Preface

The term "plankton" was coined in 1884 by Hensen to indicate organisms randomly disposed in space. In 1974, plankton distribution was assumed by Lussenhop as uniformly distributed in space. Indeed, the term plankton means wandering; basically, it is a category of organisms that are passively displaced by water, that is, they are dragged by marine currents or even by waves. Many of the organisms that compose plankton have their own movements; however, because they belong to a small-scale water movement, they cannot overcome the force of currents or waves. Plankton is strongly influenced by climate features, chemical stressors, and hydrological conditions. Their sensitivity to these fluctuations results in communities that are continuously changing and adapting to environmental factors as well as to changes in available resources. The organisms that constitute plankton are subdivided into phytoplankton (autotrophic) and zooplankton (heterotrophic) in the marine food chain. Among the main planktonic organisms, we cite protozoa, microalgae, crustacean larvae, small crustaceans, jellyfish, and larvae of various animals. The marine plankton community can also be found in limnic (freshwater) environments. Within the planktonic community, we find zooplankton (animals), bacterioplankton (bacteria), and virioplankton (viruses), among other less significant groups. An interesting pattern is the vertical distribution of the copepod community, which is a complex structured response to tidal, diel, and lunar cycles, to environmental variables (e.g., salinity, temperature, hydrostatic pressures), and to reproductive cycles of prey and predators.

Colonies of unicellular algae with poor mobility form what is called phytoplankton (vegetables). Phytoplankton contains chlorophyll and other pigments, and like terrestrial plants, they can carry out photosynthesis. Due to these characteristics, they are essential for maintaining sea life, as they are the basis of the trophic chain of the aquatic universe. Phytoplankton organisms go beyond just being organic matter (food); they are also responsible for producing oxygen. In this production process, phytoplankton plants release oxygen gas in a dissolved form in water instead of releasing it directly into the atmosphere. The oxygen dissolved in the water is used by fish and other organisms that live in the sea to breathe.

Oceans are responsible for a large part of the oxygen that is produced on Earth and thus phytoplanktons are essential organisms for maintaining not only aquatic life but also life on the planet. Just like land vegetables, aquatic plants need light and nutrients to thrive. In this case, nutrients need to be dissolved in water; the main components of which are nitrogen, phosphorus, silicon, iron, and so on. Thus, the productivity of the oceans is associated with light conditions and the availability of these nutrients.

This book is divided into three sections. Section 1, "Introduction," includes two chapters: Chapter 1, "Response of Marine Plankton Communities in Ponds to the Presence of Vertical Structures" and Chapter 2, "Plankton: Environmental and Economic Importance for a Sustainable Future."

Section 2, "Phytoplankton," includes three chapters: Chapter 3, "Remote Sensing of Phytoplankton Pigments"; Chapter 4, "First Report on the Diversity of Epizoic Algae in Larval of Shellfish Gastropod *Aliger gigas*"; and Chapter 5, "The Use of Allelochemicals of Aquatic Macrophytes to Suppress the Development of Cyanobacterial "Blooms"."

Section 3, "Zooplankton," includes three chapters: Chapter 6 "Food Webs"; Chapter 7, "Ciliates as Symbionts"; and Chapter 8, "Changes in the Fatty Acids Profile of the Zooplankton Community Reveals the Quality of Four Reservoirs in the Hydroelectric Power Plants Located in the Iguaçu River, Paraná, Brazil."
