Predicting changes in molluscan spatial distributions in mangrove forests in response to sea-level rise

Molluscs are an important component of the mangrove ecosystem, and the
vertical distributions of molluscan species in this ecosystem are
primarily dictated by tidal inundation. Thus, sea-level rise (SLR) may
have profound effects on mangrove mollusc communities. Here, we used
dynamic empirical models, based on measurements of surface elevation
change, sediment accretion, and molluscan zonation patterns, to predict
changes in molluscan spatial distributions in response to different
sea-level rise rates in the mangrove forests of Zhenzhu Bay (Guangxi,
China). The change in surface elevation was 4.76–9.61 mm yr−1 during the
study period (2016–2020), and the magnitude of surface-elevation change
decreased exponentially as original surface elevation increased. Based on
our model results, we predicted that mangrove molluscs might successfully
adapt to a low rate of SLR (2.00–4.57 mm yr−1) by 2100, with molluscs
moving seaward and those in the lower intertidal zones expanding into
newly available zones. However, as SLR rate increased (4.57–8.14 mm yr−1),
our models predicted that surface elevations would decrease beginning in
the high intertidal zones and gradually spread to the low intertidal
zones. Finally, at high rates of SLR (8.14–16.00 mm yr−1), surface
elevations were predicted to decrease across the elevation gradient, with
molluscs moving landward and species in higher intertidal zones blocked by
landward barriers. Tidal inundation and the consequent increases in
interspecific competition and predation pressure were predicted to
threaten the survival of many molluscan groups in higher intertidal zones,
especially arboreal and infaunal molluscs at the landward edge of the
mangroves, resulting in a substantial reduction in the abundance of
original species on the landward edge. Thus, future efforts to conserve
mangrove floral and faunal diversity should prioritize species restricted
to landward mangrove areas and protect potential species habitats.