INTERTIDAL ZONE

2 SPATIAL GRADIENTS:

(1) VERTICAL

(2) HORIZONTAL - WAVE EXPOSURE

VERTICAL GRADIENT:

(1) HEAT STRESS & DESICCATION

(2) GAS EXCHANGE - DISSOLVED OXYGEN

(3) REDUCED FEEDING TIME

(4) WAVE SHOCK**

(5) BIOLOGICAL INTERACTIONS: COMPETITION, PREDATION

**Affects Soft Sediments - Interaction with tide:

Tidal Migrations - Donax clam , Emerita, mole crab

Both move up and down shore and maintain position where sand is moist but not too wave washed or not too dry.

ZONATION -universal feature of rocky shores, also true of soft sediments but not as distinct (3d)

ROCKY SHORE ZONATION

Chthamalus stellatus - "southern" - Mediterranean to Shetland Islands

Semibalanus balanoides - "northern" - Arctic to southern Spain

Joseph Connell expt.

(1) transplant newly settled CH to all tidal levels

(2) cage some transplants, excluded Nucella

(3) allow SB to settle and clean SB cyprids off some rocks

Soft Sediments

Zonation - not as distinct as on rocky shores - 3rd dimension within the sediment

Competition - demonstrated by experiments

e.g., mud flat polychaetes studies by Sarah Woodin

burrowing Armandia brevis versus tube builders

Cage with Screen: tube builders settled on screen, Armandia burrowed through and reached higher densities than when screen was absent and tube builders settled directly in sediment and established tubes.

Spartina Salt Marshes

East and Gulf Coast of North America

Spartina:

<10 percent consumed by herbivores

most --> detritus

creeks - very rich nurseries for fish

Export of detritus to continental shelf?

Spartina marsh zonation

Juncus gerardi

Distichlis spicata

Spartina patens

Spartina alterniflora

Why is there zonation: Hypothesis: Spartina alterniflora can't survive high on shore.

Bertness transplants all to high shore - when alone, they all grow faster!

In Distichlis zone, Distichlis outcompetes all other species

Transplant Distichlis to lower shore: It does more poorly. Same when you transplant Spartina patens to level of S. alterniflora

DISTURBANCE - COMPETITION

Wrack covers area in high intertidal, kills all plants. Salt formed from evaporation in summer - forms salt pan, which prevents seed germination.

TWO ALTERNATIVE STABLE STATES:

SALT PAN

GRASS

ESTUARIES

SOME GENERALIZATIONS:

(1) GEOLOGICALLY EPHEMERAL

(2) NUTRIENT RICH

(3) IN SLUGGISH SITUATIONS, CAN HAVE HYPOXIA, ANOXIA ASSOCIATED WITH SUMMER STRATIFICATION

(4) DIVERSITY DECREASES UP THE ESTUARY TO A MINIMUM IN THE SO-CALLED CRITICAL SALINITY RANGE, THEN DIVERSITY INCREASES AGAIN IN FRESH WATER.