The genus Lobophora is a notable benthic algal component of tropical coral reefs, capable of dominating large reef areas following coral mortality and herbivory declines. The alga, however, has been the object of contradictory observations in terms of susceptibility to herbivory. Unaware of the species-richness of this genus, most studies referred to Lobophora variegata, a species assumed to present various morphotypes and chemotypes, occupying diverse ecological niches. Variation in susceptibility to herbivory has been consequently interpreted as intraspecific variation in terms of morphology and chemical composition as well as differences in herbivore guild compositions and diet across different locations (e.g., habitat, reef, region). Recent taxonomic studies of Lobophora disclosed a high species diversity, which could explain previous conflicting observations. The present study tested the grazing susceptibility of seven species of Lobophora (L. dimorpha, L. hederacea, L. monticola, L. obscura, L. rosacea, L. sonderi and L. undulata), which differ in growth form as well as in their chemical composition and fine-scale ecological niche on coral reefs in the southern lagoon in New Caledonia, to two important herbivores in New Caledonia, the rabbitfish Siganus lineatus and the sea urchin Diadema setosum using tank, cage, and in situ experiments. All seven Lobophora species were markedly consumed in situ and by the two herbivores. Differences in consumption among the Lobophora species were small but statistically significant. Lobophora rosacea, characterized by a distinct secondary metabolome, was significantly more consumed by the two herbivores. Conversely, L. sonderi was always among the least consumed species. These results point to the possible role of chemical defense, and suggest that L. rosacea may produce less or different chemical deterrents than the other Lobophora species, and that L. sonderi may produce deterrents active over a wider range of herbivores. However, the limited interspecific differences in consumption point to the greater importance of associational and spatial refuges as defense strategies against herbivores over chemical or morphological defenses in the genus Lobophora. Highlights► This is the first experimental study to specifically test interspecific grazing susceptibility in the brown alga Lobophora. ► Grazing susceptibility of seven Lobophora species was tested in situ and in controlled systems to two herbivores. ► All Lobophora species were markedly consumed by the herbivorous fish Siganus lineatus and the sea urchin Diadema setosum. ► Limited interspecific differences in consumption were observed between the seven Lobophora species in all experiments. ► Results indicate limited effects of morphology and chemical composition among species in their grazing susceptibility.

Stable isotopes of carbon and nitrogen characterize trophic relationships in predator–prey relationships, with clear differences between consumer and diet (discrimination factor Δ13C and Δ15N). However, parasite–host isotopic relationships remain unclear, with Δ13C and Δ15N remaining incompletely characterized, especially for helminths. In this study, we used stable isotopes to determine discrimination factors for 13 parasite–host pairings of helminths in coral reef fish. Differences in Δ15N values grouped according to parasite groups and habitat within the host with positive Δ15N values observed for trematodes and nematodes from the digestive tract and variable Δ15N values observed for cestodes and nematodes from the general cavity. Furthermore, Δ13C values showed more complex patterns with no effect of parasite group or habitat within host. A negative relationship was observed between Δ15N and host δ15N values among different host-parasite pairings as well as within 7 out of the 13 pairings, indicating that host metabolic processing affects host-parasite discrimination values. In contrast, no relationships were observed for Δ13C values. Our results indicate that parasite group, habitat within host, and host stable isotope value drive Δ15N of helminths in coral reef fish while their effect on Δ13C is more idiosyncratic. These results call for use of taxon- or species-specific and scaled framework for bulk stable isotopes in the trophic ecology of parasites.

27Stable isotopes of carbon and nitrogen characterize trophic relationships in predator-prey 28 relationships, with clear differences between consumer and diet (discrimination factor, Δ 13 C, 29 Δ 15 N). However, parasite-host isotopic relationships remain unclear, with Δ 13 C and Δ 15 N 30 remaining incompletely characterized, especially for helminths. In this study, we used stable 31 isotopes to determine discrimination factors for 13 parasite-host pairings of helminths in coral 32 reef fish. Δ 15 N differences grouped according to phylogeny and attachment site on the hosts: 33 Δ 15 N was positive for trematodes and nematodes from the digestive tract and varied for 34 cestodes and nematodes from the general cavity. Δ 13 C showed more complex patterns with no 35 effect of phylogeny or attachment site. A negative relationship was observed between Δ 15 N 36 and host δ 15 N value among different host-parasite pairings as well as within 7 out of the 13 37 parings, indicating that host metabolic processing affects host-parasite discrimination values. 38In contrast, no relationships were observed for Δ 13 C. Our results indicate that host phylogeny, 39 attachment site and host stable isotope value drive Δ 15 N of helminths in coral reef fish while 40 Δ 13 C is more idiosyncratic. These results call for use of taxon-or species-specific and scaled 41 framework for bulk stable isotopes in the trophic ecology of parasites. 42 43 44

International audienceBackground: Most of the 29 Siganidae species are widely distributed through the Indo-Pacific area. In New Caledonia, these family was represented by 12 species. The present report is the first record of Siganus randalli in New Caledonian waters and provide information on its diet. Methods: Three specimens of Siganus randalli were caught in shallow mangrove waters of the southern part of New Caledonia. Their stomach contents and isotopic signatures (carbon and nitrogen) were analyzed and compared to others siganids species. Results and conclusion: This note provides the most southerly record of the rabbitfish Siganus randalli, which extends its distribution range by 1200 km southward and 1300 km southwest. The data on its diet, when compared with other co-occurring or more reef-associated siganid species, provide information on feeding processes and ecological functions associated with its mangrove habitat