Scale of disturbance and the structure of a temperate fish guild

Although it is acknowledged that the spatial scale of sampling and experime ntation mentation is important in assessing the degree of stability of a co mmunity, multiple scales are rarely incorporated into the same study. We co mpared the persistence and resilience of a temperate blennioid fish guild a t three scales spanning an order of magnitude. Replicate permanent square q uadrats of three sizes (4 m(2), 25 m(2), 100 m(2)) were delimited within co ntiguous tracts of reef in two habitats: broken reef and macroalgal forest. Two forms of disturbance were applied to the treatment quadrats. Direct di sturbance (fish removal) was applied to treatments in the broken reef habit at. Indirect disturbance (macroalgal removal) was applied to treatments in the macroalgal forest. Both experiments identified several scale-dependent effects. Large quadrats were less variable than smaller quadrats, probably due to reduced edge effects due to movement of fish in and out of the quadr ats. The smallest quadrats did not adequately represent the available subst ratum types within the reef zone. This interacted with species-specific beh avioral factors such as mobility and habitat association to consistently bi as the blennioid composition within the smallest quadrats toward dominance of the most sedentary blennioid species. Fish responded to disturbance in d ifferent ways depending on the stage of their life cycle. Adult fish respon ded at scales within their motility range of only a few meters. In contrast , newly settling fish responded to the habitat at larger scales. Quadrat si ze also determined which assemblage dynamics could be measured. Within-year changes in guild composition due to species-specific settlement timing and survivorship could be measured only at larger scales. We conclude that dif ferent scales of monitoring and manipulation will determine what can be per ceived by the researcher as well as how the organism will respond to distur bance.