Marine Ecosystems: A Unique Source of Valuable Bioactive Compounds

The water covers about 71% of the earth's surface and occupies an area of about 361 million km2 and a volume of about 1370 million km3 of water. Oceans and seas are responsible for maintaining the global climate by regulating air temperature and supplying moisture for rainfall. They play a major part in the global carbon cycle, removing almost 25% of the carbon dioxide released by human activity. Furthermore, life would not have begun on Earth without seas, which support the planet's highest biodiversity. They also offer social and economic goods and services, as well as tourism and recreation, maritime transportation, security, and coastal protection. Marine ecosystems include the open ocean, the deep-sea ocean, and coastal marine ecosystems, each of which has different physical and biological characteristics. The variability of the marine ecosystem is the result of the wide array of habitats in seas and oceans. Coral reefs, seagrasses, estuaries, and mangroves are the most important types of marine ecosystems. Variations in the characteristics of the marine environment create different habitats and influence what types of organisms will inhabit them. The marine environment can be divided into zones based on physical features such as depth, temperature, light penetration, and other several factors. There are two main marine realms or provinces, a pelagic realm that includes the water column and a benthic realm that represents the sea floor. Each of these two domains has also been divided into other smaller domains or regions based on the prevailing environmental conditions. Pollution, habitat alteration, and overfishing are the most destructive impacts on the marine environments and their threats are very clear. So, marine ecosystems in oceans and seas should be protected through planned management in order to prevent the over-exploitation of these resources.

The marine ecosystem is the greatest of all ecosystems. Marine ecosystems cover approximately seventy-one percent of the Earth's surface; moreover, they contain approximately ninety-seven percent of the planet's water. Thirty-two percent of the world's net primary production is generated by them. There are many marine ecosystems environmental problems, which include marine pollution, unsustainable exploitation of marine resources (as overfishing to certain species), building on coastal areas, and climate change. From the trophical standpoint, a marine ecosystem has two groups of components: autotrophic components and heterotrophic components. The primary or basic productivity of an ecosystem could be defined as the storing rate of radiant energy by producers (chemosynthetic and photosynthetic) activity as an organic substance that can be utilized as food. The productivity of marine ecosystem greatly refers to the organic matter production by producers or autotrophs “phytoplanktons and algae,” the produced organic carbon is supplied to “heterotrophs,” which obtain their energy only from the organic matter respiration. There are many carbon-nested cycles associated with marine productivity including Grass and Net Primary Productivity (GPP and NPP, respectively) as well as Net community and Secondary productivity (NCP and SP, respectively). Fisheries depend on secondary productivity; thus they rely on both Net primary productivity and the organic matter transferring efficiency to the food web. Environmental factors as well as the change of climate may strongly impact NPP in many ways that rely on the regional as well as local physical settings, ecosystem structure, and functioning medium. 

An aquatic ecosystem is a water-based environment. Aquatic ecosystems include the marine ecosystem and freshwater ecosystems. Two-thirds of the total surface area of the planet is covered by marine water. These ecosystems can be classified into two main categories; i) water/pelagic environment (including; neritic and oceanic zones) and; ii) bottom/benthic environment (including; supra-littoral, intertidal/littoral, and sublittoral zones). Biotic and abiotic factors mean all the living and non-living components of any ecosystem. Biotic factors also include the interactions between organisms and the way they live with or rely on each other. Abiotic factors include all the non-living components, which the living inhabitants rely on to live, grow and thrive. Factors affecting aquatic biomes greatly differ from one water body to the other as the water itself has different properties. Abiotic factors that influence aquatic biomes include light availability, depth, stratification, temperature, currents, and tides.

Marine ecosystems encompass around 70% of the earth's surface and contribute significantly to human well-being by giving social, economic, and environmental advantages to the world's growing population. Marine ecosystems provide a variety of different services that are crucial for human well-being, in addition to being a major source of food, income, and employment. Coastal protection, marine biodiversity, and carbon sequestration are among them. Human activities, on the other hand, place diverse stresses on marine ecosystems, which are predicted to increase, resulting in cumulative impacts on marine ecosystems and biodiversity. As a result, significant efforts have been made around the world to create marine protected areas (MPAs) in order to safeguard and preserve biodiversity, as well as natural and cultural resources. They're usually made by designating zones and prescribing permissible and prohibited activities within those zones. MPAs include the Open Ocean, coastal areas, intertidal zones, and estuaries, among other habitats. The United Nations Convention on the Law of the Sea (UNCLOS), which established the worldwide framework for marine governance in 1982, obligated all governments to protect and conserve the marine environment. In 2000, MPAs covered 0.7% of the Ocean; since then, MPA coverage has increased by more than tenfold to 7.68%. The MPA network will need to be ecologically representative, equitably and efficiently maintained, and of particular importance for ecosystem services in order to meet the aim.

There is a wide variety of plant, animal, and microbial life in mangrove forests because of their location at the boundary between terrestrial and marine environments. Because of their central role in the development and upkeep of the mangrove ecosystem, microbes also serve as a useful and significant source of biotechnologically engineered materials. Microbes are essential to the health of the mangrove ecosystem's productivity by aiding in the decomposition and mineralization of leaf litter at a number of different phases of the process. They are capable of recycling nutrients; they can generate or consume gases affecting the global climate; they can remove contaminants; they can process anthropogenic trash. Mangrove environment microorganisms provide a large supply of antimicrobial substances and also create a broad spectrum of major health-boosting chemicals such as enzymes, antitumors, insecticides and immune modulators. However, unlike other ecosystems, mangrove ecosystems have never had their microbial diversity described. Despite the rich diversity of microbiological conditions in mangrove ecosystems, only around 5 percent of species have been classified, and many of them remain enigmas in terms of their ecological importance and practical use. Microbial diversity must be fully utilised to reach its potential, and modern molecular biology and genetics technologies show considerable promise. This Chapter, therefore, attempts to examine and analyze the microbial diversity of mangrove ecosystems in many aspects, such as agricultural, pharmaceutical, industrial, environmental, and medical possibilities.

In the marine rocky intertidal ecosystem, macroalgae (seaweeds) serve ecosystem engineers that create, modify, or maintain the physical habitat for their own and other species. Intriguingly, most marine macroalgal species evolved with microbial colonization and biofilm formation on their surface. The macroalgae (basibiont) and associated epiphytic microbiota (epibiont) act as a functional unit known as a “macroalgal holobiont,” characterized by its complex chemical interactions. In this non-trophic association, the epiphytic microbial biofilm forms a protective layer essential in host defense against foulers, consumers, or pathogens. In addition, antimicrobial activity is widespread among these epiphytic microbes. However, due to their thinness and often negligible biomass, the chemo-ecological impact of this epiphytic microbiome is severely underestimated. This chapter aims to review the antimicrobial potential of the “macroalgal epiphytic microbiome” and introduce the application of “meta-omics” approaches for further exhaustive exploitations of this unique microbiome for future drug discovery. 

With the advent and rapid progress of the novel blue economy, the prospect of large-scale commercial production of diverse natural bioactive compounds from aquatic biota is likely to be realized in the near future. The biodiversity of the marine biota represents a potentially abundant source of new biomolecules with potentially different economical applications. Most of these biotas are able to survive under stress conditions, as a result, they produce complex metabolites with unique biological properties. These natural substances could be used as functional constituents in the food sector. Moreover, they could aid in the treatment of a broad range of different diseases, including antitumor, antioxidant, antiaging, anti-inflammatory, and antimicrobial. The special properties of these compounds make them an attractive group deserving increasing scientific interest. It is interesting to note that there are some biomolecules exclusively found in marine biota, including phlorotannins and sulfated polysaccharides. This chapter explains the bioactive molecules from different marine biota as well as illustrates their chemical structure and highlights their new biologically active form.

Of the several types of aquatic ecosystems, marine ecosystems are the largest and are characterised by high salt concentrations. Therefore, aquatic flora, fauna and microbes which are highly halophilic can be found here abundantly. Apart from oceans and seas, there are various other types of marine habitats like salt marshes, estuaries, intertidal areas, coral reefs, lagoons and mangroves . Bioactive compounds are those chemicals produced typically in small quantities by plants, animals or microbes for their own protection or functioning, but have beneficial effects on human health. Since marine ecosystems are exceptionally rich in biodiversity, the prospect of availability of the bountiful bioactive agents can easily be conjectured. Primary producers like microalgae and phytoplanktons are rich sources of various pigments like carotenoids, beta-carotene and polyunsaturated aldehyde. Sea-weeds are abundant in vitamins A and C, and also in phenolic compounds, terpenes, etc. Primary consumers like crustaceans and molluscs are reported to produce steroids having high medicinal potential. Carnivorous fishes like herring, shad and mackerel are the secondary consumers. Mackerel is a great source of the amino acid taurine, which is considered to have beneficial effects on heart health. Top carnivorous fishes like the haddock or cod belong to the category of tertiary consumers. Cod is popular for its “cod-liver oil” which has high contents of vitamins A, D and E and omega-3-fatty acids whose health benefits are familiar to all. Even the decomposers like marine bacteria and fungi are effective manufacturers of alkaloids, terpenes, peptides and mixed biosynthetic compounds derived from polyketides. Thus, it will not be an exaggeration to say that the marine ecosystem has a plethora of bioactive compounds, and it can easily be proclaimed that collective efforts in the form of copious research and documentation are required to enable sustainable utilisation of this untapped bioresource. This review is presented here as a small step to reach that goal. 

Marine organisms offer a delicate, yet plentiful source for a vast array of novel products whose unique structural features make them suitable drug candidates, pesticides, marine anti-fouling agents, and more. There are many challenges that threaten the marine ecosystems like climatic change, biological invasions, overexploitation, overfishing, and water pollution. These challenges negatively affect the marine biodiversity and then productivity. So, they must be overcome for potential preservation of various lives in the marine environment. The current chapter will present various opportunities in marine drug discovery and will also discuss the problems encountered in marine drug discovery.

The bulk of today's medicines have been derived from natural sources in the past. In the last 50 years, more than 20,000 inspirational natural resources have been found in the aquatic world. The field of marine natural product chemistry is a relatively new field, with roots in the 1960s and an emphasis on drug development in the 1980s. Marine species constitute a significant portion of the oceanic community, and they play an essential role in the production of medicinal molecules and cosmeceutical with naturally effective moieties. They're full of potential antimicrobial, immunosuppressive, anti- carcinoma, anti- viral, and protease inhibitory compounds that could be used in new therapeutics. Numerous compounds which care possibly about the photoprotective mechanisms of strong pharmaceutical and cosmeceutical value have previously been isolated from diverse marine sources like cyanobacteria strains, lichens, fungi, algae, animals, plants and phytoplankton. Due to public concern about ecosystem health and the consequent increase in aquaculture's supply of seafood in industrialized nations, several marine-based medications are actively being developed for commercial use. Corallina pilulifera extracts, for example, showed anti-photoaging properties or photoprotective properties derived from marine sources. To combat UV-A-induced oxidative stress in human dermal fibroblast (HDF) cells, these extracts were developed to provide high antioxidant activity and protection against DNA damage while also inhibiting matrix metalloproteinases (MMPs), a key player in skin photoaging caused by UV-A exposure. Natural bioactive products are up against vast chemical libraries and combinatorial chemistries in a fight for market share. As a result, each stage of a natural product program, from environmental sampling and strain selection to metabolic expression, genetic exploitation, sample processing, and chemical dereplication, must be more effective than ever. Hence, in the presented review, attempts have been made to illustrate more on the effective strategy of drug discovery from the marine ecosystem.

The marine world expresses a great scope for diverse novel scaffolds with unusual skeleton nature. Polyphenols, phycocolloids, pigments, fucoidans, peptides, pigments, and phlorotannins are the main classes of compounds provided by marine resources. Some of these structures displayed astonishing biological activities and successfully proceeded to marketed drugs for the treatment of different human diseases. There are many examples of successful commercially available marine-derived drugs such as cytarabine (Cytosar-U®) for acute myelocytic leukemia, trabectedin (Yondelis®) for ovarian cancer, Eribulin (Halaven®) for metastatic breast cancer, Ziconotide (Prialt®) for severe chronic pain, and Vidarabine (Ara-A) for viral infections. Oceans and their immense biodiversity have gifted humanity with a pathway out of the obstacles of health care. The constant need for innovation has been a great challenge for the pharmaceutical industry especially in finding new sources of active compounds. This chapter discussed the clinically approved marine-derived compounds and their impact on different diseases, focusing on those with granted approval in the last decade from 2011 to 2021. We also highlighted the underlying mechanism of actions through in vivo, in vitro, and computational in silico studies. Hopefully, this chapter will help scientists to develop a novel marine-derived drug.

Many opportunities, from many marine secondary metabolites including some of the most interesting candidate drugs, have to be used for development in marine drug discovery in parallel to the updated technologies, procedures and protocols. The hope and the net result, in such a manner, are related to the acceleration and management of marine drug discovery as an integrated process from obtaining the sampling until the launch of the drug. The recent protocols targeted gene sequencing methods for identifying secondary metabolic pathways to be used in the biosynthesis of marine natural products (MNP) discovered from marine isolates. Afterward, the synthesis processes for replenishing inventories of compounds and analogs is a critical step. Moreover, the cheminformatics and computer screening of MNP for protein targets have been used to some extent. On the other hand, the collaboration allows sharing of knowledge, tools, finances, and administrative processes, therefore increasing the innovation potential of all parties, playing a greater role. Seriously, the future prospects for developing marine drug discovery involve the collection of relevant information and the evaluation of available opportunities to establish goals through government initiatives and finally to invest and market the drug products from marine origin. In the current chapter, the advanced approaches to marine drug discovery will be explained. Furthermore, this chapter will present both collaboration and innovation in marine drug discovery to increase the effectiveness of drug discovery and advance the production process.