Resilience and restoration of soft-bottom near-shore ecosystems

Abstract

Throughout the world, intertidal near-shore eco-systems are largely threatened by human impacts(Naylor et al., 1998; Jackson et al., 2001). Man-grove forests and seagrass meadows are majorvegetation types of these ecosystems (Hogart,1999; Hemming & Duarte, 2000). These mangroveforests and seagrass meadows constitute dominantplant communities in these ecosystems and play acrucial role in the coastal environment. Generally,both mangrove forests and seagrass meadows arecharacterisedbyhighbiomassproduction(RileyK Green & Short, 2003), and they arewidely recognized as key ecosystems in temperateand tropical near-shore ecosystems (Valiela, 1987;Hogart, 1999; Hemminga & Duarte, 2000). Inter-tidal near-shore ecosystems with mangrove andseagrass cover are important for biodiversity (DeIonghet al.,2007),theyhelptostabilizesediments(De Boer, 2007), provide nursery habitats for fish(Pollard, 1984; Nuraini et al., 2007), contribute totheprimaryproduction,andplayanimportantrolein the nutrient cycling of the coastal marineecosystems (Oshima et al.,1999; Gras et al.,2003).Storms and monsoon rains are frequent distur-bances that affect mangrove and seagrass cover(Preen et al., 1995; Ferwerda et al., 2007a). Inresilient intertidal near-shore ecosystems, thepioneer seagrass species for example can recoverquickly after such disturbances (De Iongh, 1996).Many seagrass species are, however, highly sen-sitive to environmental changes, and losses ofseagrass-vegetated areas are now a worldwideproblem (Walker & McComb, 1992; Short W Gordon, 2007). Thedecline in most areas can be related to humanactivities such as industrial and urban sewagedischarges, fish farming, trawl fishing, coastalworks (as shown for mangroves by Vaiphasaet al., 2007). The main problems in intertidalnear-shore ecosystems have an abiotic naturesuch as increased turbidity, erosion and increasednutrient load (Fourqurean & Zieman, 2002; Ruiz& Romero, 2003; De Boer, 2007). However, alsobiotic disturbances affect mangrove and seagrasscover, such as overgrowth with epiphytes andmacroalgae. The causal relationships betweenindividual factors and observed changes in man-grove and seagrass cover and biomass are difficultto establish due to the complex array of interac-tions between physical and biological factors thatcan be simultaneously induced in a same coastalarea under influence of human impacts (Terradoset al., 1999; Ruiz & Romero, 2001). Understand-ing the effect of disturbances and mechanisms of