Routes to Ocean Sustainability and Blue Prosperity in a Changing World: Guiding Principles and Open Challenges

Abstract

In December 2017, the United Nation decided to proclaim the United Nations Decade of Ocean Science for Sustainable Development for the 10-year period beginning on 1 January 2021.

Introduction

In December 2017, the United Nation decided to proclaim the United Nations Decade of Ocean Science for Sustainable Development for the 10-year period beginning on 1 January 2021 [1].

This important decision has a multifaceted meaning. From one side it reaffirms and stresses the importance of constraining human actions to the sustainability principles. Further, it emphasizes the central role of the Ocean as both a driver of future economic growth and an essential resource to be preserved. Finally, and quite relevantly, it states the need to base human activities on scientific knowledge.

In fact, the UN declared the Ocean Decade as a “once in a lifetime opportunity for nations to work together to generate the global ocean science needed to support the sustainable development of our shared ocean”, with the specific underlying goals of: (i) to provide Ocean science, data and information to inform policy for a well-functioning ocean in support of all sustainable development goals of the Agenda 2030; and (ii) to generate scientific knowledge and underpinning infrastructure and partnerships.

The importance of ocean and seas for the planet ecosystem health and for human well-being is so large that cannot be overestimated. They cover over 70% of the planet, regulate its climate by absorbing a massive amount of heat and carbon dioxide from the atmosphere, sustain the hydrological cycle and its components (including rain over land and forest), host an amazing variety of habitats and marine organisms, ranging in size and ecosystem function from the microscopic photosynthetic organisms that fuel marine life and produce half of earth’s oxygen and biomass to large marine mammals and top predators, from sandy coastal areas to deep sea hydrothermal vents, and more. They provide food, energy, transportation routes, genetic and mineral resources, job opportunities, recreational, cultural and social services [2]. Preserving ocean and ocean life is such a relevant task that it is—per se—one of the UN Sustainable Development Goals (SDG 14), but the ocean role is so relevant that many other SDGs cannot be achieved without preserving ocean health [3].

However, the ocean is challenged by a number of co-occurring pressures, and it is easy to foresee that the number and intensity of those co-occurring threats will increase in the near future, driven by the demands of the expanding blue economy sectors and the related society components.

It is therefore mandatory to monitor and understand how the ocean is responding to the cumulative impact of these multiple coexisting pressures [4], and to use this knowledge to identify safe operational thresholds—i.e. pressure levels not to be exceeded to guarantee the resilience of the marine ecosystems, ensuring their proper functioning and the persistence of good ecological state and proper functioning of marine systems—as well as effective ways to enforce the respect of those limits.

Blue economy can be instrumental in increasing the quality of life of billions of persons, and it is of crucial importance to promote its development. Of the same importance is to learn from the past and to avoid the errors made while promoting land base economy, which developed with too little or no awareness and attention to potential adverse consequences on the environment at the local or global scale. As we now know very well, overexploitation of the natural capital and/or excessive level of environmental impact cause ecosystem deteriorations with—sooner or later-cascading consequences also on the economic activities and the related social dimensions. To build the knowledge to find a proper and workable trade-off between minimization of environmental impact and maximization of socio-economic benefits, also accounting for the need and rights of other countries and future generations, remains a formidable challenge to be won. To enforce effective policies to reach that balance might be an even larger challenge.

Blue Economy

From an economic perspective, the ocean and seas represent a very relevant resource. Oceans have always been a valuable component of human societies. Coastal seas provided an accessible source of food and a convenient trade and communication routes: many important cities grew and developed along the sea coasts, and most civilizations of the past relied on their capability of sea travel and exploration. Industrial plants, too, often were located near the coast, because of the possibility of efficiently delivering raw materials and goods by ships. However, the sea was also perceived as a hostile environment, and the exploitation of marine resources has been limited by the difficulty of operating at seas and the fact that land operations were easier, and in many cases economically more rewarding.

The situation is different nowadays, since technological progress makes the use of sea resources possible and cost effective, also considering that land-based resources are becoming scarcer and more costly to exploit.

Today a significant share of oil and gas is drilled at sea, and not only is such a share increasing, but also the oil industry is moving to deeper and deeper water [5].

Similarly, there is an increasing interest in deep sea mining industries [6], which aim to exploit ores of valuable minerals (sulfide, iron), nodules (manganese), crusts (cobalts) [7].

About 10 billion tons of goods are transported by ships, and possibly 40% of the global population lives less than 100 km from the sea. Sea routes usually are toll free.

Beside fossil fuels, the ocean also provides an increasing amount of renewable energy, in the form of waves, currents, heat, and experts believe this might quickly account for almost 15% of the global electricity demand. Furthermore, offshore wind turbine fields are becoming more and more frequent.

Fisheries still sustain—directly or indirectly—almost 1 billion people worldwide [8] and represent a main source of food and protein in some parts of the world.

Aquaculture is growing exponentially and is projected to match and surpass fishery production in 10 years. By 2030 fish production will reach 200 million tons, a fish out of two will be farmed, and—even if the largest share of aquaculture refers to freshwater [8]—oceans will significantly contribute to feed humanity. In doing so it will also contribute jobs and prosperity.

In agreement with most recent figures [9] the EU blue economy 2019 established sectors (marine living resources; marine non-living resources; marine renewable energy; port activities; ship building and repair; maritime transport; coastal tourism) directly employed 4.45 million people, with an average salary of €24 739, and generated a turnover of €667,2 billions. They obtained a gross profit of €72.9 billion and a gross value added (GVA) of €183.9 billion. The net investment in tangible goods resulted to be €72.9 billion, with a net investment to GVA of 3.3%.

The fastest expanding sector being living resources (increased by about 30% in 10 years), shipbuilding (+40%), emerging and innovative sectors include the marine renewable energy sector (20%, focused on EU hydrogen strategy, and offshore renewable energy strategy goals), bioeconomy, desalination and blue technological innovation.

Ecosystem Services

The emerging need of taking into consideration environmental consequences of socio-economic activities called for new tools and methodologies to assess the environmental impact of human activities and possibly related costs, as well as the development of unifying integrated frameworks.

Ecosystem services assessment and valuation exercises are attempts to take into account the value of nature in policy making. Ecosystem services are benefits that nature contribute to people: they can be actual goods produced by ecosystems and exploited by humans, such as food, raw material and the like, or services, such as air and water purification, climate regulation, mitigation of adverse effects of extreme events, or other activities that results from a healthy ecosystem functioning and are useful to humans. Ecosystem services also include intangible benefits, such as inspiration for culture, religion or recreation and more generally the ‘sense of place’ that has an intrinsic individualistic value [10].

Ecosystem services can have a market, and in this case, it is relatively straightforward to assign a value to a service, even if the market price reflects the balance between offer and demand, rather than the actual intrinsic value of a good. In many cases, however, there is no market and no market value. Water purification, nutrient recycling, carbon sequestration, and wellness related to the beauty of nature are a few examples of extremely valuable services for which there is no market value. In these cases, some experts believe it still makes sense to devise methodologies to assign a potential value to them. Some of these methodologies analyze people choices in their real life (revealed preferences), other are based on surveys to assess the willingness to pay (wtp) for keeping a service running (would you be willing to donate a given amount of money to save whales from extinction?), or—on the contrary, the willingness to accept (wta) a payment as compensation for its loss (would you accept a given amount of money as a compensation for the extinction of the last whale?).

Without entering into the technicalities of valuation exercises, it should be noted that valuing is not pricing, meaning that not always money can be a substitution for nature, but a valuation exercise always is a way to make nature value less invisible and to highlight hidden values often taken for granted.

In 1997 a seminal paper [11] Costanza et al. attempted a fist assessment of the natural capital worldwide. The results highlighted that nature provides valuable services on the order of 33,000 billion US dollars per year. Notably, oceans and seas accounted for 70% (21,000 billion dollars) of that. Coral reefs resulted the most valuable ecosystem type, followed by salt marshes and mangroves.

The paper was followed by many discussions and critiques, had a tremendous impact (30,000 citations as of today) and had the great merit to put ecosystem services on the spot for the following decades.

Following the Costanza et al. paper, other major initiatives attempted to systematically estimate the value of nature, or to assess the capability of the global ecosystem to provide services.

In 2000, the UN secretary promoted the Millenium Ecosystem Assessment [12], to assess the consequences of ecosystem change for human well-being and to define the actions needed to improve the conservation and the sustainable use of those systems. The MA involved more than 1,000 experts worldwide and provided a state-of-the-art scientific appraisal of the condition and trends in the world’s ecosystems and of their services, and the options to restore, conserve or enhance them. The MA concluded that human actions are depleting Earth’s natural capital, but also indicated that it is possible to reverse the degradation of many ecosystem services over the next 50 years.

In 2015 UN launched the Intergovernmental Panel for Biodiversity and Ecosystem (IPBES) assessment, which—similarly to the Intergovernmental Panel for Climate Change IPCC—attempted to provide rigorous and systematic reviews of scientific literature on this important topic. They released their first assessment in 2019, both for the global and 5 macro-regions. One of the results was that biodiversity is decreasing everywhere. Another evidence arising from the study was the lack of quantitative information on the ocean, in respect to land [13].

Environmental costs has been assessed also by using other methodologies and indicators, such as the Ecological Footprint, that translates the input required to build up a good or to supply a service in terms of ‘extension of equivalent area’ [14], or the embedded energy, eMergy, that translates them in solar energy equivalent [15]. In all cases, however, the overexploitation clearly appears and highlights how we are using future generation resources. In 2023, the overshoot day, i.e. the day in which humanity’s demand for ecological resources in a given year exceeds the Earth's production in a year, was the end of July, implying that for 5 out 12 months we were living on future resources. Put in another way, we would need 1.7 planets to sustain our consumption. These indicators can be applied also to value marine systems. However, since they have been developed for terrestrial systems, specific adjustments and adaptations are needed.

Ocean contributions to people do include services that do not have a market nor a direct economic value, and whose importance might be difficult to assess. Incidentally, methodologies such as wtp or wta are in these cases even more delicate, given that the value assigned to the ocean usually depends on where a person lives, and their education.

Just as an example, we can remember that ocean adsorbed about half of the CO₂ released in the atmosphere by anthropogenic activity in the last 2 centuries [16], i.e., without the ocean, the CO₂ atmospheric concentration would be now much larger than 500 ppm, and the climate change much more severe. Ocean also adsorbed a significant amount of heat (the surface ocean is adsorbing about 0.5 watts/m², equivalent to about 10²³ J per decade) so kept the atmosphere cooler than it would be otherwise, and buffer changes during the day night or seasons cycles. Ocean and seas act as giant water reservoirs and fuel the hydrological cycle, providing the crucial supply for rains and rivers all over the planet. They provide a source of multiple inspiration to artists and are perceived as beautiful and emotional (sea-view houses always have an added value) up to the point of promoting positive feelings, useful in health care.

To attempt a quantitative estimate of the value of these services on a global scale is probably meaningless since in some cases they are literally priceless.

More sensible estimates might be provided at the local scale, possibly with the aim to inform on specific local plans. Also in this case, however, to perform an assessment poses a formidable challenge, considering that it requires a quantitative knowledge of the relationships between the state of the ecosystem and its capabilities to provide services, as well as of how these services (which are flows) change in response to changes in ecosystem state. Overall, this assessment requires a fully quantitative understanding of the relationships between ecosystem state, ecosystem functioning and the capability to provide services. In fact, the valuation also depends on the starting situation, since the value of (for instance) a square meter of a given habitat surely depends on how large the habitat is, and whether or not there are other similar habitats in the region. Similarly, the value of a fish is higher if it is one of the last specimens of an endangered species. So it is the ‘marginal value’ that has to be considered and computed. Scientific literature offers examples of these studies also for the marine realm. For instance Canu et al. [50] quantified the role of plankton activity as contributor of carbon sequestration in the Mediterranean Sea by using a combination of state of the art deterministic biogeochemical and economic models, and considering the effects of different level of plankton activity; Zunino et al. [54], (2021) used food web models to assess the loss of ecosystem services related to the impact of ocean acidification on habitat forming species, [18] used surveys to assess the recreative value of seagrass and coralligenous.

Several studies can be found also on lagoons [19,20,21]. But few are the cases in which the quantitative understanding of the system with the functional relationships between pressure, functioning and services are estimated and quantified, thus allowing a proper valuation. In all cases the uncertainty of an assessment increases while propagating among physical, biological and economic dynamics (see Fig. 2.1), also because a holistic valuation exercise always includes a judgment phase that involves arbitrary and personal choices [22] for capturing cultural, ethic and social aspects that cannot be captured by purely deterministic laws.

Fig. 2.1

Direct impacts of environmental threats on physical and chemical properties of the sea have cascading effects on marine organisms, communities, food webs and ecosystems, which in turn can affect biodiversity and marine ecosystem services, with effects on their social and economic values. Uncertainties propagate and usually amplifies along this chain, so that our understanding and capabilities to produce robust assessment of impact on socio-economic components is more uncertain than for biological or physical ones

Integrating Blue Economy and Ecosystem

Our vision and policy should be based on an integrated view in which the economy is a subsystem of the finite and non-growing ecosphere [23]. There are three possible theoretical frameworks for such integration, all considering economy as a subsystem of the ecosphere, but differing in how they consider the boundaries, feedbacks and dependencies between the subsystems.

In the Economic Imperialism the economic subsystem can growth up to encompass the entire ecosphere, and everything is sees as whole macro-economic system in which external costs and benefits are internalized into prices, or ‘shadow prices’, i.e., the price they would have if traded in a competitive market, and the economic expansion is considered acceptable as long as all costs are internalized. While costs should surely be internalized, this approach has important conceptual limitations, since not always good and services having the same economic value can be regarded as equivalent, i.e. natural capital (ocean, forest, rivers, coast) is intrinsically different and not replaceable by antophogenic capital (machines, factories, industries). Moreover, not all processes and transformations (none in reality) are reversible. In principle, a perfect pricing mechanism might take into consideration and possibly compensate for some of these limitations, but in practice it is very difficult to implement them, since (once again) we would need a perfect knowledge of the complete implications of any action, including those on future ecosystem dynamic, and a continuous update of the prices. Furthermore, on a more pragmatic side, internalization has been very slow, partial, and much resisted, since firms have economic advantages to externalize costs.

In the Ecological Reductionism paradigm, the economic subsystem and its growth are considered as bounded by natural laws and constrained by ecosphere limits. Everything is seen as a whole macro-ecosystem and explained in terms of materialist deterministic actions. Also, this vision has important limitations. In fact, if it might be possible to reduce to deterministic laws the main properties of a simple natural system, it is difficult to assume that this is true also for complex systems, and even less for human activity. Granted that natural constraints exist, humans do have the possibility to freely determine their actions among the many possible courses, and are responsible for the implication of the policies they chose.

The above-mentioned paradigms are opposite monistic visions. The third remaining perspective is the Steady state subsystem, in which one treats economic and ecological systems as distinct subcomponents working on different scales and driven by different forcing, but tightly interrelated. Within these Ecological-Socio-Economic systems the ecosphere physically supplies material and energy to drive the economic subsystem, and the throughput has to be continuous to keep the subsystem working. Indeed, the economic system can be seen as a dissipative, far from equilibrium, ordered system. In this context many different steady states can exist, and the goal of sustainable economy is to minimize the throughput, and the entropy produced by the system, by adopting efficient technologies and increasing the recycling of by-products and waste [23, 24].

Economy for a Full World

The fact that human well-being depends upon the existence of a healthy ecosystem has been obvious for centuries, during which life was regulated by rhythms and constraints posed by nature, and humans simply had to accept that their very life depended upon their relationships with the planet. On the other hand, anthropogenic activities had the capability to modify the environment only to a limited extent, and mainly to a local scale, so that it was normal to perceive the environment as having a so large buffer capacity to be virtually infinite. We lived in an ‘empty world’ (see Fig. 2.2). The economic subsystem was physically small in comparison to the ecosphere, and the exchanges of matter and energy needed to sustain economic activities were small relative to the containing system. Renewable resources reproduced faster than our harvesting capabilities, mineral and natural resources were perceived as not scarce and not limiting economic growth, human footprint was limited, and ecosystems had the capability to recover from perturbations. At that time, it made sense to think that there was no conflict between economic growth and nature.

Fig. 2.2

Economy is an open subsystem of the larger ecosphere, which sustains economic activities through exchanges of matter and energy. The ecosphere is finite, close to mass exchanges, not growing and fueled by the negentropy flux related to the dissipation of the continuous solar energy throughput. Humanity moved from an ‘Empty world’ to a ‘Full world’ economy, which now requires enormous fluxes of matter and energy, diverted by their original use. The human footprint is now of planetary relevance

Since the industrial revolution, technological development gave humans the capability to modify the Earth to an extent that basically detached us from the rest of the planet and gave us the illusory perception of owning the planet and having the possibility to dispose of its resources.

Humans forgot to be animals living within ecosystems and bound by natural constraints, and started to impose anthropogenic rhythms to nature [52]. Anthropogenic driven technological transformations modified and accelerated natural cycling—e.g. by mobilizing reduced carbon from fossil fuels as oxidized carbon in atmospheric CO₂-and imposed changes at unprecedented rates. The underpinning shared belief was that, thanks to its ingenuity, mankind could grow and evolve with no limit, and technology could solve any problem [25].

Even if this attitude is still present in a part of the population and political debate, it is now increasingly recognized and widely accepted that some limits exist and have to be considered, since—in spite of any technological improvement—there cannot be an infinite growth on a finite planet, and since in our globalized era environment buffer capacity has been not only reached, but in some case also exceeded at the local, regional, and planetary levels [23, 26].

In the last two centuries the millennia balance with nature was somehow lost and the empty world quickly turned into a full world: the global population grew from 2 to 8 billions, the number of farmed animals grew even more rapidly, the mass of artificial things become larger than the living one and the maintenance of the economy subsystem requires now an enormous throughput of mass and free energy, a metabolic flow that begin with low entropy resources from the ecosphere and ends with the return of polluting high entropy output back to the ecosphere, a massive flow that impact the ecosphere at both ends and need to be considered (internalized) when assessing the net utility of an activity (see Fig. 2.3). This view also reminds us of the thermodynamic limits constraining the ecosphere and its open economy subsystem: while the first law imposes the quantitative balance of matter exchanges between the ecosphere and the economy, the second law prescribed the existence of upper limits to the efficiency of any transformation, the consequent impossibility of infinite growth, and the necessity to rely on solar and related renewable energy as the ultimate source of negentropy required to sustain the ecosphere and the economy [27].

Fig. 2.3

If environmental and external costs are internalized, production and consumption levels stop at the economic limit, before the disutility exceeds the utility, and when there still is an economic growth. The equilibrium point between utility and environmental costs occurs at different production level, depending on the shape of the marginal disutility curve: if environmental costs are highly valued, the curve increases more steeply and at lower production level, and the economic limit equilibrium point and environmental costs decreased below the ecological limit. The opposite happens when environmental costs are valued too little, and production increases at levels in which ecological limits are exceeded. If no environmental costs are considered, production and consumption levels are driven by utility alone, up to reach-or exceed—the futility limits, above which there is no marginal utility left, the growth is largely uneconomic and the impact on the environment extremely high

The view also reminds us that capital and natural capital are not interchangeable, and technological improvements cannot substitute nature in all its processes and mechanisms, and humankind will always rely on natural products and services.

Sustainability

Sustainability pertains to integrated ecological-social-economic systems, and is related to time: it implies comparing rates of human activities against rates of natural cycles, or the entity of the energy/matter throughput needed to sustain the economic subsystem dynamic in respect to the remaining ecosphere.

The concept is often illustrated also with reference to the superposition of its social, economic, and ecological dimensions, to stress the fact that it is not something related to ecology or economy only, but to the combination of the two, with the important expansion over social justice [28]. The concept is qualitatively simple: an activity can be sustained (proceed indefinitely) in time if and only if there is an economic interest in maintaining it (otherwise the owner quits it), it has a limited impact on the environment in term of resource exploitation (otherwise it runs out of resources) and pollution (otherwise is not acceptable), it is socially acceptable (otherwise it gives rise to social tensions that make it infeasible in the long run). It is clear that in all cases these requirements refer to a balance to be made over a long enough time. Indeed, the sustainability debate is deeply rooted in the intergenerational debate: to what extent people today are responsible for the wealth of future generations.

It implies also to give full considerations to the fairness of distribution of resources and services, the efficiency in their use and the capability to maintain the wellbeing for nature and humans [29].

The concept of sustainability has been rediscovered many times. It is possible to trace it back to the 1716 in silviculture treaties by von Carlowitz, then in the Malthus dissertation [30] or the Marsh essay [31] up to the environmentalist movement of the seventies, protesting for smog, acid rain and environmental degradation in Europe and North America. In 1972 the Club of Rome published the seminal ‘Limit to Growth’ [25], which introduced the concept of sustainable global system, and warned the world against the consequence of overexploitation, and in the 1987 the UN world commission on environment and development presented the Brundtland report, which defined sustainable development as ‘the development that meets the need of the present without compromising the ability of future generation to meet their own need’ [32]. In 2000 the UN launched the Millenium Goals and a few years later redefined the concept by listing the UN Sustainable Development Goals. Even Pope Francis felt the issue so relevant to devote his encyclical “Laudato sii” to the importance of preserving biodiversity and ecosystem functions from the unsustainable exploitation of the planet.

Sustainability is today a central concept deeply rooted in any political debate and agenda. What we are still missing, however, are concrete directions for political interventions.

Unfortunately, while everyone agrees on the general principles, the wording of sustainability definition is open to different interpretations by different stakeholder groups, and even the Brundtland report contains no operational indications on how to move from principle to practices. Some theoreticians developed the ‘three pillars’ model, giving equal importance to the three dimensions of sustainability. Others stressed that social and economic SDGs cannot be reached without achieving the nature-related SDGs to begin with. But we still miss a shared idea on how to move forward, and possibly—as the UN Ocean decade declaration reminds us—the science and knowledge underpinning that.

Ocean Under Multiple Threats

The ocean and sea health is currently menaced by a number of co-occurring pressures, causing a cumulative impact that is increasing and bound to growth also in the near future, as a consequence of the expansion of the blue economy.

A non-exhaustive list of current anthropogenic driven environmental threats includes climate change, ocean warming and acidification, marine litter, a countless variety of marine pollution (e.g. oil spills, heavy metals, persistent organic pollution, antibiotics, drugs, and emerging pollutants), extractive activities and deep-sea mining, underwater noise, marine litter and marine plastic, genetic contamination, overfishing. Most of these threats were never assessed before their introduction into the ecosphere, and we became aware of their individual and combined impacts only after the fact. Even now, different countries and legislation have different approaches to pollution, with more or less restrictive and environmentally sensitive approaches. Some of those threats originated globally, others locally. Most of them interact, inducing synergistic and additive impacts, locally and globally.

Climate change has extremely relevant and pervasive impacts, which unfold through direct effect and cascading processes [33]. The warming of the atmosphere causes the warming of surface water, in turn affecting water density and therefore the seasonal alternance of mixing and stratification processes occurring along the water column which are driven by density gradients. The changes in density also affect the dense water formation triggering the thermohaline circulations, with potentially extremely relevant consequences on the global ocean circulation [34] and related space redistribution of dissolved substances, including oxygen [35]. In turn this might alter the onset, phenology and spatial distribution of plankton primary production, giving rise, in combination to differential warming of surface waters, to relevant changes in the properties of the sea regions and therefore in their suitability for marine organism’s life, migration of mobile organism, possible extinction of low mobility organisms no longer fit for new conditions, invasion on new immigrant species, occurrence of new assemblages and emerging food webs. In particular, the foreseen deoxygenation of world oceans is expected to have overwhelming effects on species bioenergetics, on mortality of sessile species and eventually displacement of mobile species and their productivity [36, 37].

The other side of increasing atmospheric CO₂ is the dissolution of CO₂ into surface water, leading to formation of carbonic acid and an increase in ocean acidification, which has been already observed and estimated in about 0.3 pH units per century, i.e. doubling the concentration of acid in the ocean (the pH is a logarithmic measure of acidity concentration). Experts expect that ocean acidification will continue for at least several decades [51] with an extremely relevant impact on ocean life and related services.

Climate changes will appear not only in the monotonic increase of averages values, but also as an intensification of extreme events, with an increase in the frequency, severity and deep penetration of marine heat waves, [38, 39], cold spell, bottom hypoxia, hypercapnia [40], not to mention the impact of sea level rise.

Pollution is another dangerous, ubiquitous and pervasive impact of human activities. The seas continue to receive massive amounts of traditional contaminants, such as metals and permanent organic pollutants, that—being permanent—bioaccumulate in marine organisms, eventually biomagnificate, and move though the whole ocean. But they also are the receptacles of a variety of ‘new’ pollutants, like pharmaceutical compounds, whose impact on marine life is still to be understood, antibiotics that might trigger the selection of resistant microorganisms, and the group of so-called emerging contaminants and of contaminants of emerging concern, about which very little is known as yet. Nutrients, in particular nitrogen and phosphorus from agricultural sources and wastewater treatments, noise pollution from ships and off-shore industry, changes in light and water color as a result of artificial lightning along the coast and electromagnetic waves are other forms of pollution which are increasingly being recognized. Plastic and marine litter are becoming so abundant to make the cover page of main newspapers.

On the exploitation side, many nations overexploited the fish stocks in their coastal area and several fish stocks experienced severe declines [42]. According to FAO the share of collapsed or overfished stock is now around 30% [8], and since most stocks have been depleted in the northern hemisphere and in particular European Seas appear subjected to high fishing pressure [48], fishing vessels are now moving south, undermining stock and local population in other parts of the planet [49]. Climate change projection agrees in indicating a significant decline of total animal biomass in most part of the planet [41], (33; see Fig. 2.4).

Fig. 2.4

Projected changes in total animal biomass (including fishes and invertebrates) based on outputs from 10 sets of projections from the Fisheries and Marine Ecosystems Impact Model Intercomparison Project (FISMIP). The figure illustrated the multi-model mean change (%) in un-fished total marine animal biomass in 2085–2099 relative to 1986–2005 under RCP8.5, respectively. Dotted area represents 8 out of 10 sets of model projections agree in the direction of change (from IPCC report [41])

Having stocks overexploited is an inherent inefficiency, since at the same level of effort, the fisheries extract less catches (i.e., food for humankind) because of the depleted population biomass [43]. However, several growing efforts to include regulations, management plans and rebuilding plans are providing important results with stocks improving conditions and reduced overfishing issues [44]. Analyses also point out that only measure with great strength (like multiannual fisheries bans or moratorium) allows for a relatively fast rebuilding (approximately 10 years), while less severe measures improve fishing mortality, but do not assure rebuilding of the natural capital [45]. Once again, therefore, there is evidence that the speed of human impact is much faster than natural dynamics, and thus the effects of pressure release need quite a long time to promote recovery.

On this aspect it is appropriate to remind that given the nonlinearity in trophic relationship occurring in the marine food webs, tipping points and hysteretic effects can exist, and often the decline in fishery effort taking place after the collapse of a stock not always results in a recovery of the stock, as the cod collapse in north Atlantic exemplified.

The global increment of aquaculture also represents a threat, if pursued in its intensive form, because of the use of related input of fish food, medicine, and export of waste to the sea bottom [46]. Moreover, in many cases the farmed marine animals are not herbivorous-like in terrestrial systems, were farming regards herbivores or at maximum omnivores. Thus, most of the farmed marine species have to be fed with either fish meal, fish-oil or other farmed organisms thus impacting on wild resources indirectly. Although aquaculture is doing enormous efforts to use alternative sources (like insects), increasing efficiency of feed, or farming alternative low trophic level species, a lot has still to be done to decrease the unsustainable aspects of fish farming (see also EU 2020, Mission Starfish-Restore our oceans and waters).

Maritime transport, oil spill, bioinvasions (sometimes related to ships traffic and ballast water), loss of biodiversity, are other sources of alteration to ocean life.

Two additional factors are important to be stressed in this context: a) different stressors can co-occur and combine into cumulative impacts whose dynamics is still little known and very far from being quantitatively understood; b) the ocean has an enormous mass, which dilutes and buffers any impact, but also accumulate them, so that changes takes time, and it is difficult to assess the impact of any action by monitoring over the short term.

Managing the Last Commons

The ocean is one, has no borders, and it belongs to everyone, since everyone benefits from its contribution and everyone has the capability to negatively impact it, together with the responsibility of not doing so. Indeed, marine pollution and environmental degradation are paradigmatic examples of threats that propagate in space and time also across political boundaries, and need to be addressed by transitional coordinated actions based on evidence-rooted common understanding [2].

The ocean—as the atmosphere and the climate system—really is one of last common, i.e. a shared open system that can be impacted by everyone, and—as it is well known—in these cases the combined action of individual users acting independently according to their own self-interest does not result in an optima equilibrium point (since players do not pay costs proportional to their benefit), but rather cause the depletion of the resource [47]. The tragedy of unmanaged commons can be avoided by sustainably-oriented management and regulating access, and examples exist where members of a community co-operate to exploit shared resources prudently, and without collapse [28]. Often, however, these examples are local and context-specific, while an implementation of efficient regulating systems at a larger scale, or planetary one, is much challenging, as can be easily seen also in the discussion on climate change regulation.

A central problem in this case is who has the power to define, enforce, revise, the regulation system, and possibly monitor its efficacy. In fact, often purely top-down regulations fail, because not all players comply with the prescriptions, the control system is not efficient enough, or there is not enough faith in the proposed solutions to ensure compliance. Furthermore, there is the perception of large uncertainties that hamper easy direct decisions, thus avoidance of taking responsibility prevails. Sometimes co-management based on a shared knowledge pool, to which every player is called to contribute, is more effective. Indeed, earlier engagement of all stakeholders and their empowerment is often advocated as an essential ingredient for efficient environmental management. Also, this approach, however, is difficult to implement when dealing with global scale resources, where there is a very large number of very diverse stakeholders, often with different power and authorities and interlaced interests. Standard representative systems might be useful, but often globalization weakens the feedback loop connecting people’s response to a local impact to the global governance system, making the adaptation weak, slow and less effective.

The picture becomes even more complex in transnational areas, where the fragmentation of the governance framework implies that different authorities might have different priorities and agenda, and—paradoxically—in coastal areas, where the number of overlapping managing authorities increases significantly.

It is not surprising, therefore, that the UN stressed the urgency and the importance of knowledge, as a common shared base to define and support adaptation strategies and science-informed policy responses to global environmental crises.

These aspects highlight as the sustainability problem really requires a multi and inter—disciplinary approach, combining physical, natural, and social sciences. The integration of these approaches, long advocated, has been so far slow and difficult, and not only because of differences in languages. Other hampering factors were the existence of unrealistic expectations from other disciplines, problems related to lack of openness of data and information, the attempt of a single discipline to dominate over others, diversity in spatial scales implicitly addressed by the different disciplines, differences in the valuing system [3]. Geopolitical, historical and wealth differences, moreover, further complicate the picture. These aspects also highlight the need of using simplicity, transparency and integrity as major principle orienting and guiding future cooperative efforts [3].

Concluding Remarks

Sustainability is a key concept in today’s political agenda and an essential tool for preserving the wealth of future generations, and their rights to meet their demands. Quantitative approaches to sustainability are much needed and can help in overcoming the remaining lack of clarity in the interpretation of concepts, if any, and in providing directions for effective and sensible operationalization of the sustainability principles. Quantitative tools require an exact definition of the system to be considered, the boundaries and the relationships among its subcomponents, the space and time scale analyzed, the physical laws considered or neglected, the value choices arbitrarily adopted, and all other details. These requirements favor a transparent and rigorous dialogue among disciplines concurring to managing the problems, and also provide an ideal framework for identifying potential alternative management scenarios, to assess the expected impact of their implementation, and to offer support to decision makers.

The application of quantitative sustainability approaches is particularly relevant in the ocean, because its intrinsic global, trans and over-national dimension makes essential to have the capability to reach a shared understanding and a clear consensus on present ocean state and trends, as well as on plausible expected future dynamics under alternative policy scenarios, and eventually pathways towards desiderable states.

Blue economy has the potential to contribute to increasing the quality of life of billions of persons, but it has to be a sustainable economy, i.e., truly constrained by sustainability principles. This is still possible, since the blue economy is developing now, and there still is the time to direct its growth toward true and real prosperity.