Rocky Promontory at Eagle Cove

Erin exploring eelgrass at the promontory edge

A large rocky promontory juts out into the ocean just next to the sandy beach.  This habitat provides the clearest example of intertidal zonation at Eagle Cove.  The highest reaches of the rocky intertidal are inhabited by barnacles and a few other hardy animals that can survive extreme temperatures and desiccation. Further down the rocky slope one finds algae and invertebrates that are less resistant to environmental extremes. More abundant in this lower zone are species of invertebrate grazers and scavengers--including the gastropod Littorina scutulata, the chitons Katharina tunicata and Tonicella lineata, the isopod Idotea wosnesenskii, and gammarid amphipods--as well as predatory nudibranchs ("sea slugs") and nemerteans ("ribbon worms").

The eelgrass beds located at the bottom of the promontory provide another unique habitat. Eelgrass facilitates the accumulation of sediment and provides a habitat for many types of polychaete worms and grazers such as the gastropods Lacuna vincta and Lacuna variegata and the isopod Idotea fewkesi.

A mass of polychaetes in a cleared eelgrass quadrat


Aeolid nudibranch in a tidepool
Tidepools and crevices on the rocky promontory offer refuge for plants and animals that might not otherwise survive high intertidal exposure. During the extremely low tide series in early July 2004, we recorded temperature fluctuations in a crevice over 3 days and noted invertebrates found in these crevices that were not apparent on nearby drained surfaces. Most notable were nudibranchs, including Archidoris montereyensis and Aeolidia papillosa.

Organisms living in rocky intertidal areas, even in tidepools and crevices, often deal with variable environmental conditions during tidal exchanges. To the right is a graph of temperature in a crevice pool, recorded every 12 minutes for 3 days during an extremely low tide series .  The temperatures in rocky crevices fluctuated as dramatically as those at the surface of the sandy beach.  Notice how the temperature spiked in the early afternoon each day, just after the tide was at its lowest point (11:17 am and 12:06 pm on July 3rd and 4th, respectively).

crevice temperatures

In addition to changes in temperature, organisms in the rocky intertidal cope with fluctuation in a number of different environmental parameters. Click on these links to learn more about locomotion , feeding , reproduction & protection strategies of invertebrates living on the rocky promontory at Eagle Cove.

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