Polychaetes of Antarctic sublittoral in the proglacial zone

30 Pages·2004·0.29 MB·English

by  Sicinski, J.

vol. 25, no. 1, pp. 67–96, 2004
Polychaetes of Antarctic sublittoral in the proglacial zone
(King George Island, South Shetland Islands)
Jacek SICIŃSKI
Zakład Biologii Polarnej i Oceanobiologii, Uniwersytet Łódzki
ul. Banacha 12/16, 90−237 Łódź, Poland
<[email protected]>
ABSTRACT:NinetyeightpolychaetespecieswerefoundintheshallowsublittoralofAd−
miralty Bay. The most abundant were Leitoscoloplos kerguelensis, Tauberia gracilis,
Ophelinasyringopyge,Rhodineintermedia,Tharyxcincinnatus,Aricidea(Acesta)strel−
zovi, Apistobranchus sp.,Cirrophorusbrevicirratusand Microspio moorei. Meanabun−
danceofpolychaeteswasestimatedat120ind./0.1m2.Asaresultofclusteranalysisseveral
polychaeteassemblagesweredistinguished.Thehighlyspecificassemblagewithtwochar−
acteristicspecies,ScoloplosmarginatusandTravisiakerguelensis,fromshallowareaswith
sandy bottom situated far from glaciers; a distincly specific assemblage with Apisto−
branchussp.frompoorlysortedsedimentsinthebottomareassituatedontheslopesatthe
baseofsteeprubbleshores;therichestandmostdiverse,highlyspecificpolychaeteassem−
blagefromthecentralbasinofthebaywithTauberiagracilisasthemostcharacteristicspe−
cies,aswellastwoassemblagesfromthebottomareasneighbouringglaciersandinflu−
enced by the intensive enrichment of very small grain−sized sediments with Ophelina
cylindricaudata and Tharyx cincinnatus. Clear assemblages’ arrangement was observed
alongthegradient:sand,siltysand,silttowardsclaysilt.Otherimportantfactors,support−
ingtheproposedclassificationofassemblagesandtheircharacter,includethesortingcoef−
ficientofthesediment(So)aswellastheslopeofthebottom.Thebetween−habitatdiversity
of polychaete fauna is strongly connected with the phenomena occurring in the
neighbouring terrestrial coastal areas.
Key words: Antarctica, Polychaeta, sublittoral, bottom sediments.
Introduction
TheecosystemoftheAntarcticshelfandcoastalzonehasrecentlybecomethe
object of research recommended by the Scientific Committee of Antarctic Re−
search.Thequestionconcerningthenatureandimportanceofmutualimpactsbe−
tweenlandandseaisoneofthemostessentialissues.Sedimentationanditseffects
seemtobethemostimportantfactors.Thetypeofsedimentistheparameterwhich
Pol. Polar Res.25 (1): 67–96, 2004
68 Jacek Siciński
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Polychaetes of Antarctic sublittoral in the proglacial zone 69
Fig.2.Investigatedarea(HerveCove),withthelocationofsamplingstations(coastalareasfreeof
glaciers are shaded).
essentiallydeterminesthecharacterofsoftbottombenthiccommunities(Thorson
1957,Gray1974).Rhoads(1974)stressedthattherelationshipbetweensediment
and fauna is crucial in explaining the benthic ecology.
Bottomsedimentsaremostdiverseinthecoastalzone,whichisrelatedtothe
diversityofconditionsinwhichsedimentationoccurs.Hence,studiesonthedistri−
butionofzoobenthosinthatpartofAntarcticshelf,takingintoaccountthedyna−
mismofprocesseswhicharedifferentfromthoseoftheopenocean,deservesat−
tention.ThiswaspointedoutbyDayton(1990)andArntzandGallardo(1994).So
far very scarce initial information on the distribution and structure of the of soft
bottom Antarctic zoobenthos assemblages analysed against a background of the
character of sediments originate from Hardy (1972), Richardson and Hedgpeth
(1977)andPlatt(1979).Thedescriptionofpolychaeteassemblagesintheshallow
sandyandsiltybottomsublittoralofMorbihanBay(KerguelenIslands)waspre−
sentedbyDuchêne(1984).IntheBransfieldStraitMühlenhardt−Siegel(1989)dis−
tinguished some assemblages of mollusks and ostracods connected with the
character of bottom sediments.
Itseemsthatincreasingknowledgeofthespatialdistributionofsedimenttypes
maybeakeyforunderstanding localphenomena inthecommunities oftheAnt−
arctic benthic sublittoral. This problem was highligted by pilot studies on zoo−
benthos distribution in Admiralty Bay (Jażdżewski et al. 1986, Siciński 1986).
Amorecomprehensiveanalysisofthisproblem,aswellasanattempttoelaborate
a synthesis, constitute the main aims of the present study.
70 Jacek Siciński
Study area, material and methods
Thematerialwasgathered in1979–1988 inthecourseofseveralPolishAnt−
arcticExpeditionsofthePolishAcademyofSciencestotheH.ArctowskiAntarc−
ticStation.Thevastmajorityofthematerialwascollectedin1985.Investigations
coveredEzcurraInletandapartofthecentralbasinofAdmiraltyBay(Fig.1).Ma−
terialwascollectedintheshallowsublittoraldowntothedepthof165m,thusto
themaximalrecordeddepthintheinner,westernpartofEzcurraInlet.Thisisthe
part of the bottom with the highest diversity and variability of environmental
factors in the Admiralty Bay coastal zone.
Several authors have described the environment of Admiralty Bay. Detailed
informationonitshydrology andhydrography isgivenbyPruszak(1980),Samp
(1980),Marsz(1983),Lipski(1987)andothers.IntensiveresearchactivityofBel−
gian,Brazilian,GermanandPolishbiologistsinthebayareahasbeenrecentlytar−
getedbyitsdesignationasthekeysitefortheSCARProgramEcologyoftheAnt−
arctic Sea−Ice Zone 1994–2004.
Suspended matter and sediments
Amongthemostimportantabioticfactorsthatdetermineconditionsoccurring
attheseabottomisthecharacterandsuspendedmattercontentandtheprocessof
itssedimentation.ThemeansuspendedmattercontentinthewatersoftheSouth−
ernOceanrangesfrom1to2mg/dm3.Theamountofsuspendedmatterinthewa−
ters of Admiralty Bay exceeds several times those from open Antarctic waters
(Pęcherzewski1980). InAdmiralty Bay,inparticular initscoastalzone,surpris−
inglyhighfluctuationsarerecordedinthecontentofinorganicsuspendedmatter,
dependent on the season, region and distance from glacier. The lowest values,
about2.8mg/dm3,wereobservedinwinterinthecentralpartofthebay.Veryhigh
amountsofmineralsuspendedmatter,usuallyabove100mg/dm3,wereobserved
in summer in the front of glacier cliffs (Pęcherzewski 1980). Maximal values,
amounting to almost 270 mg/dm3 were recorded in summer in a small lagoon,
HerveCove,closetotheinflowingglacialstream(Figs1and2).Itisworthnoting
thatthewatersofEzcurraInlet,especiallyinitswesternpart,aretherichestinin−
organicsuspendedmatter.MovingfromthewesternpartoftheEzcurraInlettothe
centralareaofAdmiraltyBayasharpdecreaseininorganicsuspendedmattercon−
tentwasobserved(Fig.3).Itwascalculatedthatabout2000tonsofmineralsus−
pended matter is transfered daily from land to the bay in summer (Pęcherzewski
1980). Part of this amount is carried by surface current to the Bransfield Strait.
Another part is spread very unevenly on the bottom of the bay.
According to the data by Lipski (1987) water transparency related to sus−
pendedmattercontentrangesfrom2minthefjordsinsummerto32minthecen−
Polychaetes of Antarctic sublittoral in the proglacial zone 71
Fig.3.GradientofsuspendedmattercontentinthewatersofAdmiraltyBay(isolinesdenoteamount
of suspended matter in mg/dm3in the subsurface layer, according to Pęcherzewski, 1980).
tralareaofthebayinwinter.Thelattervalueisequivalentto2.5mgofsuspended
matter per 1 dm3of water.
There are very scarce data of the Admiralty Bay bottom sediments distribu−
tion.RudowskiandMarsz(1996)claimthatthethicknessofthesedimentedlayer
ranges from over a dozen to several dozen meters.
Samplesofsedimenttogetherwithitsfauna,usuallyweighingfromseveralto
about a dozen kilograms, were collected with a Van Veen grab with a sampling
areaof0.1m2.Partofeachsample,400–600cm3,wasseparatedforgranulometric
analysisanddesiccated.Therestofthesamplewassievedona0.5mmmesh.Ani−
malswerethenpreservedin7%neutralizedsolutionofformaldehyde.86samples
werecollectedinthisway.Intheshallowsublittoral, downto30m,withacom−
72 Jacek Siciński
pactsandybottomwhichwasdifficulttopenetratewiththeVanVeensampler,8
further samples were collected by divers with a “Tvärminne” bottom sampler
(Kangas1972) withasamplingsurfaceof565cm2.Stationdistribution andtheir
numbers is presented in Fig. 1 and Fig. 2.
The Canberra Metric was employed to classify assemblages of Polychaeta.
C(cid:1)(cid:4)n xi (cid:2)xj
(x (cid:3)x )
k=1 i j
where:
C – Canberra Metric,
x – density of individuals of a given species in station “i”,
i
x – density of individuals of a given species in station “j”,
j
| | – absolute value,
n – total number of species.
Calculationswerecarriedoutusingraw,nontransformeddata–thedensities
of90polychaetespeciesin94stations(=samples)(Siciński1998).Objectgroup−
ingwasdonewitha“flexiblesorting”methodusingthecoefficientofgroupingef−
ficiency “(cid:5)” = –0.25.
Innamingeachdistinguished Polychaetaassemblage,thenameofitsleading
species(i.e.thatonewhichobtainedthehighestresultfrommultiplyingitsdomi−
nationvaluebythevalueofdegreeofassociationindex,DAI)waslocatedbesides
itsliteralsymbol.TheDAindex(Salzwedeletal.1985)expressesthepercentage
ofindividualsofagivenspeciesrecordedinagivenstationgroup(=assemblage)
within the total number of specimens of that species in the overall study area.
Not all species recorded in the study area were considered in the analysis.
Some species of the Cirratulidae family and Euclymeniinae subfamily were ig−
nored. The specimens of these species are extremely delicate and only a small
partofthemwerepreservedwellenoughtoenableidentification,sotheycannot
becounted.AlsothefamilySpirorbidae,abundantlyrepresentedincertainbot−
tom areas, particularly in the shallows of the central bay area, were excluded
from analysis, owing to the difficulties in precise determination of the whole
spirorbidcollection.
InsomecasesthePrincipalComponentAnalysiswasemployedinthepresent
study.Itservedtoordinate47bottomsedimentsamplesagainsttheirtexturalchar−
acters (Fig. 7) as well as to ordinate 9 distinguished polychaete assemblages
againstabackground ofsomebottomcharacters(Fig.8).Thepossibility toordi−
nate objects while simultaneously estimating their dependence on variables was
also exploited (Digby and Kempton 1987, “biplot” option).
Thefollowing termsdenoting species’domination inassemblageswereused
throughoutthestudy:dominantsarespecieswhosenumberconstitutedmorethan
5% of all specimens of all species composing an assemblage, subdominants are
species with 2–5% of specimens, while influents are those which constituted
Polychaetes of Antarctic sublittoral in the proglacial zone 73
Fig.4.Bottomsedimentsin47stationsbasedontheproportionofsand,siltandclay.Stationsare
specifiedbytheletterofthestationsgroup(orpolychaeteassemblage)accordingtothedendrogram
classification in Fig. 6.
1–2%.Remainingspecies,representinglessthan1%ofspecimens,areconsidered
accessory ones (Trojan 1975).
Thepresenceandnumberofcharacteristicspecies,theirfrequencyaswellas
the value of degree of association index (DAI) of dominants and subdominants
(Table1)wereconsideredascriteriaforspecificcharacterofdistinguishedassem−
blages.So,fourcategoriesofassemblagescanbedistinguished.Anarbitrarilyse−
lected scale comprises nonspecific assemblages, weakly specific assemblages,
fairly specific assemblages and highly specific assemblages.
In 47 of all 94 zoobenthos samples sediment was also collected for granulo−
metric analysis carried out by the araeometric method. Sediment was sieved out
throughasievewith1mmmeshsize.Whatremainedonthesievewastheskeletal
fraction.Theotherpart,withgraindiameterbelow1mm,wasfurthersortedout.
On the basis of obtained results cumulative curves of granulation were con−
structed,inwhichthecontentsofsand,siltandclayfractionsweremeasured.The
74 Jacek Siciński
Fig.5.Therelationshipbetween(cid:6)unitsandsortingcoefficient(So)ofbottomdepositsin47stations.
respectiveresultsarepresentedinatriangulardiagram(Fig.4).Theclassification
andnomenclatureofsedimentsproposedbyShepard(1954)wasacceptedaspar−
ticularlyusefulforweaklysortedsediments.Fromthecumulativecurvestheval−
uesofquartiles Q1(25%), Q2(50%)andQ3(75%)werealsoreadandthenem−
ployedtocalculatethesortingcoefficient(So)andmedianofgraindiameter(Q2),
expressedsubsequentlyintheunitsof(cid:6)=–log d(Krumbein1934),where“d”is
2
themediangrainsizeexpressedinmilimeters.Thesortingcoefficientwascalcu−
latedaccordingtotheformula:So=Q3/Q1.Valuescalculatedinthiswayserved
tolocatethe47sedimentsamplesinthecoordinatesystemrepresentedbythesort−
ing coefficient and (cid:6)coefficient (Fig. 5).
Polychaetes of Antarctic sublittoral in the proglacial zone 75
Results
Sediments.—BottomsedimentsofAdmiraltyBayarecomposedofrandomlyal−
locatedclusticmaterialsofvariousfractionstransportedtothebaymostlybygla−
cialandsubglacialstreamsandoriginatingbothfromtheabrasionofshoresaswell
asfromthemelting ofdrifting icebergs. Intermsofgrain−size structure thesedi−
mentsaresands,silty−sands,silty−clay−sands, sandy−clay−siltsandclay−silts(Fig.
4).Intermsofmedianparticlediameterexpressedbyphi((cid:6))units,thesediments
representthewholerangeofpossibilities,startingfrommediumsandandending
withveryfinesilt(Fig.5).Sedimentsarepoorlyandverypoorlysorted;theyusu−
ally contain a considerable amount of very coarse sand, gravel and stones.
Classification of assemblages.—The most general division of the dendrogram
distinguishes two clusters of stations (Fig. 6). Cluster “X”’, large and internally
verydiversified,comprisesvariousareasofEzcurraInletinthewholedepthrange
ofthisbasinaswellasshallower(4–40m)stationsofthecentralbaybasin.Cluster
“Y” is almost exclusively composed of stations located in the central part of the
bay,atdepthsfrom45to150m.Thismostgeneralclassificationofthe94stations
indicates some distinctions of polychaete fauna in the Ezcurra Inlet as compared
withpolychaeteassemblagesofthecentralbayarea.Thisalsoindicatesageneral
biocenotic difference betweentheshallow coastalzoneascompared withdeeper
sublittoral areas.
In70stationsofthecluster“X”therewererecorded72specieswhereasinonly
24stationsofthecluster“Y”asmanyas81specieshavebeenfound.Meanspecies
number per 1 m2 of bottom area was 34 in cluster “Y”, while only 10 in cluster
“X”’.Anothernoticeabledifferenceisthetwicehighermeanpolychaetedensityin
cluster“Y”thanincluster“X”:203(±92SD)and92(±84SD)specimen/0.1m2,
respectively(bothmeansdifferatasignificancelevel(cid:7)=0.001).Bothclustersdif−
feralsointheirlistsofdominantspecies(ifweignoreeurytopicspecies,whichare
commonforbothareas).Indeeperpartsofthecentralbayarea(cluster“Y”)these
dominantspecieswereAricideastrelzovi,CirrophorusbrevicirratusandAsychis
amphiglypta, whereas in the area of Ezcurra Inlet and in shallow stations of the
central part of the bay (cluster “X”) the characteristic group of dominants con−
sisted ofTharyx cincinnatus, Microspio moorei andApistobranchussp.
A more detailed division of the dendrogram (Fig. 6) distinguishes 9 station
groups.Suchadivisionseemstobethemostsuitabletakingintoaccountthepossi−
bilitiesofitsplausibleinterpretationagainstabackgroundofthepatternofthebot−
tom deposits distribution.
The differences in polychaete density in given assemblages was estimated at
thesignificancelevel(cid:7)=0.05.Lowdensitiesofpolychaetesinassemblages“C”,
“E”and “D”(60 ±46SD, 30 ±26SD and 28 ±18SD ind./0.1m2respectively) do
notdiffersignificantly.Thehighmeandensitiesinassemblages“F”and“I”(136±
97SDand133±90SDind./0.1m2respectively)arealsonotsomuchdifferent.Fi−
76 Jacek Siciński
Fig.6.Dendrogramofstationsde−
rivedfromtheabundancedistribu−
tionof90polychaetespecies(ex−
43-11m planations in text).
36-13m
A 44-44m
35-10m
45- 6m
33-10m
46- 6m
D 42-12m
34-14m
40-14m
26-72m
41-16m
B 62- 4m
63- 4m
65-10m
66-15m
68-25m
C 71-38m
67-20m
70-30m
69-27m
64- 7m
22-33m
23-33m
24-34m
21-18m
30-17m
32-10m
17-26m
19-34m
F 20-15m
58-69m
29-32m
54-52m
27-40m
18-33m
28-40m
56-15m
31-12m
16-20m
72-41m
57-35m
39- 6m
G 37- 6m
38- 6m
1-65m
7-55m
12-146m
47-70m
2-65m
E 8-60m
25-68m
9-55m
10-152m
11-132m
3-62m
4-48m
6-45m
5-45m
51-90m
49-73m
52-90m
I 13-127m
48-72m
14-127m
15-129m
50-81m
59-86m
60-126m
61-165m
91-120m
92-126m
89-115m
90-119m
83-88m
85-97m
84-88m
86-100m
87- m
88-112m
93-145m
94-147m
H 73-46m
74-46m
75-50m
76-53m
77-55m
81-66m
78-55m
82-72m
79-59m
80-60m
55-56m
53-52m