Sea anemones may thrive in a high CO₂ world

Abstract

Increased seawater pCO , and in turn 'ocean acidification' (OA), is predicted to profoundly impact marine ecosystem diversity and function this century. Much research has already focussed on calcifying reef-forming corals (Class: Anthozoa) that appear particularly susceptible to OA via reduced net calcification. However, here we show that OA-like conditions can simultaneously enhance the ecological success of non-calcifying anthozoans, which not only play key ecological and biogeochemical roles in present day benthic ecosystems but also represent a model organism should calcifying anthozoans exist as less calcified (soft-bodied) forms in future oceans. Increased growth (abundance and size) of the sea anemone (Anemonia viridis) population was observed along a natural CO gradient at Vulcano, Italy. Both gross photosynthesis (P ) and respiration (R) increased with pCO indicating that the increased growth was, at least in part, fuelled by bottom up (CO stimulation) of metabolism. The increase of P outweighed that of R and the genetic identity of the symbiotic microalgae (Symbiodinium spp.) remained unchanged (type A19) suggesting proximity to the vent site relieved CO limitation of the anemones' symbiotic microalgal population. Our observations of enhanced productivity with pCO , which are consistent with previous reports for some calcifying corals, convey an increase in fitness that may enable non-calcifying anthozoans to thrive in future environments, i.e. higher seawater pCO . Understanding how CO -enhanced productivity of non- (and less-) calcifying anthozoans applies more widely to tropical ecosystems is a priority where such organisms can dominate benthic ecosystems, in particular following localized anthropogenic stress.

Trace element profiles of the sea anemoneAnemonia viridisliving nearby a natural CO2vent

“…10–40 anemones m −2 ), consistent with findings by Suggett et al (2012). At the high p CO 2 site, anemones appeared to be healthy with their tentacles fully extended and without any excess amounts of mucus (Fig.…”

Intracellular pH and its response to CO2-driven seawater acidification in symbiotic versus non-symbiotic coral cells

“…This alkalinisation demonstrates the capacity of Symbiodinium cells to strongly buffer the external environmental pH signal, probably due to a fertilising effect on photosynthesis in these normally CO 2 -limited algae (Nimer et al, 1999). An increase in photosynthetic productivity after CO 2 addition has also been observed in other symbiotic associations, most notably in the temperate sea anemones Anemonia viridis (Suggett et al, 2012) and Anthopleura elegantissima (Towanda and Thuesen, 2012), and the benthic foraminiferan Marginopora vertebralis (Uthicke and Fabricius, 2012). The application of DCMU (a photosynthetic inhibitor) reversed the increase in pH i , confirming that the change was a direct consequence of photosynthesis, as the inhibited photosynthetic machinery of the symbionts is not able to ameliorate the increasing H + concentration (Fig.…”

Coral Community Structure and Recruitment in Seagrass Meadows

“…Size-frequency of the established coral communities of each habitat was binned into size categories; larger categories were pooled together to avoid the problems associated with low expected counts (Starnes et al, 2012). The maximum diameter for each colony was used for comparison to ensure standardization among colonies with different growth forms (per Suggett et al, 2012). Fits of exponential decay across the counts in each bin were performed for both 2012 and 2013 to assess the population size-classes (Santangelo et al, 2004).…”