Invasive species can leave lake ecosystems on brink of collapse, say University of Cambridge researchers

The ecosystems of lakes can be pushed to the point of collapse by some invasive, non-native species, impacting drinking water, aquaculture and recreation, Cambridge researchers have shown.

Invasive fish such as Asian silver carp (Hypophthalmichthys molitrix) and crustaceans such as American signal crayfish (Pacifastacus leniusculus) are among the species found to reduce the abundance of important organisms in lakes significantly, degrading water quality.

The researchers, from the University of Cambridge’s Department of Zoology, warn lake ecosystems can rapidly be sent beyond a critical tipping point, suddenly shifting the water from healthy to a damage position that is hard to reverse.

There are two alternative stable states in which shallow lakes naturally exist. Healthy lakes with clear water have an abundance of vegetation, while cloudy water is dominated by algae.

The latter use up all the nutrients in the water and block sunlight, which prevents aquatic vegetation from growing, meaning the ecosystem cannot recover.

Such deteriorate freshwater ecosystems are threatening to human health and water security.

When blue-green algae - or cynobacteria - blooms, it can produce toxins, contaminating food webs and poisoning water supplies.

Such algae was found at a lake in Milton Country Park recently, leading to activities on it being closed.

Dr Sam Reynolds, from the Department of Zoology, first author of the report published in Global Change Biology, said: “Algal blooms represent one of the most significant threats to the security of the Earth’s surface freshwaters. Simply undoing the circumstances that triggered a tipping point will not restore the ecosystem - the road to recovery is slow and steep.”

Human activity and climate change are leading to the swift spread of invasive, non-native species around the globe, which prompt these conditions.

But the impact of such species is not necessarily always negative.

Invasive molluscs, such as the zebra mussel (Dreissena polymorpha), engineer the opposite biological and environmental response. They delay the collapse of lakes ecosystems and could aid the recovery of those already degraded.

“Managers of drinking water reservoirs, for example, may be able to avoid the cost of dealing with blooms of harmful algae, by removing invasive crayfish but allowing established non-native zebra mussels to remain and act as biological filters,” said Prof David Aldridge, senior author of the report and the winner of Researcher of the Year at the Cambridge Independent Science and Technology Awards in April.

The paper offers guidance on the best ways to manage waterbodies.

“Early detection and rapid response plans should always be our first line of attack,” said Prof Aldridge. “But in situations where invaders have already established and can no longer be eradicated, it may be appropriate to embrace their positive effects.”

While the research focused on shallow lake ecosystems, the researchers say their framework could be applied to other critical ecosystems experiencing catastrophic tipping points, such as coral reefs, kelp forests and desert shrublands.

This research was funded by the Biotechnology and Biological Sciences Research Council (BBSRC).

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