6 Intertidal Rocky Shores Flashcards
What is pelagic?
What is benthic?
- pelagic is the zone that begins at the low tide mark and includes the entire oceanic water column. Pelagic organisms live floating or swimming in the water column
- benthic is the bottom of an ocean or lake. Marine benthic organisms live on the sea floor
What is a rocky shore?
- intertidal area
- consists of solid rocks
- can include many different habitat types e.g. steep rocky cliffs, platforms, rock pools, boulder fields
intertidal pools
- tidal pools are rocky pools in the intertidal zone that are filled with seawater.
- they are formed by abrasion and weathering of less resistant rock and scouring of fractures and joints in the shore platform.
- this leaves holes or depressions in where seawater can be collected at high tide.
general characteristics of intertidal rocky shores
what are they?
Where can they be found?
significance?
*Transition zones between land and sea
*Globally distributed, but particularly abundant in temperate areas where erosion caused by the retreat of glaciers has removed sediments along the coast.
*They occupy a negligible portion of the globe, but have enormous ecological, social and economic importance
*Scientific value as model systems for experimental ecology and community ecology studies
*Relatively simple environment - Strong environmental gradients (i.e. wetting, exposure) in relatively small spaces
*Predominantly sessile and small organisms, relatively easy to manipulate
physical environment shaped/ dominated by
- Climate
- Tides
- Wave exposure
- Shore geometry
- Substratum morphology & mineralogy
- Climate - differences in temperate intertidal rocky shores and tropics
- Tropics defined as areas between 23.4 degrees north and south latitudes
- Less temperature variation and seasonal rainfall in tropical than in temperate intertidal
- Higher temperatures are more stressful
- Less temperature variation and fewer storms are
less stressful
- Tides
- generate strong vertical gradient
- Between high and low tide levels (range of a few cm to> 7 m)
- In a few meters we pass from a completely terrestrial environment to a completely marine environment
tidal ranges
high tide
The tide when the water is highest
low tide
The tide when the water is lowest
Spray zone
The area above the high tide mark, where the ocean periodically sprays on the land
Intertidal zone
The area along coastlines between the high and low tide
Subtidal zone
The area below the low tide mark, always underwater
Graph that shows terms used in describing tidal levels and the shape of typical spring and neap tide curves
Immersion and Emersion - is it a vertical or horizontal gradient? Why is it a gradient?
- vertical gradient
- drying stress
- climate (thermal conditions, rain, consequent osmotic stress..)
- food- and nutrient-availability
- lack of oxygen
Emersion: Aufsteigen des Landes über den Meeresspiegel
Immersion: Eintauchen in Flüssigkeit
- Waves - vertical or horizontal gradient?
both
waves - vertical gradient
waves - horizontal gradient
- refraction
- diffraction
waves and their hydrodynamic forces
- horizontal: drag force in the direction of the wave impact inertial force of impact reaction
- vertical: lifting force from bottom to top
why are very exposed shored stressful for organisms?
drag and lift forces
why are very stagnant conditions stressful for organisms?
- temperature
- oxygen
- nutrients
- shore geometry and inclination have an effect on ___ ?
- lighting
- hydrodynamics
- temperature
- sedimentation
- larval settlement
- Substratum morphology
- refers to underlying surface/ material
- morphology can vasry in composition/ arrangement of pebbles, boulders..
- sizes
- enables topography and small scale heterogeneity
- other factors that influence intertidal rocky shores
- Physical disturbance
- Sedimentation
- Salinity
- Nutrients
The biotic environment of intertidal rocky shores is mainly influenced by what? (categorization)
- dominant forms
- zonation patterns
- patch and temporal dynamics
- trophic structure
- dominant forms
features of: Sessile Benthos
- tolerant to desiccation stress (Austrocknen)
e.g. seaweeds have
- morphologies and alginate content that help retaining moisture
-complex physiological adaptations to desiccation
strategies of mobile intertidal organisms
- isophasic strategy
- isospatial strategy
most organisms have mixed complex patterns
isophasic strategy
Forms adapted to either the marine or air environment which, through a high vagility, access the intertidal zone in the periods in which it is hit by the favorable phase. Dynamic colonization of the intertidal environment
isospatial strategy
Organisms that manage to remain in the intertidal belt regardless of the temporal alternation of the two phases. The activity of these anymals is limited to the time that is suitable for moving and feeding
what is known as “vertical zonation”?
- intertidal species tat show marked distributional patterns
from high to low shore:
- marked changes in species composition
- increase of species diversity and biomass
Zonation
regular variation in the distribution and abundance of organisms along gradients in space
zonation and gradient analysis
- One of the main research topics in rocky shores has focused on understanding the relationships between environmental gradients and species distribution and the processes that generate them
- Gradient analysis: study of the effects of varying a factor on the way populations are distributed (are there clear boundaries?)
Vertical Gradients (image)
Vertical Gradientsin IRRS
favorable and unfavorable conditions on vertical gradient
what are the gradients that are more favored, the farther down it gets?
zonation models
vertical zonation along the Atlantic coast
changes in zonation patterns in relation to coast exposure to wave action
north Adriatic exposed zones
north Adriatic protected shores
different distribution along exposed and sheltered shores in UK
changes in zonation patterns in relation to climate
- small scale patchiness
- In addition to relatively predictable gradients, the distribution of organisms exhibits great small-scale heterogeneity (patchiness)
- Sometimes patchiness is prevalent to the point that we are talking about mosaic populations
“patch”-dynamics is largely related to ___ ?
disturbance.
- Disturbance events in nature (storm surges, herbivores, abrasion, etc.) that are heterogeneous in space and time originate populations consisting of patch mosaics with different colonization dynamics.
- A patch is a portion of the localized, discrete and uniform habitat in which the effect of a disturbance is homogeneous and within which the subsequent dynamics are similar
(Petraiti et al. 1989)
Patchiness and scale
patches show:
- temporal patterns (seasonal/ non seasonal)
-cyclic dynamics
patch cyclical dynamics
typical trophic structure of a temperate rocky intertidal system
what factors affect the distribution dynamics and structure (zoning) of rocky intertidal assemblages?
For many years it was believed that the structure (zoning) of intertidal rock populations was mainly controlled by ___ ?
- abiotic factors (mainly wave motion, tidal regime)
- Studies have focused on the physiological tolerance of the different species to drying, temperature, hydrodynamics, in order to identify tolerance limits
The rise of experimental ecology in the 1960s highlighted the role of ___ ?
biotic factors (interaction between species)
Competition
(shaping distribution and zoning of intertidal rocky shores)
- common resources must be limited in quantity
- damage is generated by competition on each species. Often this damage is not homogeneously distributed among the species → asymmetry
types of competition
- intraspecific
- interspecific
difficult to separate
how do species compete?
- by exploitation (indirect competition)
- by interference (direct competition)
indirect competition by exploitation
there is no direct contact between competing organisms, and competition is mediated by the resource → a resource exploited by one organism will no longer be available for another organism
direct competition by interference
There is direct contact between organisms
examples of competition by exploitation
- Competition by “consumption” (eg. of nutrients, light, etc.)
- Competition by “pre-emption” (filling of space and inhibition of recruitment)
examples of competition by interference
- Competition by “overgrowth” (competition for space)
- Competition by “allelopathy” (chemical)
- Competition by “aggression” (clash or defense of the territory)
- Competition by “physical damage”
experiment by Joseph Connell (1961)
- competition between Semibalanus and Chthamalus
hypothesis
- previous explanation was that the net boundary between the two species was determined by their different physiological tolerances to drying
- abiotic factors: hypothesis
1) Chthamalus is excluded from the lower areas because it does not tolerate long periods of immersion
2) Semibalanus is excluded from the higher areas because it does not tolerate drying - biotic factors: hypothesis
1) Semibalanus excludes Chthamalus in the competition
vertical zonation
stress tolerance vs. competition
Organisms of the lower horizons cannot survive the higher horizons, while those of the upper horizons can adapt to the environmental conditions of the lower horizons
but
are outclassed by those of the lower horizons in terms of metabolic performance, growth, ability to exploit resources
Predation
(shaping distribution and zoning of intertidal rocky shores)
- It is the consumption of an organism (the prey) by another organism (the predator), in which the prey is alive when the predator attacks it for the first time.
- It is a direct trophic interaction that implies a negative effect of the predator on the prey and a positive effect of the prey on the predator
- The predator is an agent of mortality → it influences the structure and evolution of communities
experiment by Paine 1966
Situation:
- mussel bed on a relatively flat rocky bench
- large numbers of Pisaster ochraceus at the lower part of the bed (starfish)
- they have a limited time for feeding at the time of high tide
- they tend to feed on the lower part of the mussel bed, which is here dominated by Mytilus californianus
Hypothesis:
- Pisaster causes the discontinuous zonation by preying on the competitive dominant species
Demonstration of 3 key ecological concepts:
1) predation affects not only the dynamics of prey populations but also the structure of the community
2) Pisaster is a keystone species
3) The control exerted by pisaster is an indirect interaction – keystone predation
1) predation affects not only the dynamics of prey populations but also the structure of the community
Predation can control the outcome of competition (or other interactions) between species, with outcomes that affect the diversity of communities
2) Pisaster is a keystone species
It has a much greater community structure control effect than that of other predators in the system e.g., Nucella and disproportionate to its abundance
3) The control exerted by pisaster is an indirect interaction – keystone predation
the role of herbivores in IRS (intertidal rocky shores)
- strong controlling effect
- Grazing is a method of feeding in which a herbivore predator feeds on low-growing plants such as grasses or other multicellular organisms, such as algae
- Many marine organisms are grazers, including many molluscs (e.g. limpets, chitons, snails), echinoderms (e.g. urchins) and fish species (e.g. salemas)
Jane Lubchenco (1978)
Observation:
- Jane Lubchenco observed that in her region tide pools tended to have either high density of green seaweeds or high density of red seaweeds.
- She knew that Littorina snails graze on seaweeds and in the lab it has a preference for the green Enteromorpha over the red Chondrus.
Experiment:
- She manipulated Littorina abundance in rock pools
Result:
- Enteromorpha is the competitively dominant seaweed in rock pools
- Littorina controls algal species diversity similarly to what done by Pisaster
What caused differences in Littorina densities?
- snails were in turn controlled by their predators (green crabs) which in turn were controlled by their predators (sea gulls).
- Sea gulls would quickly eat all crabs, but crabs escape by hiding in the seaweeds
Littorina-example, an example of what mechanisms?
trophic cascades + keystone predation
Trophic cascade (Paine 1980)
(graph + arrows)
S. Hawkins (1981)
- Differences along gradient of wave exposure can be explained by differences in grazing pressure
- What factors cause observed patterns on rocky shores?
- Hydrodynamic forces caused by waves?
- Biological interactions, mainly predation?
- Other abiotic stress factors, e.g. heat & desiccation?
- Do hydrodynamic forces limit macroalgae? –> Transplantation experiment
- Does limpet predation limit macroalgae? –> experiment limpet removal
- Overall Conclusion
- Hydrodynamic exposure and grazing interact to control macroalgae
- In absence of grazing, algae will recruit but waves will prune or dislodge plants
- Recruitment is prevented if limpets exceed a critical density
- Limpets are favoured by wave exposure??
experiment by Courtesy SJ Hawkins continued:
EUROROCK EXPERIMENT: How does limpet control of macroalgae vary with latitude?
- 3 treatments
- sometimes large effects on fucoid canopy algae
- results show less macroalgae in Southern Europe (picture) - why?
from Northern to Southern Europe
1) Increase in pool of grazer species
2) Increasing grazing pressure
3) Increase in physical stress - Potential explanations
1) Limpets and other grazers actually are major structuring agents in southern Europe:
-so effective at preventing development of fucoids that they eliminate the propagule supply
2) Fucoids are not adapted to increased physical stress in southern Europe
3) Combination of above reducing likelihood of fucoid establishment
fish predation: are intertidal habitats a refuge from herbivorous fish predation?
- were considered as a refuge
- experimental work shows: NOT TRUE
Facilitation
(shaping distribution and zoning of intertidal rocky shores)
facilitation is synonymous with mutualism
- facilitation is a broader term
- mutualism is most often associated with symbiosis
- Interaction between species resulting in a mutual benefit: individuals of a population of each of the mutualistic species grow and / or survive and / or reproduce at a higher rate when in the presence of individuals of another species.
- The benefit can be food resources, protection from enemies, or a favorable environment in which to grow and reproduce.
- It can occur both between individuals of the same species (density- dependent survival) and between individuals of different species. - Often asymmetrical benefits
Mechanisms of Facilitation
- direct: without the action of intermediaries (resources or other species)
- indirect: depends on the effects on an intermediary (resource or other species)
DIRECT Mechanisms of Facilitation
INDIRECT Mechanisms of Facilitation
physically-induced facilitation in intertidal habitats
- stress: desiccation (drying out)
- benefactor (has positive effect on the other): canopy forming microalga
- beneficiary (the facilitated species): barnacles
every interaction has pros and cons
the same type of interaction can change depending on the circumstances
- Survival of barnacles decreases in South when Canopy cleared
- Opposite in north
- Competition for space or food, could be both
- south: lots of stress: interaction between seaweed and barnacles is a facilitation
- In north there is not that much stress: canopy not needed
- different interaction depending on environmental factors
physically-induced facilitation in intertidal habitats
hypothesis: mussels facilitate macroalgae at exposed sites
- Macro alga could not withstand the wave exposure unless mussels there
Model of Bertness & Callaway 1994
- Greater abundant of competitive interaction in more bellin(?) environment where good conditions
- X-achse rechts: Very stressed environment
- Few that survive have a lot of positive interaction
- Less stressed zone : more negative competition
Keystone Predation
(graph + arrows)
Indirect mutualism
(Graph + arrows)
Interaction Webs
- trophic web ≠ trophic cascade
- trophic web: the transfer of energy within a system (who eats what)
Disturbance
(shaping distribution and zoning of intertidal rocky shores)
- a discrete and localized event that determines the removal of individuals from the population
- creates the opportunity for new individuals to settle (Sousa 1984)
→ frees up resources, mitigating the intensity of competition
examples of disturbance events
(physical, biological, anthropogenic)
1) Physical factors:
Sea storms
Sediment (abrasion / suffocation)
Landslides
Fires
Prolonged drying
Floods
Prolonged drought
2) Biological factors
Predation
Illnesses
3) Anthropogenic factors
Removal of organisms
Trampling
factors that determine the final disturbance regime to which the population is subjected
- Type of disturbance
- Extension
- Intensity
- Duration
- Frequency
- Localization
effects of disturbance
(Sousa 1979)
Intermediate Disturbance Hypothesis (IDH)
- suggests that ecological communities are most diverse and stable at intermediate levels of disturbance
- According to IDH, low levels of disturbance may allow competitive species to dominate and exclude less competitive species, leading to lower diversity.
- On the other hand, high levels of disturbance may prevent any species from establishing and maintaining a stable population, also reducing diversity.
- Intermediate levels of disturbance are thought to create a balance, allowing both competitive and less competitive species to coexist and maintain higher biodiversity.
- looks like curve from predation effects
- Not too different theories, matter of scale, basically the same
- If you have a with system with no disturbance there will be predators destroying the ecosystem
- Aim is to create patch
- Species can colonize a patch
Disturbance and Patch dynamics
a species will be able to (re)colonize a patch if
- It is able to reach it (dispersion)
- appropriate conditions exist (patch characteristics)
- other species do not preclude it (interspecific interactions)
colonization dynamics is affected by ___ ?
patch characteristics, such as
- size
- shape
- location
- time of patch creations
- characteristics of the substrate
the time of creation of a patch can have an effect
Dispersal
(shaping distribution and zoning of intertidal rocky shores)
Classic experiment repeated by Hawkins (1981)
Limpet Removal
fucoids –> fucales –> brown algae
- Classical experiment on rocky shores! (Hawkins)
- Seaweeds grow where limpets have been removed
- Real story: limpets removed –> empty
- After months: strip with seaweeds
- After 5 years: strip is rock and all around seaweeds
- Why??
- System keeps moving from one state to another one
- Cyclical dynamic
- State depends on patchiness
- Each patch can be at one stage they alternate
Interaction between Fucus and P.vulgata
- Fucus = algae
- P. vulgata = limpet
(–> dispersal)
- Vulgata eats fucus but also needs it for protection (special relationship)
- Vulgata tends to aggregate near fucus
complex limpet - algae . barnacle interactions
- driven by recruitment fluctuations
- Complex relationship (patella, seaweed)
- Positive in terms of food and shelter
- Seaweed and barnacle: compete for space
- Patella and barnacles: B have neg. effect in limpets
- Also the other way around
- recruitment fluctuatins
- Systems shift depending on which species recruits another one?
Limpet – Fucus – barnacle mosaic (P. vulgata and Semibalanus only shores)
- cyclical dynamic
- P. vulgata: specific aggregative behavior (near Fucus)
–> Fucus = food
–> also facilitated by Fucus (not sure exactly how) → aggregative behavior - Here: state1) dominated by barnacles
- Basically empty rock
- What recruits first? Barnacles
- They limit grazing by limpits because they are very hard
- Seaweeds can grow
- State 2) Fucus starts growing –> reduces barnacles abundance
- Also limpet grows, has a different behavior
- Limpets start growing. Fucus disappears, but limpets need fucus
- Fucus moves to side –>
Strip becomes empty again! (process of years)
Dispersal and Connectivity - Paper (example)
- Clear isolation-by-distance: populations are strongly structured
- If it increases they will be separated
- Means: needs to take into account for restauration plans
- Be careful where to do it
- Connectivity within population is very important
- Try to create stepping stones for the dispersal when trying to restore
- Restore the connectivity
- regional genetic variability bec. of stepping stone and habitat continuity
Top-down vs bottom-up control
- top-down: Density variations of top predators produce variations in population density at lower trophic levels
- bottom-up: the community structure is regulated by the basal energy trophic input
traditionally the focus on intertidal control was top-down or bottom up?
- top-down
- bottom up had little consideration
nutrient availability as bottom-up control
-Can be a limiting factor in intertidal rocky shore
- IRS as a stressful environmnet
- Nutrient availability can vary a lot on local and regional scale
(Generally Mediterranean nutrient poor –> pretty blue waters)
example that shows importance of bottom-up control on local scale (birds)
- Local: experiments: structure of IRS different where certain birds-colonies are and where not
- Birds as predators e.g. limpets (top-down)
- Diff. view: guano rich of nutrients
- Bottom-up through nutrients from the guano (verwitterung von exkrememnten von seevögeln)
- guano has positive effect on algae
- increase in algae has effect on limpets: increased growth rate, max size, max reproductive potential
- also effect on other invertebrates associated with algae
name examples, where variations in nutrient and detritus concentrations affect populations
- local scale: guano effect from bird colonies
- differences in exposed and sheltered environments
- Wide geographical difference linked to oceanographic gradients of upwelling and productivity
bottom-up-example: differences in exposed and sheltered environments
1) Filtering biomass (e.g. mussels) 10-50 times more abundant on exposed reefs than on sheltered reefs.
Possible explanations:
- Either: Lower predation and higher recruitment
- Or: greater contribution of debris material
2) They show that in exposed sites the concentration of debris is twice as high as in sheltered sites
3) Often insufficient in situ productivity → intertidal reef organisms supported by food inputs from other systems (in South Africa 60/85% food is detritus that comes from subtidal kelp beds)
bottom-up trends on a larger scale
- Strong upwelling along the western coasts
- Little or no upwelling along the eastern coasts
- Productivity gradient reflects the oceanographic gradient because:
- From west to east: grazer biomass and filter feeder biomass decreases
- less biomass –> more chlorophyll (clearer water) –> increase of shell length (limpets)
in terms of dispersal: what are threats and conservation priorities?
what are major threats to intertidal systems?
- habitat loss
- coastal population and shoreline degradation
- urban constructions
- industrial, transport and tourism infrastructure
- tourism and trampling
- pollution
- invasive species
- overharvesting
- climate changes
Coastal claim and development
- e.g. UK: claim has affected >85% of estuaries and losses if intertidal habitats between 25-80%
- e.g. Europe: > 22000 sq-km are artificial coasts
- also
example of invasive species as threat for IRS
(Mytillus galloprovinciales)
- a mussel (Mytillus galloprovinciales) introduced in South Africa in 1970’s
- growth rate rapid, desiccation-tolerance high
- has outcompeted limpet and mussel that used to dominate mid to low intertidal west coasts
- mussel and limpet interaction influenced by wave-action/-exposure
- semi-exposed: limpets dominate
- more exposed: mussel dominates
what stops further expansion of an invasive species such as Mytillus galloprovinciales?
- expansion depends on oceanographic conditions, temperature and physical barriers
- warmer waters at east-coast, cooler at west-coast –> transition between temp. as main factor limiting recruitment spread
- currents
how do introduced Norway rats indirectly alter the intertidal community in the Aleutian Islands?
! Transition from algae- to invertebrate-dominated !
- through direct predation on birds that forage in the intertidal
- rats keeps number of certain birds low
- less limpets and snails are eaten
- more limpets and snails etc that forage on algae
effect of harvesting (in IRS)
- creates lots of new space
- may create space for invasive species
- key stone species may be harvested
effects of climate changes (abiotic changes)
e.g.
- sea level rise
- changing shores –> shifting intertidal extent and slopes
changing shores due to climate changes
- sea level rise changes the proportion of vertical and horizontal surfaces that are available for colonization
- that will cause quantitative changes and qualitative changes
talking about changes in the geometry of rocky shorelines and the sea level rise. what are QUANTITATIVE changes?
Reduction of the intertidal area extent. This is likely to reduce numbers of species via species-area relationships alone.
talking about changes in the geometry of rocky shorelines and the sea level rise. what are QUALITATIVE changes?
Changes in the inclination of the substratum. This is likely to affect species composition and distribution
fixed shorelines by humans leads to so called ____ ?
–> coastal squeeze
- intertidal habitats trapped in a coastal squeeze
- trapped between human population and climate changes sea-wise (rising sea level)
- intertidal zone shrinks, no migration landwards
where are the most severe losses of intertidal habitats?
- projected losses range between 20% and 70% of current intertidal habitat
- most severe at sited where the coastline is unable to move inland (due to steep topography or seawalls)
