Low-Canopy Seagrass Beds Still Provide Important Coastal Protection Services

Abstract

One of the most frequently quoted ecosystem services of seagrass meadows is their value for coastal protection. Many studies emphasize the role of above-ground shoots in attenuating waves, enhancing sedimentation and preventing erosion. This raises the question if short-leaved, low density (grazed) seagrass meadows with most of their biomass in belowground tissues can also stabilize sediments. We examined this by combining manipulative field experiments and wave measurements along a typical tropical reef flat where green turtles intensively graze upon the seagrass canopy. We experimentally manipulated wave energy and grazing intensity along a transect perpendicular to the beach, and compared sediment bed level change between vegetated and experimentally created bare plots at three distances from the beach. Our experiments showed that i) even the short-leaved, low-biomass and heavily-grazed seagrass vegetation reduced wave-induced sediment erosion up to threefold, and ii) that erosion was a function of location along the vegetated reef flat. Where other studies stress the importance of the seagrass canopy for shoreline protection, our study on open, low-biomass and heavily grazed seagrass beds strongly suggests that belowground biomass also has a major effect on the immobilization of sediment. These results imply that, compared to shallow unvegetated nearshore reef flats, the presence of a short, low-biomass seagrass meadow maintains a higher bed level, attenuating waves before reaching the beach and hence lowering beach erosion rates. We propose that the sole use of aboveground biomass as a proxy for valuing coastal protection services should be reconsidered.

Long-Distance Interactions Regulate the Structure and Resilience of Coastal Ecosystems

“…The physical structures of these organisms provide habitats for a large number of species and alleviate abiotic stress (e.g., hydrodynamics, anoxia, and salinity). Moreover, these ecosystems are characterized by highly efficient internal cycling mechanismse.g., the stabilization of sediments, trapping of organic particles, and filtering of nutrients from the water layer (Christianen et al 2013, de Goeij et al 2013, Hendriks et al 2010). However, these local feedback mechanisms also form the basis of distinctive long-distance facilitative interactions that all three systems may depend on ( Figure 5).…”

“…Seagrasses and mangroves provide an important reciprocal service to the corals by trapping sediments and absorbing nutrients (Christianen et al 2013, Storlazzi et al 2011). These effects have important implications for corals because they decrease sediment and nutrient fluxes from the hinterland toward the reef.…”

Seagrass community-level controls over organic carbon storage are constrained by geophysical attributes within meadows of Zanzibar, Tanzania

“…system (Christianen et al, 2013) and the high lignin content of belowground tissues (Klap et al, 2000), promote OC storage.…”

Physiological Response of Thallasia hemprichii on Antrophogenic Pressure In Pari Island, Seribu Islands, DKI Jakarta

“…Seagrass community is one of coastal ecosystem which has important ecological functionsuch as food source for coastal community and marine sediment stabilization (Koch et al, 2012;Christianen et al, 2013) and as feeding area for several marine biota (Heck et al,2003;Van Tussenbroek et al,2006;Christianen et al, 2014;Kawaroe et al,2016a). Seagrass also plays important role in carbon cycle (Mcleod et al, 2011).…”