theroleof“rulesofthumb”inscience...

The Role of “Rules of Thumb” in Science-Based EnvironmentalPolicy: California’s Marine Life Protection Act as a Case Study

Mark H. CarrI, Emily SaarmanII, & Margaret R. CaldwellIII, IV

AbstractDevelopment and application of scientifically based "rules of thumb" can be an effective meansof incorporating the best available science in resource management and decision-making.We describe and analyze how scientific experts have distilled complex knowledge about marineecosystems—while capturing scientific uncertainty—to develop relevant, credible, synthetic,understandable, and timely guidelines for direct use by decision makers tasked with building astatewide network of marine protected areas under California's Marine Life Protection Act.

I. INTRODUCTION ...............................................................................................................2II. DISCUSSION ....................................................................................................................3

A. Inherent Complexity of Scientific Information.................................................................3B. Rules of Thumb in Practice .............................................................................................4C. Employing Rules of Thumb to Foster Science-Based Decision-Making ...........................6D. Case Study of “Rules of Thumb” in Science-Based Decision-Making .............................7

III. RULES OF THUMB “IN THE WATER” .........................................................................8A. Goal #1: “Protect the Natural Diversity and Abundance of Marine Life, and theStructure, Function, and Integrity of Marine Ecosystems”...................................................8B. Goal #2: “Help Sustain, Conserve, and Protect Marine Life Populations, IncludingThose of Economic Value, and Rebuild Those that are Depleted” .....................................11C. Goal #3: “Ensure that the State's MPAs Are Designed and Managed, to the ExtentPossible, as a Network” ....................................................................................................13

IV. CONCLUSION...............................................................................................................15

IVSupport for M

I Department of Ecology and Evolutionary Biology, Long Marine Laboratory, 100 Shaffer Rd., University ofCalifornia, Santa Cruz, CA 95060, [email protected] Partnership for Interdisciplinary Studies of the Coastal Ocean, Long Marine Laboratory, 100 Shaffer Rd., Universityof California, Santa Cruz, CA 95060III Center for Ocean Solutions, Stanford University, Stanford, CA 94305

. Caldwell was provided by the Center for Ocean Solutions, Woods Institute for the Environment,Stanford University and Stanford Law School. Support for M. Carr and E. Saarman was provided by the Partnershipfor Interdisciplinary Studies of Coastal Oceans (PISCO), which is supported by the Gordon and Betty MooreFoundation and the David and Lucile Packard Foundation. The authors wish to thank Ellen Medlin and Erin Prahlerfor their research assistance, and Margaret Peloso for her review of early drafts.

Published online March 2010

2010 RULES OF THUMB IN SCIENCE-BASED ENVIRONMENTAL POLICY 2

I. INTRODUCTION1

Policymakers and the public increasingly look to science to both underpin environmental policy and to inform management decisions. Similarly, scientists are examining their own role in meeting society’s needs.2 The attraction of applying science to policy stems from three attributes highly valued by decision makers: objectivity, rigor, and the explicit characterization of uncertainty. Demand for science-based decisions and policies is especially prevalent in human health and environmental policies and manifests in state, national, and international laws. Guidelines, or “rules of thumb,” for incorporating science into policy is something that benefits both scientists (their work is clearly understood) and policymakers (decisions can be made with clear scientific input). Here we describe how rules of thumb were greatly beneficial in creating California’s network of marine protected areas (MPAs).

California’s Marine Life Protection Act (MLPA) was passed in 19993 to establish a coherent network of marine protected areas in state waters to improve marine ecosystem protection. “The MLPA reflects prevailing scientific views regarding the role of MPAs in conserving biological diversity, protecting habitats, aiding in the recovery of depleted fisheries, and promoting recreation, study, and education.”4 The act exemplifies an institutional appeal for science-based decision-making because it explicitly mandates that the process to establish MPAs be based on the best readily available science. Its authors recognized that “California's [] MPAs were established on a piecemeal basis rather than according to a coherent plan and sound scientific guidelines.”5 To correct this shortcoming, the MLPA was adopted “[t]o ensure that California's MPAs have clearly defined objectives, effective management measures, and adequate enforcement, and are based on sound scientific guidelines.”6 A guiding document for the MLPA is the “Master Plan for Marine Protected Areas,” which, as stipulated by the act, “shall be based on the best readily available science”7 and subject to peer review.8

One of many national examples of a legislative call for science-based management is the foundational federal law for U.S. fisheries management—the Magnuson-Stevens Fishery Conservation and Management Act. The act requires that “the national fishery conservation and management program utilizes and is based upon, the best scientific information available.”9 It further mandates that “[c]onservation and management measures shall be based upon the best scientific information available.”10 Reinforcing a desire for science-based marine resource policy and management is President Obama’s June 2009 White House memorandum that calls

1 For general literature that inspired some of the ideas behind this article, see generally L. Falling & R. Gregory, Ten Common Mistakes in Designing Biodiversity Indicators for Forest Policy, 68 J. ENVTL. MGMT. 121 (2003); JAMES SALZMAN & BARTON H. THOMPSON JR., ENVIRONMENTAL LAW & POLICY 165-87 (2007); Cal. Dept. Fish & Game, Peer Review of the Scientific Guidelines Found in the MLPA Master Plan Framework, http://www.dfg.ca.gov/MLPA/pdfs/binder3a.pdf (last visited Feb. 16, 2010). 2 See Jane Lubchenco, Entering the Century of the Environment: A New Social Contract for Science, 279 SCIENCE 491 (1998). 3CAL FISH & GAME CODE §§ 2850-63 (West 2010). 4CAL. DEPT. OF FISH AND GAME, CALIFORNIA MARINE LIFE PROTECTION ACT MASTER PLAN FOR MARINE PROTECTED AREAS ii (2008). 5 CAL FISH & GAME CODE § 2851(a). 6 Id. § 2853(b)(5). 7 Id. § 2855(a). 8 Id. § 2858. 9 16 U.S.C. § 1801(c)(3) (West 2010). 10 Id. § 1851(a)(2).

3 STANFORD JOURNAL OF LAW, SCIENCE & POLICY Vol. 2

for a national policy for ocean, coastal, and Great Lakes resources that “incorporate[s] ecosystem-based science and management” and mandates science-based marine spatial planning.11 At the international level, the European Union’s policy on sustainable fisheries provides another case in point. In order to maintain fisheries at the maximum sustainable yield, and to move towards an ecosystem-based approach to fisheries management, the EU intends to undertake a series of long-term planning efforts to manage various fish stocks. “Impartial scientific advice will be the basis of any plan,” and the best available science is to be used.12 Taken together, these examples reflect a widespread desire to use science to inform decision-making in a variety of marine environmental policy arenas.

Development and application of scientifically based rules of thumb are a means of bringing the fruits of the scientific community’s research and collective wisdom to bear on environmental decision-making. The origin of rules of thumb is often traced back to Italian economist Vilfredo Pareto whose 1906 research showed that twenty percent of the people in Italy owned eighty percent of the wealth. The “80-20 rule”—frequently referred to as Pareto's Principle—is now commonly applied to everything from workforce or inventory management to classroom instruction.13 We define scientifically based “rules of thumb” as guidelines that capture the current consensus of the scientific community relevant to implementation of express policy. In this article we explore the complexity of converting scientific information into operational guidelines, or rules of thumb, for environmental management, and we provide examples of the application of rules of thumb with special focus on their development and use in the MLPA. In doing so, we discuss key attributes of rules of thumb for successful integration and use in environmental decision-making and how the rules of thumb developed for MLPA could help support the overall ecological network’s resilience to climate change impacts.

II. DISCUSSION

A. Inherent Complexity of Scientific Information

Some of the very same attributes that make scientific information so appealing to decision making can also prove problematic in integrating that information into decisions “on the ground,” especially when decision makers have limited familiarity with science. For example, information produced by scientific studies of social, ecological and environmental systems is complex because these systems are inherently spatially variable, dynamic, and highly complex. Such traits produce emergent properties that are dependent on the variable state of the system itself (e.g., relative abundance of species in an ecological community) and the conditions it experiences (e.g., climate regimes). Often, such complexity overwhelms and obscures the more simple and general patterns that are otherwise sufficient to inform decisions. Communicating the variability and condition-dependent qualities of a coupled human-natural system, for example,

11 White House Office of the Press Sec’y, Memorandum for the Heads of Executive Departments and Agencies Regarding Nat’l Policy for the Oceans, Our Coasts, and the Great Lakes (June 12, 2009), available at http://www.projectaware.org/knowledgebase/details.php?id=192. 12 Communication from the Commission to the Council and the European Parliament, Implementing Sustainability in EU Fisheries Through Maximum Sustainable Yield, PARL. EUR. DOC. (SEC 868) 8, 11 (2006) 13 See generally Robert Sanders, The Pareto Principle: Its Use and Abuse, 3 J. BUS. & INDUS. MARKETING 37 (1988).


typically necessitates using qualifiers of interpretation that the audience (decision-makers and interested public) often construes as a lack of understanding.14

Four fundamental sources of uncertainty—process, measurement, model, and causal—act separately and together to drive variation and complicate both our ability to predict as well as to react effectively through management actions.15 Process uncertainty reflects the varying levels of predictability of environmental, social and ecological systems. Measurement uncertainty reflects the degree of error in our estimates in a system, such as the typical abundance of a species in an ecosystem. Model uncertainty reflects uncertainty in our conceptual model of the social or ecological system that we are attempting to manage, including the accuracy of our identified key drivers in the system. Causal uncertainty is the potential error in our inference of causality in a system’s response to implementation of a management decision. All of these sources of uncertainty should be recognized and articulated for those involved in decision- making in order to understand the likelihood that systems will respond in the manner intended by policy decision or management action. Decision-makers value information that seems intuitive and sufficiently familiar to suggest “common sense.” Historically, scientists were not trained to communicate scientific information in ways that decision-makers could readily comprehend and appreciate in these terms.16 B. Rules of Thumb in Practice

Rules of thumb may take many forms and be applied in diverse contexts, but effective rules of thumb should be relevant, credible, timely, synthetic across multiple information sources, and easily understood by non-scientists. For example, debates over terrestrial reserve design have generated a diverse array of guiding principles,17 many of which are similar to those described for marine reserves below. The need for scientific guidance on terrestrial reserve size sparked the articulation of key ecological concepts, including the species-area relationship, the concept of population viability, and the role of habitat heterogeneity in supporting biodiversity. The observation that isolated larger islands tend to support a greater diversity of species than similar small islands ultimately led to the following rules of thumb for terrestrial reserve design: large is better than small, and corridors are better than no connection.18 The observation that small or isolated populations are more vulnerable to extinction led to guidance about the

14 For example, the growth and survival of salmon (and yearly success of a fishery) varies markedly in response to variable oceanic conditions. But the importance of an oceanic driver can be negated by another driver, such as the lack of freshwater in spawning grounds hundreds of kilometers inland. 15 See, e.g., R. HILBORN & M. MANGEL, THE ECOLOGICAL DETECTIVE: CONFRONTING MODELS WITH DATA (1997); JAMES S. CLARK, MODELS FOR ECOLOGICAL DATA: AN INTRODUCTION (2007); N. Cressie et al., Accounting for Uncertainty in Ecological Analysis: The Strengths and Limitations of Hierarchical Statistical Modeling, 19 ECOLOGICAL APPLICATIONS 553 (2009). 16 Despite this historical shortcoming, some groups are now making efforts to bridge the science-policy gap. See, e.g., Communication Partnership for Science and the Sea, Products and Resources, http://www.compassonline.org/resources/ (last visited Oct. 8, 2009); Aldo Leopold Wilderness Research Inst., http://leopold.wilderness.net/ (last visited Oct. 8, 2009). 17 See M. L. Shaffer, Minimum Population Sizes for Species Conservation, 31 BIOSCIENCE 131 (1981). 18 See J. M. Diamond, The Island Dilemma: Lessons of Modern Biogeographic Studies for the Design of Natural Reserves, 7 BIOLOGICAL CONSERVATION 129 (1975); M. E. Soulé, Land Use Planning and Wildlife Maintenance: Guidelines for Conserving Wildlife in an Urban Landscape, 57 J. AM. PLANNING ASS’N 313 (1991).


minimum population size that should be captured within a reserve.19 Observations that areas with multiple habitats contain more species diversity produced a rule of thumb that terrestrial reserves should encompass multiple (or heterogeneous) habitats at multiple elevations.20

Another example is the gradient approach to development and wetlands. When construction will affect nearby wetlands, federal land use gatekeepers—the EPA and the Army Corps of Engineers—adhere to a rough hierarchy of responses: avoid, restore, mitigate.21 That is, managers prefer that developers rethink project design so as to avoid impacts altogether. If avoidance is not feasible, the second-best response is to restore nearby damaged wetlands to a functioning state. Absent avoidance or restoration alternatives, wetland managers fall back on compensatory mitigation. Compensatory restoration is often accomplished, for example, through the payment of a fee in lieu of actual avoidance or restoration. The fee is usually paid to a private natural resources management organization that works with the Corps to establish and restore wetlands elsewhere.22

A slightly more nuanced example of an operational guideline is the common reliance on certain buffer zones widths for riparian areas in land use ordinances. Broadly speaking, biological condition declines as nearby paved (impervious) surface area increases.23 Land use ordinances often require that a strip of vegetation is retained or installed adjacent to riparian corridors to filter harmful runoff from nearby impervious surfaces into streams and rivers. Buffer zones or riparian “setbacks” also provide valuable wildlife habitat and can be used to reduce impacts from flood and drought. Recommended riparian buffer strip width can vary according to the feature to be protected (water quality, habitat, flood attenuation, etc.).24 Many local land use authorities adhere to a general 50-foot minimum setback for vegetated buffers.25 One hundred-foot buffers are preferred, and are implemented where possible.26

Yet another guideline used in environmental management relates to limiting impervious surface coverage. The EPA has determined that there will be degradation in water quality within a watershed if impervious surface coverage exceeds 10%.27 Beyond the 15% impervious surface threshold, a marked decline in the water quality of nearby streams and the health of associated biological communities is observed, especially in terms of species diversity.28 These observed 19 See generally M. E. Soulé, Where Do We Go From Here?, in VIABLE POPULATIONS FOR CONSERVATION 175-183 (M. E. Soulé ed., 1987); Shaffer, supra note 17; C. D. Thomas, What Do Real Population Dynamics Tell Us About Minimum Viable Population Sizes?, 4 CONSERVATION BIOLOGY 324 (1990). 20 C. L. Shafer, Terrestrial Nature Reserve Design at the Urban/Rural Interface, in CONSERVATION IN HIGHLY FRAGMENTED LANDSCAPES 345-378 (M. W. Schwartz ed., 1997). 21 See GOV’T ACCOUNTABILITY OFFICE, GAO-01-325, WETLANDS PROTECTION: ASSESSMENTS NEEDED TO DETERMINE EFFECTIVENESS OF IN-LIEU-FEE MITIGATION (2001). 22 Id. 23 See generally Derek B. Booth et al., Reviving Urban Streams: Land Use, Hydrology, Biology, and Human Behavior, J. AM. WATER RESOURCES ASS’N 1351 (Oct. 2009); X. Wang, Integrating Water-Quality Management and Land-Use Planning in a Watershed Context, 61 J. ENVTL. MGMT. 25 (2001). 24 See RICHARD A. FISCHER & J. CRAIG FISCHENICH, U.S. ARMY CORPS. OF ENGINEERS, ERDC TN-EMRRP-SR-24, DESIGN RECOMMENDATIONS FOR RIPARIAN CORRIDORS AND VEGETATED BUFFER STRIPS (2000). 25 See D. HERNANDEZ ET AL., S.C. DEPT. OF HEALTH AND ENVTL. CONTROL, VEGETATED RIPARIAN BUFFERS AND BUFFER ORDINANCES (2003), available at http://www.scdhec.gov/environment/ocrm/pubs/docs/buffers.pdf. 26Id. 27 U.S. ENVTL. PROTECTION AGENCY, 231-R-04-002, PROTECTING WATER RESOURCES WITH SMART GROWTH 9 (2004). 28 See CHRISTINE TILBURG & MERRYL ALBER, GA. COSTAL RES. COUNCIL, IMPERVIOUS SURFACES: REVIEW OF THE RECENT LITERATURE (2006), available at http://crd.dnr.state.ga.us/assets/documents/jrgcrddnr/ ImperviousLitReview_Final.pdf.


thresholds have led land use managers to focus on percentage of impervious surface coverage in water quality control efforts.29 Many state and local agencies recommend that impervious area ordinances impose extra limitations or require additional management protections where impervious surfaces exceed 15% of lot surface area30 Synthetic rules of thumb for ecosystem protection often have diverse applications. As explained below, the rules of thumb developed for MLPA—to protect marine ecosystems from the impacts of fishing—can be directly applied to mitigating another, less predictable ecosystem threat, climate change.31 Synthetic rules of thumb that accommodate complexity and uncertainty with the goal of enhancing the resilience and adaptability of ecosystems may also address the further uncertainty produced by emerging threats.32 From the synthetic nature of the rules springs a versatility that would not be found if rules were specific to an individual species or narrow goal. C. Employing Rules of Thumb to Foster Science-Based Decision-Making

One approach to addressing the hurdle of using scientific knowledge to inform science-based decision-making is to communicate scientific concepts and information in more practical and concrete terms, such as with “rules of thumb.” We believe that successful distillation and communication of complex scientific information would benefit from some simple guidelines, reinforced by examples of their successful application. The key attributes of rules of thumb track well with the recommendations for using scientific knowledge for informing decision-making identified in the NRC report “Roundtable on Science and Technology for Sustainability, 2006.”33 These include: (1) relevance: the decision directly addresses policy goals and needs; (2) credibility: the decision is supported by the scientific community (literature and expert opinion); (3) synthesis: the decision incorporates and synthesizes multiple sources of scientific information; (4) understandability: the decision links to common sense and tangible examples or analogies; and (5) timeliness: the decision uses the best available science.

A clear understanding of policymakers’ needs is a fundamental prerequisite to developing a rule of thumb. Sometimes decision-makers may not understand their information needs because of the complexity of the issue under consideration. In the examples provided below, it was necessary to communicate why the information was important to the decision-making process. As such, providing the scientific information goes hand in hand with explaining its value. The value likewise stands or falls depending on its perceived credibility. The source of information, including reference to peer reviewed literature, and the quality of the information, including any associated uncertainty, must be articulated along with the information itself. Elements of credibility involve the development of the information (e.g., how comprehensive is

29 See Poster Presentation by M. VanderWilt et al., The Relationship Between Impervious Surface Coverage and Water Quality, in PROCEEDINGS OF THE THIRD BIENNIAL COASTAL GEOTOOLS CONFERENCE (2003). 30 WIS. DEPT. NATURAL RESOURCES, (2001). 31 Brian Helmuth et al., All Climate Change is Local: Understanding and Predicting the Effects of Climate Change from an Organism’s Point of View, 2 STAN. J. L. SCI. & POL’Y (forthcoming publication, 2010). 32 See generally NAVIGATING SOCIAL-ECOLOGICAL SYSTEM: BUILDING RESILIENCE FOR COMPLEXITY AND CHANGE (Fikret Berkes et al. eds., 2003); B. WALKER & D. SALT, RESILIENCE THINKING: SUSTAINING ECOSYSTEMS AND PEOPLE IN A CHANGING WORLD (2006); T.P. Hughes et al., New Paradigms for Supporting the Resilience of Marine Ecosystems, 20 TRENDS IN ECOLOGY & EVOLUTION 380 (2005). 33 NATIONAL RESEARCH COUNCIL, ROUNDTABLE ON SCIENCE AND TECHNOLOGY FOR SUSTAINABILITY 7-15 (2006), available at http://www.nap.edu/catalog/11652.html.


the relevant body of information that has been reviewed), and how it is presented, including graphic display.34

Rules of thumb must be based on the best available science. The most recently produced information is not necessarily the best available. Indicating how the most recent findings reinforce, extend, or perhaps contradict the body of knowledge on a topic is critical to conveying that information. Preconceived notions based on historic information needs to be acknowledged (i.e. “until recently we believed…”) with an explanation of how this latest information modifies that understanding or adds yet further support with more powerful methods than were previously available. Rules of thumb should be comprehensible to those receiving the information both for its credibility, but more importantly, so it is applied appropriately in the decision-making process. If policymakers do not understand how the information should inform their decisions, it is likely not to be applied or be applied inappropriately. Therefore, rules of thumb must be comprehensible both with respect to how they are generated and to how they bear on decision-making. It is also important that the scales at which different processes occur are clear. Synthesizing how these scale-dependent processes result in a pattern relevant to informing a rule of thumb increases decision-maker understanding of the information and its credibility. D. Case Study of “Rules of Thumb” in Science-Based Decision-Making

The implementation of California’s Marine Life Protection Act has relied heavily upon rules of thumb to inform the design of a comprehensive network of MPAs within California state waters. The MLPA articulates six primary goals, the first five of which were converted into science-based rules of thumb: (1) conservation of biodiversity and the health of marine ecosystems; (2) recovery of wildlife; (3) improvements to recreational and educational opportunities consistent with biodiversity conservation; (4) protection of representative and unique habitats for their intrinsic value; (5) ensuring MPAs are managed, to the extent possible as a network; and (6) ensuring that MPAs have defined objectives, effective management and enforcement, and are designed on sound science.35 After two failed attempts to implement the act, the state entered into a public-private partnership (recorded in a series of memoranda of understanding or “MOUs”) whereby private non-profit foundations contributed millions of dollars into a fund to support MLPA implementation, and the state assumed responsibility for developing a network of MPAs pursuant to the MLPA requirements using a defined public process. The public process structure adopted through the MOUs is depicted in Figure 1.36 We focus here on the role of the science advisors (“Science Advisory Team” or “SAT”) in developing and communicating rules of thumb to address five of the six primary goals of the MLPA.

Rules of thumb are especially important to MLPA implementation for the following reasons: (1) stakeholder confidence that the MPAs are based on sound scientific principles and will have measurable conservation benefits is critical for their acceptance of the adopted MPAs. MPAs that restrict or prohibit fishing in designated areas have been notoriously challenging to implement because of their immediate perceived or realized economic impact on fishing industries. (2) The MLPA implementation process requires that stakeholders construct initial proposals for MPA network design and that policymakers with little scientific knowledge guide 34 See E. R. TUFTE, THE VISUAL DISPLAY OF QUANTITATIVE INFORMATION (1983). 35 CAL. DEPT. OF FISH AND GAME, supra note 4, at iii. 36 See infra fig.1.


and complete the design process. Both groups are informed by a dedicated science team, but no decisions about individual MPA placement are made by scientists. (3) The scientific concepts that form the basis of MPA network design are complex and require generalization across multiple sources of information and complex processes to yield meaningful guidance. Simple and intuitive rules of thumb for MPA design provide stakeholders with critical guidance as they juggle tradeoffs between conservation goals and political and economic pressures. Likewise, rules of thumb allow policy makers to interpret simple metrics of design success (e.g. how well proposals “meet the SAT guidelines”).

An added benefit of MPA network design based on generalized rules of thumb is the inherent ability of the resultant network to continue to meet its intended objectives even when subject to emerging threats. By recognizing and addressing areas of uncertainty, the rules of thumb can guide creation of an MPA network to provide robust conservation benefits in the face of an uncertain future. Climate change drives dramatic change in the coastal ocean.37 Changes in temperature, current patterns, storm frequency and intensity, ocean acidification, terrestrial runoff, and sea level rise caused by climate change are likely to affect individual species as well as entire marine ecosystems in unpredictable ways. Climate change may also drive the emergence or intensity of the impacts of new stressors such as hypoxic conditions and invasive species.38 Thus, some anticipated effects of climate change in the marine ecosystem include changes in the abundance and distribution of individual species, extinctions, and shifts in species interactions, all of which have the potential to alter the structure and function of marine ecosystems. The complexity of both climate change processes and the marine ecosystems impacted by them make it nearly impossible to predict the effects of climate change on the local scales needed to guide management decisions. MPAs, however, act to reduce the number of stressors that an ecosystem is exposed to and therefore should reduce vulnerability (increase resistance) and enhance resilience to impacts from climate change. The rules of thumb, which account for uncertainty such as that caused by climate change, lead to an MPA network that is likely to provide broad conservation benefits in an uncertain future. We provide specific examples below of how the rules of thumb developed for the California MPA network design process relates to climate change adaptability.

III. RULES OF THUMB “IN THE WATER”

A. Goal #1: “Protect the Natural Diversity and Abundance of Marine Life, and the Structure, Function, and Integrity of Marine Ecosystems”39

A rule of thumb that addresses this goal must synthesize information about the distribution of ecosystems and the diversity and abundance of the organisms they support across

37 See generally John A. Barth, Delayed Upwelling Alters Nearshore Coastal Ocean Ecosystems in the Northern California Current, 104 PNAS 3719 (2007); Scott C. Doney, Oceanic Acidification: The Other CO2 Problem, 1 ANN. REV. MARINE SCI. 169 (2009); C. Parmesan, Ecological and Evolutionary Responses to Recent Climate Change, 37 ANN. REV. ECOLOGY, EVOLUTION, & SYSTEMATICS 637 (2006); M. A. Snyder et al., Future Climate Change and Upwelling in the California Current, 30 GEOPHYSICAL RES. LETTERS 1823 (2003). 38 See R. F. Keeling et al., Ocean Deoxygenation in a Warming World, 2 ANN. REV. MARINE SCI. 199 (2009); N. N. Rabalais et al., Global Change and Eutrophication of Coastal Waters, 66 ICES J. MARINE SCI. 1528 (2009); J. J. Stachowicz et al., Linking Climate Change and Biological Invasions: Ocean Warming Facilitates Nonindigenous Species Invasions, 99 PNAS 15497 (2002); J. J. Stachowicz et al., Linking Climate Change and Biological Invasions: Ocean Warming Facilitates Nonindigenous Species Invasions, 99 PNAS 15497 (2002). 39CAL. FISH & GAME CODE § 2853(b)(1).


broad spatial scales. A successful rule of thumb will clearly guide MPA network design and allow policy makers to assess whether or not a proposed network is likely to meet this goal.

A large body of scientific literature demonstrates that unique marine communities are associated with different habitats.40 Therefore, to protect the full diversity of marine life, an MPA network must encompass the full diversity of marine habitats. This concept is intuitive and can be illustrated with a comparison of the fish species found on a rocky reef and an adjacent sandy area. Although some species may transit between the two habitats or utilize the edge habitat, the overall community of species on the rocky reef is distinct from that on the soft bottom. Likewise, the scientific literature indicates that marine communities vary across depth within a given habitat type (e.g. rocky reef).41 Although some species range across multiple depth zones, the marine communities associated with shallow and deep habitats are distinct. Most rockfish species, for example, inhabit a range of depths but are most likely to be found within a narrower preferred depth zone.42 Complex interactions between species and their adaptation to specific depth zones result in distinct marine communities at different depths. Further support for the concept that all habitats should be included in a network of MPAs comes from the life history characteristics of individual species. Many species are known to use multiple habitats or depth zones during different parts of their life cycle. Halibut and other flatfishes, for example, inhabit near-shore and estuarine habitats as juveniles, but move to deeper soft-bottom habitats offshore as they mature.43 Likewise, many species of rockfish settle in shallow habitats, gradually migrating to deeper waters as they mature.44

The two patterns of community variation described above (by habitat and by depth) provide a simple but robust mechanism for defining the ‘key’ habitats that must be represented in an MPA network to assure that the diversity of marine life is protected. More complex definitions of habitat are possible, including definitions that consider environmental factors or detailed characteristics of the substrate habitat (high vs. low relief rock, for example), however,

40 See generally Larry G. Allen & Daniel J. Pondella II, An Ecological Classification of California Marine Fishes, in ECOLOGY OF MARINE FISHES: CALIFORNIA AND ADJACENT WATERS 81-113 (Larry G. Allen et al. ed., 2006); H. S. Lenihan & F. Michelli, Soft-Sediment Communities, in MARINE COMMUNITY ECOLOGY 253-88 (M. D. Bertness et al. eds., 2001); B. A. Menge & G. M. Branch, Rocky Intertidal Communities, in MARINE COMMUNITY ECOLOGY, supra at 221-52; B. Thompson et al., Benthic Invertebrates, in ECOLOGY OF THE SOUTHERN CALIFORNIA BIGHT 369-458 (M. D. Dailey et al. eds., 1993); J. D. Witman & P. K. Dayton, Rocky Subtidal Communities, in MARINE COMMUNITY ECOLOGY 339-66 (M. D. Bertness et al. eds., 2001). 41See Allen & Pondella, supra note 40, at 81-113; M. J. Allen, Habitats of California Marin Fishes: Continental Shelf and Upper Slope, in ECOLOGY OF MARINE FISHES: CALIFORNIA AND ADJACENT WATERS, supra, at 167-204; M. H. Horn & K. L. M. Martin, Habitats of California Marine Fishes: Rocky Intertidal Zone, in ECOLOGY OF MARINE FISHES: CALIFORNIA AND ADJACENT WATERS, supra note 40, at 205-26; M. S. Love & M. Yoklavich, Habitats of California Marin Fishes: Deep Rock Habitats, in ECOLOGY OF MARINE FISHES: CALIFORNIA AND ADJACENT WATERS, supra, at 253-68; J. S. Stephens et al., Habitats of California Marin Fishes: Rocky Reefs and Kelp Beds, in ECOLOGY OF MARINE FISHES: CALIFORNIA AND ADJACENT WATERS, supra, at 227-52; Thompson et al., supra note 40, at 369-458. 42 See D. E. KRAMER ET AL., Marine Advisory Bulletin No. 47, GUIDE TO NORTHEAST PACIFIC FLATFISHES (2003); M. S. LOVE ET AL., THE ROCKFISHES OF THE NORTHEAST PACIFIC (2002); M. S. Love et al., The Ecology of Substrate-Associated Juveniles of the Genus Sebastes, 30 ENVTL. BIOLOGY OF FISHES 225 (1991). 43 See Larry G. Allen et al., Habitats of California Marine Fishes: Bays and Estuaries, in ECOLOGY OF MARINE FISHES: CALIFORNIA AND ADJACENT WATERS, supra note 40, 119-48; B. M. Gillanders et al., Evidence of Connectivity Between Juvenile and Adult Habitats for Mobile Marine Fauna: An Important Component of Nurseries, 247 MARINE ECOLOGY PROGRESS SERIES 281 (2003). 44 Love et al., The Ecology of Substrate-Associated Juveniles of the Genus Sebastes, 30 ENVTL. BIOLOGY OF FISHES 225 (1991).

2010 RULES OF THUMB IN SCIENCE-BASED ENVIRONMENTAL POLICY 10 the MLPA Science Advisory Team chose to define habitats simply and to identify geographic patterns of environmental and habitat characteristics in a separate analysis described below. To inform MPA network design, the SAT generated a list of 18 ‘key’ habitats found within California state waters and provided the following rule of thumb: “To protect the diversity of species that live in different habitats and those that move among different habitats over their lifetime, every ‘key’ marine habitat should be represented in the MPA network.”45

To provide a more nuanced look at the simple definition of habitats used in the MLPA, the SAT recognized that marine communities within a given habitat vary across environmental gradients. Variations in water temperature have a profound influence on community composition, with some species occurring exclusively in warm-water environments, others confined to cold-water areas, and some inhabiting both. A simple comparison of kelp forest communities in the relatively cold waters of San Miguel Island (where rockfish and lingcod are important predators) and those in the warmer waters of nearby Anacapa Island (where Sheephead and Kelp Bass fill similar predatory roles) illustrates the striking effect of water temperature on community composition.46 Other environmental factors and habitat characteristics that vary geographically, such as swell exposure, geology, and nutrient availability associated with oceanographic processes (e.g., coastal upwelling) also influence the composition of marine communities and ecosystem structure. Interactions between species add an additional and often unpredictable layer of complexity to the patterns of ecosystems. For example, along California’s central coast sea otters prey on sea urchins, which limits urchin grazing on kelp, but in southern California, where sea otters are rare, lobster and Sheephead play this predatory role. However, both lobster and Sheephead are subject to fishing pressure and depressed predator populations can lead to episodic explosions in urchin populations that can consume entire kelp beds. A rule of thumb that guides protection of ecosystem variation must synthesize patterns of variation that occur at multiple scales, and arise from multiple sources, to produce concrete and intuitive guidance for MPA design.

To define geographic patterns of ecosystem variation, the SAT considered oceanographic, geologic, and community patterns across broad spatial scales. A survey of the scientific literature indicates that large-scale oceanographic patterns divide the state of California into two “biogeographic” regions, with the division between warm- and cold-water regimes occurring at Point Conception.47 To characterize the more subtle patterns of ecosystem variation that occur within these broader regimes, the science team analyzed geologic maps, maps of oceanographic features (such as upwelling and retention areas), and marine community surveys. Patterns of variation in geology, oceanography, and community structure that emerged were compared across the ‘key’ habitats, and the resulting patterns of overlap were synthesized and defined as small-scale “bioregions” (on the order of 50-100 miles of coastline length). Wherever possible, statistical analyses were conducted to verify that ecological communities were indeed distinctly different in each of the bioregions. To guide development of an MPA network that encompassed the full range of ecosystem variation at large and small scales, the SAT provided

45 CAL. DEPT. OF FISH AND GAME, supra note 4, at ii. 46 See generally Scott. L. Hamilton et al., Incorporating Biogeography Into Evaluations of the Channel Islands Marine Reserve Network, PNAS, Feb. 22, 2010, available at 10.1073/pnas.0908091107. 47 See JOHN C. BRIGGS, MARINE ZOOGEOGRAPHY (1974); Michael Horn et al., Biogeography of California Marine Fishes with Emphasis on Changes from 1978 to 2003, in ECOLOGY OF MARINE FISHES: CALIFORNIA AND ADJACENT WATERS, supra note 40, at 3-25; Carol A. Blanchette et al., Biogeographical Patterns of Rocky Intertidal Communities Along the Pacific Coast of North America, 35 J. BIOGEOGRAPHY 1593 (2008).


the following two rules of thumb: (1) “To provide analytical power for management comparisons, and to buffer against catastrophic loss of an MPA, at least three to five replicate MPAs should be designed for each habitat type within each [large-scale] biogeographical region”48; (2) “To ensure that the different community assemblages, and the ecosystem functioning, representative of the [study region] are appropriately represented in the MPA network,” “it is recommended that key habitats from within each subregion are represented in MPAs.”49

The general nature of the rules of thumb for ecosystem protection and their explicit recognition of uncertainty contribute to creation of an MPA network that is likely to provide robust conservation values in the face of uncertainty, including that caused by climate change. Climate change is likely to shift environmental gradients in the coastal ocean as waters warm, shifting currents may lead to changes in patterns of upwelling and productivity, and changes in storm frequency and intensity could alter the swell environment and terrestrial runoff.50 Some species may not be able to tolerate or adapt to environmental change and their number or ecological function will become locally extinct, while other species will shift their distributions to track favorable environmental conditions. As such, the species composition of ecosystems within an MPA may change by emigration, immigration, local extinction, and changes in species interactions. The direction and strength of these species responses is uncertain and difficult to predict on a localized level. By protecting the diversity of species and their interactions within ecosystems across broad geographic gradients, the resulting MPA network has the potential to protect the genetic diversity necessary for adaptation to changing ocean conditions. By protecting functional equivalents across the environmental gradient, the likelihood that one of those functional equivalents will compensate for loss of another increases. B. Goal #2: “Help Sustain, Conserve, and Protect Marine Life Populations, Including Those of Economic Value, and Rebuild Those that are Depleted”51

A rule of thumb that addresses this goal must synthesize information about the movement of adults across a representative variety of marine species to understand how large an MPA must be to maintain local populations within its boundaries throughout their lifecycle. A successful rule of thumb will provide clear guidance for MPA network design and allow policymakers to assess whether or not a proposed network is likely to meet this goal.

A large body of scientific literature indicates that larger, more mature adults may contribute disproportionately to the reproductive output of a population.52 Simply put, big, old, fat females have the resources to produce exponentially more young than smaller females who

48 CAL. DEPT. OF FISH AND GAME, supra note 4, at ii. 49 CAL. DEPT. OF FISH AND GAME, BIOREGIONS WORK GROUP DRAFT ANALYSIS OF BIOGEOGRAPHICAL SUBREGIONS IN THE MLPA SOUTH COAST STUDY REGION, 3 (Nov. 7, 2008), available at http://www.dfg.ca.gov/MLPA/pdfs/agenda_111208a2.pdf. 50 See generally G. A. Meehl et al., Global Climate Projections, in CLIMATE CHANGE 2007: THE PHYSICAL SCIENCE BASIS, CONTRIBUTION OF WORKING GROUP I TO THE FOURTH ASSESSMENT REPORT OF THE INTERGOVERNMENTAL PANEL ON CLIMATE CHANGE 747-846 (S. Solomon et al. eds., 2007); John A. Barth, Delayed Upwelling Alters Nearshore Coastal Ocean Ecosystems in the Northern California Current, 104 PNAS 3719 (2007); N. S. Diffenbaugh, Response of Large-Scale Eastern Boundary Current Forcing in the 21st Century, 32 GEOPHYSICAL RES. LETTERS 1 (2005); Snyder et al., supra note 37. 51 CAL. FISH & GAME CODE § 2853(b)(2). 52 See S. A. Berkeley et al., Fisheries Sustainability via Protection of Age Structure and Spatial Distribution of Fish Populations, 29 FISHERIES 23 (2004).

2010 RULES OF THUMB IN SCIENCE-BASED ENVIRONMENTAL POLICY 12 have recently reached reproductive age. However, most fisheries are regulated with a minimum size limit that prevents take of small pre-reproductive fish, but allows take of larger fish. To provide substantial population benefits, an MPA must be large enough to ensure that a large portion of the individuals remain within the MPA throughout their life and grow to produce large numbers of young.

To develop rules of thumb for MPA size, the SAT surveyed the scientific literature for adult movement estimates across a wide variety of marine species. Scientific studies indicate that adult home ranges are species-specific and influenced by multiple small-scale factors such as habitat quality, prey availability, and local competition for resources.53 Although the home ranges of many species were poorly documented and movement distances often varied markedly from individual to individual within a species, a synthetic analysis of scientifically credible studies on adult movement revealed clear patterns. A large proportion (76%) of temperate rocky reef fish species, for which movement estimates exist, travel relatively short distances as adults (< 0.5 km), while some species are wider ranging, traveling tens of kilometers.54 Fish species that inhabit deeper rocky reef and soft-bottom habitats tend to have larger home ranges (tens to hundreds of kilometers), possibly due to lower concentrations of prey and shelter in deeper reef and soft bottom habitats,55 but at least some soft-bottom species are estimated to have home ranges no larger than ten to twenty kilometers.56 Other, more pelagic species, such as tunas, salmon, and some schooling fishes have been documented to travel hundreds or even thousands of kilometers in their lifetime. Based on this synthetic analysis of adult movement patterns, the MLPA science team developed an MPA size rule that would be likely to protect many rocky reef and some more sedentary soft-bottom species, but unlikely to provide benefits to the widest ranging species. “To best protect adult populations, based on adult neighborhood sizes and movement patterns, MPAs should have an alongshore extent of at least 5-10 km (3-6 mi or 2.5-5.4 nmi) of coastline, and preferably 10-20 km (6-12.5 mi or 5.4-11 nmi). Larger MPAs would be required to fully protect marine birds, mammals, and migratory fish.”57

Another important consideration for MPA size is its offshore extent. As mentioned above, many species utilize multiple habitats or depth zones at different points in their life cycle.58 Thus, in order to protect an individual from fishing pressure throughout its life, all the habitats and depth zones needed for development must be included in a contiguous MPA. To accommodate species that range across habitats and depth zones, the science team developed a complimentary rule of thumb for MPA size: “To protect the diversity of species that live at different depths, and to accommodate the movement of individuals to and from shallow nursery

53 See generally M. A. Hixon, An Experimental Analysis of Territoriality in the California Reef Fish Embiotoca jacksoni (Embiotocidae), 1981 COPEIA 653 (1981); R. J. Larson, Territorial Behavior of the Black-and-Yellow Rockfish and Gopher Rockfish (Scorpaenidae, Sebastes), 58 MARINE BIOLOGY 111 (1980); K. R. Matthews, A Telemetric Study of the Home Ranges and Homing Routes of Copper and Quillback Rockfishes on Shallow Rocky Reefs, 68 CANADIAN J. ZOOLOGY 2243 (1990); J. Freiwald, Causes and Consequences of the Movement of Temperate Reef Fishes (2009) (unpublished Ph.D. dissertation, U. Cal., Santa Clara) (on file with author). 54 See Freiwald, supra note 53. 55 See C. G. Lowe & R. N. Bray, Movement and Activity Patterns in California Marine Fishes, in ECOLOGY OF MARINE FISHES: CALIFORNIA AND ADJACENT WATERS, supra note 40, at 524-53. 56 See id. 57 CAL. DEPT. OF FISH AND GAME, supra note 4, at iv. 58 See generally Allen et al., supra note 40; Gillanders, supra note 43; Love et al., supra note 44.


or spawning grounds to adult habitats offshore, MPAs should extend from the intertidal zone to deep waters offshore.”59

For practicality, the SAT combined the alongshore and offshore MPA size rules into a single area-based guideline. Because the offshore extent of California’s MPAs is limited to three nautical miles by MLPA jurisdiction, the two size guidelines combined and simplified yield a single area measure: minimum MPA size = 9-18 square miles, preferred size = 18-36 sq. mi.

The rules of thumb developed for MPA size are clearly relevant to the policy goal of protecting marine populations, supported by the scientific literature and expert opinion, developed through a synthetic analysis of information from multiple sources, and easily understood by both stakeholders and policymakers. The simple area-based size guidelines developed by combining the two size rules provides a clear benchmark for evaluating MPA proposals. In the three regions of the California coast for which MPA planning has been completed to date, iterative refinement of MPA designs resulted in the majority of MPAs achieving at least the minimum recommended size (58% in the central coast, 78% in the north-central coast, and 61% in the south coast region), and a significant fraction of proposed MPAs in the preferred size range (42% in the central coast, 67% in the north-central coast, and 28% in the south coast region).

The synthetic nature of the size rule of thumb and its incorporation of uncertainty support an MPA network that is likely to provide robust conservation values in the face of climate change. Because adult movement distances are influenced by local variables such as habitat quality and prey availability, climate change may alter adult movement in unpredictable ways. In shallow waters, changes in water temperature, the frequency and intensity of storm events, runoff, and sedimentation, will change local habitats. Mobile species will respond by moving to more favorable habitat in deeper or more protected water. Increasing frequencies and extent of hypoxic events in deeper waters may similarly drive species into shallower waters. By creating a network of MPAs that are large enough to encompass the known home ranges of a variety of species and include contiguous areas of both shallow and deep water, the MLPA provides opportunities for organisms to respond to a changing climate while still remaining within the protective boundaries of the MPAs.

C. Goal #3: “Ensure that the State's MPAs Are Designed and Managed, to the Extent Possible, as a Network”60

A rule of thumb that addresses this goal must define what is meant by an MPA “network” and relate this goal to ecological characteristics that can be assessed across broad spatial scales. A successful rule of thumb will provide clear guidance for MPA network design and allow policymakers to assess whether or not a proposed network is likely to meet this goal.

The term “network” implies connectivity between the multiple parts, thus, in an ecological and evolutionary context; populations within a network of MPAs must be able to exchange individuals and genes. Large-scale connectivity of marine populations is realized primarily in the larval phase. Many fish and invertebrates live relatively sedentary lives as adults, but reproduce by broadcasting larvae that drift on the ocean currents for weeks or months (potentially traveling great distances) before settling down to mature. Larval dispersal distances are influenced by a number of factors, including the length of time the larvae drift freely in the water column (pelagic larval duration), ocean current patterns which vary from year to year, the 59 CAL. DEPT. OF FISH AND GAME, supra note 4, at iv. 60 CAL. FISH & GAME CODE § 2853(b)(6).

2010 RULES OF THUMB IN SCIENCE-BASED ENVIRONMENTAL POLICY 14 time of year in which spawning occurs, survivability (e.g. parentage and access to prey), and larval behavior. All of these factors add substantial uncertainty to estimates of larval dispersal. Although the exact distances and paths that individual larvae travel are largely unknown and almost certainly vary markedly from species to species, scientists have a number of ways to estimate the scales of larval dispersal. By examining the genetic differences between populations with varying distances of separation, scientists can estimate the distances that larvae travel on evolutionary timescales.61 Through knowledge of the length of time larvae spend drifting on ocean currents and the average direction and speed of those currents, scientists can likewise estimate the distance that individual larvae are likely to travel.62 A comparison of larval dispersal estimates obtained using these two independent methods shows general agreement and elucidates some interesting patterns. The majority of algal species are estimated to have relatively short dispersal distances (< 1 km). Most invertebrate species, on the other hand, are likely to disperse longer distances (1-100 km), and fish species are estimated to disperse the longest distances of all (tens to hundreds of kilometers63). By integrating estimates of larval dispersal obtained from multiple methods for multiple species, scientists are able to generate some general rules of thumb that are likely to enhance connectivity between marine reserves and maximize larval supply in adjacent non-reserve sites. Those species whose young disperse only short distances (e.g., algae and some invertebrates and fishes) will replenish their populations within each MPA. For longer distance dispersers, MPAs need to be spaced at distances that allow young from one MPA to replenish another. As the rule of thumb for MPA network design states: “To facilitate dispersal among MPAs for important bottom-dwelling fish and invertebrate groups, based on currently known scales of larval dispersal, MPAs should be placed within 50-100 km (31-62 mi or 27-54 nmi) of each other.”64

Connectivity between populations does not depend on MPA spacing alone—each of the interconnected MPAs must contain appropriate habitat, and enough of that habitat to support an ecologically viable population. Thus, the spacing rule is habitat-specific and each MPA that contributes to the network should be of sufficient overall size to protect organisms throughout their lifecycle. To determine whether an MPA contained sufficient area of a given habitat to contribute to the network, the SAT used biological surveys to assess the relationship between habitat area and the number of species contained within that area. Both the total number of available species and the area of habitat needed to encompass 90% of the biodiversity typically endemic to a habitat, lead to different minimum ecologically viable sizes for each habitat.

By interpreting a vague policy goal (that MPAs should form a network) in an ecological context, the SAT helped to more clearly define the goal and associated informational needs. The resultant spacing rule related to the conservation objectives of the MLPA and synthesized information from multiple credible scientific sources. Both the rule and its relevance were readily understood by decision-makers, as evidenced by the current status of California’s MPA 61 See generally B. P. Kinlan & S. D. Gaines, Propagule Dispersal in Marine and Terrestrial Environments: A Community Perspective, 84 ECOLOGY 2007 (2003); S. R. Palumbi, Population Genetics, Demographic Connectivity, and the Design of Marine Reserves, 13 ECOLOGICAL APPLICATIONS S146 (2003). 62 R. K. Cowen & S. Sponaugle, Larval Dispersal and Marine Population Connectivity, 1 ANN. REV. MARINE SCI. 443 (2009); A. L. Shanks et al., Propagule Dispersal Distance and the Size and Spacing of Marine Reserves, 13 ECOLOGICAL APPLICATIONS S159 (2003); D. A. Siegel et al., Lagrangian Descriptions of Marine Larval Dispersion, 260 MARINE ECOLOGY PROGRESS SERIES 83 (2003). 63 Kinlan & Gaines, supra note 61. 64 CAL. DEPT. OF FISH AND GAME, supra note 4, at iv.


network. Through iterative design, the MPA networks adopted in the central and north-central coast achieved the recommended spacing for 88% and 71% of evaluated habitats, respectively. The MPA network currently under consideration by the Fish and Game Commission for the south coast region would achieve recommended spacing for 64% of habitats. Because larval dispersal was used to determine the distances between adjacent MPAs in the network, and larval dispersal defines species ranges along the coast, MPA spacing based on larval dispersal distances should accommodate population movement from one protected area to the next as species shift their ranges in response to climate change. The generality of the network spacing rule and its explicit recognition of uncertainty can contribute to creation of a robust MPA network that supports ecological adaptation in the face of climate change. Climate change is likely to alter many of the factors that influence larval dispersal distances, including dominant current patterns, spawning times, and possibly larval behavior and/or pelagic duration if the favorability of pelagic conditions changes. Climate change may also alter the distribution of adults and thus the locations in which spawning occurs.65 The synthetic nature of the spacing rule, which was generated in consideration of multiple species with diverse life history characteristics, increases the likelihood that MPA populations will remain interconnected in spite of changing ocean conditions, and that this genetic connectivity will enhance the ability of organisms and ecosystems to respond to the changing conditions. Combined application of the various MPA network design rules of thumb ensures that (i) all habitats are represented in MPAs across broad geographic and environmental gradients to accommodate range shifts, (ii) that MPAs are of sufficient size and extend from shallow to deeper waters to accommodate shifting depth distributions and changes in adult movement, and (iii) that all habitats are contained within interconnected MPAs to accommodate shifting patterns of dispersal and allow marine organisms and ecosystems to draw upon the full diversity present in the system for adaptation to a rapidly changing world.

IV. CONCLUSION

As demonstrated above, science based rules of thumb can provide invaluable information

to guide environmental policy and decision-making. However, in order to generate relevant and concrete rules of thumb, scientists must observe broad patterns amidst the complexity of the system and communicate these patterns in ways that seem intuitive to the decision-maker. This synthetic approach is challenging, as it often requires scientists to think and communicate outside of their comfort zone, and has lead to criticisms that rules of thumb are based on intuitive reasoning alone. These criticisms are easily refuted when the science underpinning the rules of thumb retains the objectivity, rigor, and explicit characterization of uncertainty that make science so highly valued by decision-makers in the first place.

Rules of thumb may take many forms and be applied in diverse contexts, but effective rules of thumb should be relevant, credible, timely, synthetic across multiple information sources, and easily understood by non-scientists. Above, we describe the genesis and effectiveness of rules of thumb used to inform design of California’s emerging network of marine protected areas, but many other examples of rules of thumb exist in both marine and terrestrial management. 65 See N. K. Dulvy et al., Climate Change and Deepening of the North Sea Fish Assemblage: A Biotic Indicator of Regional Warming, 45 J. APPLIED ECOLOGY 1029 (2008); A. L. Perry et al., Climate Change and Distribution Shifts in Marine Fishes, 380 SCIENCE 912 (2005).


As articulated above, science based rules of thumb have and will continue to play a vital role in informing environmental policy on land and sea. Although generating and clearly articulating synthetic rules for complex ecosystems can be challenging, the benefits of such intuitive guidance are many and often extend beyond immediate policy goals or perceived needs.


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