Did you know that the ocean occupies 99% of all the living
space on our planet and houses, perhaps, the greatest variety
of living organisms? Yet when most people think of the ocean,
they think of a place that doesn't have a lot of variety.
I call this the "bucket of water" mentality. Scientists
used to think this way too, that the ocean was a fairly
homogeneous place with not a lot of places for organisms
But the ocean (and even a bucket of water) displays incredible
variations across its depths and surfaces, across its seasons
and years, in virtually all of its physical, chemical, geological
and biological variables. It's a highly dynamic place where
the environment changes in space and time over all possible
In this section, we explore further the nature of the ocean
environment, the types of habitats we may find and the multiple
forces that each endures. We also examine the variability
of these habitats as a primary factor in determining the
kinds of species we may observe at any given time and location.
The combination of these variable most certainly has given
rise to the incredible diversity of organisms that have
evolved in the ocean, a diversity still largely unknown
and perhaps unappreciated.
Topics covered here include:
A Few Helpful Ecological Definitions
Before we launch on a whirlwind, worldwide tour of the oceans,
let's make sure we are all talking the same language and
define a few useful terms.
What do we mean by the ocean environment?
The term environment is defined in the ecological sense
as the complex of physical, chemical, geological and biological
factors that act upon an organism and determine its form
and survival. So the term ocean environment refers to all
those factors in the ocean that affect an organism's ability
to live, survive and reproduce.
The term habitat is similar to environment but more general.
Most simply, a habitat is the place where an organism lives
or where it is most commonly found. We usually designate
habitats by location or physical setting.
Any given species occupies space on our globe, in what
called its area. A species' area is simply where it occurs.
We represent species areas by shaded regions on a map. Check
out an Audubon bird book sometime (or any other kind of
field identification manual). More times than not, they
include maps with shaded regions where a particular plant
or animal can be found.
A species' area may occur over a range of habitats. Thus,
an organism may live in a number of habitats. Think about
migrating birds or whales. Within the span of a year, they
may travel across and utilize resources from many very different
habitats. The point here is that a single habitat does not
always define where a particular species live. However,
just to confuse things, some species are confined to a single
habitat. Got that?
For this reason, ecologists (scientists who study the relationships
and interactions among organisms came up with what is known
as an ecological niche. A famous ecologist named G.E. Hutchinson
in 1957 defined a niche as a region (n-dimensional hypervolume)
in a multi-dimensional space of environmental factors that
affect the welfare of a species. That's a little complicated
(but useful!) so we'll use an earlier definition, that provided
by Joseph Grinnell in 1917, who defined niche as all the
sites where organisms of a species can live (where conditions
are suitable for life).
Let's explore this concept of a niche just for a moment
because I think it will help you better understand one of
the most fundamental topics of life: how an organism reacts
to and within its environment.
Hutchinson imagined the niche like a multidimensional graph.
Since most of us think in three dimensions only, let's stick
to that. Imagine, if you will, three yard sticks arranged
in three dimensions parallel to each other. Use Popsicle
sticks or pencils if it helps you but basically what you
are constructing are the axes of an X-Y-Z graph.
Let's start with just one axis, the X axis, and consider
how we might represent the range of salinities (the saltiness
of water) within which a particular fish can live. Paul
Maslin at Chico State offers on his web site at http://www.csuchico.edu/~pmaslin/limno/niche.space.html
this simple illustration for a Largemouth Bass and a Chinook
Note that the range of salinities tolerated by a Chinook
Salmon is much greater than the range of salinities tolerated
by a Largemouth Bass (you knew that, right?). Thus we might
conclude for this one-dimensional depiction of niche that
the salinity niche for a salmon is larger than the salinity
niche for a bass (and we would be correct if we concluded
Now start thinking in two dimensions. How would we plot
the range of tolerance of a species to two variables? Maslin
does it like this:
What conclusions can you draw from this graph? Which species
is more tolerant to temperature? Does it make sense that
an organism living in a lake tolerates higher temperatures?
For the grand finale of this little niche discussion we're
having, try to imagine three dimensions. This is where your
yardsticks (or Popsicle sticks or pencils) might come in
handy. In this example, we'll look at a single plant, affected
by water, fertilizer and sunlight. Here we borrow from a
Virginia Tech web page:
Spend a few moments and trace each axis. Can you pick out
the ideal conditions for this plant?
If it helps, consider this drawing, which depicts plant
growth versus water for varying amounts of sunlight.
If you're starting to think about niches as "space"
in the sense that an organism occupies a "space"
that might have multiple dimensions where each dimension
is some variable that affects how it lives and survives,
then you are starting to think like an ecologist!
Don't feel bad if these concepts totally baffle you. Come
back to them from time to time. They are very heady topics
and require simmering and meditation to fully understand
them. The point here is to get you to think about the environment
as a multi-faceted, multi-dimensional set of factors that
determine where and when an organism lives, including humans.
You may also want to consider what Dr. Seuss has to say
about the subject. (You do know Dr. Seuss, don't you?) In
On Beyond Zebra (1955), he writes:
And NUH is the letter I use to spell Nutches,
Who live in small caves, known as Niches, for hutches.
These Nutches have troubles, the biggest of which is
The fact there are many more Nutches than Niches.
Each Nutch in a Nich knows that some other Nutch
Would like to move into his Nich very much.
So each Nutch in a Nich has to watch that small Nich
Or Nutches who haven't got Niches will snitch.
Read that aloud a couple times. It definitely will get
your head spinning!
Back in two-dimensional space (this text!), we have another
couple terms that help us better understand the relationship
of organisms to their environment. Biogeography is the science
that deals with the geographical distribution of animals
and plants. Biogeographers seek an understanding of the
relationship between an organism and its environment, with
an aim towards describing the evolution of species in various
locales and habitats across the globe.
Here's a good place to mention the word ecosystem. Formally
defined, an ecosystem is a community of organisms and the
non-living environment in which they interact. For our purposes
here, it's useful to describe our ocean habitats as ecosystems
because it implies something dynamic and variable, as most
ocean habitats are.
The role of an organism in an ecosystem is one of the most
important aspects of its ecology. Ecologists ask "what
function does an organism play in an ecosystem?" And
you might answer "plants provide food, herbivores transfer
material and energy from plants to carnivores, bacteria
decompose organic matter and make it available to plants,
as so on." Some ecologists divide organisms into guilds,
a category of organisms based on their ecological role.
For example, fishes that eat zooplankton (animals that drift
in the sea), whether in the open sea or a coral reef, are
said to belong to the zooplanktivore guild. Birds that eat
insects might belong to the insectivore guild. Actors who
act might belong to the actor's guild. You get the idea.
All these ecological definitions serve a purpose: they
not only help us to speak the language of ecologists and
to better understand what we read (not only in textbooks
but in newspapers and magazines), but they get us thinking
about the interaction between physical, chemical, geological
and biological processes, which is the major theme of this
textbook and the field of oceanography. No organism is an
island, to paraphrase John Donne, and for that reason, understanding
the relationship of organisms to their environment is one
of the most fundamental ideas we can study.
Major ocean habitats and ecosystems
Armed with these succinct definitions, let's see how we
can divide the ocean into different "life zones"
or geographic provinces. These zones define the major habitats
in the ocean in which we find the major ocean ecosystems
The most basic distinction between habitats in the ocean
is the one that separates oceanic or open ocean waters from
coastal or neritic waters. Oceanic waters (also known as
the open ocean) are truly oceanic; they are not influenced
by terrigenous or land-derived factors. Terrigenous factors
include runoff of inorganic sediments (clay, silt, sand),
dissolved substances (salts, nutrients, chemicals), non-point
source pollution (oil, fertilizers, heavy metals), organic
matter (fecal matter, sewage, plant remains, food) and debris
(straws, plastic bottles, cigarette butts, etc.), which
are largely confined to coastal waters (also known as neritic
waters). Oceanic waters may receive terrigenous materials
through the atmosphere, such as dust, aerosols and even
balloons, but the influence of these factors is negligible.
Nonetheless, there are no sharp lines in the water, so to
speak, to separate these zones, so there is bound to be
Oceanographers also use the sea bottom to separate oceanic
from coastal waters. Waters above the continental shelf
(the margin of the continents) are defined as coastal waters,
while waters beyond the continental shelf (i.e., the deepest
parts of the ocean) are defined as oceanic waters.
These distinctions help to define not only the physical
and chemical makeup of the water, but the organisms that
live there as well. Coastal waters are among the most productive
on Earth; it's where the major commercial and recreational
fisheries make their haul and it's where you and I go to
the beach. Oceanic waters have been compared to deserts
but don't let that fool you. The open ocean hosts many diverse
and fascinating life forms, like blue whales, viperfish
and giant squid.
In addition to proximity to land, depth also helps us to
define major ocean habitats. But depth in and of itself
is not a factor. When we talk about depth, we are really
talking about light penetration and water pressure, physical
factors that we'll discuss in more detail later. Just keep
in mind that when you read the word "depth" that
what we are really talking about are the factors that vary
as a function of depth. (Remember your niche dimensions?)
To be continued...
Read about the new Remarkable
Ocean World...coming soon!