QUANTIFICATION OF CRYPTIC BIOTURBATION BY "BEACH HOPPERS" (TALORCHESTIA SP.) ON A CLASTIC BEACH: WATERSIDE BEACH, BAY OF FUNDY, CANADA

Cryptic bioturbation is commonly interpreted, but rarely quantified, in the backshore and upper foreshore of modern and ancient clastic depositional systems. At Waterside beach, Bay of Fundy, Canada, "Beach Hoppers" (Talorchestia sp. are a major bioturbator of the upper foreshore and proximal backshore. Thus, they represent an important mechanism of sediment reworking within these environments. Burrowing densities upto 1200/m² and burrow depths upto 25cm, result in the nightly exhumation of significant volumes of sediment. This sediment is subsequently re-exposed to winnowing by hydraulic processes over the ensuing tidal cycle.

"Beach Hoppers" excavate unlined, vertical burrows in sandy areas of the backshore and upper foreshore. During the evening or night low tide, they exit their burrows to scavenge on kelp and vegetation built-up at the high tide line. With the sunrise, Talorchestia either excavate a new burrow or deepen an existing one, flinging the exhumed sediment upto 14 cm away from the burrow opening.

Using in-situ aquaria to observe burrowing behavior, it is established that in the study area, Talorchestia prefers medium-grained then coarse-grained sand. Very coarse-, and granule-sized sediment are less favored. In areas where gravel clasts occur within a sandy matrix, "Beach Hoppers" will burrow under the clasts or use them as a component of their burrow walls.

The aquaria also reveal the discrete biogenic structures that comprise, under high population densities, cryptic bioturbation. These are comparable to biogenic textures observed in the foreshore of ancient clastic beach accumulations.