The purpleback flying squid (Ommastrephidae: Sthenoteuthis oualaniensis) is an important species at higher trophic levels of the regional marine ecosystem in the South China Sea (SCS), where it is considered to show the potential for fishery development. Accordingly, under increasing climatic and environmental changes, understanding the nature and importance of various factors that determine the spatial and temporal distribution and abundance of S. oualaniensis in the SCS is of great scientific and socio-economic interest. Using generalized additive model (GAM) methods, we analyzed the relationship between available environmental factors and catch per unit effort (CPUE) data of S. oualaniensis. The body size of S. oualaniensis in the SCS was relatively small (<19.4 cm), with a shorter lifespan than individuals in other seas. The biological characteristics indicate that S. oualaniensis in the SCS showed a positive allometric growth, and could be suitably described by the logistic growth equation. In our study, the sea areas with higher CPUE were mainly distributed at 10°–11° N, with a 27–28 °C sea surface temperature (SST) range, a sea surface height anomaly (SSHA) of −0.05–0.05 m, and chlorophyll-a concentration (Chl-a) higher than 0.18 μg/L. The SST was the most important factor in the GAM analysis and the best fitting GAM model explained 67.9% of the variance. Understanding the biological characteristics and habitat status of S. oualaniensis in the SCS will benefit the management of this resource.

Hairtail (Scombriformes: Trichiuridae) have always ranked first in single-species production in Chinese marine fishery. However, due to the confusion of species identification, in official statistics, data on hairtail production and economic value are a combination of all the different species of Trichiuridae. In this study, based on sampling along China’s coastal areas, the composition and distribution of common hairtail species, as well as their age, growth, and trophic traits, are discussed. Six species of four genera and two subfamilies were identified, and largehead hairtail (Trichiurus japonicus) and Savalai hairtail (Lepturacanthus savala) were the most important populations that constituted catch production. The growth parameter b could be divided into two groups, with values in species mostly inhabiting northern parts of Chinese seas higher than those in southern parts. Most individuals were 1–2 years of age, suggesting species sexual precocity and individual miniaturization under multiple stresses. Species of Trichiuridae are at the top of the food web and play a bottom-up role in regulating the trophic dynamics of marine food webs. Largehead hairtail showed the highest stability and the greatest impact on the stability of the trophic structure. Despite temporary resource maintenance under fishery-induced evolution, the effective recovery and reasonable utilization of hairtail resources are still the main focuses of attention for Chinese marine fishery.

Harpiosquilla harpax, a mantis shrimp, serves an important role in both commercial fisheries and benthic food webs in tropical and subtropical marine

<!-- *** Custom HTML *** --> Asian moon scallops (Amusium pleuronectes) were sampled by trawl vessels in the Beibu Gulf, South China Sea, from October 2014 to November 2015. Feeding habits and stable isotopic patterns of A. pleuronectes were examined using stomach contents and adductor muscles based on a conventional stomach analysis method and stable carbon and nitrogen isotope technology. The applicability of A. pleuronectes as a baseline indicator in marine ecosystems in the Beibu Gulf is discussed. The stomach content analyses indicated that A. pleuronectes mainly fed on Bacillariophyta (62%), a small quantity of Chlorophyta (8%), Pyrrophyta (8%), and Cyanophyta (6%). Species of Diploneis, Cyclotella, Pleurosigma, and Navicula played dominant roles in the stomach. The nitrogen and carbon stable isotope ratios were 6.41‰–12.80‰ (average 8.89‰) and –21.45‰ to –17.56‰ (average –19.54‰), respectively. Significant differences (P < 0.01) were observed among seasons in δ¹⁵N, with average values of 9.53‰, 9.80‰, 8.79‰, and 8.34‰ from spring to winter. The analysis of the feeding habits and stable isotopic patterns indicated that A. pleuronectes could be used as isotopic baseline indicators. It is recommended that A. pleuronectes can be used as a common isotopic baseline indicator for the ecology studies in the Beibu Gulf or even in the South China Sea because there is no standard baseline in this marine ecosystem.

The study of trophic relationships among closely related species plays an important role in deepening our understanding of the resource utilization characteristics, differentiation patterns, and population dynamics of co-occurring species in the same habitat. This research uses two congeneric fish species, Pennahia pawak and Pennahia anea, as examples. Based on a stomach content analysis and a carbon–nitrogen stable isotope analysis, a comparative analysis of their feeding habits and trophic niches is conducted. Additionally, a spatial niche analysis is employed to explore the coexistence and competitive mechanisms between these two closely related fish species. The results show that specialized feeding habits mitigate intraspecific competition as the population densities increase. The carbon and nitrogen stable isotope analysis reveals variations in the feeding habits and trophic levels with body length, indicating adaptive shifts in prey selection. Despite similar food resources, niche differentiation arises due to differences in dominant prey, facilitating coexistence. Differences in spatial niche further contribute to niche separation and coexistence. In resource-limited environments, species such as Pennahia utilize trophic and spatial niche differentiation to collectively exploit resources and achieve coexistence, with implications for fishery management favoring Pennahia resource occupancy capabilities.