Background
Rocky shores are dynamic intertidal shoreline habitats, which are exposed to constant wave and wind action and undergo alternating periods of air exposure and water submersion with tidal cycles. These habitats experience seasonal changes in salinity, inundation level, and temperature. Organisms such as algae, kelp, mussels, crabs, lobsters, snails, and sea urchins are characteristic of rocky shores, as well as a variety of fish. Rocky shore composition can range from large boulders to medium sized gravel and cobble; these features strongly influence the species that found at each location. For example, shores with large rock arrangements are often dominated by brown algae, barnacles, and mussels, while cobble shores host smaller, short-lived organisms, such as small marine invertebrates (beach hoppers and scuds) ².

Rocky shore zones are distinguished by their exposure to the elements:

• Splash zones are the upper sections, or highest points, of rocky shores. They are exposed to air and waves and typically dominated by dark lichen.
• The high intertidal zone is just below the splash zone, becoming submerged during high tides, and exposed to air when tides retreat. Barnacles and mussels dominate this habitat.
• The lower intertidal zone is only exposed to air briefly during low tides and is dominated by algae.

All of these zones host a dynamic community of marine organisms that are an important part of terrestrial and marine food webs. The structural integrity of these zones protects shorelines from erosion (vegetation, shellfish beds) ⁸.

Rocky shores are currently threatened by coastal development. Dredging can cause rocky shores to be smothered with sediment, which impacts resident plant and animal communities. Pedestrian trampling threatens many organisms that dwell and utilize rocky shores. Submerged rocky habitat is also vulnerable to damage from fishing gear, particularly from trawls and boat anchors ¹².

Artificial rocky shores also occur in Massachusetts for stabilization purposes such as shoreline hardening and bridge foundations. These habitats can provide similar ecosystem services to rocky shores; however, artificial habitats are susceptible to colonization by non-native marine species ¹¹. In addition, shoreline hardening may be harmful to some coastal species as hardened shores can reduce natural coastal habitats, such as salt marshes, over time ⁴.

Climate Impacts
Many organisms that live in rocky shore habitats are vulnerable to impacts associated with climate change. Ocean acidification is projected to significantly increase in the coming centuries, as a result of CO2 absorption by global oceans ¹, and have some of the greatest impacts on calcifying marine organisms that live along rocky shores, including shellfish, corals, and crustaceans ^3,6. The combination of increased ultraviolet radiation (UV rays), water temperature, and changes in salinity negatively impact the development and survival of snails and other mollusks that depend on rocky shores ¹⁰. Changes in food supply from altered plant communities and increased water temperatures can also significantly impact rocky shore mussels ⁹.

Many organisms that live in the intertidal habitats of rocky shores persisted during the last ice age and thus have evolved to accommodate a wide range of environmental conditions ⁷. However, it is unclear if these communities will be able to keep pace with projected rates of sea level rise or run out of optimal habitat and become submerged. If suitable rocky habitats exist up gradient of current intertidal zones, plants and invertebrates should be able to migrate to more elevated habitats unless human or natural barriers prevent this movement ⁵.