Seasonal dynamics of meiofauna from the oligotrophic continental shelf of Crete (Aegean Sea, eastern Mediterranean)

The response of metazoan meiofauna and nematode communities to the sedimentation of a spring phytoplankton bloom was investigated at four stations of the continental shelf of Crete (south Aegean Sea, eastern Mediterranean). The four stations were located on a transect with depths of 20, 70, 130 and 190 m, and samples were taken monthly from May 1989 to May 1990. After the onset of the spring bloom, a marked increase in sedimentary chlorophyll α values was observed (on average 1.6 μg/g). These values remained stable throughout the spring and summer period while during autumn and winter they dropped to very low levels (0.2 μg/g). Nematodes dominated in the meiofauna, ranging from 78% in March to 95% in August and January. Harpacticoid copepods were the second most abundant group, ranging from 2% in August to 18% in April. Total meiofauna biomass was lowest in January (0.03 mg/10 cm2) and highest during spring and summer after the spring bloom (1.07 mg/10 cm2). Most meiofaunal taxa displayed significant seasonal changes at the shallower stations (20, 70 and 130 m), with abundances rising during spring and autumn following the productivity of the water column. Conversely, no seasonal variability was evident in terms of abundance or biomass at the deeper station (190 m). Nematode epistrate feeders and selective deposit feeders were more abundant at the two shallower stations, increasing their numbers after the spring bloom. Among the most dominant species, some represented as much as 18% of the total nematode abundance. The nematode community structure displayed a gradual transition, with increasing depth being mostly influenced by the sedimentary characteristics of the environment as well as the overall productivity of the system. The nematode species diversity was found to be significantly lower at the intermediate station (70 m), where physical and biological disturbance were highest.