In situ growth and bioerosion rates ofLophelia pertusain a Norwegian fjord and open shelf cold-water coral habitat

Abstract

Coral reef resilience depends on the balance between carbonate precipitation, leading to reef growth, and carbonate degradation, for example, through bioerosion. Changes in environmental conditions are likely to affect the two processes differently, thereby shifting the balance between reef growth and degradation. In cold-water corals estimates of accretion-erosion processes in their natural habitat are scarce and solely live coral growth rates were studied with regard to future environmental changes in the laboratory so far, limiting our ability to assess the potential of cold-water coral reef ecosystems to cope with environmental changes. In the present study, growth rates of the two predominant colour morphotypes of live Lophelia pertusa as well as bioerosion rates of dead coral framework were assessed in different environmental settings in Norwegian cold-water coral reefs in a 1-year in situ experiment. Net growth (in weight gain and linear extension) of live L. pertusa was in the lower range of previous estimates and did not significantly differ between inshore (fjord) and offshore (open shelf) habitats. However, slightly higher net growth rates were obtained inshore. Bioerosion rates were significantly higher on-reef in the fjord compared to off-reef deployments in- and offshore. Besides, on-reef coral fragments yielded a broader range of individual growth and bioerosion rates, indicating higher turnover in live reef structures than off-reef with regard to accretion–bioerosion processes. Moreover, if the higher variation in growth rates represents a greater variance in (genetic) adaptations to natural environmental variability in the fjord, inshore reefs could possibly benefit under future ocean change compared to offshore reefs. Although not significantly different due to high variances between replicates, growth rates of orange branches were consistently higher at all sites, while mortality was statistically significantly lower, potentially indicating higher stress-resistance than the less pigmented white phenotype. Comparing the here measured rates of net accretion of live corals (regardless of colour morphotype) with net erosion of dead coral framework gives a first estimate of the dimensions of both processes in natural cold-water coral habitats, indicating that calcium carbonate loss through bioerosion amounts to one fifth to one sixth of the production rates by coral calcification (disregarding accretion processes of other organisms and proportion of live and dead coral framework in a reef). With regard to likely accelerating bioerosion and diminishing growth rates of corals under ocean acidification, the balance of reef accretion and degradation may be shifted towards higher biogenic dissolution in the future.

Broad Thermal Tolerance in the Cold-Water Coral Lophelia pertusa From Arctic and Boreal Reefs

“…The reef of origin (i.e., experiment) of the corals influenced the variance between replicates of the respiration rates, with higher variance in the corals from Nord-Leksa and lowest in corals from Hola. A similar observation was made in a recent in situ study by Büscher et al (2019) with far higher variances in the growth rates in replicates of Nord-Leksa compared to the offshore site Sula. This result may be linked to the difficult task of sampling genetically diverse colonial animals in the deep sea.…”

Climate‐induced changes in the suitable habitat of cold‐water corals and commercially important deep‐sea fishes in the North Atlantic

“…This vulnerability exists because most cold‐water corals with carbonate skeletons occur in waters supersaturated in carbonate that enable coral skeleton biocalcification. Although several experimental studies demonstrate high resilience of reef‐building scleractinian to ocean acidification (Büscher, Form, & Riebesell, ; Form & Riebesell, ; Hennige et al, , ; Maier et al, ; Maier, Watremez, Taviani, Weinbauer, & Gattuso, ; Maier, Weinbauer, & Gattuso, ; Movilla et al, ), the projected shoaling of the calcite and aragonite saturation horizons along with warming is expected to lead to the loss of suitable habitat (Davies & Guinotte, ; Perez et al, ; Sulpis et al, ; Tittensor et al, ; Yesson et al, ), weakening of the reef frameworks that may result in structural collapse of slow‐growing scleractinian corals (Büscher et al, ; Gomez, Wickes, Deegan, Etnoyer, & Cordes, ; Hennige et al, ), and increased mortality of octocorals that form coral gardens (Cerrano et al, ; Gugliotti, DeLorenzo, & Etnoyer, ). Notwithstanding genotypic variability in cold‐water corals’ response to ocean acidification (Kurman, Gómez, Georgian, Lunden, & Cordes, ; Lunden, McNicholl, Sears, Morrison, & Cordes, ), these changes may result in the loss of biodiversity and provision of ecosystem services associated with these ecosystems (Cordes et al, ).…”

“…& Gattuso, 2019; Movilla et al, 2014), the projected shoaling of the calcite and aragonite saturation horizons along with warming is expected to lead to the loss of suitable habitat (Davies & Guinotte, 2011;Perez et al, 2018;Sulpis et al, 2018;Tittensor et al, 2010;Yesson et al, 2012), weakening of the reef frameworks that may result in structural collapse of slow-growing scleractinian corals (Büscher et al, 2019;Gomez, Wickes, Deegan, Etnoyer, & Cordes, 2019;Hennige et al, 2015), and increased mortality of octocorals that form coral gardens (Cerrano et al, 2013;Gugliotti, DeLorenzo, & Etnoyer, 2019). Notwithstanding genotypic variability in cold-water corals' response to ocean acidification (Kurman, Gómez, Georgian, Lunden, & Cordes, 2017;Lunden, McNicholl, Sears, Morrison, & Cordes, 2014), these changes may result in the loss of biodiversity and provision of ecosystem services associated with these ecosystems .…”

Influence of Water Masses on the Biodiversity and Biogeography of Deep-Sea Benthic Ecosystems in the North Atlantic

“…The dissolution effect is more pronounced in dead carbonate skeletons which lack the organic protective tissue, as observed in different mollusk gastropods, CWCs (Tunnicliffe et al, 2009;Rodolfo-Metalpa et al, 2011) and tissue-free portions of skeletons of L. pertusa (Hennige et al, 2015;Wall et al, 2015). Therefore, one of the most important predicted consequences of OA is the dissolution and weakening of the reef framework that may result in their structural collapse (Hennige et al, 2015;Büscher et al, 2019).…”