8.2 Canopy Forming Seaweeds Flashcards
what are canopy forming seaweeds?
- Kelps, fucoids and other complex, erect mainly brown macroalgae that produce relatively large biogenic habitats
- They include some of the largest marine algae, with thallus divided into basal part, stem and frond.
life cycle of fucoids (Facales)
- fucoids are diploid
- life cycle is a diploid monogenetic cycle
- reproduction through gametes
- gametes produced by meiosis
- gametes carried by antheridia and oogones (found within apical male and female conceptacles)
- fertilization in water
- new diploid plants will be generated again from the zygote
life cycle of kelps (Laminariales)
- haplodiplont cycle
- alternation of two morphologically distinct phases:
1) diploid sporophyte (macroscopic)
2) haploid gametophyte (microscopic)
Distribution of canopy forming seaweeds
(facts and map)
- widespread on shallow hard substrata
- in temperate and polar coastal ecosystems
- main genera along coasts of north-west Europe: Laminaria and Fucus
- main genera in Mediterranean Sea: Cystoseira and Sargassum
facts about canopy forming FOUNDATION species
- they modify light, flow, sedimentation and nutrients
- they buffer erosion
- they are nursery areas
- highly productive
- habitat for diverse assemblages
human usage
- food
- cosmetics
- fertilizer
- stabilizers and emulsifiers
- medicines
- thalassotherapy
estimated value of canopy habitats
these systems (canopy forming seaweeds) are___ ?
- naturally dynamic
- resilient
- have a generally rapid recovery from disturbances (ms to a few years)
they are influenced by
- dispersal
- biotic interactions (competition with understory species, herbivores)
- habitat characteristics
retraction of canopies
where?
(Rückgang)
documented widespread range retractions and declines since 1900’s in
- Europe (examples of Sweden and Mediterranean Sea were shown in slides)
- North and South America
- Japan
- Korea
- South Africa
- Australia
- New Zealand
- Alaska
what are canopies replaced by?
- turfs
- ephemeral algae
- mussels
- barrens
what are algal turfs?
- they are loosely to densely aggregated thalli
- < 15cm tall
- composed of more or 1 species
- often associated with sediments (sediment-trapping morphology)
- covering large areas
global map of canopy-shifts to turf
where are losses particularly severe?
- in urban areas
- e.g. Italy:
- 13 sites around Italy
- 40% of losses of C. compress explained by urban-related indicatorsw
what are canopy-losses accelerated by?
- climatic changes
- drives shifts in species compositions (e.g. Laminaria along
- Shift from canopy to less complex systems is globally happening
- Functional consequence?
- here: example of temperate seaweeds
- System shifty in many different ways
- lost and replaced by b, c, d
b) function don’t change too much
most similar to system befor
novel system with similar function
c) d) different system , diff. species and functions
multiple stressors that drive changes in kelp forests
- pollution
- fishing
- harvesting
- invasions
- herbivory
- warming
- others
conceptual models of canopy shifts
most likely drivers of loss here:
- decreased water quality through sedimentation
- cascading effects from overfishing (as Orcas/Alaska example)
- regression of macroalgal canopies –> turfs, ephemeral algae, mussel or barrens
-2 main types of alternatives: turfs and urchin
- in the conceptual model, two pressures are always there: x + y aches
- Low water quality from canopy to turf
In one case its barren (urchin), in other one turf, different, but in both we lose
cascading effects of predator removal
graph showing temporal trends in kelp forests where otters (predators) and sea urchins are present (Alaska)
- arrows indicate the timing of change in major community-changing forcing functions
- width of arrowheads indicates magnitude of the forcing function’s impact
graph showing temporal trends in kelp forests and sea urchins (Gulf of Maine)
Urchin dominant-> loss of kelp -> fishing urchin –> kelp comes back
Northern California - trophic cascade (fishery, urchin, kelp, barrens)
- Strongly dominated by fishery
- Start of fishing urchins: kelp came back
graph showing temporal trends in kelp forests and sea urchins (Nova Scotia, Canada)
- Extremely fluctuating system
Southern California - Trophic Cascade
graph showing temporal trends in kelp forests and sea urchins (California)
- When top control removed, other factors come in to control
- Strongly dominated by el nino
what is one of the main drivers of the loss of canopy forming algae and their turf-replacement?
enhanced sedimentation
what happens when sediments interact with other types of pollution?
- other types like nutrients or acidification
- greater negative effects than alone
why are turfs so stable?
Sedimentation mediates interactions between canopies and turfs via direct and indirect effects:
- Turfs accumulate sediments and can trap large amounts
- Accumulation of sediments deters grazers: Herbivores are generally sparse in areas with high sediment loads
- Accumulation of sediments inhibits the recruitment of erect algae that compete for space with turf: Sediment virtually precludes settlement, and reduces survival of germlings by >50%
the shift from kelp forest to turf can be accelerated by ___ ?
name some negative effects on kelps
1) climatic stressors as heat
- that can delay the population recovery (germlings survival higher under low temperatures)
- ocean warming can increase herbivorous fish pressure
2) increased storminess
-storms may destroy recruitment which was consistent
3) other stressors such as herbivores
4) increased substratum instability
5) water quality/ sediment accumulation
–> Meta-analysis shows, that ultimate effect on seaweed is driven by combination of many factors (e.g. overfishing, water quality…)
can the management of local stressors remediate for the impact of global stressors?
- Systems were stressed before (local stressors)
- “now” climate change comes on top (global stressor)
- global stressor will not change but can situation be improved if local stressors are improved?
can canopies actively be restored where natural recovery is low? give examples
- If you just protect they will hardly recover
–> active restoration needed
example 1
- crayweed restoration (Sydney, 2014)
- First: driver removed but seaweeds didn’t come back
- then: Decided for active restoration
- big and worldwide success
example 2
- Kang et al. 2008 at east and south coasts of Korea
- In 2003 restoration using a combination of transplants of adults on artificial reefs
- In 2005 complete recovery of macroalgal community structure and trophic food webs
what are challenges in reforestation of canopy forming seaweeds
- biotic disturbance
- scientific challenges (e.g. herbivory very high at urban sites as compared to nearby rocky reefs)
- practical challenges (e.g. identifying cost-effective tools to protect reforestation efforts)
- economic challenges (–> expensive)
- conceptual challenges (–> what do you want to/ decide to restore in the end?
Restoration doesn’t put exactly back what used to be there before
Going back to what used to be ther?
Saving functions? /services?)
