Abstract
An 18-year database of coral reef fish expatriation poleward in South East Australia was used to estimate persistence of coal-reef fish recruits on temperate reefs. Surveys have identified over 150 coral-reef fish species recruiting to temperate reefs at latitudes of 340S (Sydney) and 60 species to 370S (Merimbula) with 20 and 5 species respectively overwintering in at least one year over the study duration. We developed indices of vulnerability of key species to drops in water temperatures, by relating drops in abundances of species to temperature drops. Twenty species were ranked according to their temperature vulnerability. Overall, the families Chaetodontidae (butterflyfishes), Acanthuridae (surgeonfishes), Labridae (wrasses) and Pomacetnridae (damselfishes) had similar cold-water tolerance. However, there was considerable variability within families, for instance in the Pomacentridae, species from the genus Abudefduf appeared to have better cold-temperature tolerance than the other species. Predicted minimum overwintering temperature varied from 15.6C to 19.8C, with some species showing lower Tzero at Merimbula, the more poleward location. There was general concordance between a species’ tolerance to cold-water and its tendency to occur as an overwinter but also notable exceptions. So while this work demonstrates the potential utility of tolerance to seasonal temperature drops as a means to predict range expansion capacity of vagrant species, the exceptional cases serve to highlight alternative factors. Specifically, tolerance to seasonal cooling of water is not the only important factor when predicting the range expansion capacity of a species. Factors affecting the general abundance of the vagrants, such as habitat suitability and competitor/predator environments will also be critical where overwinter survival becomes a lottery.
Highlights
The future of species globally, both in terrestrial and aquatic environments, is under threat through human-caused climate change (Chen et al, 2011; Poloczanska et al, 2013)
Overwinter survival was generally much more common in Sydney than in Merimbula (Figure 3A) with the highest ratio observed for the territorial damselfish Stegastes gascoynei, overwintering was much more limited for the other Pomacentridae aside from Chromis nitida
Temperatures at the peak of abundance (Tpeak) differed between 18 and 24◦C across the dataset and were generally lower at Merimbula than Sydney for the same species (Figure 3B) there was a large overlap in error bars suggesting that this is not a significant effect
Summary
The future of species globally, both in terrestrial and aquatic environments, is under threat through human-caused climate change (Chen et al, 2011; Poloczanska et al, 2013). As a result of strengthening western boundary currents under climate change, many coral reef fishes are expected to expand their ranges polewards (Figueira and Booth, 2010; Wernberg et al, 2012; Feary et al, 2014; Vergés et al, 2016). This influx into temperate ecosystems may lead to novel interactions and affect the structure and function of temperate marine communities (Vergés et al, 2014; Luiz et al, 2016). There is still relatively little understanding of factors that constrain or facilitate species’ geographic responses to climate change, including those of marine fishes (Li et al, 2011; Yang et al, 2011; Blois et al, 2013; Liancourt et al, 2013). Feary et al (2014) and Booth et al (2018a,b) showed that species metrics such as large body size, high swimming ability, large size at settlement and pelagic spawning behavior are more likely to occur in species expatriating into temperate habitats
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