I see a lot of questions lately about these wonderful little creatures that ask specifically about acclimatization and poor survival of specimens. The acclimatization of
sea stars is so important that the fact that Linckia stars have an 80 to 90% mortality shipping rate is prolly due to the improper acclimatization of the sea stars, not necessarily the shipping. If your sea stars seem to explode, it is prolly due to the acclimatization problems seen with these echinoderms.
One of the features that distinguish echinoderms from all other animals is the presence of the ambulacral system, a relatively high-pressure hydraulic system that is used to power Asteroidea body movements. This hydrovascular system is a set of vascular vessels that use body fluids/water to extend and contract their tube feet. Tube feet are extensions of the final branches of the hydrovascular system. Although is was long thought that the tube feet used the hydrovascular system to produce suction that allowed the tube feet to “grab” the substrate, etc., it is now known that the base of the tube feet use a 2 substance system of adhesive/adhesive-resolver to literally “glue” the tube feet to the objects they come in contact with and unglue them to release them.
The presence of the hydrovascular system is probably one of the major limitations for keeping asteroides in the home aquarium. The ambulacral system is made up of many membranes and delicate tissues that simply do not respond well to repeated challenges by fluctuations in the salinity of the environment. If the changes are abrupt enough, the tissues/membranes will respond by rupturing due to the osmotic gradient across these membranes. Most echinoderms simply cannot tolerate fluctuations in the salinity of the water column. Echinoderms are some of the oldest living extant spp. of marine creatures, and have over millions of years adapted to living in fully marine (as opposed to estuary or brackish or freshwater) conditions, with the salinity at 35 to 36 PPT ( 1.026 S.G.at 84° F).
Water does not enter the water vascular system passively; rather, it is actively pumped into the hydrovascular system through an as yet incompletely understood metabolic pathway. When fluctuations in salinity rupture the membranes of the hydrovascular system, death or at least the “explosion” of the sea star occurs. This demise often occurs over several days to weeks, with pieces of flesh falling off the main body mass after the damage to the ambulacral system has occurred. See
http://www.geocities.com/banggai/blinckia.html for some pictures of the effects on Linckia levegata. Some times the remaining rays will re-grow the central disk, so it is possible to maintain the pieces to recover and re-grow full bodies if there are few scavengers…
In addition to the possible assault on the hydrovascular system, Linckias have another target of salinity weaknesses. The aboral surface of stars is often covered with small, delicate, filmy projections of the main body cavity of the creature through holes in the body wall. These are the dermal gills, considered to be the primary site of gas exchange. These projections are filled with fluid from the body cavity, which is circulated through the structures by cilia. These dermal gills are also subject to osmotic rupture and damage during periods of salinity fluctuation.
Consequently, although sea stars can survive a wide number of environmental challenges, from poor water quality to temperature fluctuations, they simply cannot tolerate fluctuations of salinity. Handling these creatures may damage these dermal gills as well.
I wish that I could tell you that I have had fantastic success using the following acclimatization procedure, but often prior handling of the sea stars will determine how well they will survive in your tank. Remember that the damage to the hydrovascular system is often slow to appear in the creature. Make sure that when you select your sea star that you look for firm creatures with no strictures or pits on the dermal surfaces and well-extended tube feet on the aboral surface of the rays.
The best method of acclimatizing these wonderful creatures is to arrange a drip (get an IV tube set from the hospital if possible) and place the creature in a bucket or container large enough to hold the sea star and it’s water that it was shipped in. Place this container in another container (PLEASE, NOT the SUMP!!! This allows the introduction of the shipping water and anything else in that water into your system… …including copper…) large enough to hold 4 volumes of the first container (or use a sink). Start the drip at about 1 to 2 drops per second, and remove approximately 1/3 the volume of the container every hour. This will take about 4 to 6 hours to equalize the volume, depending on how much water you start with. I would suggest this method whenever introducing ANY echinoderm, and prolly snails as well, although most marine snails will do with a 2 hour acclimatization. If you can’t acquire an IV set from the hospital, take some
air line tubing and put a clamp on the tube to adjust the flow rate into the acclimatization chamber. Use a watch to see how many drops fall in to the container in 30 seconds (use this as 25 to50 drops per 30 seconds)
I hope this helps, I have lost a few Linckia over the years by not knowing this information. I know that most of the info here is specific to Linckia spp., but it applies to ALL echinoderms as well, urchins, sea cukes, sand dollars, and sea stars, although the Linckia spp. seem to be the most susceptible.
Sorry for the long post, I will prolly post this on reef central as well. Hope this helps.
Julie
It arrived stiff (PH shock?)...acclimated over several hours but methinks it was already too far gone. 3 of the 4 specimens in that shipment (August 2000) were dead or dying.
