Efficacy of physical removal of a marine pest : the introduced kelp Undaria pinnatifida in a Tasmanian marine reserve

The tools available for incursion response in the marine environment are limited, both in number and in situations where they can be appropriately applied. The ability to make decisions as to when and where a response should occur is limited by knowledge of the efficacy and costs. We undertook an evaluation of manual removal of Undaria pinnatifida sporophytes in a new incursion in the Tinderbox Marine Reserve in Tasmania over a 2.5 year study period. Plants were removed, from a 800 m2 area, on a monthly basis to minimise the likelihood of maturation of sporophytes and subsequent release of zoospores. While manual removal appears to have significantly reduced the number of developing sporophytes, the persistence of ‘hot spots’ through time suggests that either microscopic stages (zoospores, gametophytes or sporelings) create a ‘seed bank’ that persists for longer than 2.5 years or selective gametophyte survival in microhabitats occurs. In order for manual removal of Undaria to be effective a long term commitment to a removal activity needs to be coupled with vector management and education initiatives to reduce the chances of re-inoculation and spread, with monitoring (and response) on a larger spatial scale for the early detection of other incursion sites, and with a treatment to remove persistent microscopic stages.