Colonization of novel habitat: Tests of generality of patterns in a diverse invertebrate assemblage

Understanding colonization and use of novel habitat by diverse assemblages is increasingly important as natural habitats are disturbed or replaced. How well novel habitats will be used by biota depends on (i) how well they mimic natural habitat and (ii) how adaptable are the fauna in utilizing different types of habitat. Much of our understanding of colonization of patchy habitats is derived from studies in which colonizing fauna respond strongly to biotic stimuli. Comparisons of patterns of colonization among patches, across landscapes, over time, etc., may thus be confounded by differences in the quality of the patches themselves, which may interact with other features of the broader landscape. Intertidal boulder-fields have many features that make them ideal for extending studies of colonization by diverse assemblages because the organisms living on boulders live in naturally patchy habitats, separated by a matrix which is differentially permeable to different components of this biota. This study used standardized, novel patches of habitat as surrogates of natural boulders in order to control the physical features of these patches. These units of habitat resemble quarried rock that is frequently added to nearshore environments in the form of groynes or breakwaters, or which is commonly disposed of in urbanized estuaries. Previous work has shown that they are readily colonized and used by a similar range of taxa as are natural boulders. Here, they were added to existing boulder-fields to test specific hypotheses regarding colonization of different types of patches across replicate sites, times, periods of deployment and levels of taxonomic grouping. All tests showed extremely variable colonization, with little support for more deterministic models that have been proposed to explain species–habitat relationships. Variability in colonization mimicked natural levels of variability in these fauna reported elsewhere. Colonization of novel habitats in this system seems therefore to be strongly influenced by stochastic variation in supply of colonists and their ability of colonists to utilize and move through he surrounding matrix, rather than on the quality of habitat itself. This needs careful consideration in attempts to manage or repair damaged marine habitats.