Seasonal Dynamics of Detritus in the Benthic Turbidity Zone (BTZ); Implications for Bottom-Rack Molluscan Mariculture
Abstract:A near-bottom turbidity zone, related to tidal and storm resuspension of bottom muds, is described for Central Long Island Sound. The turbidity layer exists in the deeper parts of the Sound and extends over an area of ca. 1,000 km2. This phenomenon may be widespread among estuaries and embayments.
Suspended seston loads change with the stage of the tide, vary seasonally and are concentrated within the lower 6–9 m of the water column. Bottom turbidity increases in the spring, reaching maximum values in May, June, and July (10–40 mg–1) as measured 1 m above the bottom. Resuspension during this period may be facilitated by intensive bioturbation of the seafloor. Concentrations decrease in late summer, often falling below 10 mg–1. Bottom resuspension may also increase in the fall, related to plankton blooms or storm mixing of the water column.
Earlier studies in Buzzards Bay, Massachusetts have shown that POC, PON, and chlorophyll a are frequently higher in the near-bottom turbidity layer than in surface water. Bottom concentrations are apparently correlated with surface production.
The potential of the PON contained in the turbidity zone to support growth of commercially important molluscan species is evaluated in terms of a simulation model of Mytilus edulis deployed on bottom racks. The output of this model closely predicts the measured growth rate of an actual M. edulis deployment in the turbidity zone of Buzzards Bay, Massachusetts. The simulation model predicts that 1.5 to 3.8 g (dry wt) mussels can be obtained if 0.3 g (dry wt) spat are placed into the turbidity zone in May and cropped in late December. This range of mussel weight depends on the assigned assimilation efficiency which could range between 52 to 100%.
Document Type: Research Article
Publication date: November 1, 1984
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