Showing papers in "Marine Ecology Progress Series in 2009"

Biological Effects Within No-Take Marine Reserves: A global Synthesis

Abstract: The study and implementation of no-take marine reserves have increased rapidly over the past decade, providing ample data on the biological effects of reserve protection for a wide range of geographic locations and organisms. The plethora of new studies affords the opportunity to re- evaluate previous findings and address formerly unanswered questions with extensive data synthe- ses. Our results show, on average, positive effects of reserve protection on the biomass, numerical density, species richness, and size of organisms within their boundaries which are remarkably simi- lar to those of past syntheses despite a near doubling of data. New analyses indicate that (1) these results do not appear to be an artifact of reserves being sited in better locations; (2) results do not appear to be driven by displaced fishing effort outside of reserves; (3) contrary to often-made asser- tions, reserves have similar if not greater positive effects in temperate settings, at least for reef ecosystems; (4) even small reserves can produce significant biological responses irrespective of lati- tude, although more data are needed to test whether reserve effects scale with reserve size; and (5) effects of reserves vary for different taxonomic groups and for taxa with various characteristics, and not all species increase in response to reserve protection. There is considerable variation in the responses documented across all the reserves in our data set — variability which cannot be entirely explained by which species were studied. We suggest that reserve characteristics and context, par- ticularly the intensity of fishing outside the reserve and inside the reserve before implementation, play key roles in determining the direction and magnitude of the reserve response. However, despite considerable variability, positive responses are far more common than no differences or negative responses, validating the potential for well designed and enforced reserves to serve as globally important conservation and management tools.

Anthropogenic and natural sources of ambient noise in the ocean

Abstract: Ocean ambient noise results from both anthropogenic and natural sources. Different noise sources are dominant in each of 3 frequency bands: low (10 to 500 Hz), medium (500 Hz to 25 kHz) and high (>25 kHz). The low-frequency band is dominated by anthropogenic sources: pri- marily, commercial shipping and, secondarily, seismic exploration. Shipping and seismic sources con- tribute to ambient noise across ocean basins, since low-frequency sound experiences little attenua- tion, allowing for long-range propagation. Over the past few decades the shipping contribution to ambient noise has increased by as much as 12 dB, coincident with a significant increase in the num- ber and size of vessels comprising the world's commercial shipping fleet. During this time, oil explo- ration and construction activities along continental margins have moved into deeper water, and the long-range propagation of seismic signals has increased. Medium frequency sound cannot propagate over long ranges, owing to greater attenuation, and only local or regional (10s of km distant) sound sources contribute to the ambient noise field. Ambient noise in the mid-frequency band is primarily due to sea-surface agitation: breaking waves, spray, bubble formation and collapse, and rainfall. Var- ious sonars (e.g. military and mapping), as well as small vessels, contribute anthropogenic noise at mid-frequencies. At high frequencies, acoustic attenuation becomes extreme so that all noise sources are confined to an area close to the receiver. Thermal noise, the result of Brownian motion of water molecules near the hydrophone, is the dominant noise source above about 60 kHz.

Changing spatial distribution of fish stocks in relation to climate and population size on the Northeast United States continental shelf

Abstract: We tested the hypothesis that recent oceanographic changes associated with climate change in the Northeast United States continental shelf ecosystem have caused a change in spatial distribution of marine fish. To do this, we analyzed temporal trends from 1968 to 2007 in the mean center of biomass, mean depth, mean temperature of occurrence, and area occupied in each of 36 fish stocks. Temporal trends in distribution were compared to time series of both local- and large-scale environmental variables, as well as estimates of survey abundance. Many stocks spanning several taxonomic groups, life-history strategies, and rates of fishing exhibited a poleward shift in their cen- ter of biomass, most with a simultaneous increase in depth, and a few with a concomitant expansion of their northern range. However, distributional changes were highly dependent on the biogeogra- phy of each species. Stocks located in the southern extent of the survey area exhibited much greater poleward shifts in center of biomass and some occupied habitats at increasingly greater depths. In contrast, minimal changes in the center of biomass were observed in stocks with distributions limited to the Gulf of Maine, but mean depth of these stocks increased while stock size decreased. Large- scale temperature increase and changes in circulation, represented by the Atlantic Multidecadal Oscillation, was the most important factor associated with shifts in the mean center of biomass. Stock size was more often correlated with the total area occupied by each species. These changes in spatial distribution of fish stocks are likely to persist such that stock structure should be re-evaluated for some species.

Alternative states on coral reefs: beyond coral–macroalgal phase shifts

Abstract: Degradation of coral reefs is often associated with changes in community structure where macroalgae become the dominant benthic life form. These phase shifts can be difficult to reverse. The debate ...

Population genetics, larval dispersal, and connectivity in marine systems

Abstract: Population connectivity plays significant roles on both evolutionary and ecological time-scales; however, quantifying the magnitude and pattern of ex- change between populations of marine organisms is hindered by the difficulty of tracking the trajectory and fate of propagules. We explored biophysical correlates of population substructure to determine how well pelagic larval duration (PLD) correlates with population genetic estimates of connectivity in a sample of 300 published studies drawn pseudo-randomly from about 1600 hits on electronic searches. In direct contrast to the general expectation of a strong correlation, we find that average PLD is poorly correlated (r 2 < 0.1) with genetic structure (FST). Furthermore, even this weak correlation is anchored by non-pelagic dispersal, because removal of the zero PLD class (direct developers) from the analy- sis resulted in a non-significant relationship between FST and PLD. For species in which minimum, maximum, and mean PLDs were available, it is noteworthy that both minimum and maximum PLDs are better corre- lated with FST than the mean larval duration, which has been used in all such previous studies. A 3-way AN- COVA reveals that genetic marker class (allozymes, microsatellites, and mitochondrial DNA sequences), as opposed to habitat or swimming ability, explain most of the variation in FST (F = 7.113, df = 2, p = 0.001), with higher values of FST obtained from mtDNA than with either microsatellites or allozymes (which were not sig- nificantly different). Our meta-analysis refutes recent reviews and conventional wisdom that PLD is a good predictor of the magnitude of gene flow and geo- graphic scale of population structure in marine systems.

Acoustic masking in marine ecosystems: intuitions, analysis, and implication

Abstract: Acoustic masking from anthropogenic noise is increasingly being considered as a threat to marine mammals, particularly low-frequency specialists such as baleen whales. Low-frequency ocean noise has increased in recent decades, often in habitats with seasonally resident populations of marine mammals, raising concerns that noise chronically influences life histories of individuals and populations. In contrast to physical harm from intense anthropogenic sources, which can have acute impacts on individuals, masking from chronic noise sources has been difficult to quantify at individ- ual or population levels, and resulting effects have been even more difficult to assess. This paper pre- sents an analytical paradigm to quantify changes in an animal's acoustic communication space as a result of spatial, spectral, and temporal changes in background noise, providing a functional defini- tion of communication masking for free-ranging animals and a metric to quantify the potential for communication masking. We use the sonar equation, a combination of modeling and analytical tech- niques, and measurements from empirical data to calculate time-varying spatial maps of potential communication space for singing fin (Balaenoptera physalus), singing humpback (Megoptera novaeangliae), and calling right (Eubalaena glacialis) whales. These illustrate how the measured loss of communication space as a result of differing levels of noise is converted into a time-varying mea- sure of communication masking. The proposed paradigm and mechanisms for measuring levels of communication masking can be applied to different species, contexts, acoustic habitats and ocean noise scenes to estimate the potential impacts of masking at the individual and population levels.

Impact assessment research: use and misuse of habituation, sensitisation and tolerance in describing wildlife responses to anthropogenic stimuli

Abstract: Studies on the effects of anthropogenic activity on wildlife aim to provide a sound scien- tific basis for management. However, misinterpretation of the theoretical basis for these studies can jeopardise this objective and lead to management outcomes that are detrimental to the wildlife they are intended to protect. Misapplication of the terms 'habituation', 'sensitisation' and 'tolerance' in im- pact studies, for example, can lead to fundamental misinterpretations of research findings. Habituation is often used incorrectly to refer to any form of moderation in wildlife response to human disturbance, rather than to describe a progressive reduction in response to stimuli that are perceived as neither aversive nor beneficial. This misinterpretation, when coupled with the widely held assumption that habituation has a positive or neutral outcome for animals, can lead to inappropriate decisions about the threats human interactions pose to wildlife. We review the conceptual framework for the use of habit- uation, sensitisation and tolerance, and provide a set of principles for their appropriate application in studies of behavioural responses to anthropogenic stimuli. We describe how cases of presumed habit- uation or sensitisation may actually represent differences in the tolerance levels of wildlife to anthro- pogenic activity. This distinction is vital because impact studies must address (1) the various mecha- nisms by which differing tolerance levels can occur; and (2) the range of explanations for habituation- and sensitisation-type responses. We show that only one mechanism leads to true behavioural habitu- ation (or sensitisation), while a range of mechanisms can lead to changes in tolerance.

Interpretation of fast repetition rate (FRR) fluorescence: signatures of phytoplankton community structure versus physiological state

Abstract: Introduction of active chlorophyll a fluo- rescence protocols, in particular fast repetition rate (FRR) fluorometry, to oceanography and limnology 15 yr ago has enabled rapid assessment of photosyn- thetic physiology in situ. The FRR protocol generates simultaneous measurements of Photosystem II (PSII) effective absorption cross sections (termed σPSII) and photochemical efficiency (termed Fv/Fm). Both Fv/Fm and σPSII measurements have been utilised to examine the effects of physiological stress on the photosynthetic apparatus of phytoplankton in an ever growing num- ber of fluorescence-based studies. However, it is now becoming clearer that in situ values of Fv/Fm and σPSII also contain taxonomic information. Here, we present

Macrophytes as habitat for fauna

Abstract: Macrophyte systems, including kelp, seaweed and seagrasses, have revealed high diversity and abundance of associated fauna along the Norwegian coast. In the present study, data from a number of recent studies were assembled and supplemented with new data to elucidate the organisation of macrofaunal diversity on macrophytes. The aim was to compare faunal composition on macrophytes of different size, shape, longevity and function. Macrofaunal densities frequently exceed 100 000 individuals m -2 in macrophyte beds. Commonly, high densities of amphipods and gastropods are found. The faunal composition depends mainly on habitat architecture at a spatial micro-scale, while faunal abundances depend on habitat size. These 2 patterns are consistent over larger spatial scales. Most faunal species show high mobility and dispersal rates, and they colonize available habitats rapidly. Macrophyte longevity may, in some cases, influence faunal composition. The macrophytes function both as a habitat and as a food source, but the feeding behaviour of the majority of the faunal components prevents the fauna from overgrazing their habitat and thus destroying the primary producer and foundation species of the community. The perennial macro- phytes are mainly consumed as particulate organic matter. A high functional redundancy in both plants and animals is most likely important for the stability of the macrophyte system. The stability and diversity of macrophyte systems are found to be threatened in various ways by overgrazing, removal by storms and commercial harvesting, eutrophication and overfishing of top predators, with concurrent challenges for management.

Impacts of bottom trawling on deep-coral ecosystems of seamounts are long-lasting

Abstract: Complex biogenic habitats formed by corals are important components of the megaben- thos of seamounts, but their fragility makes them susceptible to damage by bottom trawling. Here we examine changes to stony corals and associated megabenthic assemblages on seamounts off Tasma- nia (Australia) with different histories of bottom-contact trawling by analysing 64 504 video frames (25 seamounts) and 704 high-resolution images (7 seamounts). Trawling had a dramatic impact on the seamount benthos: (1) bottom cover of the matrix-forming stony coral Solenosmilia variabilis was reduced by 2 orders of magnitude; (2) loss of coral habitat translated into 3-fold declines in richness, diversity and density of other megabenthos; and (3) megabenthos assemblage structures diverged widely between trawled and untrawled seamounts. On seamounts where trawling had been reduced to <5% a decade ago and ceased completely 5 yr ago, there was no clear signal of recovery of the megabenthos; communities remained impoverished comprising fewer species at reduced densities. Differences in community structure in the trawled (as compared to the untrawled) seamounts were attributed to resistant species that survived initial impacts, others protected in natural refugia and early colonisers. Long-term persistence of trawling impacts on deep-water corals is consistent with their biological traits (e.g. slow growth rates, fragility) that make them particularly vulnerable. Because recovery on seamounts will be slow, the benefits from fishery closures may not be immedi- ately recognisable or measureable. Spatial closures are crucial conservation instruments, but will require long-term commitments and expectations of performance whose time frames match the bio- logical tempo in the deep sea.

Management and research applications of real-time and archival passive acoustic sensors over varying temporal and spatial scales

Abstract: Defining the appropriate scale over which to conduct a study in the marine environment is critical to achieving appropriate scientific, management, mitigation and conservation objectives. This paper focuses on applications of passive acoustic technologies over a range of spatial and temporal scales. It is divided into sections dealing with archival and real-time passive acoustic sensor applications. Each section assesses the principles behind using the respective technology and pro- vides recent examples of research and management applications for marine mammals and fish. The section on archival sensors highlights the need for continued development of automated acoustic detectors to assess large data sets. Case studies are presented of detectors developed for determining seasonal occurrence and distribution of haddock sounds and humpback whale vocalizations. Also presented are studies of other applications using archival sensors: tracking singing humpback whales in Brazil, using vocalizations to assess the reproductive strategies of Arctic bearded seals and assessing regional variability in call patterns for North Atlantic right whales. The section on real-time passive acoustic sensors focuses on real-time buoys and towed arrays. Case studies presented include a real-time buoy system used for monitoring endangered North Atlantic right whales and a station- ary autonomous array providing real-time access to Antarctic acoustic data. The value of using towed arrays for real-time applications is also assessed, and a case study is provided on the use of towed arrays to improve abundance estimates of North Pacific cetaceans and to better understand vocaliza- tion behaviors.

Consequences of ecological connectivity: the coastal ecosystem mosaic

Abstract: Connectivity links habitats in space and time. It is a key process that facilitates many life-history functions of myriad species in a variety of contexts over a wide range of scales. Perhaps its most obvious application is to the multifaceted linkages among the diverse habitat units comprising ecosystem complexes like the coastal ecosystem mosaic (CEM)—the tightly interlinked coastal, estuarine, wetland and freshwater habitats at the interface of land and sea. The ability to utilise this diversity of connected habitats is integral to the life histories of a broad spectrum of organisms, with connectivity between habitats being crucial to important functions like nursery utilisation. Although connectivity is an obvious feature of the CEM, investigation of its implications has largely been restricted to the migration of organisms. However, connectivity has much broader conceptual relevance. It is a pervasive and multifaceted process affecting and enabling the lives of organisms over the full range of conceptual scales, with ecosystem components connected by a diversity of factors, including physical and biological translocation of nutrients, ontogenetic, life history, spawning and feeding migrations, food-web dynamics, predator–prey interactions, and many more. All of these play crucial roles in structuring biological populations, communities and assemblages, and in driving the biological processes that support them. Moreover, connectivity is a prominent and necessary component of ecological concepts, ranging from estuarine dependence and metapopulation dynamics to foraging arena theory. Considering connectivity as a multifaceted process leads to specific hypotheses about the functioning of the CEM and similar ecosystem complexes.

Consequences of climate-driven biodiversity changes for ecosystem functioning of North European rocky shores

Abstract: Hawkins, S. J., Sugden, H. E., Mieszkowska, N., Moore, P. J., Poloczanska, E. S., Leaper, R., Herbert, R., Genner, M. J., Moschella, P. S., Thompson, R. C., Jenkins, S. R., Southward, A. J., Burrows, M. T. (2009). Consequences of climate-driven biodiversity changes for ecosystem functioning of North European rocky shores. Marine Ecology Progress Series, 396, 245-259.

Interacting effects of elevated temperature and ocean acidification on the aerobic performance of coral reef fishes

Abstract: Concerns about the impacts of ocean acidification on marine life have mostly focused on how reduced carbonate saturation affects calcifying organisms. Here, we show that levels of CO2-induced acidification that may be attained by 2100 could also have significant effects on marine organisms by reducing their aerobic capacity. The effects of temperature and acidification on oxygen consumption were tested in 2 species of coral reef fishes, Ostorhinchus doederleini and O. cyanosoma, from the Great Barrier Reef, Australia. The capacity for aerobic activity (aerobic scope) declined at temperatures above the summer average (29°C) and in CO2-acidified water (pH 7.8 and ~1000 ppm CO2) compared to control water (pH 8.15). Aerobic scope declined by 36 and 32% for O. doederleini and O. cyanosoma at temperatures between 29 to 32°C, whereas it declined by 33 and 47% for O. doederleini and O. cyanosoma in acidified water compared to control water. Thus, the declines in aerobic scope in acidified water were similar to those caused by a 3°C increase in water temperature. Minimum aerobic scope values of ~200 mg O2 kg–1 h–1 were attained for both species in acidified water at 32°C, compared with over 600 mg O2 kg–1 h–1 in control water at 29°C. Mortality rate increased sharply at 33°C, indicating that this temperature is close to the lethal thermal limit for both species. Acidification further increased the mortality rate of O. doederleini, but not of O. cyanosoma. These results show that coral reef fishes are sensitive to both higher temperatures and increased levels of dissolved CO2, and that the aerobic performance of some reef fishes could be significantly reduced if climate change continues unabated

Carbon-to-chlorophyll ratio and growth rate of phytoplankton in the sea

Abstract: Observations from offshore regions (NW Atlantic and Arabian Sea) and from a semi- enclosed bay (Tokyo Bay) were used to study the relationships between chlorophyll and particulate carbon in the sea. A simple conceptual model was then developed to infer in situ phytoplankton car- bon as a function of chlorophyll a. This allowed indirect estimates of the carbon-to-chlorophyll ratio of phytoplankton in the sea. Using data from high-performance liquid chromatography, field samples dominated by diatoms, dinoflagellates, green algae, prymnesiophytes and cyanobacteria were iden- tified, and their carbon-to-chlorophyll ratios were established. The computations yielded conserva- tive estimates for the ratio (15 to 176 weight:weight). The results were applied to satellite data to map the carbon-to-chlorophyll ratios in the NW Atlantic. Since methods were already in place to estimate photosynthesis-irradiance parameters for the region by remote sensing (Platt et al. 2008), we showed that it was possible, using remote sensing, to compute carbon-based phytoplankton growth rates by making use of the existing information on photosynthesis-irradiance parameters and carbon- to-chlorophyll ratios. The method makes it possible to compute primary production by using either carbon-based growth models or photosynthesis-irradiance models in ways that are fully comparable with each other.

Spatial ecology and conservation of seabirds facing global climate change: a review

Abstract: In this review we detail the impact of climate change on marine productivity, on marine environmental stochasticity and cyclicity, and on the spatio-temporal match-mismatch of seabirds and their prey. We thereby show that global warming has a profound bottom-up impact upon marine top-predators, but that such effects have to be studied in conjunction with the (top-down) impact of human fisheries upon seabird food resources. Further, we propose seabird ecological features, such as memory effects and social constraints, that make them particularly sensitive to rapid environmen- tal change. We provide examples of how seabirds may nonetheless adapt when facing the conse- quences of climate change. We conclude that our understanding of the spatial ecology of seabirds facing environmental change is still rudimentary, despite its relevance for the conservation of these vulnerable organisms and for the management of marine ecosystems. We define the following research priorities. (1) Determine the factors affecting seabird distribution and movements at sea using biotelemetry, as well as colony dynamics on land. (2) Link seabird distribution patterns to those of their prey. (3) Determine further the role of historical and metapopulation processes in contribut- ing to the dynamics of the spatial distribution of seabirds. (4) Assess phenotypic plasticity and the potential for microevolution within seabird spatial responses to climate change, since both will greatly affect the quality of modelling studies. (5) Adapt existing models to define and predict the impact of climate change onto seabird spatial dynamics. (6) Synthesize all gathered information to define marine protected areas and further conservation schemes, such as capacity reduction of fish- eries. This research effort will require maintaining existing long-term monitoring programmes for seabirds, as well as developing new approaches to permit the integration of processes occurring at various scales, in order to be able to fully track the population responses of these long-lived verte- brates to environmental changes. Resale or republication not permitted without written consent of the publisher Contribution to the Theme Section 'Spatiotemporal dynamics of seabirds in the marine environment' OPENEN

Cold-water corals in the Cap de Creus canyon, northwestern Mediterranean: spatial distribution, density and anthropogenic impact

Abstract: The occurrence and density of 3 cold-water coral (CWC) species (Madrepora oculata, Lophelia pertusa and Dendrophyllia cornigera) were investigated in the Cap de Creus canyon (north- western Mediterranean) by conducting and analysing 22 video survey transects. Species distribution patterns were also investigated at 3 spatial extents (km, 100s of m and m) across 3 of the transects using spatial statistics. Additionally, the locations of snagged benthic long-line fishing gear were logged across these 3 transects. Video surveys were carried out by both remotely operated vehicles (ROVs) and the JAGO manned submersible. CWCs were present in 15 of the 22 survey transects, pre- dominantly those covering areas with hard substrate (boulders or hardrock outcrops). M. oculata was the most abundant CWC species in the survey transects, whereas L. pertusa and D. cornigera were much more sparsely distributed, with only isolated colonies observed in the majority of transects. M. oculata showed a significant contagious distribution pattern across the analysed transects, with sev- eral scales of spatial pattern and patch size being detected, whereas L. pertusa and D. cornigera were not found in sufficient numbers to apply spatial statistics. Different covariance patterns were found across the transects between snagged fishing gear and the presence of M. oculata. Further investi- gation of this relationship and the level of hazard posed by long-line fishing to M. oculata colonies is required prior to development of a protective management strategy.

Vessel noise effects on delphinid communication

Abstract: Increasing numbers and speeds of vessels in areas with populations of cetaceans may have the cumulative effect of reducing habitat quality by increasing the underwater noise level. Here, we first use digital acoustic tags to demonstrate that free-ranging delphinids in a coastal deep- water habitat are subjected to varying and occasionally intense levels of vessel noise. Vessel noise and sound propagation measurements from a shallow-water habitat are then used to model the potential impact of high sound levels from small vessels on delphinid communication in both shallow and deep habitats, with bottlenose dolphins Tursiops sp. and short-finned pilot whales Globicephala macrorhynchus as model organisms. We find that small vessels travelling at 5 knots in shallow water can reduce the communication range of bottlenose dolphins within 50 m by 26%. Pilot whales in a quieter deep-water habitat could suffer a reduction in their communication range of 58% caused by a vessel at similar range and speed. Increased cavitation noise at higher speeds drastically increases the impact on the communication range. Gear shifts generate high-level transient sounds (peak- peak source levels of up to 200 dB re 1 µPa) that may be audible over many kilometres and may dis- turb close-range animals. We conclude that noise from small vessels can significantly mask acousti- cally mediated communication in delphinids and contribute to the documented negative impacts on animal fitness.

Effects of increased pCO2 and temperature on the North Atlantic spring bloom. I. The phytoplankton community and biogeochemical response

Abstract: The North Atlantic spring bloom is one of the largest annual biological events in the ocean, and is characterized by dominance transitions from siliceous (diatoms) to calcareous (coccolithophores) algal groups. To study the effects of future global change on these phytoplankton and the biogeochemical cycles they mediate, a shipboard continuous culture experiment (Ecostat) was conducted in June 2005 during this transition period. Four treatments were examined: (1) 12 degrees C and 390 ppm CO2 (ambient control), (2) 12 degrees C and 690 ppm CO2 (high pCO(2)) (3) 16 degrees C and 390 ppm CO2 (high temperature), and (4) 16 degrees C and 690 ppm CO2 ('greenhouse'). Nutrient availability in all treatments was designed to reproduce the low silicate conditions typical of this late stage of the bloom. Both elevated pCO(2) and temperature resulted in changes in phytoplankton community structure. Increased temperature promoted whole community photosynthesis and particulate organic carbon (POC) production rates per unit chlorophyll a. Despite much higher coccolithophore abundance in the greenhouse treatment, particulate inorganic carbon production (calcification) was significantly decreased by the combination of increased pCO(2) and temperature. Our experiments suggest that future trends during the bloom could include greatly reduced export of calcium carbonate relative to POC, thus providing a potential negative feedback to atmospheric CO2 concentration. Other trends with potential climate feedback effects include decreased community biogenic silica to POC ratios at higher temperature. These shipboard experiments suggest the need to examine whether future pCO2 and temperature increases on longer decadal timescales will similarly alter the biological and biogeochemical dynamics of the North Atlantic spring bloom.

Quantity and bioavailability of sediment organic matter as signatures of benthic trophic status

Abstract: Tools used for assessing marine trophic status are generally based on water column characteristics, which, however, may provide unreliable classification of the benthic trophic status. Here, we provide evidence from the literature that quantity and bioavailability of sediment organic matter are reliable proxies to assess benthic marine trophic status. We compiled data on the protein, carbohydrate and lipid concentration of sediments from different oceanic and coastal regions and varying water depths. The concentration of these 3 components as a whole (biopolymeric carbon) was found to be significantly correlated (r = 0.84) with the total organic carbon concentration, suggesting that the biopolymeric fraction is representative of the total organic carbon pool. However, the system- atic variation of the biopolymeric fraction was higher than that of total organic carbon concentrations, suggesting that biopolymeric carbon is a more sensitive proxy of benthic trophic status than is the total carbon pool. Furthermore, biopolymeric carbon was significantly correlated to the amount of phytopigments, indicating that biopolymeric carbon accumulation in the sediment is related to inputs of algal carbon. Biopolymeric carbon concentrations were also positively correlated to the sediment community oxygen consumption, suggesting that the progressive accumulation of biopolymeric car- bon could be an additional co-factor potentially responsible for hypoxic or anoxic events. The enzy- matically digestible and algal fractions of biopolymeric carbon decreased in sediments with increas- ing biopolymeric carbon content (i.e. eutrophic systems), suggesting that organic carbon in eutrophic sediments is mostly refractory in nature. We propose that a biopolymeric carbon concentration in the sediment of >2.5 mg C g -1 , being associated with a bioavailable fraction of <10%, can be considered as a threshold level at which benthic consumers may experience mostly refractory organic carbon.

Cross-shelf benthic community structure on the Great Barrier Reef: relationships between macroalgal cover and herbivore biomass

Abstract: The Great Barrier Reef (GBR) is one of the most extensively studied coral reef systems in the world, yet to date, there has been no comprehensive multi-spatial scale evaluation of its benthic community structure. Such descriptions provide a useful reference point for evaluating future community changes. Moreover, large-scale associations between macroalgae and herbivory on the GBR are yet to be investigated. Our aim, therefore, was to quantify all major substratum categories across multiple spatial scales and investigate cross-shelf relationships between macroalgal cover and herbivore biomass. Using point-intercept transects and timed underwater censuses, individual benthic components and roving herbivorous fish densities were quantified across 3 spatial scales: latitude, continental shelf position and within-reef habitat. Principal component analysis and analysis of similarities (ANOSIM) revealed a distinct separation of inner-shelf reef habitats from all mid- and outer-shelf habitats in both northern and central regions of the GBR. Macroalgal cover was generally high on inner-shelf reefs (36 to 66%) and decreased markedly on all mid- and outer-shelf habitats (0 to 15%). A significant negative correlation was found between macroalgal cover and total herbivorous fish biomass, but no relationship was found between macroalgal cover and macroalgal browser biomass. In contrast to macroalgae, the cover of crustose coralline algae and live scleractinian corals increased markedly across the shelf in both regions of the GBR. These patterns appear to be shaped by both physical and biological factors, including wave energy, sedimentation and grazing intensity.

Studying the behaviour and sensory ecology of marine mammals using acoustic recording tags: a review

Abstract: Many marine animals use sound passively or actively for communication, foraging, predator avoidance, navigation, and to sense their environment. The advent of acoustic recording tags has allowed biologists to get the on-animal perspective of the sonic environment and, in combi- nation with movement sensors, to relate sounds to the activities of the tagged animal. These power- ful tools have led to a wide range of insights into the behaviour of marine animals and have opened new opportunities for studying the ways they interact with their environment. Acoustic tags demand new analysis methods and careful experimental design to optimize the consistency between research objectives and the realistic performance of the tags. Technical details to consider are the suitability of the tag attachment to a given species, the accuracy of the tag sensors, and the recording and attach- ment duration of the tag. Here we consider the achievements, potential, and limitations of acoustic recording tags in studying the behaviour, habitat use and sensory ecology of marine mammals, the taxon to which this technology has been most often applied. We examine the application of acoustic tags to studies of vocal behaviour, foraging ecology, acoustic tracking, and the effects of noise to assess both the breadth of applications and the specific issues that arise in each.

Quantifying habitat use and preferences of pelagic seabirds using individual movement data: a review

Abstract: Colonial seabirds are relatively easy to observe, count, measure and manipulate, and consequently have long been used as models for testing ecological hypotheses. A combination of ani- mal tracking and satellite imagery has the potential to greatly inform such efforts, by allowing seabird-environment interactions to be observed remotely. We review how this can be achieved by applying innovative statistical techniques to quantify habitat use and preferences. Seabird move- ments are now observable at scales of meters using GPS loggers, and up to several years using light- based geolocation, while satellite remote sensing systems, at resolutions of km, are capable of char- acterizing the millions of km 2 of habitat that are accessible to seabirds. Physical forcing and biological processes result in a hierarchical, patchy distribution of prey. Hence, analyses of seabird movements should be conducted at appropriate scales. Variation in habitat accessibility should also be consid- ered: this declines with distance from the colony during the breeding season, when seabirds are cen- tral place foragers, and may be limited in the nonbreeding period by migration corridors that are defined by wind patterns. Intraspecific competition can further modify spatial usage, leading to spa- tial segregation of birds foraging from different colonies. We recommend that spatial usage be mod- eled as a function of habitat preference, accessibility and, potentially, competition. At the population level, this is currently best achieved using an empirical approach (e.g. using mixed-effects general- ized additive models). At the individual level, more mechanistic models (e.g. state-space models) are more appropriate and have the advantage of modeling location errors explicitly. Contribution to the Theme Section 'Spatiotemporal dynamics of seabirds in the marine environment' OPEN

Success of constructed oyster reefs in no-harvest sanctuaries: implications for restoration

Abstract: Dramatic declines in populations of the eastern oyster Crassostrea virginica are a symp- tom of degradation in many US Atlantic and Gulf of Mexico estuaries. We sampled 94 oyster reefs (88 constructed, 6 natural) within 11 no-harvest sanctuaries in estuaries of central and northern North Carolina, USA, to evaluate the success of oyster sanctuaries as a conservation tool. The sanctuaries have been in existence from 3 to 30 yr; 10 sanctuaries protect constructed ('restored') oyster reefs and 1 sanctuary protects natural reefs. Measurements of vertical relief, live oyster density, recruitment, abundance of market-sized oysters, and biomass as well as disease prevalence and severity indicated that 7 of the 11 sanctuaries met criteria for minimal success by having vertical relief >20 cm in height, living oysters (>10 oysters m -2 ), and evidence of recent recruitment in 1 of 2 yr of the survey. Most reefs within the 7 sanctuaries far surpassed these relatively low benchmarks. For reefs that failed, burial by sedimentation appeared to be the primary cause in 2 sanctuaries, poor water quality (low dissolved oxygen) in 1, and poor oyster recruitment in another. All intertidal reefs were successful and had significantly higher densities of all size categories of live oysters (spat, adult, marketable size) than subtidal oyster reefs. Disease prevalence and severity were low in sanctuary reefs despite high oyster densities and increased longevity of oysters on these reefs. Pronouncements that restora- tion of the native eastern oyster is a failure prove incorrect when a decade-long history of oyster reef sanctuaries is evaluated. The proposed introduction of a non-native oyster into the US Atlantic coast estuaries cannot be justified by claiming failure of native oyster restoration in light of promising suc- cesses within sanctuaries.

Bycatch and discard mortality in commercially caught blue sharks Prionace glauca assessed using archival satellite pop-up tags

Abstract: Blue sharks Prionace glauca are the most frequently discarded fish species during com- mercial pelagic longline fishing operations worldwide, yet their post-release mortality rate has never been measured. A generalized linear model of 12 404 blue sharks observed during the Canadian Atlantic pelagic longline swordfishery suggested a hooking mortality of 12 to 13%, yet scientific examination of 902 of these sharks indicated that hooking mortality was actually higher. A random sample of 40 of these blue sharks were tagged with satellite pop-up archival transmission (PAT) tags, then monitored for periods of up to 6 mo after release. All of the surviving sharks exhibited a depth- holding recovery behaviour for a period of 2 to 7 d after release. All healthy sharks survived, while 33% of those that were badly injured or gut hooked subsequently died. Overall blue shark bycatch mortality in the pelagic longline fishery was estimated at 35%, while the estimated discard mortality for sharks that were released alive was 19%. Survival time models indicated that 95% of the mortal- ity occurred within 11 d of release, indicative of death by trauma rather than starvation. The annual blue shark catch in the North Atlantic was estimated at about 84 000 t, of which 57 000 t is discarded. A preliminary estimate of 20 000 t of annual dead discards for North Atlantic blue sharks is similar to that of the reported nominal catch, and could substantially change the perception of population health if incorporated into a population-level stock assessment.

Long-term and spillover effects of a marine protected area on an exploited fish community

Abstract: We assessed the development of the exploited fish community inside and around the Columbretes Islands Marine Reserve (CIMR), a marine protected area (MPA), 8 to 16 yr after fishing ceased in the reserve. Sampling was by annual lobster trammel net fishing, an experimental tech- nique used inside the CIMR, and on-board commercial operations in adjacent fishing grounds. We examined trends in combined fish abundance and biomass (catch per unit effort), species richness and diversity, size structure, trophic level and species composition of the community. Our results showed the CIMR fish community continued to change throughout the study period as (1) abundance and biomass increased, (2) mean body size and trophic level increased and (3) species composition changed according to a linear model. Relative to nearby fished areas the CIMR fish community had (1) higher abundance and biomass, (2) lower species diversity and higher taxonomic distinctness, (3) larger relative body size and (4) no difference in mean trophic level. We found clear evidence of spillover of fish from the CIMR to the adjacent fishery as commercial fish yields at the MPA border (<0.5 km from the boundary) increased continuously during the study period, despite being locally depleted due to fishing effort concentration (fishing the line). Furthermore, fish size and diversity at the border were intermediate between the CIMR and other fished zones, suggesting that this is a transitional zone influenced by this MPA. Our results show that changes in community abundance, biomass, size structure and species composition provide a clear and interpretable view of MPA recov- ery. Diversity indices are also useful; however, their interpretation is more difficult. We conclude that the creation of the CIMR has had a positive effect on the exploitable fish community and that there is evidence of exportation of biomass to the surrounding fishery. We highlight the advantage of using multiple community metrics to study changes in fish communities, yet recommend the need for caution when interpreting them.

Seagrass photosynthesis controls rates of calcification and photosynthesis of calcareous macroalgae in a tropical seagrass meadow

Abstract: Diel fluctuations in seawater pH can be >1 pH unit (7.9 to >8.9) in the seagrass meadows of Chwaka Bay (Zanzibar, Tanzania). The high daily pH values are generated by the photosynthetic activity of the bay’s submerged seagrasses and macroalgae, and maintained by the relatively low, tide-dominated, water exchange rate. Since pH in principle can affect rates of both calcification and photosynthesis, we investigated whether diel variations in pH caused by photosynthesis could affect rates of calcification and photosynthesis of the calcareous red (Hydrolithon sp. and Mesophyllum sp.) and green (Halimeda renschii) algae growing within these meadows. This was done by measuring rates of calcification and relative photosynthetic electron transport (rETR) of the algae in situ in open-bottom incubation cylinders either in the natural presence of the rooted seagrasses or after the leaves had been removed. The results showed that seagrass photosynthesis increased the seawater pH within the cylinders from 8.3–8.4 to 8.6–8.9 after 2.5 h (largely in conformity with that of the surrounding seawater), which, in turn, enhanced the rates of calcification 5.8-fold for Hydrolithon sp. and 1.6-fold for the other 2 species. The rETRs of all algae largely followed the irradiance throughout the day and were (in Mesophyllum sp.) significantly higher in the presence of seagrasses despite the higher pH values generated by the latter. We conclude that algal calcification within seagrass meadows such as those of Chwaka Bay is considerably enhanced by the photosynthetic activity of the seagrasses, which in turn increases the seawater pH.

Effects of CO2 induced seawater acidification on infaunal diversity and sediment nutrient fluxes

Abstract: A mesocosm experiment was conducted to quantify the effects of short- (2 wk) and long- term (20 wk) exposure to acidified seawater on the structure and diversity of macrofaunal and nema- tode assemblages in 2 different sediment types. The impact of acidified seawater on sediment nutri- ent fluxes was also determined. Using carbon dioxide (CO2) gas, seawater was acidified to pH 7.3 (mimicking ocean acidification), 6.5 or 5.6 (mimicking leakage from a sub-seabed CO2 store site). Control treatments were maintained in natural seawater (pH ≈ 8.0). Exposure to acidified seawater significantly altered community structure and reduced diversity for both macrofaunal and nematode assemblages. However, the impact on nematodes was less severe than that on macrofauna. While the communities in both sediment types were significantly affected by changes in seawater pH, impacts on sandy sediment fauna were greater than those on muddy sediment fauna. Sandy sediments also showed the greatest effects with respect to nutrient fluxes. In sand, the efflux of nitrite, nitrate and silicate decreased in response to increased acidification while the efflux of ammonium increased. In mud, acidification increased the efflux of ammonium but had no effect on the other nutrients. We con- clude that both leakage from carbon storage and ocean acidification could cause significant changes in the structure and diversity of coastal sediment communities. Lowered seawater pH could also affect nutrient cycling directly by altering bacterial communities and indirectly through impacts on the abundance and activity of key bioturbators.

Effects of ocean acidification over the life history of the barnacle Amphibalanus amphitrite

Abstract: Increased levels of atmospheric CO2 are anticipated to cause decreased seawater pH. Despite the fact that calcified marine invertebrates are particularly susceptible to acidification, bar- nacles have received little attention. We examined larval condition, cyprid size, cyprid attachment and metamorphosis, juvenile to adult growth, shell calcium carbonate content, and shell resistance to dislodgement and penetration in the barnacle Amphibalanus amphitrite reared from nauplii in either ambient pH 8.2 seawater or under CO2-driven acidification of seawater down to a pH of 7.4. There were no effects of reduced pH on larval condition, cyprid size, cyprid attachment and metamorpho- sis, juvenile to adult growth, or egg production. Nonetheless, barnacles exposed to pH 7.4 seawater displayed a trend of larger basal shell diameters during growth, suggestive of compensatory calcifi- cation. Furthermore, greater force was required to cause shell breakage of adults raised at pH 7.4, indicating that the lower, active growth regions of the wall shells had become more heavily calcified. Ash contents (predominately calcium carbonate) of basal shell plates confirmed that increased calci- fication had occurred in shells of individuals reared at pH 7.4. Despite enhanced calcification, pen- etrometry revealed that the central shell wall plates required significantly less force to penetrate than those of individuals raised at pH 8.2. Thus, dissolution rapidly weakens wall shells as they grow. The ramifications of our observations at the population level are important, as barnacles with weakened wall shells are more vulnerable to predators.

Spatial interaction between seabirds and prey: review and synthesis

Abstract: The Ideal Free Distribution theory predicts a close spatial match between predators and prey. Studies have shown that seabird and prey distribution seldom conforms with this prediction. In this study, I review recent theoretical advances in spatial predator-prey interactions and relate these with studies of seabirds and pelagic schooling fish and crustaceans. Studies on seabirds and prey have generally assumed that prey are nonresponsive. Predator-prey interactions should, however, be viewed as a 2-way spatial game where seabirds track concentrations of prey while prey move away from areas with high risk of predation. The outcome of the game depends on how seabirds and prey are spatially constrained. Constraints include the spatial distribution of resources, interspecific competition, the location of spawning and breeding areas, and limitations on diving depth. Although game theoretic models can explain some general aspects of the spatial interaction, the spatial distribution of seabirds and prey is generally much more aggregated and elusive than can be expected from the game theoretic equilibrium. This is because spatial pattern is formed through self- organizing behavior that includes schooling, local enhancement and area-restricted search (ARS). Schooling and local enhancement are processes with strong positive density dependence that destabilize the predator-prey interaction locally. However, the unstable local dynamics might be stabilized by spatial constraints and the effects of ARS processes at large scales.