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Marine life |
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Human activities affect marine life and marine habitats through overfishing, habitat loss, the introduction of invasive species, ocean pollution, ocean acidification and ocean warming. These impact marine ecosystems and food webs and may result in consequences as yet unrecognised for the biodiversity and continuation of marine life forms. [3]
The ocean can be described as the world's largest ecosystem and it is home for many species of marine life. Different activities carried out and caused by human beings such as global warming, ocean acidification, and pollution affect marine life and its habitats. For the past 50 years, more than 90 percent of global warming resulting from human activity has been absorbed into the ocean. This results in the rise of ocean temperatures and ocean acidification which is harmful to many fish species and causes damage to habitats such as coral. [4] With coral producing materials such as carbonate rock and calcareous sediment, this creates a unique and valuable ecosystem not only providing food/homes for marine creatures but also having many benefits for humans too. Ocean acidification caused by rising levels of carbon dioxide leads to coral bleaching where the rates of calcification is lowered affecting coral growth. [5] Additionally, another issue caused by humans which impacts marine life is marine plastic pollution, which poses a threat to marine life. [6] According to the IPCC (2019), since 1950 "many marine species across various groups have undergone shifts in geographical range and seasonal activities in response to ocean warming, sea ice change and biogeochemical changes, such as oxygen loss, to their habitats." [7]
It has been estimated only 13% of the ocean area remains as wilderness, mostly in open ocean areas rather than along the coast. [8]
Overfishing is occurring in one third of world fish stocks, according to a 2018 report by the Food and Agriculture Organization of the United Nations. [9] In addition, industry observers believe illegal, unreported and unregulated fishing occurs in most fisheries, and accounts for up to 30% of total catches in some important fisheries. [10] In a phenomenon called fishing down the foodweb, the mean trophic level of world fisheries has declined because of overfishing high trophic level fish. [11]
"It is almost as though we use our military to fight the animals in the ocean. We are gradually winning this war to exterminate them."
– Daniel Pauly, pioneer on human impacts on global fisheries, [12]
Coastal ecosystems are being particularly damaged by humans. [13] Significant habitat loss is occurring particularly in seagrass meadows, mangrove forests and coral reefs, all of which are in global decline due to human disturbances.
Coral reefs are among the more productive and diverse ecosystems on the planet, but one-fifth of them have been lost in recent years due to anthropogenic disturbances. [14] [15] Coral reefs are microbially driven ecosystems that rely on marine microorganisms to retain and recycle nutrients in order to thrive in oligotrophic waters. However, these same microorganisms can also trigger feedback loops that intensify declines in coral reefs, with cascading effects across biogeochemical cycles and marine food webs. A better understanding is needed of the complex microbial interactions within coral reefs if reef conservation has a chance of success in the future. [16]
Seagrass meadows have lost 30,000 km2 (12,000 sq mi) during recent decades. Seagrass ecosystem services, currently worth about $US1.9 trillion per year, include nutrient cycling, the provision of food and habitats for many marine animals, including the endangered dugongs, manatee and green turtles, and major facilitations for coral reef fish. [13]
One-fifth of the world's mangrove forests have also been lost since 1980. [17] The most pressing threat to kelp forests may be the overfishing of coastal ecosystems, which by removing higher trophic levels facilitates their shift to depauperate urchin barrens. [18]
An invasive species is a species not native to a particular location which can spread to a degree that causes damage to the environment, human economy or human health. [19] In 2008, Molnar et al. documented the pathways of hundreds of marine invasive species and found shipping was the dominant mechanism for the transfer of invasive species in the ocean. The two main maritime mechanisms of transporting marine organisms to other ocean environments are via hull fouling and the transfer of ballast water. [20]
Ballast water taken up at sea and released in port is a major source of unwanted exotic marine life. The invasive freshwater zebra mussels, native to the Black, Caspian, and Azov seas, were probably transported to the Great Lakes via ballast water from a transoceanic vessel. [21] Meinesz believes that one of the worst cases of a single invasive species causing harm to an ecosystem can be attributed to a seemingly harmless jellyfish. Mnemiopsis leidyi , a species of comb jellyfish that spread so it now inhabits estuaries in many parts of the world, was first introduced in 1982, and thought to have been transported to the Black Sea in a ship's ballast water. The population of the jellyfish grew exponentially and, by 1988, it was wreaking havoc upon the local fishing industry. "The anchovy catch fell from 204,000 tons in 1984 to 200 tons in 1993; sprat from 24,600 tons in 1984 to 12,000 tons in 1993; horse mackerel from 4,000 tons in 1984 to zero in 1993." [22] Now that the jellyfish have exhausted the zooplankton, including fish larvae, their numbers have fallen dramatically, yet they continue to maintain a stranglehold on the ecosystem.
Invasive species can take over once occupied areas, facilitate the spread of new diseases, introduce new genetic material, alter underwater seascapes, and jeopardize the ability of native species to obtain food. Invasive species are responsible for about $138 billion annually in lost revenue and management costs in the US alone. [23]
Marine pollution occurs when substances used or spread by humans, such as industrial, agricultural and residential waste, particles, noise, excess carbon dioxide or invasive organisms enter the ocean and cause harmful effects there. The majority of this waste (80%) comes from land-based activity, although marine transportation significantly contributes as well. [24] It is a combination of chemicals and trash, most of which comes from land sources and is washed or blown into the ocean. This pollution results in damage to the environment, to the health of all organisms, and to economic structures worldwide. [25] Since most inputs come from land, either via the rivers, sewage or the atmosphere, it means that continental shelves are more vulnerable to pollution. Air pollution is also a contributing factor by carrying off iron, carbonic acid, nitrogen, silicon, sulfur, pesticides or dust particles into the ocean. [26] The pollution often comes from nonpoint sources such as agricultural runoff, wind-blown debris, and dust. These nonpoint sources are largely due to runoff that enters the ocean through rivers, but wind-blown debris and dust can also play a role, as these pollutants can settle into waterways and oceans. [27] Pathways of pollution include direct discharge, land runoff, ship pollution, bilge pollution, atmospheric pollution and, potentially, deep sea mining.
The types of marine pollution can be grouped as pollution from marine debris, plastic pollution, including microplastics, ocean acidification, nutrient pollution, toxins and underwater noise. Plastic pollution in the ocean is a type of marine pollution by plastics, ranging in size from large original material such as bottles and bags, down to microplastics formed from the fragmentation of plastic material. Marine debris is mainly discarded human rubbish which floats on, or is suspended in the ocean. Plastic pollution is harmful to marine life.
Another concern is the runoff of nutrients (nitrogen and phosphorus) from intensive agriculture, and the disposal of untreated or partially treated sewage to rivers and subsequently oceans. These nitrogen and phosphorus nutrients (which are also contained in fertilizers) stimulate phytoplankton and macroalgal growth, which can lead to harmful algal blooms (eutrophication) which can be harmful to humans as well as marine creatures. Excessive algal growth can also smother sensitive coral reefs and lead to loss of biodiversity and coral health. A second major concern is that the degradation of algal blooms can lead to consumption of oxygen in coastal waters, a situation that may worsen with climate change as warming reduces vertical mixing of the water column. [28]Nutrient pollution is a primary cause of eutrophication of surface waters, in which excess nutrients, usually nitrates or phosphates, stimulate algae growth. This algae then dies, sinks, and is decomposed by bacteria in the water. This decomposition process consumes oxygen, depleting the supply for other marine life and creating what is referred to as a "dead zone." Dead zones are hypoxic, meaning the water has very low levels of dissolved oxygen. This kills off marine life or forces it to leave the area, removing life from the area and giving it the name dead zone. Hypoxic zones or dead zones can occur naturally, but nutrient pollution from human activity has turned this natural process into an environmental problem. [29]
There are five main sources of nutrient pollution. The most common source of nutrient runoff is municipal sewage. This sewage can reach waterways through storm water, leaks, or direct dumping of human sewage into bodies of water. The next biggest sources come from agricultural practices. Chemical fertilizers used in farming can seep into ground water or be washed away in rainwater, entering water ways and introducing excess nitrogen and phosphorus to these environments. Livestock waste can also enter waterways and introduce excess nutrients. Nutrient pollution from animal manure is most intense from industrial animal agriculture operations, in which hundreds or thousands of animals are raised in one concentrated area. Stormwater drainage is another source of nutrient pollution. Nutrients and fertilizers from residential properties and impervious surfaces can be picked up in stormwater, which then runs into nearby rivers and streams that eventually lead to the ocean. The fifth main source of nutrient runoff is aquaculture, in which aquatic organisms are cultivated under controlled conditions. The excrement, excess food, and other organic wastes created by these operations introduces excess nutrients into the surrounding water. [30]
Toxic chemicals can adhere to tiny particles which are then taken up by plankton and benthic animals, most of which are either deposit feeders or filter feeders. In this way, toxins are concentrated upward within ocean food chains. Many particles combine chemically in a manner which depletes oxygen, causing estuaries to become anoxic. Pesticides and toxic metals are similarly incorporated into marine food webs, harming the biological health of marine life. Many animal feeds have a high fish meal or fish hydrolysate content. In this way, marine toxins are transferred back to farmed land animals, and then to humans.
Phytoplankton concentrations have increased over the last century in coastal waters, and more recently have declined in the open ocean. Increases in nutrient runoff from land may explain the rise in coastal phytoplankton, while warming surface temperatures in the open ocean may have strengthened stratification in the water column, reducing the flow of nutrients from the deep that open ocean phytoplankton find useful. [31]
Over 300 million tons of plastic are produced every year, half of which are used in single-use products like cups, bags, and packaging. At least 14 million [32] tons of plastic enter the oceans every year. It is impossible to know for sure, but it is estimated that about 150 million metric tons of plastic exists in our oceans. Plastic pollution makes up 80% of all marine debris from surface waters to deep-sea sediments. Because plastics are light, much of this pollution is seen in and around the ocean surface, but plastic trash and particles are now found in most marine and terrestrial habitats, including the deep sea, Great Lakes, coral reefs, beaches, rivers, and estuaries. The most eye-catching evidence of the ocean plastic problem are the garbage patches that accumulate in gyre regions. A gyre is a circular ocean current formed by the Earth's wind patterns and the forces created by the rotation of the planet. [33] There are five main ocean gyres: the North and South Pacific Subtropical Gyres, the North and South Atlantic Subtropical Gyres, and the Indian Ocean Subtropical Gyre. There are significant garbage patches in each of these. [34]
Larger plastic waste can be ingested by marine species, filling their stomachs and leading them to believe they are full when in fact they have taken in nothing of nutritional value. This can bring seabirds, whales, fish, and turtles to die of starvation with plastic-filled stomachs. Marine species can also be suffocated or entangled in plastic garbage. [35]
The biggest threat of ocean plastic pollution comes from microplastics. These are small fragments of plastic debris, some of which were produced to be this small such as microbeads. Other microplastics come from the weathering of larger plastic waste. Once larger pieces of plastic waste enter the ocean, or any waterway, the sunlight exposure, temperature, humidity, waves, and wind begin to break the plastic down into pieces smaller than five millimeters long. Plastics can also be broken down by smaller organisms who will eat plastic debris, breaking it down into small pieces, and either excrete these microplastics or spit them out. In lab tests, it was found that amphipods of the species Orchestia gammarellus could quickly devour pieces of plastic bags, shredding a single bag into 1.75 million microscopic fragments. [36] Although the plastic is broken down, it is still an artificial material that does not biodegrade. It is estimated that approximately 90% of the plastics in the pelagic marine environment are microplastics. [33] These microplastics are frequently consumed by marine organisms at the base of the food chain, like plankton and fish larvae, which leads to a concentration of ingested plastic up the food chain. Plastics are produced with toxic chemicals which then enter the marine food chain, including the fish that some humans eat. [37]
There is a natural soundscape to the ocean that organisms have evolved around for tens of thousands of years. However, human activity has disrupted this soundscape, largely drowning out sounds organisms depend on for mating, warding off predators, and travel. Ship and boat propellers and engines, industrial fishing, coastal construction, oil drilling, seismic surveys, warfare, sea-bed mining and sonar-based navigation have all introduced noise pollution to ocean environments. Shipping alone has contributed an estimated 32-fold increase of low-frequency noise along major shipping routes in the past 50 years, driving marine animals away from vital breeding and feeding grounds. [41] Sound is the sensory cue that travels the farthest through the ocean, and anthropogenic noise pollution disrupts organisms' ability to utilize sound. This creates stress for the organisms that can affect their overall health, disrupting their behavior, physiology, and reproduction, and even causing mortality. [42] Sound blasts from seismic surveys can damage the ears of marine animals and cause serious injury. Noise pollution is especially damaging for marine mammals that rely on echolocation, such as whales and dolphins. These animals use echolocation to communicate, navigate, feed, and find mates, but excess sound interferes with their ability to use echolocation and, therefore, perform these vital tasks. [43]
The prospect of deep sea mining has led to concerns from scientists and environmental groups over the impacts on fragile deep sea ecosystems and wider impacts on the ocean's biological pump. [44] [45]
Rapid change to ocean environments allows disease to flourish. Disease-causing microbes can change and adapt to new ocean conditions much more quickly than other marine life, giving them an advantage in ocean ecosystems. This group of organisms includes viruses, bacteria, fungi, and protozoans. While these pathogenic organisms can quickly adapt, other marine life is weakened by rapid changes to their environment. In addition, microbes are becoming more abundant due to aquaculture, the farming of aquatic life, and human waste polluting the ocean. These practices introduce new pathogens and excess nutrients into the ocean, further encouraging the survival of microbes. [46]
Some of these microbes have wide host ranges and are referred to as multi-host pathogens. This means that the pathogen can infect, multiply, and be transmitted from different, unrelated species. Multi-host pathogens are especially dangerous because they can infect many organisms, but may not be deadly to all them. This means the microbes can exist in species that are more resistant and use these organisms as vessels for continuously infecting a susceptible species. In this case, the pathogen can completely wipe out the susceptible species while maintaining a supply of host organisms. [46]
In marine environments, microbial primary production contributes substantially to CO2 sequestration. Marine microorganisms also recycle nutrients for use in the marine food web and in the process release CO2 to the atmosphere. Microbial biomass and other organic matter (remnants of plants and animals) are converted to fossil fuels over millions of years. By contrast, burning of fossil fuels liberates greenhouse gases in a small fraction of that time. As a result, the carbon cycle is out of balance, and atmospheric CO2 levels will continue to rise as long as fossil fuels continue to be burnt. [47]
Most heat energy from global warming goes into the ocean, and not into the atmosphere or warming up the land. [49] [50] Scientists realized over 30 years ago the ocean was a key fingerprint of human impact on climate change and "the best opportunity for major improvement in our understanding of climate sensitivity is probably monitoring of internal ocean temperature". [51]
Marine organisms are moving to cooler parts of the ocean as global warming proceeds. For example, a group of 105 marine fish and invertebrate species were monitored along the US Northeast coast and in the eastern Bering Sea. During the period from 1982 to 2015, the average center of biomass for the group shifted northward about 10 miles as well moving about 20 feet deeper. [52] [53]
There is evidence increasing ocean temperatures are taking a toll on marine ecosystem. For example, a study on phytoplankton changes in the Indian Ocean indicates a decline of up to 20% in marine phytoplankton during the past six decades. [55] During summer, the western Indian Ocean is home to one of the largest concentrations of marine phytoplankton blooms in the world. Increased warming in the Indian Ocean enhances ocean stratification, which prevents nutrient mixing in the euphotic zone where ample light is available for photosynthesis. Thus, primary production is constrained and the region's entire food web is disrupted. If rapid warming continues, the Indian Ocean could transform into an ecological desert and cease being productive. [55]
The Antarctic oscillation (also called the Southern Annular Mode) is a belt of westerly winds or low pressure surrounding Antarctica which moves north or south according to which phase it is in. [58] In its positive phase, the westerly wind belt that drives the Antarctic Circumpolar Current intensifies and contracts towards Antarctica, [59] while its negative phase the belt moves towards the Equator. Winds associated with the Antarctic oscillation cause oceanic upwelling of warm circumpolar deep water along the Antarctic continental shelf. [60] [61] This has been linked to ice shelf basal melt, [62] representing a possible wind-driven mechanism that could destabilize large portions of the Antarctic Ice Sheet. [63] The Antarctic oscillation is currently in the most extreme positive phase that has occurred for over a thousand years. Recently this positive phase has been further intensifying, and this has been attributed to increasing greenhouse gas levels and later stratospheric ozone depletion. [64] [65] These large-scale alterations in the physical environment are "driving change through all levels of Antarctic marine food webs". [56] [57] Ocean warming is also changing the distribution of Antarctic krill. [56] [57] Antarctic krill is the keystone species of the Antarctic ecosystem beyond the coastal shelf, and is an important food source for marine mammals and birds. [66]
The IPCC (2019) says marine organisms are being affected globally by ocean warming with direct impacts on human communities, fisheries, and food production. [67] It is likely there will be a 15% decrease in the number of marine animals and a decrease of 21% to 24% in fisheries catches by the end of the 21st century because of climate change. [68]
A 2020 study reports that by 2050 global warming could be spreading in the deep ocean seven times faster than it is now, even if emissions of greenhouse gases are cut. Warming in mesopelagic and deeper layers could have major consequences for the deep ocean food web, since ocean species will need to move to stay at survival temperatures. [69] [70]
Coastal ecosystems are facing further changes because of rising sea levels. Some ecosystems can move inland with the high-water mark, but others are prevented from migrating due to natural or artificial barriers. This coastal narrowing, called coastal squeeze if human-made barriers are involved, can result in the loss of habitats such as mudflats and marshes. [72] [73] Mangroves and tidal marshes adjust to rising sea levels by building vertically using accumulated sediment and organic matter. If sea level rise is too rapid, they will not be able to keep up and will instead be submerged. [74]
Coral, important for bird and fish life, also needs to grow vertically to remain close to the sea surface in order to get enough energy from sunlight. So far it has been able to keep up, but might not be able to do so in the future. [77] These ecosystems protect against storm surges, waves and tsunamis. Losing them makes the effects of sea level rise worse. [78] [79] Human activities, such as dam building, can prevent natural adaptation processes by restricting sediment supplies to wetlands, resulting in the loss of tidal marshes. [80] When seawater moves inland, the coastal flooding can cause problems with existing terrestrial ecosystems, such as contaminating their soils. [81] The Bramble Cay melomys is the first known land mammal to go extinct as a result of sea level rise. [82] [83]
Ocean salinity is a measure of how much dissolved salt is in the ocean. The salts come from erosion and transport of dissolved salts from the land. The surface salinity of the ocean is a key variable in the climate system when studying the global water cycle, ocean–atmosphere exchanges and ocean circulation, all vital components transporting heat, momentum, carbon and nutrients around the world. [84] Cold water is more dense than warm water and salty water is more dense than freshwater. This means the density of ocean water changes as its temperature and salinity changes. These changes in density are the main source of the power that drives the ocean circulation. [84]
Surface ocean salinity measurements taken since the 1950s indicate an intensification of the global water cycle with high saline areas becoming more saline and low saline areas becoming more less saline. [85] [86]
Ocean acidification is the increasing acidification of the oceans, caused mainly by the uptake of carbon dioxide from the atmosphere. [88] The rise in atmospheric carbon dioxide due to the burning of fossil fuels leads to more carbon dioxide dissolving in the ocean. When carbon dioxide dissolves in water it forms hydrogen and carbonate ions. This in turn increases the acidity of the ocean and makes survival increasingly harder for microorganisms, shellfish and other marine organisms that depend on calcium carbonate to form their shells. [89]
Increasing acidity also has potential for other harm to marine organisms, such as depressing metabolic rates and immune responses in some organisms, and causing coral bleaching. [90] Ocean acidification has increased 26% since the beginning of the industrial era. [91] It has been compared to anthropogenic climate change and called the "evil twin of global warming" [92] and "the other CO2 problem". [93]
Ocean deoxygenation is an additional stressor on marine life. Ocean deoxygenation is the expansion of oxygen minimum zones in the oceans as a consequence of burning fossil fuels. The change has been fairly rapid and poses a threat to fish and other types of marine life, as well as to people who depend on marine life for nutrition or livelihood. [94] [95] [96] [97] Ocean deoxygenation poses implications for ocean productivity, nutrient cycling, carbon cycling, and marine habitats. [98] [99]
Ocean warming exacerbates ocean deoxygenation and further stresses marine organisms, limiting nutrient availability by increasing ocean stratification through density and solubility effects while at the same time increasing metabolic demand. [100] [101] According to the IPCC 2019 Special Report on the Ocean and Cryosphere in a Changing Climate, the viability of species is being disrupted throughout the ocean food web due to changes in ocean chemistry. As the ocean warms, mixing between water layers decreases, resulting in less oxygen and nutrients being available for marine life. [102]
Until recently, ice sheets [104] were viewed as inert components of the carbon cycle and largely disregarded in global models. Research in the past decade has transformed this view, demonstrating the existence of uniquely adapted microbial communities, high rates of biogeochemical/physical weathering in ice sheets and storage and cycling of organic carbon in excess of 100 billion tonnes, as well as nutrients. [105]
The diagram on the right shows some human impacts on the marine nitrogen cycle. Bioavailable nitrogen (Nb) is introduced into marine ecosystems by runoff or atmospheric deposition, causing eutrophication, the formation of dead zones and the expansion of the oxygen minimum zones (OMZs). The release of nitrogen oxides (N2O, NO) from anthropogenic activities and oxygen-depleted zones causes stratospheric ozone depletion leading to higher UVB exposition, which produces the damage of marine life, acid rain and ocean warming. Ocean warming causes water stratification, deoxygenation, and the formation of dead zones. Dead zones and OMZs are hotspots for anammox and denitrification, causing nitrogen loss (N2 and N2O). Elevated atmospheric carbon dioxide acidifies seawater, decreasing pH-dependent N-cycling processes such as nitrification, and enhancing N2 fixation. [106]
Aragonite is a form of calcium carbonate many marine animals use to build carbonate skeletons and shells. The lower the aragonite saturation level, the more difficult it is for the organisms to build and maintain their skeletons and shells. The map below shows changes in the aragonite saturation level of ocean surface waters between 1880 and 2012. [107]
To pick one example, pteropods are a group of widely distributed swimming sea snails. For pteropods to create shells they require aragonite which is produced through carbonate ions and dissolved calcium. Pteropods are severely affected because increasing acidification levels have steadily decreased the amount of water supersaturated with carbonate which is needed for the aragonite creation. [108]
When the shell of a pteropod was immersed in water with a pH level the ocean is projected to reach by the year 2100, the shell almost completely dissolved within six weeks. [109] Likewise corals, [110] coralline algae, [111] coccolithophores, [112] foraminifera, [113] as well as shellfish generally, [114] all experience reduced calcification or enhanced dissolution as an effect of ocean acidification.
Pteropods and brittle stars together form the base of the Arctic food webs and both are seriously damaged by acidification. Pteropods shells dissolve with increasing acidification and brittle stars lose muscle mass when re-growing appendages. [115] Additionally the brittle star's eggs die within a few days when exposed to expected conditions resulting from Arctic acidification. [116] Acidification threatens to destroy Arctic food webs from the base up. Arctic waters are changing rapidly and are advanced in the process of becoming undersaturated with aragonite. [108] Arctic food webs are considered simple, meaning there are few steps in the food chain from small organisms to larger predators. For example, pteropods are "a key prey item of a number of higher predators – larger plankton, fish, seabirds, whales". [117]
The rise in agriculture of the past 400 years has increased the exposure rocks and soils, which has resulted in increased rates of silicate weathering. In turn, the leaching of amorphous silica stocks from soils has also increased, delivering higher concentrations of dissolved silica in rivers. [118] Conversely, increased damming has led to a reduction in silica supply to the ocean due to uptake by freshwater diatoms behind dams. The dominance of non-siliceous phytoplankton due to anthropogenic nitrogen and phosphorus loading and enhanced silica dissolution in warmer waters has the potential to limit silicon ocean sediment export in the future. [118]
In 2019 a group of scientists suggested acidification is reducing diatom silica production in the Southern Ocean. [119] [120]
As the technical and political challenges of land-based carbon dioxide removal approaches become more apparent, the oceans may be the new "blue" frontier for carbon drawdown strategies in climate governance. [128] Marine environments are the blue frontier of a strategy for novel carbon sinks in post-Paris climate governance, from nature-based ecosystem management to industrial-scale technological interventions in the Earth system. Marine carbon dioxide removal approaches are diverse [129] [130] — although several resemble key terrestrial carbon dioxide removal proposals. [128] Ocean alkalinisation (adding silicate mineral such as olivine to coastal seawater, to increase CO2 uptake through chemical reactions) is enhanced weathering, blue carbon (enhancing natural biological CO2 drawdown from coastal vegetation) is marine reforestation, and cultivation of marine biomass (i.e., seaweed) for coupling with consequent carbon capture and storage is the marine variant of bioenergy and carbon capture and storage. Wetlands, coasts, and the open ocean are being conceived of and developed as managed carbon removal-and-storage sites, with practices expanded from the use of soils and forests. [128]
If more than one stressor is present the effects can be amplified. [133] [134] For example, the combination of ocean acidification and an elevation of ocean temperature can have a compounded effect on marine life far exceeding the individual harmful impact of either. [135] [136] [137]
While the full implications of elevated CO2 on marine ecosystems are still being documented, there is a substantial body of research showing that a combination of ocean acidification and elevated ocean temperature, driven mainly by CO2 and other greenhouse gas emissions, have a compounded effect on marine life and the ocean environment. This effect far exceeds the individual harmful impact of either. [135] [138] [137] In addition, ocean warming exacerbates ocean deoxygenation, which is an additional stressor on marine organisms, by increasing ocean stratification, through density and solubility effects, thus limiting nutrients, [139] [140] while at the same time increasing metabolic demand.
The direction and magnitude of the effects of ocean acidification, warming and deoxygenation on the ocean has been quantified by meta-analyses, [136] [142] [143] and has been further tested by mesocosm studies. The mesocosm studies simulated the interaction of these stressors and found a catastrophic effect on the marine food web, namely, that the increases in consumption from thermal stress more than negates any primary producer to herbivore increase from more available carbon dioxide. [144] [145]
Changes in marine ecosystem dynamics are influenced by socioeconomic activities (for example, fishing, pollution) and human-induced biophysical change (for example, temperature, ocean acidification) and can interact and severely impact marine ecosystem dynamics and the ecosystem services they generate to society. Understanding these direct—or proximate—interactions is an important step towards sustainable use of marine ecosystems. However, proximate interactions are embedded in a much broader socioeconomic context where, for example, economy through trade and finance, human migration and technological advances, operate and interact at a global scale, influencing proximate relationships. [146]
In 2024 a study [147] was released, dedicated to the impact of fishing and non fishing ships on the coastal waters of the ocean when 75% of the industrial activity occur. According to the study: "A third of fish stocks are operated beyond biologically sustainable levels and an estimated 30–50% of critical marine habitats have been lost owing to human industrialization". It mentions that except traditional impacts like fishing, maritime trade and oil extraction there are new emerging like mining, aquaculture and offshore wind turbines. It used satellite data to monitor the vessels. It found that 72% - 76% of fishing ships and 21%-30% of energy and transport ships are "missing from public tracking systems". When the data was added to previously existing information about ships that were publicly tracked, this led to several discoveries including:
Characteristic | Assumptions before the study | After the study when satellite data was added |
---|---|---|
Dispersion of fishing between continents | Europe and Asia have roughly equal fishing activity | Asia accounts for 70% of global fishing. |
Dispersion of fishing activity in the Mediterranean sea | European countries has 10 times more fishing hours than African countries | Europe and Africa has approximately equal fishing activity. |
Illegal fishing near the Korean peninsula | Most activity occurs to the east of the Korean peninsula | Most activity occurs to the west of the Korean peninsula |
Fishing ships in marine protected areas | Significant presence of fishing vessels in marine protected areas, for example, 5 per week in the Galápagos Marine Reserve and 20 per week in the Great Barrier Reef Marine Park |
The study discovered a significant increase in offshore wind turbins which had overpassed oil platforms by number already in 2021. Fishing increased only a little in the latest years and may begin to decline because fisheries are exhausted. It concluded that "transport and energy vessel traffic may continue to expand, following trends in global trade and the rapid development of renewable energy infrastructure. In this scenario, changes to marine ecosystems brought by infrastructure and vessel traffic may rival fishing in impact".
"Application of the physical and biological sciences has made today arguably the best of times: we live longer and healthier lives, food production has doubled in the past 35 years and energy subsidies have substituted for human labour, washing away hierarchies of servitude. But the unintended consequences of these well-intentioned actions — climate change, biodiversity loss, inadequate water supplies, and much else — could well make tomorrow the worst of times."
– Robert May 2006 [148]
Shifting baselines arise in research on marine ecosystems because changes must be measured against some previous reference point (baseline), which in turn may represent significant changes from an even earlier state of the ecosystem. [149] For example, radically depleted fisheries have been evaluated by researchers who used the state of the fishery at the start of their careers as the baseline, rather than the fishery in its unexploited or untouched state. Areas that swarmed with a particular species hundreds of years ago may have experienced long-term decline, but it is the level a few decades previously that is used as the reference point for current populations. In this way large declines in ecosystems or species over long periods of time were, and are, masked. There is a loss of perception of change that occurs when each generation redefines what is natural or untouched. [149]
A coast – also called the coastline, shoreline, or seashore – is the land next to the sea or the line that forms the boundary between the land and the ocean or a lake. Coasts are influenced by the topography of the surrounding landscape, as well as by water induced erosion, such as waves. The geological composition of rock and soil dictates the type of shore that is created. Earth contains roughly 620,000 km (390,000 mi) of coastline.
Southeast Asian coral reefs have the highest levels of biodiversity for the world's marine ecosystems. They serve many functions, such as forming the livelihood for subsistence fishermen and even function as jewelry and construction materials. Corals inhabit coastal waters off of every continent except Antarctica, with an abundance of reefs residing along Southeast Asian coastline in several countries including Indonesia, the Philippines, and Thailand. Coral reefs are developed by the carbonate-based skeletons of a variety of animals and algae. Slowly and over time, the reefs build up to the surface in oceans. Coral reefs are found in shallow, warm salt water. The sunlight filters through clear water and allows microscopic organisms to live and reproduce. Coral reefs are actually composed of tiny, fragile animals known as coral polyps. Coral reefs are significantly important because of the biodiversity. Although the number of fish are decreasing, the remaining coral reefs contain more unique sea creatures. The variety of species living on a coral reef is greater than anywhere else in the world. An estimation of 70-90% of fish caught are dependent on coral reefs in Southeast Asia and reefs support over 25% of all known marine species.
Marine pollution occurs when substances used or spread by humans, such as industrial, agricultural and residential waste, particles, noise, excess carbon dioxide or invasive organisms enter the ocean and cause harmful effects there. The majority of this waste (80%) comes from land-based activity, although marine transportation significantly contributes as well. It is a combination of chemicals and trash, most of which comes from land sources and is washed or blown into the ocean. This pollution results in damage to the environment, to the health of all organisms, and to economic structures worldwide. Since most inputs come from land, either via the rivers, sewage or the atmosphere, it means that continental shelves are more vulnerable to pollution. Air pollution is also a contributing factor by carrying off iron, carbonic acid, nitrogen, silicon, sulfur, pesticides or dust particles into the ocean. The pollution often comes from nonpoint sources such as agricultural runoff, wind-blown debris, and dust. These nonpoint sources are largely due to runoff that enters the ocean through rivers, but wind-blown debris and dust can also play a role, as these pollutants can settle into waterways and oceans. Pathways of pollution include direct discharge, land runoff, ship pollution, bilge pollution, atmospheric pollution and, potentially, deep sea mining.
Ocean acidification is the ongoing decrease in the pH of the Earth's ocean. Between 1950 and 2020, the average pH of the ocean surface fell from approximately 8.15 to 8.05. Carbon dioxide emissions from human activities are the primary cause of ocean acidification, with atmospheric carbon dioxide levels exceeding 422 ppm. CO2 from the atmosphere is absorbed by the oceans. This chemical reaction produces carbonic acid which dissociates into a bicarbonate ion and a hydrogen ion. The presence of free hydrogen ions lowers the pH of the ocean, increasing acidity. Marine calcifying organisms, such as mollusks and corals, are especially vulnerable because they rely on calcium carbonate to build shells and skeletons.
Marine ecosystems are the largest of Earth's aquatic ecosystems and exist in waters that have a high salt content. These systems contrast with freshwater ecosystems, which have a lower salt content. Marine waters cover more than 70% of the surface of the Earth and account for more than 97% of Earth's water supply and 90% of habitable space on Earth. Seawater has an average salinity of 35 parts per thousand of water. Actual salinity varies among different marine ecosystems. Marine ecosystems can be divided into many zones depending upon water depth and shoreline features. The oceanic zone is the vast open part of the ocean where animals such as whales, sharks, and tuna live. The benthic zone consists of substrates below water where many invertebrates live. The intertidal zone is the area between high and low tides. Other near-shore (neritic) zones can include mudflats, seagrass meadows, mangroves, rocky intertidal systems, salt marshes, coral reefs, lagoons. In the deep water, hydrothermal vents may occur where chemosynthetic sulfur bacteria form the base of the food web.
A wild fishery is a natural body of water with a sizeable free-ranging fish or other aquatic animal population that can be harvested for its commercial value. Wild fisheries can be marine (saltwater) or lacustrine/riverine (freshwater), and rely heavily on the carrying capacity of the local aquatic ecosystem.
The ocean is the body of salt water that covers approximately 70.8% of Earth. In English, the term ocean also refers to any of the large bodies of water into which the world ocean is conventionally divided. The following names describe five different areas of the ocean: Pacific, Atlantic, Indian, Antarctic/Southern, and Arctic. The ocean contains 97% of Earth's water and is the primary component of Earth's hydrosphere; thus the ocean is essential to life on Earth. The ocean influences climate and weather patterns, the carbon cycle, and the water cycle by acting as a huge heat reservoir.
Ocean deoxygenation is the reduction of the oxygen content in different parts of the ocean due to human activities. There are two areas where this occurs. Firstly, it occurs in coastal zones where eutrophication has driven some quite rapid declines in oxygen to very low levels. This type of ocean deoxygenation is also called dead zones. Secondly, ocean deoxygenation occurs also in the open ocean. In that part of the ocean, there is nowadays an ongoing reduction in oxygen levels. As a result, the naturally occurring low oxygen areas are now expanding slowly. This expansion is happening as a consequence of human caused climate change. The resulting decrease in oxygen content of the oceans poses a threat to marine life, as well as to people who depend on marine life for nutrition or livelihood. A decrease in ocean oxygen levels affects how productive the ocean is, how nutrients and carbon move around, and how marine habitats function.
Marine chemistry, also known as ocean chemistry or chemical oceanography, is the study of chemical content in marine environments as influenced by plate tectonics and seafloor spreading, turbidity, currents, sediments, pH levels, atmospheric constituents, metamorphic activity, and ecology. Marine life has adapted to the chemistries unique to Earth's oceans, and marine ecosystems are sensitive to changes in ocean chemistry.
Fisheries are affected by climate change in many ways: marine aquatic ecosystems are being affected by rising ocean temperatures, ocean acidification and ocean deoxygenation, while freshwater ecosystems are being impacted by changes in water temperature, water flow, and fish habitat loss. These effects vary in the context of each fishery. Climate change is modifying fish distributions and the productivity of marine and freshwater species. Climate change is expected to lead to significant changes in the availability and trade of fish products. The geopolitical and economic consequences will be significant, especially for the countries most dependent on the sector. The biggest decreases in maximum catch potential can be expected in the tropics, mostly in the South Pacific regions.
Human activities have substantial impact on coral reefs, contributing to their worldwide decline. Damaging activities encompass coral mining, pollution, overfishing, blast fishing, as well as the excavation of canals and access points to islands and bays. Additional threats comprise disease, destructive fishing practices, and the warming of oceans.[2] Furthermore, the ocean's function as a carbon dioxide sink, alterations in the atmosphere, ultraviolet light, ocean acidification, viral infections, the repercussions of dust storms transporting agents to distant reefs, pollutants, and algal blooms represent some of the factors exerting influence on coral reefs. Importantly, the jeopardy faced by coral reefs extends far beyond coastal regions. The ramifications of climate change, notably global warming, induce an elevation in ocean temperatures that triggers coral bleaching—a potentially lethal phenomenon for coral ecosystems.
The resilience of coral reefs is the biological ability of coral reefs to recover from natural and anthropogenic disturbances such as storms and bleaching episodes. Resilience refers to the ability of biological or social systems to overcome pressures and stresses by maintaining key functions through resisting or adapting to change. Reef resistance measures how well coral reefs tolerate changes in ocean chemistry, sea level, and sea surface temperature. Reef resistance and resilience are important factors in coral reef recovery from the effects of ocean acidification. Natural reef resilience can be used as a recovery model for coral reefs and an opportunity for management in marine protected areas (MPAs).
There are many effects of climate change on oceans. One of the main ones is an increase in ocean temperatures. More frequent marine heatwaves are linked to this. The rising temperature contributes to a rise in sea levels due to melting ice sheets. Other effects on oceans include sea ice decline, reducing pH values and oxygen levels, as well as increased ocean stratification. All this can lead to changes of ocean currents, for example a weakening of the Atlantic meridional overturning circulation (AMOC). The main root cause of these changes are the emissions of greenhouse gases from human activities, mainly burning of fossil fuels. Carbon dioxide and methane are examples of greenhouse gases. The additional greenhouse effect leads to ocean warming because the ocean takes up most of the additional heat in the climate system. The ocean also absorbs some of the extra carbon dioxide that is in the atmosphere. This causes the pH value of the seawater to drop. Scientists estimate that the ocean absorbs about 25% of all human-caused CO2 emissions.
A planktivore is an aquatic organism that feeds on planktonic food, including zooplankton and phytoplankton. Planktivorous organisms encompass a range of some of the planet's smallest to largest multicellular animals in both the present day and in the past billion years; basking sharks and copepods are just two examples of giant and microscopic organisms that feed upon plankton.
A mesophotic coral reef or mesophotic coral ecosystem (MCE), originally from the Latin word meso (meaning middle) and photic (meaning light), is characterized by the presence of both light-dependent coral and algae, and organisms that can be found in water with low light penetration. Mesophotic coral ecosystems occur at depths beyond those typically associated with coral reefs as the mesophotic ranges from brightly lit to some areas where light does not reach. Mesophotic coral ecosystem (MCEs) is a new, widely-adopted term used to refer to mesophotic coral reefs, as opposed to other similar terms like "deep coral reef communities" and "twilight zone", since those terms sometimes are confused due to their unclear, interchangeable nature. Many species of fish and corals are endemic to the MCEs making these ecosystems a crucial component in maintaining global diversity. Recently, there has been increased focus on the MCEs as these reefs are a crucial part of the coral reef systems serving as a potential refuge area for shallow coral reef taxa such as coral and sponges. Advances in recent technologies such as remotely operated underwater vehicles (ROVs) and autonomous underwater vehicles (AUVs) have enabled humans to conduct further research on these ecosystems and monitor these marine environments.
Ocean acidification threatens the Great Barrier Reef by reducing the viability and strength of coral reefs. The Great Barrier Reef, considered one of the seven natural wonders of the world and a biodiversity hotspot, is located in Australia. Similar to other coral reefs, it is experiencing degradation due to ocean acidification. Ocean acidification results from a rise in atmospheric carbon dioxide, which is taken up by the ocean. This process can increase sea surface temperature, decrease aragonite, and lower the pH of the ocean. The more humanity consumes fossil fuels, the more the ocean absorbs released CO₂, furthering ocean acidification.
The Arctic Ocean covers an area of 14,056,000 square kilometers, and supports a diverse and important socioeconomic food web of organisms, despite its average water temperature being 32 degrees Fahrenheit. Over the last three decades, the Arctic Ocean has experienced drastic changes due to climate change. One of the changes is in the acidity levels of the ocean, which have been consistently increasing at twice the rate of the Pacific and Atlantic oceans. Arctic Ocean acidification is a result of feedback from climate system mechanisms, and is having negative impacts on Arctic Ocean ecosystems and the organisms that live within them.
The poleward migration of coral species refers to the phenomenon brought on by rising sea temperatures, wherein corals are colonising cooler climates in an attempt to circumvent coral bleaching, rising sea levels and ocean acidification. In the age of Anthropocene, the changing global climate has disrupted fundamental natural processes and brought about observable changes in the submarine sphere. Whilst coral reefs are bleaching in tropical areas like the Great Barrier Reef, even more striking, and perhaps more alarming; is the growth of tropical coral species in temperate regions, which has taken place over the past decade. Coral reefs are frequently compared to the "canaries in the coal mine," who were used by miners as an indicator of air quality. In much the same way, "coral reefs are sensitive to environmental changes that could damage other habitats in the future," meaning they will be the first to visually exhibit the true implications of global warming on the natural world.
A marine food web is a food web of marine life. At the base of the ocean food web are single-celled algae and other plant-like organisms known as phytoplankton. The second trophic level is occupied by zooplankton which feed off the phytoplankton. Higher order consumers complete the web. There has been increasing recognition in recent years that marine microorganisms.
Jean-Pierre Gattuso is a French ocean scientist conducting research globally, from the pole to the tropics and from nearshore to the open ocean. His research addresses the biology of reef-building corals, the biogeochemistry of coastal ecosystems, and the response of marine plants, animals and ecosystems to global environmental change. He is also interested in transdisciplinary research, collaborating with social scientists to address ocean-based solutions to minimize climate change and its impacts. He is currently a CNRS Research Professor at Sorbonne University.
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