Benthic assemblage development and larval ecology of marine invertebrates at Adelaide Island, Antarctica

Bowden, David A. (2005). Benthic assemblage development and larval ecology of marine invertebrates at Adelaide Island, Antarctica. PhD thesis The Open University.



This thesis describes the first regularly resurveyed study of marine benthic colonisation processes at a location within the Antarctic Circle (660 30' S). Invertebrate assemblages on hard substrata were studied at 8 m and 20 m depths at three locations near Rothera Point, Adelaide Island (670 34' S, 68° 07' W). Assemblages on natural substrata were surveyed photographically and by sampling of cryptic sessile fauna. Recruitment to upper and lower surfaces of artificial substrata was monitored at monthly intervals through 1.5 yr and subsequent survival and growth of sessile assemblages was monitored photographically over 3 yr. Planktonic larvae of benthic invertebrates were surveyed at monthly intervals through 1.5 yr.

Recruitment took place throughout the year but was strongly seasonal in most taxa. Many sessile taxa recruited during winter; apparently in direct contrast to a general pattern of summer recruitment in temperate latitudes. All vagile taxa, by contrast, recruited in summer, regardless of developmental type or time of spawning. Rates of assemblage development, and maximum growth rates of individual species, were slow compared with temperate latitudes but a biotic and biotic disturbances caused realised growth rates to be highly variable at scales of m - km. Ice impacts affected substrata at 8 m but the establishment of assemblages at both depths was controlled principally by postsettlement mortality from biotic disturbances, particularly grazing by the urchinSterechinus neumayeri.

Larvae were present in all months but most taxa showed strong seasonality of occurrence. Diversity of larval types was comparable with data from other Antarctic and temperate studies but abundances were higher than in a similar study at Signy Island (60043' S, 45° 36' W). The range of larval types, durations, and times of spawning argues against any strong selective pressures a<;ting on developmental mode itself. Rather, the timing of settlement appears to be the characteristic of the life cycle that is most strongly selected for. It is suggested that differences between sessile and mobile taxa in the timing of settlement may be caused by the seasonal availability of food types for juvenile stages.

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