Ontogenetic habitat differences of Benthosema pterotum on summer in the shelf region of southern East China Sea
Ontogenetic habitat differences of Benthosema pterotum on summer in the shelf region of southern East China Sea
Abstract:
Benthosema pterotum is one of the most abundant myctophids and an important species linked in the food web between producers and consumers for the continental shelf of the southern East China Sea (ECS). This study used R/V Ocean Researcher 1 and 5 to investigate the spatial distribution of B. pterotum, associated with environmental factors affecting the continental shelf of the southern ECS between 2006 and 2017. A generalized additive model (GAM) was used to evaluate potential habitats of B. pterotum. In total, 6,690 B. pterotum larvae were collected during the nine cruises. The density varied from 0.88 to 2488.19 the number of individuals per 1000 m3 (ind./1000 m3) during the period of this study. The median density was the highest in June 2009 (65.68 ind./1000 m3) and the lowest in July 2010 (5.78 ind./1000 m3); the highest at 18.42 ind./1000 m3 in the flexion larval, but the lowest at 7.01 ind./1000 m3 in the juvenile. The density of B. pterotum in the juvenile from different sampling depth and day-night was not significantly different. That may mean the diel vertical migration begins in this stage. The GAM results indicated that the influential environmental variables including salinity, temperature, zooplankton biomass, and chlorophyll a concentration affected B. pterotum distribution on the continental shelf of the southern ECS. Benthosema pterotum distribution in the pre-flexion and flexion stages inhabits optimum temperatures of 28.2°C–28.8°C and salinity of 32–33.6 in the waters of the south and central shelf region of the southern ECS (25–29°N, 121–125°E) and then move to a relatively low temperature–salinity area in the waters of the north and peripheral shelf region. In addition, some juveniles move to the south of the Changjiang River estuary, which has high primary productivity. Overall, B. pterotum larvae might accommodate themselves through growth to their habitat relate to their survival strategy with the optimum environment and food availability during summer.