Sea snakes could slither into bull sharks' turf in Lake Nicaragua, if a canal project recently approved by the Nicaraguan government succeeds in digging a watery connection between the Pacific Ocean and Caribbean Sea via the lake. Along with sea snakes from the Pacific, changes in water saltiness and temperature could disrupt ecosystems and economies both in the lake and on the coasts.
Lake Nicaragua hosts an unusual ecosystem. Bull sharks leap salmon-style over rapids in the San Juan River to enter the lake. The lake-loving sharks swim alongside endemic fish species and non-native tilapia fish farms.
Those sharks would probably not suffer from the construction of a canal, according to Frank Schwartz, a marine zoologist at the University of North Carolina, Chapel Hill who has more than 50 years experience studying sharks.
The bull sharks may not suffer, but sea snakes entering the lake could be a more serious threat, noted Schwartz. The snake could enter the lake in ocean water brought in through locks and dams built to bridge the elevation differences across the Nicaraguan countryside.
The Caribbean lacks sea snakes, but Pacific serpents could conceivably make it across Nicaragua through a new canal. Groupers and other large Caribbean fish may then suffer after trying to make a snack of the snakes.
Beyond the impact of the invasive snakes themselves, serpent-bearing sea water could disrupt the salt and temperature balance of the lake, said Schwartz. Likewise, fresh water flowing out of the lake could have a similar negative effect on coastal mangrove forests.
Although Nicaraguan fishermen are accustomed to sharing the water with sharks, a sea snake invasion could disrupt their livelihoods along with wildlife in the lake.
"Like any invasive species, it is often difficult to predict the impact," John Murphy, herpetologist and research associate at the Field Museum of Natural History in Chicago, told Discovery News. "But, the freshwater fish of the lake would be naïve to the snakes and some could be extirpated (locally driven to extinction)."
Sea snakes depend on freshwater for drinking and many species could easily adapt to the lake, according to Murphy. However, the species most likely to colonize Lake Nicaragua has a lifestyle that makes it less capable of conquering the lake than other sea snakes.
"The only sea snake that would be likely to colonize the lake is Pelamis platura," the yellow-bellied sea snake, said Murphy.
The yellow-bellied sea snake is the only species that rides the surf of the open Pacific ocean while it waits to ambush prey, which puts the snake in a good position to enter the western side of the canal. Luckily for the fish and fishermen of Lake Nicaragua, this seagoing lifestyle also makes the yellow-bellied sea snake a poor candidate for lake colonization, according to Murphy.
Even if yellow-bellied sea snakes did manage to survive in the lake, their slow reproduction rate of only one to three offspring at a time would limit their ability to take over the lake, noted Murphy.
Ultimately, the threat of invasive species, salinity and temperature changes, along with other ecosystem disruptions depends on the way the canal is engineered.
"Lakes are sensitive systems," William Lewis, director of the Center for Limnology, or the study of lakes, at the University of Colorado, told Discovery News. "A change in one aspect of the lake system affects other parts... and those changes are often perceived as negative by people who depend on the lakes."
Digging a canal through the heart of Nicaragua and connecting the lake to marine environments on both ends would be a unique situation, Lewis explained. The potential repercussions are difficult to predict.
"Engineers could anticipate potential problems and design countermeasures," said Lewis. Or they can focus on decreasing costs, which raises the likelihood of adverse effects, such as a sea snake invasion.