MARINE ECOSYSTEM

1. Aquatic Organisms

Aquatic organisms generally fall into three broad groups: plankton, nekton, and benthos. They vary in how they move and where they live.

• Plankton are tiny aquatic organisms that cannot move on their own. They live in the photic zone. They include phytoplankton and zooplankton. Phytoplankton are bacteria and algae that use sunlight to make food. Zooplankton are tiny animals that feed on phytoplankton.
• Nekton are aquatic animals that can move on their own by “swimming” through the water. They may live in the photic or aphotic zone. They feed on plankton or other nekton. Examples of nekton include fish and shrimp.
• Benthos are aquatic organisms that crawl in sediments at the bottom of a body of water. Many are decomposers. Benthos include sponges, clams, and anglerfish.

2. The Favorable conditions for the Marine ecosystem to flourish

• Light: On land, most photosynthesis occurs at or just above ground level, and there is no easily visible change in light as altitude increases. Things are quite different in the sea! Photosynthesis can only occur when enough light penetrates down the water column. This area is called the photic zone and varies from a few metres to as deep as 150 metres in some places. The amount of light that can penetrate the surface is limited by several factors. For example, rays of light that approach at a low angle (at sunrise and sunset) are immediately reflected off the surface. Particles of organic matter and sediments from land also affect how much light is absorbed. All primary productivity occurs in the photic zone, and as a result, about 90% of all marine life lives in this upper zone.
• Oxygen: Just as it is on land, oxygen is a very important gas in the ocean because of its role in the life processes of marine organisms. Dissolved oxygen in seawater comes from mixing (where the surface meets the atmosphere) and as a byproduct of photosynthesis. As a result, the most oxygen-rich water is found near the surface, so this is where the majority of marine organisms live.
• Movement of water: The movement of water, in the form of waves, tides and currents, plays an important role in our oceans and impacts all marine organisms. Wave action is one of the most significant environmental conditions affecting life in the sea. Water in the ocean is constantly moving due to wind, waves, the tide and underwater currents. The impact of waves generally reduces with depth.
• Salinity: The salinity (or saltiness) of seawater varies considerably throughout the world’s oceans. Although most seawater has a salinity of approximately 3–4%, it can reach up to almost 40% in some areas. In estuaries, salinity is typically low, as there is regular mixing with a freshwater source, such as a river. Salinity is typically highest in isolated bodies of seawater where the evaporation rates are high and precipitation rates are low. Marine animals are adapted to keep their body salts at a constant level so that they don’t interfere with the metabolism within cells, but significant changes in salinity can cause problems for some. For example, some marine animals are described as stenohaline, which means they can’t cope with large salinity fluctuations; others are euryhaline and can tolerate a wide range of salinities.
• Density: Seawater is more than 800 times denser than air. This high density is related to salinity and temperature and means that objects that might sink in freshwater can float in seawater. This has a big effect on life in the sea. For example, the marine ecosystem has communities of plankton – vast numbers of floating organisms that are kept perpetually afloat due to the density of seawater. It also helps explain why marine animals can grow to be so much bigger than the largest animals on land.
•  pH: pH is a measure of the acidity or alkalinity of a solution. Pure water is said to be neutral. The pH of seawater is about 8, but this varies slightly throughout the world. There is scientific evidence that suggests that the pH in our oceans is decreasing and therefore becoming more acidic. This could have significant impacts on life in the sea. For example, many marine species rely on calcium carbonate to build a shell or skeleton.

3. Threats concerning the Marine ecosystem

• Ocean Dumping: The dumping of waste materials from industries, ships and sewage plants into oceans has polluted the marine ecosystem to a great extent. As mentioned earlier, for years the oceans have been targeted as dumping sites of sewage, chemicals, industrial waste, garbage, and other debris from the land. According to reports, only mining companies across the world dump 220 million tonnes of hazardous waste directly into our waterbodies every year.
• Land Runoff: One of the major sources of ocean pollution is the waste that comes from the nonpoint source, which happens as a result of runoff. Surface runoff from both agricultural land and areas carries soil and particles mixed with carbon, phosphorus, nitrogen and minerals, posing a threat to marine life on an alarming scale.
• Dredging: In this world of ever-expanding industrial activities, dredging is an important activity that enhances marine transportation and other related activities. Similarly, dredging of contaminated materials will result in the regrouping of harmful particles and contaminate large of areas of water bodies.
• NOx and SOx: Nitrogen oxides (NOx) and Sulfur oxides (SOx) – the two main pollutants found in shipping emissions- have badly affected both the marine environment and the ozone layer in several ways.
• Ocean Acidification: The issue of ocean acidification is quickly becoming a threat to both marine life and humans. Ocean acidification is the continuing decrease of seawater pH caused by the absorption of carbon dioxide (CO2) from the atmosphere.
•  Sea Water Level Rising: Global warming is alarmingly increasing seawater levels, threatening the marine ecosystem. According to reports, the annual rate of seawater rise during the past two decades has been 0.13 inches a year, which is around twice the average speed of rise over the preceding 80 years.
• Ozone Depleting Substances: Ozone-depleting substances such as CFCs and Halon along with other pollutants from ships are destroying the ozone layer. Ozone Depleting Substances omitted by ships across the world include Methyl Chloroform, Methyl Bromide, Bromochlorodifluoromethane and Bromotrifluoromethane etc.
• Waste Pollution from Ships: As we know, tens and thousands of ships are responsible for more than 90 per cent of world trade. Apart from other pollutants such as oil and gas, the waste and garbage generated on board ships pose a significant threat to the marine ecosystem.
• Noise Pollution from Ships: It has been scientifically proven that the noise generated from shipping operations is harmful to marine organisms. Harmful effects of noise pollution on marine organisms include haemorrhages, changed diving patterns, migration to newer places, damage to internal organs and an overall panic response to foreign sounds.
• Oil Spills: No discussion on the marine environment can conclude without mentioning the biggest cause of marine pollution – oil spills. The world has witnessed several oil spill disasters that have been one of the major concerns of pollution to the marine environment. Disasters such as the Exxon Valdez Oil Spill and Deepwater Horizon etc. have resulted in the extreme pollution of the marine ecosystem, killing thousands of marine species. The oil spilt destroys the insulating ability of several marine species and also the water repellency of bird feathers, exposing these creatures to life-threatening risks.
• Plastic Pollution: It is important to mention this environment degrading agent separately for the sole fact that it has and is the reason for several environmental problems both at sea and on land. Those who have read or seen the Pacific garbage patch know the extent of damage this substance is causing to the marine environment. It is estimated that around 8 million tonnes of plastic waste enters our oceans every year, and by 2050, at this rate, we will witness more plastic than fish in the water bodies across the world.

4. Marine and coastal ecosystem services

• Provisioning services: fisheries, building materials;
• Supporting services: life-cycle maintenance for both fauna and local, element and nutrient cycling;
• Regulating services: carbon sequestration and storage, erosion prevention, waste-water treatment, moderation of extreme events;
• Cultural services: tourism, recreational, aesthetic, and spiritual benefits.