ALGAL BLOOMS, NUTRIENT OVERLOAD, TEMPERATURE ANOMALIES & FISH KILLS

Ironically, the same phytoplankton that helps keep all oxygen-dependent animal and plant life alive on Earth are also the component of algal blooms that are responsible for depletion of marine plant growth and massive fish kills when conditions upset the normal balance of chemistry, temperature and light in inland waters, estuaries, coastal waters and the open ocean. Algal blooms in inland, estuarine and shallower coastal waters are usually caused by eutrophication, or nutrient pollution due to excess nitrogen and/or phosphorus in the waterway. As the algae blooms grow, less light is able to penetrate the water, and aquatic plant life such as seagrass beds starts to decay and die. The decaying process uses up dissolved oxygen in the water which, in turn, can cause massive fish kills. The oxygen levels in the deeper ocean sections are further diminished as decaying flora and fauna sink and degrade in the depths.

Nutrient pollution in the ocean can be traced back to many sources. Human sewerage, animal waste, farm fertilisers, garden sprays and fertilisers, hydrocarbons from fossil fuels, pesticides, and a variety of nutrients and chemicals in urban water runoff and wastewater treatment plants all contribute extra nutrients (among other things) to the waterways and eventually the deep ocean.

Ocean surface temperatures are rising four times faster than forty years ago⁵. For 450 days between April 2023 and July 2024, average sea surface temperatures were higher than anything seen before. The cause of this temperature anomaly that is a real threat to the whole marine ecology system is climate change driven by the burning of fossil fuel. The level of carbon dioxide, the main greenhouse gas, has doubled in 200 years. As carbon dioxide levels increase the atmosphere acts as an insulator, not allowing heat to be dispersed to the outer atmosphere. This heat is absorbed by the ocean and as resilient as the Earth’s oceans have been until now, it is really a question of how much more heat the ocean can absorb from the atmosphere before tipping point is reached and reparation is beyond our ability.

CO₂ AND THE ACIDIFICATION OF EARTH’S OCEANS

The environment is resilient and capable of change, or evolution, much like many different organisms on Earth, provided change is not too rapid. Both the physical environment and ecology systems have adapted to changes in the past history of Earth. For instance, “ice ages” on Earth have a history of at least one million years, during which time Earth has cooled and warmed through periods of glacial and inter-glacial activity in cycles of approximately 100,000 years. The interglacial, or warm periods have lasted about 20,000 years on average, and the colder periods for up to 80,000 years – the time periods are quite variable. These periods of very different climatic conditions evolved over extremely long periods of time allowing adaption by plants and other living organisms.

Through the study of cores of ancient Arctic ice and trapped air bubbles within, scientists have been able to ascertain that for the past million years, variation of the amount of sunlight reaching the Northern Hemisphere in summer have triggered past glacial and interglacial periods. As Earth warms, ice and snow melt thereby reducing the amount of sunlight that is reflected; water vapour in the atmosphere increases enhancing the development of greenhouse gases; permafrost thaws and releases stored, dissolved carbon dioxide; and warming oceans release instead of storing carbon dioxide. Before anthropocene interference, there was balance, ensuring adaption by a large part of the biosphere, between a slowly changing climate and the environment and ecological systems within, as global temperatures warmed and cooled by as much as 3°C to 8°C. The geologic era we are now in is named by many the “Anthropocene” era with a volatile climate like nothing our ancestors have seen before – it is an era being fashioned by humans.

It is the balance between release and absorption of carbon as carbon dioxide that is of paramount importance in maintaining a healthy biosphere. The diagram (figure 1) shows the levels of atmospheric carbon dioxide in parts per million (ppm) over a period from about 800,000 years ago until recently (approximately 1990). The carbon dioxide peaks and troughs represent the glacial and interglacial periods as described above, and until the late late 18th century the level of carbon dioxide peaks and troughs were of similar values. Between 170ppm and 300ppm. Since the start of the Industrial Revolution, which started gathering momentum in the mid 19th century, the amount of atmospheric carbon dioxide has surpassed and maintained a level not seen for millennia.²⁶

As of 27th May 2025, Earth’s CO₂ reports a daily average of 430.43 ppm at the Mauna Loa Observatory, a new record high!

The incessant rise of CO2 adds to greenhouse gas levels and this has had evident effects on global temperatures with an estimated rise so far of at least 1.5°C since about 1950; and on climate and atmosphere as the weather patterns have changed and become more volatile, with catastrophic weather events being reported regularly. The effects on oceans are more subtle, but at least as perilous, if not more so, than the atmospheric effects.

Of the increased carbon dioxide generated by human activities, about 25% is absorbed in the ocean. The increased CO2 absorption is on top of the what would have been a balanced, normal pre-industrial level of CO2 in the ocean. When carbon dioxide dissolves into seawater they combine to form carbonic acid (H2CO3), a weak acid that dissociates into hydrogen ions (H+) and bicarbonate ions (HCO3-). As the pH scale is an inverse of hydrogen ion concentration, the extra hydrogen ions creates higher acidity and lower pH, making the ocean less hospitable to marine life as acidic waters dissolve calcium carbonate²⁷. This acid effect is happening in all seas and on coral reefs around the world, including Australia’s Great Barrier Reef. Coral is after all primarily calcium carbonate, as are all hard shelled marine organisms. Again, there is ecologic trauma as important links in the marine food chain are compromised.

More than 90% of the excess heat due to anthropocentric causes is stored in the ocean accounting for the largest rise in ocean temperatures over the past twenty years than at any other time since records were kept. Increasing carbon dioxide absorption and content in the ocean results in a warmer ocean. Warmer oceans are able to hold less oxygen and resulting decline in biodiversity, the increase of algal blooms and ocean ‘dead zones’. Warmer ocean water exacerbates coral bleaching when stressed coral expels the symbiotic algae that provides the coral with energy through photosynthesis.²⁸

PLASTIC, MICROPLASTIC & NANOPLASTIC OCEAN POLLUTION

An unmistakable sign of abuse of our oceans are the mountains of human-made detritus deposited in the world’s oceans. Predominant among this waste is plastic.

Over 450 million tonnes of plastic are produced each year worldwide⁶. More than 20 million tonnes of plastic waste pollution enters the environment each year, 11 million tonnes of that plastic pollution is discarded into the ocean each year, and the amount is rising rapidly as the demand for plastic increases. To store the 9.5+ billion tonnes of plastic produced so far it would require an area of approximately 2000 square kilometres 25 metres deep – about the surface area of London 25 metres deep!⁷.

Estimates by Marcus Eriksen et a¹⁶ suggest that there are as many as 358 trillion microplastic particles floating on the surface of the world’s oceans, and that is less than 10% of the estimates for the total number of microplastic particles in the deeper ocean worldwide – a staggering number!

The impact of plastic pollution waste on the environment begins with fossil fuel extraction as all plastic is made from hydrocarbons. Environmental impacts of plastic on the oceans and waterways include:

• More than 1 in 3 fish caught for human consumption now contains plastic.
• 80% of all studies marine pollution is plastic (ICUN, 2021).
• The 11 million tonnes of plastic discarded in the ocean each year is equivalent to 2,000 garbage trucks dumping full loads of plastic into the world’s waterways every year (UNEP, 2025).
• There could be more plastic than fish in the sea by 2050 (EMF, 2016).
• The level of microplastic is at the bottom of food chain and works its way up, accumulating in higher quantities and increasing toxicity.⁹
• Only 9% of the plastic ever produced has been recycled.

An obvious threat to both human and marine life from plastic ocean pollution is the Great Pacific Garbage Patch, also known as the Pacific trash vortex. This patch is a country-sized wasteland of collection of swirling marine debris that by recent estimates is over 1.5 million square kilometres in size – that’s about three times the size of France! A gyre, or series of slowly rotating ocean currents, in the North Pacific collect and retain discarded waste, most of which is plastic pollution¹⁰. Oceanographer and sailor Charles Moore who first discovered and described the Great Pacific Garbage Patch estimates that without remediation the patch will double over the next ten years. There are also two other gyres in the Atlantic Ocean and one in the Indian Ocean.

The most apparent and immediate damage from oceanic plastic pollution is the threat to marine fauna and flora. The likelihood of extinctions of both plant and animal life is heightened as plastic pollution blocks the life-giving light needed by many plants; marine organisms from the smallest plankton to enormous blue whales ingest plastic, mistaking it for food; dolphins, sharks whales and fish get tangled in discarded ropes and nets from fishing vessels. The plastic in the ocean can take between 500 to 1000 years to degrade and even then it only degrades to microplastic¹¹, which are plastic pieces less than 5 millimetres in size, or to the more insidious nanoplastic, the mostly invisible plastic particles les than 1 micron in size.

As plastics degrade, they release a variety of chemicals, including styrene monomers, oligomers of styrene, and various additives like the ubiquitous BPA – Bisphenol A. These chemicals are all of concern and are known to have adverse environmental and health impacts including some being known carcinogens^12,13. The many beneficial uses of plastic and the fact that it is widespread throughout the world would suggest plastic production cannot be stopped or banned, however, single use plastic should be outlawed worldwide. Part of a solution would be to instigate rules for more ethical uses of plastic and more time and money spent to find safer, cleaner, degradable plastic with new technologies.

DEEP OCEAN MINING – A BRIDGE TOO FAR?

The world’s deep oceans are largely unexplored., with just 21% of the seabed mapped at high resolution. While we know how far away the moon and Mars are, and their different geology and general environment, we don’t yet know with any certainty the exact depth of some of our deep oceans, and two thirds of life on the seabed is unknown to science and most species are undescribed¹⁴. Most of the known and described marine species are in the upper water layers, or waters that overlie the deep ocean waters.

The difficulties associated with gaining more knowledge and understanding of the deep ocean environment are the vast area of ocean, the depth of the ocean and the related extreme pressure, and the lack of any natural light below about 200 metres deep. Perhaps more resources should be used to acquire that knowledge here on Earth before we start trying to colonise the moon or planets.

The science community is aware of the importance of the ocean in regulating Earth’s climate. As described earlier in this essay, the phytoplankton floating on or near the ocean surface is vitally important in generating oxygen and as part of the process to absorb carbon dioxide. What we can only surmise, is how important, or even critical, are the millions of different and as yet undiscovered deep sea organisms playing a role in ecological balance. Until the significance of the deep ocean environment is better understood, it would seem reasonable to curtail any potentially damaging deep sea ocean development activities until independent environmental impact studies (IES) are carried out. Decisions in this regard are in the hands of International Seabed Authority (ISA).

Jurisdiction over oceans is complex, and governance difficult. It is defined through international law under the United Nations Convention on the Law of the Sea. Each world coastal state may have a territorial right over the sea for 12 nautical miles, which is the Territorial Sea. The rights of a state under the their territorial sea area includes sovereignty over sea, airspace, seabed and subsoil. Some states are also permitted a Contiguous Zone extending up to 24 nautical miles and allowing for control over fiscal, customs, sanitary and immigration matters. Beyond the Territorial Sea of 12 nautical miles, each state is able to claim an Exclusive Economic Zone for up to 200 nautical miles, within which that state has exclusive rights for the exploitation of natural resources, but not over navigation and overflights. Outside of these defined zones are the high seas open to all states for most purposes.

The high seas accounts for two-thirds (64%) of the Earth’s oceans, which is 43% of Earth’s surface that is not owned or regulated by any country. The Jamaican-based International Seabed Authority (ISA) is the intergovernmental body established in 1994 to regulate the seabed beyond national jurisdiction. The ISA has 167 member states and the European Union and is funded by contributions from any State, contractor. international organisation, academic and scientific institution, private corporation, philanthropic entity or private individual, which would obviously give the ISA a broad range of interests to consider. The ISA has been criticised from both sides of the deep sea mining debate – scientists and environmentalists say the ISA is too mining oriented, and the miners say the ISA has been too slow in formulating the rules and regulations to govern deep sea mining. However, the primary function of the ISA should be to ensure the environmental integrity of their area of purview.

In their zeal to satisfy the ever-growing appetite for rare and critical minerals, and the competition for land-based deposits, mining companies have turned to deep ocean exploration and extraction of these minerals. A long-term, historical interest in the exploitation of deep sea minerals is today becoming a reality as the methods of extraction of the material is made possible. Deep sea mining is described as the process of mining the seabed at depths over 200 metres. The minerals being sought by the miners are copper, cobalt, nickel, zinc, silver, gold and some of the rare earth elements and critical minerals in demand for renewable technology development. These minerals are within slow-forming potato-sized poly-metallic “nodules,” as well as in poly-metallic sulphides and metal-rich crusts on underwater mountains¹⁶.

A conflict between environmental, geopolitical and mining interests in the deep sea has been brewing for some years, and is about to come to a head as the ISA is due to release findings of deliberations into the regulation of deep sea mining in July 2025. Some high-profile miners have applications for mining licences pending and are impatient for the ecosystem protection regulations to be approved so they can commence mining. The ISA is dealing with an extremely complex matter and should be allowed to complete all investigations without the commercial and also some political pressure being put on them for a decision. “The potential consequences for marine ecosystems demand rigorous scientific scrutiny,” Luisa Araúz, Panama’s representative, told delegates attending a recent two-week gathering of the ISA Council, the organisation’s policy-making body. “The abyss has waited millions of years and it can wait for us to get this right.”¹⁷

There is political pressure coming from both China and US, with Trumps ‘transactional’ White House getting ready to reap the rewards from selling the rights to offshore mining, and China ready to start testing deep sea mining technology this year, with or without regulation approval from ISA. For the marine ecosystem, and probably for the benefit of all sea and land-based life, it is unfortunate that when Trump publicly defies the long-standing rules and conventions for the deep ocean, avaricious mining company boards become emboldened to push harder for their profits regardless of environmental consequences.

The probability of terminal damage and long-term disturbance to the deep ocean bio-system is enormous. Some of the affects will be the alteration and destruction of deep-sea habitats, in particular the removal of scarce hard surface areas that some marine creatures such as sponges and sea anemones anchor to; particle, noise and light pollution; and perhaps the affect causing the most widespread damage, sediment plumes. The sediment plumes are clouds of fine sediment stirred up by the abrasive mining techniques on the sea floor, as well as the sediment from the discharge of water from the mining ship on the surface. The suspended sediment particles can be dispersed over hundreds of kilometres in the underwater currents smother filter feeding animals by clogging the filtering organs. When the particles float back to the sea floor they smother animal and plant habitats. A scientific paper by marine biogeochemist, Matthias Harckel et el gives comprehensive descriptions of consequences of sediment plume on the marine environment¹⁸.

The overwhelming evidence suggests that deep ocean mining under currently available extraction methods is definitely a step too far. Whether this evidence will be enough to delay or suspend planned deep sea mining operations is in doubt, especially with the combined efforts of transactional and profit-seeking mining companies and climate change denying politicians in the US and elsewhere pushing the mining barrow.

WHO WILL CATCH THE LAST FISH?
The inconvenient truth about fish and fishing

In 1885, the Canadian Ministry of Agriculture said it was not only impossible to exhaust the cod supply, but even to make a noticeable dent in it. “Unless the order of nature is overthrown, for centuries to come our fisheries will continue to be fertile,” the ministry declared. What the ministry did not know was that within 100 years the “inexhaustible” supply of Atlantic cod would be reduced to almost nothing, and the reason was simple, over fishing.

Since the Middle Ages cod had been a staple in the diet Vikings, Basques, English, Spanish and Portuguese. Cod were large, easy to catch and plentiful, because it released millions of eggs when it spawned. During the 19th century fishing methods became more efficient with long-lining with lines up to five miles long with hooks every three feet. Next came the steam trawlers that were able to haul six times the number of fish a sailing ship could manage. By the middle of the 20th century, fishing methods were almost completely industrialised with the introduction of freezers on ships over 100 metres long, capable of holding over 3,500 tonnes of fish. Between 1959 and 1968, cod landings in Newfoundland increased from 330,000 tonnes to 730,000 tonnes as the rapacious trawler fleets netted more and more of the cod population, including the juvenile fish that had not even had a chance to breed. By 1992 the Atlantic cod biomass dropped 93% and has never recovered. The cod boom was over and the species was near to extinct²⁰.

Fish harvests increased from 3 million tons in 1900 to 20 million in 1950 to a peak of 85 million tons in the 1980s. The world fish catch has been declining by millions of tons a year since 1988. In addition to targeted fish, fishing boats also catch large amounts of unwanted fish (by-catch). Some estimated that up to 25 percent of all fish caught are by-catch. Each year between 20 to 40 million tons of mostly dead fish are thrown back in. (Paul Greenberg – National Geographic)

Despite the lessons that should have been heeded from the collapse of cod fishing, the voracious appetite for fish and the sophistication of fishing methods with mostly privatised fishing fleets has moved on unabated. As one target species declines, the sights of the fishing industry turn to the next easy target in our fast-emptying oceans. A study from Dalhousie University, Nova Scotia led by Dr Boris Worm published in Science Magazine in 2006 concluded the world’s oceans could virtually be emptied of fish by 2048, which is now only 23 years away!

Fishing fleets exploit waters in the most remote corners of the world depleting fish stocks that are already on the brink of collapse. There are estimates that 90% of stocks of large predatory fish, such as sharks, tuna, marlin and swordfish, are gone already. This loss is enough to cause severe ecological imbalances that will in turn have devastating socioeconomic impacts on those communities dependent on a balanced, healthy marine environment²¹.

Solutions to the over-fishing crisis need to be found immediately so the very real prospect of a tipping point being reached does not happen. Recovery of fish stocks and the vast ocean ecology reliant on a healthy balance will not be possible if a tipping point is reached. Some measures that could help in avoiding a complete collapse are, the imposition of quotas; the restriction of fishing boat numbers; strict limits on fish catches of each species; fish can only be sold if harvested from sustainable sources; removal of some of the more intricate electronic methods of tracking fish; market prices should reflect the true value of the fish; and the compulsory establishment of protected marine reserves in all marine jurisdiction zones.

AQUACULTURE IS NOT THE ANSWER
If aquaculture, or fish farming, was a solution to over-fished oceans it would be wonderful. However, other than providing some relief from the pressure to supply wild-caught ocean fish, aquaculture still presents too many problems to be considered environmentally sustainable. Proponents of aquaculture invariably resort to the economic benefits and the steady improvement in environmental issues faced by aquaculture, yet there are a number of issues that have not, and will never be resolved. For example, antibiotic use in aquaculture is apparently declining, being replaced by “safe and effective” vaccinations – wild fish don’t need vaccinating; farmed fish feed on either smaller caught fish, such as anchovies, or human-processed food – one method is unsustainable, and the other unhealthy and unnatural. Why when there is an increasing shortage of wild fish are we feeding caught wild fish to farmed fish?²²

Two other contentious effects from aquaculture are; the build up of effluent and nutrients in the fish farm environment that inevitably escapes to the open ocean as a pollutant and cuts down light penetration and visibility as well as coating the seabed with a mucky, soft coating of effluent; and the other effect is the threat to the wild fish population from fish escaping the fish farms, which is a fairly common occurrence. Escaped fish bring two types of problems to the wild world – ecological and genetic. Disease is present in fish farms, hence the need for antibiotics and vaccinations. Escaping fish transfer disease to wild fish populations, as well as having an adverse effect on the health and viability of wild fish through reproduction in the wild fish environment. Negative genetic consequences from mixed reproduction could lower fitness and the ability for the mixed bred fish to adapt to any changes I environmental conditions.²³