Sonia J. Rowley

Gorgonian corals (Cnidaria: Octocorallia) are a highly diverse group and are older in the paleontological record than Scleractinia. In fact, it is estimated that of all the 5080 species of coral currently described on this planet, 64% are octocorals (Subclass: Octocorallia), with only 14% being the reef-building (hermatypic) corals that we are so familiar with (see figure below). Out of that 5080 species, 66% are found below 50 m depth and 75% of these deep-sea species are octocorals (see Cairns 2007).

Figure 1: Williams & Cairns (2018) synopsis of extanct coral species diversity.

Gorgonian corals are often conspicuous keystone species, providing secondary space to many other animals and are often used as conservation 'flagship' taxa. Symbiotic associations with charismatic creatures such as Pygmy Seahorses (Hippocampus spp.) add to their conservation appeal. Furthermore, many species harbour powerful allelochemicals, which can then be used as pharmaceuticals (e.g., hippuristanol from the zooxanthellate gorgonian Isis hippuris Linnaeus, 1758). 

Figure 2: New species of Pygmy seahorse (Hippocampus n.sp.) on a colony of Acanthogorgia sp. at 80 m (262 ft) depth, Pohnpei. Image by SJ.Rowley.

Gorgonians are colonial suspension-feeding animals, obtaining tiny particles of food from the water column. Many species are zooxanthellate (possessing zooxanthellae within their gastrodermal - digestive - tissue), however, the majority of species are azooxanthellate relying solely on particulates and dissolved organic matter in the water column and, I suspect, a nutritional interchange with their microbiome. 

Figure 3: New gorgonian species from 84 m (276 ft) depth, Pohnpei. Image by SJ.Rowley.

Species of this colonial sessile marine group can be very responsive (therefore, plastic) to changes in their environment because of their hierarchical modularity e.g., Isis hippuris Linnaeus, 1758. Other taxa may be specialised (fixed) to specific environments such as the deep-sea specialist Metallogorgia melanotrichos Wright & Studer, 1889, which is always associated with the same species of brittle star Ophiocreas oedipus Lyman (1879) (see Cho and Shank 2010).

Figure 4: A colony of the deep-sea specialist Metallogorgia melanotrichos Wright & Studer, 1889 with its associate brittle star Ophiocreas oedipus Lyman (1879). Image courtessy of Wikimedia Commons.

Gorgonian corals reproduce in a variety of ways, which can influence their distribution. Most fascinating, however, is the immense level of gorgonian diversity across the Indo-Pacific, due to a complex interplay between ecological, geological, and oceanographic processes influencing species diversification and persistence at local and regional scales. The age and diversity of this vast region means that gorgonian octocorals have had a lot of time to evolve and diverge into a variety of forms, to develop inter-species relationships and co-evolve with other organisms, and to become specialised or flexible to their environment. ​​​​​​​Yet, there is still much that we do not know about this enigmatic group of corals, most notably those throughout the Indo-Pacific. 

Figure 5: Biodiversity including a variety of gorgonian species on a deep wall at 100 m (328 ft) depth at Ant Atoll in the Federated States of Micronesia. Image by SJ.Rowley.

In summary, I seek to understand the biological success of gorgonian corals, their phenotypic responses to environmental change over ecological and geological (deep) time and, in turn, determine what, how, and in what way is natural selection working on these remarkable animals. In particular, the shear dominance and diversity of gorgonians at the mesophotic depths of the Indo-Pacific, I see, hold many keys to some of these questions. To address these questions I integrate cross-disciplinary approaches​​​​​​​ from experimental field ecology and functional morphology, to advances in genomics, robotics, and diving technology.