7) This well-studied amphipod, which lives particularly in the supralittoral zones of beaches, migrates regularly from the shoreline to the dune, to maintain the optimal zone avoiding both desiccation in the dry zone and inundation by waves. Sandhoppers carry out their life cycle on the same beach throughout the year, so they may integrate the effects of environmental variability.
Since they are strictly linked to the supralittoral environment, the responses to environmental variation represent an integration of constant updating to the environmental condition.
Sandhoppers are important elements in ecological processes that occur on sandy beaches and, more specifically they
play a key role in the food web structure, as important consumers of wrack and a food source for most of the upper levels of the trophic chains in sand-dune environments.
8) This enables them to act as a feasible keystone species (i.e. a species whose removal from the ecosystem is expected to consistently change the community composition, Mills et al., 1993).
9) The baseline of data on this species on sandy beaches makes sandhoppers good candidates for bioindicators of environmental stress.
In fact, the behavioural plasticity of talitrids enabled them to become a special bioindicator species for human perturbations on sandy beaches.
10) In our case, in the artificial dune zone, the presence of large geotubes and the amount of disrupted textiles found in the supralittoral zone (see Fig. 1b) led us to hypothesise that amphipods could not burrow in this zone and might therefore avoid this area whenever they needed to recover the optimal zone on the beach.
Accordingly, it is not surprising that the lowest number of individuals in the artificialised area in comparison to the reference one was found both in the spring and summer 2010 sampling periods.
Indeed, statistical tests detected differences in T. saltator densities especially during the warmer season, when this species recruitment occurs on the Western Atlantic coast while during the cooler period (autumn 2010 and winter 2011)
almost no individuals were recorded at either site (Fig. 2d).
Thus, successful employment of artificial dunes in this system could jeopardise the presence of this supralittoral species in this site.
11) Therefore, such behavioural changes linked to the artificial dune zone could be well suited as an early warning signal for wider negative ecological impact (as demonstrated by reduced densities of T. saltator in this zone).
This finding makes this species suitable as a baseline indicator of habitat degradation, given its sensitivity to physical variation in the beach and dune ecological conditions as demonstrated here.
Our results reinforce the notion that T. saltator could be used as a bioindicator of human changes on sandy beaches.