COASTAL RESEARCHVolume 3, Number 2

December 1999

WOODS HOLEOCEANOGRAPHIC

INSTITUTION

RINEHARTCOASTAL

RESEARCH

CENTER

Rinehart Coastal Research Center of the Woods Hole Oceanographic Institution

Flume Studies Identify Physical and Chemical Processes ThatControl Larval Dispersal and Settlement

Contributed by Cheryl Ann Butman and Richard Zimmer

Most animals—worms, snails,and crabs—associated with

sediments as adults have a plank-tonic larval stage. Dispersing inthe water column for hours tomonths, the larvae then settleonto the seabed and metamor-phose into benthic juveniles.Knowledge of the factors deter-mining when andwhere larvae settleon the bottom iscritical for under-standing the lifecycle of a speciesand ultimately forpredicting adultpopulation sizesand distributions.

Evaluating thephysical andchemical factorsthat establish larvaldistributions in thewater column andon the seafloor is amajor research fo-cus in our laborato-ries at Woods HoleOceanographic Institution andthe University of California, LosAngeles. We are conducting anextensive series of experimentsin two recirculating flumes at theCoastal Research Laboratory, the17-Meter Flume (60 centimeterswide with a 17-meter-long chan-nel) and a smaller annular flume(1.5-meter-diameter ring,10-cen-timeter-wide channel). Combin-ing several new technologies for

monitoring the movements ofindividuals within a flow field,these experiments address therelative importance of passivetransport versus larval behaviorin response to chemical orhydrodynamic cues in determin-ing suspended and benthiclarval distributions.

Estuarine parasitic trematodes(wormlike organisms) can signifi-cantly affect both the populationdynamics and community struc-ture in salt marshes through cas-tration or by inducing behaviorsin their hosts (snails, fish, crabs).To determine factors that controlthe transfer of infection from onehost to the next, JonathanFingerut and Damion Gastelumare quantifying the emergence,

transport, and settlement of thecercaria larval stage. For one spe-cies (Himasthla rhigedena), still-water assays indicate that verticalswim speeds can double over atemperature change of only 6° C(18 to 24° C, bracketing the rangethat occurs in the field). Tempera-ture-dependent swim speeds may

generate two dif-ferent verticaldistributions ofcercaria in thewater column.Such distribu-tions could affectthe probability ofcercaria encoun-tering a suitablehost (such as fishin the water col-umn or snails onthe seabed) andthus the spreadof infection.

To quantify theinteraction be-tween larval be-havior and

hydrodynamics, we are using the17-Meter Flume to study verticaldistributions of cercaria in flow.We use an infrared laser light forillumination because the larvaecannot detect it. The laser beamis reflected and then spread tocreate a very thin sheet in thealong-channel direction. Thistechnique specifies a defined

Vicke Starczak (left) and Nan Trowbridge introduce larvae to the annular flume.

FLUME –page 2

2 ~ Coastal Research

volume for determining larvalconcentrations. Two highly sensi-tive video cameras record theimages of larvae transported byor swimming in flow. The fieldof view spans the entire watercolumn. Recorded images areprocessed in near-real time on acustom-built Computer AssistedVideo Motion Analysis System.This analysis generates verticalconcentration profiles, swim-ming speeds, and trajectoriesof cercaria.

Experiments in the annularflume are designed to quantifylarval behaviors and settlementin three-dimensional flows.Cross-stream (“secondary”) circu-lations are a direct result of thecontinuously curving channeland simulate aspects of the morecomplicated near-bed flows thatoccur in nature. Surprisingly, al-though secondary flows are weakrelative to the along-channel flow,larvae of certain species are easilyentrained in these sluggish cross-stream circulations.

Victoria Starczak and NanTrowbridge are studying larvalsettlement behavior of a smallworm (Capitella sp. I) that is veryabundant in organic-rich mudsand thus indicative of disturbedor polluted conditions. Previousstudies in a large recirculatingflume showed that larvae of thisspecies were highly selective forthe high organic muds of theadult habitat. Whereas selectivitywas not affected by currentspeed, settlement rate was abouta factor of two greater in rela-tively fast versus slow flow. Con-sequently, studies of near-bedswimming and settlement in thesmall annular flume are designedto evaluate how behaviors at thescale of the individual might

Back in the early days of the Woods HoleOceanographic Institution, there were justoceanographers. There was no separate de-partment for physical oceanographers orchemical oceanographers or engineers—infact, it wasn’t until 1963 that WHOI Direc-tor Paul Fye managed to organize the scien-tific ranks of the Institution into separatedepartments.

With the ever-increasing complexity ofour science over the last several decades,

such specialization was inevitable and valuable for increasing thesophistication and rigor of oceanographic research. But…whatgoes around comes around.

I participated in the Mid-Atlantic Bight Physical Oceanographyand Meteorology Workshop in Woods Hole this fall (see article onpage 5), where probably the most exciting talk was given by ageologist talking about clams. It turns out that these lowly mol-lusks have been keeping faithful track of the salinity of the coastalocean for the last hundred years, with a temporal resolution asfine as one week! It took some fancy analysis, precision machin-ery, and a sophisticated model of the partitioning of stable iso-topes to yield this interpretation of clam shells, which indeedspeaks to the great strides that oceanographic science has madewithin the individual disiplines.

The reason this clam research is exciting is not, however, thetechnical virtuosity of the measurements, but rather the assimila-tion of ideas across different disciplines to arrive at a new view ofhow the physical, biological, and chemical processes in the oceaninteract.

That’s Oceanography. Period.

A Message from the RCRC Director:FLUME – from page 1

RCRC Calendar for January – June 2000

April 14 ––––––––––––––––––Annual RCRC Proposal Deadline

April 25 ––––––––––––––––– Nearshore Processes Symposium

June –––––––––––––––––––––––––––––––– RCRC Open House

December 1999 ~ 3

explain flow-dependent settle-ment rates.

In addition, Patrick Krug isconducting research on larval be-havior and settlement rate in re-sponse to dissolved and adsorbedchemical cues for a small seaslug (Alderia modesta). Still-waterstudies suggest that Alderia is in-duced to settle by both water-borne and substrate-adsorbedcues produced by the benthicyellow-green alga Vaucherialongicaulis. Adsorbed moleculeshave long been highly favored asthe dominant inductive com-pounds for larval settlement.

Work in author Zimmer’s labindicates, however, that dissolvedcues may also play an importantrole, particularly under condi-tions where high concentrationsof the inductive solution aremaintained very close to the sur-face of the inductive substrate.We are exploring the effects of

such conditions on settlementrate in the annular flume studies.

We quantify larval settlementof both Capitella and Alderia lar-vae on substrates (mud for theworms and algae for the slugs)placed in depressions at 10 equi-distant locations around the an-nulus. During the experiments,larval swimming in flow is videorecorded using a set-up similar tothat described above for the 17-Meter-Flume studies. We analyzethe video tapes using the sameComputer Assisted Video MotionAnalysis System that tracks thelocations of the larvae in timeand space, and also computesswim trajectories and speeds.

This research should greatlyimprove current understandingof the interplay between animalbehavior and hydrodynamics indetermining patterns of larvalsettlement. It could lead to im-proved theory on the mecha-

nisms that control larvalsupply to established popula-tions and new habitat, and thathelp regulate benthic commun-ity structure.

Cheryl Ann Butman is a SeniorScientist, Victoria Starczak aResearch Associate, and NanTrowbridge is a Research Assis-tant in the WHOI Applied OceanPhysics and Engineering Depart-ment. Richard Zimmer is a Pro-fessor in the Department ofBiology at the University ofCalifornia, Los Angeles, wherePatrick Krug is a PostdoctoralFellow, Jonathan Fingerut aGraduate Student, and DamionGastelum a Research Assistant.

Advection

Active Habitat Selection

FLOW SPEED

DISTANCE ABOVE BOTTOM

TurbulentMixing

ActiveSwimming

Frictionless Fl

Boundary-Layer Flow

GravitationalSinking

Diagrammatic representation of physical factors and behaviors affecting larval transport within near-bottom waters andsettlement on the seabed. In addition, settlement may be influenced by dissolved or substrate-adsorbed chemical cues.

Jayn

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4 ~ Coastal Research

Coastal Groundwater Discharge on Cape CodContributed by Matt Charette and Ken Buesseler

West FalmouthHarbor

Great SippewissettMarsh

VINEYARD SOUND

WaquoitBay

42°40'

Cape CodBay

Nantucket Sound

42°20'

42°00'

41°40'

71°05' 70°50' 70°30' 70°10' 69°50'

Massachusetts

Cape Ann

10

Estimated groundwater discharge (million cubic meters per year)

2.8

4.4

Jack

Co

ok

The fate of contaminants andnatural compounds in estua-

rine and near-shore environ-ments is determined by acomplex set of biological,geochemical, and physical inter-actions. Scientists have at least abasic understanding of the majorsources, sinks, and transforma-tions for many substances. How-ever, the importance of coastalgroundwater discharge in deliver-ing dissolved nutrients, such asnitrate and phosphate, to coastalwaters has often been over-looked, primarily because it isdifficult to estimate.

In the last RCRC newsletter(Vol. 3, No.1), we reported a newapproach to studying groundwa-ter discharge in the coastalocean. It is based on radium iso-topes (radium 226, radium 228,radium 223, radium 224), a setof naturally occurring nuclidesthat are enriched in groundwater.These four isotopes, with half-lives ranging from four days to1,600 years, allow us to examinethis process over a wide range oftime and spatial scales. Inaddition, the short-lived radiumisotopes show promise forestimating flushing times oflocal estuaries.

With support from the Rine-hart Coastal Research Center, theWHOI Education Office, and theOffice of Naval Research, we setout to estimate groundwater dis-charge to three local estuaries—West Falmouth Harbor, GreatSippewisset Marsh, and WaquoitBay (see figure below). By con-structing a simple mass-balancemodel for a long-lived radiumisotope (radium 226) and using ashort-lived isotope (radium 223)to gauge estuarine water resi-dence times, we were able to esti-mate groundwater fluxes of 2.8,4.4, and 10 million cubic metersper year, respectively.

The magnitude of these fluxesis large considering that these es-tuaries are only three of themany inlets that line the south-ern and eastern coasts ofFalmouth. For example, the an-nual water use for the town ofWest Falmouth is less than 20percent of discharge to the har-bor from natural sources. InWaquoit Bay, direct ground-water discharge to the bay com-prises roughly one-third of thetotal freshwater budget for theentire watershed.

The key biogeochemical prob-lem associated with coastal

groundwater flow on Cape Cod isthe introduction of “new” nitro-gen, entrained by groundwaterplumes as they pass through sep-tic tank fields located along thecoastline. In several groundwatersamples taken from aroundWaquoit Bay, total dissolved inor-ganic nitrogen (DIN) concentra-tions ranged from 100 to 125micro-moles per liter. Using ourcalculated groundwater flux, thistranslates to a DIN flux of about15,000 kilograms of nitrogen peryear, a value much greater thanthe potential contribution fromprecipitation. Since summer DINconcentrations in the bay arethree orders of magnitude less,much of the nitrogen is eitherstored as particulate nitrogen(such as macroalgae) or exportedto Vineyard Sound.

December 1999 ~ 5

As radium isotopes are intro-duced to an estuary via ground-water discharge, they are subjectto mixing and radioactive decay.The two short-lived radium iso-topes are useful because theyhave half-lives (4 and 11 days)that are on the same order as theflushing times of many estuaries.The flushing rate of an estuary isimportant because it is a proxyfor the amount of time a con-taminant spends in the system;for example, estuaries with rapidflushing rates may be less im-pacted by contaminant inputsthan systems with slower ex-change rates.

The distribution of the short-lived radium isotopes in WaquoitBay reveals that the flushing pro-cess is more complex than previ-ously believed. Previous estimatesof flushing based on a water bal-ance differ by factors of two tothree when compared to the ra-dium approach. These estimates

may have been biased by failingto account for the large ground-water input at the head of the bayas well as a strong salinity frontlocated mid-bay. The built-in“clocks” provided by these radio-isotopes are thus improving ourunderstanding of both the inputsand circulation processes ofthese harbors.

This work is critical for the fu-ture management of our estuar-ies in the event that ground-water-borne organic contaminantplumes from the MassachusettsMilitary Reservation outcropinto local harbors and along theCape Cod coastline. Our resultscan help environmental manag-ers identify specific problem ar-eas and the potential resultingimpact on local ecosystems.

Matt Charette is a PostdoctoralInvestigator and Ken Buesseleran Associate Scientist in theMarine Chemistry and Geochem-istry Department.

Mid-Atlantic BightResearch Workshop

Contributed by Jim Churchill

S ince the time of the Nixon Ad-ministration, an autumn rite

of scientists interested in physicsof the Mid-Atlantic Bight (the oce-anic region between GeorgesBank and Cape Hatteras) hasbeen the MABPOM (Mid-AtlanticBight Physical Oceanography andMeteorology) Workshop. This isunique among scientific meetingsin that it is sustained solely bythe volunteer efforts of the sci-ence community. This year’sworkshop was held in the newlyrevamped top-floor Clark Labora-tory conference room on WHOI’sQuissett Campus.

During the one-and-a-half daymeeting span (October 25–26),the roughly 50 attendees weretreated to a broad range of pre-sentations as well as a traditionalNew England style clam boil.The mix of talks included someslick high-tech presentationsgiven by students and young in-vestigators, and more traditionalfare served up by MABPOM old-timers. This year’s meeting alsocontinued the recent MABPOMtrend of expanding disciplinaryboundaries, with a number oftalks directed to the effects ofcurrents on biological communi-ties and chemical distributions.

Interest in interdisciplinarymarine science was exemplifiedby a spirited discussion regard-ing the use of radiocarbons toinfer shelf circulation, inclu-ding a question on the possibilityof cross-shelf clam transportby fishermen.

For further information, checkhttp://www.whoi.edu/MABPOM/

Jim Churchill is a Research Spe-cialist in the Physical Oceanogra-phy Department.

Mat

t C

har

ette

Gle

n C

ross

in

Matt Charette and John Andrewsprepare R/V Mytilus for field sampling

in local Cape Cod estuaries. Radiumisotopes used to trace groundwater

discharge are concentrated from 100liter samples onto manganese-coated

acrylic fibers (inset).

6 ~ Coastal Research

high density band(summer)

1999

1959

Quantification of low-frequency variability in aBermuda brain coral (Diploria labyrinthiformis)indicates a strong correlation between density andthe North Atlantic Oscillation Index (NAO). Thismay prove to be a valuable tool in reconstructingNAO variability over the past several centuries.

Reconstructing Climate with CoralContributed by Anne Cohen

It’s after hours at FalmouthHospital’s X-ray Department,

and I’m at the controls. My pa-tient: a brain coral (Diplorialabyrinthiformis) collected fromthe southern reefs of the Ber-muda platform. The X-ray imagereveals details of the coral’s skel-etal structure invisible to the na-ked eye: pairs of alternating lightand dark bands that reflectchanges in skeletal density in re-sponse to seasonal changes inlight and water temperature (seefigure above right).

Because each high- and low-density couplet represents oneyear of growth, I can tell immedi-ately that the colony is 40 yearsold and that it grew, on aver-age, 3 millimeters per year.The second specimen isolder, 79 years. On it, I canpinpoint the year I was born,the year of the first moonlanding, the invention of theFrisbee, and the introductionof television.

This built-in chronologyis one of several uniquecharacteristics that makereef corals valuable to un-derstanding and reconstruc-tion of climate of the recentpast. Beginning in the 1950s,instrument recordings pro-vide reliable data on shortterm climate change. Theyshow that the earth’s climatehas undergone fairly signifi-cant changes, reflected inboth air and sea surface tempera-tures, the frequency of Pacific ElNiño/Southern Oscillation events(ENSO), the behavior of the NorthAtlantic Oscillation (NAO), andthe frequency and intensity ofhurricanes, floods, and droughts.

However, these records are tooshort to tell us whether these

changes are unprec-edented or part of anaturally varying cli-mate system, whetherthey’re to be expectedor whether they’re un-usual and caused by hu-man activities. To put thesechanges into a longer-termperspective and to aid climatepredictions, we are turning toproxy data.

Massive reef corals are just oneof many paleoclimate archivesthat we tap for information, butthey’re particularly well-suited tothe reconstruction of continuous,multi-century records of condi-tions in the surface oceans, with

seasonal resolution. As coralsgrow, the structure, isotope com-position, and trace elementchemistry of their calcium car-bonate skeletons change in re-sponse to small variations inlight, sea surface temperature, sa-linity, turbidity, runoff, and up-welling intensity.

We are developing techniquesto measure these changes withgreater precision. Using relation-ships established in calibrationstudies, we can re-interpret thechemistry as an environmentalsignal. For example, the oxygenisotope composition (ratio ofoxygen 18 to oxygen 16) of theskeleton is sensitive to watertemperature and salinity, whilethe strontium/calcium ratio var-ies with temperature. By mea-suring both the isotope andelemental ratios using massspectrometry, a history of tem-perature and salinity changes inthe waters surrounding the coralcolony can be reconstructed forthe period in which it grew. Be-cause reef corals grow rapidly,up to 22 millimeters per year,the skeleton can be subsampledat monthly intervals to achieve

seasonal resolution. Using Ber-muda corals we are reconstruct-ing winter-time sea surfacetemperatures to study long-termvariability in the North AtlanticOscillation. Despite the relativelylow growth rate of the Bermudabrain coral, I am able to extract12 samples per growth band us-

2000 19801990 1970 1960 1950

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-6

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Coral skeletal densityNorth Atlantic Oscillation index

An X-ray image reveals seasonal anddecadal-scale changes in coral skeletaldensity. Seasonal banding is used to agethe colony and establish longchronologies.

December 1999 ~ 7

day-time

120 microns

dailygrowthband

night-time

day-time

dailygrowthband

120 microns

night-time

ing a super-fine, diamond-tippeddental drillbit, a microscope—and a very steady hand.

Corals accrete skeleton con-tinuously until the colony dies.For some of the massive species,this may mean several hundredsof years. In fact, the oldest knownliving colony reached 1,000 yearsbefore it was removed from Ber-muda in the early 1980s for pa-leoclimate reconstruction. Today,we seldom remove entire colo-nies. Instead a special underwaterhydraulic drill is used to removecore samples, often severalmeters long and up to 10 centi-meters in diameter. After coring,the hole is closed with a cementplug to prevent infection by bor-ing organisms, and new growtheventually covers the plug.

Worldwide, there are now 15 to20 coral-based climate recordsextending back further than themid-1800s. All have been gener-ated by subsampling coral coresat monthly or annual resolution.At WHOI, we’re pushing that en-velope, striving for even greaterresolution in order to extract thesignals left by short-lived, cata-

strophic events. Us-ing petrographicthin-sections andscanning electron mi-croscopy, we recentlyidentified dailygrowth bands in coralfrom the north-cen-tral Pacific, eachband about 30 mi-crons wide (see figurebelow). We’re evenable to distinguishnight-time and day-time skeletal accre-tions! Measurementof skeletal chemistryat this micro-scale re-quires a quite differ-ent technique, onethat has been used byhard-rock geochem-ists at WHOI for decades but onlyrecently applied to corals.

With the ion microprobe, thesurface of the coral is “sputtered”with a continuous stream of oxy-gen ions, leaving a tiny cavityabout 5 microns deep. The ionbeam—as small as 10 microns indiameter—can be focused onspecific regions of the coral

sample. The figure above showsthe results of our first attempt toreconstruct ultra-high resolutionstrontium/calcium-based sea sur-face temperature variability re-corded in the daily growth bandsof a colony collected in late Octo-ber. A temperature logger placednear the base of the coral re-corded half-hourly temperature,with large biweekly oscillationscoincident with the phase of themoon. Strontium/calcium ratiovariability in the top 2,400 mi-crons of skeleton correlates re-markably well with thesehigh-frequency sea surface tem-perature changes, indicating thatwe can extract information withat least sub-weekly resolution.Over the next year we’ll be devel-oping this capability for oxygenisotope analysis in order to trackpulsed signals of hurricane rain-fall in Caribbean corals, a projectfunded by the RCRC.

Anne Cohen is a Visiting Investi-gator in the Geology and Geophys-ics Department at WHOI.

A polished thin-section of skeletal elements in Porites lutea viewed in polarized,transmitted light shows daily growth bands and regions of night- and day-time skeletalaccretion.

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tem

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˚C)

microns from top of coral

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a (m

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Date (1996)

Micro-scale analysis of the section pictured below usingthe ion microprobe yields high-frequency variability inthe strontium/calcium ratio (red), which tracks the realdaily sea surface temperature variability withremarkable precision (blue).

Published semi-annually by theRinehart Coastal Research Center

Woods Hole Oceanographic Institution193 Oyster Pond Road, MS#2Woods Hole MA 02543-1525Telephone: (508) 289-2418

Fax: (508) 457-2172E-mail: crc@whoi.edu

http://www.whoi.edu/coastalresearch

Editor: Vicky CullenDesigner: Jeannine Pires

RCRC Advisory Committee:Don Anderson

Cheryl Ann ButmanDave Chapman

Cabell DavisNeal Driscoll

Wade McGillisJim Moffett

Al PlueddemannKathleen Ruttenberg

Ex Officio: Judy McDowell

RCRC Staff:Rocky Geyer, Director

Bruce Tripp, Assistant DirectorBebe McCall, Staff AssistantJay Sisson, Boat Operations

Bruce Lancaster, CRL OperationsCheryl Ann Butman, Flume Science Coord.

Former RCRC Directors:

1979 - 1981 John H. Ryther1981 - 1986 John W. Farrington1986 - 1991 David G. Aubrey1992 - 1995 Robert C. Beardsley

WOODS HOLEOODS HOLEOCEANOGRAPOCEANOGRAPHICHIC

INSTITUTIONINSTITUTION

RINEHARTCOASTASTALAL

RESEARESEARCHCH

CENTERENTER

THE RINEHART COASTAL RESEARCH CENTER is committed to thesupport and enrichment of coastal research activities within the WHOIcommunity, particularly those research activities that directly affect theprotection and enhancement of coastal resources. This mission is accom-plished through facilitating research and education, providing facilitiesand equipment, and promoting interdisciplinary communication.

RESEARCH: Annual call for proposals • Rapid response •Mini-grants • Matching funds

EDUCATION: Postdoctoral support • Student project support

FACILITIES: Small boats • Coastal Research Laboratory (CRL) •Flumes and tanks (at CRL) • Coastal instrumentation

COMMUNICATION AND OUTREACH: Newsletter • Website • Scientificseminars, meetings, and workshops • Annual Open House

Woods HoleOceanographic Institution

Woods Hole, MA 02543 USA