Distribution and Abundance of Decapod Crustacean Larvae in the York River Estuary and Adjacent Lower Cheaspeake Bay, Virginia, 1968-1969

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Abstract
Surface and bottom plankton samples taken with a Clarke-Bumpus Quantitative Plankton Sampler at monthly intervals over a two-year period were examined for decapod crustacean larvae. These samples were taken at 12 stations over a distance of about 80 miles from fresh water in the Pamunkey River, through the meso-and polyhaline York River, to euhaline conditions at the mouth of Chesapeake Bay. Some additional samples were collected with paired BCF Bongo Samplers. Planktonic stages representing at least 37 species of decapods were identified. Larvae ofUca spp.,Crangon septemspinosa, Hexapanopeus angustifrons, Neopanope sayi andRhithropanopeus harrisii were abundant in the plankton of the York River system and lower Chesapeake Bay, and larvae of a number of other species were common. Larvae ofEurypanopeus depressus, formerly one of the abundant xanthid crabs of the bay, were rarely found. This apparent decline in abundance ofE. depressus may be associated with the recent introduction of the sacculinid parasite,Loxothylacus panopaei, into Chesapeake Bay.Callianassa spp. (other thanC. atlantica),Lepidopa cf.L. websteri andNaushonia crangonoides were recorded from the bay for the first time. Decapod larvae were nemerous throughout the estuary during summer. However,Crangon septemspinosa larvae were abundant from late winter throughout the spring, and peak numbers were generally of the same order of magnitude as total concentrations of larvae of the other species at the bay stations during summer. The number of decapod species represented in the plankton and the portion of the year during which their meroplanktonic larvae were present decreased with distance upriver. These trends are in large part related to the decreasing salinity upstream, although other factors may be involved as well. The distribution data also suggest that areas of peak larval abundance probably indicate regions of abundance of breeding adults. Larvae of a number of common species were considerably more abundant in bottom collections than near the surface. This tendency of many larvae, especially later stages, to congregate near the bottom where the net flow is upstream may be one of the factors operating to insure retention of decapod larvae within the Chesapeake Bay.

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