Self-recognition in corals facilitates deep-sea habitat engineering

Abstract

The ability of coral reefs to engineer complex three-dimensional habitats is central to their success and the rich biodiversity they support. In tropical reefs, encrusting coralline algae bind together substrates and dead coral framework to make continuous reef structures, but beyond the photic zone, the cold-water coral Lophelia pertusa also forms large biogenic reefs, facilitated by skeletal fusion. Skeletal fusion in tropical corals can occur in closely related or juvenile individuals as a result of non-aggressive skeletal overgrowth or allogeneic tissue fusion, but contact reactions in many species result in mortality if there is no ‘self-recognition’ on a broad species level. This study reveals areas of ‘flawless’ skeletal fusion in Lophelia pertusa, potentially facilitated by allogeneic tissue fusion, are identified as having small aragonitic crystals or low levels of crystal organisation, and strong molecular bonding. Regardless of the mechanism, the recognition of ‘self’ between adjacent L. pertusa colonies leads to no observable mortality, facilitates ecosystem engineering and reduces aggression-related energetic expenditure in an environment where energy conservation is crucial. The potential for self-recognition at a species level, and subsequent skeletal fusion in framework-forming cold-water corals is an important first step in understanding their significance as ecological engineers in deep-seas worldwide.

Response to Referee Comment #1

“…This hypothesis is generally consistent with empirical observations of biogenic calcium carbonates, in which ν 1 peak widths increase as ambient seawater pCO 2 decreases and/or pH increases (i.e. higher Ar ) (Kamenos et al, 2013;Hennige et al, 2015;Pauly et al, 2015). However, corals exert strong control on the carbonate chemistry of their calcifying fluid by elevating pH and/or Ar at the site of calcification to facilitate more rapid crystal growth (Al-Horani et al, 2003;Venn et al, 2011;McCulloch et al, 2012).…”

“…In biogenic calcium carbonates, correlations have been reported between ν 1 peak widths and environmental conditions, including temperature and seawater pCO 2 (Kamenos et al, 2013(Kamenos et al, , 2016Hennige et al, 2015;Pauly et al, 2015). These changes potentially reflect differences in calcifying fluid carbonate chemistry.…”

Peer Review #3 of "In situ growth and bioerosion rates of Lophelia pertusa in a Norwegian fjord and open shelf cold-water coral habitat (v0.1)"

“…Manuscript to be reviewed physiological advantage or higher stress resistance of the orange colourmorph of L. pertusa. At least with regard to framework formation, colour variation does not seem to have adverse impacts on the reef development, as it was recently shown that self-recognition even between genetically distinct colonies of these two colour variants can lead to skeletal fusion (Hennige et al, 2014b). The similar skeletal densities of white and orange corals as observed here thereby probably facilitate skeletal fusion.…”

Coral calcifying fluid aragonite saturation states derived from Raman spectroscopy

“…We collected 440 spectra from various grains spread onto a glass slide. Although JCp-1 exists in ground form, we note that analysis of intact coral skeletons is also possible (Wall and Nehrke, 2012;Hennige et al, 2014) and that peak widths apparently do not depend on whether the sample is ground or intact (Zakaria et al, 2008), as long as the grain size exceeds the laser spot size.…”