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 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp . JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecological Monographs. http://www.jstor.org 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 preda- tion 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 signifi- cant 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 produc- tion 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 struc- ture (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 inter- actions in a complex community inhabiting an ap- parently 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 environ- ments 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.