Case Studies - Coastal Lagoons: Ecosystem Processes and Modeling for Sustainable Use and Development - page 396

TABLE 9.3.2
Oxygen Values (mg/l) in the Water Column on Distinct Kinds of Bottoms
and Statement of the Macrophyte Meadows in a Location off the Los Urrutias
300 m from the Coast (July 1986)

Dense Meadow of
Cymodocea nodosa-
Caulerpa prolifera on Mud

Dense Meadow of
Cymodocea nodosa-
Caulerpa prolifera on Rock

Lax Meadow of
Cymodocea nodosa
on Mud

Surface water 5.56 5.56 5.56

1 m 5.64 5.64 5.64

2 m 5.87 5.87 5.87

3 m 5.87 5.87 5.87

3.2 m (bottom) 1.76 4.12 4.04

Note: Profiles are less than 10 m from each other.

retrieving fine particles at the more exposed areas. Although sandy sediment usually
show no vegetation coverage, Cymodocea nodosa meadows are also related to these
bottoms determining slightly higher contents in the fine fraction and organic matter.
Caulerpa prolifera or mixed C. prolifera-Cymodocea nodosa beds, in contrast,
determine muddy bottoms with very high organic matter content, which also acts
as a sediment trap thus favoring fine particles and organic matter accumulation (as
stated in other places by Harlin et al . 16 or Genchi et al . 17 ).
The contribution of the macrophytes to the organic content of sediment is a
common feature in coastal lagoons, estimated by Mann 18 to be over 60% of the
macrophytic production. In the Mar Menor the macrophytic production has been
estimated as 165.6 g C/m 2 /year 19 implying an input of detritic carbon to the lagoon
bottoms of at least 13,400 mt C/year.

9.3.1.4 Biological Assemblages

Biota is characterized by eurihaline and euritherm species also present in the Med-
iterranean Sea, but they usually reach high densities in the lagoon. Many of them
are generalist species ( r -strategists) and their high density is the result of both their
rapid growth rates and lack of competitors.
From an ecological perspective, the Mar Menor differs from other Mediterranean
coastal lagoons in several aspects related to its environmental heterogeneity. Its size,
depth, availability of rocky substrates related to the volcanic outcrop and docks, and
the mediterranization process related to increased water interchanges account for
much of the richness of species and actual bionomic diversity.
Phytoplankton assemblages follow a clearly defined seasonal succession in which
four stages can be identified: (1) a winter period dominated by Rhodomonas and
Cryptomonas with Cyclotella as the main diatom represented; (2) a spring phase
where diatoms (mainly Cyclotella ) are the dominant group with some monospecific
blooms of other diatoms (mainly of Chaetoceros sp . ); (3) a summer phase charac-
terized by diatoms with blooms of Niztschia closterium; and (4) a post-summer and
fall phase where diatoms still remain the major group but dinoflagellates increase in