Alteration of the configuration of bioengineers affects associated taxa

Modification of the abiotic environment and creation of habitat by ecosystem engineers is an important ecological process. According to landscape ecology, the configuration (distance apart and spatial arrangement) of patches of engineered habitat within landscapes can also influence the physical environment and biodiversity. To examine the influence of a model engineer, the marine intertidal mussel Trichomya hirsuta, abiotic variables (sand deposition, temperature, and humidity) and biotic variables (species richness, numbers of unique species, densities of generalist species and entire assemblages) were compared between engineered and unmodified habitat and between different configurations of engineered patches. By keeping the number of habitat patches (i.e. mussels) constant, the effect of patch configuration (in terms of degree of patch aggregation) on the same abiotic and biotic variables was investigated. Mussels were found to trap large amounts of sand and engineer intertidal habitat that was cooler and, to a lesser extent, more humid during low tides. Mussels also had more species, more unique species and different assemblages compared to habitat without mussels. Different configurations of mussels had similar effects on the physical environment and had similar assemblages as a whole. Most importantly, regularly spaced solitary mussels had more edge and consequently more species, unique species and densities of generalists. These key findings suggest that the configuration of patches of habitat is a crucial factor affecting mussel bed biodiversity, and fragmentation of habitat into regularly spaced patches may have a positive influence on biodiversity due to the positive response of other species to habitat edges.