The ocean and its problems: Has the boat sunk?

Samuel Amant
Published in
6 min readNov 22, 2022


Fisheries and aquaculture already produce an astonishing 214 million tonnes of blue food, and it is predicted to grow another 15% by the time we reach 2030.

In order to make this possible, it is important that we start implementing food systems to deliver aquatic food in a sustainable way, without the current problems of overfishing, acidification, habitat loss and pollution. In the end, the ocean is of crucial importance to our economy ($3–6 trillion per year), our society (150 million direct jobs) and our environment (earth’s ecosystems rely on it). Not to mention that oceans (i.e. phytoplankton, tiny single-celled algae) produce around half of the oxygen we breathe.

The goal of this report is to highlight the main problems the ocean is facing under the human impact. Although our impact on the ocean is complex, it can be categorized as:

  • Overfishing
  • Rising ocean temperatures
  • Raising carbon dioxide levels
  • Eutrophication
  • Pollution (plastic, oil, noise, etc.)

Let’s dive into them, one by one.

  1. Overfishing

The Food and Agriculture Organisation defines overfishing and its consequences as follows:

“Overfishing — stock abundance fished to below the level that can produce maximum sustainable yield — not only causes negative impacts on biodiversity and ecosystem functioning, but also reduces fisheries production, which subsequently leads to negative social and economic consequences.”

Here it’s important to realize that “Fishing isn’t a problem, unsustainable fishing is”. Studies show that when scientifically assessed and intensively managed, fish stocks are more abundant. Currently, ineffective management policies and lack of enforcement cause marine fisheries to suffer from overcapacity, overfishing, illegal and unregulated development, pollution and habitat degradation. In 1974, only 10% of the fish stocks were overfished. Now, this is 35.4% and this number continues to increase. 92.8% of the fish stocks are fished at their maximum sustainable capacity.


With the demand for fish and other aquatic food skyrocketing, aquaculture became a tool to relieve the pressure on the fishing industry.

The state of world fisheries and aquaculture 2022, Source: FAO

From the 178 million tonnes of aquatic animals produced in 2020, 51% was captured by fisheries, and 49% was grown in aquaculture. Between 1990 and 2020, the aquaculture annual output expanded by 609%. With the current trends, it won’t take long before aquaculture becomes the largest source of sea animals.

But what is the flip side of the medal? Indeed, since the start of industrial-scale aquaculture, many conflicts have surfaced.

Open-water aquaculture, where fish are grown in pens (net cages) in natural water bodies, lacks good waste management. Large quantities of discharges from the farm (metabolic excretion, faeces, uneaten feed, chemicals and medicines) end up stressing surrounding ecosystems heavily and can push them to collapse.

Inland fish cultivation in enclosed tanks has the answer to this problem since the waste streams are easier to control, clean and even recirculate. However, similar to open-water cultivation, this industry suffers from unsustainable sourcing of feed, and large use of medicine, especially antibiotics.

2. Rising Ocean Temperatures

Most of the planet’s excess heat is absorbed by the ocean. By now, the ocean temperature already has experienced an average increase of 1°C, resulting in visible consequences. This not only causes melting arctic ice, but also impacts fauna and flora significantly. 1.5°C is seen as a critical threshold, with a projected decline of 70–90% of coral reefs if we reach this temperature. If it continues to increase till a change of 2°C, all coral reefs will be lost. Realising that half a billion people rely on fish from coral reefs as their main protein source, this critical threshold should be avoided by all means.
Bleached coral on Australia’s Great Barrier Reef, Source: NBCNews

However, some species flourish when ocean temperatures increase. Warmer water provides the perfect breeding conditions for example for jellyfish and sea urchins. Large populations of the latter dominate and destroy their surrounding ecosystems. As a result, kelp forests disappear due to rising temperatures, acidification and sea urchins, at rates up to 90% in some areas. Compared to this, we still have plenty of Amazon forest left.

3. Raising Carbon dioxide levels

The higher carbon dioxide levels in the air end up creating more acidic water, going from pH 8.2 to 8.1 or lower. Although there is always a natural fluctuation of pH of the ocean due to the earth's climate cycles, the decrease measured today occurs at a rate 100 times greater than any change in acidity experienced during the past 55 million years, indicating the significant impact of human activity.

The impact of acidification on the shell of a snail. Source: AMAP

This drop in pH is called acidification, and it dissolves the minerals, of which marine life, such as oysters, mussels, lobsters, snails, coral reefs and some seaweed species, build their shells and skeletons. Eventually, this could alter marine food chains and impact the over 100 billion USD market that the shellfish industry represents.

4. Eutrophication

Between 2011 and 2018, a strong increase in marine algae blooms is visualised in the images below. This is a result of eutrophication.

A belt of 22 million tonnes of Sargassum shows a large increase in the monthly mean sargassum density between 2011 and 2018. Source: Science

The United Nation Environmental Programme defines eutrophication as follows:

“Excess nutrient loading into coastal environments from anthropogenic sources, resulting in excessive growth of aquatic plants, algae and phytoplankton.”

The most impactful sources of nutrient effluent flows are livestock, aquaculture, fertilizer used in agriculture and sewage disposal. When they flow into the sea, they create an over-enrichment of the water with nutrients (mainly nitrogen and phosphorus). As a consequence, if the conditions are optimal (sun light, temperature, etc.), extremely large amounts of seaweed grow due to the exceptional nutritious water. This is a so-called bloom.

The main problem with blooms is caused by the bacterial degradation of this excess biomass, which consumes large amounts of oxygen. This results in low levels of dissolved oxygen (below 2–3 mg O2/L ) creating hypoxic or dead zones. The resulting stressed marine life can lead to a collapse of the ecosystem.

Mats of Sargassum seaweed off the coast of St. Martin in April 2018, Source: The Conversation

The impact of human activities is indicated by the increase of hypoxic zones, from 10 in 1960 to nearly 500 in 2010. Estimates are that around 240 000 km2 are yearly affected by eutrophication and hypoxia. Examples of dead zones can be found in various spots in the Gulf of Mexico or the Baltic Sea.

5. Other anthropogenic impacts

Next to these, there are several other problems that negatively impact our ocean.

  • Plastic pollution: An estimated 8 million tonnes of plastic annually end up in the oceans. This plastic can kill marine life if they are accidentally mistaken for food. This plastic can also end up as micro-plastics — plastics smaller the 5mm — which can be eaten by for example plankton, which then passes the problem up the food chain. Now, by eating mussels once in a while, one can now consume up to 11.000 plastic particles annually.
  • Marine Activities: Testing, drilling and oil spills impact ocean wildlife in many ways.
  • Rising sea levels: High levels cause more frequent flooding, more coastal erosion, and endangering all coastal populations.

6. How much water has our boat taken?

The list of problems the ocean is enfacing is long and depressing. Centuries of unsustainable marine activities have been building up to a point where many variables are on the verge of a tipping point of unrecoverable damage.

Knowing this, let’s not neglect these warning signs the ocean is giving. A following article describes possible solutions to the ocean’s problems. Let’s take these opportunities and push them for a more sustainable future.

Stay tuned!