Coral photosymbiosis on Mid-Devonian reefs.

The ability of stony corals to thrive in the oligotrophic (low-nutrient, low-productivity) surface waters of the tropical ocean is commonly attributed to their symbiotic relationship with photosynthetic dinoflagellates. The evolutionary history of this symbiosis might clarify its organismal and environmental roles, but its prevalence through time, and across taxa, morphologies and oceanic settings, is currently unclear. Here we report measurements of the nitrogen isotope (N/N) ratio of coral-bound organic matter (CB-δN) in samples from Mid-Devonian reefs (Givetian, around 385 million years ago), which represent a constraint on the evolution of coral photosymbiosis.

Severe cold-water bleaching of a deep-water reef underscores future challenges for Mesophotic Coral Ecosystems.

Elevated sea surface temperatures are causing an increase in coral bleaching events worldwide, and represent an existential threat to coral reefs. Early studies of Mesophotic Coral Ecosystems (MCEs) highlighted their potential as thermal refuges for shallow-water coral species in the face of predicted 21 century warming. However, recent genetic evidence implies that limited ecological connectivity between shallow- and deep-water coral communities inhibits their effectiveness as refugia; instead MCEs host distinct endemic communities that are ecologically significant in and of themselves.

Analytical improvements and assessment of long-term performance of the oxidation-denitrifier method.

Unlabelled: The analysis of the nitrogen (N) isotopic composition of organic matter bound to fossil biomineral structures (BB-δ N) using the oxidation-denitrifier (O-D) method provides a novel tool to study past changes in N cycling processes.

Methods: We report a set of methodological improvements to the O-D method, including (a) a method for sealing the reaction vials in which the oxidation of organic N to NO takes place, (b) a recipe for bypassing the pH adjustment step before the bacterial conversion of NO to N O, and (c) a method for storing recrystallized dipotassium peroxodisulfate (K S O ) under Ar atmosphere.

Results: The new sealing method eliminates the occasional contamination and vial breakage that occurred previously while increasing sample throughput.

Coral carbonate-bound isotopes reveal monsoonal influence on nitrogen sources in Southeastern China's Greater Bay Area from the mid-Holocene until the Anthropocene.

Most anthropogenic nitrogen (N) reaches coastal waters via rivers carrying increasing loads of sewage, fertilizer, and sediments. To understand anthropogenic N impacts, we need to understand historical N-dynamics before human influence. Stable isotope ratios of N preserved in carbonates are one way to create temporal N records.