PRESPAWNING BEHAVIOR, SPAWNING, AND DEVELOPMENT OF THE BROODING STARFISH LEPTASTERIAS-POLARIS

Citation
Jf. Hamel et A. Mercier, PRESPAWNING BEHAVIOR, SPAWNING, AND DEVELOPMENT OF THE BROODING STARFISH LEPTASTERIAS-POLARIS, The Biological bulletin, 188(1), 1995, pp. 32-45
Citations number
53
Categorie Soggetti
Marine & Freshwater Biology",Biology
Journal title
ISSN journal
00063185
Volume
188
Issue
1
Year of publication
1995
Pages
32 - 45
Database
ISI
SICI code
0006-3185(1995)188:1<32:PBSADO>2.0.ZU;2-Z
Abstract
Our study focused on the precise reproductive behavior of the starfish Leptasterias polaris (Muller and Troschel) before and during spawning -a subject of much speculation and evident ecological importance. Betw een the third week of December 1992 and mid-January 1993, we observed spawning in the laboratory that roughly corresponded to field observat ions in the Lower St. Lawrence Estuary. In experimental tanks provided with natural environmental conditions, the spawning was preceded by 7 to 8 weeks of complex aggregative interactions among the starfish. Th e individuals, which usually avoid each other, began to make discreet arm contact, which intensified with time and eventually led to the sup erposition of two or more starfish, independently of sex. The interact ions seem to be associated with decreasing temperature, because aggreg ative and spawning behaviors were not observed under stable temperatur e conditions. Male spawning is first initiated when the temperature fa lls to about 2 degrees C during minimum daylength (<9 h . d(-1)). In s eawater, the spermatozoa are negatively buoyant and tend to deposit as a sticky him on the substrate, where they enter a state of low activi ty. Stimulated by male spawning, females spawn on the layer of sperm, which is reactivated by contact with the oocytes, ensuring fertilizati on. In the laboratory, the fertilized eggs undergo first cleavage in 4 5 h, become brachiolaria in 40 days, and form fully developed young st arfish within 5.5 to 6 months, synchronously with populations in the f ield. The embryos develop at the same rate even when not brooded, sugg esting that the brooding behavior in L. polaris serves mainly to keep the eggs clean, healthy, and protected against predation.