Symbiont Dependent Thermal Bleaching Susceptiblity in Two Reef-building Corals, Stylophora pistillata and Platygyra ryukyuensis.

Coral species, one susceptible (Stylophora pistillata) and the other resistant (Platygyra ryukyuensis) to bleaching, were exposed to a sudden elevated temperature (33.5oC) under dim light (5 μmol quanta m-2 s-1) for 10 to 720 min in time course experiments and to temperatures varying from 30oC to 40oC at 65 μmol quanta m-2 s-1 for 10 min at each  temperature. Chlorophyll α fluorescence measurements in Symbiodinium of both coral species indicated that the maximum electron transport rate (ETRmax) and the maximum quantum yield of photosystem II (PSII) fluorescence (Fv/Fm) were sensitive to thermal stress. The non-stressed Symbiodinium ETRmax value in S. pistillata was halved earlier and at a lower temperature stress than in those of P. ryukyuensis. Denaturing gradient gel electrophoresis (DGGE) analysis of the internal transcribed spacer 2 (ITS2) region of the ribosomal DNA revealed inter-colony  diversity of Symbiodinium in both species, though each species contained genetically distinct Symbiodinium types. Heat dissipation in PSII, through non-photochemical quenching (NPQ), increased in Symbiodinium of P. ryukyuensis irrespective of Symbiodinium genotype (C60 and C55), while in S. pistillata it either increased (C59) or decreased (C1) depending on genotype. Thus distinct Symbiodinium ITS2 types exhibit diverse photo-physiological responses to thermal stress, and may partially explain the variable bleaching susceptibilities of some hermatypic coral species.Keywords: coral, PAM fluorometry, Symbiodinium, thermal stres

First field observation of a Thalassodendron ciliatum bed on the Nazareth Bank, Mascarene Plateau

Field note - N/

Sightings of sea stars (Echinodermata, Asteroidea) and a first record of crown-of-thorns starfish Acanthaster at Saya de Malha Bank, Mascarene Plateau

Field note - N/

Marine mollusc (Mollusca: Gastropoda and Bivalvia) diversity of the Saya de Malha and Nazareth Banks, Mascarene Plateau

Marine molluscs are among the largest assemblages of the animal kingdom and inhabit the marine environment from the intertidal zone to the deep sea. This study reports the diversity of marine molluscs (Gastropoda and Bivalvia) collected from sediments at 19 stations (SS) at the Saya de Malha and Nazareth Banks during the EAFNansen expedition in May 2018. Sampling was carried out using the five hydraulic Van Veen grabs mounted on a Video-Assisted Multi-Sampler (VAMS). The mollusc shells were morphologically identified using established procedures and published guides. Shannon-Wiener diversity (H’) and Pielou’s evenness (J) indices were used to assess the diversity of the molluscs at each station. A total of 56 genera of marine gastropods belonging to 34 families, and 40 genera of bivalves from 16 families were recorded. The SS8 station at the Saya de Malha Bank had the highest diversity at a depth of 79 m for Gastropoda and Bivalvia, while SS1 harbored the highest overall molluscan diversity. At the Nazareth Bank, highest gastropod diversity was recorded at SS44, while SS43 had the highest bivalve and overall molluscan diversity. This study provides new information on the molluscan diversity at the Saya de Malha and Nazareth Banks

First in-situ observation of the endemic giant clam Tridacna rosewateri from the Nazareth Bank, Mascarene Plateau

Field note - N/

First report of White Syndrome Disease on branching Acropora at Saya de Malha, Mascarene Plateau

Field note - N/

Spatial distribution of surface chlorophyll a and micro-phytoplankton density and diversity around two islands and at two banks of the Mascarene region

The present study validated the use of AquaMODIS sea surface chlorophyll a (Chla) concentrations and investigated the spatial variation in density and diversity of micro-phytoplankton around two islands and two fishing banks of the Mascarene region. The study included areas around Mauritius (MRU) and Rodrigues (ROD) Islands, at Nazareth (NZ) Bank, and in the Joint Management Area (JMA) between the Republic of Mauritius and the Republic of Seychelles, more specifically at the Saya de Malha (SM) Bank. The AquaMODIS data were based on 67 match-up data points of in-situ against satellite Chla concentrations. The micro-phytoplankton community structure was investigated by determining the density variation and using the Shannon Wiener (H’) and Evenness (Evar) diversity indices. The satellite and in-situ Chla data were significantly and positively correlated when pooled for the four sites studied (R2 = 0.441; r = 0.642, P < 0.01), and when analysed separately for islands (R2 = 0.480; r = 0.694), and banks (R2 = 0.233; r = 0.483). However, the Chla satellite values tended to be lower than the in-situ Chla data. The highest densities of micro-phytoplankton were observed in the eastern and northern regions for MRU and ROD, respectively. The most dominant genera of micro-phytoplankton were Coscinodiscus, Navicula, Chaetoceros and Ceratium. The Shannon-Wiener diversity index values for diatoms were all above 2.5 with waters around the islands having higher diversity compared to the banks. Overall, the different micro-phytoplankton around the islands, except for the group of cyanobacteria at ROD Island, were more evenly distributed (Evar > 0.6) compared to the banks. This study indicated that AquaMODIS Chla satellite data is valid and may be potentially used as a proxy for in-situ Chla concentration on the Mascarene Plateau. The results of this study also provide detailed insight into the spatial variation in micro-phytoplankton density and diversity on the Mascarene Plateau in the Western Indian Ocean. Further long-term studies are warranted to thoroughly understand the temporal (including seasonal and inter-annual) variations in Chla and micro-phytoplankton distribution for adequate and appropriate management of these ocean territories

Variable photo-physiological performance of macroalgae and seagrasses from Saya de Malha and Nazareth Banks, Mascarene Plateau

The photosynthetic performance of macroalgae and seagrasses related to their body parts, depth and colours from the poorly-studied Saya de Malha and Nazareth Banks on the Mascarene Plateau was investigated in this study. Two seagrass (Thalassodendron ciliatum and Halophila decipiens) and seven macroalgae species (Caulerpa cupressoides, Acrosorium ciliolatum, Dictyosphaeria cavernosa, Halimeda opuntia, Ulva sp., Udotea orientalis and Udotea palmetta) were collected using the five Van Veen grabs attached to the Video-Assisted Multi-Sampler (VAMS) from 29-79 m depths in May during the FAO EAF-Nansen Research Programme 2018. The photosynthetic performance was measured using a Diving-Pulse-Amplitude-Modulated (D-PAM) fluorometer and the parameters included effective quantum yield at photosystem II (PSII) (ΦPSII), relative maximum electron transport rate (rETRm), photosynthetic efficiency (α), photoinhibition (β), saturating light level (Ek), and maximum non-photochemical quenching (NPQmax). All photo-physiological parameters varied significantly in T. ciliatum and C. cupressoides across their body parts. However, variation with seawater depths was not significant for NPQmax and β in the seagrass, and ΦPSII, rETRm and β in the macroalgae. Photo-physiological functioning of the leaf of T. ciliatum was optimal at 40 m. The photosynthetic performance of the frond and stolon of C. cupressoides decreased and remained unchanged, respectively, at 79 m when compared to that at 29 m. The whitish lobes of H. opuntia at 31 m exhibited significantly lower photosynthetic performance, in terms of ΦPSII, rETRm,α and Ek, than the greenish lobes. These findings provide a first insight of seaplant body parts-, depth- and colour-related photo-physiological performance from the Mascarene Plateau

Rhodolith beds (Corallinaceae, Rhodophyta): An important marine ecosystem of the Saya de Malha and Nazareth Banks

Field note - N/

Variations in abundance, diversity, photo-physiology and estimated productivity of micro-phytoplankton with depth at the Saya de Malha Bank, Mascarene Plateau

The variations in micro-phytoplankton abundance, diversity, photo-physiology, chlorophyll a (Chla) concentration and estimated productivity were assessed at depth ranges of 0-4, 5-10, and 11-29 m with 100, 28 and 11% of irradiance, respectively, in Saya de Malha waters. The total micro-phytoplankton abundance (TMPA) differed significantly (P < 0.001) with depth ranges, and between day and night samples. Out of the 34 genera identified, 27 showed a decrease in abundance of over 40% with depth. Chaetoceros, Coscinodiscus, Navicula, Nitzschia and Ceratium were most dominant. The Shannon-Wiener (H’) diversity index did not differ among depth ranges and between samples collected during day and night, but diatoms were more diverse than dinoflagellates. The effective quantum yield (ΦPSII) and the light-use efficiency factor (α) tended to decrease, while the maximum relative electron transport rate (rETRmax), the photo-inhibitory factor (β) and the maximum non-photochemical quenching (NPQmax) varied insignificantly from morning to afternoon sampling points at all depth ranges studied. The estimated productivity, rETRmax and Chla concentration decreased with depth ranges. The higher diversity of diatoms, better photosynthetic performance in the morning hours and higher near-surface estimated productivity provide new insights into micro-phytoplankton dynamics and productivity in Saya de Malha waters