Marine Biodiversity最新文献

Abstract

Environmental DNA (eDNA) metabarcoding is revolutionizing biodiversity monitoring, but comparisons against traditional data rarely include long-term historical inventories. We targeted eukaryotes by amplifying a fragment of the 18S gene from eDNA isolated from seawater samples at 20 sites in the Gulf of California (GC) and contrasted regional taxonomic diversity against 316 simultaneous visual surveys and a historical database with over 5k species. From 61k Amplified Sequence Variants, we identified 850 eukaryotic families, of which half represent new compiled records, including 174 families of planktonic, benthic, and parasitic invertebrates. The 18S eDNA metabarcoding analysis revealed many overseen taxa, highlighting higher taxonomic ranks within micro-invertebrates, microscopic fungi, and other micro-eukaryotes from the supergroups Stramenopiles, Alveolata, and Rhizaria. The database combining all methods has doubled the number of distinct phyla, classes, and orders compared to the historical baseline, indicating biodiversity levels in the GC are much higher than previously assumed. The estimated proportion of historical taxa included in public reference databases was only 18% for species, partially explaining the small portion of 18S eDNA reads that were taxonomically assigned to species level (13%). Each method showed different taxonomic biases, with 18S eDNA metabarcoding detecting few vertebrates, visual surveys targeting only seven metazoan phyla, and the historical records focusing on macroinvertebrates, fish, and algae. Although all methods recovered the main known biogeographic regionalization, the 18S eDNA metabarcoding data did not support the historical pattern of higher diversity in the Central than Northern GC. While combining methods provides a novel view of biodiversity that is much more comprehensive than any individual approach, our study highlights many challenges in synthesizing biodiversity data from traditional and novel sources.

Populations of the subtropical coral Alveopora japonica Eguchi, 1965 are expanding, likely in response to changes in coastal water conditions caused by human activities and climatic factors. To uncover the causes of population increase, we propose the establishment of a long-term monitoring station to comprehensively assess the drivers of population dynamics. Therefore, the aim of this study was to obtain baseline information on A. japonica in Oedo at Jeju Island (Korea) by documenting benthic composition and characteristics of A. japonica populations at different depths. In Oedo, the distribution of A. japonica is mainly restricted to 15-m depth where a high density of colonies was observed (410 ± 123 colonies m⁻²). These colonies consist predominantly of small colonies with individual or few polyps and are associated with a vertical shift in benthic composition and interactions. Indeed, comparing results with shallower waters where A. japonica is absent and geniculate coralline algae dominate (66.5 ± 2.2% at 5-m and 60.5 ± 2.7% at 10-m depth), a contrasting pattern emerges at 15-m depth. Here, crustose coralline algae make up the majority of the substrate at 56.1 ± 3.4%. These possible biotic drivers are discussed in conjunction with other abiotic factors such as temperature to explain the benthic community composition in Oedo. Given the current benthic structure and accessibility of the study area, Oedo proves to be an ideal sentinel site for monitoring the effects of anthropogenic disturbances, especially global warming, on temperate marine ecosystems.

Aethozoid ctenostome bryozoans are an unusual, small group of solitary ctenostome bryozoans, occurring almost exclusively in deep-sea habitats. Currently, there are only five species belonging to four, still insufficiently known genera, which have been reported from the Atlantic and Pacific Oceans. Recent examination of sediment core samples from an active volcanic area near Mayotte revealed a high abundance of aethozoids, recorded for the first time in the Indian Ocean. A comparative approach identified the specimens as belonging to a new species, Aethozoon flavum sp. nov. There are particular characters diagnostic of this new species, such as basally oriented duplicature bands, a highly denticulate proximal vestibular wall, and a highly elongated anal tube terminating in an almost vestibular anus. This species is the first ctenostome observed at depths of over 3.000 m in the Indian Ocean. Morphological characters are compared among all aethozoids, but still require more detailed analyses in most species. Aethozoids appear to be globally distributed and often occur in high numbers, which indicates that additional efforts will increase their distribution and species range. Ultimately, additional studies will be able to show the ecological importance of these bryozoans and molecular studies should reveal more about their diversity and phylogenetic affinities.

Harpadon nehereus is an ecologically and commercially important fish species. To investigate the phylogeographic pattern and historical demography of H. nehereus, a 1073 base pair fragment of the mitochondrial cytochrome b (Cyt b) gene was analyzed in 305 individuals collected from 13 locations in China offshore. In total, 41 haplotypes and 42 polymorphic sites were detected. Mean haplotype diversity and nucleotide diversity were remarkably low with a range from 0.1630 ± 0.0990 to 0.4113 ± 0.1308 and 0.0002 ± 0.0002 to 0.0007 ± 0.0006, respectively. Insignificant genealogical branches corresponding to sampling locations were revealed both in maximum likelihood (ML) and minimum spanning (MS) trees. The AMOVA and pairwise F_st values indicated shallow genetic structure and the slight genetic variation mainly originated within individuals. Both mismatch distribution analysis and neutrality tests showed H. nehereus had undergone population expansion, which possibly occurred 0.07 million years ago. The bottleneck effect and recent population expansion, combined with larval drift in the ocean current, could be the critical factors in shaping the contemporary phylogeographic patterns and genetic structure of H. nehereus. Our result suggested that H. nehereus in China’s coastal waters may be regarded as an integrated fishery management unit from the perspective of marine resource protection and sustainable utilization. But further researches and comprehensive considerations were still necessary too.

Abstract

Seamounts and remote oceanic islands serve as valuable natural laboratories in which to study patterns and processes in marine biodiversity. A central hypothesis arising from studies of these systems is the ecological function of seamounts as stepping-stones for dispersal and population connectivity. Evidence of this mechanism exists for a range of taxa, including coral reef fishes, but is still lacking from many tropical seamounts in remote regions. In this study, we used remotely operated vehicles and baited remote underwater video systems to survey fish and benthic communities between 1 and 100 m on seamounts in the Coral Sea Marine Park (CSMP), Australia. We found evidence to support the stepping-stone model of ecological connectivity from new observations of 16 coral reef fishes which have previously not been recorded by quantitative surveys in the region. The widespread distribution of many of these species throughout the full latitudinal extent of the CSMP suggests that there is greater connectivity between mesophotic habitats in the Coral Sea and surrounding biogeographic regions than previously known. We also found a wide variety of mesophotic habitats and recorded significant depth range extensions for 78 fishes in these habitats. This further highlights the potential role of increased habitat area and heterogeneity in a stepping-stone effect throughout the region. Four of the fish occurrence records represent significant range extensions into the Coral Sea from adjacent biogeographic regions, and 13 fishes recorded by this study in the CSMP are not known from the neighbouring Great Barrier Reef, despite its close proximity. Although the Coral Sea remains relatively understudied, these findings suggest that larger-scale models of marine biogeography are relevant to communities in the region, particularly at mesophotic depths. Given the extent and the spatial arrangement of seamounts in the Coral Sea, our findings emphasise that the region is an important link between the centre of marine biodiversity in the Coral Triangle and the Southwest Pacific. Greater mesophotic sampling effort and genetic studies are necessary to understand the nature of connectivity and to establish the role of regional seamount chains, like the Coral Sea reefs, in broader marine biogeographic processes.

The sighting of giant bivalves and tubeworms at the Rose Garden vent field on the Galápagos Rift in 1977 marked the discovery of hydrothermal vents, a turning point for modern biology. The following decade saw a flurry of taxonomic descriptions of vent endemic species from the first vents. With the finding of high-temperature “black smokers” on the East Pacific Rise, exploration shifted away from Galápagos. A faunal list of Galápagos vents with 65 species was published in 1991, then updated to 74 species in 2006. Since then, few expeditions returned to the Galápagos Rift. Here, we revisited several Galápagos vents including recently confirmed high-temperature sites and inactive sulfide mounds. From our collecting efforts and observations, as well as revisions from the literature, we update the faunal list to 92 species including 15 new records, restricted to obvious vent associates. Accurate regional faunal lists are important for understanding the biogeography of vent fauna, and our list will also be valuable for setting management strategies.

The quantitative assessment of fish larvae is a key issue in determining the composition of marine food webs. However, there is still a gap in this field regarding how to efficiently sample larvae, particularly in warm and nutrient-poor waters. We evaluated the differences found in larvae caught with two mesh size nets (330 and 500 μm) sampled in the open ocean: shelf break and slope (equatorial SW Atlantic). In total, 792 larvae were sampled, representing 14 orders and 55 families. Overall, larval density was low, and no difference in density was detected between the two net sizes (ind.100 m⁻³). However, a greater number of taxa (46 families) were found in the smaller net (300 μm) than in the larger (500 μm) (37). Moreover, 30.2% of families were found only in the 330 μm net, whereas 9.4% were found only in the 500 μm net. A total of 60.4% of taxa were common to both nets. Gonostomatidae, Paralepididae, Scombridae, Carangidae, Phosichthyidae, and the reef-associated families Scaridae and Gobiidae were the most abundant taxa in the smaller net. In contrast, Myctophidae, Gobiidae, Gonostomatidae, and Stomiidae were the most abundant in the larger net. We highlight mesophotic reefs and seamounts in the South Atlantic for adult spawning and larval growth, emphasizing the need for conservation actions and appropriate fisheries management. Finally, our results also indicate that the combination of different mesh net sizes provides a better baseline of fish larval diversity in warm and oligotrophic oceans.

Abstract

Interest in deep-sea mining for polymetallic nodules as an alternative source to onshore mines for various high-technology metals has risen in recent years, as demands and costs have increased. The need for studies to assess its short- and long-term consequences on polymetallic nodule ecosystems is therefore also increasingly prescient. Recent image-based expedition studies have described the temporal impacts on epi-/megafauna seafloor communities across these ecosystems at particular points in time. However, these studies have failed to capture information on large infauna within the sediments or give information on potential transient and temporally limited users of these areas, such as mobile surface deposit feeders or fauna responding to bloom events or food fall depositions. This study uses data from the Peru Basin polymetallic nodule province, where the seafloor was previously disturbed with a plough harrow in 1989 and with an epibenthic sled (EBS) in 2015, to simulate two contrasting possible impact forms of mining disturbance. To try and address the shortfall on information on transient epifauna and infauna use of these various disturbed and undisturbed areas of nodule-rich seafloor, images collected 6 months after the 2015 disturbance event were inspected and all Lebensspuren, ‘traces of life’, were characterized by type (epi- or infauna tracemakers, as well as forming fauna species where possible), along with whether they occurred on undisturbed seafloor or regions disturbed in 1989 or 2015. The results show that epi- and endobenthic Lebensspuren were at least 50% less abundant across both the ploughed and EBS disturbed seafloors. This indicates that even 26 years after disturbance, sediment use by fauna may remain depressed across these areas.