Intertidal oyster reefs can protect estuarine shorelines from wave erosion and sea-level rise, and recognition of these ecosystem services has fueled global efforts to conserve and restore these reefs. Although intertidal oyster reefs are valued for attenuating wave erosion, little attention has been paid to the effects of wave exposure on their distribution. The present study characterized the role of wave exposure in determining the distribution of natural intertidal oyster reefs and of oysters on hardened shorelines (bulkhead and riprap revetments). Wave exposure was determined using the National Oceanic and Atmospheric Administration (NOAA)-developed Wave Exposure Model (WEMo), which integrates adjacent water depth, fetch, and processed wind information, among other variables. Field mapping of oyster reefs, defined as ≥10 oysters m−2, in Pamlico and Core sounds, North Carolina, USA, was conducted in summer 2014. Hardened shorelines and associated oyster densities were mapped for Pamlico Sound only. A narrow wave exposure threshold (~500 J m−1) was identified above which natural intertidal reefs did not occur and below which reef presence was apparently dependent on other structuring variables, such as salinity at the time of sampling and the grain size of surrounding sediments. Wave exposure was not correlated with the presence of oysters on hardened shorelines. The application of WEMo in the present study should be useful for selecting locations and materials for intertidal oyster reef restoration.
Distributions of Species
The distribution of oceanic cephalopod species is not fully understood but seabirds, which feed on cephalopods and cover vast oceanic areas, might work as samplers and mappers of the occurrence of this elusive group. We tracked 17 wandering albatrosses Diomedea exulans at Bird Island, South Georgia (54° S, 38° W) over the austral winter (breeding period) with GPS-loggers, activity recorders and stomach temperature probes. At logger retrieval, diet composition was accessed via stomach flushings of the tagged individuals. Wandering albatrosses captured circumpolar and rarer oceanic squid in all water masses of the Southern Ocean (i.e. Antarctic, sub-Antarctic and subtropical waters), complementing much of the knowledge about the cephalopod distribution in the Atlantic sector of the Southern Ocean. Some cephalopod species showed a distribution range wider than expected, with oceanic fronts not functioning as ecological barriers as previously thought. This suggests they might be capable of overcoming these frontal regimes and even take advantage of their dynamics as migration pathways.
Imagery collected from Autonomous Underwater Vehicles (AUVs) provides a novel means of monitoring changes in benthic ecosystems over large spatial scales and depth ranges. However, for many benthic ecosystems there is little baseline data to quantify temporal and spatial variance for key indicator species. This information is crucial for isolating background “noise” from long-term “signals”. Here we quantify components of variance for five key deep-water sessile invertebrate species across four long-term benthic monitoring sites in a region undergoing strong climate-driven changes. We use linear mixed models to estimate the contribution of sources of spatial and temporal variance in species covers from empirical data. We then combine this information with projected long-term climate-driven changes in the cover of these groups and test the power of various survey designs to detect change through time. Large short-term temporal and spatial variability in the cover of a gorgonian octocoral results in high components of variance that limit the detectability of the projected long-term trend for this species. Conversely, for three of the sponge species high power is achievable with revisits to the four original sites every two years until 2060. By including more sites in the revisit design, high power can be achieved with less frequent revisits. For the fifth species, we find high power is unachievable due to the small trend predicted. Overall, we highlight how examination of components of variance in a system can aid in the selection of suitable indicators and the establishment of effective monitoring programs.
The True’s beaked whale (Mesoplodon mirus, True 1913) is a poorly known member of the Ziphiidae family. Its distribution in the northern hemisphere is thought to be restricted to the temperate or warm temperate waters of the North Atlantic, while a few stranding records from the southern hemisphere suggest a wider and antitropical distribution, extending to waters from the Atlantic coast of Brazil to South Africa, Mozambique, Australia and the Tasman Sea coast of New Zealand. This paper (i) reports the first molecular confirmation of the occurrence of the True’s beaked whale at the southern limit of its distribution recorded in the northeast Atlantic: the Azores and Canary Islands (macaronesian ecoregion); (ii) describes a new colouration for this species using evidence from a whale with molecular species confirmation; and (iii) contributes to the sparse worldwide database of live sightings, including the first underwater video recording of this species and close images of a calf. Species identification was confirmed in two cases using mitochondrial DNA control region and cytochrome b gene markers: a subadult male True’s beaked whale that stranded in El Hierro, Canary Islands, in November 2012, and a subadult male found floating dead near Faial, the Azores, in July 2004. The whale that stranded in the Canary Islands had a clearly delimited white area on its head, extending posteriorly from the tip of the beak to cover the blowhole dorsally and the gular grooves ventrally. This colouration contrasts with previous descriptions for the species and it may be rare, but it exemplifies the variability of the colouration of True’s beaked whales in the North Atlantic, further confirmed here by live sightings data. The recording of several observations of this species in deep but relatively coastal waters off the Azores and the Canary Islands suggests that these archipelagos may be unique locations to study the behaviour of the enigmatic True’s beaked whale.
Artificial reefs (ARs) have long been practiced to manage and enhance fisheries resources worldwide. Here, we aimed to identify relevant indicator species for the specific environmental conditions of ARs by comparing fish diversity against control sites (Conts). We used a combination of non-metric multidimensional scaling and indicator value analysis to identify the indicator species of the specific AR environments. More individuals and species of fish were present in ARs compared to Conts. Water temperature over the seasons was the most important environmental factor associated with the trophic group composition of fish. In particular, macrocarnivores and benthic invertivores/cleaners closely reflected habitat conditions in a consistent manner. Some dominant fish species were detected at all sites, while the indicator species were more predominant under certain environmental conditions. Altogether, ARs should be monitored at regular intervals to optimize management of their health by detecting the community representativeness via indicator species.
One aim of Marine Protected Areas (MPAs) is to protect a representative portion of the environment through spatial closures to extractive practices such as fisheries. Although they usually involve the displacement of fisheries, their design rarely takes into account the effect of displacing that fishery on the target fish population. We used a spatially explicit population model of Antarctic toothfish in the Ross Sea region to investigate the effects of the endorsed Ross Sea region MPA on the fishery dynamics and the spatial distribution of the toothfish population. Our study indicates that the MPA will likely improve protection of the juvenile population residing on the Antarctic Shelf, while the number of areas with high levels of depletion is unlikely to increase compared to status quo management. Results also suggested a small increase in the catch limit under the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) harvest management rules, but with a slight reduction in catch rates. We have showed that spatial modelling tools can help inform MPA planning by simultaneously quantifying potential effects on the fish population and the ability to achieve conservation goals.
Given the major ongoing influence of environmental change on the oceans, there is a need to understand and predict the future distributions of marine species in order to plan appropriate mitigation to conserve vulnerable species and ecosystems. In this study we use tracking data from seven large seabird species of the Southern Ocean (Black-browed Albatross Thalassarche melanophris, Grey-headed Albatross T. chrysostoma, Northern Giant Petrel Macronectes halli, Southern Giant Petrel M. giganteus, Tristan Albatross Diomedea dabbenena Wandering Albatross D. exulans and White-chinned Petrel Procellaria aequinoctialis , and on fishing effort in two types of fisheries (characterised by low or high-bycatch rates), to model the associations with environmental variables (bathymetry, chlorophyll-a concentration, sea surface temperature and wind speed) through ensemble Species Distribution Models. We then project these distributions according to four climate change scenarios built by the Intergovernmental Panel for Climate Change for 2050 and 2100. The resulting projections were consistent across scenarios, indicating that there is a strong likelihood of poleward shifts in distribution of seabirds, and several range contractions (resulting from a shift in the northern, but no change in the southern limit of the range in four species). Current trends for southerly shifts in fisheries distributions are also set to continue under these climate change scenarios at least until 2100; some of these may reflect habitat loss for target species that are already over-fished. It is of particular concern that a shift in the distribution of several highly threatened seabird species would increase their overlap with fisheries where there is a high-bycatch risk. Under such scenarios, the associated shifts in distribution of seabirds and increases in bycatch risk will require much-improved fisheries management in these sensitive areas to minimise impacts on populations in decline.
Scientists increasingly rely on protected areas to assist in biodiversity conservation, yet the efficacy of these areas are rarely systematically assessed, often as a byproduct of underfunding, particularly in developing countries. Still, adaptive management strategies to maximize conservation success often rely on understanding the temporal and spatial dynamism of population therein. Environmental DNA (eDNA) has been employed as a time and cost-effective method to monitor species’ distribution, with quantitative PCR (qPCR) techniques also assisting in our knowledge about abundance of aquatic taxa. To date however, this novel methodology remains underutilized by conservation managers in assessing populations in protected areas. In this study, we used eDNA concentration of the critically endangered Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis) to circumscribe population ecology in the Tian e-Zhou National Nature Reserve in Hubei, China. We developed, validated, and optimized a qPCR-based eDNA method and applied this protocol to diagnose the geographical reserve use across seasons. Our results suggest spatio-temporal idiosyncrasies, highlighting previously undescribed site and habitat preferences, and a propensity for post-breeding population dispersal. eDNA thus presents a quick and cost-effective method for assessing population-wide utilization of a protected area and, when accounting for environmental-specific nuances, can prove useful for current and future conservation goals.
The natural, prehuman abundance of most large predators is unknown because of the lack of historical data and a limited understanding of the natural factors that control their populations. Determining the supportable predator biomass at a given location (that is, the predator carrying capacity) would help managers to optimize protection and would provide site-specific recovery goals. We assess the relationship between predatory reef fish biomass and several anthropogenic and environmental variables at 39 reefs across the Caribbean to (i) estimate their roles determining local predator biomass and (ii) determine site-specific recovery potential if fishing was eliminated. We show that predatory reef fish biomass tends to be higher in marine reserves but is strongly negatively related to human activities, especially coastal development. However, human activities and natural factors, including reef complexity and prey abundance, explain more than 50% of the spatial variation in predator biomass. Comparing site-specific predator carrying capacities to field observations, we infer that current predatory reef fish biomass is 60 to 90% lower than the potential supportable biomass in most sites, even within most marine reserves. We also found that the scope for recovery varies among reefs by at least an order of magnitude. This suggests that we could underestimate unfished biomass at sites that provide ideal conditions for predators or greatly overestimate that of seemingly predator-depleted sites that may have never supported large predator populations because of suboptimal environmental conditions.
A thorough understanding of movement patterns of a species is critical for designing effective conservation and management initiatives. However, generating such information for large marine vertebrates is challenging, as they typically move over long distances, live in concealing environments, are logistically difficult to capture and, as upper-trophic predators, are naturally low in abundance. Large-bodied, broadly distributed tropical shark typically restricted to coastal and shelf habitats, the great hammerhead shark Sphyrna mokarran epitomizes such challenges. Highly valued for its fins (in target and incidental fisheries), it suffers high bycatch mortality coupled with fecundity conservative life history, and as a result, is vulnerable to over-exploitation and population depletion. Although there are very little species-specific data available, the absence of recent catch records give cause to suspect substantial declines across its range. Here, we used biotelemetry techniques (acoustic and satellite), conventional tagging, laser-photogrammetry, and photo-identification to investigate the level of site fidelity/residency for great hammerheads to coastal areas in the Bahamas and U.S., and the extent of movements and connectivity of great hammerheads between the U.S. and Bahamas. Results revealed large-scale return migrations (3030 km), seasonal residency to local areas (some for 5 months), site fidelity (annual return to Bimini and Jupiter for many individuals) and numerous international movements. These findings enhance the understanding of movement ecology in great hammerhead sharks and have potential to contribute to improved conservation and management.