Fertilization success of the circumpolar Antarctic seastar Odontaster validus (Koehler, 1906): a diver-collected study

Broadcast spawning invertebrates in the Antarctic encounter a very arduous and unforgiving environment, where consistently low temperatures, high seawater viscosities and at times high flow conditions undermine successful sperm-egg interactions. The fertilization traits of the circumpolar Antarctic seastar Odontaster validus, were analyzed from diver-collected monthly samples from a shallow water site adjacent to the British Antarctic Survey (BAS) Rothera Research Station (Western Antarctic Peninsula). Dives were conducted using opencircuit scuba between 15–20 m depths. Successful sperm-egg interactions varied amongst seastars, however there was an optimum range in sperm concentration over which high numbers of eggs were fertilized (105–106 sperm⋅mL-1). This Antarctic seastar required 1–2 orders of magnitude more sperm to ensure optimal fertilization success compared to several comparable temperate species and the longevity of spermatozoa was moderate, retaining some activity and minimal fertilizing ability up to 24 hours after release. Eggs and sperm released by O. validus were also highly stenothermal, with extremely narrow ranges of thermal tolerance. Therefore, even small modifications in temperature dramatically reduced the number of eggs fertilized. This has important implications for the geographical distribution of Antarctic invertebrates, but also confirms the susceptibility of these species to environmental modification, making them one of the most temperature sensitive fauna on Earth. Such stenothermy is of particular relevance if ocean warming and the 1–2ºC rise in global temperature, predicted over the next century, is realized.

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