Responses of algae with different life histories to temporal and spatial variability of disturbance in subtidal reefs

Colonisation of patches disturbed at different times of the year and at dif ferent locations was investigated from November 1995 to August 1997 in subt idal, rocky-shore, algal assemblages (Mediterranean Sea, Italy). A field ex periment tested specifically: (1) whether and how the success of turf-formi ng, encrusting and erect algae are influenced by the timing of disturbance and (2) whether recovery of these species is consistent across space (from about 1 m to 100s of metres). Clearings were made at 8 different times with in 1 year, in order to identify possible temporal trends in responses of al gae to disturbance. Reproductive traits of the most abundant algae were als o investigated. Encrusting, turf-forming and erect algae responded differen tly to spatial and temporal variation in disturbance, depending on their va rying abilities to colonise available space and on spatial and temporal dif ferences in rates of recruitment and growth. Turf-forming algae colonised s pace by vegetative propagation and quickly regained spatial dominance in pa tches cleared at all times of the year and at all locations. Conversely, en crusting and erect species occupied space mostly by colonisation of propagu les; their recruitment was influenced by the timing and location of disturb ance, probably depending on the concomitant availability of bare rock, viab le propagules and favourable environmental conditions. A regime of disturba nce adverse to recruitment of erect algae was identified as the probable ca use of their low abundance in the study area. Overall, results suggested th at while recruitment by sexual propagules can be highly variable through sp ace and time, recovery by vegetative propagation can be constant and highly predictable over a range of environmental conditions, and that vegetative reproduction is likely to be fundamental to spatial dominance in a variety of habitats.