Ichthyoplankton species assemblages during the 2015–2016 El Niño in the southwest Gulf of California

Abstract This study analyzed seasonal and interannual variations in larval fish abundance in Cabo Pulmo National Park (CPNP) from January 2015 to November 2017, encompassing the 2015–2016 El Niño and subsequent thermal relaxation, to examine the impacts of climate-driven events on larval fish abundance, diversity, and species richness in a no-take marine protected area. A total of 166 larval fish taxa were identified, spanning 59 families, 94 genera and 98 species. Dactyloscopidae spp. (relative frequency: 41.7%; abundance: 9.9%), Auxis spp. (32.3%, 7.3%), Abudefduf troschelii (24%, 4.7%), Syacium spp. (17.7%, 3.9%) and Tripterygiidae spp. (12.5%, 2.8%) were the most frequent and numerically dominant taxa, after excluding 13 mesopelagic and bathypelagic species not typically found in CPNP’s shallow waters as adults. Although larval fish assemblages responded to short-term seasonal fluctuations (quarterly and semi-annual), we found that fish larvae abundance, diversity and species richness (independently of their biogeographic and habitat affinity) declined during the 2015–2016 El Niño compared to both the period before El Niño and the subsequent thermal relaxation (June 2016–November 2017). These findings highlight their vulnerability to El Niño-driven oceanographic changes, with implications for the resilience of these populations in the context of a changing climate.