Assessing warming impacts on marine fishes by integrating physiology‐guided distribution projections, life‐history changes and food web dynamics

Abstract

Rising ocean temperatures pose a continuing threat to marine fish communities. As warming has far‐reaching impacts at multiple ecological levels, incorporating multimodal data is necessary for more accurately forecasting the responses of species and communities to the warming ocean. Range shifts, life‐history changes, and alterations of trophic dynamics are three important aspects of warming impacts, yet there has not been a formal integration of all three aspects in the same analysis. Here, we present a novel framework that integrates species distribution projections, life‐history changes, and food web dynamics to assess warming impacts on marine fish communities. We first introduce a simple yet effective way of incorporating thermal physiological data into the species distribution model without the need to empirically measure thermal performance curves. We then use the dynamic size‐spectrum model as the modeling backbone to incorporate data from species distributions and population‐level life history analyses. With this framework, we evaluate how individual species are affected under two warming scenarios (RCP4.5 and RCP8.5). We also simulate large‐scale top‐down and bottom‐up perturbations to examine community resilience under rising temperatures. We find that warming generally reduces species biomass and shifts species size spectra towards larger individuals, even though the maximum size tends to decrease under warming. However, the exact responses to rising temperatures differ among species and do not exhibit strong correlations with species size and the pace of life history. More severe warming also renders the focal community more vulnerable to top‐down perturbations, even though the community remains sufficiently resilient overall. The complex nature of species and community responses result from the fact that distribution range, life history, and food web dynamics change with warming in different directions that may not be intuitive to predict a priori. Importantly, we show that neglecting changes in species distribution or life history will lead to biased assessment of species and community responses. Our analyses highlight trophic dynamics, species biomass, and community resilience as three emergent properties that our framework can uniquely quantify. This integrative framework is readily applicable to other communities of interest and can be scaled up for multi‐regional or global analyses.

Diving deep to escape the heat: the importance of mesophotic reefs as thermal refuges for New Zealand coastal fishes

“…These findings emphasise the well-evidenced negative impacts of ocean warming on fish population biomass and productivity (Capitani et al, 2022;Carozza et al, 2018;Free et al, 2019;Wilson et al, 2021), as well as the importance of species interactions and trophic cascades in determining responses to warming (Baum & Worm, 2009;Kirby & Beaugrand, 2009;Steneck, 2012) and thermal refuge availability. Reductions in biomass and fisheries yields with ocean warming have been observed using other temperature-dependent mizer models (Audzijonyte et al, 2022;Kuo et al, 2022;Lindmark et al, 2022;Woodworth-Jefcoats et al, 2019), and Kuo et al (2022) highlighted evidence of warming-induced trophic cascades as changes in spatial overlap and decreases in fish biomass resulted in species having to feed more on background resources. However, the community-wide negative response to the extreme euphotic heatwave highlights that the impacts of approaching or exceeding thermal tolerance limits outweigh the benefits of release from competition and predation.…”

“…In mizer models of fished systems, biomasses at depth are usually taken from catch data Jacobsen et al, 2017;Szuwalski et al, 2017;Woodworth-Jefcoats et al, 2019), and it would be interesting to explore the impact of mesophotic thermal refuge availability on fisheries yields specifically. In models encompassing large areas, it would also be pertinent to incorporate latitudinal range shifts as a simulation possibility (Kuo et al, 2022). Furthermore, site-attached species such as triplefins and eels (Abrams et al, 1983;Nagelkerken et al, 2016) would be less likely to move to a mesophotic reef during warming, even if one were available.…”

“…Lindmark et al (2022) modelled temperature effects on planktonic resource spectrum dynamics as well as on fish physiology and found that warming resulted in increases in size-at-age and growth rates but decreases in large fish abundance and fisheries yields. In investigating similar warming impacts, Kuo et al (2022) also incorporated species distribution models, allowing species to respond spatially with horizontal range shifts, habitat shrinkage and changes in species overlap and interactions.…”