Seasonality of harpacticoids (Crustacea, Copepoda) in a tidal pool in subarctic south-western Iceland

Seasonality of phytal harpacticoids was studied in a tidal pool in the lower rocky intertidal in south-western Iceland. Samples of the red alga Chondrus crispus were taken monthly from January 1999 to January 2000. Multidimensional scaling ordination showed a clear seasonal pattern in phytal species composition and abundance of individual species. Of more than 70 species recorded, Zaus spinatus accounted for one third of the total abundance. Many species were found only sporadically and analysis of the data was confined primarily to the eleven most common species (Zaus spinatus, Ectinosomaspp., Tisbespp., Ameira longipes, Mesochra sp. 2 and Mesochrasp. 1, Dactylopusia vulgaris, Amphiascoides debilis, Amphiascussp. 1, Parastenhelia spinosa and Amphiascus minutus). Four showed no significant variation in total abundance through the year, while the remainder had more or less pronounced peaks in summer. Most species (on which data was sufficient) had a prolonged (≥ 6 months) to a continuous breeding season, as indicated by the presence of ovigerous females. This contrasts with most shallow-water temperate and subarctic invertebrates which appear to have more restricted breeding seasons. Our results extend to higher latitudes the general conclusion that many temperate phytal harpacticoids have a long, often continuous, breeding season. The reasons for this are unclear but, presumably, involve access to continuous food supply. There is strong evidence that variations in abundance of several species in the tidal pool were not due only to recruitment, but also to migration to the pool in summer and emigration in autumn.