h93 creature double feature.p65

172 172 172 172 172 Save The Bayrsquos San Francisco Bay Watershed Curriculum

Creature Double FeatureNative vs Non-Native Species in San Francisco Bay

OverviewOverviewOverviewOverviewOverviewIn this activity studentswill learn about two non-native species and theeffects they are having onSan Francisco Bay ecosys-tems Students will readarticles and answerquestions that bring tolight some of the problemsand ethical dilemmassurrounding non-nativespecies

Estimated timeEstimated timeEstimated timeEstimated timeEstimated time 15 hours

ObjectivesObjectivesObjectivesObjectivesObjectivesStudents will be able tobull Define native and non-native speciesbull Understand the ecological problems caused

by non-native speciesbull Study specific cases where non-native

species have become a problem in the Baybull Discuss possible solutions to the problem of

non-native species

MaterialsMaterialsMaterialsMaterialsMaterialsFor each student Photocopies of Student Pagesand Articles

VVVVVocabularocabularocabularocabularocabularyyyyynon-native alien invasive introduced exotic nativeindigenous

California Science Content StandardsCalifornia Science Content StandardsCalifornia Science Content StandardsCalifornia Science Content StandardsCalifornia Science Content StandardsGrade 6Grade 6Grade 6Grade 6Grade 6

Standard Set 5c Standard Set 5c Standard Set 5c Standard Set 5c Standard Set 5c populations of organismscan be categorized by the functions they servein an ecosystemStandard Set 5e Standard Set 5e Standard Set 5e Standard Set 5e Standard Set 5e the number and types oforganisms an ecosystem can support dependson the resources available and abiotic factorssuch as quantity of light and water range oftemperatures and soil composition

Grades 9-12Grades 9-12Grades 9-12Grades 9-12Grades 9-12BiologyLife Sciences Standard Set 6aBiologyLife Sciences Standard Set 6aBiologyLife Sciences Standard Set 6aBiologyLife Sciences Standard Set 6aBiologyLife Sciences Standard Set 6abiodiversity is the sum total of different kindsof organisms and is affected by alterations ofhabitatsBiologyLife Sciences Standard Set 6b BiologyLife Sciences Standard Set 6b BiologyLife Sciences Standard Set 6b BiologyLife Sciences Standard Set 6b BiologyLife Sciences Standard Set 6b howto analyze changes in an ecosystem resultingfrom changes in climate human activityintroduction of non-native species or changesin population size

EnglishLanguage Arts StandardsEnglishLanguage Arts StandardsEnglishLanguage Arts StandardsEnglishLanguage Arts StandardsEnglishLanguage Arts StandardsGrades 6-12Grades 6-12Grades 6-12Grades 6-12Grades 6-12

Reading ComprehensionReading ComprehensionReading ComprehensionReading ComprehensionReading Comprehension(please refer to standards for details)

ListeningSpeaking StrategiesListeningSpeaking StrategiesListeningSpeaking StrategiesListeningSpeaking StrategiesListeningSpeaking Strategies(please refer to standards for details)

Additional ResourcesAdditional ResourcesAdditional ResourcesAdditional ResourcesAdditional ResourcesUSDA Invasive Species httpwwwinvasivespeciesgov

Weedbuster Game httpwwwinvasivespeciesgoveducationweedbustergamepdf

Exotic Species Quiz httpmassbaymiteduexoticSpeciesstudentquizhtml

Tara Reinertson

Save The Bayrsquos San Francisco Bay Watershed Curriculum 173173173173173

BackgroundFrom the Marine Science Institute websitehttpwwwsfbaymsiorgWithin the last 150 years increased numbers ofhumans and increased avenues open to interna-tional shipping have greatly contributed to thedecline of Bay resources One way in which theseresources have been compromised is the replace-ment of native flora and fauna with exotic spe-cies Species introductions can be intentional ornon-intentional Most of the species that havebeen introduced into our Bay during the last 150years were non-intentionally introduced One ofthe most common mechanisms of non-inten-tional introductions is the release of ballast wa-ter carried on ships from foreign ports a practicestill occuring in our Bay today Although newspecies are probably introduced into the Bay allof the time it is the species that are introducedand become established that we need to worryabout

Over the last 140 years over 200 species of non-native aquatic invertebrates have becomeestablished as a part of the San Francisco Bayfauna Most of the fish that presently occur inthe Bay are non-native species One intro-duced species the striped bass is even used asan indicator species to give us informationabout the health of our Bay

Andy Cohen a marine biologist specializing inaquatic species introductions estimates thatone new aquatic species has been introducedinto the Bay every 24 weeks since 1970

Nichols and Patmatmat (1988) stated that acci-dentally introduced species may have thrived inSan Francisco Bay because of the relatively youngage of our Bay and the predominance of a singlehabitat type soft mud throughout the Bay Theyoung age of the Bay may not have allowed adiverse fauna to evolve prior to the introductionof exotic species A single habitat type limitedthe number of niches available in the Bay for spe-cies to invade and diversify

Some of the notable introduced species into SanFrancisco Bay are the Striped Bass Asian ClamEuropean Green Crab Chinese Mitten Crab andthe marsh grass Spartina alterniflora

References Nichols F H and M MPatmatmat 1988 The ecology of the soft-bot-tom benthos of San Francisco Bay a commu-nity profile U S Fish and Wildlife ServiceBiological Report 85 (7-23) 73 ppCohen A 1997 personal communicationUniversity of Calfornia - BerkeleyMonroe M W and J Kelly 1992 State ofthe Estuary San Francisco Estuary ProjectUS Environmental Protection Agency andthe Association of Bay Area GovernmentsOakland CA

TTTTTeacher Peacher Peacher Peacher Peacher Prrrrrocococococedureduredureduredureeeee1 Have students read Alien Invasion Unwel-

come Predator Chinese Mitten Crabrsquos Lifeand History and Crab Invasion

2 Students answer questions in a writtenformat (worksheets provided)

3 Once the students are familiar with theissues lead a class discussion using theldquodiscussionrdquo questions as a starting pointTry to draw out and highlight differentpoints of view Note you may want to leadseparate discussions for the red fox issue andthe mitten crab issue then tie them to-gether at the end

UnUnUnUnUnwwwwwelcome Pelcome Pelcome Pelcome Pelcome Prrrrredaedaedaedaedator ndash Wtor ndash Wtor ndash Wtor ndash Wtor ndash Worksorksorksorksorksheeheeheeheeheet answt answt answt answt answererererersssss1 Why is the non-native red fox such a

formidable predatorAdapts easily to its surroundings lives for eightyears has many pups

2 Name five native species that are eaten bythe red foxSnowy plovers light-footed clapper railsterns western gulls egrets herons Californiaclapper rails


3 What method does the US Fish andwildlife service use to control red foxpopulationsThey trap and euthanize them

4 According to the article which methods ofred fox population control have proven tobe unsuccessful Why were they unsuc-cessfulRelocating foxes transfers the non-native preda-tion problem elsewhere Fences are ineffective incontaining foxes

DiscussionDiscussionDiscussionDiscussionDiscussion1 Why do you think animal rights activists

might oppose the method that is currentlybeing used to control red fox populations

2 How do people make the decision topreserve one species over another

3 Do you believe that humans should betrying to control the red fox populationWhy or why not

CCCCCrab Inrab Inrab Inrab Inrab Invasion ndash Wvasion ndash Wvasion ndash Wvasion ndash Wvasion ndash Worksorksorksorksorksheeheeheeheeheet Answt Answt Answt Answt Answererererersssss1 How might mitten crabs have been

introduced into the bayThey may have been purposely introduced forfishing or they may have been releasedaccidentally in ballast water

2 What do mitten crabs eatPlants and invertebrates (they are omnivorous)

3 What are some of the mitten crabrsquos preda-tors in the BayWhite sturgeon striped bass bullfrogs loonsegrets

4 Why do Mitten Crabs migrate from salt tofresh waterAdult crabs breed in salt water After hatchingthe young mitten crabs migrate to fresh water torear

DiscussionDiscussionDiscussionDiscussionDiscussion1 How is the invasion of the red fox similar

to the invasion of the Chinese mitten crabin the San Francisco Bay How is itdifferent

2 Do you think it is important to control

non-native species in order to protectnative species Why or why not

3 While quite a bit is known about thepossible economic impact of the Chinesemitten crab scientists are still not surewhat the ecological impacts might be Usewhat you have read about the mitten crabrsquoslife cycle feeding habits and migration topredict the effect the mitten crab mighthave on other forms of life in the bay Doesyour prediction show a positive or negativeeffect

4 In the article Crab Invasion the authorstates that neither Dealy nor Tsukimurawould like to allow commercial fishing formitten crabs Why do they feel that wayDo you agree with their opinion Why orwhy not

Dealy and Tsukimura believe that commercialfishing would lead to the further spread ofmitten crabs and that it would be hard todissuade people from fishing for the crabs oncethey become accustomed to doing so

5 How do you think people should deal withthe mitten crab ldquoinvasionrdquo Describe onepossible solution Make sure your solutionaddresses the various economic and ecologi-cal concerns about the mitten crab


INTRODUCTIONINTRODUCTIONINTRODUCTIONINTRODUCTIONINTRODUCTIONYou may have read or heard about problems facingSan Francisco Bay - problems such as pollutionurban development and habitat loss But did youknow that right now at this very moment SanFrancisco Bay is being invaded by aliens Itrsquos true

These aliens did not arrive in a UFO They do notcome from Mars or any far-away universe In factthese aliens are from right here on Earth Inecological terms ldquoaliensrdquo or ldquonon-nativerdquo speciesare animals or plants that do not occur naturally inan area They are plants and animals that have either been brought to an area by hu-mans or have hitchhiked on boats and larger animals

The opposite of a non-native species is a native species A native species is a plant or animal thatdoes occur naturally in an area Ecologists use historical reports museum records naturalhistory surveys and archeological studies to determine which species are native and which arenot

Non-native species are generally harmful to any ecosystem Ecosystems have a delicate balancebetween soil water plants and animals The organisms in an ecosystem are interrelated bycomplicated food webs involving predator and prey Native predators and prey evolve togethereach developing specific traits to aid in survival When a non-native species is introduced intothe mix the delicate balance is thrown off

When a non-native plant or animal is introduced into an already stressed ecosystem it often hasan advantage over native species The ecosystem of the San Francisco Bay has been severelyimpacted by loss of habitat due to the building of roads businesses homes and other develop-ments that drive Californiarsquos economy Because native species are already struggling to survivethey cannot effectively compete with or defend themselves against the non-native species thatare invading the Bay

Researchers have documented more than 200 non-native species that live and reproduce in theBay and it is likely that there are many more that we do not know about Many of the Bayrsquosnative species are now endangered or threatened due in part to the invasion of non-nativespecies Non-native species present some challenging questions for people who are trying topreserve the natural ecosystem of the Bay How do we prevent non-native species from enteringthe Bay How do we control their population Is it ethically right to eliminate an introducedspecies in order to save a native species from extinction These are complex questions that haveno clear-cut answers

Creature Double FeatureNative vs Non-native species in San Francisco Bay

Tara Reinertson


Using what yoursquove read about non-native invasion answer the following questions1 What is a non-native or ldquoalienrdquo species

2 What is a native species

3 How do non-native species enter an area

4 How are non-native species harmful to ecosystems

5 Why are non-native species particularly harmful to native species in the San Francisco Bay



Unwelcome PredatorRead the article ldquoUnwelcome Predatorrdquo by Tracy L Palazzo then answer the followingquestions

1 Why is the non-native red fox such a formidable predator

2 Name five native species that are eaten by the red fox

3 What method does the US Fish and wildlife service use to control red fox populations Whydo you think animal rights activists might oppose the method that is currently being used tocontrol red fox populations

4 According to the article which methods of red fox population control have proven to beunsuccessful Why were they unsuccessful

DiscussionDiscussionDiscussionDiscussionDiscussion1 Why do you think animal rights activists might oppose the method that is currently being used

to control red fox populations

2 How do people make the decision to preserve one species over another

3 Do you believe that humans should be trying to control the red fox population Why or whynot


Crab InvasionRead the articles ldquoChinese Mitten Crabs Life and Historyrdquo by the California Department ofFish and Game and ldquoCrab Invasionrdquo by Dennis Pollock and answer the following questions

1 How might Chinese Mitten Crabs have gotten into the Bay

2 What do mitten crabs eat

3 What are some of the mitten crabrsquos predators in the Bay

4 Why do Mitten Crabs migrate from salt to fresh water

5 What are three negative impacts the Chinese Mitten crab could have on the economy of the Bayarea

DiscussionDiscussionDiscussionDiscussionDiscussion

1 How is the invasion of the red fox similar to the invasion of the Chinese mitten crab in the SanFrancisco Bay How is it different

2 Do you think it is important to control non-native species in order to protectnative species Why or why not


3 While quite a bit is known about the possible economic impact of the Chinesemitten crab scientists are still not sure what the ecological impacts might beUse what you have read about the mitten crabrsquos life cycle feeding habits and migration topredict the effect the mitten crab might have on other forms of life in the bay Does yourprediction show a positive or negative effect

4 In the article Crab Invasion the author states that neither Dealy nor Tsukimura would like toallow commercial fishing for mitten crabs Why do they feel that way Do you agree with theiropinion Why or why not

5 How do you think people should deal with the mitten crab ldquoinvasionrdquo Describe one possiblesolution Make sure your solution addresses the various economic and ecological concerns aboutthe mitten crab

Crab Invasion (continued)


From Life on the Edge A Guide toCaliforniarsquos Endangered NaturalResources Biosystems Books SantaCruz CA and Heyday BooksBerkeley CA 1994 p 183


THE FRESNO BEEJune 1 1999



Chinese Mitten CrabsLife and History

Life History and Background Information on the Chinese Mitten CrabAugust 5 1998

from the California Department of Fish and Gamehttpwww2deltadfgcagovmittencrablife_histhtml

The Chinese mitten crab (Eriocheir sinensis) so named for the densepatches of hairs on the claws of larger juveniles and adults is native to thecoastal rivers and estuaries of the Yellow Sea It was accidentally intro-duced to Germany in the early 1900s and spread to many northern Euro-pean rivers and estuaries In San Francisco Estuary the mitten crab was firstcollected in 1992 by commercial shrimp trawlers in South San Francisco Bayand has spread rapidly throughout the estuary Mitten crabs were firstcollected in San Pablo Bay in fall 1994 Suisun Marsh in February 1996 andthe Delta in September 1996 As of August 1998 the known distribution of theChinese mitten crab extends north of Colusa to Hunterrsquos Creek (nearDelevan National Wildlife Refuge) in the Sacramento River drainage eastto Roseville (Cirby Creek) and eastern San Joaquin County near CalaverasCounty (Mormon Slough and Littlejohns Creek) and south in the San JoaquinRiver to Hiway 165 near San Luis National Wildlife Refuge The most prob-able mechanism of introduction to the estuary was either deliberate re-lease to establish a fishery or accidental release via ballast water In Asiathe mitten crab is a delicacy and crabs have been imported live to marketsin Los Angeles and San Francisco

The mitten crab is catadromous - adults reproduce in salt water and theoffspring migrate to fresh water to rear In the San Francisco Estuary themitten crab probably matures in 2 to 3 years although it reportedly maturesfrom 1 to 5 years elsewhere depending on water temperature Males andfemales grow to a maximum carapace width of approximately 80 mm (3inches) in the estuary Mating and fertilization occurs in late fall and wintergenerally at salinities gt20permil The females carry their eggs until hatching andboth sexes die soon after reproduction A single female can carry 250000 to1 million eggs After hatching larvae are planktonic for approximately 1 to 2

months The small juvenilecrabs settle in salt orbrackish water in latespring and migrate tofreshwater to rear

Young juvenile mittencrabs are found in tidalfreshwater areas andusually burrow in banksand levees between thehigh and low tide marksMitten crabs apparentlydo not burrow as exten-sively in non-tidal areasprobably because theyare not subject to desic-


cation during low tides Older juveniles are found further upstream thanyounger juveniles and in China and Europe they have been reportedseveral hundred miles from the sea We do not understand what cues thisupstream migration although high densities were reportedly a factor inGermany and the upstream migration may be tied to the monsoon seasonin southern China Maturing crabs move from shallow areas to the channelsin late summer and early fall and migrate to salt water in late fall and earlywinter to complete the life cycle

Mitten crabs are adept walkers on land and in their upstream migra-tion they readily move across banks or levees to bypass obstructions suchas dams or weirs In Germany large numbers of mitten crabs were reportedto leave the water at night when they encountered an obstruction andoccasionally wandered the streets and entered houses In Stockton 2 adultmitten crabs climbed over a levee and into a swimming pool when theyencountered a small dam blocking their downstream migration

Mitten crabs are omnivores with juveniles eating mostly vegetationbut preying upon animals especially small invertebrates as they grow Inthe Delta adult crabs have been incidentally caught by anglers using avariety of baits ranging from ghost shrimp to shad Relatively little is knownabout the predators of the mitten crab although white sturgeon stripedbass bullfrogs loons and egrets have been reported to prey upon them inthe estuary We assume that other predatory fishes including largemouthbass and larger sunfishes river otters racoons and other wading birds willconsume mitten crabs

Based on the impacts of mitten crabs in their native range and Europethey pose several possible threats The mitten crab is the secondary inter-mediate host for the Oriental lung fluke with mammals including humans asthe final host Humans become infested by eating raw or poorly cookedmitten crabs However neither the lung fluke nor any of the freshwatersnails that serve as the primary intermediate host for the fluke in Asia havebeen found in the Estuary It has been noted that several species of fresh-water snails which could possibly serve as an intermediate host are presentin the watershed

The burrowing activity of mitten crabs may accelerate the erosion ofbanks and levees In Germany burrows were reported to be up to 50 cm(20 inches) deep and some damage to levees and structures has occurredMitten crab burrow densities as high as 30m2 (27ft2) have been reportedfrom South Bay creeks with most burrows no more than 20-30 cm (8-12inches) deep The highest density of juvenile crabs was approximately 6m2(08ft2) in Suisun Marsh and 1m2 (01ft2) in the Delta in summer 1997 In theDelta large numbers of juvenile mitten crabs were also reported in waterhyacinth which is not found in Suisun Marsh San Francisco Bay or itrsquos tribu-taries

In China and Korea juvenile mitten crabs have been reported todamage rice crops by consuming the young rice shoots and burrowing inthe rice field levees Rice fields in tidally influenced areas apparently aremost subject to damage

The most widely reported economic impact of mitten crabs in Europehas been damage to commercial fishing nets and the catch when thecrabs are caught in high numbers The mitten crab has become a nuisancefor commercial Bay shrimp trawlers in South Bay as it is time consuming toremove the crabs from the nets (one trawler has reported catching over


200 crabs in a single tow several times) Shrimp trawlers have also reportedthat a large catch of mitten crabs damages and even kills the shrimpmaking them unsuitable for the bait market Shrimp trawlers have been ableto move to areas with fewer crabs but as the mitten crab populationgrows this option diminishes

The mitten crab overlaps in dietary and habitat preferences with theintroduced red swamp crayfish (Procambarus clarkii) in South San FranciscoBay creeks and negative interactions between the two species have beenobserved in the field In the Delta the mitten crab may reduce abundanceand growth rates of the introduced signal crayfish (Pacifastacusleniusculus) which supports a commercial fishery

The ecological impact of a large mitten crab population is the leastunderstood of all the potential impacts Although juveniles primarily con-sume vegetation they do prey upon animals especially invertebrates asthey grow A large population of mitten crabs could reduce populations ofnative invertebrates through predation and change the structure of theEstuaryrsquos fresh and brackish water benthic invertebrate communities

In Germany extensive efforts were undertaken by the government inthe 1920s and 1930s to control mitten crab populations in some rivers Con-trol measures often took advantage of the mitten crabrsquos migratory behav-ior traps were placed on the upstream side of dams to capture juvenilecrabs as they migrated upstream At one site as many as 113960 crabswere trapped in a single day It was hypothesized that this populationexplosion may have coincided with a reduction of predators especiallyfishes in the rivers In recent years European mitten crab populations haveapparently been stable although there are occasional reports of ldquoinva-sionsrdquo In 1981 the mitten crab population in the Netherlands increasedsubstantially resulting in serious damage to fishing nets

Information on the impacts of the mitten crab in China and Korea hasbeen more difficult to obtain Although the mitten crab damages rice cropsno control measure have been reported In some rice fields they arecultured with fish Apparently mitten crabs are stocked at a rate that doesnot damage the rice crop

Note It is illegal to import transport or possess live Chinese mitten crabs(Title 14 of the California Code of Regulations) Accidental release or es-cape will spread these crabs to uninfested waters If you keep a mittencrab it must be dead Although there are no bag or size limits methods oftake for marine and inland waters differ


BackgroundFrom the Marine Science Institute websitehttpwwwsfbaymsiorgWithin the last 150 years increased numbers ofhumans and increased avenues open to interna-tional shipping have greatly contributed to thedecline of Bay resources One way in which theseresources have been compromised is the replace-ment of native flora and fauna with exotic spe-cies Species introductions can be intentional ornon-intentional Most of the species that havebeen introduced into our Bay during the last 150years were non-intentionally introduced One ofthe most common mechanisms of non-inten-tional introductions is the release of ballast wa-ter carried on ships from foreign ports a practicestill occuring in our Bay today Although newspecies are probably introduced into the Bay allof the time it is the species that are introducedand become established that we need to worryabout

Over the last 140 years over 200 species of non-native aquatic invertebrates have becomeestablished as a part of the San Francisco Bayfauna Most of the fish that presently occur inthe Bay are non-native species One intro-duced species the striped bass is even used asan indicator species to give us informationabout the health of our Bay

Andy Cohen a marine biologist specializing inaquatic species introductions estimates thatone new aquatic species has been introducedinto the Bay every 24 weeks since 1970

Nichols and Patmatmat (1988) stated that acci-dentally introduced species may have thrived inSan Francisco Bay because of the relatively youngage of our Bay and the predominance of a singlehabitat type soft mud throughout the Bay Theyoung age of the Bay may not have allowed adiverse fauna to evolve prior to the introductionof exotic species A single habitat type limitedthe number of niches available in the Bay for spe-cies to invade and diversify

Some of the notable introduced species into SanFrancisco Bay are the Striped Bass Asian ClamEuropean Green Crab Chinese Mitten Crab andthe marsh grass Spartina alterniflora

References Nichols F H and M MPatmatmat 1988 The ecology of the soft-bot-tom benthos of San Francisco Bay a commu-nity profile U S Fish and Wildlife ServiceBiological Report 85 (7-23) 73 ppCohen A 1997 personal communicationUniversity of Calfornia - BerkeleyMonroe M W and J Kelly 1992 State ofthe Estuary San Francisco Estuary ProjectUS Environmental Protection Agency andthe Association of Bay Area GovernmentsOakland CA

TTTTTeacher Peacher Peacher Peacher Peacher Prrrrrocococococedureduredureduredureeeee1 Have students read Alien Invasion Unwel-

come Predator Chinese Mitten Crabrsquos Lifeand History and Crab Invasion

2 Students answer questions in a writtenformat (worksheets provided)

3 Once the students are familiar with theissues lead a class discussion using theldquodiscussionrdquo questions as a starting pointTry to draw out and highlight differentpoints of view Note you may want to leadseparate discussions for the red fox issue andthe mitten crab issue then tie them to-gether at the end

UnUnUnUnUnwwwwwelcome Pelcome Pelcome Pelcome Pelcome Prrrrredaedaedaedaedator ndash Wtor ndash Wtor ndash Wtor ndash Wtor ndash Worksorksorksorksorksheeheeheeheeheet answt answt answt answt answererererersssss1 Why is the non-native red fox such a

formidable predatorAdapts easily to its surroundings lives for eightyears has many pups

2 Name five native species that are eaten bythe red foxSnowy plovers light-footed clapper railsterns western gulls egrets herons Californiaclapper rails





























Tara Reinertson

























































































Tara Reinertson





























































h93 creature double feature.p65

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