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Intertidal Ecology. Rocky Shores Sandy Shores: sandy beaches Muddy Shores: mud flat. Divisions of Ocean environment. Where? Who? What are they doing there?. Why did these students have to stand in water to do the work?. Mixed, semidiurnal, and diurnal tide curves. Intertidal Ecology.

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Intertidal Ecology

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Intertidal Ecology

Rocky Shores

Sandy Shores: sandy beaches

Muddy Shores: mud flat

Divisions of Ocean environment

Where? Who? What are they doing there?

Why did these students have to stand in water to do the work?

Mixed, semidiurnal, and diurnal tide curves.

Intertidal Ecology

The intertidal zone is the zone between the highest and lowest tides

Highest tide

Lowest tide



Subtidal zone

Characteristics of the intertidal zones

  • Flood and ebb tides

  • Water-air alternative exposure

  • Rhythmic

  • Rich diversity and density within a small area

Length of maximum submergence (hours)

Rocky Shore Ecology


Factors affecting zonation

Physical Environmental Conditions

Biological Interactions

Typical Rocky intertidal zonation patterns(Pacific)Zonation: Predictable distinctive distribution pattern of marine organisms through intertidal zone

Typical Rocky intertidal zonation patterns(Atlantic)

Zonation of major species on rocky shores. The figure is a general scheme of common animals and algae found in eastern North America. Details will differ for specific locations.

Classification of zones in all habitat type (Ricketts et al., 1985)

  • Zone 1: uppermost horizon: Highest reach of spray and storm waves -- the mean of all high tides: the splash, spray, supralittoral, or Littorina zone

  • Zone 2:high intertidal: Mean high water -- a bit below mean sea level: the home of barnacles and other animals tolerating more air than water

  • Zone 3: Middle intertidal: about mean higher low water -- mean low water

  • Zone 4:Low intertidal: normally uncovered by minus tides only. This zone can be examined during only a few hours in each month


Wave action and tidal range


Heat stress


reduced feeding time

DO and gas exchange


Larval settlement

Intra- and interspecific competition

Predation and grazing

Physiological tolerance and adaptation

behavioral pattern, mobility

Factors modifying zonation of Rocky shore

Exposure-shelter diagram for Hong Kong shores. The range of the six litterine species are superimposed. 1. Nodilittorina pyramidalis; 2. Nodilitorina millegrana; Peasiella sp.; 4. Littorina brevicula; 5. Littorina scabra; 6. Littorina melanostoma.

Physical conditions of rocky intertidal areas

Tides-Periodical change the organisms' living environments

Temperature-desiccation (could be fatal), particular in tropic region

Wave action--exerts the most influence on organisms and communities

Physical conditions of rocky intertidal areas (con’t)

  • Wave action (con’t)

    • mechanical effect--smash and tear away objects;

    • acts to extend the limits of the intertidal zone by throwing water higher on the shore (splashing allows the marine organisms to live higher in exposed wave-swept areas than in sheltered areas within the same tidal range

    • change the topography of intertidal area by move substratum around

    • mix atmospheric gases into the water--increasing the oxygen content

Physical Conditions of Rocky intertidal areas (con’t)

  • Salinity-the intertidal may be exposed at low tide and subsequently flooded by heavy rains or runoff from heavy rains --- either would sense severe problems

  • Substratum topography - grain size would change

  • pH and nutrients (not very important)

General distribution patterns

  • Random distribution: distribution of organisms can be explained by random chance

  • Even distribution: organisms occur in an even manner

  • Patchiness: Organisms occur in isolated groups within a larger contiguous suitable habitat


  • Adaptation to desiccation (water loss)

    • Move to moist place or under the moist cover (crabs & snails)

    • Tolerate high % water loss (Fucus, Porphyra, Enteromorpha, up to 60-90%)

    • Reduce water loss by close shells (snails, barnacles, limpets’ home scar)

    • Build shield to cover up (sea anemone or sea urchin covered with shell fragments)

Changes in the extent of vertical zonation with change in exposure to wave action.

Diagrammatic representation of the adaptations to water loss in intertidal organisms.

Many snails of the genus Littorina live high in the intertidal zone. When exposed, the snail protects itself from desiccation by pulling back into the shell and covering the opening with the operculum. First it secretes a mucous thread that attaches the shell to the rock.


  • Adaptation to high temperature (heat)

    • Temperature shock can

      • affect, metabolic and biochemical processes, such as enzyme function and oxygen demands.

      • retard cellular activities, such as ciliary motion.

      • inhibit behavioural activities, such as feeding & protection against predators.

      • inhibit reproductive behaviour, such as egg laying and copulation.


  • Adaptation to high temperature (heat)

    • Reduce heat gain from the environment.

      • Have a relatively large body size (less surface area relative to volume and less area for gaining heat, taking longer to heat up). (Littorina spp larger at high tidal zone)

      • Reduce the area of body tissue in contact with the sbustrate (difficult to achieve – swept off by waves)

    • Increase heat loss from the body

      • Elaborated shell ridges & sculptures acting as heat radiators (snails)

      • Light-colored body (gain and lost heat slowly)

      • Water evaporation (holding extra water in mantle cavity of barnacles, limpets– exceeds the amount the animal needs to survive desiccation)

Differences in heat absorption between smooth, dark shells and sculptured, light shells.


  • Adaptation to wave action (smashing and tearing effects)

    • Limitation of size and shape (relatively small, squat bodies with streamlined shapes to minimize the exposure to the lift and drag of wave forces)

    • Flexible and bending (seaweed)

    • Firm attachment by holdfast (algae), cemented shell

    • Temprary attachments by byssal threads (which can be borken and remade)

    • Thick shells, no delicate sculpturing

    • Large foot to clamps to the substrata

    • Seek shelters (crabs)

The distribution of barnacles from shelter to exposure (from Tain Tam to Cape D’Aguilar). 1. Balanus tintinnabulum volcano; 2. Tetraclita squamosa; 3. Pollicipes mitella; 4. Balanus variegatus variegatus; 5. Balanus amphitrite amphitrite; 6. Balanus albicostatus albicostatus; 7. Euraphia withersi. A detail of the numbers and fusion of the valves of the principal genera are also given.

Algal formation of exposed vs. sheltered coasts


  • Respiration (gills highly susceptible to desiccation in air)

    • Enclose in a protective cavity to prevent them from drying (molluscs)

    • Reduction of the gill and formation of a vascularized mantle cavity

    • Mantel tissue act as lung for aerial respiration (barnacles)

    • Close up (operculum) or clamp down (chitons and Limpets) to reduce gaseous exchange

    • Remain quiescent druing low tide to conserve oxygen and water


  • Salinity (flood by fresh water or expose to extremely high salinity)

    • Osmoconformers: organisms without mechanisms to control the salt content of their body fluids – using same adaptation as to prevent desiccation.

    • Osmoregulators: organisms with physiological mechanisms to control the salt content of their internal fluids

Causes of patchiness in algae on rocky shores. (A) Sweeping action of algal fronds. (B) Irregular spatial and temporal distribution of grazers. (C) Fluctuations in recruitment. (D) Refuge from grazing provided by pits and cracks in rock. (E) Escape of spoelings from grazers.

Biological factors controlling rocky intertidal zonation

  • Competition (barnacles as examples)

  • Predation (starfish, mussels, and barnacles)

  • Grazing (sea urchin on seaweed)

  • Larval settlement

  • Interaction among the controlling factors – community ecology

Biological factors controlling rocky intertidal zonation

  • Competition (barnacles as examples)

  • Predation (starfish, mussels, and barnacles)

  • Grazing (sea urchin on seaweed)

  • Larval settlement

  • Interaction among the controlling factors – community ecology

Interspecies competition

Intertidal zonation as a result of the interaction of physical and biological factors.The larvae of two barnacles, Chthamalus stellatus and Balanus balanoides, settle out over a broad area. Physical factors, mainly desiccation, then act to limit survival of B. balanoides above mean high water of neap tides. Competition between B. balanoides and C. stellatus in the zone between mean tide and mean high water of neap tides then eliminates C. stellatus.

Effect of desiccation and competition on two species of intertidal barnacles

Controlling factors

  • High tidal zone

    • Chthamalus stelatus settled here

    • Semibalanus balanoides have no sufficient tolerance to drying and high temperatures.

  • Mid tidal zone

    • Chthamalus stelatus settled here but was overgrew, uplifted or crushed by Semibalanus balanoides

The main groups of algal grazers at different intertidal zones in temperate and tropical systems.


Effect of sea urchin removal on kelp growth on the Isle of Man, Great Britain.


Interaction of predation and physical factors in establishing the zonation of the dominant intertidal organisms on the rocky shores

Interactions among mussels (Mytilus), barnacles, and their predators on the northwester Pacific coast of North America, which allow barnacles to persist in the intertidal zone.


Succession in a northwest Pacific coast intertidal mussel bed in the absence of Pisaster.

Flow chart of Rocky intertidal “Succession”

Rocky intertidal food web.

Sandy and Muddy Shores



1. Shape up of beaches


  • Sediment size

  • Wave action

  • Slope




2. Surroundings

  • Exposed vs protected

  • Oceanic vs semi-enclosed waters, estuaries or wetlands

  • Seasonal vs non-seasonal



3. Sediment movement

  • Swash and backwash

  • Longshore transport





4. Physical conditions of intertidal flats

  • Grain size

  • Interstial space

  • Pore water

  • Water retention


Greater Fluctuation



5. Biogeochemical conditons

  • Oxygen

  • Organic matter

  • RPD


Strong, Shallower

6. Organisms


  • Diversity

  • Abundance

  • Production



Longshore Transport Processes

So sand downcast in a zigzag path

Path of sand on beach

returns straight down the beach

Water moves on shore at an angle

Net Transport of sand


Surf zone

Longshore current

Longshore transport

Some terms

  • Swash: water running up a beach after a wave breaks; this action carries particles with it, which may cause accretion of the beach if the particles remain there

  • Backwash: water flowing back down the beach; this action removes particles from the beach, depending on the particle size

  • Slope: the slope of a beach is the result of the interaction between particle size, wave action, and the relative importance of swash and backwash water.

  • Dissipative beach: occurs where wave action is strong but the wave energy is dissipated in a broad, flat surf zone located some distance from the beach surface (gentle swash, fine sediments, gentle slope

  • Reflective beach: occurs where wave action impinges directly on the beach face and the sediment is coarse (no offshore surf zone, wave produce large swashes up the beach face, steep slop). Backwash and swash collide to deposit sediment and wave energy is directed against the face of the shore and reflected off the surface.

Classification of particle sizes

The udden-wentworth particle size classification

Comparison of the physical conditions found in fine-grained and coarse-grained beaches

  • Particle size

  • Slope

  • Water retention

  • Particle retention

  • Surface to volume absorption

  • Oxygen

  • Organisms

High tide

Water drains out at low tide

Low tide

High tide

Water retained at low tide

Low tide

Environmental characteristics of coarse- and fine-particle beaches

The process of alongshore drift

Surface stability of particulate shores. Surf causes a suspension of the particles. Waves 1m in height disturb the sediments to a depth of 8 cm. Burrowing in this shifting substrate is difficult.

A transect of a sand beach showing gradients of water content, salinity at low tide






Water edge

Intertidal zone

Temperature Change at different depth during a day

A transect of a sand beach showing gradients of water content, salinity at low tide

O2 saturation

Water edge

Sandy Shores

A common sense, all public recreational beaches are usually sandy shores.

Sandy shores are usually exposed, poor in nutrients and therefore organisms.

Muddy Shores

Muddy shores usually associated with estuaries and salt marshes, enclosed bays, lagoons, harbours,

Protected from open ocean wave action


Near sources of fine sediments

Types of organisms in sandy beach

  • No macroscopic plants occur on open sand beach, but certain ephemeral algae such as Ulva or Enteromorpha may be abundant in protected sand flats

  • No sessile animals such as barnacle and mussels

Types of organisms in sandy beach

  • Small benthic diatoms may be present on the sand grains, protected sand flats support a large and diverse microtlora of benthic diatoms, dinoflagellates, and blue-green algae--form brownish or greenish film on the sediment surface.

  • Dominate by polychaetes, bivalves, and crustaceans

Zones of water content on sandy beaches

The clam Donax moves to stay in the surf zone. (A) Burial. (B) Moving. (C) Reburial.

Adaptation of organisms of sandy beach

  • Burrow deeply -organism is deeper than the depth of d by the passing wave.

  • Burrow quickly - employed by many annelid worms, small clams, burrow quickly as soon as the passing wave has removed the animals from the substrata.

Subsequent morphology changes- To burrow deeper, the clam Tivela stultorum developed heavy shell and long siphons; - To burrow fast, raxor clams of the genus Siliqua have very smooth shells, special ridges on the shell to grip the sediment to aid in penetrating into the substrata, sand dollars have much reduced spines to allow them to burrow them into the sand; sand crabs have a short body with limbs highly modified to dig quickly into wet sand;sand dollars Dendraster excentricus accumulate iron compounds in a special area of their digestive tracts, which serve as a weight belt to keep them down in the presence of wave action.

Adaptation of organisms of sandy beach

Developed special structures to prevent clogging of respiratory surface--intake siphons of sandy beach clams are often fitted with various screens; the antennae of sand crabs held together form a tube to surface through which water enters the branching chamber--densely clothed with closely spaced hairs designed to prevent entrance of sand.

Generalized scheme of zonation on sandy shores.

Generalized patterns of organism distribution for sandy beaches.

Sandy beach zonation

Generalized food web for a sand beach in California



Upper limit of wave spray and splash

Intertidal zone


Types of organisms

Flora: plant community

Fauna: animal community

Epifauna: animals dwelling on the surface of sediment

Infauna: animals dwelling below the surface of sediment

Microfauna: organisms < 0.1 mm

Meiofauna: 0.062 mm - 0.5 mm

Macrofauna: > 1 mm



Burrowing: to construct by tunneling, or digging, e.g. polychaetes,

Tubes: siphon tube, large clams-long siphons to prevent clogging respiration pathway, heavy shell to prevent storms

Mobile: move quickly with passing wave, commonly employed by many annelid worms, small clams, and crustaceans. Eg. Sand crabs populate the world beaches, have a short body with limbs highly modified to dig quickly into wet sand. As soon as they are freed from the substrate by a passing wave, they reburrow quickly again before wave motion carries them offshore

Food sources


Benthic algae (microalgae-diatoms, macroalgae-red algae, green algae, seagrass)

Detritus: small debris of organic matter, from dead organisms


Feeding Types:

Deposit feeders (by deposit feeding):

Surface deposit feeders

Burrowing deposit feeders

Suspension feeders: filter feeders

Detritus feeders


Mudflat Ecology


Adaptations of organisms

Types of organisms

Feeding Biology

Physical factors of muddy beach

  • Muddy shores are restricted to intertidal areas completely protected from open ocean wave activity--with no wave action.

    • Muddy shores are located in various partially enclosed bays, lagoons, harbors, and especially estuaries where there is a source of fine-grained sediment particles

    • The slope of mud shores is much flatter than that of sand beaches.

  • More stable than sand substrata and more conducive to the establishment of permanent-burrows.

  • Anaerobic conditions because water in the sediments does not drain away --long retention time for water, coupled with a very poor interchange of the interstitial water with the seawater above and a high internal bacterial population,--complete depletion of the oxygen in the sediments below the first few cm of the surface

  • Between the upper aerobic aver (brown or --yellow) and the lower anaerobic layer (black) there occurs transition zone called-redox potential discontinuity (RPD) layer (grey)

  • Accumulate organic material - an abundant potential food supply for the resident organisms; but abundant small organic particles "raining" down on the mud flat also have the potential to clog respiratory surfaces.

RPD layer—- reduces compounds diffuse upward from below and as soon as oxygen is available, bacteria oxidize these compounds and the oxidized end products including CO2, NO3 and SO4, in turn are incorporated into bacterial biomass and form the basis of new food chains, some compounds diffuse downward below the RPD zone and utilized by the anaerobic bacteria. These bacteria in turn produce more reduced compounds, which complete the cycle; - chemoautotrophic bacteria in the RPD zone oxidize the reduced compounds and fixing CO2 and produce more organic materials.

Aerobic: a condition with oxygen for organisms, Oxic

Anaerobic condition: a condition depleted of oxygen, Anoxic.

Redox Potential: reduction-oxidation potential, measured by an electrode. It is positive, meaning oxidizing condition; negative-reduction condition

RPD: redox potential discontinuity

RPD layer: a transition zone between the upper aerobic layer and the lower anaerobic layer, characterized by a rapid change from a positive redox potential (Eh) to a negative potential.

Decomposition of organic matter is:

by aerobic bacteria above RPD

by anaerobic bacteria below RPD

Chemoautotrophic bacteria: obtain energy through the oxidation of a number reduced compounds like H2S to produce organic matter. They are primary producers.

Diagrammatic representation of the physical and chemical characteristics of sediments across the redox discontinuity layer and the biological processes occurring in each

Physical factors of sandy beach

  • Wave action--vary with sites, seasons, as the results:

    • Particle size vary due to the wave actions--where wave action is light, the particles are fine, but where wave action is heavy and strong, the particles are coarse, forming deposits called gravel or shingle rather than sand

    • Water retention--coarse sand and gravel allow water to drain away quickly as the tide retreats while fine sand and retent water longer

    • Organisms in a coarse gravel beach suffer from desiccation

    • Fine sand is more amenable to burrowing than coarse gravel

Physical factors of sandy beach

  • Unstable constantly moving substrata--substrate movement--particles are beingcontinually moved and sorted-- a gradation of particle sizes from fine near low water to coarser at the high tide mark.

  • Since profile and shape of sand beach change so often, few large organisms have the capability of permanently occupying the surface of open sand or gravel beaches

  • Relatively uniformed topographic--the environmental factors such as T'C, desiccation, wave action, insulation act uniformly--change little in the sand

  • Saturated oxygen content

Adaptation of organisms of muddy beach

  • Burrow into the substrata

  • Form permanent tubes

  • Physical adaptation to live under anaerobic condition burrowing shrimps and clams have haemoglobin with much higher affinity of oxygen; other animals use glycogen stores for anaerobic metabolism.

  • Obtain oxygen-rich surface water and food through various burrows, holes and tubes appear on the surface of -the mud flat

Two common polychaete worms of mud flats: Arenicola (right) in its U-shaped burrow, and Capitella (left) burrowing through the substrate.

Macoma nasuta in the substrate. (B) Macoma nasuta feeding with its in-current siphon.

Types of organisms in muddy beach

  • Epifaunal primary producer--diatom (giving a brownish colour to the surface at low tide, Gracilaria (red algae), Ulva & Enteromorgha (green algae), sea grasses (Zostera) in the lowest tidal levels

  • Infaunal primary producer – large numbers of Chemosynthetic or sulfur bacteria (only abundant organisms found in the anaerobic layers of mud).

  • Dominant macrofaunal groups including polychaetes., bivalves, small and large crustaceans

Nitrogen cycle of a soft bottom marine community

What a mess!

So guess who is who in terms of feeding types?

Surface deposit feeders:

A: spionid polychaete

B: protochodate

E: spionid polychaete

Burrowing deposit feeders:

C: paraonid polychaete

D: oligochaete

H: syllid polychaete

I: orbiniid polychaete

J: Nephtyid polychaete

Suspension feeders

G: venerid bivalves

F: haustorid amphipod

K: haustorid amphipod

Generalized food web of a muddy shore.

Species richness versus tidal level.

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