by Seema Pavgi Upadhye
Despite the fact that our planet is mostly ocean and human activity is more intense than it has ever been, we know remarkably little about the state of the ocean’s biodiversity — the variety and balance of species that support healthy and productive ecosystems. And it’s no surprise — marine biodiversity is complex, human impacts are uneven, and species respond differently to different stressors.
Human impacts on marine biodiversity are increasing, dominated by fishing, direct human disturbance from land and ocean acidification. The extent to which at-risk species are facing these pressures from human activities, and the pace at which the pressures are expanding and intensifying, is worrisome. Corals are the most widely impacted marine organism on Earth.
Coral species are facing impacts across essentially their entire ranges and those impacts are only getting more intense, particularly climate-related impacts, coral bleaching is also taking place. The species of the Coral Triangle — the tropical water connecting Indonesia, the Philippines, Papua New Guinea and the Solomon Islands — are among the most affected by human impacts, as are species in the North Atlantic, North Sea and Baltic Sea.
Seabirds are a critically important distributor of nutrients for island and marine environments. They feed on fish often in the open ocean far from islands, and then return to islands to roost — depositing nitrogen-rich nutrients on the island in the form of guano — or poo. Some of the guano is then leached off the islands by rain and into the surrounding seas where the nitrogen fertilises corals and other marine species such as algae and sponges, boosting the food-chain.
The world’s oceans – their temperature, chemistry, currents and life – drive global systems make the Earth habitable for humankind.
Our rainwater, drinking water, weather, climate, coastlines, much of our food, and even the oxygen in the air we breathe, are all ultimately provided and regulated by the sea. Over 3 billion people depend on marine and coastal biodiversity for their livelihood.
There will be disastrous effect of climate change and tourism on Marine ecosystem in coming years. Highlighting the contributions of large marine ecosystems to socio-economic development and to human well-being, UNESCO said those ecosystems alone contribute an estimated $28 trillion annually to the global economy through services and benefits provided by nature, including fish for food and trade, tourism and recreation, coastal protection from flooding and erosion, and the less tangible benefits from cultural, spiritual, and aesthetic connections to nature.
Maintaining the health and resource productivity of these transboundary water systems should help countries achieve global objectives to reduce poverty and hunger, and promote sustainable economic growth.
• 60 per cent of the world’s coral reefs are currently threatened by local activities.
• 90 per cent of all coral reefs could be threatened in 2030 by the combined pressures of local activities and climate change.
• 100 international agreements currently “govern” the open ocean, signaling severe fragmentation.
Large Marine Ecosystems (LMEs):
• 64 of 66 LMEs have experienced ocean warming since 1957 (“Super-fast” warming in the Northwest / Northeast Atlantic and in Western Pacific).
• 28 per cent reduction in fish catch potential projected for high-risk LMEs in East Siberian Sea.
• 50 per cent of all fish stock in LMEs are overexploited.
Biodiversity and ecosystem is facing multiple pressures. Over the last decades to centuries, the intensive use of land, fresh water, and oceans with the extraction of marine and freshwater organisms, wood, and agricultural commodities has dominated the loss of biodiversity and the deterioration of ecosystems globally. Approximately 70–75% of the ice-free land area is affected by human use, nearly 50% intensively so. Since 1961, cropland production increased by about 3.5 times and production of animal products by 2.5 times, supported by a massive enhancement of fertilizer input (+800%) and freshwater withdrawal (+100%).
Demand for fish has increased by >3% per year thus increasing more fish capturing. In absence of strong conservation policies and changes in per capita consumption, agricultural expansion is projected to further hasten species extinctions , while the world fish production (capture and aquaculture) is projected to increase by 18% between 2016 and 2030. In addition to the pressure from direct exploitation, the detrimental impacts of multiple pollution sources all are also harmful to marine, freshwater, and terrestrial biodiversity. Continued human population growth and the concomitant increase in per capita consumption raise serious concerns about the acceleration of overexploitation and pollution of ecosystems.
The exponential rise of atmospheric greenhouse gas concentrations over the past 30 years has increased the average global temperature by 0.2°C per decade. Most of this extra heat is being absorbed by the world’s oceans, particularly by their upper layers, with the mean global sea surface temperature (SST) increasing by approximately 0.4°C since the 1950s .The warming of the oceans drives greater stratification of the water column. It is reducing mixing in some parts of the ocean, which affects oxygen and nutrient availability and so primary production and the ecophysiology of water-breathing organisms.
The increase in water temperatures which is unevenly distributed also due to increased meltwater and discharged ice from terrestrial glaciers and ice sheets. It influences the behavior of ocean currents, which play critical roles in the dynamics, local climates, and biology of the ocean . with these environmental changes, industrial fisheries have resulted in the overexploitation and decimation of about 70% of world fish stocks, resulting in changes to fish communities and marine ecosystems. Both climatic and human pressures can lead to shifts in the size, structure, spatial range, and seasonal abundance of populations, which, in turn, may alter trophic pathways from primary producers to upper-trophic levels, propagating changes throughout ecosystems in both bottom-up and top-down directions. Accordingly, climate and fishing impacts should not be treated in isolation from each other when it comes to conservation of marine biodiversity.
Therefore warming, combined with deoxygenation or food limitation, may cause reductions in the mean body size and abundance of fish and other marine ectotherms by the end of century. It will lead to negative interactions with fishing, which also reduces fish size and abundance significantly. In case of amphibians and strictly aquatic species, changes in precipitation patterns will play an additional crucial role. Where there are no barriers to movement, warmer temperatures may result in continued poleward and altitudinal shifts of species and entire biomes.
Rising levels of CO2 in the atmosphere, in addition to advancing climate change also lead to ocean and freshwater acidification, which is expected to reduce growth rates in calcifying phytoplankton and organisms like gastropods, crustaceans, shellfish, or corals, whereas some primary producers might benefit from increased CO2 . Direct effects of CO2 thus can have knock-on effects across all systems on food web structures and for the integrity of the habitats.
Industrial fisheries may pose another serious threat for the conservation of species inhabiting marine biodiversity hot spots when those areas overlap with areas of intense human fishing activity. However, fishery data are available in such poor spatial resolution that analyses of the overlap of fishing intensity with climate change effects are necessarily limited. FAO fisheries landings are available for the last 60 years, enabling us to at least evaluate trends in the exploitation of marine resources. Although fishing has been practiced for centuries, fishing pressure has intensified in recent decades as a consequence of technical developments in fishing techniques and the demands of a rapidly increasing human population, leading to overexploitation and even collapse of many fish stocks. The world’s marine fisheries resources are under enormous pressure, with global fishing effort exceeding optimum and sustainable levels by an estimated factor of 3 to 4. Observed trends showing annual increases in fishing captures suggest that this harvest pressure will continue and further exacerbate pressure on fish stocks well into the future.
Fishing activities are particularly intense at Major Fishing Areas (MFAs, according to their FAO categorization) that overlap with marine biodiversity hot spots .This is particularly true for the tropical regions of the Indian Ocean and the western Pacific Ocean, where the highest increasing rates in fishing pressure have been recorded at both the regional and the local scale. Although biodiversity conservation is an issue of global concern, fishing policies are most commonly derived from decisions taken at a national level, particularly with regard to those occurring within EEZs where bordering sovereign states have special rights regarding the use of marine resources (United Nations Convention on the Law of the Sea, 1982).
Fishing pressure differs among countries. China and Peru contribute the most to global captures (ca. 20%) and are likely to continue to do so according to the observed trends in fishing captures. However, many other countries also contribute substantially to fishing captures within MFAs that overlap with marine hot spots. Around 30 different coastal countries that collectively account for 80.5% of fishing captures in the areas of high biodiversity.
All these environmental stressors likely interact in a number of ways, but little is known about the potential for synergetic or antagonistic interactions. Marine species may also respond differently to changes in environmental conditions. Some species may benefit from shifts toward environmental conditions outside the normal range of variability, but in most cases, these environmental changes will prove suboptimal, and this will be made apparent through changes to populations and communities. Ocean warming in temperate regions, such as the southwestern Pacific Ocean or the western Indian Ocean, can affect marine species through a reduction in primary productivity and also through trophic disruptions due to shifts in species distributions and changes in the timing of ecosystem-level processes.
Changes in ocean circulation, which largely control marine patterns of productivity and food availability, may also have important global consequences for biological communities. Thus, we should expect that consequences of changing climatic variables will be species-specific and even site-specific. Fine-scale, spatially explicit measurements on the distribution of environmental stressors are therefore crucial to effectively depict those local to regional areas of special concern for the conservation of marine biodiversity in the face of climate change.
The world’s areas of highest marine biodiversity are threatened by the impacts from both global warming and human fishing pressure. Thus, it behooves the international community to find solutions that go beyond the interests and borders of various countries if we are to conserve the biodiversity in marine hot spots, in a similar way to which the world must tackle the associated causes of climate change itself.
About Coral Reef
World’s coral reefs could bleach by the end of century, unless there are drastic reductions in greenhouse-gas emissions. This warning is given by United Nations Environment Programme(UNEP). The head of UNEP’s Marine and Freshwater Branch Leticia Carvalho said that coral reefs will soon disappear.
Coral reefs are incredibly important and sustain a wide variety of marine life. They also protect coastlines from erosions from waves and storms, sink carbon and nitrogen and help recycle nutrients. Their loss would have devastating consequences not only for marine life, but also for over a billion people globally who benefit directly or indirectly from them. Coral reefs also called a s“rainforests of the sea,” support approximately 25 percent of all known marine species. Reefs provide homes for more than 4,000 species of fish, 700 species of coral, and thousands of other plants and animals.
The architects of coral reefs are hard corals. Unlike soft corals, hard corals have stony skeletons made out of limestone that is produced by coral polyps. When polyps die, their skeletons are left behind and used as foundations for new polyps. An actual coral branch or mound is composed of layer upon layer of skeletons covered by a thin layer of living polyps. Due to hardened surfaces, corals are sometimes mistaken as being rocks. Corals are alive and unlike plants, corals do not make their own food. Corals are in fact animals.
“A coral” is actually made up of thousands of tiny animals called polyps. A coral polyp is an invertebrate that can be no bigger than a pinhead to up to a foot in diameter. Each polyp has a saclike body and a mouth that is encircled by stinging tentacles. The polyp uses calcium carbonate (limestone) from seawater to build a hard, cup-shaped skeleton. This skeleton protects the soft, delicate body of the polyp.
Most reef-building corals have a unique partnership with tiny algae called zooxanthellae. The algae live within the coral polyps, using sunlight to make sugar for energy. This energy is transferred to the polyp, providing much needed nourishment. In turn, coral polyps provide the algae with carbon dioxide and a protective home.
Corals also eat by catching tiny floating animals called zooplankton. At night, coral polyps come out of their skeletons to feed, stretching their long, stinging tentacles to capture critters that are floating by. Prey are pulled into the polyps’ mouths and digested in their stomachs.
Corals reproduce asexually by budding or fragmentation. Through budding, new polyps “bud” off from parent polyps to form new colonies. In fragmentation, an entire colony (rather than just a polyp) branches off to form a new colony. This may happen, for example, if a larger colony is broken off from the main colony during a storm or boat grounding.
In terms of sexual reproduction, some coral species, such as Brain and Star coral, produce both sperm and eggs at the same time. For other corals, such as Elkhorn and Boulder corals, all of the polyps in a single colony produce only sperm and all of the polyps in another colony produce only eggs. Coral larvae are either fertilized within the body of a polyp or in the water, through a process called spawning. In some areas, mass coral spawning events occur one specific night per year and scientists can predict when this will happen.
Once in the water, larvae ‘swim’ to the ocean surface. If they are not eaten, they eventually settle to the ocean floor and attach to a hard surface. Once attached, they metamorphose into a coral polyp and begin to grow, dividing in half. As more and more polyps are added, a coral colony develops and eventually begins to reproduce.
When water temperatures rise, corals expel the vibrant microscopic algae living in their tissues. This phenomenon is called coral bleaching. Though bleached corals are still alive and can recover their algae, if conditions improve. However, the loss puts them under increased stressed, and if the bleaching persists, the corals die.
The last global bleaching event started in 2014 and extended well into 2017. It spread across the Pacific, Indian and Atlantic oceans, and was the longest, most pervasive and destructive coral bleaching incident ever recorded.
Under the fossil-fuel-heavy scenario, the report estimates that every one of the world’s reefs will bleach by the end of the century, with annual severe bleaching occurring on average by 2034, nine years ahead of predictions published three years ago.
Corals are animals that create their own skeleton to help support them. These animals live in shallow warm waters around the world using sunlight to synthesize their sugar-based food. Reefs are not just “beautiful ecosystems” renowned for their biological diversity, according to Dr. Hagedorn, they are also crucial to life on Earth. “Almost 25 per cent of all marine life lives on a reef at some point and so without them many species of fish that we eat wouldn’t exist. Corals provide a natural protection for our coastlines, for example against tsunamis. They also support people’s livelihoods in the form of fishing and tourism and contribute 350 billion annually to the global economy. So, there are many reasons we should save them.”
The underlying structures of the reefs — which are home to a multitude of aquatic life — could fracture as a result of increasing ocean acidity caused by rising levels of carbon dioxide.
Scientists observed that the skeletons of dead corals, which support and hold up living corals, had become porous due to ocean acidification and rapidly become too fragile to bear the weight of the reef above them.
Previous research has shown that ocean acidification can impact coral growth, but the new study demonstrates that porosity in corals — known as coralporosis — leads to weakening of their structure at critical locations.
This causes early breakage and crumbling, experts say, that may cause whole coral ecosystems to shrink dramatically in the future, leaving them only able to support a small fraction of the marine life they are home to today.
The findings complement recent evidence of porosity in tropical corals, but demonstrate that the threat posed by ocean acidification is far greater for deep-sea coral reefs. The research was led by University of Edinburgh scientists, under the EU-funded ATLAS and iAtlantic projects, with researchers from Heriot-Watt University and the National Oceanic and Atmospheric Administration (NOAA).
The team identified how reefs could become fractured by analysing corals from the longest-running laboratory studies to date, and by diving with submersibles off US Pacific shores to observe how coral habitat is lost as the water becomes more acidic.
Deep sea coral reefs and sponges
Corals and sponges are important foundations in ocean ecosystems providing structure and habitats that shelter a high number of species like fish, crabs and other creatures, particularly in the seamounts and canyons of the deep sea. Researchers at the University of New Hampshire have discovered that when it comes to climate change not all deep-sea corals and sponges are affected the same and some could be threatened if average ocean temperatures continue to increase in the deap sea.
These deep-sea corals and sponges are ecologically important because they are foundational species that contribute to the food web and losing them could eventually lower the biodiversity of the deep sea.
Although corals and sponges co-occur, climate-related variables temperature, salinity and dissolved oxygen contributed to the distribution of sponges, whereas seafloor properties of slope and substrate contributed to the distribution of corals. Not all deep-sea corals and sponges were influenced by the same environmental variables and each has different levels of sensitivity. Changes in temperature and dissolved oxygen, that go beyond what the deep-sea corals and sponges are used to, could stress the species’ physiology affecting growth, tissue loss and reproduction.
In general, deep-sea corals are found 200 to 10,000 feet below sea level where sunlight is nonexistent. Unlike shallow-water coral reefs, which are limited to warm tropical waters, deep-sea corals are found throughout the world’s oceans, from tropical to polar regions, forming groves of tree or fan shapes that can reach feet to meters tall. Deep-sea sponge populations can filter water, collect bacteria and process carbon, nitrogen, and phosphorus. Deep-sea corals and sponges have been found on continental shelves, canyons and seamounts in deep seas around the world but their full extent is unknown because only 15 percent of the Earth’s seafloor has been mapped with high-resolution imaging.
Deep-sea coral reefs face challenges as changes to ocean chemistry triggered by climate change may cause their foundations to become brittle and because of their special place in biodiversity we need to see the ways to protect them.
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