Oasis of the deep: Cold-water corals of the South China Sea.

Cold-water coral (CWC) communities are biodiversity hotspots on the world's deep seafloor. Although deep-sea corals in the South China Sea (SCS) have been reported before, they are only sporadic. A comprehensive and systematic understanding of the CWC in the SCS would forge the basis for future protection. Here we conducted the first systematic survey on the CWCs in the following six broad-scale sub-regions, from the northwest and northeast slopes to the seamounts in the western and central basins of the SCS, through twenty-four dives of the human-occupied vehicle ShenhaiYongshi. Statistical analysis provided detailed information on the distribution, abundance, size, diversity, and density of CWCs and the in situ environmental conditions supporting coral habitats. We found that the SCS hosted highly diversified coral communities, including twelve genera of gorgonians, six genera of black corals, and one genus of stony corals. The differences in the spatial distribution patterns of coral communities suggested that several environmental variables (depth, temperature, salinity, substrate, and geomorphology) might influence the development of CWCs in the SCS. The intermediate water layer of the SCS appeared to provide suitable habitat for deep-sea coral communities and potentially promoted connectivity. Furthermore, differences between sub-regions within the SCS may be an important factor responsible for the biogeographic patterns of CWCs. These sub-regions of CWCs were observed to range from 0.004 to 0.622 corals m-2, with an average of 0.139 corals m-2. The mean density of CWCs in the SCS was relatively high compared to well-studied CWC hotspots. Overall, the results revealed the significance of the SCS as an important CWC hotspot in the world. These findings provide a fundamental basis for the protection of deep-sea coral assemblages in the SCS.

Muscle systems and motility of early animals highlighted by cnidarians from the basal Cambrian.

Although fossil evidence suggests that various animal groups were able to move actively through their environment in the early stages of their evolution, virtually no direct information is available on the nature of their muscle systems. The origin of jellyfish swimming, for example, is of great interest to biologists. Exceptionally preserved muscles are described here in benthic peridermal olivooid medusozoans from the basal Cambrian of China (Kuanchuanpu Formation, ca. 535 Ma) that have direct equivalent in modern medusozoans. They consist of circular fibers distributed over the bell surface (subumbrella) and most probably have a myoepithelial origin. This is the oldest record of a muscle system in cnidarians and more generally in animals. This basic system was probably co-opted by early Cambrian jellyfish to develop capacities for jet-propelled swimming within the water column. Additional lines of fossil evidence obtained from ecdysozoans (worms and panarthropods) show that the muscle systems of early animals underwent a rapid diversification through the early Cambrian and increased their capacity to colonize a wide range of habitats both within the water column and sediment at a critical time of their evolutionary radiation.

Fate, source and mass budget of sedimentary microplastics in the Bohai Sea and the Yellow Sea.

As reservoirs for pollutants transported via the Yangtze and Yellow Rivers, the Bohai Sea (BS) and Yellow Sea (YS) play an important role in transporting microplastics (MPs) to the Pacific Ocean. The fate, sources and mass budget of MPs in the BS and the YS were investigated by Pearson correlation, principal component analysis-multilinear regression analysis (PCA-MRLA) and a mass balance model to sedimentary MPs data. Average MP abundances were 137 and 119 items kg-1 in the Bohai and Yellow Seas, respectively. MPs <1000 µm exhibited similar distribution patterns to total organic carbon and fine-grained sediments, while MPs >1000 µm were confined in the BS and exhibited a strong positive correlation with chlorophyll-a and polyethylene terephthalate, suggesting that larger MPs might deposit faster due to biofouling or when comprised of high density polymers. PCA-MLRA analysis indicated land-based inputs (packing materials, textile material and daily commodities) were dominant in the BS, while maritime activities (fishing and mariculture) were the main source of MPs in the YS. The mass balance model revealed that the total MP input and output to the BS and the YS was 3396.92 t yr-1 and 3814.81 t yr-1, respectively. The major input pathway of MPs to the BS and the YS were river discharge and air deposition, respectively. Notably, 94% of MPs in the BS and the YS were deposited to sediments. This study revealed that BS and YS sediments play an important role in preventing MPs from being further transported to the Pacific Ocean, thus more attention should be paid to local ecological risk assessment.

Advanced Cambrian hydroid fossils (Cnidaria: Hydrozoa) extend the medusozoan evolutionary history.

Primitive cnidarians are crucial for elucidating the early evolution of metazoan body plans and life histories in the late Neoproterozoic and Palaeozoic. The highest complexity of both evolutionary aspects within cnidarians is found in extant hydrozoans. Many colonial hydrozoans coated with chitinous exoskeletons have the potential to form fossils; however, only a few fossils possibly representing hydroids have been reported, which still require scrutiny. Here, we present an exceptionally well-preserved hydroid found in the Upper Cambrian Fengshan Formation in northern China. It was originally interpreted as a problematic graptolite with an uncertain systematic position. Based on three characteristic morphological traits shared with extant hydroids (with paired hydrothecae, regular hydrocaulus internodes and special intrathecal origin pattern of hydrocladium), we propose this fossil hydroid as a new genus, Palaeodiphasia gen. nov., affiliated with the advanced monophyletic hydrozoan clade Macrocolonia typically showing loss of the medusa stage. More Macrocolonia fossils reviewed here indicate that this life strategy of medusa loss has been achieved already as early as the Middle Devonian. The early stratigraphical appearance of such advanced hydroid contrasts with previous molecular hypotheses regarding the timing of medusozoan evolution, and may be indicative for understanding the Ediacaran cnidarian radiation.

Worldwide revision of the genus Fraseroscyphus Boero and Bouillon, 1993 (Cnidaria: Hydrozoa): an integrative approach to establish new generic diagnoses.

The morphological character of the hydrocladium and gonotheca origin from within the hydrothecal cavity has rarely been applied for generic diagnoses in hydrozoans. Its taxonomic value has been controversial for more than a century. The genus Fraseroscyphus Boero and Bouillon, 1993 (Hydrozoa: Sertulariidae) is a relatively recently debated case and it has been distinguished from Symplectoscyphus Marktanner-Turneretscher, 1890 based on this character. A review of this character in all published nominal species of the family Sertulariidae reveals that its occurrence is inconsistent at the genus level. However, phylogenetic analyses based on mitochondrial (16S) and nuclear (18S, 28S) genes support the position of Fraseroscyphus as a genus within the family Symplectoscyphidae Maronna et al., 2016. Comparisons of 16 morphological characters of 10 related species support the distinction of Fraseroscyphus from Antarctoscyphus and Symplectoscyphus by other characters in addition to the hydrocladial and gonothecal origin character. These new characters include the rarely-branched hydrocaulus, the absence of an apophysis, and the absence of an axillary hydrotheca. Furthermore, a revision based on the morphological character complex mentioned above using type and topotypic material, demonstrated that Sertularella sinuosa Fraser, 1948 (type species of Fraseroscyphus) and Symplectoscyphus huanghaiensis Tang & Huang, 1986 are junior synonyms of F. hozawai (Stechow, 1931) comb. nov. The assignment of Sertularella irregularis Trebilcock, 1928 and Sertularella macrogona Trebilcock, 1928 to Fraseroscyphus is also supported. In addition, sequence polymorphism of mitochondrial genes even within a single hydroid fragment was detected by the molecular cloning method, and is probably in part attributable to errors introduced by PCR, mitochondrial heteroplasmy and/or nuclear mitochondrial DNA (NUMTs). The adoption of the cloning method may be crucial to improve the sequence accuracy for some colonial hydrozoans.