Reproduction, energy storage and metabolic requirements in a mesophotic population of the gorgonian Paramuricea macrospina

Phosphorus addition mitigates the combined negative effects of high temperature and nitrogen stress on corals

Global warming and imbalances in nitrogen (N)-phosphorus (P) ratios due to increased human activity have had significant impacts on coral reef ecosystems. However, the underlying mechanisms of these impacts remain poorly understood. In this study, a controlled experiment was conducted on Acropora hyacinthus treated with different P concentrations at high temperature (30 °C) and high N level (9 μM nitrate), which was analyzed in terms of physical observations and physiological indices, as well as photosynthetic activity and fatty acid composition. The results indicated that nitrate enrichment significantly reduced Symbiodiniaceae density, total chlorophyll content, and photosynthetic efficiency, as well as notable coral bleaching. P addition alleviated some of these detrimental effects, enhancing symbiotic relationship and maintaining photosynthetic activity. Additionally, changes in fatty acid composition suggest that P supplementation may improve coral tolerance to the combined stress of heat stress and nitrate enrichment by enhancing coral heterotrophy. These findings underscore the importance of balanced nutrient ratio for corals and propose P supplementation as a potential strategy to mitigate the combined stress on coral reefs.

The Octocoral Trait Database: a global database of trait information for octocoral species

Trait-based approaches are revolutionizing our understanding of high-diversity ecosystems by providing insights into the principles underlying key ecological processes, such as community assembly, species distribution, resilience, and the relationship between biodiversity and ecosystem functioning. In 2016, the Coral Trait Database advanced coral reef science by centralizing trait information for stony corals (i.e., Subphylum Anthozoa, Class Hexacorallia, Order Scleractinia). However, the absence of trait data for soft corals, gorgonians, and sea pens (i.e., Class Octocorallia) limits our understanding of ecosystems where these organisms are significant members and play pivotal roles. To address this gap, we introduce the Octocoral Trait Database, a global, open-source database of curated trait data for octocorals. This database houses species- and individual-level data, complemented by contextual information that provides a relevant framework for analyses. The inaugural dataset, OctocoralTraits v2.2, contains over 97,500 global trait observations across 98 traits and over 3,500 species. The database aims to evolve into a steadily growing, community-led resource that advances future marine science, with a particular emphasis on coral reef research.

Synergistic/antagonistic effects of nitrate/ammonium enrichment on fatty acid biosynthesis and translocation in coral under heat stress

Superimposed on ocean warming, nitrogen enrichment caused by human activity puts corals under even greater pressure. Biosynthesis of fatty acids (FA) is crucial for coral holobiont survival. However, the responses of FA biosynthesis pathways to nitrogen enrichment under heat stress in coral hosts and Symbiodiniaceae remain unknown, as do FA translocation mechanisms in corals. Herein, we used the thermosensitive coral species Acropora hyacinthus to investigate changes in FA biosynthesis pathways and polyunsaturated FA translocation of coral hosts and Symbiodiniaceae with respect to nitrate and ammonium enrichment under heat stress. Heat stress promoted pro-inflammatory FA biosynthesis in coral hosts and inhibited FA biosynthesis in Symbiodiniaceae. Nitrate enrichment inhibited anti-inflammatory FA biosynthesis in Symbiodiniaceae, and promoted pro-inflammatory FA biosynthesis in coral hosts and translocation to Symbiodiniaceae, leading to bleaching after 14 days of culture. Intriguingly, ammonium enrichment promoted anti-inflammatory FA biosynthesis in Symbiodiniaceae and translocation to hosts, allowing corals to better endure heat stress. We constructed schematic diagrams of the shift in FA biosynthesis and translocation in and between A. hyacinthus and its Symbiodiniaceae under heat stress, heat and nitrate co-stress, and heat and ammonium co-stress. The findings provide insight into the mechanisms of coral bleaching under environmental stress from a fatty acid perspective.

Shallow-emerged coral may warn of deep-sea coral response to thermal stress

In the Gulf of Alaska, commercially harvested fish species utilize habitats dominated by red tree corals (Primnoa pacifica) for shelter, feeding, and nurseries, but recent studies hint that environmental conditions may be interrupting the reproductive lifecycle of the corals. The North Pacific has experienced persistent and extreme thermal variability in recent years and this pattern is predicted to continue in coming decades. Recent discovery of deep-water emerged coral populations in Southeast Alaska fjords provided opportunity for detailed life-history studies and comparison to corals in managed habitats on the continental shelf. Here we show that sperm from deep colonies develops completely, but in shallow colonies, sperm development is prematurely halted, likely preventing successful production of larvae. We hypothesize that the divergence is due to differing temperature regimes presently experienced by the corals. Compared to deep populations below the thermocline, shallow populations experience much greater seasonal thermal variability and annual pulses of suspected near-lethal temperatures that appear to interrupt the production of viable gametes. The unique opportunity to comprehensively study emerged populations presently affected by thermal stress provides advance warning of the possible fate of deep corals in the Gulf of Alaska that will soon experience similar ocean conditions.