title: Interactions between seagrass complexity, hydrodynamic flow and biomixing alter food availability for associated filter-feeding organisms.
abstract: Seagrass shoots interact with hydrodynamic forces and thereby a positively or negatively influence the survival of associated species. The modification of these forces indirectly alters the physical transport and flux of edible particles within seagrass meadows, which will influence the growth and survivorship of associated filter-feeding organisms. The present work contributes to gaining insight into the mechanisms controlling the availability of resources for filter feeders inhabiting seagrass canopies, both from physical (influenced by seagrass density and patchiness) and biological (regulated by filter feeder density) perspectives. A factorial experiment was conducted in a large racetrack flume, which combined changes in hydrodynamic conditions, chlorophyll a concentration in the water and food intake rate (FIR) in a model active filter-feeding organism (the cockle). Results showed that seagrass density and patchiness modified both hydrodynamic forces and availability of resources for filter feeders. Chlorophyll a water content decreased to 50% of the initial value when densities of both seagrass shoots and cockles were high. Also, filter feeder density controlled resource availability within seagrass patches, depending on its spatial position within the racetrack flume. Under high density of filter-feeding organisms, chlorophyll a levels were lower between patches. This suggests that the pumping activity of cockles (i.e. biomixing) is an emergent key factor affecting both resource availability and FIR for filter feeders in dense canopies. Applying our results to natural conditions, we suggest the existence of a direct correlation between habitat complexity (i.e. shoot density and degree of patchiness) and filter feeders density. Fragmented and low-density patches seem to offer both greater protection from hydrodynamic forces and higher resource availability. In denser patches, however, resources are allocated mostly within the canopy, which would benefit filter feeders if they occurred at low densities, but would be limiting when filter feeder were at high densities.
authors.affiliation: Department of Biology, Faculty of Marine and Environmental Sciences of University of Cadiz, Puerto Real, Cadiz, Spain.
authors.forename: Vanessa
authors.initials: V
authors.lastname: González-Ortiz
authors.affiliation: Department of Biology, Faculty of Marine and Environmental Sciences of University of Cadiz, Puerto Real, Cadiz, Spain.
authors.forename: Luis G
authors.initials: LG
authors.lastname: Egea
authors.affiliation: Department of Biology, Faculty of Marine and Environmental Sciences of University of Cadiz, Puerto Real, Cadiz, Spain.
authors.forename: Rocio
authors.initials: R
authors.lastname: Jiménez-Ramos
authors.affiliation: Department of Biology, Faculty of Marine and Environmental Sciences of University of Cadiz, Puerto Real, Cadiz, Spain.
authors.forename: Francisco
authors.initials: F
authors.lastname: Moreno-Marín
authors.affiliation: Department of Biology, Faculty of Marine and Environmental Sciences of University of Cadiz, Puerto Real, Cadiz, Spain.
authors.forename: José L
authors.initials: JL
authors.lastname: Pérez-Lloréns
authors.affiliation: Department of Spatial Ecology, Netherlands Institute for Sea Research, Yerseke, The Netherlands.
authors.forename: Tjeed J
authors.initials: TJ
authors.lastname: Bouma
authors.affiliation: Department of Biology, Faculty of Marine and Environmental Sciences of University of Cadiz, Puerto Real, Cadiz, Spain.
authors.forename: Fernando G
authors.initials: FG
authors.lastname: Brun
mesh_terms: D000222:Adaptation, Physiological; D035961:Alismatales / Q000502:physiology*; D000818:Animals; D059001:Aquatic Organisms; D049873:Cardiidae / Q000502:physiology*; D002734:Chlorophyll / Q000737:chemistry; D000077194:Chlorophyll A; D003198:Computer Simulation; D017753:Ecosystem; D005247:Feeding Behavior / Q000502:physiology*; D020387:Food Chain; D057446:Hydrodynamics; D008954:Models, Biological; D018520:Plant Shoots / Q000502:physiology*; D045483:Rivers
chemical_list: D002734:Chlorophyll; D000077194:Chlorophyll A