The World of Edges in Submerged Vegetated Marine Canopies: From Patch to Canopy Scale

Abstract

This review describes the world of edges in submerged vegetated marine canopies (seagrasses, saltmarshes, and seaweeds) where an edge is a boundary with a frontal area separating the vegetation from the adjacent non-vegetated zones. Plants within the vegetation are made of flexible elements pronating in the direction of the flow and oscillating back and forth in response to wave forcing. Some of them also occupy the full height within the water body. The analysis focuses on both the canopy- and local-patch scales to acquire knowledge about the hydrodynamics and the biophysical interactions in the structural shallows and deep limits of the canopies as well as on the structural edges of vegetation patches and the edges in the gaps within the canopies. The spatial arrangements of both canopy and patch edges are not only well imposed through the modification of hydrodynamics, but so too through small-scale interactions from internal structural causes and modifications. The continuous fragmentation of coastal marine habitats has reduced their structural complexity, thus making habitat edges a prevalent seascape feature, including in the shallow (or upper) and deep (or lower) limits of the canopies, the patch edges, and the edges in the gaps within the canopies. Canopy patches represent a region of high flow resistance where flow deflects and accelerates above and/or next to the canopy, resulting in an increase in water velocity and turbulence, especially at the edges of the patch. At the edges, energy transfer is found in spectral wave velocities from the longer to shorter wave period components. Likewise, at the edges, the net deposition of sediments decreases over a distance to a certain length, relative to the bare bed, which is associated with a region of vertical updraft and elevated turbulent kinetic energy. The edge effects also relate to the influence that a patch edge can have on determining species composition and predation risk, which is additionally mediated by the effect the edges have on habitat complexity within the vegetated patch. Organism feedback within the edges does not simply follow the canopy and local features and, in fact, the intricate interaction between biogeophysical processes is key in explaining the complexity of coastal submerged canopy landscapes. For example, proximity to patch edges has a greater influence on epifaunal density and community structure than structural complexity or predation do. The extent to which edges reduce predation risk depends on the extent to which they support higher structural complexities compared to patch interiors. The canopies’ shallow limits and their position in the underwater beach profile are mostly limited by light availability, the intensity of the wave action, and the local nearshore hydrodynamics, but they also depend on the local structural conditions at the vegetated side. The deep limits of the canopies, however, mainly depend on the availability of light and research findings support migration both to the deeper and shallower layers. All structural edges face changes caused by increasing nutrient inputs, development of coastal zones and the increasing impact of climate change. A considerable challenge to managing, restoring, and conserving coastal marine ecosystems stems from understanding how the canopies are able to cope with these natural and anthropogenic disturbances.

Satellite Multi/Hyper Spectral HR Sensors for Mapping the Posidonia oceanica in South Mediterranean Islands

“…However, EO based monitoring of shallow waters and seabed of the coastal environment characterized by anthropogenic impacts, still represents a challenge, due to coastal water turbidity often associated with various atmospheric effects and noises, combined with the difficulties of in situ sampling for collecting sea truth calibration data of submerged plants on the seabed by means of scuba diving. These are important limiting factors to useful exploitation of EO high resolution (HR) data for extensive mapping of PO and coastal seabed and water quality parameters [14,19], especially where the coastal sea currents are significant, as in the Southern Mediterranean islands, with consequent additional signal degradations from increased water turbidity from sediment resuspension and sun-glint presence [20][21][22].…”

Trade‐Off Between Light Deprivation and Desiccation in Intertidal Seagrasses Due To Periodic Tidal Inundation and Exposure: Insights From a Data‐Calibrated Model

“…As such, many seagrass species are intolerant to these conditions and are unable to grow in intertidal zones (Koch, 2001). However, there are some species, including a few temperate species such as Nanozostera japonica ( Zostera japonica ), Z. marina , Z. noltei ( Z. noltii ), as well as subtropical or tropical species such as Halophila ovalis and Thalassia hemprichii , that thrive in the shallow intertidal zones of estuaries, lagoons and other coastal areas (Colomer & Serra, 2021; Shafer et al., 2007). Intertidal seagrass meadows function as essential foraging habitats (Espadero et al., 2020) and blue carbon stock, yielding higher organic carbon burial rates than subtidal seagrasses (de los Santos et al., 2022).…”

Trade-off between light deprivation and desiccation in intertidal seagrasses due to periodic tidal inundation and exposure: insights from a data-calibrated model

“…As such, many seagrass species are intolerant to these conditions and are unable to grow in intertidal zones (Koch 2001). However, there are some species, including a few temperate species in the genus Zostera such as Zostera japonica , Z. marina , Z. noltii , as well as subtropical or tropical species such as Halophila ovalis and Thalassia hemprichii , that thrive in the shallow intertidal zones of estuaries, lagoons and other coastal areas (Colomer and Serra 2021; Shafer et al 2007). Intertidal seagrass meadows function as essential foraging habitats (Espadero et al 2020) and blue carbon stock, yielding higher organic carbon burial rates than subtidal seagrasses (de los Santos et al 2022).…”

“…However, there are some species, including a few temperate species in the genus Zostera such as Zostera japonica, Z. marina, Z. noltii, as well as subtropical or tropical species such as Halophila ovalis and Thalassia hemprichii, that thrive in the shallow intertidal zones of estuaries, lagoons and other coastal areas (Colomer and Serra 2021;Shafer et al 2007).…”