Perennial growth of hermatypic corals at Rottnest Island, Western Australia (32°S)

Abstract

To assess the viability of high latitude environments as coral refugia, we report measurements of seasonal changes in seawater parameters (temperature, light, and carbonate chemistry) together with calcification rates for two coral species, Acropora yongei and Pocillopora damicornis from the southernmost geographical limit of these species at Salmon Bay, Rottnest Island (32°S) in Western Australia. Changes in buoyant weight were normalised to colony surface areas as determined from both X-ray computed tomography and geometric estimation. Extension rates for A. yongei averaged 51 ± 4 mm y−1 and were comparable to rates reported for Acroporid coral at other tropical and high latitude locations. Mean rates of calcification for both A. yongei and P. damicornis in winter were comparable to both the preceding and following summers despite a mean seasonal temperature range of ∼6 °C (18.2°–24.3 °C) and more than two-fold changes in the intensity of downwelling light. Seasonal calcification rates for A. yongei (1.31–2.02 mg CaCO3 cm−2 d−1) and P. damicornis (0.34–0.90 mg CaCO3 cm−2 d−1) at Salmon Bay, Rottnest Island were comparable to rates from similar taxa in more tropical environments; however, they appeared to decline sharply once summer temperatures exceeded 23 °C. A coral bleaching event observed in December 2013 provided further evidence of how coral at Rottnest Island are still vulnerable to the deleterious effects of episodic warming despite its high latitude location. Thus, while corals at Rottnest Island can sustain robust year-round rates of coral growth, even over cool winter temperatures of 18°–19 °C, there may be limits on the extent that such environments can provide refuge against the longer term impacts of anthropogenic climate change.

Environmental and physiochemical controls on coral calcification along a latitudinal temperature gradient in Western Australia

“…Seawater DIC cf was similar at all locations based on daytime water sampling (~2,000 µmol/kg), and seawater Ω ar was 3.0–3.3 in Coral Bay, 3.3–3.9 at Rottnest Island, and 3.0 at Bremer Bay. Nutrient concentrations (total dissolved inorganic nitrogen and phosphate) were <1 M at all locations (Supporting Information Table S2 for Coral Bay; also see Ross et al, ; Ross et al, for Rottnest Island and Bremer Bay).…”

Coralline algae elevate pH at the site of calcification under ocean acidification

“…Thirty‐six individuals of all three species of coralline algae were collected from Big Salmon Bay, Rottnest Island, WA, Australia, on 31 August 2015 (see Ross, Falter, Schoepf, & McCulloch, for details of the study site). Two crustose coralline algal (CCA) rhodoliths Sporolithon durum and Neogoniolithon sp., and one articulate coralline Amphiroa anceps (Hereafter “ Sporolithon, ” “ Neogoniolithon ” and “ Amphiroa ”) were collected.…”

The Future of Coral Reefs Subject to Rapid Climate Change: Lessons from Natural Extreme Environments

“…In high-latitude corals, phenotypic plasticity may support their survival, through diverse coral symbiont communities (Wicks et al, 2010b), enhanced symbiont tolerance to extreme (low) temperatures (Wicks et al, 2010a), enhanced heterotrophic plasticity (Bessell-Browne et al, 2014) and evidence of shifted thermal optima for calcification at cooler temperatures (Ross et al, 2015). High-latitude coral communities around the world have also been found to reproduce sexually and are therefore not solely dependent on recruitment from tropical region coral stocks (e.g., Babcock et al, 1994;van Woesik, 1995;Wilson and Harrison, 2003;Miller and Ayre, 2004;Madsen et al, 2014).…”

“…Species temporal turnover can be high depending on larval supply and recruitment from lower latitudes and fluctuations in environmental conditions. Whilst coral cover (Harriott et al, 1994;Thomson and Frisch, 2010;Denis et al, 2013) and even coral growth rates can be high (e.g., Ross et al, 2015), reef accretion and development are nevertheless often limited, with corals sometimes only forming living veneers on rocky substrate and references therein). Furthermore, future reef accretion could become increasingly challenged with the percent changes in arag predicted to be greater at high-latitude reefs relative to their tropical counterparts .…”