Benthic Habitat Mapping and Substrate Characterization

Northern Estuaries, Florida

Dial Cordy and Associates Inc. Steve Dial (910) 251-9790 Mike Rice (904) 241-8821 Dawn York (910) 251-9790 Jacksonville District, US Army Corps of Engineers Andy Loschiavo (904) 232-2077

IntroductionIntroductionIntroduction

Dial Cordy and Associates Inc. was contracted by the Jacksonville District, U.S. Army Corps of Engineers to map the four Northern Estuaries [Caloosahatchee River Estuary (CAL), St. Lucie Estuary (SLE), Loxahatchee Estuary (LOX), and Lake Worth Lagoon (LWL)] in south Florida for bottom type (e.g. shell, silt, mud, muck) and location of oyster beds and seagrasses (Figure 1). In addition, densities of live oysters, as well as presence/absence of oyster reefs and seagrass beds at select locations were examined. While monitoring of oyster reef and seagrass health has been taking place since the late 1990s in many of the estuaries, the extent and distribution of oyster reefs and seagrasses in the estuaries is unknown. In addition, comprehensive substrate bottom type and morphology of each estuary was lacking. Since the spatial location and extent of oyster reefs, seagrasses, and bottom types influences the natural expansion of oyster reefs and seagrasses and success of restoration activities, mapping of the benthic habitats and bottom types is essential. This mapping is critical since increasing the coverage of healthy oyster beds and seagrasses is a Comprehensive Everglades Restoration Plan (CERP) goal.

MethodsMethodsMethods

To characterize the substrate types and benthic habitats within each estuary, a four-pronged approach was used to map each study area. These steps included: 1. Establishment of two 50-acre calibration survey areas. The calibration survey refined and validated remote sensing equipment and software used for the mapping effort. 2. Completion of the remote sensing survey incorporating previous mapping efforts, aerial photographic interpretation, and in-field remote sensing technology. 3. Field intensive groundtruthing of the data focused on classifying benthic habitat/substrate signatures identified in the remote sensing survey, verifying presence/absence of seagrass habitats and assigning attributes to habitat types in each of the four estuaries (Figure 2). 4. Extensive mapping and quantitative assessment aimed at oyster reefs/clumps was also conducted within each estuary (Figure 3).

Figure 1. Location of Northern Estuary Study Areas

Figure 3. Data Flow Approach Figure 2. Typical Raw Side Scan Sonar Mosaic

ResultsResultsResults

The mapping effort focused from the 9 ft bathymetric contour to the shoreline, resulting in over 30,692 acres of area surveyed [SLE (4,343 acres), LOX (886 acres), LWL (2,619 acres), and CAL (22,844 acres)] and approximately 2,568 miles (mi) of tracklines surveyed [SLE (414 mi), LOX (147 mi), LWL (186 mi), and CAL (1,820 mi)] (Table 1).

Table 1. Summary of assessment parameters and target metrics for each estuary.

Side-scan sonar data collected were analyzed and post-processed using Quester Tangent Corporation (QTC) Sideview seabed classification software. This approach allowed for classification of all habitats identified. QTC Sideview takes a data set representing a complex, highly variable target (the seabed) and reduces it to a minimum set of descriptors (features) while maintaining information to distinguish one seabed from another. This approach is predicated on detecting changes in substrate (Figure 4).

Assessment Parameters and Targets

Estuary Side-scan Calibration Area (ac)

Tracklines (mi.)

Groundtruthing Locations

Processed Data - Raw

(GB)

Processing Data - QTC

(GB)

1m2 Oyster

Quadrats Sampled (#)

Classified Substrate

(ac)

SLE 50 413.9 405 31 80 160 4,343

LOX * 147.1 140 4 10 108 886

LWL * 186.1 326 11 27 64 2,619

CAL * 1,820.4 959 114 294 168 22,844

Total 50 2,568 1,830 160 411 500 30,692

ConclusionsConclusionsConclusions

The overall objective of this project was to map the four northern estuaries (CAL, SLE, LOX, and LWL) in south Florida for bottom type and location/vitality of oyster beds and seagrasses. The mapping performed and data collected will serve to support several objectives, including: establishment of reference conditions, determining the status and trends in resource conditions, detecting unexpected responses in the ecosystem resulting from CERP activities, and supporting scientific investigations leading to an increased understanding of the ecosystem. The spatial location and extent (as well as health) of oyster reefs, seagrasses, and bottom types influences the natural expansion of oyster reefs and seagrasses, therefore mapping of the benthic habitats and bottom types in the subject estuaries was essential to verify the success of future restoration activities.

Figure 4. Substrate Classification Map for Caloosahatchee Estuary