DNA barcoding of marine fish species in the waters surrounding Hainan Island, northern South China Sea

IntroductionHainan Island is encompassed within the shallow waters of the tropical continental shelf in China, which is recognized as a significant hotspot for fish biodiversity. Despite extensive research conducted on marine fish taxonomy surrounding Hainan Island, there remains a substantial gap between our current understanding and the actual fish diversity within this oceanic area.MethodsIn this study, we employed DNA barcoding and molecular identification approaches to explore the species diversity and distribution pattern of marine fish in both the northern and southern sea areas of Hainan Island in the northern South China Sea.ResultsA total of 186 sequences were obtained from the collected marine fish samples in the two sea areas surrounding Hainan Island. Through DNA identification, it was confirmed that all 186 sequences corresponded to typical fish species found in the northern South China Sea, all sequences represented a total of 56 species, 47 genera, 34 families, and 17 orders. The average Kimura 2-parameter (K2P) distances within species, genus, family, order and class were 0.15%, 6.53%, 13.17%, 16.95% and 24.81%, respectively.DiscussionOur investigation in the northern sea areas of Hainan Islands identified a total of 33 distinct species, while the southern sea areas exhibited 29 distinct species, with only 5 species found to be shared between both regions. These findings clearly indicate a significant disparity in the species composition of fish communities between the northern and southern sea regions

Trophic connectivity between intertidal and offshore food webs in Mirs Bay, China

Summary: Trophic interactions are common worldwide, both within and between ecosystems. This study elucidated the trophic connectivity between intertidal and offshore zone, in Mirs Bay, China. The contributions of offshore suspended particulate organic matter (SPOM), intertidal macroalgae and epiphytes to consumer biomass were assessed, and the trophic pathways were identified through the use of stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) of basal sources and consumers. Mean δ13C values of basal sources had a wide range (−19.6‰ to −11.8‰) and were generally well separated in Mirs Bay. The average δ13C of consumers in Mirs Bay ranged from −19.2‰ to −11.8‰, reflecting a carbon source integrated from different primary producer signals. IsoSource model solutions indicated consumers assimilated organic carbon from a mixture of basal sources. Offshore SPOM carbon was the primary carbon source supporting most consumers in both intertidal and offshore zones. Intertidal macroalgae and epiphytes also accounted for a large fraction for some consumers. δ15N data indicated 5 trophic levels in Mirs Bay. Intertidal consumers, except for Capitulum mitella, had a TP (trophic position) between 2 and 3, and mainly included filter-feeders and grazers. In contrast, almost all offshore consumers had a TP of between 3 and 4 except for filter-feeders (zooplankton), planktivores (Clupanodon punctatus and Sardinella aurita) and piscivores (Gymnura japonica). The basal sources fueled consumers through two trophic pathways, each of which involved organisms of both intertidal and offshore zones, implying trophic connectivity between them in the Mirs Bay ecosystem. Keywords: Food webs, Trophic connectivity, Carbon pathways, Stable isotopes, Mirs Ba

The complete mitochondrial genome of middle-sized form of Sthenoteuthis oualaniensis (Cephalopoda: Ommastrephidae) from the South China Sea

The purpleback flying squid (Sthenoteuthis oualaniensis) is a pelagic squid with tremendous potential for commercial exploitation. Sthenoteuthis oualaniensis comprises two forms in the South China Sea, medium-sized form and dwarf form. In this study, we described the complete mitochondrial genome of medium-sized form of S. oualaniensis. The genome is 20,309 bp in length, encoding the standard set of 13 protein-coding genes, 20 tRNA genes, and two rRNA genes, with circular organization. The overall base composition of the whole mitochondrial genome was A (35.86%), T (33.36%), G (11.63%), and C (19.15%) with an AT bias of 69.22%. The longest protein-coding gene of these species was ND5, whereas the shortest ATP8

Spatial Distribution of Major Fish Species Catches and Their Relationship with Environmental Factors in the Beibu Gulf, South China Sea

This study focused on major fish species caught from different ecological habitats to analyze the habitat changes in economically important fish in the Beibu Gulf. The maximum entropy model was constructed based on the data from 26 voyages obtained through the otter trawl fishery stock surveys conducted in the Beibu Gulf from 2006 to 2018. A total of 10 taxa of major fish catches, belonging to 4 families, 1 genus, and 5 species, were analyzed for their distribution characteristics in potential habitats during various ecological periods, specifically the withered and high-water periods, as well as their relationships with crucial environmental factors. During both the withered and high-water periods, the average area under the curve was 0.927, and all models had values exceeding 0.9. Salinity was identified as the principal factor during both periods. The salinity niche of Acropoma japonicum and the primary productivity niche of Sciaenidae were identified as the most restricted factors. The total distribution area of potentially suitable regions for major fish catches extended between 106°30′–109°45′ E and 17°30′–20°45′ N, and the area was lesser during the withered period. During the withered period, the distribution areas of Sciaenidae, Leiognathidae, and Saurida increased, while the distribution area of Trachurus japonicus increased during the high-water period. Sciaenidae and Trachurus japonicus exhibited the highest rates of change at 6.22% and 10.92%, respectively. This indicates that the high-water period may expand the range of suitable habitats for large catches that have an ideal habitat status in the Beibu Gulf. Therefore, it is crucial to anticipate the potential fish habitats in the Beibu Gulf and clarify their spatial distribution patterns

The complete mitochondrial genome of the tropical oyster Saccostrea echinata (Bivalvia: Ostreidae) from the South China Sea

Saccostrea echinata is a rock perched oyster with wide distribution and tremendous potential for commercial mariculture. However, the taxonomy of this genus is confused. In this study, we described the complete mitochondrial genome of medium-sized form of Saccostrea echinata. The genome is 16,282 bp in length, encoding the standard set of 12 protein-coding genes (PCGs), 23 tRNA genes, and two rRNA genes, with circular organization. The overall base composition of the whole mitochondrial genome was A (26.78%), T (36.64%), G (21.99%), and C (14.59%) with an AT bias of 63.42%. The longest PCG of these species was ND5, whereas the shortest was ND4L