10:00 AM - 10:15 AM
[AHW22-05] Environmental Impacts of Terrestrial-Origin Phosphate Accumulation on the Coral Ecosystems of Sekisei Lagoon
Keywords:Phosphate Accumulatio, Coral Reef Ecosystems, Sekisei Lagoon
In coral reefs, it has been found that phosphates of terrestrial origin accumulate in the calcareous sediments. We defined the accumulated phosphate is being trialed as a new indicator of terrestrial load to assess coral reef ecosystems. In the Sekisei Lagoon, located between Ishigaki and Iriomote islands, a coral community monitoring project (Ministry of the Environment) has been ongoing, with 31 fixed points established and annual monitoring surveys of coral cover, etc., being conducted. This study aims to compare and examine the relationship between the accumulated phosphate data and the biological data obtained from the monitoring surveys.
Sediment collection was carried out three times: in September 2021, December 2022, and September 2023. Sediments (n=3) were collected at 31 fixed points in Sekisei Lagoon, frozen, and transported to the lab. After drying and sieving, 6 g of sediment with a particle size of 0.5-1 mm and 15 ml of filtered seawater were added to a 50 ml tube and left to soak at 30°C for 72 hours. After centrifugation, the supernatant was filtered, and the phosphate concentration was measured by colorimetry. The weight of PO4-P per gram of sediment (µg/g) was calculated as the accumulated phosphate value. The relationship between the accumulated phosphate value and the biological data, such as genus-specific density data for corals (adults, juvenile corals), the proportion of bleached corals, and the coverage of major algae, was examined using Pearson correlation.
There were no significant year-to-year changes at 31 fixed points, but high accumulated phosphate was tended to be found in points southwest and southeast of Taketomi Island, suggesting an influence from the effluent of shrimp aquaculture facilities on Taketomi Island. Similarly, high values were observed annually at points on the east side of Kuroshima Island, which are believed to be influenced by Kuroshima. In contrast, points with low values of accumulated phosphate were found outside the reef. In 2022, there was a significant negative correlation between accumulated phosphate and the coral genus-specific cover in 7 genera of corals, while no significant difference was found in 7 genera. No positive correlations were observed. For juvenile corals, a significant negative correlation was found in 3 genera of corals, and no positive correlations were seen. Significant positive correlations were observed with non-bleached corals and Sargassum species. On the coast of Kuroshima Island, high accumulated phosphate values were consistently found southeast for all three years. Kuroshima is an island where livestock farming is thriving, and the concentration of phosphates in the groundwater is also high, raising concerns about the influence of livestock excrement and other such sources.
Sediment collection was carried out three times: in September 2021, December 2022, and September 2023. Sediments (n=3) were collected at 31 fixed points in Sekisei Lagoon, frozen, and transported to the lab. After drying and sieving, 6 g of sediment with a particle size of 0.5-1 mm and 15 ml of filtered seawater were added to a 50 ml tube and left to soak at 30°C for 72 hours. After centrifugation, the supernatant was filtered, and the phosphate concentration was measured by colorimetry. The weight of PO4-P per gram of sediment (µg/g) was calculated as the accumulated phosphate value. The relationship between the accumulated phosphate value and the biological data, such as genus-specific density data for corals (adults, juvenile corals), the proportion of bleached corals, and the coverage of major algae, was examined using Pearson correlation.
There were no significant year-to-year changes at 31 fixed points, but high accumulated phosphate was tended to be found in points southwest and southeast of Taketomi Island, suggesting an influence from the effluent of shrimp aquaculture facilities on Taketomi Island. Similarly, high values were observed annually at points on the east side of Kuroshima Island, which are believed to be influenced by Kuroshima. In contrast, points with low values of accumulated phosphate were found outside the reef. In 2022, there was a significant negative correlation between accumulated phosphate and the coral genus-specific cover in 7 genera of corals, while no significant difference was found in 7 genera. No positive correlations were observed. For juvenile corals, a significant negative correlation was found in 3 genera of corals, and no positive correlations were seen. Significant positive correlations were observed with non-bleached corals and Sargassum species. On the coast of Kuroshima Island, high accumulated phosphate values were consistently found southeast for all three years. Kuroshima is an island where livestock farming is thriving, and the concentration of phosphates in the groundwater is also high, raising concerns about the influence of livestock excrement and other such sources.