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An evaluation of factors controlling the abundance of epiphytes on Zostera marina along an estuarine gradient in Yaquina Bay, Oregon, USA.
Citation:
Nelson, Walt. An evaluation of factors controlling the abundance of epiphytes on Zostera marina along an estuarine gradient in Yaquina Bay, Oregon, USA. AQUATIC BOTANY. Elsevier Science Ltd, New York, NY, 148:53-63, (2018).
Impact/Purpose:
An evaluation of factors controlling the abundance of epiphytes on seagrasses in Yaquina Bay, OR, found that in of the presence of high natural levels of nutrients, seasonal and spatial variation in epiphyte load appears to be primarily controlled by light rather than nutrients. High epiphyte loads generally have a negative impact on seagrasses, and have been proposed as a useful indicator of elevated nutrients in seagrass ecosystems. In Pacific Northwest estuaries where nutrient levels are typically high, seasonal and spatial variations in nutrients do not appear to have limiting effects. While epiphyte loads that occur are high enough to limit light available to seagrasses, seagrasses at intertidal locations, where most seagrass is found, appear able to cope with current conditions. Rising water temperatures may make epiphyte load more problematic to seagrasses, particularly in more up estuary locations.
Description:
Epiphytes on seagrass (Zostera marina) 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. Estuarine nutrient processes tend to be dominated by marine influences near the estuary mouth, and by riverine influences further upstream. Mean epiphyte biomass per unit seagrass leaf surface area (epiphyte load) peaked during the summer, and thus epiphyte load was higher during dry season than wet season in both marine and riverine dominated regions. Epiphytes load was greater in marine than in riverine dominated areas in both wet and dry seasons, although only dry season differences were significant. There was no evidence that grazers control epiphyte load differences. Annual DIN concentration was inversely related to epiphyte load, principally as a result of elevated wet season dissolved inorganic nitrogen from river inputs. While there was a positive annual relation of epiphyte load to PO4 concentration, it is not clear that phosphorus becomes a limiting nutrient for epiphyte growth. Water column light attenuation tends to increase linearly with distance from the estuary mouth, while both epiphyte load and Z. marina biomass tend to decrease. Both seagrass and seagrass epiphytes may be increasingly light limited in the upper estuary, and thus, epiphyte loads may have proportionally more impact on seagrass occurrence in this estuarine region.
