8.1 Subtidal Rocky Reefs Flashcards
what habitat types are included in subtotal rocky reefs?
- benthic rock bottoms
- rocky slopes
- steep rocky cliffs
- boulder fields
- rock slides
- submarine caves
some characteristics of SRR (subtotal rocky reefs)
- strong environmental gradients, e.g. light, hydrodynamics
- strong environmental heterogeneity
- predominantly sessile organisms
Kelp forest distribution
nutrients in SRR
- there is seasonal fluctuations
- the thermocline affects temperature changes but ALSO the availability of nutrient and organic matter
- El nino events cause nutrient depletion along Californias coasts (associated with high temp. stress)
- kelp forests at californian coasts –> extensive losses during severe events in El Niño
light as a gradient in SRR
- vertical gradient
- zones: photic, mesophytic, aphotic
gradients in SRR? vertical or horizontal?
- nutrients (both: e.g. kelp forest distribution –> horizontal, fluctuations in thermocline –> vertical)
- light (vertical+horizontal)
- temperature (vertical+hotizontal)
- hydrodynamism (vertical+ horizontal)
temperature in SRR (vertical)
two representative temperature profiles for the water column that is overlying wave-exposed rocky subtotal sites
(A) Gulf of Maine
(B) Galapagos Islands
(A)
- steep thermocline (between surface and13m depth)
(B)
- shallow layer of warm water (2-5m depth)
- smaller thermocline (begins at 20-23m depth)
- rocky subtotal organisms may be thermally stressed in the shallow zone (3-18m depth) when thermocline is up- and down welled
my notes:
- Upper part more variable
- Deeper areas more homogenious
- More stable environments are easier for organism –> easier to adapt (to more extreme)
- Thermocline is getting deeper and deeper in ocean (due to climate changes)
- a used-to-be stable environment but nowadays it changes
–> main factors for loss
hydrodynamism
- vertical gradient: tides
- horizontal gradient: currents
- Already 14m depth are affected by wave action
- Waves important and can be a natural disturbance
-bottom left: going from surface down: mg-calcium decreases
zonation in SRR
- vertical zonation
- Littoral (top)
- Sublitoral (Infralittoral & Circalittoral)
picture of infralittoral kelp forest zonation
currents and hydrodynamics as horizontal gradients
strong horizontal gradient e.g. in caves
- caves can have particularly variable hydrodynamic conditions
- open tunnels with strong currents
- dead and caves with strong hydrodynamic confinement
- caves also create strong light vertical gradient
- direct effect/ influence of hydrodynamics on organisms:
–> substrate stability
–> availability of food and oxygen
–> sediment deposition
–> larval dispersion
zonation in caves
- the zonation in caves is similar to vertical zonation
- Less organisms in dark areas because it’s a stressed type of environment
- Submerged sea caves are confined environments.
- Gradients of hydrodynamics, light, food
Disturbances in SRR
- ice scour interact with rock
- Hurricanes in particular in tropical area and have effect on rocky shores
- Anchoring as a disturbance from humans
- Trawling
-the more shallow, the greater the disturbance –> the more down, the more stable
physical disturbances
(shallow/interdidal vs deeper water)
e.g. Thermal stress:
- high in intertidal and high in thermocline-zone
- Usually Thermocline: higher temp., then stabilizes at a certain point
- Now: thermocline is not stable any longer, moving more and more deeper
- If thermocline moves it’s a stressful area
- Now it’s far more unpredictable
- it is a STRESS factor here (not disturbance)
- only above dotted line is disturbance
where is the variability of assemblages in SRR larger?
larger in shallow water than in deep water assemblages
picture:
- Blue: plot looks the same, not many transitions
- Red: every time different, a lot of changes, high number of transition
surfaces have larger wave action, lots of disturbance, different temp.
variations in shore geometry and inclination
- they have smaller scale gradients
- overhang: usually organisms with neg. phototactic type of larval behavior, where they can be attached on upside down
microhabitat heterogeneity
- Organisms create their habitat themselves (calcareous substratum is very different from the ground)
- heterogeneity in substratum
- heterogeneity in chemical composition
effects of sedimentation on rocky shore assemblages
- presence of sediments affect structure and functioning of rocky shore assemblages
- sediments can naturally be present
- sediment inputs are often altered by human activities
sources of sediment
- Discharges by rivers and river runoffs
- Coastal Namibia because of dynomite mining
- Comes a lot from poor human management
- accelerated soil erosion due to clearing of forested catchments for agriculture
- mining
- beach nourishment
predictability of spatial and temporal variability of sediment deposition
- predictability varies
- Sedimentation and amount of sediment is more predictable at a a larger scale
- Differences for shore exposure:
more predictable on shelter than exposed shores - it becomes less predictable as you narrow the scale
- Sediment distribution in a very heterogeneous way –> lot of unpredictability
how can sediment deposition be controlled?
- by organisms
- healthy canopy algae limit excess sediment deposition
- they maintain an optimal environment for their persistence
- if there is no canopy –> then there is lots of light –> high sediment cover (why??)
mechanisms by which sediments affect rocky reef assemblages
- burial / smothering (Verschüttung/Ersticken)
- scour/abrasion by moving sediments (Auskolkung/Abtragung durch bewegte Sedimente)
- changes in the physical characteristics of the
bottom surface (even a thin layer on hard-bottom can stop recruitment of macroalgae) - the sediment increases turbidity and disrupts photosynthesis
- potential interactions with organic and inorganic pollutants
- potential indirect effects by altered bathymetry, wave and current regimes
reported effects of sedimentation on rocky shore assemblages
- effects can be variable depending on many factors:
- Effects species-specific
- Direct effects on individual species or their propagules and indirect effects through mediation of competitive and/or predator-prey outcomes
- Variable effects depending on levels and composition/size of sediments
- Variable effects depending on the scale of observation
- Variable effects depending on other physical and biological factors (hydrodinamics, stage of development of recipient assemblages, etc)
spatal interactions as a biotic factor influencing the distribution ,dynamics and structure of rocky shore communities
- Spatial relationship are crucial in buildup of coralligenous assemblages
- Top: A is dominant, no matter how distributed und combined
- bottom: depending on special position A or B or C wins
classical studies on trophic cascades (as a biotic factor influencing the distribution ,dynamics and structure of rocky shore communities)
- Species from high trophic levels control the abundance and composition of species belonging to lower trophic levels (top down control)
- The removal of sea otters caused an explosion of sea urchins with a consequent increase in the grazing of macroalgae
predators control macroalgal vertical distribution
(kelp distribution with and without otters)
Vertical distribution of seaweeds
- Not only on light
- Also determined by interaction light limitation and sea urchin predation
Left graph: seaotters
- Can only dive to certain depth
- Kelps very abundant at survace bec. No urchin because seaotters eat them
- kelps controlled by light
Right: seaotters have disappeared
- Sea urchin very abundant at surface
- Kelp not controlled by light but by predation
Trophic cascades in the Mediterranean sea
- If system protected from fishery –> seaweeds come back
- Because the urchins are controlled
- if there are many urchins: clear water + problem of overfishing
facilitation in subtotal habitats
- Urchin don’t like anemonia (similar to barnacles create obstacle for limpets)
- Absolute reduction of grazing as function of (anemonia?)
- Max. facilitation when a few grazers are in system
