The
Arc
achon l
agoon (Atl
antic co
ast, SW Fr
ance) is
a mesotid
al emb
ayment where se
agr
ass beds colonize the m
ajority of intertid
al
are
as. In recent ye
ars, the surf
ace
are
a of
Zostera noltii me
adows h
as consider
ably decre
ased, with possible consequences for the sediment b
al
ance of the l
agoon. However, such inter
actions
are poorly understood,
and knowledge of the rel
ationship between hydro-sediment
ary processes
and sm
all intertid
al me
adows, such
as
Z. noltii, is limited.
An intertidal mudflat, with variable meadow coverage, was studied during an annual survey. The study consisted in continuous high-frequency monitoring of bed altimetry, tidal elevation and waves. Sediment parameters and meadow characteristics were analyzed using samples collected monthly. Acoustic altimetry was validated as an efficient method to measure bed elevation in a vegetated environment, despite the presence of leaves under the transducer. The acoustic altimeter was also shown to have the potential to accurately estimate canopy height in a submerged environment.
Our survey data showed centimetric bed accretion at all vegetated stations. Accretion was positively correlated with seasonal growth of the meadows. During seasonal degeneration, the meadow prevented erosion of the sea bed. These results highlight the important role of seagrasses as ecosystem engineers.