Testing for concordance between predicted species richness, past prioritization, and marine protected area designations in the western Indian Ocean.

Scientific advances in environmental data coverage and machine learning algorithms have improved the ability to make large-scale predictions where data are missing. These advances allowed us to develop a spatially resolved proxy for predicting numbers of tropical nearshore marine taxa. A diverse marine environmental spatial database was used to model numbers of taxa from ∼1000 field sites, and the predictions were applied to all 7039 6.25-km2 reef cells in 9 ecoregions and 11 nations of the western Indian Ocean. Our proxy for total numbers of taxa was based on the positive correlation (r2 = 0.24) of numbers of taxa of hard corals and 5 highly diverse reef fish families. Environmental relationships indicated that the number of fish species was largely influenced by biomass, nearness to people, governance, connectivity, and productivity and that coral taxa were influenced mostly by physicochemical environmental variability. At spatial delineations of province, ecoregion, nation, and strength of spatial clustering, we compared areas of conservation priority based on our total species proxy with those identified in 3 previous priority-setting reports and with the protected area database. Our method identified 119 locations that fit 3 numbers of taxa (hard coral, fish, and their combination) and 4 spatial delineations (nation, ecoregion, province, and reef clustering) criteria. Previous publications on priority setting identified 91 priority locations of which 6 were identified by all reports. We identified 12 locations that fit our 12 criteria and corresponded with 3 previously identified locations, 65 that aligned with at least 1 past report, and 28 that were new locations. Only 34% of the 208 marine protected areas in this province overlapped with identified locations with high numbers of predicted taxa. Differences occurred because past priorities were frequently based on unquantified perceptions of remoteness and preselected priority taxa. Our environment-species proxy and modeling approach can be considered among other important criteria for making conservation decisions.

Evaluación de la concordancia entre la riqueza de especies pronosticada, priorizaciones pasadas y la designación de áreas marinas protegidas en el oeste del Océano Índico Resumen Los avances científicos en la cobertura de datos ambientales y los algoritmos de aprendizaje automatizado han mejorado la capacidad de predecir a gran escala cuando hacen falta datos. Estos avances nos permiten desarrollar un representante con resolución espacial para predecir la cantidad de taxones marinos en las costas tropicales. Usamos una base de datos espaciales de diversos ambientes marinos para modelar la cantidad de taxones a partir de ∼1000 sitios de campo y aplicamos las predicciones a las 7039 celdas arrecifales de 6.25­km2 en nueve ecorregiones y once países del oeste del Océano Índico. Nuestro representante para la cantidad total de taxones se basó en la correlación positiva (r2=0.24) de la cantidad de taxones de corales duros y cinco familias de peces arrecifales con diversidad alta. Las relaciones ambientales indicaron que el número de especies de peces estuvo influenciado principalmente por la biomasa, la cercanía a las personas, la gestión, la conectividad y la productividad y que los taxones de coral estuvieron influenciados principalmente por la variabilidad ambiental fisicoquímica. Comparamos la prioridad de las áreas de conservación a nivel de las delimitaciones espaciales de provincia, ecorregión, nación y fuerza del agrupamiento espacial basado en nuestro total de especies representantes con aquellas especies identificadas en tres reportes previos de establecimiento de prioridades y con la base de datos de áreas protegidas. Con nuestro método identificamos 119 localidades aptas para tres cantidades de taxones (corales duros, peces y su combinación) y cuatro criterios de delimitación espacial (nación, ecorregión, provincia y grupo de arrecifes). Las publicaciones previas sobre el establecimiento de prioridades identificaron 91 localidades prioritarias de las cuales seis fueron identificadas por todos los reportes. Identificamos doce localidades que se ajustan a nuestros doce criterios y se correspondieron con tres localidades identificadas previamente, 65 que se alinearon con al menos un reporte anterior y 28 que eran nuevas localidades. Sólo 34% de las 208 áreas marinas protegidas en esta provincia se traslaparon con localidades identificadas con un gran número de taxones pronosticados. Hubo diferencias porque en el pasado se priorizaba frecuentemente con base en las percepciones no cuantificadas de lo remoto y prioritario de los taxones preseleccionados. Nuestra especie representante del ambiente y nuestra estrategia de modelo pueden considerarse entre otros criterios importantes para tomar decisiones de conservación.

New insights into the diversity of cryptobenthic Cirripectes blennies in the Mascarene Archipelago sampled using Autonomous Reef Monitoring Structures (ARMS).

Autonomous Reef Monitoring Structures (ARMS) are artificial mini-reefs designed for standardized sampling of sessile and small motile cryptobenthic organisms. ARMS are also effective for collecting small cryptobenthic fishes, such as the combtooth blennies of the genus Cirripectes. Recent studies discovered several Cirripectes species endemic to islands or archipelagos, in spite of the generally broad distributions of tropical and subtropical blennies. Thus, to evaluate the diversity and distribution of Cirripectes species in the Mascarene Archipelago, a little-studied region but an important biodiversity hotspot, complete mitochondrial genomes, and nuclear rhodopsin genes were sequenced for 39 specimens collected with ARMS deployed on outer reef slopes at Reunion and Rodrigues islands. Mitochondrial COI sequences were analyzed to integrate these specimens within the largest dataset of publicly available sequences. Three species were found in the Mascarene Archipelago, Cirripectes castaneus, Cirripectes randalli, and Cirripectes stigmaticus. C. castaneus and C. stigmaticus both have an Indo-Pacific distribution with several haplotypes shared among distant localities. In agreement with the literature, C. randalli shows a small-range endemism restricted to the Mascarenes. We confirmed the presence of C. castaneus, C. randalli, and C. stigmaticus in Rodrigues, and the presence of C. stigmaticus in Reunion. This study contributes to filling the gaps in taxonomic and molecular knowledge of the reef cryptobiome in the South-West Indian Ocean, and provides the first complete mitogenomes for the genus, a crucial step for future molecular-based inventories (e.g., eDNA).

Population differentiation or species formation across the Indian and the Pacific Oceans? An example from the brooding marine hydrozoan Macrorhynchia phoenicea.

Assessing population connectivity is necessary to construct effective marine protected areas. This connectivity depends, among other parameters, inherently on species dispersal capacities. Isolation by distance (IBD) is one of the main modes of differentiation in marine species, above all in species presenting low dispersal abilities. This study reports the genetic structuring in the tropical hydrozoan Macrorhynchia phoenicea α (sensu Postaire et al., 2016a), a brooding species, from 30 sampling sites in the Western Indian Ocean and the Tropical Southwestern Pacific, using 15 microsatellite loci. At the local scale, genet dispersal relied on asexual propagation at short distance, which was not found at larger scales. Considering one representative per clone, significant positive FIS values (from -0.327*** to 0.411***) were found within almost all sites. Gene flow was extremely low at all spatial scales, among sites within islands (<10 km distance) and among islands (100 to >11,000 km distance), with significant pairwise FST values (from 0.035*** to 0.645***). A general pattern of IBD was found at the Indo-Pacific scale, but also within ecoregions in the Western Indian Ocean province. Clustering and network analyses identified each island as a potential independent population, while analysis of molecular variance indicated that population genetic differentiation was significant at small (within island) and intermediate (among islands within province) spatial scales. As shown by this species, a brooding life cycle might be corollary of the high population differentiation found in some coastal marine species, thwarting regular dispersal at distances more than a few kilometers and probably leading to high cryptic diversity, each island housing independent evolutionary lineages.

DNA barcoding of reef brittle stars (Ophiuroidea, Echinodermata) from the southwestern Indian Ocean evolutionary hot spot of biodiversity.

In anticipation of the current biodiversity crisis, it has become critical to rapidly and accurately assess biodiversity. DNA barcoding has proved efficient in facilitating the discovery and description of thousands of species and also provides insight into the dynamics of biodiversity. Here, we sequenced a portion of the mitochondrial cytochrome c oxidase subunit I (COI) gene from all morphospecies of reef brittle stars collected during a large-scale biodiversity survey in the southwestern Indian Ocean (SWIO). Three methods of species delineation (Automatic Barcode Gap Discovery, Generalized Mixed Yule Coalescent model, and Bayesian Poisson Tree Processes) showed concordant results and revealed 51 shallow reef species in the region. Mean intraspecific genetic distances (0.005-0.064) and mean interspecific genetic distances within genera (0.056-0.316) were concordant with previous echinoderm studies. This study revealed that brittle-star biodiversity is underestimated by 20% within SWIO and by >40% when including specimens from the Pacific Ocean. Results are discussed in terms of endemism, diversification processes, and conservation implications for the Indo-West Pacific marine biodiversity. We emphasize the need to further our knowledge on biodiversity of invertebrate groups in peripheral areas.

Molecular species delimitation methods and population genetics data reveal extensive lineage diversity and cryptic species in Aglaopheniidae (Hydrozoa).

A comprehensive inventory of global biodiversity would be greatly improved by automating methods for species delimitation. The Automatic Barcode Gap Discovery method, the Poisson tree processes algorithm and the Generalized mixed Yule-coalescent model have been proposed as means of increasing the rate of biodiversity description using single locus data. We applied these methods to explore the diversity within the Aglaopheniidae, a hydrozoan family with many species widely distributed across tropical and temperate oceans. Our analyses revealed widespread cryptic diversity in this family, almost half of the morpho-species presenting several independent evolutionary lineages, as well as support for cases of synonymy. For two common species of this family, Lytocarpia brevirostris and Macrorhynchia phoenicea, we compared the outputs to clustering analyses based on microsatellite data and to nuclear gene phylogenies. For L. brevirostris, microsatellite data were congruent with results of the species delimitation methods, revealing the existence of two cryptic species with Indo-Pacific distribution. For M. phoenicea, all analyses confirmed the presence of two cryptic species within the South-Western Indian Ocean. Our study suggests that the diversity of Aglaopheniidae might be much higher than assumed, likely related to low dispersal capacities. Sequence-based species delimitation methods seem highly valuable to reveal cryptic diversity in hydrozoans; their application in an integrative framework will be very useful in describing the phyletic diversity of these organisms.

Shallow-water reef ophiuroids (Echinodermata: Ophiuroidea) of Réunion (Mascarene Islands), with biogeographic considerations.

Despite their importance in marine biodiversity, invertebrates are far less studied than vertebrates. Given the current global biodiversity crisis and insufficient taxonomic resources, sustained efforts need to be undertaken to assess species diversity, especially in the highly threatened 'biodiversity hotspots'. Réunion is a young volcanic island lying in the Mascarene Islands (south-western Indian Ocean, SWIO), a marine biodiversity hotspot. A substantial sampling effort was conducted around Réunion Island to document shallow water reef-associated ophiuroid (brittle-stars) diversity, a class recognised as the most diverse among echinoderms. A total of 33 species were documented, increasing the known species richness of the island by 56%. Findings include 15 new records for Réunion, 11 for the Mascarene Islands and 8 for the Indian Ocean. The most diverse family was Ophiocomidae, a family of large, abundant and conspicuous tropical species. Even in this well studied family, a new species was revealed by this survey. Morphological variants together with DNA sequence variations within several species revealed cryptic species. We compared our results with the known fauna of other Mascarene Islands and discuss biogeographic implications for the region.

Tradeoffs between fisheries harvest and the resilience of coral reefs.

Many countries are legally obliged to embrace ecosystem-based approaches to fisheries management. Reductions in bycatch and physical habitat damage are now commonplace, but mitigating more sophisticated impacts associated with the ecological functions of target fisheries species are in their infancy. Here we model the impacts of a parrotfish fishery on the future state and resilience of Caribbean coral reefs, enabling us to view the tradeoff between harvest and ecosystem health. We find that the implementation of a simple and enforceable size restriction of >30 cm provides a win:win outcome in the short term, delivering both ecological and fisheries benefits and leading to increased yield and greater coral recovery rate for a given harvest rate. However, maintaining resilient coral reefs even until 2030 requires the addition of harvest limitations (<10% of virgin fishable biomass) to cope with a changing climate and induced coral disturbances, even in reefs that are relatively healthy today. Managing parrotfish is not a panacea for protecting coral reefs but can play a role in sustaining the health of reefs and high-quality habitat for reef fisheries.

Evolutionary dynamics in the southwest Indian ocean marine biodiversity hotspot: a perspective from the rocky shore gastropod genus Nerita.

The Southwest Indian Ocean (SWIO) is a striking marine biodiversity hotspot. Coral reefs in this region host a high proportion of endemics compared to total species richness and they are particularly threatened by human activities. The island archipelagos with their diverse marine habitats constitute a natural laboratory for studying diversification processes. Rocky shores in the SWIO region have remained understudied. This habitat presents a high diversity of molluscs, in particular gastropods. To explore the role of climatic and geological factors in lineage diversification within the genus Nerita, we constructed a new phylogeny with an associated chronogram from two mitochondrial genes [cytochrome oxidase sub-unit 1 and 16S rRNA], combining previously published and new data from eight species sampled throughout the region. All species from the SWIO originated less than 20 Ma ago, their closest extant relatives living in the Indo-Australian Archipelago (IAA). Furthermore, the SWIO clades within species with Indo-Pacific distribution ranges are quite recent, less than 5 Ma. These results suggest that the regional diversification of Nerita is closely linked to tectonic events in the SWIO region. The Reunion mantle plume head reached Earth's surface 67 Ma and has been stable and active since then, generating island archipelagos, some of which are partly below sea level today. Since the Miocene, sea-level fluctuations have intermittently created new rocky shore habitats. These represent ephemeral stepping-stones, which have likely facilitated repeated colonization by intertidal gastropods, like Nerita populations from the IAA, leading to allopatric speciation. This highlights the importance of taking into account past climatic and geological factors when studying diversification of highly dispersive tropical marine species. It also underlines the unique history of the marine biodiversity of the SWIO region.

Fast growth may impair regeneration capacity in the branching coral Acropora muricata.

Regeneration of artificially induced lesions was monitored in nubbins of the branching coral Acropora muricata at two reef-flat sites representing contrasting environments at Réunion Island (21°07'S, 55°32'E). Growth of these injured nubbins was examined in parallel, and compared to controls. Biochemical compositions of the holobiont and the zooxanthellae density were determined at the onset of the experiment, and the photosynthetic efficiency (Fv/Fm ) of zooxanthellae was monitored during the experiment. Acropora muricata rapidly regenerated small lesions, but regeneration rates significantly differed between sites. At the sheltered site characterized by high temperatures, temperature variations, and irradiance levels, regeneration took 192 days on average. At the exposed site, characterized by steadier temperatures and lower irradiation, nubbins demonstrated fast lesion repair (81 days), slower growth, lower zooxanthellae density, chlorophyll a concentration and lipid content than at the former site. A trade-off between growth and regeneration rates was evident here. High growth rates seem to impair regeneration capacity. We show that environmental conditions conducive to high zooxanthellae densities in corals are related to fast skeletal growth but also to reduced lesion regeneration rates. We hypothesize that a lowered regenerative capacity may be related to limited availability of energetic and cellular resources, consequences of coral holobionts operating at high levels of photosynthesis and associated growth.

Linking coral river runoff proxies with climate variability, hydrology and land-use in Madagascar catchments.

Understanding the linkages between coastal watersheds and adjacent coral reefs is expected to lead to better coral reef conservation strategies. Our study aims to examine the main predictors of environmental proxies recorded in near shore corals and therefore how linked near shore reefs are to the catchment physical processes. To achieve these, we developed models to simulate hydrology of two watersheds in Madagascar. We examined relationships between environmental proxies derived from massive Porites spp. coral cores (spectral luminescence and barium/calcium ratios), and corresponding time-series (1950-2006) data of hydrology, climate, land use and human population growth. Results suggest regional differences in the main environmental drivers of reef sedimentation: on annual time-scales, precipitation, river flow and sediment load explained the variability in coral proxies of river discharge for the northeast region, while El Niño-Southern Oscillation (ENSO) and temperature (air and sea surface) were the best predictors in the southwest region.

Critical thresholds and tangible targets for ecosystem-based management of coral reef fisheries.

Sustainably managing ecosystems is challenging, especially for complex systems such as coral reefs. This study develops critical reference points for sustainable management by using a large empirical dataset on the coral reefs of the western Indian Ocean to investigate associations between levels of target fish biomass (as an indicator of fishing intensity) and eight metrics of ecosystem state. These eight ecological metrics each exhibited specific thresholds along a continuum of fishable biomass ranging from heavily fished sites to old fisheries closures. Three thresholds lay above and five below a hypothesized window of fishable biomass expected to produce a maximum multispecies sustainable yield (B(MMSY)). Evaluating three management systems in nine countries, we found that unregulated fisheries often operate below the B(MMSY), whereas fisheries closures and, less frequently, gear-restricted fisheries were within or above this window. These findings provide tangible management targets for multispecies coral reef fisheries and highlight key tradeoffs required to achieve different fisheries and conservation goals.

Why does the biota of the Madagascar region have such a strong Asiatic flavour?

A corollary of island biogeographical theory is that islands are largely colonized from their nearest mainland source. Despite Madagascar's extreme isolation from India and proximity to Africa, a high proportion of the biota of the Madagascar region has Asian affinities. This pattern has rarely been viewed as surprising, as it is consistent with Gondwanan vicariance. Molecular phylogenetic data provide strong support for such Asian affinities, but often not for their vicariant origin; most divergences between lineages in Asia and the Madagascar region post-date the separation of India and Madagascar considerably (up to 87 Myr), implying a high frequency of dispersal that mirrors colonization of the Hawaiian archipelago in distance. Indian Ocean bathymetry and the magnitude of recent sea-level lowstands support the repeated existence of sizeable islands across the western Indian Ocean, greatly reducing the isolation of Madagascar from Asia. We put forward predictions to test the role of this historical factor in the assembly of the regional biota. © The Willi Hennig Society 2009.

SEASONAL CHANGES IN SIZE STRUCTURE OF SARGASSUM AND TURBINARIA POPULATIONS (PHAEOPHYCEAE) ON TROPICAL REEF FLATS IN THE SOUTHERN RED SEA(1).

Seasonal variation in density, thallus length and biomass, population size structure, and allometric length-biomass relationships was investigated in populations of Sargassum ilicifolium (Turner) C. Agardh, Sargassum subrepandum (Forssk.) C. Agardh, and Turbinaria triquetra (J. Agardh) Kütz. (Phaeophyceae) on shallow reef flats in the southern Red Sea. Thallus length and biomass varied strongly with season, with the highest values occurring in the cooler months. Thallus densities showed no significant temporal variation. Log-total biomass versus log-density relationships were positive throughout the growth season without any decrease in the slope of the relationship. In two populations, biomass-density combinations approached the interspecific biomass-density line, but the massive annual shedding of modules occurred before self-thinning would set in. Allometric length-biomass relationships varied with season in all populations and were associated with seasonal module initiation, growth, and shedding. Evidence of a strong asymmetric competition was found in two high-density populations. These populations showed a predominance of small thalli during peak development, asymmetrical Lorenz curves, increasing Gini coefficients, and increasing thallus length relative to biomass during the main growth phase. In two other less crowded populations, small thalli were absent during peak development, Lorenz curves were symmetrical, and Gini coefficients decreased during the main growth phase. In these populations, size equalization appears to be due to responses at the modular level rather than size-dependent mortality. We conclude that changes in size structure in this highly seasonal environment are determined by module dynamics, modified by asymmetric competition in some populations, with a minor role of recruitment and no regulatory effect of self-thinning.

SEASONAL MODULE DYNAMICS IN SARGASSUM SUBREPANDUM (FUCALES, PHAEOPHYTA)(1).

Module dynamics of the fucoid alga SARGASSUM SUBREPANDUM (Forssk.) C. Agardh was studied in the southern Red Sea. Seasonal variation in thallus density and size was determined, and the initiation, growth, reproduction, and shedding of modules (primary laterals) were ascertained, using a tagging approach. Possible effects of different size-related parameters on module initiation, growth, reproduction, and shedding were analyzed in the context of contradicting results for other macroalgae, in comparison with terrestrial plants. Thallus density varied little; most of the seasonal variation occurred at the modular level. A restricted period of new module formation early in the cooler season was followed by fast growth and reproduction. Massive shedding of modules occurred toward the end of the cooler season leading to strongly reduced biomass in summer. There was some evidence that high module numbers inhibited new module formation and enhanced the maximum module elongation rate (fastest-growing module per thallus). On the other hand, elongation rates generally decreased, and apical tissue losses increased with increasing module length. This response was observed over a wide size range, suggesting grazing losses. There was no evidence of suppressed growth in small modules due to intraspecific competition. Elongation rates remained unaffected by reproductive status, indicating that there was no direct trade-off between growth and reproduction. Module survivorship was independent of module number and size, but fertile modules were more persistent than vegetative ones. We conclude that module dynamics are determined by seasonal changes in the environment, size-dependent processes, and interactions among the modules.