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Marine Ecology Progress Series

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MEPS 170:107-117 (1998)  -  doi:10.3354/meps170107

Impact of solar radiation on the decomposition of detrital leaves of eelgrass Zostera marina

Anssi Vähätalo1,2,*, Morten Søndergaard3, Louise Schlüter4, Stiig Markager5

1Department of Ecological and Environmental Sciences, University of Helsinki, Niemenkatu 73, FIN-15210 Lahti, Finland
2Department of Applied Chemistry and Microbiology, PO Box 56, FIN-00014 University of Helsinki, Finland**
3Freshwater Biological Laboratory, University of Copenhagen, Helsingørsgade 51, DK-3400 Hillerød, Denmark
4The International Agency for 14C Determination, VKI, Institute for the Water Environment, Agern Allé 11, DK-2970 Hørsholm, Denmark
5Department of Marine Ecology and Microbiology, National Environmental Research Institute, Frederiksborgvej 399, DK-4000 Roskilde, Denmark
**Address for correspondence

ABSTRACT: Although seagrass detritus is exposed to high solar radiation in its natural environment, the impact of solar radiation has not yet been taken into account in degradation of particulate detritus. We exposed sterilised detrital leaves of eelgrass Zostera marina L. to solar radiation. Under solar radiation the chlorophyll in leaves bleached in <5 d and other absorbing compounds within 1 mo. During a 1 mo period the organic matter content of leaves (32 g m-2 of leaves) decreased, mainly via leaching, 3 to 9% in darkness and 23 to 36% under solar radiation. First order kinetics described the loss of organic matter as a function of cumulative global radiation well. The decay coefficient was 0.00038 MJ-1 m2. Solar radiation-induced changes in the structure of leaves increased the bioavailability of detritus to bacteria 2- to 3-fold. Our results show that solar radiation is one of the major factors in the decomposition of seagrasses and has to be taken into account in degradation models of particulate detritus.

KEY WORDS: Seagrasses · Detritus · Degradation · Photochemistry · Solar radiation · Chlorophyll · Bacteria

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