ABSTRACT
Most marine invertebrates have planktonic larval forms that are dispersed by ocean currents. A tropical starfish need not crawl from Cuba to Florida’s tropical waters through the depths of the Straits of Florida. Such migration would be impossible for an adult, but the larval form can make the trip passively. In fact, this type of dispersal accounts for the prevalence of tropical marine invertebrates in the waters surrounding southern Florida, including the famous reef-building corals. At the same time, larval dispersal greatly complicates studies of the effects of overfishing on invertebrates, such as the highly valued Florida stone crab and Caribbean spiny lobster (Table 14.1), which is the tropical epicurean equivalent of the American lobster of the Northeast’s cold marine waters. Effective regulation of fishing requires an understanding of larval movements. Studies have shown that the spiny lobster population of Florida’s southeast coast is established by larvae that arrive from various local, as well as distant Caribbean, sources via the Florida Current. It is also interesting that in 1993, when huge floods occurred in the Mississippi River system, larval transport was greatly affected in the Gulf of Mexico, and was apparently the cause of abundant slipper lobster and sand crab larvae from the northern Gulf of Mexico arriving in the Florida Keys. The important generalization is that varying conditions can make large differences in the marine invertebrate larval recruitment that establishes adult populations.137,164,870-872
Not all southern Florida marine invertebrates are strictly tropical, and some are dependent on estuaries for part of their life cycles. Three commercially important examples are the blue crab, pink shrimp, and eastern oyster. The blue crab is found from Cape Cod southward around Florida and into the Gulf of Mexico. As adults, blue crabs use estuaries, where they are aggressive predators on other invertebrates and fish, but are in turn prey for certain larger vertebrates (Kemp’s ridley turtle, see Caloosahatchee section, Chapter 12, and the American Crocodile section, Chapter 18). Depending on conditions, especially in upper estuarine to nearly freshwater areas, their numbers have fluctuated widely. The blue crab is considered a possible indicator for restoration of the Caloosahatchee estuary.50
