Natural Communities of NH -- Photo Guide

Intertidal rocky shore  (S3)



Intertidal rocky shores are found in maritime environments. They are most abundant on the open coast, but they also occur intermittently around estuarine embayments. Elevationally, they range from the splash zone just above high tide down to the lowest shore exposed at low tide. They are subjected to wave action, tides, and when the tides are drawn down, sun and wind. These environmental factors have a strong influence on species composition and zonation. Vascular plants are absent in the higher elevation portions of this community, although cyanobacteria (also known as blue-green algae) and lichens may be present, coloring the rocks in the splash zone. 

A large number marine macroalgae (seaweed) species dominate the middle and lower intertidal zones. Marine algae at the Isles of Shoals and along the open coast include a broad diversity of brown algae, with fewer types of red and green algae. In the Great Bay Estuary, seaweed species dominance shifts from green to red algae with increases in salinity levels. Great Bay also supports disjunct populations of several seaweed species typically found in warmer climates. The rocky substrate also provides solid purchase for barnacles, periwinkles, and mussels. Tidepools are conspicuous ephemeral features of this community, harboring a large number of marine species.

Variants: Two variants of this community occur, distinguished by setting and algae types.

1.     Maritime variant: This variant primarily occurs in high-energy settings along the rocky maritime coastline and at the Isles of Shoals, and is the more common of the two variants. 

2.    
Estuarine variant: This variant primarily occurs along the shores of estuaries like Great Bay and contains algae species not found in the other variant. While tidal currents are sometimes strong and wave action can be significant, settings are typically low-energy compared to the other variant.  

Good examples of this community can be seen on the Isles of Shoals and at Odiorne Point State Park (Rye).

Intertidal rocky shores often occur as part of larger sparsely vegetated intertidal systems and maritime rocky shore systems.


Intertidal rocky shore at Odiorne Point State Park (photo by Ben Kimball)
Intertidal rocky shore
(maritime variant) at Odiorne Point State Park (photo by Ben Kimball)


Intertidal rocky shore at Odiorne Point State Park (photo by Ben Kimball)
Intertidal rocky shore (maritime variant) at Odiorne Point State Park (photo by Ben Kimball)

Intertidal rocky shore at Great Bay National Wildlife Refuge (photo by Ben Kimball for the NH Natural Heritage Bureau)
Intertidal rocky shore (estuarine variant) covered in seaweed
at Great Bay National Wildlife Refuge (photo by Ben Kimball)

Intertidal rocky shore at Star Island, Isles of Shoals (photo by Bill Nichols for the NH Natural Heritage Bureau)
Intertidal rocky shore (maritime variant) at Star Island, Isles of Shoals (photo by Bill Nichols)

Intertidal rocky shore in Rye (photo by Ben Kimball for the NH Natural Heritage Bureau)
Intertidal rocky shore (maritime variant) in Rye (photo by Ben Kimball)