Penaeid shrimp postlarval abundance, phenology, and links to environmental conditions over four decades

Species with complex life cycles often occupy multiple habitats during different life stages. Shrimps in the genus Penaeus are globally distributed, play important roles in food webs, and support valuable fisheries. Before recruiting to the benthos, planktonic stages (e.g. postlarvae) ingress into estuaries. We conducted biweekly collections of postlarval penaeids for 37 yr (1981-2017) in the North Inlet estuary, South Carolina, USA, which revealed seasonal and interannual patterns and trends for white Penaeus setiferus , brown P. aztecus , and pink shrimp P. duorarum . Despite being rare as juveniles or adults in our region, pink shrimp were the most abundant species as postlarvae, identifying the postlarval-juvenile transition as the population bottleneck in the region. During our 4-decade study, postlarval white and brown shrimp abundance increased, and the increase in white shrimp was positively correlated with increasing mean winter water temperature. Abundance of white shrimp was also substantially higher after warm winters. Conversely, the seasonal peak in brown shrimp abundance was more compressed following cold winters. While long-term trends in salinity were not apparent, both brown and white shrimp annual abundance declined as salinities increased, possibly indicating salinity-mediated decreases in estuarine ingress. Generally, increasing postlarval abundances as water temperatures increase suggests that long-term environmental changes have been favorable to penaeid shrimp in South Carolina, located near the northern limits of their distributions. However, changes in the timing of occurrence in response to environmental change raises questions about the structure and stability of estuarine communities considering the important roles these species play in estuaries.