A MARINE BIOTA AND SEDIMENT ANALYSIS OF RĀPAKI BAY, NEW ZEALAND

Our research aims to provide a baseline environmental survey of Rāpaki Bay from which future research and monitoring can continue. Over the past 150 years since European contact, mass deforestation has devastated the hillsides of Banks Peninsula/Te Pātaka o Rākaihautū, leaving unstable loess soils which characterise the area vulnerable to erosion. Consequently, increased rates of sedimentation have negatively impacted the biota of Lyttelton Harbour/Te Whakaraupō, which includes Rāpaki Bay. We present a survey of sediments and intertidal biota in Rāpaki Bay and catchment, where the Ngāti Wheke marae (customary meeting house) is situated. We collected sediment samples simultaneously with pipi (Paphies australis) and cockle (Austrovenus stutchburyi) data from three transects along Rāpaki Bay Beach. Rocky intertidal biota data was collected at four transects in high, mid, and low tide zones. We found three potential beach sediment sources: loess, volcanics, and calcium-rich sediment. The beach is more dominated by loess and calcium-rich sediment than volcanics. Dredging within the harbour may also contribute to the infilling of the bay. As for intertidal biota, we found that further offshore, the number of pipis declines in coordination with a shift towards finer sediment. Our data is a snapshot of the ecosystem in Rāpaki Bay in the Spring of 2023, and will be used as a baseline for future comparison to track the progress of efforts to nurture the mauri of Rāpaki and Lyttelton Harbour/Te Whakaraupō at large.