Density of Neustonic Plastics
The patch is not a visibly dense field of floating debris. The process of disintegration means that the plastic particulate in much of the affected region is too small to be seen. In a 2001 study, researchers (including Charles Moore) found concentrations of plastic particles at 334,721 pieces per km2 with a mean mass of 5,114 grams (11.27 lbs) per km2, in the neuston. Assuming each particle of plastic averaged 5 mm x 5 mm x 1 mm, this would amount to only 8 m2 per km2 due to small particulates. Nonetheless, this represents a very high amount with respect to the overall ecology of the neuston. In many of the sampled areas, the overall concentration of plastics was seven times greater than the concentration of zooplankton. Samples collected at deeper points in the water column found much lower concentrations of plastic particles (primarily monofilament fishing line pieces). (Nevertheless, according to the mentioned estimates, only a very small part of the plastic would be near the surface.)
Read more about this topic: Great Pacific Garbage Patch