Department of Animal Ecology and Systematics, Justus Liebig University Giessen, Heinrich-Buff-Ring 26-32 (IFZ), D-35392 Giessen, Germany. E-mail: Chri...@allzool.bio.uni-giessen.de
The few existing long-lived or ancient lakes in the world are famous for being evolutionary theatres often displaying an extraordinarily high degree of mollusc diversity and endemism. However, it is often overlooked that in many cases these faunas are under extreme anthropogenic pressure. In an attempt to summarize contemporary knowledge, I review current information on the conservation status of ancient lake endemic molluscs for a total of 12 well-known and 10 less recognized (putative) ancient lakes. A combination of three sources was used for data on the various lakes: literature records, recent survey data, and expert interviews.
All of the assessed lakes showed a certain degree of faunal change, including decline in population densities and loss of endemic species. The degree of these changes, however, varied widely. It appeared to be most severe in the Caspian Sea and many of the lakes of the Balkan Peninsula, for example with alarming situations in lakes Dojran and Skutari (Skadar). Our recent studies have indicated that the mollusc faunas in the major Balkan lakes are extremely vulnerable and most of the endemics are in imminent risk of extinction if not already extirpated. Very often only cosmopolitan species remain. In addition, newly introduced species have been recognized in an increasing number of ancient lakes including famous large water bodies thought to be inviolate such as Lake Malawi, Lake Titicaca or the Caspian Sea.
It appears that stenotopic and ecologically restricted species often lack recent records, despite intensive field searches. Many of the (potentially) lost species were restricted to specific stretches of coast line with particular habitat characterisics. It is apparent that many profundal species seem to disappear or become extremely rare in many lakes.
Anthropogenic pressure is most often related to population increase, as seen around the lakes of Sulawesi or the African Rift. Major environmental changes include reductions of water levels due to massive extraction for agribusiness and eutrophication from fisheries, pollution, toxification, and seasonal climatic extremes. This causes direct or indirect habitat destruction. As a consequence, benthic communities are altered and eventually food webs become interrupted. Highly adapted and specialized species cannot cope with these often rapid environmental changes.
Public awareness of the uniqueness of these ecosystems needs to improve to give sustainability to conservation efforts. For example, this may help increase acceptance of management plans for controlled water extraction and accelerate installation of sewage treatment systems. Agricultural and forestry practices should aim to become more sustainable, reducing use of fertilizers and pesticides. However, all these practices can only be effective if concerted Conservation Action Plans (CAPs) for each lake are implemented in the immediate future. An additional point of concern is the lack of complete species lists for ancient lake molluscs among IUCN Red Lists or national protection laws.
Facing a dramatic decline and loss of mollusc diversity in many worldwide ancient lakes is only one side of the coin. Using a modern phylogenetic framework, it becomes more and more obvious that there remains unrecognized diversity to be discovered in those lakes. The simultaneous trends of losing and discovering mollusc diversity should trigger increased research efforts on the remarkable malacofaunas of those unique aquatic ecosystems.