Galician estuary: entrance of the sea into the river mouth.
Main factors in the formation of the estuaries: 1 . TECTONIC . The tectonic efforts created a faults system in three directions that determinated the orientation of the North estuaries (Rías Altas) (NE-SW), Middle and South (Rías Baixas) (SW-NE). 2. FLUVIAL . The fluvial courses used these faults zones and eroded deeply the beds of the rivers. This happened in a cold period in which the coast line was off shore. 3. CLIMATIC . The change to a warm period caused ice fusion and a rise in the level of the sea, flooding the end of the fluvial valleys previously dug out,. The estuaries were created. Coast level in glaciar period Rise of the level of water in the deglaciation Current level coast
Upwelling The wind that blows from the earth to the sea removes the warm superficial water allowing the rise of the cold deep water with a lot of nutrients. The deep water has a lot of nutrients such as nitrates and phosphates which are the result of the decomposition of the organic matter that came from the superficial water. When these nutrients are carried by the cold water to the surface, they are used by the phytoplankton for (with CO2 and light) making the photosynthesis. This growth of the primary producers carries all the food chain of the ecosystem. Phytoplankton -> Filtering Zooplankton>Predator Zooplankton ->Filtering Fishes-> Predator Fishes.
The most important upwelling zones in the world match up with that phenomenon and they are the most productive fhising areas. They are, besides the Galician short estuary tidal, the coast of Namibia and South Africa, the coast of Perú and Chile in South America…
SEA RESOURCES RECURSOS DO MAR
Bivalve Mollusks: MUSSELS Filtering bivalve mollusks which live in highly populated communities fixed over a substratum. They are in tidal zones and below them, but always in shallow zones. We can find them on the rocks but the traditional method to produce them is the growing in bed. In this system, the larvae of the mussels are fixed on the ropes that hang from a floating plattform. These beds are placed inside the estuary tidal, where the mussels will stay completely submerged until they get their commercial weight.
Bivalve Mollusks:CLAMS Bivalve mollusks with a smooth shell and different colors which live buried in shallow sandy areas. Gathering shellfish on foot is the traditional way to get the mollusks on the beach (clams, cockle) or on the rocks (mussels, goose barnacle) during the low tide. It is also called « ir á seca». Gathering afloat shellfish is the proper method to capture mollusks that grow below the water. The fisherman uses a device ( raño ) with a net and a very long handle (8-9 metres) which is thrown into the sea and dragged through the sandy floor towards the boat. The shellfish is kept into the net. It is also called “ ir ao raño”.
The farming of these bivalves consists in the care of the sandy areas by removing predators as starfishes or seaweeds which avoid the entry of oxygen. The sandy areas are plowed to oxygenate the substratum and, when the population of their offspring is high, they are recollected and sowed in another plot.
The mollusks have the shortest and most productive food chain in the sea, due to their free feeding and the high performance result in their cultivation.
In the Ría de Arousa three different type of clams are growing:
- The fine clam ( ameixa fina or from Carril ). It i s the highest quality clam in the market. It has very fine lines in the shell that draw small squares.
-The slug clam ( ameixa babosa) . It has the same quality as the fine clam but more delicate. The main difference with the fine clam is that the slug clam has the siphons linked along all their length.
-The japanese clam ( ameixa xapónica). It has very marked lines drawn in the shell, which a more visible than the fine clam ones. The siphons are joined until the half of their length.
Other bivalves: cockle and razor clam.
The razor clam is a big size bivalve mollusk with a very peculiar shape.
In the longueirón , the valves are rectangular and in the navalla are a bit curved. They live buried in shallow zones inside the estuary. There, they are able to dig big holes where they hide from the potential predators. They feed like the rest of the bivalves, with plankton which is filtered through their siphons.
The capture of the razor clam is carried out by diving and detecting them by the little sandy pile that the razor clam makes to get buried.
The cockle is a small size mollusk, almost circular, that lives in muddy or sandy floors near the coast. They feed themselves with tiny seaweed or microorganisms that are found inside the sand. The capture of the cockle is carried out with a « raño» from a boat or on foot when is collected in bed on the beaches leds.
Two islands of Ría de Arousa, Sálvora and Cortegada , are included in the National Maritime-Land Park of the Atlantic Islands (with Cíes and Ons located in the estuary of the Pontevedra and Vigo).
This protection figure intends to preserve maritime ecosystems, cliffs, beach ecosystems, dune systems, coast atlantic and mediterranean bushes and all the flora and fauna associated with them. Moreover, the island of Cortegada has, the biggest laurel forest in Europe.
Punta Carreirón , in the island of Arousa, belongs to the Complexo intermareal Umia-O Grove. In this area, the fresh water from the Umia river and the salty waters from the Atlantic ocean mix together creating an amazing group of ecosystems composed of big sandy areas, intertidal plains, marshlands, and the only coast lake which exists in Pontevedra. It has included a lot of protection figures as Ramsar zone, ZEPA, LIC ….
Dune vegetation. Adaptations . The plants of dune are exposed to the hard environmental conditions; wind, salinity and high insolation. To get an appropiate adaptation to them, they develop strategies such as the white pilosity, deep roots and succulent leaves. Othantus maritimus (carrascas de San Xoán) . White pilosity. Eryngium maritimum (cardo de ribeira) . Up to five metres long roots and leaves with thorns. Cakile maritima (eiruga de mar). Succulent leaves.
Limicola birds . They feed little invertebrates, crustaceans and mollusks. They show beaks with different lengths and curvatures according to their ecological niche.
We are in risk of losing our biodiversity because of: 1. Overexploitation (overfishing or poaching). 2. Environmental destruction (town planning and tourism). 3. Introduction of exotic species.
(cat nail) :
invady plants highly spread out in the Carreirón dunes and in all the coast zone. It comes from South Africa and it was planted with ornamental purpuses because of their flamboyant flowers. Due to its expansive growth that shaped like a carpet, they do not let space for the native species, which are in decline.