The alteration of waterways is coming to extents that could not be imagined a few years ago, even by those who have personally witnessed the accelerated pace of human destructive activities on the environment. We constantly read about these facts but when it comes to experiencing them, it really makes one shiver.
Back in 2005, I made one of my frequent visits to one of my favorite aquatic places, the Nututun natural aquarium just north of the town of Palenque, in Chiapas, México. Nututun (place among rocks in the local native language) is a wonderful clearwater pool located in the Chacamax River course. Chacamax is a mountain river that flows straight to the mighty Usumacinta River in its lower part.
Nututun is a circular shaped pool about 50 meters in diameter and nine meters deep, fed by a small waterfall. It has crystal clear water running swiftly over a rocky bottom. Nututun is home to an incredible assemblage of Usumacinta fish species, including seven permanent cichlid residents (one more species, Astatheros nourissati, is sporadically seen). The place is surrounded by rainforest vegetation, trees are covered with epiphytic species (including several orchids), and beautiful birds are seen all around. It is a favorite place for visitors and certainly for people interested in aquatic life. There is a riverside restaurant overlooking the pool and also a hotel.
At that time of my visit in 2005, the river was as wonderful as I first knew it ten plus years before. I dove in the place, took pictures, and as usual had a great time. I thought to myself; “this is one unspoiled place that should prevail, what could harm it?” How far I was from knowing what was to happen. Early in 2007, a group of friends which included Dan Woodland from the United States, visited the place and were shocked with what they found. Nututun was filled with huge schools of a large invasive plecostomus species. Dan filmed what he saw and distributed the film. I was totally shocked! Thousands of plecos swimming in the place, in a way that was reminiscent in my mind to hordes of barbarians invading Rome, in the fourth century A.C.
The origin of the plecos is unknown to my knowledge, but release into the river by an unaware aquarist cannot be ruled out. Plecostomus (and many other potentially invasive species) are available for purchase in aquarium stores in México even in small cities like Palenque.
What effect would this bring? It is my experience that an invasive species, many times finding no natural resistance to colonization by natural enemies, may grow out of proportion to incredible numbers before collapsing under its own weight, but the biomass of the invading organism replaces in the meantime that of the native species, some of which are inevitably completely expelled.
During this past month I had the opportunity to visit Nututun again. I was uncertain of what was to be found, and the extent of the damage done by the invasion. I was wishing to myself that the plecos had receded. Upon getting to the wonderful pool, something struck me right away: the color. It was not blue as usual, but black. After getting close I noticed that the black color was caused by the full substrate being covered by millions upon millions of plecostomus, one beside the other. The regularly slippery rocks at the riverbank were rough enough so you could walk without fear of slipping. That was an appalling sight!
I decided I didn’t want to swim and witness the destruction myself, but my good friend and travel companion, Rusty Wessel, decided to do so as he wanted to film some cichlids. After a while he came out depressed with what he saw, as very few native fish remained in the place, and it was now inhabited almost exclusively by the plecos. I then suggested to Rusty that he walk up the river and up the falls to another pool to see if there was any difference. We did and there was no difference, Chacamax River is totally infected.
Rusty commented to me after his swim that the plecos were starting to look unhealthy and thin. This was something I could see after spotting several dead fish, both in the water and on the shore. Is this the beginning of their doom? What will it be when they recede, will there be any left? What will be of the wonderful native fauna when this happens?
Visiting other places in the lower Grijalva, we were shocked to see that the plecos have extended their presence there. We were told in Villahermosa that they are now to be found everywhere, causing problems to fishermen with their spines entangling in their nets. In some places we found them to be ubiquitous, and in others, like some rainforest creeks in the mountains of Tabasco, just a few specimens were seen, up to now.
What will the extent of the damage be? Certainly it won’t be small. Usumacinta-Grijalva River is one of the richest places in terms of aquatic biodiversity in Central America, and the damage plecos have caused to the Chacamax River can serve as an example of the effect they will eventually have on the environment. This is however not the worst, as every year, each year more than the last, we learn of new exotic introductions in waterways, causing destruction of native species as the unstopped biomass growth of the exotics replaces them.
This is true even for species native to particularly biologically important areas. Last week I visited Tamasopo River in San Luis Potosí, one of the most beautiful and interesting rivers in Central America, with eleven native fish species of which at least nine are endemic to the river. I noticed the presence of an invader to the area never seen before. On this occasion I found Poeciliopsis gracilis in large numbers. I looked around for possible effects and realized that the local molly, Poecilia mexicana limantouri (probably an endemic species as well), was only present in very small numbers, unlike before.
What comes tomorrow? What can we do to slow down this destructive trend? One small truth must be of common knowledge for every single aquarist. Do not ever, for any reason, introduce an exotic species in a natural waterway. This of course won’t solve the problem, but at least may delay it until we have better tools to fight it.
See you next month!