Selection of multiple seagrass indicators for environmental biomonitoring

Abstract

The need to monitor the environmental condition of ecosystems worldwide has resulted in a large number of potential bioindicators being proposed in the scientific literature. However, only a few have been validated at an adequate scale to monitor environmental problems and to solve management questions. Here we compiled a list of candidate seagrass indicators (n = 59) obtained from the literature. We empirically validated them on a temperate seagrass ecosystem (Posidonia oceanica) across a wide anthropogenic gradient ranging from undisturbed to severely disturbed sites. We discarded about 75% of the candidate indicators because of their lack of sensitivity at the relevant spatial scale for biomonitoring (i.e. 10s of km against 10s of m) or across the environmental quality gradient. This illustrates the need for a careful validation of indicators prior to their use in monitoring programmes. Bathymetric variability strongly influenced indicator responses to the quality gradient. Deep meadows responded more clearly to differences in environmental quality, whereas shallow meadows were more influenced by natural sources of variability such as herbivory and physical disturbances. The 16 indicators unequivocally related to the environmental status gradient were representative of physiological, biochemical, individual, and population levels of biotic organisation. Their combination was necessary to cover the entire environmental gradient and to reflect the multiple anthropogenic disturbances causing the gradient. The selection process of indicators described here is an important step that needs to take place before the integration of these indicators to extract ecologically relevant information useful for policy and management goals.

Epiphytic bryozoan community of Posidonia oceanica (L.) Delile leaves in two different meadows at disturbed and control locations

“…Nutrient concentration is potentially a limiting factor and can determine the variability of epiphytic assemblages at spatial scale (Balata et al, 2008;Martínez-Crego et al, 2008;Ruiz et al, 2009). According to our results, the mean values of NO 2 -N, PO 4 -P, and TPO 4 -P in the water column increased moderately in the control meadows where the mean value of NO 3 -N was almost two times higher.…”

“…Leaf length and shoot density are significantly influenced by epiphytic species composition (Martínez-Crego et al, 2008) and they are important characteristics for evaluating the health status of Posidonia oceanica meadows. In the control meadow, seagrass features such as adult leaf length, adult leaf surface area, and leaf area index showed an increasing trend towards deeper stations.…”

“…Direct measurement of water column nutrients is generally ineffective due to the transportation by water flow (Koch, 2001), plant uptake (Lee et al, 2004) and adsorption by particulate sediment (Koch, 2001). Nitrogen uptake of P. oceanica leaves is hindered by the increasing epiphyte load close to the sites enriched by nutrient inputs (Lepoint et al, 2007;Martínez-Crego et al, 2008;Prado et al, 2008;Apostolaki et al, 2012). Therefore, the epiphyte community has been used as an early warning indicator of stress occurred in the meadows and their environment (Leoni et al, 2006;Balata et al, 2008).…”

Individual and population indicators of Zostera japonica respond quickly to experimental addition of sediment-nutrient and organic matter

“…population biomass, shoot density) could represent characteristic imprints of environmental conditions (e.g. Hauxwell et al, 2001;Hessing-Lewis et al, 2011;Martínez-Crego et al, 2008;Wood and Lavery, 2000). We did a short term manipulative experiment because small seagrasses may rapidly recover by clonal growth after modest sediment disturbance (Han et al, 2012;La Nafie et al, 2013).…”

Disturbance and Recovery of Intertidal Mixed Seagrass Communities

“…The tidal amplitude in much of the Indo-Pacific is greater than the Caribbean, resulting in expansive meadows that are exposed to air during low tide. Also, intertidal seagrasses may be more susceptible to wind and wave driven processes (Martinez-Crego et al 2008) than are subtidal seagrasses. Furthermore, increased exposure time and proximity to anthropogenic impacts such as human harvesting activities and boat damage may selectively impact intertidal seagrasses to a greater extent.…”