Short-term physical disturbances occur amid a backdrop of longer-term biotic interactions, including predation, which shape communities. Effects of consumer interactions typically begin in early stages of assembly and continue throughout post-disturbance recovery. Despite decades of predation and disturbance research, few studies examine how consumer interactions during these different time periods may affect community responses to disturbance. Here we use replicate communities of tropical, sessile invertebrates to ask whether fish predation during initial assembly (before) and recovery (after) influences community resistance to a hurricane-level low-salinity event. Results revealed that pre-event predation determined whether communities shifted in biomass and community structure following disturbance. Communities that assembled without predators responded to the low-salinity event strongly, with large shifts in community composition and a mean loss of 54% of pre-disturbance biomass after a one-month recovery period. In contrast, those that experienced predation during initial assembly were strikingly resistant to disturbance, which had no effect on species composition or biomass. Results were driven by predator removal of a dominant competitor, which gave rise to more disturbance-resistant communities. These findings highlight the potential for past trophic interactions to shape community stability in the face of physical disturbances predicted to escalate with global change.
There is an increasing concern that anthropogenic noise could have a significant impact on the marine environment, but there is still insufficient data for most invertebrates. What do they perceive? We investigated this question in oysters Magallana gigas (Crassostrea gigas) using pure tone exposures, accelerometer fixed on the oyster shell and hydrophone in the water column. Groups of 16 oysters were exposed to quantifiable waterborne sinusoidal sounds in the range of 10 Hz to 20 kHz at various acoustic energies. The experiment was conducted in running seawater using an experimental flume equipped with suspended loudspeakers. The sensitivity of the oysters was measured by recording their valve movements by high-frequency noninvasive valvometry. The tests were 3 min tone exposures including a 70 sec fade-in period. Three endpoints were analysed: the ratio of responding individuals in the group, the resulting changes of valve opening amplitude and the response latency. At high enough acoustic energy, oysters transiently closed their valves in response to frequencies in the range of 10 to <1000 Hz, with maximum sensitivity from 10 to 200 Hz. The minimum acoustic energy required to elicit a response was 0.02 m∙s-2 at 122 dBrms re 1 μPa for frequencies ranging from 10 to 80 Hz. As a partial valve closure cannot be differentiated from a nociceptive response, it is very likely that oysters detect sounds at lower acoustic energy. The mechanism involved in sound detection and the ecological consequences are discussed.
Implementation of an ecosystem approach to fisheries management (EAFM) for forage fish requires methods to evaluate tradeoffs associated with competing management objectives that focus on supporting fishery yields or providing food for predators. We developed an Ecopath with Ecosim ecosystem model of the U.S. Northwest Atlantic continental shelf (NWACS) for the period 1982–2013 to inform an EAFM for Atlantic Menhaden Brevoortia tyrannus. The model (with 61 trophic groups and 8 fishing fleets) was parameterized and fitted to time series using data from stock assessments, surveys, and literature. Fifty-year simulations evaluated how Atlantic Menhaden fishing mortality rates (F) influenced different ecosystem indicators, including population biomasses, fishery yields, prey-to-predator ratios, and the proportion of trophic groups that were positively or negatively affected. We quantified tradeoffs associated with a range of alternative ecosystem-based reference points for Atlantic Menhaden F and biomass (B), including F for maximum sustainable yield (FMSY), 0.5FMSY, proxies for current single-species Freference points, 75% of virgin unfished biomass (B0), and 40%B0. Striped Bass Morone saxatilis were most sensitive to increases in Atlantic Menhaden fishing, largely due to their strong dietary reliance on this prey species, but other higher-trophic-level groups (birds, highly migratory species, sharks, and marine mammals) were also negatively impacted. Other commercially important predators of Atlantic Menhaden (e.g., Bluefish Pomatomus saltatrix and Weakfish Cynoscion regalis) had moderate to negligible responses at the highest levels of Atlantic Menhaden F. The alternative reference points considered resulted in (1) variable Atlantic Menhaden biomasses (40–75% of B0) and yields (54–100% of MSY), (2) up to a 60% decline in Striped Bass B and yield, (3) negative impacts on the B of ≤13% of modeled groups, and (4) positive impacts on the B of ≤6% of modeled groups. Simulations demonstrated the varied responses, potential winners and losers, and tradeoffs resulting from alternative management strategies for Atlantic Menhaden. These results and the NWACS model can help to advance an EAFM for Atlantic Menhaden and other fishes.
Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) is an endangered species that migrate through, and occupy the coastal waters of the mid-Atlantic Bight where they interact with anthropogenic activities. Measures to understand and avoid Atlantic sturgeon that take into consideration the dynamic nature of their habitat may reduce harmful interactions. In this study, we matched fisheries independent biotelemetry observations of Atlantic sturgeon with daily satellite observations to construct a time resolved spatial distribution model of Atlantic sturgeon. We determined that depth, day-of-year, sea surface temperature, and light absorption by seawater were the most important predictors of Atlantic sturgeon occurrence. Demographic factors, such as sex and river-of-origin were of secondary importance. We found strong spatial differences in spring and fall migration patterns, when anthropogenic interactions peak. Our cross-validated models correctly identified > 88% of biotelemetry observations in our study region. Our models also correctly identified ∼64% of bycatch observations throughout the year. However, during their migrations, when harmful interactions were highest, our models correctly identified ∼90% of fisheries dependent observations. We suggest that this model can be used for guidance to managers and stakeholders to reduce interactions with this highly imperiled species, thereby enhancing conservation and recovery efforts.
Fishery species that reside in no-take, marine reserves often show striking increases in size and abundance relative to harvested areas, with the potential for larval spillover to harvested populations. The benefits of spillover, however, may not be realized if the populations or habitats outside of reserves are too degraded. We quantified oyster population density and demographics such as recruitment, growth, mortality, and potential larval output as a function of two types of oyster management strategies in Pamlico Sound, North Carolina, USA: (1) natural reefs + harvested and (2) restored reefs + harvested. We compared these data to demographic data collected as a function of a third type of management strategy, (3) restored reefs + protected from harvest. Mean oyster recruitment was ~12 times higher in restored + harvested reefs than in natural + harvested reefs. Mean total oyster density was ~8- to 72-times higher in restored + protected reefs than in restored + harvested or natural + harvested reefs, respectively. Moreover, harvested reefs exhibited truncated size structure, and few or no individuals greater than legal size (75 mm), whereas protected reefs typically had a polymodal size structure, including many large individuals. We estimate that restored + protected reefs have ~4 to 700 times greater potential larval output m−2 than restored + harvested or natural + harvested reefs, respectively. After accounting for total sound-wide areal coverage of each reef type, total potential larval output from restored + protected reefs was ~6 times greater than that from natural + harvested and restored + harvested reefs. Marine reserves can potentially subsidize harvested populations via larval spillover, however, in the case of oyster reefs in Pamlico Sound, the relatively degraded conditions of natural reefs (e.g., low vertical relief, low shell volume per square meter) may not provide much in the way of suitable settlement substrate to realize the benefits of larval spillover from reserves. Restoration of oyster reefs, even with a thin veneer of substrate, may improve settlement substrate to increase the benefits of larval spillover from reserves.
Vulnerable marine ecosystems (VMEs) are ecosystems at risk from the effects of fishing or other kinds of disturbance, as determined by the vulnerability of their components (e.g., habitats, communities, or species). Habitat suitability modeling is being used increasingly to predict distribution patterns of VME indicator taxa in the deep sea, where data are particularly sparse, and the models are considered useful for marine ecosystem management. The Louisville Seamount Chain is located within the South Pacific Regional Fishery Management Organization (SPRFMO) Convention Area, and some seamounts are the subject of bottom trawling for orange roughy by the New Zealand fishery. The aim of the present study was to produce high-resolution habitat suitability maps for VME indicator taxa and VME habitat on these seamounts, in order to evaluate the feasibility of designing within-seamount spatial closures to protect VMEs. We used a multi-model habitat suitability mapping approach, based on bathymetric and backscatter data collected by multibeam echo sounder survey, and data collected by towed underwater camera for the stony coral and habitat-forming VME indicator species Solenosmilia variabilis, as well as two taxa indicative of stony coral habitat (Brisingida, Crinoidea). Model performance varied among the different model types used (Boosted Regression Tree, Random Forest, Generalized Additive Models), but abundance-based models consistently out-performed models based on presence-absence data. Uncertainty for ensemble models (combination of all models) was lower overall compared to the other models. Maps resulting from our models showed that suitable habitat for S. variabilis is distributed around the summit-slope break of seamounts, and along ridges that extend down the seamount flanks. Only the flat, soft sediment summits are predicted to be unsuitable habitat for this stony coral species. We translated a definition for stony coral-reef habitat into a S. variabilis abundance-based threshold in order to use our models to map this VME habitat. These maps showed that coral-reef occurred in small and isolated patches, and that most of the seabed on these seamounts is predicted to be unsuitable habitat for this VME. We discuss the implications of these results for spatial management closures on the Louisville Seamount Chain seamounts and the wider SPRFMO area, and future modeling improvements that could aid efforts to use habitat suitability maps for managing the impact of fishing on VMEs.
The Marine Strategy Framework Directive (MSFD) aims to achieve “Good Environmental Status” (GES) in EU marine waters by 2020. This initiative started its first phase of implementation in 2012, when each member state defined the GES and environmental targets in relation to 11 descriptors and related indicators for 2020. In 2013, the EU Commission launched the reformed Common Fisheries Policy (CFP), which aims to achieve biomass levels capable of producing maximum sustainable yield (MSY) for all commercial stocks exploited in EU waters by 2020, as well as contribute to the achievement of GES. These two pieces of legislation are aligned since according to Descriptor 3 (commercial fish and shellfish), the MSFD requires reaching a healthy stock status with fishing mortality (F) and spawning stock biomass (SSB) compatible with the respective MSY reference limits for all commercial species by 2020. We investigated whether the two policies are effectively aligned in the Mediterranean Sea, an ecosystem where the vast majority of stocks show unsustainable exploitation. For this purpose, we assessed and compared the number and typology of stocks considered by the member states when assessing GES in relation to data on stocks potentially available according to the EU Data Collection Framework (DCF) and the proportion of landings they represented. The number of stocks considered by the member states per assessment area was uneven, ranging between 7 and 43, while the share of landings corresponding to the selected stocks ranged from 23 to 95%. A lack of coherence between GES definitions among the member states was also revealed, and environmental targets were less ambitious than MSFD and CFP requirements. This could possibly reduce the likelihood of achieving fishery sustainability in the Mediterranean by 2020. These conditions limited the envisaged synergies between the two policies and are discussed in consideration of the recent Commission Decision on criteria and methodological standards for GES.
The Canary Islands, as many islands and coastal regions, are characterized by no conventional energy sources (but renewable resources, mainly wind and solar), by a high population density and land scarcity. Taking into account this context, it is crucial to determine the offshore wind energy potential as a first step for the energy planning. For this purpose, a methodology adapted to islands’ and coastal regions’ requirements has been developed. The methodology is based on GIS (Geographical Information Systems), and takes into account technical, economic and spatial constrains. Wind turbines (bottom-fixed or floating according to the bathymetry) are placed within the resulting suitable areas, quantifying also the energy production and its cost. The economic analysis includes the calculation of the LCOE (Levelized Cost Of Energy), including integration costs, and the resulting resource cost curves. The methodology has been applied to a practical case, the Canary Islands. Results show that the electricity produced by offshore wind farms exceeds the yearly electricity demand. Moreover, the offshore wind energy cost is lower than the current electricity cost. The analysis provides further useful indicators such as percentage of suitable areas, surface covered by wind turbines, array density of turbines and marginal offshore wind energy cost.
- Reef sharks are declining world-wide under ever-increasing fishing pressure, with potential consequences on ecosystem functioning. Marine protected areas (MPAs) are currently one of the management tools used to counteract the pervasive impacts of fishing. However, MPAs in which reef sharks are abundant tend to be located in remote and underexploited areas, preventing a fair assessment of management effectiveness beyond remoteness from human activities.
- Here, we determine the conditions under which MPAs can effectively protect sharks along a wide gradient of reef accessibility, from the vicinity of a regional capital towards remote areas, using 385 records from baited remote underwater video systems and 2,790 underwater visual censuses performed in areas open to fishing and inside 15 MPAs across New Caledonia (South-Western Pacific).
- We show that even one of the world's oldest (43 years), largest (172 km2) and most restrictive (no-entry) MPA (Merlet reserve) on coral reefs has between 17.3% and 45.3% fewer shark species and between 37.2% and 79.8% fewer shark abundance than remote areas in a context where sharks are not historically exploited.
- On coral reefs situated at less than 1 hr of travel time from humans, shark populations are so low in abundance (less than 0.05 individuals per 1,000 m2) that their functional roles are severely limited.
- Synthesis and applications. Remote areas are the last sanctuaries for reef sharks, providing a new baseline from which to evaluate human impacts on the species. However, there is no equivalent close to human activities even in large, old and strongly restrictive marine protected areas. As such sharks deserve strong protection efforts. The large, no-entry marine protected areas, close to humans, offer limited benefits for reef shark populations, but provide more realistic conservation targets for managers of human-dominated reefs. The exclusion of human activities on a sufficiently large area is key to protect reef shark populations. However, this strategy remains difficult to apply in many countries critically depending on reef resources for food security or livelihood.
The increasing amount of plastic littered into the sea may provide a new substratum for benthic organisms. These marine fouling communities on plastic have not received much scientific attention. We present, to our knowledge, the first comprehensive analysis of their macroscopic community composition, their primary production and the polymer degradation comparing conventional polyethylene (PE) and a biodegradable starch-based plastic blend in coastal benthic and pelagic habitats in the Mediterranean Sea. The biomass of the fouling layer increased significantly over time and all samples became heavy enough to sink to the seafloor. The fouling communities, consisting of 21 families, were distinct between habitats, but not between polymer types. Positive primary production was measured in the pelagic, but not in the benthic habitat, suggesting that large accumulations of floating plastic could pose a source of oxygen for local ecosystems, as well as a carbon sink. Contrary to PE, the biodegradable plastic showed a significant loss of tensile strength and disintegrated over time in both habitats. These results indicate that in the marine environment, biodegradable polymers may disintegrate at higher rates than conventional polymers. This should be considered for the development of new materials, environmental risk assessment and waste management strategies.