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1. Global community breaks at 60 m on mesophotic coral reefs

   https://doi.org/10.1111/geb.12940  

   Lesser, Michael P. ; Slattery, Marc ; Laverick, Jack H. ; Macartney, Keir J. ; Bridge, Tom C. ; Pandolfi, ed., John ( June 2019 , Global Ecology and Biogeography)

   Mesophotic coral ecosystems (MCEs) are unique communities that support a high proportion of depth‐endemic species distinct from shallow‐water coral reefs. However, there is currently little consensus on the boundaries between shallow and mesophotic coral reefs and between upper versus lower MCEs because studies of these communities are often site specific. Here, we examine the ecological evidence for community breaks, defined here as species loss, in fish and benthic taxa between shallow reefs and MCEs globally.

   Global MCEs.

   1973–2017.

   Macrophytes, Porifera, Scleractinia, Hydrozoa, Octocorallia, Antipatharia and teleost fishes.

   We used random‐effects models and breakpoint analyses on presence/absence data to identify regions of higher than expected species loss along a depth gradient of 1–69 m, based on a meta‐analysis of 26 studies spanning diverse photoautotrophic and heterotrophic taxa. We then investigated the extent to which points of high faunal turnover can be explained by environmental factors, including light, temperature and nutrient availability.

   We found evidence for a community break, indicated by a significant loss of shallow‐water taxa, at ~ 60 m across several taxonomically and functionally diverse benthic groups and geographical regions. The breakpoint in benthic composition is best explained by decreasing light, which is correlated with the optical depths between 10 and 1% of surface irradiance. A concurrent shift in the availability of nutrients, both dissolved and particulate organic matter, and a shift from photoautotroph to heterotroph‐dominated assemblages also occurs at ~ 60 m depth.

   We found evidence for global community breaks across multiple benthic taxa at ~ 60 m depth, indicative of distinct community transitions between shallow and mesophotic coral ecosystems. Changes in the underwater light environment and the availability of trophic resources along the depth gradient are the most parsimonious explanations for the observed patterns.

    

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2. Geological age and environments shape reef habitat structure

   https://doi.org/10.1111/geb.13691  

   Asbury, Mollie ; Schiettekatte, Nina M. D. ; Couch, Courtney S. ; Oliver, Thomas ; Burns, John H. R. ; Madin, Joshua S. ( April 2023 , Global Ecology and Biogeography)

   Habitat complexity plays an important role in the structure and function of ecosystems worldwide. On coral reefs, habitat complexity influences ecosystem services such as harvestable fish biomass and attenuation of wave energy. Here, we test how three descriptors of surface complexity—rugosity, fractal dimension, and height range—trend with the geological age of reefs (0.2–5.1 million years old), depth (1–25 m), wave exposure (1–306 kW/m), coral cover (0–80%), and three habitat types (aggregated reef, rock and boulder, and pavement).

   We surveyed across 234 sites and 4 degrees of latitude in the eight main Hawaiian Islands.

   April 2019 – July 2019.

   Reef building corals.

   We estimate three surface descriptors (rugosity, fractal dimension and height range) using structure‐from‐motion photogrammetry. We evaluate hypothesized relationships between these descriptors and geological reef age, depth, wave exposure, coral cover and reef habitat type using generalized linear models that account for survey design.

   The rugosity of reef habitats decreased with geological reef age; fractal dimension (and coral cover) decreased with wave exposure; and height range decreased with depth. Variations in these patterns were explained by the different habitat types and the way they are formed over time. Nonetheless, the three surface descriptors were geometrically constrained across all habitat types, and so habitats occupied distinctly different regions of habitat complexity space.

   This study showed how broad environmental characteristics influence the structural complexity of habitats, and therefore geodiversity, which is an important first step toward understanding the communities supported by these habitats and their ecosystem services.

    

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3. To what extent do mesophotic coral ecosystems and shallow reefs share species of conservation interest? A systematic review

   Laverick, J.H. Piango ( January 2018 , Environmental evidence)

   Abstract Background: Globally, shallow-water coral reef biodiversity is at risk from a variety of threats, some of which may attenuate with depth. Mesophotic coral ecosystems (MCEs), occurring from 30 to 40 m and deeper in tropical locations, have been subject to a surge of research this century. Though a number of valuable narrative reviews exist, a systematic quantitative synthesis of published MCE studies is lacking. We conducted a systematic review to collate mesophotic research, including studies from the twentieth century to the present. We highlight current biases in research effort, regarding locations and subject matter, and suggest where more attention may be particularly valuable. Following a notable number of studies considering the potential for mesophotic reefs to act as refuges, it is important to know how comprehensive these sources of recruits and organisms capable of moving to shallow water reefs may be. Methods: We search seven sources of bibliographic data with two search strings, as well as personal libraries. Articles were included if they contained species presence data from both shallower and deeper than 30 m depth on tropical coral reefs. Studies were critically appraised based on the number of species identified and balanced sampling effort with depth. Maximum and minimum depths per species were extracted from each study, along with study region and taxon. We quantified the degree of community overlap between shallow tropical reefs (< 30 m) and reefs surveyed at the same locations below 30 m. Proportions of shallow species, across all studied taxa, observed deeper than 30 m were used to generate log odds ratios and passed to a mixed-effects model. Study location and taxon were included as effect modifiers. Funnel plots, regression tests, fail safe numbers, and analysis of a high validity subgroup contributed to sensitivity analyses and tests of bias. Results: Across all studies synthesised we found two-thirds of shallow species were present on mesophotic reefs. Further analysis by taxon and broad locations show that this pattern is influenced geographically and taxonomically. Community overlap was estimated as low as 26% and as high as 97% for some cases. Conclusions: There is clear support for the hypothesis that protecting mesophotic reefs will also help to conserve shallow water species. At the same time, it is important to note that this study does not address mesophotic-specialist communities, or the ecological forces which would permit refuge dynamics. As we limit our analysis to species only present above 30 m it is also possible diversity found exclusively deeper than 30 m warrants protection in its own right. Further research into relatively ignored taxa and geographic regions will help improve the design of protected areas in future. Keywords: Depth, Community structure, Biodiversity, Coral reefs, Twilight zone, Refuge 

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4. Coastal squeeze on temperate reefs: Long‐term shifts in salinity, water quality, and oyster‐associated communities

   https://doi.org/10.1002/eap.2609  

   Tice‐Lewis, Maxwell ; Zhang, Y. Stacy ; Redding, S. Gray ; Lindquist, Niels L. ; Rodriguez, Antonio B. ; Fieseler, Clare M. ; Walker, Quentin A. ; Fodrie, F. Joel ( July 2022 , Ecological Applications)

   Foundation species, such as mangroves, saltmarshes, kelps, seagrasses, and oysters, thrive within suitable environmental envelopes as narrow ribbons along the land–sea margin. Therefore, these habitat‐forming species and resident fauna are sensitive to modified environmental gradients. For oysters, many estuaries impacted by sea‐level rise, channelization, and municipal infrastructure are experiencing saltwater intrusion and water‐quality degradation that may alter reef distributions, functions, and services. To explore decadal‐scale oyster–reef community patterns across a temperate estuary in response to environmental change, we resampled reefs in the Newport River Estuary (NRE) during 2013–2015 that had previously been studied during 1955–1956. We also coalesced historical NRE reef distribution (1880s–2015), salinity (1913–2015), and water‐quality‐driven shellfish closure boundary (1970s–2015) data to document environmental trends that could influence reef ecology and service delivery. Over the last 60–120 years, the entire NRE has shifted toward higher salinities. Consequently, oyster–reef communities have become less distinct across the estuary, manifest by 20%–27% lower species turnover and decreased faunal richness among NRE reefs in the 2010s relative to the 1950s. During the 2010s, NRE oyster–reef communities tended to cluster around a euhaline, intertidal‐reef type more so than during the 1950s. This followed faunal expansions farther up estuary and biological degradation of subtidal reefs as NRE conditions became more marine and favorable for aggressive, reef‐destroying taxa. In addition to these biological shifts, the area of suitable bottom on which subtidal reefs persist (contracting due to up‐estuary intrusion of marine waters) and support human harvest (driven by water quality, eroding from up‐estuary) has decreased by >75% since the natural history of NRE reefs was first explored. This “coastal squeeze” on harvestable subtidal oysters (reduced from a 4.5‐km to a 0.75‐km envelope along the NRE's main axis) will likely have consequences regarding the economic incentives for future oyster conservation, as well as the suite of services delivered by remaining shellfish reefs (e.g., biodiversity maintenance, seafood supply). More broadly, these findings exemplify how “squeeze” may be a pervasive concern for biogenic habitats along terrestrial or marine ecotones during an era of intense global change.

    

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5. Sea‐surface temperature anomalies mediate changes in fish richness and abundance in Atlantic and Gulf of Mexico estuaries

   https://doi.org/10.1111/jbi.14451  

   Oke, Tobi A. ; Zhang, Stacy Y. ; Keyser, Spencer R. ; Yeager, Lauren A. ( July 2022 , Journal of Biogeography)

   Anthropogenic warming of marine systems has caused biological and physiological responses that are fundamentally altering ecosystem structure. Because estuaries exist at the land‐ocean interface, they are particularly vulnerable to the effects of ocean warming as they can undergo rapid biogeochemical and hydrological shifts due to climate and land‐use change. We explored how multiple components of estuarine fish diversity—turnover, richness, and abundance—have changed in the North Atlantic and Gulf of Mexico estuaries across space and time and the drivers of change.

   North Atlantic and Gulf of Mexico.

   Fish.

   We compiled long‐term (>30 years), continent‐wide fisheries independent trawl surveys conducted in estuaries—from the Gulf of Maine to the Gulf of Mexico (U.S. waters)—and combined these with climate and land‐use‐land‐cover data to examine trends and ecological drivers of fish richness, abundance and turnover using mixed‐effect models.

   Species richness, abundance and turnover have increased in North Atlantic and Gulf of Mexico estuaries in the last 30 years. These changes were mediated largely by sea‐surface temperature anomalies, especially in more northern estuaries where warming has been relatively pronounced.

   The increasing trajectory of turnover in many estuaries suggests that fish communities have changed fundamentally from the baselines. A fundamental change in community composition can lead to an irreversible trophic imbalance or alternative stable states among other outcomes. Thus, predicting how shifting community structures might influence food webs, ecosystem stability, and human resource use remain a pertinent task.

    

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