Life on the Ocean
Chapter 13
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The marine environment is a hard ecosystem to study for several reasons: it's hard to get to; cruise down in a deep-sea submersible Are expensive to build, and to operate.
it's hard to get your samples back to the lab in one piece; Animals are built to withstand the huge pressures of great water depths, When they are brought to the surface they blow up. The whole system is permeated with hydrogen sulfide, which is the smell of rotten eggs
We can define each part of the ocean on the basis of the following characteristics:
1. 2. 3. 4. 5. 6. 7. temperature amount of light currents salinity nutrient supply water depth nature of the sediment on the bottom
TEMPERATURE
The most important, for all organisms, not just the coral. Most oceanic organisms are cold-blooded (poikilothermic). they cannot regulate their internal temp. Their body temperature is near the temperature of the water they live in. Animals that can maintain a warmer-thansurroundings internal temperature are homeothermic.
Only organisms that left the sea for land or freshwater and returned to the sea are homeothermic: Marine mammals Big fish like marlin, tuna, and tarpon are homeothermic.
METABOLISM
The process by which all organisms extract energy from food, is a chemical reaction that is strongly influenced by temperature. The warmer the temperature, the faster metabolism will be. Organisms that normally live in cooler waters may burn themselves up if taken to warmer water.
And organisms that normally live in warm waters won't have enough energy to power their vital organs, like the brain and heart, if they move to cooler waters. Organisms living in warmer waters tend to grow faster, have a faster heartbeat, reproduce more rapidly, swim more swiftly, and live shorter lives than those living in cooler waters.
Remember, AMOUNT OF DISSOLVED GAS in the ocean is also determined by temperature. Fast swimmers such as salmon, trout, and pike need to live in cold waters because their oxygen demand is high.
AMOUNT OF LIGHT
Determines how productive plants can be. determined by water depth and water turbidity (how much sediment is suspended in the water). Light is composed of different colors and most light penetrates only about 100 m into the water, less if there is much suspended sediment in the water Blue light can penetrate deepest, to about 450 m.
Green light can penetrate to about 300 m water depth, but plants do not use green light-they reflect green light. This is why plants look green to us.
The depth to which light can penetrate defines an important area to plants: the PHOTIC ZONE. Plants have enough light to photosynthesize in the photic zone. They can't photosynthesize in deeper water.
CURRENTS
determines how successful filter-feeders can be. They need some current to bring food particles their way, but not so much current that it just blows the food past. Currents can drag plankton along to colder or warmer waters than the plankton prefer.
SALINITY
We are all composed of cells that are surrounded by a membrane. That membrane can allow water to pass through it readily, but not salt. An organism's body fluids must be the same salinity as seawater, or the organism needs to exert energy to either keep water in its body, or keep water out.
The process whereby water moves across the membrane but salt doesn't is called OSMOSIS (fig. 13.15-16)
If an organism is less salty than seawater, water from the organism's body moves out (to increase its salinity). The organism will dehydrate if it doesn't actively drink water and get rid of excess salt that comes from drinking seawater.
If an organism is more salty than seawater, water from the ocean moves into the organism's body and it blows up. For higher marine organisms, such as the arthropods and chordates, the problem is the former: we are slightly less salty than seawater.
A marine fish
its salinity is only 18 parts per thousand. It loses water by osmosis to increase its salinity, but gains it by drinking. However, seawater is too salty for it, so it secretes salt via the gills, and produces hardly any urine.
NUTRIENT SUPPLY
Determines how abundant life can be. include organic compounds such as proteins, vitamins, and inorganic compounds, called 'minerals', such as calcium, magnesium, selenium, etc. Nutrients for plants are all inorganic and include nitrogen, phosphorus, potassium, and a host of others. The nutrient supply to plants is the more important. Without plants, there can be no nutrients for the animals.
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Nutrients for plants come from one of two places: runoff from continents products of chemical weathering. upwelling from the sea floor.
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Where upwelling occurs? divergent ocean currents eastern boundary currents
WATER DEPTH
determines the amount of pressure an organism experiences and the amount of light it has. Water depth defines ocean provinces. A province is an area where we expect to find similar plants and animals, depending on other environmental factors (temperature, current, salinity, nutrient supply)(f.13.19)
Provinces have different names depending on whether we are considering benthonic organisms or nektonic and planktonic organisms.
Pelagic Provinces
– (nekton, plankton)
Benthic Provinces
– epipelagic 0-200 m – littoral intertidal (foreshore) – mesopelagic 200-1000 m
– sublittoral 0-200 m (continental shelf) – bathypelagic 1000-4000 m – bathyal 200-4000 m (continental slope and rise; mid-ocean ridges)
– abyssopelagic 4000-6000 m – abyssal 4000-6000 m (abyssal plains) – hadalpelagic >6,000 m – hadal >6,000 m (trenches)
Most plankton live in the epipelagic, photic zone. Most light penetrates into the epipelagic and littoral to sublittoral zones. Some whales and giant squid live in the mesopelagic and even into the top of the bathypelagic province. We still have so much to learn about life in the meso-, bathy- and abyssopelagic realms!
Nature of the bottom
sediment (sandy, muddy, carbonate), or rocky. Particularly important to the benthos. All of the physical factors interplay. If the sun warms up water at the equator, water may evaporate from the ocean and raise the salinity.
Dissolved oxygen levels will go down, but plant growth will speed up which can raise oxygen levels back up during the day, but drive them down again at night.
All the physical factors together make up a province. Each province of the ocean then has a unique set of plants and animals that are adapted to that province. The set of plants and animals is a community. A community is all of the organisms living in the same environment (province) and interacting with one another.
In the ocean, we see that animals and plants fit into one of four basic lifestyles:
1. 2. 3. 4. planktonic nektonic nekto-benthonic benthonic
Each community has its share of plankton, nekton, and benthos. The really defining members of most communities would be the BENTHOS because some nektonic organisms can swim into an area and swim out of it again.
So a particular community exists because it shares the following characteristics:
• physical characteristics of the water
temperature amount of light vigor of the currents salinity nutrient supply water depth
• characteristics of the sea floor the benthos live on or in (sandy, muddy, rocky, carbonate) and • the types of animals and plants within each.