Functional diversity of mesozooplankton communities in a transitional subtropical marine system

Zooplankton and associated environmental parameters were collected in January and May 2018 to investigate the contrasting taxonomic and functional responses of the zooplankton community to environmental changes in the Strait of Hormuz and its surrounding waters in the Persian Gulf and the Gulf of Oman. Sampling was conducted along three transects perpendicular to the coastline, each transect comprising four stations. Principal component analysis identified temperature, salinity, and dissolved oxygen (DO) as key environmental drivers. Oceanographic conditions were more stable in January, whereas there was pronounced thermal and salinity stratification in May. A total of 72 zooplankton taxa were identified. Community composition differed significantly between months, with Sagitta sp. and Temora sp. dominating in January, and Oikopleura spp. and Penilia sp. being the most abundant taxa in May. Each species was assigned functional traits using six categories based on body length, reproductive mode, feeding strategy, diel vertical migration, gelatinous factor, and trophic group. Species that produce water currents to capture food—referred to as current feeders—were the dominant feeding type during the study. Broadcast spawners, which release their gametes into the water column, were more prevalent in May, whereas sac spawners, which retain their eggs attached to the female’s body, were more abundant in January. Analysis using permutational multivariate analysis of variance (PERMANOVA) revealed significant spatial differences in both taxonomic composition and trait-based structure. The relationship between habitat descriptors and zooplankton functional traits, analyzed using a combined approach of RLQ and fourth-corner analyses, revealed that salinity, temperature, and DO influenced trait composition.