Building blocks of ocean food web in rapid decline as plankton productivity plunges

Authored by cbc.ca and submitted by Bluest_waters

They're teeny, tiny plants and organisms but their impact on ocean life is huge.ā€‹

Phytoplankton and zooplankton that live near the surface are the base of the ocean's food system. Everything from small fish, big fish, whales and seabirds depend on their productivity.

"They actually determine what's going to happen, how much energy is going to be available for the rest of the food chain," explained Pierre Pepin, a senior researcher with the Department of Fisheries and Oceans in St. John's.

Pepin says over the past 3-4 years, scientists have seen a persistent drop in phytoplankton and zooplankton in waters off Newfoundland and Labrador.

"Based on the measurements that we've been taking in this region, we've seen pretty close to 50 percent decline in the overall biomass of zooplankton," said Pepin. "So that's pretty dramatic."

Measuring 5 mm or less, phytoplankton contain chlorophyll to capture sunlight and use photosynthesis to turn it into chemical energy which is later eaten by ocean creatures. (Photo courtesy of DFO)

Scientists say local testing reveals half the amount of plankton in a square metre of water today. It's not just a problem here, declining plankton numbers are a global phenomena.

It's a difficult idea to convey to the average person who might not understand the ocean ecosystem, but Pepin likens it to walking into a grocery store and instead of seeing the shelves full, they're only half full.

Listen to Jane Adey's coverage on CBC Radio's The Broadcast:

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"You know if you saw half the number of birds, if you saw half the number of fish in the water you'd pay attention. Well, this is a signal to say we need to pay attention."

So what's causing this dramatic decline?

Scientists here haven't detected anything in particular that can be linked to the plunge in productivity, but they are worried.

Phytoplankton are tiny plants and zooplankton are tiny animals. Zooplankton feed on phytoplankton near the surface of the ocean. (Photo courtesy of DFO)

"When it persists ā€” for in our case now for three or four years ā€” in the back of my mind, at the very least, little alarm bells start going off because it means that something fundamental may have changed in the food web."

Pepin says it is difficult to understand how long it takes the effect of this lack of basic food to make its way through the ocean ecosystem.

Scientists have to advise managers on how to handle fish stocks but without clear evidence of causes and effects, it becomes a very difficult job.

"How do we act on this, this is a real challenge."

Read more articles from CBC Newfoundland and Labrador

mulder_scully on December 23rd, 2018 at 19:28 UTC »

I will get lost in the comments here, but Iā€™m studying ocean biochemistry in graduate school and the ocean is probably net heterotrophic. This means that oxygen produced from photosynthesis in the surface layer is rapidly consumed by microbes and plankton. As a result the ocean does NOT provide oxygen to humans, instead it is sourced from the massive boreal forests at mid to high latitude regions in the northern hemisphere.

Of course, the ocean is afflicted by a billion other problems directly and indirectly related to anthropogenic forcings. Ocean acidification as a result of increased carbonic acid production due to the oceans uptake of increased atmospheric CO2. Ocean warming is making oxygen less soluble and enhancing stratification between less dense surface waters and saltier, deep waters. This means less of the ocean interior is being vertically mixed to the surface. Much of the nutrients needed for phytoplankton blooms is supplied by deep ocean nutrients, so that increased stratification will result in less abundant blooms.

This barely scratches the surface of the problems of climate change and the ocean, but to say that phytoplankton provide 70% of our oxygen is impossible stoichiometrically and basically a huge urban myth.

Edit:

Some sources...

Smith & Mackenzie, 1987 - The ocean as a net heterotrophic system

Giorgio and Duarte, 2002 - Respiration in the open ocean

Karl et al., 2003 - Metabolic Balance of the Open Sea

Westberry et al., 2012 - Global net community production and the putative net heterotrophy of the oligotrophic oceans

Duarte et al., 2013 - The oligiotrophic ocean is heterotrophic

Also see Sarmiento & Gruber - Ocean Biogeochemical Dynamics

Please don't consider this to be a dismissal of the immediate and real threat that faces the oceanic food web. Phytoplankton assemblages are becoming less diverse and that means a complete rearranging of the food webs which have supported normal ecosystem functioning, and essentially human fisheries. The collapse of phytoplankton abundance and diversity is actually happening right now. I happen to point out that the 70% number is often misrepresented but don't think that means the oceans are fine and dandy. They certainly aren't.

WolfWhoRules on December 23rd, 2018 at 18:42 UTC »

Here is a study from Nasa from this summer.

https://www.nasa.gov/feature/goddard/nasa-study-shows-oceanic-phytoplankton-declines-in-northern-hemisphere

Apparently the 'mixing layer' of water that phytoplankton thrive in is getting shallower. We are not sure exactly why, but changing wind conditions may have something to do with it.

suddenly_satire on December 23rd, 2018 at 18:31 UTC »

Fun Fact - in the movie Soylent Green, the ocean's plankton dying off is what led them to turning people into soylent green.