High diversity and abundance of fish and coral in an artificial breakwater in Colombo, Sri Lanka

The diversity of reef fishes and the diversity and abundance of corals in artificial breakwaters were studied between June and August 2023 in Port City, Colombo in the Western Province of Sri Lanka. Four methods were used: visual census using video, photographs, stationary point count and environmental DNA (eDNA). A total of 137 fish species, 74 coral species and 175 other species were recorded using the four methods. There were similarities and differences between the methods for recording fish, corals and other species. Only three fish species: Moon wrasse (Thalassoma lunare); Yellowtail fusilier (Caesio cuning) and Diamond fish (Monodactylus argenteus) were recorded by all methods. The highest number of fish species was recorded by video, followed by photographs, eDNA and stationary point count in the sequence. Coral cover ranged from 9 to 50.8% and mean live coral varied from 24.4% to 34.5 ± 5.2%. The dominant coral species was Pocillopora damicornis. Rare observations of coral bleaching (n=1) and frequent observations of marine debris (n=20) and coral damage (n=25) were recorded. Species detection using eDNA is a biomonitoring tool that did not add significantly to the list of fish and corals, but included many microscopic groups such as bacteria, diatoms and ciliates that were not recorded using other methods, and provided new ecological insights into marine systems. This is the first use of multiple monitoring tools to identify and compare methods for the biodiversity of marine fish, coral and other species in Sri Lankan marine waters.