Dominance of the scleractinian coral Alveopora japonica in the barren subtidal hard bottom of high-latitude Jeju Island off the south coast of Korea assessed by high-resolution underwater images

Coastal benthic communities in temperate regions have been influenced by climate change, including increasing sea-surface temperature. Nevertheless, scleractinian coral Alveopora japonica Eguchi, 1968, is thriving in shallow subtidal hard bottoms around Jeju Island, off the southern coast of Korea. The presence of this corals has negatively impacted subtidal kelp populations in Jeju Island. However, there is no study to document how the presence or absence of this coral relates to other benthic communities. This study investigated the benthos in three shallow subtidal sites (Shinheung (SH), Bukchon (BC), and Seongsan (SS)) in northern Jeju using underwater photography. Macro-benthic organisms appearing on a 1 × 20 m line transect installed at depths of 5, 10, and 15 m at each site were analyzed. Results showed that of the three sites investigated, A. japonica colonies were most abundant at BC, accounting for 45.9% and 72.8% of the total transect area at 10 m and 15 m, respectively. At SS, A. japonica occupied 15.3% of the total area at 15 m and less than 1% at 5 m and 10 m. The same at SH accounted for 10% of the total area at 5 m, and less than 1% at 10 m and 15 m. Dead and bleached colonies accounted for 1.2–11.5% and 1.8–5.7%, respectively, at 5, 10, and 15 m at three sites. At SS, canopy-forming brown algae Ecklonia cava and Sargassum spp. accounted for 20.2 and 24.3% of the total transect area, respectively, at 5 m depth. In contrast, the percent cover of E. cava and Sargassum spp. at SH and BC ranged from 0.1 to 1.8%, respectively. Moreover, non-geniculate coralline algae dominated the subtidal substrate at SH, ranging between 60.2 and 69% at 15 and 10 m. The low cover of A. japonica in SS (at 5 m) coincided with a high percent cover of canopy-forming brown algae. However, canopy-forming brown algae were rare at all depths at SH and BC and were dominated instead by coralline algae and the scleractinian corals. This study, by utilizing a non-destructive method, provides a baseline qualitative and quantitative information for understanding the site and depth-dependent distribution of A. japonica and algal populations, which is important to understand climate change related changes in benthic communities in Jeju and elsewhere.

The diversity and ecology of Symbiodiniaceae: A traits-based review

Among the most successful microeukaryotes to form mutualisms with animals are dinoflagellates in the family Symbiodiniaceae. These photosynthetic symbioses drive significant primary production and are responsible for the formation of coral reef ecosystems but are particularly sensitive when environmental conditions become extreme. Annual episodes of widespread coral bleaching (disassociation of the mutualistic partnership) and mortality are forecasted from the year 2060 under current trends of ocean warming. However, host cnidarians and dinoflagellate symbionts display exceptional genetic and functional diversity, and meaningful predictions of the future that embrace this biological complexity are difficult to make. A recent move to trait-based biology (and an understanding of how traits are shaped by the environment) has been adopted to move past this problem. The aim of this review is to: (1) provide an overview of the major cnidarian lineages that are symbiotic with Symbiodiniaceae; (2) summarise the symbiodiniacean genera associated with cnidarians with reference to recent changes in taxonomy and systematics; (3) examine the knowledge gaps in Symbiodiniaceae life history from a trait-based perspective; (4) review Symbiodiniaceae trait variation along three abiotic gradients (light, nutrients, and temperature); and (5) provide recommendations for future research of Symbiodiniaceae traits. We anticipate that a detailed understanding of traits will further reveal basic knowledge of the evolution and functional diversity of these mutualisms, as well as enhance future efforts to model stability and change in ecosystems dependent on cnidarian-dinoflagellate organisms.

Simplification, not "tropicalization", of temperate marine ecosystems under ocean warming and acidification

Ocean warming is altering the biogeographical distribution of marine organisms. In the tropics, rising sea surface temperatures are restructuring coral reef communities with sensitive species being lost. At the biogeographical divide between temperate and tropical communities, warming is causing macroalgal forest loss and the spread of tropical corals, fishes and other species, termed "tropicalization". A lack of field research into the combined effects of warming and ocean acidification means there is a gap in our ability to understand and plan for changes in coastal ecosystems. Here, we focus on the tropicalization trajectory of temperate marine ecosystems becoming coral-dominated systems. We conducted field surveys and in situ transplants at natural analogues for present and future conditions under (i) ocean warming and (ii) both ocean warming and acidification at a transition zone between kelp and coral-dominated ecosystems. We show that increased herbivory by warm-water fishes exacerbates kelp forest loss and that ocean acidification negates any benefits of warming for range extending tropical corals growth and physiology at temperate latitudes. Our data show that, as the combined effects of ocean acidification and warming ratchet up, marine coastal ecosystems lose kelp forests but do not gain scleractinian corals. Ocean acidification plus warming leads to overall habitat loss and a shift to simple turf-dominated ecosystems, rather than the complex coral-dominated tropicalized systems often seen with warming alone. Simplification of marine habitats by increased CO₂ levels cascades through the ecosystem and could have severe consequences for the provision of goods and services.

DNA-based diversity assessment reveals a new coral barnacle, Cantellius alveoporae sp. nov. (Balanomorpha: Pyrgomatidae) exclusively associated with the high latitude coral Alveopora japonica in the waters of southern Korea

In the present study, the Indo-Pacific coral associated barnacle Cantellius euspinulosum (Broch, 1931) was found to have cryptic species in Korea, Taiwan and other regions based on molecular studies. However, the original specimens of C. euspinulosum from Broch have not been previously described or illustrated, making it difficult to assign which cryptic species to the original C. euspinulosum. The original specimen of C. euspinulosum was examined and illustrated here, and the species identity of C. cf. euspinulosum collected from Jejudo Island in the present study and other cryptic species (based on literature illustrations) in the Indo-Pacific were evaluated.C. euspinulosum from Singapore, Java, Mergui Archipelago in Andaman Sea and Nha Trang represented the C. euspinulosum identified by Broch (1931). It is a generalist on Acropora, Favia, Favites, Leptoria, Montipora, Pachyseris and Pocillipora corals and distributed in the Indo-Pacific region. Morphological examination and DNA sequencing (COI, 12S DNA sequences) in the present study showed that C. cf. euspinulosum from Jejudo Island, Korea represents a distinct species, herein named C. alveoporae sp. nov. Cantellius alveroporae sp. nov. is a specialist species that only grows on Alveopora and also present in Palau, and Ogasawara Island in Japan. Cantellius cf. euspinuloum in Taiwan, the Moscos Island, and Australia belong to several other distinct species awaiting further morphological and molecular studies. At least five cryptic species of C. euspinulosum were identified in the present study, including both specialist and generalists.

Physiological plasticity of corals to temperature stress in marginal coral communities

Adaptation and/or acclimatization through various mechanisms have been suggested to help some tropical coral species to overcome temperature-induced bleaching that is intensifying with climate change; however, while much research has been done on the physiological responses of tropical and subtropical corals to stress, little is known about these responses in corals in marginal environments-e.g., high-latitude and non-reefal communities. In this study, we examined the thermal-tolerant physiology of the flowerpot coral, Alveopora japonica, endemic to the high-latitude Jeju Island (33.39°N), South Korea and Oulastrea crispata and Coelastrea aspera from the subtropical non-reefal coral community on the Penghu Islands (23.34°N), Taiwan. Analysis of physiological parameters; photochemical efficiency, Chlorophyll pigment, Symbiodiniaceae cell number and host soluble proteins - showed that A. japonica can survive through a wide range of temperature stresses (10-32 °C) over a period of 8 days without showing signs of bleaching. In addition, corals O. crispata and C. aspera withstood temperature stresses of up to 33 °C and repeated temperature fluctuations without bleaching. Our results indicate that, under large seasonal variations and asymmetrical daily fluctuations in temperature, corals currently living in marginal environments could have thermal plasticity, allowing them to survive in the future climate change scenarios. This study reiterates the importance of studying the eco-physiology of corals that are generally ignored because of their neutral or positive responses to stress.

The complete mitochondrial genome of Plesiastrea versipora (Scleractinia, Plesiastreidae) sheds light on its phylogeny and taxonomy of the family Plesiastreidae

The genus Plesiastrea used to be a member of the traditional family Faviidae, falling into the challenging 'Bigmessidae' clade, and was re-established until recent molecular phylogenies published. The entire mitogenome of the symbiotic coral Plesiastrea versipora (Lamarck, 1816), the type species of the family Plesiastreidae, was sequenced. The length of the mitochondrial genome is 15,320 bp and it includes thirteen protein-coding genes (PCGs), two rRNAs and two tRNAs. The nucleotide composition of GC is 32%. We perform phylogenetic reconstruction based on maximum likelihood (ML) and Bayesian analysis(BI) using all PCGs. Our result indicates that P. versipora clusters closely with species which belong to Mussidae, Merulinidae and Lobophylliidae. Our phylogenetic analyses provide solid evidence for phylogenetic placement of P. versipora and the evolutionary relationships among different families within the traditional robust clade of Scleractinia. In addition, the mitogenome data provide useful information for further molecular systematic investigations on Plesiastreidae as well as conservation biology research of P. versipora.