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livello medio
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ARGOMENTO: OCEANOGRAFIA
PERIODO: XXI SECOLO
AREA: OCEANO
parole chiave: Ricerca negli oceani
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2.2. The role of humans
Examination of the earliest human interactions with the marine environment in most parts of the world is beset by a major problem. The rise in sea level after the most recent ice-age has obscured or destroyed much of the earliest evidence of human exploitation along the margins of ancient shores [29]. Although in some areas such as the North Sea some evidence of early exploitation has been recovered from submarine deposits it has often been reworked by waves and currents making interpretation difficult [30]. However, there is evidence for an intensive use of marine resources by early modern humans in Pinnacle Point (South Africa) some 164,000 years ago. Gathering shellfish seems to have been part of a response to sea level fluctuations, which forced these people to expand their home ranges and to follow the shifting position of the coast [31]. Almost contemporarily, Neanderthals gathered shellfish in the coastal waters of Torremolinos in Southern Spain [32]. Archeological studies have revealed a general shift in marine resource exploitation from inshore towards offshore areas. Marine fish became increasingly important – as early as 1,500 years ago – on the Californian coast [33]. Similar patterns have been discovered in the Wadden Sea [34]. But for most of human history, the extent of anthropogenic impacts on natural environments was largely restricted to local and regional levels. Within the last 200 years, human actions reached the global level by affecting processes such as global nutrient and water cycles. The traces of human activities are not restricted to populated areas anymore, but can be found everywhere in the ocean [35]. For example, plastic debris is accumulating at the shorelines of even the most remote islands and in the deep sea [36]. Johan Rockström and colleagues [37] claim that human actions have accelerated to such an extent that they might push the Earth beyond its “planetary boundaries”. The term planetary boundary refers to thresholds between alternate states of the global system. Once crossed, the system enters a new state, and irreversible environmental change might be unavoidable. By now, the existence of thresholds has been posited for numerous ecological and social-ecological systems, including the marine realm (see the thresholds database of the Resilience Alliance and the Santa Fee Institute).
The world has entered a geological new era: the Anthropocene. In this era, an important line of research will be the study of the interaction of different human activities and their impacts on specific marine areas in the past. Cross-regional comparisons of magnitude and direction of these changes to marine life in response to multiple human pressures could also be extremely helpful in teasing apart multiple long-term drivers. For example, it was only by the late 1990s that more or less the full range of harvestable fish and invertebrates in all ecological strata of Southeast Asian waters was caught [38]. Near-pristine marine systems could still be found in some parts of the Indonesian Archipelago until the 1960s, a time at which Atlantic waters had already been affected by industrial fishing activities for more than two centuries.
In particular, data from large, isolated, late settled islands or regions such as Madagascar, New Zealand, and Antarctica, where significant human impacts became relevant much later than in the seas bordering the major continental landmasses, can play an important role in distinguishing among natural climatic variability and human drivers (including anthropogenic climate change). Recent work in Australian coral reefs has shown that it is indeed possible to differentiate natural variability from human-induced environmental change [27]. Despite the importance of similar drivers acting at the global level, most ecosystem changes are caused by a set of interactions that are more or less unique to a particular place [11]. To understand how resource and socio-economic endowments, in combination with other factors, have created specific exploitation patterns, bioregional histories of marine environments need to be developed. This will also provide a more comprehensive view of “what once was”, e.g., historical baselines of marine animal populations, enhancing our ability to articulate desirable ecological states and management recommendations [39]. In this line of research, specific attention must be paid to the role of globalisation and changing consumption patterns.
Processes of globalisation have had a significant influence on marine resource exploitation for hundreds of years. The quest for marine resources was an important aspect of European expansion into Asia, Africa and the Americas. Arctic marine mammals, sea turtles in the Caribbean, and cod from Iceland to Newfoundland are just some examples of valuable sought-after species [40]. Similarly, Asian, particularly Chinese food and medicine markets, have driven a search for marine species on a regional to global scale over the past few centuries. For example, the development of sea cucumber fishing and trading by people from Makassar, Indonesia, can be traced from its beginning more than 300 years ago to the industrialization of the fishery in the 20th century and the depletion of sea cucumbers in the 1980s [41]. Economic gain was only one side of the story. Changing preferences for certain products, the exploitation of new areas, and technical innovations all played a role in a widening search for marine resources.
Required research
How has the pattern of marine resource exploitation proceeded in each area settled by humans, and which species were affected? Was the unfolding of events in Africa fundamentally different from histories in Asia, Australia, the Americas, and Europe and recently settled remote islands? To address this will require integration of the earliest archaeological records with historical and modern information sources to determine patterns of marine resource use over the entire period of human settlement of coastal margins. Studying the role of globalisation and changing consumption patterns may improve our understanding of resource use by linking serial depletion on a global scale to local demands. We also need research into changing consumeŕs preferences, especially towards more sustainably harvested marine products. Do such changes occur on a short or long-term scale, are they caused by public advice, by economic forces, or by other cultural factors that are to date poorly understood?
Altered Marine Ecosystems
3.1. Extinctions, species declines, and habitat changes
Extinctions and resource depletions in the marine realm have been evaluated by a number of studies (eg., [41], [42], [43]). We now have a relatively precise overview of globally extinct marine mammals, birds, fish, and molluscs [42]. Many species have become extirpated, or nearly so, across part of their range, such as is the case with several shark and ray species in the Mediterranean Sea [43]. Others have been depleted to such an extent that they cannot fulfil their former role in the ecosystem, as in the case of reduced abundances of some filter feeders [44]. To truly understand the extent of these changes, long-term biodiversity loss should be studied in different regions of the oceans over various periods of time. This includes the reconstruction of decadal, centennial, and millennial dynamics of marine animal populations [45], [46]. A number of studies have provided important knowledge in this respect, for example on changes to shark populations in the West Atlantic [47], or on numbers of large predatory fish in different seas [48]. Most of the historical studies to date have concentrated on exploited higher trophic levels of marine animals, while intermediate and lower trophic levels have largely been ignored [49]. In large part this is because the evidence about large exploited species is more readily available from archaeological and historical sources. But there is also evidence for a sequential exploitation of invertebrate species in the past [41]. How this has shaped the status of ecosystems should be an important research topic in future. Changes in coastal and marine habitats are a related research topic that deserves more attention. Although this line of work has been less prominent that changes in species, important contributions have already been made. For example, Lotze and colleagues reconstructed time lines, causes, and consequences of change in several estuaries and coastal seas worldwide and found similar patterns of habitat destruction, water quality degradation, and the influence of invasive species [44]. Other work has also focused on sub-tidal algae forests in the Adriatic Sea [50], or provided a two-century perspective on changes in a Scottish coastal area [51].
Required research
In the future, a major research avenue may be to link geospatial data and historical maps showing coastal and marine habitats to information about past distribution and abundance of species derived from archaeological, historical, and genetic sources. Such research could help us to understand indirect causes and effects of habitat change and be of value to marine and coastal management. Focussed research on species across levels, including intermediate and lower levels, is required to describe the patterns and magnitudes of their exploitation, preferably from the period of first human settlements to the present day.
3.2. Recoveries of populations, habitats and ecosystems
There are many examples around the world where previously affected species, habitats and ecosystems have or are responding to new management interventions. For example, over the last 40 years of protection populations of New Zealand fur seal (Arctocephalus fosteri) have started to rebound after 600 years of exploitation first by Polynesian settlers and later by European sealers [52]. Interestingly, the same protection regime has made little impact on the recovery of New Zealand sea lions (Phocarctos hookeri). In this species the return of maturing females to their beach of birth has limited the expansion of breeding populations into their historic range [53] Research on ecological recoveries has a very clear link to providing input to decision-makers and managers, because it brings a historical perspective into the present management of marine resources and tells them what has worked so far and what not. Given that the approach to managing marine systems is evolving towards ecosystem-based adaptive management, a long-term, historical perspective to ecosystem function and change is very much needed [54], [55]. An interesting example of such work is a recent reconstruction of social-ecological interactions over the last 700 years in Hawaiian coral reefs. It reports previously undetected recovery periods related to a complex set of changes in underlying social systems resulting in the release of reefs from direct anthropogenic stressors [56].
Required research
Future investigations should continue to assess the adaptive capacity and resilience of degraded ecosystems and depleted stocks to recover from human impacts. There is already work done on how marine resources have recovered from previous exploitation-related declines [45], [57], but we need a stronger focus on which species, ecosystem traits, and management activities might facilitate recoveries.
Perceptions, Governance, and Management of Marine Systems
How people perceive and value marine environments and the resources they provide determines individual and collective preferences, actions and strategies in the marine realm. Historical descriptions of coastal and marine environments are prime examples of documented perceptions of the past. In the absence of other data, they have been successfully used to establish abundance changes of marine species in different time periods [58], [59]. Different perceptions and valuation systems also underlie the institutional structures that govern and manage marine systems. Research on governance structures must be linked with research on perceptions and values to understand what drives and has driven approaches to marine resource exploitation and its management in different periods of time. For analytical clarity, it is important to distinguish between governance and management. Governance describes a social function centered on efforts to steer the actions of humans toward achieving desirable outcomes and avoiding undesirable ones. It covers the fundamental goals, institutional processes and structures which are the basis for planning and decision-making, and sets the stage within which management occurs. Management refers to the process by which human and material resources are used to achieve a defined goal within a known institutional structure [60]. The notion of the sea as a seemingly endless source of resources has long dominated marine governance, or rather the relative absence of institutions governing the sea. However, there are also examples of long-enduring traditional management regimes which have regulated the exploitation of valuable or scarce resources such as pearl oysters, sea cucumbers, or Trochus spp. shells in many coastal areas in the Pacific and parts of Southeast Asia, long before modern fisheries management was invented. For example, the Indonesian regime of “sasi laut” regulated access to marine resources by placing temporal and spatial harvesting restrictions on them. Similarly regulations in European inshore waters such as the Limford sustained fisheries for hundreds of years [61]. While such community-based management is certainly not a panacea, studies around the world have found that traditional community-based governance regimes contain elements that may support sustainable resource use [62], [63].
Required research
How have different local perceptions of marine systems affected their governance and management, and how have these evolved over time? Can we identify elements of these historical, community-based approaches to ocean governance and management that are also relevant to modern marine management?
end part II – to be continued
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