Reproduction of Antarctic Benthic Marine Invertebrates: Tempos, Modes, and Timing

Work on the life histories of common antarctic benthic marineinvertebrates over the past several decades demands a revisionof several widely held paradigms. First, contrary to expectationsderived from work on temperate species, there is little or noevidence for temperature adaptation with respect to reproduction(gametogenesis), development, and growth. It remains to be determinedwhether the slow rates of these processes reflect some inherentinability to adapt to low temperatures, or are a response tofeatures of the antarctic marine environment not directly relatedto low temperature, such as low food resources. Secondly, contraryto the widely accepted opinion designated as "Thorson's rule,"pelagic development is common in many groups of shallow-watermarine invertebrates. In fact in some groups, such as asteroids,pelagicdevelopment is as prevalent in McMurdo Sound, the southern-mostopen-water marine environment in the world, as in central California.In other taxonomic groups, especially gastropods, there doesseem to be a genuine trend toward non-pelagic development fromtropical to antarctic latitudes. Although this trend has beenpredicted by theoretical models, its underlying causes appearto be group specific rather than general. Thirdly, pelagic lecithotrophicdevelopment, often considered to be of negligible importance,occurs in many shallow-water antarctic marine macroinvertebrates.Pelagic lecithotrophy may be an adaptation to a combinationof poor food conditions in antarctic waters most of the yearand slow rates of development. Nevertheless, some of the mostabundant and widespread antarctic marine invertebrates havepelagic planktotrophic larvae that take very long times to completedevelopment to metamorphosis. These species areparticularlyprevalent in productive regions of shallow water (<30 m),which are frequently disturbed by anchor ice formation, andthe production of numerous pelagic planktotrophic larvaemayrepresent a strategy for colonization. Although planktotrophiclarvae tend to be seasonal in occurrence, their production isnot linked particularly closely to the mid-summer pulse of phytoplanktonproduction. These larvae show no evidence of starvation, evenduring times when phytoplankton abundance is very low, and theymay depend on unusual sources of food, such as bacteria. Howthey escape the selective conditions that apparently led toa predominance of non-feeding modes of development in antarcticmarine invertebrates remains as a major challenge for antarcticmarine biology.