Growth and survival of sea scallops Placopecten magellanicus: effects of culture depth

Abstract

We combined extensive water sampling with monthly growth measurements of juvenile sea scallops held in cages 0 to 200 cm above the bottom to (1) construct predictive empirical models of shell and soft-tissue growth based on oceanographic variables, and (2) determine whether scallops on or near the bottom can derive a food supplement from resuspended sediment when seasonal phytoplankton production is low. Variation in growth was strongly dependent on depth, but this relationship was not consistent over time or tissue type. In late fall, when phytoplankton biomass was generally low (-1 pg chl I-'), the adductor muscle of scallops on the bottom lost mass (-1.5 mg dry wt d.'), but for scallops held only 20 cm higher in the water column, growth was 2.5 mg d.'. During the winter, softtissue growth on the bottom was significantly lower than that of scallops held above the sediment surface. At this time, there was no variation in shell growth with respect to depth. At the end of the study, soft-tissue weight (excluding muscle tissue) of scallops on the bottom was -40% less than that of scallops growing 250 cm above bottom. Rather than providing an energetic benefit, results suggest that high concentrations of seston near the bottom inhibit growth. Empirical regression models of scallop growth using data from water sampling every 2 wk accounted for up to 68% of growth variation, with temperature and seston quality being the most important predictor variables. Marginal improvements to the model uslng data collected hourly with In situ probes suggest that estimates of food supply should be corrected, i.e. reduced, when high flows or high seston concentrations limit filtration rates. In addition, results indicate that attention to the magnitude and variation of predictor variables without consideration of their seasonal coherence may be a primary factor limiting the ability to construct truly predictive models of bivalve growth.

Effects of suspended mussel culture (Mytilus spp.) on sedimentation, benthic respiration and sediment nutrient dynamics in a coastal bay

“…The relationship between temperature and sediment respiration was weaker at the mussel-line site than at the reference site, and there was a much stronger gradient of hydrogen sulphide in deep sediment cores. At the mussel-line site, concentrations of 10 ppm of hydrogen sulphide were measureable at 6 cm below the sediment surface, and a consistent gradient was measured which rose to 196 ppm at 44 cm depth (Grant et al 1994). In contrast, concentrations of hydrogen sulphide at the reference site were not measureable until a depth of 30 cm (2 ppm), which rose to 41 ppm at 40 cm depth.…”

“…The between-site difference was largely d u e to abundant bivalves and gastropods in the sediments under the mussel-lines, particularly Nassarius spp. and Nuculand tenuisulcata (Grant et al 1994).…”

“…The lab cultures were chosen because they closely resemble the species present in the cove. On several occasions the calculated concentrations were compared to chl a concentrations measured in water samples taken adjacent to the moored instrument, and the values always agreed wlthin 10% of each other (Emerson et al 1994).…”

Evaluation of different shallow water culture methods for the scallop Nodipecten subnodosus using biologic and economic modeling

“…Off-bottom culture functions well to improve growth and mortality over that of suspended modules, which is probably due to improved circulation as well as allowing excrement to fall more easily outside of the costales. Being slightly elevated off the sea floor may also contribute to improved performance over bottom culture through improved seston quality (Emerson et al, 1994). Fouling is a continual problem in suspended modules, which need to be cleaned thoroughly to maintain circulation.…”

Comparacion del crecimiento de Argopecten purpuratus entre cohortes obtenidas de captacion de larvas en ambiente natural y de hatchery

“…Las variaciones en las tasas de crecimiento que muestra entre sitios, estaciones del año y profundidad, se deberían a factores ambientales como la temperatura y disponibilidad de alimento (Bricelj & Shumway, 1991;Emerson et al, 1994;Lodeiros et al, 2001) que pueden determinar diferencias en el crecimiento y rendimiento en peso. Valladares (1992) cultivó bajo las mismas condiciones individuos de Chlamys patagonica provenientes de distintas localidades encontrando diferencias en la tasa de crecimiento, indicando que el origen de tales diferencias puede ser atribuido a aspectos genéticos.…”