Algae may be the cause. It is a situation we are going to continue to monitor very closely. Dissolved oxygen levels in pockets of water off Belmar, Bay Head, Barnegat and Beach Haven hovered around two parts per million yesterday. In one case, three miles off Belmar, the level fell below two, Mears said. Oxygen levels between four and five parts per million are considered healthful for marine life, scientists say.
Levels usually drop off to four during the summer because of ocean conditions.
Fish, clams and other organisms must filter oxygen from water to live. Low oxygen can be especially disastrous for bottom-dwelling species because they do not have the ability to move around and reach more highly oxygenated water, scientists say. In summer, as the ocean warms, a cap of warmer water forms on the top layers and prevents circulation. As a result, pockets of water with low levels of dissolved oxygen form along the bottom layers. Oxygen concentrations in some waters off the Shore also drop because of naturally occurring algae blooms.