1,720,999 research outputs found
Examining the successional role of a pioneer species on post-disturbance coral reefs: Are they facilitators or short-term competitive dominants?
Full text linkAs coral reefs decline globally, there is an urgent need to understand recovery pathways and trajectories to both assess reef status and intervene with reef restoration efforts. However, the ecological role of various coral taxa on reef successional pathways is poorly understood. Building on terrestrial successional frameworks, it seems logical that weedy coral species may be placeholder species that quickly colonize cleared areas after a disturbance, but that are later replaced by more competitive, slower-growing species, leading to overall more biodiverse reefs. To test the competitive ability of a common pioneer species on Pacific reefs, Montipora aequituberculata, we tracked about 600 colonies across six equatorial islands through two time points (50 colonies per site per island), examining whether this species was more typically overgrown by other species over time, or whether M. aequituberculata was a more dominant competitor capable of overgrowing other reef taxa. Using photogrammetric data, we set out to answer questions about the fates of focal colonies and their place in the competitive hierarchy. Trajectories of area change of the focal colonies varied across islands, though they did not follow geographic patterns. Many of the changes in these post-disturbance reefs sometimes differed by site, even on the same island, and were not consistent within an archipelago.
At an island scale, Howland (Phoenix Islands) and Flint (Line Islands) showed the greatest growth of focal colonies, while Enderbury (Phoenix) and Millennium (Line) lost the most coral coverage of focal colonies. Interactions between the focal colony and other coral species were more consistent across islands, with the most common interactions being with other colonies of M. aequituberculata as well as common species of Porites and Pocillopora. There was a consistent trend of focal colonies mostly being overgrown by other colonies of M. aequituberculata: this conspecific replacement suggests that this species is capable of self-perpetuating as a primary space holder in lieu of other coral interactions. In contrast, most other coral species were commonly overgrown by the focal M. aequituberculata, suggesting that M. aequituberculata is a strong competitor when vying for groundcover. Indeed, M. aequituberculata may be able to dominate reefs post-disturbance until stress-tolerant species take over. Surprisingly however, we did not see a consistent pattern of species interaction, meaning that there was not a single coral taxon that universally overgrew M. aequituberculata, suggesting that M. aequituberculata is a generalist competitor and is not a specialized facilitator of any one competitively dominant taxa. Islands with similar species interaction patterns are not the same islands with similar growth or loss patterns, suggesting that site-level ecological complexity overrules any general patterns of geography or species interactions. This study is among the first to provide detailed species interactions in a successional framework, paving the way for future studies to do the same in the hopes that we can predict the trajectory of reefs based on the community composition
Nitrogen cycling in the temperate Northern star coral, Astrangia poculata: distinguishing autotrophic from heterotrophic nutrient contributions
Full text linkCoral reefs are in a global state of decline due to coral bleaching, which is a state of dysbiosis between the coral host and its algal endosymbionts that can bring about a nutritional crisis potentially leading to mass mortality. In this study, I used a temperate coral, Astrangia poculata, to determine the effects of symbiotic state and trophic status on nitrogen acquisition. The facultatively heterotrophic nature of A. poculata allows for the decoupled analysis of host and symbiont without the induced stress of a dysbiotic event. In this study, I used δ15N labeled DIN to track the assimilation and translocation of ammonium and nitrate by fed and starved colonies of both symbiotic and aposymbiotic A. poculata. I also analyzed tissue samples for δ13C, %N, %C, and C:N. Using photosynthetic efficiency as a proxy, I analyzed changes in symbiont health before and after being treated with DIN. Stable isotope analysis suggested that corals acquire more of their nitrogen from DIN than from heterotrophy, that their symbiotic algae, Breviolum psygmophilum, are responsible for a greater amount of DIN assimilation than the host, and that ammonium is more readily assimilated than nitrate. Protein analysis was inconclusive in determining any potential advantages to symbiotic state. Photosynthetic efficiency analysis suggested that ammonium boosts symbiont activity and nitrate may adversely affect symbionts. Overall, both symbiotic state and nutritional condition influenced holobiont health, and symbionts were found to be the driving force behind nitrogen acquisition. These results suggest that dysbiosis not only inhibits corals’ mixotrophic strategy of nutrient acquisition but suggests that symbiosis has advantages across nitrogen acquisition pathways that are augmented by feeding. As such, starved, aposymbiotic corals suffer from energetic double jeopardy, and having either feeding or symbiosis alone does not fully equivocate to the energetic advantage of both
Analyzing the effects of ubiquitous urban pollutants on the metabolic physiology of a temperate coral, Astrangia poculata
Full text linkNitrogen is an essential nutrient for photosynthetic marine organisms, but it can also be an urban pollutant in coastal ecosystems due to runoff and wastewater effluent. Two forms of dissolved inorganic nitrogen (DIN), nitrate and ammonium, are readily taken up by corals and used for macromolecular synthesis, including DNA, RNA, and proteins. DIN also crosses the symbiosome, where it is an essential component of chloroplasts and other endosymbiotic organelles. However, in excess amounts, these nutrients can harm coral health, making them more susceptible to bleaching and disease. The level of DIN that triggers this shift from nutrient to pollutant remains unclear, and it is not well understood how these responses are exacerbated when coupled with urban bacterial pollutants (e.g. Escherichia coli) and temperature increases reflective of global change. Narragansett Bay (Rhode Island) is an urbanized coastal ecosystem that has a long history of anthropogenic nitrogen pollution, and is home to Astrangia poculata, a temperate scleractinian coral and emerging model species. In a 12-day multi-stressor experiment exposing A. poculata to varying levels of nitrate, ammonium, and an acute E. coli challenge, we found that A. poculata is strikingly physiologically resilient to various urban stressors. However, thermal stress (30°C) reduced A. poculata’s ability to mount a metabolic response to pathogenic E. coli regardless of nutrient input, suggesting that this multi-stressor regime may inhibit A. poculata’s immune response. As Northwest Atlantic ocean temperatures rise and coastal urban centers continue to grow, it is crucial to understand how global and local stressors interact to affect the physiology of potentially vulnerable marine organisms like A. poculata
Microplastic accumulation and impacts on eelgrass (Zostera marina L.) ecosystems throughout coastal Massachusetts, USA
Full text linkMicroplastics have been discovered ubiquitously in marine environments. While their accumulation is noted in seagrass meadows, much work is required to understand microplastic accumulation patterns and mechanisms in this ecosystem, as well as microplastic impacts on seagrass plants and their associated epiphytic and sediment communities. We pursue this effort by quantifying microplastic densities in seagrass blades, sediments, and nearby water columns across nine sites in coastal Massachusetts and exploring their relationships to morphological and anthropogenic variables. Further, we synthesize the potential impacts microplastics have on relevant seagrass plant, epiphyte, and sediment processes and functions. Microplastics were found ubiquitously at all sites regardless of proximity to anthropogenic interference, with plant epibiont density influencing their accumulation on seagrass blades, and bulk density influencing accumulation within sediments. Literature review revealed that microplastics may harm seagrass ecosystems via physical obstruction of epiphytic and plant surfaces, nutrient cycle and sediment characteristic alteration, and sediment organism ingestion, with all impacts exacerbated by seagrasses high trapping efficiency. As microplastics become a permanent and increasing member of seagrass ecosystems it will be pertinent to direct future research towards continuing to explore their impacts and patterns behind their accumulation.2023-09-28T00:00:00
Investigating patterns of deep sea coral and sponge diversity and abundance across multiple spatial scales in the Central Pacific
Full text linkThe deep sea is the largest ecosystem on the planet, comprising more than 90% of the volume that life can inhabit, yet it is the least explored biome in the world. The deep sea includes the benthos, which makes up 91.5 % of all the seafloor globally, and the water column deeper than 200 meters. It hosts a wealth of ecosystems including deep-sea vents, seamount coral gardens, abyssal plains, high-productivity whale falls, and life even in the deepest trenches. We now understand that all of these ecosystems host a variety of habitats, each with their own ecology and unique species. These ecosystems and habitats- and their associated biodiversity- provide essential ecosystem services such as carbon sequestration, nutrient regeneration, microbial processes detoxification, fisheries provisioning, and many others. However, despite the uniqueness of these ecosystems and the importance of the services they provide, we still know far less about them than we do about their shallow water and terrestrial counterparts. In this dissertation, I contribute new insights about the patterns of biodiversity in the Pacific Ocean across a large geographic area, and across a wide range of depths. To that end, in Chapter 1, I have used one of the largest ocean exploration datasets to look for patterns of the abundance and diversity across the most
common benthic invertebrate families found on Pacific seamounts: Anthozoa, Porifera, and Echinodermata across the Central and Western Pacific. In addition to quantifying the diversity and abundance of known taxa, I also documented patterns of as-of-yet unidentified taxa by region, depth, and deepwater feature (seamount shape). Building on patterns associated with seamount shape that were described in Chapter 2, I focused on the effect of seamount shape on the diversity and abundance of deep-sea coral communities in Chapter 3. The analysis presented in Chapter 3 provides strong support for the novel hypothesis that gross seamount morphology is a significant driver of community composition. In Chapter 4, I focused on a single seamount to investigate biodiversity and abundance of coral and sponge taxa on a finer spatial scale, examining the role of direction (N, S, E, W) on different flanks of a single equatorial seamount. This analysis yielded interesting consistent patterns of zonation on all sides of the seamount in terms of depth, but with differences in abundance patterns on each flank for individual taxa. Finally, in Chapter 5, I took a global perspective to investigate gaps in deepwater data, with the goal of determining what regions need further exploration to conclusively determine patterns of deep-sea biodiversity, which will be critical for determining the health of deepwater ecosystems under climate change conditions with increased exploitation pressure and cooccuring with increased conservation efforts. Merging Ocean Biogeographic Information System (OBIS) records with the largest collection of deep submergence dive records ever collected, I used proposed biogeographic provinces schema to identify areas with the least supporting data. Additionally, I coupled records from OBIS with climate change projections to identify the areas with the fewest number of biodiversity records that are likely to change the fastest under different IPCC projections. These areas of low number of records and high likelihood of change by the end of the century should become priority targets for future exploration. Taken together, this dissertation provides valuable insights and generates new hypotheses about patterns and drivers of deep-sea biodiversity, and puts forth recommendations for future research and exploration efforts
Stressed out in a changed world: investigating the strength of the temperate coral response to acute and chronic anthropogenic stress
Full text linkBoth global and local chronic environmental stressors associated with climate change and anthropogenic sources are increasing in severity, and can compromise the resilience of key marine ecosystems such as foundational coral reefs. Despite the impacts, however, there are major knowledge gaps in our understanding of direct interactive and compounding effects of multiple chronic environmental stressors on coral animals. Further, chronic stress may have sublethal, downstream impacts; for example, inhibiting the recognition and response to sudden acute stressors in the marine environment. The goal of this study was to determine the direct impacts of multiple chronic environmental stressors - elevated temperature (global), microplastic pollution, light availability, and food availability (local) - on survival and physiological performance of the emerging temperature coral model Astrangia poculata, and to determine how exposure to different chronic stressors affects their ability to deal with sudden acute stress. To achieve this, we exposed individual coral polyps to different combinations of stressors, and quantified the response of the coral host (growth) and symbiont (photosynthetic efficiency, chlorophyll a density). Coral polyps were then challenged with an acute stress near the onset, midpoint, and end of the experiment to quantify the impact of chronic environmental stress on the ability to mount a response to an acute stress. We found that the local stress of microplastic exposure had no impact on lethal or sublethal measures of the coral holobiont, while light was beneficial in maintaining coral mass. In contrast, elevated temperatures (representing global stress) reduced survival, diminished host and symbiont performance, and repressed the coral metabolic response under acute stress challenge. Feeding, however, was beneficial in preserving symbiont function, but has consequences for fitness and coral growth when presented with thermal stress, lending support to the growing hypothesis that this established mutualism shifts towards parasitism in stressful environmental conditions. Despite the magnitude of these combined stressors, over 80% of coral polyps survived, highlighting the overall resilience of A. poculata to diverse environmental challenges. These findings underline the complexity with which anthropogenic stressors interact to affect coral survivorship and resilience to future global change
Diversity of larval tuna diets across the central equatorial Pacific
No full text2025Understanding the feeding ecology of larval tuna is essential for predicting their recruitment and survival success as this directly supports the management of tuna populations across the changing ocean. To provide new insights into early-stage foraging dynamics, we investigated larval tuna gut contents collected from the Phoenix Islands Protected Area (PIPA) during its no-take period between 2016 and 2019. Using 18S sequencing, we characterized prey biodiversity, composition, and selectivity across years and tuna genera. We found that larval tunas consumed a taxonomically diverse range of zooplankton, with Katsuwonus exhibiting opportunistic foraging characterized by one or two dominant prey taxa that shifted across years, while Thunnus, despite limited sampling– consumed a broader range of prey taxa within a given year. Prey composition and selectivity varied by year and tuna genus, reflecting possible responses to shifting plankton communities and environmental conditions such as the ENSO state, as well as highlighting genus-specific trophic strategies and the potential for niche partitioning that may reduce interspecific competition for prey between tunas. This study sheds light on the ecological flexibility of larval tuna and underscores the importance of considering early-life foraging behavior in efforts to conserve and sustainably manage tuna stocks in the Western and Central Pacific Ocean, particularly in the context of marine protected areas (MPAs) and no-take zones
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
- …
