<strong>Spatial</strong> <strong>distribution</strong> <strong>and</strong> <strong>seasonal</strong> <strong>variation</strong> <strong>in</strong> <strong>Undaria</strong> p<strong>in</strong>natifida populationsaround the Corom<strong>and</strong>el Pen<strong>in</strong>sulaJuly 2012Kate James <strong>and</strong> Nick ShearsLeigh Mar<strong>in</strong>e LaboratoryUniversity of Auckl<strong>and</strong>kjam015@auckl<strong>and</strong>uni.ac.nz,A report prepared for the Waikato Regional Council
11. Executive Summary<strong>Undaria</strong> p<strong>in</strong>natifida (hereafter called <strong>Undaria</strong>) was first officially recorded <strong>in</strong> the Hauraki Gulf, on mussel farm <strong>in</strong>frastructure<strong>in</strong> the Firth of Thames, <strong>in</strong> 2002, <strong>and</strong> subsequently at Hobson West Mar<strong>in</strong>a <strong>in</strong> the Waitemata Harbour <strong>in</strong> 2004. The warmerwaters of the Hauraki Gulf had been considered to be outside the optimal range for <strong>Undaria</strong> growth. However, this hasproven to be <strong>in</strong>accurate. Prior to this report no quantitative <strong>in</strong>formation was available on the <strong>distribution</strong> or ecology of<strong>Undaria</strong> populations <strong>in</strong> the Corom<strong>and</strong>el region.Between November 2011 <strong>and</strong> February 2012 spatial surveys were carried out to <strong>in</strong>vestigate the <strong>distribution</strong> of <strong>Undaria</strong>populations <strong>and</strong> the level of <strong>in</strong>festation present on mussel farms <strong>and</strong> adjacent coastal sites around the Corom<strong>and</strong>elPen<strong>in</strong>sula. In addition, beg<strong>in</strong>n<strong>in</strong>g <strong>in</strong> June 2011 <strong>Undaria</strong> populations were monitored monthly at two sites with<strong>in</strong>Corom<strong>and</strong>el Harbour <strong>and</strong> fortnightly at two sites at Westhaven Mar<strong>in</strong>a <strong>in</strong> the Waitemata Harbour.Sites where mussel farms are established provide suitable habitat for <strong>Undaria</strong> growth. The water quality, flow <strong>and</strong> nutrientlevels required for mussel farm<strong>in</strong>g are <strong>in</strong> l<strong>in</strong>e with ideal <strong>Undaria</strong> grow<strong>in</strong>g conditions <strong>and</strong> the well-illum<strong>in</strong>ated, artificialstructures promote <strong>Undaria</strong> establishment without competition from other macroalga. A survey of <strong>Undaria</strong> was conductedacross all mussel farm sites <strong>and</strong> large areas of adjacent coastl<strong>in</strong>e around the Corom<strong>and</strong>el Pen<strong>in</strong>sula. Further areas of<strong>in</strong>terest surveyed were high use public boat ramps, sw<strong>in</strong>g moor<strong>in</strong>gs, Hannaford’s Jetty <strong>and</strong> the mussel load<strong>in</strong>g facility atTe Kouma. At each site environmental data was collected <strong>and</strong> <strong>in</strong>formation on <strong>Undaria</strong> population structure <strong>and</strong> densitywere recorded. Other <strong>in</strong>vasive species present were also recorded.<strong>Undaria</strong> was found to be widespread on mussel farms around the Corom<strong>and</strong>el Pen<strong>in</strong>sula. It is well established on musselfarm structures from Moturua Isl<strong>and</strong> to Wilson Bay on the west coast of the Corom<strong>and</strong>el Pen<strong>in</strong>sula. Although notprevalent, dur<strong>in</strong>g this survey, on mussel farms at Kennedy Bay or Port Charles, <strong>Undaria</strong> was found on artificial substrateat these sites. Thirty one mussel farms were surveyed, levels of <strong>Undaria</strong> <strong>in</strong>festation were def<strong>in</strong>ed as low to medium (1-100plants per 50 m length of mussel l<strong>in</strong>e) on seventeen, high (>100 plants per 50 m of mussel l<strong>in</strong>e) on eleven <strong>and</strong> <strong>Undaria</strong>was not seen on three farms. Higher density populations were found at poorly ma<strong>in</strong>ta<strong>in</strong>ed mussel farms <strong>and</strong> on mussell<strong>in</strong>es with large mussels, 80-120mm. The exception to this was the high densities of <strong>Undaria</strong> at all mussel farms surveyedat the Wilson Bay Mar<strong>in</strong>e Farm<strong>in</strong>g Zone (WBMFZ) <strong>in</strong> the Firth of Thames, a well ma<strong>in</strong>ta<strong>in</strong>ed site. The vigour <strong>and</strong> density ofthe population seen with<strong>in</strong> the WBMFZ, by far the largest aquaculture site surveyed, may be due to the fact that this is themost long-established population. The size <strong>and</strong> nature of the WBMFZ ensures a constant <strong>and</strong> immense supply of sporesat this site. This high propagule pressure is likely to perpetuate the dense population at this site despite differ<strong>in</strong>g stages ofmussel growth <strong>and</strong> l<strong>in</strong>e/float rotation at <strong>in</strong>dividual farms with<strong>in</strong> the site. Further <strong>in</strong>vestigation <strong>in</strong>to environmental <strong>in</strong>fluencescould reveal other factors promot<strong>in</strong>g the growth <strong>and</strong> proliferation of <strong>Undaria</strong> at this site. <strong>Undaria</strong> is likely spread betweenmussel farms, <strong>in</strong> its sporophyte or microscopic gametophyte phase, via fouled mussel barge hulls, mussel farm<strong>in</strong>gequipment (such as ropes <strong>and</strong> floats) <strong>and</strong> with mussel spat.<strong>Undaria</strong> has not extensively <strong>in</strong>vaded coastal reef areas adjacent to mussel farms. Approximately 12km of coastl<strong>in</strong>eadjacent to mussel farms was surveyed around the Corom<strong>and</strong>el Pen<strong>in</strong>sula. <strong>Undaria</strong> was found at six out of the twenty sixcoastal sites surveyed. This is the first time <strong>Undaria</strong> has been recorded on the Corom<strong>and</strong>el Coast. Total numbersrecorded at any coastal site were between two <strong>and</strong> fifty plants, <strong>in</strong>clud<strong>in</strong>g reproductively mature plants. Relatively lowdensities at coastal sites could reflect poor dispersal to coastal sites, high levels of predation <strong>and</strong> competition <strong>in</strong> theseareas, <strong>in</strong>sufficient time to allow extensive populations to establish <strong>in</strong> these coastal reef communities, or <strong>seasonal</strong> lows dueto the tim<strong>in</strong>g of some of the surveys.No <strong>Undaria</strong> was found at the mussel load<strong>in</strong>g facility/boat ramp at Te Kouma, the sw<strong>in</strong>g moor<strong>in</strong>g sites at W<strong>in</strong>dy po<strong>in</strong>t/PuheRare <strong>and</strong> Takawhare Bay, Hannaford’s Jetty or the two other boat ramp sites surveyed at Colville <strong>and</strong> Waikawau.Monitor<strong>in</strong>g studies found <strong>Undaria</strong> plants to be present, at vary<strong>in</strong>g densities, on Corom<strong>and</strong>el Harbour mussel farmstructures <strong>and</strong> at Westhaven Mar<strong>in</strong>a year round (June 2011 to July 2012). The cycle of plant growth <strong>and</strong> density wasrelated to water temperature. Size <strong>and</strong> density of <strong>Undaria</strong> plants <strong>in</strong>creased steadily from June through until lateOctober/early November when plant lengths <strong>and</strong> the presence <strong>and</strong> volume of sporophylls peaked. This peak <strong>in</strong> plant size<strong>and</strong> reproductive maturity co<strong>in</strong>cided with water temperatures reach<strong>in</strong>g ~17ºC. Average length then showed a steadydecl<strong>in</strong>e, as the mature plants degraded, with the shortest average lengths recorded at Corom<strong>and</strong>el <strong>and</strong> at Westhaven <strong>in</strong>
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