Biodiversity in the Indian River Lagoon:
 

By the early 1980s, scientists around the world had begun to recognize that species extinctions were occurring on a global scale.  The rate of these extinctions rivaled, or surpassed, those of the Cretaceous period 65 million years ago when many species, including the dinosaurs became extinct. The crisis facing species today differs in one fundamental way from any other extinction events: all other cases of mass extinction throughout global history have come about as the result of climatic change, a natural geological change or some cataclysmic event. The present crisis, however, is being driven by human influences. Throughout the 1980s and early 1990s, the scientific community, the media, the public, and governmental agencies worldwide began working to preserve the biological diversity of terrestrial systems.  Issues such as deforestation of tropical forests, overdevelopment, overexploitation of species, pollution, habitat loss, invasions by introduced species, and other issues which addressed habitat preservation and conservation were brought into public focus.  However, maintaining the biological diversity of marine and estuarine systems was largely overlooked throughout the 1980s, even though it was generally accepted that marine systems are far more species rich and have greater ecosystem diversity than terrestrial systems.  Representatives from 32 of the 33 known animal phyla can be found in ocean and coastal waters. Of these, 15 phyla occur exclusively in estuarine or marine environments.

Defining Biodiversity:

The vast wealth of life on earth is unified by a common strand: DNA. All living things owe their forms and functions to the molecular makeup of their DNA. But perhaps more intriguing than life's unity is its immense diversity. Biological diversity - biodiversity - is one of the central themes of conservation. But what exactly is biological diversity, and why should we be concerned about preserving it? Simply put, biodiversity may be defined as the measure of how healthy our ecosystems are.  Healthy ecosystems support high biological diversity;  while stressed or highly disturbed ecosystems do not.  When we consider biodiversity as a whole, we are actually addressing 3 main components: genetic level biodiversity, species richness and ecosystem diversity.

Genetic Level Biodiversity:

The term "genetic diversity" is the most fundamental level of biodiversity, and refers to the degree of variation in all the genes for all individuals within a species. Here we will define a species as a group consisting of all the collected populations of morphologically similar organisms which are able to interbreed with one another. A population is defined as consisting of all the individuals of the same species within a defined geographical area, for example, the Indian River Lagoon.

Within a species, it is theoretically possible for any individual to breed successfully with any other individual of the species. However, populations, tend to remain somewhat separated from each other. Thus, there is a higher probability that an individual within a population will select a mate from the same population. Within a large population, the effect of geographic separation of populations, which often results in reduced genetic mixing, is small.  However, within small populations, there can be a tendency toward reduced genetic diversity among members of that population. Over long periods of time, this can lead to geographically separated populations diverging genetically, each population having its own set of genetic adaptations which allow it to live optimally within a particular habitat.

This genetic divergence is the basis for evolution. Populations having greater genetic diversity are far better equipped to cope with environmental change and go on to reproduce successfully than populations with low genetic diversity. Populations with low genetic diversity can become so well adapted to local conditions that any environmental disturbance may be enough to reduce their numbers dramatically, or even destroy them entirely. Thus, in thinking about preserving biodiversity, one must consider that each population within a species may have some unique set of genetic adaptations that could potentially assist the entire species in overcoming environmental, or human influenced challenges to its survival.

Species Richness:

This term, quite simply, is the measure of the number of species which occur within a particular taxonomic level (i.e., genus level, family level, etc.) in a geographic area. In marine ecosystems, species diversity tends to vary widely depending upon latitudinal and longitudinal location.   Along a latitudinal gradient, species diversity tends to increase toward tropical areas.  Within tropical areas, species diversity tends to increase along a longitudinal gradient, with more species being found toward the Indo-Pacific region around northeastern Australia, Indonesia and the Philippines. There is a moderate amount of species diversity in the eastern Pacific and western Atlantic oceans, with lowest species diversity found in the eastern Atlantic.

Ecosystem Diversity:

Ecosystems are the collection of all the plants and animals within a particular area, each differing in species composition, physical structure and function. Even within highly diverse ecosystems, these elements can differ widely.  For example, most estuarine ecosystems, especially salt marshes, generally have high primary production. Coral reefs, an entirely different type of ecosystem, must rely on the efficient recycling of nutrients in order to maintain high productivity. Deep sea ecosystems, while rich in species, have no primary production because sunlight does not penetrate such vast depths.

Threats to Biodiversity

The factors which threaten biodiversity in estuaries and in the oceans are generally the same as those which affect biodiversity in terrestrial systems: overexploitation, physical alteration of habitat areas, alien species introductions, and changes in atmospheric composition. Many threats to the survival of life in the oceans (i.e., siltation, nutrient loading, pollution of air and water by toxic chemicals, etc) can originate on land.  Also threatening marine ecosystems, particularly coastal and estuarine systems, is the continuous increase in the size of human populations, wasteful resource consumption, lack of knowledge, and poor management.  Habitat degradation which occurs as the result of these problems, inevitably leads to loss of species from an ecosystem, and thus, a loss of biodiversity.

The Solution: Preserving Biodiversity

In order to insure biological diversity in both marine and terrestrial systems, we must finally recognize the fact that our natural resource base, our economic development, our food, our medicine, our clothing, the air we breathe, indeed our very existence on this planet is dependent on the life around us. In preserving biological diversity, we are simply insuring our own continued prosperity and survival.

Further Reading:

Norse, Elliot A. 1993. Global Marine Biological Diversity: A Strategy for Building
     Conservation Into Decision Making.  Island Press, Washington, D.C.  384 pp.

Thorne-Miller, Boyce, and J. Catena. 1991. The Living Ocean: Understanding
     and Protecting Marine Biodiversity. Island press, Washington D.C.180 pp.

Report by:  K. Hill, Smithsonian Marine Station
Submit additional information, photos or comments to:
irl_webmaster@si.edu
Page last updated: Aug. 1,  2001