How to use marine ecosystem models to improve climate change impact forecasts
Millions of people depend on oceans for food and income. A recent report from the Intergovernmental Panel on Climate Change states that at least 83 percent of the ocean's surface will continue to warm this century, which will negatively affect lives and livelihoods. Additionally, a new international study that includes research from LSU found that higher resolution data are critical to predict how ocean warming will impact various marine species and ecosystems.
The study suggests that while marine ecosystem models are the key tools used to understand how climate change could impact marine food webs and fisheries in the future, how those models represent key processes that drive the marine ecosystem's response to climate change differ widely. These researchers believe this uncertainty could be causing models to underestimate future climate change impacts on the world's marine ecosystems.
LSU scientist Cheryl Harrison co-coordinated the team of 23 international researchers from the U.S., Australia, Europe and Canada, who produced this milestone paper for marine climate change impact projections. She is an assistant professor in the LSU Department of Oceanography & Coastal Sciences within the College of the Coast & Environment and in the LSU Center for Computation & Technology.
"Global ocean modeling of marine ecosystem and fisheries impacts under climate change is a relatively new field of study, and one that is very important for understanding both societal and conservation impacts of climate change. This study aims to improve understanding of major differences in various marine ecosystem models and how they work by separating out the data on how the fish respond to changes in temperature and the amount of available food," Harrison said.
The researchers explored the many mechanisms behind how marine animals respond to climate change in eight global marine ecosystem models from the Fisheries and Marine Ecosystem Model Intercomparison Project, or FishMIP. While the models in this study generally show that climate change will cause the world's marine animal populations to decline as oceans warm, the magnitude and details of temperature impacts are uncertain due to the large number of biological and ecosystem processes that temperature controls. The implication is that the models together may be underestimating the impact of ocean warming on fisheries.
"Additionally, how marine ecosystem models respond to climate change depends greatly on assumptions about the best variable from climate models to use to represent fish food," Harrison said. "Some use new growth of marine algae while others look at the total amount of biomass or more complicated formulations. However, new growth and biomass respond very differently to climate change, mostly due to the 'tropicalization of the ocean' as it warms, which is the marine equivalent to desertification. In tropical regions, there is more growth but more turnover, and less biomass to support larger organisms. These differences are amplified in the marine ecosystem responses."
This study takes the first step in reconciling those differences. According to the study's lead author, Ryan Heneghan from Queensland University of Technology's School of Mathematical Sciences, they plan to use their results as a roadmap for the global scientific community to increase its understanding of the world's marine ecosystems now and in the future.
View ORCID ProfileChloé Pozas-Schacre, View ORCID ProfileJordan M. Casey, View ORCID ProfileSimon J. Brandl, View ORCID ProfileMichel Kulbicki, View ORCID ProfileMireille Harmelin-Vivien, View ORCID ProfileGiovanni Strona, and View ORCID ProfileValeriano Parravicini
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PNAS September 28, 2021 118 (39) e2100966118; https://doi.org/10.1073/pnas.2100966118
Edited by M. Aaron MacNeil, Dalhousie University, Halifax, Canada, and accepted by Editorial Board Member James A. Estes July 28, 2021 (received for review January 25, 2021)
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Species loss can weaken the trophic interactions that underpin ecosystem functioning. Coral reefs are the world’s most diverse marine ecosystem, harboring interaction networks of extraordinary complexity. We show that, despite this complexity, global coral reef food webs are governed by a suite of highly consistent energetic pathways, regardless of regional differences in biodiversity. All networks are characterized by species with narrow dietary preferences, arranged into distinct groups of predator–prey interactions. These characteristics suggest that coral reef food webs are robust to the loss of prey resources but vulnerable to local extinctions of consumer species.
Abstract
Ecological interactions uphold ecosystem structure and functioning. However, as species richness increases, the number of possible interactions rises exponentially. More than 6,000 species of coral reef fishes exist across the world’s tropical oceans, resulting in an almost innumerable array of possible trophic interactions. Distilling general patterns in these interactions across different bioregions stands to improve our understanding of the processes that govern coral reef functioning. Here, we show that across bioregions, tropical coral reef food webs exhibit a remarkable congruence in their trophic interactions. Specifically, by compiling and investigating the structure of six coral reef food webs across distinct bioregions, we show that when accounting for consumer size and resource availability, these food webs share more trophic interactions than expected by chance. In addition, coral reef food webs are dominated by dietary specialists, which makes trophic pathways vulnerable to biodiversity loss. Prey partitioning among these specialists is geographically consistent, and this pattern intensifies when weak interactions are disregarded. Our results suggest that energy flows through coral reef communities along broadly comparable trophic pathways. Yet, these critical pathways are maintained by species with narrow, specialized diets, which threatens the existence of coral reef functioning in the face of biodiversity loss.
food web
coral reef
interaction network
Footnotes
↵1To whom correspondence may be addressed. Email: valeriano.parravicini@ephe.psl.eu or pozaschloe@gmail.com.
↵2G.S. and V.P. contributed equally to this work.
Author contributions: C.P.-S., J.M.C., G.S., and V.P. designed research; C.P.-S., J.M.C., S.J.B., G.S., and V.P. performed research; M.K. and M.H.-V. contributed new reagents/analytic tools; C.P.-S., G.S., and V.P. analyzed data; and C.P.-S., J.M.C., S.J.B., M.K., M.H.-V., G.S., and V.P. wrote the paper.
The authors declare no competing interest.
This article is a PNAS Direct Submission. M.A.M. is a guest editor invited by the Editorial Board.
This article contains supporting information online at https://www.pnas.org/lookup/suppl/doi:10.1073/pnas.2100966118/-/DCSupplemental.
Data Availability
All data and scripts have been deposited in a publicly accessible GitHub repository (https://github.com/ChloePZS/foodweb) and are also available on Zenodo (https://zenodo.org/record/5341340#.YS3ikt8682w). All other study data are included in the article and/or supporting information.
Accepted July 28, 2021.
Published under the PNAS license.
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