Invasive seaweed provides inadequate shelter from predators

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Invasive seaweed provides inadequate shelter from predators

May 22, 2018 - 21:42
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As invasive seaweed species overrun kelp habitats, fish in recent decades have been finding it more challenging to locate a safe refuge from predators, according to a study.

Cunner in Nahant, Massachusetts looking for refuge. The photo shows a mix of algae species, including Dasysiphonia japonica (red seaweed in foreground) and Saccharina latissima (golden blades in background).

Fish often use kelp forests to hide from potential predators. In recent decades, kelp forests have been taken over by invasive, turf-dominated seaweed species.

Being shorter and less dense, the invasive species gives the fish less protection and makes them more visible to predators; this may consequently affect their behaviour.

This is the finding of a study by researchers from the University of New Hampshire (UNH), as published in the recent issue of Journal of Experimental Marine Biology and Ecology.

In the study, three experiments were conducted in the Gulf of Maine involving the cunner (Tautogolabrus adspersus), a species of wrasse: in situ video observations, a refuge choice study and a foraging efficiency study.

According to the University's press release, "The video of cunner, a residential mid-trophic level fish, in their habitat showed that the fish preferred the kelp almost three times as much. The refuge choice experiment, where different seaweed scenarios were created for them to hide, supported the video observations that in all cases, kelp was the refuge of choice. The foraging efficient study showed very little difference between seaweed habitats."

Jennifer Dijkstra, research assistant professor in UNH's Center for Coastal and Ocean Mapping said that the cunner repeatedly chose to hide in the kelp or similar seaweed species: "Over and over, they gravitated to the kelp that is taller and because of its blade-like structure, provides a canopy to hide under. Because these new species are lower, this makes it harder for the fish to hide themselves from predators.

"Our results suggest that the refuge-seeking behaviour of the cunner may be impacted by the ongoing shift we have seen in our earlier studies of the increased dominance of the Dasysiphonia japonica (invasive seaweed) in the southern Gulf of Maine," she added.

The impact of the invasive species may prove to be more detrimental to juvenile cunner, as they tend to seek refuge more often. The researchers warn that continued reduction in kelp cover may lead to density-dependent mortality in the cunner population, and this may result in cascading effects on other species in the local ecosystem.

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