Relationships between linear extension, calcification rate, skeletal density, and nutrients with coral bioerosion: A case study in the Persian Gulf

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The balance between reef growth and physical and biological erosion that underlies the coral reef framework can be disrupted by environmental disturbances. The variation in macroborer assemblages and the bioerosion intensity in four scleractinian corals (Porites harrisoni, Platygyra daedalea, Cyphastrea microphtalma and Dipsastraea pallida) were investigated at Kharg and Khargo islands in the northern Persian Gulf. Macroborers in five-mm-thick sections of the longest central axis of each coral colony in each species were identified and counted. Five groups of macroborers were identified including bivalves, polychaetes, sponges, barnacles and vermetid snails. Boring bivalves accounting for 63.3% of the total internal macrobioerosion and were the most abundant macrobioeroder group in all coral species. There were significant differences in macrobioerosion intensity among coral species and locations (P≤0.05). Barnacles were only detected in P. daedalea. Boring sponges were marginally found in P. harrisoni, C. microphtalama and D. pallida. Polychaetes were the second-most important macroborers after bivalves, particularly in C. microphtalma and P. harrisoni. Vermetid snails were recorded from all four coral species but to lesser extend in P. harrisoni. Higher linear extension rate was positively correlated to higher bioerosion intensity, but was significant only in C. microphthalma. We detected no significant correlation between coral calcification rate and macrobioerosion intensity. Skeletal density was negatively correlated with the bioerosion intensity in all coral species. Macrobioerosion was most abundant at the site with highest pollution levels and increased with nutrients. Nutrients and skeletal density were the most important factors influencing macrobioerosion intensity. We found that northwestern part of the Persian Gulf experienced high bioerosion intensity compared to other parts. We concluded that Khargo Island possessed higher water quality compared to Kharg Island.