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ABSTRACT:The mechanisms by which non-indigenous species overcome resistance in native communities are not well understood but are fundamental to the ability of invaders to persist and spread once they reach alien shores. One of the most widespread invaders is the kelp Undaria pinnatifida. Here we test disturbance, competition and facilitation in its recruitment into intertidal algal communities in southern New Zealand. In field-based experiments, we manipulated native fucoid and U. pinnatifida canopies, as well as the abundance and type of understory turfing species, and provided various gap sizes in native communities. Undaria pinnatifida recruitment occurred almost exclusively on coralline turf and in the absence of canopies, both native and conspecific. Where the native fucoid canopy was removed, U. pinnatifida recruited into gaps of all sizes (5 × 5 cm, 25 × 25 cm, 50 × 50 cm), but the smallest gaps recovered their native canopy within several months and precluded further recruitment. Experimental manipulations of coralline turf showed that recruitment of U. pinnatifida was orders of magnitude greater where turf was present, regardless of the timing or sizes of clearances. Facilitation did not occur with other turfing species. Overall, native fucoids showed high resistance to invasion, but there was great facilitation by native coralline turf. Furthermore, as annual U. pinnatifida canopies disappear over summer, it is clear that coralline turf harbors the microscopic stages of U. pinnatifida that will form the following year's populations. As turfing species increase and persist following disturbances of native canopies worldwide, it can be expected that the recruitment dynamics of non-indigenous species will also change.

Heterozius rotundifrons is a New Zealand endemic crab that lives in the intertidal zone and is found under rocks during low tides. We investigated the role of the local sex ratio (= under rock) in affecting movement patterns of this crab. In the laboratory, male crabs moved more when the sex ratio was male biased. Field surveys suggested that there is an upper limit to the number of males found under rocks, even as the number of females increases. Field manipulations demonstrated that when the sex ratio under a rock is female biased there is no effect on female movement but when the ratio is male biased, males move away more frequently and move further. This increased movement by males is probably related to avoidance of male-male competition for females.

The Belliidae are a small family of crabs whose relationships with other families are enigmatic and whose composition is controversial. It is by no means certain whether their genera form a monophyletic group. One member of this family is Heterozius rotundifrons, a New Zealand endemic crab that lives in the intertidal zone, sheltering under rocks. In the present study the mating behaviour of this species was examined under laboratory conditions. Mating and moulting are closely linked because H. rotundifrons females only mate immediately after moulting. Females remain attractive to males for almost 3 days. A female-derived water-borne pheromone seems to be the basis of this attraction. Prior to moulting males guard females for up to 5 days. During the female moult some males were observed to assist the female. During copulation both males and females exhibited an unusual limb quivering behaviour and afterwards males guarded the females for 10.5 h, which was extended to 37 h when other males were present. Field studies showed that females moulted during early spring over a period of 1 month. Throughout the year very few females moulted, suggesting that there may be intense competition for mates during the early spring. At all times the operational sex ratio was biased in favour of males. In terms of the evolution of reproductive characters among the Belliidae, Atelecyclidae, Cheiragonidae and Corystidae, H. rotundifrons occupies an intermediate position between the ancestral condition and that seen in Corystes cassivelaunus.

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