intertidal ecology rocky shores sandy shores: sandy beaches muddy shores: mud flat
TRANSCRIPT
Highest tide
Lowest tide
Intertidal
Flat Subtidal zone
The intertidal zone is the zone between the highest and lowest tides
Flood and ebb tides
Water-air alternative exposure
Rhythmic
Rich diversity and density within a small area
Characteristics of the intertidal zones
Rocky Shore Ecology
Zonation 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
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
Factors modifying zonation of Rocky shore
Abiotic Wave action and
tidal range Desiccation Heat stress Salinity reduced feeding
time DO and gas
exchange
Biotic Larval settlement Intra- and
interspecific competition
Predation and grazing
Physiological tolerance and adaptation
behavioral pattern, mobility
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
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)
Physical Conditions of Rocky intertidal areas
(con’t)
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 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)
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 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 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)
Adaptation 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.
Adaptation 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
Adaptation 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
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.
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
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.
Sandy and Muddy Shores
1. Shape up of beaches
Sediment sizeWave actionSlope
2. Surroundings Exposed vs protectedOceanic vs semi-enclosed
waters, estuaries or wetlandsSeasonal vs non-seasonal
3. Sediment movement
Swash and backwashLongshore transport
Sandy Muddy
LargerStronger
Slopy
Exposed
Oceanic
Seasonal
Applicable
4. Physical conditions of intertidal flats
Grain sizeInterstial spacePore waterWater retention
5. Biogeochemical conditons
OxygenOrganic matterRPD
6. Organisms
Sandy Muddy
LargerLarger
Greater Fluctuation
Weaker
ShallowerAnoxic
RichStrong, Shallower
DiversityAbundanceProduction
HighLarge
High
Water moves on shore at an angle
returns straight down the beach
So sand downcast in a zigzag path Net
Transport of sand
Longshore current
Longshore transport
Longshore Transport ProcessesPath of sand on beach
ShorelineSurf zone
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.
Some terms
High tide
Low tide
Water drains out at low tide
High tide
Low tide
Water retained at low tide
• Particle size
• Slope
• Water retention
• Particle retention
• Surface to volume absorption
• Oxygen
• Organisms
Comparison of the physical conditions found in fine-grained and coarse-grained beaches
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.
<5%
5-10%
10-15%
15-20%
20%
Water edge
Intertidal zone
A transect of a sand beach showing gradients of water content, salinity at
low tide
O2 s
atur
atio
n
Water edge
A transect of a sand beach showing gradients of water content, salinity at low tide
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
Flat
Near sources of fine sediments
Sandy Shores
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
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
Types of organisms in sandy beach
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.
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.
Adaptation of organisms of sandy beach
OrganismsTypes 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
OrganismsAdaptations
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 sourcesPhytoplankton
Benthic algae (microalgae-diatoms, macroalgae-red algae, green algae, seagrass)
Detritus: small debris of organic matter, from dead organisms
Bacteria
Feeding Types:
Deposit feeders (by deposit feeding):
Surface deposit feeders
Burrowing deposit feeders
Suspension feeders: filter feeders
Detritus feeders
Scavengers
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.
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.
Redox Potential: reduction-oxidation potential, measured by an electrode. It is positive, meaning oxidizing condition; negative-reduction condition
Decomposition of organic matter is: by aerobic bacteria above RPD
by anaerobic bacteria below RPDChemoautotrophic 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
Unstable constantly moving substrata--substrate movement--particles are being continually 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
Physical factors of sandy beach
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.
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
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