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.
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Introduction 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.
Methods 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 sacross 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.
Results and discussion 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 coldest temperature, lobsters had almost no metabolic activity and at the highest temperature, 33% of lobsters died. Our results suggest 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.
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Abstract How strongly predators and prey interact is both notoriously context dependent and difficult to measure. Yet across taxa, interaction strength is strongly related to predator size, prey size and prey density, suggesting that general cross‐taxonomic relationships could be used to predict how strongly individual species interact.
Here, we ask how accurately do general size‐scaling relationships predict variation in interaction strength between specific species that vary in size and density across space and time?
To address this question, we quantified the size and density dependence of the functional response of the California spiny lobster
Panulirus interruptus , foraging on a key ecosystem engineer, the purple sea urchinStrongylocentrotus purpuratus , in experimental mesocosms. Based on these results, we then estimated variation in lobster–urchin interaction strength across five sites and 9 years of observational data. Finally, we compared our experimental estimates to predictions based on general size‐scaling relationships from the literature.Our results reveal that predator and prey body size has the greatest effect on interaction strength when prey abundance is high. Due to consistently high urchin densities in the field, our simulations suggest that body size—relative to density—accounted for up to 87% of the spatio‐temporal variation in interaction strength. However, general size‐scaling relationships failed to predict the magnitude of interactions between lobster and urchin; even the best prediction from the literature was, on average, an order of magnitude (+18.7×) different than our experimental predictions.
Harvest and climate change are driving reductions in the average body size of many marine species. Anticipating how reductions in body size will alter species interactions is critical to managing marine systems in an ecosystem context. Our results highlight the extent to which differences in size‐frequency distributions can drive dramatic variation in the strength of interactions across narrow spatial and temporal scales. Furthermore, our work suggests that species‐specific estimates for the scaling of interaction strength with body size, rather than general size‐scaling relationships, are necessary to quantitatively predict how reductions in body size will alter interaction strengths.
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A major challenge in sustainability science is identifying targets that maximize ecosystem benefits to humanity while minimizing the risk of crossing critical system thresholds. One critical threshold is the biomass at which populations become so depleted that their population growth rates become negative—depensation. Here, we evaluate how the value of monitoring information increases as a natural resource spends more time near the critical threshold. This benefit emerges because higher monitoring precision promotes higher yield and a greater capacity to recover from overharvest. We show that precautionary buffers that trigger increased monitoring precision as resource levels decline may offer a way to minimize monitoring costs and maximize profits. In a world of finite resources, improving our understanding of the trade-off between precision in estimates of population status and the costs of mismanagement will benefit stakeholders that shoulder the burden of these economic and social costs.more » « less
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Abstract Marine Protected Areas (MPAs) are designed to enhance biodiversity and ecosystem services. Some MPAs are also established to benefit fisheries through increased egg and larval production, or the spillover of mobile juveniles and adults. Whether spillover influences fishery landings depend on the population status and movement patterns of target species both inside and outside of MPAs, as well as the status of the fishery and behavior of the fleet. We tested whether an increase in the lobster population inside two newly established MPAs influenced local catch, fishing effort, and catch-per-unit-effort (CPUE) within the sustainable California spiny lobster fishery. We found greater build-up of lobsters within MPAs relative to unprotected areas, and greater increases in fishing effort and total lobster catch, but not CPUE, in fishing zones containing MPAs vs. those without MPAs. Our results show that a 35% reduction in fishing area resulting from MPA designation was compensated for by a 225% increase in total catch after 6-years, thus indicating at a local scale that the trade-off of fishing ground for no-fishing zones benefitted the fishery.more » « less
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Abstract Multispecies mutualisms are embedded in a network of interactions that include predation, yet the effects of predation on mutualism function have not been well integrated into mutualism theory. Where predators have been considered, the common prediction is that predators reduce mutualist abundance and, as a consequence, decrease service provision. Here, we use a mathematical model of a predatory fish that consumes two competing coral mutualists to show that predators can also have indirect positive effects on hosts when they preferentially consume competitively dominant mutualists that are also lower in quality. In these cases, predation reverses the outcome of competition, allowing the higher quality mutualist to dominate and enhancing host performance. The direction and strength of predator effects depend on asymmetries in mutualist competition, service provision, and predation vulnerability. Our findings suggest that when the strength of predation shifts (e.g., due to exploitative harvest of top predators, introduction of new species, or range shifts in response to climate change), mutualist communities will exhibit dynamic responses with nonmonotonic effects on host service provision.
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null (Ed.)Abstract A suite of processes drive variation in coral populations in space and time, yet our understanding of how variation in coral density affects coral performance is limited. Theory predicts that reductions in density can send coral populations into a predator pit, where concentrated corallivory maintains corals at low densities. In reality, how variation in coral density alters corallivory rates is poorly resolved. Here, we experimentally quantified the effects of corallivory and coral density on growth and survival of small colonies of the staghorn coral Acropora pulchra . Our findings suggest that coral density and corallivory have strong but independent effects on coral performance. In the presence of corallivores, corals suffered high but density-independent mortality. When corallivores were excluded, however, vertical extension rates of colonies increased with increasing densities. While we found no evidence for a predator pit, our results suggest that spatio-temporal variation in corallivore and coral densities can fundamentally alter population dynamics via strong effects on juvenile corals.more » « less
