Chapter 11 Between the Tides Intertidal or Littoral

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 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

• 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 • H 2 S – 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 ……