Seagrasses and eutrophication

Cover versus recovery: Contrasting responses of two indicators in seagrass beds

“…However when nutrients, particularly nitrogen, are in excess, the plant physiological and growth response are negatively affected. This is due to nitrogen toxicity, and in aquatic or marine systems additional algal overgrowth, which both lead to a higher demand of carbon skeletons, thus causing physiological imbalance, ultimately leading to mortality and collapse (Pearson and Stewart, 1993;Marschner, 1995; for seagrasses reviewed in: Touchette and Burkholder, 2000;Burkholder et al, 2007). Along this eutrophication trajectory, prior to collapse, increasing plant cover thus may coincide with increasing physiological imbalance, which likely diminishes plant recovery potential.…”

Combined nutrient and macroalgae loads lead to response in seagrass indicator properties

“…One of the most important threats to seagrasses is eutrophication, which could result from increased fertilizer use and marine cultivation (Burkholder et al, 2007;Orth et al, 2006). Nutrient enrichment can accelerate seagrass loss through direct effects, such as toxicity, increased system respiration and sediment anoxia (Burkholder et al, 2007;van Katwijk et al, 1997), but also through indirect effects via algal proliferation that could cause shading and/or smothering (Burkholder et al, 2007;Hauxwell and Valiela, 2004;van Katwijk et al, 2010).…”

“…Seagrass decline in temperate estuaries under high nutrient enrichment often coincides with high macroalgae biomass (Burkholder et al, 2007;Hauxwell et al, 2001;Short and Burdick, 1996;Thomsen et al, 2012;Valiela et al, 1997). The negative effects of macroalgal blooms on seagrasses have been documented in many areas of the world, such as Australia, Japan, America and Europe (e.g.…”

“…Small-statured seagrass species are more impacted than larger species, and the effect is often proportional to the biomass of macroalgae (Thomsen et al, 2012). Shading by the macroalgae causes light reduction and is one of the most common mechanisms resulting in seagrass decline (Burkholder et al, 2007), which is indicated by reduction in the depth of the meadows, lowered shoot densities, poor recruitment, slower growth rates and decreased overall production of seagrasses (Krause-Jensen et al, 2000;McGlathery, 2001). Additionally, decomposition of macroalgae mats may decrease oxygen content in eutrophicated waters and further abate seagrass survival (McGlathery et al, 2007).…”

“…Fewer studies have investigated the effect of nutrients on the interaction between seagrasses and macroalgae beyond the effect of light reduction (but see Burkholder et al, 2007;Vonk et al, 2008). In general, when nutrient concentrations are low in seawater, seagrasses are dominant over macroalgae (Fourqurean et al, 1995), due to the competitive advantage conferred by roots and rhizomes in absorbing nutrients from sediment porewater (Hemminga, 1998;Vonk et al, 2008).…”