5.3 Shifting baseline, global climate changes and human disturbances
Imagine this scenario. You have been living in a city near the sea and watching the shorelines from your boat. What can you see? The coast is lined with concrete. Several human activities are present. There are fishes in the water, but they are rare. Hopefully the majority of people viewing this seascape will perceive its unnaturalness, but it is not always so simple. Probably once there was a softer shoreline, perhaps dominated by marshes, tidal inlets and dunes, and large fish in the water. What has happened?
On one hand, when a person or a society is not able to connect the impoverished present with a rich and bio-diverse past, the result is called the ‘shifting baseline’ (Video1_Ses5.3_Jeremy Jackson TED talk; (Jackson et al. 2001)). On the other hand, many temperate coastal rocky reefs have few large predators. If you go back some human generations, you can find reports and photos of abundant large predatory fish (Video2_Ses5.3_Enric Sala TED talk). Some studies have highlighted that the shift we are observing todayt is related to the overfishing of top predators in the past. These two sides could lead to difficulties in establishing clear and common aims for an ecological restoration that resembles the pristine state. Indeed if the environment is impacted through years of several human disturbances, it is entirely possible that future generations are unable to remember the original pristine state.
Global climate change can have biological effects both at an individual organisms level and at the biodiversity one. The increase of the sea surface temperature could affect physiological function, migration patterns, and geographical range. The elevated temperature will affect oxygen demand, which may be limited by the seasonal water stratification (thermocline). It may also influence migration patterns (i.e. meridionalization of the Mediterranean Sea) or change the geographical distribution of marine species(i.e. tropicalization of the Mediterranean Sea). The spread and effect of diseases could also be altered by the increasing seawater temperature (e.g. mass mortality events). Moreover there is evidence of the influence of rising acidification on the calcification in organisms, ranging from calcifying plankton to corals.
Global climate change is a fundamental and grave problem, but the most direct impact of man on the sea is through fishing and hunting, and we should not forget about pollution, physical damage due to marine transport and tourism, and invasions of new species, all factors causing extremely serious changes to our sea.
Indeed the threats to natural habitats are often multifactorial and frequently involve anthropogenic damage interacting with natural events, as you have seen in the previous sections.
Jackson JBC, Kirby MX, Berger WH, Bjorndal KA, Botsford LW, Bourque BJ, Bradbury RH, Cooke R, Erlandson J, Estes JA, Hughes TP, Kidwell S, Lange CB, Lenihan HS, Pandolfi JM, Peterson CH, Steneck RS, Tegner MJ, Warner RR (2001) Historical overfishing and the recent collapse of coastal ecosystems. Science 293:629-638
5.3.1 The definition of shifting baseline.
To understand the shifting baseline, we need to know what the term baseline means. A baseline is a state of a system with a description of its existing conditions that can be used for comparison in the future. However, people tend to easily forget about the ecosystem baseline in the past and create a new perception. In other words, due to faulty memories, humans have a bad perception of how much nature is changing.
This phenomenon of change is called shifting baseline and was first used by biologist Daniel Pauly in 1995. There are two types of shifting baseline: generational amnesia and personal amnesia. Generational amnesia occurs because new generations don't know how ecosystems used to look like and take the current version as normal. Knowledge is not passed from older generations, therefore what to us seems natural, to older generations seems degraded or reduced. On the other hand, personal amnesia occurs much faster. It is when people forget how things used to be. For example, you may not remember that in your childhood there used to be much more trees in the forest you live near to. Since baseline is changing slowly, it is hard for people to notice the difference, and there lies a problem. It is hard to convince people that the environment is changing if they don't see it themselves. Another issue is lack of scientific data from the past which supports the theory of shifting baseline.
But even with a lack of information, it is very clear that human activity is massively changing the environment. General perception about this topic can be, and should be, changed with education. If the awareness is not raised, we could destroy the Earth's ecosystem without even knowing about it.
5.3.2 The definition of pristine ecosystem.
The definition of pristine ecosystems
Pristine ecosystems are defined as ecosystems that have never been impacted by humans. That definition relies on the idea that humans are not a part of the natural environment and that all change caused by humans makes an ecosystem no longer pristine. In reality, humans have been changing the natural world for thousands of years and have impacted the environment so greatly that nature untouched by humans is almost entirely gone.
As of the year 2000, it is estimated that about 95% of the world’s oceans and 99% of the ocean floor has yet to be explored. So how come new studies show that 87% of the ocean is no longer pristine? Studies have shown that many oceanic ecosystems cannot function like they used to due to commercial shipping, fertilizer runoff and fishing. Polar biomes like the Antarctic and Arctic are believed to be the only untouched marine ecosystems. Unfortunately, they are in danger because of melting ice caps caused by climate change. Other human activities that badly affect oceans are overfishing and plastic pollution. Overfishing causes unwanted change in the food chain while plastic pollution jeopardizes the lives of innocent and even endangered species.
The Millennium Atoll was believed to be one of the last pristine ecosystems in the world. The remote coral reef belonging to the Republic of Kiribati was discovered and observed in 2009. Because coral reefs are so delicate its condition has already been affected by the scientists’ observation and presence. Another example of an area mostly untouched by humans is the Ross Sea in Antarctica. The sea was quite suitable for scientists to study such an environment filled with life but became especially put at risk when an international fishing fleet came because commercial fishing can permanently modify the fragile ecosystem.
5.3.3 An example of meridionalizationof the Mediterranean Sea.
Meridionalization is the movement of a warm-water species to cold northern waters, because of climate change and global warming caused by the population growth. It's a phenomenon because usually warm-water species gravitate towards warmer waters as we can see from their name. Common warm-water species are catfish, largemouth bass, bluegill, crappies and others from the Centrachidae family.
Mediterranean species usually spread southwards to warmer sectors of the Mediterranean Sea but lately, they have been moving northwards to colder waters, mostly the British Sea. Meridionalization is particularly evident in fish. If the Mediterranean Sea continues to warm up at the same rate, most of the Mediterranean marine species will rapidly disappear and will be replaced with a tropical ecosystem. Meridionalization is caused by the northward movement of surface isotherms (curves joining equal temperatures on a diagram), due to climate warming which causes a change in water circulation that allows warm-water species to cross the Straits of Sicily and to penetrate the sub-basins where they were formerly absent. And because of that, the wall between West and East has been torn off and species from the Atlantic Ocean are coming through Gibraltar and have reached the Levant Sea, while species from the Red Sea have reached the Western Mediterranean.
Because of such changes, most of the species will become extinct because food that grows in the northern sea is not intended for species that lived in the Mediterranean Sea, so we must be smart and we need to change the way people think and act towards the environment because if we don't change now, our marine ecosystem
5.3.4 An example of tropicalization of the Mediterranean Sea.
The process of tropicalization is something that is currently being observed and assessed on the Mediterranean Sea. As we all know, climate change is an ongoing problem in the whole world, and it is believed that it could reduce marine biodiversity in the Mediterranean Sea. The temperature which is steadily rising due to the change in the climate correlates with the spread of invasive species and marine diseases. These two very present and concerning problems are the reason we are experiencing the process of tropicalization in the Mediterranean Sea.
Over the past few decades severe cases of massive marine invertebrates mortalities have been recorded, and these occurrences are becoming more common in temperate seas. The cause of these terrible events is most commonly attributed to these newer climatic anomalies during the later summer and early autumn months (extraordinarily high and perpetual temperatures which can keep going for a whole month).
For example, the Madracis pharensis, a stony coral of the Astrocoeniidae family, suffered great losses after the incredibly hot summers of 2003, 2007, 2008, 2009, 2011 and 2012, when up to 30% of the specimens in the colonies (which are located on the eastern and southern coasts of Spain and France respectively, coasts of Turkey, and the coasts of some Greek islands) were affected by diseases. The most severe of these diseases are polyp bleaching and polyp tissue necrosis. In the majority of cases bleaching has been caused by the elevated temperatures. Nevertheless there are some cases where the population had recovered after these bleaching events, which indicates the fact that these corals obviously have some adaptability to these unwelcome changes in the environment and thus possibly can adapt to the ever-rising changes in the climate.
THE STATUS OF MEDITERRANEAN SYMBIOTIC CORALS IN THE FORTHCOMING “TROPICALIZATION”
Kružić, Petar ; Lipej, Lovrenc ; Mavrič, Borut ; Rodić, Petra
5.3.5 An example of species that have experience mass mortality caused by the increasing of the water temperature in the Mediterranean Sea.
Water temperature is measured on the surface. A minimal value of 4.1 °C was measured from 1911 to 1964 and the maximum value of 28.8 °C on the surface of the Adriatic Sea. Water temperature has sometimes even increased up to 30 °C in the last 10 years.
Some sensitive organisms like corals and sponges are becoming endangered because of the increase in temperature. However, there are some invasive species that favor the increase of temperature. One of them is Sparisoma cretense (papigača) who’s feeding on corals. Scomber scombrus (skuša) and Sarda sarda (palamida) are now living in deeper layers than before and they are withdrawing from upper layers because it’s colder the more you go down. Every year in late spring and summer thermocline occurs. It is a thin layer in which temperature changes more rapidly with depth than in layers above or below. 20 years ago it used to develop at 20 meters of depth but nowadays it is created even at 50 meters of depth sometimes. “Bleaching” is the process of corals dying out because of temperature increase. High temperature is threatening zooxanthellae algae most and they live in symbiosis with polyp. These algae are using products of the polyp’s metabolism and in return doing photosynthesis, feeding the polyps. Zooxanthellae algae are dying out because of climate change, therefore polyps are losing their main source of food and becoming vulnerable.
Finally, Balanophyllia is a species of corals that are experiencing total mortality in some places on the island of Mljet. On the coral reef of Mljet whole colonies have died. One of the consequences of increasing water temperature is also the arrival of tropical species into the Mediterranean Sea.
5.3.6 An example of species that could have problems in calcifying caused by the increasing of the water acidification in the Mediterranean Sea.
Ocean acidification is sometimes called “climate change’s equally evil twin”. It's a significant and harmful consequence of excess carbon dioxide in the atmosphere that we don't see or feel because its effects are happening underwater. At least one-quarter of the carbon dioxide (CO2) released by burning coal, oil and gas doesn't stay in the air, but instead dissolves into the ocean. Since the beginning of the industrial era, the ocean has absorbed some 525 billion tons of CO2 from the atmosphere. When carbon dioxide dissolves in seawater, the water becomes more acidic and the ocean’s pH (a measure of how acidic or basic the ocean is) drops. Even though the ocean is immense, enough carbon dioxide can have a major impact. In the past 200 years alone, ocean water has become 30 percent more acidic—faster than any known change in ocean chemistry in the last 50 million years.
Construction of skeletons in marine creatures is very sensitive to acidity. One of the hydrogen bonded molecules is carbonate, a key component of calcium carbonate shells. To create calcium carbonate, marine animals that build shells like corals combine the calcium ion with carbonate from the surrounding sea water. Like calcium ions, hydrogen bonds bind to carbonate - but they have a greater attraction to carbonate than calcium. When hydrogen is bonded to carbonate, a bicarbonate ion is formed. Organics that build shells cannot extract the carbonate ion they need from bicarbonates. In this way, hydrogen bonds carbonate ions, making it difficult to build their homes. Even if animals can build shells in acidic water, they may have to spend more energy to do so by subtracting resources from other activities such as reproduction.
While it is important to understand how ocean acidification will change ocean chemistry and marine organisms, it is equally critical to understand how these effects may grow and start to affect populations, communities, and entire marine ecosystems.
5.3.7 A definition of global climate change.
Experts agree that the Industrial Revolution was the turning point when emissions of greenhouse effect gases entering the atmosphere began to levitate. The Industrial Revolution was itself born out of smaller revolutions: agricultural, technological, demographic, transport, finance… reating a new model of production and consumption.Climate change also increases the appearance of more violent weather phenomena, drought, fires, the death of animal and plant species, flooding from rivers and lakes, the creation of climate refugees and destruction of the food chain and economic resources, especially in developing countries.
The global temperature increase brings disastrous consequences, endangering the survival of the Earth’s flora and fauna, including human beings. The worst climate change impacts include the melting of the ice mass at the poles, which in turn causes rising sea level, producing flooding and threatening coastal environments through which small island states risk disappearing entirely.
How can we avoid climate change?
First, it is important to be clear that climate change cannot be avoided. We can mitigate its effects and adapt to its consequences, we can fight it through the application of small and large scale measures that help to slow down climate change. These actions are known as climate change mitigation and adaptation measures.
In conclusion, climate change cannot be stopped but we need to contribute to keep our planet clean for next generations. Consequences could be horrible if we dont start with that. People act like it is not their problem but it actually is. it affects everyone and everyone is equally responsible.
5.3.8 Which are the main effects of global climate change in the marine environment?
The rising problem of modern society brought up more and more with new movements arising faster than people can keep track of is global warming: the climate changer of the century. As Earth warms up, the life on it has to adapt and many humans, feeling responsible for the drastic climate change, have realized it is their responsibility to protect the many endangered species finding themselves unable to cope with the sudden shift of nature.
It seems that the area most affected by the warm-up is the ocean and the seas. The sea levels are rising and the water temperature as well which is affecting the seafloor and many temperature-sensitive creatures are finding themselves unable to adapt. Except for the obvious issue of rising temperatures which is evident to the naked eye a massive problem comes in the form of greenhouse gasses, especially carbon dioxide. Rising levels of the gas mean a significant change in the seawater pH, specifically a decrease making it more acidic.
All of these changes are already taking effect and causing problems in our marine ecosystems: plankton, the basis of the marine food chain is starting to become scarce, the corals are losing their colouring or “bleaching” as a consequence of extreme stress, polar bears are finding themselves lost in the sea because of the melting ice and a numerous number of other species are forced to move their chosen residence because of the ideal water temperature they need and the consequences keep piling up. A change is happening and only time will tell how many will be able to adapt.
5.3.9 What could happen if large predatory fish disappear?
When you hear "large predatory fish", you first think of sharks. Sharks play a vital role in ocean ecosystems. Every year 100 million sharks are killed by humans and that number is only increasing. As an example, we can look at coral reefs. A study published in PLOS ONE in 2013 showed that sharks were crucial for the health of coral reefs.
Algae grow on coral, which is eaten by herbivorous fish. Herbivorous fish are then eaten by larger predatory fish which are eaten by sharks. When sharks are dying, less of the large predatory fish are eaten, which means that less of the herbivorous fish are eaten, and in turn, less of the algae is eaten. The algae compete directly with the coral, and too many algae kill coral reefs. After studying 185 miles of coral reef, the information on sharks the scientists found showed that declining shark populations as a result of overfishing have had a disastrous impact on coral reefs. So, if all sharks disappeared, coral reefs would also vanish.
Another problem is that the large growth of algae would suffocate the ocean. Algae suck the oxygen out of the water creating low oxygen levels. Without oxygen, marine life will suffocate to death. Also, some algae can also make toxins that get into the water. These toxins are incredibly harmful to marine life and can lead to mass die-offs. Algae can also be very toxic for people.
The global commercial fishing industry employs 200 million people and generates up to $90 billion dollars a year. If sharks disappeared, there would be a massive collapse in the ocean’s food chain. A collapse that would dramatically impact the commercial fishing industry. Due to reduced animal rich habitats like coral reefs, declining and extinct populations, and algae creating toxic fish, commercial fishing would be destroyed.