Growth and feeding of deep-sea coral Lophelia pertusa from the California margin under simulated ocean acidification conditions

Abstract

The global decrease in seawater pH known as ocean acidification has important ecological consequences and is an imminent threat for numerous marine organisms. Even though the deep sea is generally considered to be a stable environment, it can be dynamic and vulnerable to anthropogenic disturbances including increasing temperature, deoxygenation, ocean acidification and pollution. Lophelia pertusa is among the better-studied cold-water corals but was only recently documented along the US West Coast, growing in acidified conditions. In the present study, coral fragments were collected at ∼300 m depth along the southern California margin and kept in recirculating tanks simulating conditions normally found in the natural environment for this species. At the collection site, waters exhibited persistently low pH and aragonite saturation states (Ω_arag) with average values for pH of 7.66 ± 0.01 and Ω_arag of 0.81 ± 0.07. In the laboratory, fragments were grown for three weeks in "favorable" pH/Ω_arag of 7.9/1.47 (aragonite saturated) and "unfavorable" pH/Ω_arag of 7.6/0.84 (aragonite undersaturated) conditions. There was a highly significant treatment effect (P < 0.001) with an average% net calcification for favorable conditions of 0.023 ± 0.009% d^-1 and net dissolution of -0.010 ± 0.014% d^-1 for unfavorable conditions. We did not find any treatment effect on feeding rates, which suggests that corals did not depress feeding in low pH/ Ω_arag in an attempt to conserve energy. However, these results suggest that the suboptimal conditions for L. pertusa from the California margin could potentially threaten the persistence of this cold-water coral with negative consequences for the future stability of this already fragile ecosystem.

Keywords: Carbonate saturation; Climate change; Deep-sea; Ocean acidification.

Figure 1. Map of the South California Bight showing the sampling station (red dot).

Yellow dots refer to the CalCOFI stations used to complement the characterization of the carbonate chemistry of the area where L. pertusa was collected.

Figure 2. Water column profiles for (A) temperature (T °C), (B) total alkalinity (A_T), (C) aragonite saturation (Ω_arag) and (D) pH_T(total scale) in the study site plotted against depth.

Solid line indicates the average (±SD) of the seawater chemistry approximated from the CalCOFI database spanning a whole year from Nov 2014 to Nov 2015 the red dots represent the seawater chemistry from discrete water samples taken in the area of the collection sites. pH${}_{\mathrm{T}}^{\mathrm{es}}$ and A${}_{\mathrm{T}}^{\mathrm{est}}$ where obtained from the empirical model proposed by Alin et al. (2012) for the South Atlantic Bight for pH_T and A_T.

Figure 3. Cross-sectional profiles of in-situ carbonate chemistry parameters.

Profiles are for (A) total pH (pH_T), (B) total alkalinity (A_T) (C) and aragonite saturation (Ω_arag) in the South California Bight where L. pertusa were collected.

Figure 4. Growth (% day⁻¹) of L. pertusa fragments in the different treatment conditions.

Aragonite saturation (Ω_arag) and total alkalinity (A_T) treatments used in the study. Values are reported as mean ± SD (n = 8).

Figure 5. Average capture rates of Artemia standardize per polyp per hour.

Aragonite saturation (Ω_arag) and total alkalinity (A_T) treatments used in the study. Values are reported as mean ± SD (n = 8).