Biological diversity - biodiversity - is a central theme 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.

The factors that threaten biodiversity in estuaries and in the oceans are generally the same as those that affect biodiversity in terrestrial systems: overexploitation, physical alteration of habitat areas, and alien species introductions.  Many of the current threats to aquatic species originate on land.  Siltation, nutrient loading, air and water pollution,   human population growth, and wasteful resource consumption all contribute to habitat degradation, which inevitably leads to loss of species from an ecosystem, and thus, a loss of biodiversity.

The Indian River Lagoon had long been purported to be one of the most, perhaps the most, biologically diverse estuary in the continental United States.  The compilation of the IRL Species Inventory in 1995, provided the first evidence of the IRL's vast biodiversity.  

The original Species Inventory listed a total of 2493 different species of plants, animals and protists.  Of these, animals comprised the greatest proportion of species in the Inventory, approximately 71%.  Plants comprised 12% of the species, and the single-celled Protozoa accounted for the remaining 17%.  No data were available for insects, bacteria or the fungi.  Since 1995, over 500 additional species have been added to the Inventory, and this work is still not complete. 

Total Biodiversity in the Indian River Lagoon based on the original Species Inventory information.

Animal Biodiversity in the Indian River Lagoon based on the original Species Inventory information.

Plant Biodiversity in the Indian River Lagoon based on the original Species Inventory information.

The figure below shows a comparison of the Indian River Lagoon to another large, regional ecosystem for which we have robust scientific information:  the Chesapeake Bay.  Just over 3,000 species have been documented to occur in the IRL, which has a total area of approximately 2,280 square miles.  Despite its much larger size, the Chesapeake Bay has approximately half the total species number of the IRL, with 1,500 species known to occur there.  While ecologists would expect species numbers to increase the closer one moves toward the equator, the comparison is nevertheless illustrative of the IRL's vast biodiversity.
 

Indian River Lagoon vs. Chesapeake Bay
Indian River Lagoon		Species Group	Chesapeake Bay
	429	Mollusks	177
	381	Fishes	197
	220	Crabs, Shrimps, Lobsters	63
	143	Segmented Worms	145
	141	Algae	112
	35	Isopods	21
	33	Jellyfish, Corals, Anemones	73
	31	Sea Stars, Sea Urchins, Sea Cucumbers	14
2,280 sq. mi.                                                                                                                    3,237 sq. mi.