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

Abstract

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.

Carryover effects of temperature and pCO2 across multiple Olympia oyster populations

“…Those modeling larval recruitment (Wasson et al. , Kimbro et al. ) should consider including winter temperature as a factor influencing spatiotemporal recruitment patterns.…”

“…Whether larvae released earlier in the spring can survive to recruitment will greatly depend on many factors including food availability and predation. Those modeling larval recruitment (Wasson et al 2016, Kimbro et al 2019) should consider including winter temperature as a factor influencing spatiotemporal recruitment patterns.…”

“…For instance, large interannual variability in larval recruitment and frequent recruitment failures were recently reported (Wasson et al. , Kimbro et al. ).…”

“…Restoration efforts are afoot, but O. lurida populations continue to struggle, and may be further challenged by changing conditions (Feely et al 2008, Barton et al 2012. For instance, large interannual variability in larval recruitment and frequent recruitment failures were recently reported (Wasson et al 2016, Kimbro et al 2019). This variability is presumably related to inconsistent spawning success, larval survival, and retention, and governed predominantly by local conditions (Kimbro et al 2019).…”

“…This variability is presumably related to inconsistent spawning success, larval survival, and retention, and governed predominantly by local conditions (Kimbro et al 2019). It is unknown how the intensity, timing, and duration of local environmental conditions can predict recruitment failure (Wasson et al 2016). If winter conditions significantly influence recruitment through direct changes to adult reproductive capacity or timing, or indirect changes through parental carryover effects, population densities and distributions will inevitably shift with conditions.…”