Showing papers in "Marine Ecology Progress Series in 2005"

Eutrophication of Chesapeake Bay: historical trends and ecological interactions

Abstract: This review provides an integrated synthesis with timelines and evaluations of ecological responses to eutrophi- cation in Chesapeake Bay, the largest estuary in the USA. Analyses of dated sediment cores reveal initial evidence of organic enrichment in ~200 yr old strata, while signs of increased phytoplankton and decreased water clarity first appeared ~100 yr ago. Severe, recurring deep-water hypoxia and loss of diverse submersed vascular plants were first evident in the 1950s and 1960s, respectively. The degradation of these benthic habitats has contributed to declines in benthic macro- infauna in deep mesohaline regions of the Bay and blue crabs in shallow polyhaline areas. In contrast, copepods, which are heavily consumed in pelagic food chains, are relatively un- affected by nutrient-induced changes in phytoplankton. Intense mortality associated with fisheries and disease have caused a dramatic decline in eastern oyster stocks and associated Bay water filtration, which may have exacerbated eutrophication effects on phytoplankton and water clarity. Extensive tidal marshes, which have served as effective nutrient buffers along the Bay margins, are now being lost with rising sea level. Although the Bay's overall fisheries production has probably not been affected by eutrophication, decreases in the relative contribution of demersal fish and in the efficiency with which primary production is transferred to harvest suggest funda- mental shifts in trophic and habitat structures. Bay ecosystem responses to changes in nutrient loading are complicated by non-linear feedback mechanisms, including particle trapping and binding by benthic plants that increase water clarity, and by oxygen effects on benthic nutrient recycling efficiency. Observations in Bay tributaries undergoing recent reductions in nutrient input indicate relatively rapid recovery of some ecosystem functions but lags in the response of others.

Effects of long-term moderate hypercapnia on acid-base balance and growth rate in marine mussels (Mytilus galloprovincialis)

Abstract: In the context of future scenarios of progressive accumulation of anthropogenic CO2 in marine surface waters, the present study addresses the effects of long-term hypercapnia on a Mediterranean bivalve, Mytilus galloprovincialis. Sea-water pH was lowered to a value of 7.3 by equilibration with elevated CO2 levels. This is close to the maximum pH drop expected in marine sur- face waters during atmospheric CO2 accumulation. Intra- and extracellular acid-base parameters as well as changes in metabolic rate and growth were studied under both normocapnia and hypercap- nia. Long-term hypercapnia caused a permanent reduction in haemolymph pH. To limit the degree of acidosis, mussels increased haemolymph bicarbonate levels, which are derived mainly from the dissolution of shell CaCO3. Intracellular pH in various tissues was at least partly compensated; no deviation from control values occurred during long-term measurements in whole soft-body tissues. The rate of oxygen consumption fell significantly, indicating a lower metabolic rate. In line with pre- vious reports, a close correlation became evident between the reduction in extracellular pH and the reduction in metabolic rate of mussels during hypercapnia. Analysis of frequency histograms of growth rate revealed that hypercapnia caused a slowing of growth, possibly related to the reduction in metabolic rate and the dissolution of shell CaCO3 as a result of extracellular acidosis. In addition, increased nitrogen excretion by hypercapnic mussels indicates the net degradation of protein, thereby contributing to growth reduction. The results obtained in the present study strongly indicate that a reduction in sea-water pH to 7.3 may be fatal for the mussels. They also confirm previous obser- vations that a reduction in sea-water pH below 7.5 is harmful for shelled molluscs.

Patterns, processes and regulatory mechanisms in sandy beach macrofauna: a multi-scale analysis

Abstract: Physical and biological factors govern com- munity and population features of sandy beach macro- fauna. At the macroscale, species richness decreases from tropical to temperate beaches, and from macrotidal dissipative to microtidal reflective beaches. At the species level, life history traits are highly plastic over latitudinal gradients; large-scale variations in environmental vari- ables modulate intraspecific phenotypic differentiation. At the mesoscale, alongshore and across-shore distribu- tions tend to be unimodal, bell-shaped within a beach, with abundance varying from the central region to the boundaries, even though environmental gradients (wave exposure, salinity) can cause asymmetries. Zona- tion is highly dynamic and not sharply defined. This is attributed to short- (hourly, daily) or medium- (seasonal) term reactions to environmental conditions, passive transport and sorting by the swash (e.g. recruits), active micro-habitat selection (e.g. adults), and intra- and inter- specific interactions. Across-shore distribution may be- come multimodal due to intraspecific segregation by sizes during recruitment. At the microscale (individual neighbourhood or quadrat scale), behavioural factors and intra-/interspecific interactions become more important as density increases. Human induced impacts also gener- ate variability in population demography, structure and dynamics. We identify physical-biological coupling at dif- ferent temporal and spatial scales, emphasizing the role of life history traits in order to assess alternative regula- tory mechanisms and processes. Our synthesis suggests that: (1) biological interactions are more important regu- latory agents than previously thought: in benign dissipa- tive beaches or undisturbed sites, intra- and interspecific competition can be more intense than in reflective beach- es or disturbed sites, where the populations are physi- cally controlled; (2) supralittoral forms are relatively inde- pendent of the swash regime and show no clear response to beach type; (3) marked long-term fluctuations are noticeable in species with planktonic larvae structured as metapopulations, due to environmental disturbances and stochasticity in reproduction and recruitment.

Perspectives on mucus secretion in reef corals

Abstract: The coral surface mucus layer provides a vital interface between the coral epithelium and the seawater environment and mucus acts in defence against a wide range of environmental stresses, in ciliary-mucus feeding and in sediment cleansing, amongst other roles. However, we know surpris- ingly little about the in situ physical and chemical properties of the layer, or its dynamics of formation. We review the nature of coral mucus and its derivation and outline the wide array of roles that are pro- posed for mucus secretion in corals. Finally, we review models of the surface mucus layer formation. We argue that at any one time, different types of mucus secretions may be produced at different sites within the coral colony and that mucus layers secreted by the coral may not be single homogeneous layers but consist of separate layers with different properties. This requires a much more dynamic view of mucus than has been considered before and has important implications, not least for bacterial colonisation. Understanding the formation and dynamics of the surface mucus layer under different environmental conditions is critical to understanding a wide range of associated ecological processes.

From wind to whales: trophic links in a coastal upwelling system

Abstract: Blue whales Balaenoptera musculus meet the highest prey demands of any predator that has ever existed by feeding exclusively upon dense but patchy schools of pelagic euphausiids. We examined the role that seasonally high primary production supported by coastal upwelling com- bined with topographic breaks off California play in creating, collecting, and maintaining euphausi- ids at densities sufficient to allow exploitation by whales. We used concurrent ship- and mooring- based oceanographic, hydroacoustic, and net sampling, whale-sighting records, visual surveys, and time-depth recorder deployment to examine temporal and spatial linkages between (1) intensity of upwelling, (2) primary production, (3) development, density and distribution of euphausiids, and (4) the distribution, abundance, and foraging behavior of blue whales in Monterey Bay, California between 1992 and 1996. Blue whales fed exclusively upon adult euphausiids Thysanoessa spinifera and Euphausia pacifica that were larger than those generally available in the Bay. Foraging whales dove repeatedly to dense euphausiid aggregations between 150 and 200 m on the edge of the Mon- terey Bay Submarine Canyon. Euphausiid aggregations where whales were foraging averaged 153 g m -3 , approximately 2 orders of magnitude greater than mean euphausiid densities in the Bay (1.3 g m -3 ). High euphausiid densities are supported by high primary production between April and August (249 mgC m -3 d -1 ) and a submarine canyon that provides deep water down-current from an upwelling region. Peak euphausiid densities occur in late summer/early fall, lagging the seasonal increase in primary production by 3 to 4 mo. This lag results from the temporal development of euphausiids spawned around the spring increase in primary production and the shoreward collapse of productivity due to decreased upwelling in late summer. The migratory movements of the Califor- nia blue whale probably reflect seasonal patterns in productivity in other foraging areas similar to those we describe for Monterey Bay.

Low energy values of fish as a probable cause of a major seabird breeding failure in the North Sea

Abstract: Many seabirds in the North Sea feed on lesser sandeels Ammodytes marinus during the breed- ing season. Unprecedented breeding failures were recorded at many seabird colonies on the east coast of Britain in 2004. We used demographic, dietary and behavioural data from a long-term study of a colony of common guillemots Uria aalge, the most abundant seabird species in the North Sea, to set the 2004 season in context. Birds at this colony showed greatly reduced breeding success and those chicks that did survive left the colony in very poor condition. The main prey item fed to chicks in 2004 was sprat Sprattus sprattus rather than sandeels, and parents increased the amount of time spent foraging, frequently leaving chicks unat- tended in order to maintain a normal feeding rate. The calculated daily food intake of chicks derived from these values did not differ markedly from previous years and therefore the magnitude of the impact on chick growth and breeding success appeared dispro- portionately large. However, nutrient analyses of fish collected from birds in 2004 revealed them to be of sig- nificantly lower energy value than expected. Poor food quality therefore appeared to be the proximate cause of seabird breeding failure in 2004 giving support to the 'junk-food' hypothesis. Single-prey loaders such as guillemots will be particularly sensitive to reductions in the energy value of food items. The reasons for the poor fish condition in this part of the North Sea are currently unknown, but the results provide further evidence of major changes in the North Sea food web.

Organic carbon content of sediments as an indicator of stress in the marine benthos

Abstract: While organic matter in sediments is an important source of food for benthic fauna, an overabundance can cause reductions in species richness, abundance, and biomass due to oxygen depletion and buildup of toxic by-products (ammonia and sulphide) associated with the breakdown of these materials. Moreover, increasing organic content of sediment is often accompanied by other chemical stressors co-varying with sediment particle size. In the present study, synoptic data on the structure of macroinfaunal communities and total organic carbon (TOC) content of sediment were obtained from 951 stations representing 7 coastal regions of the world: the northern Black Sea (Crimean and Caucasian coasts); eastern Mediterranean Sea (Greece); North Sea (Ekofisk oil field); Firth of Clyde and Liverpool Bay, UK; Seto Inland Sea, Japan; Boston Harbor and Massachusetts Bay, USA and estuaries of the southeastern USA. Macroinfaunal and TOC data were examined to look for patterns of association consistent with conceptual model predictions and to identify TOC critical points corresponding to major shifts in the benthic data. Species richness, Hurlbert's E (Sn), was selected as the primary response parameter. Results suggested that risks of reduced species richness from organic loading and other associated stressors in sediments should be relatively low at TOC concentrations less than about 10 mg g -1 , high at concentrations greater than about 35 mg g -1 , and intermediate at concentrations in between. Predictive ability across these ranges was high based on results of re-sampling simulation. While not a measure of causality, it is anticipated that these TOC critical points may be used as a general screening-level indicator for evaluating the likelihood of reduced sediment quality and associated bioeffects over broad coastal areas receiving organic wastes and other pollutants from human activities.

Stable isotope food web studies: a case for standardized sample treatment

Abstract: The enrichment of the stable isotopes 13C and 15N across trophic levels is a commonly used tool in studies on organic matter flow and food webs. An accepted standard for pre-analysis sample preparation, however, is still missing. Thus, potential methodological bias in single studies may hamper comparability and scalability of data from different sources. Sample CaCO3 content introduces a positive bias in ?13C measurements and a negative bias in ?15N measurements. The acidification of samples to remove inorganic carbonate significantly reduces both ?13C and ?15N. As a standard procedure we recommend (i) to acidify samples with as little hydrochloric acid (HCl) as possible using the drop-by-drop technique and (ii) to restrain from rinsing after HCl application.

Satellite Tracking and Analysis Tool (STAT): an integrated system for archiving, analyzing and mapping animal tracking data

Abstract: Despite the obvious power and advan- tages of the Argos system to track animals by satellite, the data generated are difficult for many biologists to exploit. A broad range of skills is required to efficiently download, collate, filter and interpret Argos data. Inte- gration of animal movements with other physical (e.g. remote sensing imagery) and anthropogenic (e.g. fish- ery distributions) datasets presents additional technical and computing challenges. The Satellite Tracking and Analysis Tool (STAT) is a freely available system de- signed for biologists who work on animal tracking; it includes a set of standardized tools and techniques for data management, analysis, and integration with envi- ronmental data. STAT logs in to the Argos computer network each day and downloads all available loca- tions and associated data for each user. These data are parsed and stored in a relational database and auto- matically backed up to an offsite location. A number of data filtering options are available, including setting maximum speed, time or distance between consecutive points, Argos location class, and turning angle. A vari- ety of environmental data layers, including bathymetry, sea surface temperature, sea surface height, ocean cur- rents and chlorophyll, can be sampled for all locations in the STAT database and can be downloaded and incorporated into tracking maps and animations. STAT also facilitates collaboration and the sharing of animal tracking information with the wider public and funding organizations. We hope that STAT will act as a catalytic foundation, fostering collaboration among users of satellite telemetry, and ensuring maximum value from these studies.

Phytoplankton community ecology: principles applied in San Francisco Bay

Abstract: In his seminal 1961 paper 'The paradox of the plankton' Am Nat 95:137-147, G E Hutchinson asked why many species of phytoplankton can coexist while competing for a small num- ber of limiting resources in an unstructured habitat Hutchinson anticipated the resolution of his paradox, recognizing that communities are organized by processes beyond resource competition including species interactions, habitat variability and dispersal Since 1961 we have made funda- mental discoveries that have revolutionized our conceptual understanding of pelagic ecology, includ- ing (1) habitat heterogeneity at all scales relevant to plankton population dynamics, (2) community shifts in response to global climate cycles, (3) fast and selective predation as a powerful top-down force to shape phytoplankton communities, (4) turbulent mixing as a physical process that selects species on the basis of their size and form, (5) mixotrophy that allows some algal species to tap organic nutrient pools and function at multiple trophic levels, (6) taxon-specific life cycles including alternating vegetative and resting stages, and (7) the pelagic as an open system where communities are continually reshaped by species immigration Here we synthesize these discoveries to show how they validate and amplify Hutchinson's hypothesis that phytoplankton communities are assembled by many processes Our synthesis is built around observations of phytoplankton species composition from a decade of study in San Francisco Bay, used as a case study to illustrate the contemporary prin- ciples of phytoplankton community ecology We apply these principles to address 2 central questions: (1) What processes assemble phytoplankton communities? (2) How does phytoplankton community composition influence ecosystem functions such as production in pelagic and benthic food webs?

Patterns of distribution of marine assemblages from rocky shores: evidence of relevant scales of variation

Abstract: Increasing evidence indicates that spatial and temporal patterns in ecological systems are not independent of the scale of measurement In this study we used a hierarchical sampling design to examine spatial patterns in assemblages of algae and invertebrates in midshore and lowshore habitats of rocky coasts in the Mediterranean Sea, increasing the range of scales usually covered by this type of study in marine habitats To put our results in a broader context, we also conducted a review of the literature, targeting studies that explicitly investigated spatial patterns with hierarchical designs We addressed 2 main questions: (1) To what extent does small-scale variability contribute to large-scale patterns of variation? (2) Is there a pattern of variability that can be generalised across species and habitats? The review of the literature indicated that hierarchical analyses of spatial pattern have been limited to a narrow range of habitats and taxa and that very few studies have addressed regional scales of variation (1000s of kilometers) The available data, however, did identify a general pattern: variability was larger at small spatial scales (meters) in almost all habitats, whereas variation over larger spatial scales (10s to 100s of kilometers) depended on the specific habitat and taxa examined In our case study, we obtained measures of spatial variability through the use of 2 alternative methods: hierarchical nested design and independent estimate of spatial variance between pairs of quadrats Both approaches provided further support to the patterns displayed by the analysis of the literature Most response variables exhibited large variation over small spatial scales, while the significance of mid- to large-scale variability differed between midshore and lowshore habitats and among taxa Although a proper understanding of large-scale patterns will require additional comparisons across wide geographical areas, small-scale variability emerges as a general property of benthic assemblages in marine coastal habitats We suggest that this pattern is common to a wide range of natural systems where assemblages are influenced by complex sets of physical and biological processes like those operating in the marine environment

Ocean temperature oscillations enable reappearance of blue mussels Mytilus edulis in Svalbard after a 1000 year absence

Abstract: We report the first observations of settled blue mussels Mytilus edulis L. in the high Arctic Archipelago of Svalbard for the first time since the Viking Age. A scattered population was discovered at a single site at the mouth of Isfjorden in August 2004. Our data indicate that most mus- sels settled there as spat in 2002, and that larvae were transported by the West Spitsbergen Current northwards from the Norwegian coast to Svalbard the same year. This extension of the blue mussels' distribution range was made possible by the unusually high northward mass transport of warm Atlantic water resulting in elevated sea-surface temperatures in the North Atlantic and along the west coast of Svalbard.

Effects of habitat complexity on Caribbean marine fish assemblages

Abstract: Sets of artificial reefs were replicated in 5 bays off Tortola in the British Virgin Islands to investigate the effects of habitat complexity on fish assemblages. Increasing percentage hard sub- strate and the number of small reef holes increased fish abundance on reefs. The observed number of species (Sobs) occurring on each reef increased with increasing rugosity, variety of growth forms, percentage hard substrate, and variety of refuge hole sizes. A rarefied or abundance-corrected spe- cies richness measure (Srare) was calculated to take the varying fish abundances into account. After this correction, rugosity was the only variable that significantly increased fish species-richness. Experimental reefs of different height (20 and 60 cm) did not have significantly different fish abun- dance or species richness. The presence of long-spined sea urchins Diadema antillarum increased Sobs and total fish abundance on artificial rock-reefs and in seagrass beds, but the effect was most pronounced in seagrass beds where shelter was a strongly limiting factor. These results indicate that complex habitats or animals such as D. antillarum that provide shelter to fish are essential for main- taining fish biodiversity at local scales. The most important aspects of complexity are rugosity, hard substrate and small refuge holes. Artificial reefs may be used to mitigate habitat damage in impacted areas, and if management objectives are to increase local fish abundance and species richness, the reefs should provide a stable substrate where this is unavailable, have a rugose surface with many small refuge holes, and have a variety of growth forms.

Upwelling, downwelling, and cross-shelf transport of bivalve larvae: test of a hypothesis

Abstract: Larval supply affects the structure of marine communities. Cross-shelf transport of larvae by upwelling and downwelling may cause variation in larval supply. We tested the hypothesis that slow- swimming bivalve larvae are swept offshore during upwelling and shoreward during downwelling. We sampled a transect at Duck, North Carolina during a period when currents shifted from upwelling to down- welling and back to upwelling. During each shift, nearshore water was exchanged with offshore water and currents were 10 to 100 times faster than larval swimming speeds. Larval Spisula solidissima and Ensis directus were found below the thermocline and, con- trary to prediction, were swept onshore during up- welling and offshore during downwelling. When S. solidissima larvae were found above the thermocline, cross-shelf transport was as predicted. Larval Tellina spp. and Mulinia lateralis remained within 5 km of shore despite cross-shelf currents and the exchange of nearshore waters with offshore waters. They did not behave as passive particles; they were not swept off- shore by upwelling or onshore by downwelling. For these taxa the hypothesis was rejected. These larvae may have remained close to shore by using behaviors analogous to those displayed by animals concentrated at convergent fronts. Given the relatively slow swim- ming speed of bivalve larvae, there is no reason to expect that any larval type is swept offshore by up- welling. The effect of upwelling and downwelling on larval distributions varies with larval behavior and ver- tical distribution. Without careful sampling, one cannot invoke offshore transport of larvae by upwelling as a cause of variations in larval settlement.

Stable isotopes from multiple tissues reveal diet switching in sharks

Abstract: Food web relationships in marine systems have traditionally been defined through stomach content analysis, but biochemical techniques have recently emerged to validate and broaden temporal diet patterns. Stable isotope analysis has become a practical tool for evaluating these relationships in aquatic systems; however, routine sampling of muscle tissue captures only part of the trophic information available from each animal. We compared δ 15 N and δ 13 C values among liver, muscle and cartilage in the blue shark Prionace glauca, shortfin mako Isurus oxyrinchus, and common thresher Alopias vulpinus from the northwest Atlantic to show how multiple-tissue sampling captured feeding relationships which would have been invisible to muscle tissue alone. Specifically, we demonstrated evidence of a cephalopod to bluefish Pomatomus saltatrix diet switch in the short- fin mako in spring, and found that the blue shark and common thresher have consistent diets throughout the year. We concluded that consistency observed among stable isotope values in multi- ple tissues implied that the fish were in steady-state with the isotope ratios of their diet and that multiple tissues should be used in trophic assessments of large pelagic fishes. Further experiments to quantify the turnover of stable isotopes in different tissues and species are needed to improve the accuracy of stable-isotope analyses .

Indo-Pacific seagrass beds and mangroves contribute to fish density and diversity on adjacent coral reefs

Abstract: There is a long-standing debate whether mangrove and seagrass habitats in the Indo- Pacific region function as nurseries for coral reef fishes. We studied the use of all major shallow-water habitat types by juvenile coral reef fish using visual census surveys at 4 islands along the Tanzanian coast (East Africa) and at the island of Grande Comoros (Comoros archipelago). We investigated the value of mangroves, seagrass beds, coral reefs, macroalgae and intertidal flats as a juvenile habitat for fish by studying density distribution patterns of juveniles and adults of 76 reef fish species in these habitats. We assessed (1) which part of the reef fish community used mangrove-seagrass habitats as juvenile or adult habitats, (2) whether adult fish densities and diversity on adjacent reefs were related to the presence of these shallow habitats, and (3) whether adults of species that use these habitats when juvenile were less abundant on coral reefs situated far away from these juvenile habitats. Sea- grass beds and coral reefs were the most important juvenile fish habitats. Ontogenetic migrations between seagrass beds and reef habitats possibly occur, since several species showed their highest juvenile densities on seagrass beds, whereas adults showed their highest densities on reefs adjacent to these seagrass beds. The presence of areas with seagrass beds positively influenced adult densi- ties of many reef fish species on adjacent coral reefs. Of the 36 fish species whose juveniles were observed in seagrass beds along the Tanzanian coast, 32 species were absent from or showed low densities on coral reefs of the island of Grande Comoros (lacking seagrass beds or mangroves). On reefs far from seagrass beds and mangroves along the Tanzanian coast, 25 of these 36 species were absent or showed low densities in comparison with reefs adjacent to these habitats.

Regime shifts in marine ecosystems of the North Sea and Wadden Sea

Abstract: Wide-scale and sudden shifts in several biological and environmental systems of NW Europe have been reported in recent years, and attributed to a range of factors, both climatic and anthropogenic. To examine whether there is any evidence of coinciding region-wide environmental shifts, we gathered existing long-term data series on a wide range of physical and biological para- meters from the 1960s to the present and, following the methods of a similar recent study on North Pacific regime shifts, we analysed the data using principal component analysis and regime shift analysis to identify the extent and timing of regime shifts in NW Europe. The end-point of a regime (i.e. the year) was determined using a sliding window in regime shift analysis. Additionally we applied chronological clustering to the (1) combined data, (2) biological data and (3) environmental data. In all 3 cases, the same regimes were identified. Our results indicate that substantial regime shifts occurred in the marine ecosystem in 1979 and 1988 and perhaps also in 1998, although results were less clear-cut in the latter case. These regime shifts were most evident among the biological data series, but they appeared to have been triggered by earlier shifts in a number of environmental factors. Salinity and weather conditions played an important role in the 1979 shift, while in the 1988 shift, temperature and weather conditions were the predominant factors. Our results confirm those of the North Pacific study, with concomitant changes in physical and biological indices. This indicates a shift in climate-ocean interactions throughout the entire temperate zone of the Northern Hemisphere.

Mitochondrial DNA variation and cryptic speciation within the free-living marine nematode Pellioditis marina

Abstract: An inverse correlation between dispersal ability and genetic differentiation among populations of a species is frequently observed in the marine environment. We investigated the population genetic structure of the free-living marine nematode Pellioditis marina. A total of 426 bp of the mitochondrial cytochrome oxidase subunit 1 (COI) gene were surveyed on a geographical scale of approximately 100 km during spring 2003. Nematodes were collected from 2 coastal locations in Belgium, and from 2 estuaries and a saltwater lake (Lake Grevelingen) in The Netherlands. Molecular variation was assessed with the single-strand conformation polymorphism (SSCP) method. In total, 32 different haplotypes were observed, and sequence divergence among 452 individuals ranged from 0.2 to 10.6%. We discovered 4 distinct mitochondrial lineages, with low divergences within the lineages (0.2 to 1.6%) and high divergences between the lineages (5.1 to 10.6%). The nuclear ribosomal ITS (internal transcribed spacer) region showed concordant phylogenetic patterns, suggesting that nematode species diversity may be considerably underestimated. Analysis of molecular variance (AMOVA) indicated a strong genetic differentiation among populations. The Lake Grevelingen population was clearly differentiated from all other populations, but genetic structuring was also significant within the Westerschelde and was correlated with gradients in salinity and pollution. The observed population genetic structure is in accordance with the limited active dispersal capacity of P. marina, but is at variance with its significant potential for passive dispersal. We therefore suggest that autecological characteristics, including short generation time, high colonization potential and local adaptation, may be at the basis of this nematode's population genetic structure.

Variability of diet-tissue isotopic fractionation in estuarine macrobenthos

Abstract: Juveniles of bivalves Mactra veneriformis and Ruditapes philippinarum, and ghost shrimps Nihonotrypaea japonica and N. harmandi were reared on a microalga of a constant isotopic value to quantify their diet-tissue isotopic fractionation. The weights of the animals increased by >7-fold, resulting in isotopic equilibria with their diet. Fractionation for bivalve soft tissues was 0.6 to 0.9‰ for carbon and 3.4 to 3.6‰ for nitrogen, which fell within the range of the currently accepted fractionation values (0 to 1 and 3 to 4‰). Examinations of acid-treated or untreated whole body, mus- cle and exoskeleton of the ghost shrimps showed (1) large variations in δ 13 C for untreated exoskele- tons, (2) reduced δ 13 C for acid-treated exoskeletons by 3.5 to 6.2‰, (3) confined ranges in 13 C and 15 N fractionations for muscles (2.0 to 2.2 and 3.6 to 4.0‰), (4) only slight effects of acid treatment on 13 C and 15 N fractionation for muscles (≤0.3‰ differences), (5) a significant difference in 13 C fractionation for acid-treated whole bodies between N. japonica (-0.3‰) and N. harmandi (-1.7‰), and (6) 2.3 to 3.0‰ of 15 N fractionation for whole bodies, which were smaller than for muscles due to negative frac- tionation for exoskeletons (-3.0 to -1.9‰). These findings suggest that carbonates in exoskeletons should be removed by acid and that muscle is the most appropriate tissue for isotopic analysis. Although 15 N fractionation for ghost-shrimp muscle was within the above-mentioned accepted range, 13 C fractionation was outside this range. The present study highlights that fractionation is species- and tissue-specific, and that the accepted fractionation values may not be universally applicable.

Habitat degradation from intermittent hypoxia: impacts on demersal fishes

Abstract: As eutrophication of estuaries and coastal oceans increases worldwide, the resulting expansion of hypoxic zones represents an increasingly frequent form of habitat degradation. Although impacts of prolonged hypoxia on benthic invertebrate species are well-documented, there is little understanding of how those effects subsequently influence the motile upper trophic levels in estuarine ecosystems. Quantitative nekton surveys in the Neuse River Estuary and field experiments in June and August 1999 using Atlantic croaker Micropogonias undulatus demonstrated that inter- mittent hypoxia decreased habitat quality for juvenile, demersal fish through 3 pathways: (1) hypoxia restricted the fishes in estuaries to shallow, oxygenated areas, where in the early part of the summer about 1 ⁄3 fewer prey resources were available. (2) This contraction of suitable habitat crowded the fish into smaller areas and may have resulted in density-dependent reduction of growth rates. (3) Most importantly, mortality of sessile infauna in deeper areas exposed to intermittent hypoxia decreased prey densities about 8-fold between the June and August experiments. Through these mechanisms, intermittent hypoxia may result in ecological crunches or bottlenecks. Field data collected from May to October in 3 yr (1998 to 2000) with differing levels of hypoxia support the conclusion that intermit- tent hypoxia may decrease habitat quality and result in ≥50% declines in juvenile fish growth rate. Incorporation of these indirect effects of hypoxia on juvenile growth rates into a population model demonstrated the potential for significant (~4%) reductions in population growth rate. Thus, sub- lethal effects of hypoxia-driven habitat degradation may impact fisheries production not only through reduced size at age, but also through reduced abundance of demersal fish populations.

Feeding ecology of eastern North Pacific killer whales Orcinus orca from fatty acid, stable isotope, and organochlorine analyses of blubber biopsies

Abstract: Blubber biopsy samples from eastern North Pacific killer whales Orcinus orca were ana- lyzed for fatty acids, carbon and nitrogen stable isotopes and organochlorine contaminants. Fatty acid profiles were sufficiently distinct among the 3 reported ecotypes ('resident,' 'transient' or 'offshore') to enable individual animals to be correctly classified by ecotype and also by mitochondrial DNA (mtDNA) haplotype. Profiles of PCBs also enabled unambiguous classification of all 3 killer whale ecotypes, but stable isotope values lacked sufficient resolution. Fatty acid, stable isotope and PCB profiles of the resident and transient ecotypes were consistent with those expected for these whales based on their reported dietary preferences (fish for resident whales, marine mammals for transients). In addition, these ecotype profiles exhibited broad similarity across geographical regions, suggesting that the dietary specialization reported for resident and transient whales in the well-studied eastern North Pacific populations also extends to the less-studied killer whales in the western Gulf of Alaska and Aleutian Islands. Killer whales of the same ecotype were also grouped by region of sample col- lection. The mean stable isotope ratios of various regional groups differed considerably, suggesting that the prey preferences of these North Pacific killer whales may be both region and ecotype spe- cific. Furthermore, 3 specific ecotypes of killer whales were found to have measured stable isotope values that were consistent with dietary preferences reported in the literature. Finally, although the offshore population had blubber fatty acid profiles implicating fish as its primary prey, contaminant and stable isotope results were equally congruent with predation on marine mammals.

Residency pattern of bottlenose dolphins Tursiops spp. in Milford Sound, New Zealand, is related to boat traffic

Abstract: A population of bottlenose dolphins inhabits 7 of the 14 fjords that compose Fiordland, New Zealand. One of these fjords, Milford Sound, supports a large tourism industry that results in intense boat traffic. Bottlenose dolphins regularly visited Milford Sound and tour boats interacted with them during these visits. I studied the factors affecting the frequency of visits to Milford Sound by relating the residency pattern of dolphins in this fjord to oceanographic parameters and variations in boat traffic between December 1999 and February 2002. Boat traffic was the only variable that could explain the frequency of dolphin visits to Milford Sound. Dolphins spent less time in Milford Sound during seasons of intense boat traffic. Moreover, when dolphins visited this fjord, they spent more time at the entrance of the fjord when boat traffic was intense, out of the reach of tour boats. It seems that dolphins avoid Milford Sound when traffic is heavy. This avoidance could have long-term implications for the demography of the population.

Decline of recruitment success in cockles and other bivalves in the Wadden Sea: possible role of climate change, predation on postlarvae and fisheries

Abstract: In the last ~15 yr, frequent recruitment failures in the main bivalve species in the western Wadden Sea led to insufficient food supply for some specialised bird species, sharpening conflicts be- tween nature conservationists and fishermen. To study possible causes of the recent recruitment failure in bivalves, we compare long-term data sets (1973 to 2002) of annual abundance of spat of 3 of the most important species of bivalves (cockle Cerastoderma edule, gaper clam Mya arenaria, and Baltic tellin Macoma balthica) on Balgzand, a tidal-flat area in the westernmost part of the Wadden Sea. In the 3 spe- cies, recruitment success declined significantly over the period of observation, particularly at offshore sampling sites which were characterized by low intertidal levels and sandy sediments. In these areas, we found high biomass values of a predator of bivalve postlarvae, the shrimp Crangon crangon. In each of the 3 bivalve species, annual recruitment (estimated as numerical density of spat in August) in these areas was negatively related to shrimp biomass at the time of settlement of postlarvae (May/June). Shrimp biomass has increased over the last ~30 yr. High near-shore flats showed invariably low shrimp biomass values and appear to serve as a refuge for postlarval bivalves in years of high predation pres- sure. Only in this coastal part of Balgzand was no decline in bivalve recruitment found; in fact, cockle re- cruitment even increased. Alternative explanations for the observed changes in recruitment of bivalves are discussed, including changes in sediment composition and bottom-disturbing fishing for cockles, mussels and lugworms. It is concluded that the recruitment trends on Balgzand (and other parts of the Wadden Sea) are governed primarily by natural processes, in particular increases in predation pressure on early benthic stages, which in turn appears to be largely governed by the warming climate.

Nature and consequences of biological connectivity in mangrove systems

Abstract: Mangroves are important nursery and feeding areas for fish. Their rich invertebrate faunas render them productive feeding areas, while their shallow waters and structural complexity provide sanctuary habitats at a variety of scales. However, in most parts of the world mangroves are available to fish for only part of the time because they are alternately inundated and exposed by the high-tide/low-tide cycle. As a result, few fish can use mangroves exclusively but must migrate in and out of the mangroves with the tide, occupying alternative habitats when mangroves are unavailable. These movements connect the mangroves and the alternative habitats to form an ‘interconnected habitat mosaic’. Living in a habitat mosaic puts limits on the patterns of life possible in mangrove systems, complicates trophic structures, and creates the need for tactics and strategies to meet the challenges imposed by movement among components of the mosaic. Moreover, this biological connectivity means that understandings of trophic relationships, life-history strategies, predation and mortality, and patterns of distribution and abundance must be set in a spatially and temporally variable context. Despite the obvious consequences and importance of biological connectivity in mangrove ecosystems, it has often not been given appropriate consideration in the development of theories and paradigms.

Coral disease outbreak: pattern, prevalence and transmission in Acropora cervicornis

Abstract: A rapidly progressing disease outbreak affecting Acropora cervicornis (staghorn coral) was recently observed over a wide geographic range (>200 km) in the Florida Keys, USA. Original observations made at White Bank Dry Rocks revealed colonies with tissue rapidly sloughing from multifocal lesions. Over the course of the epizootic at least 72% of tagged colonies were affected, live tissue cover of these colonies decreased from 96 ± 1% to 12 ± 5% (mean ± SE), and 28% of the colonies suffered complete mortality. Observed rates of tissue loss were highly variable, ranging from 2 to 43 cm 2 d -1 , but the mean was a rapid 13 ± 11 cm 2 d -1 or about 4 cm branch length d -1 . Field exper- iments demonstrate that this disease is transmissible not only by direct contact between affected and healthy staghorn coral tissue but also by the corallivorous snail Coralliophila abbreviata. The disease was also transmissible, although less effectively so, to the congener A. palmata (elkhorn coral). No transmission was observed in indirect contact treatments designed to simulate diver interaction. Transmissibility implies that the condition is indeed a biotic disease and the demonstration of effec- tive vector transmission suggests that predation may exacerbate disease outbreaks in remnant Caribbean acroporid populations, further impeding their potential recovery.

Temperature and salinity effects on magnesium, manganese, and barium incorporation in otoliths of larval and early juvenile spot Leiostomus xanthurus

Abstract: The use of otolith chemistry to delineate fish populations and trace migration pathways is premised on a significant correlation between the elemental composition of otoliths and physico- chemical properties of the ambient environment. However, few experiments have been rigorously designed to address the effects of temperature and salinity on the elemental composition of otoliths. We examined the effects of temperature and salinity on the incorporation of magnesium (Mg), man- ganese (Mn), and barium (Ba) in the otoliths of larval and early juvenile spot Leiostomus xanthurus by rearing fish in the laboratory under controlled environmental conditions. L. xanthurus are an estu- arine dependent species that traverse varying temperature and salinity regimes throughout their life histories. It is important, therefore, to understand the influence of physicochemical properties of dif- ferent water masses before attempting to reconstruct important life history transitions based on vari- ations in otolith chemistry. Both (Mg/Ca)otolith and the Mg partition coefficient, DMg, were not signifi- cantly affected by either temperature or salinity, but were correlated with otolith precipitation and somatic growth rates. Temperature and salinity had significant interaction effects on DMn, but not on (Mn/Ca)otolith. Finally, DBa was influenced by salinity but not temperature. These results highlight the complex nature of elemental deposition in otoliths, and suggest that both environmental and physio- logical effects likely influence elemental ratios in fish otoliths.

Hearing in fish and their reactions to sounds from offshore wind farms

Abstract: The current knowledge on detection of, and reaction to, sound by fish is reviewed, with special emphasis on underwater noise from offshore wind farms. The detection distance to wind farms for 3 species of fish representing various hearing capabilities varies between 0.4 and 25 km at wind speeds of 8 to 13 m s -1 . The detection distance depends on the size and number of windmills, the hearing abilities of the fish, background noise level, wind speed, water depth and type of sea bot- tom. The noise from windmills may decrease the effective range for sound communication of fish; however, it is not known to what extent this decrease affects the behaviour and fitness of fish. Wind- mill noise does not have any destructive effects upon the hearing abilities of fish, even within dis- tances of a few metres. It is estimated that fish are consistently scared away from windmills only at ranges shorter than about 4 m, and only at high wind speeds (higher than 13 m s -1 ). Thus, the acoustic impact of windmills on fish is restricted to masking communication and orientation signals rather than causing physiological damage or consistent avoidance reactions. These conclusions must be viewed with great caution, however, as the existing data are prone to large uncertainties. Further studies on more detailed measurements of the sound-field and of fish behaviour around windmills are needed.

Modelling diatom and Phaeocystis blooms and nutrient cycles in the Southern Bight of the North Sea: the MIRO model

Abstract: The link between anthropogenic nutrient loads and the magnitude and extent of diatom and Phaeocystis colony blooms in the Southern Bight of the North Sea was explored with the complex ecosystem model MIRO. The model was adapted for resolving the changing nutrient loads, the com- plex biology of the bloom species and the tight coupling between the benthic and pelagic compart- ments that characterise this shallow coastal shelf sea ecosystem. State variables included the main inorganic nutrients (nitrate (NO3), ammonium (NH4), phosphate (PO4) and dissolved silica (DSi)), 3 groups of phytoplankton with different trophic fates (diatoms, nanophytoflagellates and Phaeocystis colonies), 2 zooplankton groups (copepods and microzooplankton), bacteria, and 5 classes of detrital organic matter with different biodegradability. The capability of the MIRO model to properly simu- late the observed SW-NE gradient in nutrient enrichment and the seasonal cycle of inorganic and organic C and nutrients, phytoplankton, bacteria and zooplankton in the eastern English Channel and Southern Bight of the North Sea is demonstrated by running the model for the period from 1989 to 1999. The MIRO code was implemented in a simplified multi-box representation of the hydrody- namic regime. These model runs give the first general view of the seasonal dynamics of Phaeocystis colony blooms and nutrient cycling within the domain. C, N and P budget calculations show that (1) the coastal ecosystem has a low nutrient retention and elimination capacity, (2) trophic efficiency of the planktonic system is low, and (3) both are modulated by meteorological forcing.

Population characteristics of a recovering US Virgin Islands red hind spawning aggregation following protection

Abstract: Many species of groupers form spawning aggregations, dramatic events where 100s to 1000s of individuals gather annually at specific locations for reproduction. Spawning aggregations are often targeted by local fishermen, making them extremely vulnerable to over fishing. The Red Hind Bank Marine Conservation District located in St. Thomas, United States Virgin Islands, was closed seasonally in 1990 and closed permanently in 1999 to protect an important red hind Epi- nephelus guttatus spawning site. This study provides some of the first information on the population response of a spawning aggregation located within a marine protected area. Tag-and-release fishing and fish transects were used to evaluate population characteristics and habitat utilization patterns of a red hind spawning aggregation between 1999 and 2004. Compared with studies conducted before the permanent closure, the average size of red hind increased mostly during the seasonal closure pe- riod (10 cm over 12 yr), but the maximum total length of male red hind increased by nearly 7 cm fol- lowing permanent closure. Average density and biomass of spawning red hind increased by over 60% following permanent closure whereas maximum spawning density more than doubled. Informa- tion from tag returns indicated that red hind departed the protected area following spawning and mi- grated 6 to 33 km to a ca. 500 km 2 area. Protection of the spawning aggregation site may have also contributed to an overall increase in the size of red hind caught in the commercial fishery, thus increasing the value of the grouper fishery for local fishermen.