The world’s oceans cover over 70% of the Earth’s surface, supporting diverse ecosystems and providing numerous resources. While international shipping facilitates a significant portion of global trade, large vessels introduce various pressures on marine ecosystems. This article explores the specific ways large ships can negatively affect the ocean, from chemical contamination to physical habitat disruption.
Contamination from Discharges and Waste
Large ships release harmful substances and waste directly into the marine environment. Oil pollution can occur through accidental major spills, but also through routine operational discharges such as oily bilge water. Bilge water, a mixture of water, oil, grease, and chemicals collected in the ship’s lowest part, can poison marine organisms and form surface films that obstruct sunlight and oxygen, disrupting food chains. These pollutants can float to the surface and be blown to shorelines, physically covering plants and animals and interfering with their life cycles and respiration. Even small amounts of oil can spread widely and impact marine life, including birds whose feathers lose waterproofing, leading to hypothermia.
Chemical discharges also pose a threat, particularly from cleaning agents and anti-fouling paints used to prevent marine growth on hulls. These paints, containing compounds like copper or booster biocides, leach harmful chemicals into the water. These biocides can contaminate the food chain, disrupt marine life growth, and accumulate in sediments, affecting benthic organisms.
Solid waste, especially plastics, discharged or lost from ships contributes significantly to marine debris. Despite regulations prohibiting plastic disposal at sea, it remains a concern as plastic debris can entangle marine animals and break down into microplastics, which absorb toxins and enter the food web upon ingestion. Furthermore, greywater and blackwater, wastewater from sinks, showers, and toilets, are discharged, potentially introducing excess nutrients and pathogens into coastal waters, leading to localized pollution.
Noise and Air Pollution
Beyond direct waste, large ships contribute to environmental burdens through their emissions into both the atmosphere and the underwater acoustic environment. Exhaust gases from burning heavy fuel oil release sulfur oxides (SOx), nitrogen oxides (NOx), particulate matter, carbon monoxide, and greenhouse gases like carbon dioxide and methane. These atmospheric pollutants contribute to air quality issues such as acid rain, which damages crops and buildings, and smog, and they are linked to respiratory problems and cardiovascular diseases in humans. Greenhouse gas emissions also intensify climate change.
Underwater noise generated by ship propellers, machinery, and sonar systems profoundly alters the marine soundscape. The global merchant fleet has contributed to a substantial increase in background noise levels underwater over the past decades. This continuous noise disrupts marine animals that depend on sound for essential life functions, including communication, navigation, foraging for food, and avoiding predators. Whales and dolphins, for instance, use echolocation to find food and navigate, and increased ship noise can mask their sounds, interfere with their ability to communicate, and even cause temporary hearing loss or displacement from habitats.
of Invasive Species
Large ships serve as significant vectors for transporting non-native species across vast ocean distances. The primary mechanism for this biological invasion is ballast water, which ships take on at one port for stability and then discharge at another. This process inadvertently transfers thousands of aquatic organisms, including bacteria, viruses, algae, invertebrates, and fish larvae, from their native habitats to new ecosystems. Billions of tons of ballast water are transported globally each year.
Organisms can also attach to ship hulls, a phenomenon known as hull fouling, and be carried to new regions. Once introduced, these non-native species can become invasive, outcompeting local organisms for resources, disrupting established food webs, and introducing new diseases or parasites. Such biological invasions can lead to declines in biodiversity, alter habitats, and cause economic harm to fisheries and aquaculture.
Physical Damage to Habitats and Marine Life
Direct physical harm to marine ecosystems and individual organisms results from various ship-related activities. Collisions between large vessels and marine animals, known as vessel strikes, are a leading cause of human-induced mortality for several whale populations, dolphins, and sea turtles. These incidents often result in severe injuries, such as blunt trauma or propeller cuts, or immediate death, and due to the large size of many commercial ships, operators may not even detect a strike. The substantial increase in global shipping traffic, combined with higher vessel speeds, significantly increases the likelihood and severity of these collisions.
Anchors and their chains can inflict substantial physical damage on sensitive seabed habitats. Dropping or dragging anchors can break or dislodge corals, sponges, and sea fans on coral reefs, which grow very slowly, making recovery from damage a lengthy process. A single anchor drop can damage a significant area, potentially hundreds of square meters of reef. Seagrass beds, which serve as nurseries and feeding grounds for many species, are also vulnerable to damage from anchors and propeller scouring, leading to habitat fragmentation. This destruction can take decades to recover.
Furthermore, propellers themselves can directly injure marine life, particularly in shallow areas where animals may not detect or avoid the approaching vessel. Lastly, dredging operations, necessary for maintaining navigable shipping channels and expanding port facilities, physically alter and destroy marine habitats. This process involves removing sediments and debris, which can increase water turbidity, smother delicate coastal vegetation and benthic organisms, and release contaminants like heavy metals from disturbed sediments, impacting the marine food web.