Structural Changes of Seagrass Seascapes Driven by Natural and Anthropogenic Factors: A Multidisciplinary Approach

Seascape ecology has been widely applied to marine habitats, including seagrass
meadows, through various approaches all over the world for the past 30 years. However,
these methods mainly study seagrass meadows on a single spatial scale and monitor
a single driver of heterogeneity. Additionally, few assess the seascape’s structural
evolution. This creates gaps between the scientific data provided and those required by
environmental managers and stakeholders in charge of seagrass meadow conservation.
To meet their expectations, in this paper we developed a new multidisciplinary approach
based on the coupling of mapping techniques, particle flux, and biometric investigations
in a Mediterranean Bay, the Calvi Bay (Corsica, France), to assess the structural changes
of Posidonia oceanica (L.) Delile meadows subject to disturbances. We focused our
investigations on the structural characteristics, the spatial dynamics, and the particle
fluxes of natural sand areas generated by bottom currents and dead matte patches
which ensued from anchoring damages at 10, 15, and 20m depth. Natural sand patches
and anchoring patches differed in size, the first the largest. They also displayed different
erosion-colonization dynamics. Natural sand patches were eroded at a mean speed of
12 cm.a−1 and colonized at a rate of 7 cm.a−1. Anchoring patches showed a mean
erosion speed of 3.5 cm.a−1 and a colonization rate of 6.5 cm.a−1. Regarding particle
fluxes, continuous meadow, and natural patch sedimentation and resuspension rates
were 3.7 gDW.m−2.d−1 and 4.1 gDW.m−2.d−1 in average, respectively. In contrast,
anchoring patches at 20m depth acted as sediment traps (112.60 gDW.m−2.d−1 in
winter) and showed a higher particle resuspension rate. Our results highlighted the
dichotomous dynamics of seagrass seascapes influenced by natural and anthropogenic
factors. Thus, the smallest anchoring patch will take about 27 years to be recolonized
while the biggest requires 60 years to be covered by the plant. With an upscaling
approach, together with the newest mapping tools of marine habitats, we suggest a
new method to study the evolution of seagrass meadows at a large spatial scale.