Diversity and distribution of the shallow water (23-50 m) benthic habitats on the Saya de Malha Bank, Mascarene Plateau

Abstract

The Saya de Malha Bank (SMB) is one of the largest and least studied marine banks on the Mascarene Plateau. This study aimed to examine the diversity and distribution of the main benthic habitats in the shallow waters of the SMB (23 to 50 m). The survey was carried out in May 2018 during the EAF-Nansen Indian Ocean Research Expedition using a Remotely Operated Vehicle (ROV) deployed at 15 stations. Four main benthic habitats were investigated and their relative abundance determined during the survey. The 143,110 m2 surveyed area revealed proportional benthic habitat cover of 43.6 ± 22.4, 24.5 ± 21.9, 21.2 ± 27.8, and 10.5 ± 12.6 % for seaweed, abiotic substrate, seagrasses and corals, respectively. The seaweed habitat (43.6 %) was mainly composed of Halimeda spp. It represented up to 77 % of the habitats observed at SS34 (4553 m2). Even though seaweeds are considered seasonal, their dominance at all stations creates an important habitat structure for many organisms. The seagrass habitat (21.2 %) was dominated by Thalassodendron ciliatum. This habitat covered up to 93 % of the area investigated at SS38 (5950 m2) and was found mainly on the eastern side of the bank. The live hard coral habitat (10.5 %) was the highest at SS36-2 (35% of 9819 m2) and was more homogenously spread within the shallow areas. The unstable and the stable bare bottom substrate habitat (24.7 %) characterized as abiotic habitat was mainly composed of bedrock, sand, and rubble. It dominated at SS42 where it constituted 72.5 % of the 5114 m2 investigated and was recorded at all stations. Further research is warranted to better understand the diversity and the distribution of benthic habitats within the shallow waters of the SMB, along with collection of targeted benthic organisms for identification at higher taxonomic levels, to better formulate conservation and management measures and strategies.

Remote submerged banks and mesophotic ecosystems can provide key habitat for endangered marine megafauna

“…Our approach of tracking a marine vertebrate also informs on the distribution of its prey and points to an abundance of benthic invertebrates at mesophotic depths, since hawksbill turtles are thought to feed primarily on sponges and other invertebrates (11). This conclusion adds to the growing evidence that mesophotic depths and submerged banks might support rich benthic biodiversity, including sponges [e.g., (3,12,13)] with, for example, both sponge growth rates and biomass reported to increase with depth (14). Furthermore, fishing fleets are known to target submerged banks, such as the Saya de Malha Bank, suggesting high fish abundance.…”

The red coralline alga Hydrolithon onkodes, an attractor of coral larvae, is photosynthetically more susceptible to thermal stress than Lithophyllum incrustans

“…Moreover, no study has documented the effect of steadily increasing temperature on non-geniculate RCAs, under current and predicted climate change scenarios. It is noteworthy that limited studies on RCAs have been conducted around Mauritius in the Western Indian Ocean, though studies on other macroalgae of the Republic of Mauritius have been documented (Bolton et al 2012;Somanah et al 2012;Mattio et al 2013;Ramah et al 2014Ramah et al , 2021aKaullysing et al 2016;Bhagooli and Kaullysing 2019;Gopeechund et al 2020;Bhagooli et al 2021a,c,d;Narrain et al 2023). To explore the effect of temperature on the photo-physiology of non-geniculate RCAs, two species were used to assess the photo-physiological thermal tolerance in laboratory-based experiments.…”

Ocean circulation over the Saya de Malha Bank in the South West Indian Ocean

“…This paper focuses on the latter which will be hereafter referred as Saya de Malha (SDM). The SDM has been the target of various scientific research works during recent years due to the uniqueness of its ecosystems (Bergstad et al, 2021;Ramah et al, 2022), the complexity of its oceanographic processes (da Silva et al, 2011;New et al, 2013;Lindhorst et al, 2019) as well as its geological nature and biogeochemistry (Lindhorst et al, 2019). The oceanographic conditions that develop over SDM and their impact on local biological productivity are strongly influenced by a superposition of the steady SEC flow with barotropic tides (da Silva et al, 2015) upon interacting with the relief of the bank.…”