Anchors aweigh: Fragment generation of invasive Caulerpa taxifolia by boat anchors and its resistance to desiccation

We use two experiments to assess the role of anthropogenic activities in disseminating the invasive alga, Caulerpa taxifolia. First, we tested the hypothesis that the removal of fragments of C. taxifolia from an estuary would be dependent on anchor type (sand versus rock) and anchor attachment (chain versus rope). Second, we hypothesised that the viability of different sized clumps (1, 5 and 10 g dry weight) of C. taxifolia would be dependent on aerial exposure (1 h, 1 day and 3 days) and environmental conditions (sun versus shade, damp rope versus no rope). Fragments of C. taxifolia were consistently removed by anchors regardless of the anchor type; overall, 82% of anchors lowered into C. taxifolia beds removed fragments. Rock and sand anchors removed similar sized clumps of C. taxifolia (up to 15 g dry weight), while chain attachments removed significantly larger clumps compared to ropes (up to 0.5 g dry weight). Once removed from the water, fragment survivorship increased with clump size, protection from desiccation (i.e. greatest under damp shaded ropes) and decreased with length of aerial exposure. Most shaded clumps survived 1 h of aerial exposure, while none, irrespective of their size, survived 3 days. Our study confirms that the anchoring of vessels removes fragments of C. taxifolia from estuaries and that conditions inside anchor lockers may enhance fragment survivorship. Thus, vessels may be an important vector for dispersal of C. taxifolia within and between estuaries.