Manutenção do coral de águas profundas Lophelia pertusa (Linnaeus, 1758) em laboratóprio e experimentos de exposição com barita usando sistema de recirculação de água

Abstract

The maintenance of corals, especially deep-sea species, under artificial conditions and experimentation imply in high cost and complexity, but it is necessary for conducting studies of offshore oil and gas activities impacts. Waste material from these activities contains barite as a weighting agent (>50%), which is composed by fine particles that can physically affect these organisms. In the present study, the first goal was to maintain Lophelia pertusa in aquaria systems with recirculating natural or artificial seawater, comparing their success, and secondly, to assess the effects of barite smothering on this coral in an aquaria-based experiment with water recirculation system. Corals were collected by ROV from Santos Basin, at 206-247 m depth, during SENSIMAR Project-PETROBRAS. Colonies were acclimated for 80 days prior to the experiments in 700 L and 300 L natural filtered (0.5µm) and 300L synthetic seawater aquaria systems, with controlled salinity (35±1) and temperature (12±1°C) in darkness. The experiment was conducted in 23L cone-shaped aquaria, adapted with an individual water recirculation system (12L.h-1), using synthetic seawater. Each exposure to suspended barite particles (50 and 100mg.L-1) plus a control group were maintained in triplicate. Three nubbins with 3-8 polyps were accommodated vertically in the aquaria and acclimated for 7 days before experiments start. They were fed three times a week with 300 Artemia sp. nauplii.L-1 (<24 h). The experimental design simulated two cycles of discharge, followed by a recovery cycle of 7 days each, totalizing 35 days. The barite was added continuously with a peristaltic pump (0.18L.h-1). Survival was checked after the experiment. Three polyps in each nubbin (9 per treatment) were monitored twice a day regarding behavior levels (1 = fully or partially extended polyps; 0 = fully retracted). In relation to the use of synthetic seawater in the maintenance system, it showed promising results for L. pertusa. After 35 days, total polyp survival in control was 100% (n = 47), while in 50mg.L-1 and 100mg.L-1 were 94.2% (n = 52) and 93.6% (n = 47), respectively, with no significant difference between treatments (Kruskal-Wallis chi-squared = 1.1667, p = 0.558). Polyp activity was different between treatments (Kruskal-Wallis chi-squared = 142.83, p<2.2e-16), with both exposed aquaria displaying higher activity than control. It is probably related to the natural cleaning behavior of L. pertusa. Mucus production was observed after the first cycle of discharge in both treatments, and none in control, which is also possibly related to cleaning behavior. L. pertusa showed tolerance to sedimentation of barite. The recirculated system designed for this experiment was adequate for barite exposure.