Andres Felipe Navia

Intraspecific niche variation shapes the structure and function of food webs, but we still know little about the magnitude and drivers of trophic variation within species in species‐rich communities. Here, we examined how intrinsic (sex and life stage) and extrinsic (locality and season) factors affect the diet composition and trophic niche width of tropical fish species. Specifically, we studied co‐occurring species with benthopelagic (Stellifer ericymba, S. melanocheir, S. zestocarus, and Larimus argenteus) and benthic feeding habits (S. strabo, Cathorops manglarensis, Notarius troschelii, and Urotrygon rogersi) on the central Pacific coast of Colombia. Overall, we observed strong spatial and seasonal effects driving variation in the consumption of (i) amphipods, copepods, and decapods for benthopelagic species and (ii) mollusks and polychaetes for benthic species. As expected, we observed little sexual diet variation; however, surprisingly, most species showed little ontogenetic diet variation. Seasonality strongly shaped the trophic niche width for most species, but effects were species‐specific, suggesting no general pattern of seasonal niche expansion across species. In turn, spatial effects on the trophic niche width were congruent across species, which might be related to differences in the diversity of available resources between bays. Our results reveal the complex interplay between intrinsic and extrinsic factors in shaping resource exploitation by coastal fish. This high level of trophic plasticity may be a critical component for both the persistence of marine populations and the stability of local food webs.Abstract in Spanish is available with online material.

Aim: To examine the species richness, distribution and macroecological patterns of elasmobranch assemblages across a broad latitudinal gradient in the Eastern Pacific Ocean (EPO).Location: The study area encompasses the Pacific coast of the American continent, spanning from 65°N to 60°S, and extending from the coastline to approximately 1000 km offshore, encompassing the oceanic archipelagos.Taxon: Elasmobranchs.Methods: Utilising the established distribution ranges of 190 elasmobranch species (comprising 89 sharks and 101 rays), we assessed the richness and spatial distribution of these species across the EPO. Subsequently, three macroecological patterns were scrutinised: Rapoport's rule, the Mid Domain Effect with its association to Mean Sea Surface Temperature, and the correlation between body size and latitudinal distribution.Results: The analysis of species richness along latitudinal gradients unveiled a bimodal pattern, reaching peaks between 30° to 20°N and 10°N to 5°S. A decline in species richness was observed from tropical to polar regions. Contrary to Rapoport's Rule, Stevens' and midpoint methods demonstrated higher geographic range values at lower latitudes, diminishing towards higher latitudes. Additionally, the mid‐domain effect model exhibited a robust correlation with the mean sea surface temperature. Exploring the interspecific relationship between body size and extent of occurrence, it was found that 29 out of 190 species are more susceptible to extinction.Main Conclusion: Marine elasmobranchs of the EPO defy conventional latitudinal richness patterns and deviate from Rapoport's rule. Furthermore, our findings indicate a robust correlation between observed richness and both sea surface temperature and environmental heterogeneity. The proportion of species vulnerable to human or stochastic impacts potentially leading to extirpation in relation to their geographic range was low across the majority of examined provinces.

Climate change is an environmental emergency threatening species and ecosystems globally. Oceans have absorbed about 90% of anthropogenic heat and 20%–30% of the carbon emissions, resulting in ocean warming, acidification, deoxygenation, changes in ocean stratification and nutrient availability, and more severe extreme events. Given predictions of further changes, there is a critical need to understand how marine species will be affected. Here, we used an integrated risk assessment framework to evaluate the vulnerability of 132 chondrichthyans in the Eastern Tropical Pacific (ETP) to the impacts of climate change. Taking a precautionary view, we found that almost a quarter (23%) of the ETP chondrichthyan species evaluated were highly vulnerable to climate change, and much of the rest (76%) were moderately vulnerable. Most of the highly vulnerable species are batoids (77%), and a large proportion (90%) are coastal or pelagic species that use coastal habitats as nurseries. Six species of batoids were highly vulnerable in all three components of the assessment (exposure, sensitivity and adaptive capacity). This assessment indicates that coastal species, particularly those relying on inshore nursery areas are the most vulnerable to climate change. Ocean warming, in combination with acidification and potential deoxygenation, will likely have widespread effects on ETP chondrichthyan species, but coastal species may also contend with changes in freshwater inputs, salinity, and sea level rise. This climate‐related vulnerability is compounded by other anthropogenic factors, such as overfishing and habitat degradation already occurring in the region. Mitigating the impacts of climate change on ETP chondrichthyans involves a range of approaches that include addressing habitat degradation, sustainability of exploitation, and species‐specific actions may be required for species at higher risk. The assessment also highlighted the need to further understand climate change's impacts on key ETP habitats and processes and identified knowledge gaps on ETP chondrichthyan species.

The deep ocean is the last natural biodiversity refuge from the reach of human activities. Deepwater sharks and rays are among the most sensitive marine vertebrates to overexploitation. One-third of threatened deepwater sharks are targeted, and half the species targeted for the international liver-oil trade are threatened with extinction. Steep population declines cannot be easily reversed owing to long generation lengths, low recovery potentials, and the near absence of management. Depth and spatial limits to fishing activity could improve conservation when implemented alongside catch regulations, bycatch mitigation, and international trade regulation. Deepwater sharks and rays require immediate trade and fishing regulations to prevent irreversible defaunation and promote recovery of this threatened megafauna group.

La distribución conocida del tiburón espinoso negro del Pacífico Echinorhinus cookei en el Pacífico Oriental se extiende desde Oregón (EE.UU.) hasta Costa Rica y desde Ecuador a Chile, con vacíos en las zonas costeras de Panamá y Colombia. El presente documento confirma la presencia de E. cookei en el Pacífico costero colombiano y verifica que su distribución es continua a lo largo del rango latitudinal en el Pacífico Oriental.

Ecosystem-based management for marine life conservation is of growing consensus, although the focus on protecting either charismatic or commercially important species still persist, understating species playing key functional roles. Here we quantified the topological importance of species with high economic or conservation value by simulating extinction scenarios in the Gulf of California trophic network. We found food web robustness against removals of charismatic or commercially important species. Instead, other species suggest strong roles on food web functioning. Invertebrates such as squids and crustaceans are in crucial intermediate positions, making them key bottlenecks for energy transfers. A mixed ecosystem control is at play in the food web, which is dominated by species controlling the indirect effects in top-down forcing as white sharks and hammerheads and bottom-up forcing imposed by the phytoplankton. Direct effect transmission is regulated by the silky shark due to its diverse diet. Only two charismatic removals, blue whale and white shark affected the closeness centrality patterns, whereas only blue shrimp and Monterrey sardine are commercially important species with functional relevance roles in the food web. We hope our network analysis will help decision makers in the development of novel conservation policies. Our results highlight in fact the importance of loliginid squid and blue shrimp populations, having beneficial indirect effects for the protection of charismatic species. This study is particularly timing since islands and protected areas of the Gulf of California were upgraded to the highest level of concern by the UNESCO World Heritage Convention in 2020.

Sharks and rays are key functional components of coral reef ecosystems, yet many populations of a few species exhibit signs of depletion and local extinctions. The question is whether these declines forewarn of a global extinction crisis. We use IUCN Red List to quantify the status, trajectory, and threats to all coral reef sharks and rays worldwide. Here, we show that nearly two-thirds (59%) of the 134 coral-reef associated shark and ray species are threatened with extinction. Alongside marine mammals, sharks and rays are among the most threatened groups found on coral reefs. Overfishing is the main cause of elevated extinction risk, compounded by climate change and habitat degradation. Risk is greatest for species that are larger-bodied (less resilient and higher trophic level), widely distributed across several national jurisdictions (subject to a patchwork of management), and in nations with greater fishing pressure and weaker governance. Population declines have occurred over more than half a century, with greatest declines prior to 2005. Immediate action through local protections, combined with broad-scale fisheries management and Marine Protected Areas, is required to avoid extinctions and the loss of critical ecosystem function condemning reefs to a loss of shark and ray biodiversity and ecosystem services, limiting livelihoods and food security.