73
6
K. E. Havens ()
Florida Sea Grant and University of Florida School of Forest
Resources and Conservation, Gainesville, 32611 FL, USA
e-mail: khavens@ufl.edu
Abstract
The plankton food web comprises microscopic organisms that transport carbon and energy
from producers to consumers in the water column of aquatic ecosystems. In lakes, the food
web includes bacteria, phytoplankton, protozoa, micro- and macrozooplankton, and the trophic links between them. Structure of the plankton food web in lakes is affected in a predictable manner by eutrophication: phytoplankton biomass becomes relatively greater, while
macrozooplankton biomass declines. The relative biomass of protozoa also may increase.
Food web function also is affected: ecological transfer efficiency is lowest in ultraoligotrophic lakes and hypereutrophic lakes and highest in mesotrophic lakes. The relationship
between the size of producers and grazers drives this unimodal pattern. In ultraoligotrophic
lakes, cooccurrence of picoplankton with copepods that cannot directly graze such small
particles results in long, energetically inefficient food webs with multiple steps including protozoa and microzooplankton. In hypereutrophic lakes, similar food webs occur, but
owing to cooccurrence of cyanobacteria and small macrozooplankton that cannot handle
those large and sometimes toxic phytoplankton. The dominance of large cyanobacteria in
hypereutrophic lakes can be directly linked to enrichment with nutrients, particularly nitrogen and phosphorus, while the small size of zooplankton is attributed most often to intense
fish predation. Long-term studies indicate that the changes in plankton food web structure
and function can be reversed if nutrient loads are substantially reduced.
Keywords
Eutrophication · Plankton food web · Lake management · Fish · Plants
eutrophication, is most often owing to an overenrichment of
lakes with phosphorus (P) and/or nitrogen (N; Conley et al.
2009) and recent evidence suggests that its symptoms may
be exacerbated by climate change (Moss et al. 2011) making
the rehabilitation of culturally eutrophic lakes an even greater challenge in the future. One impact of eutrophication on
lakes is a change in the structure and function of their food
webs. The aim of this chapter is to provide a concise overview of how cultural eutrophication affects plankton food
webs, drawing on research from the 1960s through studies
completed in recent years. The chapter is divided into the
A. A. Ansari, S. S. Gill (eds.), Eutrophication: Causes, Consequences and Control,
DOI 10.1007/978-94-007-7814-6_6, © Springer Science+Business Media Dordrecht 2014
Lake Eutrophication and Plankton
Food Webs
Karl E. Havens
6.1 Introduction
Thousands of lakes around the world have been impacted
by excessive inputs of nutrients from human-related uses of
the land, and as a result have experienced changes in their
ecological structure and function. This phenomenon, cultural
6
K. E. Havens ()
Florida Sea Grant and University of Florida School of Forest
Resources and Conservation, Gainesville, 32611 FL, USA
e-mail: khavens@ufl.edu
Abstract
The plankton food web comprises microscopic organisms that transport carbon and energy
from producers to consumers in the water column of aquatic ecosystems. In lakes, the food
web includes bacteria, phytoplankton, protozoa, micro- and macrozooplankton, and the trophic links between them. Structure of the plankton food web in lakes is affected in a predictable manner by eutrophication: phytoplankton biomass becomes relatively greater, while
macrozooplankton biomass declines. The relative biomass of protozoa also may increase.
Food web function also is affected: ecological transfer efficiency is lowest in ultraoligotrophic lakes and hypereutrophic lakes and highest in mesotrophic lakes. The relationship
between the size of producers and grazers drives this unimodal pattern. In ultraoligotrophic
lakes, cooccurrence of picoplankton with copepods that cannot directly graze such small
particles results in long, energetically inefficient food webs with multiple steps including protozoa and microzooplankton. In hypereutrophic lakes, similar food webs occur, but
owing to cooccurrence of cyanobacteria and small macrozooplankton that cannot handle
those large and sometimes toxic phytoplankton. The dominance of large cyanobacteria in
hypereutrophic lakes can be directly linked to enrichment with nutrients, particularly nitrogen and phosphorus, while the small size of zooplankton is attributed most often to intense
fish predation. Long-term studies indicate that the changes in plankton food web structure
and function can be reversed if nutrient loads are substantially reduced.
Keywords
Eutrophication · Plankton food web · Lake management · Fish · Plants
eutrophication, is most often owing to an overenrichment of
lakes with phosphorus (P) and/or nitrogen (N; Conley et al.
2009) and recent evidence suggests that its symptoms may
be exacerbated by climate change (Moss et al. 2011) making
the rehabilitation of culturally eutrophic lakes an even greater challenge in the future. One impact of eutrophication on
lakes is a change in the structure and function of their food
webs. The aim of this chapter is to provide a concise overview of how cultural eutrophication affects plankton food
webs, drawing on research from the 1960s through studies
completed in recent years. The chapter is divided into the
A. A. Ansari, S. S. Gill (eds.), Eutrophication: Causes, Consequences and Control,
DOI 10.1007/978-94-007-7814-6_6, © Springer Science+Business Media Dordrecht 2014
Lake Eutrophication and Plankton
Food Webs
Karl E. Havens
6.1 Introduction
Thousands of lakes around the world have been impacted
by excessive inputs of nutrients from human-related uses of
the land, and as a result have experienced changes in their
ecological structure and function. This phenomenon, cultural