**4. Marine biodiversity and chemodiversity today**

Water is an extraordinary medium and, in many respects, mysterious. Its outstanding solvation properties are due to the capacity of the water dipoles (H-OH) to dissociate, reorientate and accommodate salts and polar compounds in a monophasic system [27]. Salts are essential to maintain osmotic balance and membrane polarization. Hydration is essential for the catalytic properties of enzymes. Semiotic (communication) substances are usually released as pheromones (intra-specific signaling) or allomones (against defense or predation). In addition, apolar (long chains or cyclic) molecules can be associated with mucus and dispersed. Some chemical cues are surface-adsorbed on dead substratum and serve as transgeneration signaling, e.g. for the settlement of larvae near adult colonies. Fish have extraor‐ dinarily sensitive and selective receptors that allow them to detect specific chemical signatures that influence their behavior.

Water participates in all life-essential molecular processes, from the most basic (e.g. Miller's experiment) to the most complex enzymatic processes, and it has allowed virtually all types of interatomic and molecular interactions that have resulted in the highly complex and diverse chemical diversity observed in our oceans today.

#### **4.1. Minerals and geochemical cycles**

conditions found outside the biosphere. The biosphere represents a very narrow region less than one thousand times thinner than the globe's diameter, and comparable conditions have not been found on any other planet so far. This does not mean that dormant bacterial spores could not withstand intersidereal journeys - lichens have successfully resisted prolonged exposures in outer space during space craft experimentations. High biodiversity environments are usually found in warm, stable environments where nutrient cycling is efficient (without accumulation of wastes) - this is at least true for tropical rainforests and shallow water coral

"Any lasting change in the biogeochemistry of any of the three components (atmosphere, seawater and land) will disrupt the interfacial equilibrium that supports the many thousands of life forms that interact constantly within an ecosystem. This has happened several times in the history of our planet since it became life-supporting. Changes in soil mineral strata indicate the occurrence of biodiversity-modifying events such as occupation by seas or the occurrence of an ice-age. Discrete organic layers may indicate the presence of a tropical rainforest or of a dry land savannah. Datable fossil evidence within these strata, together with paleontological reconstructions, point out the floristic and faunistic peculiarities of the times. Core drills in ice provide datable evidence of biogeoclimatic episodes within the last few millennia, while core drills in massive scleractinian corals give accurate calendar-like records of recurrent or of

Speciation usually goes along with occupation of new territories and new habitats, the first colonizers having acquired the necessary adaptations to cope with evolving external demands – the Cambrian explosion (545 million years ago) being the most dramatic example of such

Along with this, evidences of accidental episodes of massive species extinctions are witnessed by the sudden "disappearance" of terrestrial and of marine life, that are attributable to tectonic, telluric or meteoritic impacts and to their profound and lasting climatologic and geochemical consequences. The most significant mass extinction is undoubtedly the Permian-Triassic Great Dying [23] where a 96% loss of all non-microbial marine life occurred within ten million years. The precise causes of mass extinction events may be in connection with continuous tectonic movements with their telluric and volcan‐ ic outbreaks and their climatic consequences, to collisions with meteoritic bodies, and to a lesser extent to the appearance of dominant predators, parasites or microbial diseases, or to combinations thereof. Common with many extinction events, however, is the massive release of greenhouse and of toxic gases (carbon dioxide, methane, hydrogen sulfide etc.). The water solubility of CO2 being nearly 30 times that of oxygen, water acidification occurs that impacts preferentially all calcifying organisms with low metabolic rates and weak respiratory systems: most coral genera died out during the Great Dying, along with

Interestingly, profound taxonomic changes in all major phyla seem to follow extinction events, resulting in a better adapted biodiversity. Nothing is known, however, on the consequence of

calcareous sponges, calcifying algae, echinoderms, bryozoans etc. [24].

reefs.

*Biodiversity explosions and mass extinctions (from [26])*

78 Biodiversity - The Dynamic Balance of the Planet

accidental climatic events affecting their biotope.

adaptive diversification at all scales.

The mineral world is massively involved in global geochemical processes, and in the compo‐ sition of solutes in the oceans, as salts and inorganic carbon sources. The cycling of elements is both tectonic and biogenic. Metals are essential catalysts of many organic reactions, and salts are actively involved in osmotic balance and membrane polarization. The availability of heteroatoms (P, S, halogens in particular) is (and has been originally) fundamental in the evolution of natural organic chemistry, because of their involvement in life-essential processes.

#### **4.2. Prokaryotes and prokaryote chemistry**

"Creative" chemistry is the work of living creatures, and Eubacteria and Archaea are probably the best organic chemists ever. Microbes are the drivers of global biogeochemical processes, and their genes have survived the great extinction events [28]. They have set the stage for other organisms to adapt and evolve. The capacity for pioneer organisms to modify their environ‐ ment for the benefit of other life forms is termed metabiosis, and it has been largely docu‐ mented in soil biology [29], but somewhat overlooked in aquatic ecosystems. They can occupy every niche of the biosphere, utilize different carbon and/or energy sources available in order to generate ATP, the energy currency of all biochemical processes.

A distinction is made between chemotrophs and phototrophs as primary producers of organic molecules.

Photosynthesis began as an anoxygenic process that later evolved to produce oxygen, thus allowing the evolution of aerobic metabolism. Photoautotrophs include most producers of primary biomass, from cyanobacteria to algae, plants and are involved as photosymbionts in vegetal (e.g. lichen) and animal (e.g. coral) biological photosystems. They are the base of simple

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Many bacteria derive their energy from the breakdown of organic substances produced by living or dead multicellular organisms. They are instrumental in the recycling of dead organic matter, and many strains live as commensals or symbionts of most eukaryotes, to help the host's digestion with nutrient assimilation or with the energy-yielding catabolism of proteins, carbohydrates and lipids into small, usually water-soluble monomers. A highly diverse microflora is generally associated with good health at the single host's level as well as whole ecosystems. Pathogens are maintained but their numbers are regulated by complex peerinduced antibiotic and bacteriostatic pressure. In corals, metabolic efforts to adapt or com‐ pensate lasting stress (temperature, salinity, hypoxia sometimes in combination) will affect the host's resistance, favor the dominance of opportunistic and aggressive strains and dramatically reduce microbial diversity, leading to a range of necrotic diseases. In humans, obesity and consequential diabetes and cardiovascular diseases strongly correlate with poor feeding habits

Some strains are downright lethal after acquiring multi-resistance to existing antibiotics, and if provided with conditions that trigger their inherent but normally unexpressed pathogenic‐ ity. Some exciting scientific advances have been made since the discovery of quorum sensing in bacteria, the detailed study of microbial biofilms, and in the understanding of lethal epidemics (e.g. caused by *Vibrio* species). However, by and large, metagenomic studies have clearly shown that eukaryotic and prokaryotic biodiversity (and hence chemodiversity) are

Cyanobacteria are thought to have enriched the primitive atmosphere in oxygen, promoting biodiversity through repeated endosymbioses, i.e. successive fusion-acquisition processes that led to the complex metabolic machineries of higher plants (origin of plastid organelles) while ancestral bacteria became incorporated as mitochondria in most eukaryotes. Other organelles are suspected to have generated from similar mechanisms. Many eukaryotes have successfully

This increase in biodiversity has itself led to competition for existing resources: food, space,

In non-motile organisms (algae, halophytes and some benthic invertebrates) in which escape responses are not possible, species-specific assortments of physical protections and/or chemical defenses have evolved to discourage predators. Their remains are collectively termed

biominerals. Some growth forms (encrusting, massive, cryptic) may also

or highly complex marine and terrestrial food chains.

**4.3. Eukaryotes and Eukaryote-associated chemistry**

colonized non-aquatic environments.

*4.2.3. Heterotrophs - the good, the bad and the ugly*

and deficient gut microflora [31].

strongly correlated.

access to light etc.

#### *4.2.1. Chemotrophs*

Chemotrophic Archaea and Bacteria that live in oxygen-depleted environments (e.g. in the vicinity of hydrothermal vents) derive their energy from the oxidation of reduced inorganic compounds and use (i) carbon dioxide as sole carbon source or (ii) lipids, sugars or proteins to form their own organic compounds. Many scientists believe that life originated in the oceans, in the absence of light and in the vicinity of underwater tectonic/volcanic activity, under similar conditions to post-Hadean times.

Archaea are recognized among the most abundant living entities in the oceans, participating in major biocheochemical cycles, such as the Methanogens that produce most the atmospheric methane greenhouse gas. Halophilic Archaea thrive in hyper saline environments like in the Dead Sea, sometimes in hyper alkaline conditions (pH around 12). On the other hand, extremophilic Archaea can be found in hot sulfur springs under pHs as low as 2. They are either anaerobic and reduce hydrogen sulfide to sulfur, or aerobic and oxidize sulfur to sulfuric acid. Thermophilic (50-70°C) and hyperthermophilic (70 to 118°C) Archaea produce thermo‐ stable enzymes of major biotechnological importance, e.g. in DNA amplification using polymerase chain reaction (PCR), in food industry, etc.

Chemotrophic Eubacteria include chemoautotrophs which utilize inorganic sources and environmental CO2, (like nitrogen-fixing soil bacteria, iron and manganese-oxidizing hydro‐ thermal bacteria) and chemoheterotrophs which degrade existing organic substrates. Many bacteria (Gram-positive Actinomycetes, Bacillus, Gram-negative gamma-Proteobacteria) are chemotrophs, and produce a wide array of bioactive compounds, many of which have strong antibiotic potential (examples are given in [30] vol.1, chapter 7). Interestingly, hydrothermal vents are crowded with invertebrates (mollusks, crustaceans and worms) that cultivate chemotrophic bacteria that provide them with organic nutrients.

#### *4.2.2. Phototrophs*

Phototrophs harvest solar photons as the energy source to carry out their cellular energy processes.

Most phototrophs carry out photosynthesis, a process by which carbon dioxide is converted into organic material, used structurally (generally as polymers or supramolecular complexes) or functionally for the regulation of cellular processes, or stored as reserves.

A trans-membrane electrochemical gradient is created, which is utilized by ATP synthase, to create ATP (adenosine triphosphate), the key molecule that fuels biochemical processes in the cell, from the oxidation of glucose. Oxygen is generated in the process. Archaea may fix carbon and some use light as energy source to create metabolic energy but none is capable is capable of photosynthesis with the use of complex electron- transfer chains. Halophilic archaea use bacteriorhodopsin instead - a pigment that activates a transmembrane proton pump.

Photosynthesis began as an anoxygenic process that later evolved to produce oxygen, thus allowing the evolution of aerobic metabolism. Photoautotrophs include most producers of primary biomass, from cyanobacteria to algae, plants and are involved as photosymbionts in vegetal (e.g. lichen) and animal (e.g. coral) biological photosystems. They are the base of simple or highly complex marine and terrestrial food chains.

#### *4.2.3. Heterotrophs - the good, the bad and the ugly*

A distinction is made between chemotrophs and phototrophs as primary producers of organic

Chemotrophic Archaea and Bacteria that live in oxygen-depleted environments (e.g. in the vicinity of hydrothermal vents) derive their energy from the oxidation of reduced inorganic compounds and use (i) carbon dioxide as sole carbon source or (ii) lipids, sugars or proteins to form their own organic compounds. Many scientists believe that life originated in the oceans, in the absence of light and in the vicinity of underwater tectonic/volcanic activity, under similar

Archaea are recognized among the most abundant living entities in the oceans, participating in major biocheochemical cycles, such as the Methanogens that produce most the atmospheric methane greenhouse gas. Halophilic Archaea thrive in hyper saline environments like in the Dead Sea, sometimes in hyper alkaline conditions (pH around 12). On the other hand, extremophilic Archaea can be found in hot sulfur springs under pHs as low as 2. They are either anaerobic and reduce hydrogen sulfide to sulfur, or aerobic and oxidize sulfur to sulfuric acid. Thermophilic (50-70°C) and hyperthermophilic (70 to 118°C) Archaea produce thermo‐ stable enzymes of major biotechnological importance, e.g. in DNA amplification using

Chemotrophic Eubacteria include chemoautotrophs which utilize inorganic sources and environmental CO2, (like nitrogen-fixing soil bacteria, iron and manganese-oxidizing hydro‐ thermal bacteria) and chemoheterotrophs which degrade existing organic substrates. Many bacteria (Gram-positive Actinomycetes, Bacillus, Gram-negative gamma-Proteobacteria) are chemotrophs, and produce a wide array of bioactive compounds, many of which have strong antibiotic potential (examples are given in [30] vol.1, chapter 7). Interestingly, hydrothermal vents are crowded with invertebrates (mollusks, crustaceans and worms) that cultivate

Phototrophs harvest solar photons as the energy source to carry out their cellular energy

Most phototrophs carry out photosynthesis, a process by which carbon dioxide is converted into organic material, used structurally (generally as polymers or supramolecular complexes)

A trans-membrane electrochemical gradient is created, which is utilized by ATP synthase, to create ATP (adenosine triphosphate), the key molecule that fuels biochemical processes in the cell, from the oxidation of glucose. Oxygen is generated in the process. Archaea may fix carbon and some use light as energy source to create metabolic energy but none is capable is capable of photosynthesis with the use of complex electron- transfer chains. Halophilic archaea use

bacteriorhodopsin instead - a pigment that activates a transmembrane proton pump.

or functionally for the regulation of cellular processes, or stored as reserves.

molecules.

*4.2.1. Chemotrophs*

*4.2.2. Phototrophs*

processes.

conditions to post-Hadean times.

80 Biodiversity - The Dynamic Balance of the Planet

polymerase chain reaction (PCR), in food industry, etc.

chemotrophic bacteria that provide them with organic nutrients.

Many bacteria derive their energy from the breakdown of organic substances produced by living or dead multicellular organisms. They are instrumental in the recycling of dead organic matter, and many strains live as commensals or symbionts of most eukaryotes, to help the host's digestion with nutrient assimilation or with the energy-yielding catabolism of proteins, carbohydrates and lipids into small, usually water-soluble monomers. A highly diverse microflora is generally associated with good health at the single host's level as well as whole ecosystems. Pathogens are maintained but their numbers are regulated by complex peerinduced antibiotic and bacteriostatic pressure. In corals, metabolic efforts to adapt or com‐ pensate lasting stress (temperature, salinity, hypoxia sometimes in combination) will affect the host's resistance, favor the dominance of opportunistic and aggressive strains and dramatically reduce microbial diversity, leading to a range of necrotic diseases. In humans, obesity and consequential diabetes and cardiovascular diseases strongly correlate with poor feeding habits and deficient gut microflora [31].

Some strains are downright lethal after acquiring multi-resistance to existing antibiotics, and if provided with conditions that trigger their inherent but normally unexpressed pathogenic‐ ity. Some exciting scientific advances have been made since the discovery of quorum sensing in bacteria, the detailed study of microbial biofilms, and in the understanding of lethal epidemics (e.g. caused by *Vibrio* species). However, by and large, metagenomic studies have clearly shown that eukaryotic and prokaryotic biodiversity (and hence chemodiversity) are strongly correlated.

#### **4.3. Eukaryotes and Eukaryote-associated chemistry**

Cyanobacteria are thought to have enriched the primitive atmosphere in oxygen, promoting biodiversity through repeated endosymbioses, i.e. successive fusion-acquisition processes that led to the complex metabolic machineries of higher plants (origin of plastid organelles) while ancestral bacteria became incorporated as mitochondria in most eukaryotes. Other organelles are suspected to have generated from similar mechanisms. Many eukaryotes have successfully colonized non-aquatic environments.

This increase in biodiversity has itself led to competition for existing resources: food, space, access to light etc.

In non-motile organisms (algae, halophytes and some benthic invertebrates) in which escape responses are not possible, species-specific assortments of physical protections and/or chemical defenses have evolved to discourage predators. Their remains are collectively termed biominerals. Some growth forms (encrusting, massive, cryptic) may also

resist whole-organism or whole-colony predation, or restrict their access.

Algae are generally non-toxic, but may contain antifeedants such as organohalogens or polyphenols that are distasteful to fish [32].

**5. Uses of marine natural products**

**5.1. Housing and transportation matters**

mineral sand and crushed rocks or debris.

million times slower the consumption rate.

biomass of high-diversity systems in tropical zones.

*5.1.1. Construction materials*

*5.1.2. Fossil fuels and biofuels*

**5.2. Health and well-being**

sources.

Marine biogenic molecules are used in a large variety of applications, industrial, medical,

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These include the use of fossilized or detritic materials for construction and as chemical energy

Biogenic sand and rocks (e.g. sandstone) are used to create building, roads and associated structures. Urban architecture is mostly made of concrete structures, i.e. cemented biogenic or

Fossil fuels are consumed at the rate of 88 million barrels a day, in heat engines, to produce electricity, domestic heating, and in petrochemical chemistry (plastics, clothing, lubricants, polymers). Fossil fuels are non-renewable energy, since the production rate is about one-

This includes the use of biomineral or bioorganic materials in surgery, of cosmetics and skin care substances, and most of all of anticancer, antiviral, anti-pain, antibiotic, anti-inflamma‐ tory, as well as insecticidal, anti-malarial or anthelminthic molecules, not to mention other

The exploitation of marine natural products in folk medicine is very limited and concerns a few organisms that did not necessitate special underwater investigations, nor entail storage and conservation problems - of paramount importance since desiccation, oxidation and fermentation occur so rapidly. Exceptions are the occasional use of specific algae as insecticides and for ringworm treatment, or the ceremonial use of toxic or venomous organisms. Fixed and fleshy organisms were generally distasteful or toxic, sparing them for being considered as remedies. Corals, sponges and a few others have no nutritional value and represent the largest

It is only since just after WW2 that marine organisms emerged as a complementary source to traditional plant remedies, thanks to the co-occurrence of several factors, among which (i) the recent discovery of fungal antibiotics and the use of bacterial enzymes in bioprocesses, (ii) the development of adequate screening procedures, (iii) SCUBA exploration and later robotsampling in oceanic depths. The development of synthetic chemistry soon became necessary to provide alternative sources for rare organisms, but also to find better analogues (more active,

domains of growing interest, such as Alzheimer's disease and schizophrenia.

less toxic, more soluble, better tolerated, easier and cheaper to synthesize…).

pharmaceutical, cosmetological, as food or associated to food, decoration…

Not all sessile, slow-moving and sedentary organisms enjoy an efficient physical protection. Fleshy invertebrate species and those that must be exposed to sunlight to perform photosyn‐ thesis may produce toxic or distasteful substances to discourage feeding by fish, crustaceans or other carnivores. Alcyonarian octocorals shelter photosymbiotic dinoflagellates, and are able to produce complex bouquets of cyclic terpenoids that are dissuasive against predators and efficient against space competitors. Sponges shelter biodiverse archaean, eubacterial and cyanobacterial communities and produce an amazing variety of metabolites (many are nitrogen containing and halogenated) as a functional consortium. Bryozoans shelter bacteria that produce highly complex and toxic molecules (e.g. bryostatins). Ascidians can produce highly bioactive molecules, such as the depsipeptidic didemnins, in association with pro‐ chloron, i.e. cyanobacteria which they cultivate in their tissues. The purpose here is not to list the thousands of amazing molecules that are produced by benthic marine invertebrates, to which we must add the recently discovered highly diverse repertoire of planktonic organisms: [31] and its updated version [33] in press) and [34] are probably the most recent and compre‐ hensive texts on the subject.

Evolutionary reflections of chemical defenses in marine symbiotic systems have been recently proposed by [35]. Symbiotic and photosymbiotic systems that associate an invertebrate or algal host and its specific microbial consortium are common in tropical shallow water reefs, which concentrate at least one third of the total marine biodiversity and certainly the largest propor‐ tion of all known "secondary" metabolites [26]. To these must be added marine fungi and actinobacteria that live in marine sediments.

A generally overlooked component of marine chemodiversity is mucus, sometimes constantly and abundantly produced by epithelial goblet cells of cnidarians, and also found in other sessile invertebrates, and also in fish. No two muci are alike. In fish, it helps protecting scales from unwanted fouling by encrusters or parasites, as well as having intrinsic antibacterial and antiviral properties. Coral mucus has species-specific composition and plays a role equivalent to the organ-forming mesoderm of triploblastic organisms, in managing a highly biodiverse microbial fauna that recycles carbon, nitrogen and sulfur and provides an energy complement to symbiotic photosynthesis. To the coral associated bacteria mucus plays the role of a biofilm in which complex antibiotic interactions are at play to maintain microbial diversity.

Behavioral adaptations like "advertising" (aposematic) colors and body shapes make use of colored metabolites borrowed from the prey organisms and concentrated into superficial diverticula. Specialist predators like shell-less mollusks like dorid nudibranchs are beautifully colored and highly toxic. Several aeolid nudibranchs on the other hand use camouflage for similar reasons.
