The Spawning of Neanthes Succinea in the Salton Sea

Abstract

The spawning of the polychaetous annelid Nereis ii;:bata was observed in the Woods Hole region by Lillie and Just (1913) who reported considerable uniformity in swarimiing periods in accordance with phases of thie on10011. Lillie and Just concluded that periodicity in Nereis IiPJIbata belongs to the large class of phenomena of which lunar spawning of the Pacific palolo, Eutnice viridis, is a well-known example. Korringa (1947) in a review of the relations between the moon and periodicity in the breeding of marine animals pointed out that Nereis liUtbata wcas not a clear cut case of lunar periodicity. The synonymiy of this species is extensive (see Hartman 1951). What Lillie and Just referred to as Nereis linibata is probably the same species currently known as Ncanthles .succinea (Frey and Levc 'art). Since the time when Near thes was first reported present in the Salton Sea by Hartman (1936), it has become very prevalent and is the main food of the croaker, Bairdiella icistius, a fish introduced into the Salton Sea from the Gulf of California in 1951. The life cycle of Neanthes was studied during 1955-1956 as part of a study of the Sea as a sport fishery. The ichthyological aspects of the study are to be published as a Fish Bulletin by the California Department of Fish and Game. Because the pheniomenon of periodicity may be of general interest, the following note is submitted for wider dissemination of evidence that, at least in the Salton Sea, the spawning of Neanthes does not seem to follow a monthly cycle. Observations in the field and in the laboratory indicate that spawning takes place as described by Lillie and Just. Spawning can be observed at night because mature Neantthes are attracted to light. Epitokes appear shortly after sunset, swimming at the surface; maximum numbers are seen about an hour after sunset; numbers then decrease until, about 3 hours after sunset, epitokes are no longer attracted to the light and their spawning, appar.ently, ceases for the night. Fertilization takes place immediately after eggs are spawned. At temperatures between 20-25? C, the eggs begin to cleave within 20 -minutes after fertilization, develop into ciliated, freeswimming larvae in about 13 hours, and into trochophore larvae within 24 hours after fertilization. Thus, the presence of eggs in the plankton would seem to be presumptive evidence for spawning within the previous 24 hours. Eggs were found by the senior author in quantitative plankton samples taken at all phases of the moon. For example, eggs were present in all samples collected *during a 4-month period on the dates and at the phases of the moon indicated in the following list: It was mentioned above that within 24 hours after fertilization developmelnt has proceeded to the trochophore stage. A day and a half after fertilization, the larva has developed 2 segments v%ith setae, and after 2 days there are 3 seta-bearing segments. The larva2 renmain planktonic and continue to add segments until, after about 2 weeks, they have attained 6-9 segments and settle to bein