Population dynamics, biomass and productivity of Limapontia depressa (Gastropoda, Opisthobranchia) at Bull Island, Dublin, Ireland

Abstract

Limapontia depressa was present in the saltmarsh pools at Bull Island, Dublin from October to June each year. Numbers peaked in December, with a secondary peak in April, and the maximum density recorded was just under 23000 indiv m−2. The strong population seasonal cycle was not linked to salinity or chlorophyll-a cycles but did coincide with the drying of the pools. Average production (P) was 233 kJ m−2 y−1, with a P:B ratio of just 2:1, which is rather low for such a small animal and may be a function of the low growth rate. These conclusions must be treated with caution due to uncertainty over recruitment mechanisms. Gamete output (G) was calculated at a maximum of 28.6 kJ m−2 y−1. This is a higher secondary production than previously reported for saltmarsh herbivores, and may be an important link into the wider estuarine trophic system and a vital food resource for small waders. The low G:P ratio suggests that not all semelparous species necessarily adopt an r-strategy of ‘reproductive recklessness’.