The implications of marine invasive species for tropical biodiversity hotspots.
Over the years ecologists have noticed a global pattern, which generally demonstrates that more different kinds of species exist in the tropics than in the temperate and polar regions of the planet. The observed latitudinal diversity gradient (LDG) which describes a decline in overall biodiversity corresponding with increasing distance in both directions from the equator, seems to have been operating for quite some time. Although the ocean basins and continents looked very different than they do today, evidence from the fossil record suggests that tropical regions have served as a cradle of biodiversity for many life forms since at least the early Triassic Period some 250 million years ago.
The Liquid Jungle Lab (LJL), situated less than 8 degrees north of the equator on the Pacific coast of Panama, is surrounded by ecosystems highly representative of the remarkable biodiversity found in tropical Central America. In fact several new terrestrial plants, fungus, and insect species have been discovered at LJL since its inception in 2004. These include a fungus (Opegrapha pigozziana), a lichen (Pyrenula lutepruinosa), an epiphytic plant from the family Aracea (Monstera sp.), a wasp (Foxita cambrai) and a never-before described male spider (Amphidraus sp.). Similarly, an international team of phycologists (scientists who study algae and seaweed) believe they have discovered 2 new species of algae at the LJL in 2010, and are currently conducting additional laboratory cultures and genetic testing to verify their findings.
Many competing theories attempt to explain why overall biodiversity is greatest in tropical and equatorial regions; however the spread of invasive (exotic) species, virulent disease vectors, habitat degradation and certain negative effects of rapid climate change are also influencing the natural distribution of biodiversity especially in the tropics where rates of biodiversity loss and species extinctions are now exceptionally high.
Recently, a group of scientists visiting Panama from the USA and Brazil have been studying the distributions and taxonomy of a group of filter feeding marine animals commonly referred to as Sea Squirts. These sessile (non-moving) tunicates normally attach themselves to rocks, coral reefs, and other hard substrate on the ocean floor but often find homes on more temporary structures such as docks, moorings, and boat hulls.
Identifying and collecting tunicates from the bottom a mooring float near the Panama Canal. Photo courtesy Mary Carman.
Because these normally sessile organisms can in fact move with the unwitting help of humans, part of this study has focused on the implications of maritime traffic through the Panama Canal by attempting to create a regional inventory of endemic (native to the area) and exotic (invasive) tunicates found on both the Caribbean and Pacific coasts of Panama. Besides characterizing the baseline geographic distributions of these animals, results of this investigation have also led to the discovery of two new species of Sea Squirts found in subtidal areas near the Liquid Jungle Lab including (Ascidia panamensis) (Bonnet and Rocha 2011) and (Pyura sp.) which is undergoing genetic analysis for a more detailed taxonomic description.
Blue and Red color morphs of the ascidian species Rhopalaea birkelandi, a common tunicate in the Gulf of Chiriqui Panama. Photo courtesy Rosana Rocha.
Study of invasive species in the marine environment is of special interests to many scientists because it includes a wide range of aquatic microbes, viruses, plant and animal species which, when suddenly introduced, can swiftly disturb or adversely affect natural coastal and benthic (sea floor) ecosystems which have been evolving as specific ecological communities under various and often regionally isolated natural selection pressures for millions of years. New techniques in Molecular Biology, Paleobiology, and Marine Ecology have helped advance Biogeographic theories which explain to some degree the biodiversity gradients we observe in many natural systems around the world.
Divers using a quadrat to conduct tunicates diversity study. Photo Luis Camilli
These discoveries also have profound implications for contemporary models of habitat and species conservation and natural resource management, particularly in tropical biodiversity “hotspots” such as coastal zones along the Isthmus of Panama where relatively small areas, exhibiting high biodiversity, experience frequent human perturbations. Broader scope studies focusing on aspects of species diversity, relative abundance and habitat structure for entire suites of organisms will help to determine how these subtidal communities change over time, and continuous monitoring efforts and experimental study will be required to understand the distribution patterns and functional operation of the myriad of emergent ecologic interactions produced under these new conditions beneath the inscrutable surface of the sea.
Luis CamilliScience Director Liquid Jungle LaboratoryWoods Hole Oceanographic Institution
Jablonski, D., Roy, K., and Valentine, J. W. (2006). Out of the tropics: Evolutionary dynamics of the latitudinal diversity gradient. Science 314(5796):102-106.Stevens, George C. (1989) The Latitudinal Gradient in Geographical Range: How so Many Species Coexist in the Tropics. The American Naturalist Vol. 133, No. 2, pp. 240-256Carman, Mary R. , Stephan G. Bullard, Rosana M. Rocha, Gretchen Lambert, Jennifer A. Dijkstra, James J. Roper, Anne Goodwin, Mimi M. Carman and Elisabete M. Vail (2011) Ascidians at the Pacific and Atlantic entrances to the Panama Canal. Aquatic Invasions (2011) REABIC Volume 6, Issue 4: 371–380
Tunicate study group at the Liquid Jungle Lab.
The lead scientists Mary Carman, Stephan Bullard and Rosana Rocha wish to thank the Autoridad Nacional del Ambiente (ANAM) Panama for research and collection permits granted for this scientific investigation.