Scale-dependent impact on diversity of Antarctic benthos caused by grounding of icebergs

Abstract

Analysis of seabed video-strips on the Weddell Sea shelf provided evidence that the effects of iceberg scouring on megabenthic assemblages differ, depending on spatial scale. At a local scale (1 to 100 m), undisturbed glass sponge-associated habitats were significantly more diverse than disturbed ones; at a regional scale (1 to 100 km), increased habitat heterogeneity caused by iceberg scouring enhanced species diversity. The pace and succession of the recolonization exhibits high variability and is difficult to predict. The results not only underpin the concept that disturbance events are essential factors in the regulation of ecosystem dynamics, but also emphasize the relevance of scale in the evaluation and explanation of diversity patterns.

On the origin of Antarctic marine benthic community structure

“…Figure Ib). These processes are likely to have had structuring effects of catastrophic dimensions on benthic communities [2].…”

“…However, Dimakis et al [44] estimated that mass wasting on a glaciated continental slope in the northern hemisphere typically occurred at least once every 95 to 170 years. If this is a reliable estimate, and such conditions are applicable to glaciated continental margins elsewhere, the Antarctic slope fauna would have been severely affected during glacial periods, because it might take one hundred to several hundreds of years for the Antarctic benthos to reach community equilibrium following physical destruction [2,5,45,46]. Although we do not yet have good methods for dating the age of most Antarctic invertebrates, Polar invertebrates are known to have slow growth rates, longevity and delayed age at first maturity, as a consequence of adaptation to cold conditions [9,36].…”

“…We consider that the few broadcasters with pelagic larvae, which have the ecological advantage of a quick recolonization of highly disturbed intertidal or sublittoral habitats [2,45], might be at a disadvantage in the longer term, especially during glacial periods, when intertidal habitats are broadly erased. Again the question arises as to how these intertidal communities with a narrow depth distribution range, from the intertidal to shallow subtidal, survived.…”

“…During glacialinterglacial cycles, most ecosystems experience significant environmental change, although the magnitude of recurrent direct mechanical destruction of environments by ice on the Antarctic continental shelf during the later part of the Cenozoic era (65 million years ago to the present day) is unparalleled anywhere else on Earth. During the present interglacial, iceberg scouring or ploughing, caused by an iceberg running aground on the shelf, is the main physical process affecting the benthic communities (see Glossary) in shallow waters on the Antarctic continental shelf [1,2]. Effects of iceberg scouring vary locally and, on a larger geographical scale, intermediate levels of disturbance by icebergs can even enhance benthic diversity on the Antarctic continental shelf [1,3,4].…”

“…Effects of iceberg scouring vary locally and, on a larger geographical scale, intermediate levels of disturbance by icebergs can even enhance benthic diversity on the Antarctic continental shelf [1,3,4]. Enhanced habitat structuring through local disturbance has been frequently used to explain Antarctic species richness and community structure [2].…”