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
water quality is declining, why?
- Oceans long regarded as a dumping ground for humans
- Changes are more difficult to see and so are easy to ignore
changes to water quality can include ___ ?
- increased nutrient loads
- enhanced sedimentation rates
- turbidity
- reduced light penetration (needed
for photosynthesis) - increased temperatures
- altered salinity regimes
- harmful algal blooms
- toxins, herbicides and heavy metal
pollutants
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
examples of recovery from barrens
1)
- in southeast Alaska
- kelp beds recovered after reestablishment of sea otters
- due to local protection
2)
- over-fishing in a Reserve, New Zealand
- declared unproductive when sea urchins und unproductive barrens habitat was dominating (1997)
- by 2003 , large predaory fish and lobsters had returned, urchin populations had declined, and lush kelp forests returned
- But: this community change was recent and highlighted a time-lag effect of protection
loss of canopy forming algae in the mediterranean sea due to ___ ?
- date mussel fishery
recovery from barren to canopy can be difficult, why?
- Many habitats have not recovered yet as the empty holes enhance sea urchins recruitment
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%
feedback mechanisms that pave the shifts between canopies and turfs
- pulse sedimentation events (e.g. beach nourishment) remove canopy algae
- sediment no longer removed by canopies accumulates
- accumulation of sediments favours development of turfs which further bound and stabilize sediments
- algal turfs replace and prevent re-establishment of productive canopy forests
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…)
synergistic
Synergistic: resulting effect is greater than the sum of independent effects (greater effect)
prevalence of synergistic interactions between nutrients and other global stressors leads to ___ ?
- Synergistic interactions between nutrient
enrichment and the presence of competitors, low light, and increasing temperature, leading to amplified negative effects on canopy- forming algae. - Synergistic interactions between nutrient enrichment and increasing CO2 and temperature leading to amplified positive effects on mat-forming algae.
—-> Nutrients are major player in issues of our system: if you can improve that factor, it has a major effect and improvement because it acts synergistic with so many others
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?
experiment: can the management of local stressors improve the resilience of Marine Canopy Algae to global stressors?
- yes
- different climatic scenarios and management scenarios were tested in an experiment
- Cystoseira doesn’t recruit when there is sediment (NM = no management)
- Ranking: sediment removal, because it has a high effect on recruitment
- Also Nutrients
- is is a matter of HOW to manage climate change factors, because systems can (!)
- Connectivity as very important gradient (be aware when managing)
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 the most common approaches to restore canopy forming seaweeds
- adult-plant transplantation on either natural or artificial substrata
- transplantation of juveniles either collected or intercepted in the field by using artificial panels or cultured indoor
- seeding of germling in the field (generally associated with creation of artificial habitats)
- use of “fertile mesh-bags” packed with fertile, adult plants suspended over rocky substrata or artificial reefs during the reproductive season
- Enhancement of natural recruitment e.g. by using chemical fiber fabrics
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?)
what can buffer the impact of global stressors?
coordinated remediation of local stressors (e.g. water quality) - at least temporarily
