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Life on our planet arose from water, which covers about 72 % of the earth's surface. And just as water is not always the same everywhere on Earth – it has different chemical properties, pH, temperature, density and flow rate – so is the life found in it and dependent on it, also variable.
Regarding the wealth and number of species, 80 % of all species can be found on land. The aquatic world comprises about 15 % of species in the oceans and 5 % living in fresh water. Although it may seem that there are fewer aquatic than terrestrial animals, in terms of total biomass (amount of living biological organisms), about 78 % can be found in the aquatic environment.
What is an Aquatic Ecosystem? It is an umbrella term for all ecosystems that depend most or part of the time on water, whether marine or fresh water. We can divide them into two main groups:
The life in these aquatic ecosystems can be found in different zones – on the surface of water bodies, in the middle, or on the bottom.
What is an Aquatic Animal? An aquatic animal is any animal (whether vertebrate or invertebrate) that lives in water for all or most of its life. It can breathe air or extract oxygen from water through specialized organs called gills, or directly through its skin.
Water organisms generally fall into four wide groups, and differ in the way they live and move. They are listed below according to the layers (from top to bottom) in which they are most often found in the water ecosystem.
Neuston Neuston is a group of organisms that live on the surface or attached to the underside of the surface film of water. They can also exist in the surface microlayer that forms between the upper side and the lower side. Unlike neuston, plankton is only occasionally associated with the surface film accidentally. These organisms include:
Neuston can be found in all types of aquatic environments, from lakes and rivers to oceans and seas. Neuston is most abundant in shallow waters with moderate temperature and good mineralization. It is an important part of the aquatic food chain and is a food source for many animals, including fish, insects and reptiles. Neuston also breaks down organic matter that falls into the water from the air or from shores, releasing nutrients that are available to other organisms.
Plankton These are small animals that float in the upper layer of water (fresh or salty) and cannot move on their own. They live in the upper layers of water where there is enough light. The collective term “plankton” refers to all such organisms, such as certain algae, bacteria, protozoa, crustaceans, molluscs, and coelenterata.
Plankton is thus the basis of marine and freshwater ecosystems and provides essential food for larger animals and, of course, indirectly for humans. Many planktonic organisms are neither clearly plant nor animal, yet we divide them into:
There is a vast range of sizes of individual organisms in plankton. This ranges from more than 20 cm large representatives of megaplankton (for example, jellyfish; ctenophores; salps and pyrosomes) to the smallest representatives of femtoplankton with a size of less than 0.2 µm (marine viruses).
Did you know… phytoplankton produce almost one-half of the oxygen in the atmosphere through photosynthesis?
Nekton Representatives of nekton include aquatic organisms that can actively move through the water and are not just carried along by the current, like plankton. Of course, this classification has its flaws, as some animals may begin their life cycle as plankton and gradually develop into nekton.
Most nekton are chordates, animals with bones or cartilage. Nekton representatives include:
Benthos Benthos is a collective name for all animals that live at the bottom of seas, rivers, lakes or streams. It comes from the Greek (bénthos) “the depths (of the sea)”.
These organisms can live even at great depths, where practically no light penetrates. The source of energy for benthic ecosystems is usually organic matter from the higher parts of the water column. Dead and decaying matter that sinks to the bottom sustains the benthic food chain. Most organisms in this zone are scavengers or detritivores. Benthos also help to keep the water clean. The types are:
Fresh Water vs. Salt Water We also divide aquatic animals according to the type of water in which they live – sweet, salt or borderline. Each aquatic animal has a unique adaptation to the specific environment in which it thrives. There are important differences between aquatic animals that will not allow them to live in a different environment.
Why should we care about aquatic animals? The diversity of aquatic life that is found in oceans, rivers and lakes is irreplaceable. These animals are a source of food for many people and other animals; they help to cleanse the water and participate in the nutrient cycle. They play a vital role in ecosystems and are also important for recreation and entertainment. And most importantly, they are living creatures that deserve their own space.
Aquatic animals as a food source According to a 2022 Food and Agriculture Organization of the United Nations (FAO) report, more than 600 million human lives depend in some way on fisheries and aquaculture. In some parts of Africa and Asia, aquaculture constitutes more than 50 % of the protein source for the population. Other important sources of food from aquatic animals include crustaceans, molluscs, amphibians and reptiles.
Aquatic animals help cleanse the water Fish and other aquatic animals filter the water and help to remove dirt and debris from the water. Aquatic plants also help to purify water by absorbing carbon dioxide and releasing oxygen.
Aquatic animals participate in the nutrient cycle Aquatic animals help to break down organic matter and convert it into nutrients that are available to other organisms. Aquatic plants also absorb nutrients from the water and use them for their growth.
Aquatic animals play an important role in ecosystems Aquatic animals are part of the food chain and help to maintain the balance in ecosystems.
Aquatic animals are important for recreation and entertainment People keep aquatic animals as pets, go hunting and fishing, and visit zoos and aquariums. Aquatic animals also play an important role in the cultures and traditions of many nations. For example, in Japan, the Koi Carp is a symbol of luck and prosperity.
We take water as a natural part of our environment and treat it only as a commodity. At the same time, the aquatic environment is the location in which life flourishes, whether it is a forest stream, a small pond or a huge ocean. We are accustomed to using this wealth only for our own benefit, but by our intervention, we are irreversibly destroying this environment.
Did you know... 80 % of plastic in the world's oceans enters the ocean via rivers and the coast? The remaining 20 % comes from marine sources, such as fishing nets, ropes and vessels.
Plastic Pollution It is estimated that about 8 million tons of plastic waste enter our oceans every year. At this rate, there will be more plastic than fish in the oceans by 2050. Plastic pollution has a direct impact on Nature. Plastic bags, fishing nets and other waste suffocate thousands of seabirds and sea turtles every year. Microplastics threaten fish and other species and also pose a risk to humans. An estimated 81 % of ocean plastic comes from Asian rivers. The Philippines alone contribute about one-third of the global total.
Did you know... the Great Pacific Garbage Patch (an area in the Pacific Ocean with a huge concentration of garbage) is 1.6 million square kilometers in size? This means it is 2x the size of Texas and 3x the size of France.
Ocean Dumping For several decades, the oceans have been regarded as a dumping ground for garbage, sewage, chemicals, industrial waste and other items not required by humans. Mining companies alone around the world dump 220 million tons of hazardous waste directly into the Earth's water bodies every year. About 2/3 of the world's marine animals are threatened by the chemicals we use every day, including household cleaners. Due to the fact that humans utilize aquatic animals as a food source (and in many cases the main source), they naturally threaten themselves secondarily.
Soil Erosion Trash in the sea is not only composed of trucks full of garbage. Pollution can also take the form of soil erosion. From agricultural areas, surface water carries soil that is mixed with phosphorus, nitrogen, carbon and minerals, posing a huge threat to marine life. A cocktail of these toxic chemicals causes algae blooms in the oceans and threatens fish, turtles, shrimp, – as well as humans, who are at the top of the food chain. Another effect is sediment deposition. This can accumulate, suffocating the seabed and killing creatures living in the mud.
Oil Pollution Oil spills, either during extraction or as a secondary effect of shipping, kill thousands of marine species. Oil destroys corals, has a toxic effect on the nervous system of animals and the insulation and water repellency of birds’ feathers. For example, more than 160 000 sea turtles alone died in the 2010 Deepwater Horizon disaster.
NOx and SOx Pollution Nitrogen oxides (NOx) and Sulfur oxides (SOx) are the two main pollutants found in shipping emissions. These affect the marine environment, as well as the ozone layer. According to recent studies, this type of air pollution from shipping is responsible for thousands of premature deaths each year.
Climate Change and Ocean Acidification The issue of ocean acidification is quickly becoming a threat to marine life and humans. Ocean acidification is the ongoing lowering of seawater pH, caused by the absorption of carbon dioxide (CO2) from the atmosphere. Ocean acidification has the potential to significantly threaten the lives of marine organisms, as well as the people who depend on fish and fish products for their daily sustenance. Studies have shown that reduced pH levels affect the behavior of several marine species, putting them at life-threatening risk.
Natural Disasters Natural disasters such as floods, droughts and storms can also have a negative impact on aquatic life. These events can destroy the aquatic environment and of course can also kill the animals themselves. For example, in 2011, the Tsunami in Japan killed up to 25 000 marine animals.
Noise Pollution Sources of shipping noise include everything from engine noise to cruise ship entertainment. Noise generated by shipping contributes to damage to the internal organs of animals that rely on their hearing as part of underwater orientation. Shipping alone has contributed to an estimated 32-fold increase in low-frequency noise along major shipping routes over the past 50 years, driving marine life away from vital breeding and feeding grounds. In addition, the use of sonar has been linked to the stranding of whales on beaches.
Overfishing Humans have always used the sea as a source of food. However, with better equipment, larger boats, and an increasing number of people, fishing has become excessive. For example, trawling can cause extensive damage to the seabed and the creatures that live there. Other species (known as bycatch) are also caught, which are then discarded. Almost 1/3 of the global fish population suffers from overfishing.
Invasive Species Invasive species are a threat to all ecosystems – including the marine system. Not all invasive species will spread or even survive, but if they do become established, they can be difficult or impossible to remove and can compete with native species.
Physical Damage to the Seabed Physical damage to the seabed is caused by ship anchors, trawl nets, fishing and mining. This damage disrupts the unique natural environment that is home to benthic organisms.
Water is not only important as a vital sustenance for humans and for irrigation of crops in the fields. Water is the only home for millions of animals who cannot survive without it. Moreover, water is also important for each of us. By protecting aquatic animals, we also protect ourselves.
Limit the Use of Plastics Plastics do not simply disappear from Nature after being thrown away. They stay with us for hundreds of years. They can pose a danger to wildlife and leach toxins into the environment as they gradually decompose. Stop using unnecessary single-use plastic products! Buy items with less packaging. Do not use single-use plastic items, such as straws, cups and cutlery. Try to use reusable cloth bags, instead of plastic shopping bags where possible.
Buy Fish and Seafood from Sustainable Fisheries Fishing significantly affects the aquatic ecosystems. And it doesn't matter if we are discussing fishing itself, the processing of the products or the subsequent transportation – each of these activities leaves its mark. Even though being vegan is the best option for the environment, you can still choose from the more sustainable methods if you eat fish. If you eat seafood, eat what has been caught sustainably, i.e. eating species that have healthy populations and the fishing of which minimizes bycatch. And if you can, use local resources. In this way, you minimize the carbon footprint that comes from transportation.
Clean Up! Don't look at the trash around you as someone else's problem. Even if you're not the cause of the mess, you can be part of the solution. Every bit of trash collected means that a little less waste gets into the environment and can mean one saved animal life. And it doesn't matter if you live right next to the beach or so far away that you haven't ever seen the sea. Because even waste hundreds of miles away from the shores of rivers and oceans can eventually end up in them.
Bear in Mind your Carbon Footprint Even small things can reduce the effects of climate change. Think about using resources that increase CO2 in the atmosphere. There are a few things you can do to get started today. You can turn off the lights and the TV when you are not in the room. You can replace light bulbs with more energy-efficient ones. You can leave the car in the garage if you can walk or cycle. You can think about how you travel. The less electricity or fuel you use, the less CO2 will enter the atmosphere and the slower will be the melting of the glaciers.
Don't buy Items that Abuse Aquatic Life There are items that we like to take with us as souvenirs from vacations or that we buy for pleasure. But some products contribute to damaging the marine ecosystem. These include coral products, turtle hair accessories and shark products. Before you buy something, try to think about how the item was made.
Educate Yourself The more you know about the amazing aquatic ecosystem, and the problems it faces, the more you will feel the need to protect it. Increased knowledge can broaden your horizons and find a way of getting involved in helping. More knowledge will also help you to inspire others in this good cause.
Support the Correct Laws There are still laws and rules that need to be changed or modified. Electing public officials who support the correct environmental policy can effectively help to protect aquatic life. Of course, this also helps terrestrial life and our own as well. When choosing your representatives, try to think about how they want to help Nature, and if they are interested in creating a better future. Alternatively, you can remind the already elected representatives what their election program was and what their voters really care about.
Spread your Knowledge Even though the world seems to be open to information, there is still a huge group of people who just don't get the connection. Become a “spokesperson” for the oceans and tell your friends and family what's really happening to the marine ecosystems. Sometimes it is enough to show your friends and acquaintances a different point of view to open their minds. Discuss the issue and be part of the solution together.
Support Organizations that Aid Aquatic Animals There are many institutions and organizations that fight for the protection of aquatic animals. These include volunteers tending forest streams and ponds, and people aiding sea turtles. Find an organization that protects your favorite animal species or works in an area you love, and support it. You can support them financially, or actively participate in their events as a volunteer.