Historical Reconstruction of Phytoplankton Composition in Estuaries of Fiordland, New Zealand: the Application of Plant Pigment Biomarkers

Abstract

Phytoplankton pigments in sediment cores from four New Zealand fjords were quantified to investigate community composition and primary production in this pristine and remote region. Downcore sediment records from Doubtful Sound, Fiordland, were also compared with phytoplankton pigments in sediment traps to investigate pathways of phytodetritus flux from the upper water column to the sediment. Historic primary production was estimated using downcore chlorophyll a (Chl a) and β-carotene as proxies for total algal biomass. Sedimentary Chl a was similar across Fiordland (p = 0.09), but β-carotene was significantly different in Broughton Arm (Kruskal–Wallis p < 0.01). Dominant transformation products of Chl a were steryl chlorin esters and carotenol chlorin esters, indicating the importance of grazing as a sink for phytoplankton in Fiordland. Carotenoids indicative of diatoms and dinoflagellates were recovered in the sedimentary records of Doubtful Sound. Pigment biomarkers were observed in higher quantities in the sediment traps than in the surface sediment. In particular, grazing biomarkers were abundant in the sediment, highlighting the importance of fecal pellet export in phytodetritus preservation. Phytoplankton pigment preservation in Fiordland sediments is good as indicated by little variation in Chl a/pheopigment ratios throughout the cores. This research supports other new work, which has shown that carbon preservation in southern hemisphere fjord ecosystems is more efficient than previously thought.