Acerca del seguimiento, monitoreo y evaluación

Even though spore dispersal alone may explain the scale of spread at Karaka Point, other natural mechanisms, such as the drift of sporophytes or fragments that release

were noted in the Karaka Point survey area during the course of this study, particularly in early summer when sporophytes began to senesce and were easily displaced by waves generated naturally and by vessel traffic. In areas of strong water current in Tasmania, drifting sporophytes are believed to facilitate the dispersal of Undaria over scales of up to 10 km (Sanderson 1997).

Our findings also suggest another potential mechanism of longer range dispersal. High densities of spores near the water surface (e.g., because of surface tension) may lead to clumping, as was observed in the laboratory. Clumping during dispersal could increase the likelihood of male and female gametophytes maturing in close proximity, promoting fertilization and the initiation of a new sporophyte generation; Santelices (1990) has discussed the potential benefits of dispersal of aggregated seaweed propagules. However, while clumping of spores may circumvent problems caused by the physical ‘dilution’ of propagules, other factors may become limiting during long-range dispersal. For example, grazing in the water column may reduce propagule densities, or propagules may lose their ability to attach over time. Suto (1950) notes that Undaria spores lose the ability to attach after several hours, although attachment was evident after fourteen days in the present study.

Hence, Undaria may exhibit multiple dispersal strategies, as has been noted for many other macroalgae, including invasive species such as Sargassum muticum (Hoffmann 1987; Norton 1992). Spore dispersal in Undaria is probably a key mechanism for short- range (metres to hundreds of metres) spread from fixed stands. Short-range dispersal would maintain established stands of sporophytes and increase densities adjacent to such stands, as observed at Karaka Point. Dispersal via whole sporophytes or fragments, and possibly via spore clumping, is likely to be particularly important in range extensions of Undaria over scales of hundreds of metres to kilometres, with episodic or chance events potentially leading to spread at even greater scales (Reed et al. 1988). Subsequent short-range dispersal of spores around the more distant and scattered ‘frontier’ individuals at the boundary of the population would establish a new sporophyte stand by gradual infilling and enhance the propagule supply for further spread. The multiple dispersal strategies for Undaria described here may play an especially significant role in facilitating rapid spread within regions where human-

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