Data from: Ecological effects of habitat complexity vary with intertidal elevation: Implications for seawall eco-engineering

Coastal urbanisation is replacing natural shoreline habitats with built
structures, such as seawalls. Built structures often lack complex habitat
features that provide protective and cool microhabitats for biodiversity.
We conducted field experiments to assess whether the addition (or
eco-engineering) of complex habitat panels to seawalls influenced benthic
community assemblages across the intertidal range, at panel and site
scales. We expected: (i) effects of habitat complexity to vary with tidal
elevation, reflecting spatial variation in the identity and magnitude of
stressors from which habitat complexity provides protection; (ii) positive
effects of complexity on functional groups of organisms with exposed soft
tissues that make them prone to desiccation and predation, and especially
on the high shore where temperature and desiccation is greatest, and (iii)
increases in the upper vertical limit of key taxa inhabiting
eco-engineered seawalls to match reference reefs, and exceed control
seawalls, depending on the type of habitat complexity provided. Effects of
habitat complexity increased with tidal emersion and varied by functional
group. In the mid- and high-intertidal, across which temperatures
increased, complex panels supported over two times the abundance of key
taxa than flat control panels. In the low-intertidal, brown algae were
more abundant on flat than complex panels, whereas mobile invertebrates
with exoskeletons responded positively to complexity in the
high-intertidal, and mobile soft-bodied invertebrates were only found in
complex habitats of the mid-intertidal. Cool microhabitats (pools, shaded
depressions) of complex habitat panels were important in supporting key
taxa and functional groups at higher intertidal elevations than on flat
surfaces, and that, often, matched natural rocky shores. Synthesis and
applications: Our results demonstrate that the addition of habitat
complexity through eco-engineering can promote key functional groups of
algae and invertebrates on seawalls, but effects vary across tidal
elevation gradients and with the type of complexity provided.
Consequently, to achieve desired outcomes, eco-engineering interventions
must be applied with knowledge of key limiting factors to target taxa, and
of spatial variation in these limiting factors across small-scale
gradients such as intertidal elevation, as well as sites.