Chapter 11 Between the Tides
Intertidal or Littoral Zone Best known Narrow fringe along the shoreline that lies between the highest high tide and the lowest low tide Easy to study No specialized equipment needed Can return to the exact same spot again
A unique environment Regularly exposed to air – organisms must have a way to cope Emersion – being out of water and exposed to air Immersion – being submerged Bottoms vary and determine the community that lives there
Substrate or substratum – material on or in which organisms live Can be hard and rocky or soft and muddy or sandy
Rocky Shore Communities
Occur on steep coasts without large amounts of sediment Active margins – west coast Glaciers moving over land and scraping away sediments Waves and currents can carry sediments away Hawaii – rocky because it is geologically young
The Organisms Live right on the rock’s surface Epifauna – live on the surface of the substrate Sessile – stay attached to the rock Living on the rock’s surface, the organisms in the rocky intertidal are fully exposed to the elements – great physical stress
Exposure at Low Tide
Low tide – left high and dry, exposed to air which is much harsher environment than water Highest part of the intertidal (only wet on high spring tides) is almost never immersed and kept wet by wave splash
Low intertidal – submerged most of the time So the higher the organisms live in the intertidal, then, the more time they have to spend out of the water
Water Loss Desiccate – dry out if left out of the water too long To live in the intertidal an organism must be able to prevent desiccation, tolerate it or both They either run and hide or “clam up”
Organisms that run and hide Shore crabs Hermit crabs Snails Huddle in moist shady crevices
Tide Pools Depressions in the rocks that hold sea water after the tide goes out Good places to hide at low tide
Organisms that can’t run and hide Seeweeds and sessile animals Must live in moist areas all the time
Organisms that Clam up Have a protective covering like a shell that they can close to hold water Barnacles Mussels Limpets – clamp to the rock Limpets can also carve out shallow depressions or “home scars” to make a more effective seal – use their radula
Littorina or periwinkles clamp to rocks and also seal the opening of their shelf with their operculum
Organisms that do nothing Chitons – just dry up – can survive a loss of 75% Intertidal seaweeds – Fucus – can withstand a water loss of 90% - get practically crunchy
Temperature and Salinity
Temperature Sea temperatures are relatively constant and mild because of high heat capacity Air temperatures can be much more extreme – hot and cold
Dealing with Temperature Moist hiding places also have lower temperatures Nerita plicata – tropical snail has pronounced ridges to help radiate heat Color can help deal with high temperatures
Salinity Fluctuates widely When it rains salinity decreases, even have to deal with fresh water Tide pool residents – high salinity when there is a lot of evaporation – low salinity when it rains
Restriction of Feeding Little sediment accumulates so deposit feeders are rare Deposit feeder – animals that eat organic matter that settles to the bottom Most are sessile filter feeders – can not feed when the tide is out Filter feeders – animals that actively filter food particles from the water
The Power of the Sea
When the tide is in life is still hard in the intertidal Ocean waves expend tremendous energy as they crash on the shore Rocky intertidal organisms are exposed to the full power of the sea
There is tremendous variation in the intensity of wave impact (wave shock) from place to place along the shore Exposure to waves strongly affects intertidal organisms
Coping with Wave Shock
Some organisms can’t withstand wave shock and are only found in sheltered locations Some deal with wave shock by firmly anchoring themselves to the rocks
Ways to Anchor Seaweeds use their holdfasts or crust on the rock Mussels hold on with byssal threads (strong fibers made of protein) Limpets and Chitons use their muscular foot as a suction cup Intertidal fishes lack swim bladders so they sink and stay on the bottom
Other Adaptations to deal with Wave Shock Thicker shells Compact shape to reduce impact Low profiles that keep them close to the rocks (barnacles, mussels, limpets and chitons) Seaweeds are flexible and can go with the flow
The Battle for Space
The intertidal has plenty of food Shallow coastal water provide lots of light and nutrients – photosynthesis – lots of food for animals Plankton rich water moves in at high tide Detritus moves in with the tide
Limiting Factor Space Nearly all of the space is occupied Organisms may attach to each other because space is so limiting
Competition for Space A dominant biological factor Several ways to compete for space One – get there first - be the first to colonize the area (which means an organisms must have an effective means of dispersal) Two – take over a space that is already occupied – uncut or bulldoze the off (barnacles and limpets)
Three – grow over the competitors making them vulnerable to waves, smothering them, or blocking their sunlight
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
Organisms of the Upper Intertidal Lichens Cyanobacteria (Calothrix) Filamentous green alga (Ulothrix) Periwinkles (Littorina) which graze on algae Limpets – hardy grazers Predators- birds raccoons and rats from land
Organisms of the Intertidal Acorn barnacles Little gray barnacles (Chthamalus) Rock Barnacles (Balanus, Semibalanus) Little gray barnacles live higher up than rock barnacles – upper limit physical factor – emersion Lower limit – biological factors (competition and predation) – rock out compete little gray – rock are eaten by Whelks
Brown seaweeds –rock weeds (Fucus, Pelvetia) Mussels Gooseneck barnacles Brown seaweeds –rock weeds (Fucus, Pelvetia) Sea stars (Pisaster, Asterias) eat mussels Lower limit of mussels is set by predation of sea stars Spiny lobsters – eat mussels Pelvetia
Gooseneck Barnacles Pisaster
Lower Intertidal Organisms Seaweeds Light and space are important resources Green alga (Entromoropha) Irish moss (red alga) Chondrus crispus Kelps Coralline algae (Corallina, Lithothamnion) Sea urchins
Chondrus crispus Corallina
Sea anemones (Metridium, Anthopleura) Polychaete worms (Spirorbis, phragmatopoma) Snails (Tegula, Nucella) Sea Slugs (Aplysia, Dendronotus) Gobies, clingfishes, sculpins, pricklebacks and gunnels
Spirorbis Metridium Spirorbis Sculpin Aplysia
Soft-Bottom Intertidal Communites
Soft bottom – bottom composed of sediment – organisms can burrow in it easily Whether and what type of sediment accumulates depends on how much water motion there is and on the source of the sediment The type of sediment strongly influences the community
The Shifting Sediments
Unstable, constantly shifting Organisms do not have a solid place to attach Few seaweeds, some areas have sea grass beds Most burrow in the mud – infauna (live in the sediment)
Important Physical Factor of Soft Bottom Communities Kind of sediment Size of the grains (gravel, sand, silt, clay) Sediment composition is directly related to the degree of water motion Fine sediment remains suspended longer and can be kept suspended with a small amount of water motion
Living in the Sediment
Advantages Stays wet when the tide goes out Desiccation is not as critical Course sand however will dry out quickly
Oxygen Availability Amount of organic matter in bottom sediments is particularly important to deposit feeders Few primary producers, detritus is the main source of food Deposit feeders extract this organic matter from the sediments Smaller grain sizes contain more organic matter
Grain size also affects the amount of oxygen available in the sediments Oxygen is used through respiration and decay bacteria
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
Adaptations of Infauna to low oxygen levels Pump oxygen rich water from the sediment surface with siphons or through their burrows Adaptation of hemoglobin to low oxygen levels – can extract as much oxygen as possible Sluggish – reduces the need
Getting Around Muscular foot pulls the organism into the sediment Burrow or plough along Jointed appendages to dig – crustaceans Eating their way through the sediment – sea cucumbers and certain worms
Feeding Detritus is the main food source Diatoms sometimes form highly productive mats Plankton brought in by the tides Deposit feeding – burrowing through the sediments and eat them Tube feet to pick up particles – sand dollars Siphons to filter feed
Plankton Diatoms Sand Dollar
Zonation Not as obvious as it is on the rocky intertidal Best seen on sandy beaches where water drains quickly Hardiest to see in muddy areas where the area is flat
The End ……