intertidal mussels as ecosystem engineers: maintenance of invertebrate assemblages amid intertidal stress gradients

In this study, we measured univariate and multivarite metrics of mobile invertebrate assemblages along the midlittoral vertical range of four replicate rocky shores, aiming a control habitat (barnacle cover) and a facilitated habitat (barnacle cover plus a secondary mussel cover). At any given shore height, differences between assemblages would indicate realized facilitation. Temperature and desiccation potential increase from the bottom to the top of this range, and increased facilitation higher on the shore would support the stress-gradient hypothesis. Along with invertebrate data, we provide key environmental data at study sites that could underlie any spatial structure on top of local vertical trends.

Methods
Environmental parameters at study sites were estimated following standard techniques in intertidal ecology (i.e. shore characteristics). A  compass was used to estimate shore orientation. A digital clinometer measured shore inclination. Measuring tapes, water hoses and rulers were used to measure shore inclination, shore height and mussel bed cross-shore size. A digital thermometers coupled to a pointed probe was used to measure interstitial temperature.

In the lab, mobile invertebrates were sorted out from samples through washing and sieving and counted/identified under a dissecting microscope.