In general, approximately 80% of litter found in the ocean and on beaches, collectively called marine debris, is from land-based sources, and 20% is ocean-based. This generally means fishing and shipping. Land-based sources of plastic pollution can make its way to our oceans through waterways, stormwater and drains connected to beaches or can be transported by wind, animals or careless individuals to the beach and dragged in with the rising tide. In isolated bays throughout Australia, like Gulf St. Vincent here in South Australia, much of the plastic is thought to be from local sources. However, coastlines exposed to open ocean can accumulate offshore sources through ocean currents. We are connected to all other oceans worldwide by many ocean currents, so some of the floating plastic could be coming from areas like Indonesia/South East Asia; although this is difficult to analyse and prove. Look at the KESAB interactives about ocean currents to find out more.
There are numerous reports each year of animals that are affected by plastic pollution in our oceans; primarily sea birds, turtles and marine mammals such as whales and dolphins. WWF estimates that globally, 100 000 marine mammals die as a result of plastic pollution every year. There would also be many other creatures affected, but larger, air-breathing animals who may travel near the coast allow us to more easily observe the impacts. Injury or death due to plastic pollution are a result of either ingestion or entanglement; both of which can block airways and cause choking. Entanglement can cause infection at wound sites, blood loss or loss of appendages, or the inability to move around and feed when the entanglement becomes severe. Pollution commonly causing entanglement include discarded fishing nets, fishing line, and plastic bags.
Ingestion of plastic by marine animals can cause a wide variety of issues. Stomach acids and digestive tracts are not able to break down the polymers in most plastics and given that harder plastics can take up to 500 years to break up when exposed to sunlight, these plastics will remain in the gut of animals that ingest them indefinitely. This causes false feelings of satiation or feeling full, which leads to decrease in body fat stores and ultimately starvation. Larger plastics can also block or obstruct parts of the digestive tract. Another negative impact of consumption of plastics is the leaching of toxic chemicals into the digestive fluids and the tissues of the animals, some of which are known endocrine disruptors and neurotoxins (e.g. PCBs), and so can also alter the behaviour of some animals. Oceanic plastics also have the opportunity to pick up additional water-borne pollutants which wash into the waters as a result of human activity. These include heavy metals, polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs). All of these can easily adhere to the surface of debris in the ocean and will enter into the food chain when the plastic is ingested. The contaminants can build up over time through bioaccumulation, or can be concentrated in higher order animals such as whales and dolphins due to biomagnification. The chemicals or heavy metals cannot be processed and pass from one animal to another as it is eaten. For example, small crustaceans eat microplastics, many of these are eaten by fish, many of these are eaten by seals and many of these are eaten by toothed whales. This causes a large accumulation of plastics and associated toxins.
A 2015 study by Australian and British scientists determined that 90% of sea birds living today have ingested some form of plastic. If the trend continues, 99% of sea birds will have plastic in their guts by 2050. Luckily, on our marine trails on Henley Beach, we have never encountered an injured or dead animal as an obvious result of plastic pollution.
We actually don’t have coral reefs in South Australian oceans. South Australia has temperate marine habitats, as opposed to tropical marine habitats in Queensland, Northern Territory and Western Australia where coral reefs are found. Temperate waters are cooler and more nutrient rich than tropical marine waters. Coral reefs generally form only when winter water temperatures exceed 18 degrees Celsius and light levels are high. South Australia’s cooler and nutrient rich waters mean that only three species of hard corals occur here. So, while some hard and soft corals can be found in SA, they are not common or and cannot built up enough to form reefs. We are lucky enough to have seaweed reefs, rocky reefs and shellfish reefs here in SA which create shelter, food and habitat for many marine creatures just as coral reefs do in tropical habitats. This network of rocky reefs is known as the Great Southern Reef.
Coral reefs that make up the Great Barrier Reef in Queensland or the Ningaloo Reef in Western Australia are amongst the reefs worldwide that are threatened by a number of human impacts which work together to cause coral bleaching and the loss of coral reefs.
Ocean warming: Increases in global sea surface temperatures over long periods as a result of climate change causes the tiny algae present in coral tissue to be expelled, disrupting the relationship between the algae and the coral polyp which allows coral reefs to survive. These single-celled algae called zooxanthellae are photosynthetic, and so convert light energy from the sun into chemical energy, which is used by the host coral. This reaction is what causes coral bleaching, as the algae will give the coral polyps their various colours. Coral bleaching may be intensified with changes in salinity and increases in water pollution. If these stressors occur for an extended period of time, the algae do not return to the coral polyps and the coral dies. High stress also means the coral is less likely to survive wave erosion, predators and disease.
Ocean acidification: Another impact of climate change is the absorption of carbon dioxide from the atmosphere by the ocean. Increased dissolved CO2 in the water locks up carbonates and creates carbonic acid. This not only makes the ocean more acidic, but also takes away carbonate and other minerals needed by corals and shell-forming animals to build their skeletons and shells. This means corals won’t have the building blocks needed to build reef, and will have weaker skeletons, making them more vulnerable to predators or wave action in extreme storms.
Run-off pollution and sedimentation: The algae in coral polyp tissues need sunlight to create chemical energy. If the water is too nutrient-rich or polluted, this can cause cloudy or less clear water, and prevent the zooxanthellae from accessing as much sunlight. Excess nutrients or chemicals can enter our oceans through rivers or stormwater drains that empty into the sea. This water can contain animal poo, leaves and lawn clippings, or pesticide, herbicide and fertilisers from farms. Sedimentation caused by land or coastal erosion can also bury or smother these sessile (not moving) animals. This is made worse when forests are cut down on the land to make room for farms, and the soil washes away down rivers into our oceans. Plumes of sediment can also be caused by dredging to clear shipping channels and harbours.
Overfishing: Herbivorous fish species are important in coral reef ecosystems as they eat the algae that grows on coral structures. Some of these species have been observed to disappear from the ecosystem due to overfishing; taking too many fish or fish that are too small, so that the population does not have the chance to recover. Weedy algae will then overgrow and smother corals, shielding the zooxanthellae from any light and causing the coral to die. Overfishing of any species causes a shift in the balance of an ecosystem. It disturbs food chains and causes many flow-on effects for not only other animals, but also plants and the habitat itself. For example, it is thought that overfishing of a sea snail, the giant triton, on the Great Barrier Reef could have been part of the cause for Crown of Thorn starfish outbreaks. These snails are natural predators of the starfish, but with a decline in their population, the starfish population is able to rapidly increase.
Marine parks have been implemented globally to preserve and look after pristine marine habitats both onshore and offshore. These act similarly to national parks on land and establish a set of rules and guidelines regarding the types of activities allowed or banned in the area. This includes fishing, trawling, building structures, snorkelling, diving and mining. These marine park areas have been established in Western Australia, Northern Territory and Queensland in order to protect our very valuable coral reefs which are under threat. They also occur in other important areas around Australia's coastline to preserve a wide variety of marine habitats and ecosystems.
A map showing Commonwealth Marine Reserves around Australia
It is also important to protect habitats adjacent or connected to coral reef ecosystems. Seagrass beds that often grow in the shallow, sunlit waters near coral reefs stabilise the sand, resulting in clear water that corals need to survive. Mangrove forests which grow on the fringe of the coasts and along rivers leading to the ocean provide nursery habitats for many fish that live on coral reefs as adults. Some of these important species wouldn’t be able to thrive without the shelter and protection of mangrove roots as babies.
Crown of Thorn starfish outbreaks have been managed by culling programs on the Great Barrier Reef, using injections to kill the starfish that eats vulnerable corals.
There is also emerging work regarding the research and ‘planting’ of hardy and adaptable coral species which may be more likely to survive as the climate changes.
Shelter and habitat for many marine animals: Coral reefs occupy 0.1% of the area of the ocean but they support 25% of all marine species on the planet because of their complex physical structures.
Benefits for fishing and industry: Many people globally rely on fish for their main source of protein in food, or as their main source of income. Many fish and invertebrate species that spend all or part of their life on a coral reef are important for fisheries. Some examples in Australia include coral trout and red emperor.
Protection of coastlines from storms: Coral reefs protect shorelines by absorbing constant wave energy from the ocean, and therefore protect people living near the coast from increased storm damage, erosion of beaches and flooding.
Tourism: Many coastal communities rely on tourism income from people visiting coral reefs in the area. The popularity of reefs and the sandy beaches that accompany them also create jobs for coastal communities, in Australia and worldwide. The Great Barrier Reef supports an estimated 64,000 jobs. In 2017, Deloitte Access Economics in conjunction with the Great Barrier Reef Foundation estimated that the total economic, environmental and icon asset value of the reef is $56 billion and contributes over $6 billion to Australia’s economy every year.
In order to save coral reefs, we should move to renewable energy sources to reduce our greenhouse gas emissions and slow the changing climate. This will reduce the number of high sea surface temperature days, as well as slow ocean acidification and increased storm damage. We need to ensure that recreational and commercial fishing are done responsibly and sustainably so that we don’t upset the balance of the ecosystem. We also need well managed land practices that can reduce the pollution of waters from run-off including controlled fertiliser, pesticide and herbicide use. The more we understand our reef systems and the threats that they face, the better prepared we are to look after them so that future generations can enjoy them. It is important to understand we are all connected to the ocean, no matter how far away we are, so everyday actions like energy use and reducing our waste can have helpful positive impacts for our marine life.
Sharks are top predators in many marine ecosystems. Some sharks are bottom feeders which prey on invertebrates on the ocean floor, while others are scavengers or hunters, feeding on herbivorous fishes, mammals or reptiles. These species help to keep the balance of living organisms in check in a coral reef ecosystem, as well as protecting other creatures from disease, bacteria and pathogens by eating the carcasses of dead animals. Generally, the loss of top predators in an ecosystem will cause trophic cascades, changing the abundance and roles of prey species below then in the food chain, and altering ecosystem functioning. However, studies in comparison of trophic structure between protected and fished sites show that loss of reef sharks usually coincides with fishing of herbivorous fishes or mesopredators (middle level predators). Mesopredatory sharks and other fish predators often have functional overlap, in that the loss of reef sharks will not result in a trophic cascade as their prey will be eaten by other animals. This is due to the biodiversity and complexity of interactions found in coral reef ecosystems.
The effect of shark loss will depend on the strength of association with coral reef ecosystems, whether they migrate between pelagic, coastal and reef habitats, or are strongly reef dependent. Sharks can also apply ‘fear’ effects that disrupt the foraging of potential prey and the modification of behaviours in other sharks or fishes. Reef shark loss may also have alternate impacts if the coral reef ecosystem is also under pressure from additional human impacts such as coastal sedimentation, nutrient runoff, invasive species, warming ocean temperatures or ocean acidification.
Around a quarter of all marine fish species rely in some way on coral reef ecosystems during their life cycle. Many of these species are important in commercial, recreational and subsistence fisheries, feeding millions of people worldwide. Aside from apex predators keeping prey species in check, other roles of sharks on coral reefs include nutrient cycling among nearby habitats, scavenging, habitat disturbance allowing for diversity of coral structure and the removal of invasive species. Coral reefs emerged around 45 million years ago, and sharks have since evolved and adapted to the prey and habitat diversity associated with these ecosystems. Consequently, reefs provide many shark species with food sources, nursery habitats for their young, safety from predation and parasite removal.
Biodiversity means the range of different living things that occur together in an environment and the balance of these living things; plants, animals and bacteria. Biodiversity in an ecosystem stems from the occupation of various ecological niches by these living organisms. An ecological niche is the space and role a living thing can fulfill as part of the wider ecosystem, which includes relationships with other plants and animals. Without balance, these ecosystems lose some of these relationships and functions, and an imbalanced ecosystem becomes degraded. This in turn could have an impact on other relationships to our world such as regulated climate, weather, oxygen production, food production, nutrient recycling and water quality.
It is estimated that around 80% of our oceans are still unmapped and 90% of marine species are yet to be classified. So, while there are around 225 000 described marine species that make up its biodiversity, there could be many more.
Marine ecosystems are any aquatic ecosystem with high salt content in water. These ecosystems are characterised by their biological and physical components which form habitats and their living community.
These marine ecosystems can include those classified by the type of plant or vegetation that make up the habitat, such as kelp forests, seagrass meadows, mangrove forests and seaweed reefs. They can also be made of colonies of animals such as coral reefs or sponge gardens.
Other marine ecosystems are characterised by their physical features and their location in the ocean environment, such as seafloor habitats, open ocean, deep ocean, hydrothermal vents, rocky reefs, intertidal reefs, sandy shores, rock pools and mudflats.
It is important to realise that all of these different marine ecosystems are connected, and some marine animals move and migrate between different ecosystems and habitats.
All food chains in any ecosystem rely on the capture of the sun’s energy by photosynthesising plants, which are then eaten by animals. Therefore, the richness and diversity of plant life is essential to the living animals of any marine ecosystem. This includes phytoplankton; tiny floating algae that create up to 70% of the oxygen on earth. Other marine plants include seaweed or macroalgae, seagrass and mangrove trees.
There are three levels of biodiversity that are also important in sustaining ecosystems; genetic diversity within a species, species diversity between species and ecosystem diversity between ecosystems. Each of these contributes to the health and longevity of an ecosystem by allowing species to survive and adapt to changes in their environment (genetic) and allowing complex relationships between species to occur (species and ecosystem) so that the transfer of nutrients, energy and water flows throughout our environment.
The ocean covers 70% of the Earth’s surface and provides us with 50-70% of the world’s oxygen. We need the ocean to survive. However, with advances in industry and technology, humans have increasingly exploited and over-utilised resources from our oceans, as well as negatively impacted habitats and the plants and animals that call them home.
Overfishing: This occurs when there are more animals being taken from the ocean than the population can replace, and the fishery is not given a chance to recover. This can change the behaviours of marine animals whose food source has been depleted or taken away, forcing them to forage or hunt for food in different areas, change migration patterns or for some of these animals to become more vulnerable to malnourishment. This can have cascading effects in food webs and food chains.
Pollution: Chemical or effluent pollution discharged into waterways and oceans have the potential to change behaviour by increasing chances of reproductive abnormalities. Some of these compounds are known as endocrine disrupting chemicals, which if absorbed or ingested by animals can overstimulate systems by mimicking naturally occurring hormones. This could alter interactions between animals or feeding or breeding behaviours. Marine debris such as fishing nets and other plastics could entangle animals which changes their swimming behaviours.
Climate Change: A rapid and dramatic increase in the emissions of carbon dioxide and other greenhouse gases by humans is causing climate change, which affects both land and ocean habitats. In the ocean, climate change leads to increase in ocean temperatures, and ocean acidification caused by the absorption of carbon dioxide by the oceans. This can alter fish and other animals’ migration patterns as well as changing the behaviours of snails and other molluscs by not allowing them to build strong shells. This can make them more vulnerable to predation. Increasing ocean temperatures means that coral reefs are losing their symbiotic algae that grows within coral cells, and bleaching. This causes animals to change reproductive, feeding and swimming behaviours when their habitats are lost.
Invasive species: As shipping and travel across oceans increases, animals and plants are being transported across wide oceans to other countries, increasing the number of invasive, non-native species in many marine habitats. This can mean animals are now interacting with other plants and animals they do not usually live with, and can compete for food, shelter, spread disease or even prey on these native species. This can severely change the behaviours and survival of native marine species. For example: the Asian Paddle Crab, the European Fan Worm or the Northern Pacific Sea Star in Australia.
Lost at Sea: the story of a baby fish: https://www.youtube.com/watch?v=g3cIr9RomPM
We can do a lot at home or school to try and reduce carbon emissions that threaten the health of our marine ecosystems. If you can walk or ride to school, try doing this once a week, or even every day. Host a safe walk, ride or scoot to school week at your school and see if people enjoy it and choose to change from using a car. You can also do an electricity audit of your school and see how much power is used. Check if lights are being left on, and if air conditioners and heaters are at the right temperature to be energy efficient. See if your school can get a grant from the government to get solar panels if you haven’t got them already, and you can get your own power from the sunlight.
Use the climate clever website to see what actions you could take at your school. https://www.climateclever.org/
Many of the world’s fisheries are currently fully exploited or over exploited, which means that fish are being taken out of the oceans faster than the remaining breeding population can replace. This leads to the collapse of fisheries production; which is bad news for the approximately 40% of the world’s population that relies on fish for protein. The technologies now used in fisheries, paired with the high demand in developed countries importing fish from developing countries, means that we are quickly depleting our oceans and not allowing populations to recover. For countries with alternate sources of protein, fish as a food source could become more expensive, and it is likely that people with fish as a staple in their diets in developing countries will suffer the consequences of fewer fish or exerting more effort for catch. Paired with other human impacts such as climate change, habitat destruction and pollution, many fish populations could be at high risk of collapse. The omega 3s in some fish which many people are eating fish for, are obtained by the fish by eating seaweed or algae, and we can get so many more omega 3s by eating the seaweed directly.
There have already been range shifts for many marine species, which means as the average ocean temperature rises, even by a few degrees, different species will change their geographic distribution to keep in line with their preferred and tolerated temperature. This can mean encounters of species that usually don’t live side by side, and more competition for space or food. This shift is usually from the equator to the poles, with some tropical fish in Australia shifting their range down towards Sydney. This means that we may observe different behaviours and interactions between migrating animals as new species move into the areas they migrate to. We may also observe migrations further poleward, toward the north or south pole, if migrating animals and their food sources shift their range due to higher ocean temperatures.
Natural changes generally occur over a long time period, and through the fossil record we can observe changes to species through evolution to adapt to changes in environment, weather and habitat. The changes we experience and will experience with climate change however are occurring much, much faster, with species unable to adapt. We are already beginning to see an increase in some species with short life cycles which are able to cope with the increasing changes happening to temperatures and other stressors. In the ocean, this is jellyfish and cephalopods; octopus, squid and cuttle and a decrease in the diversity of marine animal and plant species.
Our oceans absorb around 30% of the carbon dioxide in our atmosphere, and carbon dioxide has increased by 40% in the last 200 years due to the industrial revolution and the burning of fossil fuels. Ocean acidification is the increasing acidity of sea water caused by dissolved carbon dioxide absorption by the ocean. Carbon dioxide binds with sea water to become carbonic acid, changing the water chemistry of our oceans. The ocean is not becoming an ‘acid’ as we would know it, like lemon juice or vinegar, but slowly lowering in pH to its current level of 8.1, which is 0.1 units in the last 200 years. This may not sound like much, but the pH scale is logarithmic, which means a shift of 0.1 pH units is a 30% increase in acidity. If today’s global CO2 emission trends continue, scientists estimate that by the end of this century, oceans will be more acidic than they have been for more than 20 million years.
Image source: https://www.britannica.com/science/ocean-acidification
In order to build shells and skeletons, marine animals such as snails, clams, corals and crustaceans extract calcium and carbonate from seawater, combining them into solid crystals of calcium carbonate that are used to make shells.
As carbonic acid is formed with the absorption of dissolved carbon dioxide, excess hydrogen ions are created. These hydrogen ions bind with carbonate, making it less available in seawater for marine organisms to build and maintain their shells, and must spend more energy getting rid of excess hydrogen ions. This may result in weaker shelled animals who are less able to thrive, and ultimately a decline in their population.
This could be larger animals such as crabs and shellfish, which may cause an imbalance in the ecosystems food web and create a domino effect towards the populations of other living organisms within that ecosystem. It is also already showing signs of affecting smaller animals such as pteropods, small sea snails which form the base of many marine food chains and food webs in Antarctic ecosystems
If the oceans continue to become more acidic, it may even begin to dissolve the already built shells and skeletons on some marine animals More acidic oceans have also been shown to affect the behaviours of some fish species, including recognising predators or finding suitable habitats.