The pearl oysters, Pinctada maxima and P. margaritifera, respond in different ways to culture in dissimilar environments

Abstract

Growth, Condition Index (CI) and survival of the pearl oysters, Pinctada maxima and P. margaritifera, were measured in three size groups of oysters over 14 months at two dissimilar environments in the Great Barrier Reef lagoon. These were the Australian Institute of Marine Science (AIMS) in a mainland bay and Orpheus Island Research Station (OIRS) in coral reef waters. Temperature, suspended particulate matter (SPM) and particulate organic matter (POM) were monitored during the study. Temperature at AIMS fluctuated more widely than at OIRS both daily and seasonally, with annual ranges 20–31 °C and 22–30 °C, respectively. Mean SPM concentration at AIMS (11.1 mg l − 1) was much higher than at OIRS (1.4 mg l − 1) and fluctuated widely (2–60 mg l − 1). Mean POM level was also substantially higher at AIMS, being 2.1 mg l − 1 compared with 0.56 mg l − 1 at OIRS. Von Bertalanffy growth curve analyses showed that P. maxima grew more rapidly and to larger sizes than P. margaritifera at both sites. For the shell height (SH) of P. maxima, growth index ϕ′ = 4.31 and 4.24, asymptotic size SH ∞ = 229 and 205 mm, and time to reach 120 mm SH ( T (120)) = 1.9 and 2.1 years at AIMS and OIRS, respectively. While for P. margaritifera, ϕ′ = 4.00 and 4.15, SH ∞ = 136 and 157 mm, and T (120) = 2.5 and 3.9 years at AIMS and OIRS, respectively. P. maxima had significantly lower growth rates and lower survival of small oysters during winter compared with summer. There were, however, no significant differences between the two sites in growth rates of P. maxima and final CI values. In contrast, P. margaritifera showed significant differences between sites and not seasons, with lower growth rates, survival of small oysters, final CI values and asymptotic sizes at AIMS. The winter low temperatures, but not high SPM at AIMS, adversely affected P. maxima. Conversely, the high SPM levels at AIMS, but not temperature, adversely affected P. margaritifera. This was in accordance with earlier laboratory-based energetics studies of the effects of temperature and SPM on these two species. P. maxima has potential to be commercially cultured in ca. > 25 °C waters with a wide range of SPM levels, including oligotrophic coral reef waters with appropriate particle sizes. It is possible to culture P. margaritifera in turbid conditions, but its poor performance in these conditions makes commercial culture unlikely.