Marine algae are of high importance in their natural habitats and even more now in the world of green technology. The sprouting interest of the scientific community and industries in these organisms is driven by the fast-growing world of modern biotechnology. Genomics, transcriptomics, proteomics, metabolomics and their integration collectively termed here as ‘marine algal-omics’ have broadened the research horizon in view of enhancing human’s life by addressing environmental problems and encouraging novelty in the field of pharmaceuticals among so many more. Their use in the human society dates back to 500 B. C. in China and later across the globe; they are still being used for similar purposes and more today. There is a hiking interest in marine algae and their derivatives—from phycoremediation, food supplements, pharmaceuticals to dyes. Marine algae are currently considered as an emerging panacea for the society. They are being studied in a multitude of arenas. The multi-use of marine algae is enticing and promises to be a boon for industrial applications. Yet, most marine algae face challenges that might variably constrain their commercialisation. This chapter gives an overview of marine algae including all the ‘omics’ technologies involved in studying marine algae and it explores their multitude applications. It also draws the various successful industries budded around them and presents some of the challenges and opportunities along with future directions.
- marine algae
- ‘marine algal-omics’
Algae can be generally categorised into two large sub-groups, namely, microalgae (microscopic) and macroalgae (macroscopic). Although both groups have common traits such as the ability to carry out photosynthesis, they differ in various ways from their size to their phylogeny. Yet, they are of common interest to scientists and industries around the globe as part of biotechnological development and the exploitation of their metabolites of high economic values. Their use as food dates back to 500 B.C. in China and the ninth century A.D. in Chad . Eventually, the purpose of their exploitation has expanded to other avenues. Since the nineteenth century or so, several marine macroalgae have been used as a natural fertiliser in several countries, for instance,
At the very beginning of the twenty-first century, genomics marked the dawn of a different epoch of biological research providing a blueprint for genetic engineering for the optimisation of productivity of marine algae, reassembling the puzzle of evolution and the discovery of genes of interest coding for biological compounds of high significance. For instance, Stephenson et al.  provided an insight of several genes that have the potential to improve the solar conversion efficiency in mass culture of marine algae for biofuel production. Although genomics provide a static view of the capacity of a marine algal cell, the integration of transcriptomics, proteomics, metabolomics and system biology allows the study of its gene expression in response to environmental stresses [6–8], evolution among others. Examples range from the upregulation of gene coding for proteins of several pathways of the microalga
The Economist Intelligence Unit Limited  acknowledges the emergence of several ocean industries including marine biotechnology, e.g., the commercial production of β-carotene from the microalga
This chapter describes the taxonomic classification of marine macroalgae and microalgae as well as gives a brief description of their characteristics. It also discusses the phycoremediation technology using marine algae and the study of the metabolites of interest using the ‘omics’ technologies for their subsequent commercial/industrial applications. In addition, it points out the main challenges that their associated industries are facing and discusses future directions in both the research and commercialisation/industrialisation arenas.
2. Description of marine algae: morphological and genetic characterisation
More than 71% of the world’s surface is covered by oceans that serve as habitats to a diversity of marine organisms including marine algal species [18, 19]. Ecologically, marine algae are at the base of most aquatic food chains and are important in biogeochemical cycling and, in addition, serve as habitats for many organisms in aquatic ecosystems [20–22]. Marine algae can be prokaryotic or eukaryotic. They usually inhabit shallow waters and belong to two main sub-groups (Figure 1), namely, macroalgae (also commonly known as seaweeds) and microalgae. The macroalgae are macroscopic and consist of three main groups: Chlorophyta (green macroalgae), Rhodophyta (red macroalgae) and Phaeophyta (brown macroalgae) . They are thallophytes (non-vascular plants). They constitute of leaf-like structures known as blades, stem-like structures known as stipe and root-like structures such as rhizoids and holdfasts. In contrast, microalgae are microscopic and are grouped as follows: Cyanophyta (blue‒green algae), Pyrrophyta (dinoflagellates), Chrysophyta (diatoms and golden-brown algae) and Chlorophyta (green algae) [23, 24, 26]. Marine algae are taxonomically classified using diverse methods including analyses of their morphological key features and molecular characteristics—pigments (phycocyanin, phycobilins, β-carotene and chlorophyll) , genetic molecules, fatty acids distribution, secondary metabolites distribution [28, 29], and diffraction, light scatter and fluorescence parameters (through flow cytometry). The choice of use or the extent of the use of the different methods is dependent upon the level of difficulty in identifying a particular species.
3. Applying biotechnology tools to explore the hidden properties of marine algae
The ‘omics’ technologies have revamped biological research and have led the twenty-first century into the post-genomic era that goes beyond the static state of genomics. Organisms being subjected to such high-throughput technologies include marine algae and hence the expression: ‘marine algal-omics.’ Analogous to other organisms and cellular omics studies, ‘marine algal-omics’ include essentially genomics, transcriptomics, proteomics, metabolomics and system biology tagged along with miscellaneous ones (e.g., fluxomics) which deepen our understanding of the respective organisms . In this chapter, we use the expression ‘marine algal-omics’ to illustrate the advanced technologies involved in the study of marine algae.
Marine algae have built up their profiles exponentially in the omics world: their significance as primary producers of the blue planet, their impacts on global productivity as well as biogeochemical cycling are acknowledged . ‘Marine algal-omics’ provide better understanding of biological system as well as commercially important molecules for marine macroalgae and microalgae alike [1, 32–34]. Hitherto, the marine algae had to satisfy a set of criteria before being considered as potential candidates for such endeavours , but with the advent of meta-omics, the possibilities now seem endless.
Genomics, the first of the ‘omics’ technologies, defines an organism’s native biosynthetic and metabolic capacities as a potential microbial cell factory, and provides a blueprint for engineering and optimising productivity. Although during the early genomics era studies were focused mainly on bacterial and mammalian organisms for biomedical applications and subsequent improvement to the human health sector, genomics has been a key technology involving several steps (Figure 2) in unlocking the biocatalytic potential of marine algae.
The advent of the next-generation sequencing technologies such as sequencing by litigation, pyrosequencing and real-time sequencing has revolutionised the field of genomics . It has helped in the rapid, reliable and accurate sequencing of a number of marine algal species at a comparative cost [31, 37]. Successively, after more than a decade following the human genome project, scientists around the world have sequenced many different organisms including marine algae . About 8000 organisms’ genomes from different kingdoms have been completely sequenced and published with thousands more in the pipeline [Genome OnLine Database (GOLD)]. The first marine alga to be sequenced is
Genome sequencing provides a sequence of nucleotides which should be assembled and analysed for gene annotation. It indicates genes encoding proteins and functional RNAs available to the cell along with their associated regulatory elements . Gene sequencing of the microalga
Evolution study is another prime element of genomics providing a description of the phylogenetic relationship of all organisms on Earth. The comparative genomics analysis of the genome sequence of the filamentous brown marine macroalga
In addition, marine algal genomics encourages the understanding of algae allowing them to serve as model organisms . Subsequently, studies have used several marine algae as model organisms such as the microalga
The term ‘transcriptomics’ refers to the study of transcriptome, the whole set of transcribed RNAs, at a certain period of development as well as under a specific biological condition. Transcriptomics gives insights into genome expression that lends a view on gene structure, gene expression regulation, gene product function and the dynamics of the genome. Over the years techniques used for transcriptome analysis have evolved from the initial expression sequencing tag (EST) strategy to gene chips, and now the RNA-seq and bioinformatics analysis (Figure 3) . Dong and Chen  and Morozova et al.  provide an in-depth review of transcriptomics techniques.
The integration of transcriptomic studies in ‘marine algal-omics’ assists the elucidation of gene expression in response to environmental stresses [6, 7], evolution , biochemical pathways  and the characterisation of genes of those biochemical pathways . The relevance of transcriptomics exemplified by the studies herein mentioned ranges from the understanding of overexpression of respective enzymes in a particular biochemical pathway for pertinent applications to that of carbon capture.
The ability of marine algae to produce secondary metabolites in response to an environmental change is well understood. Radical changes are observed at the first gene expression level (i.e., transcription level). Transcriptomics studies on the response to environmental variability include
Furthermore, the transcriptome analysis of marine macroalgae of economic importance in China covering two groups Rhodophyta and Phaeophyta—3 classes, 11 orders and 19 families—helped to decipher the proteins involved in the ability of these macroalgae to cope with extreme environmental variabilities . The study reported three types of phycobiliproteins in
In a broad sense, the term ‘proteomics’ can be defined as the study of proteins coupled with transcriptomics and genomics for they are complementary . A cell’s Proteome – the whole cell protein – is dynamic: proteins extracted and studied at a particular point in time and under certain physiological condition(s) represent the cell’s immediate response to its environment, transcriptome alike. While there is a fine line of distinction between the classical and contemporary proteomics, the aim remains the global study of a cell’s proteome—protein‒protein interaction, protein modifications, protein function and location of proteins among others. Proteomics involves different separation techniques to multiple analyses and different identification tools (Figure 4). Graves and Haystead  provide an in-depth review of proteomics techniques.
For the past decade or so, several novel marine algal proteins have been identified by two-dimensional electrophoresis (DE) and mass spectrometry (MS) including proteins from the macroalga
Proteomic studies on algae are still relatively limited compared to higher plants. So far, it is the freshwater Microalga –
The shotgun proteomics technique is being profusely applied to the study of marine algal proteome. The first shotgun proteomics analysis of
Le Bihan et al.  investigated the effect of nitrogen deprivation on the biosynthetic pathways of
It is noteworthy that marine macroalgal proteomic studies are relatively uncommon and studies of those under stress are further limited but there are some whose expressed proteome in response to an environmental stress has been explored and these include
Additionally, proteomic studies are also being carried out to investigate the biosynthesis mechanism of harmful marine algae particularly in relation to human health and safety . Saxitoxin, for instance, is associated with paralytic shellfish poisoning. For a long time, little was known of the biosynthetic pathway of saxitoxin synthesis but studies are now revealing the enzymes implicated . Marine algal toxins are being considered for potential commercial applications such as the use of saxitoxin and tetrodotoxin as an anaesthetic  and insights of their production would be an advantage for the industry.
Owing to the relationship between genes and proteins, proteomics became the main focus of the post-genomic era. However, being of subordinate relevance to the evaluation of phenotypic responses of organisms, proteomics gradually took the backseat while metabolomics was brought in the limelight . Akin to the definition of the other ‘omics’ terms, ‘metabolomics’ refers to the study of the metabolome that is the complete set of metabolites of an organism. The metabolites of an organism can be categorised as primary (fundamental for cell development and are continually produced, e.g., amino acids and polysaccharides) or secondary (produced in response to a stimulus such as an environmental distress, e.g., sterols). Secondary metabolites of marine algae are of major interest but not all can be expressed at all times. Their synthesis must be triggered by a stimulus—mostly physiological and/or environmental. Verpoorte et al.  advocated that the prime goal of metabolomics is the qualitative and quantitative analysis of all the metabolites present in an organism. They mentioned five major approaches including high-performance liquid chromatography/thin layer chromatography‒ultraviolet (HPLC/TLC‒UV), gas chromatography‒MS (GC‒MS), LC‒MS, MS and nuclear magnetic resonance (NMR) spectrometry. Roessner and Bowne  summarised metabolomics approaches as follows: target analysis, metabolite profiling, metabolomics and metabolic fingerprinting (Figure 5).
As metabolomics depicts the physiological states of any organism including marine algae, the research database of this omics surpasses that of proteomics as well as transcriptomics in the functional genomics arena. The exometabolome and endometabolome of both marine microalgae and macroalgae have been thoroughly studied for multiple purposes including ecology , physiological states  and applications in multiple sectors such as health [34, 74] and energy .
Barofsky et al.  explored the exometabolomes of the marine microalgae (diatoms)
Barre et al.  depicted several analytical methods used to study the marine macroalgal metabolites including coupling MS with GC, coupling MS with HPLC and NMR spectroscopy. Several applications of those analytical methods for the understanding of species like the macroalga
The understanding of metabolisms (e.g., fatty acids) and identification of respective metabolites go beyond the mere comprehension of the marine algal world. Its application as a panacea for the benefits of the society is what is mostly driving the marine algal metabolomics. A concrete example is the quest for cancer remedy. Cancer is the gangrening scourge of the modern world and is on the forefront in the research arenas of several organisms including marine algae. Studies on the red macroalga
The metabolome composition is affected by mutations and endogenous as well as exogenous stimuli. There are some metabolites that can even induce perturbations at the transcriptional level and, consequently, modify the proteins’ activities. Goulitquer et al.  reported on a broad spectrum identification of several metabolites using GC‒MS of marine microalgae including
As is the case with proteomics, the nature and concentration of metabolites vary with respect to environmental stress conditions. An inexhaustive list of such metabolomic studies includes defence response of the macroalga
3.5. System biology
System biology is a multidisciplinary field of study with the integration of the ‘omics’ promoting the holistic approach and condemning the reductionist one . The integration of the ‘omics’ results is imperative for the appreciation of an organism at the system level. The aim of system biology is to establish a profound understanding of the behaviour of and the interaction between the individual components of the organisms . The basic principle of system biology is modelling, which unveils the dynamics of the organisms. To date, studies on marine macroalgal and microalgal system biology are very limited.
System biology is unravelling the novelty of metabolic capabilities and potential bioproducts of marine algae. Genomics, transcriptomics, proteomics and metabolomics are leading to the discovery of innumerable novel molecules, which are proving to be crucial resources and assets in emerging industries such as nutraceuticals, biofuels, pharmaceuticals and cosmeceuticals based on marine algae.
In this section, we have attempted to address the majority of ‘marine algal-omics’ research that has been conducted to date. However, it is far from being an exhaustive review. ‘Marine algal-omics’ have the potential to further develop a whole range of relevant industrial products including commodity and specialty chemicals and enzymes, biopolymers and pigments as well as application to the examination of marine algal bioremediation.
4. Existing and potential applications of marine algae
The array of marine algae and their derivatives are gaining increasing recognition worldwide. In addition to the panoply of ecosystem services that marine microalgae and macroalgae provide, the extensive range of biotechnological exploitation and the subsequent industrial applications of these organisms as biological factories are thoroughly documented. Marine algae are being widely used (Figure 6)—both at the molecular and organismal levels—as food [85, 86] and nutraceuticals , animal and fish feed [86, 88], biofertiliser , bioplastics , pharmaceuticals , cosmeceuticals [91–93], fluorophores , food colourants and textile dyes [95, 96], and biofuels  as well as for phycoremediation [97–99] (Table 1).
Phycoremediation is the use of algae to destroy or biotransform pollutants to innocuous level . Marine algae are being considered for their multiple advantages. Marine algae can remediate heavy metal contamination [97, 98, 108], contribute to wastewater treatment , lower the atmospheric carbon dioxide [14, 15] via photosynthesis  and produce biomass for industrial applications [15, 108].
Carsky and Mbhele , Lawton et al.  and Imani et al.  investigated the potential of several marine algae to be considered for heavy metal contamination remediation. S
Increasing atmospheric carbon dioxide concentration is another major environmental threat environmental threat affecting the balance of nature. Brennan and Owende  enumerated three sources of CO2, namely, the atmosphere, industrial power plants and soluble carbonate. The desirable traits of microalgae, we assume which applies to algae in general, were considered to be the high growth rates, high metabolism of CO2, high tolerance to SO
Sydney et al.  reported that the freshwater microalga
Chung et al.  mentioned that over half a million tonnes of carbon is removed from the sea yearly within commercially harvested macroalgae (seaweeds). They stated that large-scale seaweed cultivation is attractive owing to their decades-proven, low-cost technologies and the panoply uses of their products. They provided an overview of the Korean Coastal CO2 Removal Belt which promotes the removal of atmospheric CO2 via marine forests—approximately 10 tonnes of CO2 per hectare yearly for the brown macroalga
Kaladharan et al.  investigated the carbon sequestration ability of the following marine algae:
The phycoremediation through marine algae is still at an infancy stage and it is unclear whether marine macroalgae or microalgae will monopolise this sector. So far, taking into consideration the literature cited, it is of opinion that marine macroalgae will be the first monopoly of this sector as it has been for the other sectors since the advent of marine algal industrialisation.
4.2. Food and nutraceuticals
The consumption of marine algae originates from countries such as Japan, China and the Republic of Korea [2, 89] where several genera of marine macroalgae, such as
The high nutritional value and rich source of phycocolloids of several genera of marine macroalgae have been reported to be used as food. In this chapter, the term ‘phycocolloid’ refers to three commercially important high molecular weight polysaccharides, namely, alginate, carrageenan and agar. Sulphated galactans—agar and carrageenan—are extracted from Rhodophytes , whereas alginate (composed of mannuronic acid and guluronic acid ) is extracted from Phaeophytes. They are vastly used in the food industry as cost-effective gelling, viscosifying or thickening agents in ice creams and jellies . The global value of these phycocolloids approximates to US$1 billion . Other economically important phycocolloids extracted from macroalgae are ulvans and fucoidans .
Marine microalgae have also been reported to contain proteins, carbohydrates and lipids in substantial amounts , which have been widely utilised as nutritional supplements and health food.
Polyunsaturated fatty acids (PUFAs) such as omega-3 eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)  and omega-6 arachidonic acid (ARA)  are sourced from marine microalgae. Presently, focus is being laid on
4.3. Animal and fish feed
Strains of marine microalgae with high EPA/DHA levels used as a component of aquaculture and livestock feed  have been observed to augment its nutritional value [85, 128], increase the digestion capability, and induce positive growth and reproductive results to a certain extent . Shifting from the conventional use of fish meal, a protein-rich product made from processing remainder fish after human consumption, fish bones and offal, microalgae are now progressively being used as constituents of animal feed. Furthermore, farmed carnivorous fish species fed by a marine microalgae-based diet obtain ample amount carotenoids, lipids, vitamins, proteins and energy for enhanced growth and reproduction . Among cyanobacteria (blue-green algae), species of the genus
The marine microalgae
Marine macroalgae have long been used as a natural fertiliser on the shore and nearby land:
4.5. Cosmeceuticals and pharmaceuticals
The bioprospecting of marine algae has gained momentum in the development of products for cosmeceuticals and pharmaceuticals. Significant marine algal compounds of the cosmeceutical industry include phlorotannins (also used in the food industry), sulphated polysaccharides, tyrosinase inhibitors and suppressors of matrix metalloproteinase (MMP). The marine algal extracts have recently received bouncy attention especially for their antimicrobial properties and in the treatment of the skin related issues (skin anti-aging, skin whitening and pigmentation reduction) . Examples of such extracts from marine algae include
Furthermore, marine algae are the most abundant source of natural polysaccharides—fucoidans, Carrageenans and ulvans. Those polysaccharides are used in some cosmetics as moisturising and thickening agents, rheology modifiers, suspending agents, and hair conditioners among others [93, 138]. Polysaccharides extracted from the macroalgae
4.6. Food colourants, natural dyes and fluorophores
Marine microalgae have also been explored for and used as a renewable source of natural food colourants and dyes. The bright red pigmentation exhibited by the carotenoids of
Microalgae are also sources of phycobiliproteins (phycoerythrin and phycocyanin and allophycocyanin) and chlorophylls that are used as natural dyes in various industries and as food colourants [94, 102]. These proteins are brightly coloured and fluorescent constituents of cyanobacteria and red macroalgae (
Both sub-groups of marine algae have the potential to contribute towards the world’s future energy security, at the same time helping to reduce CO2 emissions and mitigate global climate change impacts as compared to conventional fuels. The biomolecules for the biofuel industry are carbohydrates and lipids for the production of bioethanol and biodiesel respectively. Several strains of marine algae which produce carbohydrates and lipids via photosynthesis have the potential to be exploited as biofuel feedstock . The choice of marine algae as biofuel feedstock is dictated by a number of advantages: relatively rapid growth rate and high productivity compared with other conventional oil crops, high photosynthetic efficiency, great potential for CO2 fixation, low percentage of lignin and a high content in carbohydrates and lipids (20–50%) [143–147]. Microalgae can provide several types of renewable biofuels, for example, methane — produced by the anaerobic digestion of the algal biomas; biodiesel — derived from microalgal oil; and biohydrogen – produced by photobiologically [16, 144]. Several studies have focused mostly on eukaryotic species such as
Delving into the potential applications of marine macroalgae, many authors have reported the use of algae-sourced cellulose in papermaking, a field of application still at an infancy stage. In general, wood-based pulp utilised in the papermaking industry has to undergo a lignin removal process to liberate the cellulose, which is the desired component for producing high quality bleached paper. Lignin is a polymer intercalated between the cellulose fibres in cell walls. Lignified pulp is normally used for low-quality papermaking, for instance, newsprints. Owing to the lack or substantially low amount of lignin in the cell walls of algae [150, 151], the lignin removal process is omitted when using algae , making them potential candidates for sustainable and profitable papermaking as long as cultivation methods are cost effective. This can be achieved by mass cultivation of raw material for a fully established algae-based papermaking industry. Seo et al.  attempted to use lignin-free red macroalgae
Bioplastics have been derivative from organic sources such as potatoes, corn, vegetable oil, and most recently from marine algae. Polysaccharides from macroalgae – carrageenan, agar and alginate – can be used to make bioplastics . Marine algae–based bioplastics have the following advantages: no competition with food resources, ease of growth in a wide range of environments, high yield/biomass, cost-effectiveness, address the issue of excessive CO2 emissions and is environment-friendly [2, 154]. The various types of plastics that are derived from marine algal feedstock include the following:
|Product||Level of exploitation||Applications||Genus|
|Biofertiliser, organic compost, soil conditioner|
|Extract/molecule||Stabilisers and thickeners in food industry, wound dressing, prosthetic devices, matrices to encapsulate and/or release cells and medicine, medical sutures|
|Phycocolloids—agar||Extract/molecule||Gelling agent in food industry, food gums, thickener in ice creams, excipient in pills, growth media for bacteria culture, biotechnological applications|
|Phycocolloids—carrageenan||Extract/molecule/algal biomass (for bioplastics)||Food industry, gel formation and coatings in the meat and dairy industries, stabilisers and thickeners in cosmetics, binders in toothpaste and tablets, smoothers in feed, paint industry, bioplastic|
|Phycobiliproteins||Molecule||Natural dyes in cosmetics, natural food colourants, fluorophores in immunodiagnostics|
|Organism/molecule||Health food, food supplement, feed, natural food colourant|
|Carotenoids—lutein||Organism/molecule||Natural colour enhancer in aquaculture|
|Fatty acids||Organism/molecule||Health food, food supplement, cosmetics, prevention of disease|
|Organism||Live feed, mixed algal diets|
|Polysaccharides||Molecule/extract||Pharmaceuticals, cosmetics, nutrition|
|Phycobiliproteins||Molecule||Natural dyes in cosmetics, natural food colourants, fluorophores in immunodiagnostics|
|Organism/molecule||Nanotechnology, optical systems, semiconductor, nanolithography, drug delivery, medical|
5. Challenges and opportunities in biotechnological applications of marine algae
‘In the end, the objective of microalgal biotechnology is to make money by selling a product for a higher price than it costs to produce.’—Olaizola 
‘Marine algal-omics’ studies have given rise to new opportunities and subsequent industrial applications. While the prospects of those organisms are huge, there are multiple challenges that this sector has been facing since its foundation. Olaizola  presented one of the major issues that the field of marine algal biotechnology faces and why many marine algal applications have not yet reached the commercial and industrial scale. As a whole, for this chapter’s scope, the challenges and prospects are discussed under the following umbrellas: marine algae taxonomic classification, ‘marine algal-omics’ and applications of marine algae.
5.1. Marine algae taxonomic classification
The taxonomic classification of marine algae has been tedious for the past decades. Morphological identification (using both microscopic and macroscopic features) of algae engenders various limitations such as change in morphology due to environmental factors , presence of similar morphotypes, complex cellular structure , lack of characteristics morphological features of the organisms as well as time-consuming and expertise-requiring in this field . The ambiguities of identification using morphological keys have been found in most microalgal genera following phylogenetic analyses of ribosomal genes (SSU and ITS rDNA sequences) .
Identification of marine algae is highly problematic. In this view, taxonomic classification of marine algae is being reviewed through phylogenetic studies supported by analyses of cell division processes, physiological products (pigments and oils produced) and genetic characterisation . For example, the taxonomy of the
As aforementioned, phylogenetic analyses help in categorising species which are difficult to identify. However, from a taxonomic point of view, DNA sequence information without other corroborating evidence can never be used by itself as an indicator for species delimitation . In conjunction, molecular phylogenetic studies often address such issues. Nonetheless, it is still unclear whether the detected sequence differences may be used for delimitation of different species. This is explained by the progress of lineage sorting . The use of different tools as well as sorting out of all lineages of algae is imperative for the identification of marine algae and further enhances their taxonomic exploration.
5.2. Marine algal-omics
‘Marine algal-omics’ are subjected to pretty much the same challenges that other microbial ‘omics’ agonise over. Graves and Haystead  put forward that the foremost challenge of proteomic studies is the analysis of low-abundance proteins and further deplored the archaic methods used to study proteins including the dearth of bioinformatics tools for data interpretation. They also advocated that there is an urgency for new algorithms and that the mundane technologies should retreat while other technologies involving large-scale analyses need to be conceived.
On the other hand, transcriptomics experiences challenges of both worlds—genomics and proteomics. Dong and Yan  summarised the challenges as being experimental, technological and at the level of data interpretation to address issues like unveiling the regulating targets for each non-protein coding RNA and to decipher the complexity of the transcriptome. Bioinformatics is the resonance factor in all the ‘omics’. The advancement in high-throughput technologies of metabolomics is gaining momentum. Nevertheless, there is still an echo of data interpretation difficulties: identification of a panoply of unknown metabolites and transformative agents of metabolism, and data mining .
We are certainly past the genomics era; however, it is only recently that marine algal genomics took off. It has multiple challenges with an echo of bioinformatics especially in the context of the acquisition of growing amounts of data. It is further to be noted that significant advances in algal bioinformatics tool development, such as the Algal Functional Annotation Tool  and GreenCut2 , are therefore unequivocally important drivers in the study of ‘omics’ in marine algae. ‘Marine algal-omics’ also represents a major challenge at organismal level for a set of criteria, such as
In addition, ‘marine algal-omics’ encounters pronounced issues with respect to macroalgae and microalgae. Contreras-Porcia and Lopez-Cristoffanini  underlined that protein extraction of algae follows no common protocol and pointed out that it is particularly difficult to extract proteins from macroalgae due to their low concentration and the co-extraction of contaminants. In the years to come, the proteomics studies of marine algae are expected to increase by multiple folds taking into account their commercial/industrial implication and the will of many countries to develop their blue economy. Such ‘omics’ studies are also opening a plethora of opportunities for several algal species in multiple fields such as
The ‘omics’ technologies detailed in this review are the most commonly used in ‘marine algal-omics.’ Conversely, earlier on, we deplored the static nature of the results that they provide. We also brought the perspective of other avenues (e.g., fluxomics) to the attention of the readers for a dynamic distinction in this arena. Many metabolomics studies provide a snapshot of the targeted or untargeted metabolome at a specific time and can be altered at any given time in response to stimuli or different life stages and growth conditions . Metabolomics allows scientists to catch a glimpse of such a dynamic nature which in fact makes the static picture a limitation in itself. The curiosity even more importantly the urgency to discover the function of several metabolic pathways is now taking over the post-genomic era leading to the field of fluxomics, which is the study of metabolites fluxes. Fluxomics is still in its infancy stage and demands more research in this area for an understanding of how the system works.
5.3. Applications of marine algae
As a consequence, only a few species have been able to reach the industrial and commercial level while many marine algae still remain largely untapped as an asset due to an apparent lack of utility as a primary active ingredient . While some advocate for the industrial application of marine macroalgae, others favour the marine microalgae. However, literature shows that both the marine macroalgae and microalgae can be useful to different industries. Nonetheless, marine macroalgae are currently more appealing for industrial application as they are readily accessible and easy to harvest compared to microalgae  but also have lower cost of production  and biosynthesise commercially important molecules such as the phycocolloids . Marine microalgae, on the other hand, are attracting more attention as a feedstock for biodiesel production and other products such as β-carotene. However, as listed in Table 2, marine algal applications face many challenges that need to be addressed prior to commercialisation.
of marine algae
|Biomass production||High cost of production due to significant cost implication with respect to resource supply: water, carbon dioxide and nutrients|||
|In-sea cultivation||Alterations to biosynthesis of molecules of interest due to spatial and seasonal variations, location and depth|||
|Biomass harvest||Energy intensive process: centrifugation*||[16, 17, 173]|
|Oil extraction||Use of petroleum derivatives||[16, 17, 173]|
|Algal strain||In-breeding leads to negative alteration of trait of economic importance such as decline in yield and quality||[17, 172, 173]|
|Algal diseases||Affect the candidature of strain to be considered as a feedstock|||
|External factors affecting production||Impact of microbial interactions with marine algae on bioactivity|||
|Land use||Non-arable land hosting marine algal mass production increases proportionately with increase in demand||[147, 173]|
|Carbon dioxide input||Contribute to high cost of production due to purchased carbon dioxide|||
|Nutrient supply (especially nitrogen and phosphorus)||Limited nutrient supply limits algal mass production|||
|Dehydration||Energy intensive||[17, 128]|
|Water use||Limited by freshwater||[17, 173]|
|Light||Optimal production limited by shading as well as photo inhibition|||
As a whole, the numerous challenges mentioned (Table 2) can be addressed by genetically enhancing the algal strains, improving the production of high-value products and lowering its cost. Hybridisation of marine macroalgae  and genetic engineering  of both macroalgae and microalgae are promising tools assuring expression of important traits such as disease resistance and overproduction of specific compounds of interest. The compounds of interest may be targeted molecules as well as by-products. Furthermore, the in-sea culture exercise should be carried out along a standard for cultivation to circumvent issues such as inconsistent depth, environmental changes and others which may impact the production of bioactive compounds and composition . In view of lowering the cost of production of marine algae, the by-products of macroalgae biomass production such as protein, alginates and phenolic compounds should be considered as an integral part of commercialisation to enhance the economic value of marine algal biofuel production process. The nutrients can be recycled while wastewater can also be used to some extent .
The last few decades have witnessed several developments in biotechnological applications of marine algae on three scales: research, commercial and industrial. However, the inexhaustive list of challenges mentioned here has hindered the Full-fledged application of marine algae. The challenges are being progressively addressed and opportunities are being generated. It is with confidence that we advocate the determinant role ‘marine algal omics’ will play in the marine algal economy.
The authors are thankful to Mr. Sundy Ramah and Mr. Yohan D. Louis, and Drs I. Yakovleva, R. Bholah and P.K. Chumun for their insightful comments on an earlier version of the manuscript as well as Mr. Sarvesh Pilly Mootanah for the technical support.