BENTHIC RESTING EGGS OF CALANOID COPEPODS IN NORWEGIAN ENCLOSURES USED IN MARICULTURE - ABUNDANCE, SPECIES COMPOSITION AND HATCHING

Abundance, species composition and viability of benthic resting eggs o f calanoid copepods were investigated in the sediments of seven Norweg ian enclosed pond systems used in mariculture as well as in the sedime nts of the nearby open sea. The ponds represented different types of m orphometry and zooplankton communities and were located from approxima tely 60 to 70 degrees N. Differences in environmental conditions in de ep water were also typical with anoxia and the presence of hydrogen su lphide at most of the localities. The lowest and highest egg densities in the enclosures were 7.5 +/- 6.4 x 10(4) and 5.5 +/- 2.5 x 10(6) m( -2), respectively, higher than in the sediments of the nearby open sea . Highest densities were found at larger or median depths. Altogether, egg densities higher than 10(3) m(-2) were found of only four calanoi d species; Eurytemora affinis, Acartia teclae, Acartia clausi, Temora longicornis. Hatching success was variable (0-92%), and no significant correlation to the presence of anoxia and hydrogen sulphide was found . This high hatching success was achieved with eggs exposed to hydroge n sulphide for several months. The recruitment potential to the plankt on of nauplii was estimated from 4.8 to 1682 nauplii l(-1) for the dif ferent localities. The results showed that resting egg production is a common life history characteristic of some neritic calanoid species i n Norwegian waters. In addition to copepod eggs, low densities (< 10(3 ) m(-2)) of eggs from rotifers and 'cladocerans' were found in most of the localities.