Effects of Changing Environmental Conditions on Lagoon Ecology - Coastal Lagoons: Ecosystem Processes and Modeling for Sustainable Use and Development - page 208

S

B

A

Increasing organic input

FIGURE 5.7 Changes in abundance (A), biomass (B), and species richness (S) of macrobenthic
assemblages with increasing organic input, according to the Pearson-Rosenberg model. (Adapted
from Pearson, T.H. and Rosenberg, R., Oceanogr. Mar. Biol. Annu. Rev., 16, 229, 1978. With
permission.)

progressive decline in species richness and biomass when eutrophication increases,
while abundance (mainly of opportunistic species) continues to rise.
Effects of nutrient enrichment can usually be detected earlier and more obviously
in meiofaunal populations, with a lifecycle that is usually shorter than in the mac-
rofauna, thus responding more quickly to small changes in the organic content of
sediment. On the other hand, compared to macrobenthic fauna, meiofauna is also
less affected by physical disturbance of sediment (such as humans digging up
sediment to capture bivalves). 85,86 The joint study of macro- and meiofauna can be
useful to discriminate between two disturbance factors: pollution or organic content
increase and physical disturbances.
A moderate organic enrichment usually increases the secondary production of the
affected communities, supporting larger numbers of fishes and waterfowl. However,
when the origin of the load is sewage it can produce significant public health problems.
Filter feeders, such as mussels and clams, may accumulate and increase concentrations
of sewage-derived pathogens. Many beds of shellfish cannot be exploited or can only
be eaten after depuration. Pollution, whether chronic or acute, usually tends to favor
short-lived opportunistic species. 66

5.2.2.4 Fish Assemblages (Pelagic/Benthic)

As a result of increasing benthic invertebrate biomass and planktonic biomass, fish
production can also increase. This phenomenon was clearly observed in the Baltic
Sea. Elmgren 87 estimated that the pelagic energy flows in the Baltic increased by
30 to 70% in the 20th century and the fish catches increased more than tenfold. In
some areas of the Mediterranean, in the Adriatic and the Aegean Seas, eutrophication
extended offshore, increasing primary production and associated production of
pelagic fish, such as anchovies. 88