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
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.