LONG-TERM CHANGE OF TEMORA-LONGICORNIS (COPEPODA, CALANOIDA) ABUNDANCE IN A DUTCH TIDAL INLET (MARSDIEP) IN RELATION TO EUTROPHICATION

Eutrophication of the coastal marine ecosystem of the western Wadden Sea and the adjacent coastal North Sea has led to increasing spring and summer levels of flagellates in the period 1973 to 1991. This was observed in the Marsdiep area, where in recent years the typical April bloom of Phaeocystis sp. started earlier and had a broader seasonal distribution than ever before. In the same years, the average abundance of successive developmental stages of the herbivorous pelagic copepod Temora longicornis increased by factors between four and eight in the period March to June. The seasonal peak of this species, originally between March and the end of May, widened into the summer months. Daily egg production per Temora female reached a peak at the highest Phaeocystis density. Apparently, eutrophication had a stimulating effect on the productivity and the development of Temora. Because Temora did not ingest high quantities of Phaeocystis itself, an alternative food source growing together with Phaeocystis or even in response to Phaeocystis, must have been available for Temora longicornis to sustain its high egg production and its enhanced abundance..