open. The spines of sea urchins and the pedicellariae of brittle and basket stars are also
controlled by the internal hydraulic pressure generated by this system.
Echinoderms are highly sensitive to rapid changes in salinity and other water quality
parameters. The water vascular system may help explain this; the organisms have little
ability to regulate the speed of osmotic acclimation, as their bodies are essentially open
to the surrounding water. Take great care when acclimating any new echinoderm. Drip
methods are preferred and should occupy the span of several hours to limit osmotic
shock. Hyposaline (low salinity) conditions, which are often found in dealer aquariums
or during some disease treatment regimes, are not tolerated by most spiny skins.
The Power of regeneraTion
My favorite story of the power of regeneration hails from the New England seaboard at
a time when sea stars were being blamed for dwindling oyster crops. As the story goes,
oyster fishermen became aggravated by these benthic competitors and feverishly began
cutting the sea stars in half and throwing the pieces overboard to cull the population and
regain control of the oyster fishery. Soon thereafter, the sea star population exploded.
Sea stars and some sea cucumbers are well known for their ability to regenerate, a
trait thought to have evolved as a defensive mechanism. Regeneration allows an animal
to re-grow a single limb that has succumbed to predation, but in many cases entire new
animals are formed from dismembered arms. Many brittle stars offered for sale are missing sections of arms or entire arms. When the animal is handled during collection, the
animal may itself detach an arm as a predator deterrent. These arms quickly grow back.
As echinoderm popularity increases, this natural trait may be advantageous in culturing
the organisms. Could we not propagate desirable sea stars as we do corals?
STarS of The Sea (aSTeroidS)
The dietary requirements of coral-reef sea stars are not well understood. In captivity,
most species seem to waste away slowly within months from suspected malnutrition.
Most sea stars are considered to be specialized feeders, but species-specific diets are rarely
known. In the aquarium, most common sea stars will accept meaty foods such as Mysis
shrimp, chunks of clam, and even prepared pellets. Often, captive sea stars will become
omnivorous, consuming whatever is available—but without specific species of sponges,
bryozoans, and corals, the preferred prey items of many echinoderms, they rarely survive
beyond 18 months. Target feeding with meaty foods, a mature aquarium with live rock,
and exchange of live rock seem to stretch the captive life span.
