Vegetation variety affected by local environments in a coral reef lagoon

From shore to sea, coral reefs can generally be divided into a lagoon zone, a reef crest, and a fore reef. Environmental variables, such as nutrient fluxes, light availability, and water temperature, vary among the zones and influence the biodiversity of submerged macrophytes. Additionally, the biodiversity of vegetation within the lagoon appears to be affected by multiple and extremely localized conditions. We investigated the impact of small-scale variations on vegetation diversity, and implemented an ecological survey within a well-defined area inside of a lagoon at Bise Point, Okinawa, Japan. A total of 20 macroalgal species (four green algae, six brown algae, and ten red algae) and four seagrass species were identified from the surveyed quadrats over a period of 19 months, from October 2019 to March 2021. Patterns in species occurrence were spatially and temporally heterogeneous. Notably, water motion and sediment flux were highly variable among the monitoring sites. Redundancy analysis allowed us to evaluate the significance of environmental factors on the vegetation of each monitoring area. Six environmental factors were considered in this study, but their impacts on local vegetation were not equivalent. Redundancy analysis suggested that water depth, flow velocity, and the ratio of the small fraction of deposition particles were the three factors with the strongest influence on local vegetation. This study provides some crucial insights into the determinants of vegetation in a coral reef lagoon. Our findings suggest that the factors we examined exert more influence on the vegetation than seasonal effects.