Spatial distribution of Undaria 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. 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 study no quantitative information was available on the distribution or ecology of Undaria populations in the Coromandel region. Results of the survey showed that sites where mussel farms are established provide suitable habitat for Undaria growth. 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. 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.Higher density populations were generally found at poorly maintained mussel farms and on mussel lines with large mussels, 80-120mm. Undaria has not extensively invaded coastal reef areas adjacent to mussel farms. Monitoring studies found Undaria plants to be present, at varying densities, on Coromandel Harbour mussel farm structures and at Westhaven Marina year round (June 2011 to July 2012). Results indicate that the warmer waters of the Hauraki Gulf may produce smaller plants with a slower growth rate than those found in cooler waters. 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. It is apparent that introducing mussel farm infrastructure to a site will likely result in the introduction of Undaria that site. If mussel farms are to be placed in High Value Conservation sites or sites near marine reserves it must be taken into consideration that Undaria will then be introduced to these sites. Purpose: The study had two main objectives: 1. Investigate the spatial distribution of Undaria populations and levels of infestation on mussel farms and adjacent coastal sites around the Coromandel Peninsula. 2. 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 surveys were carried out between November 2011 and February 2012 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 and fortnightly at two sites at Westhaven Marina in the Waitemata Harbour. At each site environmental data (water clarity, temperature, nitrate, nitrite and ammonia) was collected and information on Undaria population structure and density were recorded. Other invasive species present were also recorded. Approximately 12km of coastline adjacent to mussel farms was surveyed around the Coromandel Peninsula.

Coromandel Peninsula

Between November 2011 and February 2012

Mussel farm locations: outermost lines at each end of each mussel farm and some inner lines assessed. Numbers of mussel lines surveyed at each farm was generally relative to the total number and size of lines present. Surveys of lines were conducted with snorkel and/or SCUBA. Effort concentrated near the surface. A total of 268 transects were run along 132 mussel lines at 31 different mussel farms. Notes were taken on the size distribution and reproductive status of the Undaria surveyed at each line. other invasive species was also noted. Representative photographs were taken of Undaria and/or other invasive species present. A minimum of five mussels were measured on every line surveyed and the average mussel size was calculated for each of these lines. Coastal reefs: 50 x 10m transects were run along sections of coast adjacent to all mussel farm locations on the Coromandel Peninsula. A total of twenty six coastal reef areas were surveyed via SCUBA and/or snorkel. Sampling was concentrated on the shallow-subtidal margin of the reef, typically just below the low-tide mark. The depth of the surveys conducted ranged from one to five metres, depending on habitat and tide levels, with an average depth across the total 244 transects of 2.4m. Frequency of collection: One off data collection

see report Gaps in collection: Some farms were surveyed less thoroughly than others due to poor weather conditions and some farms did not have lines in the water at the time of surveying. Data quality: see report

Report available in electronic form at Regional Council website (see below) Digital Format: Available as .pdf at http://www.waikatoregion.govt.nz/tr201315

Report freely available online. Sensitivity/Confidentiality: None

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