Table Of ContentREPORTS ON RESEARCH FROM THE WOODS HOLE OCEANOGRAPHIC INSTITUTION
Vol. 39. No. 1 • Spring/Summer 1996 • ISSN (1029-8182
Marine
Biodiversity
II
—
Biodiversity & the World Ocean
Comments from the Editor
As Earth's human population grows and its environments. It included an update on marine mam-
activities profoundly affect the planet's diver- mal biodiversity and tookus to the deep sea, where
sityofanimal life, it is important to considerthe sediment samples collected in the 1980s revealed that
significance ofbiodiversity and howwevalue it. These this habitat may rival tropical rainforests in the numbers
are not easyjudgements. Sheerdiversity itselfmaybe of ofspecies present. Ourauthors also described new mo-
inestimablevalue as a foundation for a healthyplanet leculartechniquesthatofferpowerful tools for probing
and human well-being. Manyecologists nowbelieve that biodiversity, discussed howscientists go about estimat-
richly diverse ecosystems are more resilient and better ingdiversity, and described a national research agenda
able to recoverfrom such stresses as drought or human- on marine biodiversitydrawn up by aspecial National
induced habitat destruction than less diversesystems. Research Council Ocean Sciences Board committee.
Somedescribe biodiversityas nature's insurance policy This issue's authors continue the Marine Biodiversity
against catastrophe, because greater diversity offers a theme by offering a lookat the myriad forms ofphy-
range ofpathways forprimaryproduction and ecological toplankton and zooplankton and atthesaltmarsh habi-
—
processes such as nutrient recycling ifone pathway is tat, and introducingtaxonomists, those important
damaged ordestroyed, alternatives are available to allow people who undertake species description.
the ecosystem to continue functioning at its usual level. The Biodiveritysidebars and thesecond section,
The human activities that most affect biodiversity called "WHOI and theWorld Ocean," offeryou a peek
coastal development, logging, transport ofspecies from into the laboratories oftheWoods Hole Oceanographic
—
one habitatto another in ships' ballasttanks are Institution (WHOI). The authors discuss awidevariety
unlikelyto stop. Butwe can think aboutwhatwe do, ofoceanographic topics that range from robots to fish
and we can make some choices. We can learn more feedingbehaviorand air-sea interaction to sound recep-
about the great web oflife and its interconnectedness tion in seals. Geographically, the articles range from
in orderto make wisechoices. Earth would be a lonely Block Island Sound to the the Arabian Sea and thewest-
place for humans without a bird call, the hope ofsee- ern equatorial Pacific.
ing a fish jump, or just knowing that elephants and At anygiven time, there aresome 350 research
tigers still roam free (tigers only in Asia, not in Africa projects underwayatWHOI as each scientistpushesthe
as we mistakenly suggested in the introduction to the marine frontier, describingan organism that is newto
—
last issue thanks to the sharp-eyed readerwho human knowledge, elucidatinga puzzlingprocess, or
pointed out ourerror!). developinga new research technique. Theytravel the
This issue ofOceanus continues ourcelebration ofthe world to work aboard the research vessels ofthe United
sea's wonderful diversityoflife. Marine Biodiversity I States and othercountries, attend international meet-
(Vol. 38, No. 2) discussed new insights on marine bacte- ings, andworkwith colleagues on today's majormarine
rial diversityand on midwateranimals that live in avast, questions. Heretheyshare theirworkwith you.
stable habitatthat is one ofourplanet's least explored —Vicky CuUcn
Oceamisispublishedsemi-annuallybytheWoodsHoleOceanographicInstitution,WoodsHole,MA02543.508-289-3516.http://www.whoi.edu/oceanus
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Oceanus
REPORTS ON RESEARCH FROM THE WOODS HOLE OCEANOGRAPHIC INSTITUTION
Vol. 39, No. 1 • Spring/Summer 1996 • ISSN 0029-8182
DielVertical Migration inZooplankton 19
ByStephenM. Bollens
ABEMakesFirstScienceDivestoStudyMagneticAnomalies
AnAB(L)EBodiedVehicleProvesItsWorth 20
ByDanaR. Yaerger, AlbertM. Bradley, andBarrieB. Walden
From theBeginning: MonitoringChangein aYoungLava Flow 21
ByMaimceA. Twey
MarineGcophysicistsStudyShallowandDeepContours
ScientistsStudyStorm & Human Effeasin BlockIslandSound 22
ByNealDnscoll
Volcanoes, Earthquakes, & Mountain BuildingUndertheAtlantic 23
ByHanLin
ScientistsRangetheWorldToStudyOceanPhysics
ChangingWinds&Ocean Mi.xing:TheArabianSeaMonsoon 24
ByKennethH. BrinkandFrankBahr
NewFindingsOnTheWestern Equatorial Pacific'sWarm Pool 25
ByStevenP.AndersonandRobertA. Weller
BobberFloatsMeasureCurrents'VerticalComponent 26
BylamesF. Price
Air-SeaInteractionStudiesEmployUniqueVesselFLIP
ImprovingWeatherForecastswith BetterMarineMeasurements 27
BylamesB Edson
ExperimentComparesDirectJS RadarMeasurementsofInternalWaves 28
ByErikI. Bock
Marin ChemistsExamineSurfaceExchangeRates&Sediments
£j£]i7ij'::ii7
RadionuclideStudiesIndicatean HistoricallyHardy"ConveyorBelt" 29
ByRogerFrancois, Ein-Fen Yii, andMichaelBacon
PBohxyets,opSplhaenrkest,onSpiBrialosd,iavnerdsSiutnybursts•* EsrimaringAir-SeaGasExchangewithSatelliteDataMethod .., 30
ByNelsonM. Frew
ByAnyuM. Wane
LifeCyclesandPopulation Dynamics .x^jf^^^l
Protozoan Grazers
ByHalCaswell
MayInfluencetheBiologicalAvailabilityofIron
HowASealHearstheWorld
\amei W, MoffettandKathenneA. Barheau
ByPeterTyack
Zooplankton Diversity A-USailsOffintotheSunset InsideBackCover
A Bizarre—andChanging—ArrayofLifeForms
ByCabellS. Dam, CarinI.Ashjian, andPhilipAlatalo
GulfofMaine Physics
LinkingLargeandSmallMarineAnimals
ByAn W. Epstein
Measuring Diversity ofPlanktonic Larvae 12 1930
Catch'Em(andIdentify'Em) IfYouCan Editor: VickyCullen • Designer: Jim Canavan
ByElizabethD. GarlandandCherylAnnButman
Woods Hole Oceanographic Institution
Salt Marshes 13
RobertB.Gagosian,Director
TheyOfferDiversityofHabitat FrankV.Snyder,ChairmanoftheBoardofTrustees
ByJohnM. Teal lamesM.Clark,PresidentoftheCorporauon
DescribingDiversity 16 RobertD. Harrington, If.,PresidentoftheAssociates
TooManyUev/Species,TooFev^'Taxonomists WoodsHoleOceanographicInstitution
ByRudolfs.Scheltema isanEqualEmploymentOpportunityandAffirmativeActionEmployer
OCEANUS
'
Phytoplankton Biodiversity
Boxes, Spheres, Spirals, and Sunbursts
Ecosystems, like well-madeairplanes, tend to have redundantsidisystemsandother "design"features thatpermit
them tocontinuefunctioningafterabsorbinga certain amountofabuse. A dozen rivets, ora dozen species, might never
be missed. On theotherhand, a thirteenth rivetpoppedfrom a windflap, ortheextinction ofa keyspecies involved in
thelyclingofnitrogen, could lead to a seriousaccident.—Ehrlich and Ehrlich, 1981
Anya M. Waite protozoans thatpull individual picoplankton
1992-94 Postdoctoral Scholar, 1994-95 Postdoctoral Fellow into theirhairymouths, to crustacean copepods
Slip a drop ofseawaterundera simple light and larval fish thatcan bite through whole chains
microscope, andthediversityofmarine and clusters ofultra-phytoplankton.
phytoplankton is spectacular: Thousands The keyto the overwhelmingdiversityof
oftinyboxes, spheres, spirals, and sunbursts float marine phytoplankton may be the highlyvari-
orswim by, packed with brightgreen able marine environment inwhich they live.
and brown pigments analogous to Phytoplankton have responded in dozens of
those found in land plants. These are, \\\ differentways overevolutionary time to
literally, the "plant" plankton, thebase .tlternatingpatches ofvigorous ocean
V ofthe oceanic food chain and prey forthe mixing and calm waters, to the patchy
innumerable small animal plankton that abundance ofpredators, and to chang-
Thethree ^^
watercolor ^k V _ cruise the coastal ocean to feed. Each phy- ingvertical gradients in tlie light intensityand
J^^^
illustrationson toplankter is a single cell thatgrows and nutrients they need forgrowth. Each species has
^B^B
thispageshow divides into two new cells, eventually capitalized on different combinations ofthese
someofthewon- ^Pi^ populatingwhole sectors oftheworld factors, selectingauniqueshape, size, and physi-
dedrifaultosmhsapeexshitbihta.t ocean. They range in size from the ultra- ologyto maintain survival. Some phytoplankton
Theyare normally phytoplankton, about one-tenth ofa millimeter can be extremely flexible in their response to the
visibleonlyunder in diameter, down to the pico-plankton that are environment, developingtolerance to a wide
a microscope. thousands oftimes smaller.Theirpredators in- range ofpossible habitats, while others' require-
clude every herbivore, from small, cup-shaped ments are highlyspecific. The result is an enor-
mouslydiversespecies assemblage.
The logical outcome ofthis is that anychanges
in the ocean that create uniform conditions
acrosswideareas, includingheavy nutrient in-
puts from sewage orlarge-scale industrial pollu-
tion, can potentiallyreduce the diversity ofspe-
cieswithin them.The Ehrlichs tell us in Extinction
that a rich biodiversity increases the abilityof
ecosystems to respond to, and recoverfrom, such
stresses. Essentially, we depend on high
biodiversityfor protection from extreme biologi-
cal responses to external forces, including pollu-
tion, overfishing, and global warming. But our
understandingofexactly howthese responses
occur is rudimentary atbest. Our intuitive grasp
ofthe ecologyofmarinespecies is often poor
compared to ourfeel formore familiarterrestrial
RestingcystsofthetoxicdinoflagellateAlexaiulriuin tamarense.Thesedormant
cellsoverwinterinthesedimentlikeseeds, germinatingaswaterswarm to pro- •rhrlich.PR,andEhrlich,AH. 1981.Evlimtitin.ThecMisesandconse-
videtheinoculumfor "red tide" blooms.Theymeasureabout30 by50 microns. ijuencesoftheduappearanceofspecies. RandomHouse,NewYork.
SPRING/SUMMER 1996
A mid-ocean phytoplankton sampleshows thediversity in form that typifiesoceanic regions.The largecell in thecenterisadinoflagellate,
about 80 microns long, in thegenusOrnUocenis (ornitho=bird, cercus=tail).The largeappendagesmayactas flotationdevicesormayin-
creasecell surfaceareatoenhance nutrientuptake.
systems, and phytoplankton's tinysize com- Dinoflagellates have a unique \
pounds the problem. form ofhighlyabundant DNA that
However, as soon aswe begin to explore remains condensed into chromosomes
how different phytoplanklon species have Y^ throughout theircell cycle. Some
adapted to theirenvironment, we can see 1 l^W species form a pigmented structure
how intricatelythese organisms are "> I ^N,^^ thatis almostthe perfect analogof
—
caught up in the global scale ofthe \ a human eye—but thousands of
marine ecosystem. These adaptation times smaller formed within a single
differences are typified bytwo ofthe ^^-^cell.There arespecies ofdinoflagellates
majorgroups oflarge ultra-phytoplankton, that are partiallyorwholly herbivorous,
the dinoflagellates and the diatoms, which sometimes actuallyeatingother phytoplankton
haveeach adapted verydifferentlyto ocean dy- manytimes theirsize byimpalingthem, envelop-
namics. Dinoflagellates are one ofthe mostun- ingthem in a membrane, and siphoning
usual groups in theworld ocean. Up to one-fifth outthe contents. v
ofa millimeterin diameter, with a membrane- Mostfamous ofthedinos arethespecies
covered organic shell, theysport a pairofbeatinj that gather in high densities at the surfaceto
tlagella that make them twistand spin as they form what is known as a "red tide." Manyof Tchhaersaectserhiaspteiscaorfedi-
move. "Dinos" prefercalmwaterwhere these red tide species are known tor their potent noflagellates. Note
they can gather at the surface to photo- toxins, which can become concentrated when theflagella.
synthesize in bright sunshine and then theyare eaten by filter-feedingshellfish,
plunge down to imbibe the rich nutri- eventuallypoisoning human consumers 1 millimelerequals
ent cocktail available in deeperwaters. as (forexample) Paralytic Shellfish one-thousandthofa
meter(.03937inch)
Though mostlysolitary, dinos can form Poisoning, or PSP.
chains ofcells that swim as a unit, their Such spectacular and lethal events o1nmei-ctrhoonuseaqnudatlhsofa
longitudinal flagella beating in tandem. do not characterize all species ot di- millimeter
OCEANUS
noflagellates, but monitoring their occur- access, to understand more fully how
rence on a global basis gives us clues as large pulses ofproduction occurred
to how these ciiverse organisms move in the past. Understanding how
around the world in response to '.W differentspecies react to chang-
changes in the marine environ- < ^ ingclimaticconditions, how
ment. Some scientists suggestthat \' theyare transported to the
the frequency and intensity ofred A /". seafloor, and what factors
^
tides are increasingworldwide, and govern theirpreservation in
'f\
it is becoming more and more im- *" 4P ^'^ a'' the sediments are critical for
portant to understand and ^ '^ ^ the reconstruction ofEarth's
—
monitorthe dynamics of climate history and thus for
individual species. The in- predictions ofglobal climate change.
crease in red tides is cited as Forexample, scientists use the chemical compo-
evidence for an increase in coastal pollution, sition oforganisms found in sediments to make
since calm, nitrogen-rich waters are ideal for estimates ofthe carbon dioxide concentrations
dinos' growth. In addition, the recent appear- thatexisted thousands ofyears ago. Recent work
ance ofnorthern species in southern waters by lack BaldaufatTexasA & M Universityhigh-
highlights the necessity ofmonitoring ship bal- lights how mass sedimentation ofdiatoms can
last water for the errant phytoplankton actuallydisrupt the sedimentary fossil record,
species that can be transported thou- insertinglarge matsofdiatoms between the
sands ofmiles and emptied into foreign more regular layers ofsediment. Heated debate
harbors to find new habitat. Even a also continues on exactlywhat source ofcarbon
quickevaluation ofdinoflagellate ecol- phytoplanktonuse forgrowth. Different carbon
ogy leads us to the conclusion that un- sources can radicallyalter how the chemical
derstanding their biodiversity is ofim- makeup ofphytoplankton is related to the car-
mense practical importance. bon dioxideconcentration ofthe ocean in which
The diatoms are anothersort oforganism theygrow. Thus back-calculatingto reconstruct
Coccolithophores altogether. With their heavyglass shells (called Earth's ancientclimate becomes a complicated
aresingle-celled frustules), diatoms can sinkquicklyoutofthe matter indeed. Work attheAlfredWegener Insti-
pwlaalnltssawrehoesmebecdel-l surface layeronce they have used up all the avail tute in Bremerhaven, Germany, by UlfRiebesell,
ded with small cal- able nutrients, waiting in dark cool waterto be suggests that different—diatoms actually use dif-
careousplatesor mixed upward again, in some cases ferentcarbon sources with an enormous poten-
coccoliths.These on an annual cycle. Diatoms tial impact on the sort ofsignature the cells
are magnified
about4,000times. generally depend on vertical preserve. The species diversity ofdiatoms has
mixingto reach the ocean also changed overthe ages, and these
,
surface again, and keep them- changes themselves mayyield clues as to how
selves there onlywhen condi- the upperocean has changed overthe ages.
tions are favorable to their But as it turns out, the tools scientistsuseto
growth, by pumpingan internal determine species composition are only now
vacuole full ofsubstances lighter reaching a stage wherewe can fully understand
than seawater. During favorable periods, they how individual species evolve and how they are
maximize theirgrowth rates to optimize the related to one another.
limited time theyspend at the surface, and can Diatoms' dependence on ocean mixingto
reach high densities, especially in the springtime reach the surface has led them to develop a wild
coastal ocean. Some predators depend entirely assortment ofmorphologies to catch the cur-
on this early springbloom as a food source, and rents, rhis allowed scientists initially to describe
the timingofthe bloom can influence the sur- thousands oflivingdiatom species and catego-
vival oflarval fish and copepods critical forthe rize them in a frameworkthat identifies how
nextyear's productivity. Once theysink to the each species is related to another based on their
seafloor, diatoms can become food for inverte- morphology alone.The frustule itselfcan be
brates that in turn feed everything from fish to fantastically ornate, covered in patterned ridges
graywhales. When diatoms reach the bottom in and pores in geometric designs. One group, the
such numbers that theycannot all be eaten, they Chaetoceros species (see illustration above head-
accumulate in ocean sediment layers, leaving a line on page 2), are known for the formation of
record oftheir pulse ofproductivity forthou- enormous glass spines with sharp triangular
sands ofyears. With them is preserved a chemi- barbs extendingout from theirfrustules. In nu-
Photoscourtesy cal signature that can tell scientists a great deal merous species, many cells adhere to one an-
DonAnderson.
about how the phytoplankton grew. other, forming longchains and clusters. Chains
Illustrationsby
E.PaulOberlander. It is this record that paleoceanographers tryto can takeon a spiral form, be elongated and flex-
SPRING/SUMMER 1996
ibie, orentirely rigid. Some clusters are spherical species, and indeed, identifying important spe-
and held togetherwith a dense mucus that fills cies both morphologicallyand with DNA finger-
the spaces between the cells. printing, will be critical to a betterunderstanding
Recently however it has become clear that ofsuch global processes.
classifyingsuch organisms on the basis ofmor- Anyn WaitecompleteiiherWHOlpcstdoctcratappointments in
phologyalone can be misleading. The definition September1995andtookapositionasReiearch Fellowatthe
ofa specieswas originallydeveloped for land SchoolofBiologicalSciences in Wellington, NZ. Heroceano-
mammals forwhom that definition ofa species graphicwanderings havetaken hertothecoastsofAustralia,
holds fairlywell (verygenerally, anytwo animals Canada, Spain, Germany, Chile, the US, andmostrecently
NewZealand. Inaddition toworkinginscience, shehaspub-
that cannot mate successfullywith each another lishedmagazinearticlesonscienceandtheenvironmentaswell
are considered differentspecies). Mammals mul- asclassicalmusicreviews. Sheis, shesays, alsocunentlyat
tiply exclusivelythrough sexual reproduction, workon theGreatCanadian Novel!
allowingthem to shuffle theirgenes with each
generation and potentiallycreate an enormous
amount ofgenetic diversitywithin a population.
However, phytoplankton are single cells that
multiplythrough binaryfission.Theyshuffle
genetic material only rarely, and each generation
is a clonal replicate ofthe last. Then, when they
do actually have sex, the matingpatterns can be
complicated. In some cases, two similarstrains
can exchange genetic material with each other,
but onlyoneofthemwill successfully mate with
a third, and so on.Thesame cells grown under
different conditions can change the length ot
theirspines and chains and even the shape of
their frustule. So understandingwhat a species
means becomes difficulteven though the idea of
a "species" is one ofthe most recognizable and
practical units ofbiodiversity for field biologists.
New techniques are revolutionizingthe study
ofphytoplankton biodiversity. Optical tech-
niques like flow cytometry, which allow scien-
tists to count and characterize hundreds ofthou-
sands ofphytoplankton cells per minute, are
being perfected in the laboratoryofRob Olson.
In 1988 Olson and Penny Chisholm (MIT) dis-
covered a new and highly abundant group of
picoplankton in the open ocean called
"prochlorophytes." These previouslyunknown
organisms are now understood to be responsible
fora huge fraction ofthe productivity ofopen
ocean systems.
Newly available molecular techniques that
probe the DNAofeach organism offer the possi-
bilityoflookingdirectly atthe organisms' genes
to see exactly how related they are. Important Thetopphoto shows,Me.\andrnun tainarensccellsfrom theGulfofMaine
work has been done in the laboratoryofDon gplroowbsedbrwiigthhtgarsemeanllunfdreargmaenntepoifflDuoNrAescceonutplmeidcrtooscaofpleu.orAesscpeenctiaclloymspyonuthnedsitzheadt
Anderson on dinoflagellates and by Michelle DNAprobeisbindingtospecificsequenceson RNAinsidethecells, allowing
Wood (University ofOregon) on diatoms. Such theobservertoeasilyidentifythem.Thebottom photoshowsa negative result
workshows furtherthat identical-lookingspecies when thesameprobe isused on a strain ofAlexwidnum tatnarensefrom Europe.
maynot actuallybethesame, orthat species wEoveunldthloouogkhthtehescaemllesuinndtehreatwnoorpmhaolt,osbriagrhetc-foinesliddemriecdrotshceopsea,methsepDecNieAsparnodbe
whose appearances are entirelydifferent may in easilydistinguishesthem on the basisofgeneticdifferences.
fact have close ancestors. It is to these tech-
niques, especiallywhen used in combination
with the more classical morphological analyses,
that wewill look for future progress in under-
standingphytoplankton biodiversity. Under-
standingthe growth responses ofthe myriad
Protozoan
Grazers
May
They Influence the
Biological Availability of Iron
to Phytoplankton
JamesW. Moffett it is subjected to harsh chemical treatment involving
AssociateScientist, MarineChemistry& GeochemistryDept. digestive enzymes and acidic conditions. We are inter-
KatherineA. Barbeau ested in howthis process can affectparticulate forms of
MIT/WHOI loint ProgramStudent various trace metals, including iron, byaccelerating
Iron is an essential micronutrient for marine life, dissolution processes that would not occursignificantly
yetitis highlyinsoluble in seawater. Dissolved in seawater. Nanoprotozoans could be particularly im-
iron concentrations in the oceans are exceedingly portant since theyingest particles in the 0.2 to 1 mi-
low, and much ofthe iron that is present occurs in rela crometersize class, which represents a large pool of
tivelyrefractoryforms, such asveryfine particles (col- particulate metals.
loids), which are difficult fororganisms to assimilate. Our laboratory studies ofwhat happens to colloidal
Some scientists propose that, in manyareas ofthe iron oxides ingested byprotozoans show that protozoan
world's oceans, iron mayactually limit the growth of grazers can greatly accelerate the produrtion ofdis-
marine phytoplankton, the primaryproducers in the solved and chemically reactive iron from colloidal iron
oceanic watercolumn. Biolo- oxides in seawater. Most sig-
gists and chemists atWHOI nificantly, our research indi-
and elsewhere are currently cates thatprotozoan grazers
investigating the mechanisms can convert refractorycolloidal
phytoplankton useto obtain iron oxides into a form ofiron
the iron theyneed. Consider- that is biologicallyavailable to
able attention is focused on diatoms, a majorgroup of
howtherefractoryforms of phytoplankton. Given the
iron, including iron oxide abundance ofprotozoans in
minerals and iron bound to the upperocean, this maybe a
dissolved orcolloidal organic significant mechanism forthe
matter, are converted into production ofbiologically
forms that phytoplankton can Epitluorescence micrograph ofadiversityofprotists available iron. The nextstep
use.Two processes thathave found in coastal watersofVineyard Sound (above) and will beto conduct field experi-
been particularlywell-studied scanningelectron micrographs (top) oftwospeciesot ments, studyingcolloidal iron
heterotrophicprotistsunderhigh magnification.These
arethe dissolution ofrefrac- organisms areless than 20 microns in size. dissolution in freshlycollected
toryironbysunlight through seawatersamples spikedwith
a photochemical mechanism, and the dissolution of tracers and incubated underavarietyofconditions. We
refractory iron bysiderophores, compounds produced will also study the ability ofprotozoans to dissolve
bybacteria and some phytoplankton. atmosphericdust panicles, which are a primary source
Recently, research in our laboratory has identified an oftrace metals to the open ocean.
additional mechanism that maycontribute to the sup- Protozoans may play an even widerrole in ocean
plyofavailable iron forphytoplankton. We are studying chemistry.Through theirdigestive process, theycreate a
how heterotrophic nanoprotozoans, tinygrazers less chemical "microenvironment" verydifferent from that
than 20 micrometers in size, can influence iron chemis- ofbulkseawater. Marine chemists are onlybeginningto
try in seawater.These organisms are ubiquitous, essen- study processes occurringwithin this microenviron-
tial components ofmarine food chains: The principle ment that may include dissolution ofanthropo-
fate ofbacteria in seawater is to be consumed by genically produced particles such as fly ash, transforma-
nanoprotozoans! Protozoans engulftheir preyand tion oforganiccontaminants, and production ofnew
incorporateit into a foodvacuolewithin the cell where colloidal phases.
Zooplankton, pri-
marilycopepods,
collectedin May
1996 on Georges
BankduringaGlo-
bal Ocean Ecosys-
tems Dynamics Pro-
gram (GLOBEC)
cruise. Copepods
arethemostplenti-
ful membersofthe
zooplanktonand
possiblythemost
abundantanimal
grouponearth.
Zooplankton
Diversity
— —
A Bizarre and Changing Array of Life Forms
Cabell S. Davis array oflife forms.
AssociateScientist, BiologyDepanment Notall zooplankton
Carin Ashjian are larvae offamiliar
J.
PostdoctoralScholar, Biology Department largeranimals. In fact,
Philip Alatalo thezooplankton is
ResearchAssociate, BiologyDepartment dominated numerically,
Thegreat majorityofanimal species in the and in total mass, by
seaspend at leastpartoftheirlives as animals that spend their
members ofthe plankton.The term plank- entire lives as plankion
ton comes from the Greekword "planktos," and are unfamiliarto
meaning "drifter," so plankton are generally most people. Such animals are termed Adultfemale
small, passivelydriftingcreatures (although holoplankton, while the temporary residents of o(lfatrhgeer)coapnedpomdale
some, like the jellyfish, can be quite large). The the plankton (such as the larval forms) are called species
animal orzoo- (pronounced zoh) plankton in- meroplankton. Pseudodiaptomas
clude theyoung life stages offish, crabs, lobsters, One group ofholoplankton, the copepods coronatus.Thefe-
barnacles, clams, starfish, conchs, squid, and (coh' pah pods), deserves special mention. Cope- mmiallleimisetaebroulotng1. In
nearly all othergroups offamiliarsea animals pods are more numerous than anyothergroup of thisspecies, thefe-
(except mammals) aswell as otherless familiar, animals on earth (with the possible exception of malecarriesher
but abundant, groups. roundworms), yetthe average person has never eggs in aclutch at-
Many larval forms heard ofthem.The numberofcopepods residing toafchheerdbaotdtyh.ebase
look nothinglike their undereach square meterofsea surface can range
—
parents forexample, from one thousandto overone million (and they
who would guess that arealso abundant in freshwaterenvironments). Larvalcrab (zoea
the larva at rightwould Since the ocean covers 70 percent ofthe earth's stage) collected
metamorphose into an surface, or 137 million square miles, thereare with a plankton
netofftheWHOI
adult crab? Remarkable about one quintillion (10''') copepods on earth! pierduringMay
adaptations in body In addition to beingplentiful, copepods are 1996.Thelarva is
form among the plank- Earth's fastestanimals fortheirsize. Usinga high about2 millime-
ton result in a bizarre speedvideo microscope mounted on an ROV ters long.
OCEANUS
—
Thecopepod Copepods need to be
Calanusfinmar- able to move fast to avoid
chicitscolleaedon
Georges Bank(May theircountless predators.
1996).Thisspecies While feeding, copepods
dominatesthe assume a chararteristic
zooplankton mass
posture (photo at left);
in latespringand
isthe main foodof With their long anten-
manyspecies in- nules extendedwidely
cludingcod and apart, theyoften hoveror
haddocklarvae as
cruise slowlyas they filter
well asnorthAtlan-
tic rightwhales ; food from the waterwith
(seeboxbelow). 1 their feedingappendages.
Thisspecimen is £ The antennules detect
shown in thechar- " vibrationsgenerated by
acteristicfeeding
posturewith its (Remotely Operated Vehicle), researchers have oncomingpredators, which, iftoo close for
longantennules found that copepods can swim atspeeds of500 comfort, cause the copepod to cease feeding and
spread farapartto body lengths persecond. Bycomparison, a chee- initiate an escape response.To escape, the cope-
detectoprnecdoamtoirnsg. tah would have to run 2,000 miles perhourto pod rapidly folds its legs and antennules down
attain the same relative speed. In fact, an F-16 alongthe sides ofits body, creating a stream-
fighterjetonly moves about 50 bodylengths per lined bulletshape and propelling itselfinstantly
second. Even more amazing is thatcopepods through thewaterto a location several body
achieve their rapid movement through water, a lengths away. Copepods can repeat this escape
much heavierand moreviscous medium than air. response several times in a row before tiring.
Gulf of Maine Physics
Linking Large and Small Marine Animals
Ari W. Epstein species Calanusfinnuirchicus (photo above).The existence
VisitingAssistantProfessor, Physics Department, BowdoinCollege ofthese dense patches is extremelyimportantto the
andVisitingScholar, NewEnglandAquarium whales: Rightwhales feed byswimmingwith their mouths
Everyspring, most (and perhaps all) oftheright open, filtering prey out ofthewaterwith their baleen. Be-
whales known to existin the NorthAtlantic causeoftheadditional hydrodynamicdraginvolved, open-
—
about 300 to 350 individuals migrate to the shal- mouth swimmingcosts a whale much more energythan
low GreatSouth Channel ofthe GulfofMaine, which di- closed-mouth swimming, and so unless there is a very high
vides Georges Bankfrom NantucketShoals.Theretheyfeed concentration ofprey in thewater, thewhale can actually
forabouttwo months on dense patches ofthezooplankton loseenergyby attemptingto feed. Rightwhales may not
T T feed at all duringthe Buoyantplume
Wilkinson winter, so it is crucially
Basin important forthem to
GulfofMaine
find a large numberof
dense Calanus patches
duringthe spring and
summer.
Whatcauses dense
clumps ofC(i/(!m(5 to
form in the Great
Georges
Bank South Channel? One
clue maybe found in
the figure at left, which (Top)Abuoyantplumeadvancesover
heavierwaterinwhich plankton are
whalesighting shows large numbers
salinitycontour distributed in athin layer.
ofwhale sightings (red (Bottom) Plankton thatareswept un-
dots) and hence, prob- dertheplumeseektheirpreferred
depth, swimmingupward to join
ably, Calanus patches,
plankton alreadywithin theplume.
justat the edge ofa Eventuallyadensepatch ofplankton
plume ofrelatively accumulatesattheedgeoftheplume.
SPRING/SUMMER 1996
