Past and present grazing boosts the photo-autotrophic biomass of biofilms

Skov, Martin W., Volkelt-Igoe, Megan, Hawkins, Stephen J., Jesus, Bruno, Thompson, Richard C. and Doncaster, C. Patrick (2010) Past and present grazing boosts the photo-autotrophic biomass of biofilms. Marine Ecology Progress Series, 401, 101-111. (doi:10.3354/meps08481).


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Little is known about the long-term consequences of grazing effects on microphytes. This study tested for density-dependent responses to grazer removal on the biomass (Chlorophyll a: ‘Chla’) and composition of natural high rocky-shore biofilms over a 7-month period. Gastropod snails Melarhaphe neritoides graze entirely within circular halos generated in biofilms surrounding their refuges. The experiment crossed 3 levels of original snail density per halo with 3 levels of grazing intensity (generated by 100%, 50% and 0% snail removal). Areas inside halos from which all snails had been removed sustained significantly higher Chla than never-grazed control areas outside the halos. This effect of grazing history was still present after 7 months, suggesting that past grazing had an enduring positive influence on biofilm biomass. Against expectation, Chla-biomass was not increased by removing snails, regardless of original grazer density. Half- and fully-grazed halos peaked to a higher Chla than ungrazed halos in spring. Grazing did not affect the presence of major biofilm taxonomic groups, although it did alter their relative contributions. Never-grazed areas were covered by thick biofilm detritus and had proportionally more filamentous cyanobacteria than grazed areas, which sustained abundant clusters of coccoid cyanobacteria and lichen within micro-pits inaccessible to snail radulae. The study shows that effects of grazing history are not exclusive to macrophytic systems. Grazers boosted the concentration of micro-autotrophs relative to non-Chla biofilm constituents, probably by removing an unproductive biofilm canopy and facilitating light and nutrient penetration for new growth.

Item Type: Article
Additional Information: REF
ISSNs: 1616-1599 (electronic)
0171-8630 (print)
Keywords: standing stock, epilithic biofilm, micro-algae, grazing, refuge, rocky shore, detritus, littorina
Divisions: University Structure - Pre August 2011 > School of Biological Sciences
University Structure - Pre August 2011 > School of Ocean & Earth Science (SOC/SOES)
ePrint ID: 142549
Date Deposited: 31 Mar 2010 15:45
Last Modified: 27 Mar 2014 19:04

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