MEPS 272:131-140 (2004)  -  doi:10.3354/meps272131

ABSTRACT: The reproductive biology of the common Antarctic ascidian Cnemidocarpa verrucosa (Lesson) (Tunicata, Ascidiacea) was studied in a shallow-water population at Potter Cove, South Shetland Islands. Samples were taken monthly by SCUBA diving over a 15 mo period during 1996 and 1997. The reproductive cycle was examined by histological analysis of the gonads and gonad index measurements. Mean oocyte diameter peaked in June and showed a sharp decrease in August. A similar pattern was exhibited by gonad indices, which suggests a strong seasonality in reproduction. Gametogenesis was continuous year-round, although vitellogenesis, mature oocytes and mature spermatocytes were mainly observed during the austral winter. It is interesting that reproduction of this suspension feeder seems to be decoupled from the pulses of primary production characteristics of Antarctic systems and was not related to the slight, but present, temperature changes. It was striking since these 2 factors are usually among the most important in determining reproductive cycles, especially in suspension feeders. This suggests either that winter time is not so stressful, in energetic terms, at least in the Potter Cove ecosystem, or that this ascidian species is able to store energy in some organs during favorable periods to later fuel reproduction. This later idea is supported by the higher gonad production observed in 1997 compared to 1996, which coincided with higher levels of chl a that year.

KEY WORDS: Antarctica · Ascidians · Reproductive strategies · Cnemidocarpa