These are heterotrophic dinoflagellates. This particular species is nocturnal. But dinoflagellates and diatoms dominate zooplankton that along with phytoplankton, represent the bottom of the ocean food chain. Everything in the ocean is ultimately nourished by them. So they are very important to ocean ecosystems.
But more alarmingly interesting is what happens to them when an oil spill occurs such as the Deepwater Horizon disaster of 2010 in the Gulf of Mexico. Shortly after that spill, articles appeared indicating the contribution of oil-spill eating bacteria to clean the site. Referred to as nature’s janitors, it was commonly thought that biology could help fight a disaster of this magnitude. But what if biology could spread the toxicity of the spill even further?
In a paper appearing in the journal, Nature, published December 19th and authored by scientists from University of Texas Austin and Technical University of Denmark, the researchers cast serious doubt on our previous assumptions. They note that even oil spills treated with chemical dispersant suspend the hydrocarbon as small droplets in the water column, and those droplets are small enough to be ingested by creatures like the one you see above because they cannot distinguish the oil from real food. That’s because the droplets mimic the size of their normal food.
Initially of course at the site of a spill oil concentrations are so high that much of the zooplankton and phytoplankton dies. But as dispersant is applied the oil breaks up into finer droplets with secondary implications for surviving and new blooms of dinoflagellates. Thinking this is food the creatures gobble up the oil. This ingestion leads to many consequences one of which is the entry of microscopic hydrocarbons into the entire ocean food chain.
The authors note, “dinoflagellate cells containing crude oil can be prey for consumers, such as crustacean zooplankton and fish larvae which would enhance biotransfer of highly toxic, low-solubility petroleum hydrocarbons through marine food webs during crude oil spills.”
In other words dinoflagellates in making the mistake of thinking oil droplets are food unwittingly spread the oil throughout the food chain.
But it doesn’t end there. The authors of the study calculate that a single bloom of dinoflagellates like the ones seen above “has the potential to ingest, in one day, most of the dispersed crude oil droplets in the area covered by the bloom when oil concentrations are ~1-2 ppm [parts per million].”
What happens to that ingested oil? Well it appears that dinoflagellates have a fairly high tolerance to crude oil and dispersant once the levels of concentration decline. They can digest some of it but in processing it they also defecate the oil. These eliminated fecal pellets contain insoluble portions of the crude oil and it is not fully understood how its composition is altered by dinoflagellate digestion. The researchers suggest further study is needed. But one thing was noted by the researchers. The fecal pellets do not remain suspended in the water column because in digestion the oil loses its buoyancy. So the material sinks further into the water column bearing its toxic oil load.
Why is this significant? In the past scientists saw the digestion of oil by zooplankton as a natural means of eliminating oil spills. But contaminated fecal pellets descending to the depths was not considered as a source of secondary oil pollution in the marine environment.
In their conclusions, the researchers state, “our study highlights that ingestion of crude oil by heterotrophic dinoflagellates is a significant path by which crude oil pollution enters marine food webs and an important mechanism affecting the fate of dispersed crude oil in the sea after oil spills. Our results emphasize the need to understand and quantify crude oil ingestion and defecation by zooplankton, both protozoans and metazoans, to determine the fate and impact of petroleum pollution in marine environments.”
In other words, we don’t know, in the aftermath of an oil spill, after cleanup and after natural biological processes have worked on the oil, what is the full extent and duration of the environmental damage.
]]>
The mercury inventory was gathered by several oceanographic expeditions from the Atlantic, Pacific, Antarctic and Arctic Oceans. Measurements were obtained throughout the water column in these locations and showed variation in concentration both by location and depth. Two-thirds of the mercury present is found in water of less than 1,000 meters (3,300 feet) in depth.
The proximity to surface waters is a good clue as to how the mercury gets into the ocean and we are the offenders. Yes, there are natural sources of mercury. These include volcanoes and some minerals in which mercury is present. But the increases in concentration are wholly human created and the major sources include mining and the burning of fossil fuels.
Mercury would be even more concentrated in coastal areas if it weren’t for ocean currents and wind which help to disperse it to some degree. That may be the saving grace in this story because deeper water sequesters the chemical. But marine geo-chemists believe that sequestering capability will soon come to an end as humans put an equal amount of mercury to that of the last 150 years in the next 50.
The problem of mercury is one well understood by the scientists and the fishing industry. Mercury concentrations in large game fish like marlin, swordfish and tuna make them less desirable as a food source. People are cautioned to eat these large game fish no more than once in awhile. That’s because as an example, the average tuna contains levels of mercury 10 million times higher than the water in which they swim.
Sea and freshwater fowl who derive much of their diet from fish are also contaminated by high levels of mercury. The impact it has on them includes reduced reproductive rates and birth defects.
What does it do to us? For children it effects brain development leading to lower IQs and other cognitive deficits. Mercury toxicity in adult humans can lead to headaches, insomnia, tremors, memory loss, depression, tingling in the hands and feet and many more central nervous system related conditions. Minimata disease, named after Minamata City in Japan, was first identified as assoociated with mercury contamination in 1956. The residents of that city ate fish and shellfish from the bay where wastewater discharge from a chemical plant contained high volumes of methylmercury {MeHg). The population exhibited cognitive, sensory and and vision loss. Children born to mothers exposed to the wastewater presented as having mercury poisoning. More than 2,200 citizens of Minimata City were afflicted.
Mercury never breaks down. It just continues to build up but if we humans can reduce our output we can at least control One good thing coming out of the report. Because mercury is not evenly distributed throughout the ocean there is still the opportunity for humans to put less of it into the environment.
So don’t tell me – you had a tuna sandwich for lunch today?
