A guide for planners and managers - IUCN

2.8 General Information Needs
PART II
Protected Areas for Lagoons and Estuaries
Planning for MPAs in estuaries or lagoons requires detailed ecological knowledge. The
protected area manager should have a thorough knowledge of the physical, chemical,
and biological parameters of the estuarine ecosystem and when possible participate
in research in the field (see Boxes II-2 and II-3). Research and monitoring studies and
periodic management plan revisions are the basis for the most successful management
of lagoons and estuaries. But only occasionally has sufficiently detailed research
preceded protected area design.
Box II-2. Physical Information for Lagoon and Estuary MPAs.
Geomorphology of a basin reveals a wealth of information on the likely functions
and characteristics of the ecosystem. Classifying the estuary by type requires little more
than visual inspection.
Bottom topography can yield features of ecological significance (shape of bottom
affects currents; shallow areas have higher photosynthetic rates, etc.). Depths can be taken
by a cheap electronic meter or simple lead line.
Bottom types reveal biological activity types that are particularly diagnostic for
estuaries. Samples of bottom sediments are easily obtained by simple methods; a bamboo
tube would be sufficient in many cases to distinguish among sand, mud, gravel, and ooze.
Salinity gradient (seasonal and sporadic) is easily determined with a direct reading
salinometer (see Chemical in Box X), although “presence or absence” can be learned from
the “taste test.”
Tidal flux in most estuaries is a dominant hydrological force. Measure diurnal
changes by use of water level gauges (marked stick), tidal velocities (movement of a float)
and extent of substrate exposed and flooded. Tide tables are usually available for navigable
estuaries.
Current patterns influence the degree of mixing between seawater and sedimentation.
Currents may be powered by tides, external marine currents, rivers, and wind. Surface
currents can be plotted with floating objects, like bottles or coconut husks.
Turbidity results from suspended particles of silt, organic detritus, and plankton.
It influences light penetration and photosynthesis. Turbidity can be measured with a Secchi
disc (a white-and-black painted, weighted disc lowered from the surface by cord).
Geomorphological dynamics indicate stability of different substrates in the basin
which may be shifting or filling. An outlet may silt up or a sandbar form or a new outlet
may open, seasonally, over a few years or overnight during storms. The MPA manager
can monitor these dynamics using trees, buildings, etc as visual benchmarks, or stakes
driven into the ground. More sophisticated survey techniques (remote sensing) may also
be used.
Seasonal considerations, including rainfall, air and water temperatures, insulation
(sunshine), tides, and hydrology are all important.
Source: Carr, 1982b.
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