Differential response mechanisms of kelp aquaculture in Rongcheng and Changdao, Shandong Province, to abnormal coastal currents in autumn 2021

Abstract

In the autumn of 2021, an unprecedented kelp mortality event occurred in the Rongcheng kelp aquaculture area of Shandong Province, China, triggered by the invasion of an anomalous North Shandong Coastal Current (NSCC) following an extreme inland rainfall and subsequent environmental anomalies. In contrast, the Changdao kelp aquaculture area, located near the northern coast of the Shandong Peninsula, did not experience such mortality. The reasons behind this differential response remain unclear. In this study, we utilized remote sensing satellite images and open-access datasets to analyze the differential responses and environmental driving mechanisms of the Rongcheng and Changdao kelp aquaculture areas to the coastal current invasion. The results indicate that the severe kelp mortality event in Rongcheng during autumn 2021 did not impact the Changdao kelp aquaculture area because the Northern Five Islands (NFIs), the primary kelp-producing region, were not exposed to the anomalous coastal waters characterized by low suspended sediment concentration (SSC) and high chl-a levels. The anomalous intrusion of the NSCC in November 2021, driven by a sea surface height difference and eastward wind stress established by an autumn Yellow River flood and exacerbated winter northwesterly winds, accounted for the significantly low SSC and high chl-a concentrations in Rongcheng. Conversely, the NFIs in Changdao remained outside the impact zone of this anomalous NSCC. The long-term analysis also confirmed that the NFIs were typically unaffected by the NSCC, with synoptic-scale variations in SSC primarily governed by sediment resuspension due to wind waves. This study reveals the contrasting impacts of climate change on adjacent coastal ecosystems and aquaculture industries, highlighting the necessity for focused assessments and tailored adaptive strategies that consider specific environmental contexts to effectively mitigate climate-induced impacts.