Chapter 11 Between the Tides
Location Narrow fringe along the shoreline that lies between the highest high tide and the lowest low tide
Easy to study
A unique environment Organisms are regularly exposed to air Emersion – being out of water and exposed to air Immersion – being submerged
Bottom Type (Varies) Sand, mud, rock Substrate – material on or in which organisms live
Types of Communities
Rocky Shore Communities Organisms are attached to rocks Sessile – permanently attached Epifauna – live on the surface of the substrate
Challenges of the Environment Exposure at low tide – can lead to desiccation (drying out), temperature changes, salinity change Adaptations: clam up, run and hide (tide pool or crevice), tolerate it High tide – wave shock, restrictions on feeding Adaptations: flexible, low profile, strong anchors (muscular foot, holdfast, byssal threads), thick shell, compact shape
Plentiful Resources Plenty of nutrients, light and food High tides bring plankton and detritus (decaying organic matter)
The Battle for Space
Limiting Resources There is not enough space – all areas are occupied – competition for space
Vertical Zonation
The rocky intertidal community is usually divided into distinct bands or zones at characteristic heights in the intertidal Vertical zonation - A given species is only found in a particular vertical range
Zonation is Caused by: Complex interaction of physical and biological factors Upper limit determined by physical factors Lower limit determined by biological factors
Soft-Bottom Intertidal Communites
Substrate: Sand or mud Organisms are buried in the sand or mud (substrate) Infauna – live in the sediment
Challenges of the environment Size of particles determines many physical characteristics of the habitat
Problems for Sandy Bottoms Sediments are constantly shifting – nowhere to attach Water drains quickly Can have a lot of water motion
Problems for Muddy Bottoms More organic matter to decay and use up oxygen Flow of water that brings in new oxygen is reduced Except for the upper few centimeters of mud the interstitial water (water between the grains) is deficient of oxygen
Anoxic – sediments with absolutely no oxygen Anaerobic bacteria can break down organic matter without oxygen – hydrogen sulfide is produced as a byproduct H2S – smells like rotten eggs and turns things black