**Abstract**

Plankton is composed by unicellular, filamentous or colonial organisms that may have prokaryotic or eukaryotic cell structures. These organisms have an extreme ecological importance in the different water bodies worldwide, as they fix carbon dioxide, produce oxygen and are an important key element in the basis of various food chains. Through an industrial perspective, phytoplankton species have been used as a feedstock for a wide range of applications, such as wastewater treatment, or production of high value compounds; and commercial products, such as food and feed supplements, pharmacological compounds, lipids, enzymes, biomass, polymers, toxins, pigments. Zooplankton is commonly used as live food for larval stages to the period of termination of fish, shrimp, mollusks and corals. These types of organisms have characteristics such as a valuable nutritional composition, digestibility, buoyancy, ease of ingestion and attractive movement for post-larvae, thus presenting economic importance. This book chapter aims to demonstrate the several advantages that plankton have, their ecological and economic importance, targeting the production of add-value products.

**Keywords:** phytoplankton, zooplankton, bioactive compounds, industrial products

### **1. Introduction**

Oceans cover 71% of the surface of the Earth and have a huge diversity and high percentage of the earth biota [1]. Oceans take a key role in the global carbon cycle, therefore openly influence the speed and magnitude of climate changes, which can be observed in the aquatic organisms [2]. Moreover, the biota of the oceans have huge socioeconomic value, through food and feed production, nutrient recycling and carbon dioxide regulation [3]. Climate changes impacts on the ocean biota will provoke economic implications, so there is a need to understand the key drivers to understand the ecological change and how some to exploit the ocean organisms without putting pressure in the surrounding ecosystem [4]. In which, phytoplanktonic microorganisms develop the basis to the food chain status quo and greatly contribute for oxygen production and carbon dioxide sequestration, this organisms are mainly composed and denominated as plankton [5].

Plankton comprises single-celled algae – phytoplankton (which realizes photosynthesis) - and generally small animals (mm or less) – zooplankton (secondary producers, herbivores), which are drifting in marine currents. Phytoplankton is responsible for about 45% of the global annual primary production and serve as food for zooplankton, which in its turn is an ideal size food for several commercially important fish and large aquatic mammals. Plankton is a vital component of marine and freshwater ecosystems. Besides, they also make important contributions to the global biogeochemical cycle and improve the accumulation of carbon dioxide in the atmosphere, 'pumping' carbon into the deepest regions of the sea [5].

Planktonic communities are frequently used as bioindicators to monitor ecological changes in aquatic ecosystems [6]. Thus, being a management tool to supervise the ecological system quality and to be a tool to take actions, for example to prevent algal blooms, toxic contamination from undisclosed source. This happens, because plankton reacts at the lowest variation of surrounding ecosystem. Plankton species and planktonic communities varies incited by many abiotic factors (light availability, temperature, salinity, heavy metals, pollutants, pH and nutrients concentration) and biotic factors (predators, parasites) [7]. These variations are being studied through ecological data to help policy makers, for example, where the plankton community varies and there is harmful plankton species that grows rapidly due the excessive nutrients in water [8].

However, the plankton interest is not only as ecological tool, but also holds industrial and biotechnological potential to be used in commercial products. Through an industrial perspective, phytoplankton and zooplankton species have been used as a feedstock for a wide range of applications, such as wastewater treatment, or production of high value compounds; and commercial products, such as food and feed supplements, pharmacological compounds, lipids, enzymes, biomass, polymers, toxins, pigments. Zooplankton is commonly used as live food for larval stages to the period of termination of fish, shrimp, mollusks and corals [9–11]. However, to exploit these organisms at a commercial and industrial level, there is a need to understand the ecological data to cultivate this organisms in a controlled methods to have a best effective method with reduced cost, due the impossible control in the wild ecosystems (where commercial exploitation provokes a negative impact) [12, 13].

This book chapter aims to analyze the several advantages that plankton, specifically phytoplankton and zooplankton, their qualities, ecological and economic relevance, as well as their cultivation techniques, aiming the production of addvalue products.

## **2. Plankton ecological relevance**

Plankton is a key-element to form the base of the aquatic food chain [14]. Every organism in the ocean habitat depends on plankton for their survival. Without them, the food chain will broke extensively provoking a shortage of the food basis [14]. For instance, bacterioplankton holds a key role to recycle compounds, minerals and energy within the food chain [15]. Due to climatic changes, plankton communities can change rapidly provoking diverse problems in the food chain, causing a bottom-up effect up to the fish, which is explored as a food source by humans. So, there is a need to monitor wild plankton communities to identify structural changes and, if necessary, to take actions in order to mitigate some of the negative changes, for example toxic algal blooms in marine ecosystems [4].

Plankton species are mostly short live forms and consequently, plankton communities are not greatly influenced by the persistence of older individuals from

*Plankton: Environmental and Economic Importance for a Sustainable Future DOI: http://dx.doi.org/10.5772/intechopen.100433*

previous years. This can allow the joint of environmental changes and plankton dynamics, enabling fast analyzes unlike other aquatic organisms, such as fish species. Moreover, plankton can demonstrate dramatic changes within abiotic and biotic parameters variation (such as temperature, pH, salinity, nutrients and metals concentration, or even biotic changes, as bacteria or fungi proliferation) [16]. Regarding monitoring plankton communities, there are Continuous Plankton Recorders around the globe, aiming the development of studies about plankton dynamics (with abiotic and biotic data to understand plankton responses), and to contribute with updated data that will be pivotal to assist the management decisions of the stakeholders. In a large scale, this method has revealed itself, cost effective and essential to obtain data to understand the aquatic ecosystems [14].

### **2.1 Phytoplankton**

Phytoplankton is one of the primary producers of the aquatic ecosystem, as well as the first organisms to produce energy, which they generate from light sources, such as solar. Phytoplankton converts light energy into carbohydrates through photosynthesis. The energy not auto consumed by them for survival and maintenance is available as food for herbivores or omnivores that feed on these microorganisms. Phytoplankton can absorb about 3% of the light energy that penetrate in the ocean. In fact, a low percentage when compared with terrestrial plants, which can absorb about 15% of the accessible sunlight. This divergence is triggered by the ocean itself, which absorbs sunlight in fluctuating grades. The sunlight is a limiting factor and a key source for phytoplankton survival and reproduction. If there is not enough sunlight, phytoplankton will diminish up to stable population [15].

#### **2.2 Zooplankton**

Zooplankton is composed by heterotrophic organisms that feed on phytoplankton, being mainly secondary consumers and aquatic herbivores. Thus, their energy is acquired from consuming the primary producers. The energy disposal is identical for tertiary consumers, as well as for phytoplankton, only the energy stored is available for predators. This predator can be a different zooplanktonic organism or a larger animal that grazes on plankton [15].

### **3. Specificities of the plankton**

To fully understand plankton biotechnological potential, there is a need to evaluate their ecological specifications, according to the species and geographical habitat. Phytoplankton can be an useful and promising feedstock, due to their resilience and quick adaptation to environmental changes, which incontestably has consequences on their secondary metabolism [17].

#### **3.1 Phytoplankton**

There are evidences of the existence of microalgae since the Precambrian period, approximately 3.5 billion years ago. These microorganisms, mainly marine species, are responsible for the production and maintenance of atmospheric oxygen [18]. Algae have a fundamental role on ecological balance maintenance. Moreover they have a pivotal economic and social importance by supporting fauna, which is a source of food for humans [19] and other organisms [20].

Algae are considered a pool of several compounds with biological activities [21, 22]. The algal composition varies according to environmental conditions, thus there are species with different concentrations of proteins, polysaccharides, pigments and fatty acids [23].

Microalgae retains about 50% of carbon in their biomass, which is obtained in most cases from atmospheric carbon dioxide. Therefore, they are attracting interest for carbon sequestration in industrial processes [24, 25]. Nitrogen and phosphate compounds are essential nutrients for microalgae to protein and cell membrane synthesis. In this context, the application of microalgae in water bioremediation is a sustainable application to remove high amounts of these compounds from water bodies, mitigating their negative impacts [26].

#### **3.2 Zooplankton**

Zooplankton is offered as live food since the larval stages until the period of completion of fish, shrimp, mollusks and corals. They are organisms that have characteristics such as a rich nutritional composition, digestibility, buoyancy, ease of ingestion and attractive movement for post-larvae [27]. Rotifers are among the most widely used, mainly the genus *Brachionus* (Animalia, Monogononta), as an important source for the first zooplanktonic feeding for larvae of aquatic organisms, because they contemplate all the characteristics mentioned above, they have a high dietary value, being rich on polyunsaturated fatty acids and essentials amino acids, in addition to the appropriate size for the animal's feeding apparatus [28, 29].

Artemia or brine shrimp is an aquatic crustacean genus with nonselective feeding habit, which can feed on tiny particles of food like microalgae, bacteria, detritus and small organisms [30]. Artemia is a good model organism for ecotoxicological studies because they have a short life cycle and can be cultured in a large scale [31, 32].

The rotifers *Brachionus plicatilis* and *Brachionus rotundiformis* can be also cultivated at a large scale, meeting the demand for fish and shrimp larviculture [33]. Although they are considered a resource with a high nutritional value, it is important to note that this occurs due to the improvement of secondary cultivation techniques such as bioencapsulation, a technique in which the rotifer is enriched with foods with a high content of essential compounds, being fed for a time period less than 24 h and immediately offered in the larvae diet. Bioencapsulation allows rotifers to incorporate the nutritional characteristics of algae, subsequently transporting these elements to the fed larvae [34].

Copepods, used as live food, contribute to a better performance of fish larvae when compared to larvae fed with rotifers and Artemia [35, 36]. In general, copepod feeding results in an increase in survival, growth and a decrease in larval deformities [37, 38].

Due to a relatively high protein and nutrient content, *Moina* spp. (Branchiopoda, Cladocera) is a superior live food compared to *Artemia* [39, 40]. Cladocerans of the genus *Moina*, and *Moina macrocopa* in particular, are progressively important in aquaculture and ecotoxicology [41].

## **4. Plankton wild exploitation**

There are commercial exploitation of plankton wild resources to provide marine food sources for human consumption, mainly zooplankton (example copepods and krill) [42]. This plankton presents a great economic potential because they are enriched biochemical profile, such lipids, proteins, pigments and other bioactive

*Plankton: Environmental and Economic Importance for a Sustainable Future DOI: http://dx.doi.org/10.5772/intechopen.100433*

compounds. However, even at the lower food chain level they can accumulate heavy metals, organo-chlorides, dioxins and other harmful compounds, thus can be a problem if not analyzed rigorously [43]. However, at low quantities their risk is minimum when compared to higher food chain levels [44].

In this case, there are plankton specialized fisheries, where the harvest of the targeted species uses scientific data to harvest the adults in one specific season, with equipment to collect the plankton desired. For example, this happens in the Norwegian region from 1950 until today [44].

Although the plankton wild harvest needs a strong marine strategy to not cause environmental problems and to promote a sustainable plankton fishery, with reduced by-catch [44]. The economic importance and valorization are identical to the cultivated plankton, see Section 6. In this case, the most advantage is for animal feed due to: i- Greater diversity of organisms and possibility of compatibility with the larvae's and organism digestive apparatus; ii- The captured organisms will find themselves in different stages of development, and therefore, there must be some that have an adequate size to the requirements of apprehension of the cultivated larvae/organism; iii- The cost of capture is much lower than the cost of production of organisms used as live food. However, when compared to the cultivated, wild harvest demonstrates the consequent problems: i-the instable productivity rate due to the environment changes; ii- seasonality; iii-presence of parasite species, such as *Argulus* sp. e as *Lerneae* sp.; iv- maintenance of biochemical profile between harvests; v- possibility of accumulation of heavy metals, toxins, pollutants and harmful compounds.

### **5. Plankton cultivation**

To avoid natural resources overexploitation, emerged the need to evolve plankton cultivation techniques. In this way, it is possible to produce enough biomass to supply industrial applications without putting pressure under marine ecosystems [45].

#### **5.1 Phytoplankton**

In aquaculture, microalgae serve as food and help to maintain water quality, as they produce oxygen, consume carbon dioxide and nitrogen compounds, especially ammonia [46]. In addition, they can still be used as bioindicators of the level of eutrophication of water bodies [47].

Microalgae are highly efficient photosynthetic organisms, and due to their high biotechnological potential, makes them one of the hot research topics of the moment [48]. Microalgal biomass can be commercially explored in different areas such as nutrition, human and animal, wastewater treatment, biodiesel production and to obtain compounds of interest to food, chemical and pharmaceutical industry [49, 50].

The main physico-chemical factors that affect the growth of microalgae are light, temperature, salinity and availability of nutrients [50].

Microalgae energy reserve substances consists in compounds of high molecular weight such as α-1,4 glucans, β-1,3 glucans and others of low molecular weight such as (glycosides and poly oils). In algae, the lipid reserve is needed for thee synthesis of lipoprotein membranes [51], and is also used to regulate the fluctuation of cells in water.

Lately, microalgae have been attracting the attention of researchers worldwide due to their resilience and high commercial interest [52].

#### *Plankton Communities*

The production of microalgal biomass, through photosynthetic growth, requires carbon dioxide, water, inorganic salts and temperatures generally between 20 to 30°C. To reduce the costs of microalgae biomass production, sunlight should be used, through outdoor cultivations, considering that the contamination is minimal, using essential nutrients such as nitrogen, phosphorus, iron and, in some cases, silica [49].

Currently, raceway ponds are the most used technique in the upscale production of microalgae to obtain biofuel. However, for this production to be more effective, technological advances must occur to develop photobioreactors which use light more efficiently, reducing the costs associated [53].

Microalgae cultivation is advantageous because it is possible to obtain metabolic products, which are used in feed of marine and terrestrial organisms, food supplements for humans, or for use in environmental processes, such as wastewater treatment, fertilization soil, biofuels and phytoremediation of toxic waste [54].

Species bioprospecting is very important to select the best strains that can produce the most desirable metabolic products. Several studies have evaluated the use of different microalgae for different purposes [55–57], but this field of research needs is currently evolving and much research still needs to be done.

Lourenço [58] reports that the interaction of microalgae with the culture medium and its physical environment results in significant changes in cell density, which tends to increase numerically in large proportions after inoculation. On the other hand, the concentrations of nutrients dissolved in the culture medium tend to decrease with their multiplication, reaching the point of complete exhaustion, depending on the time of development of the culture, stressing it.

The choice of the culture medium is extremely important for mass production of microalgae. Its improper use can affect the growth rate and the biochemical composition of cells [59, 60]. For each microalgae species, the productivity and the biochemical composition of the cells strongly depend on the type of cultivation and the nutrient profile of the medium [61].

According to Lourenço [58], the choice of the culture medium should consider the operational costs involved, since often low-cost culture media may be deficient in some components and do not allow the maximum production of algal biomass.

The microalgae possess various antioxidant properties and they are potential oxidative stress control alternatives in Artemia and, perhaps, other aquatic organisms used in aquaculture [62].

#### **5.2 Zooplankton**

Fiore and Tlusty [63] studied the incorporation of *Artemia* in commercial diets for larval diets of the American lobster (*Homarus americanus*) and found greater survival in stage IV post-larvae (19–25%) and subsequent juvenile performance when compared with a combination of *Artemia nauplii* with frozen *Artemia* incorporated in the diet. A diet 100% formulated resulted in reduced larval survival (6%) and post-larval size, while a larval diet of 100% of frozen adult *Artemia* resulted in reduced post-larval quality and early juvenile performance.

Vinh et al. [64] cite that the profitability of Artemia producing farms in the Mekong Delta, Vietnam, was significantly influenced by the geographic location and their interaction with the scale of production. To improve farm productivity, besides maintaining optimal stocking densities, moderate increases of organic fertilizer, feed and chemical inputs are recommended to supply Artemia with more nutrients and create better water environment for the optimal development and reproduction. Additionally, a periodic harvest of *Artemia* biomass (adult *Artemia*)

#### *Plankton: Environmental and Economic Importance for a Sustainable Future DOI: http://dx.doi.org/10.5772/intechopen.100433*

is required to minimize food and space competition and provide more incomes to farmers.

Prusińska et al. [65] proved that the use of Artemia enriched in polyunsaturated fatty acids (PUFAs) in the larval cultivation of the freshwater fish (*Barbus barbus*), is an effective method to improve growth rates and feed utilization. Besides that, histological analyzes revealed better development of the active area of intestines, as well as an increase in the neutrophil count in the blood.

When cultivated, rotifers are relatively poor in eicosapentaenoic acid (EPA: 20: 5ω-3) and docosahexaenoic acid (DHA: 22: 6ω-3), and it is essential and therefore a common practice to enrich the culture with marine oil emulsions. Novel production techniques, such as closed recirculation systems are offering new possibilities for continuous supply of high-quality rotifers at densities 10 times greater than batch cultures. The increase in production in these systems is explained by the better water quality [66].

Yoshimura et al. [67] obtained a high density of rotifers (1.6 x 105 individuals mL−1) using continuous filtration of water developed for ultra-high density production, equipped with a membrane filtration unit (pore size: 0.4 μm) and set inside a culture vessel. The culture performance of this system was tested by feeding with freshwater *Chlorella* (Chlorophyta) paste in a 4-day batch culture.

Alver et al. [68] used a system for automatic control of the growth and density of rotifer. The system computes feeding rates based on a setpoint for rotifer density and provides a fast growth period followed by rapid stabilization of the rotifer density. At the same time, overfeeding is prevented, thereby reducing the risk of cultivation crashes. Feeding rates are automatically computed based on measurements of the cultivation density and egg rate, and internal setpoints for growth rate and egg rate. The authors obtained densities in all tanks increasing from 60 to 90 mL−1 to the setpoint densities of 500 and 1000 mL−1 in 5–7 days, after insignificant growth on the first day. Gross growth rates slowed down considerably towards the end of the experiment, as the controller reduced feed rations in order to stabilize densities.

Han and Lee [69] studied the effects of salinity changes on the marine monogonont rotifer *Brachionus plicatilis* and found that a significant decrease in population growth was observed when the rotifers were grown in high salinity (35‰), leading to growth retardation and modulation of the antioxidant defense system. These findings provide a better understanding on the adverse effects of salinity changes on lifecycle parameters and oxidative stress defense mechanism in rotifers.

Chilmawati and Suminto [70] observed the performance of copepod *Oithona* sp. in different diets with microalgae *Chaetoceros calcitrans* (Bacillariophyta), *Chlorella vulgaris*, *Nannochloropsis oculata* (Ochrophyta, Eustigmatophyceae) and *Isochrysis galbana* (Haptophyta, Coccolithophyceae). The results showed that the diet of phytoplankton cells was significantly different in the growth performance of *Oithona* sp. The diet of *C. calcitrans* gave the best growth performance of *Oithona* sp., when reached 6,963 ± 0.38 ind mL−1 of total density (0.121 ± 0.003) and specific growth rate and egg production (16.50 ± 2.74 ind−1).

Knuckey et al. [71] cultivated the copepod *Acartia sinjiensis* in a variety of mono and binary algal diets and observed that there were significant differences in the rate of development of copepods between diets. *Rhodomonas* (Cryptophyta) was confirmed as an excellent algal diet for *Acartia* (Crustacea, Copepoda), but it is often unpredictable in mass culture. The cryptophyte, Cryptomonad sp. (CS-412) showed to support an equally rapid development rate with the advantage of being more stable in mass culture. The algal feed concentration for maximal copepod development rate was dependent on the algal feed species.

Puello-Cruz et al. [72] cultivated the copepod *Pseudodiaptomus euryhalinus* (Crustacea, Copepoda) in a mono-microalgae culture (*Chaetoceros muelleri*, *Nannochloropsis oculata*, *Isochrysis galbana*, *Tetraselmis suecica* (Chlorophyta), or a commercial frozen concentrate of *Tetraselmis* sp.) and in binary diets (*C. muelleri*: *I. galbana* in 1: 1 and 2: 1 cell ratios and *C. muelleri*: *I. galbana*: frozen *Tetraselmis* sp. in 2: 2: 1 ratio). These gave better results than the cultures of *N. oculata*, *I. galbana*, *T. suecica* and the frozen *Tetraselmis* concentrate, but the production was similar to that obtained with *C. muelleri* supplied as a monoalgal diet, showing that the addition of *C. muelleri* may improve the performance of other monoalgal diets, whereas the addition of other microalgae is unlikely to improve the results obtained when *C. muelleri* is supplied as a monoalgal diet.

Using relatively simple culture techniques, in transparent plastic boxes (32 × 47 × 14.5 cm) containing 4.5 L of filtered aerated seawater at room temperature (28 to 32°C) and a salinity of 35‰, Ribeiro and Souza-Santos [73] cultivated the copepod *Tisbe biminiensis* fed with commercially available ornamental fish food and every two days following water exchange, with 500 mL of one of the following diatoms: *Phaeodactylum tricornutum* or *Thalassiosira fluviatilis* (Bacillariophyta). The collection of *T. biminiensis* from the 5 L cultures produced a mean of 28,000 nauplii and copepodites L−1 day−1 over a 130-day period.

Sarkisian et al. [74] used an innovative design for an intensive culture system of the calanoid copepod *Acartia tonsa*, a prime candidate for use as a live food item. The system output was on average 22 million eggs day−1 (21,955,420 ± 8,709,668) with an average hatch rate of 49% (49.1 ± 14.8) over three seasons.

Poynton et al. [41] cultivated females of the cladoceran *Moina macrocopa* in a situation of flagellate infection associated with mortality. At day 10, all *M. macrocopa* were alive in uninfected cultures, whereas in untreated infected cultures, the survival was significantly lower: only 26% of cladocerans were alive. In infected cultures treated with humic substances (25 mg L−1 of dissolved organic carbon), mortalities were comparable to those in the untreated infected cultures; in contrast, in the infected cultures treated with 4 g L−1 sea salt, mortalities were interrupted, and 76% of the *M. macrocopa* were alive at day 10.

Liu et al. [75] studied the effects of a polystyrene nanoplastic on physiological changes (e.g., survival, growth, and reproduction) and expression levels of stress defense genes (oxidative stress-mediated and heat shock proteins) in the freshwater flea *Daphnia pulex*. The results showed that the digestive organs of *D. pulex* were strongly fluorescent after exposure to the nanoplastic particles and the 48 h median lethal concentration (LC50) of the nanoplastic was determined to be 76.69 mg L−1. The time to brood was delayed, and total offspring per female and number of broods were decreased in all the treatment groups. In addition, the offspring per brood were significantly decreased in the 0.1 mg L−1 group.

Raymundo et al. [76] compared the sensitivity of temperate and tropical cladocerans to different insecticides. The order of sensitivity of the native cladocerans to chlorpyrifos was: *Ceriodaphnia silvestrii* (0.039 μg L−1) > *Diaphanosoma birgei* (0.211 μg L−1) = *Daphnia laevis* (0.216 μg L−1) > *Moina micrura* (0.463 μg L−1) = *Macrothrix flabelligera* (0.619 μg L−1). A regulatory acceptable concentration based on temperate cladoceran toxicity data of both chlorpyrifos and other insecticides also appeared to be sufficiently protective for tropical cladoceran species.

Jaikumar et al. [77] described that the sensitivity to microplastics can differ between different species of cladocerans and can be drastically influenced by the temperature, although in high concentrations of exposure.

Hansen [78] cultivated the planktotrophic larvae of the boreal capitellid polychaete *Mediomastus fragile*, fed with the microalgae *Isochrysis galbana* and concluded that the larvae were able to capture and ingest particles in the size spectrum between 2 and 10 μm. However, the optimal particle size was 7 μm. The larvae enter the plankton in the early spring, when the phytoplankton size spectrum is typically dominated by large algal cells, exceeding the size for efficient uptake. The physical limitations for particle capture are therefore a potential limit for feeding. The ability to delay larval development is an advantage for a planktotrophic larvae functioning as a growing dispersive organism.
