Mesophotic Coral Ecosystems (MCEs), often referred to as the ‘Twilight zone’, extend from 30 to over 150 meters depth and are among the most unexplored realms on the planet. With technological advances in closed circuit rebreathers’ (CCR), these deeper habitats reveal a reservoir of biodiversity that has been poorly known. MCEs are typically dominated by gorgonian (sea fan) octocorals and, therefore, will be the main subject of this seminar. Exploratory and archival records across the Indo-Pacific show a frequently documented biogeographic pattern of an eastward attenuation in shallow water gorgonian diversity, yet this diversity is consistently high at mesophotic depths. Ecological research using CCR include field surveys and transplant experiments on the shallow and mesophotic reefs of Pohnpei island and the atolls Ant and Pakin in Micronesia. Surveys reveal a depth transition between two primary benthic groups: photosynthetic scleractinians and filter-feeding azooxanthellate gorgonians. Ubiquitous taxa, including the gorgonian Annella reticulata (Ellis & Solander 1786), was abundant across >20ºC temperature range. Subsequent transplant experiments from 30 – 130 m using A. reticulata suggest diurnal thermal tolerance, and a species-specific association between the host and it’s microbiome. This preliminary work provides proof of concept in terms of methodology, and insights into the biological success of gorgonian taxa on Indo-Pacific MCEs.
Sonia Rowley is a postdoctoral research fellow at the University of Hawai’i at Manoa working with evolutionary paleontologist Prof. Steven M. Stanley. She is also a research affiliate at the Bishop Museum in Honolulu. She received her PhD in 2014 from Victoria University Wellington, New Zealand on gorgonian responses to environmental change on coral reefs in SE Sulawesi, Indonesia. Prior to that she received her BSc(hon) in Marine Biology at Plymouth University, UK. Raised in the diving industry throughout the British Isles, Sonia eventually decided to pursue a career in Marine Biology combining over 3 decades of diving experience with scientific research. She now uses closed circuit rebreather (CCR) technology to address questions of diversity, evolution, and the responses of gorgonian octocorals to environmental change across bathymetry (from shallow to mesophotic depths). Sonia recently received the Sir David Attenborough award for fieldwork for this research.