Revealing the Systematic Nature of Coral Attachment to Reef Substrates

Abstract

Reef-building coral colonies propagate by periodic sexual reproduction and continuous asexual fragmentation. The latter depends on successful attachment to the reef substrate through modification of soft tissues and skeletal growth. Despite decades of research examining coral sexual and asexual propagation, the contact response, tissue motion, and cellular reorganisation responsible for attaching to the substrate via a newly formed skeleton have not been documented. Here, we correlated fluorescence and electron microscopy image data with ‘live’ microscopic time-lapse of the coral tissue biomechanics and developed a multiscale imaging approach to establish the first “coral attachment model” (CAM) - identifying three distinct phases that determine the timing and success of attachment during asexual propagation: (i) an initial immune response, followed by (ii) fragment stabilisation through anchoring by the soft tissue and (iii) formation of a “lappet appendage” structure leading to substrate bonding of the tissue for encrustation through the onset of skeletal calcification. In developing CAM, we provide new frameworks and metrics that enable reef researchers, managers and coral restoration practitioners to evaluate attachment effectiveness needed to optimise species-substrate compatibility.

Horizon scan of rapidly advancing coral restoration approaches for 21st century reef management

“…In all cases, research has turned to addressing a key aspect of coral biology that has long remained obscure - how material actually attaches to substrates - to further optimise attachment protocols (e.g. the first ‘coral attachment model'; [ 98 ]). Practicalities of attachment are equally critical in innovations such as micro-fragmentation to establish rapid growth of outplants (and notably of massive corals; [ 99 ]) needed for ‘re-skinning' of large substrate areas.…”