The Interannual Variations of Summer Ichthyoplankton in the Pearl River Estuary as a Response to Climate Change

The impacts of climate change on ichthyoplankton have barely been examined in the Pearl River estuary (PRE). Using the fish larvae and eggs caught in the estuary in the summer from 2003 to 2018 (except for the years 2004 and 2008), the spatial and temporal variations in ichthyoplankton’s abundance, species composition, and community structure were examined and linked to the variability of the climate system. A positive/negative correlation was found between the abundance and taxonomic diversity of the fish larvae and the monthly Oceanic Niño Index. However, the variation in larval fish’s species diversity was in phase with climate change, while the variation in larval fish’s abundance had a 3-month lag behind the climate variability. The different phases of the correlations reflect a progressive change in the ichthyoplankton dynamics under the influence of climate. Furthermore, during the period of the study, the regional climate underwent an obvious transition from a “cold” to a “warm” state in the early 2010s. Associated with that, it was found that both the abundance and species composition of the ichthyoplankton exhibit a significant change around that time, particularly for the fish larvae. A further examination of the ichthyoplankton’s horizontal distributions suggests that the assemblage of ichthyoplankton in the PRE is sensitive to the La Niña conditions. This leads to an overall reduction in ichthyoplankton’s abundance and less seaward spreading of the assemblage, implying the possible impact of climate change on river discharge and then the estuarine environment.