Quality as well as quantity can change as an evolutionary response to intensive harvesting of algae

Intensive production of algae for biofuels, new bio-products and animal feed is of increasing commercial interest. Land based systems commonly cultivate single species of algae at high densities with periodic removal of biomass for commercial uses. While we know that such intense harvesting regimes can effect the evolution of size and growth rates, we don’t know if there are evolutionary consequences for the ‘quality’ of the commercial yield.

Recent research has investigated whether the overall productivity of desirable biochemical components in algal culture, such as oils (particularly omega 3 fatty acids) and amino acids, will evolve differently with different harvesting regimes.

To do this, the team used three strains of a freshwater filamentous algae Oedogonium, which they cultured in buckets at James Cook University in Queensland. For each strain of algae, 10 replicates were assigned to a high yield (approximately 70% of the biomass was removed each week) or a low yield (approximately 20% of the biomass was removed each week) harvest regime. After 12 weeks all replicates were treated the same, in that approximately 50% of the biomass was removed weekly for a further four weeks.

The research team included colleagues from The Centre for Geometric Biology (Dustin Marshall and Keyne Monro) working with scientists from James Cook and Southern Cross Universities.

Dustin and his colleagues found that there were a number of changes in the biochemistry of the algal strains after 12 weeks of different selection regimes (high yield and low yield) but more importantly, after a further four weeks of identical selection, differences persisted for one amino acid (lysine) and most fatty acids, implying an evolutionary shift.

Intensive harvesting of algae is becoming more common but the evolutionary implications are not completely understood.

Experimental cultures of algae were maintained at different harvesting regimes (high yield and low yield) to explore the consequences for the production of commercially important biochemical components of the algae.

Researchers found that certain desirable products, such as the amino acid lysine had lower productivity when subject to an intense harvesting regime (red bar).

These findings present a conundrum for producers: on the one hand intensive harvesting leads to more rapid growth rates, higher protein production (initially at least) and higher biomass yields over all. On the other hand, productivity of other desirable products (such as fatty acids and lysine) goes down.

While this study suggests that the burgeoning algal culture industry should pay attention to the role of evolution in intensively harvested cultures, it also suggests a solution. By maintaining ‘mother cultures’ of algae held under a low harvest regime, the operators will be able to restart their cultures periodically to minimise the negative consequences of biochemical evolution.

This research was published in the journal Evolutionary Applications.