Case Studies - Coastal Lagoons: Ecosystem Processes and Modeling for Sustainable Use and Development - page 412

4

1981

1987

3.5

1997

3

2.5

2

1.5

1

0.5

0

J FMAMJ J ASOND

FIGURE 9.3.18 Interannual monthly variation of chlorophyll a concentration in the Mar
Menor waters in three different trophic states: 1981 oligotrophic state; 1987 oligotrophic state
with increasing urban pressure in summer time without urban waste treatments and without
jellyfishes; and 1997 eutrophic state with continuous flow through the Albujón watercourse,
with urban waste treatments and with top-down jellyfishes control. J through D represent the
months of the year.

large gelatinous zooplankton. On the other hand, removing large diatoms has a direct
effect on nutrient loads as they uptake inorganic nutrients from the water column,
but the simultaneous removal of grazers such as ciliates and copepods reduces the
predation pressure on smaller phytoplankton. The feeding preference of jellyfish
imposes a combination of direct and indirect effects on the planktonic structure at
different size levels. The trade-off between competition for available resources (bot-
tom-up) and predation (top-down) control mechanisms 60,61 results in a planktonic
size structure different from that thought to occur under eutrophic conditions.
The presence of such direct and indirect mechanisms controlling the planktonic
food web makes it necessary to know in depth the nature of those processes in order
to establish causal relationships to be included in the eutrophication models. Knowl-
edge about many of these relationships can only be acquired after implementation
of long and detailed monitoring and scientific programs.

9.3.4 S UGGESTIONS FOR M ONITORING AND M ODELING P ROGRAMS

Obviously, to control the processes that lead to the degradation of the Mar Menor or
any other natural environment, it is necessary to have in-depth knowledge of the nature
of such processes and the causal relationships between them and human activities that
cause them. Such cause-effect relationships, in general, are unknown and to establish