BROODING BIOLOGY OF THE SEA STAR PTERASTER-MILITARIS (MULLER,O.F.) - ENERGETIC AND HISTOLOGICAL EVIDENCE FOR NUTRIENT TRANSLOCATION TO BROODED JUVENILES

Adaptations of the sea star Pteraster militaris (O.F. Müller) for brooding postmetamorphic juveniles in an aboral chamber are examined. Brooding was extremely widespread among adult females, occurring in 75 of 99 individuals examined between February 1986 and July 1987. Premetamorphic offspring comprised > 80% of all brooded progeny. Offspring may be brooded to a juvenile size of R = 4.5 mm from an egg of ≈ 1.1 mm in diameter, although the majority of juveniles left the brood chamber at sizes less than R = 2.1 mm. There is a size-independent upper limit on the number of juveniles that can be successfully brooded by a female. The mean energetic content of freshly spawned eggs (10.2 J) was considerably less than that of brooded juveniles (54.2 J). This suggests that there must be some postvitellogenic transfer of nutrients from parent to brooded juvenile. Histological examination revealed the presence of a complete and apparently fully functional digestive system in brooded juveniles as small as R = 1 mm. Thus, both histological and energetic analyses indicate the possibility of active feeding by brooded juveniles. There are numerous potential mechanisms by which nutrients may be procured by the brooded juvenile. Observations indicate that brooded juveniles are cannibalistic ectoparasites, grazing on irritation-induced hyperplastic regions of the maternal dermis. Direct ingestion of other maternal tissues, such as pyloric caeca that has been extruded into papullae and on the epithelium lining the brood chamber, may also occur. Brooded juveniles may also ingest particulate organic matter derived from abortive embryos or larvae, faecal material and mucus secreted by the epithelium of the brood chamber. Uptake of dissolved organic matter may also be of importance to brooded juveniles. © 1990.