Spatial distribution and seasonal variation in Undaria pinnatifida populations around the Coromandel Peninsula

Abstract

Undaria pinnatifida is a large laminarian kelp. Undaria is an annual with several different life stages. It was introduced to New Zealand waters in the 1980s by Asian fishing vessels. It is known to have direct negative impacts on indigenous biota and it can change the entire structure of marine ecosystems. Since its detection in Wellington in 1987, Undaria has spread rapidly around New Zealand coasts and is now widespread around most of New Zealand’s eastern and southern coastlines from Auckland to Bluff. Vessel hulls and aquaculture equipment are known to be the main dispersal pathways. Quantitative data on the extent and nature of Undaria populations in the wider Hauraki Gulf including the Coromandel area are currently lacking. The potential exists for this highly invasive species to spread to regions regarded as having high conservation values such as marine reserves and Hauraki Gulf islands. Data on the distribution and biology of Undaria in the Hauraki Gulf is necessary to determine the risks of future spread, the potential impact on environmental values and on marine farming, and in general to inform management decisions regarding this invasive species. The present study has two main objectives: Investigate the spatial distribution of Undaria populations and levels of infestation on mussel farms and adjacent coastal sites around the Coromandel Peninsula. Investigate seasonal variation in the structure and biology of Undaria populations at sites around the Coromandel Peninsula and at Westhaven Marina in the Waitemata Harbour. Sites at Coromandel and Westhaven were monitored from June 2011 to July 2012.