Showing papers in "Marine Ecology Progress Series in 2015"

Marine animal behaviour in a high CO2 ocean

Abstract: Recently, the effects of ocean acidification (OA) on marine animal behaviour have garnered considerable attention, as they can impact biological interactions and, in turn, eco system structure and functioning. We reviewed current published literature on OA and marine behaviour and synthesize current understanding of how a high CO2 ocean may impact animal behaviour, elucidate critical unknowns, and provide suggestions for future research. Although studies have focused equally on vertebrates and invertebrates, vertebrate studies have primarily focused on coral reef fishes, in contrast to the broader diversity of invertebrate taxa studied. A quantitative synthesis of the direction and magnitude of change in behaviours from current conditions under OA scenarios suggests primarily negative impacts that vary depending on species, ecosystem, and behaviour. The interactive effects of co-occurring environmental parameters with increasing CO2 elicit effects different from those observed under elevated CO2 alone. Although 12% of studies have incorporated multiple factors, only one study has examined the effects of carbonate system variability on the behaviour of a marine animal. Altered GABAA receptor functioning under elevated CO2 appears responsible for many behavioural responses; however, this mechanism is unlikely to be universal. We recommend a new focus on determining the effects of elevated CO2 on marine animal behaviour in the context of multiple environmental drivers and future carbonate system variability, and the mechanisms governing the association between acid-base regulation and GABAA receptor functioning. This knowledge could explain observed species-specificity in behavioural responses to OA and lend to a unifying theory of OA effects on marine animal behaviour.

Herbivory and the Resilience of Caribbean Coral Reefs: Knowledge Gaps and Implications for Management

Abstract: Herbivory is a key process on coral reefs that can facilitate reef-building corals by excluding algae that otherwise negatively impact coral settlement, growth, and survivorship Over the last several de cades, coral cover on Caribbean reefs has declined precipitously On many reefs, large structurally complex corals have been replaced by algae and other non-reef-building or- ganisms, resulting in the collapse of physical structure and the loss of critical ecosystem services The drivers of coral decline on Caribbean reefs are complex and vary among locations On many reefs, populations of key her- bivores have been greatly reduced by disease and over- fishing, and this has resulted in the proliferation of algae that hinder coral recovery following major disturbances Yet, evidence that increases in herbivory can promote coral recovery on Caribbean reefs has been mixed Here, we discuss key contingencies that will modify the rela- tionships between herbivores, algae, and corals and identify critical knowledge gaps that limit our ability to predict when and where herbivores are most likely to facili tate coral persistence and recovery Impacts of her- bivores on coral reef ecosystems will vary greatly in space and time and will depend on herbivore diversity and species identity While there are still a large number of knowledge gaps, we make several management rec- ommendations based on our current understanding of the processes that structure reef ecosystems Reversing the fate of Caribbean coral reefs will require the de - velopment of integrated management strategies that simultaneously address multiple stressors in addition to the impacts of fisheries on herbivore assemblages

Spatial scale and geographic context in benthic habitat mapping: review and future directions

Abstract: Understanding the effects of scale is essential to the understanding of natural eco - systems, particularly in marine environments where sampling is more limited and sporadic than in terrestrial environments. Despite its recognized importance, scale is rarely considered in benthic habitat mapping studies. Lack of explicit statement of scale in the literature is an impediment to better characterization of seafloor pattern and process. This review paper highlights the impor- tance of incorporating ecological scaling and geographical theories in benthic habitat mapping. It reviews notions of ecological scale and benthic habitat mapping, in addition to the way spatial scale influences patterns and processes in benthic habitats. We address how scale is represented in geographic data, how it influences their analysis, and consequently how it influences our under- standing of seafloor ecosystems. We conclude that quantification of ecological processes at multi- ple scales using spatial statistics is needed to gain a better characterization of specieshabitat relationships. We offer recommendations on more effective practices in benthic habitat mapping, including sampling that covers multiple spatial scales and that includes as many environmental variables as possible, adopting continuum-based habitat characterization approaches, using statistical analyses that consider the spatial nature of data, and explicit statement of the scale at which the research was conducted. We recommend a set of improved standards for defining benthic habitat. With these standards benthic habitats can be defined as 'areas of seabed that are (geo)statistically significantly different from their surroundings in terms of physical, chemical and biological characteristics, when observed at particular spatial and temporal scales'.

Similar effects of bottom trawling and natural disturbance on composition and function of benthic communities across habitats

Abstract: Bottom trawl fishing has widespread impacts on benthic habitats and communities. The benthic response to trawling seems to be smaller or absent in areas exposed to high natural disturbance, leading to the hypothesis that natural and trawl disturbance affect benthic communities in a similar way. However, systematic tests of this hypothesis at large spatial scales and with data from sites spanning a large range of natural disturbance do not exist. Here, we examine the effects of trawl and natural (tidal-bed shear stress) disturbance on benthic communities over gradients of commercial bottom trawling effort in 8 areas in the North and Irish Seas. Using a trait-based approach, that classified species by life-history strategies or by characteristics that provide a proxy for their role in community function, we found support for the hypothesis that trawl and natural disturbance affect benthic communities in similar ways. Both sources of disturbance caused declines in long-living, hard-bodied (exoskeleton) and suspension-feeding organisms. Given these similar impacts, there was no detectable trawling effect on communities exposed to high natural disturbance. Conversely, in 3 out of 5 areas with low bed shear stress, responses to trawling were detected and resulted in community compositions comparable with those in areas subject to high natural disturbance, with communities being composed of either small-sized, deposit-feeding animals or mobile scavengers and predators. The findings highlight that knowledge of the interacting effects of trawl and natural disturbance will help to identify areas that are more or less resilient to trawling and support the development of management plans that account for the environmental effects of fishing.

Invasive Pacific lionfish Pterois volitans reduce abundance and species richness of native Bahamian coral-reef fishes

Abstract: Pacific red lionfish Pterois volitans, introduced to Atlantic waters in the 1980s, represent a particularly successful invasive marine predator with strong effects on native prey. Previous experiments examining the effects of lionfish on native fish communities have been conducted on small patch reefs. However, the effects of lionfish on native reef-fish communities over larger spatial scales — scales at which conservation and management efforts are typically applied — have not been examined experimentally. Beginning in June 2009, I conducted a large-scale field experiment near Lee Stocking Island, Bahamas. Ten large (1400 to 4000 m2) coral reefs were paired based on location and similarity of habitat, and baseline surveys of their fish communities were conducted. Quarterly removals of lionfish were then conducted on 1 reef in each pair, while the densities of lionfish on the other reefs were standardized at typical post-invasion levels. Through August 2010, quarterly surveys showed that lionfish caused significant changes in native reef-fish communities, including reductions in the total density (up to 46.3 ± 13.7%, mean ± SEM), biomass (31.9 ± 10.7%), and species richness (21.4 ± 9.1%) of prey-sized fishes (all individuals <10 cm total length). Lionfish also caused substantial reductions in the biomass of prey-sized herbivorous fishes (33.9 ± 16.0%) and piscivores (98.6 ± 39.5%). However, these negative effects on small fish did not translate to observable declines in a larger size-class (all individuals 10 to 20 cm total length) over the 14 mo study period.

Coral reef species assemblages are associated with ambient soundscapes

Abstract: Coral reefs provide a wide array of ecosystem services and harbor some of the highest levels of biodiversity on the planet, but many reefs are in decline worldwide. Tracking changes is necessary for effective resource management. Biological sounds have been suggested as a means to quantify ecosystem health and biodiversity, but this requires an understanding of natural bioacoustic variability and relationships to the taxa present. This investigation sought to characterize spatial and temporal variation in biological sound production within and among reefs that varied in their species assemblages. Multiple acoustic recorders were deployed for intensive 24 h periods and longer-term (~4 mo) duty-cycled deployments on 3 reefs that varied in coral cover and fish density. Short-term results suggest that while there were statistically significant acoustic differences among recorders on a given reef, these differences were relatively small, indicating that a single sensor may be suitable for acoustic characterization of reefs. Analyses of sounds recorded over approximately 4 mo indicated that the strength of diel trends in a low frequency fish band (100 to 1000 Hz) was correlated with coral cover and fish density but the strength of highfrequency snapping shrimp (2 to 20 kHz) trends was not, suggesting that low-frequency recordings may be better indicators of the species assemblages present. Power spectra varied within reefs over the deployment periods, underscoring the need for long-duration recordings to characterize these trends. These findings suggest that, in spite of considerable spatial and temporal variability within reef soundscapes, diel trends in low-frequency sound production correlate with reef species assemblages.

Movements and foraging of predators associated with mesophotic coral reefs and their potential for linking ecological habitats

Abstract: Marine predators will often perform diel and seasonal movements associated with specific habitats. In tropical areas, mesophotic coral reefs may be an important habitat type for many predators, but their use of these areas has rarely been investigated. We used results of acoustic telemetry and stable isotope analyses to investigate the diel and seasonal movements of Galapagos sharks Carcharhinus galapagensis and giant trevally Caranx ignobilis captured from a mesophotic reef (depth: 50 to 70 m) at an uninhabited Pacific atoll. All predators associated with mesophotic reefs performed horizontal and vertical movements over seasonal and diel time frames. Galapagos sharks performed reverse diel vertical movements, diving deeper during the night than during the day, while giant trevally displayed a mix, with some individuals performing regular diel movements (deep during the day, shallow at night) and others performing reverse vertical diel movements. Trevally used very shallow water during the summer spawning periods. The isotopic compositions of predators suggest they primarily forage in shallow reefs, although approximately 35% of resources came from mesophotic reefs. Similar to their variability in vertical movement strategies, giant trevally occupied a wide range of trophic positions, potentially due to individual specialization in diet and high levels of intra-specific competition. Mesophotic reefs may provide some prey to upper level predators but also serve as a refuge habitat. The frequent movements between habitats suggest that marine predators may function as significant trans- porters of nutrients, particularly from shallow to mesophotic reefs.

Seasonal and interannual phytoplankton production in a sub-Arctic tidewater outlet glacier fjord, SW Greenland

Abstract: This study describes seasonal patterns and proposes likely drivers of an unusual phytoplankton primary production pattern in the outer-sill region of a tidewater outlet glacier- influenced fjord (Godthabsfjord) in SW Greenland. It is based on monthly measurements of pelagic primary production and hydrographic conditions during a 7 yr period. Total annual primary production during 2005 to 2012 was between 84.6 and 139.1 g C m �2 yr �1 . Two phyto- plankton blooms of similar magnitude reoccur in the fjord every year. A 'classical' spring bloom of up to 1743 mg C m �2 d �1 occurred in late April/early May in a water column almost fully mixed due to tidal forces at the fjord sill. After the spring bloom, primary production decreased in June, after which a summer bloom of up to 1383 mg C m �2 d �1 built up. This bloom coincided with the devel- opment of a pycnocline caused by substantial runoff from the Greenland Ice Sheet every year during midsummer. This observation supports a hypothesis that fjord circulation modes and subglacial freshwater discharge, leading to upwelling of nutrient rich water, stimulate primary production in the fjord. Future changes in the timing or magnitude of meltwater runoff from the Greenland Ice Sheet are thus likely to affect phytoplankton dynamics in the fjord.

Sexual segregation in a wide-ranging marine predator is a consequence of habitat selection

Abstract: Sexual segregation, common in many species, is usually attributed to intra-specific competi- tion or habitat choice. However, few studies have simultaneously quantified sex-specific foraging be- haviour and habitat use. We combined movement, diving, stable isotope and oceanographic data to test whether sexual segregation in northern gannets Morus bassanus results from sex-specific habitat use. Breeding birds foraging in a seasonally stratified shelf sea were tracked over 3 consecutive breeding seasons (2010�2012). Females made longer trips, foraged far- ther offshore and had lower δ 13 C values than males. Male and female foraging areas overlapped only slightly. Males foraged more in mixed coastal waters, where net primary production (NPP) was relatively high (>3 mg C m �2 d �1 ) and sea-surface temperature (SST) was relatively low ( 15°C) more than females, possibly as a consequence of foraging in productive mixed waters over offshore banks. Females foraged most frequently in stratified offshore waters, of intermediate SST (12�15°C), but exhibited no consistent response to NPP. Sex-specific differences in diving behaviour corresponded with differences in habitat use: males made more long and deep U- shaped dives. Such dives were characteristic of inshore foraging, whereas shorter and shallower V-shaped dives occurred more often in offshore waters. Heavier birds attained greater depths during V-shaped dives, but even when controlling for body mass, females made deeper V-shaped dives than males. Together,

An integrated ecosystem approach for assessing the potential role of cultivated bivalve shells as part of the carbon trading system

Abstract: The role of bivalve mariculture in the CO2 cycle has been commonly evaluated as the balance between respiration, shell calcium carbonate sequestration and CO2 release during bio- genic calcification. However, this approach neglects the ecosystem implications of cultivating bi- valves at high densities, e.g. the impact on phytoplankton dynamics and benthicpelagic coupling, which can significantly contribute to the CO2 cycle. Therefore, an ecosystem approach that accounts for the trophic interactions of bivalve aquaculture, including dissolved and particulate or- ganic and inorganic carbon cycling, is needed to provide a rigorous assessment of the role of bivalve mariculture in the CO2 cycle. On the other hand, the discussion about the inclusion of shells of cultured bivalves into the carbon trading system should be framed within the context of ecosystem goods and services. Humans culture bivalves with the aim of producing food, not se- questering CO2 in their shells, therefore the main ecosystem good provided by bivalve aquaculture is meat production, and shells should be considered as by-products of this human activity. This reasoning provides justification for dividing up respired CO2 between meat and shell when con- structing a specific bivalve CO2 budget for potential use of bivalve shells in the carbon trading sys- tem. Thus, an integrated ecosystem approach, as well as an understanding of the ecosystems goods and services of bivalve aquaculture, are 2 essential requisites for providing a reliable assessment of the role of bivalve shells in the CO2 cycle.

Post-release survival of juvenile silky sharks captured in a tropical tuna purse seine fishery

Abstract: Juvenile silky sharks Carcharhinus falciformis comprise the largest component of the incidental elasmobranch catch taken in tropical tuna purse seine fisheries. During a chartered cruise on board a tuna purse seine vessel conducting typical fishing operations we investigated the post-release survival and rates of interaction with fishing gear of incidentally captured silky sharks using a combination of satellite linked pop-up tags and blood chemistry analysis. To identify trends in survival probability and the point in the fishing interaction when sharks sustain the injuries that lead to mortality, sharks were sampled during every stage of the fishing procedure. The total mortality rates of silky sharks captured in purse seine gear was found to exceed 84%. We found survival to precipitously decline once the silky sharks had been confined in the sack portion of the net just prior to loading. Additionally, shark interactions recorded by the scientists were markedly higher than those recorded by vessel officers and the fishery observer. Future efforts to reduce the impact of purse seine fishing on silky shark populations should be focused on avoidance or releasing sharks while they are still free swimming.

Changes in pteropod distributions and shell dissolution across a frontal system in the California Current System

Abstract: We tested the sensitivity of the vertical distributions and shell dissolution patterns of thecosome pteropods to spatial gradients associated with an eddy-associated front in the southern California Current System. The aragonite saturation horizon (Ωarag = 1.0) shoaled from >200 to 1.4, while peak dissolution occurred in depths where Ωarag = 1.0 to 1.4. Vertical habitat compression and increased shell dissolution may be expected to accompany future shoaling of waters that are undersaturated with respect to aragonite.

Soundscapes and living communities in coral reefs: Temporal and spatial variation

Abstract: Acoustic landscapes, or soundscapes, can vary due to biological (‘biophony’), geophysical (‘geophony’) and anthropogenic (‘anthrophony’) components, and in some environments, such as many coral reefs, biophony dominates the soundscape. We compared 126 sound recordings from 3 different times of day (day, dusk and night) at 42 locations with concurrent fish and habitat surveys to investigate the relationships of acoustic parameters with biological and physical characteristics of coral reefs in the Gambier Archipelago, French Polynesia. Principal Component Analysis revealed that most of the variability in soundscapes could be described using only 4 factors: (1) full bandwidth root mean squared sound pressure level (SPL; 0.01 to 22.5 kHz in dB re 1 μPa); SPL of frequencies (2) >0.63 kHz and (3) between 0.16 and 2.5 kHz; and (4) the number of snaps made by snapping shrimp. Number of snaps in a recording and SPL above 0.63 kHz were negatively related to live coral cover, and the density and diversity of adult and juvenile fish, but positively related to dead coral cover and time of day (as the day progressed from day to dusk to night). Full bandwidth SPL and midrange SPL were positively related to sea state, depth, Porites coral, the coral forms ‘branched’ and ‘massive’ and whether the bottom was coverd by coral (live or dead). Soundscape recordings can contribute to a more complete assessment of ecological landscapes and, in cases where logistical constraints preclude traditional survey methods, passive acoustic monitoring may give valuable information on whether habitats are changing over time.

Extreme increases in natural mortality prevent recovery of collapsed fish populations in a Northwest Atlantic ecosystem

Abstract: Improved understanding of the dynamics of populations at low abundance is needed in the face of global biodiversity loss. We examined the dynamics of depleted demersal fish populations in the southern Gulf of St. Lawrence, Canada. Twenty years ago, a number of these populations collapsed due to overexploitation. Since then, others have declined to low abundance. Despite negligible levels of fishing mortality and strong rates of production of small juvenile fish, these populations have shown no sign of recovery and some continue to decline. Lack of recovery is due to dramatic increases in the natural mortality of larger individuals in these populations. In some of these fishes, natural mortality has risen to levels typical of high-turnover forage fishes rather than long-lived demersal fishes. We hypothesize that these high levels of mortality reflect a ‘predator pit’ or predation-driven Allee effect, resulting from the severely depleted abundance of these fishes and the high and rising abundance of their marine mammal predators, in particular grey seals. Recovery of collapsed demersal fish populations does not appear to be possible under current conditions in this ecosystem, even in the absence of fishing. Our results indicate a need for more precautionary management regimes in order to avoid population collapses that are not reversible by reducing exploitation.

Shark and ray provisioning functional insights into behavioral, ecological and physiological responses across multiple scales

Abstract: The use of olfactory stimuli and the provision of food are a common practice to prompt artificial aggregations of emblematic wild species and ensure the economic viability of the wildlife-watching industry. Several elasmobranch species have been targeted by such operations in a variety of locations for over 4 decades. A recent review succinctly addressed the potential effects of shark diving tourism, including shark provisioning, on shark individual behavior and ecology, but the paucity of data on the ecology of elasmobranchs precluded general statements. By using a functional framework, we reviewed the findings of the 22 available studies that investigated the behavioral, physiological, and ecological response of 14 shark and 3 ray species targeted by artificial provisioning. Focusing on the underlying processes that rule the response of targeted elasmobranch species, we report further effects acting beyond the individual scale. We suggest that the most commonly described alterations of individual movement patterns have cascading effects through the group and community scales, ultimately resulting in altered health condition and individual behavior toward humans. We conclude by stressing the potential for provisioning activities to support the investigation of complex ecological and behavioral processes in elasmobranchs.

Differing responses of three Southern Ocean Emiliania huxleyi ecotypes to changing seawater carbonate chemistry

Abstract: The invasion of anthropogenic carbon dioxide into the surface ocean is altering seawater carbonate speciation, a process commonly called ocean acidification. The high latitude waters of the Southern Ocean are one of the primary and most severely affected regions. Coccolithophores are an important phytoplankton group, responsible for the majority of pelagic calcium carbonate production in the world’s oceans, with a distribution that ranges from tropical to polar waters. Emiliania huxleyi is numerically the most abundant coccolithophore species and appears in several different ecotypes. We tested the effects of ocean acidification on 3 carefully selected E. huxleyi ecotypes isolated from the Southern Ocean. Their responses were measured in terms of growth, photosynthesis, calcification, cellular geometry, and stoichiometry. The 3 ecotypes exhibited differing sensitivities in regards to seawater carbonate chemistry when cultured at the same temperature (14°C) and continuous light (110 µmol photons m-2 s-1). Under future ocean acidification scenarios, particulate inorganic to organic carbon ratios (PIC:POC) decreased by 38-44, 47-51 and 71-98% in morphotype A ‘over-calcified’ (A o/c), A and B/C, respectively. All ecotypes reduced their rate of calcification, but the cold-water adapted ecotype (morphotype B/C) was by far the most sensitive, and almost ceased calcification at partial pressure of carbon dioxide ( pCO2) levels above 1000 µatm. We recommend that future surveys for E. huxleyi cells in the Southern Ocean should include the capability of recognising ‘naked cells’ by molecular and microscopic tools. The distinct differences in the physiological responses of these 3 dominant Southern Ocean coccolithophore ecotypes are likely to have consequences for future coccolithophore community structures and thereby the Southern Ocean carbon cycle.

Influence of environmental variability and age on the body condition of small pelagic fish in the Gulf of Lions

Abstract: Endogenous and environmental variables are fundamental in explaining variations in fish condition. Based on more than 20 yr of fish weight and length data, relative condition indices were computed for anchovy and sardine caught in the Gulf of Lions. Classification and regression trees (CART) were used to identify endogenous factors affecting fish condition, and to group years of similar condition. Both species showed a similar annual cycle with condition being minimal in February and maximal in July. CART identified 3 groups of years where the fish populations generally showed poor, average and good condition and within which condition differed between age classes but not according to sex. In particular, during the period of poor condition (mostly recent years), sardines older than 1 yr appeared to be more strongly affected than younger individuals. Time-series were analyzed using generalized linear models (GLMs) to examine the effects of oceanographic abiotic (temperature, Western Mediterranean Oscillation [WeMO] and Rhone outflow) and biotic (chlorophyll a and 6 plankton classes) factors on fish condition. The selected models explained 48 and 35% of the variance of anchovy and sardine condition, respectively. Sardine condition was negatively related to temperature but positively related to the WeMO and mesozooplankton and diatom concentrations. A positive effect of mesozooplankton and Rhone runoff on anchovy condition was detected. The importance of increasing temperatures and reduced water mixing in the NW Mediterranean Sea, affecting planktonic productivity and thus fish condition by bottom-up control processes, was highlighted by these results. Changes in plankton quality, quantity and phenology could lead to insufficient or inadequate food supply for both species.

Behavioural drivers of the ecological roles and importance of marine mammals

Abstract: Marine mammals feed at a variety of trophic levels, occur from freshwater to openocean ecosystems and are found across virtually all latitudes. Due to their high historical, and sometimes present-day, abundances, capability for large-scale movements and high metabolic rates, they have the potential to affect the structure and function of ecosystems through a variety of mechanisms over both ecological and evolutionary time. Usually, the effects of marine mammals on ecosystems are explicitly or implicitly considered to occur through their ability to remove prey through direct predation. Recent empirical studies and a rich theoretical framework, however, demonstrate that marine mammals can affect ecosystems through more diverse pathways, including those that are driven by marine mammal behaviour. Thus, non-consumptive effects of and on marine mammals may be critical in shaping their ecological importance. Nonconsumptive effects may include risk effects, whereby predators induce costly changes to prey behaviour that impact prey population sizes or the magnitude and spatiotemporal patterns of prey impacts on communities (e.g. behaviour-mediated trophic cascades). Changes in the abundance of large apex predators (both marine mammals and sharks) and the introduction of perceived and real risks (human disturbance) may also affect behaviours of marine mammals and their prey that cascade to the wider ecosystem; the conditions under which such cascading effects might be most important, however, remain poorly understood. Other behaviour-driven ecological roles of marine mammals may include foraging tactics that facilitate the foraging of other species (especially seabirds), translocating nutrients and linking the dynamics of spatially distinct food webs.

Unravelling the ecological role and trophic relationships of uncommon and threatened elasmobranchs in the western Mediterranean Sea

Abstract: Deficiencies in basic ecological information on uncommon and endangered elasmobranch fishes impair the assessment of their ecological role in marine ecosystems. In this study, we examined the feeding ecology (diet composition and trophic level) and trophic relationships of 22 elasmobranchs (2 Carcharhiniformes, 1 Hexanchiformes, 1 Lamniformes, 3 Myliobatiformes, 6 Rajiformes, 6 Squaliformes and 3 Torpediniformes) present in the western Mediterranean Sea. To obtain a comprehensive view of the feeding ecology of these species, we combined different approaches: stable isotope analyses (delta C-13 and delta N-15 values), stomach content analyses and published sources. Our results revealed differences in feeding strategies among elasmobranch groups: skates (Rajiformes) mainly consume crustaceans; sharks (Carcharhiniformes, Hexanchiformes, Squaliformes and Lamniformes) prefer mixed diets composed of cephalopods, crustaceans and fishes; electric rays (Torpediniformes) feed mostly on fishes; and the diet of stingrays (Myliobatiformes) varies between species. Sharks and electric rays show higher trophic positions than skates, and the former occupy similar positions to other apex predators. Skates are more similar to other mesopredator fishes. These new findings offer essential information on the ecological role of several elasmobranchs in the western Mediterranean Sea and provide useful data for managers for future conservation strategies.

Community response of deep-sea soft-sediment metazoan meiofauna to the Deepwater Horizon blowout and oil spill

Abstract: The Deepwater Horizon (DWH) blowout and oil spill of 2010 released an estimated 4.9 million barrels of oil into the Gulf of Mexico. Spill-related contaminants that sank to the seafloor pose risks to benthic fauna living within bottom substrates that are unable to avoid expo- sure due to their relatively sedentary existence. Metazoan meiofauna are abundant and diverse members of deep-sea soft-sediment communities and play important roles in ecosystem function. We investigated the deep-sea metazoan meiofauna community response to the DWH blowout and oil spill at 66 stations ranging from <1 km to nearly 200 km from the Mississippi Canyon Block 252 wellhead. Metazoan meiofauna abundance, diversity, and the nematode to copepod ratio (N:C) varied significantly across impact zones. Nematode dominance increased significantly with increasing impacts, and N:C spiked near the wellhead. Conversely, major taxonomic diversity and evenness decreased in zones of greater impacts that were in closer proximity to the DWH well- head. Copepod abundance and the abundance of minor meiofauna taxa decreased where impacts were most severe, and at these severely impacted stations the abundance of ostracods and kinorhynchs was negligible. Increasing abundance and dominance by nematodes with increasing impacts likely represent a balance between organic enrichment and toxicity. Spatial analysis of meiofauna diversity and N:C at 66 stations increased our spatial understanding of the DWH ben- thic footprint and suggests expanded spatial impacts in areas previously identified as uncertain.

Coral reef benthic regimes exhibit non-linear threshold responses to natural physical drivers

Abstract: We assessed the independent effects of natural physical drivers in structuring coral reef benthic communities at a remote oceanic atoll in the central equatorial Pacific with minimal local human impacts. High-resolution bathymetric data combined with in situ oceanographic measurements and a nearshore hydrodynamic model revealed complex intra-atoll gradients in geomorphic complexity, wave forcing, currents, and temperature. For example, maximum wavedriven bed shear stress spatially varied on the forereef (15�20 m depth) by over 2 orders of magnitude, peaking in areas exposed to multiple wave regimes. Benthic community composition, quantified via towed-diver imagery collected in a complete circumnavigation of the atoll (~40 km), also exhibited considerable spatial heterogeneity. Benthic competitors showed distinct, non-linear threshold-type responses to variations in physical drivers. For example, at a wave-driven bed shear stress threshold of 18 N m�2, calcifying crustose coralline algae lost relative dominance and were replaced by non-calcifying fleshy turf algae. Hard coral communities also demonstrated considerable flexibility in response to physical drivers, with distinct shifts in the relative dominance of different growth morphologies along gradients of wave forcing, presumably as a means of local adaptation. Our results highlight (1) the importance of natural gradients in physical drivers in determining dominant benthic regimes on coral reefs (e.g. calcifying vs. fleshy), (2) that non-linear thresholds (or tipping points) exist between key benthic competitors in response to key physical drivers, and (3) that coral assemblages show inherent flexibility and can reorganize in response to physical drivers rather than exhibit wholesale changes in overall cover.

Trophic cascades in the western Ross Sea, Antarctica: revisited

Abstract: We investigated mesopredator effects on prey availability in the Ross Sea, Antarctica, as sessing the reasons why Adelie penguin Pygoscelis adeliae foraging trip duration (FTD) increases and diet changes from krill to fish as numbers of foraging penguins and competing cetaceans increase in the penguins’ foraging area. To investigate penguins’ seasonally changing FTD as a function of foraging-population size—previously investigated indirectly—we used bio-logging to determine the penguins’ 3-dimensional foraging volume, while an autonomous glider quantified the depth, abundance, and distribution of potential prey. As numbers of foraging penguins and cetaceans increased, penguins spent more time on foraging trips, traveling farther and deeper, and their diet included more fish, as average maximum depth of krill increased from 45 to 65 m, and that of small fish also deepened, but only from 51 to 57 m. With a need to forage at greater depths for in creasingly over lapping prey, the penguins consumed more of the energydense fish. Krill depth was negatively correlated with chlorophyll (a proxy for krill food), indi cating an uncoupling between the two and the overwhelming importance of predation avoidance by the krill relative to food acquisition. Results support the hypotheses that (1) predators remove the grazers from Ross Sea surface waters, controlling their ver tical distributions; and (2) the food web has a ‘waspwaist’ structure, in which middleand upper-trophic levels are controlled top-down, whereas phytoplank ton production and accumulation are regulated bottom-up, largely independent of grazer control. Ross Sea models need revision to reflect this food web structure.

Long-term effects of an offshore wind farm in the North Sea on fish communities

Abstract: Long-term effects of the Horns Rev 1 offshore wind farm (OWF) on fish abundance, diversity and spatial distribution were studied. This OWF is situated on the Horns Reef sand bank in the North Sea. Surveys were conducted in September 2001, before the OWF was established in 2002, and again in September 2009, 7 yr post-establishment. The sampling surveys used a multi- mesh-size gillnet. The 3 most abundant species in the surveys were whiting Merlangius merlan- gus, dab Limanda limanda and sandeels Ammodytidae spp. Overall fish abundance increased slightly in the area where the OWF was established but declined in the control area 6 km away. None of the key fish species or functional fish groups showed signs of negative long-term effects due to the OWF. Whiting and the fish group associated with rocky habitats showed different dis- tributions relative to the distance to the artificial reef structures introduced by the turbines. Rocky habitat fishes were most abundant close to the turbines while whiting was most abundant away from them. Species diversity was significantly higher close to the turbines. Overall, these results indicate that the artificial reef structures were large enough to attract fish species with a prefer- ence for rocky habitats, but not large enough to have adverse negative effects on species inhabit- ing the original sand bottom between the turbines.

Climate-associated changes in prey availability drive reproductive dynamics of the North Atlantic right whale population

Abstract: Considered one of the most endangered cetacean species, the North Atlantic right whale Eubalaena glacialis suffered declining abundance during the 1990s due to a high rate of anthropogenic-associated mortality and a low rate of reproduction. Previous studies have sug- gested that the reproductive rate is tightly coupled to the abundance of Calanus finmarchicus in the Gulf of Maine (GOM), which has been shown to respond to ecosystem regime shifts associated with decadal-scale climate forcing from the Arctic. Given the endangered status of the right whale population, it is vital to determine how climate-associated changes in prey availability will affect this species in the future. Here, we investigate a 3-state reproduction model that explores multiple environmental proxies as potential predictors of annual calf production during the period from 1980 to 2007. The model achieves its best fit to observations using temporally and spatially resolved C. finmarchicus abundance data derived from Continuous Plankton Recorder (CPR) sur- veys of the GOM. Building on previous research, this prey-dependent model, which uses bi- monthly and geographically specific abundance anomalies of C. finmarchicus, significantly improves estimates of annual calf production relative to a null model. The temporal and geo- graphic distributions of prey objectively chosen for inclusion in the new version of the model cor- respond well with observed right whale seasonal distribution patterns, providing further evidence that the model captures essential features of right whale reproductive ecology.

Direct seeding of mass-cultured coral larvae is not an effective option for reef rehabilitation

Abstract: We thank Steven Victor and staff of the Palau International Coral Reef Center for the use of facilities and their support in the field; we also thank 3 anonymous reviewers, whose insightful comments improved the original manuscript. We are particularly grateful to Geory Mereb and Charlie Boch for invaluable field assistance. This research was supported by the Global Environment Facility/World Bank funded Coral Reef Targeted Research and Capacity Building for Management program.