EXPERIMENTS ON EMBRYO SURVIVORSHIP, HABITAT SELECTION, AND COMPETITIVE ABILITY OF A STICKLEBACK FISH (GASTEROSTEUS) WHICH NESTS IN THE ROCKY INTERTIDAL ZONE

Like other 'white' sticklebacks, those nesting intertidally at Spry Ba y: Nova Scotia, Canada, remove fertilized eggs from the nest, disperse them over the surrounding area, and ss provide no subsequent parental care. However the breeding substrate at Spry Bay is devoid of the fil amentous algae which are the normal breeding substrate of the white st ickleback and which elsewhere facilitate survival of abandoned embryos . Experiments show that embryos dispersed in the intertidal zone al Sp ry Bay survive surprisingly well despite the complete absence of paren tal care and the periodic absence of water. Intertidal embryos general ly develop faster than embryos in the adjacent subtidal zone, but ther e are exceptions to this pattern. Intertidal males show site fidelity to their nests despite interrupted access to territory, and they show consistent preference for nesting in the intertidal zone in the field. In the laboratory, and in the absence of tidal flux and competition, males taken from the rocky intertidal zone generally prefer to breed o n bare rock substrate even when filamentous algae are freely available . When white stickleback males from an adjacent population which breed s subtidally in filamentous algae are introduced into the experimental aquaria as competitors, they exclude the males that breed on bare roc k. The surprisingly high survivorship of embryos in the rocky intertid al zone, the habitat selection of males for bare substrate, and their exclusion by males that breed subtidally on algae, all suggest that th e highly unusual breeding behaviours of intertidal white males form an effective alternative breeding repertoire. Because breeding habitat s election has implications for mate selection, the possibility exists t hat sticklebacks with different breeding repertoires at Spry Bay may m ate assortatively.