We will now begin the second half of the class, focusing in on the complex life that abounds in the oceans. Rather than merely cataloguing the various critters, we will first look at the general aspects (benefits and difficulties) of life in the ocean, and then discuss the organisms in terms of their role in various nutrient pathways and community interactions. Through it all, keep in mind all of the various geological, chemical, and physical processes in the oceans we have been discussing.

Building blocks of life

In a simple definition, one can view life as "when organized collections of elements utilize energy and produce new forms of life." This is of course vague, but we are trying to sum up 3500 million years of activity in one sentence! There are some characteristics shared by all "life forms" on our planet:

Most organic matter is composed of the elements Carbon, Oxygen, Nitrogen, and Hydrogen in various amounts and combinations. Together, these four elements comprise 99% of the mass of all living things. The movement of carbon from the oceans or atmosphere, into one organism, and then into another, etc., is called the "carbon cycle." Similarly, we can think of a similar movement, although through different pathways of nitrogen in a "nitrogen cycle." One key step in both is the release of organic carbon or nitrogen (as opposed to inorganic elements) into the ocean as "dissolved organic carbon" (DOC) or "dissolved organic nitrogen" (DON). The importance of DOC and DON will be discussed later.

In addition, there are a number of other elements that are in relatively very small amounts but vital to life processes. These include Sodium, Magnesium, Phosphorus, Sulfur, Chlorine, Potassium, Calcium, Iodine, Silicon, Iron, Copper, and Zinc.

Since organisms need these various elements to differing degrees for food, reproduction, skeleton formation, and other functions, if the element is not available it "limits" growth and could cause death. Generally speaking, most limiting factors are "not having enough" of a substance, but having "too much of a good thing" can also be limiting.

Other Limiting Factors

In addition to the availability of the important elements listed above, the presence and success of life in the oceans is also dependent on various physical and chemical factors. These include: Light, Temperature, Salinity, pH, Dissolved Gases, and Hydrostatic Pressure. The following is a brief summary of why each of these factors is important:

Light-Needed by photosynthetic plants, algae, and bacteria as well as by (some) animals to see. Limited to the upper several hundred meters of the ocean, called the "photic zone."

Temperature-Most organisms, other than mammals and birds, do not have internal temperature regulation, but rely on the external temperature to stoke the chemical processes. Too cold a temperature, and the various processes move too slowly, but too warm, the organism cooks.

Salinity-Changes in salinity can damage cells, affect the buoyancy of organisms, and alters the osmotic pressure of cells, which regulates how water flows into and out of cells.

pH-Great changes can affect the structure of vital proteins. Also, the pH is related to the dissolved CO2 of the seawater, so changing the pH will change the amount of CO2 and most ions in the water.

Dissolved Gases-Colder water can hold more dissolved gases (increased solubility) which all organisms need.

Hydrostatic Pressure-The pressure built up under the weight of the ocean water. This pressure is regulated by pressure built-up inside an organism to make sure it doesn't explode or implode.

How Organisms Deal With the Ocean

Living in salt water has its advantages and its difficulties. In addition to the factors listed above, here are some additional biological factors that marine organisms have to deal with:

Osmosis-Diffusion of water from one side of a cell to the other (i.e., inside to out or visa versa). Water wants to move from the site of low salinity to the site of high salinity. If ocean water is too salty, the cells give up their water and dehydrate (hypotonic). If the ocean becomes too un-salty, than the cells would swell and maybe burst (hypertonic)!

Gravity/Buoyancy-Organisms in the ocean need to choose whether to be the same density as the part of the ocean they live in (neutral buoyancy) or alter their density by the addition or subtraction of material to float up or down in the water column. Most commonly, this is done with gases, but in some cases, the organisms change their density by altering their skeletal structure, or changing the types of ions in the solutions they contain. Some floating organisms want to be permanently positively buoyant so they retain lots of waxes and oils in their bodies.

Viscosity-Water is more viscous (harder to move through) than air. Organisms that live in the ocean deal with this by having streamlined shapes, and having surface textures that are not perfectly smooth to reduce the drag.

Water Movement-Organisms can either passively or actively move through the water column. They do this for a variety of reasons including feeding, mating, or dispersal of newborns.

Brief Overview of Environmental and Life Organizational Categories

Life on Earth first began about 3.5 billion years ago in the warm shallow seas on the edges of the early continents, based on available fossil evidence. Over the following 3,500 million years, life has grown more complex and the various life forms have been able to occupy more positions in the ocean (and on land). In order to assess the patterns of this historical development, we need to come up with a scheme for classifying the various environments in the ocean and to classify life itself.

Environmental Classification-By light, can be defined by the zone well-lit (Photic Zone), and the zone below that is without light (aphotic zone). The upper part of the photic zone in which plants, algae, and bacteria can photosynthesize is called the Euphotic Zone. The lower part where the same critters cannot photosynthesize, but there is a little light is the Dysphotic Zone. We also classify the ocean based on geographical/depth location (*this is important for when we begin to discuss various organisms so learn this!). Organisms which swim about live in the Pelagic Zone. The alternative is to live on the sea floor, or in the Benthic Zone. The Pelagic Zone is divided into the shallow, Neritic Zone, and the deep, Oceanic Zone. The Benthic Zone is divided into the intertidal or Littoral Zone, the deeper Bathyal Zone of the continental slope, the Abyssal Zone of the deep ocean floor, and the Hadal Zone, or deep DEEP zones in the trenches.

Life Classification-Of the various possible ways to classify life, we have chosen to use a system based on natural connections. Although it was not known why this occurs when Linneas first proposed the system, we now know it is due to evolution. The Linnean system is hierarchical, that is, each group can be nested within a larger group, and is composed of other, lesser groups. From most inclusive to least inclusive, the Linnean system is as follows:

Kingdom (Five mostly used: Animalia, Plantae, Monera, Protista, and Fungi)
Phylum
Class
Order
Family
Genus
species

Species, the fundament unit of this system, refer to a unique group of interbreeding (or presumed interbreeding) organisms that do not breed with any other organisms. Since this is a hierarchical, one or many species can belong to the same Genus, and one or many Genera (plural of Genus) can belong to one Family. The opposite never occurs, such as where the same Genus belongs to several Families. Note two rules are that the "Genus" and "species" is always written in italics or underlined, and the Genus is always Capitalized and the species is never capitalized. An example of this system is the classification of Blue Whale:

Kingdom-ANIMALIA
Phylum-CHORDATA
Class-MAMMALIA
Order-MYSTICETI
Family-BALAENOPTERIDAE
Genus-Balaenoptera
Species-musculus

Note that a Fin Whale, is a different species, physalis, but the same Genus, Balaenoptera. Also, our friendly local Grey Whale, is also of the Order MYSTICETI, but is in the Family ESCHRICHTIIDAE. Now, the Sperm Whale belongs to the same Class MAMMALIA, but belongs to a different Order, ODONTOCETI.
The benefit to using this system is that it is global so all interested people can communicate about the same thing!! If we use "common names," such as "slipper shell," our foreign colleagues may not know what we are talking about.

Key Points:

1. 99% of all organic matter is composed of Carbon, Oxygen, Nitrogen, and Hydrogen in various amounts and combinations.

2. Carbon and Nitrogen are cycled through the oceans and atmosphere, and various organisms in the "carbon cycle" and "nitrogen cycle."

3. "Dissolved organic carbon" (DOC) and "dissolved organic nitrogen" (DON) are organic compounds of carbon and nitrogen in the ocean.

4. Other important elements, vital to life, are Sodium, Magnesium, Phosphorus, Sulfur, Chlorine, Potassium, Calcium, Iodine, Silicon, Iron, Copper, and Zinc.

5. The lack of or overabundance of a vital element or other necessary factor for life will limit growth or cause death. Therefore, these forces are called "limiting factors."

6. In addition to the vital elements, limiting factors include: Light, Temperature, Salinity, pH, Dissolved Gases, and Hydrostatic Pressure.

7. Osmosis is the process by which water moves from inside of a cell to the outside or visa versa.

8. Organisms in the ocean can alter their density (buoyancy) in order to float up or down in the water column.

9. Water is more viscous (harder to move through) than air, so ocean creatures need to have more streamlined shapes to reduce drag when moving.

10. Organisms can either passively or actively move through the water column for feeding, mating, or dispersal of newborns.

11. The Photic Zone is the zone in the ocean that light penetrates. Below the photic zone lies the aphotic zone. The upper part of the photic zone where photosynthesize takes place is the Euphotic Zone; the lower part of the photic zone is the Dysphotic Zone.

12. The open ocean, or Pelagic Zone, can be divided between the shallow Neritic Zone and the deep Oceanic Zone. The seafloor is called the Benthic Zone and is divided into the intertidal or Littoral Zone, the deeper Bathyal Zone of the continental slope, the Abyssal Zone of the deep ocean floor, and the very deep Hadal Zone.

13. The Linnean system is a hierarchical classification that is composed of naturally related categories.

14. From most inclusive to least inclusive, the Linnean system is composed of Kingdoms, Phyla, Classes, Orders, Families, Genera, and Species.

15. Most scientists believe that life can be divided among five kingdoms: Animalia-multicellar organisms that eat other life forms for energy, Plantae-multicellar organisms that gain energy from sunlight, Monera-single-celled organisms lacking a nucleus that gain their energy from a variety of sources, Protista-single-celled organisms with a nucleus that also gain their energy from a variety of sources, and Fungi-multicellar organisms that gain energy by absorption.

16. Species are unique groups of interbreeding (or presumed interbreeding) organisms that do not breed with any other organisms.

17. One or many species can belong to the same Genus, and one or many Genera (plural of Genus) can belong to one Family, etc.