From 30st of July to 2st of August we were in Manija, a beautiful island in Pärnu bay. In this talgud we were working for the benefit of Bufo calamita, natterjack toad. On the first day, we released young frogs, coming from the Penijõe amphibian restoration centre. A few months ago we were building tents for them in Penijõe, you can read more about it here.
On this island the small scale agriculture is ecological and frogs are a good help because they eat insects that influence some agricultural crops. We were cutting common reed grass because natterjack toad needs open habitat. They live on the ground so if the grass is too high they have difficulties to find food.
In shorter vegetation it is also easier for them to move. It is especially crucial in the reproduction moment, when the males are calling females. If the grass is too high, females cannot reach male frogs. The cut reed was accumulated in small piles to dry. Later these piles will be burned as there is no use for the reed.
The international camps are focusing on restoring the habitat for freshwater pearl mussel (latin name Margaritifera margaritifera). Also this year is about flowing rivers so here’s some information about this species.
The freshwater pearl mussel is one of the longest-living invertebrates in existence. This species has been exploited until the mid- twentieth century for the production of beads for jewelry, before the discovery in the eighteenth century tropical pearl oysters. Now it only can be founded in one river in Estonia. The longevity of this species is remarkable, as it varies between 20 and 30 years for individuals who live in warmer waters of Southern Europe, to more than 150 years for those living in Scandinavia.
The native distribution of this species is Holarctic. The freshwater pearl mussel can be found on both sides of the Atlantic, from the Arctic and temperate regions of western Russia, through Europe to northeastern North America.
The life cycle of the pearl oyster is associated with the trout and Atlantic salmon because these shellfish larvae grow to coat the gills of the fish, and only them. Once the fertilization (the sexes are separated), the larva, called a glochidium is incubated by the female for four weeks. When it reaches the size of 0.05 mm, the larva is released into the river and fixed on the gill apparatus of a brown trout or an Atlantic salmon. This parasitic phase usually lasts several weeks (up to 10 months), after which the glochidium becomes a real bivalve miniature 0.5 mm. The mollusk is then fixed on the substrate and continues to grow, reaching sexual maturity at age 20.
They require fast-flowing streams and clean rivers, where it lives buried or partly buried in fine gravel and coarse sand, generally in water at depths between 0.5 and 2 metres, but sometimes at greater depths. Clean gravel and sand is essential, particularly for juvenile freshwater pearl mussels, for if the stream or river bottom becomes clogged with silt, they cannot obtain oxygen and will die. Also essential is the presence of a healthy population of salmonids, a group of fish including salmon and trout, on which the freshwater pearl mussel relies for part of its life cycle.The freshwater pearl oyster is a filter animal that feeds on particles carried by currents.
Threats and conservation:
Once the most abundant bivalve mollusc in ancient rivers around the world, numbers of the freshwater pearl mussel are now declining in all countries and this species is nearly extinct in many areas. The causes of this decline are not fully understood, but alteration and degradation of its freshwater habitat undoubtedly plays a central role. The negative impacts humans have on rivers and streams come from a wide range of activities such as river regulation, drainage, sewage disposal, dredging, and water pollution, including the introduction of excess nutrients. Anything that affects the abundance of the fish hosts will also affect the freshwater pearl mussel; for example, the introduction of exotic fish species, such as the rainbow trout, reduces the number of native fish hosts. Introduced species are also directly affecting the freshwater pearl mussel; the invasion of the zebra mussel (Dreissena polymorpha), which has been spread to new locations by being transported on the bottom of boats or in ballast waters, has impacted freshwater pearl mussel populations in all countries it has invaded.
The freshwater pearl mussel, which is completely protected in most European countries, has been the focus of a significant amount of conservation efforts. Measures have included the transfer of adult mussels to areas where it had gone extinct, the culture of juvenile mussels, and the release of juvenile trout, which have been infected with glochidia, into small rivers, but mainly the freshwater pearl mussel has benefited from habitat restoration projects in some areas. Due to the essential role salmonid fish play in the life of the freshwater pearl mussel, the conservation of salmon and trout is also central in the survival of this endangered freshwater mussel.