Plankton: Environmental and Economic Importance for a Sustainable Future

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.

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, 10, 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 add-value 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 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 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].

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, 56, 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) 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.

6. Plankton economic importance

In diverse industry areas, microalgae have been widely used as a source for a variety of practices and potential metabolic products, such as food supplements, pharmacological substances, lipids, enzymes, biomass, polymers, toxins, pigments or tertiary sewage treatment. They are also important in aquaculture as a source of nutrients and are of great importance in the production of oxygen, carbon dioxide sequestration and nitrogenous compounds removal, such as ammonia [46, 54, 58]. They are also used as bioindicators, reporting water bodies ecological quality status [47]. However, it is considered that the plankton biotechnology is still young when compared to macroalgal and terrestrial plant biotechnological exploitation and knowledge [79]. Nevertheless, when compared with this two biotechnology branches, it is estimated that plankton have specimens and more suitable, due to their reduced form, being mainly aquatic, a life cycle shortened and rapid adaptation of the metabolism which is capable to produce various interesting compounds [9, 13, 80].

The production of microalgae in different sectors generates social, environmental and economic benefits. For example, in the USA and India, Haematococcus lacustris (formerly Haematococcus pluvialis) (Chlorophyta) production aims the extraction of astaxanthin, used as a food coloring and also as a powerful anti-oxidant in the pharmaceutical and cosmetic industry [81].

According to Wijffels [53], marine biotechnology aims to discover new products that can contribute to the health of human beings, such as, for example, new nutraceuticals obtained from algae for use in human and animal feed industries, besides the contribution also in the energy sector, such as the production of biofuels. According to the author, the ω-3 fatty acids, provenly beneficial for human health, can also be a potential source of biofuels. Therefore, the biggest challenge is to obtain these products with quality, in enough quantities and in a sustainable way.

6.1 Food and nutraceuticals

The search to food sources are advancing as an indispensable resolve the feed problem, with the continuous world’s population grow restricted, by the global restrictions [82]. Phytoplankton aquaculture in an industrial large-scale to human food usage begin with the cultivation of Chlorella vulgaris during World War II [80].

According to Pulz and Gross [79], the functional food market using microalgae, in pasta, breads, yoghurts and beverages, is rapidly developing in countries, such as France, United States, China and Thailand. The most common application has been in aquaculture, for the direct or indirect feeding of some species of fish, mollusks, crustaceans and other organisms of economic interest [83].

The consumption of ω-3 obtained from microalgae is beneficial for neural development, in addition to preventing coronary problems, cancer, hypertension, diabetes, cystic fibrosis, arthritis, asthma, schizophrenia and depression. Marine microalgae are capable of synthesizing ω-3 fatty acids, eicosapentaenoic (EPA, C20: 5) and docosahexaenoic (DHA, C22: 6), which enter the marine food chain and are available in fish oil. These fatty acids are considered important in the development of brain tissue and visual function [84].

Microalgae are the main producers of biomass that accumulate in higher organisms through the food chain. For several centuries, they are used as food in Southeast Asian countries, mainly due to their high protein content. Recently, microalgae have attracted the interest of many researchers due to their structurally diverse bioactive compounds, efficient photosynthetic machinery, greater mass productivity and the absence of competition with arable land and drinking water. They can withstand adverse environmental conditions, producing a variety of biologically active primary and secondary metabolites, such as polysaccharides, carotenoids, omega-3 and 6 fatty acids and phenolic compounds. These metabolites exhibit a series of pharmacological activities, which include therapeutic, drug-carrying and physiochemical properties, including gelation, swelling and emulsification. These may be a new source of functional compounds in the food and pharmaceutical industries [85].

Currently, microalgae are being incorporated into many food formulations. Most of them use microalgae as a marketing strategy or as a coloring agent. As for example, the cyanobacterium Spirulina is not only in fashion, but is rich in several valuable and highly nutritious compounds, such as proteins, PUFAs and bioactive pigments, including chlorophylls, carotenoids and phycobiliproteins. One of the main advantages of natural pigments derived from Spirulina, when compared to their synthetic counterparts, is that the former has several health benefits, and can be used as an ingredient in the development of new functional foods. Proteins from Spirulina have proven to be excellent sources of bioactive peptides with potential application in the functional food industry as antihypertensive, anti-diabetic, anti-obesity and antioxidant ingredients [86] immunomodulatory and anti-inflammatory among other positive bioactivities [87].

Some of the prerequisites for using algae biomass for humans and animals include determining the chemical composition; toxic biogenic substances; non-biogenic toxic compounds; protein quality studies; biochemical nutritional studies; supplemental value of algae to conventional food sources; health analysis; safety assessments (animal feeding tests); clinical studies (safety test and suitability of the product for human consumption) and acceptability studies [88].

The microalgae used as a food supplement are generally sold in the form of tablets, capsules and liquids or are incorporated in pasta, snacks, candy bars, ice cream, chewing gum, in mixtures of drinks and dyes for natural foods [88, 89]. Foods supplemented with microalgae biomass, when properly processed, can make foods more colorful and tasty, adding not only nutritional value, but also new, unique and attractive flavors [50].

The reasons for this recent growth in interest are cost-effective cultivation and a short cultivation time until the desired compost is obtained. In addition, they have the status generally considered safe and as such do not contain any toxins or pathogens that can be transmitted to humans. [90].

6.2 Feed

The plankton is a natural source for various animals’ species, which are cultivated. Consequently, they are a standard feed source to various farmed species. To other animals, they are non-natural feed source, which is used supplement to be incorporated with normal feed, similarly the plankton usage as human food supply, due to the high quality of protein, minerals, vitamins, carbohydrates and also essential fatty acids to be a high quality feed for fish and others animals [91].

Phytoplankton is a vital player in aquaculture (mariculture) as they are the natural food bases to larvae life stage of various types of mollusks, crustaceans, and fish. The utmost phytoplankton used in aquaculture worldwide belong to the genera: Chlorella, Tetraselmis, Isochrysis, Pavlova (Haptophyta, Pavlovophyceae), Phaeodactylum, Chaetoceros, Nannochloropsis, Skeletonema, and Thalassiosira (Bacillariophyta) [92].

The use of plankton as feed improver was attainment further attention by the I&D research teams and industry to develop feeds to diverse animals (mainly in aquaculture). Which, the main results are the animals feed with plankton gain weight, enhance of triglyceride profile and the protein deposition in muscle, the animal digestibility, starvation tolerance and carcass quality [91, 93].

Phytoplankton can be cast-off as a source of natural pigments for the culture of prawns, salmonid fish, and ornamental fish [91].

6.3 Cosmetic

The cosmetic area is the third major commercial segment for phytoplankton application, due to the research of natural products to substitute synthetic ingredients. Thus, with cosmetic consumers turning their mindset, the cosmetic segment is one of the main actives to explore the biotechnological potential of the plankton. The natural and ecofriendly predispositions in this area, give an new input to find new high value, innovative and natural formulations for new products, without the imposition of reduced costs as the other areas [80]. The microalgae were not very common in cosmetic, nonetheless, microalgae and their derivatives are in beginning to be integrated in diverse formulas to skin and hair products, through a wide range of functions, such as excipient (stabilizer or emulsifier) or active ingredient. The phytoplankton is usually used in moisturizing, skin whitening, anti-aging, and sun protection creams formulations. However, the pigments from phytoplankton is cast-off as colorant agent for varied cosmetic products [94].

6.4 Bioremediation

The application of microalgae to bioremediate wastewaters shows a great potential to complement traditional wastewater treatment processes. Furthermore, this approach addresses the need to reduce the costs associated with the growth media expenses for microalgae biomass production [95], through wastewater recycling to obtain microalgal biomass instead of culture medium [96].

Nevertheless, it is necessary to consider possible sources of growth medium contamination, such as grazers which feed on microalgae (Figure 1a and b), as well as the presence of other microalgae species that can compete or inhibit the target species production.

Figure 1.

Microscopic observations of Chlorella vulgaris cultivation in municipal wastewater sludge centrate, (a) with the presence of other microalgae species and (b) with the presence of grazers.

Bioremediation of numerous pollutants of different characteristics and properties released from the domestic, industrial, agricultural and aquaculture sectors [97, 98]. Moreover, promoting microalgae cultivation in wastewater will help mitigate the environmental impacts of treated effluents since this biological method will complement conventional wastewater treatment and improve not only the removal of organic and inorganic load but also the removal of emerging pollutants, such as pesticides, metals, pharmaceuticals or household cleaning chemicals [99, 100, 101, 102].

In addition, they are also capable of removing metals, incorporating them in their cell wall [103] and other noxious compounds such as phenols and chlorophenols [104].

6.5 Renewables energies

An emerging area for microalgae biotechnology is environmental applications. This is mainly due to its carbon dioxide mitigation capacity, reducing greenhouse gas emissions that are related to global warming and climate change; and its ability to grow in an effluent liquid that allows wastewater treatment. Today, there is a focus on the use of microalgae in renewable energy as a potential source for the production of biofuels, such as biodiesel, bioethanol, biohydrogen and biogas [105].

It is worth mentioning the importance of the production of biofuels through microalgae. Microalgae naturally contain about 10% lipids. These lipids are mainly present in photosynthetic membranes. Microalgae accumulate lipids in high concentration under “stress” conditions, caused, for example, by the depletion of nutrients such as nitrogen. In the absence of these nutrients, growth is hampered, while energy is continuously received in the form of light. Microalgae channel excess energy into large macromolecules, such as lipids or starch. In these cases, the lipid content can reach 60%. Under stressful conditions, these lipids accumulate in body lipids such as triacylglycerides or neutral lipids. The neutral lipids can be used as raw material for the production of biofuels [106].

During the past few decades, many research studies have covered different technologies to produce biodiesel from lipid-rich microalgae. Under controlled cultivation conditions, microalgae can accumulate metabolites intended to produce various biofuels. For example, starch and various types of oils can be bioaccumulated. Starch extracted from algae is easily hydrolyzed to glucose and used for fermentation in the production of bioethanol. Currently, commercial production of bioethanol from algae is not a viable choice due to the low yield of the product compared to other terrestrial biomasses. The high costs of algae cultivation systems are due to several complex steps: (i) algae cultivation; (ii) harvest; (iii) pre-treatment of biomass; (iv) fermentation; and (v) extraction of bioethanol. By linking all possible improvements at each stage of the process, a substantial advance towards cost-effective algae systems can be achieved in the future [107].

7. Conclusions

This chapter covered the many advantages that plankton have, specifically phytoplankton and zooplankton, their qualities, ecological and economic relevance, as well as their cultivation techniques, aiming the production of add-value products with industrial interest.

It is of great need to use all the knowledge presented and apply it in the different branches of ecology, industry or science, aiming the discovery of new products or directing it to a specific study area, being a subsidy of great importance for the environment and/or for the human being.

Acknowledgments

This work is financed by national funds through FCT - Foundation for Science and Technology, I.P., within the scope of the projects UIDB/04292/2020 – MARE - Marine and Environmental Sciences. This work was financed by the Live Food Production Laboratory (LABPAV) and the Tropical Aquaculture Study Group (GEAQUI) of the Federal Institute of Education, Science and Technology of Ceará —IFCE, Campus Aracati, Ceará, Brazil. João Cotas thanks to the European Regional Development Fund through the Interreg Atlantic Area Program, under the project NASPA (EAPA_451/2016). Diana Pacheco thanks the PTDC/BIA-CBI/31144/2017—POCI-01project -0145-FEDER-031144—MARINE INVADERS, co-financed by the ERDF through POCI (Operational Program Competitiveness and Internationalization) and by the Foundation for Science and Technology (FCT, IP).

Conflict of interest

The authors declare no conflict of interest.