Is this the equivalent of a crayfish selfie?
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The iconic Murray River crayfish
Murray River crayfish are the largest freshwater crayfish on mainland Australia. Characterised by their large size and formidable large white claws, Murray River crayfish are iconic throughout south eastern Australia where they exist. However, they have been in decline for decades, and overfishing, river regulation and pollution are all likely to have played a part in their demise. Despite their broad appeal and totemic status, we know very little about the biology and behaviour. During 2009, we employing underwater video systems in clear, montane streams in the ACT region, where we were able to gain a new insight into the population structure of Murray River crayfish, in addition to some neat behaviours never before reported.
This research has been published in Australian Journal of Zoology. |
What do they eat?
Study site on the Goodradigbee River
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Murray River crays are considered to be 'ecosystem engineers' in that they perform key ecosystem functions. Crayfish are believed to do this by consuming detritus - dead and decaying aquatic material, or terrestrial material that has fallen into the water. As such, declines in Murray River crayfish may have deleterious impacts on freshwater ecosystems. In this study, we observed crayfish feeding on small patches of terrestrial plant matter, made up predominantly of She-oak (Casuarina) needles and sticks, that had formed in back eddies of the Goodradigbee River. Getting up close and personal with cameras revealed the crayfish were eating the biofilm off the terrestrial material, and not consuming the plant matter itself. More questions are raised than answered!
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Social crayfish?
A female crayfish carrying eggs under her tail
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We also noted that crayfish were feeding in loose aggregations on these patches of terrestrial detritus. This was surprising, as it is widely considered that crayfish are aggressive, solitary animals. Instead, our cameras revealed that crayfish were willing to share the space on this restricted food source, and no escalation of aggression was observed. Sampling of the individuals on these patches revealed them to be mostly females, or immature males. Could it be that adult males are the agro individuals? Further research is needed to answer this question. I would suggest that crayfish hold many more surprises, just waiting to be uncovered.
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Starrs, D., Ebner, B.C., and C.J. Fulton (2015) Cease-fire: Minimal aggression among Murray River Crayfish feeding on patches of allochthonous material. Australian Journal of Zoology 63: 115-121 doi: 10.1071/ZO14081 LINK
