Marine Ecology Chapter 10

Ecology The study of the interactions between organisms and their environment. Also studies how these interactions affect the abundance and distribution of populations.

How populations grow When conditions are right, populations will grow exponentially. That means, with unlimited food, shelter and space- there is a population explosion. Abiotic (environmental) factors can reduce population growth. Biotic factors (crowding, competition, disease) can affect population growth.

Unchecked population growth in dinoflagellates

Exponential growth

Explosions in the population of sea urchins can affect the entire ecosystem.

As the population increases, the amount of nutrients decreases.

Carrying capacity The largest population that can be sustained by available resources. Limiting resource- a resource whose short supply restricts population growth. Once the carrying capacity is reached, the population growth levels off.

Competition Organisms constantly compete for resources. Competitive exclusion- when one species outcompetes another and eliminates it. Resource partitioning- sharing of resources by specialization.

Hermit crabs compete for the best shells for protection.

Ecological niche- everyone plays a part Niche- an organisms’ role in the community. bacteria recycle nutrients, predators reduce population growth, etc. Predation- affects both the numbers of predators and the number of prey. They rely on each other.

This whale shark’s mouth is well adapted for taking in large volumes of water for filter feeding.

Predation

The ‘Arms Race’ For every predator strategy, prey evolve defenses to combat them. Ex.- spines, nematocysts, lures, camouflage. Natural Selection- favors the best predators and also the prey that can get away!

Symbiosis- one more time! Commensalism- one organisms benefits, the other is ‘indifferent’. ex- barnacles growing on the skin of whales. Mutualism- both species benefit. Ex.- coral and zooxanthellae. Parasitism- the host is harmed. Usually does not kill the host. Ex.- tapeworms in the gut of whales.

More on symbiosis Facultative symbiosis- both partners can survive without each other if they have to. Obligate symbiosis- One or both partners depend upon each other.

Energy flow through ecosystems Trophic levels- feeding levels in the pyramid of energy. “Steps in the food chain” Primary producers- phytoplankton, kelps and other seaweeds. First level, or primary consumers- eat algae. Second level, or secondary consumers- feed on the primary consumers. Third level or tertiary consumers- feed on second level. Top predators- animals like killer whales

Three step food chain in Antarctica

Food webs- a more complete picture Food webs show many different feeding relationships. Many animals have more than one food source There may be many types of primary producers.

A marine food web

Biomass and energy Each time an organism is eaten, only 10% of its energy is passed on to the predator. 90% is recycled by decomposers into the ecosystem. 1 million calories if energy in krill, only 100,000 are obtained by the whales. It takes a massive amount of primary production to sustain those at higher trophic levels.

Measuring primary productivity Productivity- expressed as the amount of carbon fixed under one square meter of sea surface in a day or a year. Includes phytoplankton and producers on the ocean floor. Gross production- total amount produced through photosynthesis. Net production- what is ‘left over’ for other organisms to eat.

Productivity is a measure of the amount of carbon compounds produced in the water column.

Methods for measuring primary productivity

A view of global primary production

Nutrient cycles Carbon cycle- Begins as carbon dioxide, is ‘fixed’ into organic compounds by photosynthesis. Passed to other consumers, is returned to environment through respiration, excretion or decomposition. Bacteria and other decomposers return carbon to carbon dioxide dissolved in seawater.

The carbon cycle in the ocean

Nitrogen cycle Nitrogen gas dissolves in ocean water. It is ‘fixed into nitrogen compounds by bacteria, then absorbed by plankton. Is passed on to consumers in the food web. Returns to nitrogen gas through death and decomposition.

Nitrogen cycle in the ocean.

Ecological Zones of the Marine Environment. Classifying the lifestyles of marine life- Benthos- organisms that live on the sea floor. Ex.- lobsters, sponges, crabs. Pelagic- live in the water column. Two types: Nekton- Pelagic free swimmers that can swim against a current. Ex. – most fish, sharks, turtles, squid. Plankton- any pelagic organism that is at the mercy of ocean currents. Ex. Phytoplankton, jellies, zooplankton.

Classifying marine environments by location- The benthic zones. Intertidal or littoral zone- between the tides. Subtidal or Sublittoral zone- Benthic area on the continental shelf. Deep sea floor- include the bathyl, abyssal, and hadal zones.

Marine environments- the Pelagic zones Neritic zone- pelagic environment above the continental shelf. Oceanic zone- past the shelf break. Divided into several ‘subzones’. Epipelagic- near the surface, first 100-200 meters. Most photosynthesis occurs here. Mesopelagic- the ‘twilight zone’. 200-1000m deep Deep sea – includes bathypelagic, abyssopelagic. Total darkness.

Figure 10.22