-- MAIN LINKS --

-- EVOLUTION & ADAPTATION -- BALEEN WHALE SPECIES --
-- CLASSIFICATION -- CHARACTERISTICS OF BALEEN WHALES --
-- TOOTHED WHALE SPECIES -- DOLPHINS -- SEALS --
-- ENDANGERED SPECIES -- THREATS -- GAMES --

-- DOLPHINS --

. Anatomy . Senses . Feeding . Behaviour . Reproduction .
. Communication . Marine ecosystem . Dolphines on display . Training .

DOLPHINS: Place in the marine ecosystem

--- Life's many faces or biodiversity

The oceans, which cover about 70% of the Earth's surface, is home to the largest variety of species of living creatures. There are more than 40 different main divisions of life forms, of which about 15 occur only in the oceans. The seas teem with a multitude of mammals, fishes, shrimps, corals, algae and a host of micro-organism, both animal and plant, and bacteria. All those life forms are adapted for living in the salt water of the oceans.

The salt contents of the oceans water is about 35 ‰ or 35 gr/l. The Baltic Sea is brackish water with a salt content of only 13 ‰. The enormous diversity of life in the seas is not surprising, if you keep in mind that life on Earth started in the water some 670 million years ago.

The ocean environment is very diverse. It is a complex of smaller communities or ecosystems. These together form the larger marine ecosystem. An ecosystem is the whole of the biotic community (all the living organisms together, including animals and plants) and its abiotic environment (which includes physical and chemical factors, such as temperature, light, salinity, nutrients, etc.).

The diversity of species in an ecosystem can be expressed in a diversity index. There are several formulas for calculating this index, but all take into account the number of species and the number of individuals in each of the species. Also within a species, there is diversity. Each individual has a unique set of genes which set it apart from other individuals. The level of diversity within a species is important for the survival of the species. If there is a high level of genetic variation, the species is more likely to be able to survive changes in the environment, since it is more likely that there are individuals that can adapt to the changes.

There are a number of marine mammal species, including blue whales, bowhead whales and elephant seals, that have been hunted close to extinction. Some populations have recovered but because the number of animals that were left when the hunt stopped was low, the genetic diversity of those populations is low: only a small number of individuals contributed to it.

An extreme case is the Northern elephant seal. In 1890, after a period of intensive hunting, less than 100 individuals (maybe even less than 20!) were left. Since then the population has increased in
size to about 127,000. All these animals have descended from those 20 animals in 1890, so they are all closely related and the level of genetic diversity in this species is very low. This species can therefor be very sensitive to environmental changes.

On a large scale, the Earth as a whole can be considered one big ecosystem, the biosphere, which contains a large number of interacting smaller ecosystems. Changes in one system will affect the other systems and consequently the whole. People, animals and plants are all part of the biosphere and are thus connected. What we do to our environment, will affect other animals and plants, and
ultimately, ourselves.

For more information on threats to and protection of the marine ecosystem, look at Conservation and protection.

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--- Food chains

Every ecosystem consists of biotic (living) and abiotic (dead) components. The living elements depend on each other and are connected through food chains and (more complex) food webs. Each
food chain or - web contains producers and consumers.

The primary producers are green plants, algae and phytoplankton. They can produce organic material from inorganic matter (salts, water, carbon dioxide) under the influence of sunlight. In this process, called photosynthesis, sugars and oxygen are produced. The sugars are used in their own metabolism and are converted to proteins, cellulose and other building blocks of their own cells.

There are 3 types of consumers:

primary consumers: The most obvious members of this group are the herbivores, feeding on plants, the primary producers. But also fungi, that digest plant material, belong to this group.

secondary consumers: To this group belong carnivores and parasites. They feed mainly on the primary consumers.

tertiary consumers: To this group belong the higher carnivores and hyper-parasites, that feed on secondary and other tertiary consumers

A special group of consumers are the reducers, saprophytic plants and animals (fungi, molds, and some insects). They digest dead plant and animal material and turn it into inorganic matter. This
matter can then be taken up again by the primary producers, and in this way, the circle is closed.

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--- Marine food chain

The marine ecosystem is diverse and contains a large number of food chains and - webs. There are no large green plants in the seas, like on land, but instead, the main plants are large algae and microscopic algae (phytoplankton).

The following is an example of how a marine food chain, which includes the bottlenose dolphin, might look:

primary producers: This group consists mainly of microscopic algae, which contain chlorophyll and can produce their own food using dissolved matter in the water, dissolved carbon dioxide and
sunlight. This phytoplankton lives in the upper layers of the water, because it depends on sunlight and the light does not penetrate very deeply into the water.

primary consumers: This diverse group contains small copepods,medusae, crab and shrimp larvae, krill and a whole lot more.

secondary consumers: These are animals, that feed on the zooplankton.They include worms, squid, fishes like herring and also baleen whales, such as the blue whale, which feed mainly on krill.

tertiary consumers: These include predatory fishes, such as mackerel, tuna and sharks. Also dolphins, that feed on mackerel and herring, belong to this group. The killer whale, which feeds on fishes and dolphins is the top predator in the seas, along with the larger shark species.

reducers or saprophytic organisms: These are mostly bottom dwellers, such as crustaceans and worms. Also a wide range of marine bacteria belong to this group. They break down the dead material that sinks to the bottom to dissolved organic matter. Upwelling along coastal ledges and deep sea canyons will bring these dissolved nutrients back to the higher layers and make them available again to the primary producers.

When going through a food chain, some mass and energy is lost at every level. Not all of the material consumed contributes directly to mass in the next level. Some of it is lost. For a gain of say 1 kg of biomass in primary consumers, several kilos of primary producer material is needed. Because of this, pollutants can concentrate in the higher levels of the food chain. This effect is called bioaccumulation or bioamplification. One of the pollutant groups which is known for its bioaccumulation effects is the PCBs. These poisonous substances are present in low concentrations in algae (phytoplankton), which pick it up from the water.

The zooplankton that feeds on the phytoplankton then concentrates the PCBs and consequently they contain higher levels of PCBs. The fishes feeding on zooplankton have even higher levels and the highest level consumers, such as seals, dolphins and porpoises have the highest concentrations in their bodies, so high even, that they may get poisoned by it. The possible effects of PCBs include reduced immunity and reduced fertility (the decline of the seal populations in the North Sea and Baltic Sea was caused by reduced pup births and reduced pup survival, because of the high PCB levels in the seals).

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