 Intertidal zone o Littoral zone o Narrow fringe along shorelines
 Between highest high and lowest low tides o Only part of marine world that we can experience firsthand without leaving our own natural element
 Best studied and understood community o Tiniest fraction of marine environment o Unique because its regularly exposed to air
 Organisms must cope with exposure
 Sometimes have to give up characteristics that would be advantageous below the tides
 Emersion: out of water
 Immersion: submerged in water o Effects of the tide (aka nature of the community) depend on the type of bottom
 The bottom is referred to as the substrate
 Differ greatly depending on whether they have rocky or soft bottoms
ROCKY SHORE INTERTIDAL COMMUNITIES
 Rocky shores generally happen on o Steep coasts o With a lot of sediment o Areas that have recently been uplifted or rising
 These haven’t had time to accumulate sediment o WEST COAST OF USA
 Rocky because its active margin has been uplifted by geological processes
 Active continental margin = colliding with another plate and therefore has a lot of geological activity

o EASTERN CANADA AND NEW ENGLAND
 Once covered by huge sheets of ice during the last ice age
 Ice sheets scraped sediment from the continental shelf
 Exposing bare rock beneath
 Weight of ice sank down into the mantle
 Mantle = one of three main internal layers of the earth (middle layer)
 Ice melted and the coast rebounded and rose
 Left a coastline of exposed rock
 Sea level began to rise and overtook the rebound
 This explains the beautiful flooded rocky coast of Cape
Cod
 Only place in in Atlantic coast that has rocky shore o SOUTHERN ATLANTIC COAST & GULF COAST
 Sinking or subsiding
 Weighed down by huge amounts of sediment accumulating on the passive continental margin
 Rocky areas uncommon o Not all rocky shores are formed by uplift. Other ways:
 Waves carry sediment away leaving bare rock
 Outcrops of hard, erosion-resistant rock may be left behind after softer surrounding rocks erode away
 Hawaii is rocky because it is geologically young
 Formed by successive lava flows into the sea o Hasn’t had time to accumulate sediment
 Coast is still being formed by periodic eruptions of
Kilauea volcano o Organisms that live on rock
 Clams that can burrow through soft rock like sandstone
 Epifauna: most organisms that live on surface of substrate
 Some move

 Some are sessile and stay attached to the rock
 Exposed to the elements o Subjects them to great physical stress
EXPOSURE AT LOW TIDE
 Upper part of the intertidal isn’t normally submerged o Even during really high spring tides
 Sidenote about other types of tides
 Neap tides= tides with small range that occur when the moon is in quarter
 Tidal range= difference in height between a high tide and the next low tide o Highest part of intertidal is only wet bc of wave splashes
 WATER LOSS o Desiccate = dry out
 Must be able to prevent or tolerate it to live in intertidal
 Do this in 2 ways o Run and hide o “Clam up” o Run and hide = tide goes out and organism goes somewhere wet and wait for the tide to come back
 Shore crabs
 Hermit crabs
 Snails o Its not unusual to see crabs and snails all huddled up in moist crevices
 Tide pools = depression in the rocks that hold seawater after the tide goes out
 Some areas are kept moist because of
 Spray from waves
 Tide pool leaks
 Hiding places can be provided by other organisms
 Mussels form dense clumps that retain moisture for themselves and others

o Sessile animals and seaweed cant run so they hide in moist areas all the time
 Possibly because
 Larvae or spores settle only in moist shady places
 Those that settle elsewhere dry and die out o Organisms that “clam up”
 Protective covering they can close and hold in water
 Completely enclose and can seal in moisture o Barnacles o Mussels
 Some have an opening that cannot shut completely o Limpets o Clamp next to the rock to cover the opening o Use mucus to make a better seal o Carve out shallow depressions using their shell (=radula)
 Disadvantage = hard to obtain air and food o Some use a combination of both hiding and clamping up
 Periwinkles
 Clamp themselves to the rock to seal moisture
 Seal off opening of shell by closing the operculum
(= stiff plate that fits the opening like a door)
 Congregate in moist, shady places o Some use neither run-and-hide nor the “clamp up” approach
 Tolerate it
 Chitons (=molluscs w. 8 overlapping plates) can survive
75% water loss in tissues
 Some seaweeds survive 90% water loss
 TEMPERATURE AND SALINITY o Temperature
 Animals that live at sea experience constant water temperature because of the high heat capacity of water

 Heat capacity = amount of hear energy required to raise the temperature of a substance o Ability to hold heat o Water has the highest HC
 Air temperatures are MORE extreme than water temp.
 Intertidal orgs can tolerate a wide temperature range in their own ways
 Periwinkles are tough and show high heat tolerance
 Snails in the tropics have pronounced ridges on their shells o Help snail lose excess heat
 Snails also have light colored shells to keep cool o Brown shelled snails = shores heavy wave action
 Their neighbors are dense mussel beds o Sheltered shores = white shell
 Wave sprays help keep cool o Sheltered coasts have few
 Mussels
 Wave spray o Salinity
 Rain = freshwater that is deadly to most marine orgs
 Must clam up
 This is bad during low tides because tide pools get diluted by rain
 On hot days salinity increases because of evaporation
 To cope with these ups and down they:
 Burro or reduce activity to ride out extreme conditions and wait for high tide
 Restriction of feeding o Deposit feeders = animals that eat organic matter that settles to the bottom

 Rare in the rocky intertidal because little sediment accumulates o Sessile animals are filter feeders (=suspension feeder)
 When the tide is out they cant eat because
 They have to be underwater to filter it
 Theyre clammed up and cant filter or pump o Even animals that aren’t filter feeders have trouble feeding at low tide
 Many are grazers that scrape
 Algae
 Bacteria
 Others feed on seaweed and
 Detritus = particles of dead organic matter
 Some are predators and move over rock
 But when the tide is low they cant move around to find food
 However they’re normally immersed
THE POWER OF THE SEA
 Waves are powerful
 THE DISTRIBUTION OF WAVE ENERGY ALONG THE SHORE o Enclosed bays are protected from wave action
 Used for harbors for this reason o When a wave enters shallow water it “feels” the bottom and slows down o Waves come at an angle
 One end reaches shallow water before the other
 Shallow end = water slows down
 End in deep water = travels at its original speed
 The wave bends like a two wheeled cart will turn to one side if a wheel sticks

 Refraction = bending of the wave causing the waves to become parallel to the shore o Produces complex wave patterns when the coast is not a straight line o Wave action tends to focus at headlands
 Why Bays get less wave energy o Offshore bottom features can influence the effect of waves on the coast
 Submarine canyons
 Reefs
 Sand bars o Result = variation in the intensity of wave shock (=wave impact)
 Strongly affects intertidal organisms
 COPING WITH THE WAVE SHOCK o Some cant deal with it
 Found in sheltered location
 Sediment collects here o Organisms cope with sedimentation better than those who live on exposed shores
 Often delicate or cant keep a grip o Ways sessile organisms anchor to rocks
Organism
Seaweeds
Barnacles
How they deal with it
Use holdfast or encrust on rocks
Secure themselves with glue
Mussels Attach with their byssal threads(=strong fibers made of protein produced in a special gland in its foot)

o Mobile animals also cling to rocks o
Organism How they deal with it
Limpets and Chitons Use muscular foot like a powerful suction cup
Gobies and clingfishes
Intertidal fishes
Suction cups formed by modified fins
Can swim home if dislodged.
Tend to lack swim bladders so they sink and stay on the bottom. o Rather than resist the waves many find shelter
 True of highly mobile animals
 Shore crabs
 Trade off between moving fast and having a strong grip on the rocks
 Holding tightly slows an animal down
 Snails are easier to knock form the rocks when moving than when they stop and clamp down
 usually stop and hold on when wave action is heavy
 limits feeding
 prevent some species from living in exposed areas o Intertidal organisms have adaptations to withstand wave shock

Adaptation
Thick shells
Compact shape
Low profiles close to the rocks
(mussels, barnacles, limpets & chitons)
Colonies of sand-castle worm dome shape
Seaweeds are flexible
Large number of population
How it helps withstand wave shock
Reduces impact
Reduces impact
Withstand wave shock
Can go with the flow
Safety in the numbers o Waves sometimes hit loose rock that crush things o Waves can also turn over rocks
 Organisms on top get smashed or buried
 Sunlight for algae is buried
 Underside of the rock supports different organisms which also suffer
 Exposure to sun
 Predators o Sheltered and exposed areas have distinct communities
 Bars are different from headlands
 Orgs in sheltered crevice differ from those on exposed rocks nearby
THE BATTLE FOR SPACE
 Rocky intertidal populations are often limited by space, not food or nutrients o Intertidal organisms generally have plenty of food o High light levels and nutrient rich coastal waters supply reqs for photosynthesis o High tides bring in plankton and seaweed fragments (detritus)

o EXCEPTION: limpets, snails and other small, slow moving animals that graze algar from rocks are limited by food availability because of small range o Sessile animals dont consider food a limiting resource
 Though feeding time can be restricted near upper end of animals range
 Unoccupied space is often in short supply o Even in sheltered areas intertidal orgs will drift away or be smashed on the rocks if they cant attach to the substrate o Orgs may attach to each other instead of to the rocks
 Many ways to compete for space o Be the first to get open spots
 Requires effective means of dispersal(=getting themselves or their offspring from place to place)
 Via larvae or spores o Take over occupied space
 Barnacles undercut neighbors
 Owl limpets bulldoze intruders
 Seaweeds block sunlight
 Grow over their competitors
 Make them vulnerable to waves
 Smother them
 Grow in colonies o Two species of mussels provide an example of how competition and physical factors can interact to determine the distribution of organsisms
 WEST COAST NORTH AMERICA
 Blue mussel = found in sheltered locations
 California mussel = found on wave-exposed coast
 Thicker shell
 Attaches more strongly to rock
 HOWEVER

 Blue mussel does good when the California mussel is absent
 Its not that the blue mussle cant handle open coasts o Its that it is out-competed by the California mussel o California mussel’s thicker shell crushes the blue mussel when they grow together
 On the other hand blue mussels tolerate a lot of silt so they survive in calm bays
VERTICAL ZONATION OF ROCKY SHORES
 One feature that is always present in rocky intertidal o Divided into distinct bands, or zones
 At characteristic heights in the intertidal
 A given species isn’t usually found throughout the intertidal o Rather only within a particular vertical range
 Vertical zonation
 Evenly sloping rock = zones are sharply defined o Distinguished by colors of organisms
 Uneven rocks w/ boulders, channels, and gullies = zonation not as obvious but exists nonetheless
 CAUSE: o Upper limit of a zone = physical factors o Lower limit = biological factors
 Ex. Predation and competition o EXCEPTIONS:
 Can also be caused if larvae of a species settle only at a particular height on the shore
 Can be a combination of physical and biological
 Ex. Some filter feeders don’t live high in intertidal bc they aren’t submerged long enough to feed o Physical factor = emersion

o Biological factor = feeding
 V.Z. is similar in general nature but highly variable in its particulars o Areas are named after dominant organism
 Ex. Mussel zone: can include worms, crabs, snails, seaweeds, and many other species o Types of organisms vary from place to place
 Ex. On the EAST COAST OF NORTH AMERICA the mussel zone is replaced by a rockweed zone
 UPPER INTERTIDAL o Mostly above the high tide line
 Affected by wave splash and highest spring tides o Lichens and cyanobacteria = primary producers (=organisms that manufacture organic matter from CO2) o Inhabitants must be able to withstand air exposure o Splash zone
 More splash on expose coasts = higher high tide line compared to sheltered coasts
Organism
Lichens (=mutualistic association between fungi and algae) that form black, tar-like blotches on rocks
Dark green mats
Cyanobacteria
Adaptation to air exposure
Fungus part soaks up water & stores it for long dry periods
Jelly coat prevents drying out.
Able to fix nitrogen
(=conversion of nitrogen gas into nitrogen compounds that can be used by primary
Small tufts of filamentous green alga producers as nutrients) from the air
Resistant to drying out

Green, brown, and red algae
(Encrusted
Periwinkles
Live in moist spots
Breath air like snails.
Live out of water for months.
Tolerate extreme temperatures. o Periwinkles graze on algae
 Scarping it with radula
 So common that the upper intertidal is often called the
“Littorina” zone
 MOST COMMON/DOMINANT o Limpets
 Grazers like periwinkles o Shore crabs
 Eat limpets and periwinkles o Sea lice/Sea roaches
 Breath air and live about the water’s edge o Unicorn snails sometimes benture o Often visited by predators from land
 Birds that eat oysters, limpets and snails
 Middle intertidal o Submerged o Uncovered by the tides on a regular basis
 Diurnal tide = exposes the organisms once a day
 Semidiurnal tide = exposed the organism twice a day
 Mixed tide = 2 low tides and 2 high tides; each of unequal height
 lower of the two successive high tides may not submerge the high part of the zone; higher of the two lows may not expose the bottom part
 Therefore, even in parts of the middle intertidal zone may be submerged or exposed only once a day

o Upper boundary is almost always marked by a band of acorn barnacles
 Little gray (Chthalamus)= higher
 Rock Barnacles (Balanus)= lower
 This zonation is caused by:
 Larval settlement pattern o larvae of both settle over a wider range; those that settle too high die out
 Desiccation tolerance o Little gray tolerate it better so they can live higher
 Competition o At lower levels rock barnacles outcompete little gray
 Predation o Lower limit is determined by biological factors
(predation and competition)
 Lower limit of rock barnacles is determined by biological factors
 Kinda like little grey barnacles
 Mussels = predators
 Dog Whelks = predators o Only thing protecting barnacles from dog whelks is that whelks do their feeding during high tide and when above water they lose too much water hunting barnacles o

 Snails = predators w their radula to drill holes in barnacle shells o Note that in the upper intertidal the snails don’t have enough time at high tide to eat barnacles o Seastars also have this problem
 Summary: acorn barnacles usually occupy the top of the middle intertidal zone. Their upper limit is determined by how high they can live without drying out. Their lower limit is set by competition with other barnacles or mussels or by snail or sea star predators
 o Other organisms live among or below barnacles
 Which orgs depend on physical and biological factors
Physical factors Biological factors
-Patterns of the tides
-steepness of the shore
-Exposure to the waves
-local weather
-Predation
-Competition
-larval settlement patterns

 Organisms that dominate the middle intertidal under barnacles
 Mussels o Common on stormy exposed shores o Cant live as high as barnacles because they dry out and cant filter feed o Where they CAN live they dominate
 Smothering
 Crowding
 Goodneck barnacles
 Brown seaweeds (rockweeds) o Have air bladders called pneumatocysts that float their fronds closer to light o Form an algal turf that shelters small animals
 Sea stars (Pisaster, Asterias) are voracious predators of mussels o Insert their stomach into the shell and digest the mussel from the inside o Shell opens when mussel is weakened o THUS mussels live above sea stars
 Lower limit is set by biological factor: predation of sea stars
 Upper limit is set by desiccation and filter feeding o Also eat dog whelks
 Which does barnacles a favor because if the barnacles live long enough, they get too big for the dog whelks to eat. By reducing the dog whelks, the sea stars give the barnacles more of a chance to grow before a whelk eats them o Absent from areas with extremely strong wave action

 Mussels take over and outcompete other sessile organisms
 THUS many species can live in the middle intertidal only if seastars keep mussel numbers in control
 Note that many intertidal species are more abundant than the sea stars but the sea stars have a BIG impact on the entire community
 Keystone predators = predators whose effects on their communities are proportionally much greater than their abundance

 Lobsters (instead of sea stars) are the main predators of mussels o Can eliminate mussels altogether
 Opens up space for other organisms
 Acorn barnacles
 Gooseneck barnacles

 Seaweeds o Natural disturbances can have effects similar to those of predation (open up space)
 Mussel beds get too thick = clumps torn away by waves
 Drifting logs batter the rocks
 Ice or freezes in cold places
 IMPORTANT BECAUSE = prevents mussels from taking over ; allows other organisms to persist o Ecological succession = when a space is cleared, new organisms move into the patch and get replaced
 Typical steps of ecological succession in the middle intertidal
 Bacterial and algal film (diatoms)
 Settling larvae prefer surfaces with film
 Seaweeds
 Barnacles
 Climax mussel community
 But this pattern may deviate for reasons
 Grazers like limpets and chitons may remove newly settled larvae and spores o If they move in too early then the other steps may not happen and may even limit film
 Predators n other disturbances determine whether the final stage is a solid mussel bed or a mixture of species
 Steps may be skipped o Seaweeds may never colonize a patch if barnacle larvae get there first
 Time of the year the patch is created is important
 If the patch opens when barnacle larvae are abundant and seaweed spores are rare, barnacles have the upper hand

 Thus an element of chance
 If the bare patch is small and in the middle of a mussel bed it may be taken over by other mussels that move from the sides
 Disturbances can thus increase the number of species that live in an area (Diversity) by interfering with competitive exclusion (= the elimination of one species by another as a result of competition)
 Can be thought of as a mosaic of patches that were cleared at different times and are in different stages of succession
 Each patch supports a different set of organisms o The # of species in the area as a whole increases
 On the other hand, if predation and other disturbances happen too often the community keeps getting knocked back to the starting point o Never gets a chance to develop and many species are NOT able to live there
 Highest point of diversity=
 enough disturbances to prevent the dominant competitors from taking over
 but not so much that the community is unable to develop


 Lower intertidal o Immersed most of the time
 Making it easy for sea stars and dog whelks to feed
 So mussles and barnacles are rare o Grazing and competition are important
 Space as well o Seaweeds compete by outgrowing and blocking the light
 Lower intertidal is dominated by red, green and brown seaweeds o ON THE COAST OF NEW ENGLAND
 Green alga Enteromorpha
 Dominates by overgrowing
 Red alga Irish moss
 Most common seaweed in many tide pools
 Because grazing prevent enteromorpha from taking over o Periwinkle eats enteromorpha but doesn’t eat irish moss
 If a tidepool ha a lot of snails they eat the enteromorpha and make way for irish moss
 If snails are transplanted into an enteromorpha pool, enteromorpha disappear and irish moss takes over
 Enteromorpha soon moves in after periwinkles are removed from an irish moss pool
 THE STORY DOESN’T END THERE
 Periwinkles actually don’t like moving around to go find enteromorpha pools
 Young periwinkles are eaten by green crabs
 Crabs are eaten by seagulls
 Enteromorpha provide cover for the crabs, protecting them from gulls.
 Crabs then eat young periwinkles, preventing them from colonizing the pool

o
 In Irish moss pools, the crabs lack cover and are eaten by gulls
 Without crabs, young periwinkles can survive in the tide pools o o Other seaweeds in lower intertidal
 Delicate reds and greens
 Tough kelps

 Mark the lower limit of the intertidal and continue down into the subtidal zone (=the part of the continental shelf that is never exposed by low tide) o However, there is not precise boundary between the lower reaches of the intertidal and the upper edge of the subtidal
 Coralline algae = red algae that deposit calcium carbonate (CaCO3) in their tissues
 Abundant in lower intertidal
 Surf grass = flowering plant also common in lower intertidal on the PACIFIC COAST NORTH AMERICA
 Small animals live among the seaweeds
 Sea urchins = common grazers
 Sea anemones
 Polychaeta worms
 Snails
 Sea slugs
 Most rocky intertidal fishes live in the lower intertidal or in tide pools o These are all small fishes adapted to the environmental extremes of the intertidal o Most are carnivorous
SOFT-BOTTOM INTERTIDAL COMMUNITIES
 Introduction o Soft-bottom = composed of sediment, as opposed to rock
 Dividing line isn’t always clear
 Ex. Boulder fields are usually thought of as rocky, but how small the rocks have to be before the bottom is considered soft is not precisely defined
 SO in this text a soft bottom is one where organisms can burrow easily
 Occur where sediments accumulate
 NORTH AMERICA

o East coast south of cape cod o All of the gulf coast o Rocky west coast is interrupted by sandy beaches and mud flats
 Near river mouths
 How much and whether sediment accumulates depends on o how much water motion there is and the source o source of sediment
 Type of sediment strongly influences the community
THE SHIFTING SEDIMENTS
 Unstable o Waves, tides and currents
 Do not have a solid place for attachment o Few seaweeds adapt to this o Seagrasses most common primary producers
 Form dense intertidal beds
 IN THIS CHAPTER WE DEAL ONLY WITH INTERTIDAL
SOFT-BOTTOM COMMUNITIES THAT LACK SEAGRASSES
 Epifauna= animals that live on sediment surface
 Infauna = animals that burrow in the substrate/sediment
 Sand, silt, and clay refer to sediments of particular grain sizes o Sand = coarsest
 Followed by silt and then clay o Mud = silt and clay together

 o Most sediments are a mix of different particle sizes
 But described according to the most common grain size in the area
 Ex. Sand may have small amounts of mud or a few large rocks
 Sediment composition is directly related to the degrees of water motion
Fine sediments remain suspended with even a small amount of water motion o Coarse sediments settle out o Bottom sediment = prevailing conditions
 Calm, sheltered areas have muddy bottoms because fine sediments can settle out
 Particles of organic matter sink at the same rate as clay
 The two settle out together
 Clay sediments are organic rich
 Places with strong waves and currents have coarser bottom sediments
 If strong enough it can carry away all the loose material leaving rocks or boulders
LIVING IN THE SEDIMENT

 Advantages: o Stay wet after the tide is out
 Desiccation problem not critical as in rocky intertidal
 Depends on grain size though
 Coarse sands drain and dry out fast o Why there is little animal life
 Oxygen availability o Amount of O2 available is important to deposit feeders o Few primary producers
 Detritus is the main source of food for intertidal softbottom communities
 Deposit feeders extract this organic matter from the sediments
 Amount of detritus depends on grain size o Coarse sand = very little organic matter
 SAND = CLEAN o Silt and clay = rich in detritus
 Smelly o Grain size (and the degree of sorting) affects amount of available oxygen in sediments
 Oxygen in sediments is used up by the respiration of animals and decay bacteria
 No light or photosynthesis in sediment
 Infauna depend on circulation of water through the sediment to replenish the oxygen supply o Water flows more easily through sand and clay
 Muddy bottoms have 2 issues
 The first is that they have more organic material to decay and use up oxygen
 The second is that the flow of water that should bring in new oxygen is reduced

 Except for the interstitial water (=upper few centimeters of mud or water between the grains) the rest is deficient in oxygen
 If you go very far down there is no oxygen at all
(Anoxic) o Anoxic conditions are no problem for bacteria because they’re capable of anaerobic respiration(=they break down organic matter without oxygen) o A noxious gas called hydrogen sulfide (H2S) is produced as a by product
 Produced when bacteria continue to decompose organic material after all the oxygen has been used up
 Distinct black layer appears where anoxic conditions begin in the sediments
 SUMMARY: The decay of organic matter in the sediments uses up oxygen.
Because of this, the interstitial water beneath the sediment surface is often depleted of oxygen, especially in fine sediments
 Infauna must adapt to the short supply of oxygen
 Especially in muddy bottoms
 Many animals pump oxygen-rich water from the sediment surface with siphons or through their burrow o So they’re never exposed to low oxygen levels o Bioturbators = infauna that burrow through, turn over, or disturb sediment
 Help oxygenate the sediment w their burrows

 Special hemoglobin = red protein in the blood of vertebrates and some invertebrates that transport oxygen o Extract as much as possible of the little oxygen there is in the interstitial water
 Some are sluggish = reduces oxygen consumption
 Limited capability to carry out anaerobic respiration
 Symbiotic bacteria that help them live in low oxygen sediments
 Even so, hydrogen sulfide is really toxic
 Anoxic sediments have little animal life o GETTING AROUND
 Methods to burrow through the sediments:
Organism
Clams and cockles
Method of burrowing
Change the shape of their muscular foot,
Make it thin, reach forward. Then the end
Soft bodied animals
Worms
Heart urchins of the foot thickens and acts as an anchor
Similar to clams but use their body the way clams use the foot.
Force their pharynx into cracks in the sediment to expand the crack before pulling their bodies along behind
Burrow or plough through the sediment with their spines and tube feet

Crustaceans such as amphipods, sand/mole crabs, ghost/mud shrimps
Use jointed appendages to dig
 Deposit feeders solve two problems at once
 Eat their way through the sediment
 Sea cucumbers & certain worms
 Move kinda like the clams and worms previously talked about except instead of pushing through the sediment they push the sediment
them
 Digest the organic matter and leave the rest of the sediment behind
 Meiofauna = so small that instead of burrowing through the sediments they live in the interstial spaces between the grains
 Most have worm like shape o FEEDING
 Detritus is the main source of food
 Diatoms = form highly productive mats on the sediment surface
 Most animals don’t distinguish between diatoms and detritus
 Doesn’t account for much primary production
 Plankton = brought in by tides & make a small contribution to the food supply
 Many different methods of deposit feeding have been evolved
 The more common method is the same one used by sea cucumbers and worms o More common on mud bottoms than sand because
 Mud contains more organic material

 Sand is more abrasive on digestive system
 On the upper layer of sediment where detritus accumulates: o Sand dollars = use their tube feet to pick up organic particles o The bent-nosed clam
 Uses a long siphon to suck up food particles
 Other animals catch particles as they settle out and are thus on the line between
 suspension feeding
 deposit feeding
 Polycheate worms have:
 long, sticky tentacles they spread to the bottom to get food
 mucus net ^ for same reason
 important predators
 Suspension feeders filter food from the water
 Don’t wait for detritus to settle
 Olive shell from central America o Mucus net it holds up to filter food
 Sand/Mole crabs o Hold a pair of large bushy antennae up into the water to trap food o Bury and uncover themselves
 Combine feeding and locomotion o Surf waves to get to shore
 Predators in the soft bottom
 Moon snails: burrow through the upper sediments looking for clams to drill a hole into
 Birds can be major predators during low tide
 Fishes can be predators during the high tide

 dont eat the whole animal only nip off clam siphons or other bits that stick out o ZONATION
 Its hard to see zonation patterns because everything is inside the sediment
 However zonation does exist
 Especially on sandy beaches
 Upper part of the beach is dryer because the beach is sloped
 Beach hoppers/sand fleas o Really amphipods
 Isopods
 In warmer areas beach hoppers and isopods are replaced by ghost and fiddler crabs o Catch smaller animals o Scavenge dead meat o Detritus
 Polychaets and clams
 Lower on the beach
 Zonation is even less obvious in muddy areas
 Flat bottom
 Fine sediments retain water
 Habitat doesn’t change too much between high and low water marks
 Intertidal communities here are similar to the subtidal ones in the next two chapters
