Abstract
Cold-water corals (CWC) can be found throughout a wide range of latitudes (79°N–78°S). Since they lack the photosymbiosis known for most of their tropical counterparts, they may thrive below the euphotic zone. Consequently, their growth predominantly depends on the prevalent environmental conditions, such as general food availability, seawater chemistry, currents, and temperature. Most CWC communities live in regions that will face CaCO3 undersaturation by the end of the century and are thus predicted to be threatened by ocean acidification (OA). This scenario is especially true for species inhabiting the Chilean fjord system, where present-day carbonate water chemistry already reaches values predicted for the end of the century. To understand the effect of the prevailing environmental conditions on the biomineralization of the CWC Tethocyathus endesa, a solitary scleractinian widely distributed in the Chilean Comau Fjord, a 12-month in situ experiment was conducted. The in situ skeletal growth of the test corals was assessed at two sites using the buoyant weight method. Sites were chosen to cover the naturally present carbonate chemistry gradient, with pH levels ranging between 7.90 ± 0.01 (mean ± SD) and 7.70 ± 0.02, and an aragonite saturation (Ωarag) between 1.47 ± 0.03 and 0.98 ± 0.05. The findings of this study provide one of the first in situ growth assessments of a solitary CWC species, with a skeletal mass increase of 46 ± 28 mg per year and individual, at a rate of 0.03 ± 0.02% day. They also indicate that, although the local seawater chemistry can be assumed to be unfavorable for calcification, growth rates of T. endesa are comparable to other cold-water scleractinians in less corrosive waters (e.g., Lophelia pertusa in the Mediterranean Sea).
Highlights
More than 50% of the approximately 5,100 recent coral species are deep and cold-water corals (CWC) (Roberts et al, 2009)
Knowledge on skeletal growth rates of other CWC species, especially solitary and nonhermatypic corals, is very limited (Jantzen et al, 2013a), some of these species may constitute a major component of the benthic community and provide three-dimensional structures and habitat for other species
This study provides one of the first in situ assessments on skeletal growth rates of a solitary cold-water scleractinian species, Tethocyathus endesa
Summary
More than 50% of the approximately 5,100 recent coral species are deep and cold-water corals (CWC) (Roberts et al, 2009). In the absence of light-enhanced calcification processes (Falkowski et al, 1984), growth rates of scleractinian CWCs largely depend on other prevailing environmental factors, including food availability, currents, temperature, and in particular seawater carbonate chemistry (Mortensen et al, 1998; Flögel et al, 2014) As a result, their skeletal mass is reported to increase relatively slow (Orejas et al, 2011; Büscher et al, 2017, 2019) in comparison to that of their photosymbiotic tropical conspecifics, with only a few exceptions (see e.g., Desmophyllum dianthus in Jantzen et al, 2013a). While the factors influencing growth and biomineralization rates of tropical, photosymbiotic corals have been intensively studied in recent decades (see e.g., Gattuso et al, 1998; Allemand et al, 2011; Chan and Connolly, 2013), growth rates of their coldwater and deep-sea congeners are less well known This lack of information is mainly due to the difficulty of accessing their habitats, and there are few studies on the longterm growth of CWCs, especially in situ. Crucial to understand their general ecology, and their vulnerability to regional and global impacts, and their likely resilience in future scenarios (Jaap, 2000; Rinkevich, 2014)
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