Wednesday, 2 July 2008


Biodiversity is the quantity, variety and distribution across biological scales ranging through genetics and life forms of populations, species, communities and ecosystem. Biodiversity affects the capacity of living systems to respond to changes in the environment, underpins ecosystem function and provides the ecosystem goods and services that support human well-being (e.g., nutrient cycling, clean water. As well as having intrinsic value, biodiversity has aesthetic value: many of us have admired the wonderful colors and shapes of fishes on coral reefs and in other coastal habitats. Some benefits of biodiversity are not apparent today but may be unlocked in the future (known as the option value): compounds derived from marine animals and plants may serve as medicine to prevent and cure more of our ills in the future. Biodiversity also has cultural value when it is directly linked to the cultural fabric of human societies.

Human efforts, especially over the past 50 years, to meet rapidly growing demands for food, fresh water, timber, fiber, and fuel have resulted in an array of extensive changes to terrestrial, freshwater, and marine ecosystems. These changes, in turn, have resulted in an ongoing, widespread, and largely irreversible loss in the number and variety of organisms on Earth as well as the degradation of ecosystem services. The effects of pressures that arise from social and economic aspirations have been particularly severe on freshwater ecosystems. An index of the world’s freshwater species shows a more rapid decline between 1970 and 2000 than for terrestrial and marine indices during the same period. Similarly, South Africa’s first National Spatial Biodiversity Assessment examined the terrestrial, river, estuarine, and marine environments, and highlighted the fact that the country’s river ecosystems are now in a much poorer state overall than its terrestrial ecosystems.

Protected Areas represent one management instrument to balance the conservation and use of natural resources.

Fish species can be divided into at least eight group of feeding guilds (based on Inger and Chin, 1962), although it should be remembered that some species change their dietry preferences with age, season, and with the availability of alternative food items.

It can be difficult to determine directly what a particular fish has been feeding on. The gut of a fish may frequently be empty, but some indication of diet can be gain by examining the length of the gut in the relation to the length of the body. Thus herbivore generally have a gut which is 4-10 times the length of the body, whereas predator guts are much straighter and may be only as long as or even shorter than the body.

This technique can be useful to differentiate between herbivoures that fed on microscopic plants, filamentous algae etc. and primary predator that feed on nematode worm and other small animal living in the sediment. Both types of fish generally have stomach filled with mud or sand, but the gut length to body length ratio provide a guide to their preferred food.


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