Impacts of rising sea temperature on krill increase risks for predators in the Scotia Sea

PLOS ONE, Nov 2019

Climate change is a threat to marine ecosystems and the services they provide, and reducing fishing pressure is one option for mitigating the overall consequences for marine biota. We used a minimally realistic ecosystem model to examine how projected effects of ocean warming on the growth of Antarctic krill, Euphausia superba, might affect populations of krill and dependent predators (whales, penguins, seals, and fish) in the Scotia Sea. We also investigated the potential to mitigate depletion risk for predators by curtailing krill fishing at different points in the 21st century. The projected effects of ocean warming on krill biomass were strongest in the northern Scotia Sea, with a ≥40% decline in the mass of individual krill. Projections also suggest a 25% chance that krill biomass will fall below an established depletion threshold (75% of its unimpacted level), with consequent risks for some predator populations, especially penguins. Average penguin abundance declined by up to 30% of its unimpacted level, with up to a 50% chance of falling below the depletion threshold. Simulated krill fishing at currently permitted harvest rates further increased risks for depletion, and stopping fishing offset the increased risks associated with ocean warming in our model to some extent. These results varied by location and species group. Risk reductions at smaller spatial scales also differed from those at the regional level, which suggests that some predator populations may be more vulnerable than others to future changes in krill biomass. However, impacts on predators did not always map directly to those for krill. Our findings indicate the importance of identifying vulnerable marine populations and targeting protection measures at appropriate spatial scales, and the potential for spatially-structured management to avoid aggravating risks associated with rising ocean temperatures. This may help balance tradeoffs among marine ecosystem services in an uncertain future.

A PDF file should load here. If you do not see its contents the file may be temporarily unavailable at the journal website or you do not have a PDF plug-in installed and enabled in your browser.

Alternatively, you can download the file locally and open with any standalone PDF reader:

https://journals.plos.org/plosone/article/file?id=10.1371/journal.pone.0191011&type=printable

Impacts of rising sea temperature on krill increase risks for predators in the Scotia Sea

January Impacts of rising sea temperature on krill increase risks for predators in the Scotia Sea Emily S. Klein 0 1 2 Simeon L. Hill 2 Jefferson T. Hinke 1 2 Tony Phillips 2 George M. Watters 1 2 0 Farallon Institute, Petaluma, California, United States of America , 3 British Antarctic Survey , Natural Environment Research Council , Cambridge , United Kingdom 1 Antarctic Ecosystem Research Division, Southwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration , La Jolla, California , United States of America 2 Editor: Heather M. Patterson, Department of Agriculture and Water Resources , AUSTRALIA Climate change is a threat to marine ecosystems and the services they provide, and reducing fishing pressure is one option for mitigating the overall consequences for marine biota. We used a minimally realistic ecosystem model to examine how projected effects of ocean warming on the growth of Antarctic krill, Euphausia superba, might affect populations of krill and dependent predators (whales, penguins, seals, and fish) in the Scotia Sea. We also investigated the potential to mitigate depletion risk for predators by curtailing krill fishing at different points in the 21st century. The projected effects of ocean warming on krill biomass were strongest in the northern Scotia Sea, with a 40% decline in the mass of individual krill. Projections also suggest a 25% chance that krill biomass will fall below an established depletion threshold (75% of its unimpacted level), with consequent risks for some predator populations, especially penguins. Average penguin abundance declined by up to 30% of its unimpacted level, with up to a 50% chance of falling below the depletion threshold. Simulated krill fishing at currently permitted harvest rates further increased risks for depletion, and stopping fishing offset the increased risks associated with ocean warming in our model to some extent. These results varied by location and species group. Risk reductions at smaller spatial scales also differed from those at the regional level, which suggests that some predator populations may be more vulnerable than others to future changes in krill biomass. However, impacts on predators did not always map directly to those for krill. Our findings indicate the importance of identifying vulnerable marine populations and targeting protection measures at appropriate spatial scales, and the potential for spatially-structured management to avoid aggravating risks associated with rising ocean temperatures. This may help balance tradeoffs among marine ecosystem services in an uncertain future. - Funding: This work was supported by funding from the Pew Charitable Trusts, contract ID #29068. This funder had no role in study design, data collection and analysis, or preparation of the manuscript, Publication under peer review was a requirement of this funding source, although the Introduction Marine ecosystems provide important provisioning, regulatory and cultural services, but climate change may threaten their sustainable delivery (e.g., [1±3]). The impacts of climate change can propagate through food webs as changes affecting one species also influence its funder had no say in where this manuscript would be submitted. competitors, predators, and prey [ 4 ]. This can further alter the various services an ecosystem provides for people, potentially motivating the re-assessment of tradeoffs between these services [ 1 ]. In addition, the consequences of climate change may be compounded by fishing or other human uses. Reducing such uses (and possibly accepting a cost in other ecosystem services, such as provisioning) might help compensate for the negative impacts of climate change on marine biota (e.g. reduced population sizes). For example, where climate change increases the risks of negative outcomes associated with exploited and overexploited fisheries, these risks may be offset by reducing overall catch [ 5 ]. The Scotia Sea, in the southwest Atlantic sector of the Southern Ocean (Fig 1), presents a case study to explore how the potential effects of climate change on an important forage species might affect higher trophic levels, and how fisheries-management actions might interact with broader climate impacts to affect tradeoffs among ecosystem services. The Scotia Sea provides provisioning services via fisheries, including one targeting Antarctic krill, Euphausia superba, and cultural services via an array of charismatic predators that are important for ecotourism and of wider conservation concern [ 6 ]. These predators include numerous penguins, seals and whales, which feed primarily on Antarctic krill [ 7 ]. Several studies suggest that climate change could have negative impacts on the krill population (e.g. [8±10]), although at least two identify potential positive effects [ 11, 12 ]. Any negative outcomes are likely to reduce the biomass of krill, with potential consequ (...truncated)


This is a preview of a remote PDF: https://journals.plos.org/plosone/article/file?id=10.1371/journal.pone.0191011&type=printable

Emily S. Klein, Simeon L. Hill, Jefferson T. Hinke, Tony Phillips, George M. Watters. Impacts of rising sea temperature on krill increase risks for predators in the Scotia Sea, PLOS ONE, 2018, Volume 13, Issue 1, DOI: 10.1371/journal.pone.0191011