INSIGHTS FROM BENTHIC FORAMINIFERA ON LYTTELTON HARBOUR, NEW ZEALAND, SEDIMENT CONDITIONS AND ANTHROPOGENIC IMPACTS

Benthic foraminifera are shelled protists that are common in marine sediments and are an ideal tool for monitoring and characterizing the health of marine ecosystems. Lyttelton Harbour, New Zealand, hosts the Port of Lyttelton and has undergone frequent dredging, yet the anthropogenic impacts of these activities on the Harbour remain poorly understood. This study characterized the benthic foraminifera in Lyttelton Harbour to investigate sediment conditions and organic pollution impacts on preservation of forams in Harbour sediments and to determine living depth of forams in the Harbour. Three 20-cm push cores were collected in Charteris Bay, Lyttelton Harbour, subsampled, and stained to reveal live and dead forams at the time of collection. Forams were picked and characterized by species, density per gram of sediment, size, live or dead status, and corrosion (for calcareous taxa). Results are compared to the neighboring Avon-Heathcote/Ihutai Estuary, which has higher pollutant levels from nearby Christchurch wastewater treatment plants. Charteris Bay cores were dominated by Ammonia aoteana and exhibited low diversity, typical of marginal marine environments. Foram density decreased up the cores, which could be indicative of increasing sedimentation rates in Lyttelton Harbour due to dredging and sediment redistribution from the Port of Lyttelton. Foram densities in Lyttelton Harbour were high compared to the Avon-Heathcote/Ihutai Estuary, suggesting heathier sediment conditions in Lyttelton Harbour. Corrosion of calcareous taxa increased with depth, likely due to increasing decomposition and pore-water acidity with depth. Living depth did not deepen moving inshore due to less frequent inundation as had been hypothesized. This trend could be due to a surface bloom of Trochammina inflata in the highest intertidal core. Future work should sample Lyttleton Harbour foraminifera and geochemistry over greater spatial and temporal gradients, potentially to establish a baseline for future monitoring efforts.