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Identification of environmental factors affecting growth and survival of the mangrove oyster, Crassostrea rhizophorae (Guilding, 1828), in suspended culture at La Restinga lagoon, Margarita Island, Venezuela

Abstract:

Mangrove oyster, Crassosterea rhizophorae, is one of the mollusks with greatest perspectives for aquaculture development in the Caribbean and the tropical Atlantic coast. Even though, many studies have been carried out to establish its culture, there has not been established which and how environmental factors influence its growth under culture condition. Spats with a mean size of 30 mm were suspended in "Spanish baskets" at a depth of 4 m during 6 months. The experiment was carried on at La Restinga lagoon, Margarita Island, Venezuela. Each month oysters were measured (ventral-dorsal and antero-posterior), and weighted (dry weight from conch, tissue and fouling). Survivorship was also evaluated. Water temperature was recorded continuously and weekly measurements of Secchi depth, salinity, oxygen, total, organic and inorganic seston, and chlorophyll a were determined. Results show 89% increase in ventral-dorsal size reaching sizes of 54.5 mm. Dry weight of tissue at the end of the study period was 0.48 g after a decrease during the warmer months of august and september, indicating temperature as an important factor controlling spawning. The high and constant phytoplanktonic biomass present in La Restinga lagoon showed that food availability was not a limiting factor, which together with the small variability in the studied environmental variables, made impossible to identify factors controlling growth and survival of Crassostrea rhizophorae in long-line suspended culture. The exception was the occasional predation by Cymatium snails.