Structure-building, autogenic ecosystem engineers are recognized worldwide as potential tools for coastal protection, which depends on long-term sustainability and persistence of their structures. For reef-building oysters, reefs are maintained through accumulation of shell material, which depends on recruitment and growth and which provides substrate for new generations. Knowledge of the fundamental niche of oysters in relation to biotic and abiotic conditions helps define the area where ecosystem engineers grow and survive well and where their structures are likely to persist and be effective for coastal protection. Response curves of different life-history stages (larvae, juveniles and adults) of the Pacific oyster Crassostrea gigas were investigated along a tidal emersion gradient in a manipulative field study. Density of juvenile oysters was maximal around 36% tidal emersion. Shell growth of juveniles and adults, condition index (CI) of adults and mortality of adults were negatively related to tidal emersion, whereas mortality of juveniles was positively related to tidal emersion. Tidal emersion had a strong effect on oyster survival and growth, with the most favourable being around 20 to 40% tidal emersion, as indicated by recruit density and the CI of adults. These findings suggest that the area of 20 to 40% tidal emersion is optimal for reef development, which is in line with other investigations of C. gigas and the eastern oyster C. virginica across different systems, supporting a broader geographical application of these findings.
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