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1. Metabarcoding as a tool to examine cryptic algae in the diets of two common grazing surgeonfishes, Acanthurus triostegus and A . nigrofuscus

   https://doi.org/10.1002/edn3.206  

   Nalley, Eileen M. ; Donahue, Megan J. ; Toonen, Robert J. ( June 2021 , Environmental DNA)

   Surgeonfishes (Acanthuridae) are an important group of herbivores that are abundant on reefs globally. Acanthurids consume macroalgae that can compete with corals for space, turf algae that can proliferate on degraded reefs, and detritus that may smother adult corals or inhibit settlement. For these reasons, they are of particular interest at present to resource managers seeking to restore and conserve reefs that are facing a myriad of stressors. To contribute to our understanding of the diet breadth and potential vulnerability of these important fishes, we employed metabarcoding to identify and compare the algal diets of two common Hawaiian surgeonfishes, the convict tang or manini (Acanthurustriostegus) and the brown surgeonfish or maʻiʻiʻi (A. nigrofuscus). These species serve important biological and cultural roles in Hawaiian coral reef ecosystems, and manini, in particular, constitute an essential component of traditional Hawaiian diets. Although diet richness was not significantly different between the species, with 64 unique taxa identified from the gut contents of 89A. triostegusand 57 taxa from 73A. nigrofuscus,A. nigrofuscusexhibited greater diet diversity as measured by the Simpson's Diversity Index.A. nigrofuscushad a greater relative read abundance of brown algae, cyanobacteria, and material from the epilithic algal matrix.A. triostegushad a taxonomically more specialized diet, consuming primarily red algae.A. triostegusshowed greater variabilitymore »between sites in diet composition thanA. nigrofuscus, and when grouped at the site, shore, or species level,A. triostegustended to have greater diet overlap among individuals. Conversely,A. nigrofuscusexhibited greater variation in diet among individuals, with less diet variability between sites. Grazing surgeonfishes such as these are critical components of existing and future herbivore management plans, making their diet breadth and consequent vulnerability to habitat loss or disturbance of great interest to resource managers.

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2. Multi-omic characterization of the thermal stress phenome in the stony coral Montipora capitata

   https://doi.org/10.7717/peerj.12335  

   Williams, Amanda ; Pathmanathan, Jananan S. ; Stephens, Timothy G. ; Su, Xiaoyang ; Chiles, Eric N. ; Conetta, Dennis ; Putnam, Hollie M. ; Bhattacharya, Debashish ( January 2021 , PeerJ)

   Background Corals, which form the foundation of biodiverse reef ecosystems, are under threat from warming oceans. Reefs provide essential ecological services, including food, income from tourism, nutrient cycling, waste removal, and the absorption of wave energy to mitigate erosion. Here, we studied the coral thermal stress response using network methods to analyze transcriptomic and polar metabolomic data generated from the Hawaiian rice coral Montipora capitata . Coral nubbins were exposed to ambient or thermal stress conditions over a 5-week period, coinciding with a mass spawning event of this species. The major goal of our study was to expand the inventory of thermal stress-related genes and metabolites present in M. capitata and to study gene-metabolite interactions. These interactions provide the foundation for functional or genetic analysis of key coral genes as well as provide potentially diagnostic markers of pre-bleaching stress. A secondary goal of our study was to analyze the accumulation of sex hormones prior to and during mass spawning to understand how thermal stress may impact reproductive success in M. capitata . Methods M. capitata was exposed to thermal stress during its spawning cycle over the course of 5 weeks, during which time transcriptomic and polar metabolomic data were collected.more »We analyzed these data streams individually, and then integrated both data sets using MAGI (Metabolite Annotation and Gene Integration) to investigate molecular transitions and biochemical reactions. Results Our results reveal the complexity of the thermal stress phenome in M. capitata , which includes many genes involved in redox regulation, biomineralization, and reproduction. The size and number of modules in the gene co-expression networks expanded from the initial stress response to the onset of bleaching. The later stages involved the suppression of metabolite transport by the coral host, including a variety of sodium-coupled transporters and a putative ammonium transporter, possibly as a response to reduction in algal productivity. The gene-metabolite integration data suggest that thermal treatment results in the activation of animal redox stress pathways involved in quenching molecular oxygen to prevent an overabundance of reactive oxygen species. Lastly, evidence that thermal stress affects reproductive activity was provided by the downregulation of CYP-like genes and the irregular production of sex hormones during the mass spawning cycle. Overall, redox regulation and metabolite transport are key components of the coral animal thermal stress phenome. Mass spawning was highly attenuated under thermal stress, suggesting that global climate change may negatively impact reproductive behavior in this species.« less
3. Cladocopium community divergence in two Acropora coral hosts across multiple spatial scales

   https://doi.org/10.1111/mec.15668  

   Davies, Sarah W. ; Moreland, Kelsey N. ; Wham, Drew C. ; Kanke, Matt R. ; Matz, Mikhail V. ( October 2020 , Molecular Ecology)

   Many broadly‐dispersing corals acquire their algal symbionts (Symbiodiniaceae) “horizontally” from their environment upon recruitment. Horizontal transmission could promote coral fitness across diverse environments provided that corals can associate with divergent algae across their range and that these symbionts exhibit reduced dispersal potential. Here we quantified community divergence ofCladocopiumalgal symbionts in two coral host species (Acropora hyacinthus, Acropora digitifera) across two spatial scales (reefs on the same island, and between islands) across the Micronesian archipelago using microsatellites. We find that both hosts associated with a variety of multilocus genotypes (MLG) within two genetically distinctCladocopiumlineages (C40, C21), confirming thatAcroporacoral hosts associate with a range ofCladocopiumsymbionts across this region. Both C40 and C21 included multiple asexual lineages bearing identical MLGs, many of which spanned host species, reef sites within islands, and even different islands. Both C40 and C21 exhibited moderate host specialization and divergence across islands. In addition, within every island, algal symbiont communities were significantly clustered by both host species and reef site, highlighting that coral‐associatedCladocopiumcommunities are structured across small spatial scales and within hosts on the same reef. This is in stark contrast to their coral hosts, which never exhibited significant genetic divergence between reefs on the same island. Thesemore »results support the view that horizontal transmission could improve local fitness for broadly dispersingAcroporacoral species.

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4. Habitat attributes mediate herbivory and influence community development in algal metacommunities

   https://doi.org/10.1002/ecy.3976  

   Srednick, Griffin ; Cohen, Alyssa ; Diehl, Olivia ; Tyler, Kaela ; Swearer, Stephen E. ( February 2023 , Ecology)

   Understanding the drivers and impacts of spatiotemporal variation in species abundance on community trajectories is key to understanding the factors contributing to ecosystem resilience. Temporal variation in species trajectories across patches can provide compensation for species loss and can influence successional patterns. However, little is known about the underlying mechanisms that lead to patterns of species or spatial compensation and how those patterns may be mediated by consumer–resource relationships. Here we describe an experiment testing whether habitat attributes (e.g., structural complexity and spatial heterogeneity) mediate the effects of herbivory on tropical marine macroalgal communities by reducing accessibility and detectability, respectively, leading to variable trajectories among algal species at community (within patch) and metacommunity (i.e., among patch) scales. Reduced accessibility (greater habitat complexity) decreased the effects of herbivory (i.e., depressed consumption rate, increased algal species richness), and both accessibility and detectability (spatial heterogeneity) influenced algal community structure. Moreover, decreased accessibility at the community scale and a mosaic of accessibility at the metacommunity scale led to variation in community assembly. We suggest that habitat attributes can be important influencers of consumer–resource interactions on coral reefs, which in turn can increase species diversity, promote species succession, and enhance stability in algal metacommunities.
5. Comparative demography of commercially important species of coral grouper, Plectropomus leopardus and P. laevis , from Australia's great barrier reef and Coral Sea marine parks

   https://doi.org/10.1111/jfb.14491  

   Payet, Samuel D. ; Lowe, Jake R. ; Mapstone, Bruce D. ; Pratchett, Morgan S. ; Sinclair‐Taylor, Tane H. ; Taylor, Brett M. ; Waldie, Peter A. ; Harrison, Hugo B. ( September 2020 , Journal of Fish Biology)

   Understanding the spatial and environmental variation in demographic processes of fisheries target species, such as coral grouper (Genus:Plectropomus), is important for establishing effective management and conservation strategies. Herein we compare the demography ofPlectropomus leopardusandP. laevisbetween Australia's Great Barrier Reef Marine Park (GBRMP), which has been subject to sustained and extensive fishing pressure, and the oceanic atolls of Australia's Coral Sea Marine Park (CSMP), where there is very limited fishing for reef fishes. Coral grouper length‐at‐age data from contemporary and historical otolith collections across 9.4 degrees of latitude showed little difference in lifetime growth between GBRMP and CSMP regions.Plectropomus laevispopulations in GBRMP reefs had significantly higher rates of total mortality than populations in the CSMP. Mean maximum lengths and mean maximum ages ofP. laeviswere also smaller in the GBRMP than in the CSMP, even when considering populations sampled within GBRMP no‐take marine reserves (NTMRs).Plectropomus leopardus, individuals were on average smaller on fished reefs than NTMRs in the GBRMP, but all other aspects of demography were broadly similar between regions despite the negligible levels of fishing pressure in the CSMP. Similarities between regions in growth profiles and length‐at‐age comparisons ofP. laevisandP. leopardussuggest that the environmental differences between the CSMP and themore »GBRMP may not have significant impacts on lifetime growth. Our results show that fishing may have influenced the demography of coral grouper on the GBR, particularly for the slower growing and longer lived species,P. laevis.

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