• Views from Penobscot Mountain summit.

    Acadia

    National Park Maine

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  • Temporary Road Closure

    A section of the Western Mtn Road in Southwest Harbor will be closed until 8/18 while park crews replace a culvert with a new fish-friendly open bottom culvert. For more information and a map visit our Getting Around Page. More »

  • Trail Closure: Gorge Path weekdays, 7 am - 4 pm

    The section of the Gorge Path between the Hemlock Path intersection and the A. Murray Young Trail intersection is closed until rehabilitation work is completed. The closure will be in effect Mondays through Fridays only, from 7 am to 4 pm.

Field Guide to Marine Invertebrates - Arthropods - Crustaceans

Jonah Crab
Cancer borealis
Cancer borealis ("Jonah crab") is found in the mid- to lower intertidal zone under algae and among rocks. This predator eats blue mussels and other invertebrates. The remains of this crab are often found in the upper intertidal zone, evidence of bird predation.
 
Green Crab
Carcinus maenas
Carcinus maenas ("green crab") is found under algae and small rocks, and it eats other invertebrates in the mid- to lower intertidal zones. This crab is native to Europe and is an invasive species. The green crab is smaller than the Jonah crab.
 
Lobster on rocks
Homarus americanus
Homarus americanus ("American lobster") is a bottom-dwelling predator and scavenger. The American lobster is found throughout the Gulf of Maine, where it is commercially important. The lobster is found in rocky, subtidal habitats but, rarely, can be observed in lower intertidal pools.
 
Isopod on aglae
Idotea balthica
This herbivorous crustacean, an isopod, feeds on a variety of algae including large rockweeds (Ascophyllum, Fucus). It is common in the mid- and lower intertidal zones but is hard to see because its color usually matches the algae it is feeding on. This behavior helps it resist predation by fish. Individuals vary in color from yellow to brown to deep burgundy.
 
Close-up view of barnacles

Semibalanus balanoides
S
emibalanus balanoides ("barnacles") are sessile filter feeders. Larvae settle in the spring and attach head down to the rock. They make heavy calcified plates, which protect them from predation and drying stress, and begin to sweep phytoplankton into their digestive system by catching them with modified, feathery limbs that sweep out into the seawater from the plates. Semibalanus balanoides can be found from the low to high intertidal zones. Individuals lower in the intertidal zone and in high intertidal pools are larger than individuals that settled in the high intertidal zone. The larger individuals are in habitats where they are covered by water for a longer period of time each day, and this protects them from stress and provides them with more opportunities to feed.

 
All photos by Sarah Hall, except for American lobster (NPS/Todd Edgar photo).

Did You Know?

A girl stands along the stone steps of the Kurt Diederich Path in this historic image taken around 1920.

Acadia National Park contains more than 120 miles of historic hiking trails. Many of these trails were established by local village improvement societies in the late 1800s and early 1900s. Today many of the historic features, such as stonework, are still visible.