Temperature

Lophelia pertusa is typically found in water temperatures of 4-12°C (Rogers, 1999 and references therein), and can be exposed to rapid temperature changes in some locations (Ellet et al., 1986; Mienis et al., 2014; Davies et al., 2009). Brooke et al., (2013) observed L. pertusa reefs exposed to temperatures of up to 15°C, whilst some reports suggest up to 18°C. In the field, usually single point measurements of temperature are taken and give little indication to any temporal or spatial variation (Brooke et al., 2013), so even more extreme temperatures may be experienced by L. pertusa.

Metabolism, growth, fecundity and behaviour among many other biological traits of organisms are strongly influenced by temperature changes. Davies et al. (unpublished) noted an increase of the polyp retraction of L. pertusa during a 0.5°C increase, suggesting either increased feeding rates or a resting state due to unsuitability of feeding. Dodds et al. (2007) observed a 50% increase of oxygen consumptions when an increase of 2°C was induced in laboratory experiments and high Q10 values, suggest high sensitivity to temperature change. A two-fold increase in metabolism was also observed when temperature increased by 1°C (Dodds et al., 2007). Furthermore mortality rates of L. pertusa greatly increases at high temperatures (20°C), though they do survive brief exposures (Brooke et al., 2013; fig 4). It appears when exposed to temperatures above 14°C for seven more days, high mortality is observed (Lunden et al., 2014; Brooke et al., 2013). Calcification rates decline with decreasing temperature by as much as 58% over a 6°C decrease from 12°C (Naumann et al., 2014).

fig. 4.  Mean survival of Lophelia pertusa when exposed to different temperatures for 24 hours (black bars) and 7 days (grey bars). Error bars indicate standard deviation.

fig. 4. Mean survival of Lophelia pertusa when exposed to different temperatures for 24 hours (black bars) and 7 days (grey bars). Error bars indicate standard deviation. Brooke et al., 2013.

Even the deep ocean is not immune to global warming, with temperatures in the first 700m of the ocean being found to have increased by 0.18°C between 1955 and 2010 (Levitus et al., 2012; Barnnet et al., 2005; fig 5), which may have consequences for cold-water corals. Although the temperature increase seems minute, metabolism rates

Fig. 5. Change of heat content in the first 2000m at 100m intervals. (Levitus et al., 2012)

Fig. 5. Change of heat content in the first 2000m at 100m intervals. (Levitus et al., 2012)

would still increase and would need to be met by sufficient food supply, or the effects may be highly detrimental. In past rapid warming events 11,500 years ago after the Younger Dryas period, the Mediterranean deep water environment increased by up to 3°C (Delibrias and Taviani, 1984; Luz, 1982). Cold-water coral abundance greatly reduced at this time and is likely linked to the rapid temperature change and its indirect impacts (Delibrias and Taviani, 1984).

Evidence from laboratory experiments and geological records demonstrate the sensitivity of L. pertusa to temperature change and its importance to behavioural and physiological processes. Whilst L. pertusa appear tolerant of short term temperature fluctuation, the long term effect of sustained elevated temperatures, on cold-water corals is unknown, but evidence from past geological times suggests global warming could potentially further limit their range and may cause loss of some reef habitats.

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