Biorealms of life on Earth

Biorealms of Planet Earth

By Dr J Floor Anthoni (2001)
www.seafriends.org.nz/issues/cons/realms.htm

In the Seafriends web site you will learn about the sea and how life is radically different there. The link between the land and the sea is very important in order to understand why we are losing so much in the sea. Thus studying soil, how it is made and how it is lost, is critical to understand what is happening. On this page we'll make a comparison between the main biomes of our planet, the soil, the land flora and fauna, the fresh water, and the saltwater ecosystems.

The geographically large and separate ecosystems are referred to as biomes, such as the boreal forests, temperate forests, savannahs, tropical rain forests and so on. For larger groupings, it is common to use the word sphere, and the following spheres are distinguished:

biosphere: (bios=life) the total of the planet's envelope containing life. It covers both land and sea.
lithosphere: (lithos= stone) the inside of the earth, consisting of rock.
pedosphere: (pedon=ground) the soils.
atmosphere: (atmos=vapour) the gases above soil and sea.
hydrosphere: (hydros=water) the water on earth, but mainly applied to the water cycle. It includes the oceans, lakes and rivers, and water vapour, clouds, ice caps, glaciers and so on.

Although the above spheres divide the planet into identifiable parts, they do not describe the major living parts of the world, for which I will introduce the new concept of biorealm.

realm: (L: regere= to rule; regimen= a system of government or rule; Old French: réaume= kingdom) A kingdom. A sphere or domain. An area under the same rule.
We'll define the word biorealm likewise as a major ecosystem type, like the land, the sea, the fresh water. These all work under different rules, while they are also quite separate from each other. Organisms exist which live their lives in two biorealms, but the key players in each biorealm belong to one biorealm only. Biorealms have their own nutrient and energy cycles, but may cycle nutrients and energy to other biorealms as well.

In the table below, the major biorealms of the world have been placed side by side to allow comparison. By looking at the living world in this manner, one can get a good feel for what is going on, and how they are affected by human existence.

Main differences between the four most important biorealms of the planet

Factors	Soil	Land flora/fauna	Fresh water	Sea and ocean
size	large. About 0.5-4m deep, covering all land, where water is available some time of the year.	large. About 0.5-40m tall, covering all land where moisture is found but no ice.	very small. 0.5-1000m deep, surrounded by land. Water flows to the sea, but much evaporates.	very large. Continental shelves 20-200m and oceans 1000-10,000m deep; average about 4000m.
natural fragment- ation	very high. Soils are fragmented by mountains, rivers, lakes and changes in habitat, moisture, temperature and rock type.	high. Dissected by freshwater rivers, tall mountain ranges and oceans. Islands.	very high. Every watershed is physically isolated from every other. Interconnected only by the sea, which is a barrier to most freshwater species.	low. All seas and oceans are interconnected. Currents flow shallow and deep. Habitats and regions form by temperature and depth.
species diversity	very high. Due to fragmentation. Most species unknown. In the dark no plants can live. Many types of soil exist and interdependent guilds of species.	very high. many phyla, species and guilds. Many biomes and habitats. Island speciation. Separate continents.	very low. Due to small habitat, difficult living conditions, availability of water, seasons.	low/high. Low in productive areas and in the open ocean, due to interconnectedness. High on the deep sea floor due to it being a stable environment. High around islands and sea mounts.
long-lived species	very low. The soil's function is mainly that of breaking down, for which small species are best suited. Small animals can creep more easily through the soil. Fungi can grow large. Cells need to die to pass on nutrients.	low. Many trees can grow very old (200-2000y). Niche specialists such as orchids too. The bulk of the species is short-lived because they are insects. Mammals and birds 5-100y.	low. Most freshwater species are small and live short. Sturgeons, catfish, carp, can live to 100y. Many species have adapted to aestivate in mud during the dry season.	low/high. Productive areas have short-lived species. Many predator fish can grow to 80y. Age of deep sea life not known. Some phyla have no age, and could live forever, like anemones, sponges and more.
dispersal	very difficult. Bacteria, nematodes, etc. must be spread by other animals. Fungi can disperse by wind.	difficult. Plants can't move and rely on special adaptations for seed dispersal. Most animals can migrate easily.	easy. Eggs and larvae float suspended in the water, but currents may carry them off too quickly. Most spawning attached to grass or under stones. Juvenile fish swim upstream.	very easy. Eggs and larvae float suspended in the water, dispersed easily. Mass spawning is common. Most marine species reproduce prolificly.
environ- mental fluctuation	low-high: moisture, temperature. Barren soils suffer high fluctuations but forest soils stay moist and enjoy the stability of the forest microclimate. Soil organisms recover readily after drought. Seasons may bring sudden leaf loss. Dry soil can become lifeless.	high-very high: temperature, moisture, wind, sunshine, seasons. Land cools and warms up rapidly, especially when little moisture is present like mountain rock, desert. Moisture is highly variable in most places. Wind can affect growth. Seasons can cause leaf loss.	high: rainfall, temperature, sediment, nutrients. The temperature of freshwater stays more constant than the land, but depends on precipitation which is unpredictable in most places. Freshwater life is well adapted to high variations in suspended sediment (mud) and nutrients.	low: waves, seasons, currents. The seas and oceans are very stable due to their water mass. Waves affect life close to the surface. Currents may oscillate, bringing colder or warmer water or upwellings. Sea life is not well adapted to temperature variations, and suspended sediment (mud).
metabolic rate	very high. Small organisms have high metabolisms. They must suddenly adapt to opportunity, a fallen leaf, a dead animal.	low-high. Plant metabolic rate depends very much on temperature and moisture (up to 40x). Some plants are adapted to live slowly in difficult places. Metabolic rate of animals varies with size and whether they are warm-blooded. Some mammals hibernate.	low. With body temperatures matching that of the water, animals are energy-economic, which can lead to good growth rates (carp) and the ability to aestivate. Very few freshwater plants. Many animals depend on other animals falling into the water.	low-high. Some areas in the sea have high productivity with high growth rates, such as estuaries, the intertidal zone, coastal zone and areas with upwellings. Many slow-growing fish have low metabolic rates, live frugally and can grow old. Plankton organisms grow and cycle profusely.
knowledge of these realms	poor. Not only poor knowledge of the soil species but also about how soil works.	good. Most research has focussed on the terrestrial world, its plants and animals. Due to the very high number of species, large gaps in knowledge exist. Ecosystems still poorly understood.	fair. Freshwater research is making good progress. Because of its poor species diversity, knowledge about species is good; about aquatic ecosystems poor.	poor. The sea is difficult to get to, very large, very deep and hostile to humans. Most fish species have been described, but the lower organisms are poorly known. Fished species are known very well. Marine ecosystems not well understood.
affected by humans	very high. Soil organisms are immediately affected by habitat destruction and farming or cropping, but new communities develop. When built on or paved over, soil is lost.	high. Habitat loss and introduced species are the main causes of the disturbance of communities and habitats. Over 50% of photosynthesis now used by humans.	very high. Damming, canalisation, habitat destruction, introduced species, development, pollution. Almost everything humans do, negatively affects freshwater life. It is highly threatened. Many introduced species: carp, trout, mosquitofish, etc.	low. Exploitation, pollution, erosion, habitat destruction. The oceans are very large and mix reasonably well. Human influences have a minimal effect, compared to the other biorealms. However, the coastal zone is under threat, mainly from exploitation and mud.
extinctions	unknown. Due to poor species knowledge. However, when calculated from the area changed, it must be very high.	high. Due to human intervention, an estimated 12% of 2-10 million species is endangered or extinct.	unknown/high. Freshwater knowledge is too recent to know the losses.	low/unknown. Most of the ocean is unknown territory, but extinctions are deemed low due to its interconnectedness and stability and people not living there.
worst human activities	deforestation, farming, particularly ploughing, building, roading.	habitat modification, introduced species,	soil runoff, pollution, dams, cropping, feedlot farming, eutrophication, acid rain, aquaculture.	exploitation, soil runoff, pollution, farming, cropping, aquaculture.

Source: Floor Anthoni, 2001

A number of other very special biorealms exist on the planet, worth mentioning:

deep sea floor: although part of the oceans, it could well be considered a separate biorealm because life is so different there. This biorealm is as large as the oceans, but covers only the bottom surface. A steady rain of dead organisms in all sizes from whales to bacteria, supplies it with both energy and nutrients. Being disconnected from the ocean's surface, oxygen is in short supply. Plant life is of course not possible. Bacteria in the sea bottom digest the dead organisms and they become food for filterfeeding organisms. In the process, oxygen is used and carbondioxide released. A foodweb is formed, which exists on the seabottom only. Excess nutrients dissolve back into the water column, and eventually find their way back to the surface, either by gradual diffusion or by deep currents ending in upwellings at the ocean's surface. Very little is known of this environment, but we know that it is very stable in temperature. It has existed for thousands of millions of years, hardly affected by the massive extinctions that happened on the land. As a result, it houses an unexpectedly varied community of (often ancient) organisms, which live very frugally and which can grow very old. Note that the movement of the sea bottom, spreading away from mid-ocean ridges towards where they are subducted under continents, takes about 200 million years. So the youngest communities are found near the ridges, and the oldest in the deep trenches.
deep sea vents: in the vicinity of the spreading seafloor ridges in the middle of the oceans, hot magma comes close to the seafloor. In places, where the crust is broken and active, it heats the seawater, sending 'smoking' plumes of boiling hot water up. These hot plumes are loaded with minerals and hydrogensulphide (H2S). As the water cools, some minerals precipitate to form pipes or smoke stacks surrounding the plumes of hot water. Bacteria use the energy in hydrogensulphide to synthesise carbohydrates and compounds edible to planktonic organisms. These in turn are filtered out of the water by a community of filter feeders such as tube worms and clams. On these prey other species. It is a true ecosystem, functioning in the sunless depths of the ocean floor, and unlike any other.
hot water pools: where hot water, loaded with minerals reaches the sunlit surface, such as is the case in many geothermal pools, some (thermophile) bacteria and algae are able to live in unbelievably hot circumstances. They photosynthesise carbohydrates in normal ways, but constitute small biorealms unlike any other.
brine pools: where seawater evaporates, it leaves behind salty pools which are too salty for ordinary life. But some (halophile) organisms manage to live even here, capable of photosynthesising in warm and very saline conditions. Animals like brine shrimps feed on these algae, and bacteria complete the nutrient loop.

f027537: A snorkeldiver holds on to a moss-covered stick in the clear currents of Pupu Springs, NZ. Clear water and healthy aquatic weeds are hard to find, now that most rivers have been polluted by farm run-off.

f210117: in the saturated salt water of a salt pan, grows salt-loving phytoplankton, eaten by salt tolerant brine shrimps. Salt-tolerant bacteria close the food web. It is a simple but stable ecosystem.

Reader, please note that the above distinctions have been gleaned from many sources, and have also been inferred by myself. It is possible therefore, that errors have crept in. Please email me for discussion.
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