Distinguishing impacts of climate change and human activities on phytoplankton communities in remote coastal waters: A paleoecological perspective

• Published in: Marine pollution bulletin Vol. 217; p. 118057
• Main Authors: Zhou, Chongran, Liu, Dongyan, Keesing, John, Masqué, Pere, Yuan, Zineng
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.08.2025
• Subjects: Anthropogenic Effects; Bays; Climate Change; Community structure; Diatom; Diatoms; Ecosystem; Environmental Monitoring; Eutrophication; Geologic Sediments; Human Activities; Humans; Nitrogen - analysis; Phytoplankton; Sediment; Silicoflagellate; Temperature; Silicoflagellate; Community structure; Diatom; Temperature; Sediment; Eutrophication
• ISSN: 0025-326X; 1879-3363; 1879-3363
• DOI: 10.1016/j.marpolbul.2025.118057

Distinguishing between climatic and anthropogenic influences to accurately assess their respective impacts on coastal phytoplankton dynamics remains a complex challenge. Northwestern Australia (NWA), largely free from direct human disturbances, presents a unique natural laboratory for disentangling these factors. This study reconstructs phytoplankton community dynamics over the past century by analyzing sedimentary diatoms and silicoflagellates from sediment cores in Roebuck Bay, which experiences mild eutrophication, and Cygnet Bay, which remains relatively pristine. Total nitrogen (TN) and stable nitrogen isotopes (δ15N) were employed as proxies to trace anthropogenic nutrient inputs. Results suggest that shifts in the Pacific Decadal Oscillation (PDO) and variability in the Indonesian Throughflow (ITF) contributed to increased phytoplankton biomass and a rise in silicoflagellate dominance during 1950–1970 and after 2000. Meanwhile, anthropogenic nutrient enrichment in Roebuck Bay, evident from elevated TN and δ15N levels after 1967, correlated with increased Shannon Diversity Index and a shift in community structure, favoring planktonic over benthic species. These findings highlight the distinct interconnected roles of climatic variability and human activities in shaping the NWA ecosystem, underscoring the need for continued monitoring and research. •Nitrogen isotopes identified anthropogenic nutrient input processes.•Climate change likely dominated shifts in algal biomass.•Nutrient inputs increased planktonic algae but reduced benthic species.•Silicoflagellates may serve as effective climate reconstruction proxies.