Functional diversity in marine ecosystems

Functional diversity refers to the variety of biological processes, functions or characteristics of a particular ecosystem.

Functional diversity reflects the biological complexity of an ecosystem. Some scientists argue that examining functional diversity may in fact be the most meaningful way of assessing biodiversity while avoiding the difficult and usually impossible task of cataloging all species in marine ecosystems. By focusing on processes, it may be easier to determine how an ecosystem can most effectively be protected. Protecting biological functions will protect many of the species that perform them. However, the exact function of most of the species is hardly known to date.

.There are several ways in which ecological classifications group organisms according to common functions: classification according to their habitat, to their position in the food web or to their functional feeding mechanism.

1.2.1 Classification by ‘habitat’

Aquatic organisms can be divided into four major groups: pelagic, benthic, neuston and fringing, according to the water body which they inhabit.

PELAGIC ORGANISMS

Pelagic organisms are those that live in ocean water (not associated with the bottom) thus in the water column and can be divided in plankton and nekton. Plankton are organisms that are suspended, (they float or are weakly self-propelled) in the water and drift with it as it moves. Plankton is either passive and includes algae, bacteria and variety of animals. Plankton is usually subdivided in phytoplankton (photosynthethic organisms like algae) and zooplankton (animals), what refers to their ecological function. Plankton can also be subdivided in holoplankton and meroplankton. Holoplankton are permanent members, represented by many taxa in the sea. Meroplankton are temporary members, spending only a part of their life cycle in the plankton. They include larvae of anemones, barnacles, crabs and even fish, which later in life will join the nekton or the benthos. Meroplankton are very much a feature of the sea, particularly coastal waters, as the often sedentary adult forms of coastal species use their planktonic stage for dispersal. Nekton are organisms swimming actively in the water, it includes a variety of animals, mostly fish.

BENTHIC ORGANISMS.

Benthos comprises organisms on the bed of the water body. Animals attached to or living on the bottom are referred to as epifauna, while those which burrow into soft sediments or live in spaces between sediment particles are described as infauna. Attached multicellular plants and algae are referred to as macrophytes, while single-celled or filamentous algae are called as periphyton or microphytobenthos. Epiphytic algae are those which grow on macrophytes. Benthic consumers can be divided by size into macrofauna (>500 μm), meiofauna (10-500 μm) and micro-organisms (<10 μm).

NEUSTON

Neuston are those organisms associated with the water surface, where they are supported by surface tension. Most neuston require very still water surface and is therefore very restricted in the sea.

FRINGING COMMUNITIES

Fringing communities are floral communities that occur where the water is shallow enough for plentiful light to reach the bottom, allowing the growth of attached photosynthesisers, which may be entirely submerged or emergent into the air. Marine communities are composed mostly out of algal seaweeds. Wetlands are composed of this type of vegetation.

There are a lot of other habitat classifications, for example the EUNIS Habitat types classification.. This is a comprehensive pan-European system to facilitate the harmonized description and collection of data across Europe through the use of criteria for habitat identification; it covers all types of habitats from natural to artificial, from terrestrial to freshwater and marine.

An example of the EUNIS habitat classification: marine habitats at level 1 is the following:

A1 Littoral rock and other hard substrata

A2 Littoral sediment

A3 Infralittoral rock and other hard substrata

A4 Circalittoral rock and other hard substrata

A5 Sublittoral sediment

A6 Deep-sea bed

A7 Pelagic water column

A8 Ice-associated marine habitats