4.2 Effects of environment factors on the distribution ofT. maxima
Land distance and light at bottom were important variables of habitat suitability for T. maxima(Fig. 5), consistent with studies on species distributions ofAcropora tenuis in the Great Barrier Reef (Strahl et al., 2019) and T. maxima in the Central Red Sea (Rossbach et al., 2019). The most unique biological feature of T. maxima is its nutritional relationship withZooxanthellae , whereby the majority of their required nutrients and energy are obtained through photosynthesis (Lucas, 2014; Yonge, 1975). This symbiotic relationship has significant ecological and morphological significance for T. maxima . On the one hand, the distribution of T. maxima is limited by their symbiotic dinoflagellates, which require sufficient light for photosynthesis. Land distance is generally shallow with high transparency and ample sunshine, meeting the basic conditions for maintaining the symbiotic relationship. In addition, T. maximaattach themselves to coral reefs or live freely. Their habitat is mainly in the low tide zone near coral reefs in tropical waters or in shallower reefs, making them an important component of coral reef ecosystems. Giant clams support overall reef biodiversity and functionality, making them flagship taxa for coral reef conservation efforts (Killam et al., 2023; Lee et al., 2022). A significant decline in the number of T. maxima in a particular area indicates damage to the coral reef ecosystem. Conversely, a relatively stable population size and species composition of T. maxima indicate good health of the coral reef ecosystem (Dewiyanti et al., 2021). Interestingly, the distribution range of coral reefs highly coincides with that of T. maxima , as shown in the Allen Coral Atlas (Lyons et al., 2020), further explaining why T. maxima are found at a close land distance and verifying the accuracy of species distribution models in predicting their distribution. We speculate that coevolution of these species in this shared environment has led to similar response patterns among associated species in the face of climate change (Chen et al., 2023). This also provides an ideal system for studying how each species in Tridacninae , corals, andZooxanthellae utilizes local climate adaptation, dispersal, and other strategies to mitigate the risks of climate change in the future. In addition, light directly or indirectly affectsTridacninae physiological activities, such as growth and energy metabolism (Ip et al., 2006). Studies have shown that the oxygen production rate in T. croceagradually increases with rising light intensity within an experimental range. Light intensity significantly impacts the metabolic synthesis ofT. crocea and other symbiotic dinoflagellates, promoting their photosynthetic activity and growth (Liu et al., 2018; Liu et al., 2021).