Temporal and spatial distributions of calanoid copepod eggs in intertidal sediment of a tropical coastal lagoon

Abstract

This study examined the temporal and spatial distributions of calanoid copepod eggs in the intertidal sediment of Tapong Bay, a tropical lagoon in southwestern Taiwan. Copepod and sediment samples were collected from five stations across dry, rainy, and post-rainy seasons in 2020-2021, alongside measurements of salinity, temperature, and precipitation. Benthic calanoid egg abundance in sediment was estimated using a sucrose flotation protocol, while the abundances of ready-to-hatch egg- and resting egg-derived copepods were assessed through experimental incubations. Taxonomic analysis identified the isolated benthic eggs and egg-derived copepods as Acartia cf. tsuensis, a species known to be introduced into Tapong Bay from nearby brackish aquaculture ponds. For temporal distribution, abundances of benthic eggs in sediment were higher during the dry and post-rainy seasons, correlating with increased numbers of resting egg-derived copepods, likely a response to salinity stress on the copepod population. In contrast, warmer and brackish conditions during the rainy season favored the emergence of ready-to-hatch egg-derived copepods, resulting in reduced benthic egg accumulation. Spatially, higher abundances of benthic eggs and egg-derived copepods were documented in the inner-bay area, where poor tidal water exchange and inflows from aquaculture ditches may limit their dispersal. This is the first study to document the temporal and spatial distributions of A. cf. tsuensis eggs in Tapong Bay, suggesting how environmental conditions shape their reproductive patterns and distribution in this tropical ecosystem.