Deteriorating water quality, invasive species and the practise of draining lakes is now bringing the axolotl, a neotenic mole salamander native to central Mexico, to the brink of extinction. According to researchers the species could disappear in just five years and it is currently listed as Critically Endangered on the IUCN Red List of Threatened Species.

“If the axolotl disappears, it would not only be a great loss to biodiversity but to Mexican culture, and would reflect the degeneration of a once-great lake system,” says Luis Zambrano, a biologist at the Universidad Nacional Autónoma de México (UNAM).

The axolotl (Ambystoma mexicanum) is native to no more than two lakes, Lake Xochimilco and Lake Chalco, and Lake Chalco was drained in the 1970s to prevent flooding. The only surviving wild population of axolotl is therefore to be found in Lake Xochimilco; a lake that is rapidly vanishing due to draining efforts. Today, Lake Xochimilco can not even be accurately described as a lake anymore; it is just a series of canals and scattered lagoons. As if this wasn’t bad enough for the axolotl, this salamander also has to combat severe pollution and the introduction of alien species. Mexico City has been pumping its wastewater into the remains of Lake Xochimilco since the 1980s, and both African tilapia and Asian carp have been deliberately introduced to serve as food fish. These alien species compete for prey items with the axolotl and are also fond of eating its eggs.

The exact number of axolotls left in the wild remains unknown, but a survey conducted by Zambrano shows a sharp drop from roughly 1,500 specimens per square mile in 1998 to no more than 25 per square mile in 2008.

One way of improving the situation for the remaining axolotls may be to create a series of axolotl sanctuaries in canals cleared of invasive species, but this would of course require some type of barrier to keep the aliens from returning. A pilot sanctuary is planned to open in Mexico City in 2009.

Repopulating Lake Xochimilco with captive reared specimes has also been suggested, since the axolotl is a popular house pet known to readily breed in captivity. Unfortunately, it is always risky to re-introduce a species into the wild since captive specimens may be carriers of genetic problems or hosts of malicious organisms like parasites, viruses and bacteria.

During the Aztec empire, the axolotl was an important food item as well as an integral part of numerous myths and legends. According to legend, the Aztec god Xolotl – who was in charge of death, lighting and monstrosities – suspected the other gods of plotting to banish or even kill him, and turned himself into a salamander in order to fool them. He moved to Lake Xochimilco where he could stay hidden from the other gods and Xolotl became a-xolotl, blessing the Aztecs with an important source of food. If you visit markets in Mexico City today you can still find axolotls being sold as food. Cooked axolotl is however becoming a more and more scarce dish on Mexican dinner tables, mainly because fishermen almost never find them.

Outside Mexico, the axolotl is more popular as a pet than a snack. It can today be found in pet shops world-wide, sometimes being offered under other names such as Wooper Rooper or Mexican Water Monster. The axolotl is also famous for its ability to regenerate most body parts and is extensively used in scientific research on regeneration and evolution.

As we release more and more carbon dioxide from fossil fuel into the atmosphere, the world’s oceans become more and more acidic. Exactly how this will affect marine life remains unknown, but a paper published this week by marine chemists Keith Hester and his co-authors at the Monterey Bay Aquarium Research Institute is now shedding some light on how a change in acidity affects sound waves under water.

Beluga Whale

So, why is the speed of sound underwater of any interest to Monterey Bay Aquarium researchers? As sounds travel faster, the amount of background noise in the sea will increase and this could affect the behaviour of marine mammals. Many marine mammals, such as whales, dolphins, and porpoises, relay on sounds for communication and food location.

According to conservative projections by the Intergovernmental Panel on Climate Change (IPCC), the chemistry of seawater could change by 0.3 pH units by 2050. According to Hester and his colleges, such a change in acidity would allow sounds to travel up to 70 percent farther underwater in some areas, especially in the Atlantic Ocean. The paper also states that sound may already be travelling 10 percent farther in the oceans than it did a few centuries ago.

According to Hester et al, a change by 0.3 pH units by 2050 will have the greatest effect on sounds below about 3,000 cycles per second. This range includes most of the low frequency sounds that marine mammals are known to use, but it also includes a lot of sounds produced by human activity, such as boating, shipping, and certain military activities. As if acidification of the ocean wasn’t enough, the amount of underwater sound produced by human activities has increased dramatically over the last 50 years. So, even if acidification would make it possible for sound produced by marine mammals to travel farther than ever before, it might also cause these sounds to be effectively drenched by a cacophony of human generated low frequency noise. In such a noisy sea, a marine mammal’s ability to locate prey animals and a suitable mate and could be severely impinged on.

The paper will be published in the October 1, 2008 issue of Geophysical Research Letters.

Scuba diving tourists are an important source of income for Egypt, but now the tourism sector might be sawing off the branch on which they’re sitting by over-exploiting the sensitive coral reefs of the Red Sea. According to a study by Hasler and Ott, heavily dived dive sites near the town of Dahab have a significantly lower level of coral cover compared to areas without recreational diving.

Located off the south-eastern coast of the Sinai Peninsula, the reefs of Dahab is one of Sinai’s most treasured and well visited diving destinations. Dahab is still a fairly small town, but it is situated no more than 80 km (50 miles) from Sharm el-Sheik, a bustling tourist hub which attracts tens of thousands of visitors each year. Some of the dive sites off Dahab are among the world’s most heavily dived sites with over 30,000 dives per year.

According to Hasler and Ott, heavily dived sites in the studied area exhibited a reduced coral cover compared to non-dived sites and there were also significantly higher levels of broken and damaged corals. Differences could also be observed within the same reef, with coral communities located on reef crest areas being significantly more damaged than coral communities growing on reef slopes.

Divers are not only causing trouble by damaging corals directly; they can also stir up the sand around the reefs, thereby promoting sedimentation on top of the corals. Attached corals cannot free themselves of sediment particles and being covered in sand is therefore very dangerous for them.

In order to combat the problems faced by heavily exploited reefs, Hasler and Ott have suggested implementing ecologically sustainable dive plans for individual sites and limiting the total amount of dives per year. According to the authors, it is also very important to educate dive guides and divers.

For more info, read the results of the study which are due to be published shortly in Marine Pollution Bullentine. “Hasler H and JA Ott (2008) – Diving down the reefs? Intensive diving tourism threatens the reefs of the Northern Red Sea. Marine Pollution Bulletin, 2008 Aug.”