Chapter 8 Continental shelves!!!. Intro! Only 8% of global sea surface Mostly falls in the euphotic zone o Its shallow Areas that have narrow shelves.

Chapter 8Continental shelves!!!

Intro!• Only 8% of global sea surface• Mostly falls in the euphotic zone

o Its shallow

• Areas that have narrow shelves there is also upwelling which helps the production

• The shelves fuel of 90% world’s fisheries• Are affected by human influences

Continental shelves!• The shelf goes from the extreme low-water mark on

the shore line about 200 m deep• Its considered neritic

• Continues till shelf break (anywhere from 0-1500km offshore )• Usually has a shallow gradient of 1˚• Strongly influenced by physical forcing (physical processes like waves)

because they are really close to shore

• Waves affect ecology of the shallower parts of the shelf

• Effects on benthic ecology go to about 80m • Fetch is the uninterrupted distance over which winds

exert friction at the sea surface• http://www.youtube.com/watch?v=v0OYJzyxAZc

Currents and water… • Currents are increased when a water mass moves

through or around land bounded restrictions, or across irregularities in seabed topographyo Straights and estuaries typically have typically have the strongest tideso Headlands and bedrock cause tides to be strong around the apex of the

headlando Irregularities in seabed cause friction so the current slows down

Fronts!• Fronts occur at a point where stratified water and

mixed water meet• Results in density gravity dient between the two

bodies of water• Causes an influx of nutrients • Causes more productivity• Can also happen near estuaries

o mixing of waters with different densities. o Causes a frontal systemo Can deflect the current away from the shore with aid from the

Coriolis affect o Called Regions Of Freshwater Influence (ROFIs)

Depth and turbitity• Depth and turbidity are important determining

factors of the locations of benthic algae• Areas affected by estuarine plumes are usually very

light limited• Caused by suspended sediment and photodetritus

o These places are mostly lived in by animals

• Coastal areas that are open to the ocean are much clearero Algae can be found almost everywhere there

• Clear zonation from the shallow water to the deepero Green (shallow), brown, red (deep)o In these situations algae are dominant in biomasso Width of algae dominance depends on water clarity and slope of

sea bed

Animals and stuff• Processes vary with morphology of the seabed and

coast• Body size affects both production processes and how

much a specific life form is associated with a specific placeo Size of animals living on seabed is constrained by ability to burrow and respireo Size of attached animals are limited by physical processes

• Sheer due to current speed • Mobility of organism varies

o Highly mobile fish and o Anemones that can move a few mm a dayo Others cemented to the rock

• Mobility affects the ability to respond to environmental change

• Places a limit on how much they can use the enviroment

More animals…• Grouping are based on body size

o Macrofauna • Anything larger than meiofauna• Most research has been done on them

o Easiest to study o Meiofauna

• Organisms that would pass through a sieve with a mesh diameter of .5mm but would be restrained by mesh of .063 mm

• Least studied but most diverse • Rates of production is much higher than larger macrofauna

• Make very indication of environmental stress• http://www.youtube.com/watch?v=x_xyQFGId3g

Yaaay.. Yet more animals

Microbiota• Contribution is often underrepresented

o In tropics can be much greater than the others combined

• Body size and longevity are factors that affect recovery time

• Smaller organisms take less time to recover• Organisms are also categorized by relative

position on seabed• http://www.youtube.com/watch?v=t8nodTdbRqc

Things that live in sand…

Epibiota organism• Emergent organisms that are anchored in or on substratum or free

living organisms that move on surface of substratum• Algae are almost exclusively epibenthicGrow attached to

substratumo Sometimes calcareous algae form their own habitats

Infaunal organisms• Live buried within substratum

o Entirelyo Partialy

Movement! • Sessile organisms show seasonal patterns of

growth at high latitudes• Mobile organisms show varying level of inshore/

offshore movement due to temperature • Many crabs and lobsters move inshore during

spring and summer to find mateso Then move back during winter to avoid storms

• Distribution of bottom dwelling fish in regional seas are linked to certain habitat types

Yay fish and movement• At mid-high latitudes fish are associated with a

range of habitatso Variation can be attributed to different behavioral characteristics at

different life stages• Juveniles are vary picky of sediment grain sizes

o Needs more protectiono Limits places it can live

• Adults are less picky o They can live more places

Feeding• Nearly all predators will also eat carrion

o Even herbivorous sea urchins and suspension feeders will eat carrion• They are known as facultative scavengers. (Will eat carrion if there

is nothing else). • Obligate scavengers are debated to exist. (Only eats carrion)

o Candidates would have to be <6 mm o There have been lots of possible species but no conclusive

evidence.

Food… again• Maintain diversity within algal-dominated

community.• Herbivory in fish is more common toward lower

Lat. In higher lat. Herbivores are mostly invertebrates.o In systems where a specific species is the predominant grazer they can

have a key-stone role or eco-engineering role because they eat certain algae.

• Grazers also include carnivores• Evolutionary arms race:race for one species to

evolve into something that the predator can’t eat vs. the predator trying to evolve to beat those defenses

Feeding.. Yet again• Filter Feeders: extract phytoplankton from water

column and suspended mater from just above the seabed (suspension feeding)o Individual animal (about 1g dry weight) filters about 57 liters of water a

day o Have an important role in Bento-pelagic coupling

• Waste is rich in organic material that is processed by microbial community which feeds the suspension feeders and bulk sediment processers

More things• Organisms can have both a stabilizing and

destabilizing role in communities. o Cumulative effect of all sediment disturbances known as bioterbation.

• They left what’s called trace fosils in rocks • They enhance the passage of oxygen rich water deeper than into

the sediment than it usually would go. • Increases sediment porosity

o Burrows made by high density organisms can expose 1.4 m2 o Sediment conveyors- transfer nutrients deeper into the sediment

• http://www.youtube.com/watch?v=9SK5amoShPE

Cascades and stuff• The flexibility in feeding patterns leads to

compicationso if you remove species from system, the system isn’t likely to cause

significant cascade effects at either end.

o Resilience can weaken when human interference and environmental change happen simultaneously.

o Simple systems like this are expected in high diverse systems that are characterized by specilized feeding interactions

o Interactions in cascades are between organisms from major trophic levels ithin systems(Predator-Herbivore-Primary producer)

o Key predators or herbivores in trophic cascades are usually the dominent organisms in their trophic level

Organisms• Often can be ecosystem-engineering biota.

• They are organisms that due to their abundance or feeding or other activities, exert a strong influence on the structure of the ecosystem

• When the link between one trophic level is strong that means that when there is a significant decrease in the pop of a predator/herbivore, there are few others to take their place

• Habitat is composed of :o Non biologic material

• Biogenic material• Things that came from living things (broken shells)• biota(living things)• Prevailing water-column conditions above

o Normally depends on interaction between seabed hardness and stability o Sediments dominate the seabed habitat of the continental shelf

• Very according to:o Tectonic historyo quantity and quality of the inputs from riverso transport by currents and waves

Surfaces• Hard substrata is rather rare

o Strata categorized as:• hard (bedrock to cobble• Soft (gravel to mud) • Biogenic habitats

• Bedrock is most stable • Provides an archer for sessile life forms

o Occupied by crusting things

• Really important for algaeo Creates the ability for kelp forrests

• Rocks with lots of relief, such as rock reefs also create microhabitats

• http://www.youtube.com/watch?v=GcbU4bfkDA4

Fooooood• Dominated by particle feeders

o The crevices permit the exchange well oxygenated water• provide a hiding place from predators

o Many species of fish use these places for refuge when they are growing up

• Fishery’s have tried to increase the available habitats by creating artifical reefs

• The size of substrata is mostly determined by physical processes and are subject to frequent disterbances o When the physical processes weaken and there are less physical forces

• There are more biological and chemical sedimentso Stability of sedimentary habitats depends on interaction of physical,

chemical and biological processes

• http://www.youtube.com/watch?v=XiSU0n0EFoE

Size of things in the ocean

• The size of substrata is mostly determined by physical processes and are subject to frequent disterbanceo When the physical processes weaken and there are more fine

sediments• There are more biological and chemical sediments

o Stability of sedimentary habitats depends on interaction of physical , chemical and biological processes

• Typically described by their partical size• We can only get partial info from this technique• Doesn’t tell us about how the different types of sediment pack

togethero We can’t tell the porosity or anything that we can learn from

knowing the porosity

Sediments… yaay..• Near-shore sediments less than 30m deep are

often moved by wave actionso Almost no sessile life formso Highly mobile organisms most common

• In deeper water (more than 50m deep) or in shallow sheltered areas:o Finer sediments settle out due to redused physical forcingo Lots of burrowing amimals that shape seaflooro Mostly crustaceans and shrimp live here

• Many semi-enclosed seas and fjordic areas have mud communities o Weak currentso Sheltered o Heavy stratification durring summer

Reefs…. kinda….o Can be made entirely by reef building organisms

• Formed by bivalves, corals (hermatypic vs. ahermatypic) and sponges

• Can be made by accumulations of things , inorganic or organic material