Infrequent Fluctuations in Temperature and Salinity May Enhance Feeding in Pisaster ochraceus (Asteroidea) but Not in Dendraster excentricus (Echinoidea) Larvae.

AbstractIn recent years, low-salinity events characterized by high temperatures (18-23 °C) and low-salinity waters (20‰-22‰) have increased during late spring and summer, when many marine invertebrate larvae are developing. The present study examines the effects of low-salinity events on particle ingestion for larvae of two echinoderm species, the sea star Pisaster ochraceus and the sand dollar Dendraster excentricus. Larvae were exposed to high temperatures and low salinities for 24 hours, followed by feeding on the alga Isochrysis galbana in high or low salinity for another 10 minutes. Exposing Pisaster larvae to high temperatures and low salinities, followed by feeding in low salinity, did not impair ingestion rates. In fact, these larvae ingested particles at similar and sometimes higher rates than those in the controls. In sharp contrast, a 24-hour exposure to a high temperature and low salinity, followed by continued exposure to low salinity to feed, led to a decrease in the number of particles ingested by 8-arm Dendraster larvae. Larvae of both species captured very few particles when returned to 30‰ after a low-salinity event, indicating that continuous interruption of larval feeding by low-salinity events during development could be deleterious. Sand dollar larvae may have responded negatively to low-salinity events in our experiments because they are found in protected bays, where they may seldom experience these events.

Arms of larval seastars of Pisaster ochraceus provide versatility in muscular and ciliary swimming.

Larval swimming with cilia, unaided by muscles, is the presumed ancestral condition for echinoderms, but use of muscles in swimming has evolved several times. Ciliation and musculature of the arms of brachiolaria-stage larvae in the family Asteriidae provide unusual versatility in the use of muscles in swimming. The muscles affect swimming in two different ways. (1) Contraction of muscles moves the arms, propelling the larva. (2) Contraction of muscles changes orientation of the arms, thereby changing direction of ciliary currents and direction of swimming. New observations of the brachiolaria of the asteriid seastar Pisaster ochraceus demonstrate more versatility in both of these uses of muscles than had been previously described: the posterolateral arms stroke in more ways to propel the larva forward and to change the direction of swimming, and more pairs of the arms point ciliary currents in more directions for changes in direction of swimming. Morphology of brachiolariae suggests that these uses of muscles in swimming evolved before divergence of the families Stichasteridae and Asteriidae within forcipulate asteroids. This versatile use of muscles for swimming, both alone and in combination with ciliary currents, further distinguishes the swimming of these brachiolariae from swimming by larvae of other echinoderms and larvae of acorn worms in the sister phylum Hemichordata.

Culturing echinoderm larvae through metamorphosis.

Echinoderms are favored study organisms not only in cell and developmental biology, but also physiology, larval biology, benthic ecology, population biology and paleontology, among other fields. However, many echinoderm embryology labs are not well-equipped to continue to rear the post-embryonic stages that result. This is unfortunate, as such labs are thus unable to address many intriguing biological phenomena, related to their own cell and developmental biology studies, that emerge during larval and juvenile stages. To facilitate broader studies of post-embryonic echinoderms, we provide here our collective experience rearing these organisms, with suggestions to try and pitfalls to avoid. Furthermore, we present information on rearing larvae from small laboratory to large aquaculture scales. Finally, we review taxon-specific approaches to larval rearing through metamorphosis in each of the four most commonly-studied echinoderm classes-asteroids, echinoids, holothuroids and ophiuroids.