Tridacna maxima (T. maxima) are widely distributed in shallow areas near coral reefs and hold significant commercial value as a food source and for marine tourism. However, it has been extensively harvested and depleted in many regions, leading to it being listed as endangered species by the International Union for Conservation of Nature (IUCN). While marine protected areas (MPAs) are considered effective conservation tools, it remains uncertain whether existing MPAs adequately protect these vulnerable giant clams. Here, we employed a Species Distribution Models (SDMs) approach, combining occurrence records of T. maxima with environmental variables, to predict their distribution and capture spatiotemporal changes. The findings revealed the importance of land distance and light at bottom in determining the distribution of T. maxima, with suitable habitats predominantly found in shallow coastal waters rather than deep sea areas. Furthermore, we modeled potential distribution areas for T. maxima in 2050 and 2100 under different climate change scenarios, highlighting varying impacts on suitable habitats across different model predictions. To evaluate current conservation gaps, we conducted an analysis by overlaying suitable areas with existing protected areas. The results showed that the potential distribution area of T. maxima is 1,519,764.73 km2, accounting for only 16.10% of the total protected areas. It became evident that the existing protected areas are insufficiently large or well-connected, suggesting their ineffectiveness in safeguarding giant clams. Therefore, management efforts should focus on establishing a network of MPAs along the coastlines of West Pacific-Indonesia, matching the dispersal capability of giant clams. These findings provide valuable insights for the conservation of endangered giant clams, offering a scientific foundation for designing MPA networks in the Indo-Pacific region.

Stable isotope analysis is a universally recognized and efficient method of indicating trophic relationships that is widely applied in research. However, variations in natural isotopic abundance may lead to inaccuracies due to the effects of complex environmental conditions. This research compared the carbon and nitrogen isotopic niches of fish communities between diverse biotopes around the Yellow River estuary and adjacent sea areas, with the aim of revealing distinctions in stable isotopic niche metrics, trophic positions, and feeding preferences. Stable isotopic niche results indicated that the communities of estuarine habitants were compatible in most study biotopes, and may provide a corridor for energy and material transportation between Laizhou Bay and the open water. Local biocoenosis was embodied in the wider isotopic niche corresponding to frequent environmental changes and abiotic gradients. This implied that they used various food sources to adapt to the fickle environment, including marine-terrestrial boundaries and the estuary. Our analysis of the food source contribution indicated that allochthonous sources were considered major energy sources in estuarine areas directly affected by Yellow River-diluted water, while autochthonous benthic and pelagic producers dominated carbon input into the food web in Laizhou Bay and the open water. A significant variation in the fish δ15N characteristic was found within estuarine adjacent regions, so, together with the results from previous studies, we deemed the local high concentration of dissolved inorganic nitrogen as the original trigger of the abnormal δ15N characteristic in fishes via a transport process along food chains. These results provide a new perspective on the natural distinction of carbon and nitrogen isotopic niches. The detailed data reported here enhance our understanding of variations in fish communities in estuarine ecosystems.