Of great importance in the understanding of present-day biomes is that
humans have now heavily influenced the mix of species over the planet. Natural
parts of biomes are quite rare in the populated parts of Earth. Illinois had many
acres of prairie but corn and soybean farming has reduced this to a very few
hectares. In manyregionsof Earth deforestation has changed the landscape over
to crops.Urbanizationis an unrelenting fact of social geography so that much
land is paved over and/or revegetated with human-placed species such as lawn
grasses.
Similar to climates and soil classifications, there are several biome classifica-
tions with various “flavors” and, thus, different numbers of biomes and various
complexities. For thisHandbookwe will use a simplified classification while
appreciating that there are other ways with greatly increased complexity to spa-
tially sort life on Earth.
Biomes are divided into aquatic and land-based varieties. Aquatic biomes cover
most of Earth. Three marine (saltwater) biomes are usually recognized. The first is
ocean. The world’s oceans are deep as well as extensive, so oceans represent the
most diverse biome. Plants and animals range from microscopic zoo- and phyto-
plankton to whales that can measure over 30 m in length.
The ocean biome is usually divided into four zones: abyssal, benthic, pelagic, and
intertidal. The abyssal portion is the part of the ocean deeper than 4,000 m yet con-
tains some plant and animal species in the lightless, highly pressurized, cold (2°Cto
3 °C) water. Here, the biomass is much less than other oceanic biomes but can be
locally rich where methane, sulfides, or thermal energy seep out of the sea bottom.
The benthic zone is generally between 1,000 and 4,000 m depth and ranges
from 4°Cto8°C around the world. This is a lightless zone with pressures exceed-
ing 200X those in the air above. Life is a bit more diverse than in the abyssal zone
but the relative lack of plankton limits life.
Above the benthic zone is the pelagic zone, sometimes called the open ocean.
This is the first 1,000 m or so in which sunlight penetration directly fuels the food
chain anchored by plankton. This zone, particularly the first few hundred meters,
is directly affected by climate and exchanges mass and energy with the atmos-
phere. Lack of nutrients causes many pelagic areas to be unproductive in terms
of biomass and biodiversity. Selected areas, such as off the western coast of South
America, are subject to upwelling, which brings benthic nutrients to the pelagic
waters and are hugely productive.
The intertidal zone is the area between the lowest and highest tides. Generally,
the lower intertidal locations have a greater biodiversity than the higher locations
because the higher locations are less often covered by water. Rocky coasts tend
to have greater biodiversity than sandy coasts because sand makes it more difficult
for plants and animals to gain a permanent foothold at a single spot.
Biomes 33