•
Submerged edge of the continents
Richest part of the ocean
•
Includes world’s most important fishing grounds (90% of total global catch)
•
Oil and minerals have been found on it
Profoundly affected by pollution on other activities of humans on land

•
Never exposed at low tide
•
Extends from the low tide level on shore to the shelf break (outer edge of continental shelf)
•
Benthos of the continental shelf live in the subtidal zone
•
Plankton and nekton over the continental shelf are part of the nertic zone

Factors that affect subtidal organisms are linked to two of the shelf’s fundamental characteristics:

• temperature varies from place to place one of the most important factors effecting distribution of organisms
•
Bottom affected by waves and currents – prevents stratification and nutrients do not concentrate in the bottom layer

•
Nutrients are brought in by rivers
Water over the continental shelf is far more productive and plankton rich than the open ocean
•
Water has a greenish tint from the phytoplankton and the decaying organic matter
•
Freshwater runoff can lower the salinity

•
Of great influence because of the proximity to land and the shallow water
•
The settling of sediment particles from the water
•
Most sediments are lithogenous (sediment that comes from the physical and chemical breakdown of rocks on land)

1.Wind transported
2. Shore erosion
3. Transport by rivers
4. Transport by ground water
5. Yields of biological and chemical processes
6. Transport by icebergs and floating ice
7. Volcanic eruptions

•
Abundant phytoplankton and the sediment from rivers and stirred up by waves and currents make shelf water murkier than the open ocean
•
Light does not penetrate as deeply which reduces the depth that primary producers can live

•
The type of substrate is very important in determining which particular organisms inhabit the floor of the continental shelf

Soft-Bottom Subtidal Communities
•
Sandy and muddy substrates dominate the world’s continental shelves
•
There are distinct communities whose distribution is greatly influenced by such factors as the particle size and stability of the sediments, light and temperature

•
Infauna predominate, some epifauna, sessile organisms are rare
•
There are higher numbers of organisms on soft bottoms in the subtidal zone as compared to the intertidal zone

•
Desiccation is not a problem
•
No drastic temperature changes
Minimal salinity changes
•
Stable environment

•
Patchy
•
Organisms are in distinct clumps
•
Caused by different sediment types

Unvegetated Soft-Bottom Communities
•
Lack significant amounts of seaweeds or sea grasses
•
Main primary producers are diatoms
•
Detritus is a very important food source for many inhabitants

•
Polychaets
Trumpet worms ( Pectinaria ) •
Bamboo worms (
Lugworms (
Clymenella
Arenicola )
)
•
Heart Urchins (
Sand Dollars (
Spatangus
Dendraster )
)
•
Echiurans, peanut worms, sea cucumbers and ghost shrimps (Callianassa)

Trumpet worm
Lugworm
Bamboo Worm
Sea Cucumber

Heart Urchin
Ghost Shrimp

Suspension Feeders (Filter Feeders)
•
Clams
Razor clams •
Quahog (
Cockles
Mercenaria mercenaria )
•
Soft-shelled clam (
Amphipods
Mya arenaria )
•
Polychaetes (parchment worms and terebellids)

Quahog
Soft Shell clam

Distribution of burrowing deposit and suspension feeders is influenced by several factors:

•
Deposit feeders predominant in muddy sediments
•
Suspension feeders – sandy bottoms

2. Type of Organisms present affects the establishment of others
•
Deposit feeders exclude suspension feeders
Bioturbators – move sediment while burrowing or feeding

•
Deposit Feeders
–
Brittle stars amphipods •
Scavengers
Shrimps ( Penaeus ) •
Predators
Whelks ( Nassarius
Moon snails (
)
Polinices )

•
Blue crab (
Lady Crab (
Callinectes sapidus
Ovalipes ocellatus )
)
•
Hermit crabs
Lobsters • octopuses
Sea Stars ( Astropecten ) prey on:
•
–
–
Clams
Brittle stars
Polychaetes
Predatory amphipod

Bottom Dwelling fishes of the soft bottom community
•
Rays
Skates
•
Flounders
Halibuts
•
Soles
Tubots

Ray
Flounder
Sole

Skate
Skate

Halibut

•
Soft bottoms along the coast are occasionally carpeted by seagrasses
•
Flowering plants, grass-like in appearance but unrelated to true grasses
•
Develop best in sheltered, shallow water along the coast
•
Also found in estuaries and association with mangrove forests

•
50 to 60 species of sea grasses
Most are tropical and subtropical
•
Several species are common – Eelgrass
(
•
Zostera marina )
Form thick luxuriant beds
•
Their roots keep them anchored in the face of turbulence

Eel Grass

•
Stabilize the soft bottom
Leaves cut down wave action and currents
•
More and finer sediment can be deposited which affects colonization by other organisms

•
Sea grass beds have a higher primary production than anywhere else on soft bottoms •
Rank among the most productive communities in the entire ocean •
Part of the reason: true roots – able to absorb nutrients from sediment •
Increased by algae growing on the surface of the sea grass - epiphytes

•
Sea turtles
Mantees
•
•
Sea urchins (
Parrotfishes (
Birds
Diadema, Lytechinus
Sparisoma )
)

Diadema

Ways that animals take advantage of high primary production of seagrasses:
•
Feed on the large amounts of decaying leaves and seaweeds
•
Offer shelter
•
Animals live on the leaves: hydroids, snails, tiny tube dwelling polychaetes, amphipods, shrimps

Larger animals that live among the plants:
•
Queen conch ( Strombus )
•
Clams
Pen shell ( Pinna carnea )
•
Nurseries for commercially available species

Queen conch (Strombus)
Pen shell (Pinna carnea)

•
Relatively small portion of the continental shelf
•
In some cases a significant component of the hard substrate is provided by calcareous algae, tubes of polychaete worms and oyster shells
•
Often called reefs

•
Never subject to desiccation
Wider variety of organisms
• are rich and productive
Seaweeds – most conspicuous inhabitants

•
Brown and red
Filamentous ( Chordaria, Ceramium )
•
Branched ( Agardhiella, Desmarestia
Thin and leafy ( Porphyra, Gigartina )
)
•
Encrusting ( Lithothamnion
All have holdfasts
)

Chordaria Agardhiella

Lithothamnion

•
One of the main problems for seaweeds and sessile animals in the subtidal is to find a place to attach
•
There is intense competition for living space
•
Rich epifauna and poor infauna

•
Sponges
Hydroids •
Sea anemones
Soft corals •
Bryozoans
Tube-dwelling polychaetes •
Barnacles
Sea squirts

Bryozoans

Sea Squirts

•
Small, slowing moving invertebrates
Sea urchins ( Arbacia, Diadema,
Stronglyocentrotus )
•
Chitons
•
Limpets
Sea hares
•
Abalones

Abalones

Seaweed defenses against grazing
•
Chemicals such as sulfuric acid and phenols
Can rapidly regrow
•
Tough and leathery
Calcareous algae ( Lithothamnion,
Clathromorphum, Halimeda ) deposit calcium carbonate in their cell walls

•
Feed on attached invertebrates
Sea urchins – seaweeds and flimsier attached invertebrates
•
Crabs
•
Lobsters
Fish
•
Grazers and predators strongly influence the composition of hard-bottom communities

•
Kelps are a group of large brown seaweeds that live in relatively cold water and are restricted to temperate and sub polar regions
•
True giants
Home to a vast assortment of organisms

•
North Atlantic and Asiatic coast
Blades 3 m or 10 ft long

•
Macrocystis
•
Pacific coasts of north and south America
•
Stipe – 20 to 30 m in length

•
Kelp beds – large dense patches of kelp
•
Kelp forests – when the fronds of the kelp beds float at the surface
•
Canopy – floating tops of kelps at the surface

Physical Factors that influence kelp
Communities
•
Temperature – must be cool
Do not do well where there is heavy wave action – fragile
•
Prefer to attach to deep bottoms where wave action is reduced

•
Kelps can grow very fast with the giant kelp growing as fast as 50 cm/day ( 20 in/day)
•
Kelp communities are very productive

Organisms found within the kelp beds
•
•
Polychaetes
Small crustaceans
Brittle stars
Tube-dwelling polychaetes •
•
Lace-like bryozoans (
Sponges
Sea squirts
Lobsters
Membranipora )
•
Crabs
Hermit crabs •
•
Sea stars
Abalones octopuses

•
Rockfishes (
Kelp bass (
Sebastes )
Paralabrax clathratus )
•
California sheephead ( Semicossyohus pulcher ) eats sea urchins, crabs)
•
Surf perches (
Topsmelts (
Rhacochilus, Brachyistius
Atherinops ) – plankton
) feeders

•
Snails
•
Crabs
Sea urchins
•
Fishes
Few eat kelps

•
Most important grazers in kelp communities
•
Most important species – red
( Strongylocentrotus franciscanus ), purple ( urchin (
S. purpuratus ) and green sea
S. droebachiensis)

•
Populations sometimes explode (known as plagues)
•
Normally urchins feed on drifting kelp
During a plague urchins eat attached kelp and can clear large areas – urchin barrens or urchin deserts
•
Sea otters can help maintain urchin populations