Benthic Cover Research Articles

Structuring patterns of the epilithic algal matrix cryptofauna in a tropical oceanic reef

Reef systems are one of the most biodiverse and complex marine ecosystems. Invertebrate cryptic epifaunal communities (i.e, cryptofauna) associated with the epilithic algal matrix make up a large part of the reef biodiversity and play a critical role in their food webs. Yet, few studies have investigated the composition and abundance of the cryptofauna associated with EAM and the major drivers influencing patterns of community structure. Algae biomass, rates of predation, depth, and trapped particles (detritus and sediment) are among the main drivers of cryptofauna composition changes. In the South Western Atlantic, the epilithic algal matrix composes up to 70% of the benthic cover both in tropical (biogenic) and subtropical (non-biogenic) reefs, but information about the associated cryptofauna is limited. We sampled the epilithic algal matrix (EAM) of two sites in an equatorial Brazilian oceanic island, at three depth strata. In total, 106 operational taxonomic units (OTUs) belonging to 14 taxa were recorded (Foraminifera, Gastropoda, Bivalvia, Polyplacophora, Amphipoda, Tanaidacea, Cumacea, Ostracoda, Decapoda, Polychaeta, Cnidaria, Sipuncula, Echinodermata and Chironomidae). Gastropods were the most diverse group (48 OTUs) and second most abundant (n = 1585). Total invertebrate abundance and composition, as well as abundance of each taxa, were influenced by EAM characteristics (algae biomass and coarse particulates) and depth. Foraminifera abundance increased as algae biomass increased, due to the presence of Large Benthic Foraminifera (LBF) which may associate with algae for sunlight protection. Mollusks were mainly represented by the detritivorous Barleeia rubrooperculata. Richness of taxa in EAM observed here was similar to values observed in frondose macroalgae elsewhere despite the low taxonomic resolution applied, indicating its potential as a cryptofauna biodiversity reservoir.

Satellite-derived bathymetry from WorldView-2 based on linear and machine learning regression in the optically complex shallow water of the coral reef ecosystem of Kemujan island

Shallow coastal water bathymetry information is required for various navigation, management, conservation, and research purposes. Bathymetry data modeled through satellite remote sensing (SDB) is considered more effective and efficient because it is cheaper, can cover a large area, and can be done routinely. In this study, we assess the linear (LR) and machine learning regression performance of bathymetry mapping in the optically shallow water of a coral reef ecosystem. We selected random forest regression (RFR) and support vector machine regression (SVR) machine learning regression models. All three regression models were trained using field bathymetry data, and different tuning parameter scenarios were applied to each model to obtain the best bathymetry map. Independent field bathymetry data were used for the assessment, which included root mean squared error (RMSE), a plot between reference and predicted depths, and an underwater topographic profile in three unique areas. Each unique area represented different water depths, underwater topography, benthic cover variations, and water clarity. This highlights and provides a comprehensive insight into how each model performs under different underwater topographic conditions. Kemujan Island, which has various coral reef geomorphic classes and underwater topographic variations, was selected as the study site. The RMSE of the SDB mapping accuracy obtained in this research ranged from 0.82 to 0.87 m for RFR, 0.96–1.17 m for SVR, and 1.00–1.23 m for LR. Overall, RFR produced SDB with higher accuracy and precision compared to SVR and LR. RFR managed to estimate the depth that follows the underwater transverse profile accurately and precisely in three sites and does not require a band ratio to produce accurate SDB in areas with various benthic covers. LR competes well with RFR in predicting water depths of up to 6 m but cannot accurately predict depths beyond 6 m. The study results provide a comprehensive reference for developing robust automated mapping models for producing SDB, increasing the availability of optically shallow water bathymetry information worldwide while reducing the cost of conducting bathymetric surveys.

The green macroalga Caulerpa prolifera replaces seagrass in a nitrogen enriched, phosphorus limited, urbanized estuary

The Indian River Lagoon (IRL) on Florida’s east-central coast is a highly developed eutrophic estuary, experiencing harmful algal blooms (HABs). Beginning in 2011, the IRL experienced multiple phytoplankton HABs that were followed by widespread seagrass losses and expanding blooms of the rhizophytic macroalga Caulerpa prolifera. To better understand factors related to the changing benthic cover, long-term monitoring data spanning 2011–2020 for seagrass and C. prolifera percent cover at six locations in the northern IRL and Banana River Lagoon were considered in multivariate analyses with environmental parameters (temperature, salinity, pH, dissolved oxygen, etc.), dissolved nutrient and chlorophyll-a concentrations, and macroalgal carbon (δ13C) and nitrogen (δ15N) stable isotopes, elemental composition (%C, %N, %P), and nutrient ratios (C:N:P). Data reduction using the global Bio-Env + STepwise (BEST) procedure followed by linkage tree (LINKTREE) analyses indicated the variable most correlated to annual differences in benthic cover was macroalgal C:P. Following seagrass losses, P availability increased, as the result of heavy rainfall, increased sediment flux, and/or more bioavailable P due to seagrass losses. The most correlated variables among differences in location were C:P, δ13C, and salinity, which could be related to less urbanization at the northernmost sites that had lower percent cover of C. prolifera. While not identified as a significant variable, the increase in C. prolifera was associated with four years (2016–2019) of high ammonium concentrations (6.26 µM) and macroalgal δ15N values (+8.67 ‰), linking the blooms to the influence of human waste. The variables identified in this work as related to benthic cover suggest that reducing stormwater runoff and inputs of human waste will promote the recovery of seagrasses in the IRL. These findings have implications for urbanized estuaries experiencing seagrass loss globally.

Divergent recovery trajectories of intertidal and subtidal coral communities highlight habitat-specific recovery dynamics following bleaching in an extreme macrotidal reef environment.

Coral reefs face an uncertain future punctuated by recurring climate-induced disturbances. Understanding how reefs can recover from and reassemble after mass bleaching events is therefore important to predict their responses and persistence in a rapidly changing ocean. On naturally extreme reefs characterized by strong daily temperature variability, coral heat tolerance can vary significantly over small spatial gradients but it remains poorly understood how this impacts bleaching resilience and recovery dynamics, despite their importance as resilience hotspots and potential refugia. In the macrotidal Kimberley region in NW Australia, the 2016 global mass bleaching event had a strong habitat-specific impact on intertidal and subtidal coral communities at our study site: corals in the thermally variable intertidal bleached less severely and recovered within six months, while 68% of corals in the moderately variable subtidal died. We therefore conducted benthic surveys 3.5 years after the bleaching event to determine potential changes in benthic cover and coral community composition. In the subtidal, we documented substantial increases in algal cover and live coral cover had not fully recovered to pre-bleaching levels. Furthermore, the subtidal coral community shifted from being dominated by branching Acropora corals with a competitive life history strategy to opportunistic, weedy Pocillopora corals which likely has implications for the functioning and stress resilience of this novel coral community. In contrast, no shifts in algal and live coral cover or coral community composition occurred in the intertidal. These findings demonstrate that differences in coral heat tolerance across small spatial scales can have large consequences for bleaching resilience and that spatial patchiness in recovery trajectories and community reassembly after bleaching might be a common feature on thermally variable reefs. Our findings further confirm that reefs adapted to high daily temperature variability play a key role as resilience hotspots under current climate conditions, but their ability to do so may be limited under intensifying ocean warming.

Sea‐weeding: Manual removal of macroalgae facilitates rapid coral recovery

Abstract Coral reef ecosystems globally are under threat, leading to declining coral cover and macroalgal proliferation. Manually removing macroalgae (i.e. ‘sea‐weeding’) may promote local‐scale coral recovery by reducing a biological barrier, though the impact of removal on community composition of benthic reef organisms has not been quantified. In this three‐year study (2018–2021), fleshy macroalgae (predominantly Sargassum spp.) were periodically removed from 25 m2 experimental plots on two inshore fringing reefs of Yunbenun (Magnetic Island) in the central Great Barrier Reef. By the end of the study, coral cover in removal plots (n = 12 plots) assessed through in‐field transects increased by at least 47% (2019 mean: 25.5%, 2021 mean: 37.4%), and macroalgal cover decreased by more than half. In contrast, in control plots (n = 12 plots), there was no change in macroalgal cover while coral cover remained stable (2019 mean: 16.4%, 2021 mean: 13.6%). Changes in benthic cover were supported by photoquadrat data, with Bayesian probability modelling indicating a 100% likelihood that coral cover more than doubled in removal plots over the study period, compared to only a 29% chance of increased coral cover in control plots. Synthesis and applications. Manual macroalgal removal can provide rapid benefits and enhance inshore coral reef recovery. Through involvement of community groups and citizen scientists, larger scale removal of macroalgae is a low‐tech, high‐impact, and achievable method for local reef management.

Alacranes reef: A refuge for structurally complex coral species from increasing stressors

Coral reefs worldwide are being exposed to an interconnected myriad of anthropogenic stressors degrading their structure and functions. Therefore, global coral cover and coral reef ecosystem services have declined by half since the 1950s. Yet, remote reefs represent a time capsule to study ecological processes on minimally disturbed reefs, and these findings can steer management decisions and actions to enhance resilience. Combining in situ and satellite-derived data from the remote Alacranes Reef system located in the Gulf of Mexico, we evaluated benthic cover data and coral structural complexity together with physical drivers and direct coral stressors to better understand the current reef conditions of this remote system. Our main results show that 57% of the reef sites have >10% hard coral cover and are dominated by structurally complex species. Moreover, sites with >20% coral cover were associated with significantly shallower depths, smaller wave significant height, fewer bleaching impacts, as well as fewer macroalgae and cyanobacteria cover. Despite cumulative stressors impacting the Alacranes reef system, coral species assemblages and conditions are still driven by natural physical gradients, and the system hosts potential refuges for structurally complex species in the wider Caribbean. However, not all these refuges are fully protected, and strategic local management is key to maintaining and enhancing coral resilience in the context of increasing global stressors.

Roles of depth, current speed, and benthic cover in shaping gorgonian assemblages at the Palm Islands (Great Barrier Reef)

Gorgonians are a diverse and conspicuous component of coral reef ecosystems, providing habitat structure that supports unique assemblages of fishes and invertebrates. Evaluating their overall importance as ecological engineers requires an understanding of their spatial patterns of distribution, abundance and assemblage composition, and the biophysical factors that drive these patterns. No baseline data are available on the spatial patterns of distribution of gorgonians for the Great Barrier Reef. In this study, we quantified the abundance, genera richness, and composition of gorgonian assemblages using video surveys at three depths (5, 10, and 15 m) at 16 locations at the Palm Islands, an inshore island group in the central Great Barrier Reef. We compared gorgonian abundance and genera richness between depths and assessed the role of benthic habitat in structuring gorgonian communities. We also conducted a preliminary investigation of the potential role of water currents in driving gorgonian spatial patterns in the Palm Islands, using in situ current meters. Gorgonian abundance and genera richness consistently increased with depth, although the magnitude of the depth effect varied among locations. Abundance increased with increasing percent cover of rubble and conversely declined with increasing cover of hard corals. The composition of gorgonian assemblages also varied among depths, with whip (Junceella, Viminella) and fan (Acanthogorgia, Anthogorgia, Annella) growth forms being dominant at depths of 5 and 10 m, and branching (Dichotella, Icilogorgia) and candelabrum (Ctenocella) forms being dominant at 15 m. The shallow gorgonian assemblage was associated with high coral cover, whilst the deeper assemblage was associated with high per cent cover of rubble, turf and/or macroalgae. This study highlighted that the abundance, diversity, and composition of gorgonian assemblages on coral reefs in the Palm Islands are determined by a range of biophysical factors linked to depth. Further work is required to isolate the primary drivers of these depth-related effects and evaluate their relative importance.

Establishing historical benthic cover levels for coral reefs of the Western Indian Ocean

Data on coral reef health prior to large-scale disturbances are unavailable in most parts of the world including the Western Indian Ocean (WIO). Robust coral reef health baselines could improve the understanding of changes occurring to reefs in the 21st century and prevent the “shifting baseline” phenomenon, enabling researchers and managers to evaluate the success of management measures, and set achievable targets for new interventions. To make this data accessible to the WIO coral reef community, a literature review was conducted to identify and compile data collected prior to 2008 for two principal measures of reef health; hard coral and fleshy algae cover. Baseline hard coral and algae cover levels were calculated using data from selected sites that were known to be in healthy condition prior to (or just after) the 1998 bleaching event. Mayotte had the highest mean hard coral cover with 80.9 % (95 % bootstrap confidence interval (95 % CI) =65.8-95.9 %), followed by Comoros with 62.1 % (95 % CI=53.2-78.8 %) and Madagascar with 55.6 % (95 % CI=49.8-62.5 %). Mean fleshy algae cover varied from 8.4 % in Mayotte (95 % CI=2.4-17.4 %) to 35.4 % in Mozambique (95 % CI=20.6-50.8 %). At a regional scale, mean baseline hard coral cover is estimated to be between 41 and 47 %; reefs were in a coral-dominant state, with more than double the amount of coral compared to algae.

Remote sensing of Antarctic polychaete reefs (Serpula narconensis): reproducible workflows for quantifying benthic structural complexity with action cameras, remotely operated vehicles and structure‐from‐motion photogrammetry

AbstractQuantifying the structural complexity provided by biogenic habitat structures is important in ecology, conservation and management, and yet remains a challenging task, particularly in deep sea and polar environments, that current photogrammetry tools can alleviate. In this study, we demonstrate how small remotely operated vehicles and compact underwater GoPro® action cameras can be easily integrated into coastal Antarctic surveys to quantify structural complexity of under‐ice benthos via underwater photogrammetry. Forty‐four pairs of 1 m2 quadrats at 1 cm resolution, each comprising an orthomosaic and three‐dimensional reconstructions, were analyzed to describe relationships between benthic cover and structural complexity metrics. The study case provided insights into a unique biogenic habitat, highlighting the role of integrating structural complexity metrics in Antarctic benthic surveys. Although no clear relationships between structural complexity and biodiversity were found, high cover of live reef‐building polychaetes was associated with higher levels of structural complexity, particularly fractal dimension (D). Further, broken biogenic structures, product of disturbance events retain habitat structural complexity known to be associated with larvae settlement and biogenic reef growth. This suggests that D can be used as a metric for detecting subtle changes in biogenic structural complexity. We build from available open‐source code, a reproducible scientific workflow that is expected to facilitate the acquisition and analysis of structural complexity metrics. The workflow presented aims to encourage and accelerate the use of photogrammetry tools for benthic studies aiming to quantify biogenic structural complexity across depths and latitudes.

Efficacy of algaecides for the proactive treatment of overwintering cyanobacteria

Once established within a water resource, harmful algal blooms (HABs) can occur seasonally with an intense and rapid onset, giving water resource managers limited time to respond to lessen risks. An attractive strategy to decrease human, ecological, and economic risks from HABs is to implement proactive algaecide treatments applied to overwintering cyanobacteria (i.e., akinetes and quiescent vegetative cells) in sediments prior to the formation of a HAB; however, this approach is novel and very limited efficacy data exist. Therefore, the specific objectives of this research were to 1) evaluate copper- and peroxide-based algaecides, applied as single and repeat treatments at the bench scale, to identify effective proactive treatments, and 2) compare correlations between cell density and other response measurements (i.e., in vivo chlorophyll a and phycocyanin concentrations and percent benthic coverage), to identify informative metrics to assess overwintering cyanobacteria responses. Twelve treatment scenarios using copper- and peroxide-based algaecides were applied to sediments containing overwintering cyanobacteria prior to a 14 d incubation under favorable growth conditions. Responses of cyanobacteria in the planktonic (i.e., cell density, in vivo chlorophyll a and phycocyanin concentrations) and benthic (percent coverage) phases after a 14 d incubation were evaluated in treatments and controls. The HAB-forming cyanobacteria present after a 14 d incubation were: Aphanizomenon, Dolichospermum, Microcystis, Nostoc, and Planktonthrix. Successive treatments of copper sulfate (CuSulfate) followed by sodium carbonate peroxyhydrate (PeroxiSolid) (second algaecide applied after 24 h) as well as repeat applications of a single algaecide, PeroxiSolid (second treatment applied after 24 h) resulted in statistically significant (p ≤ 0.05; α = 0.05) declines in cell density relative to untreated controls. Planktonic cyanobacteria responses measured in terms of phycocyanin concentrations were strongly correlated with cyanobacteria density measurements (Pearson’s correlation coefficient (r) = 0.89). Chlorophyll a concentrations and percent benthic coverage did not correlate with planktonic cyanobacteria density measurements (r = 0.37 and −0.49, respectively) and therefore, were unreliable metrics for cyanobacterial responses in this study. These data provide initial evidence of the efficacy of algaecides for treating overwintering cells in sediments and contribute to our overarching hypothesis that proactive treatments may delay the onset and intensity of HABs in impacted waterbodies.

Zonation of The Waters of Spermonde Archipelago Base on Nutrient Concentration and Its Impact to Coral Reef Ecosystem

The Spermonde Archipelago is divided into four zones, the division of zones is based on the distribution of coral reefs, distance from the mainland, and water depth, but this condition tends to change as a result of high anthropogenic activity in the Spermonde Islands. Based on this, it is very necessary to re-zoning the Spermonde Archipelago Waters based on the condition of nutrient distribution. The research method uses the integration of remote sensing data analysis, field surveys, and secondary data which are then analyzed using the Boleean method for re-zoning. The results showed that the nutrient, in this case, chlorophyll-a, was concentrated in the deep zone (near the mainland) and the concentration was higher during the rainy season, this condition affected the coral reef cover in the Spermonde Islands. Based on these conditions, the Spermonde Islands waters are divided into three zones, namely the inner zone with high nutrient conditions with a benthic cover dominated by fleshy macroalgae, the middle zone with low nutrient conditions with crustose coralline dominance, and the outer zone with low nutrient conditions with algal turf dominance turf alga/corals.

Decadal stability in coral cover could mask hidden changes on reefs in the East Asian Seas

Coral reefs in the Central Indo-Pacific region comprise some of the most diverse and yet threatened marine habitats. While reef monitoring has grown throughout the region in recent years, studies of coral reef benthic cover remain limited in spatial and temporal scales. Here, we analysed 24,365 reef surveys performed over 37 years at 1972 sites throughout East Asia by the Global Coral Reef Monitoring Network using Bayesian approaches. Our results show that overall coral cover at surveyed reefs has not declined as suggested in previous studies and compared to reef regions like the Caribbean. Concurrently, macroalgal cover has not increased, with no indications of phase shifts from coral to macroalgal dominance on reefs. Yet, models incorporating socio-economic and environmental variables reveal negative associations of coral cover with coastal urbanisation and sea surface temperature. The diversity of reef assemblages may have mitigated cover declines thus far, but climate change could threaten reef resilience. We recommend prioritisation of regionally coordinated, locally collaborative long-term studies for better contextualisation of monitoring data and analyses, which are essential for achieving reef conservation goals.

Persentase Tutupan Karang Di Perairan Teluk Akle Kecamatan Semau Selatan Kabupaten Kupang Nusa Tenggara Timur

Akle Bay is one of marine aquaculture area in Semau island and it has coral reef potention. The coverage percentage of coral reef in the ocean might be decline by human activities and also by nature itself. The aimed of this research was analyzed to know the percentage of coral reef coverage in Akle Bay, South Semau District. This study conducted in Akle Bay, South Semau District on May 18, 2023st . Underwater Photo Transect (UPT) was used to take a sample in five meter depth at two different sites in Akle Bay waters. Data was analyzed by software CPCe 4.1. Result showed the highest benthic coverage percentage is soft coral. There were eleven genus of hard coral was found and its dominated by Porites genera. The percentage of hard coral coverage in S1 was 9.14%, while in S2 was 6.11% and was categorized in worst condition. The decline of coral reef coverage percentage in this area was expeted due to of human activities such as coral removal, the usage of anchor and the destructive fishing gear like a bomb, and also a sedimentation. According to the lifeform, covarage percentage of hard coral was dominated by coral branching. The average of current velocity in Akle Bay was 0,417 m/s with the range of waves was 0.1 to 0.5 meters. Conclusion of this research is the percentage of coral coverage in Akle Bay is worst. It was becacuse of human activities and sedimentation.

Characterization of the populations of upside-down jellyfish in Jardines de la Reina National Park, Cuba.

Upside-down jellyfish are a group of benthic scyphozoans belonging to the genus Cassiopea, whose members are in symbiosis with dinoflagellates and inhabit tropical and subtropical waters. Although there are some studies of the genus in the Caribbean, these are limited. In Cuba, the group's studies are restricted to reports on taxonomic lists and, as far as we know, no one has performed any analyzes of the densities of these jellyfish in seagrass or mangrove ecosystems in Cuba. In this work, the populations of Cassiopea spp. in Jardines de la Reina National Park (JRNP) were characterized, for the first time for this Marine Protected Area and Cuba. One hundred 1m2 square frames were placed at 14 JRNP sites. For each site, the species, density, size of the individuals and abiotic factors were determined. Density and diameter comparisons were made between sites, zones and regions within the JRNP. The percentage of the benthic cover was determined and a correlation was made between density and diameter. A total of 10,803 individuals were recorded, of which 7,618 belong to Cassiopea xamachana and 3,185 belong to Cassiopea frondosa. Both species share a niche and no evident segregation was detected according to abiotic variables. Significant differences were detected in comparisons of density and size across sites and zones. Density and size in the JRNP were negatively correlated, and higher aggregations of the species were observed at lower sizes. Density mean values ranged from 2.18 to 14.52 ind. /m2 with maximum values of 79 ind. /m2. Cayo Alcatraz was the site found to have the highest density while Cachiboca was the site with the lowest density. The average bell diameter size of the individuals ranged from 9.34 to 15.31 cm for the sampled sites, with minimum and maximum values of 2.5 cm and 32.6 cm. The smallest size was recorded at Cayo Alcatraz while the largest size was reported for Boca de las Anclitas. The environmental factors evaluated showed no significant relationship with the density or diameter of Cassiopea, while the Thalassia testudinum cover was negatively correlated with Cassiopea density at all fourteen sites in the JRNP. The percentage of Cassiopea coverage was higher than those reported in the literature, with four sites exceeding 20% coverage. In general, the populations of Cassiopea spp. in the JRNP did not differ greatly, although a higher density was observed towards the eastern region of the park. It was shown for the first time for the species that density and size have a negative correlation. Future studies are required to quantify the impact of Cassiopea on coastal marine ecosystem processes, and to further determine how anthropogenic changes may be altering the function of these tropical ecosystems.

Coral reef degradation at an atoll of the Western Colombian Caribbean.

Coral reef decline is an issue of concern around the globe. Remote and uninhabited coral areas are not exempt from facing changes in species composition and functionality due to global drivers. Quitasueño is a remote atoll within the Seaflower Biosphere Reserve, in the Southwestern Caribbean Sea. To evaluate the current status of the coral reefs in Quitasueño we sampled 120 stations through Rapid Ecological Assessment and evaluated four stations through Planar Point Intercept to compare the current percent cover of benthic groups with previous studies in the area. We found pronounced changes in coral and macroalgae covers in time, and great conspicuousness of multiple conditions of deterioration along Quitasueño, including diseases, coral predation, and aggression and invasion of coral colonies by macroalgae and sponges. The reef ecosystem seems to be facing a phase shift, in which the benthic cover previously dominated by hard corals is currently dominated by fleshy macroalgae. It is essential to evaluate the possible drivers of the extent of degradation of Quitasueño to understand the process of deterioration and mitigate the impacts.

Community-managed coral reef restoration in southern Kenya initiates reef recovery using various artificial reef designs

Monitoring of reef restoration efforts and artificial reefs (ARs) has typically been limited to coral fragment survival, hampering evaluation of broader objectives such as ecosystem recovery. This study aimed to determine to what extent AR design influences the ecological recovery of restored reefs by monitoring outplanted coral fragments, benthic cover, coral recruitment and fish and invertebrate communities for two years. Four AR designs (16 m2), unrestored controls and natural reef patches as reference (n = 10) were established in Mkwiro, Kenya. ARs consisted either of concrete disks with bottles, layered concrete disks, metal cages or a combination thereof. A mixture of 18 branching coral species (mainly Acropora spp.) was outplanted on ARs at a density of 7 corals m-2. After two years, 60% of all outplanted fragments had survived, already resulting in coral cover on most ARs comparable (though Acropora-dominated) to reference patches. Coral survival differed between ARs, with highest survival on cages due to the absence of crown-of-thorns sea star predation on this design. In total, 32 coral genera recruited on ARs and recruit densities were highest on reference patches, moderate on concrete ARs and low on cages. ARs and reference patches featured nearly twice the fish species richness and around an order of magnitude higher fish abundance and biomass compared to control patches. Fish abundance and biomass strongly correlated with coral cover on ARs. AR, reference and control patches all had distinct fish species compositions, but AR and reference patches were similar in terms of trophic structure of their fish communities. Motile invertebrates including gastropods, sea urchins, sea cucumbers and sea stars were present at ARs, but generally more abundant and diverse at natural reference patches. Taken together, all studied ecological parameters progressed towards reef ecosystem recovery, with varying influences of AR design and material. We recommend a combination of metal cages and layered concrete ARs to promote high fragment survival as well as natural coral recruitment. Ultimately, a longer period of monitoring is needed to fully determine the effectiveness reef restoration as conservation tool to support coral reef ecosystem recovery.

Diversity, density and photo-physiology of micro-phytoplankton from degraded and non-degraded reefs around Rodrigues Island, Western Indian Ocean

Abstract. Soondur M, Kaullysing K, Ramah S, Bhagooli R. 2023. Diversity, density and photo-physiology of micro-phytoplankton from degraded and non-degraded reefs around Rodrigues Island, Western Indian Ocean. Indo Pac J Ocean Life 7: 108-121. This study aimed at investigating the variations in micro-phytoplankton diversity, density and photo-physiology between a degraded, Anse Aux Anglais (AAA) in the north, and a non-degraded, Port Sud-Est (PSE) in the southeast, reefs around Rodrigues Island, Republic of Mauritius. Sampling was carried out in summer and winter seasons from 2016 to 2019 at the two sites, PSE and AAA. Micro-phytoplankton samples were collected using a plankton net of 5µm and conserved with Lugol’s solution. Physico-chemical parameters namely temperature, dissolved oxygen, salinity, and ph were recorded in situ. Seawater samples were collected for nutrient and chlorophyll-a concentration analyses. The Total Micro-Phytoplankton Densities (TMPD) did not differ seasonally for the whole period from 2016 until 2019 but there was a significant difference station-wise (P < 0.01), with higher TMPD recorded at the non-degraded reef of PSE. PSE exhibited the higher species diversity. Diatoms and dinoflagellates were more abundant at PSE while the cyanobacteria showed higher densities at AAA. Genera like Licmorphora, Gonyaulax, Polykrikos, Trichodesmium, and Lygnbya, reported worldwide to possibly cause mortality and/or changing community structure of corals, were recorded at both PSE and AAA though not at blooming densities. Photo-physiological assessment of micro-phytoplankton, using a Diving Pulse-Amplitude-Modulated (D-PAM) fluorometer, varied significantly both seasonally and spatially. These findings indicated that the non-degraded reef site had higher micro-phytoplankton density, diversity and photo-physiological performance than the degraded one, implying that degraded reefs may not only be characterized by the benthic cover and/or their health status but also the biological parameters from the water column.

CORAL REEF HEALTH INDEX CALCULATION FROM REMOTE SENSING DATA: A REVIEW

The coral reef ecosystem plays an important role as a provider of ecosystem services and has various economic benefits to the coastal community. However, the coral reefs ecosystem continues to degrade by 19% globally. This degradation caused some coastal and archipelagic countries have developed methods of calculating coral reef health index, including Indonesia. However, some literature shows that there is no common standard method for coral reef health index as the analysis depends on the data availability and the purpose of the study. Remote sensing technology that currently provides much open-source data is a potential method /tool to calculate the health index of coral reefs if the required parameters are met. This article review aims to identify remote sensing data used in the existing coral health indexes and then analyze the integration of all spatial data for coral reef health index calculation. Reference searches are sourced from the SCOPUS database combined with search engines Harzing and Mendeley. There are five coral reef health index calculation models from 25 references consisting of 19 publications and six reports out of 209 filtered references using keywords of Coral Reef Health Index. As a result, coral reef cover and algae are commonly used data obtained from remote sensing imagery. However, remote sensing technology cannot estimate other important parameters such as fish biomass. In addition, physical information of the waters, such as sea surface temperature (SST) and water clarity indicators (turbidity and diffused attenuation coefficient), are parameters contained in the five indexes that can be obtained from remote sensing data. In general, the literature review shows that coral reef health indicators (e.g. index or individual benthic cover) are significantly related to the various parameters affecting coral reef degradation such as algae cover, rubble cover, SST and river plump either as an individual or multivariate factors.

Heatwave hit phase shifted coral reefs: Zoantharian mass mortality record

Phase shift is characterized by an abrupt change in the structure of a community in response to a disturbance that can break its resistance, displacing it from its natural variation. This phenomenon has been recognized in several ecosystems and often points to human activities as the main cause. However, reactions of shifted communities to anthropogenic impacts have been less studied. In recent decades, heatwaves resulting from climate change have strongly affected coral reefs. Mass coral bleaching events are recognized as the main cause of coral reef phase shifts on a global scale. In 2019, an unprecedented heatwave hit the southwest Atlantic Ocean causing mass coral bleaching in non-degraded and phase-shifted reefs of Todos os Santos Bay, at an intensity never recorded in a 34-year historical series. We analyzed the effects of this event on the resistance of phase-shifted reefs, dominated by the zoantharian Palythoa cf. variabilis. Using benthic coverage data from 2003, 2007, 2011, 2017, and 2019, we analyzed three non-degraded reefs and three phase-shifted reefs. We estimated the coverage and bleaching of corals and P. cf. variabilis on each reef. There was a reduction in coral coverage in non-degraded reefs before the 2019 mass bleaching event (i.e., heatwave). However, there was no significant coral coverage variation after the event and the structure of non-degraded reef communities did not change. In phase-shifted reefs the coverage of zoantharians did not change significantly before the 2019 event, however, after the mass bleaching, there was a significant reduction in the coverage of these organisms. Here we revealed that the resistance of the shifted community was broken, and its structure was altered, indicating that reefs in this condition were more susceptible to bleaching disturbance than non-degraded reefs.

How herbivores reshape a macroalgal community on a Little Cayman coral reef: The role of herbivore type and density

Many coral reefs throughout the world continue to decline in health and resilience. In the Caribbean, much of this decline has been attributed to increases in algal cover due to the loss of herbivores such as herbivorous fishes, especially large parrotfish, and the sea urchin Diadema antillarum. In recent years, the combination of protections and natural recovery has helped these herbivores, particularly parrotfishes, to recover in some areas. This recovery has led to questions about how different herbivores affect both the overall benthic cover of macroalgae and the specific composition of algal communities. Toward that end, we designed a caging experiment in Little Cayman to manipulate density and type of grazers. Treatments included full cages (1.27 cm wire mesh) with 4 D. antillarum/m2 added, full cages with 1 D. antillarum/m2, lidless cages (fences) open to herbivorous fishes without D. antillarum, full cages (herbivore exclosures) that excluded most fishes and urchins and open cageless controls. Benthic cover was quantified to assess differences in percent cover and community structure of macroalgae and benthic invertebrates throughout the 5-month study. As the experiment proceeded, both percent algal cover and algal community structure in the full herbivore exclosures, treatments open to fishes (open plots and fences), and treatments with D. antillarum (both densities) diverged. No changes were observed in percent cover of corals or other benthic invertebrates. Overall, reductions in percent algal cover were greater in the high density (4/m2) D. antillarum treatment compared to the low density (1/m2) D. antillarum treatment or those treatments where fishes were allowed access. As expected, greater densities of sea urchins reduced algal cover more quickly. However, these high density treatments also affected the D. antillarum themselves. The condition of the urchins (assessed as ratio of mass to test diameter) at the conclusion of the experiment declined in the 4 D. antillarum/m2 treatment compared to urchins in the 1 D. antillarum/m2 treatment and natural populations. Moreover, high densities of D. antillarum were better able to reduce the abundance of the brown macroalgae Lobophora spp. and Dictyota spp. compared to natural assemblages of herbivorous fishes. These findings suggest that these different types of herbivores, i.e., fishes and D. antillarum, exert different pressures on available algae. Their relative abundances will likely dictate macroalgal community structure on Caribbean coral reefs, and thus the suitability of a reef for the settlement of vital sessile organisms, especially corals.