Modelling ocean acidification effects with life stage-specific responses alters spatiotemporal patterns of catch and revenues of American lobster, Homarus americanus Ocean acidification (OA) affects marine organisms through various physiological and biological processes, yet our understanding of how these translate to large-scale population effects remains limited. Here, we integrated laboratory-based experimental results on the life history and physiological responses to OA of the American lobster, Homarus americanus, into a dynamic bioclimatic envelope model to project future climate change effects on species distribution, abundance, and fisheries catch potential. Ocean acidification effects on juvenile stages had the largest stage-specific impacts on the population, while cumulative effects across life stages significantly exerted the greatest impacts, albeit quite minimal. Reducing fishing pressure leads to overall increases in population abundance while setting minimum size limits also results in more higher-priced market-sized lobsters (> 1 lb), and could help mitigate the negative impacts of OA and concurrent stressors (warming, deoxygenation). However, the magnitude of increased effects of climate change overweighs any moderate population gains made by changes in fishing pressure and size limits, reinforcing that reducing greenhouse gas emissions is most pressing and that climate-adaptive fisheries management is necessary as a secondary role to ensure population resiliency. We suggest possible strategies to mitigate impacts by preserving important population demographics. Ocean acidification (OA) and climate change drivers are affecting marine environments, altering species’ performances, distribution and abundance1, and in turn the supply and access to marine resources that we depend on for food, livelihoods, and economic development2,3,4. While these global changes pose risks to society’s dependence on marine fisheries resources, management strategies to reduce pressures on fisheries stocks could mitigate negative effects of global ocean changes5,6,7,8. Understanding how marine organisms respond to multiple stressors, shift their geographic distribution and change their local abundance is essential to manage added pressures of fishing.Research on OA effects has significantly increased in the past two decades, fundamentally improving our understanding of its direct and indirect impacts on marine life9,10,11. Despite the diversity of responses to OA, we have identified organisms that are likely to be most sensitive to changes in ocean pH. Shell forming organisms—such as corals, mollusks, and crustaceans—appear particularly sensitive to changes in ocean chemistry linked to OA, as they can be severely impacted by high dissolution rates and increased energy costs linked to the need to increase the effort for homeostasis and mineralisation to form and maintain calcium carbonate shell components12,13. Organisms at early stages in their life cycle (i.e. larval and juvenile) appear to be more sensitive to OA14,15,16,17,18,19,20. In species with complex life history traits, such as marine invertebrates, different life stages represent a sequence of biotic filters21 that are expected to have life-stage specific sensitivity to OA. These biotic filters cumulatively affect species’ recruitment and survival.Implications of OA and climate change present new and complex challenges for fisheries. These phenomena together increase the uncertainty for fisheries as rapidly changing environmental conditions drastically affect seasonal recruitment of many stocks22. This in turn increases the risks to the livelihoods of > 260 million people that depend on marine capture fisheries as a source of employment23,24. Ocean acidification is expected to have the greatest effects on invertebrates12,25, which will affect global shellfish fisheries, some of the most valuable fisheries in the world valued at over 50 billion USD and one third of the value of internationally traded seafood26,27. Furthermore, many developing nations rely on invertebrates as an important ‘backup’ source of nutrition, and account for up to 50% of animal protein intake in some countries (e.g. Fiji)28,29.In this study, we use a multi-disciplinary approach to link biological responses to global change drivers to downstream effects on fisheries using the American lobster, Homarus americanus (H. Milne-Edwards), as our model organism, within the context of the Canadian fisheries. Canada’s lobster fishery is one of the most economically lucrative fisheries, valued at over $1.6 billion CAD annually and further contributes over $2 billion CAD to the Canadian economy as exports30. First, we integrated experimental evidence of biological responses to OA amongst other stressors (i.e. ocean warming, de-oxygenation) to model future global change effects on various life stages of H. americanus. We explored the added effects of OA on mortality of larval, juvenile and adult stages. Next, we model these changes in a dynamic bioclimatic envelope model (DBEM) to observe changes in distribution, abundance, and fisheries catch. Lastly, we explored various broad fisheries management measures—specifically fishing pressure and size limits—that affect the dynamics of populations and the sustainability of fisheries. We tested the sensitivity of our model to uncertainties surrounding the structure and parameter selection. This is a continuation of the development of integrating OA effects into a dynamic bioclimatic envelope model31,32 to improve our understanding of OA effects on population dynamics and fisheries in a multi-stressor framework, and advance the general application of these models to broad scale fisheries analyses.Global ocean changes (including ocean warming and ocean acidification) are projected to have negative effects on the abundance and maximum catch potential (MCP) of the American lobster, with elevated impacts (more than 20% decrease in abundance and MCP) when climate change is accelerated (RCP 8.5; Fig. 1). Even with strong mitigation of carbon emissions (RCP 2.6), abundance and maximum catch potential are projected to decrease by up to 10% by 2100 relative to 2010. Mean body size of lobsters is also projected to decrease by 10 and 45% by the end of the twenty-first century for RCP 2.6 and RCP 8.5, respectively.Figure 1Alternative model parameter settings and their effects on abundance, maximum catch potential, and body size for the American lobster, Homarus americanus. While exploring change for each parameter, other parameters were held constant, such that: earth system model = GFDL; climate change scenario = RCP 8.5; OA effect size = 15%; OA effects on life stage = all; fishing pressure = MSY; fishing size limit = none. Dashed lines are the relative value in 2010, while coloured lines are temporal trends in the first three columns, and a snapshot of the population’s body size distribution in year 2095 in the far-right column. Values are relative to 2010 and are smoothed with 10-year running means.Changes in OA effects on mortality had very small effects overall on abundance and catch potential. However, there was a clear negative relationship with OA and mean body size of the population—mean body size decreased by an additional 10% by the end of the century under a high climate change scenario when OA effect size (see methods) was 15%, and another 10% decrease when the effect size was doubled (Fig. 1). When considering the effects of OA on mortality for various life stages, the effects on the juvenile stages had the greatest impacts on mean body size at the population level, suggesting that population demographics are most sensitive to impacts on juveniles.When fishing rate is reduced, there were initial increases in abundance and catch potential as expected. At the lowest fishing level explored (i.e. assuming fishing at 0.8 times the maximum sustainable yield or MSY), abundance initially increased by 15% (Fig. 1), but then decreased by 20% to a change of − 5% by the end of the twenty-first century due to environmental stressors, relative to 2010 under RCP 8.5. Alternatively, fishing at the long-term sustainable level (i.e., assuming fishing at MSY) under RCP 8.5 resulted in an overall decrease of 20% in abundance by 2100. Furthermore, scaling back fishing at 0.8 times the MSY resulted in an initial decrease in catch potential, but was only 2% lower than fishing at MSY by the year 2100 under RCP 8.5.Limiting the minimum size that the fisheries could target had a greater effect on abundance, but much smaller effect on catch potential (Fig. 1). While, implementing body size limits considerably increased overall abundance and reduced climate effects on abundance, over time there was no projected benefits to overall catch potential compared to the no fishing size limit scenario. Implementing fishing size limits had a large effect on the mean body size compared to no size limit, but minimal effects at different levels of size limits. Smaller mean body sizes with the implementation of size limits resulted from a relative increase in smaller individuals as larger individuals were removed from the population. Current fishing size limits vary based on region—more northern regions (e.g. Northumberland Strait) have smaller size limits—and are based on length, resulting in canner-sized lobsters (0.5–1 lb; market-sized lobsters are greater than 1 lb). We used weight for size limits to streamline our analyses for the two lobster market size classes.Projections of high climate change (including all global change drivers) on MCP show that future catch is expected to remain on continental shelf areas, but with much less biomass at lower latitudes (Fig. 2a). Changes in MCP show a shift in distribution poleward (north), and losses at lower latitudes (south) under a high climate change scenario (Fig. 2b).Figure 2Effects of environmental change on the distribution of maximum catch potential for H. americanus at the end of the twenty-first century (2091–2100) in a high climate change scenario (RCP 8.5). The top two panels show the null model effects of environmental change without any OA effects (i.e. changes due to temperature, oxygen content, primary production): (a) estimated maximum catch potential in year 2100, and (b) the change in maximum catch potential relative to 2010. Panels (c)–(f) represent the change in catch potential due to the added effects of OA, relative to the null model (panel a), on the different life stages (larval, juvenile, adult). Results are from simulations using the GFDL Earth system model and are the annual average across 10 years. Other parameter values (Table 1): OA mortality effect size = 15%; fishing pressure = MSY; fishing size limit = none.The effects of OA on MCP show geographical differences based on which life history stage we model OA effects on. Ocean acidification effects on early life stages (larvae and juvenile) affect the ability for the population to shift their distribution to new, more favourable habitats (Fig. 2c,d), while OA effects on adult size classes show more homogenous effects across the entire range (Fig. 2e). Early life stages are known to be more sensitive to environmental stressors18,19,20, and our results show that OA can have major implications on range shifts. Specifically, cumulative OA effects on all life stages of lobster may restrict migration to suitable habitat as well as reduce abundance across the entire distribution (Fig. 2f).Interestingly there are considerable differences in the effects of fishing body size limits for the two lobster market size classes. While canner-sized lobsters see no change in catch potential with no fishing size limit under a high climate change scenario by year 2100, catch potential for market-sized lobsters decreased by almost 60% (Fig. 3), averaging out to the overall decrease in catch potential of ~ 15% (Fig. 1). Implementing and increasing size limits results in decreased catch potential for canner-sized lobsters, while market-sized lobsters showed increases in catch potential (Fig. 3)—an increase of > 100% in catch potential of market-sized lobsters (relative to current catch of market-sized lobsters) with the largest fishing size limit of 1 lb. However, the combined overall (by biomass) change in catch potential was negligible with implementation of increasing size limits (Fig. 1).Figure 3The effect of implementing different fishing size limit on change in maximum catch potential for the two market size categories of H. americanus by end of twenty-first century (2091–2100, relative to 2010) under a high climate change scenario (RCP 8.5), and the effects of implementing fishing size limits. Points represent multi-model means from simulations from three Earth system models and error bars represent the minimum and maximum of the three outputs. Null parameter values were used (Table 2): climate change scenario = RCP 8.5; OA mortality effect size = 15%; OA effects on life stage = all; fishing pressure = MSY.Continuing with a high climate change scenario, there is a positive relationship with an increase in fishing size limits on catch potential by the end of the twenty-first century, regardless of the proportion of canner-sized lobsters in catch (Fig. 4a). However, the margin of increase in catch potential due to fishing size limits lessens if the proportion of canners in fishing catch increases (Fig. 4a). The large increase in catch potential for fishing size limits set at > 1 lb is exclusively due to an increase in market-sized lobsters (Fig. 3). Price differences between canner- and market-sized lobsters have a very minimal effect on the landed value (Fig. 4b). Nonetheless, restricting fishing limits to > 1 lb increases the abundance of market-sized lobsters (Fig. 3), increases their catch potential (Fig. 4a), and increases the landed value (Fig. 4b). Our results here show that fishing size limits can have considerable benefits for mitigating OA and climate change impacts.Figure 4The effect of implementing different scenarios of fishing size limits on: (a) maximum catch potential based on different catch proportions of canner lobsters, and (b) landed value potential with different price ratios of market to canner lobsters. Values are the change weighted by tonnage of the different priced lobster sizes by end of twenty-first century (2091–2100) under a high climate change scenario (RCP 8.5), relative to 2010 for American lobster biomass. Proportion of canners in catch were kept constant at 0.2 (the current value) for the analysis in panel b, except for when size limits were > 1 lb (thus no canners in catch). Points represent multi-model means from simulations from three earth system models and error bars represent the minimum and maximum of the three outputs. Parameter values were used from our null model (Table 2): climate change scenario = RCP 8.5; OA mortality effect size = 15%; OA effects on life stage = all; fishing pressure = MSY.The American lobster will likely be affected by projected climate change scenarios, and while OA shows little impacts to overall abundance, it may have major implications for population demographics, as already observed in systems that are naturally characterised by high CO2 levels33,34. Previous research on crustaceans, including the American lobster, has shown that individuals in the juvenile stage may be most sensitive to OA18,19,20,35,37,37, and our results further support this notion, suggesting that lobster populations are most sensitive to OA during juvenile stages with resulting impacts on mean body size in the population (Fig. 1). Geographical responses of the population are most sensitive when OA affects larval and juvenile stages (Fig. 2c,d). Furthermore, our findings of poleward shifts in distribution due to ocean changes are consistent with changes observed (e.g. lobster nurseries off the East c
https://www.nature.com/articles/s41598-021-02253-8
Modelling ocean acidification effects with life stage-specific responses alters spatiotemporal patterns of catch and revenues of American lobster, Homarus americanus
