Ontogenetic differences in the response of the cold-water coral Caryophyllia huinayensis to ocean acidification, warming and food availability

Cold-water coral energy reserves and calcification in contrasting fjord environments

The relationship between energy reserves of cold-water corals (CWCs) and their physiological performance remains largely unknown. In addition, it is poorly understood how the energy allocation to different metabolic processes might change with projected decreasing food supply to the deep sea in the future. This study explores the temporal and spatial variations of total energy reserves (proteins, carbohydrates and lipids) of the CWC Desmophyllum dianthus and their correlation with its calcification rate. We took advantage of distinct horizontal and vertical physico-chemical gradients in Comau Fjord (Chile) and examined the changes in energy reserves over one year in an in situ reciprocal transplantation experiment (20 m vs. 300 m and fjord head vs. mouth). Total energy reserves correlated positively with calcification rates. The fast-growing deep corals had higher and less variable energy reserves, while the slower-growing shallow corals showed pronounced seasonal changes in energy reserves. Novel deep corals (transplanted from shallow) were able to quickly increase both their calcification rates and energy reserves to similar levels as native deep corals. Our study shows the importance of energy reserves in sustaining CWC growth in spite of aragonite undersaturated conditions (deep corals) in the present, and potentially also future ocean.

Ecophysiological and behavioural response of juveniles of the Chilean cold-water coral Caryophyllia (Caryophyllia) huinayensis to increasing sediment loads

Chilean Patagonia is a hotspot of biodiversity, harbouring cold-water corals (CWCs) that populate steep walls and overhangs of fjords and channels. Through anthropogenic activities such as deforestation, roadworks, aquafarming and increased landslide frequency, sediment input increases in the fjord region. While the absence of CWCs on moderately steep slopes has been suggested to reflect high vulnerability to sedimentation, experimental evidence has been lacking. Here, we investigated the sensitivity of CWCs to sediment stress, using juvenile Caryophyllia (Caryophyllia) huinayensis as a model. A 12-week aquarium experiment was conducted with three sediment loads: the average natural sediment concentration in Comau Fjord, 100- and 1000-fold higher sediment levels, expected from gravel road use and coastal erosion. Changes in coral mass and calyx dimensions, polyp expansion, tissue retraction and respiration were measured. For CWCs exposed to two and three order of magnitude higher sediment concentrations, 32% and 80% of the animals experienced a decrease in tissue cover, respectively, along with a decrease in respiration rate of 34% and 66%. Under the highest concentration corals showed reduced polyp expansion and a significantly reduced growth of ~ 95% compared to corals at natural concentration. The results show that C. huinayensis is affected by high sediment loads. As human activities that increase sedimentation steadily intensify, coastal planners need to consider detrimental effects on CWCs.