Saline lagoons, State 2 - intermediate salinity levels

In lagoons maintained at a higher salinity (18-24%) there is a greater likelihood of the development of a specialist fauna. Under these circumstances marine derived species represent a large proportion of specialist lagoonal species. From the analysis undertaken in the Saline Lagoon Guide (Section 3.3) an optimal range of habitat parameters for a hypothetical saline lagoon which supports specialist, marine, lagoonal species has been derived:

• At least 60% of the water of the lagoon persisting at all times of year and states of tide;
• Salinity varying, over a range between 15% and 40%;
• Sea-water input exceeding freshwater input.

These together with the following other attributes provide the preferred State for saline lagoons of biological value:

• Muddy-sand to sandy-mud substratum;
• Rocky substratum for specialist hard substratum biotopes;
• Shelter from wind effects;
• >1 ha, and if >10 ha then of high length to breadth ratio, aligned across rather than along the prevailing wind direction;
• To one metre deep, but the majority less in smaller lagoons and over substantial marginal areas of larger lagoons such as found in Scotland;
• Shallow margins except where this may encourage deleterious reed encroachment.

Comment: These lagoons are sensitive to drying out and to salinities <10% or >40%. If these conditions persist for much more than a week mortality will occur. As the generation time of the more marine species is longer than, for example the chironomids present in State 1 Lagoons (Nereis can take over a year to reach maturity) biomass levels can be depressed for over a year after mortality events.