Seasonal abundance and distribution of chaetognaths in the northern Gulf of Mexico: The effects of the Loop Current and Mississippi River plume

Abstract

We examined the effect of mesoscale oceanographic conditions on the seasonal abundance and distribution patterns of chaetognaths, a major component of the zooplankton community in the northern Gulf of Mexico, with data collected in late spring (May/June) and summer (July) from 2015 to 2017. Overall, 13 chaetognath species from six genera were observed in the samples. Significant pairwise associations were found between some species of chaetognaths, e.g. Flaccisagitta enflata and Sagitta bipunctata, which were affected by the distance of sampling stations to the Loop Current front. Flaccisagitta hexaptera observed in the samples appeared as an indicator species of high salinity water. Additionally, the abundance of chaetognaths showed an increasing trend as the distance increased from the Loop Current front. The potential effects of environmental factors (e.g. SST, salinity, and dissolved oxygen) and oceanographic features (i.e. the Loop Current front) on abundance and distribution of chaetognaths were further examined using non-metric multidimensional scaling (NMDS) and generalized additive models (GAM). The NMDS ordination showed significant differences in chaetognath assemblages between the cruises. Furthermore, the GAM modeling displayed species-specific impacts of salinity, dissolved oxygen, and distance to the Loop Current front on the abundance of key chaetognaths in the region. Given the critical roles of zooplankton communities, this three-year study of chaetognaths contributed to the understanding of the processes and drivers of zooplankton dynamics in relation to environmental factors in the northern Gulf of Mexico to further explore how these changes would affect fisheries production and ecosystem functions in the areas.