Biological Accommodation in the Benthic Community at Mcmurdo Sound, Antarctica Author(S): Paul K

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Biological Accommodation in the Benthic Community at McMurdo Sound, Antarctica Author(s): Paul K. Dayton, Gordon A. Robilliard, Robert T. Paine and Linnea B. Dayton Reviewed work(s): Source: Ecological Monographs, Vol. 44, No. 1 (Winter, 1974), pp. 105-128 Published by: Ecological Society of America Stable URL: http://www.jstor.org/stable/1942321 . Accessed: 15/11/2012 17:29

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This content downloaded by the authorized user from 192.168.52.62 on Thu, 15 Nov 2012 17:29:57 PM All use subject to JSTOR Terms and Conditions E(eological MAlionoapl.s ( 1974) 44: pp. 105-128

BIOLOGICAL ACCOMMODATION IN THE BENTHIC COMMUNITY AT McMURDO SOUND, ANTARCTICA'

PAUL K. DAYTON Seiipr,. Iisititttioi of Oceanotroaphv, La Jolla, California 92037 GORDON A. ROIL-LIARD Woo(lul(ar-Elwicoll, 3489 Kurtz Sreet, Sall Die-o, Califolrlia 92110 ROBERT T. PAINE 1D)parltmnnt of Zoology, UlniV(EitV of Wa.s/illctbo;, Seattle, Wa.shliiiigtoln98105 IINNEA B. DAYTON 608 Barbara A vaeim, Sol/aia Beach, California 92075

Abstraet. Studies of the benthos between 30 and 60 m at Cape Armitage, McMurdo Sound. Antarctica, reveal an epifatinal community in which sponges and their asteroid and nUdibranchpredators predominate. Field experiments demonstrated that, with the exception of MveN(caleaeerata, the growth rates of the sponges are too slow to measure in one year. Aleal/e, however, was observed to increase its mass as much as 677%. Because of its more rapid growth rate, Mveale appears to be the potential dominant in competition for substraturm space, the resource potentially limiting to the sessile species. This conclusion is supported by observations of Alxeale growing over and, in some cases, apparently having smothered many other sessile species representing at least three phyla. The densities and size frequency distributions of all the predators were measured; numerous feeding observations allowed an accurate appraisal of dietary compositions. Because of the predators' very slow consumption rates, however, direct measures of ingestion and its impact on prey populations were not possible. Estimates of the ingestion rates were derived from measurements of predator respiration rates, growth rates, and gonad growth. Data from the field surveys and the energetics studies suggest that M ycale is prevented from dominating the space resource by the predation of two asteroids, Perkimaster fusel.s antar(tietsc and A eolontaster eonrspieuits. Adult Perkianster specialize on Mycale, and the sponge provides a small proportion of the diet of A. (onispicutts. Aeo(lontaster conspietuis and the dorid nUdibranch Austrod(oris tiwtnmetdensis are the most important predators on three species of rossellid sponges (Romsella racovitzae, R. nwt/a, and Seolynia.stra joubilli). Despite this relatively heavy consumption and despite the fact that none of these sponges has a refuge in growth from potential mortality from A. eonspicims, very large standing crops of the rossellid sponges have accumulated. This accumulation appears to result from predation on larval and young A. eonlspieitus and Austrodloris by 0(dontasterl vali/Wus, which is primarily a detrital feeder and apparently acts as a filter against the settlement and survival of the A. Colispicims and Ainstro(lolis larvae. In addition, predation upon adult A. conspiculis by 0. iva/ihlas and the actinian Urticillopsis atllarctitis anntlally kills approximately 3.5%'c of the A. eon.spiettt.s population. This mortality exceeds the apparent rate at which A. c-onspietlt.s escape the larval filter.

KeY wvords: Acconmnmodation- Aniitarcticai asteroit; benlt/hos; ('O)i)illllit\' (0olpetitioll; Porifi-ea: /)-re(latioll, preitltabilitY:. ta/ui/it.

INTrOI)UC'riON degree of physical predictability. That these com- nuinities have received less attention than most others Environmental predictability is assuiming an in- can he attributed to their relative inaccessibility or creasingly important position in theoretical considera- limited geographic distribution, or both. tions of the species composition and organizational Superimposed on the strictly physical components maintenance of natural communities because of the of community organization is a hierarchy of biologi- widely held assuLImptionamong ecologists that such cal events that may either amplify or minimize the predictability and community stability muLst be re- variation initiated by changes in the physical environ- lated. The physical environment of most natural ment. These biological events are an commuILinitiesis markedly variable- only a few com- equally significant component of the total predictability picture. mun_1ities,suIch as carves ( POLI1SOn1and CuLlver 1969) The simplest of these are the annual pulses of the deep sea (Sanders 1968). or the ,antarcticbenthos production characteristic of cave and antarctic deeper than 3() m ( Dayton et al. 1.969), are suIf- ecosystems. More complex and subtle are the in ficiently invariate to justify the aSssumption of a high changes patterns induced by biological interaction (Paine 1966a, Day- I Received October 5. 1972: accepted April 17. 1973. ton 1 971 ) suLch as competition and various levels of

This content downloaded by the authorized user from 192.168.52.62 on Thu, 15 Nov 2012 17:29:57 PM All use subject to JSTOR Terms and Conditions 106 PAUL K. DAYTON FT AL. Ecological Monographs Vol. 44, No. I biological disturbance. It is these biologically based events that, within the broad limits established by physical parameters, probably determine the structure (pattern, abundance, trophic structure) of most assemblages (Connell 1961, Paine 1966a, Harper ROSS SEA 1967, Janzen 1970, Dayton 1971). We believe that an evaluation of biological interactions in a complex community inhabiting an apparently physically predictable environment is im- Mc MURDO portant to an eventual understanding of community X SOUND J/ RROSS ISLAND " organization. Further, we think that the most satis- factory understanding will be a mechanistic one, in which the known confounding physical and biological influences are separated by experimental means. Two ROSS ICE SHELF of the most physically predictable natural environments of broad geographic extent are the benthic communities of the deep sea and the antarctic. The FIG. 1. Map of McMurdo Sound and Ross Island inadequacy of explanation made in the absence of showing the Cape Armitage study area in the inset. direct observation/experimentation is exemplified in the former of these by the assumption of opposed Most of the conspicuous species in the benthic ecological mechanisms-competitively derived micro- community at depths between 33 and 60 m are niches by Sanders (1968) and cropping disturbance sponges and their asteroid and molluscan predators by Dayton and Hessler (1972)-to explain the (Dayton et al. 1970). The community is relatively organic diversity. The present paper gives details of amenable to ecological study for two reasons. First, an initial attempt to examine, by both experimenta- the sessile species, almost exclusively sponges, appear tion and direct observation, the role played by to share primary substratum as their most important biological interactions such as competition and pre- potentially limiting resource, and the successful dation in the organization of a shallow-water benthic utilization of this resource can be easily quantified. community in the physically constant environment Second, the predators on the sponges are conspicuous, at McMurdo Sound, Antarctica. move slowly, and digest their prey externally, making The major source of physical variation in the it possible to quantify predator distribution, abun- McMurdo Sound benthic community is the forma- dance, and diet. tion of anchor ice, which, in conjunction with the ice scour, effectively zones the community (Dayton DESCRIPTION OF COMMUNITY et al. 1970). Thus the shallowest zone (0-15 m) is essentially devoid of sessile organisms because of This paper describes work done between McMurdo the annual certainty of the ice disturbance from both Station and Cape Armitage on Ross Island in Mc- anchor ice and the scouring action of drift ice. An Murdo Sound, Antarctica (Fig. 1). The field pro- intermediate zone (15-33 m) is below the limit of gram was carried out between October I and Decem- ice scour but is still influenced by anchor ice forma- ber 15, 1967, and September I and December 16, 1 tion capable of removing objects weighing as much 968. All the data were collected at McMurdo as 25 kg (Dayton et al. 1969). Competition for Sound, except for the caloric values, which were space does not seem to be important in either of the measured during 1969 and 1970 in Seattle, Washing- upper two zones, and it is difficult to differentiate ton. the effects of physical disturbances, such as uplift by The substratum below 33 m is a mat of siliceous anchor ice and scour, and biological disturbance re- sponge spicules, which varies in thickness from a few sulting from the presence of predators. Below 33 m, cm to more than 2 m (cf. Koltun 1968). Below the however, anchor ice does not form, and scouring and sponge spicule mat is usually a layer of bivalve shells other physical disturbances rarely occur. The physi- (mostly Limatula hodgsoni). Sponges, the most cal environment below 33 m has been described by conspicuous sessile species, cover almost 55% of the Littlepage (1965), who found that at 75 m the surface area and provide almost all the vertical temperature (annual x- -1.87' C SD 0.11I N structure in the community. The sponges exhibit a 31), salinity (annual X = 34.7",; SD 0. 9: N remarkable diversity, both in the number of species 30), dissolved oxygen concentration (annual X and in the many growth forms. Some aspects of the 6.79m1/ I; SD = 0.38: N = 31 ), and concentrations natural history of the more conspicuous and abun- of various mineral elements are very predictable. dant species can be found in Appendix L. The

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FIG. 2. Photographs of the sponge assemblage at 60 m at Cape Armitage. The two round sponges in the foregroundof the left plate are Tetilla leptoderma; all the other recognizable sponges are "Volcano" sponges. The large "Volcano" sponge (probably Scolyanstra joihini) was slightlyover 2 m tall and 1.5 m in diameter. The right plate shows a large Mycale acerala (approximately I m tall) overgrowingHaliclona d(lacoi in the center and a small "Volcano" sponge on the right. sponges, sonie of which resemble staghorn corals, identified aeolids (possibly Eibhranchus sp. and large fans, bushes, volcanoes, spheres, etc., contribute Coryphella sp.), while Clavularia is preyed upon by a remarkable vertical structure to the community 7ritoniellabelli and Notoeolidia gias. Hydroidsand (Fig. 2). Much of this structure is used by the actinians are also eaten by pycnogonids,especially fishes as refuge from seal predation, and many ani- Thavinasopycnon striata and various species of mals, including fish, holothurians, crinoids, and Colossendeis. The only predator on ascidians ob- ctenophores, use the sponges as elevated perches. servedwas an unidentifiedchrome yellow lamellarian In addition to the sponges there are scattered gastropod which frequentlydrills them and deposits individuals of many other macroscopic species, in- eggs there. Limnatulahodlgsoni is consumed by the cluding the actinians Stomiphia selaginella, Artemni- asteroids Diplasterias hrucei and Odontaster validus, dactis i'ictrix. Urticinopsis antarcticus, Isotealia ant- and the gastropod Trophon langstaffi. The urchin arctica. and Hormaath/ia lacunifera: the alcyonarian Sterechinus neumayeri, and especially Odontaster Akcyoniumypaesvleri; the hydroids Lamnpra parviula, valid(usare conspicuous detritusfeeders, whereas 0. L. mnicrorhiza, 7'ubularia ho(dgsoni, Halecium ar- vaili(dusand the nemertean Lineus corrugatlusare horeum, and a number of unidentified species: some efficientscavengers. The relativelylarge and rare bryozoans, especially Hippmclenella carsonae. 7'ere- asteroid Macroptychast'r accrescens consumes 0. pora frigida, and Caherea dlarwinii; some ascidians, valkius and Sterechinus neuinayeri. The actinian especially Cnemi(locarpa verrucosa; the pterobranch Urticinopsi-santarcticus is an efficientpredator of Cephalodi.scus antarcticus: the bivalve Limnatula echinodermsand medusae that brush against it. hod'svoni; and a few unidentified sabellid polychaetes. In addition to Cape Armitage, we also studied The asteroids Perknaster fuscus antarcticus, Aco- areas north of Hut Point, along Arrival Heights to dontaster conspicWuis, A. hodgsoni. Odonlaster the Cinder Cones, and at Turtle Rock, Cape Evans, imeri(lionalixv, and Odontaster validus and the dorid Cape Royds, Backdoor Bay, and the Dailey Islands. nud ibranch A ultro(loris memur(lensis are the most The sites between Hut Point and the Cinder Cones conspicuous predators on sponges. Several other are increasinglysubject to sedimentation;other sites nudibranchs prey on the stoloniferan Clavutlaria have unstable substrate(Turtle Rock) or are sub- frankliniana and hydroids: specifically, Lam pra spp. ject to intenseice scour ( Dailey Islands). The other are eaten by two unidentified aeolids, and Halecium more northerlysites exhibit very differentspecies by Doto sp. (e.g. D. anltarctiwts) and by two un- complexes dominated by algae, scallops, sea urchins,

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TABLE 1. Abundance of sponges at 33-60 m, Cape in which we expected to he able to measure, for Armitage, McMurdo Sound, in terms of percent cover example, growth rates of prey species and consuimp- of benthic surface and percent of total biomass (wet weight). Total percent cover of sponges = 55.5% of tion rates of predators. the remaining cover; bryozoans, actinians, hydroids, etc. = 5.4%; free space = 39.1%. Total area sur- 7'Ixono 7 , veyed = 410 m2 Many taxonomic prohlems are encountered in any Percentof broad ecological study of an unfamiliar environ- Sponge Percent Sponge ment. We were fortunate that, because of the Species Cove r Biomass thorough and competent collections made by Hodg- Rossella racovitzae 41.8 70.9 son ( 1907) during the first British National Antarctic Volcano" sponge 3.8 18.3 Expedition, taxonomic literature on the organisms Tetilla leptodermna 3.2 6.7 and most Cinachyra antarctica 1.2 0.6 of this community is remarkably complete, Haliclona dlancoi 1.1 0.2 of the larger animals are adequately described. Also, Mycale acerata 1.1 2.4 we were fortunate to have outstanding cooperation Polymastia invaginata 1.0 0.5 Dendr-illa nemnranosa (.8 0.08 from many taxonomic specialists (named in Acknowl- Gellius ten/lla 0.6 edgments). Nevertheless, while we were actually in Spliacrotylusantarcticus 0.5 0.3 the field we were unaware of the species names of Leucetta leptorliapsis 0.2 0.04 Gellins benedeni 0.08 many of the animals: we therefore created colloquial Calyx arcitarius 0.03 names to use in our field notes. This approach has 0.02 Isoclictya setifera certain risks, and we made two errors: the first was Kirkpatrickia variolosa 0.02 Kirkpatrickia coulmnani 0.01 failing to differentiate two species of rossellid lsodictya erinacea 0.01 sponge, Ros.sella nudai and Scolvu.isstra joithini, and Pachychalina pedunculata 0.01 lumping them as "Volcano" sponge. Because "Vol- . Less than 0.01. cano" sponge is one of the most important and conspicuous members of the community, it is unfortunate and high densities of Odlontaster va/i/mits. For these that we are not able to discuss these two species reasons and because of logistic problems involving separately. The second, but less damaging, error travel to some of these sites, we have restricted this was that we split the asteroid species Perknaster paper to data collected at Cape Armitage, unless fu.scits cintcroti(-usinto two groups which look very otherwise stated. Hedgpeth ( 1971 ) summarizes de- different but which we later learned represent juve- scriptions of other communities at many different niles and adults of the same species. This artificial localities around the Antarctic continent, indicating splitting was to our advantage, as the two age groups that the species complex at McMurdo Sound is have markedly different diets. We have maintained circum-Antarctic in occurrence. the separation of these two sets of data in appropriate sections. Diving We made a total of 525 man-dives in 1967 and .Spon,ce (( 0ier on(lI smln(lin,L,( rap 1968. The dives at Cape Armitage, Hut Point, and The abundance, size frequency, and space utiliza- Arrival Heights were made from heated huts placed tion of the sponges were calculated from photo- over holes blasted in the annual sea ice. Other dives transects taken (at I--m intervals along a 20-m line were made from open tide cracks, seal holes, or, most on which each meter was clearly marked) along commonly, open holes which we had blasted. particular depth profiles. We placed the weighted There are some disadvantages associated with the line along the bottom by blindly dropping one end study of this environment. Our diving was some- of the line from the surface and placing the other what inefficient because of the limited bottom time end in such a position that the depth of the line at the depths studied. Furthermore, even a minor remained constant. The photographer was approxi- change of locality necessitated blasting a hole in mately 2-3 m above the substratum, and the total the ice, clearing it, and moving the diving hut over area of each photograph was approximately 6-9 in2: the new hole. Probably the most significant prob- there was no parallax problem when approximately lems with this study arose because of our limited I m2 in the center of each photograph was analyzed. field research season and the relative isolation of All the species could be recognized, and individuals McMurdo Station from outside sources of supplies as small as I cm in diameter could be identified. and references. These restrictions greatly reduce the potential for "trial and error" modification of a us as we program, which might have been useful to FIG. 3. Size-frequency histograms of major benthic approached a functionally undescribed community. sponge species. 33-60 m deep at Cape Armitage.

This content downloaded by the authorized user from 192.168.52.62 on Thu, 15 Nov 2012 17:29:57 PM All use subject to JSTOR Terms and Conditions 40- Kirkp4tria , j~korchi rQylmonj Cola srsWt= a N=6 N=62 3 301 0 30N Sphaerotylus antorci&cs N=73 201 0 20 20

N 48 Ilo lo

20 |i 210 N0 20 40 60 70 I0 20 30 l0 20 40 50 Length Length 301 Mean Diameter Maximum Diameter

2 ajls olclona dSono Ratiii"1 OCovtzae 50i 201 N=769 2YN see text 4oticlN

40 40 q 2or Isodictyx eenticr H r 2 17 1 i I ~~~~~~~~~~~~~~~~~~~~~~~~~~~N=23 10Z [fl In 9'59 10 N=230 30 10 20 30 40 10 20 30 40 50 60 70 W Length Lnt w 2-2012 20. 202 I Teti.I Lrmfa1 H Dendrillamembranosa ~ ~~ o~~~~~N=708 No42 o- w cx W 1_4. 0 0 50 so I0 20 30 I 20 30 40 60 70 Ig 0 I0 20 30 2 Diameter Mean Length Length slLengt

e IMIrttaim volcano'VE sponge N(6 N=59 N-I02o

41Cinachyraantarctica rf-Vlr-v~~~~~~~~~~Ffi.N 441 I0 I 20 30 40 ID 20 30 40 50 60 70 80 30 3 0 Height MaximumDiameter Poyatia inagata~ N- 479 ______201 20 20- 20 Pachychalinapeduncuktat Mycxleacerata N=I 0 N= 31 0- lo-~lo K vvI 10- IO

0 60 20 30 40 20 30 40 ~ 70 80 90 10 20 10 20 I10 ID0 Ia0 Length Mean Diameter Mean Diameter MeanDiameter (without spicules) Mean Basal Diameter LINEAR DIMENSION(cm)

This content downloaded by the authorized user from 192.168.52.62 on Thu, 15 Nov 2012 17:29:57 PM All use subject to JSTOR Terms and Conditions 10 Homnoxonellasp 8- Y=0276 X1862 400/ Lfcfg Intblgais 8001 t13- 802 / Y-0.844 XI.863

700 Spaerotylua antarccu 6- *t73.70 Y=0.435 X~~~2646 4 - 3* 600Ptynasgano~laaEa 0 t13 =14 83 30 50J Y-0714 X2 318 50 2 2-

40 53 140 20 2 300/ 30(} 'Twig Length

2001 * 100- 100 lo/ ?in0* 1L40., X r 20L w 1 20 L Y= (12B03) (1.042)80- 0 20 10 20 l 4. 3 50 10 20 30 Mean Basal Diameter Mean Diameter 60- Height 0 Coaoh antanctln 4. 287 700, Y= 1007 X2 30 60 t'6 =1130 ,1200 2

500' 1000 Kirkpatrickiovarioloso , I 20 30 40 50 2 Y=0.109 donco 40C0 Y=0.477 200, X134 62.408 Length y=3- 30 / *' 6~~~~~~~~~~~013t13-7.60 * t13=7.33 200 , 4/l 1 ~~~~~~~~~~200- ~ Y=0 '33X

10 20 10 20 1t03 /, Length Mean Denmeter(without spicules) 4000 L0 20th Leng E 2800 -~i etdro *Datc~ c19. Te - 2400 Rossella rncocavtza 3000= Y-32l lpodem - X2.244 240 flossel4roco~~~ltr~e 30001 Y=0 453 10--- 1200 Y=0.127 132 X3 j1 | 0 20 ?0 t - X2.648 = =407* 2000- r=0.245 t7 1057 Length 1000- 10 4 / 0 UI 16001 2000- 800/ 1200/ Iscdictya ennrae 600 UJI / X2_211 800- l00 200- Y=0-060t 40031 800- 20000*20

100 20 10 20 203040 Length AQ0 50 60 70 Mean Diameter * Finger Length

l8,00C l0 20 0o '40 i6,00- 10 Length 16 LLatrunculia aoicalis 16,000] Mvcale acerota /Q000 Y=(14.850) (1.345) / 14,000 Y=0.486 Xno Volcano spong t o209 - 6 02 12,CO Vlaospne600 120 12,000) t~o 3 02 1 20,000- Y=0.348 X2.880 11 10,0 tio 89 500~ CaILU UArcilagoOOO 400 Y=0028 X2.348 8000- 20,00 t2= 750 80

6000 z / 300. 600 4000 ** 10,O00 200 400t 200 I 1 , 200 ri 7~~~~~~~~~~~~~~~~~~~~ r * , i ' _ , , ' I0 20 30 40 50 60 70 20 30 40 5010 20 50 Mean Diameter IQ 20 MaximumDiameter Length Height 50 L A D LINEAR DIMENSION (cm) z _05

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TABLE 2. Composition of living sponges. N1 = number of specimens used for determinationof proportion H20 (A); N2 = number of specimens used for determinationof proportionfalse ash (C). True ash is false ash/0.93. The composition of a living sponge is given by the summation of (A) + (D) + (E)

C Proportion E of dry D Propor- B weight Propor- tion true A Proportion that is tion true organic Proportion dry false ash ash (B) x matter Species N1 H2O SD (1.000-A) N2 + SD (C)/0.93 (B-D) Rossella racoi'itzae* 3 .920 + .003 .080 9 .802 + .047 .069 .011 "Volcano" sponge* 9 .890 + .021 .110 8 .707 ? .035 .084 .026 Tetilla leptodernia" 5 .811 + .045 .189 5 .714 + .105 .145 .044 Cinachyra antarctica1 3 .768 + .027 .232 6 .655 ? .071 .163 .069 Haliclonta dancoi 3 .913 + .004 .087 3 .544 ? .032 .051 .036 Mycale acerata 4 .889 + .023 .111 3 .777 ? .039 .092 .019 Polymnastiainbaginataa1 3 .743 ? .017 .257 4 .791 ?.044 .219 .038 Dendrilla mnembranosa 3 .882 + .004 .118 3 .262 ? .015 .033 .085 Gellius tenella 0 3 .657 ? .014 Sphaerotylus antarcticus" 3 .766 + .044 .234 3 .790 ? .015 .199 .035 Leucetta leptorhapsis 3 .906 + .044 .094 3 .599 ? .016 .056' .038 Calyx arcuarius 3 .870 + .022 .130 3 .576 ? .127 .081 .049 Isodictya setfera 0 2 .640 .106 Kirkpatrickia itariolosa 3 .887 + .008 .113 3 .574 ? .034 .070 .043 Isodictya erinacea 3 .856 ? .010 .144 3 .744 ? .018 .115 .029 Pachychalina pedunculata 3 .902 ? .008 .098 3 .597 + .101 .063 .035 Latrunculia apicalis 0 3 .502 ?.122 Inflatella belli 3 .888 + .025 .112 4 .678 ? .086 .082 .030 Homraxonella sp. 4 .901 + .009 .099 3 .580 ? .033 .062 .037

. For this non siliceouLs species, proportion true ash = (B) (C).

The percent cover of each species was determined (assumed to be all SiO2 for the siliceous sponges), by a planimeter or random dots as described by organic fractions, and water of hydration fractions. Dayton ( 1971 ) This photographic technique yielded The ash values for siliceous sponges have been cor- percent free space and percent cover of every benthic rected for water of hydration, based on the findings species and a measure of the size of each individual of Vinogradov (1953) and Paine (1964). We deter- as either a length or a series of diameters, which were mined the percent hydration characteristic of two averaged. antarctic species as follows. The material was We obtained length (or diameter) to wet weight cleaned in distilled water, and then subjected to two regressions of sponges by collecting specimens, or three digestions in hydrogen peroxide, accom- making the appropriate linear measurements, and panied by further washings. When a clean prepara- weighing them after allowing them to drip dry for I tion was obtained, the spicules were dried at 80? C, minute. After wet weights were determined, the weighed, and then incinerated at 500? C for 3 to 4 sponges were oven dried to a constant weight at hours. The weight loss was assumed to be caused by 80? C, allowing a wet weight to dry weight ratio to evolution of bound water from the spicules. The be computed. The dry residue is composed of ash values for "Volcano" (x = 7.2%; SD = 1.I N = 5) and Cinachyra antarctica (#x= 6.8%; SD 0.4%; N - 5) have been averaged (7.0%) and this value assumed to characterize all our siliceous sponge material. Therefore, true ash = false ash/0.93. Dried wet weight and linear FIG. 4. Relationship between samples of each species were pulverized, stored, and dimensions of sponge species. Length = total length later burned in a Parr semi-micro bomb calorimeter of sponge; height = total height; mean diameter = average of two or more diameters of spherical or discoid (Model 1411). In most cases, portions of the same species; "twig" length = length of one twig-likeprojec- pulverized sample were used for ash determination tion of Homaxonella sp, and wet weight given is that and calorimetry. But for six species we found it im- of a "twig"; "finger" length = length of one finger-like projection of Haliclona dancoi and wet weight given is possible to pulverize adequately the dried material that of a "finger." t values given (N-2 df) are for the to be used for calorimetry without first removing as significanceof the differenceof b, the regression coeffi- many of the glass spicules as possible. Therefore, cient from zero in the equations written in the form correct ash values for those species were determined InY - In a + b ln X or lnY = In a + x In b as appropriate. All b values show a highly significantdifference from samples other than those to be used for (p < .01), except those of PachlYchliliua pedutln- from zero calorimetry. The caloric values for the calcareous (111t(1(1 p < .05 ) and La!;miculia (Icia li.s ( p < . It))

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TABLE 3. Caloric values of sponges. N_ number of Cages specimens used to determine caloric values. For each species except those denoted with :, the kcal/dry g Fifty cages, each with an adjacent control, were value = mean of N determinations,and the kcal/ash- established in 1967 at HLut Point and Cape Armitage - freeg value mean of N determinationsof kcal/dryg/ with the objective of defining relative growth rates (1.00-proportion ash), where proportion ash = true ash per dry weight for each sample burned of sponges and the feeding rates of their predators. These cages were made of 6.3-mm steel mesh panels Mean Mean that had been dipped in epoxy and baked. The top kcal/ kcal/ash panels were 0.9 X 0.9 m and the side panels were dry g free g Species N (?SD) (?SD) 0.3 X 0.9 m. The panels were held together by stainless steel wire and plastic poultry bands. With Rossella side panels added, the cages were made 0.3, 0.6, racovitzaew' 3 1.086 6.209 ? 0.668 "Volcano" 0.9 m high. All the cages survived without loss or sponge" 4 1.415 5.986 ? 0.826 fouling during the I year on the bottom. Tetilla Thirty of the cages excluded all predators from leptoderina: 5 1.407 6.043 ? 0.679 Cinachyra sponge species or species complexes, and 18 included anlarctica: 4 1.762 5.924 ? 0.236 predators. However, seven of these 18 cages en- Haliclolna dancoi 3 2.635 ? 0.091 6.380 ? 0.489 closed only the echinoid Stereclinits neuniayeri or Mycale 1.001 ? 0.184 6.220 ? 0.75(0 the asteroid Diplvsterias /brlu(ei; we later learned that acerata 3 (0.519) (3.222) neither of these predators eats sponges. Therefore, Polyinastia ilnaginata5 3 1.008 6.815 ? 0.651 those seven cages were also considered to have ex- Dendjilla cluded sponge predators. We established two three- ? ? Inemnbrano.sa 3 4.086 0.119 5.690 0.037 sided cages to evaluate potential cage artifacts, but Gellius tenella 3 1.634 ? 0.044 5.575 ? 0.162 none was observed. The predator exclusion cages Sphliarotyvlls were designed to measure differential growth rates alitareticuls: 3 (.911 6.094 ? 0.068 Leucetta of sponges and in many cases to test hypotheses that leplorhap.si-s 3 1.785 ? 0.261 4.440 ? (1.486 certain sponge species would monopolize the avail- Calyx able space and exclude other species. The predator arcuarius 3 2.161 ? 0.742 5.708 ? 0.241 Isoadicty enclosures were designed to evaluate consumptions setifera 2 1.878 ? 0.622 6.069 ? 0.221 rates of sponges by their predators and in some cases Kirkpatrickil to test preferences of a predator given two sponge v'ariolosa 3 2.144 ? 0.134 5.614 ? 0.370 IYodlic t N(a species it was known to eat. Each cage area and erilnacCa 3 1.384 ? 0.083 6.929 ? 0.323 adjacent control was photographed in 1967 and Palch~l Ciallia~ again upon our return in 1968. pe(dluculatl 3 2.076 ? ().616 5.801 ? 0.082 Latrunculia apicalis 3 2.656 ? 0.799 5.755 ? 0.266 Pre(lator dliet~s,a1hutndance, an(l size frequency 1ifla/tel/(l The diets of the predators were determined both belli 4 1.510 ? 0.498 5.625 ? 0.506 Homxolie//(a by noting the percent feeding and the prey items of sp. 3 2.576 + ().196 6.854 ? 0.174 the various predators on dives made with that specific

t For each species denoted 4, the hardness and large size of the objective, and, more commonly, by making such siliceouIs SpICUIles present made it impossible to prepare samples observations dives with other objec- for calorimetry without first removing some of the spictles. incidentally on Theietore, the ash contents of the samples burned were low. tives (e.g., setting tip cages, laying out transect lines, For this reaison, the caloric vailu.e per dry g obtained from the sample was divided by (1.00-proportion ash for the sample) to etc.). Since the latter did not yield data on the obtain kcal/ash-free g; the values from samples of N individuals were averaged to provide the mean given. The mean kcal/ash-free abundance or size frequency of the predators, unless g value was then multiplied by (1.00-mean proportion true ash. (C)/.93 Iroia Table 2), to obtain mean kcal/dry g. The caloric otherwise noted this second class of feeding data is valutes for Leicetta leptorliap.sis, a calcareous sponge, have been corrected according to Paine (1966) for endothermy caused by used only for quantifying description of the total CaCO. Caloric vailu.es in parentheses for MYcale acerata aie diet, so that we can discuss the percentage con- calories useful to predators; 48.2%c (N = 2 samples) of the dry weight of this sponge is spongin, which the predators do not tributed by a given prey species to the total observed ingest but which provides caloric valukte in the bomb calorimetry determinat ions. diet of a particular predator. With the exception of the very common Odontaster vralidutlsand the very rare Ac(alontastel Iodlgwsoni, data a were corrected for sponge Le-ettu leptorlhapsis on the percent feeding, abundance, and size-fre- endothermy following Paine ( 1966h). For Mycale quency of the predators were obtained from transects a correction has been made based on the observation in which a 50-in weighted line was dropped blindly that starfish fail to consume the sponge's organic on a given depth profile and two divers crawled (spongin) skeleton, and that this accouLnts for 48.2%/ along the line recording the diets of and collecting (N -= 2) of the total dry weight. all the predators within I m of each side of the line

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TABLE 4. Results of cage experimentsand their controls; estimated growthof sponges and consumptionby asteroids over a 1-year period

Diam- Original eter diam- after 1 Estimated Sponge eter year Estimated amount kcal Species (cm) (cm) increase" Predator species eaten derived

Mycale acrIata 45 Perknasterfuscus 85% 602b an tarcticus (2, large, caged in) Mycale acerata 45 10-15% biomass Perknasterfuscus piece, 20 cm 83b - 142-213 kcal antarcticus in diameter (still present) Mycale acerata 74 78 15% biomass Perknasterfuscus piece, 10 cm 121' 792 kcal antarcticus in diameter (still present) Mycale acerata 35 40 43% bio-mass Excluded none 305 kcal Mycale acerata 40 Perknaster fuscus 70% 369b antarcticus (2 still present) Mycale acerata 30 unknown 60% 146b Mycale acerata 66 80 67% biomass Excluded none = 2593 kcal

Mycale acerata 25 unknown 60% gob

"Volcano" sponge 55 A co(lontasterconspicuus 55% e 3065 (3, large, caged in) Kirkpatrickia 35 PelrknasterfJuscis piece, 8 cm 17 iariolosa antarcticus in diameter (juvenile, caged in)

Estimated kcal presented are total kcal including those in spongin. Useful kcal derived; calories contained in spongin (estimated to be 48.2% of the total, see Table 3) not included. 55% is the final estimate ot dead sponge and an overestimate of the amount consumed by these three large asteroids during the period of the experiments, as the three were found on the sponge and had already consuLmnedpart of it before the experiment was begun.

(100 m2 total area per transect). The predators mating the diet, percent feeding, density, and size- were later measured and weighed. We eliminated a frequency of this predator. possible artificialsampling bias that would have in- The means used to estimate actual amounts of creased or decreased the apparentdensities, by having sponge biomass consumed by these predators are the diver on the shallow side of the transectcollect discussed in the predator energetics section. only the predators that fell completely within the RESULTS meter belt while the diver on the deep side of the transectcollected all of the predatorseven partially Distributionand abundance of sponge species withinthe belt. In this way we collected reasonably The space utilization by each sponge species is unbiased percent feeding, abundance, and size- presented as percent cover of the substratum in frequencydata. Table 1. The size of each individual as either a The abundance and size-frequency data for length or series of diameters is presented in size- Acodontaster hodgsoni were collected in the same frequency histograms in Fig. 3. In order to estimate manner, but the species was so rare that it was biomass of each sponge species, length (or diam- necessary to utilize most of the individuals in the eter) to wet weight regressions (Fig. 4) were summed entire study area, rather than along transect lines over the size-frequency histogram of each species. only, in order to obtain an adequate sample size. The only exception to this method of estimating the Feeding observationson all the observed individuals standing crop was used in the case of Rossella were used to calculate theirdiet and percentfeeding. racovitzae. This species grows under the surface of We sampled the relatively common Odontaster the spicule mat, where it is hard to see in the photo- validus by haphazardly dropping I-m2 quadrats at graphs and where it anastomoses and buds in such differentlevels: 49 such quadrats were used in esti- a way that individual colonies can rarely be identi-

This content downloaded by the authorized user from 192.168.52.62 on Thu, 15 Nov 2012 17:29:57 PM All use subject to JSTOR Terms and Conditions 114 PAUL K. DAYTON ET AL. Ecological Monographs Vol. 44, No. I TABLE 5. Density, percent feeding, and dietary composition of predators on sponges, except Odontaster validus. Densities are based on 9 transectsof 100 m2each at Cape Armitage below 33 m in depth; 95% confidence intervals (? t df X SD) are given. N1 = number of individuals checked to determinepercent feeding; N2 = numberof feeding individuals on which the dietary composition (prey species and percenteaten) is based

PREY SPECIES Percent eaten

Predator = Qn Z> '

Odontaster 12.8 33.1 130 25.0 14.5 1.3 11.8 3 1.6 2.6 5.3 6.6 1.3 76 meridionalis + 1.9

Acodlontaster 5.6 48.5 132 10.7 38.2 39.7 8.4 2.3 0.8 131 conspicuous +1.7 Acodontaster 0.3 41.2 1 7 16.7 33.3 16.7 33.3 12 htodgsoni +0.5

Perknaster fuscus 60.9 23 2.4 2.4 95.2 41 antarcticus ( adult ) 1.0

P. fuscus antarcticus + l .0 (juvenile) 20.0 135 14.3 14.3 42.9 14.3 14.3 7 Austrodoais 3.3 51.2 217 42.9 36.6 1.9 4.5 1.3 3.8 8.3 0.6 156 mcmurdensis 2.1

fied in the photographs, although it is usually pos- Competitionfor space by sponges sible to evaluate the percent cover of R. racovitzae. Substratum space, the resource for which the It is unfortunate that this major (42%) user of space sessile species are most likely to compete, was esti- is also the one whose biomass must be estimated mated in two ways. The estimate of unoccupied by the most derived, least direct, technique. The substratum (39.1% available free space) from the problem of estimating standing crop biomass results photographic transects (discussed under Methods) because individual size cannot be measured for all is in reasonable agreement with a second estimate Rossella racovitzae. However, the photo-transects made by direct visual observation. A 1 m2 quadrat yielded 39 measures of individual length and area divided into 100 sections was dropped haphazardly covered. By assuming that these 39 individuals are and two divers estimated the percent free space in a representative sample of the total population in the the area it covered. As these estimates never differed 410-M2 area surveyed, we estimated the total wet by more than 10% and were usually within 5% of weight of the standing crop by converting their each other, the estimates were averaged for 102 lengths to wet weights and multiplying by a factor quadrats, yielding a mean of 45% free space. The of 113. This value was derived as follows: Rossella two independent estimates suggest that unoccupied racovitzae occupied 190 m2 in the 410 m2 surveyed, substratum is not a scarce resource. and the 39 measured individuals covered an area of Total free substratum space may not be an ap- 16,865 cm2: 190/1.6865 = 113. All the percent propriate measure of available settling space for the cover and biomass data are summarized in Table 1. larvae of a few sponge species that may settle only on The biomass data for all sponge species were con- bivalve shells rather than directly on the spicule mat verted from wet to dry weight, and the ash, water of (Appendix 1); however, bivalve shells are abundant hydration, and organic fractions were calculated in the spicule mat. Therefore, for all sponge species, (Methods section) and are presented in Table 2. competition for space probably is not an important Data from bomb calorimetry then allowed computa- factor influencing existing patterns of distribution tion of standing crop for most of the species in terms and abundance of the populations. of kcal per unit dry weight and ash-free weight This apparent lack of competition for space does (Table 3). not, however, eliminate the existence of competitive

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dominance, often expressed in sessile organisms as TABLE 6. Dietary composition, density, and percent the ability to undercut or overgrow and smother feeding of Odontaster validus. Sponges (first three food items) comprise 29.9% of the diet individuals of another species (Connell 1961, Paine 1966a, Dayton 1971). One of the principal objec- ODONTASTER VALIDUS tives of the cage experiments was to define relative Density-2.67/m2 growth rates of the sponges at McMurdo Sound, the implication being that the competitive dominance Percent feeding-20.7 (N - 140) hierarchy is a function of growth rates. Colonies of Percent most of the sponges were protected from predators of diet with cages, and marking stakes were placed close Food item (N = 60) to the sponges, so that very small growth increments Rossella racovitzae 8.8 would be detectable in photographs. Unfortunately, "Volcano" sponge 5.3 with the exception of one species, 1 year is insufficient Tetilla leptoderma 15.8 time to measure any growth by these methods. Lirnatulaliodgsoni 21.1 Laturnellaelliptica 12.3 was a measurable The one species for which there Halecium arboreum 1.8 growth rate is Mycale acerata (Table 4). In two Bryozoan 1.8 predator exclusion cages Mycale colonies grew Filter feeding 8.8 through the mesh in their cages and gained a calcu- Detritus 24.6 lated 2,744 g wet weight (437% of the estimated original weight) and 23,337 g wet weight (67%); hydroids, bryozoans, and detritus. We recorded as two colonies in uncaged control quadrats lost small filter feeding those individuals that had all five rays pieces to unknown predators but still exhibited net curled aborally in what is a characteristic filter feed- growth of 7,126 g (15%) and 1,280 g wet weight ing pose (Mauzey et al. 1968). The diet of Diplas- ( 10%). terias brucei in this area consists only of molluscs, In contrast to Mycale, no growth was observed particularly Limatula hodgsoni; since its diet does in any of the following sponges: "Volcano" sponge, not include sponges, we assume its effect on the Tetilla leptoderma, Cinaclzyra antarctica, Haliclona sponge species to be negligible. dancoi, Polymastiainvaginata, Dendrilla membranosa, In most cases the cage experiments failed to yield Gellius tenella, Sphaerotylus antarcticus, Leucetta a direct measure of the predators' effects on individ- leptorhapsis,Calyx arcuarius, Isodictya setifera, L. ual prey items. In two cases the predators (a Kirkpatrickia variolosa. While data erinacea, and Perknasterand an Acodontasterhodgsoni) occupied are insufficient to define a competitive hierarchy, identical positions and showed identical body con- these cage experiments strongly support the hypothesis figurations in October 1968 as when they were last that Mycale acerata is a competitive dominant in this observed in December 1967. The only measurable community because it has a much higher growth predation effects observed in the cage experiments rate than any of the other sponges. are recorded in Table 4. Three of these observations We do have field evidence that there are competi- represent cases in which Perknaster were observed tive interactions between Mycale acerata and other eating Mlycale in control plots. In two of the latter sessile animals. On numerous occasions we observed cases the Perknaster probably had come rather re- that Mycale had grown over and apparently killed, cently, as the sponges showed a net growth despite or was in the process of killing, other sponges such the predation. The Acodontaster conspicuus preda- as "Volcano" sponge, Rossella racovitzae, Haliclona tion on "Volcano" sponge is almost certainly an over- invaginata, Kirkpatrickia vario- dancoi, Polymastia estimate, as an unmeasured part of the sponge had the anemones Hormathia losa, and Calyx arcuarius; been consumed, apparently by the three A. con- Artemidactis and the solitary lucuniferaand victrix; spicuus, before the experiment was begun. verrucosa (Fig. 2). tunicate Cnemidocarpa The size-frequency distributions of all predators including Diplasterias, which broods its young, are Predator abundance, diet, and size-frequency presented in Fig. 5. The observed densities, percent feeding, and dietary composition of the sponge predators are presented Predator energetics in Table 5. These predator populations tend to be Upon examining predator exclusion and inclusion characterized by low densities and broad diets. Simi- cages after they had been in place for a year, we lar data are presented separately (Table 6) for found that we could not use direct measures of the Odontaster validus because less than 30% of feeding impact of the predators on their prey because of observations of this species involved sponge prey. very slow and erratic feeding behavior of the preda- The rest of the observed diet includes molluscs, tors. Consequently, we estimated indirectly the in-

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4 8 12 16 20 24 28 32

Qdontoster meridionalis 20 N=56 I 0

1 2 3 4 5 6 7 8 9 10 11

40 Acodontaster hodgsoni N=6

20- Acodontoster conspicuus 20 N =52 I

LL r T-F-41X 18 100 200 300 400 500 600 700 800 900 20 40 60

'701

50, Diplosterios brucei z 40- N= 159 w t t 3:L Perknaster fVscus ontorcticus

40 0 10 10 2 20 100 200 300 400 500 600 700 2Y N=19

30 ~~~Austrodoris mcmurdoensis

40 80 10 160 200 240 2 0

WET WEIGHT (gm)

FIG. 5. Size-frequency histograms of predator populations, 33-60 m deep at Cape Armitage. The dark Perknaster histogram represents juveniles.

gestion rates of the predator population from obvious to us that there was a very large standing energeticsdata. From estimates of the abundance crop of many prey species (i.e., some prey species of the predators,the compositionof their diets, and appear to have escaped their predators), and we their annual energyrequirements, we calculated the wished to be conservative in estimatingthis over- amount of each prey species ingested annually by abundance of food. In each case, realisticdeviations each predator population. Reliable abundance and fromour assumed values would have relativelyslight dietarydata were obtained by sampling in the field, effectson our calculations. but the energeticsdata are much more derived.There The energy requirementsof the predators were are several importantfactors, such as assimilation estimatedby summingfor each predator species the efficiency and energy utilized in production of kcal/l0O m2'yr utilized for respiration,growth, and gonads, which were impossiblefor us to measure in reproduction,and dividingby assimilationefficiency the available time period. In each such situationwe to yield an estimate of annual ingestion. Equations used estimatesthat basically are intelligentguesses. estimatingenergy per year channeled into respiration, Our methodsof arrivingat these estimatesare clearly growth,and reproductionfor a given species were defined below. In most such uncertain cases, we summed over the size-frequencydistribution for that biased our calculations toward an overestimateof species,assuming that this distribution was representa- predator ingestion. This was done because it was tive of the population as a whole. The values thus

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TABLE 7. Oxygen consumption, as a functionof dry weight, by predators; t values given (N-2 df) are for the significance of the differenceof b, the regression coefficient,from zero in the equations written in the form In O= In K + b In W

Oxygen con- Range No. of Mean coeffi- sumption No. of of dry runs/ cient of regression speci- weight speci- variation 02 = KWb Species mens (g) men of 02 (mg/hr) (dry g) t

OdoItwaster ialidus 21 0.3- 5.5 1-7 0.176 (N -20) 02- 0.0253W0920 13.82** Odontaster ineridliona/is 18 0.5- 4.2 2-10 0.125 (N - 18) 0 = 0.0255W0 020 7.30*" Acodtontasterconspicuus 9 2.6-19.2 1-9 0.188 (N -8) 02- 0.0305W00, 10.15*> Acodontaster hIodsonti 9 1.3-11.3 1-9 0.097 (N -7) 02 0.0275WO"10 4.73* PI-erkizasterfuscus antarcticus 21 2.7-14.1 1-9 0.152 (N 20) 0, 0.0265W0 74 3.83** Austrodoris nmcniurdensis 9 0.6- 7.7 1-4 0.143 (N -8) 02 0.0860W043" 3.270

* Significance at the 5% level or better. significance at the 1%7 level or bettei. obtained were divided by N, the number of in- evidence of oxygen consumptionconforming to the dividuals used to determinethe size-frequencydis- level of oxygen in the chamber (Prosser and Brown tribution,to find weighted mean values for energy 1961). Unfortunately,there was a lack of chambers used in respiration,growth, and reproductionper large enough for heavy individuals of some of the individual. For each predator these three mean larger species. Extrapolatingrespiration rates fron' values were summed and the total was multiplied small to large animals tends to result in an over by the density (number of individuals per 100 m2) estimateof the large animal respiration.This means of the predatorto give a final estimate of kcal/100 our estimatedingestion rates may be somewhathigher m* yr ingestedby that species. than the actual rates. The results of the respirationmeasurements are Respiration shown in Table 7. All species showed statistically Respirationdata for the predatorswere collected significantincreases in oxygen consumptionper ani- by placing them in glass respiration chambers of mal with increasing weight. The slope (b) of the appropriatesizes and thenputting the chambersback respirationequations in log-log form were tested for on the sea bottom so that measurementscould be differencefrom 0.75, the value discussed by Zeuthen made under conditionsas nearly natural as possible. (1953) as an average value for poikilotherms,and The oxygen content of the water in each chamber by Hemmingsen (1960) for unicellular organisms, was determinedbefore and after each run by the plants,poikilotherms, and homiotherms.Only those Winkler technique. Control blanks were run by of Austrodoris mctnurdensis (.05 > p > .02) and means of two empty chambers per run. As a con- Odontaster validus (p .02) were found to differ trol against bias caused by oxygen dependency,only significantlyfrom 0.75. In the case of Austrodoris, those runs in which the final oxygen contentwithin the small sample size may have contributedto this the respirometerwas 50%, or more of the original departure, but the sample size for 0. validus was value were used in calculating the respirationrates. large, and the slope of the respirationequation was Respiration data from the runs used showed no the most highlysignificant of those of all the preda-

TABLE 8. Wet to dry weight conversions and whole body caloric values for predators; N. - number of specimens used to determine the wet to dry weight regressionequation; t values given (N, - 2 df) are for the significanceof the differenceof b from zero, for the wet to dry weight equations in the form Y - a + bx or In Y - In a + b In x, as appropriate; N2- number of specimens used to determine caloric and ash values; kcal/ash-free g (kcal/dry g) /(1.00-proportion ash)

Dry weight regression (Y --dry weight,g; X = wet kcal/ dry g Proportionash kcal/ash-freeg Species N. weight,g) t N., + SD ? SD + SD

Odontaster ialidus 75 Y = 0.444 X 7 33.20 7 2.699 ? 0.339 .501 ? 0.054 5.400 ? 0.223 0. meriidionalis 18 Y (0.326 X " 6.12 5 2.383 ? 0.175 .521 ? 0.027 4.977 ? 0.207 Acodotauster conispicutis 12 Y 0.225 XV'9 18.19 2 4.822 ? 1.133 .282 ? 0.138 6.693 ? 0.294 A. hodgsoni 9 Y -2.2 17 + 0. I 59X 3.51 Perknasterfuscus antarcticus 21 Y = 0.398 XI'73 9.00 3 3.671 ?0.617 .354 0.083 5.671 ?0.411 A ustrodoris mcwmurdensis 21 Y 2= 0.113 X' ST 21.52 4 3.240 ? 0.316 .348 ? 0.044 4.966 + 0.228

This content downloaded by the authorized user from 192.168.52.62 on Thu, 15 Nov 2012 17:29:57 PM All use subject to JSTOR Terms and Conditions 118 PAUL K. DAYTON ET AL. Ecological Monographs Vol. 44, No. I tors. Therefore, the difference of b from 0.75 may TABLE 9. Results of asteroid tagging experiments; 128 indicate unusual relationships among metabolism, Odontaster validus were tagged and released (18% recovered) at Cape Armitage and 11 were tagged, body weight, and surface functions, which Hem- caged, and recovered at Cape Evans; 11 Acodontaster mingsen (1960) postulated as the interacting factors conspicuus (82% recovered), 7 A. hodgsoni (29%), and 6 0. meridionalis (O recovered) tagged and re- selecting for the 0.75 value. leased at Cape Armitage To assess the amount of energy used for respiration per 100 m2 per year by each predator species, we performed calculations as follows. First we obtained the size-frequency distribution in terms of dry > weight, by applying the wet to dry weight conversion (Table 8) to the wet weight size-frequency distribution (Fig. 5). The respiration equation (Table 7) Species 3- 0 < E was then summed over this distribution to give a yearly caloric value for the individuals in a 100-M2 Odontaster 44 32.8 33.8 12.5 2.9 10 validus 48 27.5 30.2 12.5 9.4 8 area: 54 12.8 8.2 11.5 -37.5* 10 57 16.3 16.6 11.0 2.0 5 kcal/100 m2-yr - (8760 hr/yr) (.0034 kcal/mg O.) 71 12.0 8.3 10.0 -37.0* 3 76 9.1 10.5 10.5 17.5 1 > (k)(g dry wt) jb mg O.,/hr 95 15.5 17.6 11.0 14.7 11 99 15.4 16.2 12.0 5.1 3 N *#/100 m2. 104 15.6 12.0 12.0 -23.0* 5 110 19.1 20.0 10.5 5.3 3 Growth 115 15.7 16.0 12.0 1.9 8 128 16.2 18.3 12.0 12.9 5 Energy used by predators in growth was derived 133 10.3 10.8 12.0 4.8 7 as follows. A total of 176 asteroids were weighed to 151 24.9 24.3 11.0 -2.6 0 nearest 0.1 g and tagged with spaghetti tags held by 152 15.5 14.5 11.0 -7.0 0 156 16.6 18.4 10.5 12.3 0 a nylon monofilament loop inserted through the base 158 9.6 10.4 11.0 9.0 4 of one of the rays. After tagging, the asteroids were 159 10.7 10.4 11.0 -3.0 2 160 25.1 24.6 11.0 -2.1 NRW suspended in the water column in a nylon mesh box 169 17.6 18.0 11.0 2.4 NR for 10-14 days in order to reduce the probability of 170 16.5 18.0 11.5 9.4 NR their being eaten by Odontaster validus and the 174 7.2 7.8 12.0 8.3 NR 185 10.9 8.5 10.5 -25.1* 2 nemertean Lineus corrugatus, which are efficient = 5.4 scavengers adroit at finding and consuming injured Odontaster 0 13.0 15.6 12 20.0 asteroids (details in Discussion). The boxes were validus 1 12.0 16.0 12 33.3 then opened and placed at two known locations at caged at 3 10.0 14.7 12 47.0 Cape Evans 4 11.0 18.6 12 69.1 depths of 30 and 40 m. We did not observe any 6 13.0 14.7 12 13.1 tagged asteroids to be eaten by 0. validus or Lineus. 7 9.0 12.4 12 37.8 A year later we found some of the same asteroids 8 8.0 14.2 12 77.5 11 5.5 10.0 12 81.8 in their original boxes, and the maximum observed 12 8.0 11.9 12 48.8 distance between release and recovery sites was 27 m 13 9.0 12.7 12 41.1 14 6.0 11.0 12 83.3 (Table 9). These data may represent a conservative x - 50.3 estimate of the asteroid mobility, as many of the un- Acodontaster 18 166.4 194.2 10.0 20.0 14 recovered individuals may have moved farther and conspicuus 19 166.4 186.2 11.0 12.9 2 escaped detection; this is particularly true of those 20 173.2 167.2 11.0 -3.1 NR 21 457.4 558.5 11.0 24.1 8 individuals that went into deeper water where our 22 194.2 179.6 12.0 -7.5 5 search time was more limited. We have no good 31 94.4 96.1 10.5 2.0 3 estimate of the mortality of the tagged starfish; how- 34 67.5 63.5 12.0 -5.9 7 35b 351.0 434.0 12.0 23.6 5 ever, we know that some were eaten by the sea 36C 89.6 67.5 10.5 -28.1* 1 anemone Urticinopsis antarcticus, as we recovered x= 8.3 two tags from the coelenterons of these anemones Acodontaster 27d 33.1 20.1 10.5 -44.8* 0 hodgsoni 78C 42.1 40.6 10.5 -4.0* 3 and two more adjacent to their pedal discs. Three Perknaster 23 149.8 171.0 11.0 15.4 27 of these asteroids were Odontaster validus and one fuscus 37 160.0 135.3 12.0 -15.4 NR was Acodontaster conspicuus. We have no means antarcticus 38K 250.0 363.2 11.5 47.2 5 of estimating tag loss, but we did not see any loose 41 31.7 33.7 11.0 6.8 8 .=- 13.5 tags other than those associated with Urticinopsis. * Value omitted because animal obviously injured by tag. Thirty-eight of the asteroids tagged at Cape Armitage a NR - not recorded. were b Observed feeding on "Volcano" sponge for 7 weeks. recovered and weighed about a year later (Table e Large scar at tag site indicates tagging injury. 9). Eleven more 0. validus were (I Lost end of ray in tagging process. similarly tagged v Observed feeding on Mycale acerata for 7 weeks.

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TABLE 10. Determinations of caloric values of reproductivematerial of predators. N - number of specimens

kcal/dryg Proportion kcal/ash-freeg Species N Sex + SD ash + SD Odontaster v'alidus 1 4.707 0.188 5.797 Acodontaster conspicuus 3 O 7.659 ? 0.073 0.059 ? 0.000 8.137 ? 0.045 Acodontaster conspicuus 2 4.715 ? 0.018 0.149 ? 0.019 5.542 ? 0.151 Perknaster fuscus antarcticus 4; 7.402 ? 0.188 0.072 ? 0.016 7.975 ? 0.171 Perknaster fuscus antarcticus 2b 0 4.477 ? 0.438 0.156 ? 0.023 5.302 ? 0.373 All asteroids sampled 7 7.512 ? 0.196 0.066 ? 0.013 8.044 ? 0.151 All asteroids sampled 5 4.618 ? 0.254 0.160 ? 0.022 5.497 ? 0.288 Austrodoris rncmurdensis 2 egg masses 4.458 ? 0.100 0.150 ? 0.003 5.242 ? 0.148

;13 adults, 1 juvenile. b 1 adult, 1 juvenile. and placed in a cage (in order to insure recovery) Reproduction at Cape Evans, approximately22 km northof Cape Energy used per year for gonad growth by each Armitage, which appears to have a much higher asteroid predator species was estimated by summing productivityof 0. validus food than does Cape its gonad index (weight of gonad/weight of individ- Armitage (Pearse 1965). These Cape Evans 0. ual) over the dry weight size-frequency distribution, validus doubled their weight despite the facts that making the conversion to a 100-M2 area, and multi- theywere the firstanimals tagged (before we refined plying by mean kcal/g dry wt of gonad (Table 10), our technique) and that they were transferredto determined by calorimetry as described for sponges. Cape Evans in an open bucket. These data indicate For each species the overall mean value for kcal/g thatthe taggingprocedure was not unreasonablyhard dry wt of gonad was used, because (1) sample sizes on the animals and that the low growth values at per species were small for the determination of Cape Armitageare probably realistic. kcal/gm dry wt of gonad, (2) within sexes, no sig- Estimates of percent growth per year for Aco- nificant differences in caloric values were found dontasterconspicuus (8.3%), Perknasterfuscus ant- among the species, and (3) a sex ratio of 1.0 was arcticus (13.5%), and Odontaster validus (5.4%) assumed for each predator population. were determinedfrom field observations of tagged N animals at Cape Armitage (Table 9). For 0. kcal/ 100 m2 * yr , (g dry wt) i meridionalis,A. hodgsoni, and Austrodorismcmur- of gonad used gonad index* N densis, no accurate field observations were made. in reproduction Growth was estimatedto be 5.4% per year for 0. wt. rneridionalis(based on the similarityof this species #/100 m2 -mean kcal/g dry to 0. validus) and 5% per year for Acodontaster For our purposes, it was assumed that each individual hodgsoni and Austrodoris,which, in the absence of spawned once annually. This assumption was verified empirical evidence, is used as a conservative esti- by Pearse (1965) for Odontaster validus, and our mate. own observationsof Acodontasterhodgsoni, Perknas- The estimated mean growth per individual per ter, and Odontaster meridionalis, which were es- year was summed over the dry weightsize-frequency sentially spawned out in November. Again, the error distribution, again using the conversion to a 100-M2 in this assumption is toward an overestimate of inges- area. The value obtained (grams drywt/ 100 m2 yr) tion. Because all Odontastervalidus, 0. meridionalis, was then multipliedby the mean value for kcal/g Acodontasterhodgsoni, and Perknasterfuscus antarc- dry wt for that species (Table 8). Calorimetrywas ticus had at least partially spawned before our arrival done as described for sponges, on samples of pul- each season, it was necessary to derive estimates of verized whole predator bodies. No calorimetrywas their gonad indices. carried out on the rare Acodontaster hodgsoni; its Gonad indices used were as follows: Odontaster caloric value was considered to be the same as that validus, 0.07 (derived from Pearse 1965); 0. of A. conspicuus. meridionalis, assumed 0.07 because of its similarity N to 0. validus; Acodontaster conspicuus, 0.155 (de- kcal/ 00 m2 yr growth E (g dry wt)1 termined from two males and two females); A. used in growth = * _ and Perknaster antarcticus,assumed yr N hodgsoni fuscus 0.15 based on our own estimates, the values for A. wt, #/100 m2.kcal/g dry conspicuus, and the fact that other similar asteroids new wet wt - old wet wt are near 0.155 (Farmanfarmaian et al. 1958). For where growth - ld=wet old wet wt Austrodoris mcmurdensis, gonad index and kcal/g

This content downloaded by the authorized user from 192.168.52.62 on Thu, 15 Nov 2012 17:29:57 PM All use subject to JSTOR Terms and Conditions PAUL K. DAYTON ET AL. Ecological Monographs 120 Vol. 44, No. 1 TABLE 11. Estimated annual energy requirements of predators per IO0mM per year

Energy (kcal/lOOm2 yr) utilized in: Total energy Gonad Assimilation utilized (kcal/ Species Respiration Growth growth efficiency* 100 m2 yr)

Odontaster meridionalis 7.69 1.27 4.21 0.75 17.56 Odontaster v'alidus 377.00 67.31 196.08 0.75 853.85 255.30 fromsponge 29.9 7 Acodontaster conspicius 172.47 150.49 353.47 0.75 901.92 Acodontaster hodgsoni 1.26 0.54 2.12 0.75 5.24 Perknasterfuscus antarcticus (adult) 7.03 11.05 19.74 0.75 50.43 Perknasterfuscus antarcticus (juvenile) 1.52 1.80 3.19 0.75 8.68 Austrodoris mncmurdensis 13.76 2.03 19.93 0.66 54.12 Total 1293.25

* True values unknown. were not measured. Instead the mean weight of an used for A ustrodoris is that calculated by Paine egg mass (2.71 g dry; n -2) and the kcal/dry g (1965) for Chelidoneura (Navanax) inermnis,an- egg mass (4.458 kcal; n - 2) were used. It was other carnivorous opisthobranch. estimatedfor our calculations that each hermaphro- The calculated energy requirements of each preda- ditic Austrodorisindividual produced one egg mass tor population in units of kcal/100 m2'yr are sum- after 2 years. This is probably an overestimateof marized in Table 11. The relatively large amount their reproductiveoutput; time of firstreproduction ingested by Odontaster validus results from its high may be much later than 2 years, possibly as long density, whereas that of Acondontaster conspicuus as 5 to 6 years after settling. Further, in 1968 we results partly from the large individual size. Adult observed eight caged Austrodoristo be in the same Perknaster are also large, but are relatively rare. places and feeding postures as they had been when Our estimate of a total of 1293.25 kcal/100 m2-yr caged in 1967; most of these individualsapparently sponge ingestion is probably high, because each of neithercopulated nor produced the conspicuous egg the estimates of energy requirements is biased in masses characteristicof the species. It seems likely that direction. The effects of predator populations thatif Austrodorisactually does reproducein 2 years, on the standing crop of individual prey species have we would have seen at least one egg mass laid by one been calculated (Table 12) by multiplying the annual of the 15 individualsunder observation. This prob- ingestion of the predator population from Table 11 able overestimateagain errs toward an overestimate by the percent of the predators' diets provided by the of the ingestion. given prey species (Table 5 and 6). The pattern in Table 12 suggests that many of the sponge popula- Ingestion tions have low standing crops and have not escaped Assimilation efficiencywas assumed to be 0.75 heavy predation. However, the rossellids and Tetilla for the asteroid predatorsand 0.66 for Austrodoris. lepto(lerma have accumulated a very large standing Because real data on assimilation efficiencywere crop and appear less affected by their predators. impossibleto obtain, we use these figuresas realistic The cage experiments provide an indication of the estimates. The 0.75 value for the asteroids is prob- accuracy of our derived estimates of annual inges- ably conservative(low), as they appear to consume tion. The rate of predation of Perknaster on Mycale all the organic material (except spongin) in the can be estimated from one predator inclusion cage sponges and to digest almost everythingthey ingest. in which two large Perknaster ate 602 kcal of Mycale We have seen egestion twice for Acodontastercon- and from three control quadrats in which Perknaster spicuus and once for Perknaster:the feces were thin, ate 369 (2 Perknaster), 83, and 12 kcal of Mycale almost invisiblestrings up to 25 cm long. The rate in slightly less than a year (Table 4). In these of egestionis probablyvery low, and the feces prob- three instances the Perk naster were still feeding when ably have little, if any, caloric content. The 0.75 we returned in 1968. The other two Mycale in con- figure is comparable to but somewhat higher than trol quadrats were also subjected to some predation, those of other higher order carnivores that egest a probably also by Perknaster (Table 4). The mean significantfraction of what they ingest (summarized amount (116 usable kcalh N - 4) consumed by the by Welch 1968), but Paine has found asteroid uncaged Perknaster is consistent with our calculated efficienciesas high as 0.90. The assimilationvalue annual ingestion by Perknaster. The calculated value

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TABLE 12. Estimated annual effects of predators on their sponge prey; standing crop of sponges in terms of kcal/ 1OOm' and years' supply

Predator O species x r _____2_ Odontaster mteriioliali's 4.39 2.55 0.23 2.07 5.55 0.46 0.93 1.16 0.23- Odouloi ater v'alidus 75.14 45.25 134.91 Acodontaster (ol0SpiCOulls 96.51 344.53 358.06 75.76 20.74 7.22 2 AcoIontaister 11od(isolli 0.88 1.74 0.83 1.74 Q. Perknasterfuscus c anttarcticus (adult) 1.21 1.21 48.01 tE8 Perkliasterfuscus anttarcticls C( (juvenile) 1.24 1.24 3.72 1.24 1.24 1 A ust'rolorisi tncmiurdensi.s 23.22 19.81 1.03 2.44 0.70 2.11 4.49 0.32 E TOTAL 200.14 413.35 496.45 81.41 74.54 7.49 3.45 7.16 1.48 8.46 0.23 Standing crop (kcal/1OOm2) 277,398 128,629 80,698 1667 61414 5532 Not 15 12 66 12 known Standing crop (Number of years' supply) 1386 311 163 20 82*1 739 Not 2 8 9 50 known

* kcal useful to predators; this figure is 51.8% of the kcal/100mn2 as determined by bomb calorimetry, since 48.2% of the dry weight of Mrcale acerata is spongin, which is not consumed by the predators but which contributes to the caloric value as determined by bomb calorimetry. ** also corrected for the presence of spongin. for adult Perknaster is 50.43 kcal/ 100 m'-yr (Table for juvenile Perknaster, since it was for this caged 11); the density of adult Perknaster is 11 / 19 (adult: individual 100%7 of the available prey, we can com- total ratio; Fig. 5) X 1.0/100 m' (total Perknaster pare calculated and observed ingestion as above for density; Table 5) = 0.58 adult Perknaster per 100 adults: 8/19 (juvenile: total ratio; Fig. 5) X 1.0/ mi . Using this value, the calculated kcal/yr re- 100 m2 (total density; Table 5) = 0.42 juvenile quired by one adult Perknaster would be 50.43/ Perknasterper 100 m2: 0.58 = 87 kcal, reasonably close to the 1 16 kcal ob- 8.68 kcal/0.42 individuals - 21 kcal per individual. served value. The high mean value (301 kcal) for the caged Perknaster probably resulted from the fact The observed 17 kcal is not inconsistent with this that (I) the animals were caged in with their prey, value. thus restricting movement and reducing the search In only one other cage situation was predation time necessary to find prey, and (2) the two Perknas- observed. In a Hut Point experiment three Aco- ter used were larger than average adults. dontaster conspicutus observed eating a "Volcano" In another cage experiment, a juvenile Perknaster sponge were caged in with it. It is difficult to assess ate a small (diameter - 8 cm; 17 kcal) piece of a the amount of this sponge eaten by asteroid preda- Kirk patrickia variolosa colony soon after being tors, because they digest it externally, leaving a com- placed in the cage. But the Perknaster than crawled plete spicule skeleton that is somewhat difficult to into an upper corner of the cage and did not move differentiate visibly from the uneaten portion of the again for the 7 weeks of observation in 1967. It colony. The best method of identifying the digested occupied the same position and had the same body areas of the sponge is to light the sponge from inside conformation in October 1968, suggesting that it had the osculum with a hand light; much more light not moved during the year. The 17-kcal value agrees penetrates the digested than the nondigested por- quite well with our calculated annual requirements tions. We used this field technique when we checked for this starfish. Ignoring the fact that Kirkpatrickia the sponge in 1968 and estimated that 50% of it variolosa normally comprises only 14.3% of the diet had been eaten. We later found that color photo-

This content downloaded by the authorized user from 192.168.52.62 on Thu, 15 Nov 2012 17:29:57 PM All use subject to JSTOR Terms and Conditions 122 PAUL K. DAYTON ET AL. Ecological Monographs Vol. 44, No. 1 graphs allow measurement of the digested portion. probability of encounter by predators) and the di- Our 1968 photographs suggested an estimate of 60% etary composition of Odontaster validus and Aco- as the total amount of this colony eaten by the three dontaster conspicuus, two of the predators consum- Acodontaster conspicuus. Unfortunately, our 1967 ing the most kcal of sponge. The three commonest photographs were less clear, so it was impossible to sponges comprise most of the diets of these two decide what proportion of the 50% to 60% had been predators, the ash, water, and organic proportions eaten during the experimental (caged) period and of the sponges notwithstanding. However, Tetilla what proportion had been eaten previously. Using and Cinachyra are both moderately common 55% as a compromise maximum value, we can sponges (Table 1), are ranked four and two in the calculate that the three caged A. conspicuus ate at proportions of organic matter potentially available most 3,065 kcal (or 1,022 kcal each) of "Volcano" to a consumer (Table 2), and yet Tetilla is the most sponge during the year they were caged (Table 4). important item in the diets of the two major starfish This value is 6.3 times the mean calculated ingestion predators, and Cinachyra was not observed to be 902 kcal/5.6 individuals - 161 kcal; 1022/161 - 6.3. eaten (Table 5 and 6). The fact that the three observed animals (1) were The effectiveness of sponge predator-defense large, (2) were caged and remained on the sponges mechanisms is highly variable. Long, externally con- during the period of observation, and (3) had eaten spicuous spicules appear to be generally ineffective, as at least some and probably a considerable amount they are well developed in the rossellids and Tetilla, of the 3,065 kcal prior to the period of the experi- and yet these species are the major dietary com- ment, suggests that the calculated annual ingestion ponents of the predators (Table 5). The one case for this species is reasonable. in which spicules may provide some defense is that of Cinachyra antarctica, which has spicules long DISCUSSION enough to prevent the predators from actually reach- ing the sponge colony itself. However, the simi- The organization of the artarctic sponge com- larities in abundance of spicules, percent cover of munity can best be understood by examining the substratum and percent organic matter available to to which predation by starfish and a nudi- degree a consumer between Tetilla and Cinachyra suggest the competitive relationships among branch alters that there is some other as yet unknown explanation utilizers, sponges. Mycale acerata the primary space for the latter's observed absence from predator diets. rate than the other sponge has a much faster growth Another well-known defense is the secretion of and has been seen to overgrow some of them. species, mucus; this is the response of Mycale to perturba- the potentially dominant It is, therefore, probably tion, but it is not an effective deterrent to its preda- is relatively competitor for space. However, Mycale tors. Most sponges that were never observed to be abundance of available free rare, and there is an eaten, such as Leucetta leptorhapsis, Dendrilla mem- for does space in the community; competition space branosa, and Isodictya erinacea, have neither ap- the sessile not seem to affect many of populations. parent spicules nor mucus and may instead have A few of the sponges, such as Gellius tenella, Calyx chemical defense similar in effect to those of many arcuarius, Isodictya erinacea, and Pachychalina plant species (Whittaker and Feeny 1971). All of pedunculata, appear to have morphological adapta- the latter sponges are relatively rare; it would be tions such as arborescent growth forms which may interesting to know why they are not more common, reduce the effect of competition by allowing them particularly if the apparent lack of predation is real. to grow on relatively narrow bases above the sub- Mycale populations are, in part, regulated by stratum. This may ameliorate competition with the predation. We have seen from the cage experiments more prostrate forms and at the same time reduce that Perknaster has a fairly high Mycale consump- the probability of predation because of the smaller tion rate and, judged by the fact that two-thirds of area of encounter for predators moving on the spicule the Mycale colonies in control quadrats for the cage arborescent have use- mat. While these sponges may experiments were found and preyed upon by Perk- ful morphological adaptations, they are among the naster, this asteroid appears to be an efficient rarest of the local sponge species. Therefore, the searcher. Because Perknaster specializes on Mycale question of population regulation of sponges must and is the only predator to include it as a major por- remain open, with the possible exception of Mycale. tion of its diet (95% of adult diet; 48 kcal/ IOOm2 *yr), We will discuss only predator-related possibilities, it is tempting to conclude that Perknaster predation since we have seen little evidence of importance of effects of competition, and our observations were is responsible for preventing Mycale from dominating designed to be below the level of physical disturbance. the space resource. While this is partially true, There is a general correlation between percent Acodontaster conspicuus also consumes a significant cover of sponge (assumed to be equal to the amount of Mycale. Although A. conspicuus takes

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only 2.3% of its diet from Mycale, this asteroid is A ustrodoris. Both predator species have size-fre- large and common enough so that it consumes 21 quency distributions skewed toward the larger sizes kcal/ 10Om2 yr. The combined predation appears to (Fig. 5), suggesting that filters imposed by plankton be responsible for preventing Mycale from exerting mortality and/or this consumption of settled larvae its potential dominance of the spatial resource. Addi- and juveniles by Odontaster has an important effect. tional evidence suggests that the density of adult Because Acodontaster, at least, has a slow growth Perknaster would be higher given a greater abun- rate (Table 9), the skewed size distribution suggests dance of AMlycale. For example, we observed that a that few larvae of any year class survive. Another tagged juvenile that was recovered eating a Mycale indication that this skewed size distribution results had grown and attained the adult form, whereas from larval mortality can be seen by comparing the juveniles caged without access to Mycale and tagged histogram of Acodontaster conspicuus to that of juveniles that did not find a Mycale grew little, if Diplasterias brucei (Fig. 5), which broods its larvae any, and retained the juvenile form. to a size at which they are probably immune to A somewhat different situation seems to be true Odontaster predation. for the populations of the four most abundant The Odontaster filter effect probably has different sponges, the rossellids Scolymastra joubini + Rossella implications for Acodontaster than for Austrodoris nuda, (= "Volcano" sponge), and R. racovitzae, and because of the differences in life history patterns. the demosponge Tetilla leptoderma. Despite the fact Asteroids tend to be long-lived, iteroparous animals, that we have seen as many as 18 Austrodoris eating whereas dorids are generally short lived and semel- one "Volcano" sponge, apparently without seriously parous (Miller 1962, Thompson 1964, observations damaging it, we know that these sponges can be of the authors). Thus an efficient filter might pre- killed by their predators. We have observed several vent the Austrodoris population from increasing sig- instances in which one to four A. conspicuus were nificantly because the individuals that escape the in the process of killing large rossellid sponges, and "filter" die after a single reproduction; but, because we have seen numerous skeletons of relatively re- of its longevity and iteroparity, the occasional cently killed rossellids and Tetilla. We know from Acodontaster escape could lead to a gradual increase one of our cage experiments that three A. conspicuus in density. can eat up to 55% of a very large "Volcano" sponge In addition to acting as an effective larval filter, within I year. Thus a small number of A. con- Odontastervalidus also kills adult Acodontastercon- spicuus are capable of killing the largest rosselids. spicults. The observation of this predation surprised There is, therefore, no secure refuge in growth from us, because the biomass of an adult 0. validus is only this predation. Despite this predation load however, about 5% of that of an adult A. conspicuus. In an there is an estimated 1,386 years' supply of Rossella attack on A. conspicuus, a single Odontaster first racovitzae, 311 years' supply of "Volcano" sponge, climbs onto the aboral surface of an Acodontaster and 163 years' supply of Tetilla leptoderma available ray, everts its stomach, and digests a hole in the to consumers (Table 12). Acodontaster. During an attack by one Odontaster, Although Acodontaster conspicuus, at least, can the Acodontaster moves rapidly along the substratum kill even the largest sponges, the large rossellid but makes no apparent effort to dislodge the standing crop strongly suggests that these sponge Odontaster. An attack by a single Odontaster is populations at this locality have escaped overexploita- probably never, by itself, fatal to the much larger tion by their consumers. For these sponge species, Acodontaster. In fact 19/ 112 healthy Acodontaster which live in a physically predictable and homo- collected for tagging or size-frequency measurements geneous environment and seem to have no size refuge had scars on their rays which probably resulted from from their predators, the apparent escape from preda- Odontaster attacks. However, in all the cases of these tion must result from some source of mortality to attacks observed in progress, other nearby Odontaster, the predators. probably responding to the release of Acodontaster An important question, then, is What regulates the coelomic fluid, also attacked the fleeing victims. growth of populations of Acodontaster conspicuus Eventually the A codontaster were forced to slow and Austrodoris ;ncmurdensis, the two most im- their movement, and invariably the large nemertean, portant predators on these large sponges, in the Lineus corrugatus, again probably responding to presence of the great excess of their food resources? release of coelomic fluid, moved into the holes made Our observations suggest the hypothesis that the by the Odontaster and appeared to be digesting the small but ubiquitous asteroid, Odontaster validus, is organs of the Acodontaster. On four occasions, we partially responsible, in two ways. First, since it is an observed within a few hours after the initial attack, abundant detritus-feeder, it may act as an effective that Acodontaster up to 40 cm in diameter were filter by consuming the larvae of Acodontaster and completely buried under piles as high as 20 cm of

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FIG. 6. Sequence of Odontaster v'alidus and Liteius cotrrugatuspredation on Acodontaster conspicuuts. Plate A shows one 0. validits on the ray of an A. conspicuus. The 0. vali(li.s had its stomach everted and was digestingthe A. conspicuuis,which was otherwise healthy and was moving rapidly in the other direction. Plate B shows a pile of 0. validuis on 3 of the rays of the A. (-olnspicUUs. The large nemerteanworm, Line'. corrugatus has moved into the body of the Acodontaster. This photo was taken approximately 16 hours after the first photo. Plate C shows the large AcoCdontast'rcompletely covered with 0donitastcrand Lineus. Plate D shows the star-shaped ossicle pile remaining a few weeks later. The dark specks in these photos are amphi- pods. which play no role in this interaction.

Odontaster and Lineus. Within 2 weeks the scaven- no more than 9 months previously. In 1968 we gers dispersed, leaving a starshaped pile of Aco- counted successful O(lontawter attacks on Aco(lonta- dontaster ossicles (Fig. 6). Another observed cause ster as well as recent kills evidenced by the ossicles of adult Acodontaster mortality is consumption by in a site of known area. We observed 14 Aco- the sessile anemone Urficinopsis antarcticus. Oc- (lontaster kills in an 8,375-in2 area at Cape Armitage. casionally Ac(odonltaster and other echinoderms The Acotlont.ster density here is 0.056/rm2 (Table blunder into an Urticinopsis., which then bends over 5). Thus we determined that the Odlontaster had and engulfs them (Dayton 1972). killed 37 of the Acodlonaster population within I We can estimate the rate of Acodlonhisier mor- year. In addition, we saw one Ac(odontaster brush tality. The star-shaped aggregations of A(o(dontaster against and be killed by an Urticinopsis antlarticus, ossicles remaining after an Odont aster massacre are and at the base of another Urticinopsis we found a clean and white and therefore stand out sharply tag which had been firmly sewed onto an Aco- against the dark-brown substratum: they are thus (lontasler in 1967. strongly suggesting that the tagged easily counted. Apparently the plankton debris Aco(lontaister suffered a similar fate. The Odontaster from the late November-January phytoplankton and Urticinopsis, then, had killed 3.5% of the Cape bloom and the surface diatoms eventually cover the Armitage Amodoniaster population in I year. This ossicles, which are then dispersed by the detritus is a minimal estimate because it omits Odlontaster feeders. We know that these ossicles disappear, be- kills during and perhaps sometime after the summer cause we marked ossicle aggregations in 1967 and plankton bloom which covers the ossicle aggregation: found no trace of them in 1968. While it is not this estimate also underestimates the loss from known exactly how long the star-shaped ossicle anemones, which usualiv leave no evidence of a aggregations persist, the ones we observed in October kill. and November 1968 represented Aco(dontaster killed We believe that larvae amounting to something

This content downloaded by the authorized user from 192.168.52.62 on Thu, 15 Nov 2012 17:29:57 PM All use subject to JSTOR Terms and Conditions Winter 1974 ANTARCTIC COMMUNITY ORGANIZATION 125 less than 3.5%7, of the Acodontaster population an- that this species, much like Perknaster, may be food nually escape mortality imposed by the larval filter. limited at Cape Armitage. Given the density of 0.056 Acodontaster/m2, in the 8,375-m2 area intensively surveyed, there should CONCLUSION have been 469 Acodontaster, of which 16 should When the observations discussed in this paper are have been in the 1st-year class and 32 in the first synthesized, a pattern in common with other marine 2-year classes (maximum diameter probably 7-10 epibenthic communities, such as the rocky intertidal cm), assuming a steady state in which an equal (Connell 1961, 1970, Paine 1966, 1971, Dayton number are recruited as are lost to O(lontaster and 1971) and perhaps coral reefs (Branham et al. 1971, Urticinopsis. We searched this area carefully for Porter 1972) emerges, as this comlnunity also is small Acodlontaster and found none smaller than 5 structured by biological interactions, especially preda- cm and only three between 5 and 10 cm. Since we tor-prey relationships. In all these communities, al- often found O(lontaster less than I cm in diameter though space is potentially limiting, the cardinal fac- and because of the clear water and sharp contrast tor in preventing space monopolization by a single between the white Acodlontaster and the dark sub- species is predation. The intertidal communities are stratum, it is unlikely that we missed as many as certainly more influenced by physical factors than 16 of the Ist-year class Acodontaster, the number is the antarctic epibenthic community, although that would be necessary to replace adults removed whether they are physically controlled in the sense from the population at the observed annual mor- of Sanders (1969) remains to be seen. The basis of tality rate. Clearly these data are not conclusive, organization held in common appears to be indepen- but they do suggest that Odlontaster kills the adult dent of the supposed rigors and relative predictability Acodontaster as fast as or faster than the larvae of the respective environments. escape their Odontaster detrital feeding filter. If this In the antarctic sponge community selective preda- is true, the dramatic escape of the rossellid sponges tion tends to counter the more effective growth and from their predators is probably the result of the greater competitive abilities of AMIycaleacerata. A effective larval cropping and adult predation by the competitive hierarchy of sponges may exist, but same generalized predator. Furthermore, because the other than the existence of conspicuous morphologi- Odontaster population probably derives the bulk of cal differences of unknown functional significance, its energy from detrital feeding, this system is un- there is little evidence for competitive niche differ- usual in that its most influential carnivore is probably entiation. controlled by the availability of detritus (Pearse This order exists in a system characterized by low 1965). In most predator-prey interactions there is a biological rate processes set in a very predictable and negative feedback effect on the predators when they constant physical environment. A comparison of the begin to overeat their prey: however, in this system antarctic with the deep sea is appropriate, as the the Odontaster can cause a severe reduction of latter system is also essentially unaffected by physical A codontaster populations without such feedback perturbation. Sanders (1968, 1969), using entirely control. indirect methods of studying the deep sea, has em- We know less about the population dynamics of phasized the concept of biological accommodation, other predators. One extremely rare tertiary carni- to which he delegates an increasingly significant role vore, the asteroid Macro ptvchaster accrescens, was for interspecific competition along a gradient of de- seen twice in the study area: one of these was found creasing physical stress. to contain the remains of nine Odlontaster x'alidits. We believe that the term "biological accommoda- In other areas it was observed to eat urchins, and it tion" can aptly be applied to almost any ecological may well eat other asteroids as well. A weak case can association characterized by even a small number be made for food limitations of Perknaster. We of species (e.g., Dodson 1970). Experimental studies found no other predator consuming it, and the transi- of such a physically stressed community as that of tion from immature to mature morphology seems the rocky intertidal have demonstrated that most of to he associated with a substantial meal of Mycal/. the populations are regulated by biological inter- The asteroid Acodlontaster lo(dgsoni is uncommon, actions (Dayton 1971). The intertidal biological which reduced the probability of observation, and interactions are similar to those of this antarctic it and Odontaster meridionalis are characterized by community, with the exception that competition skewed size distributions (Fig. 5). This latter observa- seems to play a more important role in the lives of tion could indicate that the proposed 0. validlus many intertidal species, which are more influenced larval filter plays a significant role in their dynamics. by competition for space than are the sessile antarctic The regional comparisons of 0. *a//lids growth species. In general, predation pressure is certainly (Table 9) and reprodLction (Pearse 1965) indicate an important component of biological accommoda-

This content downloaded by the authorized user from 192.168.52.62 on Thu, 15 Nov 2012 17:29:57 PM All use subject to JSTOR Terms and Conditions 126 PAUL K. DAYTON ET AL. Ecological Monographs Vol. 44, No. 1 tion in the antarctic and temperate zone intertidal tions of the barnacle Balanus balanoidles. Ecol. communities (Connell 1961, Paine 1966a, Dayton Monogr. 31: 61-104. 1971), high altitude, tropical, and experimental lakes 1970. A predator-preysystem in the marine intertidal region. 1. Balanus glandula and several (Dodson 1970, Zaret 1972, Hall et al. 1970), tropi- predatory species of Thais. Ecol. Monogr. 40: 49-78. cal plant-held water communities (Maguire 1971), Dayton, P. K. 1971. Competition, disturbance, and tropical forests (Janzen 1970), and coral reef com- community organization: the provision and sub- munities (Branham et al. 1971, Porter 1972). This sequent utilization of space in a rocky intertidalcom- fact has been elucidated by combining extensive nat- munity. Ecol. Monogr. 41: 351-389. 1972. Toward an understanding of commu- ural history observations with varying degrees of nity resilience and the potential effectsof enrichment experimental manipulation. The product is a power- to the benthos at McMurdo Sound, Antarctica. p. 81- ful approach to the complexities of the real world. 95. In B. C. Parker [ed.] Proceedings of the colloquium In the present paper, it has lead to a suggestion that on Conservation Problems in Antarctica. Allen Press. 356 p. the association of organisms in a physically stable Dayton, P. K., and R. R. Hessler. 1972. Role of environment can be considered to be biologically biological disturbance in maintaining diversity in the accommodated, and that the term must include deep sea. Deep-Sea Res. 19: 199-208. easily measurable components of both predation and Dayton, P. K., G. A. Robilliard, and A. L. DeVries. 1969. Anchor ice formation in McMurdo Sound, competition. We suspect that when the same tech- Antarctica, and its biological effects. Science 163: niques of in situ observation and experimentation are 273-274. applied to deep-sea ecological systems, the conclu- Dayton, P. K., G. A. Robilliard, and R. T. Paine. 1970. Benthic faunal zonation as a result of anchor ice at sions about community organization will not be sig- McMurdo Sound, Antarctica. p. 244-258. Vol. 1, nificantly at variance with those derived from most Antarctic Ecology. Academic Press, London. other communities. Dodson, S. I. 1970. Complementary feeding niches sustained by size-selective predation. Limnol. ACKNOWLEDGMENTS Oceanogr. 15: 131-137. Farmanfarmaian, A., A. C. Giese, R. A. Boolootian, and We gratefullyacknowledge the diving and laboratory J. Bennett. 1958. Annual reproductivecycles in four assistance of Charles Galt and the outstanding coopera- species of west coast starfishes. J. Exp. Zool., 138: tion of the U.S. Navy Photographic Laboratory at 355-367. McMurdo Station. A project such as this depends upon Hall, D., W. Cooper, and F. Werner. 1970. An ex- the cooperation of many taxonomists; we acknowledge perimental approach to the production dynamics and our gratitudeto the following specialists: V. M. Koltun, structure of freshwater animal communities. Limnol. who promptlyidentified our large collections of porifera, Oceanogr. 15: 839-928. and P. Bergquist, who helped with later porifera collec- J. L. A tions and questions; C. Hand, who identifiedmost of our Harper, 1967. Darwinian approach to plant ecology. J. Ecol. 55: 242-270. coelenterates; J. Dearborn for patiently helping us plan the project and identifyingthe echinoderms; J. Hedgpeth Hedgpeth, J. W. 1971. Perspectives of benthic ecology for many interesting discussions and assistance with in Antarctica. p. 93-136. In L. 0. Quam [ed.] Re- pycnogoinid taxonomy; and J. Bullivant, R. Dell, and A. search in the Antarctic. Am. Assoc. Adv. Sci. Publ. Brinckmann-Voss, who promptly identified our bryo- No. 93. 968 p. zoans, molluscs, and hydroids, respectively. We thank Hemmingsen, A. M. 1960. Energy metabolism as re- D. Tinklepaugh for supplying us with a formula for lated to body size and respiratory surfaces, and its thermal cream to use while diving; W. R. Curtsinger evolution. Rep. Steno. Mem. Hosp. 9: 1-110. for making many dives with us, and W. Warriner for Hodgson, T. V. 1907. On collecting in Antarctic seas. drawing Fig. 1. Finally, it gives us pleasure to acknowl- BritishNational Antarctic Expedition, 1901-1904. Nat. edge the continuing help and encouragement of many Hist. 3. friends,especially R. L. Fernald, P. I. Illg, G. and N. Janzen, D. L. 1970. Herbivores and the number of MacGinitie, B. Menge, M. Mullin, J. Pearse, T. Poulson, tree species in tropical forests. Am. Nat. 104: 501- B. Rabbit, R. Root, H. Reiswig, D. Rivera, and an un- 528. identifiedreviewer. Koltun, V. M. 1968. Spicules of sponges as an element This research was supported by NSF Grant GA-1187. of the bottom sediments of the Antarctic, p. 121-3. Some of the calorimetry was supported by NSF Grant In Symposium on Antarctic Oceanography, Scott Polar GA-25349 and much of the preparation of this manu- Res. Inst., Cambridge. script has been supported by NSF Grants GA-30877 and Littlepage, J. L. 1965. Oceanographic investigations GV-32511 and Sea Grant GH-112. We are grateful to in McMurdo Sound, Antarctica. Antarct. Res. Ser., Woodward-Envicon, Inc., for supporting a share of the NAS, 5: 1-37. page charges. Maguire, B. 1971. Phytotelmata: biota and community structure determination in plant-held waters. LITERATURE CITED Annu. Rev. Ecol. Syst. 2: 439-464. Branham, J. M., S. A. Reed, J. H. Bailey, and J. Mauzey, K., C. Birkeland, and P. Dayton. 1968. Caperon. 1971. Coral-eating sea stars Acaniutia~tcr Feeding behavior of asteroids and escape responses planci in Hawaii. Science 172: 1l55-57. of their prey in the Puget Sound region. Ecology 49: Connell, J. 1961. Effect of competition, predation by 603-619. Thais lapillus, and other factors on natural popula- Miller. M. C. 1962. Annual cycles of some Manx

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nudibranchswith a discussion of the problem of migra- Tetilla leptoderma; Basketball Sponge; white; Zone III, tion. J. Anim. Ecol. 31: 545-569. rare in Zone II; a spherical sponge firmly attached to Paine, R. T. 1964. Ash and calorie determinations spicule mat by long spicules; occasionally found grow- of sponge and opisthobranch tissue. Ecology 45: ing on "Volcano" sponge; distribution often clumped; 384-387. sponge may be elevated by long spicules at base. 1965. Natural history, limiting factors and energetics of the opisthobranch Navanax inermis. Cinachyra antarctica; Spiky Sponge; grey; Zone III, rare Ecology 46: 603-619. in Zone II, somewhat spherical, usually protectedby long * 1966a. Food web complexity and species clumped spicules; firmlyattached to rocks or attached to diversity. Am. Nat. 100: 67-75. spicule mat by long spicules; often partially buried 1966b. Endothermy in bomb calorimetry. in spicule mat. Limnol. Oceanogr. 11: 126-9. Sponge; white, Zone III, base 1971. A short-termexperimental investigation Haliclona dancoi; Finger mat; often clumped, but clump of resource partitioningin a New Zealand r6cky inter- diffused through spicule rhizoidal growth; exudes mucus and tidal habitat. Ecology 52: 1096-1106. may result from crumbles easily when collected. Pearse, J. 1965. Reproductive periodicities in several validus Koehler, contrastingpopulations of Odontaster Mycale acerata; Slimy Sponge; white; Zone III; weakly Antarct. Res. Ser., a common Antarctic asteroid. attached by spongin to rocks or spicule mat; grows over NAS, 5: 39-85. and around other sessile animals; exudes copious Porter, J. W. 1972. Predation by Acanthaster and its quantities of mucus when disturbed. effect on coral species diversity. Am. Nat. 106: 487-492. Polymastia invaginata; Cone Sponge; grey; Zone II and Poulson, T., and D. Culver. 1969. Diversity in ter- III; solidly attached to rock in Zone II, without obvious restri'alcave communities. Ecology, 50: 153-158. attachment in spicule mat; often overgrown by other Prosser, C., and F. Brown. 1961. Comparative animal sponges in Zone III; has only one osculum, which can be physiology. W. B. Saunders Co. 661 p. retracted when disturbed. Sanders, H. 1968. Marine benthic diversity: a comparative study. Am. Nat. 102: 243-282. Dendrilla membranosa; Cactus Sponge; bright yellow; base diffusedthrough spicule mat; base 1969. Benthic marine diversity and the Zone III; spongin to Limatula hodgsoni valve; rubber-like stability-timehypothesis. Diversity and stability in often attached ecological systems.Brookhaven Symp. Biol. 22: 71-81. texture. cycles Thompson, T. E. 1964. Grazing and the life Gellius tenella; Staghorn Sponge; white; Zone III, rare [ed.] of Britishnudibranchs, p. 275-297. In D. J. Crisp in Zone II; weakly attached by spicules, forms large, 4. Grazing in British Ecological Symposium No. anastomosing structureabove substratum. terrestrialand marine environments. Blackwell, Ox- ford. Gellius benedeni; Pink Staghorn Sponge; pink; Zone III; Vinogradov, A. P. 1953. The elementary chemical weakly attached by spicules; similar to G. tenella but composition of marine organisms. Sears Found. Mem., less massive. This sponge harbors an isopod that some- 2: 1-647. times kills the sponge. Welch, H. E. 1968. Relationships between assimilation efficiencies and growth efficiencies for aquatic con- Splhaerotylus antarcticus; Tubular Sponge; dark grey; sumers. Ecology 49: 755-759. Zone II and III; similar to Polymastia but has many Whittaker, R. H., and P. P. Feeny. 1971. Allelo- tube-like oscula that can be retracted when disturbed. chemics: Chemical interactions between species. Science 171: 757-770. Leucetta leptor12apsis; Rubber Sponge; light tan; Zone often attached to Linmatulavalves and small rocks; Zaret, T. M. 1972. Predator-prey interactions in a III; convoluted appearance with very rubbery texture. tropical lacustrine ecosystem. Ecology 53: 248-257. related to Zeuthen, E. 1953. Oxygen uptake as body Calyx arcuarius; Fan Sponge; white; Zone III; attached size in organisms. Q. Rev. Biol. 28: 1-12. to rocks, shells, and spicule mat by thin stalk; forms large compressed fan-shaped structure.

APPENDIX I Isodictya setifera; Stringy Sponge; pink; Zone III; at- to rocks or Limatula List of the conspicuous sponges at McMurdo Sound tached by compact rhizoidal base including species name, common name, color, zone valves; delicate fibrous structure. (Dayton et al. 1970: 2), and natural history notes. Isodictya erinacea; Polychaete Sponge; yellow; Zone III; which Rossella nuda/Scolymastra joubini; Volcano Sponge; attached to spicule mat by long strand of spongin fibrous white; Zone III, rare in Zone II; weakly attached to appears to be dead sponge; characterized by long sponge spicule mat by dermalia; might bud or have "spines." low dispersal larvae as young sponges often clustered Red Zone II, rare around adults; very large sponge up to 2 m tall by 1.5 m Kirkpatrickia variolosa; Sponge; red; to rocks and shells broad wide. in Zone III; attached by base; conspicuous deep-red color. Rossella racoi'itzae; Root Sponge; light grey; Zone III; found in sponge spicule mat anchored by long spines; Kirkpatrickia coulmani; Wafer Sponge; yellow; Zone "budding" commonly seen; often lies buried beneath III; sits on spicule mat; crumbly but somewhat rubbery spicule mat with osculum extending above surface. structure.

This content downloaded by the authorized user from 192.168.52.62 on Thu, 15 Nov 2012 17:29:57 PM All use subject to JSTOR Terms and Conditions 128 PAUL K. DAYTON ET AL. Ecological Monographs Vol. 44, No. I Pachychalina pedunculata; Pencil Sponge; pale pink; Zone firmlyto large rocks; oscula appear as tuberances; soft III; long thin and unbranched stalk often deeply buried insides of sponge fall out when sponge is pulled off in spicule mat; stands upright. basal attachment; inside full of what appear to be eggs.

Latrunculia apicalis; Green Sponge; green; Zone II; Honiaxonella sp.; Bush Sponge; white to pale yellow; attached firmlyto large rocks; soft, globose shape; con- Zone II; rare in Zone III; attached to rocks or shells; spicuous dark green color. often has many small individuals around base of adult; 'branches" of adult fall off easily, may become attached Inflatella belli; Knob Sponge, brown, Zone II; attached and grow.

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