Coast-wide recruitment dynamics of Olympia oysters reveal limited synchrony and multiple predictors of failure.

Recruitment of new propagules into a population can be a critical determinant of adult density. We examined recruitment dynamics in the Olympia oyster (Ostrea lurida), a species occurring almost entirely in estuaries. We investigated spatial scales of interannual synchrony across 37 sites in eight estuaries along 2,500 km of Pacific North American coastline, predicting that high vs. low recruitment years would coincide among neighboring estuaries due to shared exposure to regional oceanographic factors. Such synchrony in recruitment has been found for many marine species and some migratory estuarine species, but has never been examined across estuaries in a species that can complete its entire life cycle within the same estuary. To inform ongoing restoration efforts for Olympia oysters, which have declined in abundance in many estuaries, we also investigated predictors of recruitment failure. We found striking contrasts in absolute recruitment rate and frequency of recruitment failure among sites, estuaries, and years. Although we found a positive relationship between upwelling and recruitment, there was little evidence of synchrony in recruitment among estuaries along the coast, and only limited synchrony of sites within estuaries, suggesting recruitment rates are affected more strongly by local dynamics within estuaries than by regional oceanographic factors operating at scales encompassing multiple estuaries. This highlights the importance of local wetland and watershed management for the demography of oysters, and perhaps other species that can complete their entire life cycle within estuaries. Estuaries with more homogeneous environmental conditions had greater synchrony among sites, and this led to the potential for estuary-wide failure when all sites had no recruitment in the same year. Environmental heterogeneity within estuaries may thus buffer against estuary-wide recruitment failure, analogous to the portfolio effect for diversity. Recruitment failure was correlated with lower summer water temperature, higher winter salinity, and shorter residence time: all indicators of stronger marine influence on estuaries. Recruitment failure was also more common in estuaries with limited networks of nearby adult oysters. Large existing oyster networks are thus of high conservation value, while estuaries that lack them would benefit from restoration efforts to increase the extent and connectivity of sites supporting oysters.

Phylogeography of the genus Epiplatys (Aplocheiloidea: Cyprinodontiformes).

There are six major genera of aplocheiloid killifishes endemic to West Africa. Five of these are largely restricted to the two major blocks of rainforest. Two are found within the Eastern rainforest block (Nigeria to the central Congo) while three are found within the Western rainforest block (Sierra Leone to Togo). The sixth genus (Epiplatys) has a range that exceeds that of the combined area of the other five genera. Phylogenetically this genus is related to the Western rainforest taxa. Phylogeographic analysis of this genus suggests that it escaped the confines of the Western block by first expanding into lowland habitats exposed after a sea level drop and then dispersed along coastal habitats to the east. One lineage managed to penetrate the interior of the Eastern rainforest block and one derivative of this lineage penetrated the Congo basin. A second route out of the Western rainforest block was to the north through what is now savannah habitat. The greater phylogeographic range of Epiplatys is hypothesized to be due to retention of ancestral morphology related to a greater adaptability compared to the other five genera.