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Development of an epiphyte indicator of nutrient enrichment: A critical evaluation of observational and experimental studies
Citation:
Nelson, Walt. Development of an epiphyte indicator of nutrient enrichment: A critical evaluation of observational and experimental studies. ECOLOGICAL INDICATORS. Elsevier Science Ltd, New York, NY, 79:207-227, (2017).
Impact/Purpose:
An extensive review of the literature on epiphytes on submerged aquatic vegetation (SAV) concluded that measurement of epiphytes may be a useful indicator of persistent nutrient enhancement in many situations. Evidence from field observational studies together with laboratory and field mesocosm experiments was assembled from the literature and evaluated for evidence of a hypothesized positive response to nutrient addition. Results confirmed that elevated nutrients tended to increase the load of epiphytes on the surface of SAV, in the absence of other limiting factors. Patterns of epiphyte response to nutrient load tend to be less evident as the spatial and temporal scale of data sets expand. Careful selection of appropriate temporal and spatial constraints for data collection, and concurrent evaluation of confounding factors will help increase the signal to noise ratio for this indicator.
Description:
An extensive review of the literature on epiphytes on submerged aquatic vegetation (SAV), primarily seagrasses but including some brackish and freshwater rooted macrophytes, was conducted in order to evaluate the evidence for response of epiphyte metrics to increased nutrients. Evidence from field observational studies together with laboratory and field mesocosm experiments was assembled from the literature and evaluated for evidence of a hypothesized positive response to nutrient addition. There was general consistency in the results to confirm that elevated nutrients tended to increase the load of epiphytes on the surface of SAV, in the absence of other limiting factors. In spite of multiple sources of uncontrolled variation, positive relationships of epiphyte load to nutrient concentration or load (either N or P) were often observed along strong anthropogenic or natural nutrient gradients in coastal regions, although response patterns may only be evident for parts of the year. Mesocosm nutrient studies tended to be more common for temperate regions and field addition studies more common for tropical and subtropical regions. Addition of nutrients via the water column tended to elicit stronger epiphyte responses than sediment additions, and may be a factor in the lack of epiphyte response reported in some studies. Mesograzer activity is a critical covariate for epiphyte response under experimental nutrient elevation, but the epiphyte response is highly dependent on factors such as grazer identity, density, nutrient and ambient light levels. The balance of evidence suggests that epiphytes on SAV will be a useful indicator of persistent nutrient enhancement in many situations. However, patterns of epiphyte response to nutrient load tend to be less evident as the spatial and temporal scale of data sets expand. Careful selection of appropriate temporal and spatial constraints for data collection, and concurrent evaluation of confounding factors will help increase the signal to noise ratio for this indicator.
