Feast and famine in the abyssal plain – sciencedaily

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Animals living in the abyssal plains, miles below the ocean’s surface, usually don’t have much to eat. Their main source of food is “sea snow” – a slow drift of mucus, fecal pellets and body parts – which drains from surface waters. However, researchers have long been puzzled by the fact that, in the long run, regular falling sea snow cannot account for all the food consumed by animals and microbes living in the sediment. A new article by MBARI researcher Ken Smith and colleagues shows that population booms of algae or animals near the sea surface can sometimes result in huge pulses of organic matter sinking into the seabed. In a matter of weeks, such deep-water “feasts” can provide as much food for deep-sea animals as would normally get in years or even decades of typical sea snow.

For more than 20 years, Smith and his fellow researchers have studied animals living in the Abyssal Plain of Station M, a deep-water research site about 220 kilometers (140 miles) off the central California coast. The muddy bottom of M Station – 4,000 meters (13,100) feet below the surface – is home to a variety of deep-sea animals, from sea cucumbers and urchins to pomegranate fish. In addition, a myriad of small animals and microbes live buried in the mud.

Researchers have long wondered how all of these animals and microbes get enough food to survive. The slow trickle of sea snow coming down from above does not provide enough food to feed all the organisms that live there. However, in a new article from Proceedings of the National Academy of Sciences, Smith and his co-authors show that occasional feasting could provide enough food to sustain deep-sea communities for years to come.

Smith and his colleagues used several instruments to study the amount of sea snow arriving at Station M, as well as its impacts on life in the depths. They hung conical “sediment traps” above the seabed to collect and measure the amount of sea snow falling into the water. They also used automated camera systems to take time-lapse photographs of the seabed. This allowed them to track the behavior, numbers and sizes of large deep-sea animals such as sea cucumbers. Finally, they used a seabed crawling robot, the Benthic Rover, to measure the amount of water. oxygen consumed by animals and microbes in sediment. These oxygen measurements allowed researchers to estimate how much food these organisms were consuming.

Using data from 1989 to 2012, Smith and his colleagues compared the amount of sea snow arriving at Station M with estimates of microscopic algae populations observed at the surface using satellites. For most years, the amount of food reaching the seabed peaked annually in summer and fall, but remained relatively low.

However, in 2011 and 2012, researchers observed three dramatic events that delivered huge amounts of relatively fresh food to the deep seabed. The first took place from June to August 2011, when a large number of diatoms (a type of microscopic algae) bloomed near the surface, then quickly sank to the bottom of the sea.

The second event occurred from March to May 2012, when salps – gelatinous pelagic animals that eat algae – reproduced rapidly in surface waters. These salps became so abundant that they blocked the seawater intake at the Diablo Canyon Nuclear Power Plant, located on the California coast east of Station M. When the salps in the surface waters of the station M died, they sank so quickly that they covered the seabed. , four kilometers below. In the third event, in September 2012, another algal bloom created so much dead algae that it clogged researchers’ sediment traps, but was captured by a time-lapse camera.

The excess food that came to the seabed during these feasts was not wasted. Instead, it was quickly consumed by deep-sea animals and sea-floor microbes, which used it to thrive and reproduce. Some of the organic carbon in food was released into the surrounding seawater through respiration. Most of the rest was incorporated into deep-sea sediment, where it could be recycled by animals and microbes that feed on the mud. In this way, large, intermittent pulses of food could help sustain life in the depths for years, if not decades.

Smith and his colleagues are still studying the biological effects of these extreme food impulses. They have already seen changes in the number and types of deep-sea animals living at Station M that appear to be a result of the 2011 and 2012 holidays. They will report these findings in a later article.

The researchers note that the frequency of deep-sea feasting may increase off California’s central coast, as well as at other deep-sea study sites around the world. Over the past decade, the waters off central California have seen stronger winds, which bring more nutrients, such as nitrates, to the ocean surface. These nutrients act as fertilizers, triggering algal blooms, which in turn sometimes fuel salp blooms. The fallout from all of this increased productivity ends up on the seabed.

The authors also note that changes in ocean conditions that provided more food for deep-sea animals at Station M could be linked to global warming. Alternatively, these changes could simply reflect long-term natural cycles in the ocean.

These findings remind us once again that the deep sea is directly affected by events on the ocean surface, as well as human activities on land. In fact, information from high seas studies like this one will be critical to improving computer models of the global carbon cycle and climate change.


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