Effects of water dynamics on Zostera marina: transplantation experiments in the intertidal Dutch Wadden Sea

Abstract

Pilot experiments in the tidally dominated Dutch Wadden Sea indicated a negative relationship between Zostera marina L. transplantation success and tidal depths. As light availability was sufficient, we hypothesised that water dynamics (particularly waves) and ensuing sediment mobility (movement or resuspension of the sediment) were the major cause for the loss of transplants at larger depths. Transplantation experiments were carried out at intertidal flats and depths under conditions of normal and reduced water dynamics and sediment mobility, using exclosures that reduced water dynamics and shells that stabilised the sediment. To test bioturbation effects, cages that excluded large biota were used. Without protection, Z. marina plants were successfully established in a belt within the intertidal zone (0 to -0.20 m mean sea level, MSL) at 2 out of 3 transplantation sites during the first growing season. Reduced water dynamics by exclosures prevented the loss of plants in the zone -0.40 to -1.15 m MSL; removal of the exclosures after 1 mo resulted in loss of all plants within a few days. Neither light limitation nor bioturbation could explain these results. We conclude that prevalent water dynamics, particularly the relative period of exposure to wave dynamics, were too high for establishment and maintenance of intertidal Z. marina at depths below -0.20 m MSL at these sites of intermediate exposure. At the third, exposed, transplantation site, water dynamics prevented transplantation success along the entire depth gradient studied. Reduction of sediment mobility by shells had a positive effect on transplant survival, particularly at -0.20 m MSL. Shell armour can therefore be recommended in transplantations near the lower limit of potential intertidal habitats of Z. marina. Anchorage of the plants with pegs had no positive effect. Depth limitation of intertidal Z. marina populations by water dynamics can explain zonation patterns that occur in several tidal systems in northwest Europe.

Direct effects of current velocity on the growth, morphometry and architecture of seagrasses: a case study on Zostera noltii

“…Leaf detachment was previously suggested to be the main mechanism for variable leaf morphometry among environments with contrasting hydrodynamic conditions (van Katwijk & Hermus 2000, Schanz & Asmus 2003, Peralta et al 2005. In our study, this mechanism was unlikely to have affected leaf morphometry: reduced leaf loss rate was observed in all the treatments.…”

“…On one hand, it is well known that hydrodynamic energy from waves or currents that is too high will restrict seagrass distribution (e.g. see Fonseca & Bell 1998, van Katwijk & Hermus 2000, Schanz & Asmus 2003, and on the other hand, that some water movement is needed to sustain growth (Ackerman & Okubo 1993, Koch 1994, Thomas & Cornelisen 2003. However, the ef-fects of intermediate ranges of velocities are not well understood.…”

New evidence for habitat-specific selection in Wadden Sea Zostera marina populations revealed by genome scanning using SNP and microsatellite markers

“…In the Wadden Sea area, eelgrass is subtidally almost extinct after the wasting disease in the 1930s (den Hartog 1970). Recovery never occurred, possibly due to ongoing pollution of coastal waters and changes in water movement and climate (van Katwijk and Hermus 2000). However, some fragments in permanently submerged creeks remained, situated on the low lying islands of the northern Wadden Sea (the 'Halligen', Reusch 2002).…”

Waves and high nutrient loads jointly decrease survival and separately affect morphological and biomechanical properties in the seagrass Zostera noltii

“…Depending on the environment, an enhanced nutrient load may sometimes have a positive (Perez et al 1991;Brun et al 2002) or no effect (Harlin and Thornemiller 1981;Lee and Dunton 2000) on seagrasses. However, nutrient enrichment generally has a negative effect on seagrass growth and survival either directly due to the toxic effect of nitrate (Burkholder et al 1992) or ammonium (van Katwijk et al 1997;Brun et al 2002) or indirectly due to algal overgrowth, which causes light deprivation and enhanced organic matter fluxes to the sediment (Short et al 1995;Brun et al 2003). Hydrodynamic conditions from waves and currents are also known to have direct and indirect effects on seagrass ecosystems.…”

“…Hydrodynamic conditions from waves and currents are also known to have direct and indirect effects on seagrass ecosystems. For example, increased wave energy can directly reduce survival and number of seagrass shoots (van Katwijk and Hermus 2000), while increased flow velocity can directly affect plant growth and morphometry (Schanz and Asmus 2003;Peralta et al 2006;de los Santos et al 2010). In addition, increased flow velocity and/or waves can have indirect effects on the photosynthetic rates and nutrient uptake by reducing boundary layers (Koch 1994).…”