The turbulence we have put into our reef aquariums with propeller pumps and random flow created by wavemakers is an efficient way to create water flow, yet a recent bit of research finding boat turbulence killing zooplankton in channels and estuaries may also have some bearing on our reef aquariums as well. Experiments with copepods have shown that one third of copepods in areas frequented by propeller-driven boats are dead– significantly higher than in waters with no boat traffic. The 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. “But to my knowledge, no one had explored the idea that the intense turbulence generated by boats could have an adverse impact on zooplankton.”
Prior studies had showed that even a small amount of turbulence can affect a copepod’s ability to feed and grow and Bickel and her colleagues postulated that the sudden and intense turbulence created by a boat could harm or even kill copepods.
With colleagues Kam Tang, and Joseph Hammond of Virginia’s Hampton University, Bickel conducted experiments to test whether that was the case. By using a dye that colored the live animals red and left the dead ones unstained, the team collected and studied different samples.
What did the team find? Areas with high boat traffic did have a higher occurrence of copepod fatalities. Samples had shown 34% of copepods were dead in a highly-traveled channel while only 5-6% were dead in a marina and along a shoreline. The team discovered more copepod carcasses were found inside boat wakes (14%) than outside boat wakes (7%) and the amount of dead copepods increased with increasing turbulence intensity.
“This suggests that turbulence generated by boats can be an important source of mortality among copepods,” Bickel added. “This could have a number of important impacts within aquatic systems.”
As we know, zooplankton are a critical link between phytoplankton and fish in aquatic food chains. The less copepods can mean less zooplankton to chow down on phytoplankton blooms and reduce the amount of food available to smaller fish that eat zooplankton.
Another thought too, if the dead copepods are not consumed the addition of rich organic material into the bottom sediment or be consumed by bacteria. “So the zooplankton biomass that would normally go towards feeding fish would be diverted to feed bacteria instead,” she said.
While the overall global levels of copepods and zooplankton killed by boats may be minimal, on the local level and in closed water systems where pollution and other manmade influences have hindered water quality, this could become a greater problem to the ecology of those water systems.
As far as reef aquariums, the chaotic flow and turbulence from propeller-style pumps probably does have an effect on copepod and other “bug” populations in our aquariums. As we’ve found out over the years, your most successful refugiums go well beyond a ball of chaetomorpha wedged between the overflow side of a sump and your return pump. The most successful ‘fuges are when incorporated into an area of low flow but with the great variety of foods available on the market today, live ‘pods are not essential but are definitely beneficial to the overall system.