Assessing the impact of climate variability on exposure indices of Portunid crabs in the Southern East China sea

Abstract

Climate-driven variability is altering Taiwan's marine ecosystems, with implications for Portunid crabs (Charybdis feriatus, Portunus pelagicus and Portunus sanguinolentus). This study assessed species-specific exposure to climate-driven changes using an exposure index (Ex) derived from five key environmental variables: chlorophyll-a (Chl-a), sea bottom temperature (SBT), sea surface salinity (SSS), sea surface height (SSH) and sea surface temperature (SST). Fishery-dependent data (2013-2022) were standardized using the Vector Autoregressive Spatio-Temporal (VAST) model, while individual exposure scores for each environmental variable were weighted by variable importance in projection (VIP) through partial least squares regression (PLSR). Results showed that exposure was strongly seasonal and species-specific; high exposure index (Ex >= 0.6) occurred mainly in spring - summer, overlapping with spawning periods and peak fishing effort, compounding risks to recruitment and population stability. Exposure differed among species, with SSH carrying the greatest weight for C. feriatus and P. sanguinolentus, and SSS most prominent in winter, while SST, SSS and SSH carried the greatest weight for P. pelagicus. Among climate indices, Ni & ntilde;o 3.4 aligned positively with winter - spring exposure (most evident for C. feriatus). The NPO provided short leads (1-4 months) to higher Ex, while the PDO co-varied with exposure in spring and summer, especially for C. feriatus and P. sanguinolentus. Overall, understanding how climate variability raises exposure is essential for adaptive management; real-time monitoring to trigger short closures during vulnerable periods can protect recruitment and support SDG-14.