Coral reefs entice marine life, providing rich biodiverse habitats, and protect one-quarter of all marine organisms across the world. In the last few decades, these aquatic ecosystems have been under acute pressure from ships, marine vessels, and the consequences of marine pollution. Coral reefs face a lot of threats from humans. For these fragile animals that build their own limestone homes underwater, oil spills only add insult to injury.

Shipping Threat

Incidents including grounding of ships on coral reefs threaten aquatic life, while often causing significant harm to flora and fauna associated with the reef. Moreover, there is still fear of oil spills or release of contaminants as a result of such events, which could lead to extreme destruction or irreversible loss of coral reefs due to the insidious impact of bioaccumulation within invertebrates.

Apart from grounding and oil spills, underwater operations such as recovery attempts, anchoring, dredging, propeller wash and towing cable drags also contribute to the degradation of coral reef stability and the loss of marine habitat. Even piers, docks and luxury homes are built right on top of coral reefs, causing serious harm by destroying and covering the biota.

The issues of grounding and anchoring have been recorded since the 1970s. This is further exacerbated by medium-sized and huge cruise ships, most of which are capable of breaching shallow, vulnerable areas and, in the process, causing serious damage to coral reefs, with their huge anchors and anchor chains. What is more terrifying is that an anchor-damaged reef may never recover ,and even if it does, it may take at least 50 years to begin recovery.

Cruise ships have also been observed flushing a massive amount of sewage , food waste and oily bilge water as a stream of insoluble particles into the ocean. In 2008, an EPA study on the disposal of pollutants from cruise ships reported that this toxic waste and ocean pollution generates acid in the waters and drastically reduces the level of oxygen. This results in a rise in toxic algae blooms, another major threat to coral reefs.

How Does Spilled Oil Reach Coral Reefs? And What Are The Effects?

Several accidents in the past, both by cruise and container boats, have posed a significant danger to coral reefs by ship grounding. In August 2010, within eight days, two container vessels and a cargo ship caused major damage to the coral reef near Mumbai and off Kavaratti Island in Lakshadweep, which is second to Andaman and Nicobar Islands for the largest number of reefs in Indian waters. 

In yet another incident, in April 2010, a container ship was taken into custody by the Australian Federal Police for landing on the Douglas Shoal at the Great Barrier Reef. In addition, the world’s largest underwater conservation park has encountered three big ship-landing incidents in the last decade.

Whether oil spills affect corals depends on the species and age of the coral (e.g. early life stages are very susceptible to oil) as well as the method and degree of exposure to oil. Coral exposure to small quantities of oil for a prolonged period of time can be just as toxic as huge amounts of oil over a short period of time.

Coral reefs can be impacted by oil spills in three major ways:

  1. Oil settling on the surface of the ocean will be deposited directly on the corals in the intertidal zone as the water level decreases at low tide. 
  2. Stormy weather can mix lighter oil substances in the water column where they can descend onto the coral reefs. 
  3. When heavy oil blends with sediment, it may become thick enough to sink beneath the surface of the water.

When oil comes into contact with corals, it may kill them or disrupt their reproduction, growth, activity and productivity. The whole reef environment may be impacted by oil spills, affecting numerous species of fish, crabs, and other aquatic invertebrates dwelling in and surrounding coral reefs.

Reefs At Peril

Currently the coral reefs in Southeast Asia, off Indonesia and Philippines, are found to be the most threatened ones, where many pristine reefs require utmost protection from the heavily populated adjacent areas. The Caribbean ‘Blue Jewels’ coral reefs have experienced incredible pressure from maritime tourists, untreated wastewater and overfishing. In SouthEast Florida, expanded maritime operations and a major rise in deep-water ports and their impact on coral reef systems are pervasive.

The Great Barrier Reef – the world’s largest preserved coral reef system, despite being a UNESCO World Heritage Site, is still threatened by underwater contamination, which makes the waters more acidic and prevents corals from being able to generate calcareous skeletons.

Preventive Measures

A variety of factors have been taken into consideration in the conservation of coral reefs. The expansion of marine protected areas, the control of shipping pressure, the development of integrated sewage treatment, the introduction of a waste management strategy and the elimination of harmful activities are of serious importance. While illegal entry or negligent grounding in coral reef areas is subject to a high degree of prosecution, the primary duty is to differentiate these areas as conservation areas in order to limit shipping and intrinsic harm. Pressure is also associated with excavation of propeller wash, harbor dredging and off-shore anchorage.

Friends of the Planet, a multinational environmental watchdog organization, has reviewed large cargo ships and found that most of the new cruise ships that have been sailing since 2006 lack sophisticated sewage treatment facilities. 

Another separate program is the Florida Keys National Marine Sanctuary (FKNMS) – developed by the United States Environmental Protection Agency (EPA) in partnership with the National Oceanic and Atmospheric Administration (NOAA) and the State of Florida. Since 1981, FKNMS has been pursuing the construction and management of mooring buoy, which are replacements to anchoring vessels that can harm or even break off coral reef fragments. These buoys offer information and navigation support in areas with complex legislation. Furthermore, the dumping of toxins or other harmful substances from ships in the associated area is strictly forbidden.


The effect of these incidents is devastating, but there is some positive news. We are seeing a drop in oil use at the moment, but it needs to come sooner. The move to more sustainable lifestyles and clean energy technologies is far more important than ever before in order to counteract the climate crisis.