Print PagePopulation connectivity is a key factor in the causes and consequences of fluctuations in abundance and geographic distribution of estuarine and marine invertebrates and helps modulate metapopulation responses to floods, droughts, and many other disturbances. Many marine invertebrates have a two-part life cycle featuring mobile larvae and sessile adults, with connectivity manifested via dispersal during the larval stage and habitat quality most directly influencing the sessile stage. Disruptions to habitat quality can influence connectivity in several interacting ways, including effects on adult survivorship and growth, adult fecundity, quality and quantity of larvae produced, and selection of settlement sites by larvae.
We investigated population dynamics and larval dispersal patterns of the Pacific oyster Ostrea lurida in San Francisco Bay using a combination of population surveys, recruitment monitoring, and trace elemental fingerprinting methods. We examined oyster populations during the low flow season at the end of a three-year drought (Fall 2009) and during higher flow conditions (Spring 2010). Our specific aims were to (1) identify source and sink populations or regions for oysters within the Bay, (2) estimate regional connectivity patterns, (3) and link habitat quality of source and sink areas to recruitment, growth, and survivorship.
Results/Conclusions
Oyster abundance and size distributions differed significantly along the salinity gradient from upstream sites (lower salinity) toward the mouth of the Bay (higher salinity). Maximum oyster density occurred in brackish waters near China Camp State Park with over 1000 oysters / m2. Significant regional variation in temperature and salinity conditions were correlated with differences in the onset of fecundity and settlement as well as their peak levels. Juvenile oyster recruitment varied significantly around the Bay, with greatest settlement (15,250 oysters / m2) in upstream areas, coinciding with areas of maximum adult density, especially during warmer periods in summer and fall. While fecundity was relatively low throughout the Bay, with an average of 5.6% of oysters brooding at any one time, late-stage shelled larvae were found most frequently on the opposite side of the Bay from the sites of maximum recruitment, possibly suggesting that different factors may control each process. Connectivity patterns show some movement of larvae between upstream and downstream areas, with many appearing to originate at sites of maximum adult growth. These patterns indicate that habitat quality may influence both the production and settlement of larvae, with higher quality sites supplying larvae to lower quality sites.
