Breeding season and egg morphology of echinoderms in Balsfjorden, northern Norway

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Abstract
Reproduction has been investigated in echinoderms from selected localities in an arctic-boreal fjord (c. 70° N). Three echinoids (Strongylocentrotus droebachiensis, S. pallidus, and Echinus esculentus) and three ophiuroids (Ophiopholis aculeata, O. sarsi, and O. albida) all produce large numbers of small eggs that develop plankto-trophically in the pelagic zone during spring and summer. So does one of the six asteroids examined, Asterias rubens. Five other asteroids (Leptasterias muelleri, Asterias lincki, Ctenodiscus crispatus, Pteraster militaris, and Solaster endeca) and the one holo-thurioid examined (Cucumaria frondosa) all produce fewer numbers of large eggs. A. lincki, C. crispatus, S. endeca, and C. frondosa develop lecithotrophically in the pelagic zone. S. endeca and C. frondosa reproduce during spring whereas A. lincki and C. crispatus have main reproductive peaks in mid-winter. L. muelleri and P. militaris develop by brood protection; the former reproduces in winter, the latter in spring. Eggs from the different species can generally be distinguished morphologically. Large, red/orange lecithotrophic eggs that develop either in the pelagic zone or by brood protection have numerous large lipid-like globules that are not conspicuous in small planktotrophic eggs. Chemical analyses confirmed the high content of lipid in ovaries of asteroids producing large, yolk-rich eggs. Distinctive reproduction strategies in arctic-boreal asteroids are indicated.