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Understanding an animal’s movement, distribution and activity pattern is vital for effective delivery of evidence-based management; however, such data are sparse for many economically important fishery targets, particularly the European lobster Homarus gammarus. This study aimed to elucidate high-resolution movement and activity patterns of a large cohort (n = 44; carapace length = 65–98 mm) of adult European lobsters, using a passive fine-scale acoustic telemetry VEMCO Positioning System (VPS) off Northumberland (UK). This is the first application of VPS on this species and the first offshore VPS study within the UK, providing novel positional data generated via triangulation based on time difference of arrival of acoustic signals. Individual home-ranges using kernel density and minimum convex polygons showed seasonal variation: 95% utilisation distribution ranged from 244 to 7722 m² during spring (mean ± SE: 11 104 ± 397 m²), and declined to 237–784 m² during autumn (mean ± SE: 455 ± 66 m²s.e.). The study also provides evidence of behavioural differences between sexes, with males using more space than females. Daily cumulative step-length and daily minimum convex polygons highlighted that while space-use decreased during the autumn, daily distance moved increased for the majority of lobsters observed, coupled with longer durations of diel activity during autumn. These results suggest that using home-range analyses alone to describe lobster movement may inadequately represent its full behaviour. This study demonstrates the potential for passive acoustic telemetry tracking of otherwise cryptic and difficult to study marine benthic animals.

Aspects of between-individual trophic niche width can be explored through the isotopic niche concept. In many cases isotopic variability can be influenced by the scale of sampling and biological characteristics including body size or sex. Sample size-corrected (SEAc) and Bayesian (SEAb) standard ellipse areas and generalised least squares (GLS) models were used to explore the spatial variability of δ13C and δ15N in Kiwa tyleri (decapod), Gigantopelta chessoia (peltospirid gastropod) and Vulcanolepas scotiaensis (stalked barnacle) collected from 3 hydrothermal vent field sites (E2, E9N and E9S) on the East Scotia Ridge (ESR), Southern Ocean. SEAb only revealed spatial differences in isotopic niche area in male K. tyleri. However, the parameters used to draw the SEAc, eccentricity (E) and angle of the major SEAc axis to the x-axis (θ), indicated spatial differences in the relationships between δ13C and δ15N in all 3 species. The GLS models indicated that there were spatial differences in isotope–length trends, which were related to E and θ of the SEAc. This indicated that E and θ were potentially driven by underlying trophic and biological processes that varied with body size. Examination of the isotopic niches using standard ellipse areas and their parameters in conjunction with length-based analyses provided a means by which a proportion of the isotopic variability within each species could be described. We suggest that the parameters E and θ offer additional ecological insight that has so far been overlooked in isotopic niche studies.

The magnitude of different sources of variation in coral reef fish abundance data needs to be known if temporal changes in population and community data are to be correctly estimated. A particularly important missing component of the variability is the ‘instantaneous’ change in fish, largely caused by the interaction between fish movement and observer recognition. This variation occurs at a time scale less than that influenced by the focus of previous studies, including time of day, tides, migration, or birth and death processes. Without this measure of variance, estimates of temporal change are confounded. To determine the magnitude of this instantaneous variance, belt-transect visual counts of damselfish, surgeonfish, and parrotfish were conducted during a short interval at midday during neap tides over consecutive days in the calm season and compared to similar samples in 1992 and 2003. Within-site, or our estimate of instantaneous variation, was the greatest source of variability for the whole assemblage and for the surgeonfish/parrotfish group but not for damselfish. Direct between-year comparisons produced estimates of population change over time that were twice as high as those derived by an indirect method where the instantaneous spatial component was subtracted from the total variation. Because the inherent spatial component of variability makes it difficult to detect site change over time, we recommend sampling designs that use random sampling and have greater statistical power to detect change. Furthermore, aggregate metrics, such as numbers of species or density at the family, community, or the functional group, will have greater potential to detect change for sample sizes typical of coral reef studies. Otherwise, when life history traits and species level change are important, high replication will be required.

As one of the most diverse and productive ecosystems known, and one of the first ecosystems to exhibit major climate-warming impacts (coral bleaching), coral reefs have drawn much scientific attention to what may prove to be their Achilles heel, the thermal sensitivity of reef-building corals. Here we show that climate change-driven loss of live coral, and ultimately structural complexity, in the Seychelles results in local extinctions, substantial reductions in species richness, reduced taxonomic distinctness, and a loss of species within key functional groups of reef fish. The importance of deteriorating physical structure to these patterns demonstrates the longer-term impacts of bleaching on reefs and raises questions over the potential for recovery. We suggest that isolated reef systems may be more susceptible to climate change, despite escaping many of the stressors impacting continental reefs.

Overfishing and habitat degradation through climate change pose the greatest threats to sustainability of marine resources on coral reefs. We examined how changes in fishing pressure and benthic habitat composition influenced the size spectra of island-scale reef fish communities in Lau, Fiji. Between 2000 and 2006 fishing pressure declined in the Lau Islands due to declining human populations and reduced demand for fresh fish. At the same time, coral cover declined and fine-scale architectural complexity eroded due to coral bleaching and outbreaks of crown-of-thorns starfish, Acanthaster planci. We examined the size distribution of reef fish communities using size spectra analysis, the linearized relationship between abundance and body size class. Spatial variation in fishing pressure accounted for 31% of the variation in the slope of the size spectra in 2000, higher fishing pressure being associated with a steeper slope, which is indicative of fewer large-bodied fish and/or more small-bodied fish. Conversely, in 2006 spatial variation in habitat explained 53% of the variation in the size spectra slopes, and the relationship with fishing pressure was much weaker ( 12% of variation) than in 2000. Reduced cover of corals and lower structural complexity was associated with less steep size spectra slopes, primarily due to reduced abundance of fish <20 cm. Habitat degradation will compound effects of fishing on coral reefs as increased fishing reduces large-bodied target species, while habitat loss results in fewer small-bodied juveniles and prey that replenish stocks and provide dietary resources for predatory target species. Effective management of reef resources therefore depends on both reducing fishing pressure and maintaining processes that encourage rapid recovery of coral habitat.

Visual assessments of topographic habitat structure and benthos on coral reefs were appraised using quantitative data collected from 16 replicate surveys within each of 21 sites on Seychelles reefs. Results from visual assessments of reef benthos were similar to those obtained using techniques frequently used to assess benthic complexity and composition. Visual estimates of habitat topography were correlated with rugosity, reef height and holes of 10-70 cm diameter, whilst visual estimates of benthic composition were very similar to those obtained from line intercept transects. Visual estimates of topography correlated strongly with species richness of fish communities and explained 42% of the variation in these data. The relationship between visual estimates of topography and species richness is strongest with fish 10-30 cm total length (TL), abundance of fish within this size category also correlating positively with topographic visual assessments. Visual techniques are prone to observer bias, however with regular training they can be used to quickly provide a reliable and effective means of assessing habitat complexity and benthos on coral reefs. [PUBLICATION ABSTRACT]

1. An assumed constant trophic fractionation of ¹⁵N/¹⁴N between consumer and diet (usually 3·4 for diet-muscle tissue differences) allows inferences to be made about feeding interactions and trophic level in food web studies. However, considerable variability surrounds this constant, which may conceal subtle differences about the trophodynamics of consumers. 2. The feeding ecologies of herbivores and carnivores differ in terms of diet quality (in C : N terms) and food processing mechanisms, which may affect fractionation. 3. We present a new model that explores how consumer feeding rates, excretion rates and diet quality determine the ¹⁵N/¹⁴N ratios in the consumer's tissues and hence influence the magnitude of trophic fractionation. 4. Three herbivorous reef fish Acanthurus sohal, Zebrasoma xanthurum and Pomacentrus arabicus were chosen as study organisms. Empirical estimates of diet-tissue stable isotope fractionation were made in the field, and model parameters were derived from feeding observations and literature data. 5. The trophic fractionation values of A. sohal, Z. xanthurum and P. arabicus were 4·69, 4·47 and 5·25, respectively, by empirical measurement, and 4·41, 4·30 and 5·68, respectively, by model, indicating that herbivores have a higher trophic fractionation than the currently accepted value of 3·4. 6. The model was most sensitive to the excretion rate, which may differ between herbivores and carnivorous animals. This model is the first to determine stable isotope signatures of a consumer's diet mixture without applying a constant fractionation value.

Carbon and nitrogen stable isotope ratios are used to assess diet composition by determining bounds for the relative contributions of different prey to a predator's diet. This approach is predicated on the assumption that the isotope ratios of predator tissues are similar to those of dominant food sources after accounting for trophic discrimination (Δ x X), and is formulated as linear mixing models based on mass balance equations. However, Δ x X is species- and tissue-specific and may be affected by factors such as diet quality and quantity. From the different methods proposed to solve mass balance equations, some assume Δ x X to be exact values whilst others (based on Bayesian statistics) incorporate variability and inherent uncertainty. Using field data from omnivorous reef fishes, our study illustrates how uncertainty may be taken into account in non-Bayesian models. We also illustrate how dietary interpretation is a function of both absolute Δ x X and its associated uncertainty in both Bayesian and non-Bayesian isotope mixing models. Finally, collated literature illustrate that uncertainty surrounding Δ x X is often too restricted. Together, these data suggest the high sensitivity of mixing models to variation in trophic discrimination is a consequence of inappropriately constrained uncertainty against highly variable Δ x X. This study thus provides guidance on the interpretation of existing published mixing model results and in robust analysis of new resource mixing scenarios.

Cousin Island marine reserve (Seychelles) has been an effectively protected no-take marine protected area (MPA) since 1968 and was shown in 1994 to support a healthy herbivorous fish assemblage. In 1998 Cousin Island reefs suffered extensive coral mortality following a coral bleaching event, and a phase shift from coral to algal dominance ensued. By 2005 mean coral cover was <1%, structural complexity had fallen and there had been a substantial increase in macroalgal cover, up to 40% in some areas. No clear trends were apparent in the overall numerical abundance and biomass of herbivorous fishes between 1994 and 2005, although smaller individuals became relatively scarce, most likely due to the loss of reef structure. Analysis of the feeding habits of six abundant and representative herbivorous fish species around Cousin Island in 2006 demonstrated that epilithic algae were the preferred food resource of all species and that macroalgae were avoided. Given the current dominance of macroalgae and the apparent absence of macroalgal consumers, it is suggested that the increasing abundance of macroalgae is reducing the probability of the system reverting to a coral dominated state.

1. Body size determines rates of respiration and production, energy requirements, mortality rates, patterns of predation and vulnerability to mortality. Body size distributions are often used to describe structure and energy flux in communities and ecosystems. 2. If clear relationships can be established between body size and trophic level in fishes, they may provide a basis for integrating community and ecosystem analyses based on size spectra, food webs and life histories. 3. We investigated relationships between the body sizes (weight and length) of north-east Atlantic fishes and their trophic level. The abundance of15N, as determined by stable isotope analysis, was used as an index of trophic level. 4. Cross-species and comparative analyses demonstrated that body size was unrelated or weakly related to trophic level. Thus allometric relationships between body size and trophic level could not be used to predict the trophic structure of fish communities. 5. The results of the cross-species analyses contrasted with patterns in the size and trophic structure of entire fish communities. When fish communities were divided into size classes, there were strong positive relationships between size class and trophic level. The slope suggested a mean predator: prey body mass ratio of 80: 1. 6. Our results suggest that body size does not provide a useful surrogate of trophic level for individual species, but that body size is an excellent predictor of trophic level within the community, providing an empirical basis for integrating community analyses based on models of trophic structure and body size distributions.