Dynamics of epiphyton on eelgrass (Zostera marina L.) leaves: Relative roles of algal growth, herbivory, and substratum turnover1

Abstract

Biomass accumulation of epiphytic algae on eelgrass leaves with leaf age was measured during three periods in Roskilde Fjord, Denmark. Epiphyte biomass increased exponentially with leaf age during the first 10–14 d of colonization. On older leaves epiphyton gradually approached a phase with only small changes in biomass. Algal doubling times, calculated from biomass accrual, were between 3.6 and 4.6 d on young leaf segments and increased to more than 14 d on old leaves. When corrected for biomass losses due to invertebrate grazing, algal doubling time was only 5.8 d on old leaves in August 1983. In this period grazing accounted for the bulk of epiphyte biomass losses and was a more important factor than eelgrass leaf renewal in reducing epiphytic load. As a conservative estimate, the epiphyte community contributed 4–5 times more to total aboveground production in the eelgrass bed than was indicated by its biomass contribution.

Distribution of the epiphytic organisms on Posidonia australis and P. sinuosa, two seagrasses with differing leaf morphology

“…The time available for the accumulation of biomass is also regarded as an important factor in the establishment of zonation of epiphytic organisms on macrophyte hosts (e.g. Ballantine 1979, Borum 1987, Mazella & Russo 1989. Significant differences in the species richness and coverage of epiphytic organisms on Posidonia leaves of different ages provide circumstantial evidence to support this hypothesis.…”

“…The progressive increases in the mean percentage cover and species diversity of the epiphytic algae as the leaves age has also been reported for Posidonia oceanica (L.) Delile (Van der Ben 1971, Borum 1987, Phyllospadix torreyi Watson (Willcocks 1982), Zostera marina L. (Jacobs et al 1983), Heterozostera tasmanica (Martens ex Ascherson) den Hartog (Bulthuis & Woelkerling 1983), Amphibolis antarctica (Bramwell & Woelkerling 1984), A. g~iffithii (Borowitzka et al 1990) and Thalassia hemprichii (Heijs 1985a). The time available for the accumulation of biomass is also regarded as an important factor in the establishment of zonation of epiphytic organisms on macrophyte hosts (e.g.…”

“…Epiphytic algae are exposed advantageously to light and nutrients and are less subject to sedimentation at the leaf apices as the leaves move back and forth with the current (Keough 1986, Borowitzka et al 1990). Self shading, reported to exceed 90% by some workers (Borum & Wium-Andersen 1980, Borum et al 1984, also affects algal growth toward the leaf base more than competition for space by sessile animals (Sand-Jensen 1977, Borum 1987. On the other hand, nutrient exchange is increased through enhanced water mcvement near the leaf apex (Harlin 1975, Fonseca et al 1982, Fonseca & Kenworthy 1987, Horner 1987).…”

“…Competition for Light plays an important role in structuring marine communities (e.g. Sand-Jensen 1977, Reed & Foster 1984, Borum 1987, and there is circumstantial evidence to indicate that light is a primary factor influencing algal recruitment and growth. Epiphytic algae are exposed advantageously to light and nutrients and are less subject to sedimentation at the leaf apices as the leaves move back and forth with the current (Keough 1986, Borowitzka et al 1990).…”

Effects of grazing and fertilization on epiphyte growth dynamics under moderately eutrophic conditions: implications for grazing rate estimates

“…The lack of a major consistent impact of nutrient enrichment on epiphyte biomass in our trials could be due to the background eutrophic conditions in our mesocosms and in the seagrass beds where the samples were collected (Cebrian et al 2008, Anton et al 2009, Plutchak et al 2010. Consistent with these naturally eutrophic levels, the levels of epiphyte biomass in the samples incubated in the mesocosms were high in comparison with values reported in the literature (Borum 1987, Neckles et al 1993, Cebrian et al 1999, Hauxwell et al 2001, Stutes et al 2007, Jaschinski & Sommer 2010, even when those levels were reduced under the presence of grazers. High levels of epiphyte biomass may imply thick and dense canopies, which through intense self-shading and limited nutrient and gas diffusion may dampen a positive response of epiphyte biomass to nutrient enrichment (Sand-Jensen & Borum 1984, Duarte 1995.…”