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Virginia Marine Resource Bulletin Sea Grant

Summer 7-1-1996

Marine Resource Bulletin Vol. 28, No. 2 & 3

Virginia Sea Grant

Virginia Institute of Marine Science

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Recommended Citation Virginia Sea Grant and Virginia Institute of Marine Science, "Marine Resource Bulletin Vol. 28, No. 2 & 3" (1996). Virginia Marine Resource Bulletin. 67. https://scholarworks.wm.edu/vimsmrb/67

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DR. L. DONELSON WRIGHT

Dean and Director

Virginia Institute of Marine Science

School of Marine Science

The College of William and Mary

DR. WILLIAM RICKARDS

Director

Virginia College Sea Grant Program

DR. WILLIAM D. DUPAUL

Director

Marine Advisory Services

Summer/Fall1996 Vol 28, No.2 & 3 Contents The Experiment 3 I

Native : Its ComplicatedDemise 4 Oyster Shell Use

Oyster Biology 8 In Some Sort of Regard The Geographical Distribution of C. virginica, C. gigas and C. rivularis

Change,Change, Change Crassostreagigas, Under Scrutiny Mosaics The Plan

RecentPublication

SUSAN C. W A 1ERS, Editor, Writer and Designer KA Y B. STUBBLEFIELD, Graphic Designer

The photographyand illustrationsin the Virginia Marine ResourceBulletin arecopyrighted. Permissionto use artwork must be obtainedfrom the originatorsof the artwork. Artwork credits: cover, IS, 18, Bill Jenkins,Virginia Instituteof Marine Science (VIMS); 4,5,7,9, VIMS archives;pages 8,23, TheAmerican Oy,\'ter:Cra,\'so.\'trea vir~inica, by Paul Galtsoff, U.S. Departmentof the Interior, Fish and Wildlife Service,Bureau of CommercialFisheries (the illustrationson the front cover are also from Galtsoff's book); page 1O,Diana Taylor,VIMS; page 13, SusanC. Waters,Virginia SeaGrant, VIMS; page IS, SusannaMusick; page 16, 17, Lee Larkin, Virginia SeaGrant, VIMS; page20, G. B. Ramusio;page 2, JohnGerard; page22, Dover Publications;back cover, John Tenniel,from Alice:\' Adventuresin Wonderland,1865. The Virginia Marine Resource Bulletin is a publication of Marine Advisory Services of the Virginia Sea Grant College Program which is administered by the Virginia Graduate Marine Science Consortium with members at the College of William and Mary, Old Dominion University, University of Virginia and Virginia Polytechnic Institute and State University. Subscriptions are available without charge upon written request. The Bulletin is intended as an open forum for ideas. The views expressed do not imply endorsement, nor do they necessarily reflect the official position of Sea Grant of the Virginia Institute of Marine Science. Sea Grant is a partnership of university, government and industry focusing on marine research, education and advisory senrice. Nationally, Sea Grant began in 1966 with passage of the Sea Grant Program and College Act.

Cover photo (from top, clockwise): Crassostreavirginica, Crassostrearivularis, Crassostreagigas,

12Virginia's1011Introductions.7 with scientific assistance from the Shellfish Genetics and Breed:ing-Technology Transfer Services at the Haskin Shellfish Research Laboratory, Rutgers University. This issue of the Virginia Marine Resource Bulletin is intencled as an informational tool, to provide an overview of the current situation, and to explain the experiments which will be conducted by the Institute.

......

... r~e status of the native had to filter through a great deal oyster, Crassostrea of non-nutrients (sediments,for virginica, is bleak. In instance)to obtain their suste- less than a century, the Chesa- nance, higher in the peake Bay's abundant resource water column usually had better dwindled to almost non-existent accessto favorable food condi- levels. The Bay bivalve which tions. Becauseof overfishing prompted the oyster wars, the and shell mining,* the oyster bivalve which was so popular reefs of yesteryeardo not exist. that it was shippedas far as Without these structures, it Europe and Australia during the would be difficult for oystersto 19th century--for all practical feed, fight off diseasesand purposesvanished. developa resistanceto patho- The culprit, or culprits? The gens. causeis bandied about, and is Unfortunately, the already usually diplomatically attributed beleagueredoyster population to a combination of overfishing, faced another challenge,in the disease,and environmental form of two pervasivediseases, stress. While it is true that the Perkinsus marinus and resource'sdemise was the result Haplosporidum nelsoni. The of factors, it is probably more diseases,which do not harm accurate to say that one factor humans, causeearly mortality in led to another until it was too the bivalves, leaving few oysters late. to harvest. Environmental conditions during some of the crucial years favored the disease, Overfishing, were years of high salinity in the Disease, Bay. Despite more than 30 years Environmental of diseaseactivity, the native oyster developedneither toler- Stress ance nor absoluteresistance to The ChesapeakeBay, as we the diseases. In diseaseendemic know it now, is far different than it was 30 or more years ago. *Seethe "Oyster Shell Use" article on page 7 for a fewways shells were utilized. Habitat characteristics have changed. At one point in time, the oyster reefs were a promi- On the right: nent topographicalfeature. Even though oysters on or near in former days of plenty. the bottom of the reef may have areas of Virginia, Crassostrea Filter Feeders Not only is an oyster an virginica did not show any excellentfilterer, it is a habitat recovery. In addition, repletion Extraordinaire, creator, providing niches for all programs failed to restore Habitat Creators sorts of life, forms that will feed permanent production to areas someanimals higher in the food lost to disease. An oyster is a filter feeder. chain. Barnacles,sea anemones, Environmental degradation Stationary in its adult life, the fan worms, hookedmussels, causedby the growth in popula- manner in which it obtains oyster spat, cockles,mud crabs, necessary nutrients is by filter- tion and in land use in the skilletfish, gobies,blennies, ChesapeakeBay region further ing them out of the water. At nudibranches,bryozoans, small complicatesthe picture. The the same time an oyster obtains hydroids, sponges,and sea problems are not limited to sustenance, it may filter out squirts are someof the sedimentsand nutrients; many other substances and, depending inhabitors of oyster reefs in the other elements,and sometoxi- on the substance, may concen- ChesapeakeBay. Benthic, or cants, are part of the mix. trate it. This is basic biology, yet bottom dwelling life, is neededin Toxicants are suspectedof it was not until recent times that the Bay to sustain resident or making oysters more susceptible the benefits of the oyster's migratory fish and crustaceans to diseaseat certain stages,and feeding mechanism were more which rely on this part of the may also interfere with growth fully appreciated. It became Bay for food. and survival.** evident, after the oysters had ... In the best of all possible been depleted in the Chesapeake estuarine worlds, there are many Bay, that the bivalves had been a environmental factors-such as substantial player in improving nutrient availability and tem- water quality. A number of perature-which can have an estimates have bee!l quoted impact on the bivalve during any calculating the amount of time it On the right: one life stage. A whole host of would take the 1870s stock and predators are also part of the that, of a few years ago to filter Oyster shells outside system. Crassostreavirginica the Bay. The much quoted figure a shucking house. has beena resilient animal, for filtering potential contrasts a surviving at least 3.5-4 or more capacity to filter the entire If the oysters were million years.*** Yet it may be volume of the of to be used for that too many natural and man- a few days in the 1870s, to reshelling a bed almost a year in the very recent made factors may have consti- (young oystersprefer tuted an overwhelming set of past. Debate exists about the to settle upon adult shells), estimates, yet there is no doubt obstaclesfor the animal's contin- they would be that filtering the Bay today takes ued level of abundancein the loaded onto a barge. much, much longer than before. ChesapeakeBay.

**The exact relationship of pollutants to the onset of diseasein the Virginia oysterhas not beenfully established. In most cases, toxic substancesin low dosesdo not causethe immediate death of an organism. Instead,the substancesmay stressbiota by interfering with normal physiologicalfunctions or by depleting energy or other crucial reserves.Experiments conducted at various times at the Virginia Institute of Marine Scienceindicated that the more the oysterwas stressed,that is exposedto toxins, the more susceptiblethe animal wasto disease. ***C. virginica maybe older than this. While it is found in the Pliocene,some 3.5 to 4 million years ago,occurrences have been locatedelsewhere in the geologicrecord.

The following article summarizes C. irginica grows approximately with it food suspended in the some of the biological aspectsof one inch per year. water: small microscopic plants the , Crassostrea he oysterfeeds by using its and animals (plankton) along virginica. Most of the informa- gill. Small, hairlike projections with other small pieces of or- tion also pertains to the Pacific on he gills called cilia beat and ganic material and microorgan- oyster, Crassostrea giga.~. How- dra water into the shell and isms such as bacteria. The food ever, variations may exist, for als act to expelit. The water material filtered out of the instance, in fecundity levels, pas es through the oyster's circulating water is trapped by sexual maturation, and growth par ially open shell carrying the mucus that is secreted by the rates.-ed. gland cells on the gills. This process is called filter feeding. rvrassostrea virginica Food is transported from the .A is a member of the gills to the mouth as a mucus '-/ phylum Mollusca, class -~m. thread moves /"" Bivalvia. The most obvious ),C, via the cilia. 'j visual feature of the oyster is its ~~. This filtering shell, which is laid down in action is rather growth rings and varies in efficient and \. length dependingon age. .~~ large oysters _00" 0".," /' Elements necessaryfor h. = ._per:- have been II';',... shell construction are l" - "I' 1:"111. known to pump extracted from the water an.- ,,-A-o!" ."""'- g, up to 10.6 and convertedinto shell l.m. I ;, '- ad. m. gallons of water material by the mantle, an T' sh per day through ~- JI ,J#. ~t, .their gills. internal organ. Approxi- '1;~}. . ~ mately 98% of the shell ~ Consequently, material is calcium areas of signifi- carbonate. cant oyster ChesapeakeBay oystersgo -../ abundance, such as oyster reefs \ / through two growth periods per or bars, may :have significant

year, one from April to May and I I I I I I water filtering capacity. 0 .5 a secondafter the fall spawning Centimeters season,sometime in October. Shell growth is somewhat Org ns of C. virginica seenafter the removal of right valve. temperature dependent,as no ad. .-adductor muscle,' an.-anus,' c.g.-cerebral ganglion; f. shell growth occurs in waters -fi sion of two mantle lobes and gills,' g.-gills; h.-heart,' l.m. colder than 40°F. Shell growth -le mantle; l.p.-labial palps; m.-mouth,' per.-pericardium,. r.- ectum,' r.m.-right mantle, sh.-shell; t.-tentacles. The doestake place in summer, but rig t mantle contracted and curled up after the removal of the to a far lesserextent sincethe rig t valve, exposing the gills. Portion of the mantle over the oyster expendsmost of its energy hea region and the pericardial wall were removed. on reproduction at this time. In [llus ation from Paul Galtsoffs book, The American Oyster: Crassostrea vireinica. many placesin ChesapeakeBay, 8

~T a " Oyster Larvae t Oysters are protandrous hermaphro- dites*; they are capable of being either male or '" Spat settle and female, changingfrom attach to the cultch. Oysters one sexto the other at different times during

their life cycle. C. virginica :~:"~::::' usually becomesreproduc- .',.-::

tively viable within a year. f When first mature, the ) Crassostreaspecies usually function as males. Anytime after this and between spawning season,the sex organs of the male transform into functional ovaries. Therefore, by the time an oyster is legally harvestable, i.e. three inches long and ap- is considered a larva. The cilia Spat have been called gregari- proximately three years old, it enables the larva to swim to a ous because of their tendency to has usually made the change limited degree in the water settle in places where there are from male to female. Females column. During the next 15-20 already other newly-settled spat. spawn severaltimes during one days the oyster larva feeds on It is generally believed that seasonwith estimates of fecun- plankton in the water column oyster larvae are induced to dity ranging from 15-115million and searches for an appropriate settle by the release of a chemical eggsper spawn. settling location. The term substance by larger oysters on The Crassostreaspecies "setting" is used to describe the the bottom. This factor, plus the reproduce by expellingeggs and process of settling and attaching observation that oysters prefer a sperm directly into the water to a firm substrate via an ex- hard, stable substrate to set on, column where fertilization creted chemical cement. Larvae is one explanation for the natu- occurs. Within four to six hours that have recently set are called ral propagation of oyster reefs. after fertilization, the embryonic "spat." During this sensitive -The Sea Grant advisory which bivalve has developeda rudimen- time in the animal's life cycle, contained this segment was tary shell and a row of cilia, and many larvae are lost to predation authored by Dave Smith and or inhospitable environmental Michelle Monti. conditions. The Virginia Marine * A true hermaphroditepossesses fully ... Resources Commission estimates functioning male and female sexorgans simultaneously. A potandroushermaph- that, "approximately one of rodite is an animal which changesfrom every three million eggs survive one sexto anothe]~. to become spat." 9 .~pa:wning1 t might seemprosaic to S ationary, an adult oyster is males by their first winter. In marvel at the adaptability of liter lly glued to the bottom or another year they will change ~n oyster to changesin the to 0 her shells in a reef. What, into females. environment since this is a the, about reproduction, and Conclusiveinformation about feature of most, if not all life on the eed to produce prolific the rhyme and reasonbehind an Earth. Yet, it seemsappropriate amo nts of larvae to ensure the oyster's sexchanges, and the sex to at least pausein some sort of exis ence of future generations? ratio when oysters mature does No roblem. Reproduce all at regard. not appearto exist--not exactly. Among animals, a number of once and as broadcast spawners, A few substantial question options exist for growing and rele sing great quantities of eggs marks canbe found in the protecting internal organs. and perm into the water column literature. It may be that local Humans contain an internal conditions, suchas temperature skeleton, which grows along with and food availability, have a the internal organs. Crabs grow bearing on the sex of the animal. by sheddingan outer protective In Paul Galtsoff's encyclopedic shell; in optimal conditions the book on C. virginica he reports new, soft shell will harden that, "In the warmer waters fairly quickly into an of Beaufort, N.C. young armor-like covering. oystersare more apt to Bivalves, suchas oysters, developdirectly into protect internal organs via femalesthan in the an external shell. Growth is northern cold waters of New achievedby the accretion of England." The commonwisdom material secretednear the edge about the oyster is that most of of the shell. the older onesare female. This A substantial external shell so fe tilization can take place.* would make somesense, since provesa successfulstrategy for a The ues for the oysters' syn- the larger animal could produce stationary animal which lives in chro ous spawningare believed far greater amounts of eggs. a highly variable environment. to b a combination of environ- However,exceptions have been Faced with adverseconditions, men al conditions-including reported.

... suchas cold temperatures, low wat r temperature and food . . . salinity, or low dissolvedoxygen, avai ability--conditions which the oyster will closeits shell, would be conducivefor survival. and, if necessary,begin a tempo- S me oyster speciesare *Not all oystersreproduce in exactlythis rary state of hibernation. An her aphroditic and someare fashion. Oysters fall into two categories: eith r male or female, with sex nonincubatoryand incubatory. In the oyster can even live without first case,the eggsare dischargedinto dissolvedoxygen for a few days if cha ges taking place several the water and are fertilized outside the it is able to keepits valves closed. time within the animal's life- female. In the secondcase, the fertiliza- tion takes place in the gill cavity. The Somepredators are evadedby time. In the caseof the Chesa- larvaeare incubatedand dischargedafter the healthy oyster's ability to pe e Bay's C. virginica, oysters they reachan advancedstate of develop- ment. keepits shell securelyclamped are bisexualwhen only a few shut. mon~hsold. They will become

10 ... Crassostrea virginica unfavorable to the establishment one of the most important food The easternoyster's natural of an industry. oysters in many parts of the range is from the Gulf of St. Thousandsof miles away world and is widely cultivated, Lawrence, in Canada,southward from the natural range of the especiallyin Japan, Korea, the to the Gulf of Mexico, Panama, easternoyster, in the middle of west coastof the United States, and the CaribbeanIslands. the Pacific Ocean,the introduc- Canada,and Europe. It also is However, introductions of this tion was successfulin Hawaii. A being produced commercially in popular bivalve to regions large population exists there Brazil, Chile, and Ecuador. outside of its range have been today. persistent in history. Researchersbelieve that the Crassostrea rivularis As early as the mid-19th failure of C. virginica introduc- This bivalve can be found from century, recordsindicate that tions to becomeestablished may the Philippines and Taiwan to attempts were madeto introduce be due to a number of factors, Formosa,Thailand and North the eastern oyster to France. and are mainly site dependent. Borneo. An occasionalspecimen Later in the 19th century, and in The factors range from not high may occur at low tide, but most the 20th, similar efforts to enoughtemperatures for success- seemto have beendredged from introduce the eastern oyster ful spawningand a lack of few to 100 m. Somedebate exists were made in England, Wales, suitable substrate for spat about its classification. It has Ireland, the Netherlands, and settlement, to poor water qual- been placed in Ostrea, Denmark. The populations ity, a want of suitable food, and Crassostreaand under the new failed to becomeestablished. not enougheffort by fishermen genusPlanostrea. Introductions to the Pacific to husbandthe resource. -The last two entries about .Q.. ~ and C. rivularis are derived Coast of North America were Crassostrea gigas from the new, extensive book, Ib.e. slightly more successful. In The is found Eastern Qyster: Crassostrea virginica. produced by the British Columbia, a small throughout much of the world. population still exists. During Sea Grant Program. Seepage 23 for It is located in the Indo-West an overview of the books's contents. the late 1890s, freight trains Pacific, from Pakistan to Japan ... hauled carloads of eastern and Korea, and the Philippine oysters to Washingtonstate; Islands, Borneo,and Sumatra, however,World War I disrupted and alongthe Chinesecoast. It the industry and a red tide killed has beenintroduced into many most of the rest of the popula- counties, including the west tion. Introdu(:ed oysters in coastof Canada,United States, Oregondemonstrated some Mexico, as well as to Chile, reproduction, but ultimately the Korea, Taiwan, New Zealand, bivalve did not becomeestab- Australia, and coastalEuropean lished. For a while, introduc- countries. The Pacific oyster is tions into California had limited commonin shallow protected initial success,but apparently waters in optimal salinities of 23 environmental conditions proved to 28ppt. Crassostreagigas is 1or manyyears the terns were such that seasonal satellite shoppingmalls-and it ~ ChesapeakeBay and runrff was controlled by forest is not difficult to understand the coastallagoons of the covrr and beaverdams, and large magnitude of the forces that Virginia Eastern Shore were influxes of silt laden water or have changedand shapedthe prime growing areas for oysters, freshets were probably rare, even Bay, as the recipient of the clams and other shellfish species in extendedrainfall periods. cumulative impacts of an evolv- of commercialand ecological Wa~erentering the Bay was ing society. Add to this the interest. Within recent memory, clearer with lower nutrient historic developmentof commer- however,there has been a leve;ls.This was probablythe cial marine activity, including significant decline in the shell- casewell after the establishment someof the largest ports in the fish stocks in both locations. In of e rly settlements. Ships' logs world and accessorymainte- developinga plan to reversethis com ent on mariners being able nanceactivity, suchas dredging, trend it is important to under- to s e the bottom of the James and the continually changing stand the long term (recent Riv r. In such an environment, pressuresfor freshwater diver- geologicaland within recorded the liter-feeding activity of sion and control, and the result human settlement) history of the oyst rs and clams would have is an environment that bears region in order to developa bee optimal. little resemblanceto that en- picture of the environment ith time, colonistssettled counteredby the first colonists before human impact. Oysters, m of the ChesapeakeBay only a few hundred years ago. clams, and other mollusks are wat rshed and beganto remove The cumulative impact of human members of a very old lineage the orest coverand develop activity is marked, and changes that is well representedin the agri ulture. Important natural in the ecosystemshould not be fossil record. The Chesapeake floo controls were eliminated viewed with surprise. The once Bay and seasidelagoons as (not bly beaverdams). In clear waters are no longer clear, known today are very geologi- com ination with poor soil and a regime of increasedsilt cally young-approximately ma agementpractices, increased and nutrient loads prevails. 10,000years old. The Bay filled sedi ent runoff was inevitable. Neither is it ideal for filter with sea level rise, conditions Thi processcontinued at an feedingshellfish. Consequently, becamesaltier, and oysters and incr asingpace with urbaniza- it should not be surprising that other mollusks invaded the Bay. tion and use of Bay tributaries as shellfish populations have With increasingsea level, oyster con enient disposalconduits. diminished, even in the absence reefs grew as three dimensional Ima 'ne the progressionto a of diseaseor fishing pressure. structures. The Bay has an wat rshed that is now hometo Against this background of enormouswatershed, extending more than 14 million people-all environmental changethere as far north as New York State. im~ersed in an energyintensive remains the problem of optimiz- Prior to colonial settlement this lifes yle, supportedby intensive ing conditions for growth of region was predominantly fa ing, involved in numerous native shellfish speciesor, forested with a sparsenative ind strial pursuits, with surface alternatively, seekingto restore American population. Dense water infiltration inhibited by the Bay's badly degradedecosys- forests and their complexecosys- resi4ential developmentsand tem using filter feeding shellfish 12 from other g'eographiclocations. support commercially important directly harvestableresource, The importaJtlceof environmen- finfish and crab species.These improving water quality, and tal reparation cannot be under- important food-webinteractions maintaining a diverse and stable scoredenough; without commen- often are underestimatedin foodweb. Unfortunately, four surate and parallel reparative current attempts to "manage" centuries of exploitation and efforts, any attempts to rejuve- finfish and crab stocks on a wholesalemining of the oyster nate shellfish specieshave species-specificbasis. Further, resource,both living and shell limited chanc:esof success. the filtering role of the oyster in (the latter for industrial pur- Why should an attempt be controlling primary productiv- poses),has resulted in the made to restclreor rejuvenate the ity. in ChesapeakeBay should present situation, in which oyster resour,ceof Chesapeake .not be minimized. The calcula- sparsepopulations survive in Bay? An init:ial, and perfectly tions offered by Newell in 1989 disparate, low salinity sanctuar- defensibleres:ponse to this are illuminating-a two order of ies from endemicdiseases as question would probably be magnitude decreasein filtration subtidal crusts of living material becauseit supports a commer- capacitycompared to pre-1870 overlaying a base of reef mate-

cially valuable industry. It can oysterstocks! _Whereasthe pre- rial. Ecologicallyand economi- as well be arglled, however,that 1870 oyster population had the cally, the importance of the direct commercialexploitation is potential to filter all the waters oyster as a cornerstonespecies in of secondaryimportance. of the Bay in approximately ChesapeakeBay likely surpasses Benthic comm.unitiesof Chesa- three days,the present stocks that of the directed fishery. peake Bay in pre-colonialtimes only managethat task in ap- -From the Virginia Institute of were highly influenced by proximately 325-and stocksare Marine Sciencereport to Virginia's intertidal oyster reefs. Oyster still declining. A healthy and General Assembly reefs were important geological substantial oyster stock in ... as well as biological structures. ChesapeakeBay may be a most They supporte!dextensive effective mechanismof simulta- * Primary productionis a term usedto associatedcommunities that, in describethe first level of a food chain. In neously harvesting microplank- an aquatic system,the primary producers turn, provided the baselevels of ton, reducing the impact of are phytoplankton,minute plants. food websthai; eventually excessnutrients, sustaininga

13 experimentsdied from heavy terminated in February of 1994 review of the environ- infections of P. marinus. These after confirmation that someC. ..L~ ..:i.. mental requirements of resrlts demonstratethat C. gigas individuals were mosaics, various oyster speciesaround the gigas can acquireP. marinus that is possessingboth diploid world, the Pacific oyster infections, but there is no and triploid cells (seefootnote). (Crassostreagigas)was chosenas adverseeffect. H. nelsoniproved to be a prob- the specieswhose requirements fhe next stepwas to investi- lem in the Virginia and Mary- reasonablymatched those of the gate the susceptibility of C. land oysters. The maximum lower ChesapeakeBay. Impor- gigas to Haplosporidium nelsoni prevalenceof the diseasewas 84 tantly, the Pacific oyster has no (MSX). Researchershave not percent in the Virginia oysters, significant diseasesin its native been able to infect oysters with and 92 percent in the Maryland range, and it has been resistant thi diseaseunder laboratory controls, with a high proportion to local diseaseswherever it has co ditions.** After appropriate of moderateand heavyinfec- been introduced for aquaculture de ate about the risks and tions. None of the C. gigas were purposes. be efits of a limited introduc- infected. The other oyster The first investigation with C. tio of C. gigas for disease disease,Perkinsus marinus, took gigas involved diseasesusceptibil- ch llenge, the experimentwas its toll amongthe native oyster; ity. If it were as susceptibleto ap roved for the summer,1993. the maximum prevalencewas 96 local diseasesas the native oyster, On y triploid C. gigas were used percent in the Virginia oysters, then it would be of no value to to inimize the risk of spawn- 100 percent in the Maryland aquaculture or to the rehabilita- ing. Two hundred triploid C. controls. C. gigas fared better; tion of the public fishery. Initial gigas and 400C. uirginica P. marinus infected 24 percent of diseasechallenge experiments cot rOI oysters were deployed at the Pacific oysters. A high involved diploids and triploids.* the Virginia Institute of Marine proportion of heavyand moder- C. gigas and C. virginica were Sci nce dock, lower York River, ate infections occurred in the held side-by-sidein quarantine Virginia. The C. uirginica were Virginia and Maryland control flumes and exposedto Perkinsus from the RappahannockRiver groups, but all P. marin us marin us over one summer. In in Virginia, and from Wye River, infections in C. gigas were of low these experiments,64% of the C. Maryland. intensity. Mortality rates among gigas becameinfected with P. Weeklytests were made for the Virginia and Maryland marin us, but all the infections diseasediagnoses and mortality oysterswere of plague-like remained low in intensity and est,mates. The experimentwas dimensions:90 percent. In the there was no disease-associated Pacific oyster, the rate was 25 mortality. All C. virginica in the **The entire life cycle ofH. nelsoni percent and was not attributable is umknown. An intermediate host apparentlyplays a role in the to disease. *Very tersely, with the caseof this transmissionof the disease.If the The growth rate of the Pacific animal, a diploid is sexuallyviable, a intermediate host, or hosts,were oyster was also an aspectof this triploid is sterile. A mosaicpossesses known, it might be possibleto infect both diploid and triploid cells. Whether it oysters in the lab. This is why in- experiment. The C. gigas is able to reproduceis thought to be field testing is a necessityin increasedin size and weight unlikely, but is unknown to date. See determining whetherC. gigas is page16 for a more in-depth explanation. resistant to the disease. during summer, but did not grow

14 during the fall, as expected, Results from this short Because of the short duration of experiment suggestthat the the experiment, no spring Pacific oyster of this size are not growth data w'e available for the susceptibleto the major oyster Pacific oyster. diseasesof the ChesapeakeBay. ... C. giIfas. by Susanna Musick 15

months with mortality less than 15 percent in the presenceof high pressure from both Haplosporidum nelsoniand Perkinsusmarinus.** After two summers of exposure,mortality in this group was 50 percent, much less than the mortality in the other two groups under evaluation. However, 50 percent may be too high for this strain to Measuring shell growth. be given consideration. A related project is being regionally conductedby Rutgers of the Virginia has been part of the VIMS plan University, the University of Institute of Marine to r vive the fishery. This is not Maryland, and VIMS, with Science(VIMS) in the a n w venture. Attempts were support from the National possibleintroduction of a non- ma e in the past. However, at Oceanicand Atmospheric native oyster is not one of policy tha time the oyster fishery was Administration. This breeding making. Rather, VIMS' role is to stiI viable, even if sometimes program will utilize H. nelsoni- provide a science-basedfounda- ma ginally, and support for the resistant oystersdeveloped by tion from which decisionscan be pri r programs was minimal. Rutgers and the Delaware Bay most ten years ago, a new made by state agenciesand strain that is apparently resis- sele tive breeding program legislative entities. tant to both H. nelsoni and P. Even though researchersare beg n at VIMS, with funding marinus. Diseaseresistant testing a non-native species,they fro the Virginia Sea Grant oysters still becomeinfected with have not given up on the native Col ege Program until 1992. A the parasites,but intensity oysters, Crassostreavirginica. nu ber of strains have been remains low and mortality is The intention is not to outright eva uated and discarded because greatly reduced. supplant the local bivalve. of igh mortality. Presently, A central question in the test Instead, in light of the oyster's thr e strains are being exam- plan is resistanceto disease. The economicand ecologicalimpor- ine , and one, a third generation tests will compareresults be- tance to the ChesapeakeBay Del ware Bay oyster,* shows tween the diseaseresistant region, scientists are exploring pro ise. The Delaware Bay strains of the native oyster and severalresearch avenues. str in reached market size in 18 the non-native species. Three Selectivebreeding of the native oyster, that is crossing the*Th ~ ameDelaware as the Baynative oysterbivalve. is obviouslyIt is just **The diseasescan not be transmitted to animals with disease-resistant fou d in a different location and is humans. They are harmful to oysters traits for stronger individuals, con idered a different strain. alone. 18 strains of the species Crassostrea gigas, and the species Crassostrea rl:vularis will be tested for the:ir resemblance to the native species as reef-form- ing species which are tolerant of mid- to sub-tropical latitude and high stress environments, and are resistant 1;0Chesapeake Bay diseases. The purpol~e of the plan is to first screen for the candidate species most likely to succeed in the local estuarine environment. Second, the results from the tests will enable an assessment of environmentaJ risk. That is, the geographic range of likely reproductive success will be estimated. Quarantined, hatchery-raised progeny from imported brood stock will be used. This last procedure ensures that the Commission and which would be duction of non-native species offspring are Jree of parasites conducted by VIMS. if introduced in substantial and disease which the parent numbers. may have carried. ..;0 A series of comparative ~ Upon review, and ifaddi- To the extent possible, all studies in laboratory quaran- tional tests are neededto field tests will utilize natural tine to evaluate larval and settle ambiguities, limited in- triploid stockElof the non-native post-settlement response to a water testing of diploid species.*** OLlrrent results range of environmental hatchery-rearedstock with indicate that 1;hisstrategy conditions. small lots under secure minimizes ris]k.sfor reproductive ..;0 A series offield challenges, conditions. capacity. As ,veIl, utilization of under secured conditions, of Specifically, eachspecies will triploid stockElin field challenge native oysters and triploid be examinedfor the follow- allows testing under a range of non-native species to com- ing qualities: more natural conditions not pare disease resistance, ~ Growth rate and longevity available in a laboratory setting. growth characteristics, and comparableto the native, For example, researchers have susceptibility to invasion of ChesapeakeBay species. been unable tI:>infect oysters macro organisms under a ~ Resistanceto endemic with H. nelsoni in a laboratory. range of environmental disease. The follow:ing constitutes the conditions. ~ Growth and survival in local strategy whic]tt was approved by ..;0 Evaluation of the likely conditions of temperature, the Virginia Marine Resources success of candidate species salinity, and su,spended and an assessment of likely sediments. ***Triploidy is e1:plainedin depth on geographic range of repro- page16. {Continuedon Page22. ..J 19 t is fairly modern thinking norm, and not just on continents. were at a premium. Explorers to question the introduc- Even Iislands, including the then collectingplants were often held -' of a plant or animal. remote Pacific islands, were not in high regard for their "discov- Right or wrong, introductions left untouched. Sailors oftentimes eries" could be crucial to a have been an important part of left ahimals with the assumption country or a region. Example: in human history. Many of the that ~he animals would proliferate the 1870s,Henry Wickham species we associate with a and ~rovide food for their, or smuggled70,000 rubber seeds country, or part of a country, anotHer sailor's next visit. out of the Amazon. Theseseeds originated elsewhere. In fact, It wasn't until the last half of were germinated in England, the foundation of the U.S.'s the 2()th century that introduc- transported to Ceylonwhere food base is made up of non- tions Iwere sometimes viewed they becamethe basis of the indigenous crops and live- ask~ce. Unexpected results southeastAsia rubber industry. stock-in the form of soybeans, undermined confidence in even In a fairly short time, the south- wheat, and cattle. At least man8ged introductions. Kudzu is eastAsia industry would supply 4,500* species of foreign origin a prime example. A vine native to 90 percent of the world's natural have established populations Japan, kudzu literally took over rubber. The advent and popu- within the United States, landscapes in the South. Some- larity of the automobile made according to the federal Office times the introductions were rubber, until a synthetic was of Technology Assessment. virtu~l escapeesfrom human found, a valuable commodity. The re-inventing of the culti'jation; loosestrife, an attrac- How valuable? The World War natural ecosystem started early tive nursery plant, ended up a II war machine was highly in the New World. When major wetland weed. In recent dependenton rubber for its colonists arrived, they brought history, a disastrous introduction vehicles. When the Japanese the plants and animals they arrived in the Great Lakes via conqueredsoutheast Asia, the knew, with full intentions of ballast water: zebra mussels. In United Stateswas cut off from establishing these life forms in an amazingly short time, the 98 percent of its rubber source. their new home. World-wide, bivalve spread, wreaking expen- The race to find a synthetic this type of behavior was the sive damage as it colonized. substanceintensified.

"Man has literally rem,ade the green face of *This numberincludes plants, terrestrial the ~arth." vertebrates,insects and arachnids,fish, -Melville Bell Grosvenor mollusks,and plant pathogens.Insects and arachnids (spiders,scorpion, mites, ticks), and plants predominate,each It was not an exaggeration accountingfor approximately2,000. Manyunintended plant introductions whe~ Grosvenormade that wereliteral escapeesfrom cultivated state~ent almost 40 years ago in a gardens. book about plant discoveryand An exhaustivestudy of the introduc- tion and spreadof harmful non- introductions. Worldwide, the indigenousspecies in the U.S. was exte~t of introductions is over- conductedby the TechnologyAssessment Board of the 103rd Congress.The book, whelming. Beforethe widespread Ear of corn,from G. B. Ramusio, Harmful Non-IndigenousSpecies in the manufacture and use of synthetic Navigationi et Viaggi, Venice,1556. United States(OT A-F -565) was pub- materials, somenatural materials lished in 1993. 20 Non-Inten.tional, danger of non-indigenousorgan- intentional introductions have Intentionau isms has increased,little thought been recognized in the scientific Introductilons is given, by at least a good community and were suggested portion of the generalpublic, to as guidelines when the introduc- Increasingly, the general the spreadof non-indigenous tion of Crassostrea gigas was public seems 1;0make little speciesfrom one area to another first proposed in Virginia. distinction between different within the United States. Ac- Very briefly, the protocol types of introductions. Instead, cordingto the federal Office of requires the following: there is a per(:eption that they all TechnologyAssessment, "The .a clear rationale for intro- are detrimental. Perhaps this is current popular interest in duction; due to the n01;oriety of some non- 'wildflowers' for ornament~l .selection of candidate species, intentional, harmful introduc- usesand 'native grasses'for including a consideration of tions like the zebra mussel. In livestockand wildlife forage may associated pests, parasites and actuality, introductions should inadvertently be fueling wide- diseases; fall into two categories: inten- spreadplants of non-indigenous .testing, utilizing quarantine tional and nol:l-intentional. Both speciesin natural and semi- systems, before a decision to kinds have rel~ulted in good and natural areas." Even if an proceed with introduction; harm. This is because our introduction is not overt, organ- and, understanding of ecosystems, isms can find ingenious path- .introduction using quarantine and of the potential to upset a ways. Take the garlic mustard, procedures and monitoring system by intJroducing or remov- first reported in 1918 in Illinois. after release to provide data ing a species, is relatively new. Via flood waters, mowers,trains, for subsequent considerations Plus, never bE~forein human cars, and on the boots, clothes for introductions. history have distances been so and hair of hikers, the weed To ensure that fellow travel- short. World transportation is madeits way across42 counties ers-that is, pests, parasites and constant and ,often rapid, open- in Illinois. Boats,vans, and diseases-are not brought into ing new, and sometimes unsus- motor homescan be vectors for the Bay, the parents will be pected avenuE!s. Who would have organisms,too. destroyed. Only offspring will be ever thought 1;hatthe Asian tiger used in the experiments. Also, mosquito would arrive in the International when researchers perform the U.S. via a containerized ship- Guidelines for Marine initial in-field testing, sterile ment of used 1;ires? The insect, a Non-Indigenous Species animals will be used to eliminate carrier of denjsue fever and the possibility of an uninten- encephalitis, breeds in small, The International Council for tional introduction. protected pooJlsof water, the the Exploration of the Seas kind that can form inside tires. (ICES) developeda "code of Today, a ruumber of national practice" to reducethe risks 'The apples of and international agencies are associatedwith marine non- love' (the tomato plant), involved in the process of indigenousspecies. The ICES from John planned introlductions, and in Working Group on Introductions Gerard, 11le. the preventiol:l of harmful non- and Transfers of Marine Organ- Herball of generall indigenous in1~roductions. Now isms works in an advisory historie of it requires ext;ensive research capacitywith the country consid- lliantes. London, 1633. and planning for an intentional ering an introduction. The introduction. Ironically, while guidelinesdeveloped by the ICES the awareness of the potential Working Group pertaining to 21 Introductions, A Global Phenomena

The following is a short, short list of some plant origins-meant to give an idea of how global introductions have been historically. The list representsthe common knowledge about origins and does not reflect any recent scientific or archeological findings. Also, a plant might occur naturally in two areas, but the introduction is from a specific place.

Brazil-rubber, pineapple (the pineapple is not native to Hawaii) Mexico-poinsettia, zinnia The Americas-sweet potato, potato, maize, common bean, lima bean, tomato, garden peppers, tobacco Africa-geranium, okra, gladiolus, African violet, coffee (through the Arabian port of Mocha) Asia Minor-tulip Persia (and to a far lesser extent India)-muskmelon Afghanistan (and adjacent areas)-carrot India-.:.--cucumber,eggplant, cowpea (the last, the cowpea, came to the Americas through Africa aboard slave ships) Southern Asia-banana Northern Burma (and possibly easternIndia)-lemon, lime China-chrysanthemum, camellia, clematis, azalea, rhododendron (the last two were also in the New World), hollyhock, forsythia, peach, apricot, orange (the last also in Indochina) Japan-wisteria Australia -strawflowers

The Plan. (Contulued from Page 19.) Whether or not a non- deliver that information to the native species should be intro- governmental groups which .30 Ability to reproduce in local duce"dto Bay waters on a large oversee fishery regulations and waters (this indicates that scale is for policy makers to natural resources in the Com- they would develop self- decide. VIMS will conduct the monwealth. sustaining populations). science and evaluate risks, and . . . .30 Lack of ability to reproduce in local waters (this would be an advantage if it were determined that a non- native oyster would be used, but only in hatcheries. .30 Reef-forming habits (the ability to form reefs would be necessary in the Chesa- peake Bay). .30 Lower susceptibility to predators. .30 Suitability as a commercial product.

22

... The Eastern Oyster: Crassostrea... v~rg~n~ca

Albert F. Eble, Victor S. Kennedyand RogerI.E. Newell, editors $95.00

This comprehensivevolume of Mechanisms;Culture: Applica- researchon many aspectsof the tion; Transfers and World-Wide eastern oyster was published by Introductions; and Management Maryland Sea Grant Collegein of Natural Populations. July 1996. The book is aimed at the specialist,but should be of This book can be ordered from value to scientists, managersand the Maryland Sea Grant Pro- commercialaquaculturists. gram, 0112 Skinner Hall, Uni- Chapters in the book include: A versity of Maryland, College Catalogueof SelectedSpecies of Park, Maryland 20742. Living Oysters (Ostracea); GeneralAnatomy; The Shell and Ligament; Adductor and Mantle Musculature; Mechanismsand Physiologyof Larval and Adult Feeding; Digestion and Nutrition of Larvae and Adults; the Circu- latory System;Hemocytes: Form and Function; Reproductionand Early Development;Larval Biology; Biochemicaland Popu- lation Genetics;Cytogenetics and Evolution; Environmental Factors: Responseto Metals; The Bioaccumulationand Biological Effects of Lipophilic Organic Contaminants; Predators and Pests;Diseases and Defense Oysters, long part of human fare, appear in all sorts of art forms, from painting to poetry. Lewis Carroll's oysters fell prey to the fast-talking Walrus, a character who. along with the Carpenter, lured the bivalves away from the oyster bed only to feast upon them. -Drawing by John Tenniel, from Alice'sAdventures in Wonderland,1865.

"0 Oysters,come and walk with us!" The Walrus did beseech. '~ pleasant walk, a pleasant talk, Alon~c the briny beach. .."-Lewis CalToll

Sea Grant Communications NONPROFITORGANIZATION US POSTAGEPAID Virginia Institute of Marine Science GLOU.PT.. VA 23062 PERMITNUMBER 6 PO Box 1346 Gloucester Point, Virginia 23062

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