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Life at the Ocean’s Edge Activity 11 Donnelly Science 6. Who would build their home on shifting sand, jagged rocks, or sticky mud? Who would choose a life pounded by surf, abraded by wind, water, and sand, and alternately covered with water and exposed to air and sunlight each day?.
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Who would build their home on shifting sand, jagged rocks, or sticky mud? • Who would choose a life pounded by surf, abraded by wind, water, and sand, and alternately covered with water and exposed to air and sunlight each day?
Intertidal Zone • This harsh, ever-changing environment is called the intertidal zone, and thousands of organisms thrive here and nowhere else.
Intertidal Zone • Located at the edge of the ocean, between the highest high-tide line and the lowest low-tide line. • It may be rocky, sandy, marshy, or muddy. • During periods of low tide, it is possible to explore the ocean floor in the intertidal zone. • Most thoroughly studied, and best-known, ocean area.
Habitats within the Intertidal Areas • Even within the intertidal areas, the cycle of exposure to air varies markedly—so much that four different habitat bands have been identified: 1) the spray zone, 2) the high-tide zone, 3) the mid-tide zone, 4) the low-tide zone
The Spray Zone • Also known as the splash zone • Rarely covered completely by water (only during the highest high tides) • Organisms living here need the salty spray of ocean water but would not thrive if submerged.
The High-Tide Zone • Exposed most of the time and under water only during high tides.
The Mid-Tide Zone • Regularly covered and uncovered by the tide twice each day • This area is under water about half the time.
The Low-Tide Zone • Submerged for all but a few hours each month, during the lowest low tides.
Tidal Zones • Depending on location, the range of the tidal zones can be small or great. • In flat areas where the tide can spread over smooth, open beaches, as in the Gulf of Mexico, the tide may rise and fall only a few inches each day, and the intertidal zone is broad but shallow. • Where the tide cannot spread out, as in Nova Scotia’s narrow Bay of Fundy, high tide may be over 20m (70 ft) higher than low tide, but the intertidal zone may be very narrow.
Tidal Zones • Each type of zone is home to organisms that have adapted to their environment in some remarkable ways. • Most intertidal animals stay in the zone that supplies the amount of water, food, and air they need. • Many move from zone to zone.
How the Animals Adapt? • One way the animals are adapted to the pounding breakers, hot sun, rain, snow, and even ice of the tidal area is by having a hard exterior. • The shells that we see on the beach are the discarded homes of once-living mollusks, aword that means “soft-bodied.” • These shells, which the animals make from calcium carbonate in seawater, are the external skeletons, or exoskeletons, of the animals. • Without their shells, the animals would never survive in the intertidal zone.
Bivalves • Mollusks with two shells.
Bivalves • Use muscles to open and close their shells. • Open their shells to let in food and water and close them to rest or to protect themselves. • Have two siphon tubes. The bivalves take in water through one tube (from the water the animal absorbs oxygen and filters microscopic food particles) , and waste water leaves through the other siphon tube.
Bivalves • Most live in sand or mud, although some attach themselves to rocks and pilings. • Most move by extending and then contracting their large muscular foot, although some can move through a kind of “jet propulsion” by opening and then clamping shut their shells. • Large colonies of bivalves are often referred to as “beds”
Univalves • Mollusks with one shell.
Univalves • Also known as gastropods.(Gastropod comes from words that mean “stomach” and “foot.”) • All univalves are gastropods, but not all gastropods are univalves (slugs, for example). • Gastropods are abundant and diverse, outnumbered in the animal kingdom only by insects.
Univalves • Have a well-developed head with eyes, a mouth, and tentacles, just like ordinary pond or land snails. • Have a rough, scraping tongue, called a radula, which is used to shred vegetable or animal matter. • Many live among rocks and coral reefs, while others dwell in the shallow water along sandy shores.
Univalves • Like bivalves, they have one or more siphon tubes and move by extending and contracting a muscular foot. • To protect themselves, they retract their soft bodies into their shells and seal the opening with a plug called an operculum.
