Deep Sea Research I

Virginie Riandeya

Description

Deep-Sea Research I ] (]]]]) ]]]–]]] ARTICLE IN PRESS Corresponding author. Tel.: ; fax: . [phone]/$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.dsr.2005.06.004 E-mail address: (V. Riandey). 1Present address: UR 098, IRD, Centre de Bel Air, BP 1386, 18524 Dakar, Senegal. Abstract This work represents a first step in understanding the impact of hydrodynamic features on the zooplankton dynamics in the Algerian Basin (southwestern Mediterranean Sea). The mesoscale distribution of mesozooplankton abundance, biomass, specific composition and size structure was investigated during ELISA-1 campaign (1997) in the framework of the program ELISA (Eddies and Leddies Interdisciplinary Study off Algeria, 1997–1998), partly dedicated to study the mesoscale features during 1997. Physical, biogeochemical and biological measurements were made on transects through two hydrodynamic features, one anticyclonic eddy and a small secondary shear cyclonic eddy. The use of combined zooplankton descriptors, i.e. biomass, abundance, size structure (e.g. NB-SS slope) and taxonomic structure, and of cumulative function allowed us to extract spatial trends in the anticyclonic eddy (AE 96-1).

• mesoscale dynamical


• distance between successive


• eddies


• station


• mediterranean sea


• algerian current


• western mediterranean


• ctd-rosette


• created between


• size structures

Sujets

• IFREMER
• Eddy (fluid dynamics)
• Station
• Mediterranean Sea

Informations

• Publié par: pefav
• Nombre de lectures: 56
• Poids de l'ouvrage: 1 Mo

Extrait

ARTICLE IN PRESS
Deep-SeaResearchI ](]]]]) ]]]–]]]
www.elsevier.com/locate/dsr
Zooplanktondistributionrelatedtothehydrodynamic
featuresintheAlgerianBasin(westernMediterraneanSea)
insummer1997
a, a,1 aVirginieRiandey ,GiseleChampalbert ,Franc -oisCarlotti ,
b cIsabelleTaupier-Letage ,DelphineThibault-Botha
aLaboratoire d’Oce ´anographie et de Bioge ´ochimie, UMR 6535 CNRS/Universite ´ de la Me ´diterrane ´e,
OSU/centre d’Oce ´anologie de Marseille, Station marine d’Endoume, rue de la batterie des lions, F-13007, France
bLaboratoire d’Oce ´anographie et de Bioge ´ochimie, UMR 6535 CNRS/Universite ´ de la Me ´diterrane ´e, d’Oce ´anologie de Marseille, Antenne de Toulon, c/o IFREMER, BP 330, F-83507 La Seyne, France
cLaboratoire d’Oce ´anographie et de Bioge ´ochimie, UMR 6535 CNRS/Universite ´ de la Me ´diterrane ´e,
OSU/centre d’Oce ´anologie de Marseille, Campus de Luminy, Case 901, F-13288 Marseille Cedex 09, France
Received10December2004;receivedinrevisedform6June2005;accepted15June2005
Abstract
Thisworkrepresentsafirststepinunderstandingtheimpactofhydrodynamicfeaturesonthezooplanktondynamics
intheAlgerianBasin(southwesternMediterraneanSea).Themesoscaledistributionofmesozooplanktonabundance,
biomass,specificcompositionandsizestructurewasinvestigatedduringELISA-1campaign(1997)intheframeworkof
theprogramELISA(EddiesandLeddiesInterdisciplinaryStudyoffAlgeria,1997–1998),partlydedicatedtostudythe
mesoscalefeaturesduring1997.Physical,biogeochemicalandbiologicalmeasurementsweremadeontransectsthrough
two hydrodynamic features, one anticyclonic eddy and a small secondary shearcyclonic eddy. The use of combined
zooplankton descriptors, i.e. biomass, abundance, size structure (e.g. NB-SS slope) and taxonomic structure, and of
cumulativefunctionallowedustoextractspatialtrendsintheanticycloniceddy(AE96-1).Itishypothesizedherethat
theeasternedgeofAE96-1,characterizedbythicklayerofchlorophyll(between100and150m)duetothedownward
entrainment of chlorophyll down to 200m, was favorable for small organisms (Paracalanus/Clausocalanus,
Calocalanus, and Calanus) while higher abundance of large active swimmer such as chaetognaths was observed in
thecenter.Inthecycloniceddy,thehighestoffilter-feeders(ostracods,cladocerans,doliolidsandsalps)was
3related to enhance trophic conditions, i.e. highest chlorophyll concentration (4–8mgm ).Theseresultsshowthat
cyclonicandanticycloniceddiesstronglyinfluencethemesoscalecharacteristicsofzooplanktonintheAlgerianbasin
Correspondingauthor.Tel.:[phone];fax:[phone].
E-mail address:[e-mail](V.Riandey).
1PresentUR098,IRD,CentredeBelAir,BP1386,18524Dakar,Senegal.
0967-0637/$-seefrontmatterr2005ElsevierLtd.Allrightsreserved.
doi:10.1016/j.dsr.2005.06.004
`´´ARTICLE IN PRESS
2 V. Riandey et al. / Deep-Sea Research I ] (]]]]) ]]]–]]]
duringsummer.Higherchlorophyllconcentrationsobservedinspringsuggestthatsucheddiescanhaveanevenmore
pronouncedimpactonthestructuringoftheecosystemduringhighproductiveseason.
r2005ElsevierLtd.Allrightsreserved.
Keywords: Mesoscale eddies; Zooplankton; Size distribution; Optical plankton counter; Pelagic environment; Cumulative sums
method;MediterraneanSea;AlgerianBasin
1. Introduction filamentsandsubmesoscale cyclonicsheareddies.
Suchsheareddieshavediametersofafewtensof
Numerousstudiesshowtheimpactofmesoscale kilometers, vertical extents of 100m, and life-
physical oceanic processes such as fronts, rings timesofafewweeks.TheAEcorrespondtolarge,
andeddiesonplanktonicecosystems(Owen,1981; highly oligotrophic areas during the summer-
LegendreandDemers,1984;WishnerandAllison, stratified conditions, because their anticyclonic
1986; Huntley et al., 1995; Huskin et al., 2001). structure maintains the nutricline at depths close
Studies based onthe warm-corerings intheGulf tothatoftheeuphoticzoneinthecentralpartof
Streamhighlightedthatzooplanktonbiomasswas the AE. On the other hand, the cyclonic plumes
higherintheircenters(Wiebeetal.,1985;Cowles sometimes associated with AE and shear eddies
et al., 1987). Fronts (Seguin et al., 1993, 1994; correspondtoricher,ephemeralspotsduetotheir
Thibaultetal.,1994;YoussaraandGaudy,2001) cyclonic doming structure (Moran et al., 2001;
and eddies (Pinca and Dallot, 1995; Pakhomov Taupier-Letageetal.,2003).
and Perissinotto, 1997) have been also known to The ELISA operation (Eddies and Leddies
enhance zooplankton biomass and to influence Interdisciplinary Study off Algeria, 1997–1998—
zooplanktonhorizontaldistribution. see Taupier-Letage et al., 2000, part of the
The Algerian Basin is a place where the MATER /MAST3-MTP2 European program)
mesoscale dynamical activity is intense. The was dedicated to the study of: (i) the general
instability of the Algerian Current generates circulation of the water masses, (ii) the origin,
meanders enclosing anticyclonic eddies (for a structure and trajectories of the eddies, (iii) the
reviewsee Millot and Taupier-Letage, 2005a), biological response associated with the mesoscale
which propagate downstream (i.e. eastward) at a dynamic phenomena, and (iv) the biological
fewkilometerperday.Attheentranceofthe consequences of the mesoscale dynamics for the
Channel of Sardinia the bathymetry narrows and functioning of the Algerian Basin. Throughout
shallows, so that the deeper and larger eddies that experimental year, 4 main campaigns were
cannot go through. They are guided by the organizedinordertotracktwomainAE(96-1and
bathymetry northward along the western Sardi- 97-1)andtosamplethematdifferenttimesofthe
nian slope, and thus detach from their parent year. Their general hydrodynamic characteristics
current.Thentheyfollowacounter-clockwise and associated chlorophyll, and nitrate distribu-
circuit in the eastern part of the Algerian basin, tionsarepresentedinTaupier-Letageetal.(2003).
possibly completing up to three loops. The Mesoscale hydrodynamic features play an im-
Algerian Eddies (hereafter AE) are 50–250km in portant role on the structuring of the organic
diameter, can have a vertical extent down to the matter compartment in oceanic regions. The
bottom (3000m; Ruiz et al., 2002; Millot and impact of such structures is clearly shown on
Taupier-Letage,2005b),andappeartolastupto3 phytoplanktonbyremotesensing,butthestudyof
years (Puillat et al., 2002). When returning in the their influence on the zooplankton compartment
Algerian coastal zone (CZ) AE interact with the still need to be assessed through mesoscalen Current, and the intense shear created sampling. Here, the distribution of zooplankton
between the eastward Algerian Current and the related to mesoscale hydrodynamic features was
westward current south of the eddy generates investigatedforthefirsttimeintheAlgerianBasinARTICLE IN PRESS
V. Riandey et al. / Deep-Sea Research I ] (]]]]) ]]]–]]] 3
1during the cruise ELISA-1 (summer 1997), using 200m to the surface at 1ms . No flowmeters
both microscope counts and bench-top optical were available but special care was taken while
planktoncounter(OPC).ELISA-1focusedontwo sampling to keep the cable vertical. Intervals
features, the (anticyclonic) eddy AE 96-1 and its between stations ranged between 2 and 13.5
associated(cyclonic)sheareddyC.Moststudiesof nautical miles (Table 1). Samples were preserved
zooplanktonresponsetophysicalchangeslookat directly upon collection (5% buffered formalin
a couple of indexes, i.e. biomass and abundance. solution) and quantitatively split with a Motoda
Inthispaper,weproposedanintegratedapproach boxoncebackinthelaboratory.
by considering together zooplankton biomass,
abundance, population structure (e.g. slope of 2.2. Processing of zooplankton samples: abundance
normalized biomass size spectra (NB-SS)) and and biomass
taxonomicstructure.
Mesozooplankton community characteristics
weredescribedfollowingtwodifferentapproaches,
2. Methods i.e. studies based on traditional taxonomic deter-
minations and size structures. Taxonomic
2.1. Sampling mination was done using a dissecting microscope
(Leica); three subsamples were counted per net
ThesamplingstrategyduringtheELISAexperi- and at least 600 individuals were enumerated per
ment was based on the near real time analysis of subsamples. Identifications were done for cope-
satellite thermal images, which were received on pods to genus level and to taxa level for other
board the RV Le Suroıˆt in order to locate the majorzooplankton(e.g.chaetognaths,ostracods).
mesoscale features. Then transect locations were Microscopecounts(MC)werenotdoneforstation
determined and run using a fine sampling interval 110duetohandlingproblems.Sizestructureofthe
o5 nautical miles (10km) for the CTD stations. same subsamples was studied using a bench-top
The ELISA-1 3rd leg (23/07–04/08/1997, in the versionoftheOPC-1L.
region 37–401N and 4–91E) was dedicated to the TheOPCsetupwassimilartotheonedescribed
time-demanding biological and biogeochemical by Beaulieu et al. (1999). Organisms were gently
sampling(Fig.1andTable1).DuringtheELISA- introduced into the water circulation system. To
1 cruise, the AE 96-1 (diameter 150km) was avoidcoincidence,weimposedamaximumcount
1
sampled along its southern (‘‘S-9