A Suite of Adaptations for Intertidal Spawning

Abstract

Salt marshes and similar tide-dominated habitats present an unusual challenge for reproduction of resident aquatic organisms. Strong currents, siltation and hypoxia can potentially contribute to reproductive failure through mortality of the eggs or flushing of the eggs and larvae from the habitat. Fundulus heteroclitus , a small brackish water killifish, is a common resident of tidal marshes along the east coast of North America from Newfoundland to Florida. The reproductive strategy of this and related species is based on aerial incubation of eggs in the high intertidal zone. The eggs are resistant to desiccation and, when fully developed, hatch on immersion. Copulatory behavior and anatomy of accessory reproductive structures are adapted to placement of eggs in protected incubation sites. The gonads of both males and females mature rhythmically with an endogenous circasemilunar period, which is synchronized with the “spring” tides of new and full moons. Spawning occurs on high tides. Embryos develop in 9–15 days, and usually hatch on the succeeding spring tide series. Reproductive cyclicity in F. heteroclitus and related fishes ensures that spawning fish will have access to the high intertidal zone, thereby permitting aerial incubation of eggs.