Natural patches in Posidonia oceanica meadows: the seasonal biogeochemical pore water characteristics of two edge types

Seagrass meadows can be assimilated to seascape
matrixes encompassing a mosaic of natural and
anthropogenic patches. Natural patches within the Mediterranean
Posidonia oceanica meadows show a structural
particularity which consist in a duality of their edge types.
One edge is eroded by bottom currents, while the adjacent
meadow colonizes the bare sediments. This study aims to
study the dynamics of these two edges through the investigation
of the biogeochemistry (pH, total alkalinity, dissolved
inorganic carbon, CO2,
CH4,
N2O,
H2S,
dissolved
inorganic nitrogen, PO4
3−) within vegetated and unvegetated
sediments. These observations are compared with
the adjacent meadow to have a better understanding of the
colonization processes. Our results reveal that the P. oceanica
matrix shows differences from the vegetated edges of
sand patches, especially with regard to nutrient availability,
which is generally more important at the colonized edge
(dissolved inorganic nitrogen up to 65.39 μM in June). A
clear disparity also occurs between the eroded and colonized
edge with both a seasonal and bathymetrical variation of leaf
biomass with higher disparities at 10 m in June (colonized
edge 1415 gDW m−2; eroded edge 1133 gDW m−2). Themost important contrasts during this study were assessed in
June, suggesting that the warm period of the year is more
suitable for sampling to highlight disparate characteristics in
temperate seagrass meadows. These findings put into light
the potential importance of biogeochemical processes in
the dynamics of natural patch edges. We hypothesize that
they may influence the structural dynamics of P. oceanica
seascapes.