First records of illegal harvesting and trading of black corals (Antipatharia) in Madagascar

Black corals (Cnidaria: Antipatharia) have been used all around the world for a long time, whether as money or for medicinal purposes and jewellery manufacturing. Except in Hawaii where these fisheries are well known, black coral harvests are usually made without any control or any management. This is the case in many tropical islands and particularly in Madagascar, where the illegal trade is continually expanding. Since 2011, an illegal traffic of black corals has been occurring in the main cities of the southern and coastal regions of Ambovombe and Tolagnaro. In 2014 and 2015, hundreds of kilograms of black coral skeletons and a lot of diving material were seized by the authorities in the Anosy and Androy regions. Despite this and the continual harvesting of these natural resources, there has been no study of the excessive exploitation in this region. This paper is the first to talk about this new threat and to analyse and discuss the benefits of these fisheries. The first seizures and the efforts carried out on the island to stop the trade are explained. This paper highlights the urgency of studying these corals before making an appropriate conservation and management plan

Stable isotope ratios suggest limited trophic importance of seagrasses for invertebrate consumers from Malagasy tropical polyspecific seagrass meadows

Polyspecific seagrass meadows are of critical ecological importance in tropical coastal zones. These ecosystems provide a wide range of socio-economical services to local populations. Meadows however undergo multiple threats linked to human activities (increased nutrient input, overfishing, invertebrate overharvesting, etc.). It is currently difficult to assess how seagrass meadows could respond to anthropogenic impacts due to poor knowledge of their functional ecology. Here, stable isotope ratios of carbon, nitrogen and sulfur were used to unravel trophic interactions ruling the food webs associated to seagrass beds of the Toliara Great Reef (SW Madagascar). The contributions of various potential food items (sediment-associated and suspended particulate organic matter, plankton, leaves, roots and epiphytes of 7 seagrasses and thalli of 7 dominant macroalgae) to the diet of 20 invertebrate taxa (one sea urchin, 2 sea stars, 2 sea cucumbers, 5 gastropods including one sea hare, one bivalve, 2 amphipods, one leptostracan, one cumacean 2 hermit crabs and 3 shrimps) were assessed using a Bayesian stable isotope mixing model. Model outputs revealed that important trophic diversity existed among the invertebrate assemblage. In some groups (e.g. hermit crabs and amphipods), resource use by morphologically and taxonomically close taxa was markedly different. Many of the dominant taxa heavily relied on macroalgae for their nutrition. On the other hand, few species apparently consumed seagrass tissues. Moreover, when they did, seagrass generally accounted for a minor portion of the diet only. Overall, our results suggest that seagrass grazing in meadows of the Toliara Great Reef could be lower than in other tropical areas. These discrepancies could be linked with seasonal variation in resource availability or with eutrophication. Higher nutrient load is indeed known to cause ecosystem phase shifts and it may induce diet shift to algivory in some invertebrate consumers

Review of fisheries and management of sea cucumbers in the Indian Ocean

Several sea cucumber species (Echinodermata: Holothuroidea) are fished, mostly for export of the dried product for Oriental consumers. Previous studies had analysed the historical trends at the world-scale until 2014. In the Western Indian Ocean (WIO) holothurian fisheries have a long history and several programmes have tried to ameliorate their management. Information has been recently gathered through a questionnaire and access to the most recent, yet unpublished available data (2015 to 2021) from different countries, through the evaluation of catches and/or processed product, present management systems, the imports of beche de mer and other products from Indian Ocean (IO) countries into the major market hub of Hong Kong SAR, and the Food and Agricuture Organisation (FAO) yearly statistics. The results are first presented for WIO countries, highlighting recent improvements in management. Imports from 16 WIO countries into the Hong Kong market (2017-2020 data) indicate the importance of the hub. The FAO world statistics are used to present the changes for the last few years, concentrating on the WIO countries. The recent trends show that demand for holothurians is still very high. Inconsistencies in the unit used in the reported statistics (fresh or dry weight) exist, and this needs to be addressed. The national data should be collected at the species level, to be able to follow the changes and the stock status. A regional approach is needed to encourage use of comparable management tools and follow future trends

Stable isotope ratios reveal trophic niche partitioning among hermit crabs from tropical polyspecific seagrass meadows

Polyspecific seagrass meadows are ubiquitous features of tropical coastal zones. These ecosystems are of critical ecological importance, and provide a wide range of socio-economical services to local populations. Meadows however undergo multiple threats linked to human activities (increased nutrient input, overfishing, invertebrate overharvesting, etc.). It is currently hard to assess how seagrass meadows could respond to anthropogenic impacts due to poor knowledge of their functional ecology. In an effort to unravel trophic interactions ruling the food webs associated to seagrass beds of the Toliara Great Reef (SW Madagascar), we studied resource segregation between two common Diogenidae hermit crabs (Dardanus scutellatus and Ciliopagurus tricolor) using stable isotope ratios. Interspecific differences were noted in isotopic composition of carbon (δ13C = -12.22 ± 1.73 ‰ for D. scutellatus, δ13C = -14.55 ± 0.73 ‰ for C. tricolor), nitrogen (δ15N = 4.73 ± 0.53 ‰ for D. scutellatus, δ15N = 5.20 ± 0.61 ‰ for C. tricolor) and sulfur (δ34S = 14.08 ± 2.32 ‰ for D. scutellatus, δ34S = 16.73 ± 1.49 ‰ for C. tricolor), suggesting that the two species do not feed on the same items. In addition, SIBER (Stable Isotope Bayesian Ellipses in R) modeling based on C and N data clearly showed that no overlap was present in the core isotopic niches of the two species. It also indicated that the isotopic niche of D. scutellatus was greater than the one of C. tricolor, implying that the former feeds on a greater number of items than the latter. While hermit crabs are generally considered as omnivorous species, this study highlighted differences in the foraging ecology of D. scutellatus and C. tricolor. These differences could help to limit competition for food between these two species, and facilitate their coexistence in Malagasy seagrass beds

Use of C, N and S stable isotope ratios to highlight resource segregation among hermit crabs from tropical seagrass meadows

Polyspecific seagrass meadows are ubiquitous features of tropical coastal zones. These ecosystems are of critical ecological importance, and provide a wide range of socio-economical services to local populations. Meadows however undergo multiple threats linked to human activities (increased nutrient input, overfishing, invertebrate overharvesting, etc.). It is currently hard to assess how seagrass meadows could respond to anthropogenic impacts due to poor knowledge of their functional ecology. In an effort to unravel trophic interactions ruling the food webs associated to seagrass beds of the Toliara Great Reef (SW Madagascar), we studied resource segregation between two common Diogenidae hermit crabs (Dardanus scutellatus and Ciliopagurus tricolor) using stable isotope ratios. C, N and S stable isotope ratios of bulk muscle tissue were measured via CF-EA-IRMS (Elementar Vario MicroCube EA coupled to an Isoprime 100 MS). Interspecific differences were noted in isotopic composition of carbon (δ13C = -12.22 ± 1.73 ‰ for D. scutellatus, δ13C = -14.55 ± 0.73 ‰ for C. tricolor), nitrogen (δ15N = 4.73 ± 0.53 ‰ for D. scutellatus, δ15N = 5.20 ± 0.61 ‰ for C. tricolor) and sulfur (δ34S = 14.08 ± 2.32 ‰ for D. scutellatus, δ34S = 16.73 ± 1.49 ‰ for C. tricolor), suggesting that the two species do not feed on the same items. In addition, SIBER (Stable Isotope Bayesian Ellipses in R) modeling based on C and N data clearly showed that no overlap was present in the core isotopic niches of the two species. It also indicated that the isotopic niche of D. scutellatus was greater than the one of C. tricolor, implying that the former feeds on a greater number of items than the latter. While hermit crabs are generally considered as omnivorous species, this study highlighted differences in the foraging ecology of D. scutellatus and C. tricolor. These differences could help to limit competition for food between these two species, and facilitate their coexistence in Malagasy seagrass beds

Isotopic tracing of sediment components that are assimilated by epibiontic juveniles of Holothuria scabra (Holothuroidea)

Despite H. scabra’s wide distribution and status as one of the best candidates for sustaining the development of tropical sea cucumber aquaculture, very few data are available regarding the organic fraction it assimilates in practice. In this study we report experimental results where H. scabra’s diet was supplemented with various 15N-labelled organic fractions of sediment. We used juveniles weighing between 38- 88 mg at the beginning of the experiment (ca. 2 cm long and 30 days old). Their growth was measured over a four week period and their 15N composition recorded. The results showed that H. scabra juveniles assimilated all added organic components from both dissolved and particulate fractions of the sediment. Bacteria seem to be an important food source for juveniles, even more so than microphytobenthos (diatoms).Holothurian aquaculture and nutritio

Carbon and nitrogen incorporations by the farmed seaweed, Kappaphycus alvarezii and its epiphytes (EFA)

editorial reviewedFaced with the decrease in the fishery resources that they catch, coastal villagers communities in Madagascar are turning to the red algae cultivation, with the species, Kappaphycus alvarezii to diversify and improve their sources of income. However, the production is disrupted by the appearance of the EFAD or Epiphytic Filamentous Algae Disease, which can reduce the algal production up to 90 %. The EFAD is induced by the epiphytic red algae Polysiphonia sp. which kill the infested host at the end of the disease. The mechanism by which host weakness arises is presently not well understood and it is not clear if Polysiphonia sp., at initial stage of the infestation, competes with its host to acquire inorganic carbon and nitrogen. The present work aims to assess the effects of Polysiphonia sp. on its host in term of nutrients uptakes in situ at initial infestation stage. Using 15N and 13C labeled substances, we have measured experimentally in situ the incorporation of nitrogen (NH4+) and inorganic carbon in infested algae in K. alvarezii at two different sites, Tampolove (S 22°13'29.7''; E 43°15'37.3'') and Lambohara (S 22°10'46.2"; E 43°15'3.1"), both located in Baie des Assassins, (Southwestern region of Madagascar). Solutions of sodium bicarbonate (13C, 99 %, Eurisotop, France) and ammonium chloride (15N, 99 %, Eurisotop, France) were injected in transparent plastic bags containing thallus of healthy (n = 5 per experience) and infested K. alvarezii by Polysiphonia sp. (n = 5 per experience). After one hour, sample were collected and dried (60°C, 48h). Host and epiphytes were separated, weighted precisely (i.e. 0.01 mg) and their 13C and 15N contents were measured using EA-IRMS (Elemental Analyzer – Isotope Ratio Mass Spectrometer). The quantity of 13C and 15N uptaken by K. alvarezii were far greater than those by EFA. K. alvarezii (i.e. 2.03 vs. 0.190 g mgDW of 13C and 10.22 vs. 0.018 mgDW of 15N for host and epiphytes, respectively). This is due to larger biomass of cultivated algae at this early stage of infestation. In term of biomass turnover, 13C and 15N uptake by both organisms differed significantly (0.009 vs. 0.0003 % per hour for C and 0.07 vs. 0.15 % per hour). This indicates that Polysiphonia sp. relatively to its biomass incorporate nitrogen faster than its host. At the start of infestation, this is probably not a problem but quickly it could drive to outcompete host for the acquisition of N and therefore contribute to decrease cultivated algae growth.14. Life below water12. Responsible consumption and production8. Decent work and economic growt