Abstract
Marine ecosystems are vulnerable to climate driven events such as marine heatwaves yet we have a poor understanding of whether they will collapse or recover. Kelp forests are known to be susceptible, and there has been a rise in sea urchin barrens around the world. When temperatures increase so do physiological demands while food resources decline, tightening metabolic constraints. In this case study, we examine red abalone (Haliotis rufescens) looking at sublethal impacts and their prospects for recovery within kelp forests that have shifted to sea urchin barrens. Abalone are a recreationally fished species that once thrived in northern California’s bull kelp forests but have recently suffered mass mortalities since the 2014–2016 marine heatwave. Quantitative data exist on the health and reproduction of abalone both prior to and after the collapse. The survivors of the mass mortality show a 2-year lag in body and gonad condition indices. After the lag, body and gonad indexes decreased substantially, as did the relationship between shell length and body weight. Production of mature eggs per female declined by 99% (p< 0.001), and the number of eggs per gram of female body weight (2,984/g) declined to near zero (9/g). The number of males with sperm was reduced by 33%, and the sperm abundance score was reduced by 28% (p= 0.414). We observed that these reductions were for mature eggs and sperm while immature eggs and spermatids were still present in large numbers. In the lab, after reintroduction of kelp, weight gains were quickly lost following a second starvation period. This example illustrates how climate-driven declines in foundation species can suppress recovery of the system by impacting body condition and future reproduction of surviving individuals. Given the poor reproductive potential of the remaining abalone in northern California, coupled with ongoing mortality and low kelp abundances, we discuss the need to maintain the fishing moratorium and implement active abalone restoration measures. For fished species, such as abalone, this additional hurdle to recovery imposed by changes in climate is critical to understand and incorporate into resource management and restoration.
Highlights
Climate driven impacts to marine systems are occurring around the world and human mediated warming is the major contributor to these changes (Frölicher and Laufkötter, 2018)
Some regions and habitats are going to be sensitive to these changes (Hobday and Pecl, 2014), such as large marine ecosystems (Belkin, 2009), coral reefs (Hughes et al, 2017; Fordyce et al, 2019), seagrass meadows (Marbà and Duarte, 2010), and kelp forests (Cannell et al, 2019; Arafeh-Dalmau et al, 2020)
The case study of red abalone in northern California illustrates how climate stressors may result in ongoing changes to productivity which need to be accounted for in management of natural resources
Summary
Climate driven impacts to marine systems are occurring around the world and human mediated warming is the major contributor to these changes (Frölicher and Laufkötter, 2018). Some regions and habitats are going to be sensitive to these changes (Hobday and Pecl, 2014), such as large marine ecosystems (Belkin, 2009), coral reefs (Hughes et al, 2017; Fordyce et al, 2019), seagrass meadows (Marbà and Duarte, 2010), and kelp forests (Cannell et al, 2019; Arafeh-Dalmau et al, 2020). The collapse of marine ecosystem structuring species has the potential to impact the foundation species and the structure, function, and services provided by entire ecosystems (Harley et al, 2012; Arafeh-Dalmau et al, 2019; Smale et al, 2019). A warming climate will lead to a narrowing of metabolically suitable habitats in marine systems (Deutsch et al, 2015)
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