Stolonifera from shallow waters in the north-western Pacific: a description of a new genus and two new species within the Arulidae (Anthozoa, Octocorallia)

The Biology and Evolution of Calcite and Aragonite Mineralization in Octocorallia

Octocorallia (class Anthozoa, phylum Cnidaria) is a group of calcifying corals displaying a wide diversity of mineral skeletons. This includes skeletal structures composed of different calcium carbonate polymorphs (aragonite and calcite). This represents a unique feature among anthozoans, as scleractinian corals (subclass Hexacorallia), main reef builders and focus of biomineralization research, are all characterized by an aragonite exoskeleton. From an evolutionary perspective, the presence of aragonitic skeletons in Octocorallia is puzzling as it is observed in very few species and has apparently originated during a Calcite sea (i.e., time interval characterized by calcite-inducing seawater conditions). Despite this, octocorals have been systematically overlooked in biomineralization studies. Here we review what is known about octocoral biomineralization, focusing on the evolutionary and biological processes that underlie calcite and aragonite formation. Although differences in research focus between octocorals and scleractinians are often mentioned, we highlight how strong variability also exists between different octocoral groups. Different main aspects of octocoral biomineralization have been in fact studied in a small set of species, including the (calcitic) gorgonian Leptogorgia virgulata and/or the precious coral Corallium rubrum. These include descriptions of calcifying cells (scleroblasts), calcium transport and chemistry of the calcification fluids. With the exception of few histological observations, no information on these features is available for aragonitic octocorals. Availability of sequencing data is also heterogeneous between groups, with no transcriptome or genome available, for instance, for the clade Calcaxonia. Although calcite represents by far the most common polymorph deposited by octocorals, we argue that studying aragonite-forming could provide insight on octocoral, and more generally anthozoan, biomineralization. First and foremost it would allow to compare calcification processes between octocoral groups, highlighting homologies and differences. Secondly, similarities (exoskeleton) between Heliopora and scleractinian skeletons, would provide further insight on which biomineralization features are driven by skeleton characteristics (shared by scleractinians and aragonitic octocorals) and those driven by taxonomy (shared by octocorals regardless of skeleton polymorph). Including the diversity of anthozoan mineralization strategies into biomineralization studies remains thus essential to comprehensively study how skeletons form and evolved within this ecologically important group of marine animals.

Corrigenda: Hanah, a replacement name for Hana Lau, Stokvis, Ofwegen & Reimer, 2018 (preoccupied name)

[This corrects the article DOI: 10.3897/zookeys.790.28875.].

Zooxanthellate, Sclerite-Free, and Pseudopinnuled Octocoral Hadaka nudidomus gen. nov. et sp. nov. (Anthozoa, Octocorallia) from Mesophotic Reefs of the Southern Ryukyus Islands

Shallow water coral reefs are the most diverse marine ecosystems, but there is an immense gap in knowledge when it comes to understanding the diversity of the vast majority of marine biota in these ecosystems. This is especially true when it comes to understudied small and cryptic coral reef taxa in understudied ecosystems, such as mesophotic coral reef ecosystems (MCEs). MCEs were reported in Japan almost fifty years ago, although only in recent years has there been an increase in research concerning the diversity of these reefs. In this study we describe the first stoloniferous octocoral from MCEs, Hadaka nudidomus gen. nov. et sp. nov., from Iriomote and Okinawa Islands in the southern Ryukyus Islands. The species is zooxanthellate; both specimens host Cladocopium LaJeunesse & H.J.Jeong, 2018 (formerly Symbiodinium ‘Clade C’) and were collected from depths of ~33 to 40 m. Additionally, H. nudidomus gen. nov. et sp. nov. is both sclerite-free and lacks free pinnules, and both of these characteristics are typically diagnostic for octocorals. The discovery and morphology of H. nudidomus gen. nov. et sp. nov. indicate that we still know very little about stoloniferous octocoral diversity in MCEs, their genetic relationships with shallower reef species, and octocoral–symbiont associations. Continued research on these subjects will improve our understanding of octocoral diversity in both shallow and deeper reefs.

A first phylogenetic study on stoloniferous octocorals off the coast of Kota Kinabalu, Sabah, Malaysia, with the description of two new genera and five new species

Sabah, Malaysia, is well known for its extensive and diverse coral reefs. It is located on the northwestern edge of the Coral Triangle, the region with the highest marine biodiversity. Much of the marine fauna here is still unknown, especially inconspicuous animals, such as small stoloniferous octocorals, which are common on coral reefs. Here, we describe two new monospecific genera of the family Arulidae found off the coast of Kota Kinabalu, Sabah, East Malaysia; Bunga payung gen. nov. et sp. nov. and Laeta waheedae gen. nov. et sp. nov. As well, the stoloniferan genus Phenganax Alderslade & McFadden, 2011 belonging to the family Clavulariidae is expanded with three new species, P. marumi sp. nov., P. subtilis sp. nov., and P. stokvisi sp. nov., which are all sclerite-free. Additionally, we report a possibly undescribed species, closely related to the clavulariid genera Azoriella Lopez-Gonzalez & Gili, 2001 and Cervera Lopez-Gonzalez et al., 1995. As this and other recent studies have shown, discoveries of small stoloniferous octocorals are helping to fill gaps in our knowledge of the overall systematics of Octocorallia.

Digging for DNA at depth: rapid universal metabarcoding surveys (RUMS) as a tool to detect coral reef biodiversity across a depth gradient

Background

Effective biodiversity monitoring is fundamental in tracking changes in ecosystems as it relates to commercial, recreational, and conservation interests. Current approaches to survey coral reef ecosystems center on the use of indicator species and repeat surveying at specific sites. However, such approaches are often limited by the narrow snapshot of total marine biodiversity that they describe and are thus hindered in their ability to contribute to holistic ecosystem-based monitoring. In tandem, environmental DNA (eDNA) and next-generation sequencing metabarcoding methods provide a new opportunity to rapidly assess the presence of a broad spectrum of eukaryotic organisms within our oceans, ranging from microbes to macrofauna.

Methods

We here investigate the potential for rapid universal metabarcoding surveys (RUMS) of eDNA in sediment samples to provide snapshots of eukaryotic subtropical biodiversity along a depth gradient at two coral reefs in Okinawa, Japan based on 18S rRNA.

Results

Using 18S rRNA metabarcoding, we found that there were significant separations in eukaryotic community assemblages (at the family level) detected in sediments when compared across different depths ranging from 10 to 40 m (p = 0.001). Significant depth zonation was observed across operational taxonomic units assigned to the class Demospongiae (sponges), the most diverse class (contributing 81% of species) within the phylum Porifera; the oldest metazoan phylum on the planet. However, zonation was not observed across the class Anthozoa (i.e., anemones, stony corals, soft corals, and octocorals), suggesting that the former may serve as a better source of indicator species based on sampling over fine spatial scales and using this universal assay. Furthermore, despite their abundance on the examined coral reefs, we did not detect any octocoral DNA, which may be due to low cellular shedding rates, assay sensitivities, or primer biases.

Discussion

Overall, our pilot study demonstrates the importance of exploring depth effects in eDNA and suggest that RUMS may be applied to provide a baseline of information on eukaryotic marine taxa at coastal sites of economic and conservation importance.

Molecular phylogeny and diversity of sea pens (Cnidaria: Octocorallia: Pennatulacea) with a focus on shallow water species of the northwestern Pacific Ocean

The order Pennatulacea, commonly known as sea pens, are colony-forming benthos belonging within subclass Octocorallia (Anthozoa, Cnidaria). Sea pens are found worldwide from shallow to deep waters, and they are important components in sandy and muddy environments. Thus far, there has been only one molecular study focusing on the phylogenetic relationships within the order Pennatulacea, which mainly treated deep-sea species, and thus information on shallow water species is still lacking. On a regional scale, the diversity of sea pens in the northwestern Pacific, including Japan and Palau, has not been well investigated. In this research, we aimed to: (1) more accurately resolve the phylogenetic relationships of sea pens with the inclusion of shallow water species, and (2) obtain a better understanding of the diversity of sea pens in Japan and Palau. Specimens were collected by SCUBA and dredging from the Ryukyu Islands in southern Japan, and from mainland Japan and Palau, and identified to at least the genus level by their morphological traits. Construction of phylogenetic trees with concatenated sequences including the mitochondrial mutS-like protein DNA mismatch repair gene mtMutS and the NADH dehydrogenase subunit 2 ND2 region were performed. The p-distances of mtMutS were calculated for estimation of species number following McFadden et al. (2011). Molecular data for 12 families and 20 genera of sea pens were used in this study. This most comprehensive study including shallow water taxa provided us with more knowledge of phylogenetic relationships. The resulting phylogenetic trees showed a topology distinguished by four large clades (clades 1-4). Families Veretillidae and Echinoptilidae are shown as not the earliest-diverging taxa. Virgulariidae and Scleroptilidae are shown as polyphyletic groups, and our results reconfirm that families Pennatulidae, Kophobelemnidae and Umbellulidae are not monophyletic groups. Overall, we collected and examined an estimated 18 species from the Ryukyu Islands, 16 species from mainland Japan, and five species from Palau. Some of these specimens represented new records from Ryukyu Islands and Palau. Previous records of these sea pens did not exist likely due to a lack of diversity research in sandy and muddy areas. These results demonstrate that many sea pens discoveries likely remain in shallow waters of the Pacific.