Jogee SY, Jeetun S, Ricot M, Taleb-Hossenkhan N, Mattan-Moorgawa S, Kaullysing D, Riemann P, Blanc L, Casareto BE, Suzuki Y, Bhagooli R. 2023. Photo-physiology of healthy-looking and diseased/health-compromised hard corals from Mauritius Island, Western Indian Ocean. Indo Pac J Ocean Life 7: 27-37. The spatial photo-physiological responses of in hospite zooxanthellae in hard corals, including coenosarc and polyps, healthy-looking and affected parts in four coral diseases, namely Brown Band, Black Band, Skeletal Eroding Band and White Band on the coral Acropora muricata, and two health-compromised conditions such as the Pink Pigmentation Response and its differentiated morphology, the Pink Line Syndrome, on the coral Porites were investigated using the Imaging-PAM fluorometry. A significantly lower F_v/F_m was observed in case of Black Band, White Band, Brown Band and Pink Pigmentation Response affected parts compared to the healthy-looking parts. The F_v/F_m had the highest decline in Brown Band disease. Both the polyps and coenosarc had significantly lower F_v/F_m in White Band and Brown Band diseased parts compared to their healthy-looking parts. The rETR_max did not change significantly between diseased/health-comprised parts and healthy-looking parts. NPQ_max declined significantly in White Band, Black Band and Pink Pigmentation Response cases. ? and ? generally did not tend to be affected in diseased/health-compromised conditions. The photo-physiology of in hospite zooxanthellae was least affected in Pink Line Syndrome. These findings suggest that diseased/health-compromised parts of corals behave differently in terms of their photo-physiology in different diseased and health-compromised coral conditions in important reef-building corals species such as A. muricata and Porites species, with important implications for the productivity and thus adaptive management of coral reefs in a globally warming ocean.

Coral diseases represent a prominent menace to coral reefs and to the associated ecological services they provide to the surrounding coastal communities. Studies on diseases and compromised health conditions (CHCs) on hard corals in the Southwest Indian Ocean (SWIO) are scarce, and their consequences are often overlooked. This study aimed to establish the baseline prevalence of diseases and CHC of hard corals around Rodrigues Island. Coral disease and CHC prevalence were visually assessed using 2 m × 50 m belt transects at eight sites around the island. This is the first report of four coral diseases, namely White Plague (WP), White Syndrome (WS), Black Band (BB), and Growth Anomalies (GA), and two CHCs, two forms of Pink Pigmentation Responses (PPR)—Pink Patches (PP) and Pink Line Syndrome (PLS)—observed on six genera of hard corals from the island of Rodrigues. PP on Fungia (15.92 ± 5.65%), followed by the WS on Montipora (4.67 ± 3.72%) and GA on Gardineroseris (4.16 ± 4.16%), so far unreported from the SWIO, were the most prevalent around the island. The least prevalent disease was BB on Montipora (0.13 ± 0.13%). Although the overall disease and CHC prevalence for Rodrigues Island (0.98 ± 0.30%) were much lower than the surrounding islands in the SWIO, the observations of these diseases and CHCs on hard corals and relevant environmental parameters warrant further in-depth characterization to better inform coral reefs management and conservation actions.

Crown-of-Thorns starfish (CoTS, Acanthaster spp.) are major coral predators capable of driving significant reef degradation, yet their occurrence and impact remain poorly documented in parts of the Western Indian Ocean. This study documents the occurrence of CoTS within the South East Marine Protected Area (SEMPA), Rodrigues, and characterizes the ecological and environmental conditions associated with their localized occurrence. Roving visual surveys across four reef sites recorded CoTS exclusively at Couzoupa, where four adults (mean diameter: 35.8 ± 2.2 cm) and 30 feeding scars were observed, with predation affecting multiple coral taxa, particularly Montipora and Acropora. Coral assemblages differed significantly among sites, while Montipora accounted for 86.6% of feeding scars recorded at Couzoupa. Nitrate concentration also varied significantly among sites, with the highest concentrations recorded at Couzoupa (0.246 ± 0.053 mg L⁻¹). Couzoupa was further distinguished by its greater depth and open reef-pass setting, while spatial mapping showed that the CoTS occurrence was located within SEMPA Conservation Zone 3, adjacent to other protected reef sectors. The co-occurrence of adult CoTS, active coral predation and distinct environmental conditions identifies Couzoupa as an important site for continued surveillance, although the processes underlying this localized occurrence require further investigation. Given its location within a protected reef system, early detection and targeted monitoring of Couzoupa and neighboring conservation zones, together with timely intervention where necessary, may be important for reducing potential ecological impacts and supporting long-term reef resilience and restoration efforts.

Understanding the factors influencing the variability in the composition of fish assemblages is essential for bolstering the resilience of coral reef ecosystems, effective coral reef management and maintaining sustainable fisheries. The benthic composition and reef fish assemblages at eight sites at the poorly studied St. Brandon, also known as a bank fisheries area in the Indian Ocean, were assessed to discern distribution patterns, including differences between channel (Passe Grand Capitaine, Passe Ile Longue-Canal Coco and Passe La Cayane) and non-channel (Chaloupe, Anchor Points 1 and 2, Bain des Dames, Pearl Island) sites and fisheries sustainability. The benthic composition exhibited clusters, revealing the distinct separation of Chaloupe which predominantly featured sand (75.26%) interspersed with sporadic coral patches characterized by live and dead corals and rubble. The three channel sites composed a cluster. Coral species across eight families were identified, with significant variability (p < 0.05) observed in their benthic cover, particularly live coral cover (LCC). Fish density and diversity analyses unveiled 58 fish species from 12 families, with no statistically significant disparity in density among sites. Total fish biomass (TFB) and target fish biomass (TB) ranged from 138.02 ± 65.04 to 4110.16 ± 3048.70 kg/ha and from 28.31 ± 24.52 to 3851.27 ± 2753.18 kg/ha, respectively. TFB and TB differed significantly (p < 0.05) among sites irrespective of channel and non-channel sites, with Pearl Island recording the highest biomass. TFB and TB recorded at five out of the eight surveyed sites exceeded the mean biomass benchmark (B₀) for the Western Indian Ocean, set at 1150.00 and 560.00 kg/ha for TFB and TB, respectively. Functional group analysis unveiled six discrete groups influencing TFB, with scrapers being the most dominant. This study presents the first report on fish biomass surveys in St. Brandon, highlighting a case for sustainable fisheries in the waters of the Republic of Mauritius.