Bioerosion and its relationship with skeletal density of Platygyra daedalea and Porites harrisoni in Larak Island, Persian Gulf

Abstract Due to the extreme environmental conditions in the Persian Gulf, the bioerosion rate in the coral reefs of the region deem to be higher than the other regions, which may disturb the balance between the processes of the reef growth and destruction. The bioerosion rate in Platygyra daedalea and Porites harrisoni in three stations of Larak Island (Hormuz Strait, 56°39′35.7″ E & 26°88′65.17″ N) was assessed in 2017. This study also examined the effect of skeletal density on the severity of bioerosion rate. For this purpose, five coral pieces of each species were collected from the stations. Each piece was cut in the direction of the longest central axis with a thickness of about 7 mm, and their photographs were taken. The bioeroded area was evaluated by ImageJ 1.44 software, and the freezing method was used to measure the skeletal density. A total of four groups of macrobioeroders were found in both coral species, including bivalves, polychaetes, sponges, and barnacles. Also, increased skeletal density was positively correlated with bioerosion in P. daedalea, but not in P. harrisoni. This indicates that some bioeroders prefer denser corals for various reasons. Evidence from this research suggests that skeletal density was the most important factor affecting the degree of bioerosion rate. However, other environmental factors such as depth may also affect the bioerosion rate to certain degrees.