Effects of Changing Environmental Conditions on Lagoon Ecology - Coastal Lagoons: Ecosystem Processes and Modeling for Sustainable Use and Development - page 196

Macroalgae

Seagrass

Phytoplankton

Epiphytes

Bottom Light Intensity

Nutrient load

Short Residence Time

Long Residence Time

P

M P

M

S

S

Low High

Low High

Nitrogen loading rates

Nitrogen loading rates

FIGURE 5.2 Representation of changes in the lagoon ecosystem with increasing nutrient

loads. Top: In the oligotrophic state submerged aquatic vegetation is dominated by seagrasses
and the planktonic food web is based on the microbial loop. At moderate nutrient loads—
mesotrophic state—macroalgae outcompete seagrasses and small phytoplankton grow. At high
nutrient loads, large-celled phytoplankton dominates in the water column. Light is strongly
trapped becoming the limiting factor for macroalgae and benthic fauna turns to deposit feeders.
Middle: Evolution of the abundance of submerged aquatic vegetation, epiphytes and phy-
toplankton, with nutrient load and light reaching the bottom. (Adapted from Nienhuis, P.H.,

, 42, 59, 1992. With permission.) Bottom: Relative changes from benthic to pelagic
dominated vegetation with nutrient load and residence time of the water in the lagoon
(S = seagrass; M = macroalgae; P = phytoplankton). (Adapted from Valiela, I. et al.,

Vie Milieu

Limnol .

Oceanogr ., 42, 1105, 1997. Copyright 1997 by the American Society of Limnology and

Oceanography, Inc. With permission.)