Main threats

Gizani is threatened by the continuing environmental degradation of the streams of Rhodes island, that is caused by both the adverse impacts of human activities and natural processes.

More specifically, the main threat to the survival of gizani is summer drought and concomitant over-abstraction of water for domestic use and irrigation that dry up the streams of the island.

Drought occurs as a result of the arid climate with the limited rainfall. However, even when it rains, the flow of rainwater is fast (due to the steep slopes of the island's mountains) and thus the enrichment of the underground aquifer is poor. Furthermore, most forests in Rhodes were destroyed by fires in the recent past, hence decreasing the underground water sources, since the trees prevent soil erosion and retain the rainwater.

Severe degradation of the island's freshwater resources, and therefore of the habitats of gizani, has taken place in recent years, due to human activities. Tourist development has increased water consumption considerably (230,000 tourists visited the island in 1970 and more than 1,000,000 in 1990), while local domestic use also increased significantly (70 L/day in 1970 and more than 150 L/day in 1994). The above factors, along with abstraction (most often unregulated) of water for irrigation, contribute to the over-abstraction of the island's freshwater resources and to the seasonal drying up of the island's streams.

The disposal of litter and various solid wastes at the streams and the collection of sand and gravel from the streambeds alter the natural water flow and further degrade gizani habitats. Most of the island's streams do not suffer significant pollution, since streamside farming is limited and domestic liquid wastes from nearby villages are drained into absorbent sewers.

As a result of climate, geomorphology and man induced impacts, the streams of Rhodes often flood during rainy winters, whereas they dry up for most of their length during the prolonged dry seasons.

In fact, the size of each gizani population fluctuates according to the water quantity available at a given time. Population size is usually drastically decreased during the dry season of each year. The fish that survive reproduce massively the following spring, and thus the population size is usually regenerated at the beginning of the summer. However, the mass mortality of fish that occurs by the end of summer, leads also to the reduction of the population's genetic diversity.

The reduction of genetic diversity poses a serious threat to a population, as it can lead to genetic collapse and extinction.