Characterising Stylophora from Mauritius and their photo- physiological responses to heat stress

Ranjeet Bhagooli1,2,3*, Grégory Philippart4, Nawsheen Taleb-Hossenkhan1, Sruti Jeetun1, Anne Sophie Virassamy1, Arvind Gopeechund1, Mouneshwar Soondur1, Jean- François Flot4, Todd C. Lajeunesse5

1. Department of Biosciences and Ocean Studies, Faculty of Science & Pole of Research Excellence in Sustainable Marine Biodiversity University of Mauritius, Réduit 80837, Republic of Mauritius 2. The Biodiversity and Environment Institute, Réduit, Republic of Mauritius 3. Institute of Oceanography and Environment (INOS), Universiti Malaysia Terengganu, 21030 Kuala Terengganu, Terengganu, Malaysia 4. Evolutionary Biology & Ecology - C.P. 160/12, Université Libre de Bruxelles, Avenue F.D. Roosevelt 50, B-1050 Brussels – Belgium 5. Department of Biology, 327 Mueller Laboratory, Pennsylvania State University, University Park, PA 16802, USA

*Corresponding author: Email - [email protected] ; Tel: (Office) 403-7916 Mobile (57579420)

Abstract

Stylophora is a coral found in the WIO region and is widely distributed. It is also known to be one of the bleaching-vulnerable coral to climate change-driven warming events. We present the first detailed study of the reef-building coral Stylophora from the waters of the Republic of Mauritius. Our main objectives were 1) to characterize morphologically the Stylophora coral colonies colonies recently discovered in Mauritius; 2) to characterize genetically the coral and their symbionts; and 3) to test the thermal photo-physiological responses of the different morphs observed in the field. Surveys were conducted around the islands of Mauritius and Rodrigues in 2017 and 2018, during which Stylophora colonies were found only at Ilot Longue and Plateau Ile aux Bernaches adjacent to Amber Island, as well as at Flat Island in the north of Mauritius. Though few in numbers, Stylophora colonies dominated the scleractinian coral community at Ilot Longue, where most of the other corals were dead. The other surviving corals at Ilot Longue and Plateau Ile aux Bernaches included massive Porites, Favia, Favites and Fungia species along with some soft corals. Colony morphology and scanning electron microscopy (SEM) analyses revealed multiple morphs, while genetic characterisation of the mitochondrial open-reading frame (ORF), the mitochondrial control region (CR) and the nuclear internal transcribed spacer 2 (ITS2) revealed a perfect match for ITS2 and near-perfect matches for ORF and CR with published sequences of Stylophora madagascarensis from Toliara in Madagascar, the type locality of this species. Genetic characterisation of the symbionts was carried out by amplification and sequencing of the 28S large ribosomal subunit (LSU_RNA) gene, and those results were partly confirmed via PCR- RFLP of the 18S small ribosomal subunit (SSU_RNA) using zooxanthellae-specific PCR primers. The results indicate the presence of as single species of Durusdinium sp., (this genus was formerly referred to as Clade D). The photo-physiological responses of the different Stylophora morphs were determined by exposing coral nubbins to 28, 30 and 32oC for a 12-hr duration then using a Diving Pulse-Amplitude-Modulated (D-PAM) fluorometer to measure changes in chlorophyll a fluorescence. Variable photo-physiological responses to thermal stress were observed among the Stylophora colonies habouring both species of symbionts. The different morphologies may partially explain the differential responses to thermal stress. Identification of thermally vulnerable morphs is imperative in a globally warming ocean for appropriate adaptive management strategies so as to better conserve and manage rare and thermally vulnerable reef-building coral species. Keywords: Cladocopium, Durusdinium, Mauritius, Stylophora madagascarensis, Thermal stress