Award: OCE-1458188

The overall goal of this project was to test whether differences in larval transport among regions in the Gulf of Maine results in the formation of different intertidal communities. The Downeast Institute's portion of this collaborative project focused on larval transport processes, while collaborators at other institutions focused more on the community dynamics. We found that larval transport differed greatly along the coast. While larvae along most of the coast are mainly transported to the southwest, the very northeastern most portion of the coast (the Grand Manan Channel) experiences a seasonal (summer) reversal in the direction of transport. Barnacles and mussels exhibit latitudinal gradients in the release of gametes or larvae, with release beginning in the southwest and subsequently spreading to the northeast. These latitudinal gradients interact with the seasonal flow reversal to send larvae in fundamentally different directions. Larvae from the earlier spawning southwestern populations are transported to the southwest (as expected from previous work), but larvae from northeast populations are transported to the northeast (into Canadian waters). As a consequence, a section of the northeastern coast (the Grand Manan Channel) receives very few larvae, and mussels and barnacles are very rare in this region. The higher relative abundance of organisms with limited propagule dispersal (mainly algae) results in very different intertidal communities in this region. As a by-product of our work on the transport of larval mussels, we monitored mussel beds for several years. Contrary to popular beliefs, mussels are quite abundant in large beds that form on soft sediment well up the estuaries (near clam flats). Although open coast rock-living mussels appear to have declined, we found that the mud populations were quite robust, though the recruitment of seed mussels varied quite a bit from year to year. Although these mud populations are commercially harvested, the state of Maine has not traditionally assessed the stocks. Our data provided some preliminary stock assessments during a time when the regulators and industry were debating whether to move toward more active management of the industry. Last Modified: 06/02/2020 Submitted by: Philip O Yund