Hansen BW, Drillet G, Kristensen RM, Sorensen TF, Tottrup MT
Calanoid copepods, hatching, egg production, SEM, mesocosm, Limfjord, Denmark, 2000 m3
Close to 50 species of marine Calanoid copepodshave been reported to produce diapause eggs (Engeland Hirche in J Plankton Res 26:1083–1093, 2004); eggsthat are viable but require a refractory phase before theyhatch, sometimes after months. Diapause eggs are oftendescribed as morphologically diVerent with respect to eggmembrane ultrastructure and having a thicker egg shellwith surface ornamentation as opposed to the smooth shellfound in subitaneous eggs that hatch within days (Belmontein J Mar Syst 15:35–39, 1998; Chen and Marcus in MarBiol 127:587–597, 1997; Castro-Longoria in Crustaceana74:225–236, 2001). Egg production rates, egg surface ornamentation,and hatching success were monitored in largeaquaculture Wsh enclosures during winter with close to zerowater temperatures (N57°). Surprisingly, all female copepods(Acartia spp.—presumably A. tonsa, and Centropageshamatus) produced eggs all through the winter with noobvious pattern with respect to light, temperature and foodavailability, and no diapause eggs were observed. However,individual females produced several categories of eggs withor without surface spines even within the same egg batch asevidenced by scanning electron microscopy (SEM). Fouregg categories were distinguishable: ‘no spines’, smootheggs; ‘short spines’, 5–15 m long; ‘truncated spines’, withthe spine tips cut-oV