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This study aimed to test the effects of rainfall-driven nutrient loading on the microphytoplankton dynamics in the shallow water at Trou aux Biches lagoon on the northwest coast of Mauritius. Changes in density, diversity and estimated productivity of microphytoplankton were monitored in three zones—coast, lagoon and reef—during two rainfall periods of 4 and 3 days' duration, respectively, in March–April 2017. The average nutrient loading from terrestrial runoff was 15.5% and the salinity decreased by 2.5%. Following the two rainfall events, a 3-fold increase in total microphytoplankton density (TMPD), with a dominance of diatoms, was noted within a week at the coast and lagoon, while it remained relatively unchanged at the reef. These changes in microphytoplankton densities were concomitant with adequate levels of silicate (>2 µM) and high nitrate:silicate ratios (2.84–6.93). During this study, the numbers of genera of diatoms, dinoflagellates and cyanobacteria observed were 28, 12 and 3, respectively. The Shannon–Wiener, equitability and evenness indices showed high diversity values for diatoms and cyanobacteria prior to the rainfall events and for dinoflagellates after the events. The chlorophyll a content, relative electron transport rate, and estimated productivity of microphytoplankton increased during and after the rainy periods. TMPD and chlorophyll a were correlated significantly and positively with nutrients, salinity and temperature. Toxic algal species such as the dinoflagellates Alexandrium, Dinophysis and Tripos were recorded, although not in bloom densities. These findings indicate that rainfall-driven nutrient loading led to an increase in microphytoplankton density and estimated productivity, and a change in its diversity. [ABSTRACT FROM AUTHOR]

Damselfish of the genus Stegastes inhabit territories and cultivate algal gardens on branching corals of the genus Acropora, aggressively protecting their territories from other fish and preventing predation upon corals within the territory. This behaviour has important ecological impacts and could also be useful in reducing predation on outplanted corals during reef restoration efforts. However, the degree of protection from predators may depend on the ability of Stegastes spp. to recolonise outplanted or newly established coral colonies. Protection of bleaching-resilient massive corals within territories may be of particular importance due to the role of these corals in maintaining coral cover following bleaching events. This study examined whether the presence of Stegastes spp. reduces predation on the massive bleaching-resilient coral Porites lutea in the Mauritian lagoon, and whether Stegastes spp. readily colonise outplanted branching coral fragments and provide adjacent massive corals with indirect protection from predation. Predation levels on wild-occurring and outplanted P. lutea within and outside Stegastes spp. territories were measured. In addition, Acropora muricata branches were outplanted adjacent to wild P. lutea colonies outside Stegastes spp. territories, and recolonisation of these outplants by Stegastes spp. and the impacts of recolonisation on predation were monitored. Both wild and outplanted P. lutea colonies within Stegastes spp. territories sustained less predation damage compared to colonies outside territories. Stegastes spp. recolonized outplanted A. muricata colonies within six months of outplanting, and in doing so returned predation protection to adjacent P. lutea colonies. The ability of Stegastes spp. to colonise outplanted corals and provide indirect protection to adjacent massive bleaching-resilient corals may inform coral outplanting efforts in systems where Stegastes spp. are common. Encouraging Stegastes spp. recolonisation may help to reduce predation damage to corals within territories and potentially improve the success of rehabilitation efforts. [ABSTRACT FROM AUTHOR]

B Correction to: Coral Reefs (2021) 40:1549-1561 b https://doi.org/10.1007/s00338-021-02147-1 Final line of the results section "Fish and coral assemblage at study sites" should read: "A total of 1085 individual corallivorous fish of 20 species were observed on transect surveys, with a further five species observed off transects (Table 1)." Numbers of corallivorous fish observed on transect surveys in the lagoon of Mauritius, and all species observed at sites (including off transects).". [Extracted from the article]

Coral cell aggregates (tissue balls) from four species (Acropora muricata,Fungia repanda,Pavona cactusandPocillopora damicornis) were used as an indicator to investigate the effects on the corals of thermal stress and of chemical extracts from three sponges (Adociasp.,Haliclonasp. andLissodendoryxsp.) and one ascidian (Didemnum molle). The formation and disintegration of tissue balls were studied through exposure to a temperature range of 23–30 °C at time intervals of 0–90 min, and to sponge and ascidian crude extracts at concentrations of 50–200 µg ml−1at temperatures of 23 and 30 °C and at time intervals of 10, 60 and 120 min. The negative effect of temperature on overall tissue ball density (number per cm2of coral surface) was greatest at higher temperatures (28 and 30 °C) but varied among coral species. Tissue balls ofP. damicorniswere the most robust whereas those ofA. muricatawere the most sensitive. High concentrations of extracts ofAdociasp.,Haliclonasp. andLissodendoryxsp. generally inhibited the formation of tissue balls or caused their disintegration, or both, most markedly at 30 °C.Adociasp. induced the least negative effects andHaliclonasp. the most. No tissue balls were formed in the presence ofD. molleextracts (50 and 100 µg ml−1), indicating a high level of interference with tissue ball formation. The differential susceptibility to thermal and chemical stressors exhibited by the corals under study have possible implications for the interactions of the corals with other sedentary reef organisms under climate change-driven ocean warming. [ABSTRACT FROM AUTHOR]

Spatial and temporal (seasonal and interannual) variation in microphytoplankton was investigated at two tropical coral reef sites off Mauritius (Belle Mare [BM] and Flic-en-Flac [FEF]), from 2010 to 2012. Each site was divided into three zones: coast, lagoon and reef. Microphytoplankton, nutrient and chlorophyllasamples were collected, and physico-chemical parameters were measuredin situ. A total of 56 microphytoplankton genera were identified (43 diatoms, 8 dinoflagellates and 5 cyanobacteria). Total microphytoplankton density exhibited spatial and temporal variation, being higher at BM and near the coast, and mostly high in summer. Nutrient concentrations were highest near the coast as a result of run-off events and anthropogenic inputs, especially during heavy rainfall, and this resulted in elevated total microphytoplankton density. There were no clear diversity patterns at the two sites or within the different zones. At both sites,Navicula, CocconeisandFragilariawere the dominant diatoms, andGymnodinium, AlexandriumandProtoperidiniumwere the dominant dinoflagellates. There was a shift in dominance fromNaviculain summer toFragilariain winter. This seasonal shift may reflect how these species respond differently to environmental change, which could have implications for primary production at spatial and temporal scales. [ABSTRACT FROM AUTHOR]

Micro-phytoplankton density, genera composition, chlorophyll a concentration, and physico-chemical parameters were investigated at five stations (S1-near the coast; S2 and S4-at the edges of the aquaculture set-up; S3-in the center of the set-up; and S5-nearby patch of corals) in and around a coastal channel-based fish farm. The highest total micro-phytoplankton density (TPD), including diatoms, dinoflagellates and cyanobacteria, was recorded at S3 ((6.28±2.00)×10 cells/L) followed by S4 ((5.87±2.81)×10 cells/L), S1 ((4.92×10±8.70×10) cells/L), S5 ((3.54×10±5.33×10) cells/L) and S2 ((2.60±1.14)×10 cells/L). Chlorophyll a and nutrient concentrations were highest at S3 and were positively correlated with TPD. Among the 35 genera documented in this study, Chaetoceros spp. was the dominant diatom while Peridinium spp. was the most dominant dinoflagellate. Very low densities of toxic bloom-forming dinoflagellates were encountered during this study. These results suggest that occurrence of non-bloom densities of micro-phytoplankton, possibly due to the natural flushing of the existing lagoonal channel at the aquaculture site, yielded in little environmental impact and can represent an appropriate sustainable approach for future aquaculture development. [ABSTRACT FROM AUTHOR]

Gene expression biomarkers can enable rapid assessment of physiological conditions in situ, providing a valuable tool for reef managers interested in linking organism physiology with large-scale climatic conditions. Here, we assessed the ability of quantitative PCR ( qPCR)-based gene expression biomarkers to evaluate (i) the immediate cellular stress response ( CSR) of Porites astreoides to incremental thermal stress and (ii) the magnitude of CSR and cellular homeostasis response ( CHR) during a natural bleaching event. Expression levels largely scaled with treatment temperature, with the strongest responses occurring in heat-shock proteins. This is the first demonstration of a 'tiered' CSR in a coral, where the magnitude of expression change is proportional to stress intensity. Analysis of a natural bleaching event revealed no signature of an acute CSR in normal or bleached corals, indicating that the bleaching stressor(s) had abated by the day of sampling. Another long-term stress CHR-based indicator assay was significantly elevated in bleached corals, although assay values overall were low, suggesting good prospects for recovery. This study represents the first step in linking variation in gene expression biomarkers to stress tolerance and bleaching thresholds in situ by quantifying the severity of ongoing thermal stress and its accumulated long-term impacts. [ABSTRACT FROM AUTHOR]

Damage to zooxanthellae photosynthetic apparatus has been proposed to be the underlying mechanism of coral bleaching, but how the expulsion of zooxanthellae is triggered is still not understood. The present study compared the photosystem II (PSII) functioning and overall photosynthesis of retained and released zooxanthellae from the reef-building coral Galaxea fascicularis exposed to high temperature stress. The use of pulse-amplitude-modulated (PAM) fluorometry for isolated zooxanthellae was validated and used to measure photosynthesis. There was no significant difference in PSII functioning and the overall photosynthesis between retained zooxanthellae, which were isolated immediately after stress treatment, and those released from the coral exposed to either 30 or 32°C, while the zooxanthellae population released at 28°C showed significantly lower PSII functioning than those retained in the polyps. The release of healthy-looking zooxanthellae by polyps exposed to elevated temperatures was significantly higher than those in the control (28°C). Higher release of undischarged cnidae, indicative of host cell necrosis or detachment, was observed in 32°C treatments. These findings indicate that the zooxanthellae released in 30 or 32°C treatments exhibited normal morphology and intact photosynthetic activity. The present results strongly suggest that the release of zooxanthellae from G. fascicularis at 30 or 32°C is a non-selective process with respect to the zooxanthellar PSII functioning and thus the host seems to be the first partner to be physiologically affected in temperature-induced bleaching. [ABSTRACT FROM AUTHOR]

Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Correction to: Coral Reefs https://doi.org/10.1007/s00338-021-02147-1 The erratum is published as several corrections were overlooked by author during proofing. [Extracted from the article]