Like a Rolling Stone : the Mobility of Maerl ( Corallinaceae ) and 1 the Neutrality of the Associated Assemblages 2

Beds of non-attached coralline algae (maerl or rhodoliths) are widespread and 15 considered relatively species rich. This habitat is generally found in areas where there is 16 chronic physical disturbance such that maerl thalli are frequently moved. Little is known, 17 however, about how natural disturbance regimes affect the species associated with maerl. This 18 study compared the richness, animal abundance and algal biomass of maerl-associated species 19 over a two year period in a wave disturbed and a sheltered maerl bed. Changes in associated 20 species over time were assessed for departures from a neutral model, where the dissimilarity 21 between samples reflects random sampling from a common species pool. Algal biomass and 22 species richness at the wave exposed site and on stabilized maerl at the sheltered site were 23 reduced at times of higher wind speeds. The changes in species richness were not 24 distinguishable from a neutral model, implying that algal species were added at random to the 25 assemblage as the level of disturbance lessened. Results for animal species were more mixed. 26 Although mobile species were less abundant during windy periods at the exposed site, both 27 neutral and non-neutral patterns were evident in the assemblages. Artificial stabilization of 28 maerl had inconsistent effects on the richness of animals, but always resulted in more attached 29 algal species. While the results show that the response of a community to disturbance can be 30 neutral, the domain of neutral changes in communities may be relatively small. Alongside non31 neutral responses to natural disturbance, artificial stabilization always resulted in an 32 assemblage that was more distinct than would be expected under random sampling from a 33 common pool. Community responses to stabilization treatments did not consistently follow the 34 predictions of the dynamic equilibrium model, intermediate disturbance model or a facilitation 35 model. These inconsistencies may reflect site-specific variation in both the disturbance regime 36 and the adjacent habitats that provide source populations for many of the species found 37 associated with maerl. 38 39