Publications > In Dead Water > The Cumulative Impacts

In Dead Water

The Cumulative Impacts

One of the main obstacles to assessing the state of the oceans and in planning for the conservation, protection and sustainable management/use of the marine environment is the slow responses of the seas to pressures. Many processes and changes in the oceans take place below the surface, silently, on large scales and over long time periods, i.e. they are not on the ‘radar screen’ of human perception. It can take more than 100 years for a deep-sea water molecule to come to the surface. The signal from the increased CO2 released by anthropogenic activities in the last 50–100 years has so far penetrated to only around 3,000 meters water depth. An example of the time lag in response is the absorption of CO2 in the oceans, with the signal of increased CO2 concentrations. The oceans have a huge capacity to cope with impacts and change without apparent effect. However, once their resilience threshold has been overstepped, and effects are detected and becoming obvious, it is often too late to reverse the trend. Even if CO2 emissions would stop today, it would take the oceans many decades to respond.

The combined effects of the ‘Big Five’ environmental threats provide a grim outlook to the sustainable future of the World’s oceans, and the billions of people who depend on marine resources. Many marine areas and species may be exposed and impacted simultaneously by all or several stressors, often acting in synergy and thereby amplifying their effects and impacts (Harley and Rogers-Bennett, 2004). Climate change will provide numerous changes in oceans. It will affect physical parameters such as temperature, strength of currents and the chemistry of the oceans, which, in turn, will invariably impact fisheries (MacKenzie et al., 2007). Climate change is increasingly likely to put substantial strain on the productivity of the World’s oceans, along with pollution, over-harvesting and unchecked coastal development. Disease and infestations often follow in the wake of the other stressors.

However, of perhaps even greater concern, is the fact that in the light of the accelerating climate change, the natural resilience of the oceans, such as their capacity to act as natural buffers, is likely to diminish in future. Heavily harvested fish stocks and populations will be even further reduced by impacts on their vulnerable spawning grounds from other activities. As long as deep-water seamounts and the continental shelves remain nearly completely unprotected, their important roles as nursery grounds is threatened by the expansion of fishing and mineral resource exploitation (Thrush and Dayton, 2002;  Pusceddu et al., 2005; Tillin et al., 2006; Hixon et al., 2007). Projections show that the coral reefs of the World are likely to meet, in the worst case, biannual bleaching events within a few decades. Healthy reefs might be able to recover from these impacts, but reefs already stressed and degraded by other factors (e.g. coastal development and pollution, overfishing etc.) will most likely succumb. It is critical that the areas with projected high risk to coral bleaching become priority zones for reductions in coastal pollutions to prevent a collapse of the reefs and the associated loss of their functions.

Similarly, it is also evident that the majority of the Worlds most damaging marine infestations have taken place in areas with large stresses and diminished resilience due to human activities (e.g. in heavily harvested fishing grounds with extensive trawling/dredging). Hence, building resilience and strengthening the natural buffers of marine (eco)systems has to become an essential element and consideration in the conservation, protection and sustainable management/use efforts at all levels, such as in the creation of system of marine protected areas spanning from coastal waters to the high seas.

Of critical concern is the current lack of policies and protected areas covering deeper waters on the continental shelves and the high seas, including seamounts (Davies et al., 2007; Mossop, 2007). On average, around 70% of the waters under national jurisdiction (e.g. within the EEZs of coastal states) are deeper than 200 meters, rising to over 95% in some island states. However, few countries are aware of their deep-waters and the need to explore, protect and manage the important services and resources these areas provide.

Figure 31:Climate change may, inter alia through effects on ocean currents, elevated sea temperatures, coral bleaching, shifts in marine life, ocean acidification, severely exacerbate the combined impacts of accelerating coastal development and pollution, dead zones, invasive species, bottom trawling and over-harvest. These impacts will be the strongest in 10–15% of the World’s oceans, which harbour the most productive fishing grounds today, responsible for more than half of the marine landings globally.

Biodiversity hotspots form the basis of the Worlds fisheries, but have currently no basis in either marine protected areas or in specific management. It is absolutely crucial that the management of these hotspots becomes an international environmental priority with regard to identifying areas where multiple stressors are likely to leave these water as death zones, lost fisheries and lost recreational and tourist income regions. While there are projections of collapse in the World’s fisheries alone as a result of over-harvest, it is far more likely that such collapse may arise even earlier as a result of the rapid growth of multiple stressors, including climate change, acting in combination. Unless these interlinked and synergistic processes are seen and addressed together, the environmental and socio-economic impacts, particularly for impoverished coastal populations, may become severe. Building resilience by giving climate impact hot-spots priority with regard to reducing other stressors should become focus for future environmental programmes.

The impacts of climate change on the marine environment are growing rapidly, and are likely to become much severe in coming decades. The lack of marine information and easy observation by man as a land-living organism has permitted these and other pressures to progress much farther than anything we have yet seen or would have permitted without intervention on land, in spite of the fact that the oceans are crucial for life on Earth and represent a significant share of global economies and basic food supply.

Unless other pressures are reduced in some of the primary fishing grounds, including bottom trawling and pollution, the impacts may become catastrophic, resulting in wide-spread death or strongly depleted fishing grounds, with severe impacts on countries, coastal economies, livelihoods and food supply. There are currently no international or widespread implemented national policies in place to ensure that such disaster is prevented. The urgency and relation to the continental shelves is critical, given the short time frame, severity and catastrophic nature of the already emerging impacts.