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Seashore

Intertidal Zone

The intertidal zone is an extremely important part of the marine community because it harbors such a large number of species. There is a huge diversity of organisms, not only due to upwelling but also because of the abundance of different habitats and niches.

There are four different types of coastline. These are divided by designations of wave shock, tidal exposure, and bottom type. Wave shock is probably the most important factor because it determines the types of organisms that can live in a coastal habitat. Organisms who live in areas with high wave shock must have some protection to avoid being crushed, and are usually securely attached to a rock or other stable object to avoid being washed away. Organisms that live in areas with a lower degree of wave shock can afford to have softer bodies, and are not required to be "fixed" because it is less likely that they will be washed away.

ZONE
Wave Shock

Effect on Organisms

Protected Outer Coast
force of surf is somewhat dissipated Protected outer coasts harbor a large number of diverse organisms because of the lessened degree of wave shock.

These shores are generally concave and protected by headlands, a close lying island, or even an underwater reef or kelp bed a long ways offshore, anything to break the waves before they hit the land.

Open Coast
entirely unprotected, surf-swept shores There is a very low number of animals because this is the area with the highest degree of wave shock. Only animals who have learned to tolerate surf or even require it can exist in this zone.

These shores are generally convex, and usually have very deep water lying close offshore. There are only rocky shores and sandy beaches. There is no mud because it would get washed away.

Bays and Estuaries
very low to no wave shock because of the enclosed nature of this zone Since the animals in this area have the higest degree of protection from wave shock, the animals are very diverse and are different from the species that exist in the protected outer coast and the open coast.

The shores in this area are sharply concave, having a large protected area with a relatively small opening into the sea. There is a greater variety in types of shore in this zone, including rocky shores, sand flats, eelgrass, and mud flats.

Wharf Piling
can vary with the location of the wharf The wooden pilings in this area support a great number of species

Wharf pilings provide a habitat for many organisms, especially things like barnacles and mussels that require a solid stationary object to attach themseves to.

The coastline is also divided into a different set of zones in relation to the balance between water and air exposure.

Zone

Boundaries

Organisms

1- Spray Zone from the highest reach of spray to the mean of all high tides Periwinkles and Pillbugs

2- High

Intertidal
from the mean of all high tides to the mean flood of the higher of the two daily low tides Barnacles and other organisms that are accustomed to more air than water and have a way to keep from drying out

3- Middle

Intertidal

from the mean of the higher low tides to the mean of the lower low tides

This area is covered and uncovered twice a day.

Sea Cucumbers and Anemone

Would you like to know more about Sea Anemone? See my other page.

4- Low

Intertidal
only uncovered by negative tides a few hours a month Sea Stars, Sea Urchin, Clams Mussels Oysters and other filter feeders

These are some pictures of our oceanography class trip to Duxbury Reef, CA.

Above: a Sea Star, purple Sea Urchin, and a view of the underside of another Sea Star

Below: some Barnacles, Turban Snails, and a Turban on Eel Grass

Bottom: two Limpets, Mussels and Gooseneck Barnacles, and a pink Algae from the underside of a submerged rock

Would you like to see pages from the Bishops College Intertidal Zone Field Trip?

Would you like to know more about the major plants or animals in the intertidal zone?

Would you like to know more about the intertidal zone in general?

Go to the University of Michigan Animal Diversity Web.

Go to my page on Sea Anemone.

Go to my bibliography.

Go to the MA Oceanography Class Home Page.

ZONE	Wave Shock	Effect on Organisms
Protected Outer Coast	force of surf is somewhat dissipated	Protected outer coasts harbor a large number of diverse organisms because of the lessened degree of wave shock.
	These shores are generally concave and protected by headlands, a close lying island, or even an underwater reef or kelp bed a long ways offshore, anything to break the waves before they hit the land.
Open Coast	entirely unprotected, surf-swept shores	There is a very low number of animals because this is the area with the highest degree of wave shock. Only animals who have learned to tolerate surf or even require it can exist in this zone.
	These shores are generally convex, and usually have very deep water lying close offshore. There are only rocky shores and sandy beaches. There is no mud because it would get washed away.
Bays and Estuaries	very low to no wave shock because of the enclosed nature of this zone	Since the animals in this area have the higest degree of protection from wave shock, the animals are very diverse and are different from the species that exist in the protected outer coast and the open coast.
	The shores in this area are sharply concave, having a large protected area with a relatively small opening into the sea. There is a greater variety in types of shore in this zone, including rocky shores, sand flats, eelgrass, and mud flats.
Wharf Piling	can vary with the location of the wharf	The wooden pilings in this area support a great number of species
	Wharf pilings provide a habitat for many organisms, especially things like barnacles and mussels that require a solid stationary object to attach themseves to.

Zone	Boundaries	Organisms
1- Spray Zone	from the highest reach of spray to the mean of all high tides	Periwinkles and Pillbugs
2- High Intertidal	from the mean of all high tides to the mean flood of the higher of the two daily low tides	Barnacles and other organisms that are accustomed to more air than water and have a way to keep from drying out
3- Middle Intertidal	from the mean of the higher low tides to the mean of the lower low tides This area is covered and uncovered twice a day.	Sea Cucumbers and Anemone Would you like to know more about Sea Anemone? See my other page.
4- Low Intertidal	only uncovered by negative tides a few hours a month	Sea Stars, Sea Urchin, Clams Mussels Oysters and other filter feeders