ELEMENTS OF OCEANOGRAPHY

 

Topic 18 - Marine Biological Ecosystems

Overheads (three lectures):

Biological Definitions
Plankton - organisms that float suspended in the water column and have insufficient swimming ability to avoid transport by ocean currents
Nekton - strongly swimming organisms such as fish, mammals, and squid
Benthos - organisms that live in intimate contact with the ocean floor

Ecology of Open Ocean Ecosystems
Plankton live in photic zone
Herbiverous plankton and nekton live in photic zone, some graze on plant material throughout the water column
Carnivorous nexton live mostly below the photic zone, move vertically in search of food
Omnivorous nekton are most common at bathyl depths
Detritus feeders tend to occur at depths greater than carnivores

Phytoplankton in Open Ocean Ecosystems
Types of phytoplankton (autotrophs)
cyanobacteria - blue-green algae
diatoms (siliceous shells)
silicoflagellates (siliceous shells)
coccolithophores (carbonate shells)
Key factors in phytoplankton growth
nutrients
light
temperature
means of staying afloat in photic zone

Zooplankton in Open Ocean Ecosystems
Types of zooplankton (heterotrophs)
foraminifera (carbonate shells)
radiolarians (siliceous shells)
copepods and krill (crustaceans)
Key factors in zooplankton growth
must efficiently find food
must maintain position in water column
must avoid predators

Plankton and Predation
There are two basic ways for phytoplankton to avoid getting eaten
by their small size (hard to see)
by their translucent color (hard to see)
There are two extra ways for zooplankton to avoid getting eaten
schooling (harder for bigger predators to get at them)
vertical migration - stay in aphotic zone during daylight hours, rise to eat at night

Nekton in Open Ocean Ecosystems
Types of nekton (free swimmers)
Fish - bony fish (most common), catilaginous fish (sharks, rays)
Sea mammals - whales, seals, porpoises, dolphins
Birds
Reptiles - sea snakes, turtles
Squid

Nekton Growth Factors
Swimming ability - need streamlined cross-section for minimal drag
Buoyancy - need specialized adaptations to help keep afloat (air sacs, liquid fats)
Search for prey - most food searches occur at night or in aphotic zone; need sonar or keen eyesight to find prey

Deep Sea Ecosystems - I
Distinctive and controlling factors are:
cold water (-1° to 5°C)
aphotic environment
very high pressure (200-2000 times P at sea level)
typically muddy bottoms
regionally strong currents
Biomass decreases with depth in open ocean and distance from coastline - most organisms are detritus or filter feeders

Deep Sea Ecosystems - II
Benthos
epifaunal - crabs, star fish, sea urchins
infaunal - worms and molluscs
sessile benthic - sea fans, sea anemones
Nekton
deep sea fish (phosphorescent)
squid (giant squid)

Unusual Deep-Sea Benthic Ecosystems
Degree of anoxia controls type and number of benthic organisms
Bacterial mats and little else grows in truly anoxic basins
Hydrothermal vent type systems can grow around whale carcasses and oil seeps

Hydrothermal Vent and Cold Seep Ecosystems
These are deep sea benthic ecosystems that depend on chemosynthetic bacteria for food
Bacteria commonly live in symbiosis with giant clams and worms
Strong venting of hot or cold nutrient-rich brines is the controlling factor on the community growth potential
Very limited spatial domains but extremely high biomass per unit area - how do new communities develop?

Coastal Marine Ecosystems
All have plant and animal communities which extend from euphotic zone to ocean bottom
Key factors which control diversity and biomass are
wave activity
range of daily and seasonal temperature
amount of light
supply of nutrients
substrate
Rocky Shore Ecosystem
Typical of high relief coastlines
Biological zones are defined on the basis of degree of exposure during daily tidal cycle
Key factors in growth
avoid drying out
avoid overheating
avoid getting broken up by wave action

Rocky Shore Biological Zones
Periwinkle zone - edge of high tide; many small snails which brows on algae; live in rock cracks, under rocks, or in rock borings
Barnacle zone - below Periwinkle zone, high density populations attached to hard surfaces; filter feeders
Predatory snail, limpet, mussel, and barnacle zone - Snails feed on mussels and barnacles; limpets browse on algae; mussels and barnacles are filter feeders
Tide pools - contain animals that require more protection from wave action; sea anemones, fish, crabs

Kelp Forests
Kelp forests develop on rocky coastlines in the sublittoral zone
Key factors are cool temperatures (<18°C), currents and wave activity, hard substrate
Dominant organisms are giant algae called kelp; anchored at bottom and grow like trees
Many animals live on and below kelp and use kelp forest as protection from predators
Main consumer of kelp are sea urchins - kept in check by sea otters

Sandy Shore/Shelf Ecosystem
Substrate is unconsolidated sand and silt due to moderate/strong wave action
Prime of most animals is burrowing; either filter or deposit feeders
Most common inhabitants are clams, snails,sand dollars, and crabs
Predators are mostly birds, sea otters, seals

Muddy Shore/Shelf Ecosystem
Distal shelf below wave action, protected estuaries or lagoons
Key factors for growth - high organic flux, limited oxygen
Dominant organisms are infaunal clams, worms, snails

 

Return to Table of Contents