Abstract
MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 238:73-79 (2002) - doi:10.3354/meps238073 Direct measurements of light attenuation by epiphytes on eelgrass Zostera marina Mark J. Brush*, Scott W. Nixon Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island 02882-1197, USA *E-mail: brush@vims.edu ABSTRACT: Declines in the seagrass Zostera marina L. in estuaries and lagoons have been attributed in part to reductions in irradiance reaching the seagrass blades. Epiphytes growing on Z. marina have the potential to attenuate a large fraction of the light that would otherwise reach the blades. This problem has previously been studied by measuring light penetration through homogenized epiphytic slurries or through glass slides fouled with epiphytes. However, the latter may not represent the natural succession or species composition found on live Z. marina leaves and the former does not preserve the structure of the epiphytic complex. Further, past studies have not measured attenuation across the full range of epiphytic densities found in the field. In this study, we measured light penetration across a wide range of epiphytic densities by holding scraped and unscraped Z. marina blades over a submerged light sensor. Results compared well with past studies at low epiphyte densities, with strong reductions in light penetration as density increased. However, at higher densities, penetration leveled off to a relatively constant value as the epiphytes floated out from the edges of the blade. Studies using slurries did not capture this phenomenon and thus predicted decreasing penetration down to 0%. KEY WORDS: Epiphytes · Light attenuation · Seagrass · Zostera marina Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 238. Online publication date: August 08, 2002 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2002 Inter-Research.
Highlights
The well-known and widespread decline of submersed aquatic angiosperms in shallow lakes and coastal marine waters around the world is commonly attributed, at least in part, to shading by excessive growths of epiphytes (e.g. Sand-Jensen 1977, Phillips et al 1978, Borum & Wium-Andersen 1980, Kemp et al 1983, Orth & Moore 1983, Twilley et al 1985, Silberstein et al 1986, Valiela et al 1990, Neckles et al 1993)
The epiphytic community found on such plants is a heterogeneous and varying complex of bacteria, micro- and macroalgae, heterotrophic organisms, and organic and inorganic detritus and debris that is usually characterized in terms of total dry weight (DW), ash free dry weight (AFDW), and/or the weight of chlorophyll per unit area of leaf substrate
All previous studies have used indirect approaches by which light attenuation has been measured as the light passed through an epiphyte matrix grown on artificial transparent substrates, or as the light passed through a suspension prepared from naturally occurring epiphytes removed from the leaves of various submersed plant species (Table 1)
Summary
The well-known and widespread decline of submersed aquatic angiosperms in shallow lakes and coastal marine waters around the world is commonly attributed, at least in part, to shading by excessive growths of epiphytes (e.g. Sand-Jensen 1977, Phillips et al 1978, Borum & Wium-Andersen 1980, Kemp et al 1983, Orth & Moore 1983, Twilley et al 1985, Silberstein et al 1986, Valiela et al 1990, Neckles et al 1993). The epiphytic community found on such plants is a heterogeneous and varying complex of bacteria, micro- and macroalgae, heterotrophic organisms, and organic and inorganic detritus and debris that is usually characterized in terms of total dry weight (DW), ash free dry weight (AFDW), and/or the weight of chlorophyll per unit area of leaf substrate. Because of the obvious potential for shading when the epiphytic. All previous studies have used indirect approaches by which light attenuation has been measured as the light passed through an epiphyte matrix grown on artificial transparent substrates, or as the light passed through a suspension prepared from naturally occurring epiphytes removed from the leaves of various submersed plant species (Table 1)
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