Aim: Climate change is affecting the geographic distributions of many species and researchers are increasingly relying on species distribution models (SDMs) to forecast species' redistributions under climate change. Such modelling studies, however, often ignore biotic interactions that shape species' geographic ranges. This is especially problematic for coral reefs, which host a high diversity of species and interactions. We tested how biotic interactions affect the distribution patterns of obligate coral-dwelling Trapezia crabs. Location: Global coastal ocean. Time Period: 2000-2014, 2040-2050, 2090-2100. Major Taxa Studied: Corals and coral-dwelling Trapezia crabs. Methods: We determined the symbiotic relationships between 22 crab species in the genus Trapezia and corals via field survey and extensive literature review. We first developed SDMs for coral and crab species using exclusively abiotic variables (abiotic-only models for corals and crabs). Then we constructed a second set of models where we accounted for coral distributions into crab predictions by combining model predictions for the two taxa a posteriori (abiotic-plus-biotic models for crabs only). Results: We obtained 30 commonly accepted coral-crab symbiotic relationships from nine Trapezia crab and six stony coral species. The abiotic-only model predictions showed that six corals may lose approximately one-sixth of suitable ranges under RCP 8.5 in 2040-2050. The two types of models for crabs yielded largely different habitat suitability predictions and accounting for biotic interactions into SDM predictions exacerbates the predicted impacts of climate change on coral-dwelling crabs. Main Conclusions: Our results show large discrepancies in crab spatial distribution patterns with and without accounting for symbiotic interactions. Our findings highlight the important role of modeller's decision on accounting for biotic interactions when predicting the geographical ranges of coral-dwelling species, with important implications for designing future conservation and management strategies for marine species.

Coral reef environments are threatened by multiple anthropogenic stressors. To inform more efficient local management strategies that support coral reef resilience, high-resolution spatial data of key environmental parameters is critically needed. High-resolution maps of, for example, coral type distribution, reef structural complexity, bleaching, and water quality would be highly useful in the selection of priority sites for coral reef protection and restoration action. Excitingly, new remote-sensing technologies are increasingly enabling such maps to be produced at low cost and over large spatial scales. Importantly, understanding the optical properties of different species of corals is a key condition for the development of advanced remote-sensing applications: in clear and shallow coral reef environments, benthic reflectance makes a major contribution to the total optical signal retrieved by a remote-sensing instrument. Here, we present initial results from a fieldwork campaign in summer 2022 at Tetiaroa, a low-lying atoll in French Polynesia. Coral reef reflectance was measured at 21 sites using TriOS RAMSES hyperspectral sensors (optical resolution: 3.3 nm). The coral reflectance data indicates differences between coral species and corroborates previous findings in the literature. The next step of this research project is to complement these initial findings with the analysis of the inherent optical properties of water constituents. This will allow for forming a comprehensive understanding of the different factors contributing to the total optical signal detected by remote-sensing instruments. Ultimately, better understanding the optical properties of coral reef environments will enable the production of high-resolution spatial-temporal shallow water products. Future work will build on these results to map and monitor the flows and hotspots of nutrients across the coral reef seascape using multispectral/hyperspectral drone and satellite imagery.

The Sentinel-2A and 2B Multi-Spectral Instrument (MSI) offers a specification of potential value toward a number of objectives in remote sensing of coral reefs. Coral reefs represent a unique challenge for remote sensing, being highly heterogeneous at metre scales and occurring at variable depths and water clarity regimes. However, conservation initiatives, such as the United Nations Sustainable Development Goals, add urgency to the need for the large scale environmental monitoring information that remote sensing can provide. In the quest to meet this challenge a range of satellite instruments have been leveraged, from Landsat to high spatial resolution sensors such as WorldView-2, toward objectives such as: mapping of bottom types, bathymetry, change detection, and detection of coral bleaching events. Sentinel-2A and 2B offer a new paradigm of available instruments, with a 5-day revisit, 10 m multispectral spatial resolution and freely available data. Pre-launch simulation analyses by several of the authors suggested Sentinel-2 would have good performance for reef applications, in this paper we follow up on this study by reviewing the potential based on the substantial archive of actual data now available. First we determine to what extent the World's reefs are covered by Sentinel-2, since the mission requirements do not by default include all reefs. Secondly we review how a 5-day revisit translates to a usable acquisition rate of clear images, given that cloud and surface glint are common confounding factors. The usable acquisition rate is the real determinant of the objectives to which the data can be applied. Finally we apply current processing algorithms to Sentinel-2 data of several sites over the Great Barrier Reef, including physics-based bathymetry inversion and object-orientated benthic mapping. Landsat 8 OLI is most comparable current sensor to Sentinel-2 MSI, so direct comparisons and the possibilities for data synthesis are explored. Our findings confirm that Sentinel-2 has excellent performance for meeting several essential coral reef scientific and monitoring objectives. Taking into account cloud and sun glint, the usable acquisition rate for a large proportion of reefs is likely to be around 20 clear images a year on average, giving a new potential for evaluation of short time-scale disturbances and impacts. The spatial resolution of 10 m is a key threshold for delineating benthic features of interest such as coral structures, and there is evidence from image and field data that bleaching is detectable. Radiometrically Sentinel-2 data can support good results in physics-based methods, such as bathymetric mapping, comparable to Landsat 8 and WorldView-2. In addition the large scale acquisition area, provided by the 290 km wide swath, offers advantages over high spatial resolution imagery for mapping at multi-reef scales. Sentinel-2 data can be immediately leveraged with existing methods, to provide a new level of reef monitoring information compared to that previously available by remote sensing. Combined with Landsat 8 and the historical Landsat archive, the data collected today will be invaluable for decades or even centuries to come. In this context, the main downside of the Sentinel-2 mission is that approximately 12% of the World's reefs currently lie outside the acquisition plan and are not imaged. Surprisingly, for a European initiative, coral reefs in European governed territories are among the worst served globally. These omissions, approximately only 1/200th of the currently imaged area, limit the global scope which otherwise would be one of Sentinel-2's greatest strengths.

Sentinel-2 (S2) offers a great potential coral reef mapping as its spatial resolution up to 10 m is comparable to the patchy distribution typically met in coral environments, and data acquired in 13 spectral bands offer improved spectral diversity for assessing the variety of coral colors. With a revisit time of five days with two satellites in orbit, S2 will enable the observation of ecosystems processes such as coral bleaching, coral mortality or shifts to macroalgal domination. Nevertheless, the acquisition plan needs adjustments to include coral reefs globally in remote oceanic reef environments, particularly those in European governed territories.

The global erosion of biodiversity presents unique challenges for identifying major changes in population dynamics, establishing their causes, and managing and conserving affected ecosystems at broad spatial scales. Adaptive learning approaches connecting different spatial scales through the transfer of hierarchical information are powerful tools to address such challenges. Here, we use a Semi-Parametric Bayesian Hierarchical (SPa-BaH) model to estimate coral cover trajectories using 16 years of a broad-scale survey on Australia's Great Barrier Reef (GBR). The spatiotemporal variability of coral populations has been considered by separating three-tiered spatial scales and allowing for alternating phases of increasing and decreasing in the estimation of their trajectories. Model estimates revealed coral cover trajectories that were highly variable according to location but that fairly consistently declined at a regional spatial scale. Notwithstanding this general trend, individual reefs within subregions in the central part of the GBR often displayed different trajectory types between sites separated by only a few hundred meters. These coral dynamics were also associated with reduced recovery rates in the Cairns and Swain subregions. Our study highlights the importance of accounting for local variation in coral cover when estimating the spatiotemporal trends in coral cover trajectories, in this case, at the GBR scale. By retaining information at different hierarchical spatial scales, our SPa-BaH model supports better estimation of large-scale coral cover trajectories. The quantitative approaches developed here can also be applied to other species with complex dynamics thereby enhancing estimations of their trajectories at local- and larger-scales and options for their management.

Elevated carbon dioxide (CO2) has recently been shown to affect chemosensory and auditory behaviour, and activity levels of larval reef fishes, increasing their risk of predation. However, the mechanisms underlying these changes are unknown. Behavioural lateralization is an expression of brain functional asymmetries, and thus provides a unique test of the hypothesis that elevated CO2 affects brain function in larval fishes. We tested the effect of near-future CO2 concentrations (880 mu atm) on behavioural lateralization in the reef fish, Neopomacentrus azysron. Individuals exposed to current-day or elevated CO2 were observed in a detour test where they made repeated decisions about turning left or right. No preference for right or left turns was observed at the population level. However, individual control fish turned either left or right with greater frequency than expected by chance. Exposure to elevated-CO2 disrupted individual lateralization, with values that were not different from a random expectation. These results provide compelling evidence that elevated CO2 directly affects brain function in larval fishes. Given that lateralization enhances performance in a number of cognitive tasks and anti-predator behaviours, it is possible that a loss of lateralization could increase the vulnerability of larval fishes to predation in a future high-CO2 ocean.

Somalia has the longest national coastline (3025 km) in Africa with an estimated shelf area (depth 0-200 m) of 32500 km2. The country is divided into the northern coastal plain of Guban, which has a semi-arid terrain; the northern highlands with rugged mountain ranges containing the country's highest peak (2407 m); and the Ogaden region which descends to the south from the highlands and which consists of shallow plateau valleys, wadis and broken mountains. The latter region continues to the Mudug plain in central Somalia. From Ras Caseyr to the Kenya border, the coast runs north-east to south-west, coinciding with the displacement caused by the Mesozoic marginal subsidence. This general structure is complicated by sedimentary troughs crossing the Horn of Africa, and by large sedimentary basins, cutting the coastline and extending inland into Southern Somalia and Northern Kenya (Juba-Lamu embayment, Mogadishu basin). Offshore, the western Somali Basin extends from Socotra to the Comores. The open shelf environments developed along the Somali coast are a consequence of an extensive marine transgression, connected to coastal subsidence or inland uplift. The rocks along the southern coastal belt are Pliocene-Pleistocene, and are characterized by a sequence of both marine and continental deposits of skeletal sands, coral build-ups, eolian sands and paleosols. As well as eolian and biogenic sedimentary processes, sea-level fluctuations, Holocene climatic changes and neotectonic movements have combined to produce the modern coastline. A notable feature is an ancient dune ridge complex, known as the Merka red dune, which rims the coast extending beyond the Kenyan border and which separates the narrow coastal belt from the Uebi Shebeli alluvial plain. Two features of note are the Bajuni Archipelago, which consists of islands, islets and skerries, forming a barrier island separated from the coast by a narrow marine sound, and a braided, channelized coastal area, which originated from the drowning of a paleofluvial net. The southern Somali coast, with that of Kenya and Tanzania, forms part of the Somali Current Large Marine Ecosystem, encompassing 700000 km2, and extending 800 km between Dar es Salaam and Ras Hafun. Abundant biomass develops here due to upwelling. The shelf area has a wide variety of coral reefs, mangroves, seagrass meadows, beaches and estuaries. In shallow water areas the abraded flats are colonized by scattered coral communities with variable cover. A true fringing reef is achieved in places only in the Bajuni archipelago. All along the southern Somali coastal shelf there are spreading meadows of Thalassodendron seagrass, and benthic communities typical of mobile sandy substrates are limited to beach ridges and shoals developed along the coastline. Around the Bajuni barrier island and the channelized area there is more diversity. Mangroves grow on the tidal belts of the channels, and there are expanses of salt flats. Large-scale alteration produced by man on the Somali coast is relatively recent, but has accelerated in the last few decades, especially around major cities. This alteration affects especially backshore areas where the Pleistocene coral reefs are quarried. At present, the continental shelf is not adequately monitored or protected, so coastal habitats are being degraded, living marine resources are overexploited, and pollution levels are increasing, all of which affect natural resources and biodiversity. Somalia is one of the world's poorest and least developed countries, with few resources and devastated by civil war, but since 1993 it has been part of the Common Market for Eastern and Southern Africa (COMESA). This will affect fisheries and aquaculture in terms of the investment, production, trade and fish consumption of the member states. There are currently no marine protected areas and no legislation concerning their establishment and management, although the World Conservation Monitoring Centre (WCMC) Protected Areas Database lists Busc Busc Game Reserve as an MPA. In 1992, The WCMC also listed the following coastal sites as proposed protected areas: Zeila (important sea bird colonies on offshore islets), Jowhar-Warshek, Awdhegle-Gandershe. The area from Kisimayo to Ras Chiambone is probably of highest priority, as it is important for coral reefs, marine turtles, and mangrove resources, although it is still poorly known. (C) 2000 Elsevier Science Ltd.