Changes In Benthic Communities Research Articles

Depth variation in benthic community response to repeated marine heatwaves on remote Central Indian Ocean reefs.

Coral reefs are increasingly impacted by climate-induced warming events. However, there is limited empirical evidence on the variation in the response of shallow coral reef communities to thermal stress across depths. Here, we assess depth-dependent changes in coral reef benthic communities following successive marine heatwaves from 2015 to 2017 across a 5-25 m depth gradient in the remote Chagos Archipelago, Central Indian Ocean. Our analyses show an overall decline in hard and soft coral cover and an increase in crustose coralline algae, sponge and reef pavement following successive marine heatwaves on the remote reef system. Our findings indicate that the changes in benthic communities in response to elevated seawater temperatures varied across depths. We found greater changes in benthic group cover at shallow depths (5-15 m) compared with deeper zones (15-25 m). The loss of hard coral cover was better predicted by initial thermal stress, while the loss of soft coral was associated with repeated thermal stress following successive warming events. Our study shows that benthic communities extending to 25 m depth were impacted by successive marine heatwaves, supporting concerns about the resilience of shallow coral reef communities to increasingly severe climate-driven warming events.

Short-term temporal variability in offshore benthic biodiversity across hydrographic regions at a sub-Antarctic archipelago

AbstractCommunity composition is one of the main factors influencing the ecological functioning of any given ecosystem, with a more diverse community providing a larger set of services. Benthic community composition can vary at spatial and temporal scales, with the dynamics of primary production and benthic food availability being key determinants of community structure of a given system. Studies have indicated shifts in benthic community composition at sub-Antarctic Islands over a period of 30 years, linked to variability in food availability driven by climate change. Here, we aim to evaluate possible short-term variability in benthic community composition at the sub-Antarctic archipelago Prince Edward Islands (PEIs), sampling stations across three hydrographically dynamic regions over two consecutive years, 2016–2017. The results indicated significantly higher species richness and abundance in 2017 than in 2016, with some taxa also showing variation among regions around the PEIs. Such effects can be linked to different substratum type or hydrographic regime. This study further contributes to understanding variability and changes in benthic communities in the near future, an essential information to develop efficient management strategies for this vulnerable marine system.

Ecosystem function modified by an invasive species: Density and distance dependent changes in sediment characteristics, fluxes, and benthic communities

Coastal marine benthic ecosystems are considered hotspots for biodiversity and productivity. However, the introduction of bio-engineering non-indigenous species can alter the delivery of key functions and services provided by these systems. Here, we investigated the influence of Sabella spallanzanii, a large structure-forming invasive polychaete, on a marine soft-sediment system in New Zealand, examining effects on sediment characteristics (organic matter and chlorophyll a content), solute fluxes, and benthic communities near and far from low-, medium-, and high-density clumps of Sabella. Fluxes of dissolved oxygen and inorganic nitrogen near (<10 cm) Sabella clusters were significantly lower to those 1 m away, and fluxes differed between low-, medium-, and high-density clumps. Larger densities of Sabella and clumps with greater overall biomass were associated with increased sediment oxygen consumption, particularly in areas 1 m distant from the Sabella clumps. Similarly, ammonium production (efflux from the sediment) increased with increasing Sabella biomass at the 1 m ‘distal’ sites (from 0 μ to 40 μmol/m2/h), but NOx efflux decreased (from 5 to 0 μmol/m2/h) with distance. The flux results were consistent with findings of higher organic matter content and finer grain size sediment in ‘distal’ plots to Sabella clusters. We also showed how benthic diversity and abundance increased with increasing Sabella clump biomass. Our investigation suggests that the building of biogenic structures and the filter feeding activity by Sabella may alter near-bed flows and concentrations of organic rich biodeposits in surrounding sediments, with ramifications for organic matter distribution and nutrient recycling rates. The continuous expansion and colonisation of Sabella could reshape local benthic communities and increase oxygen consumption rates in affected marine sediments.

Protected yet unmanaged: insights into the ecological status of conservation priority stony reefs in Belgian waters based on the integrative use of remote sensing technologies

Stony reefs are ecologically important, providing irreplaceable ecosystem services. These fragile environments are recognised as conservation priorities by all relevant global and European policies. Bottom-contacting fisheries are an important source of anthropogenic disturbance to the seafloor’s physical and ecological integrity having immediate and destructive consequences on stony reefs and compromising ecological functions. This study, aimed to assess the ecological status (community composition and functions) of two stony reef areas -Northwest and Hinder Banks study sites -in Belgian waters using multiple remote sensing tools. Insights on the study sites’ geomorphological context and fishing patterns were gained using echo-sounding and publicly available satellite data. Video-based benthic community data were assessed against the exposure to fishing pressure using a trait-based approach linked to the biotas’ resistance and recovery potential. In the Northwest study site, between 2019 and 2022 there was a significant decline in the abundance of benthic species classified with low resistance and recovery potential to trawling. Conversely, there was a notable increase in species with moderate scores. During the same period, this site experienced an eight-fold increase in fishing effort and the hydroacoustic data revealed the presence of several trawl-marks in 2022. Similar changes in benthic communities were observed in the Hinder Banks too. Here, the abundance of species with low resistance and recovery potential was significantly lower in locations that were geomorphologically exposed to trawling compared to sheltered ones. Exposed locations had a higher abundance of opportunistic species, with moderate to high scores. The presence of several trawl marks on the seafloor was observed in the exposed locations, corresponding to fishing hotspots identified in the satellite data. Trawling activities marginally impacted richness and total abundance, but negatively altered benthic functional composition. The findings of this study provide scientific evidence of the detrimental impact of bottom-contacting fisheries on conservation priority biotopes and argues against the coexistence of such activities with Marine Protected Areas. The results of our investigation are of interest to environmental managers for the adequate implementation of environmental legislation in the face of rapid and widespread anthropogenic changes.

Integrative taxonomy approach to detect spatial and temporal variability of the Mediterranean benthic communities through artificial substrate units (ASUs)

Monitoring spatial and temporal changes of marine benthic communities using standardized procedures is essential to take necessary steps towards conservation of marine ecosystems. In this study we combined Artificial Substrate Units (ASUs) for sampling of benthic communities, with integrative taxonomy approach that incorporated morphological identification of organisms and COI DNA metabarcoding, to characterize the diversity of communities at three locations across the Central Mediterranean Sea (Livorno and Palinuro, Italy; Rovinj, Croatia) in 2019 and 2020. Significant differences in the communities’ structure were observed both at large spatial scale between sampled locations, and at small spatial scale (less than ten kilometers) between sites. Moreover, significant temporal variability in species richness and structure of benthic assemblages was detected, with higher richness in 2020. Revealed variability can probably be attributed to the peculiar geomorphological, oceanographical, and ecological features of locations, but also to the influence of interplaying local chemical and physical factors and biological processes such as species settlement, competition, and migration that can act at small spatial and temporal scales. The similarity in the species composition and community structure accessed by morphological and metabarcoding approaches was low, with only 16% of the species (out of 133 species identified overall) commonly detected by both approaches. This is mostly both due to a lack of data on COI sequences of numerous benthic invertebrates in the public barcoding databases on the one hand, and difficulties in detecting small and cryptic taxa through morphological analyses on the other. This suggests that combining of two approaches is required to fully describe the biodiversity of benthic assemblages. Finally, comparison of the spatial variability of the benthic communities’ structure with two approaches at different taxonomic levels, indicated that genus and family levels give results that are consistent to those obtained by the species level. This suggests that family level might be satisfactory in monitoring the spatial-temporal variability of Mediterranean hard bottom benthic communities.

The Impact of Sea Ice Cover on Microbial Communities in Antarctic Shelf Sediments.

The area around the Antarctic Peninsula (AP) is facing rapid climatic and environmental changes, with so far unknown impacts on the benthic microbial communities of the continental shelves. In this study, we investigated the impact of contrasting sea ice cover on microbial community compositions in surface sediments from five stations along the eastern shelf of the AP using 16S ribosomal RNA (rRNA) gene sequencing. Redox conditions in sediments with long ice-free periods are characterized by a prevailing ferruginous zone, whereas a comparatively broad upper oxic zone is present at the heavily ice-covered station. Low ice cover stations were highly dominated by microbial communities of Desulfobacterota (mostly Sva1033, Desulfobacteria, and Desulfobulbia), Myxococcota, and Sva0485, whereas Gammaproteobacteria, Alphaproteobacteria, Bacteroidota, and NB1-j prevail at the heavy ice cover station. In the ferruginous zone, Sva1033 was the dominant member of Desulfuromonadales for all stations and, along with eleven other taxa, showed significant positive correlations with dissolved Fe concentrations, suggesting a significant role in iron reduction or an ecological relationship with iron reducers. Our results indicate that sea ice cover and its effect on organic carbon fluxes are the major drivers for changes in benthic microbial communities, favoring potential iron reducers at stations with increased organic matter fluxes.

Spatial and temporal changes of subtidal benthic communities in Antofagasta Bay (SE Pacific) stressed by permanent human disturbances

Human activities have impacted the coastal area of Antofagasta Bay for decades, particularly miners’ activities (loading of mineral concentrates of Cu, Zn, Pb, and Mg), port operations, tourism, desalination plants, artisanal fishing, and sewage discharge. Subtidal coastal benthic communities were assessed in 7 sectors with different magnitudes of anthropogenic disturbances between the years 2008 to 2011 at Antofagasta Bay. Transennella pannosa, Incatella cingulata, Crassilabrum crassilabrum, and Leukoma thaca dominated the communities in all years of study. Based on the type of feeding behavior, the highest biomass was evidenced for the suspensivore group in all years of study, followed by the carnivore species. The highest average richness and average Shannon diversity were observed in sectors with medium and high levels of disturbances. In contrast, the highest average species dominance was registered in a sector with low disturbances. Community structure differed significantly between the seven sectors over the four years. The analysis of classification and ordination showed the conformation of three groups of sectors based on their dissimilarities. The differences were best explained by the sectors with low and high disturbances and by the presence of bivalves, ascidians, gastropods, and algae. It was demonstrated that the reduction or absence of fishing pressure could explain species’ high richness and diversity. Likewise, the sectors under low disturbance pressure showed the highest biomass and dominance of species. The information obtained in the current work could be used to design management strategies for conservation, monitoring, and restoration programs.

Faunistic and Structural Changes in Shallow Coastal Benthic Communities of the Ebre Delta (NW Mediterranean Sea)

The Ebre Delta (NW Mediterranean), which is considered a highly vulnerable ecosystem, is one of the most important European wetlands and belongs to the Natura 2000 network. The present study aims to characterize the benthic megainvertebrate communities inhabiting the Ebre Delta soft-bottom infralittoral to acquire faunistic and biological knowledge for two periods of time, 23 years apart. Experimental trawls were conducted during the two periods (1992–1993 and 2016–2017) in three depth strata, between 5 and 25 m. A total of 139 and 170 taxa were collected at each period, respectively. Our results showed that community species composition and structure varied between periods and among depth strata. Overall, a large decrease in density and biomass was detected for most species in all three depth strata examined (0–5, 15–20, and 20–25 m) in 2016–2017, especially in the shallowest stratum. Species richness was higher in 2016–2017 than in 1992–1993, and the lowest values were found at the shallowest stratum in both periods. The significant biomass losses herein reported highlight the need to increase, in time and effort, the monitoring of large marine invertebrates in coastal areas, where many taxa provide important ecosystem functions and services.

Spatial variation in the community structure and response of benthic macroinvertebrates to multiple environmental factors in mountain rivers

Exploring the response between benthic community changes and environmental variables has significance for restoring the health of river ecosystems. However, little is known of the impact on communities of interactions between multiple environmental factors, and frequent changes in the flow of mountain rivers are different from those in the flow of plain river networks, which also impact differently the benthic community. Thus, there is a need for research on the response of benthic communities to environmental changes in mountain rivers under flow regulation. In this study, we collected samples from the Jiangshan River in the dry season (November 2021) and the wet season (July 2022) to investigate the aquatic ecology and benthic macroinvertebrate communities in the watershed. Multi-dimension analyses were used to analyze the spatial variation in the community structure and response of benthic macroinvertebrates to multiple environmental factors. In addition, the explanatory power of the interaction between multiple factors on the spatial variation of communities, and the distribution characteristics of benthic community and their causes were investigated. The results showed that herbivores are the most abundant forms in the benthic community of mountain rivers. The structure of benthic community in Jiangshan River was significantly affected by water quality and substrate, whereas the overall community structure was affected by river flow conditions. Furthermore, nitrite nitrogen and ammonium nitrogen were the key environmental factors impacting the spatial heterogeneity of communities during the dry and wet season, respectively. Meanwhile, the interaction between these environmental factors showed a synergistic effect, enhancing the influence of these environmental factors on community structure. Thus, controlling urban and agricultural pollution and releasing ecological flow would be effective strategies to improve benthic biodiversity. Our study showed that using the interaction of environmental factors was a suitable way to evaluate the association between environmental variables and variation in benthic macroinvertebrate community structure in river ecosystems.

Changes in reef benthic communities in Sumba Timur, East Nusa Tenggara, Indonesia

Abstract. Utama RS, Hadi TA, Hermanto B, Giyanto, Budiyanto A. 2022. Changes in reef benthic communities in Sumba Timur, East Nusa Tenggara, Indonesia.Biodiversitas 23: 677-687. Anthropogenic impacts and coral bleaching due to rising sea surface temperature have been severe and often, as of late on the worldwide scale, influencing the composition of coral reef benthic communities from coral to algal-ruled reefs (phase shift). In any case, coral reef phase shift does not continuously happen, considering corals can recoup when stressors occur. This considers points to examine the alteration in coral reef benthic communities and the relationship among benthic categories. The study was carried out in 2018 and 2021 at 10 stations within East Sumba, and East Nusa Tenggara. Underwater photo transect (UPT) was used to examine benthic cover at a depth of 6 to 9 m in reef slope. The result demonstrated that the benthic communities were slightly altered, especially hard coral, sponge, and other biotas. A slight recovery of hard coral cover is shown in 2021, followed by the decline of sponge and fleshy seaweed cover, which is shown in most observation sites. Acropora spp., Seriatopora spp., and Stylophora spp. were the three genera that increased in cover. The study also found the relationship between the benthic gradient and species richness and the number of colonies, which is gradient changes in benthic composition were in line with the change in hard coral species richness and colony numbers. Although hard coral increase significantly changes over time, it's not altered the coral communities.

Succession of macrozoobenthic communities and its drivers in Meiliang Bay of Lake Taihu during the past 40 years

梅梁湾是太湖北部最大湖湾,也是太湖生态环境问题最严重的区域之一,近年来对太湖治理力度不断加大,然而对其生态状况演变的认识尚不清晰。本文基于长期监测及文献资料,获得1980s以来太湖梅梁湾底栖动物及环境因子数据,分析底栖动物种类组成、优势种、丰度的时空变化,应用非度量多维尺度分析(NMDS)和随机森林(RF)分析群落结构演变及其与环境因子的关系。结果表明,梅梁湾1980-2019年共记录到44属(种)底栖动物,以摇蚊幼虫和软体动物为主,总丰度年际变化显著,40年来底栖群落结构发生显著变化,优势种经历了由较敏感的软体类为主到以耐污寡毛类、摇蚊幼虫等为主的转变。综合NMDS和随机森林分析结果,梅梁湾底栖动物群落演变大致可分为4个阶段:1980s及以前,物种多样性丰富,以河蚬(Corbicula fluminea)等大型软体动物为优势种;1990s-2007年,底栖动物群落快速退化,以耐污种占优;2008-2016年,水生态略有恢复,河蚬等清洁种略有回升;2017-2019年,耐污种优势度和丰度反弹。近40年来梅梁湾底栖动物群落变化主要受底质氮磷、有机质和水体营养盐、蓝藻水华等环境因子变化的影响,此外水生植物演替也是影响底栖动物群落变化的重要因素。;Meiliang Bay is the largest bay in the northern Lake Taihu which has the most serious ecological and environmental problems. In recent years, while the governance of Lake Taihu has been strengthened, the understanding of the succession of its ecological status remains unclear. Based on the long-term monitoring data and historical literature, this study analyzed the temporal and spatial variation of macrozoobenthos composition, the dominant species and density in Meiliang Bay since 1980s. Community succession and its relationship with environmental factors are examined by non-metric multidimensional scale analysis (NMDS) and random forest (RF). The results showed that 44 taxa were recorded in Meiliang Bay from 1980 to 2019, mainly composed of chironomid larvae and molluscs, with substantial interannual changes in total density. The benthic community structure has changed significantly in the past 40 years, with the dominant species have changed from sensitive species dominated by molluscs to pollution tolerant species characterized by oligochaetes and chironomids. Based on the results of NMDS and random forest analyses, the benthic community succession in Meiliang Bay can be roughly divided into four stages. Stage 1 (before 1980s) had Corbicula fluminea and other large molluscs dominated the community characterized by high species diversity. In stage 2 (1990s-2007), the benthic community degenerated rapidly, dominated by pollution-tolerant species. From 2008 to 2016 (stage 3), the ecological condition showed a recovery trend, with the sensitive species increased slightly. Stage 4 from 2017 to 2019, the dominance and density of pollution tolerant species rebounded. The changes of benthic communities in Meiliang Bay in recent 40 years are mainly regulated by sediment nitrogen and phosphorus, organic matter and water column nutrients, followed by aquatic macrophytes degradation.

Long-term changes in benthic communities following the invasion by an alien octocoral in the Southwest Atlantic, Brazil

Invasive alien species are considered one of the main threats to marine biodiversity. We used a BACI design to investigate the changes in rocky reef benthic communities related to the invasion of the octocoral Latissimia ningalooensis in the Southwest Atlantic. Drastic changes in benthic community structure were restricted to the invaded site and associated with the growth of L. ningalooensis on turf algae. Conversely, the zoanthid Palythoa caribaeorum remained stable coverage along the 9-year study period, indicating a greater biotic resistance against the octocoral. Latissimia ningalooensis spread from large and well-established patches to new areas of the reef, increasing turf-octocoral interactions. This study warns of the great invasive potential of the octocoral, due to its high abundance, competitive and expansion ability. The decline in abundance of turf-forming algae following the emergence of L. ningalooensis threatens the structure and functioning of macroalgal-dominated rocky reefs.

Dominance of the scleractinian coral Alveopora japonica in the barren subtidal hard bottom of high-latitude Jeju Island off the south coast of Korea assessed by high-resolution underwater images.

Coastal benthic communities in temperate regions have been influenced by climate change, including increasing sea-surface temperature. Nevertheless, scleractinian coral Alveopora japonica Eguchi, 1968, is thriving in shallow subtidal hard bottoms around Jeju Island, off the southern coast of Korea. The presence of this corals has negatively impacted subtidal kelp populations in Jeju Island. However, there is no study to document how the presence or absence of this coral relates to other benthic communities. This study investigated the benthos in three shallow subtidal sites (Shinheung (SH), Bukchon (BC), and Seongsan (SS)) in northern Jeju using underwater photography. Macro-benthic organisms appearing on a 1 × 20 m line transect installed at depths of 5, 10, and 15 m at each site were analyzed. Results showed that of the three sites investigated, A. japonica colonies were most abundant at BC, accounting for 45.9% and 72.8% of the total transect area at 10 m and 15 m, respectively. At SS, A. japonica occupied 15.3% of the total area at 15 m and less than 1% at 5 m and 10 m. The same at SH accounted for 10% of the total area at 5 m, and less than 1% at 10 m and 15 m. Dead and bleached colonies accounted for 1.2-11.5% and 1.8-5.7%, respectively, at 5, 10, and 15 m at three sites. At SS, canopy-forming brown algae Ecklonia cava and Sargassum spp. accounted for 20.2 and 24.3% of the total transect area, respectively, at 5 m depth. In contrast, the percent cover of E. cava and Sargassum spp. at SH and BC ranged from 0.1 to 1.8%, respectively. Moreover, non-geniculate coralline algae dominated the subtidal substrate at SH, ranging between 60.2 and 69% at 15 and 10 m. The low cover of A. japonica in SS (at 5 m) coincided with a high percent cover of canopy-forming brown algae. However, canopy-forming brown algae were rare at all depths at SH and BC and were dominated instead by coralline algae and the scleractinian corals. This study, by utilizing a non-destructive method, provides a baseline qualitative and quantitative information for understanding the site and depth-dependent distribution of A. japonica and algal populations, which is important to understand climate change related changes in benthic communities in Jeju and elsewhere.

Utilization of riverine organic matter by macrobenthic communities in a temperate prodelta

Macrobenthos is an important component of organic carbon storage and energy flow in marine systems, including these impacted by riverine discharge and high share of allochthonous organic matter (OM). Changing environmental conditions, such as lower precipitation and snow cover duration, may affect patterns of riverine input, therefore it is crucial to know how benthic communities utilize different OM sources in areas affected by rivers. Using Bayesian stable isotope mixing models, we assessed the diet composition of common macroinvertebrates forming benthic communities in the transition zone of one of the largest river outlets in the Baltic Sea region, the Vistula River prodelta. Furthermore, we analyzed the spatial and temporal variability in the biomass-weighted resource utilization by those communities. Contribution of riverine OM to the particulate OM in Vistula prodelta decreased with increasing depth. Despite similar distances to the river mouth, the relative contribution of riverine OM to the diet of all studied taxa also decreased with increasing depth, which corresponded to organic matter composition in prodelta waters. Nevertheless, due to synchronous structural changes in benthic communities, and changes in the feeding modes of dominant species, particularly Macoma balthica and Hediste diversicolor, the riverine organic carbon share in the biomass of benthic communities often remained the highest in the deepest prodelta parts. Our study corroborates that benthic primary consumers act as a gateway for riverine organic matter into the marine food web and illustrates that sediment properties and resource partitioning affects spatial structure of benthic communities and their abilities to utilize allochthonous OM.

Benthic Foraminiferal and Sedimentologic Changes in the Pliocene Yorktown Formation, Virginia, USA

ABSTRACTThe Pliocene Yorktown Formation consists of four lithologic units that record three marine transgressive sequences along the U.S. mid-Atlantic margin. These units were deposited during a time when average sea-level and mean global temperatures were ∼25 m and ∼3°C higher than the pre-industrial, respectively, and global atmospheric CO2 concentrations were similar to present. Forty-five samples were collected along the James River near Rushmere, Virginia, and Spring Grove, Virginia, and were analyzed for benthic foraminifera community and sedimentological changes between each member of the formation. These data are useful for developing boundary conditions for shallow, near-shore environments for paleoclimate modeling. Foraminiferal analysis distinguishes six biofacies across the entire formation. The most notable change in grain-size occurs at the conformable boundary between the Rushmere and Morgarts Beach members, where the average percentage of sand decreases from ∼60% in the Rushmere Member to &amp;lt;40% in the Morgarts Beach Member.

Characterizing the Biological Community before and after Partial Removal of an Offshore Gas Platform in the Northwestern Gulf of Mexico.

High Island A-389-A (HI-A-389-A) is a gas platform situated in 125 m water within Flower Garden Banks National Marine Sanctuary in the northwestern Gulf of Mexico, and provides habitat to a diverse array of benthic organisms and fish species. Platform production ceased in 2012, beginning the decommissioning process for structural removal. Rather than complete removal of the structure, the lower portion was left intact as an artificial reef and the upper 21 m was removed. The biological communities (benthic and fish) were characterized during diver and remotely operated vehicle surveys, both before and after removal of the upper structure. The platform's benthic community, primarily categorized as fouling organisms, was mainly composed of sponges, hydroids, macroalgae, bivalves, zoanthids, and stony corals. The dominant stony coral was orange cup coral (Tubastraea sp.), an exotic species, while native coral species were rare. Fish species were predominantly demersal planktivores. Analyses of the benthic and fish communities documented four distinct biological zones strongly associated with depth. Significant differences in the benthic community were observed after partial removal and varied with depth, including the loss of hydroids, increase in macroalgae cover, and sponge and coral community changes. Both demersal and pelagic fish communities exhibited significant differences by depth after removal but no significant changes were observed in federally managed species. Results reflect changes in benthic and fish communities after partial removal of the platform that is likely, in part, influenced by structure removal and temporal variations.

Sr isotope variations in Oligocene–Miocene and modern biogenic carbonate formations of Koko Guyot (Emperor Seamount Chain, Pacific Ocean)

The Hawaiian–Emperor Seamount Chain, a major topographic feature of the Pacific Ocean floor, is composed of seamounts capped with fossil coral reef deposits that originally formed close to sea level but are now covered by hundreds of meters of water owing to prolonged subsidence. These fossil reef deposits are important archives of paleoenvironmental change and yield information on the subsidence history of the seamounts. We studied the Sr isotope compositions of Oligocene–Miocene coral reef limestone from Koko Guyot in the southern Emperor Seamount Chain to assess the dynamics of the subsidence. The ages of the studied samples containing coral fragments established by Sr isotope stratigraphy vary from 26.3 to 20.1 Ma. In contrast, the youngest samples (15.3 Ma), which were deposited in water depths of >120 m, are barren of corals and are composed exclusively of bryozoans and coralline algae. The subsidence rate of the Koko Guyot volcanic structure was not constant over time. Integration of our new data with the results of previous studies reveals that the subsidence rate was 0.046 ± 0.005 mm/yr during the first 25–30 Myr (from 49–44 to 20 Ma). During this period, Koko Guyot was in a bathymetric interval favorable for coral reef development, and its subsidence was compensated by rapid vertical growth of the reef. Subsequently, the subsidence rate decreased to an average value of 0.019 ± 0.003 mm/yr from 20 to 15 Ma. The decrease in the rate of bottom subsidence coincided with unfavorable environmental conditions for coral reef development, leading to the disappearance of corals. The average subsidence rate has been 0.015 ± 0.002 mm/yr since 15 Ma, comparable to the present-day subsidence rate. We also analyzed the stable Sr isotope ratios (δ88/86Sr) of warm-water coral samples formed at 25–20 Ma (0.32‰ ± 0.1‰), as well as carbonate of large benthic foraminifera, coralline algae, and other non-coral species for the period 20–15 Ma (0.10‰ ± 0.09‰). We suggest that the large difference in carbonate δ88/86Sr between 25–20 and 20–15 Ma corresponds to a difference in the fractionation factor caused by environmental and benthic community change.

A remote coral reef shows macroalgal succession following a mass bleaching event

Coral reefs worldwide are exposed to increased levels of thermal stress due to global warming. A coral reef at the remote island of Kapou (Lisianski) in Papahānaumokuākea experienced an unprecedented level of heat stress in 2014, which resulted in coral bleaching and subsequent mass mortality that resulted in nearly 100 % loss of live coral cover. Here, we describe successional changes in benthic communities occurring on the reef from 2014 to 2021 based on our surveys utilizing underwater photogrammetric techniques. Despite having > 85 % Montipora live coral cover before the bleaching event, the newly available substrata created by the loss of coral were quickly colonized by the green macroalga Halimeda, along with an ephemeral bloom of the green macroalga Boodlea in 2016. While Halimeda continued to increase in benthic cover, other algae (Neomeris, Asparagopsis and unidentified filamentous red and green algae) also started colonizing the reef between 2017 and 2021. Erosion of the reef substrata was evident in both in-situ and three-dimensional surveys in 2015 following the bleaching event and has continued to progress through time. The high abundance of Halimeda may indicate a slow process of coral recovery, but the overall benthic diversity increased in 2021 due to the presence of other algae and an increase in hard substrata and turf algal cover. New colonies of Montipora coral were also observed during annual surveys following the bleaching-induced mortality. Future monitoring efforts should continue to track coral and algal communities and survey herbivorous fish and reef binders that play important ecological roles in algal control, reef erosion and sediment binding. Such efforts should reveal interactions among these different ecological processes that enable reef succession following mass coral mortality.

Small Hydropower—Small Ecological Footprint? A Multi-Annual Environmental Impact Analysis Using Aquatic Macroinvertebrates as Bioindicators. Part 1: Effects on Community Structure

The increasing incentives stemming from many international initiatives that target sustainable energy production have led to the global success of small hydropower plants. However, there is a growing debate about the actual environmental impact these structures have on riverine ecosystems, to the extent that some researchers argue that they could have a proportionally greater impact than large hydropower plants; nevertheless, an empirical evaluation applying a long-term true “Before-After-Control-Impact (BACI)” approach has never been conducted. In a true “BACI” experiment applying generalized linear mixed models, we assessed changes in benthic macroinvertebrate communities—taxonomic composition, spatial and temporal β-diversity, and possible indicator taxa—along 6 sites located in a glacier-fed stream in the Italian Alps before and after the installation of a small “run-of-river” hydropower plant. The “BACI” results over the 5-year study showed no significant variation in the benthic macroinvertebrate communities stemming from the activity of the hydropower plant. Moreover, spatial β-diversity showed, in relation to the “control” site, a constant dissimilarity pattern throughout all the sampling years, exhibiting a constant increase proceeding downstream. On the other hand, temporal β-diversity showed changes in the benthic macroinvertebrate communities, but these changes were largely caused by variation in densities and not by the appearance or disappearance of new taxa. In summary, we were unable to detect a significant impact of the small “run-of-river” hydropower plant on the benthic macroinvertebrate communities of the glacier-fed stream under study. Despite the need of further studies that consider the different features and operational measures of small hydropower plants, our findings illustrate that, when correctly managed, small hydropower plants and the energy they produce may represent an added resource for strategic debates on energy planning processes, especially in light of the commitments at the international level of many countries in developing strategies toward a “carbon-neutral” energy sector.

Santonian deep sea benthic foraminifera from IODP Site U1513, Mentelle Basin (SW Australia): Reactions of benthic foraminiferal assemblages to surface water cooling at southern high latitudes

International Ocean Discovery Program (IODP) Expedition 369 recovered a stratigraphically complete, Santonian-aged, pelagic sedimentary sequence at Site U1513 on the Naturaliste Plateau (33°47.6084′S, 112°29.1338′E) at ~2800 m water depth. The site was located at ~60°S paleolatitude in Cretaceous times. A total of 59 samples studied from Holes 1513A and 1513B yielded 140 calcareous and nine agglutinated benthic foraminiferal taxa. Gavelinellids (Notoplanulina, Gavelinella, Anomalinoides) and Gyroidinoides spp., are the most abundant taxa overall and also dominate most samples. We also report 382 foraminiferal stable isotopic measurements and infer cooling [of ~5 °C in surface waters and 2 °C at the seafloor] based on changes in δ18O values for benthic and planktonic taxa through the Santonian at Site U1513. Inferred cooling was accompanied by changes in planktonic and benthic foraminiferal assemblages. At Site U1513, benthic foraminiferal taxonomic richness declines by 15 species (from 20– 25 to 5–10 taxa) towards the upper Santonian. Within this interval, epifaunal, oxic foraminifera diminish in absolute and relative abundance, and there is a parallel relative increase in opportunistic taxa and infaunal foraminifera. Changes in benthic foraminiferal communities indicate a shift from oligotrophic to eutrophic conditions in the bottom water despite the general cooling trend. This paper explores the causes and effects of the paleoenvironmental changes in the bottom waters.