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Regrowth or dispersal? Recovery of a freshwater red alga following disturbance at the patch scale
Author(s) -
DOWNES BARBARA J.,
STREET JODIE L.
Publication year - 2005
Publication title -
austral ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.688
H-Index - 87
eISSN - 1442-9993
pISSN - 1442-9985
DOI - 10.1111/j.1442-9993.2005.01467.x
Subject(s) - quadrat , disturbance (geology) , ecology , biological dispersal , algae , habitat , seed dispersal , biology , ecological succession , colonisation , colonization , paleontology , population , demography , shrub , sociology
Disturbance is an important factor in species coexistence. Disturbance models require knowledge about whether disturbed patches must be colonized anew from dispersal or whether species left behind can dominate, hence altering recovery trajectories of patches. The red, filamentous alga Audouinella hermannii Roth is a common macroalgal species present at sites in the Steavenson River, a stony, upland stream in south‐eastern Australia. We conducted an experiment in which we contrasted the recovery trajectory of the alga on overturned rocks compared with those that were not overturned, and for rocks that had remnants of the alga left behind compared with others where the alga was scrubbed off completely. Rocks had either a rough or smooth texture. Experimental rocks were set out in riffles and algal recovery monitored in 8 × 8 cm quadrats at approximately 4–6 weekly intervals for 8 months. We found that overturning caused a lasting impact on A. hermannii cover, whereas rocks that were abraded by scrubbing recovered very quickly, suggesting that this alga can re‐grow quickly from fragments (a result confirmed by a second experiment). Both surface texture and resident algae affected recovery on abraded substrata. Quadrats surrounded by resident algae on rough‐textured rocks had lower algal cover compared with all other treatments. We hypothesize this effect is caused by higher densities and grazing intensities of herbivorous macroinvertebrates on those sorts of substrata, analogous to findings for marine habitats. Abrasion does not kill A. hermannii , whereas overturning likely does, necessitating new colonization. Floods often create a mix of abrasion and overturning, producing a mosaic of patches, the complexity of which is not represented well by measures of average disturbance intensity over a whole site. The use of the latter may explain some recent contradictory results among stream disturbance studies. A patch‐level perspective is needed when disturbance creates mosaics over the landscape.