Temperate Rocky Reefs

Reef - ridge of jagged rock, sand, coral above or below surface of sea - supports flora and fauna

Consist of hard substrate - non-living and various types e.g. volcanic, sedimentary

Found along continental shelves - bare rock and high primary production

Mostly temperate and subtropical areas but also tropical arewas where corals can't grow e.g. deep, murky waters

Structurally complex habitats w/ lots of crevices and algae found attached to rocks

Rocky reefs with macroalgae

Forests - found when canopy-forming kelps reach sea surface

Beds - have shorter kelps don't reach surface

Both highly productive and add additional structual complexity to complex rocky reefs

Macroalgae can have zonation based on competiton an light requirements 

Kelp imporant as it:

• Maintains significant primary production and carbon sequestation
• Regulates recruitments of coastal species - provide food/shelter
• Habitat for juvenille fish (nurseries)
• Buffering and protection against waves and storms

Foundation species - species that has strong role in structuring community

Kelp = foundation species - structure and presence changes environment for others

Order Laminariales

Large, brown subtidal seaweeds

Strong holdfasts to stay attached

Dense forests on west North American coast

Brown algae = mix of different types of photosynthetic pigments

Kelp forests refer to any type of brown seaweed forming a canopy

Kelp species show convergent evolution - similar morphologies in distantly realted species

Lack 'true' leaves, stems or roots

Flat blades

• Chlorophyl concentrated here
• High SA:V = maximise nutrient absorption

Pneumatocysts - air filled to allow blades to float close to surface

• Grape to volleyball sized
• = blades closer to light

Stipe - strong, flexible link between blades and holdfast

• Shock absorption
• Photosynthetic

Holdfasts - root-like structures that keep seaweeds anchored to bottom

• Don't absorb nutrients

Algal communities change with water depth

Canopy - fronds lying on surface/midwater

• Most light
• Most wave action

Understory - front erect or close to bottom

• Less light
• Less wave action
• Highest diversity in forest
• Area of stipes

Algal turf - short clumps, filaments and encrusting algae

• Least light 
• Little/no wave influence 
• Area of holdfasts of larger kelp, invertebrates and red algae

Species requiring substrate colonise stipes e.g. tube forming polychaetes, bryzoans

Surf perches - eat small crustaceans

Topsmelt and blue rockfish - feed off plankton

Larvae of benthos

Organisms feed off kelp holdfast - small invertebrates, brittle stars, polychaetes, sea urchins, crabs

Species of adult rockfishes and kelp bass (herbivores)

California Sheephead - predator that eats crabs and sea urchins

Diversity - lower species diversity but similar functional diversity

Reproductive patterns - more livebearers and fewer sex changing species

Longevity and maturity - longer and slower due to cold temperatures slowing down life history

Diet - reduced herbivory

Factors controlling distribution:

• Substrate - hard substrates to attach
• Light - kelp needs light to photosynthesise
• Nutrients - lots of dissolved inorganic nutrients for photosynthesis
• Temperature - colder temperatures preferred

Polar systems unable to support kelp forests = ice scour and light limitation

Tropics = too hot and nutrient poor

= Limitation to temperate zones

Distribution extended in upwelling zones - riches in these places with good climate e.g. Peru

Upwelling important for kelp beds - brings cold nutrient rich waters to surface

Upwellings seasonal - vary among years e.g. El-Nino = changes in ocean currents and upwelling

El-Nino - intrustion warm waters to west = sea surface temperature increase/nutrients decrease

Causes:

• Anomalies of physical conditions = push physiological tolerance of kelps
• Storms - removes kelp and/or sea urchins
• Sea urchins getting out of control due to predators, food limitations etc.

Sea urchins = herbivores and destructive to kelp

• Normally passively feed of drift kelp 
• When drift kelp limited - feeding behaviour changes
• Aggregate into feeding 'front' = feed on live kelp and disloge them from bed floor
• = Urchin barren - kelp deforestation and replaced by crustose coraline algae
• = Change community and other species begin to colonise e.g. invertebrates
• Urchins get out of control = phase shift in ecosystems

Shifts are widely distributed - sometimes reversible - and vary in duration

Understanding tipping points for phase shift = important in maintaining ecosystems for fishing

Phase shift - large, abrupt, persistent changes in structure and function of system

Healthy abundant kelps - provide abundant detritus for urchins

Keep them in check - whiplash motion deters urchins from entering forest = prevents attachment to kelp

Physiological or environmental source of stress for kelp = promote urchins

Bottom-up control - nutrient supply and produtivity and type of primary producers = controls ecosystem structure

Top-down control - top predator controls stucture or population dynamics of ecosystem (trophic cascade)

Trophic-cascade - chain reaction within food webs = changing population densities at higher trophic levels, shifting dominance and impact of consumers in lower levels

Effects of trophic cascades - stronger in simple systems (marine)

3 different case studies

Ecosystems shift between dominated by kelp forests and urchin barrens

Frequency and duration of phases differ between regions

All these barrens are recent historical phenomenon

Sea-otter driven trophic cascade - simple food web with intermediate diversity

Sea otters feed on urchins - direct negative effect

Sea urchins feed on kelp - direct negative effect

By reducing urchin abundance, otters - indirect positive effect on kelp

When otters are hunted = kelp barrens occured

Interannual variability in top predators (killer whales) - induce interannual differences in otters, urchins, kelps

Whales begun to eat more otters - other food sources declining (most recent increase in urchin barrens could be cause

Cod - functionally similar to sea otters

Human-induced loss of predators/herbivores via fishers = increase in barrens

Humans replace top predator

Disease cycles - kill urchins and causes recovery of kelp

Recovery of kelp also encouraged crabs to migrate

• Feed on urchin larve = prevent recruitment
• Feed on diseased adult urchins

Marine fisheries create large crabs and invertebrates - feed on more larvae

California - delayed phase shifts

Otters removed many years ago but phase shifts aparent recently 

May be as many diverse consumers functionally replace otters or urchins = buffering ecosystem from change

Humans systematically remove consumers = more urchin barrents

El-Nino events cause storms, weak/no upwellings and warmer temperatures = less nutrients delivered to coast and large predators removed = more urchin barrens

Continous (linear) phase shifts:

• Paths same backwards as forward
• F1 and F2 = tipping points

Tipping points - point at which series of small changes/incidents become significant enough to cause larger, more important change

Discontinous (non-linear) phase shifts:

• Backward path not same as forward
• Hard to predict and harder to reverse

Patterns influencing kellp recolonisation and urchin feeding influences phase shifts

Threshold - change in system that leads to shift from 1 phase to other

Urchin density - threshold for creation of urchin barren phase

Reducing urchin density back not always enough to switch system back = discontinous phase shift

Feedback processes stabilise phases

Healthy kelps - processes that limit urchins = positive feedback for kelp bed and negative feedback for urchin barrents

• Spore production
• Detritus
• Whiplash

Urchins in barrents promote conditions for local urchin reproductive success and recruitment - prevent kelp from settling/thriving 

• Urchin fertilisation and settlement

Tasman sea - ocean warming hotspot

Scientists investigated changes in reef fish abundance in control fished site and MPA site - effects of climate change

Reserve sites - distinguished from fished sites by displaying:

• Recovery of large-bodied temperate species
• Resistance to colonisation by subtropical vagrants
• Less pronounced increases in community thermal index