Box jellyfish will destroy future oceans by gobbling up the food

8 September 2017

Who ate all the copepods?

Nature Production / NaturePL

By Christie Wilcox

As the oceans become more acidic, box jellyfish may start eating a lot more. Their greedy appetites could have a huge impact on marine ecosystems.

Some of the carbon dioxide we release is dissolving in the oceans, where it becomes carbonic acid – making the oceans less alkaline and more acidic. Scientists are scrambling to identify which species will be most impacted.

They are particularly concerned about organisms that play pivotal roles in marine food webs, because if they disappear, entire ecosystems may collapse.

Copepods are particularly critical. These tiny crustaceans are the most abundant animal on earth by mass. They swarm in vast numbers in some regions of the ocean, where larger animals feast on them.

What happens to copepods affects all that depend on them, “which is pretty much everything,” says Edd Hammill of Utah State University in Logan.

Previous studies have found copepods may be fairly resistant to ocean acidification. However, these have largely focused on single species, so community-level effects may have been missed.

To find out, Hammill and his colleagues collected zooplankton and one of their gelatinous predators, the box jellyfish Carybdea rastoni, from the waters around Australia. They kept the plankton in tanks containing either ambient seawater or seawater acidified at levels predicted for 2100, then added box jellyfish to half of the tanks. After 10 days, they counted what survived.

Continued

'Flying plankton' escape predatory fish

Tiny shrimp-like creatures called copepods break through the ocean's surface and leap through the air to escape predators, US scientists say.

They have been investigating how the brightly-coloured Pontellid copepods, which live close to the surface, are so abundant yet so conspicuous to fish.

Writing in Proceedings of the Royal Society B, the scientists say copepods travel further in air than in water.

Predators are also left confused about where they will land, they say.

Almost all commercially important fish, including cod, pollock and whiting, feed on copepods.

There are reports from the late-19th Century of copepods breaking through the water surface but observers at the time thought this was to allow them to moult.

A later report proposed jumping was part of an escape from predators but was not confirmed.

Read on:  http://www.bbc.co.uk/news/science-environment-17430640

Motor boat turbulence kills zooplankton in estuaries

Tuesday, 19 April 2011 09:32 UK
By Matt Walker
Editor, Earth News

Turbulence generated by speeding motor boats kills significant numbers of zooplankton, a study has revealed for the first time.

Experiments on copepods, tiny crustaceans that live and float in water, show that a third die in waters frequented by propeller-driven boats.

That is significantly more than in bodies of water not used by boats.

Zooplankton play a crucial role in water ecology and their death may have hitherto unknown impacts.

Details of the discovery are published in the Journal of Experimental Marine Biology and Ecology.

"A number of studies have been performed that looked at the impacts of much smaller scale turbulence on zooplankton," said Samantha Bickel, a PhD student at the Virginia Institute of Marine Science in Gloucester Point, US.

"But to my knowledge, no one had explored the idea that the intense turbulence generated by boats could have an adverse impact on zooplankton."

These prior studies had showed that even a small amount of turbulence can affect a copepod's ability to feed and grow.

So "it seemed intuitive that the sudden and intense turbulence created by a boat could harm or even kill copepods".

With colleagues Kam Tang, and Joseph Hammond of Hampton University, Virginia, US, Ms Bickel conducted experiments to test whether that was the case.

The researchers stained the copepods using a dye, which colours live animals red, while dead ones remain unstained.

That allowed them to quickly identify how many were alive and how many were dead in each sample.

"Regions with high boat traffic exhibited a higher occurrence of copepod carcasses," Ms Bickel told BBC News.

For example, 34% of copepods were dead in a channel while only 5-6% were dead in a marina and along a shoreline.

More copepod carcasses were found inside boat wakes (14%) than outside boat wakes (7%) and the fraction of dead copepods increased with increasing turbulence intensity.

"This suggests that turbulence generated by boats can be an important source of mortality among copepods," Ms Bickel said.

"This could have a number of important impacts within aquatic systems."

Zooplankton are a critical link between phytoplankton and fish in aquatic food webs.

High mortality in copepods could reduce the ability of a zooplankton population to graze down phytoplankton blooms and reduce the amount of food available to smaller fish that eat zooplankton, says Ms Bickel.

Also, if copepod carcasses are not consumed, they could transport high quality organic materials to the sediments or be decomposed by bacteria within the water column, she adds.

"So the zooplankton biomass that would normally go towards feeding fish would be diverted to feed bacteria instead."

The scientists have not yet been able to establish how many boats might cause a problem, and much would depend on their size and speed, which have a large effect on the turbulence they create.

"When viewed at a global scale, the portion of zooplankton killed by boat-generated turbulence is probably minimal," she says.

However, turbulence could have a significant impact on zooplankton, and therefore water ecology, at a local scale.

This may be particularly so in areas of high boat traffic and in closed freshwater systems such as lakes.

http://news.bbc.co.uk/earth/hi/earth_news/newsid_9449000/9449070.stm
(Via Dawn Holloway)