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 ……