Interaction between hydrodynamics and seagrass canopy structure: Spatially explicit effects on ammonium uptake rates

Abstract

The hypotheses that (1) different seagrass morphologies may facilitate different nutrient uptake rates under similar hydrodynamic forcing and (2) this effect on nutrient uptake rates is spatially explicit, with the highest uptake rates at edges of patches, where currents and turbulence are highest, were examined under unidirectional flow conditions. Homogeneous patches (2 m long) of two seagrass species (Cymodocea nodosa and Zostera noltii) with contrasting shoot size and density were placed in a race track flume. 15 NH z 4 uptake and hydrodynamic properties along a gradient from outside to inside the patch were measured at a range of current velocities (0.05 to 0.3 m s 21 ). For each velocity we also determined the height and bending of the canopy. Water velocity affected the ammonium uptake rate of both species. The almost double uptake rates of C. nodosa shoots, compared to those of Z. noltii, were mainly attributed to a twofold difference in the within-canopy water flow (Q c , m 3 s 21 ). Spatial patterns in canopy water flow were highly correlated with spatial patterns in NH z 4 uptake, thereby explaining the 20% higher uptake rates at the leading edge of both canopies. The correlation between spatial patterns in canopy water flow and ammonium uptake rates underlines the role of canopy and patch configuration in determining the functioning of seagrass landscapes and their associated ecosystem services, such as nitrogen assimilation.

Role of two contrasting ecosystem engineers (Zostera noltii and Cymodocea nodosa) on the food intake rate of Cerastoderma edule

“…Our results clearly demonstrate for both seagrass species Cymodocea nodosa and Z. noltii that Cerastoderma edule living within seagrass beds in a zone with a relatively high hydrodynamic energy, is able to increase the food intake rate relative to that in non-vegetated areas. No signiWcant diVerences were found between both seagrass species, despite that earlier studies indicated that their contrasting canopy properties caused a factor two diVerence in canopy Xuxes (Morris et al 2008). To our surprise, both our hypotheses were rejected.…”

“…In order to elucidate the eVect of canopy properties on the food supply to Wlter feeding organisms inhabiting vegetated areas, we compared the food uptake of Cerastoderma edule in two seagrass species with contrasting canopy properties (Zostera noltii Horneman vs. Cymodocea nodosa (Ucria) Ascherson) and in the non-vegetated surroundings. Previous studies demonstrated that diVerences in canopy properties (shoots density, height and stiVness) caused the water Xux through the canopy of C. nodosa to be approximately double of that through a Z. noltii canopy (Morris et al 2008). Therefore, we hypothesised that (a) both seagrass species will decrease the food intake rate of C. edule compared to non-vegetated areas and, (b) that the Wltration rate will be the lowest for cockles inhabiting Z. noltii beds.…”

Uptake of dissolved inorganic nitrogen by shallow seagrass communities exposed to wave-driven unsteady flow

“…Isotopically labeled nutrients have been used to measure nutrient uptake for individual organisms within a community (Cornelisen & Thomas 2006, Morris et al 2008, to determine the relationship between seagrass and epiphyte nutrient uptake (McRoy & Goering 1974, Lepoint et al 2007, and to trace distribution of nutrients among community components (Koop et al 2001, Cornelisen & Thomas 2006, Gribsholt et al 2006). …”

“…The interaction between water column hydrodynamics and submerged vegetated canopies affects the coupling of benthic and pelagic nutrient cycling (Lemmens et al 1996, Thomas et al 2000, Morris et al 2008) and affects stresses imposed at the sediment/ water interface (Fonseca & Fisher 1986, Fonseca & Cahalan 1992, Gacia et al 1999. Seagrass communities provide important ecosystem services: they filter the water column (Szmant & Forrester 1996, Lapointe et al 2004, feed grazing marine species (Fry & Parker 1979, Moncreiff et al 1992, Connolly et al 2005, and shelter organisms during early stages of their development (Eggleston et al 2004, Gullström et al 2008.…”

Effects of seagrasses and algae of the Caulerpa family on hydrodynamics and particle-trapping rates

“…The surface area of Caulerpa taxifolia was calculated (n = 95) with Jimage TM image analyses software after processing the images in Adobe Photoshop TM . Parameters for Cymodosa nodosa were extracted from Morris et al (2008), while data for Posidonia oceanica were derived from (Hendriks et al 2008). All parameters are summarised in Table 1. Hydrodynamic properties of the canopy Hydrodynamic properties and particle-trapping rates of the canopies were measured under controlled conditions in a racetrack flume (described in detail in Hendriks et al 2006; also see http://www.nioo.nl/science/facilities/flume/flume.…”