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Changes in sea urchin behavior following detection of chemical cues from predatory fishes may influence key ecological dynamics but have rarely been experimentally quantified. Here, we measured feeding rates on a habitat-forming macroalgae by two size classes of the New Zealand sea urchin ( Evechinus chloroticus ) exposed to either ambient seawater or seawater carrying excretions from a predatory fish (blue cod; Parapercis colias ). We created a Bayesian model that combined uncertainty in kelp growth rates and probability of urchin feeding to generate robust estimates of fish-exposure effects on multiple feeding metrics. We then compared our results to re-analyzed data characterizing behavioral responses of E. chloroticus to lobster cues ( Jasus edwardsii ). Larger urchins (6–8 cm test diameter) consumed ~ 40% less kelp in both predator treatments, exhibiting indistinguishable responses to blue cod and lobster despite being less susceptible to fish predation. Responses of smaller urchins (3–5 cm test diameter) to both predators were equivocal, though were more consistent with reduced feeding in the presence of lobster. Here we provide novel evidence that fish cues can suppress urchin feeding rates, even in the absence of urchin alarm cues, and discuss our findings in the context of the specificity of predator cue detection-reception pathways and possible mechanisms for risk-induced reductions in urchin feeding.

In the face of an accelerating extinction crisis, scientists must draw insights from successful conservation interventions to uncover promising strategies for reversing broader declines. Here, we synthesize cases of recovery from a list of 362 species of large carnivores, ecologically important species that function as terminal consumers in many ecological contexts. Large carnivores represent critical conservation targets that have experienced historical declines as a result of direct exploitation and habitat loss. We examine taxonomic and geographic variation in current extinction risk and recovery indices, identify conservation actions associated with positive outcomes, and reveal anthropogenic threats linked to ongoing declines. We find that fewer than 10% of global large carnivore populations are increasing, and only 12 species (3.3%) have experienced genuine improvement in extinction risk, mostly limited to recoveries among marine mammals. Recovery is associated with species legislation enacted at national and international levels, and with management of direct exploitation. Conversely, ongoing declines are robustly linked to threats that include habitat modification and human conflict. Applying lessons from cases of large carnivore recovery will be crucial for restoring intact ecosystems and maintaining the services they provide to humans.

Sea urchins can strongly reduce their mobility, exposure to predation, and feeding rates upon detection of chemical cues produced by predators, driving behavioral effects on grazing activity that may contribute to macroalgal community dynamics. However, the extent of chemically induced antipredator behaviors in urchins can vary by predator–prey species pair and ecological context and is therefore important to characterize in novel settings. Additionally, the effect of predator and prey size on urchin reactions to predator cues has rarely been considered, with the few existing examples yielding mixed conclusions. Here, we used a replicated split‐plot experiment to measure the effects of red rock lobsters (Jasus edwardsii) on consumption of macroalgae by the New Zealand sea urchin (Evechinus chloroticus) across a range of predator and prey body sizes. Overall, per‐capita consumption rates of kelp by urchins declined by 30% in the presence of lobsters, though feeding activity varied widely among individuals. Based on mass‐specific measurements of feeding rates, responses to predator cues appeared similar across all urchin sizes but only yielded distinguishable differences in the amount of kelp consumed in trials with larger urchins due to their considerably higher feeding capacity. Conversely, consumption rates of kelp by urchins had no apparent relationship with lobster size, likely due to chemical cue saturation in our experimental setting or a risk gradient that was insufficient to elicit a graded behavioral response. Our findings provide new evidence for a nonconsumptive effect of lobsters on feeding rates of an important grazer that can potentially reinforce the ecological role of this key predator in New Zealand kelp beds.

Fishes can undergo dramatic social and morphological changes throughout development that drive ontogenetic shifts in diet and habitat association. Measurements of trophic ontogeny at the individual level often complement population‐level assessments, detailing foraging strategies that have underpinned long‐term growth and survival. Using stable isotope measurements from muscle and eye lenses, we modeled size‐based patterns in basal resource use and trophic position across multiple levels of organization for three New Zealand reef fishes ( Notolabrus fucicola , Odax pullus, and Parapercis colias ). From lens‐derived data series, we were able to estimate trends and variability in lifetime trophic ontogeny of each species, as well as size‐structured changes in breadth and interspecific overlap of resource use. For adults, broadly similar trophic shifts were reflected in isotopic composition of both muscle tissue and lens layers, with subtle differences between tissues for some combinations of species and ecological metric. Critically, only samples from eye lenses yielded estimates of resource use that supported early growth. Specifically, our measurements suggested heightened reliance on macroalgal food webs during post‐settlement dispersal of two carnivores ( N. fucicola , P. colias ), as well as variable peaks in omnivory at small sizes for O. pullus , a primary herbivore. Trophic shifts modeled from eye lenses of carnivorous species were generally similar throughout early development, but highly inconsistent among juvenile O. pullus . Analyses of eye lenses also yielded evidence of trophic breadth contraction around size‐at‐maturity of all three species, coincident with apparent differentiation of adult resource use between sampled carnivores. Finally, in addition to high‐resolution assessments of trophic ontogeny, we provide analytic considerations that may strengthen use of eye lenses for investigation of fish life history, particularly through examination of calibration assumptions in a novel system.

Changes in temperature can fundamentally transform how species interact, causing wholesale shifts in ecosystem dynamics and stability. Yet we still have a limited understanding of how temperature-dependence in physiology drives temperature-dependence in species-interactions. For predator-prey interactions, theory predicts that increases in temperature drive increases in metabolism and that animals respond to this increased energy expenditure by ramping up their food consumption to meet their metabolic demand. However, if consumption does not increase as rapidly with temperature as metabolism, increases in temperature can ultimately cause a reduction in consumer fitness and biomass via starvation. Here we test the hypothesis that increases in temperature cause more rapid increases in metabolism than increases in consumption using the California spiny lobster (Panulirus interruptus) as a model system. We acclimated individual lobsters to temperatures they experience across their biogeographic range (11, 16, 21, or 26°C), then measured whether lobster consumption rates are able to meet the increased metabolic demands of rising temperatures. We show positive effects of temperature on metabolism and predation, but in contrast to our hypothesis, rising temperature caused lobster consumption rates to increase at a faster rate than increases in metabolic demand, suggesting that for the mid-range of temperatures, lobsters are capable of ramping up consumption rates to increase their caloric demand. However, at the extreme ends of the simulated temperatures, lobster biology broke down. At the cold end, lobsters stopped their hearts and at the highest temperature, 50% of lobsters died. Our results suggest that that temperature plays a key role in driving the geographic range of spiny lobsters and that spatial and temporal shifts in temperature can play a critical role in driving the strength of species interactions for a key predator in temperate reef ecosystems.

Photogrammetry is an emerging tool that allows scientists to measure important habitat characteristics of coral reefs at multiple spatial scales. However, the ecological benefits of using photogrammetry to measure reef habitat have rarely been assessed through direct comparison to traditional methods, especially in settings where manual measurements are more feasible and affordable. Here, we applied multiple methods to measure coral colonies (Pocillopora spp.) and asked whether photogrammetric or manual observations better describe short-term colony growth and links between colony size and the biodiversity of coral-dwelling fishes and invertebrates. Using photogrammetry, we measured patterns in changes in coral volume that were otherwise obscured by high variation from manual measurements. Additionally, we found that photogrammetry-based estimates of colony skeletal volume best predicted the abundance and richness of animals living within the coral. This study highlights that photogrammetry can improve descriptions of coral colony size, growth, and associated biodiversity compared to manual measurements.

Patterns of stable isotopes recorded in metabolically stable, serially synthesized, structures such as eye lenses can yield robust descriptions of resource use across the life histories of individual fish. We performed stable isotope analysis of eye lenses sampled from invasive lionfishes Pterois spp. and a potentially competitive native mesopredator, the graysby Cephalopholis cruentata, to compare lifelong patterns of trophic resource use on a coral reef ledge in Biscayne National Park, Florida, USA. In both lionfishes and graysby, stable isotope values increased logarithmically with eye-lens radius, likely reflecting increases in trophic position with growth. Tissue samples toward the interior of the lens were the most isotopically similar between lionfish and graysby, suggesting interspecific resource use overlap may be strongest in smaller fish. We observed substantial variation in isotopic chronologies around the underlying logarithmic trend within individual fish, potentially driven by patterns of movement across measured environmental isotopic gradients, intraspecific variation in resource use specificity, or other ecological variables of interest. These results are the first to describe patterns of size-structured resource use across the life of individual lionfish, an important objective for researchers studying the interactions of this highly invasive species with the surrounding ecological communities. Additionally, through this example, we illustrate analytical approaches and considerations for the application of eye-lens stable isotope analysis to the study of vertebrate ecology.

Biological invasions threaten ecosystems worldwide, with invasive predators such as lionfish (Pterois spp.) altering marine communities through predation, competition, and habitat disruption. Since their introduction to the western Atlantic in the 1980s, lionfish have rapidly expanded their range and contributed to declines in native reef fish populations. In response, management agencies have implemented targeted removal programs, although their effectiveness, particularly across broad spatial and temporal scales, remains uncertain. We evaluated the effects of removals (culls) at two temporal frequencies by quantifying the densities of both lionfish and potential prey over two years at experimental and non-removal control sites in Florida's Biscayne National Park (BNP). Removals conducted at one-month intervals resulted in moderate reductions in lionfish density but removals at four-month removals did not result in appreciable changes in density. Neither treatment produced substantial changes in lionfish biomass or native prey abundance. Importantly, the magnitude of change in lionfish density following removals depended on the initial lionfish density at a site. Together with previous work, these results suggest that removals are less effective at reducing lionfish densities and enhancing prey assemblages once lionfish densities are already low. Our findings underscore the importance of monitoring lionfish density when evaluating the ecological efficacy of removal programs.

In marine ecosystems, little is known about how competition with invasive fishes may affect the resource use of native predators. Throughout the western Atlantic, invasive Indo-Pacific lionfishes (Pterois spp.) are likely to compete with native mesopredators such as the graysby Cephalopholis cruentata, an ecologically similar serranid. In conjunction with a before-after-control-impact lionfish removal experiment, this study measured whether graysby population size, diet, and condition varied in relation to cohabitant lionfish biomass. Lionfish, graysby, and prey populations were surveyed and sampled along a contiguous reef ledge in Biscayne National Park, south Florida. Mesopredator diet was measured with stable isotope (δ13C and δ15N) and gut content analyses, and isotopic niches were used to compare patterns of inter- and intraspecific resource use diversity. The isotopic niches of graysby and lionfishes overlapped by 67%, suggesting similar population-level resource use. On sites with higher lionfish biomass, graysby isotopic niche was 34% smaller and overlapped 47% less with that of lionfishes, possibly indicating both a narrower breadth of resource use and associated interspecific niche segregation. Although gut content analyses suggested that graysby may consume less fishes on high lionfish biomass sites, prey fish populations did not vary accordingly, potentially inferring interference by lionfishes on graysby foraging behavior. However, graysby condition was not related to lionfish biomass, so the 2 species ultimately did not fit the classic definition of competitors. By discussing potential influences of lionfishes on graysby resource use, our research contributes useful information to the study of how invasive lionfishes may affect native predator communities.