Plant Cuttings

The lachrymatory tale of the barnacle and the bacterium

For Valentine's Day Nigel Chaffey finds a tale of an unlikely couple who have set up home together, though it ends in tears.

Ever intrigued by, and interested in sharing, stories which show how plants – or organisms with plant-like properties – help other less well-off forms of life, this is a tale that might well bring a tear to the eye. Investigating formations in sandstone blocks on the coast near the Lakes Entrance holiday resort on the coast of Victoria (SE Australia), John Buckeridge and William Newman have uncovered what appears to be the first record of mutualistic symbiosis between a ‘higher invertebrate’ and cyanobacteria.

Chthamalus stellatus
Sadly Chthamalus antennatus couldn’t be with us today, so here’s a cousin Chthamalus stellatus. Photo: Michael Maggs / Wikipedia

The rock features, which have the appearance of crying eyes and have been named the ‘Tears of the Virgin’, are apparently the work of cyanobacteria [bacteria that undergo photosynthesis similar to green plants (and are therefore sufficiently plant-like for Mr Cuttings’ purposes)] that dissolve away some of the rocky substrate to produce depressions and the elongated tear-like ‘tails’. The depressions are occupied by the barnacle Chthamalus antennatus, which is thereby better able to withstand the desiccating conditions when uncovered by the receding tide.

The cyanobacteria – which have yet to be fully identified although may involve Rivularia sp(p).– are presumed to benefit from access to the barnacle’s nitrogenous waste products. An additional bonus for the barnacle is that these dehydration-defying depressions allow it to survive in areas higher on the shore than they could otherwise occupy so it is less likely to be prey to crabs and other predators.

Barnacles and blue-green algae in binary biological harmony? That’s just bonzer!