Bhagooli, Ranjeet

Kaullysing, Deepeeka

Ramah, Sundy

English

AJOL - African Journals Online

197WIO Journal of Marine Science  Special Issue 2/ 2021 197-201Sea stars or starfish, belonging to the phylum Echino-dermata and class Asteroidea, are ecologically impor-tant and diverse members of marine ecosystems. They are found at various depths ranging from the intertidal to abyssal zones (Gale, 1985). The estimated number of species in this class is 1900, belonging to seven extant orders (Mah and Blake, 2012). The rich fossil history of sea stars dates back to the early Pale-ozoic (Gale, 1985). Sea stars predate mostly on benthic invertebrates (Wells et al., 1961; Mauzey et al., 1968; Sloan and Robinson, 1983; Magnesen and Redmond, 2012), and are known to regenerate damaged parts or lost arms (Mladenov et al., 1989). The ecologically important corallivorous crown-of-thorns starfishes (COTS) Acanthaster spp. have gained particular attention among the sea stars due to their significant contribution to the loss of hard coral cover globally (Conand, 2001; Emeras et al., 2004; Conand et al., 2016; Pratchett et al., 2017; Conand et al., 2018; Caragnano et al., 2021). The displacement of COTS principally occurs at night, ranging between less than 1 m to 19 m day-1. This wide difference in the daily movement is dependent on the availability of the preferred coral prey, Acropora spp. (Ling et al., 2020). Despite the uncertainty about the main causes leading to COTS outbreaks, Babcock et al. (2016) proposed that elevated nutrients leading to phytoplankton blooms, acting as abundant food sources for Acanthaster larvae, and removal of key predators can cause or exacerbate an outbreak, eventually resulting in a decrease in coral cover. They also suggested that multiple factors act together to initiate an outbreak.Numerous reports on the devastating effect of COTS have emanated from various regions globally, particu-larly from the Indo-Pacific region. The Great Barrier Reef (GBR) has witnessed four outbreaks since the 1960s (in 1962, 1979, 1993 and 2009) (Babcock et al., 2016; Pratchett et al., 2017), resulting in the average hard coral cover across the GBR halving during the period from 1985–2012, largely attributed to Acan-thaster cf. solaris (Babcock et al., 2020; Westcott et al., 2020). Saponari et al. (2015) reported an average den-sity of 120±51 COTS per 900 m2 at Mama Ghiri, Ari Atoll in the Republic of Maldives. This led to approxi-mately 70 % coral mortality comprised almost entirely of tabular Acropora mainly belonging to the species A. cytherea, A. clathrata, and A. hyacinthus. Moreover, Plass-Johnson et al. (2015) noted high densities of COTS reaching up to 37 individuals per 250 m2 in a region close to two river mouths, which resulted in the loss of half the live coral at 2 out of the 12 islands studied in Indonesia.In the Western Indian Ocean (WIO) region, there have been some reports of high densities of COTS; for instance in Seychelles in 1997 and 2014 (Obura et al., 2017). In 1994, a COTS outbreak was reported on the reefs of northern KwaZulu-Natal, South Africa, with the hard coral genera Acropora, Montipora and Fungia being initially favoured, followed by the fre-quently avoided colonies of Pocillopora (Schleyer, 1998). This was in contradiction with other observa-tions where Pocillopora was found to be one of the pre-ferred coral genera of COTS (Pratchett, 2001, 2007; De’ath and Moran, 1988). There appears to be a gap in Sightings of sea stars (Echinodermata,  Asteroidea) and a first record of crown-of-thorns starfish Acanthaster at Saya de Malha Bank, Mascarene PlateauSundy Ramah 1,2*, Deepeeka Kaullysing 2, Ranjeet Bhagooli 2Field Note1 Albion Fisheries Research Centre,  Ministry of Blue Economy, Marine Resources, Fisheries and Shipping, Albion, Petite Rivière 91001, Republic of Mauritius2 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* Corresponding author: sundy.ramah@gmail.com http://dx.doi.org/10.4314/wiojms.si2021.2.17198 WIO Journal of Marine Science  Special Issue 2/ 2021 197-201  |  S. Ramah et al.Figure 1. A, B. Crown-of-thorns starfi sh Acanthaster sp. spotted on a rhodolith bed at 38.11 m at Saya de Malha Bank; C–N. Sea stars spotted at Saya de Malha Bank. C. Culcita sp. 1 - Location 36 at a depth of 38.71 m and 25.07 m, respectively; D, E. Culcita sp. 2 - Location 39 at a depth of 37.84 m; F. Protoreaster lincki - Location 13 at a depth of 31.5 m; G. Linckia sp. - Location 39 at a depth of 33.09 m; H. Linckia sp. - Location 36 at a depth of 26.11 m; I. Protoreaster lincki - Location 39 at a depth of 41.81 m; J. Culcita schmideliana - Location 39 at a depth of 32.74 m; K. Culcita sp. 3 - Location 40 at a depth of 43.42 m; L. Linckia sp. - Location 36 at a depth of 26.16 m; M. Rathbunaster sp. - Location 38 at a depth of 175.23 m.Figure 1. 199S. Ramah et al.  |  WIO Journal of Marine Science  Special Issue 2/ 2021 197-201the scientifi c information available in the WIO region on COTS species. Although research has shown the occurrence of Acanthaster mauritiensis in this region (Haszprunar et al., 2017), additional information is required to provide a broader understanding on the phylogeography and evolution of these species.In May 2018, the Indian Ocean Research Expedition conducted under the EAF-Nansen Programme at the Saya de Malha Bank of the Mascarene Plateau enabled the sighting of one Acanthaster sp. individual (Fig. 1A, B) using the Argus Remotely Operated Vehicle (ROV). A total of 12 transects at 7 locations for an average of 30 min to 1 hour were covered. The Acanthaster sp. was observed at locations 38 (SS38) on a rhodolith bed at a depth of 38.11 m. The presence of the coralline green macroalga Halimeda on the bed was also noted while the corals in the vicinity were widely spaced and included Porites sp., branching Acropora sp., Pocillopora sp., Heliopora coerulea and other massive hard corals. Fur-ther visual inspection revealed the presence of at least 17 other individuals of non-corallivorous sea stars (with Protoreaster sp., Linckia sp. and Culcita spp. being more dominant) during the cruise at depths ranging between 23 m to 50 m (Fig. 1 C-M) at locations at locations SS34, SS36, SS37, SS38, SS39, SS40 and SS42 (Fig. 2). The substrata on which the sea stars were spotted were sand, rhodolith beds, corals, macroalgae and seagrass beds.Koonjul et al. (2003) reported 28 COTS around Mau-ritius Island, spread over a reef area of 0.6 km2 (about 4.67 x 10-5 per m2, or 0.01 per 250 m2, or 0.04 per 900 m2) with a substrate mix comprising corals, algae, sand, and coral rubble. The fi rst observation of only one individual of Acanthaster sp. at one location (out of 7) aft er 30 min of video time at Saya de Malha Bank does not signify any warning of signifi cant damage to corals in that region. However, this information is noteworthy as it brings forth new knowledge on Aster-oids from the Saya de Malha Bank, an unexplored region of the WIO which appears to harbour a high diversity of sea stars. There are considerable challenges to addressing the knowledge gaps relating to the biology, ecology and genetics of Acanthaster spp. Diff erences in morphol-ogy, in particular colour patterns, among COTS spe-cies reported from the Pacifi c and the Indian Oceans suggest divergent biology and ecology (Haszprunar, 2017). Further research on and exploration of the sea-bed is required to build a more robust and in-depth understanding of the sea star distribution at the Bank, especially the corallivorous COTS. Thorough morphological, morphometric, and genetic analy-ses are necessary to characterize the COTS from this region to assist any future development of key actions required for management.AcknowledgementsThe underlying work was made possible with the support of the EAF-Nansen Programme “Supporting the Application of the Ecosystem Approach to Fish-eries Management considering Climate Change and Pollution Impacts” executed by Food and Agriculture Figure 2. Map showing the seven locations (SS where the sea stars were observed indicated in yellow and red border stars. Map prepared using the GEBCO Bathymetry Grid layer data 2020.Figure 2. 200 WIO Journal of Marine Science  Special Issue 2/ 2021 197-201  |  S. Ramah et al. Organization of the United Nations (FAO) and funded by the Norwegian Agency for Development Cooper-ation (Norad). The authors are thankful to FAO for funding and supporting the Indian Ocean research expedition 2018 on the Saya de Malha Bank and Naza-reth Bank with the R/V Dr Fridtjof Nansen, the Depart-ment of Continental Shelf, Maritime Zones Admin-istration & Exploration of Mauritius for co-leading and coordinating the scientific expedition, the Mau-ritius-Seychelles Joint Commission of the Extended Continental Shelf for their support and assistance and granting the necessary authorisations, the Min-istry of Blue Economy, Marine Resources, Fisheries & Shipping for hosting and spearheading the Habi-tat Mapping Workshop in Mauritius and for grant-ing necessary authorization to carry out research in the Nazareth Bank; the Institute of Marine Research, Norway for leading the expedition and providing the technical and logistic support. 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Sightings of sea stars (Echinodermata, Asteroidea) and a first record of crown-of-thorns starfish Acanthaster at Saya de Malha Bank, Mascarene Plateau

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

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