Linking physical and biogenic habitats to reveal Kapiti Island's submarine landscape

Abstract

Kapiti Island is one of New Zealand's most important small islands, hosting an ecologically important nature reserve that is juxtaposed by an equally important marine reserve. Although the geology surrounding Kapiti Island is dynamic with several active faults, information about seafloor morphology dates from the 1990s and has a low level of detail. Identifying the geomorphology and biogenic habitats of an area are essential to understanding the processes influencing species' distributions, ecological interactions and managing the marine environment. Through a collaborative mapping initiative, we mapped the seafloor using a Kongsberg EM2040 Multibeam Echosounder (MBES) to produce highly detailed maps of the reserve and surrounding area. Preliminary bathymetry data was visually analysed and segmented into 18 habitat types that were used to ground-truth the multibeam and define biogenic habitats. Ground-truthing included 214 camera drops, 12 sled tows and 46 dives distributed over the 18 habitat types. We present here the compilation of ground-truthing and multibeam data to reveal the diversity of physical and biogenic habitats that comprise the submarine landscape surrounding Kapiti Island, which include: soft sediments with associated infaunal communities, large areas of rock rubble and gravels with mobile invertebrates, extensive anemone and rhodolith beds, boulder fields with dense macroalgal stands, flat and complex rocky reefs encrusted with a diversity of invertebrates and algae. This multidisciplinary and scalar approach supports a greater ability to effectively manage the area and promote awareness of the richness, diversity and complexity of the seafloor of the Kapiti Island region and the biota it supports.