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Herbivory and nutrient availability are fundamental drivers of benthic community succession in shallow marine systems, including coral reefs. Despite the importance of early community succession for coral recruitment and recovery, studies characterizing the impact of top-down and bottom-up drivers on micro- and macrobenthic communities at scales relevant to coral recruitment are lacking. Here, a combination of tank and field experiments were used to assess the effects of herbivore exclusion and nutrient enrichment on micro- to macrobenthic community succession and subsequent coral recruitment success. Herbivore exclusion had the strongest effect on micro- and macrobenthic community succession, including a community shift toward copiotrophic and potentially opportunistic/pathogenic microorganisms, an increased cover of turf and macroalgae, and decreased cover of crustose coralline algae. Yet, when corals settled prior to the development of a macrobenthic community, rates of post-settlement survival increased when herbivores were excluded, benefiting from the predation refugia provided by cages during their vulnerable early post-settlement stage. Interestingly, survival on open tiles was negatively correlated with the relative abundance of the bacterial order Rhodobacterales, an opportunistic microbial group previously associated with stressed and diseased corals. Development of micro- and macrobenthic communities in the absence of herbivory, however, led to reduced coral settlement. In turn, there were no differences in post-settlement survival between open and caged treatments for corals settled on tiles with established benthic communities. As a result, open tiles experienced marginally higher recruitment rates, driven primarily by the higher initial number of settlers on open tiles compared to caged tiles. Overall, we reveal that the primary interaction driving coral recruitment is the positive effect of herbivory in creating crustose coralline algae (CCA)-dominated habitats, free of fleshy algae and associated opportunistic microbes, to enhance coral settlement. The negative direct and indirect impact of fish predation on newly settled corals was outweighed by the positive effect of herbivory on the initial rate of coral settlement. In turn, the addition of nutrients further altered benthic community succession in the absence of herbivory, reducing coral post-settlement survival. However, the overall impact of nutrients on coral recruitment dynamics was minor relative to herbivory.

AimResearch on mesophotic coral ecosystems (MCEs) has increased exponentially in recent decades, and the significance of this ecosystem has been recognised both in terms of biodiversity and distribution. However, this research has mostly focussed on corals and is globally sporadic, with the Indian Ocean remaining largely unexplored and overall MCEs under protected. Hence, baseline data on MCE benthic communities is lacking, but nonetheless essential for developing adequate management strategies. Here, we assess the variation in diversity and community structure of MCEs along the depth gradient and among sites in the Indian Ocean and the environmental parameters that are potentially driving these differences.LocationEgmont Atoll, Chagos Archipelago, central Indian Ocean.Time PeriodPresent.Major Taxa StudiedMarine benthic invertebrates, plants.MethodsUsing a remotely operated vehicle, we collected video transects between 15 and 160 m. We analysed the diversity and composition of benthic communities and used DistLM analysis to determine the environmental drivers of the community structure over the depth gradient and between sites.ResultsWe observed distinct benthic communities along the depth gradient, with a strong community break observed at ~60 m. We also identified a clear zonation of the benthic taxa with depth. This zonation was primarily driven by downward irradiance and temperature, with additional environmental processes playing a minor role in structuring the benthic communities.Main ConclusionsWe show that MCEs in the Chagos Archipelago are distinct communities, and their distribution is driven primarily by irradiance and temperature. Our results highlight the variability in benthic community structure of MCEs, both along the depth gradient and at local geographical scales for the study region. This study showcases the uniqueness of MCEs and will aid in predicting their distribution, potential refugia for shallow reefs, and in developing evidence-based protection for MCEs, to maintain overall marine biodiversity.

Ecosystem macroscopic properties given by Ascendency theoretical framework were compared between two multispecies mass-balanced trophic models of the coastal benthic ecosystem along Mejillones Bay in northern Chile (SE Pacific). The models were constructed with a similar number of components representing system conditions for years 2006 and 2018 using Ecopath with Ecosim (EwE) software. The most relevant change was that the macroalgae (principally Rhodophyta group) increased notably over 12 years. In terms of Ascendency, the larger increase in Total System Throughput (TST) compared to the null increment in the Average Mutual Information would indicate that the benthic ecosystem of Mejillones Bay is moving towards eutrophic conditions. This is consistent with the reduction in the TST cycled, Finn’s cycling index, and a two-fold increase in the flow of detritus. Likewise, the Keystone Species Complex seems to be sensitive to changes in the properties of ecosystems, reducing the number of components in cases of deteriorated ecosystem. Based on the results obtained, it is suggested the implementation of management strategies that allow reversing this trend towards eutrophication, such as, to strengthen environmental policies and monitoring programs in order to conserve the benthic communities of Mejillones Bay.

Acute disturbances and chronic pressures have an important and increasing influence on the structure of coral reef communities. For the viability of benthic taxa such as stony corals, a balance between loss following disturbance and recovery is vital. Coral populations on reefs with lower exposure to chronic pressures are often presumed to have increased resilience, enabling them to recover quickly following disturbance, but decades of anthropogenic stress and degradation may undermine the systematic recovery and reassembly of benthic communities. This study explored spatiotemporal changes in benthic community structure over a 15 yr period at three distinct coral reef regions with a gradient of chronic pressures in Florida, USA, (southeast Florida, the Florida Keys and the Dry Tortugas). We specifically assessed the spatial scale, potential drivers of change and resilience in stony coral, octocoral, sponge and macroalgae cover. Spatiotemporal changes were assessed at four different scales: among regions, habitats, sub-regions, and habitat types within regions. Cover of stony corals remained very low or declined in every region from 2004 to 2018, with corresponding increases in macroalgae cover. Stony coral recovery was limited regardless of regional differences in chronic pressure. Octocorals exhibited greater resilience due to increased recovery following disturbance and generally had higher cover than stony corals on Florida’s Coral Reef, while sponge cover was very stable over the study period. Acute disturbances, which affected sites on average once every 3 yr, negatively impacted stony coral and/or octocoral cover in every region and habitat, contributing to the regionwide proliferation of macroalgae. This study determined that high disturbance frequency and chronic anthropogenic pressures on Florida’s Coral Reef have led to sustained declines in stony corals and corresponding proliferation of macroalgae. Stony corals were expected to recover during inter-disturbance periods, but in Florida, even in locations with lower chronic pressure, recovery is severely limited.

Temperate mesophotic ecosystems (TMEs) typically occur between 30 and 150 m depth and support rich benthic communities. However, despite their widespread distribution and ecological importance, TMEs are one of the most poorly studied marine ecosystems globally. We measured changes in the benthic community composition of rocky reefs through the infralittoral and mesophotic zone from 5 to 120 m at 6 locations across New Zealand (the Poor Knights Islands, the inner, mid-, and outer regions of the Fiordland Marine Area [FMA], and the North and South Taranaki Bights) which we considered as potential shallow-water TME surrogates due to these sites having environmental conditions and biological communities similar to deeper-water communities. Benthic community data were analysed from videos and photographs collected using SCUBA (<30 m) and a remotely operated vehicle (ROV) (>30 m). We found significant changes in community composition with depth at all locations, suggesting that TMEs provide habitats different from those in shallower water. We consistently found that TME benthic communities were dominated by sponges, but their abundance varied significantly with depth at 3 out of 4 locations, while the morphological composition of these assemblages changed with depth at all locations. Given their particularly high abundance and morphological complexity, we suggest that sponge assemblages make an important contribution to habitat complexity in benthic TME communities.

The objectives of the present study were to characterize the benthic invertebrate communities at the Marine Protected Area (MPA) Namuncurá/Burdwood bank (created by the National Law 26875, year 2013) and their different sub-areas, to compare these benthic communities with nearby sub-areas, and to detect sites that meet the criteria of Vulnerable Marine Ecosystems (VMEs) to highlight the importance of this particular and rich sub-Antarctic region. We used quali- and quantitative data obtained from research cruises developed by Argentina in 2016 and 2017. The results showed that Porifera was the most important component (in terms of wet biomass) of these benthic communities, followed by Cnidaria and Echinodermata. The evidences regarding general composition of the main taxonomical groups of the benthic invertebrate community did not support the maintenance of the original zoning of the MPA (core, buffer, and transition), considering that only a weak differentiation was found among the sub-areas designed in the creation Law. Additionally, the analyzed evidences also demonstrated that this MPA was different from other neighboring areas. Vulnerable and fragile organisms recorded in many locations led to the detection of fourteen sites located inside the MPA Namuncurá that meet the characteristics of VMEs (wet biomass of ≥ 10 kg 1200 m−2 of vulnerable and fragile species). These evidences reinforce the conservation value of these particular and susceptible sub-Antarctic benthic communities, composed of both Antarctic and Magellanic species.

Oxygen depletion is well recognized for its role in the degradation of tropical coral reefs. Extreme acute hypoxic events that lead to localized mass mortality and the formation of ‘dead zones’ (a region where few or no organisms can survive due to a lack of oxygen) are particularly concerning as they can result in wide-ranging losses of biodiversity, ecosystem productivity and functioning, economic prosperity, and wellbeing. In March of 2022, the annual coral spawning event at Bills Bay (Coral Bay, Ningaloo Reef, Western Australia) coincided with elevated seawater temperature, calm weather conditions and a flood tide resulting in coral spawn becoming trapped in Bills Bay. Immediately after, there was a mass fish kill, which is believed to have been caused by local eutrophication resulting in severe oxygen depletion. The impact the deoxygenation and thermal stress event had on benthic communities has not yet been quantified; hence, the principal aim of this study is to document the extent of change that occurred in the benthic communities before and after the 2022 coral spawning event over a spatial gradient from the nearshore to mid-reef. Percent coral cover in the Bay decreased from 55.62 ± 2.26% in 2016–2018 and 70.44 ± 5.24% in 2021 to 1.16 ± 0.51% in 2022. Over the same period, the percent cover of turf algae increased from 27.40 ± 2.00% in 2016–2018 and 24.66 ± 6.67% in 2021 to 78.80 ± 3.06% in 2022, indicating a dramatic phase shift occurred at Bills Bay. The abundance of healthy coral colonies recorded on replicated belt transects at nine sites declined from 3452 healthy individuals in 2018 to 153 individuals in 2022 and coral generic richness decreased by 84.61%, dropping from 26 genera in 2018 to 4 genera in 2022. Previously dominant genera such as Acropora, Montipora and Echinopora, were extirpated from survey sites. Isolated colonies of massive Porite s spp. and encrusting Cyphastrea sp. survived the event and understanding the mechanisms underpinning their greater survivorship is an important area of future research. Long-term monitoring is recommended to track the community recovery process and improve our understanding of the longer-term implications of this acute mortality event on the ecological, socio-economic and cultural values of Ningaloo Reef.

Information on the ecology of invertebrate communities populating Macrocystis pyrifera forests in the Falkland Islands is scarce. Indeed, the factors influencing diversity, distribution and community structure have never been studied here. Benthic photoquadrats were collected along three permanent 20 m transects at three depth strata (shallow 5–10 m; middle 10–15 m; deep 15–20 m) off the coast of Kidney Island, Falkland Islands from Austral summer 2009 to Austral spring 2010. 146 taxa comprising 10 phyla and 21 classes were recorded during the surveys, with the most abundant sessile and vagile taxa being Spirorbinid worms and the hermit crab Pagurus comptus, respectively. Community structure was influenced by depth, with highest species richness in the middle depth stratum, and strong contrasts between the communities in the shallow and deep depth strata. Influence of season on community structure was evident, though not as strong a factor as depth. Spring and summer months were most species rich, demonstrating a difference between the shallow subtidal regions of Patagonia where species richness was reported to be highest in Austral autumn and winter. The effect of substrate and depth was also investigated for the abundance of individual taxa. This study provides the first description of the fauna and flora of shallow rocky reefs in the Falkland Islands, describing how these communities change over small spatial and temporal scales. The outcomes of this investigation contribute to better understanding ecological patterns of the Falklands shallow benthic environments and adds knowledge to the biogeography of the South Atlantic.

Marine protist diversity inventories have largely focused on planktonic environments, while benthic protists have received relatively little attention. We therefore hypothesize that current diversity surveys have only skimmed the surface of protist diversity in marine sediments, which may harbor greater diversity than planktonic environments. We tested this by analyzing sequences of the hypervariable V4 18S rRNA from benthic and planktonic protist communities sampled in European coastal regions. Despite a similar number of OTUs in both realms, richness estimations indicated that we recovered at least 70% of the diversity in planktonic protist communities, but only 33% in benthic communities. There was also little overlap of OTUs between planktonic and benthic communities, as well as between separate benthic communities. We argue that these patterns reflect the heterogeneity and diversity of benthic habitats. A comparison of all OTUs against the Protist Ribosomal Reference database showed that a higher proportion of benthic than planktonic protist diversity is missing from public databases; similar results were obtained by comparing all OTUs against environmental references from NCBI's Short Read Archive. We suggest that the benthic realm may therefore be the world's largest reservoir of marine protist diversity, with most taxa at present undescribed. Sampling RNA in near-shore marine environments along the European coast shows that benthic protist communities are extremely diverse with many species currently unknown. Graphical Abstract Figure. Sampling RNA in near-shore marine environments along the European coast shows that benthic protist communities are extremely diverse with many species currently unknown.

Coral reefs are crucial ecosystems for marine biodiversity but are increasingly threatened by anthropogenic pressures and climate anomalies. The 2016 global bleaching event resulted in widespread coral mortality, altering reef structure and benthic communities. Here, we examine the evolution of Maldivian reefs from 2015 to 2023 using long-term monitoring data to assess post-disturbance dynamics. Analyses of 26 benthic descriptors revealed severe impacts from thermal stress, with heterogeneous recovery patterns. Reef-building capacity, which reflects the reef’s accretion potential and is mainly sustained by primary (e.g., Acropora branching corals) and secondary constructors (e.g., Tridacna spp.), rebounded substantially, while binders (e.g., coralline algae) and bafflers (e.g., erect sponges) remained depleted. Among growth forms, fast-growing branching and digitate corals, despite substantial declines, drove rapid recovery. Massive corals were less affected and continued growing, while encrusting corals declined steadily over the period. Post-bleaching community composition shifted markedly toward increased abiotic cover and reduced coral dominance, with partial reversion by 2023. Despite the 2016 collapse in constructional capacity, most reefs exhibited notable recovery within seven years. These findings underscore the moderate yet promising resilience of Maldivian reefs, exceeding previous bleaching events, and emphasize the importance of long-term monitoring to understand ecosystem responses under accelerating climate stress.