16 research outputs found
Early recruitment and growth of the American oyster Crassostrea virginica (Bivalvia: Ostreidae) with respect to tidal zonation and season
Survival and growth of newly settled oysters were measured at sub- and intertidal treatment levels during the first month of post-settlement life in the York River, Virginia, USA. Controlled settlement of hatchery-reared larvae in the laboratory and image analysis techniques allowed for individual oysters grown in the field to be tracked through time. High mortality occurred within 1 wk postsettlement at ah tidal heights in 3 experiments which spanned the natural recruitment period. This initial mortality strongly influenced later abundance, as weekly mortality rates decreased sharply after 2 wk. Additionally, all recruits were eliminated from the mid-intertidal zone and above (\u3e25% aerial exposure) during high temperature periods. Only in autumn did recruitment occur in the intertidal area occupied by natural oyster populations. In contrast, low intertidal and subtidal populations persisted through the month long experiments where adult oysters were rare. Growth (shell area) of intertidal oysters exposed \u3e25% was reduced relative to more immersed oysters. Density-dependent growth was not observed. While the natural oyster population appeared to be relegated to the suboptimum intertidal, successful recruitment to this zone was limited on a seasonal basis by lethal air temperatures \u3e30 degrees C. The mortality agents which structure the intertidal population affect recently settled and juvenile oysters
Coastal Upwelling Supplies Oxygen-Depleted Water to the Columbia River Estuary
Low dissolved oxygen (DO) is a common feature of many estuarine and shallow-water
environments, and is often attributed to anthropogenic nutrient enrichment from
terrestrial-fluvial pathways. However, recent events in the U.S. Pacific
Northwest have highlighted that wind-forced upwelling can cause naturally
occurring low DO water to move onto the continental shelf, leading to
mortalities of benthic fish and invertebrates. Coastal estuaries in the Pacific
Northwest are strongly linked to ocean forcings, and here we report observations
on the spatial and temporal patterns of oxygen concentration in the Columbia
River estuary. Hydrographic measurements were made from transect (spatial
survey) or anchor station (temporal survey) deployments over a variety of wind
stresses and tidal states during the upwelling seasons of 2006 through 2008.
During this period, biologically stressful levels of dissolved oxygen were
observed to enter the Columbia River estuary from oceanic sources, with minimum
values close to the hypoxic threshold of 2.0 mg L−1. Riverine
water was consistently normoxic. Upwelling wind stress controlled the timing and
magnitude of low DO events, while tidal-modulated estuarine circulation patterns
influenced the spatial extent and duration of exposure to low DO water. Strong
upwelling during neap tides produced the largest impact on the estuary. The
observed oxygen concentrations likely had deleterious behavioral and
physiological consequences for migrating juvenile salmon and benthic crabs.
Based on a wind-forced supply mechanism, low DO events are probably common to
the Columbia River and other regional estuaries and if conditions on the shelf
deteriorate further, as observations and models predict, Pacific Northwest
estuarine habitats could experience a decrease in environmental quality
Recruitment Constraints in Singapore's Fluted Giant Clam (Tridacna squamosa) Populations - A Dispersal Model Approach
10.1371/journal.pone.0058819PLoS ONE83
Can artificial substrates enriched with crustose coralline algae enhance larval settlement and recruitment in the fluted giant clam (Tridacna squamosa)?
10.1007/s10750-008-9698-0Hydrobiologia625183-90HYDR