Oceans are crucial to life on earth, whose 70% of the surface is covered by water. As confirmed by the 2013 IPCC report, climate change events such as atmospheric warming, the warming of the oceans, sea level rise, the acidification of the oceans and the increase in the incidence of extreme weather events, are the results of the increase in greenhouse gas emissions. What and how is this happening?
Acidity and coastal erosion
“In 1998, one mass coral bleaching event killed 16% of all the world’s tropical coral reefs”
Corals are marine creatures whose exceptional colors come from the symbiotic algae that they feed on. Sea temperature rise stress the corals who lose their algae and bleach, and without these algae the corals have difficulties to nourish, their growth and reproductive capacity declines, and their vulnerability rises. If the stress occurs for a prolonged period, the corals die. The acidity and temperatures of the oceans’ surface water is increasing, causing water levels to rise, increasing coastal erosion, and affecting fish migration routes.
The oceans have absorbed roughly half of anthropogenic CO2 atmospheric emissions in the past 200 years. The rate of absorption is estimated at 22 million tons per day. Carbon dioxide reacts in the seawater to form carbonic acid (H2CO3), and the concentration of this gas have significantly increased. This is how the high levels of CO2 in the atmosphere cause the acidity of the oceans to increase, altering the pH and threatening the marine flora and fauna. The acidification of the ocean leads to the depletion of crucial minerals necessary to the formation of skeletons and shells, threatening the development of coral, crabs, starfish, sea urchins, plankton and other creatures. Thus, increases in atmospheric CO2 concentration, alters the chemical composition of ocean surface waters causing acidification, with a number of negative implications for marine life (UNEP, 2012). This could have serious consequences for the food web, destabilizing the ecosystems and damaging fisheries, tourism and other sea-related human activities. Coral reefs have been disappearing at an alarming rate over recent decades, principally because of contamination by waste and agricultural residues. In 2008, the report published by the Global Coral Reef Monitoring Network predicted that if current rates of emissions were maintained, many coral reefs would disappear within the next 40 years (GCRMN, 2008). Nineteen percent have already died. In the Caribbean, for example, researchers of the Catlin Seaview Survey reported the dramatic loss of 80% of coral reefs.
Water pollution and biodiversity loss
Industrial agriculture threatens marine biodiversity, which is currently in a critical condition. Biodiversity – the variety of life present in a particular habitat or ecosystem – is fundamental to allow nature to adapt to external pressures, such as climate change, environmental changes and pathogens. As reported by FAO (2006), the principal source of water pollution is the livestock industry: these operations release a deadly mix of chemical substances (fertilisers, antibiotics, phytopharmaceuticals) as well as manure and other animal wastes.
Agriculture is also the principal source of ammonia release into the environment. Livestock operations, especially bovine, generate 44% of the emissions, while another 17% derives from fertilisers. Given that ammonia has an even stronger acidifying effect than nitrogen oxides and sulphur dioxide, these emissions are particularly dangerous for the health of our seas (FAO, 2012). Fertilisers, of which we now apply some 1,550 tons per year to our crops, provide nutrients to plants and boost the fertility of soils. On the other hand, these fuel-derived chemical compounds lead to eutrophication – an excessive supply of nutrients into aquatic ecosystem causing excessive growth of its plant components with the consequent depletion of oxygen – and increase the release of powerful greenhouse gases such as nitrous oxide (UNEP, 2012).
Fertiliser runoff into watercourses and their transport into the oceans stimulate the growth of small plants known collectively as phytoplankton. When this type of algae dies, it is deposits on the sea bottom where it is decomposed by microbes that consume the oxygen dissolved in the water, leading to an increased bacterial activity. The increased depletion of oxygen levels in the seawater forces fish, crustaceans and other organisms to migrate, but also causes the death of clams and other molluscs and bottom-dwellers. Microbes thus become dominant in these oxygen-depleted zones and form vast blooms that produce sulphuric acid, a toxic gas. Thus, the lack of oxygen compromises marine life and leads to the creation of so-called “dead zones”. There are currently some 405 dead zones around the world and they are expanding rapidly, with the largest covering as much as 20,000 square kilometres (SWC, 2011).
An example of the changes in the fauna of aquatic ecosystems lays in the surprising proliferation of jellyfish. Dr. Anthony Richardson wrote that “Mounting evidence suggests that open-ocean ecosystems can flip from being dominated by fish, to being dominated by jellyfish”. Agricultural fertilisers running off into the oceans favour the growth of plankton on which jellyfish feed. This is compounded by the fact that uncontrolled fishing activity driven by increased consumer demand for fish has seriously depleted the stocks of small fish that feed on plankton (e.g. sardines). When these fish disappear, this opens up further opportunities for the proliferation of jellyfish.
However, the industrial operation of livestock is not the only issue. Aqualculture developed after the continuous decline and over-exploitation of marine resources, and as a solution to the higher demand of fish from the population worldwide. Between 1980-2010 in fact, global production of fish from aquafarming, expanded 12 times at an annual rate of 8,8% (FAO, 2012). Fish farms release enormous quantities of toxic residues and organic wastes (faeces) to the environment. According to Slow Food, taken together, the Scottish salmon farms generate an amount of faecal substance equivalent to that of the 600,000 inhabitants of Edinburgh.
Since the 1950s, global fish consumption has tripled and entire families of marine organisms are literally collapsing. Scientists predict that if we continue fishing at the current rate, all existing fish stocks will be depleted by over 90% by 2050 (SWC, 2011). Subject to the dictates of the market, overfishing and unsustainable capture methods are damaging the ecosystem and biodiversity: in fact, most of the fish stocks now on the market are over exploited or literally on the verge of collapse. Industrial fishing is based on various technologies and techniques. A common method is the use of dragnets, which are quantitatively very effective but have heavy impacts on the ecosystem. By dragging the nets across the sea floor, these nets capture indiscriminately everything in its path, including species that are not a target, which are then thrown back into the sea wounded or dead. It has been estimated that these non-targeted animals account up to the 40% of the catch in each net. These nets also cause a sort of desertification of the sea floor, damaging the ecosystem at the passage of the nets, and reducing the life of several marine species below their limit for survival.