Abstract

Increases in frequency and intensity of physical disturbances under climate change will result in increases in microhab-itat fragmentation and episodic mortality of resident fish populations, freeing previously occupied space. It is important to understand how the fragmentation of unoccupied habitat will affect the replenishment of fish populations, particularly soon after settlement, when fishes are most vulnerable. This study looks at the effect of microhabitat patch size on the abun-dance, survivorship and growth of newly settled bicolour damselfish Stegastes partitus in the absence of older resident fishes. We used standardized microhabitat settlement units arranged in two different patch size configurations, i.e. small (1 unit) and large (2x3 units), to monitor the abundance of bicolour recruits onto replicate size patches during a large natural settlement pulse. We expected that smaller patches would exhibit lower recruit abundance but higher density than larger patches because of their higher perimeter-to-area ratio. Consequently, we also expected stronger intra-cohort density-dependent effects on recruit growth and early-post settlement mortality in the small patches. Over a three-week period, we recorded a total 225 bicolour recruits onto the experimental patches. As predicted, we found that the smaller patches had higher densities than larger patches, resulting in higher intra-cohort aggression in the smaller patches. However, we found no difference in recruit growth or mortality between patch sizes, indicating no measurable aggression effects on these demographic rates. Overall, our results indicate that bicolours readily tolerate high crowding soon after settlement and so this species might be little affected by fragmentation of unoccupied habitat when it is most vulnerable to mortality.

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