Introduction to Marine Rocky Intertidal

HabitatMasochistic Organisms and the

Students Who Love Them

Physical Challenges

Inhabitants of the rocky intertidal habitat must deal with some of the most extreme envirnmental fluctuations on earth. These include:

• Wave action• Substrate• Slope• Exposure to the sun• Dessication• Extremes of salinity• Extremes of

temperature

Rocky Substrate

Organisms must adhere to solid rock. Examples of such mechanism include:

• Holdfasts (multicellular algae)

• Super adhesives (barnacles)

• Suction (sea stars, sea urchins)

Byssal threads (mussels)

Wave Action

Strategies for coping with relentless battering include:

• Clinging rigidly to rock.• Maintaining a low profile.• Inhabiting crevices protected from waves.• A flexible but tough tissue consistency.

Slope

The jumble of surfaces exposed as rock of the intertidal zone weathers and breaks up range from horizontal to vertical to inverted.

Exposure to the Sun

• Ultraviolet rays can damage tissue and genetic material of unprotected organisms.

Dessication• Intertidal inhabitants are marine organisms, but some are exposed to air daily by the receding tide for hours at a time.

• To avoid dessication, they must be able to seal unprotected tissues in a watertight surrounding in order to survive.

Temperature Extremes• Throughout the year, intertidal organisms must

cope with air temperatures ranging from sub-freezing to over 35oC (mid 90’s Fahrenheit).

• On a daily basis,

sudden immersion

in and withdrawal

from ocean water

can involve a

difference of

20oC or more.

Salinity Extremes

• As the mid-day sun heats tide pools, water evaporates, but its salt remains behind.

• Salinity can increase dramatically before the next flush of fresh sea water.

• At the opposite extreme, tide pools with a direct influx of fresh water from the land can have a much lower salinity than ocean water.

Zonation on Maine’s Rocky Shore

• Physical and biological factors create regular patterns in the ecology of the rocky littoral zone. These effects are displayed as wide bands, each containing certain species.

Subtidal Zone• Not “intertidal.”• the extreme

low margin of shore that is always submerged. Large kelps (brown algae) are dominant here along the zone's upper edge.

Red Algae Zone

• The first intertidal zone, dominated by Irish moss and tufted red weed.

"In the calm world of the deeper rock pools, undisturbed by the tumult of incoming waves, crabs sidle along the walls, their claws busily touching, feeling, exploring for bits of food. The pools are gardens of color composed of the delicate green and ocher-yellow of encrusting sponge, the pale pink of hydroids that stand like clusters of fragile spring flowers, the bronze and electric-blue gleams of the Irish moss, the old-rose beauty of the coralline algae."

- Rachel Carson, The Edge of the Sea

Brown Algae Zone

• Brown algae, such as rockweeds and knotted wrack, dominates.

"Meadows of brown rockweeds appear on the gently sloping rocks of the shore as the tide imperceptibly ebbs. Smaller patches of green weed, stringy as mermaids’ hair, begin to turn white and crinkly where the sun has dried them." - Rachel Carson, The Edge of the Sea

Mussel Zone• Dominated by the

edible mussel, Mytilus edulis.

• Many other species live in the mussel bed attached to the mussels' byssal threads, or attached to the mussels' shells.

Barnacle Zone

“Like drifts of old snow no longer white, the barnacles come into view; they blanket rocks and old spars wedged into rock crevices, and their sharp cones are sprinkled over empty mussel shells and lobster pot buoys and the hard stipes of deep water seaweeds, all mingled in the flotsam of the tides.” - Rachel Carson, The Edge of the Sea

Black Zone• Dominated by various blue-green bacteria

(Cyanobacteria) that appear as a slimy, black film on the rock surfaces (beware! slippery when wet!)

Lichen Zone

• Organisms living here are exposed to salt water as spray from crashing waves rather than from tidal inundation.

• lichens tolerant of occasional salt spray dominate this zone.

Common Intertidal Residents

Sessile algae (Protista)

Hollow green algae (Enteromorpha intestinalis)

Sea lettuce (Ulva lactuca)

Green seaweed (Spongomorpha sp.)

Green fleece (Codium fragile)

Irish moss (Chondrus crispus)

Coral weed (Corallina officinalis)

Tufted red weed (Gigartina stellata)

Dulse (Rhodymenia palmata)

Rockweed (Fucus sp.)

Knotted wrack (Ascophyllum nodosum)

Brown kelp (Laminaria sp.)

MollusksBlue Mussel (Mytilus edulis)

Common periwinkle (Littorina littorea)

Dog whelk (Thais lapillus)

Tortoiseshell limpet (Acmaea testudinalis)

ArthropodsNorthern Rock

Barnacle (Semibalanus balanoides)

Rock crab (Cancer irroratus)

Hermit crab (Pagurus longicarpus)

Scud (Gammarus sp.)

Echinoderms

Northern Sea Star (Asterias vulgaris)

Blood Star (Henrica sp.)

Green Sea Urchin (Strongylocentrotus droebachiensis)

Sponges

• Crumb-of-bread Sponge (Halichondria panacea)

Tide Pool FishesEnough said.