The effects of ocean acidification on living marine resources present serious challenges for managers of these resources. An understanding of the ecosystem consequences of ocean acidification is required to assess tradeoffs among ecosystem components (e.g.fishery yield, protected species conservation, sensitive habitat) and adaptations to this perturbation. We used a marine ecosystem model for the Northeast US continental shelf to address direct and indirect effects of species responses to ocean acidification. Focusing on upper trophic level groups that are primary targets of fishing activity, we projected changes for systemic ecological and fisheries indicators. We modeled effects of ocean acidification as either fixed changes in mortality rate or production for select species groups over twenty years. Biomass and fishery yield of species groups that were modeled to have direct acidification impacts and groups that were not directly impacted both declined, due to both increased mortality/decreased growth and a decrease in availability of food for groups that prey on shelled invertebrates. Our analyses show that food web consequences of ocean acidification can extend beyond groups thought most vulnerable, and to fishery yield and ecosystem structure. However, the magnitude and precise nature of ocean acidification effects depend on understanding likely species’ responses to decrease in pH. While predicting the effects of ocean acidification is difficult, the potential impacts on ecosystem structure and function need to be evaluated now to provide scientists and managers preliminary assessments for planning and priority setting. Scenario analysis using simulation models like ours provides a framework for testing hypotheses about ecosystem consequences of acidification, and for integrating results of experiments and monitoring.
Recent eustatic sea level rise (SLR) is one of the most striking manifestations of recent climate change as it directly impacts coastal activities and ecosystems. Although global SLR is well-known, local values differ due to vertical land motion, and changes in atmospheric pressure, ocean currents and temperatures. Although a reliable estimation of local SLR trends is needed to assess coastal zone vulnerabilities and plan adaptation strategies, instrumental records are usually short or sparse, especially in developing countries. Here we show that 210Pb-dated sedimentary records from mangrove saltmarshes can provide useful decadal records of local SLR trends. We quantified sediment accretion rates in sediment cores from remote mangrove saltmarshes of the Yucatan Peninsula. Best SLR records were observed for cores collected near mean sea level (MSL). During most of the XX century the SLR rate ranged from 1-2 mm yr-1, increased to a maximum of 4.5 ± 0.6 mm yr-1 and the acceleration was 0.13 mm yr-2. Assuming either a constant SLR rate or acceleration, by the end of this century MSL level will be 39 cm or 91 cm above the present value. Both coastal infrastructures and ecosystems will be negatively affected by SLR and society will need to adapt relatively fast to the new conditions.
Increasingly frequent severe coral bleaching is among the greatest threats to coral reefs posed by climate change. Global climate models (GCMs) project great spatial variation in the timing of annual severe bleaching (ASB) conditions; a point at which reefs are certain to change and recovery will be limited. However, previous model-resolution projections (~1 × 1°) are too coarse to inform conservation planning. To meet the need for higher-resolution projections, we generated statistically downscaled projections (4-km resolution) for all coral reefs; these projections reveal high local-scale variation in ASB. Timing of ASB varies >10 years in 71 of the 87 countries and territories with >500 km2of reef area. Emissions scenario RCP4.5 represents lower emissions mid-century than will eventuate if pledges made following the 2015 Paris Climate Change Conference (COP21) become reality. These pledges do little to provide reefs with more time to adapt and acclimate prior to severe bleaching conditions occurring annually. RCP4.5 adds 11 years to the global average ASB timing when compared to RCP8.5; however, >75% of reefs still experience ASB before 2070 under RCP4.5. Coral reef futures clearly vary greatly among and within countries, indicating the projections warrant consideration in most reef areas during conservation and management planning.
Increasing disturbance frequency and severity on coral reefs has caused declines in the abundance of structurally complex corals and many fish species that depend on them. However, most studies have focused on the shallowest 10 m, despite coral habitat extending to >30 m in many regions. Reefs in deeper water and offshore locations are less exposed to many stressors associated with coral decline, and may offer a refuge for coral-associated fishes. Understanding how distributions and species-specific fish–habitat relationships vary along depth and distance-from-shore gradients is critical for assessing refuge potential. Here we examined the community structure, distributions and coral habitat associations of 123 reef fish species along a depth gradient from <1 to 40 m, from coastal to offshore reefs in Kimbe Bay, Papua New Guinea. Overall fish density and species richness declined with increasing depth but increased with distance offshore, such that deep offshore assemblages supported similar richness to shallow inshore sites. The most distinctive fish assemblage occurred at depths <1 m and ~25% of species were observed in only the shallowest 5 m. However, ~60% of species occurred at or below 20 m and 24% were broadly distributed from <1 to 30 m, with depth ranges of many species increasing with distance offshore. Strong relationships between fish abundance and coral habitat were observed, and 85% of species that were strongly associated with coral occurred at depths ≥20 m. Our results suggest that while many species are restricted to vulnerable shallow depths, deep offshore reefs provide a potential refuge for a substantial proportion of coral-associated fishes threatened by degradation of shallow coastal reefs, and deep reefs should be afforded greater consideration in conservation planning for coral reef fishes.
The Vulnerable Marine Ecosystems: Processes and Practices in the High Seas catalogues the achievements that have been made since 2006 on the identification and protection of vulnerable marine ecosystems (VMEs) from significant adverse impacts caused by fishing with bottom contact gears in the high seas. It is a consolidated output of the FAO VME Portal and DataBase (www.fao.org/in-action/vulnerable-marine-ecosystems/en/), which was requested by the UNGA in Resolution 61/105 (Paragraph 90) to support States and regional fisheries management organisations and arrangements (RFMO/As) in protecting VMEs.
The introductory chapter explains the international instruments applicable to the management of bottom fisheries in the high seas, the regional conventions and agreements establishing regional fisheries bodies, and the UNGA Resolutions pertaining to VMEs. This provides the global framework for managing certain fisheries to safeguard VMEs.
The main chapters describe the actions taken in the following ten regions: Atlantic Ocean (northwest, northeast, western central, central eastern, southwest and southeast), Mediterranean and Black Sea, Pacific Ocean (north and south), Indian Ocean, and Antarctic and Southern Ocean. These are divided into separate chapters. The regions approximate to the areas covered by RFMO/As, but also include regions where there are no regional management bodies. The seabed features are broadly described in each chapter to provide an indication as to where VMEs may be present and where they may overlap spatially with bottom fisheries. The functions and responsibilities of RFMO/As are described, as are detailed accounts of measures adopted and implemented to protect VMEs from significant adverse impacts by fisheries using bottom contact gears. The measures implemented by each regional body are divided into general measures that mostly apply to the whole region and are typically precautionary in nature to allow sustainable fisheries to continue in certain areas and to identify VME areas, and specific measures typically involving the closure of areas to bottom fishing that are known or likely to contain VMEs. Domestic measures applied by States to their flagged high seas fishing vessels are included when particularly relevant, such as in areas where there are no current measures from a regional body.
The final chapter synthesises the regional measures into a global summary and thus provides an overview of the various approaches that have been taken.
Unmanned aerial vehicles (UAVs) are being increasingly used in studies of marine fauna. Here, we tested the use of a UAV (DJI Phantom II®) to assess fine-scale variation in densities of 2 elasmobranchs (blacktip reef sharks Carcharhinus melanopterus and pink whiprays Himantura fai) on reef systems off Moorea (French Polynesia). We flew parallel transects designed to sample reef habitats (fringing, channel and sandflat habitats) across 2 survey blocks. Block 1 included a shark and ray provisioning site with potentially higher elasmobranch densities, whereas Block 2 most likely had lower densities with no provisioning activities. Across 10 survey days in July 2014, we flew 3 transects (400 m) within each survey block (n = 60 total transect passes). As expected, densities (animals ha-1) were significantly higher in Block 1 than in Block 2, particularly where provisioning activities occur. Differences between habitats surveyed were also found. Our study provides the first direct estimates of shark and ray densities in coral-reef ecosystems and demonstrates that UAVs can produce important fishery-independent data for elasmobranchs, particularly in shallow-water habitats.