Predicting changes in molluscan spatial distributions in mangrove
forests in response to sea-level rise
Abstract
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 two
dynamic empirical models based on measurements of surface elevation
change, sediment accretion and zonation patterns of molluscs 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
a−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 (marker-horizon model: 2–4.57 mm a−1; plate
model: 2–5.20 mm a−1) by 2100, with molluscs moving
seaward and those in the lower intertidal zones expanding into newly
available zones. However, as SLR rate increased (marker-horizon model:
4.57–8.14 mm a−1; plate model: 5.20–6.88 mm
a−1), our models predicted that surface elevations
would decrease beginning in the high intertidal zones and gradually
spreading to the low intertidal zones. Finally, at high rates of SLR
(marker-horizon model: 8.14–16.00 mm a−1; plate
model: 6.88–16.00 mm a−1), surface elevations were
predicted to decrease across the elevation gradient, with molluscs
moving landward and species in higher intertidal zones would be blocked
by landward barriers. Tidal inundation and the consequent increase in
interspecific competition and predation pressure were predicted to
threaten the survival of many molluscan groups in higher intertidal
zones, especially species at the landward edge of the mangroves. Thus,
future efforts to conserve mangrove floral and faunal diversity should
prioritize species restricted to landward mangrove areas.