Abstract Chaetognaths are abundant carnivorous zooplankters that play a pivotal role in structuring and regulating the pelagic ecosystem, yet long-term studies of their ecological dynamics in the Mexican Pacific are limited. We investigated the chaetognath community structure in a tropical coastal system of the Mexican Pacific from 2010 to 2016 using monthly zooplankton samples collected across two contrasting hydroclimatic seasons (mixed and stratified) and three interannual ENSO phases: La Niña (Nov 2010–Mar 2012 and Aug–Dec 2016), neutral (Apr 2012–Oct 2014), and El Niño (Nov 2014–May 2016). Our analytical approach integrated: univariate, multivariate, and taxonomic diversity analyses. A total of 145,077 chaetognath specimens were identified from 110 zooplankton samples. Fifteen species were recorded, Zonosagitta bedoti , Parasagitta euneritica , and Flaccisagitta enflata being numerically dominant (73.2% of total abundance) across all seasons and ENSO phases, indicating ecologically resilient local populations. RDA revealed that Z . bedoti and P. euneritica were associated with high 15-CUI values and low temperatures, whereas S. bierii , A. septata , A. regularis , and S. pacifica were linked to moderate-to-high temperatures. Chaetognaths had low mean numerical abundance and diversity during La Niña, high species richness during El Niño 2015–2016, and maximum abundance values during ENSO neutral conditions. These patterns suggest strong local dominance of these predators under anomalously warm conditions.
Franco-Gordo et al. (2026) studied this question.