Climate change and species introductions are altering native distributions and abundances of organisms world-wide. When these changes involve ecosystem engineers, cascading shifts in ecosystem function are expected. Predicting how ecosystem engineers will respond to novel or changing habitats is therefore critical to predicting ecosystem-level responses to climate change and species introductions. Ecosystem engineering polychaetes in the Diopatra genus are undergoing range shifts in Western Europe. We (i) assess the species diversity underlying these shifts, (ii) link biogeographic patterns to sea surface temperature patterns, and (iii) predict possible ecosystem-level outcomes of Diopatra's poleward expansion. We use molecular phylogenetic and morphological evidence to assess species diversity and biogeographic ranges. We compare biogeographic patterns to historical sea surface temperature patterns to draw links between range shifts and climate change. Finally, we review published data to predict potential ecological changes as Diopatra invades new habitats.
The native D. neapolitana range has contracted 150 km to the south. A cryptogenic species, Diopatra sp. A, has extended the northern limit of the genus 300 km poleward to the southern Brittany peninsula. A third species, the Moroccan D. marocensis, now occurs in Portugal. Diopatra species density correlates with sea surface temperatures, and both shifts can be explained by historical sea surface temperature anomalies. The Diopatra sp. A expansion is predicted to continue into the English Channel and the North Sea, introducing large tube structures to sheltered sedimentary habitats that currently lack such structures. As climate change intensifies, the sediment-stabilizing Diopatra sp. A will invade habitats dominated by the bioturbating lugworm Arenicola marina. The resulting interaction between functionally different ecosystem engineers will likely cause ecological changes in Northern European coastal waters. Existing data for Diopatra species and arenicolids suggest that the diversity and biomass of macroalgae, vascular plants, infauna and epibenthic fauna may increase, while microbial activity may decrease. Net changes in productivity will depend on the relative rates of these changes.