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

TR 2013/15
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Report: TR 2013/15

Author: K James and N Shears (Leigh Marine Laboratory, University of Auckland)

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.

Spatial distribution and seasonal variation in Undaria pinnatifida populations around the Coromandel Peninsula [PDF, 2.3 MB]

Contents
1 Executive summary 1
2 Introduction 1
3 Methods 5
3.1 Spatial distribution survey 5
3.1.1 Mussel farm locations 5
3.1.2 Coastal reef locations 6
3.1.3 Other "high risk" locations 6
3.1.4 Semi-quantitative measurements of Undaria abundance 6
3.1.5 Other invasive species 7
3.2 Seasonal monitoring of Undaria populations 8
3.2.1 Coromandel monitoring 8
3.2.2 Westhaven monitoring 9
3.3 Environmental data 9
4 Results 10
4.1 Spatial distribution survey 10
4.1.1 Coastal survey 10
4.1.2 Mussel farm survey 13
4.1.3 "High risk" sites 15
4.1.4 Other invasive species 16
4.1.5 Environmental data 16
4.2 Seasonal monitoring of Undaria populations 17
4.2.1 Environmental variation at monitoring sites 17
4.2.2 Temporal distribution and population dynamics of Undaria populations 19
5 Discussion 23
5.1 Spatial distribution of Undaria around the Coromandel Peninsula 23
5.2 Temporal distribution and population dynamics 25
5.3 Other invasive species 26
5.4 Implications and considerations 26
  References 28
  Appendix 1 - Maps of Undaria infestation at mussel farms, high risk and coastal survey sites 30
  Appendix 2 - Summary of coastal transect information 34
  Appendix 3 - Summary of mussel farm survey information 36
  Appendix 3A - Mussel farm invasive species information 36
  Appendix 3B - Mussel farm site environmental information 38
  Appendix 4 - Size frequency distribution of monitoried Undaria populations 39