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Biological feasibility of suspended Pacific oyster (Crassostrea gigas Thunberg) and California sea cucumber (Parastichopus californicus Stimpson) polyculture Paltzat, Debbie Lynne

Abstract

The potential for California sea cucumber (Parastichopus californicus Stimpson) growth and production when in polyculture with suspended Pacific oysters (Crassostrea gigas Thunberg) was investigated. A 12-month field study was undertaken at two oyster culture sites in British Columbia, Canada, to examine the rates of oyster biodeposition and the utilization of this particulate material as a food source by P. californicus. Peaks in sedimentation rates (93.6 g dry wt m⁻² d⁻¹ ) through 8.5 m water depth were observed in April 2004 and July 2004. At the two study sites, fluxes of particulate organic carbon (POC) through 8.5 m in July amounted to 3123 mg C m⁻² d⁻¹ and 4150 mg C m⁻² d⁻¹ and fluxes of total nitrogen (TN) amounted to 441 mg N m⁻² d⁻¹ and 633 mg N m⁻² d⁻¹ . Mean C/N ratios of particulate material in the sediment trap samples ranged between 5.93 and 8.39 and may be classified as being of high nutritional value. Growth and survivorship of sea cucumbers held in experimental trays below the suspended oysters was measured quarterly using total body weight and muscle and skin wet weights. Sea cucumbers grown in trays successfully utilized biodeposits from the cultured oysters and showed a mean weight increase of 42.9 g in approximately 11 months. Growth rates ranged from 0.061 to 0.158 g d⁻¹. Overall growth was affected the absence of visceral organs and the cessation in feeding activity in the November 2004 sampling period. Values for organic content were significantly higher in the foregut (233.0 mg g dry sediment⁻¹) than in the sediment (64.3 mg g dry sediment⁻¹) or in the hindgut (142.8 mg g dry sediment⁻¹) due to digestion and assimilation. Organic material deposited in the trays was utilized by P. californicus with an average efficiency of 48.4%. The successful utilization of the naturally available biodeposits from the cultured oysters does suggest the feasibility of successful culture of this commercially important species in a polyculture system. Feeding activities of P. californicus were examined in laboratory experiments designed to assess the rates of sediment ingestion and organic matter uptake. Sea cucumbers fed natural marine bottom sediment ingested sediment and removed organic matter at an average rate of 9.17 g dry sediment d⁻¹ and 50.3 mg (g dry sediment) ⁻¹ d⁻¹. From these rates, it was determined that this species of sea cucumber could survive and grow on the amount of organic matter deposited

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