Abstract
Aquatic structure-formers have the potential to establish mosaics of seston in shallow water if they modify the relative amounts of deposition (or filtration) and resuspension of particles. By sampling surface water adjacent to Lagrangian drifters traveling 0.1 to 2 m above the bottom, we tested the modification of seston in water masses flowing over two biogenic marine species (native eelgrass, Zostera marina; introduced oysters, Crassostrea gigas) in comparison to unstructured tidal flats. Water properties were examined at five intertidal sites in Washington State, USA, each with 27 drifts (three drifts at different stages of the tidal cycle in each of three patches of three habitat types; drift distance 116 m (109SD), duration 24 min (15SD)). At the initiation of each drift, habitat differences in water properties were already apparent: chlorophyll-a and total suspended solid (TSS) concentrations were greater in structured habitats than bare, and TSS was also inversely related to water depth. Water flowed more slowly across eelgrass than other habitat types. As water flowed across each habitat type, TSS generally increased, especially in shallow water, but without habitat differences; chlorophyll-a in these surface-water samples showed no consistent change during drifts. At higher TSS concentrations, quality in terms of organic content declined, and this relationship was not habitat-specific. However, quality in terms of chlorophyll-a concentration increased with TSS, as well as being greater in water over eelgrass than over other habitat types. These results support widespread mobilization of seston in shallow water ebbing or flooding across Washington State’s tidal flats, especially as water passes into patches of biogenic species.
Highlights
Intertidal organisms, in addition to spending time in both water and air, experience short-term variation because coastal water fluctuates in such properties as dissolved gas concentrations (Duarte et al, 2013) and particle loads (Ralph et al, 2007)
For water properties of total suspended solids and chlorophyll-a, we evaluated both the static differences among habitat types based on point samples and the dynamic changes as water transited over bare tidal flat, eelgrass, or oysters
Higher concentrations of total suspended solid (TSS) and Chl were present in both biogenic habitats than over bare tidal flat, the oyster-bare comparisons had P-values closer to α = 0.05 that should be interpreted cautiously in linear mixed effects models
Summary
Intertidal organisms, in addition to spending time in both water and air, experience short-term variation because coastal water fluctuates in such properties as dissolved gas concentrations (Duarte et al, 2013) and particle loads (Ralph et al, 2007). The amount and composition of suspended particulate matter, termed seston, has important implications for the productivity of macrophytes via light limitation (DeBoer , 2007) and for benthic suspension feeders via food resources (e.g., Kang et al, 2003). Quantifying how biogenic species influence the mobilization and removal of particles improves understanding of the feedbacks governing local heterogeneity in water properties Comparison of shallow-water seston among biogenic habitats on tidal flats. We track water properties across tidal flats and compare unstructured habitat to two dominant structure-forming species: eelgrass (Zostera marina) and oysters (Crassostrea gigas)
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