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1. Spatial distribution, diversity, and taphonomy of clypeasteroid and spatangoid echinoids of the central Florida Keys

   https://doi.org/10.7717/peerj.14245  

   Grun, Tobias B.; Kowalewski, Michał (January 2022, PeerJ)

   Background Irregular echinoids are ecosystem engineers with diverse functional services. Documenting present-day distribution of those widespread organisms is important for understanding their ecological significance and enhancing our ability to interpret their rich fossil record. Methods This study summarizes SCUBA surveys of clypeasteroid and spatangoid echinoids conducted in 2020 and 2021 along the central part of the Florida Keys. The survey included observations on both live and dead specimens, their distribution, habitat preferences, abundance, and live-dead comparison. Results Echinoids were found at 17 out of 27 examined sites (63%) and occurred across a wide range of habitats including coastal seagrass meadows, subtidal sand and seagrass settings of the Hawk Channel, backreef sands, and fine muddy sands of deeper forereef habitats. The encountered species, both dead and alive, included Clypeaster rosaceus (four sites), Clypeaster subdepressus (five sites), Encope michelini (three sites), Leodia sexiesperforata (eight sites), Meoma ventricosa (nine sites), and Plagiobrissus grandis (four sites). All sites were dominated by one species, but some sites included up to five echinoid species. Live-dead fidelity was high, including a good agreement in species composition of living and dead assemblages, congruence in species rank abundance, and overlapping spatial distribution patterns. This high fidelity may either reflect long-term persistence of local echinoid populations or fragility of echinoid tests that could prevent post-mortem transport and the formation of time-averaged death assemblages. Regardless of causative factors, the live-dead comparisons suggest that irregular echinoid assemblages, from settings that are comparable to the study area, may provide a fossil record with a high spatial and compositional fidelity. The survey of live fauna is consistent with past regional surveys in terms of identity of observed species, their rank abundance, and their spatial distribution patterns. The results suggest that despite increasingly frequent hurricanes, active seasonal fisheries, massive tourism, and urban development, irregular echinoids continue to thrive across a wide range of habitats where they provide diverse ecosystem services by oxygenating sediments, recycling organic matter, supporting commensal organisms, and providing food to predators. Results reported here document the present-day status of local echinoid populations and should serve as a useful reference point for assessing future regional changes in echinoid distribution and abundance. 

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2. An asynchronous Mesozoic marine revolution: the Cenozoic intensification of predation on echinoids

   https://doi.org/10.1098/rspb.2021.0400  

   Petsios, Elizabeth; Portell, Roger W.; Farrar, Lyndsey; Tennakoon, Shamindri; Grun, Tobias B.; Kowalewski, Michal; Tyler, Carrie L. (March 2021, Proceedings of the Royal Society B: Biological Sciences)

   Predation traces found on fossilized prey remains can be used to quantify the evolutionary history of biotic interactions. Fossil mollusc shells bearing these types of traces provided key evidence for the rise of predation during the Mesozoic marine revolution (MMR), an event thought to have reorganized global marine ecosystems. However, predation pressure on prey groups other than molluscs has not been explored adequately. Consequently, the ubiquity, tempo and synchronicity of the MMR cannot be thoroughly assessed. Here, we expand the evolutionary record of biotic interactions by compiling and analysing a new comprehensively collected database on drilling predation in Meso-Cenozoic echinoids. Trends in drilling frequency reveal an Eocene rise in drilling predation that postdated echinoid infaunalization and the rise in mollusc-targeted drilling (an iconic MMR event) by approximately 100 Myr. The temporal lag between echinoid infaunalization and the rise in drilling frequencies suggests that the Eocene upsurge in predation did not elicit a coevolutionary or escalatory response. This is consistent with rarity of fossil samples that record high frequency of drilling predation and scarcity of fossil prey recording failed predation events. These results suggest that predation intensification associated with the MMR was asynchronous across marine invertebrate taxa and represented a long and complex process that consisted of multiple uncoordinated steps probably with variable coevolutionary responses. 

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3. Mapping Past Distributions of Marine Mollusks Using Shell Death Assemblages

   https://doi.org/10.58782/flmnh.cpmy8278  

   Herbert, Gregory S; Kramer, Andrew M; Geiger, Stephen P; Jimenez_Bustos, Ana; Sanders, Stephanie A; Seiden, Nicole; Rogers, Jaime A (February 2023, Bulletin of the Florida Museum of Natural History)

   Marine species assessments rely heavily on baseline surveys conducted after the 1960s, long after many anthropogenic pressures began, which could lead to misinformed management decisions and poor conservation outcomes. In this study, we collaborated with Florida Fish and Wildlife to conduct stock assessments for mollusks of the west Florida shelf that incorporate shell death assemblages. One of our first assessments was of the Florida Fighting Conch, Strombus alatus, an abundant gastropod that is also under consideration as a replacement fishery for the threatened Queen Conch. Live and dead shells were collected from >300 dredge tows between 2008-2018 covering the entire west Florida shelf. Shells were age-partitioned by 14C- and AAR-calibrated taphonomic criteria. Counts were converted to densities per m2. Inverse distance weighting interpolation of S. alatus death assemblages reveals multiple population centers along the coast and a rapid decrease in density with depth from 25-120 m. In contrast, live conchs were absent in our dredge samples from shelf depths deeper than 40 m. These differences are confirmed by single-visit occupancy methods that account for variation in detectability across the samples. Live-dead differences in spatial distribution are probably influenced by time averaging in death assemblages, which increases detectability of conchs in deeper habitats, where they may be too rare to be sampled alive. However, extirpation of offshore populations was also indicated by independent natural history collection occurrence records, which show numerous live-collected conchs from 1940-1980 but none afterwards, despite an increase in sampling effort. These results suggest that live-dead comparisons can reveal biodiversity loss at the scale of large marine ecosystems. 

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4. Trace elements in mollusc shells and benthic foraminifera

   Brooks, HL; Cruz-Uribe, AM; Stone, JS (May 2019, North American Workshop on Laser Ablation 2019 Abstracts)

   Throughout the course of an organism’s life, the chemical signatures of environment, food consumption, and weather are recorded into their carbonate structures; these signatures can be directly linked to a time-resolved lifespan. Here we present trace element data from benthic foraminifera and tropical molluscs determined using an ESI NWR193UC excimer laser coupled with an Agilent 8900 triple quadrupole mass spectrometer in the MicroAnalytical Geochemistry and Isotope Characterization (MAGIC) Laboratory at the University of Maine. Benthic foraminifera are protists that live on the sea floor and produce calcite shells, progressively adding chambers. Changes in Mg/Ca in foraminifera are used as a proxy for ocean temperature. Laser ablation ICP-MS data for 18 trace elements were collected in individual growth chambers in foraminifera of the genus Uvigerina from the Bay of Plenty. Line scans were performed within thin (~10 µm) chamber walls using a spot size of 8 µm, beam energy density of 3 J/cm2, repetition rate of 12 Hz, and scan speeds of 2-3 µm/s. Concentrations were determined relative to the NIST610 glass. Ratios of Mg/Ca and other trace elements record the same range of values as those determined via bulk wet chemistry analysis of ~10 foraminifera for a given population, which suggests that LA-ICP-MS may be a viable alternative to wet chemistry. Trace element data were collected across shells of the warm-tropical mollusc species Chione subrugosa from the Ostra Base Camp area, Peru (78°37’22”W, 8°54’46”S). Previous studies of the area have suggested that a large climate transition occurred, transforming a warm water tropical bay into a desert surrounded by a coastal stand with cool waters. This area was occupied by humans at 6250-5450 radiocarbon years BP. This study examines Chione subrugosa, which were found in the living position at the fossilized Ostra Beach and are thought to have been the final living warm-tropical molluscs in the bay. Studies of modern molluscs have revealed that molluscs record massive climatic changes, such as El Niño, in their chemistry. Laser ablation provides a unique opportunity to examine chemical changes directly related to the changing coastal environment. Line scans transverse growth bands along the length of the shell, providing a high resolution record of daily variation in trace element chemistry over the lifespan of the mollusc. Eleven elements were analysed with a beam energy density of 2.4 J/cm2, repetition rate of 15 Hz, spot size of 5 x 25 µm, and a scan speed of 5 µm/s. Preliminary data suggest the preservation of yearly oscillations in trace elements, with high concentrations of La, Ce, U, and Pb during early shell growth. Continued study will examine catastrophic mollusc life events in an effort to link these with environmental climate changes over daily timescales. 

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5. Death Assemblages Record Significant Range Contraction in a Molluscan Species of Concern from the Eastern Gulf of Mexico

   https://doi.org/10.58782/flmnh.gxlr7897  

   Sanders, Stephanie A; Herbert, Gregory S; Trobbiani, Gastón; Seiden, Nicole; Rogers, Jaime A (February 2023, Bulletin of the Florida Museum of Natural History)

   Marine habitats are in decline due to increasing anthropogenic pressures, but baseline data on species distributions needed to manage and conserve populations are lacking. Incorporating death assemblages into species assessments can create a more accurate understanding of pre-anthropogenic communities than survey records alone. In this study, we conducted a live-dead analysis on mollusks from a new 2008-2018 dredge survey in the eastern Gulf of Mexico. We selected the predatory banded tulip snail, Cinctura hunteria, as a test case for assessment because this species is one of several designated by the Florida Fish and Wildlife as a species of concern. Using spatial count data for shells in our samples, we estimated density values for each taxonomic grade over the sampled area using IDW spatial interpolation. These maps reveal large areas of occupation across the west Florida shelf for two taxonomic grades of dead shells but loss of offshore occurrence for live records. One explanation for the lack of occurrences in offshore habitats is that, unlike dead shell records, there is no time averaging accumulation of live shells. Time averaging increases detectability of species in habitats where they are rare. However, independent fisheries data from live-only animal surveys not only mirror our live-dead results but suggest that habitat loss in our live-dead comparisons was rapid and occurred in the late 1980s or early 1990s. Thus, live-dead comparisons reveal both natural baselines as well as anthropogenic changes in distribution without being significantly distorted by time-averaging biases. Including live-dead data can greatly improve species assessments when long-term survey records are unavailable and provide a key tool in combatting biodiversity loss across marine ecosystems. 

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