Health status assessment of gorgonian species in an artificial reef in Gibraltar’s waters

Awantha Dissanayake¹, Livia Lang¹Jaime Davies^{1, 2}

¹University of Gibraltar, Gibraltar, ²University of Plymouth, UK

Gorgonians are among the most important habitat-forming species of benthic communities in the Mediterranean Sea. Through their three-dimensionality they create underwater forests, so called coral gardens. These coral gardens provide structural complexity and biomass of a habitat and moreover enhance surrounding species diversity. Gorgonians are sessile colonial organisms that can be found in reef habitats all around the world. Being sessile organisms with slow growth rates and general longevity, gorgonian gardens represent highly vulnerable marine ecosystems. Healthy gorgonian gardens are associated with an array of ecosystem goods and services, thus adding value to the ecosystems in which they are found. The present study represents a first-ever quantitative health assessment of gorgonian species in Gibraltar’s waters using a modified standardised monitoring protocol. The main aim of this project was to assess the health status of gorgonian species, focussing on four representative species that inhabit the Mediterranean Sea: the white gorgonian - Eunicella singularis, the pink gorgonian – Eunicella verrucosa, the red gorgonian – Paramuricea clavata and the sea fan Leptogorgia sarmientosa.
The health assessment was carried out on an artificial reef in Gibraltar. All four species were highly represented at the study area, with E. singularis as the most predominant species. In total, 158 individual colonies were investigated were it was found that over 63 % of the total amount of colonies were affected by epibiosis, 9 % were found to be dead with less than 28 % were perceived healthy. Eunicella verrucosa exhibited the highest percentage of injury with a value of 81 %. Overall, gorgonians exhibited a high epibiotic cover by predominantly two non-indigenous invasive algae species; Rugulopteryx okamurae and Womersleyella setacea. Epibionts also consisted of hydrozoan, poriferan, bryozoan and even other encrusting anthozoan. Multivariate statistical results indicated that epibiosis, abundance of healthy and of affected/injured species are the main factors leading to differences across the research site. In general, findings of this study indicate an overall poor ‘health’ condition of the species investigated at the artificial reef in Gibraltar. By assessing the current health status of gorgonian corals, this research hopes to improve the current knowledge and policy gaps about coralligeneous communities and the main abiotic and biotic factors responsible for the observed poor health status.