When it comes to meal time, sea slugs, or nudibranchs, attack prey that have just eaten in order to access their meals, new research has found.
The researchers say they are the first to have observed this feeding strategy in the natural world and have named the behavior ‘kleptopredation.’
The tiny, brightly colored sea slugs live and feed on hydroid colonies – a super organism distantly related to corals, which consist of individual polyps that capture and feed on plankton and small crustaceans.
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When it comes to meal time, sea slugs, or nudibranchs, attack prey that have just eaten in order to access their meals, new research has found. This is the nudibranch, or sea slug, that feeds on hydroid colonies.
WHAT ARE NUDIBRANCHS?
Nudibranchs, also called sea slugs, are an order of marine mollusks that lack the shell, gills and mantle cavity typical of other mollusks.
Their delicately colored bodies have bizarre outgrowths called cerata, which serve a defensive function, dishcharging stinging cells (nematocysts) that they ingest from cnidarians (jellyfish).
Cerata also function in gas exchange.
They have antenna-like organs (rhinophores) in their heads, and can reach lengths of 43 centimeters (16 inches).
They live and feed on hydroid colonies – a super organism distantly related to corals, which consists of individual polyps that capture and feed on plankton and small crustaceans.
The study, published in the Royal Society journal Biology Letters, was conducted by researchers at the University of Portsmouth.
‘This is very exciting, we have some great results here that rewrite the text book on the way these creatures forage and interact with their environment,’ said Dr Trevor Willis, who led the research into the behavior of nudibranchs off the coast of Sicily.
The researchers studied the nudibranch Cratena peregrina, finding that the creature preferred to eat polyps that had recently eaten and that over half of the nudibranch’s diet was made up of zooplankton – the prey of the polyp they were consuming.
The research showed that the nudibranchs doubled their attack rate on prey that had eaten zooplankton, compared to their hungry counterparts.
‘Effectively we have a sea slug living near the bottom of the ocean that is using another species as a fishing rod to provide access to plankton that it otherwise wouldn’t have,’ said Dr Willis.
‘People may have heard of kleptoparasitic behaviour – when one species takes food killed by another, like a pack of hyenas driving a lion from its kill for example.
‘This is something else, where the predator consumes both its own prey and that which the prey has captured.’
According to the researchers, the behavior is a combination of kleptoparasitic competition and direct predation.
Dr Willis first became interested in nudibranch feeding behavior while pondering how a species of nudibranch in his native country of New Zealand seemed to have evolved to live and feed on hydroid colonies at the risk of depleting them.
He said that there would always be the risk that the food would run out before the nudibranchs could reproduce.
‘A colleague in Sicily had data to indicate that there was something going on other than a simple predator-prey relationship,’ says Dr Willis.
Dr Willis’ research into Cratena peregrina aimed to investigate how the species balanced energy intake with the preservation of habitat.
To do this, his team looked at stable nitrogen isotope levels in the nudibranchs, hydroid polyps and zooplankton, discovering that the nudibranchs had a significantly lower level than expected if the polyps were their only prey.
This indicated that the hydroid polyp represented a relatively low percentage of the total prey ingested.
This implies that by consuming fewer hydroid polyps and increasing energy intake from their prey’s plankton diet, nudibranchs may be able to extend the life of the hydroid colony on which they live, feed and shelter.
It’s uncertain how widespread this behavior might be but it’s hoped this and future research could contribute to a better understanding of the marine environment.
‘Our ability to understand and predict ecosystems in the face of environmental change is impeded by a lack of understanding of trophic linkages,’ said Dr Willis, but he added there was still a lot to learn from research.
‘While we have some great results, like any science worth its salt, it raises more questions than it answers.’
Nudibranchs, also called sea slugs, are an order of marine mollusks that lack the shell, gills and mantle cavity typical of other mollusks