Numerical Simulations of Blue Crab Larval Dispersal and Recruitment
Abstract:Wind- and current-induced drifts of blue crab larvae hatching near the mouth of Chesapeake Bay, Virginia, are simulated using numerical models to examine the relationship between larval recruitment and environmental forcing. The circulation is produced with a three-dimensional model of the bay and adjacent continental shelf. The circulation is then used by a drifter advection model to produce Lagrangian drift tracks. Observed winds at Norfolk, Virginia, predicted tides from harmonic analysis, and daily river discharges from major tributaries are used as driving forces. The model includes both density and wind forced circulation. We model the release of near-surface drifters from 132 hatch locations in and near the bay mouth. Because higher numbers of larvae have been observed at some locations than at others, each location of a simulated hatch is given a probability weighting. Model hatches occur on three different days in both 1980 and 1982, and drifters are tracked for 45 days. At the end of that time, the location of each drifter is analyzed. Those within the bay are categorized as recruited. Weighted recruitment ranges from 3 to 67%, with a mean of 42% of the total larvae. Although in the simulations some larvae are retained in the bay and never leave (averaging 13%), a majority of larvae leave the bay (87%) and a large number (29%) leave the Bay and later return in the surface waters. In cases where drifters are moved to the bottom after 35 days, subsequent recruitment is severely reduced. By alternately removing forcing by winds, river flow, and density differences, the relative influence of the three forcings is also evaluated. The wind component is found to have the greatest effect on larval recruitment, although wind can either increase or decrease recruitment. River flow and gravitational circulation each have a smaller influence.
Document Type: Research Article
Publication date: 1990-01-01
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