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CONTROLS OF SEAGRASS EPIPHYTE ABUNDANCE: DOES LIGHT TRUMP NUTRIENTS?
Citation:
NELSON, W. G. CONTROLS OF SEAGRASS EPIPHYTE ABUNDANCE: DOES LIGHT TRUMP NUTRIENTS? Presented at Benthic Ecology Meeting, Atlanta, GA, March 21 - 25, 2007.
Description:
Epiphytes on seagrass growing in the lower intertidal were examined along an estuarine gradient within Yaquina Bay, Oregon over a period of 4 years. The Yaquina Estuary receives high levels of nutrients from the watershed during the wet season and from the ocean during the dry season, with each source dominating nutrient processes within an estuarine zone. Zone 1 is marine dominated, while Zone 2 nutrients are watershed dominated. Mean epiphyte biomass per unit seagrass blade surface area peaks during the summer, and thus biomass was higher during dry season than wet season in both zones. Biomass of epiphytes was greater in Zone 1 than Zone 2 in both wet and dry seasons, although only dry season differences were significant. There is no evidence that grazers control epiphyte biomass differences. Over the portion of the estuary where epiphytes were collected, wet season DIN showed elevated median values in Zone 2, but there was no spatial pattern during the dry season. While PO4 decreased with distance up estuary, levels would not appear to be limiting for epiphyte growth. However, water column light attenuation increases linearly with distance from the estuary mouth. Hence, both seagrass and seagrass epiphytes may be increasingly light limited in the upper estuary. Because of lower light levels in Zone 2, the smaller epiphyte loads in the upper estuary may have proportionally more impact on seagrass occurrence.