Underwater fauna of the Gironde estuary in France.
The Gironde estuary in the department of Charente-Maritime in West of France consists of a mixture of saltwater and freshwater very beneficial for underwater fauna that is very specific. It is marked by all estuaries physical characteristics (turbidity, salinity) and biological. The waters are very nourishing for the underwater fauna. The Gironde estuary is the largest estuary system in Europe. It is also the most open to marine influences. Biodiversity, even if it is low colonized by species able to withstand high environmental variations, including salinity. Changes in salinity are primarily due to strong tides and currents very important.
An estuary is the portion of the mouth of a river where the effect of the sea or ocean in which it flows is noticeable. For some, it is all part of the river where the water is brackish or salt, for others, it is the presence of the dynamic effect of the tide on the river water that defines it. By convention, we do not speak of estuaries to rivers that flow into inland seas that have no tide. In the case of the Gironde estuary, it is rivers: the Garonne and Dordogne. It is 75 km long for 12 kilometers wide at the widest. It covers 635 km square.
The Garonne and Dordogne rivers bring from 800 to 1000 m3 / s freshwater sediment-laden and at the same time, twice a day the tide brings 15 000 to 25 000 m3 of seawater, which promotes the formation of sandbanks and islands of vasards. Meet the fresh water rich in alluvium, with salt water is flocculated clay particles that form a "turbidity maximum" characteristic of estuarine waters. Gironde carries each year from two to eight million tonnes of suspended particles. A portion of the suspended solids (1.5 to 3 million tons per year) is deposited, forming sandbars, and islands of vasards. The Gironde estuary is highly subject to the ebb and flow of the tides. Another characteristic of the Gironde estuary north for the presence of a river Seudre. It fills and empties with the tides. The waters are then loaded silt and mud that come further fuel the ecosystem of the region so special.
These photos of fish were taken during the summer of 2012 at the mouth of the Gironde estuary off the city Royan. Diving conditions are very difficult because the currents are very violent. Divers can get water at the stall current. Temperatures hover around 16 degrees Celsius. The number of species even though it is far from reaching the tropical waters is still important with blennies, gobies, rays, crabs, crabs, eels, lobsters ... The main problem for underwater photographer and scuba diver is that visibility is completely unpredictable. It can reach 10 centimeters as 15 meters. Many statistics and measurements were made during the last ten years by divers but for now, it is impossible to predict water conditions.
It is a lottery!
Yet despite these specific conditions, the mouth of the Gironde estuary is one of the most exciting places we've photographed.
Click on a thumbnail to enlarge the image.