Abstract
Trace metal dynamics have not been studied with respect to growth increments in octocorals. It is particularly unknown whether ontogenetic compartmentalization of trace metal accumulation is species-specific. We studied here for the first time the intracolonial distribution and concentrations of 18 trace metals in the octocorals Subergorgia suberosa, Echinogorgia complexa and E. reticulata that were retrieved from the northern coast of Taiwan. Levels of trace metals were considerably elevated in corals collected at these particular coral habitats as a result of diverse anthropogenic inputs. There was a significant difference in the concentration of metals among octocorals except for Sn. Both species of Echinogorgia contained significantly higher concentrations of Cu, Zn and Al than Subergorgia suberosa. We used for the first time exponential growth curves that describe an age-specific relationship of octocoral trace metal concentrations of Cu, Zn, Cd, Cr and Pb where the distance from the grip point was reflecting younger age as linear regressions. The larger colony (C7) had a lower accumulation rate constant than the smaller one (C6) for Cu, Zn, Cd, Cr and Pb, while other trace metals showed an opposite trend. The Cu concentration declined exponentially from the grip point, whereas the concentrations of Zn, Cd, Cr and Pb increased exponentially. In S. suberosa and E. reticulata, Zn occurred primarily in coenosarc tissues and Zn concentrations increased with distance from the grip point in both skeletal and coenosarc tissues. Metals which appeared at high concentrations (e.g. Ca, Zn and Fe) generally tended to accumulate in the outer coenosarc tissues, while metals with low concentrations (e.g. V) tended to accumulate in the soft tissues of the inner skeleton.
Highlights
Coral reefs are fragile ecosystems, characterized by high biodiversity and high productivity [1]
The most important forms of anthropogenic disturbance to coral reefs include additional threats such as damages associated with fishing activities, euthrophication and pollution caused by sewage discharge, heat stress caused by effluents from power plants, and sedimentation from dredging and mud dumping
The general aim of this study was to evaluate whether octocorals, especially Subergorgia suberosa, Echinogorgia complexa, and E. reticulata, are suitable for the monitoring of trace element pollution
Summary
Coral reefs are fragile ecosystems, characterized by high biodiversity and high productivity [1]. The most important forms of anthropogenic disturbance to coral reefs include additional threats such as damages associated with fishing activities, euthrophication and pollution caused by sewage discharge, heat stress caused by effluents from power plants, and sedimentation from dredging and mud dumping (as reviewed by [10, 11, 12]). The coral reefs around Taiwan are characterized by high species diversity [13]. Coastal areas around Taiwan are intensively disturbed by urban development, industry, aquaculture and agriculture [12]. When bottom sediments in coastal areas are dredged to open up channels for ships, or when mangrove forests are removed to provide areas for aquaculture, metals are resuspended and the health of coral reefs is threatened [3, 22]. A recent survey of Taiwan’s coastal areas revealed a general trend for the decline of coral species diversity and coral cover [24]
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