Microboring
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Recent papers in Microboring
The study of microbial fossils involves a broad array of disciplines and covers a vast diversity of topics, of which we review a select few, summarizing the state of the art. Microbes are found as body fossils preserved in different modes... more
The study of microbial fossils involves a broad array of disciplines and covers a vast diversity of topics, of which we review a select few, summarizing the state of the art. Microbes are found as body fossils preserved in different modes and have also produced recognizable structures in the rock record (microbialites, microborings). Study of the microbial fossil record and controversies arising from it have provided the impetus for the assembly and refining of powerful sets of criteria for recognition of bona fide microbial fossils. Different types of fossil evidence concur in demonstrating that microbial life was present in the Archean, close to 3.5 billion years ago. Early eukaryotes also fall within the microbial realm and criteria developed for their recognition date the oldest unequivocal evidence close to 2.0 billion years ago (Paleoproterozoic), but Archean microfossils >3 billion years old are strong contenders for earliest eukaryotes. In another dimension of their contribution to the fossil record, microbes play ubiquitous roles in fossil preservation, from facilitating authigenic mineralization to replicating soft tissue with extracellular polymeric substances, forming biofilms that inhibit decay of biological material, or stabilizing sediment interfaces. Finally, studies of the microbial fossil record are relevant to profound, perennial questions that have puzzled humanity and science—they provide the only direct window onto the beginnings and early evolution of life; and the methods and criteria developed for recognizing ancient, inconspicuous traces of life have yielded an approach directly applicable to the search for traces of life on other worlds.
The study of bioerosion, a widespread process greatly impacting reef biodiversity, structural complexity, and sediment production, has largely focused on shallow-water reefs with no review of this process in deeper environments. In this... more
The study of bioerosion, a widespread process greatly impacting reef biodiversity, structural complexity, and sediment production, has largely focused on shallow-water reefs with no review of this process in deeper environments. In this first synthesis of bioerosion literature for mesophotic reefs (subtropical and tropical ecosystems in low-light conditions at depths of ~30 to 150 m), we show that the distribution of key bioeroder taxa, their abundances , and overall bioerosion rates are considerably different on mesophotic reefs compared to their shallow-water counterparts. In particular, carbonate grazing and photo-trophic microboring rates decline with depth from shallow to mesophotic reefs. In the absence of significant erosive action by grazers, sponges are hypothesized as the primary long-term bioeroders on lower mesophotic reefs (60-150 m) and possibly on some upper mesophotic reefs (30-60 m). Given these factors, we postulate that meso-photic reef substrates experience slower bioerosion rates and lose less carbonate than shallower reefs over the same timeframe. This likely stems from differences in photo-synthetically active radiation and other factors such as temperature, sedimentation, bioeroder food abundance and quality, substrate characteristics, and exposure time for bioerosion. There is a critical need to document meso-photic bioeroders via taxonomic inventories, as well as quantify their bioerosion rates across mesophotic depths in terms of specific bioeroder guilds using experimental substrates. These data will aid management efforts to maintain positive net carbonate budgets on mesophotic reefs, ensuring that sufficient three-dimensional structure is available to support biodiversity at mesophotic depths.
A process-based carbonate budget was used to compare carbonate framework production at two reef sites subject to varying degrees of fluvial influence in Rio Bueno, Jamaica. The turbid, central embayment was subjected to high rates of... more
A process-based carbonate budget was used to compare carbonate framework production at two reef sites subject to varying degrees of fluvial influence in Rio Bueno, Jamaica. The turbid, central embayment was subjected to high rates of fluvial sediment input, framework accretion was restricted to ≤30 m, and net carbonate production was 1,887 g CaCO3 m−2 year−1. Gross carbonate production (GCP) was dominated by scleractinians (97%), particularly by sediment-resistant species, e.g. Diploria strigosa on the reef flat (<2 m). Calcareous encrusters contributed very little carbonate. Total bioerosion removed 265 g CaCO3 m−2 year−1 and was dominated by microborers. At the clear-water site, net carbonate production was 1,236 g CaCO3 m−2 year−1; the most productive zone was on the fore-reef (10 m). Corals accounted for 82% of GCP, and encrusting organisms 16%. Bioerosion removed 126 g CaCO3 m−2 year−1 and was dominated by macroborers. Total fish and urchin grazing was limited throughout (≤20 g CaCO3 m−2 year−1). The study demonstrates that: (1) carbonate production and net reef accretion can occur where environmental conditions approach or exceed perceived threshold levels for coral survival; and (2) although live coral cover (and carbonate production rates) were reduced on reef-front sites along the North Jamaican coast, low population densities of grazing fish and echinoids to some extent offset this, thus maintaining positive carbonate budgets.
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