Corals evolved by establishing symbiotic relationships with various microorganisms (the zooxanthellae, filamentous algae, cyanobacteria, bacteria, archaea, fungi and viruses), forming the ‘coral holobiont'. Among them, the endolithic community is the least studied. Its main function was considered to be translocation of photo-assimilates to the coral host, particularly during bleaching. Here, we hypothesize that (i) endolithic algae may show similar primary production rates in healthy or bleached corals by changing their pigment ratios, and therefore that similar production and translocation of organic matter may occur at both conditions and (ii) diazotrophs are components of the endolithic community; therefore, N2 fixation and translocation of organic nitrogen may occur. We tested these hypotheses in incubation of Porites lutea with 13C and 15N tracers to measure primary production and N2 fixation in coral tissues and endoliths. Assimilation of the 13C atom (%) was observed in healthy and bleached corals when the tracer was injected in the endolithic band, showing translocation in both conditions. N2 fixation was found in coral tissues and endolithic communities with translocation of organic nitrogen. Thus, the endolithic community plays an important role in supporting the C and N metabolism of the holobiont, which may be crucial under changing environmental conditions.

Tropical seagrass meadows and coral reefs often function as interconnected marine habitats, but they are often studied and managed as homogenous units. As macrohabitats, seagrass meadows provide important benefits to adjacent reef ecosystems by acting as natural filters of sediments and nutrients, and by providing critical feeding, nursery, and refuge habitats for reef fishes and other fauna. Whilst the macrohabitat functions of seagrass meadows have been often acknowledged, their microhabitats functions have largely been neglected. The purpose of the study is to explore how seagrass meadows provide multiple benefits to adjacent coral reefs through various microhabitat functions. The paper reveals some of the diversity of microhabitats that seagrass meadows contain, such as macroalgal mats, rubble cavities, sand patches with sparse seagrass, anemone gardens, hard substratum, and sponges mixed with seagrass. We highlight the ways in which reef creatures have diversified and specialized in using these different microhabitats, and postulate that seagrass microhabitat diversity enhances the habitat function and faunal diversity of seagrass meadows.

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Demersal zooplankton (DZ) appear in the water column at night, and are highly abundant in mangrove, seagrass, and coral reef habitats; however, few studies have discussed their role in aquatic food webs, considering different consumers and their preferences on different DZ' size classes. This study elucidates the role of DZ as a food source for higher trophic levels in an estuarine area, particularly with respect to the food preference and size selection of their consumers. The study was conducted in the mangrove forest of Fukido Estuary and an adjacent reef lagoon (with seagrass-dominated and seagrass-coral mixture areas) on Ishigaki Island, Japan. The abundance of demersal zooplankton was 4.0, 5.4, and 11.3×10 4 ind.m -2 for seagrass, mangrove, and seagrass-coral mixture habitats, respectively. The lowest DZ biomass was recorded in mangroves and mainly dominated by smaller organisms, because their consumers in this habitat prefer large-sized prey. The δ 13 C and δ 15 N signatures showed that, in mangroves, demersal zooplankton constituted a higher proportion of the diet of fishes than in lagoon habitats; however, demersal zooplankton did not have a significant role in the diet of fishes and macroinvertebrates in the lagoon. Consistency among biomass, stomach contents, and the proportions of DZ of all size classes in the diet of mangrove fishes indicated that DZ serve as a major food source. In contrast, fishes in lagoon habitats consumed more crabs, shrimps and mollusks than DZ. In conclusion, our analytical approach allowed us to demonstrate that DZ of different body sizes serve as food sources for different consumers in different habitats of the estuarine ecosystem.