Case Studies - Coastal Lagoons: Ecosystem Processes and Modeling for Sustainable Use and Development - page 388

9.3 THE ECOLOGY OF THE MAR MENOR COASTAL

LAGOON: A FAST-CHANGING ECOSYSTEM
UNDER HUMAN PRESSURE

Angel Pérez-Ruzafa, Concepción Marcos Diego,
and Javier Gilabert

9.3.1 F UNCTIONAL T YPOLOGY

9.3.1.1 Location, Origin, Climate, and Hydrography

The Mar Menor is a hypersaline coastal lagoon, with a surface area of 135 km 2 and
a perimeter of 59.51 km. It is located on the southwestern Mediterranean coastline
(37 W) with a mean depth of 3.6 m and a maximum depth of

6 m. La Manga, a sandy bar 22 km long and 100-900 m wide, acts as a barrier
between the lagoon and the Mediterranean Sea. It is crossed by five more or less
functional inlets called golas . Four are shallow (less than 1 m deep) and one of
them, the El Estacio, was widened and dug to a 5-m depth to make it a navigational
channel. Altogether the total width of lagoon entrances is about 645 m, giving Mar
Menor a restriction ratio of 0.015. Mar Menor is therefore a restricted lagoon
according to the classification proposed by Kjerfve 1 ( see Chapter 6). There are two
main islands and three other smaller islands, one of which is artificially connected
to La Manga. Figure 9.3.1 and Figure 9.3.2 show the location of the Mar Menor
Lagoon and its main physiographic characteristics.
The origin and evolution of the Mar Menor Lagoon have been greatly influenced
by the changing levels of the sea since the Tortonian, the volcanic activity that
occurred during the Pliocene and formed the small hills and islands in the Mar
Menor basin, and the Quaternary compressive system that helped shift the sandy
barrier that encloses the Mar Menor. 2,3
At present, the main geomorphological elements that determine the lagoon dynam-
ics are (1) the sandy barrier enclosing the Mar Menor; (2) the inlets or golas that
determine the entrances from the Mediterranean Sea and its hydrography and confine-
ment; (3) the islands and volcanic outcrops that constitute the only natural rocky sub-
strates and generate environmental diversity for biological assemblages; (4) the gullies
or ramblas that contribute waters and materials from agricultural run-off and mining
mountains; and (5) marginal lagoons, now transformed into salt flats or salt mines.
The lagoon basin is located in a semi-arid region with low rainfall, 4 an annual
mean of 300 mm, and high potential evapotranspiration (close to 900 mm) that
results in a deficit of the net annual hydric balance that exceeds 600 mm/m 2 year
(Figure 9.3.3) . The orographic configuration of the basin, the scant vegetation, the
impermeability of marly sectors, and the precipitation concentration all make tor-
rential rainfall a characteristic of the area. 5 Winds show a well-defined and regular
pattern during the year primarily from the east ( levantes ) followed by winds from
the west and southwest ( lebeches ) ( Figure 9.3.4) . The annual mean velocities of the
weakest winds (west and west-southwest) range from 9 to 12 km/h and the strongest

° 42 ′ 00 ′′ N, 00 ° 47 ′ 00 ′′