A freshwater biodiversity hotspot under pressure – assessing threats and identifying conservation needs for ancient Lake Ohrid

摘要

Immediate conservation measures for world-wide freshwater resources are ofeminent importance. This is particularly true for so-called ancient lakes.While these lakes are famous for being evolutionary theatres, oftendisplaying an extraordinarily high degree of biodiversity and endemism, inmany cases these biota are also experiencing extreme anthropogenic impact.Lake Ohrid, a major European biodiversity hotspot situated in atrans-frontier setting on the Balkans, is a prime example for a lake with amagnitude of narrow range endemic taxa that are under increasinganthropogenic pressure. Unfortunately, evidence for a "creepingbiodiversity crisis" has accumulated over the last decades, and majorsocio-political changes have gone along with human-mediated environmentalchanges.Based on field surveys, monitoring data, published records, and expertinterviews, we aimed to (1) assess threats to Lake Ohrids' (endemic)biodiversity, (2) summarize existing conservation activities and strategies,and (3) outline future conservation needs for Lake Ohrid. We compiled threatsto both specific taxa (and in cases to particular species) as well as to thelake ecosystems itself. Major conservation concerns identified for LakeOhrid are: (1) watershed impacts, (2) agriculture and forestry, (3) tourism andpopulation growth, (4) non-indigenous species, (5) habitat alteration or loss,(6) unsustainable exploitation of fisheries, and (7) global climatechange.Among the major (well-known) threats with high impact are nutrient input(particularly of phosphorus), habitat conversion and silt load. Otherthreats are potentially of high impact but less well known. Such threatsinclude pollution with hazardous substances (from sources such as mines,former industries, agriculture) or climate change. We review and discussinstitutional responsibilities, environmental monitoring and ecosystemmanagement, existing parks and reserves, biodiversity and species measures,international conservation activities, and ongoing research on conservationand raising of public awareness. Following this summary, we evaluate thestatus quo and future of Lake Ohrid and its biota. A comprehensiveconservation strategy should include measures that result in an immediatereduction of nutrient input, particularly with phosphorus, in order to slowdown the ongoing eutrophication process. The existing watershed managementshould become more effective. Implementation and particularly with a view tothe enforcement of national laws should be enhanced. Increased research onthe lakes' limnology, biodiversity, and conservation management practicesare necessary. The latter research should identify conservation priorities.Public awareness should be enhanced. Facing these parallel needs to protectthe unique biodiversity of Lake Ohrid, we suggest urging (a) implementationand enforcement of the General Management Plan that would ensure long-termintegrated and sustainable use of the lake and its watershed, (b) scientificstudies on ecology, biodiversity and effects of human impact, (c) theestablishment of Core Conservation areas (CCA), including underwaterreserves, and (d) Coastal Zone Management (CZM) areas that would constitutebuffer zones for the CCAs around the lake. Given the number of identifiedthreats, it is clear that only concerted international action can stop or atleast slow down further degradation of Lake Ohrid and the creepingbiodiversity crisis already evident. All conservation activities should,among others, ultimately lead to a trans-boundary major conservation area ofthe Ohrid-Prespa region that would allow long-term integration of bothhumans and nature.