This study presents the first report of variable photo-physiology of healthy-looking and bleached corals from the upper mesophotic waters of the Mascarene Plateau. In May 2018, during the FAO EAF-Nansen research expedition cruise, coral bleaching was visually observed. Five coral species from Saya de Malha Bank, namely Heliopora coerulea, Favites sp. and Porites sp. from 27 m and Acropora sp. and Lithophyllon repanda from 30 m, and three coral species from the Nazareth Bank, namely Acropora sp. and Galaxea fascicularis from 36 m and Stylophora-like species from 58 m were studied using the Video-Assisted Multi-Sampler (VAMS) and collected using a Van Veen grab. Chlorophyll a fluorescence parameters such as effective quantum yield at photosystem II (ΦPSII), relative maximum electron transport rate (rETRm), photosynthetic efficiency (α), photoinhibition (β), saturating light level (Ek), and  maximum non-photochemical quenching (NPQm) were measured using a Diving-Pulse-Amplitude-Modulated (D-PAM) fluorometer to study variable photo-physiology in bleached and non-bleached corals. All photo-physiological parameters varied significantly among coral species tested and between coral conditions, except for β. The interaction between species and coral conditions was only significant in the case of β, but generally not significant. A two-way ANOVA indicated significant effects of depth and coral conditions in Acropora sp. on almost all photo-physiological parameters, except for β, and the effect of depth on rETRmax and α, and the effect of depth along with its interaction with coral conditions on Ek. ΦPSII did not differ in bleached and healthy-looking coral parts of Porites and Lithophyllon from 27 m, Galaxea and Acropora from 36 m while it decreased significantly in Heliopora and Favites at 27 m, Acropora from 30 m, and Stylophora-like at 58 m. NPQm did not change for Porites, Acropora (30 m) and Galaxea but it tended to increase for Heliopora, Acropora (36 m), Lithophyllon, Galaxea, and decrease for Favities, Acropora (30 m) and Stylophora-like. The thermally tolerant coral Porites exhibited normal photo-physiology even in bleached conditions while the bleached parts of Favites, Acropora (30 m) and Stylophora-like corals exhibited photo-physiological dysfunctioning. This study revealed that the seven studied corals from the upper mesophotic waters of the Mascarene Plateau are not spared from the bleaching phenomenon and exhibit variable photo-physiology in bleached and non-bleached conditions. Further studies are warranted to thoroughly understand the coral bleaching patterns and severity during summer periods at the Saya de Malha and Nazareth Banks.

Abstract. Fai ALY, Kaullysing D, Jeetun S, Soondur M, Bhagooli R. 2023. Diplosoma simile (Ascidiacea: Didemnidae) distribution and its photosynthetic thermal stress responses from Mauritius: Implications for invasive or opportunistic behavior. Indo Pac J Ocean Life 7: 16-26. This study aimed to investigate the morphological identity of the ascidian Diplosoma, its distribution, experimental thermal stress responses, and its characteristics of being potentially invasive or opportunistic in Mauritian waters. The Diplosoma species were anesthetized in menthol, fixed, and preserved in a formalin-seawater solution. Isolated zooids and embryos were examined under a microscope for distinct morphological characteristics, which revealed their identity as D. simile (Sluiter, 1909). The D. simile percentage cover studied at seven sites in 2019 around Mauritius tended to be high at the near-reef zone, with a high percentage of dead coral cover per 0.5 m2. At Flic en Flac, long-term observations in 2008, 2010, 2016, and 2019 indicated a significant decrease and increased from 61.25±3.31 to 6.15±0.60 % and 0.08±0.05 to 2.50±090% for the percentage covers of live coral and D. simile, respectively. The D. simile was recorded on five coral species, and its percentage occurrence increased from 2008 to 2019 in Acropora muricata, A. cytherea, Pocillopora damicornis, and Montipora aequituberculata with the highest levels occurring in Acropora while Porites lutea was not found to be covered by D. simile during the study. Visual observations from the thermal exposures at 27ºC, 30ºC, and 33ºC during 19 hrs revealed that D. simile was more affected by increasing temperature and exposure time. Using four observed conditions of normal, bleached/paled, tissue sloughing, and mortality, D. simile suffered from only bleaching/paling at 33ºC at 19 hrs exposure. Variable visual responses were noted for corals, with P. lutea appearing normal at all trials while A. cytherea was suffering from mortality both at 30ºC and 33ºC at 19 hrs exposure. The effective quantum yield (?PSII), measured using a Diving-PAM, declined significantly at 33ºC treatments at 6 and 19 hrs of exposure. D. simile generally tended to be more thermally tolerant than corals like P. lutea, P. damicornis, M. aequituberculata, A. muricata, A, cytherea, though the ?PSII thermal responses were variable among the tested corals. When considering the reported behavioral characteristics of D. simile, namely the lack of broad dispersal range and wide environmental tolerance, it is tempting to deduce that the species is potentially invasive. However, in this study, D. simile’s significant distribution on dead corals, its presence in zones of high anthropogenic activities, and its relatively more robust thermal stress responses than corals colonized suggest an opportunistic behavior.

Abstract. Ricot M, Jeetun S, Joggee S, Kaullysing D, Taleb-Hossenkhan N, Bhagooli R. 2023. Thermal photo-physiological responses of massive heat-resistant coral Porites lutea under fish predated versus non-predated conditions. Indo Pac J Ocean Life 7: 38-47. Fish predation on corals leading to polyp and tissue loss has been identified as a significant stressor to corals and is often associated with reduced growth, reproduction, and even mortality. However, how climate change-driven ocean warming may impact such a biological stressor is yet to be thoroughly understood. This study aimed to assess elevated temperature’s effects on the photo-physiology of fish-predated and non-predated parts of the thermally resistant coral Porites lutea (Quoy & Gaimard, 1833). The objectives were to assess the photo-physiological parameters such as effective quantum yield at photosystem II (FPSII), relative maximum electron transport rate (rETRmax), maximum photo-chemical quenching (NPQmax), photosynthetic efficiency (?), photoinhibition (?) and Ik at fish bite-affected (BA) and non-affected (NA) coral parts at temperatures of 28°C and 32°C under low-light (10 µmol quanta m-2s-1) and moderate-light (110 µmol quanta m-2s-1) conditions for a duration of 48hr. FPSII, rETRmax and NPQmax were not negatively affected by fish predation conditions. Under moderate light, the rETRmax increased in the non-predated condition at 28°C but not at 32°C while the NPQmax exhibited a more pronounced increase at 32°C compared to the 28°C treatment. The absence of significant declines in FPSII and rETRmax accompanied by a significant increase in NPQmax at 32°C is indicative of a lack of photo-inhibition and an active quenching of energy in a non-harmful way at PSII. No significant interactions of temperature and predation condition and light and predation condition were found, indicating that short-term exposure of 2 days to an elevated temperature of 32°C and moderate light intensity of 110 µmol quanta m-2s-1 did not result in any exacerbated negative photo-physiological impacts of fish predation in P. lutea. These findings suggest that both fish-predated and non-predated conditions in P. lutea are equally tolerant to the tested elevated temperature level. Thus, ocean warming events may not differentially impact their photosynthetic activities.

Abstract. Kaullysing D, Jogee SY, Mundil SP, Soondur M, Gopeechund A, Ricot M, Jeetun S, Chinta T, Chockalingum J, Mungur D, Kowal B, Kristnama L, Gunness V, Balgobin A, Fakun ZR, Munbodhe V, Nohur MB, Ramdhun D, Ramsurrun LK, Rase S, Seetohul TK, Mattan-Moorgawa S, Ramah S, Bhagooli R. 2023. Variations in photo-physiological responses of shaded and non-shaded mangrove, Rhizophora mucronata tree parts from Mauritius Island, western Indian Ocean. Indo Pac J Ocean Life 7: 71-78. This study assessed and compared the photo-physiological responses of the tree parts of juvenile and adult mangrove, Rhizophora mucronata, under shaded and non-shaded conditions in the northern coast of Mauritius Island. Chlorophyll a fluorescence of mature (dark) leaves, young and mature propagules, lichen, buds, and sepal of adult R. mucronata trees, and of mature and young (pale) leaves of juveniles under natural shaded and non-shaded conditions was measured using a field-portable Diving Pulse-Amplitude-Modulated (D-PAM) fluorometer. Commonly used chlorophyll fluorescence parameters such as Fv/Fm, rETRmax, NPQmax were calculated. The tree parts of adult and juvenile R. mucronata showed considerable variations in their photosynthetic responses. Fv/Fm of adult tree leaves was 30% higher in shaded condition as compared to non-shaded condition. The combined effect of mangrove tree parts and conditions (shaded; non-shaded) resulted in significant differences in mean values of Fv/Fm (three-way ANOVA, p<0.001). Leaves of adult trees had 52% higher rETRmax in shaded condition. While a significant difference (p<0.001) was noted in the mean rETRmax values of various tree parts, the shaded and non-shaded conditions did not have any significant effect on rETRmax (p>0.05). Non-shaded parts of R. mucronata, including the leaves, exhibited higher NPQmax values as compared to shaded conditions. Mean NPQmax varied significantly among mangrove parts (p<0.001), between tree stage (p<0.001) and between conditions (p<0.05). These findings revealed differences in the photosynthetic activities of various mangrove parts of juvenile and adult trees under shaded and non-shaded conditions, a first attempt for the tropical island of Mauritius.

Abstract. Munbodhe V, Jeetun S, Ricot M, Jogee S, Kaullysing D, Bhagooli R. 2023. Photo-physiological responses and thermal tolerance of regionally endemic/rare and morphologically different corals of the Western Indian Ocean. Indo Pac J Ocean Life 7: 100-107. Intensification in climatic variations is causing major alteration in ecosystem functionalities and an overall decline in reef biodiversity. Underlying the ongoing cumulative threats and the vulnerability to biodiversity loss in the reefs, this study aims to determine the photo-physiological response and the thermal tolerances of the morphologically different coral species namely, Porites lutea, Porites cylindrica, Acropora hyacinthus, Galaxea fascicularis, Seriatopora hystrix including the two regionally endemics of the Western Indian Ocean, Acropora branchi and Pocillopora indiania. Coral fragments from three colonies per species were collected from the south and southeast of Mauritius Island and treated at 27°C, 30°C and 32°C for 19 hours. Using a diving Pulse-Amplitude-Modulated (D-PAM) fluorometer, the effective quantum yield at photosystem II (FPSII) was recorded from the coral fragments initially and following 3, 6 and 19 hours of treatment. This experiment determined the thermal threshold of the understudied A. branchi and P. indiania, and detected the unexpectedly enhanced thermal tolerance of S. hystrix and G. fascicularis. Overall, it provides a preliminary insight into potential thermal stress tolerance in some Mauritius corals and has shown that these corals might have strategized to enhance their thermo-resilience while others are still struggling to withstand such stresses. These findings on the thermal resilience of regionally endemic/rare and morphologically different coral species are essential for further reef conservation efforts and the selection of coral species for reef restoration.