an introduction to zonation. rocky intertidal ecology rocky - hard substrate intertidal - area...

An Introduction to Zonation

Rocky Intertidal Ecology

• Rocky - hard substrate

• Intertidal - area between high tide and low tide marks

• Ecology - the study of the interactions that determine the distribution and abundance of organisms.

* Interactions can be between organisms or between organisms and their environment

Intertidal zone • This area is is exposed to the air usually twice a

day as the tides ebb and flood

• Tides create a partly aquatic and partly aerial environment

• Locally the tidal range is about 3 meters

• Rocky, sand, estuaries, mangroves, coral reefs, etc.

• Patterns are similar worldwide

Vertical zonation

• Banding pattern on the rocky shore as a result of the rise and fall of the tides

• The distribution of organisms is in horizontal bands

• Upper, middle and low zones

• Caused by differing tolerances of organisms to stresses, both biotic and abiotic

• Examples?

Limits of organisms

• Upper limits are set by abiotic factors such as desiccation, temperature, salinity, food and oxygen availability, light

• Lower limits are set by biotic factors such as competition, predation, herbivory

Abiotic factors

1. Desiccation • = water loss; drying out

• Occurs at low tide due to air exposure

• Can increase with wind

• Some species are more tolerant to being in the air (e.g. limpets, Fucus, Porphyra) and can live higher in the intertidal zone

• Adaptations:- close up e.g. barnacles, mussels- lose water then rehydrate e.g. Fucus

2. Temperature • Water temperature varies only slightly over the

year (7-12oC)

• Air temperature, however, can vary drastically (0-30oC)

• Organisms out of the water are subject to greater variations in temperature

– Adaptations:

– Evaporative cooling by mussels

– Eurythermal enzymes

3. Salinity

• Salinity can increase with evaporation or decrease with fresh water input (e.g. rain)

• Euryhaline - tolerant to wide variations in salinity e.g. mussels, barnacles

• Stenohaline - can only tolerate a narrow range of salinities e.g. sea stars

• Adaptations:

• Close up e.g. barnacles, mussels

• Ion pumps e.g. crabs

4. Food & oxygen availability

• Many marine organisms get their food from the water (as plankton!) they can only feed when underwater

• Also, many marine organisms obtain oxygen from the water

• Organisms living high in the intertidal zone have a limited time in which they can feed and acquire oxygen

• Adaptations:- scaleless fish e.g. clingfish- feed whole time they are underwater

5. UV light

• Marine organisms can get sunburns too

• Especially when out of the water

– Adaptations:

– Sun screen - natural compounds that absorb UV

– Protective shell

Biotic factors

1. Competition

• = use or defense of a resource that reduces its availability to other individuals

• Interference - direct interaction

• Exploitative - differential use of resource

• Interspecific - between species

• Intraspecific - between individuals of the same species

2. Predation

• Animals eating other animals

• Predators can be generalists (eat a wide range of food) or specialists (eat a single prey type)

• Refuges from predation:

• Size e.g. some mussels are too big to be eaten by Pisaster

• Space e.g. limpets living on vertical surfaces to avoid predation by birds

• Height in the intertidal e.g. Pisaster / mussel interactions (Paine experiments)

3. Herbivory

• Animals eating plants

• Similar to predation interactions

• Refuges from herbivory:

• Chemical defenses e.g. sulphuric acid in Desmarestia, bromine in Prionitis

• Physical defenses e.g. calcium carbonate in coralline algae

• Height in the intertidal e.g. Ulva and Porphyra live very high to avoid being eaten

A reminder…

• Upper limits are set by abiotic factors such as desiccation, temperature, salinity, food and oxygen availability, light

• Lower limits are set by biotic factors such as competition, predation, herbivory