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In marine and freshwaterecology, aparticle is a small object.[1][specify] Particles can remain in suspension in the ocean or freshwater. However, they eventually settle (rate determined byStokes' law) and accumulate as sediment. Some can enter theatmosphere through wave action where they can act ascloud condensation nuclei (CCN). Many organismsfilter particles out of the water with unique filtration mechanisms (filter feeders). Particles are often associated with high loads oftoxins 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 (seebioaccumulation). Very little is known about the dynamics of particles, especially when they are re-suspended bydredging. They can remain floating in the water and drift over long distances. The decomposition of some particles by bacteria consumes muchoxygen and can cause the water to becomehypoxic.
Particle levels in water (or air) can be measured with aturbidity meter and analyzed with aparticle counter. They can also be scanned with an underwater microscope, such asecoSCOPE.
It takes a few days untilplankton organisms have filtered the particles and incorporated the toxins into their body fat andtissue: In the southwards flow of the waters of the Hudson off the coast ofNew Jersey, the highest levels of mercury incopepods have not been found directly in front of the river offNew York but 150 km south, offAtlantic City.
Many copepods are then captured bymysidae,krill and smallestfish like the juveniles ofatlantic herring - and in each step of thefoodchain the toxin concentrations increase by the factor of 10.
Filter ofkrill: The first degreefilter setae carry in v-form two rows of second degreesetae, pointing towards the inside of thefeeding basket. The purple ball is one micrometer in size. To display the total area of this fascinating particle filtration structure one would have totile 7500 times this image.
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 forherring,cod,flounder,striped bass. In polluted areas they have high toxin levels in their tissue but they are very robust and require much poison to die.
