3.2. Oil and Gas
The depletion of gas and oil resources on land was among the factors leading to the exploration and exploitation of gas and oil in the deep sea, the so-called offshore oil and gas industry
[135][30]. The operations consist of four stages: geological and geophysical investigation, exploration, production and decommissioning. Every step is associated with potential environmental impact, including chemical, physical and biological disturbance
[136][31]. Due to the absence of sufficient data related to deep-sea ecosystems, the environmental impact assessment of such activities is still limited
[137][32]. In addition, environmental management is challenging as deep-sea biological systems operate at a slower pace compared to shallow waters
[138][33]. Anthropogenic stressors resulting from deep-water oil and gas operations in such fragile ecosystems may influence habitats and species, making re-colonization and recovery difficult
[139,140][34][35].
3.3. Deep-Sea Minerals
Deep-sea mineral extraction is identified as an alternative source of metals of economic interest and is claimed to be a future clean sector
[154][36], unlike terrestrial mining, which generates pollutants into water and land
[155][37]. On the other hand, the risk and sustainability of such activities is still undefined because the ecological aspects of the deep-sea are unknown and studies are very few
[78][38]. The interest in this industry sector is substantially growing, but the risks associated with this kind of deep-sea operations remain immeasurable
[53,156][7][39]. Commercial mining tests and scientific investigations on the disturbance of polymetallic nodules have shown that the impact is severe after dredging operations, especially on habitat and biodiversity
[157[40][41][42],
158,159], and restoration is far from being implemented
[160][43]. The technologies and procedures for exploiting the deep sea for mining purposes could seriously harm the marine environment, including habitats, marine resources, biogeochemistry cycling and environmental quality and blue economy sectors (e.g., fisheries
[161][44]). Even subtle changes in the morphology of deep-sea abyssal plains have the potential to cause severe changes in benthic habitats
[162][45]. Furthermore, not only habitat and biodiversity in abyssal regions will be impacted by nodules operations, but the impact will also touch midwater and mesopelagic species together with biota through the entire water column, especially during the lifting of nodules to the surface
[163][46].
3.4. Marine Renewable Energy (MRE)
MRE, the so-called ocean-based energy, looks promising in tackling dioxide emissions, meeting the growing energy demand, and reducing the human contribution to global warming
[176][47]. MRE include offshore winds farms (OWFs), solar energy, wave and tidal energy, in the latter case, the mattresses that stabilize submarine power cable may enhance benthic megafauna habitat capacity and increase artificial habitats for a range of fish and crustacean species
[177][48]. On the contrary, Dannheim et al.
[178][49] reported that MRE installations might impact the benthic compartment during the construction, operational or decommissioning stages.
The deep-sea OWE industry exerts potential associated risks and stressors on the environment that were defined by Boehlert and Gill
[179][50] and Copping et al.
[180][51]. These can be summarized as follows: (i) atmospheric and oceanic dynamics changes resulting from energy modification and removal; (ii) habitat alterations; (iii) electromagnetic field influence on deep-sea species from cables; (iv) underwater noise effects on marine species; (v) water quality changes.
3.5. Biotechnology and Chemical Compounds for Industrial and Pharmaceutical Uses
Chemicals from anthropogenic sources tend to harm the ocean and human health
[192][52]. The increase of human activities around and in the ocean, including oil and gas exploitation, deep-sea mining operations, fishing, coastal tourism and shipping contribute largely to the accumulation of toxic chemicals in marine ecosystems such as heavy metals
[193][53], persistent organic chemicals (POC)
[194][54] and radioactive elements
[195,196][55][56]. In many coastal areas around the world, the concentrations of toxic chemicals are extremely high. Therefore, new biotechnology approaches represent the fundamental solution for tackling the challenge of “human need growing” vs. “pressure on marine resources” and are an efficient tool for environmental bioremediation
[197][57].