Distribution of Undaria pinnatifida populations on the Coromandel Peninsula.

Undaria pinnatifida (Undaria) was first officially recorded in the Hauraki Gulf, on mussel farm infrastructure in the Firth of Thames, in 2002, and subsequently at Hobson West Marina in the Waitemata Harbour in 2004. The warmer waters of the Hauraki Gulf had been considered to be outside the optimal range for Undaria growth. However, this has proven to be inaccurate. Prior to this report no quantitative information was available on the distribution or ecology of Undaria populations in the Coromandel region. A survey of Undaria was conducted across all mussel farm sites and large areas of adjacent coastline around the Coromandel Peninsula. Further areas of interest surveyed were high use public boat ramps, swing moorings, Hannaford’s Jetty and the mussel loading facility at Te Kouma. At each site environmental data was collected and information on Undaria population structure and density were recorded. Other invasive species present were also recorded. Undaria was found to be widespread on mussel farms around the Coromandel Peninsula. It is well established on mussel farm structures from Moturua Island to Wilson Bay on the west coast of the Coromandel Peninsula. Although not prevalent, during this survey, on mussel farms at Kennedy Bay or Port Charles, Undaria was found on artificial substrate at these sites. Thirty one mussel farms were surveyed, levels of Undaria infestation were defined as low to medium (1-100 plants per 50 m length of mussel line) on seventeen, high (>100 plants per 50 m of mussel line) on eleven and Undaria was not seen on three farms. Higher density populations were found at poorly maintained mussel farms and on mussel lines with large mussels, 80-120mm. The exception to this was the high densities of Undaria at all mussel farms surveyed at the Wilson Bay Marine Farming Zone (WBMFZ) in the Firth of Thames, a well maintained site. The vigour and density of the population seen within the WBMFZ, by far the largest aquaculture site surveyed, may be due to the fact that this is the most long-established population. The size and nature of the WBMFZ ensures a constant and immense supply of spores at this site. This high propagule pressure is likely to perpetuate the dense population at this site despite differing stages of mussel growth and line/float rotation at individual farms within the site. Further investigation into environmental influences could reveal other factors promoting the growth and proliferation of Undaria at this site. Undaria is likely spread between mussel farms, in its sporophyte or microscopic gametophyte phase, via fouled mussel barge hulls, mussel farming equipment (such as ropes and floats) and with mussel spat. Undaria has not extensively invaded coastal reef areas adjacent to mussel farms. Approximately 12km of coastline adjacent to mussel farms was surveyed around the Coromandel Peninsula. Undaria was found at six out of the twenty six coastal sites surveyed. This is the first time Undaria has been recorded on the Coromandel Coast. Total numbers recorded at any coastal site were between two and fifty plants, including reproductively mature plants. Relatively low densities at coastal sites could reflect poor dispersal to coastal sites, high levels of predation and competition in these areas, insufficient time to allow extensive populations to establish in these coastal reef communities, or seasonal lows due to the timing of some of the surveys. No Undaria was found at the mussel loading facility/boat ramp at Te Kouma, the swing mooring sites at Windy point/Puhe Rare and Takawhare Bay, Hannaford’s Jetty or the two other boat ramp sites surveyed at Colville and Waikawau. Two other invasive species were prevalent on mussel farm structures. The clubbed tunicate Styela clava was found on all the mussel farms surveyed and the green seaweed Codium fragile ssp. tomentosoides was present on twenty eight out of the thirty one farms surveyed. The Asian paddle crab Charybdis japonica was found at two coastal sites. Purpose: Between November 2011 and February 2012 spatial surveys were carried out to investigate the distribution of Undaria populations and the level of infestation present on mussel farms and adjacent coastal sites around the Coromandel Peninsula. In addition, beginning in June 2011 Undaria populations were monitored monthly at two sites within Coromandel Harbour.

Records of Undaria at five (non-mussel farm) sites on the western Coromandel Peninsula (present in 5 out of 26 sites surveyed). Description/observations. Also description of infestations at mussel farm sites (Undaria found at all farm sites surveyed on western Coromandel Peninsula). Seawater nutrient and plant length data presented.

Coromandel Peninsula. The mussel farms around the Coromandel Peninsula were split into twelve survey locations. Ten locations are on the western side of the Peninsula and the other two are on the eastern coastline at Kennedy Bay and Port Charles (Figure 1).

between November 2011 and February 2012

The starting point for this survey was mussel farm structures. Mussel farm locations were identified from Waikato Regional Council survey maps and although not all individual mussel farms could be surveyed at least one farm at each geographic grouping of farms was inspected. The possible spread of Undaria from mussel farm infrastructure to adjacent coastal reef systems was examined by surveying coastal sites adjacent to every mussel farm or group of mussel farms around the Coromandel Peninsula. Mussel farms and adjacent reef habitats were accessed from the University of Auckland research vessel R.V. Hawere. A combination of snorkelling and diving observations were used as required. Other “high risk” areas for Undaria colonisation are those frequented by recreational and commercial boat traffic (Hay and Luckens, 1987; Hay, 1990, Russell et al, 2007; Verlaque, 2007). Areas with high boat traffic such as swing mooring sites and boat ramps were surveyed. In-water surveys were carried out at most sites. Some shore and kayak based inspections were also carried out. Frequency of collection: One-off survey

Data in report listed below. Digital Format: Unknown.

None Sensitivity/Confidentiality: None.

Complete