Post provided by Chi-Yun Kuo

Predicting the effects of ocean warming is vital for understanding the likely impacts of climate change on marine ecosystems. In this post, Chi-Yun Kuo shares insights from his recent publication in Methods in Ecology and Evolution which develops a framework for estimating the effects of warming water on communities of marine fishes, and discusses the implications for conservation, food security, and other ecosystem services. 

Global warming is causing sea temperatures to rise, and this alarming trend is projected to persist to the end of the century and beyond. Since marine fishes are important sources of food and provide other ecosystem services, assessing what would happen to these communities in a warming ocean is a pressing task at the intersection of ecology, conservation, and fisheries.

Four of the species represented in analyses, including species important for commercial fisheries such as Atlantic cod and haddock. Credit: Wikimedia Commons

Warming can impact marine fishes in a multitude of ways, but most notably it will change (1) where species occur, (2) their pace of life (or life history), and (3) how they interact with other species. One cannot fully assess warming impacts on marine fishes without taking these three important aspects into account.

An integrative framework for evaluating warming impacts

Realizing the necessity for an integrative framework to evaluate warming impacts, we developed a method that uses information from distribution projections, life-history changes, and food web dynamics to examine how species and communities would respond to a warming ocean.

Our framework stands on the shoulders of several well-established methods, including the species distribution models , global-scale life-history analyses , and the size-based food-web model with the R package mizer. Integrating these methods into the same analysis, our framework allows us to examine how size distribution of individuals would change within species under warming and how resistant the community would be as a whole to large-scale disturbances.

Integrating existing models into a new framework. Arrows show how information on species distribution and life history are incorporated into size-based food webs. Variables in red are directly influenced by temperature. Credit: Kuo et al. 2022

We applied our method to the community inhabiting the continental shelf along the east coast of the United States and found:

  1. Warming generally reduces species biomass, the proportion of smaller individuals within species, and the maximum size.
  2. The exact responses to warming differs among species.
  3. More severe warming makes the community more vulnerable to disturbances, especially disturbances that eliminate larger individuals from the community. Eventually, the community is still able to return to the pre-disturbance state.

Who could use our method?

Our method would be of interest to researchers and various policy makers. Ecologists might use our method to address questions such as: what type of species would be impacted the most by warming. Is this associated with specific taxonomic groups? Species living in tropical, subtropical, or temperate regions? Or species living at particular depths in the water column?  

Conservation biologists, fisheries scientists, and policy makers might use our method as a heuristic tool to envision the future of their communities of interest under warming and develop conservation measures for species that might be the most vulnerable. Given the fact that marine fish constitute an essential food source in many regions of the world, results from our method can be used in conjunction with economic models to evaluate the impact on food production. Even though our method can be readily applied to any marine community, a global dataset would harness the full potential of our method to answer the large-scale questions: what would happen to marine fishes if warming continues, and what that might mean for human populations?

Relative distribution of different-sized individuals within each species. Red curves are the
sizes under current climate, green curves are those under less severe, and the blue
curves are those under more severe warming.

You can read the full paper in Methods in Ecology and Evolution:

Assessing warming impacts on marine fishes by integrating physiology-guided distribution projects, life-history changes, and dynamic food webs