Better together…

A study shows coral polyps actively generate micro-currents and eddies to promote nutrient inflow and exchange of materials using externally located cilia.
Image: pixabay.com.
Image: pixabay.com.

No, this is not a belated bit of biased support for the Scottish referendum on independence from England  (which was rejected by those who voted and thereby prevented the United Kingdom becoming the anagrammatically amusing Untied Kingdom…). Rather, it is recognition that – at least in nature – sometimes things do work better when two partners co-operate rather than work against each other. Take for example the reef-building corals – an intimate mutualistic symbiosis between a unicellular alga, a dinoflagellate and an animal, the coral polyp. Put very simply, the alga provides much of the polyp’s food requirements by dint of its photosynthesis, which ultimately allows it to make the massive coral reefs. Although warm-water coral reefs are the basis of extremely rich and biodiverse ecosystems, they are nutritionally poor. This ‘nutrient paradox’ – originally recognised by Charles Darwin (is there any branch of biology that doesn’t have a contribution from this venerable Victorian?) – has traditionally been presumed to be due to very tight cycling/recycling of nutrients within the ecosystem (and the abundance of mutualistic symbioses therein, amongst other factors…). However, a new twist to this nutrient tale has recently been proposed by Orr Shapiro et al. They have revealed that, far from being static structures dependent upon the vagaries of currents to bring nutrients to them and remove waste products, the coral polyp actively generates micro-currents and eddies that promote nutrient inflow and exchange of materials. Using externally located cilia, these miniature structures whip up ‘vortical flows’ immediately adjacent to the epidermal surface, which reduces the exchange-limiting boundary layer at that site thereby facilitating mass transport between coral and the ocean. And in the way of all good discoveries, there are potential spin-offs to other areas of study. In this instance the team posits that investigation of these surface-situated cilia could be used as an alternative to the study of more-inaccessible, internalized cilia, e.g. those in the airways of animals. Thus, there may be unpredictable benefits for biomedicine from this photosynthetically dependent marine mutualism (I know, plants lighting up the path for others to follow – again!!). I’ve oftentimes wondered what the polyp brought to this relationship – aside from providing a chalky castle for the enslaved, hard-working alga. Well, I guess we now know, and it’s reassuring to discover (finally…?) that this intriguing symbiosis is much more mutual than we might previously have imagined.

 

[A video of this phenomenon can be seen on YouTube. The irony of internalization of the dinoflagellate symbiont – which, as its name implies, usually has flagella (two in this case, like much bigger versions of cilia)  – within the coral polyp and its consequential loss of its flagella on the one hand, and the importance of the polyp’s cilia (pale imitations of flagella?) in and to this relationship on the other, is not lost on Mr P. Cuttings. And this item gives a whole new meaning to the phrase ‘on the lash’ because cilium is Latin for eye-lash… – Ed.]