TRACING ALGAL INVASIONS ACROSS THE
PANAMA CANAL
Brian Wysor
1997 Fulbright Proposal
Brian's Home Page | C.V. | Smithsonian Tropical Research Institute
Increases in transworld shipping in the last 200 years have lead to an increase in the extent and diversity of introduced marine floral and faunal species around the world. The ability to transport coastal marine organisms across oceans or other barriers over short periods of time facilitates the introduction of foreign species to new environments (1). Introduced species could have devastating ecological impacts by replacing native species (which could lead to extinctions) and decreasing biological diversity. Studies which reveal biogeographical patterns of invasive species offer valuable insight into the mechanisms of introduction and subsequently into measures which can minimize the extent and impact of introduced species. The Panama Canal is an ideal system in which to study the biogeographical relationships of introduced species because it is a high traffic shipping zone and, in effect, is a breach in a natural, physical barrier (the Isthmus of Panama) through which transoceanic introductions could be easily accommodated. I propose using molecular tools to ascertain the biogeographical affinity of marine seaweeds from both sides of the Panama Canal and to test the null hypothesis that similar species of algae on both sides of the canal are native.
Biological invasions are the arrival, establishment and diffusion of non-native species which occur through range expansions and introductions (2). Range expansions result from dispersal events governed by natural mechanisms over evolutionary time scales. In contrast, introductions result from the anthropogenic transport of species across natural physical barriers and remain largely unpredictable. Milestone cases of marine bioinvasions include the introduction of Mnemiopsis leidyi, a small but voracious zooplanktivorous comb jelly, which reduced the anchovy landings of the Black Sea from hundreds of thousands of tons to tens of thousands in just seven years (3, 4). The toxic macroalga, Caulerpa taxifolia, believed to have escaped from the aquarium industry, now dominates the shallow sublittoral zone of vast regions of the Mediterranean Sea where a diverse assemblage of marine life once flourished (5). The weedy green alga, Codium fragile, has progressively invaded temperate coasts around the world for the better part of the last century (6). These classic examples represent a fraction of the number of human mediated invasions. The number of documented cases of introduced species continues to increase as methodological improvements allow for the recognition of previously undetected cases (7) and as anthropogenic alterations of ecosystems continue to diversify (8).
Mechanisms for anthropogenic dispersal of marine organisms include the transport of fouling and boring communities on ship hulls and the transport of organisms in ballast water of transient ships (1, 2, 7, 9). Because ships serve as temporary microecosystems, transplanting species from one environment to another, high traffic shipping routes are particularly susceptible to invasions. The varied reproductive strategies of marine algae make those species growing on bulkheads and ship hulls well suited to invasions. Spores, gametes, and vegetative fragments can be collected in ships' ballast water (1) and subsequently discharged at a new location. Additionally, the algal flora attached to the hull of a ship may release reproductive cells or attached thalli may fragment while en route. As primary producers, algae provide food, habitat and substrate for other organisms such that introductions of exotic marine algae may have cascading effects through the trophic hierarchy of an ecosystem.
The Panama Canal is an ideal system in which to study marine bioinvasions because it is a global convergence of ships that may be carrying exotic organisms. Completed in 1914, the Panama Canal remains one of the most commercially and militarily strategic waterways ever built. The 51-mile long waterway, designed to cut the transit of circumnavigational ships by as much as 8,000 miles (10), connects the Pacific Ocean to the Atlantic Ocean by a lake-and-lock system (11). Ecologically, the Panama Canal serves as a freshwater bridge between two distinct marine ecosystems; however, the freshwater presents a physiological stress to most marine organisms and consequently serves as a barrier to dispersal between Pacific and tropical Atlantic communities. Although few interoceanic colonizations have been documented (12, 13) the potential for biological invasions is great due to the extensive use of the canal. Some Caribbean species of macroalgae and animals have been shown to tolerate fresh water submersion for durations of time typical of canal transit (12, 14). Conservative estimates indicate that as much as 252 metric tons of fouling biota are transported across the canal annually (14), and while the odds of survival for most of these organisms are poor, conditions may be appropriate for some aggressive or opportunistic species to establish a population. If such an introduction is successful, as in the case of Mnemiopsis in the Black Sea, the ecological impact on the canal system may be severe because the physical and biological controls that once kept the organism (presumably) in check in its natural range may not be present in the new system (13).
Tracking biological invasions can be difficult due to poor historical records and a lack of understanding (ecologically and biologically) of donor and recipient regions (8, 12). The use of molecular biological techniques in phylogenetic (evolutionary history) studies has elucidated biogeographical relationships in many different groups of organisms, including introduced species which may have no inherently obvious origin (6, 15-19). Advancements in sequencing technologies (e.g., the Polymerase Chain Reaction (PCR) for amplifying DNA and automated DNA sequencers) have greatly simplified DNA sequencing methodologies, especially in cases where limited quantities of DNA are available (15, 20 ) (such as might occur when using samples from archived collections). As a result, alternatives now exist to examine differences in populations of marine algae which are independent of phenotypic plasticity (acclimation of a genotype to variable environmental conditions) . Nuclear ribosomal DNA (rDNA) sequences have been used to infer phylogenetic relationships across different taxonomic classifications in protists, fungi, higher plants and animals. In particular, the internal transcribed spacer (ITS) regions of the rDNA cistron has been identified as a preferred sequence region because it evolves rapidly, allowing for the delineation of species and subspecies (15).
I propose conducting sequence analyses of the ITS region of macroalgal rDNA from both sides of the Panama Canal to determine the biogeographical affinity of similar species and test the null hypothesis that similar species of algae on both sides of the Panama Canal are native. The Smithsonian Tropical Research Institute (STRI) offers a state of the art molecular biological laboratory where the proposed research would be completed. STRI is a valuable platform from which to work both due to its proximity to the Panama Canal and due to the emphasis placed on comparative biological studies of marine organisms found on both coasts of Central America (e.g. 21-24).
This research will serve to emphasize the potential impact of biological invasions in the region of the Panama Canal. In light of turning over governing authority of the canal to Panama in 2000, alternative uses of the coastal regions of the Panama Canal Zone currently used as naval stations are being considered. One promising proposal is the mariculture of economically important seaweeds which are native to the area and may currently occur in harvestable abundances (25). The impact of an invasive species in a controlled, mariculture setting would be quickly realized as an economic disaster. Molecular biological techniques used in conjunction with available ecological data will be paramount to determining the extent and diversity of invasive species in the vicinity of the Panama Canal and will also be instrumental to developing control measures to aid in the preservation of valuable marine resources.
Brian's Home Page | C.V. | Smithsonian Tropical Research Institute
LITERATURE CITED