Proliferation of the invasive kelp Undaria pinnatifida at aquaculture sites promotes spread to coastal reefs

摘要

Aquaculture is a significant vector for the introduction of invasive species worldwide. Understanding factors influencing the proliferation and spread of invasive species from aquaculture sites to native habitats is necessary to develop management strategies aimed at mitigating their spread and subsequent impacts. This study compares population dynamics of the invasive kelp Undaria pinnatifida between mussel farms and a natural reef site in northern New Zealand (36 degrees 35'S 175 degrees 05'E) and investigates how the abundance of U. pinnatifida on mussel farms, and its presence on adjacent reefs, relates to different environmental variables and physical attributes of mussel farms. Monitoring from 2011 to 2014 found that U. pinnatifida on mussel farms were larger and more seasonally and reproductively persistent compared to populations on adjacent reefs. Region-wide surveys found U. pinnatifida at all mussel farming sites examined (n = 25) and at eight adjacent reefs. Coastal populations were most abundant in reef habitats lacking native macroalgal canopies. Abundance of U. pinnatifida on mussel farms was related to the size of mussels present, but not strongly related to wave exposure, turbidity or spatial attributes of farms. Undaria pinnatifida was found on a number of native reefs adjacent to mussel farms, but its presence on these reefs was not related to the size of farms or distance from shore. These results demonstrate how marine farms provide an optimal environment for the proliferation of invasive species, and management strategies must consider that farms of any size or position relative to shore pose a risk of introducing invasive species to native habitats.