Showing papers in "Marine Ecology Progress Series in 2008"

Ecosystem effects of ocean acidification in times of ocean warming: a physiologist’s view

Abstract: Ocean warming and acidification occur at global scales and, in the case of temperature, have already caused shifts in marine ecosystem composition and function. In the case of CO2-induced ocean hypercapnia and acidification, however, effects may still be so small that evidence for changes in the field is largely lacking. Future scenarios indicate that marine life forms are threatened by the specific or synergistic effects of factors involved in these processes. The present paper builds on the view that development of a cause and effect understanding is required beyond empirical observations, for a more accurate projection of ecosystem effects and for quantitative scenarios. Identification of the mechanisms through which temperatureand CO2-related ocean physicochemistry affect organism fitness, survival and success, is crucial with this research strategy. I suggest operation of unifying physiological principles, not only of temperature but also CO2 effects, across animal groups and phyla. Thermal windows of optimized performance emerge as a basic character defining species fitness and survival, including their capacity to interact with other species. Through effects on performance at the level of reproduction, behaviour and growth, ocean acidification acts especially on lower marine invertebrates, which are characterized by a low capacity to compensate for disturbances in extracellular ion and acid–base status and sensitivity of metabolism to such disturbances. Available data suggest that one key consequence of these features is a narrowing of thermal tolerance windows, as well as a reduced scope for performance at ecosystem level. These changes in bioenvelopes may have major implications for the ranges of geographical distribution of these organisms and in species interactions.

Effects of CO2-driven ocean acidification on the early developmental stages of invertebrates

Abstract: CO2 emissions arising from the burning of fossil fuels have altered seawater chemistry far more rapidly than the Earth has previously experienced, and the rate and extent of this change are expected to affect shallow water marine organisms. The increased CO2 diffuses from the atmos- phere into ocean surface waters, resulting in increased partial pressure of CO2, and reduced (CO3 2- ) and pH. The CO2-driven ocean acidification leads to a decrease in calcium carbonate (CaCO3) satu- ration state in the ocean surface waters and has potential impacts on calcifiers. The present study focuses on the effects of ocean acidification on early developmental and reproductive stages of calci- fiers, both of which are believed to be the most vulnerable stages to environmental change within a life cycle. Laboratory experiments revealed that ocean acidification has negative impacts on the fer- tilization, cleavage, larva, settlement and reproductive stages of several marine calcifiers, including echinoderm, bivalve, coral and crustacean species. There appear to be significant ontogenetic impacts and species-specific differences in tolerance to the high CO2 levels. The conclusion is that future changes in ocean acidity will potentially impact the population size and dynamics, as well as the community structure of calcifiers, and will therefore have negative impacts on marine eco- systems. Further studies are needed to evaluate the potential impacts on non-calcifiers, as well as the synergistic impacts of ocean acidification and climate change. Studies should also focus on the adaptive capability of marine organisms, which will be crucial to the ability to forecast how marine organisms and ecosystems will respond to the world's oceans as they warm and acidify.

Invasive Indo-Pacific lionfish Pterois volitans reduce recruitment of Atlantic coral-reef fishes

Abstract: The Indo-Pacific lionfish Pterois volitans, introduced to Florida waters in the early 1990s, is currently spreading rapidly throughout the Caribbean region This invasive carnivore may cause deleterious changes in coral-reef ecosystems via predation on native fishes and invertebrates as well as competition with native predators We conducted a controlled field experiment using a matrix of translocated coral and artificial patch reefs to examine the short-term effects of lionfish on the recruit- ment of native reef fishes in the Bahamas Lionfish caused significant reductions in the recruitment of native fishes by an average of 79% over the 5 wk duration of the experiment This strong effect on a key life stage of coral-reef fishes suggests that invasive lionfish are already having substantial nega- tive impacts on Atlantic coral reefs While complete eradication of lionfish in the Atlantic is likely impossible, it would be prudent to initiate focused lionfish control efforts in strategic locations

Sensitivity of phytoplankton to future changes in ocean carbonate chemistry: current knowledge, contradictions and research directions

Abstract: Despite their microscopic size, marine phytoplankton are responsible for about half of the global primary production and represent the basis of the marine food web. This diverse group of organisms drives important biogeochemical cycles, exporting massive amounts of carbon to deep waters and sediments, and strongly influencing ocean–atmosphere gas exchanges. Anthropogenic climate change will result in significant alterations in the marine environment over the next 100 yr and beyond. The increase in atmospheric CO2 has already caused significantly higher aquatic CO2 concentrations and lower pH values (‘ocean acidification’) than in pre-industrial times. Rising temperatures will also impact surface ocean stratification, which in turn will affect the surface-water light regime and nutrient input from deeper layers. Phytoplankton will be affected by these environmental changes in many ways. In this article we assess the possible responses of different phytoplankton groups with regard to the expected physico-chemical changes. In addition to summarizing laboratory and field studies, we outline the current understanding of the underlying mechanisms that cause processes such as photosynthesis, calcification, and nitrogen fixation to be sensitive to ocean acidification. We describe different approaches to manipulate carbonate chemistry (e.g. acid/base or CO2 addition), discuss their potential to simulate future ocean acidification, and allude to common problems in experiments caused, for instance, by high biomass or the use of buffers. In addition to guidelines for CO2 perturbation experiments, we argue that it is essential to look at multiple environmental factors in combination with CO2, to aim for process-understanding rather than correlation, and to assess a wider diversity of phytoplankton species both in laboratory and field studies.

Life on the margin: implications of ocean acidification on Mg-calcite, high latitude and cold-water marine calcifiers

Abstract: Future anthropogenic emissions of CO2 and the resulting ocean acidification may have severe consequences for marine calcifying organisms and ecosystems. Marine calcifiers depositing calcitic hard parts that contain significant concentrations of magnesium, i.e. Mg-calcite, and calcify- ing organisms living in high latitude and/or cold-water environments are at immediate risk to ocean acidification and decreasing seawater carbonate saturation because they are currently immersed in seawater that is just slightly supersaturated with respect to the carbonate phases they secrete. Under the present rate of CO2 emissions, model calculations show that high latitude ocean waters could reach undersaturation with respect to aragonite in just a few decades. Thus, before this happens these waters will be undersaturated with respect to Mg-calcite minerals of higher solubility than that of aragonite. Similarly, tropical surface seawater could become undersaturated with respect to Mg- calcite minerals containing ≥12 mole percent (mol%) MgCO3 during this century. As a result of these changes in surface seawater chemistry and further penetration of anthropogenic CO2 into the ocean interior, we suggest that (1) the magnesium content of calcitic hard parts will decrease in many ocean environments, (2) the relative proportion of calcifiers depositing stable carbonate minerals, such as calcite and low Mg-calcite, will increase and (3) the average magnesium content of carbonate sedi- ments will decrease. Furthermore, the highest latitude and deepest depth at which cold-water corals and other calcifiers currently exist will move towards lower latitudes and shallower depth, respec- tively. These changes suggest that anthropogenic emissions of CO2 may be currently pushing the oceans towards an episode characteristic of a 'calcite sea.'

Oceanic circumpolar habitats of Antarctic krill

Abstract: Surveys of Euphausia superba often target localised shelves and ice edges where their growth rates and predation losses are atypically high. Emphasis on these areas has led to the current view that krill require high food concentrations, with a distribution often linked to shelves. For a wider, circumpolar perspective, we compiled all available net-based density data on postlarvae from 8137 mainly summer stations from 1926 to 2004. Unlike Antarctic zooplankton, the distribution of E. superba is highly uneven, with 70% of the total stock concentrated between longitudes 0° and 90°W. Within this Atlantic sector, krill are abundant over both continental shelf and ocean. At the Antarctic Peninsula they are found mainly over the inner shelf, whereas in the Indian–Pacific sectors krill prevail in the ocean within 200 to 300 km of the shelf break. Overall, 87% of the total stock lives over deep oceanic water (>2000 m), and krill occupy regions with moderate food concentrations (0.5 to 1.0 mg chl a m–3). Advection models suggest some northwards loss from these regions and into the low chlorophyll belts of the Antarctic Circumpolar Current (ACC). We found possible evidence for a compensating southwards migration, with an increasing proportion of krill found south of the ACC as the season progresses. The retention of krill in moderately productive oceanic habitats is a key factor in their high total production. While growth rates are lower than over shelves, the ocean provides a refuge from shelf-based predators. The unusual circumpolar distribution of krill thus reflects a balance between advection, migration, top–down and bottom–up processes.

Near-future level of CO2-driven ocean acidification radically affects larval survival and development in the brittlestar Ophiothrix fragilis

Abstract: The world's oceans are slowly becoming more acidic. In the last 150 yr, the pH of the oceans has dropped by ~0.1 units, which is equivalent to a 25% increase in acidity. Modelling pre- dicts the pH of the oceans to fall by 0.2 to 0.4 units by the year 2100. These changes will have signif- icant effects on marine organisms, especially those with calcareous skeletons such as echinoderms. Little is known about the possible long-term impact of predicted pH changes on marine invertebrate larval development. Here we predict the consequences of increased CO2 (corresponding to pH drops of 0.2 and 0.4 units) on the larval development of the brittlestar Ophiothrix fragilis, which is a key- stone species occurring in high densities and stable populations throughout the shelf seas of north- western Europe (eastern Atlantic). Acidification by 0.2 units induced 100% larval mortality within 8 d while control larvae showed 70% survival over the same period. Exposure to low pH also resulted in a temporal decrease in larval size as well as abnormal development and skeletogenesis (abnormali- ties, asymmetry, altered skeletal proportions). If oceans continue to acidify as expected, ecosystems of the Atlantic dominated by this keystone species will be seriously threatened with major changes in many key benthic and pelagic ecosystems. Thus, it may be useful to monitor O. fragilis populations and initiate conservation if needed.

Gelatinous plankton: irregularities rule the world (sometimes)

Abstract: In spite of being one of the most relevant components of the biosphere, the plank- ton-benthos network is still poorly studied as such. This is partly due to the irregular occurrence of driving phenomena such as gelatinous plankton pulses in this realm. Gelatinous plankters rely on their life cycles and histories to exploit temporarily abundant resources with an undeniable, but often overlooked, impact on marine food webs. Dramatic increases of gelatinous filter-feeders and/or carnivores (both native and nonindigenous species) are frequently observed, and explana- tions of these blooms alternatively invoke ecosystem variability, climate change, unspecified anthropogenic perturbation or removal of top predators from trophic networks. Gelatinous plank- ters, however, are not anomalies in plankton dynamics: the recognition of the ecological impor- tance of their pulses, based on their life cycle patterns (often involving benthic stages), is a critical breakthrough to understand the cycling diversity of plankton in space and time. The current study focuses on the many neglected aspects of the ecology and biology of gelatinous zooplankton, describes how life cycle patterns are central in marine ecology, as are the pulses of gelatinous organisms, and highlights how such a dramatic lack of knowledge can affect our understanding of the marine ecosystem as a whole.

Vertical swimming behavior influences the dispersal of simulated oyster larvae in a coupled particle-tracking and hydrodynamic model of Chesapeake Bay

Abstract: Because planktonic organisms have swimming speeds that are orders of magnitude lower than horizontal current velocities, it is unclear whether behavior of weak-swimming bivalve larvae could influence dispersal distance, encounters with suitable habitat, or subpopulation connec- tivity. We used a numerical approach to investigate whether these processes could be affected by species-specific differences in larval vertical swimming behavior of 2 oyster species (Crassostrea vir- ginica and C. ariakensis) in Chesapeake Bay, a partially mixed estuary. A coupled particle-tracking and hydrodynamic model was forced with observed winds and freshwater flow and included the best available estimate of present-day oyster habitat. Model scenarios were conducted with hydrody- namic predictions from June to September, 1995 to 1999, to simulate a range of environmental con- ditions. Simple larval swimming behaviors were parameterized for the 2 oyster species with results from preliminary laboratory experiments and literature. To isolate the effect of circulation, settlement habitat, and larval behavior on the spatial trajectories of particles, vertical swimming velocity was the only biological process represented in the model; egg production and larval growth were not included. Differences in larval swimming behavior had significant consequences for particle trans- port in Chesapeake Bay by influencing dispersal distances, transport success, and the degree of con- nectivity between 'subpopulations' in different tributaries. Most particles (>96%) did not return to the same reef on which they were released, and there were behavior-dependent differences in spa- tial patterns of the 'source' and 'sink' characteristics of oyster reefs. Simulated larval behavior had greater influence on spatial patterns of transport success than did interannual differences in circula- tion patterns. These model results have implications for fisheries management and oyster restoration activities.

Recovering a lost baseline: missing kelp forests from a metropolitan coast

Abstract: There is concern about historical and continuing loss of canopy-forming algae across the world's temperate coastline. In South Australia, the sparse cover of canopy-forming algae on the Adelaide metropolitan coast has been of public concern with continuous years of anecdotal evidence culminating in 2 competing views. One view considers that current patterns existed before the onset of urbanisation, whereas the alternate view is that they developed after urbanisation. We tested hypothe- ses to distinguish between these 2 models, each centred on the reconstruction of historical covers of canopies on the metropolitan coast. Historically, the metropolitan sites were indistinguishable from con- temporary populations of reference sites across 70 km (i.e. Gulf St. Vincent), and could also represent a random subset of exposed coastal sites across 2100 km of the greater biogeographic province. Thus there was nothing 'special' about the metropolitan sites historically, but today they stand out because they have sparser covers of canopies compared to equivalent locations and times in the gulf and the greater province. This is evidence of wholesale loss of canopy-forming algae (up to 70%) on parts of the Adelaide metropolitan coast since major urbanisation. These findings not only set a research agenda based on the magnitude of loss, but they also bring into question the logic that smaller metropolitan populations of humans create impacts that are trivial relative to that of larger metropolitan centres. Instead, we highlight a need to recognise the ecological context that makes some coastal systems more vulnerable or resistant to increasing human-domination of the world's coastlines. We discuss challenges to this kind of research that receive little ecological discussion, particularly better leadership and administration, recognising that the systems we study out-live the life spans of individual research groups and operate on spatial scales that exceed the capacity of single research providers.

Impact of coral predators on tropical reefs

Abstract: It is well known that herbivores have numerous and diverse impacts on plant and algal fitness, community structure and ecosystem function. The importance of corallivory as a selective force, however, has been underestimated. Corallivores, or consumers of live coral tissue, employ a wide variety of feeding strategies and can be obligate or facultative coral feeders. Our literature review reveals a complex array of corallivores across the globe, represented by 11 families of fishes and 5 invertebrate phyla and totaling over 160 species known to consume scleractinian corals world- wide. Importantly, although these corallivores span a wide taxonomic range, we found that they have been reported to feed on relatively few genera of hard corals, specifically, on only 28 scleractinian genera worldwide. Damage by corallivores ranges from minor to lethal, but there is a growing body of evidence to support that even limited removal of tissue or skeletal structures has growth and/or fit- ness consequences for a scleractinian coral colony. In light of increasing reef stressors and diminish- ing coral populations, we suggest that the role of corallivores in reef trophodynamics is more complex than appreciated previously.

Biological responses in marine no-take reserves versus partially protected areas

Abstract: Marine Protected Areas (MPAs) are a common tool for conserving and managing marine and coastal ecosystems. MPAs encompass a range of protection levels, from fully protected no-take reserves to restriction of only particular activities, gear types, user groups, target species, or extrac- tion periods. There is a growing body of scientific evidence supporting the ecological benefits of full reserve protection, but it is more difficult to generalize about the effects of other types of MPAs, in part because they include a range of actual protection levels. However, it is critical to determine whether partial protection and no-take reserves provide similar ecological benefits given potential economic costs of lost fishing grounds in no-take areas, common sociopolitical opposition to full pro- tection, and promotion of partially protected areas as a compromise solution in ocean zoning dis- putes. Here we synthesize all empirical studies comparing biological measures (biomass, density, species richness, and size of organisms) in no-take marine reserves and adjacent partially protected and unprotected areas across a range of geographic locations worldwide. We demonstrate that while partially protected areas may confer some benefits over open access areas, no-take reserves gener- ally show greater benefits and yield significantly higher densities of organisms within their bound- aries relative to partially protected sites nearby.

Increasing relative abundance of Porites astreoides on Caribbean reefs mediated by an overall decline in coral cover

Abstract: On most coral reefs, the percentage cover of scleractinian corals has declined greatly over the last 30 yr; some species that are more resistant to mortality have been less affected than others. Porites astreoides is one species that has become a more prominent com- ponent of coral reef communities throughout the Caribbean. Analyses of coral reefs in shallow water (5 to 6 m depth) at 6 locations spanning a 4100 km arc of the Caribbean were used to evaluate the contri- bution of P. astreoides to contemporary reefs. Photo- quadrats recorded in 2003/2004 were used to esti- mate the percentage cover and colony density of P. astreoides, and colony size-frequency structure was analyzed to gain insight into demographic processes. At all locations, reefs were characterized by <15% coral cover, but 16 to 72% of this cover was P. astreoides, at mean densities of 1.76 colonies per 0.25 m 2 . Most of these colonies (62%) were ≤50 cm 2 in size, demonstrating that the populations were young and influenced strongly by recruitment. Comparison to historical data collected between 1974 and 1992 suggests that the relative percentage cover of P. astreoides in shallow water reef habitats has increased at a rate of 1.5% yr -1 , from <20% in the 1970s to 50% in 2003/2004. These findings indicate that community structure of Caribbean coral reefs is changing on a decadal time scale to become dominated by 'weedy' corals that form rapidly growing, small colonies that are short lived and quickly replaced.

Fishes in high-CO2, acidified oceans

Abstract: Research interest in CO2-driven ocean acidification has been centered on certain groups of calcifying marine organisms, but knowledge on the possible impacts of ocean acidification on fish is limited. Our survey of the existing literature on the effects of increased pCO2 on fish (total of 116 papers) revealed that few studies were conducted under pCO2 conditions relevant to the future scenarios of ocean acidification. Information is nearly absent on reproduction, early development, and behaviour of marine fish. The short experimental durations of these studies preclude forecasting of how mortality and growth of marine fish would be affected by future increases in seawater CO2. Fish have been shown to maintain their oxygen consumption under elevated pCO2 conditions, in contrast to declines seen in several marine invertebrates, in spite of possible additional energetic costs incurred by higher pCO2. Impacts of prolonged CO2 exposure on reproduction, early development, growth, and behaviour of marine fish are important areas that need urgent investigation. There is also a need to rapidly advance research into possible acclimation of marine fish to high pCO2 environments, endocrine responses to prolonged CO2 exposure, and indirect influences through food availability and quality on fish growth, survival and reproduction. Useful guidance could be gained from the rich literature on the effects of freshwater acidification.

Importance of genetic diversity in eelgrass Zostera marina for its resilience to global warming

Abstract: Effects of global warming on marine ecosystems are far less understood than they are in terrestrial environments Macrophyte-based coastal ecosystems are particularly vulnerable to global warming, because they often lack species redun- dancy We tested whether summer heat waves have negative effects on an ecologically important eco- system engineer, the eelgrass Zostera marina L, and whether high genotypic diversity may provide re- silience in the face of climatic extremes In a meso- cosm experiment, we manipulated genotypic diver- sity of eelgrass patches fully crossed with water temperature (control vs temperature stress) over 5 mo We found a strong negative effect of warming and a positive effect of genotypic diversity on shoot densities of eelgrass These results suggest that eel- grass meadows and associated ecosystem services will be negatively affected by predicted increases in summer temperature extremes Genotypic diver- sity may provide critical response diversity for main- taining seagrass ecosystem functioning, and for adaptation to environmental change

Experimental assessment and modeling evaluation of the effects of the seagrass Posidonia oceanica on flow and particle trapping

Abstract: Retention of particles in seagrass canopies is usually attributed to only the indirect, attenuating effects canopies have on flow, turbulence and wave action, promoting sedimentation and reducing resuspension within seagrass meadows. Yet recent evidence suggests that seagrasses are also able to affect particle flux directly through loss of momentum and increased path length derived from collisions with leaves and binding of particles. We evaluated the role of Posidonia oceanica on flow and associated particle trapping through flume experiments. Our results confirm the existence of 2 dynamically different environments, viz. (1) the below-canopy habitat, with low shear stress and reduced turbulence, and (2) the canopy-water interface region, characterized by high shear stress and turbulence intensity, where vertical transport of momentum is enhanced. At relatively low free stream velocities (i.e. 0.05 and 0.10 m s -1 ) sediment concentration decreased much faster when a Posidonia meadow was present in the flume, indicating major particle trapping in the seagrass canopy. Fluxes to the sediment (as shown by large negative peaks in Reynolds stress inside the Posi- donia meadow) indicated 2 to 6 times more sediment transport to the bottom when a meadow is pre- sent. However, calculations based on the experimental results point to loss rates an order of magni- tude larger in a Posidonia meadow. We hypothesize that direct effects of particle collisions with leaves are responsible for this discrepancy, and we explore possible interactions with a simple model. Using only collisions as a loss factor, the model predicts that the probability a particle is lost from the flow upon a collision is 2 to 3%. Previously observed leaf density and flow velocity effects on particle loss rates were explained by the model. Fitting the model to our experimentally obtained particle dis- appearance rates in vegetation indicated that around 27% of particle momentum is lost upon each collision with a leaf. We hypothesize that physical filtration by sediment collisions with plant struc- tures plays a role in particle removal in aquatic systems.

Life strategies of fishes in European estuaries: the functional guild approach

Abstract: The structure and functioning of estuarine fish assemblages have been analysed using data sets for 38 transitional waters covering all European latitudes, including NE Atlantic estuaries, Mediterranean lagoons and Scandinavian fjords. The fish species were assigned to functional guilds covering estuarine use, mode of feeding and reproductive strategy, thus describing the use made of transitional waters by fishes. The importance of estuaries as temporary biotopes (migration and nurs- ery routes) for fish species has been identified together with the predominance of feeding on the detritivorous hyperbenthos and infauna. The high incidence of protective breeders in estuaries, as a mechanism to prevent the flushing out of young, has also been identified. These findings allow the validation of the functional guild approach, emphasising its use for the understanding of the function- ing of estuaries and for their management and the protection of their ecological goods and services.

Differences in fish-assemblage structure between fished and unfished atolls in the northern Line Islands, central Pacific

Abstract: We describe the abundance, biomass, size composition, and trophic structure of fish assemblages of shallow (10 m depth) fore reef habitats at 2 US Pacific atolls (Kingman, Palmyra) and 2 Kiribati-owned atolls (Tabuaeran, Kiritimati) in the northern Line Islands. Our characterization spans several coincident gradients (in human habitation and exploitation, latitude, and nutrient upwelling) from uninhabited, presently unfished, and oligotrophic Kingman to relatively densely populated, fished, and equatorially upwelled Kiritimati. Major findings are most consistent with direct effects of extraction on large-bodied predators and indirect effects on lower-level assemblage structure. Fish assemblages at Palmyra and especially Kingman atolls were characterized by high total standing biomass, large average body sizes, a preponderance of apex predators and other pis- civorous fishes in an inverted biomass pyramid, few and small planktivorous fishes, and herbivores dominated by non-territorial species. Median body sizes at color change from initial to terminal phase (an index of sex change in parrotfishes) were also small for 4 species of parrotfish at Kingman and Palmyra. Fish assemblages at Tabuaeran and especially Kiritimati atolls had starkly contrasting char- acteristics: piscivorous and other fisheries-targeted fishes were depauperate, lower-trophic levels dominated fish biomass, planktivorous fishes were larger-bodied and more numerous, territorial her- bivores were better represented, and size at maturation in parrotfishes was proportionately larger. Our results show the effects that even modest fishing effort can have on assemblage structure and indicate the importance of reefs like Kingman as increasingly rare relicts of natural coral reefs, pro- viding insights into the natural structure and function of these ecosystems.

Loss of fucoid algae along a gradient of urbanisation, and structure of benthic assemblages

Abstract: Canopy-forming macroalgae of the genus Cystoseira are being lost in several areas of the Mediterranean Sea. Cystoseira amentacea var. stricta and C. compressa are common species in the Ligurian Sea; they are distributed in patches, but their abundance and distribution is locally vari- able. We investigated changes in relative cover, biomass and morphology of Cystoseira amentacea var. stricta and C. compressa with increasing urbanisation, and effects of the presence or absence of Cystoseira species on the composition and structure of understorey assemblages. C. amentacea var. stricta habitats were lost close to urban areas, while C. compressa slightly increased. The morpholog- ical characteristics of these 2 species were very variable in space and time, and did not vary with urbanisation. Assemblages lacking canopy differed markedly from Cystoseira-dominated assem- blages, particularly assemblages dominated by Corallina elongata, the species most responsive to changes in habitat structure and urbanisation, which forms dense turfs in urban habitats lacking canopies. Marked species-specific differences between the assemblages dominated by the 2 Cysto- seira species were detected. C. amentacea var. stricta is a key species maintaining habitat complex- ity and species diversity in Mediterranean rocky shores and we recommend additional conservation actions, such as habitat restoration by transplantation of this endangered species.

Spillover from six western Mediterranean marine protected areas: evidence from artisanal fisheries

Abstract: This study investigated spillover (biomass export) around 6 marine protected areas (MPAs) in the western Mediterranean based on catch and effort data from artisanal fisheries. The selected MPAs were Cerbere-Banyuls and Carry-le-Rouet in France, and Medes, Cabrera, Tabarca, and Cabo de Palos in Spain. These MPAs had been functional for more than 8 yr and incorporate areas of fisheries closure and restricted use where fishing is limited. We based our study on the hypotheses that, in the presence of biomass export, (1) fishing effort would concentrate close to MPA boundaries, and (2) fishery production, expressed as catch per unit area (CPUA), would be highest near MPA boundaries and decrease with dis- tance. We selected data from 14 'fishing tactics' using gill nets, trammel nets and bottom long-lines target- ing sparids, mullids, serranids, scorpaenids and palinurids. We analyzed the spatial distribution of effort, fishery production and revenues per unit area, using generalized additive models (GAMs), and we tested regression slopes of effort density and CPUA with distance to closure boundaries, using generalized lin- ear models (GLMs). GAMs allowed us to recognize habitat discontinuities or 'hot spots' of high production in the vicinity of the MPAs, and to identify the extent of potential spillover effects in order to implement GLMs. We found evidence of effort concentration and high fishery production near fisheries closures for all fishing tactics analyzed and significant negative slopes for most. Revenues generally followed trends similar to CPUA. Significant negative slopes from GLM of effort density and CPUA with distance from fisheries closures were indicative of biomass export where habitats across closure boundaries had some degree of continuity. The spatial extent of spillover was consistent with species mobility and fisheries effi- ciency and extended 700 to 2500 m from fishery closure boundaries. Our results suggest that coastal MPAs can be an effective management tool for artisanal fisheries in the region and can be extended to the rest of the western Mediterranean, as the fishing tactics studied are typical of the region.

High connectivity of Indo-Pacific seagrass fish assemblages with mangrove and coral reef habitats

Abstract: Marine ecosystems throughout the Indo-Pacific region are highly threatened by anthropogenic stressors, yet the faunal interaction between different component habitats remains poorly understood. This information is vital as stress on one inter-connected habitat may have cascade effects on other habitats. The present study focused on the impact of inter-habitat connectivity on seagrass fish assemblages, specifically between seagrass, mangrove and reef habitats. Fish were sampled using a seine net within 3 seagrass habitats (seagrass near to reef, seagrass near to reef and mangrove, and seagrass near to mangrove) within eastern Indonesia. Visual surveys were also conducted within mangrove habitats. Fish abundance and species richness in seagrass beds in close proximity to mangroves was at least twice that found in seagrass beds that were distant from mangrove habitat. The trophic structures of seagrass fish assemblages change from being dominated by predators and omnivores close to the reef, to assemblages high in planktivores and herbivores close to mangroves. We found that mangroves enhance the fish assemblages of nearby seagrass beds probably by increasing the availability of shelter and food provision. This study indicates that Indo-Pacific seagrass beds play an important fish nursery role, which is influenced by the availability of nearby reef and mangrove habitats. Our research supports the need for ecosystem-level management of shallow water tropical habitats, but also suggests that successful management requires local-level knowledge of habitat interactions to successfully enhance or conserve fish assemblages. © Inter-Research 2008.

Wave exposure indices from digital coastlines and the prediction of rocky shore community structure

Abstract: Topographical wave exposure indices allow objective assessment of the degree of wave action at coastal sites. We present a grid-based method for rapidly calculating indices at fine spatial resolutions along whole coastlines, and evaluate the power of candidate indices in predicting composi- tion of rocky shore communities. The method has 3 stages: (1) a grid is created from a vector-based digital coastline using geographical information systems (GIS) software; (2) for every coastal cell, wave fetch is determined as the distance to the nearest land cell in 16 angular sectors, using coarse-, medium- and fine-resolution searches of the surrounding cells up to a distance of 200 km; (3) wind energy (average wind speed and propor- tional occurrence) in each sector is calculated for nearby coastal sites. We calculated the average fetch in each sector ( F) and the sum of products of fetch and wind energy ( W) . A total of 57 species were surveyed at 185 sites in west Scotland for determination of trends with wave indices. Average wave fetch with a 200 m scale grid explained > 50% of the variation in the first principal compo- nent of the species-sites abundance matrix, with shore extent explaining another 10%. Incorporating wind data in the indices had a negligible effect on predictive power. Species diversity explained 61% of the variance in the second principal component and declined from low to high pelagic primary pro- ductivity. Separating direct physical effects from biological effects, such as food supply or grazing could potentially help us better understand the pro- cesses structuring biological communities on rocky shores.

Tidal dynamics, topographic orientation, and temperature-mediated mass mortalities on rocky shores

Abstract: Temperature is among the main structuring agents on rocky intertidal shores. Although infrequent mortality events associated with high temperatures have been observed in several inter- tidal taxa, careful documentation of these events is rare, and small-scale variability in mortality patterns remains poorly understood. In Bodega Bay, California, USA, 2 mortality events occurred on exposed rocky shores during the spring of 2004 when low tides occurred around mid-day. Limpets Lottia scabra were killed during unseasonably warm weather in mid-March. In late April, record- high temperatures resulted in widespread mortality of the mussel Mytilus californianus. Levels of mortality for both species were closely associated with small-scale variability in temperature, which in turn was closely associated with substratum orientation. Invertebrates occupying surfaces facing the sun when stress was most intense were much more likely to die than those living on surfaces angled ≥45° away. Because the within-day timing of thermal stress varied seasonally, the highest mortalities were recorded on southwest-facing surfaces on the March afternoon low tide and on southeast-facing surfaces on the April morning low tide. Limpets and mussels showed little mortality during the events that were harmful to the other taxon, suggesting that these different taxa respond to different aspects of their thermal environment. If climate change results in more frequent and more severe episodes of thermal stress, future ecological change may also be heavily dependent on tidal dynamics and small-scale variation in substrate orientation.

Stable isotopes reveal the trophic position and mesopelagic fish diet of female southern elephant seals breeding on the Kerguelen Islands

Abstract: Trophic interactions between organisms are the main drivers of ecosystem dynamics, but scant dietary information is available for wide-ranging predators during migration. We investi- gated feeding habits of a key consumer of the Southern Ocean, the southern elephant seal Miroun- gia leonina, by comparing its blood δ 13 C and δ 15 N values with those of various marine organisms, including crustaceans, squid, fishes, seabirds and fur seals. At the end of winter, δ 13 C values (-23.1 to -20.1‰) indicate that female elephant seals forage mainly in the vicinity of the Polar Front and in the Polar Frontal Zone. Trophic levels derived from δ 15 N values (trophic level = 4.6) show that the southern elephant seal is a top consumer in the pelagic ecosystem that is dominated by colossal squid. The mean δ 15 N value of seals (10.1 ± 0.3‰) indicates that they are not crustacean eaters, but instead feed on crustacean-eating prey. Surprisingly, most of the previously identified prey species have isotope δ 13 C and δ 15 N values that do not fit with those of potential food items. The most singular pattern to emerge from δ 15 N values of predators and prey is that female seals are likely to feed on myctophid fishes, not squid or Patagonian toothfish. We therefore suggest that they occupy a unique trophic niche amongst the guild of air-breathing, diving vertebrates by feeding on mesopelagic fish at great depths. In turn, this finding emphasizes the role of myctophids in oceanic waters and will help to quantify and model fluxes of matter and energy within the pelagic ecosystem of the Southern Ocean.

Migration patterns of white sharks Carcharodon carcharias tagged at Guadalupe Island, Mexico, and identification of an eastern Pacific shared offshore foraging area

Abstract: Pop-up satellite archival tags (PSATs) were used to study the migration patterns and habitat preference of 56 white sharks tagged off Guadalupe Island, Mexico, between 2000 and 2008. Nine tags were recovered, providing 1021 d of high resolution (2 min) archival data. Two individual sharks were tagged in consecutive years, providing 2 yr of tracking data for each individual. White sharks were found to make long-range, seasonal migrations from Guadalupe Island to an offshore pelagic habitat, sometimes traveling as far west as the Hawaiian Islands. The pelagic region inhabited by Guadalupe Island white sharks corresponds with that reported for sharks tagged off central Cali- fornia; thus we have termed it the Shared Offshore Foraging Area (SOFA). Sharks spent at least 5 mo off Guadalupe Island before beginning their migration around 15 February on average (earliest 21 December, latest 5 May). They traveled through a migration corridor in an average time of 16 d at an average speed of 3.2 km h -1 and remained in the SOFA for an average duration of 140 d. Males and females began their offshore migrations around the same time and traveled to the same area, but males were found to return to Guadalupe Island on average around 22 July (earliest 15 July, latest 30 July), while females remained in the SOFA into early autumn. Diving profiles of sharks in the SOFA strongly suggest feeding behavior; however, the targeted prey species are unknown at this time.

Major bulk dissolved organic carbon (DOC) removal by encrusting coral reef cavity sponges

Abstract: We studied the removal of dissolved organic carbon (DOC) and bacterioplankton by the encrusting sponges Halisarca caerulea, Mycale microsigmatosa and Merlia normani in coral reefs along Curacao, Netherlands Antilles. Sponge specimens were collected from coral reef cavities and incubations were done on the fore-reef slope at 12 m depth. The concentrations of DOC and bacteri- oplankton carbon (BC) were monitored in situ, using incubation chambers with sponges and without sponges (incubations with coral rock or ambient reef water only). Average (±SD) DOC removal rates (in μmol C cm -3 sponge h -1 ) amounted to 13.1 ± 2.5, 15.2 ± 0.9 and 13.6 ± 2.4 for H. caerula, M. micro- sigmatosa and M. normani, respectively. The DOC removal rates by the 3 sponges were on average 2 orders of magnitude higher than BC removal rates and accounted for more than 90% of the total organic carbon removal. Total organic carbon removal rates presented here were the highest ever reported for sponges. In an additional experiment with H. caerulea, the fate of organic carbon was reconstructed by measuring dissolved oxygen (O2) removal and dissolved inorganic carbon (DIC) release in a laminar flow chamber. H. caerulea respired 39 to 45% of the organic carbon removed. The remaining 55 to 61% of carbon is expected to be assimilated. We argue that H. caerulea may have a rapid turnover of matter. All 3 sponge species contained associated bacteria, but it is unclear to what extent the associated bacteria are involved in the nutrition of the sponge. We conclude that the 3 sponge-microbe associations are (related to the availability of dissolved and particulate carbon sources in the ambient water) 'dissolved organic matter (DOM)-feeders' and encrusting sponges are of quantitative importance in the removal of DOC in coral reef cavities.

Ontogenetic changes in diet and habitat use in green sea turtle (Chelonia mydas) life history

Abstract: Green turtles Chelonia mydas are endangered, long-lived marine reptiles that display an ontogenetic shift in diet and habitat use during development. During their early life stage, juvenile green turtles in the southwestern Pacific inhabit the pelagic zone where they feed omnivorously on neustonic material. At approximately 44 cm curved carapace length they recruit to inshore foraging habitats where they become primarily herbivorous. In this study we investigate the change in stable isotope (δ13C and δ15N) composition of green turtle epidermal tissue throughout their life history to examine this ontogenetic shift in diet and habitat as it occurs in a southwestern Pacific green turtle population. Turtles that had recently recruited to foraging grounds in Moreton Bay, Australia had significantly higher δ15N isotopic signatures when compared with all other life history groups examined and significantly lower δ13C when compared with all age classes other than pelagic juveniles. Adult and large immature turtles had similar isotopic signatures and were both significantly enriched in 13C when compared with hatchlings and small immature turtles. These results support previous observations that suggest pelagic juveniles are foraging in a different habitat and at a higher trophic level than turtles captured in the neritic environment. This is the first study to capture the entire life history of green turtles in terms of foraging ecology and supports the ontogenetic shift previously observed in traditional diet and behavioral studies of green turtles.

Drifting fish aggregation devices could act as an ecological trap for tropical tuna species

Abstract: Purse seine fishing on fish aggregating devices (FADs) has expanded considerably during the last 15 yr in tropical tuna purse seine fisheries, and FADs currently account for about 70 % of their reported tuna catches. The scientific community has expressed concern over the consequences of this fishing practice in terms of yield per recruit and suspected detrimental effects on FAD-associated tunas. To explore possible detrimental effects, we compared stomach fullness, fish plumpness, growth rate, and migration behaviour between free school and drifting FAD-associated tunas for skipjack tuna Katsuwonus pelamis and yellowfin tuna Thunnus albacares caught in the Atlantic and Indian Oceans. Significant differences in fish plumpness and individual growth rates were found, suggesting that individuals associated with drifting FADs were less healthy than those in free schools. Since stomach fullness indicated that tunas associated with FADs eat less than those in free schools, the difference in growth rate and condition could be the consequence of altered feeding patterns. For each species, significant changes in migratory direction and displacement rates were observed in the presence of drifting FADs. These findings support the hypothesis that FADs act as a super-stimulus, misleading tunas to make inappropriate habitat selection. However, further studies are required to investigate the long-term effect of FADs on the entire life cycle of tunas.

Foraging ecology of loggerhead sea turtles Caretta caretta in the central Mediterranean Sea: evidence for a relaxed life history model

Abstract: In the central Mediterranean Sea, gut contents and feces of 95 turtles captured by bottom trawlers and pelagic longliners fishing in neritic and oceanic areas, respectively, were examined. Ben- thic prey were more abundant than pelagic, a probable bias due to the higher digestibility of the latter. Animal and plant taxa belonging to 12 Phyla and 20 Classes were observed, with 63 new records of prey species, and Malacostraca, Gastropoda, and Echinoidea were the most commonly occurring animal classes. Results showed a highly opportunistic foraging behavior by the turtles on both live and dead ma- terial in the epipelagic zone as well as on all types of seafloor. Benthic taxa were found in turtles as small as 26 cm curved carapace length (CCL), indicating an early use of benthic resources, and also among turtles over a wide size range caught by pelagic longliners. The lack of evidence of a strict oceanic/ pelagic stage and of a clear habitat shift in the observed size range (25 to 80.3 cm CCL), when consid- ered together with other recent findings, challenges the current ontogenetic model of life history for the species. A relaxed model is proposed, with an early short obligate epipelagic stage due to limited div- ing capacity, followed by the main opportunistic amphi-habitat stage, with a tendency to prefer benthic prey as turtles grow and their benthic foraging efficiency improves. Under this model, temporary or per- manent association or fidelity to specific oceanic or neritic zones would vary among individuals or pop- ulations according to food availability and oceanographic features in the foraging or migratory areas.