3/10/2024 0 Comments Common retrospect for life tidalHowever, biogenic species might block the sediment surface and therefore reduce the surface area subject to resuspension. Similarly, benthic animals that bioturbate sediment or graze biofilms are associated with increased erodability of sediments ( Widdows et al., 2008 Guizien et al., 2014). Bivalves such as hard clams can intensify erosional processes and accordingly augment seston, even while drawing down phytoplankton biomass overall ( Porter, Mason & Sanford, 2013). Seagrass contributes tall, flexible structure, whereas oysters are stiff and typically shorter (although reefs can build up from gregarious settlement and particle trapping Walles et al., 2015). However, effects on flow velocity and turbulence within and around structure are sensitive to a variety of parameters that naturally vary in the field, including the fraction of the water column occupied by structure ( Moore, 2004 Hasegawa, Hori & Mukai, 2008 Luhar, Rominger & Nepf, 2008), and the density and flexibility of structural elements ( Adhitya et al., 2014 Houser, Trimble & Morales, 2015). Empirically, seagrass beds buffer against water motion and accumulate fine particles ( Fonseca et al., 1982 Kenworthy, Zieman & Thayer, 1982). Seagrass influences seston predominantly as a side effect of altering water motion, since more rapid flow or turbulence can lift and transport larger, denser particles ( Widdows et al., 2008 Wilkie et al., 2012). Away from the footprint of oysters, mixing and compensatory phytoplankton dynamics obscure this trophic effect ( Dame & Libes, 1993 Plutchak et al., 2010). As suspension-feeders, oysters remove particles, and water passing across oyster beds typically declines in chlorophyll concentration ( Grizzle et al., 2006 Grizzle, Greene & Coen, 2008 Grangere et al., 2010 Plutchak et al., 2010 Wheat & Ruesink, 2013. These two species are expected to modify water properties in different ways. In this study, we track water properties across tidal flats and compare unstructured habitat to two dominant structure-forming species: eelgrass ( Zostera marina) and oysters ( Crassostrea gigas). Quantifying how biogenic species influence the mobilization and removal of particles improves understanding of the feedbacks governing local heterogeneity in water properties ( Widdows et al., 2008 DeBoer, 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). 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). 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. 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. At higher TSS concentrations, quality in terms of organic content declined, and this relationship was not habitat-specific. 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. Water flowed more slowly across eelgrass than other habitat types. 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 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)). 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. 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.
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