Particle (ecology)

In marine and freshwater ecology, a particle is a small object. Particles can remain in suspension in the ocean or freshwater. However, they eventually settle (rate determined by Stokes' law) and accumulate as sediment. Some can enter the atmosphere through wave action where they can act as cloud condensation nuclei (CCN). Many organisms filter particles out of the water with unique filtration mechanisms (filter feeders). Particles are often associated with high loads of toxins which attach to the surface. As these toxins are passed up the food chain they accumulate in fatty tissue and become increasingly concentrated in predators (see bioaccumulation). Very little is known about the dynamics of particles, especially when they are re-suspended by dredging. They can remain floating in the water and drift over long distances. The decomposition of some particles by bacteria consumes a lot of oxygen and can cause the water to become hypoxic.

Particle analysis

Particle levels in water (or air) can be measured with a turbidity meter and analyzed with a particle counter. They can also be scanned with an underwater microscope, such as ecoSCOPE.

Particlekils
Particles scanned with the ecoSCOPE microscope. The blue frame is a 1 mm contrast grid.

Contaminant kinetics

It takes a few days until plankton organisms have filtered the particles and incorporated the toxins into their body fat and tissue: In the southwards flow of the waters of the Hudson off the coast of New Jersey, the highest levels of mercury in copepods have not been found directly in front of the river off New York but 150 km south, off Atlantic City.

Many copepods are then captured by mysidae, krill and smallest fish like the juveniles of atlantic herring - and in each step of the foodchain the toxin concentrations increase by the factor of 10. The milk of mothers (Homo sapiens) consuming fish and related products like margarine and eggs in such areas have so high toxin levels that it would be impossible to sell such milk on markets - their babies have much more birth-defects and/or retarded brains and have later difficulties to learn and/or reproduce. Many die at an early age.

Krillfilter2kils
Filter of krill

Filter of krill: The first degree filter setae carry in v-form two rows of second degree setae, pointing towards the inside of the feeding basket. The purple ball is one micrometer in size. To display the total area of this fascinating particle filtration structure one would have to tile 7500 times this image.

Mysis2kils
Filter basket of a mysid.

Filter basket of a mysid. These 3 cm long animals live close to shore and hover above the sea floor, constantly collecting particles. Mysids are an important food source for herring, cod, flounder, striped bass. In polluted areas they have high toxin levels in their tissue but they are very robust and take a lot of poison before they die. Such filter-feeding organisms are the reason that much of the materials we throw in the oceans comes back to us in our food.

Copepod

Copepods (; meaning "oar-feet") are a group of small crustaceans found in nearly every freshwater and saltwater habitat. Some species are planktonic (drifting in sea waters), some are benthic (living on the ocean floor), and some continental species may live in limnoterrestrial habitats and other wet terrestrial places, such as swamps, under leaf fall in wet forests, bogs, springs, ephemeral ponds, and puddles, damp moss, or water-filled recesses (phytotelmata) of plants such as bromeliads and pitcher plants. Many live underground in marine and freshwater caves, sinkholes, or stream beds. Copepods are sometimes used as biodiversity indicators.

As with other crustaceans, copepods have a larval form. For copepods, the egg hatches into a nauplius form, with a head and a tail but no true thorax or abdomen. The larva molts several times until it resembles the adult and then, after more molts, achieves adult development. The nauplius form is so different from the adult form that it was once thought to be a separate species.

EcoSCOPE

The ecoSCOPE is an optical sensor system, deployed from a small remotely operated vehicle (ROV) or fibre optic cable, to investigate behavior and microdistribution of small organisms in the ocean.

Environmental impact of shipping

The environmental impact of shipping includes air pollution, water pollution, acoustic, and oil pollution. Ships are responsible for more than 18 percent of some air pollutants.It also includes greenhouse gas emissions. The International Maritime Organization (IMO) estimates that carbon dioxide emissions from shipping were equal to 2.2% of the global human-made emissions in 2012 and expects them to rise 50 to 250 percent by 2050 if no action is taken. The First Intersessional Meeting of the IMO Working Group on Greenhouse Gas Emissions from Ships took place in Oslo, Norway on 23–27 June 2008. It was tasked with developing the technical basis for the reduction mechanisms that may form part of a future IMO regime to control greenhouse gas emissions from international shipping, and a draft of the actual reduction mechanisms themselves, for further consideration by IMO's Marine Environment Protection Committee (MEPC).The fact that shipping enjoys substantial tax privileges has contributed to the growing emissions.

Filter feeder

Filter feeders are a sub-group of suspension feeding animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Some animals that use this method of feeding are clams, krill, sponges, baleen whales, and many fish (including some sharks). Some birds, such as flamingos and certain species of duck, are also filter feeders. Filter feeders can play an important role in clarifying water, and are therefore considered ecosystem engineers. They are also important in bioaccumulation and, as a result, as indicator organisms.

Aquatic ecosystems

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