Population biology and reproductive ecology of Chlorostoma (Tegula) funebralis, an intertidal gastropod

Abstract

The trochid gastropod Chlorostoma (Tegula) funebralis is found in rocky intertidal habitats along the west coast of North America from Baja California to Vancouver Island. Size-frequency distributions of populations were analyzed along a latitudinal gradient from northern Oregon to Baja California. Populations in California and southern Oregon were dominated by individuals in the juvenile size classes (0.1g-2g). Along the Oregon coast, populations dominated by juveniles were correlated with coastline topography, with protected areas having large numbers of juveniles and exposed areas dominated by larger size classes. The largest size classes (>9g) were rarely present in southern populations.

The seasonality of reproduction was investigated in a southern California population and an Oregon population to determine whether continuous reproduction in southern populations increases recruitment success over the year and decreases inter-annual variation in reproductive success. Constant recruitment may cause populations to have a large number of juveniles, the observed pattern in southern populations. Although individuals capable of reproduction were found year-round in both populations, the southern population experienced multiple spawning events over the year, while the northern population experienced only one such event. Constant recruitment may be a strategy to compensate for shorter life spans and smaller sizes of individuals in southern California.

To investigate whether variations in predation rates on large adult C. funebralis affect the size structure of populations, the main predators and predation rates for different populations in Oregon were identified. All observed predation events were by the intertidal seastar Pisaster ochraceus . Predation pressure by P. ochraceus varied significantly with site and between sampling dates but did not remove enough C. funebralis from the adult population to have a significant effect on population size structure.

To determine the connectivity between populations and the maximum dispersal potential, the mitochondrial gene COI was sequenced from individuals from nine populations ranging from southern California to northern Oregon. Although haplotype diversity was high, no genetic structure was found between populations. Rather than an indication of high dispersal potential and a panmictic species, the lack of isolation by distance may be a result of range expansion following the last glacial maximum.