Temporal variability in embryonic development and mortality in the southern calamary Sepioteuthis australis: a field assessment

This study describes the incidence of embryonic mortality and differential development in southern calamary Sepioteuthis australis eggs. Late-stage S. australis egg strands harbouring multiple embryos close to hatching were sampled from shallow (<4 m) Tasmanian spawning grounds from early November 2000 to January 2001. Sepioteuthis australis embryos were found to develop asynchronously within individual egg strands with proximal embryos developing slower and suffering higher mortality than their distal siblings. The magnitude of asynchrony, however, differed throughout the season with greater within-strand differences observed when embryos were exposed to broader incubation temperatures. Unexpectedly, embryos developed more synchronously within biologically fouled strands and displayed a significantly lower incidence of mortality compared to those developing in unfouled strands. Embryonic mortality was initially low (4%) and significantly increased to 20% in late November, remaining above 10% until late December. This dramatic increase in mortality was not strongly associated with increasing water temperatures, but coincided with a period of heavy rainfall alluding to potential salinity effects.