Regenerative bioturbation by intertidal burrowing crabs modifies microphytobenthic composition and enhances primary production in SW Atlantic mudflats

Abstract

In coastal systems, benthic microalgae are important primary producers that significantly contribute to global primary production. Microphytobenthic (MPB) community structure and the ecosystem functions that it mediates are modulated by biotic and abiotic factors. Through burrowing activity, different types of bioturbators can impact MPB in different ways. Through directed sampling and field experiments performed at the Mar Chiquita coastal lagoon (Argentina), we evaluated the effect of regenerative bioturbation (continuous digging and maintenance of burrows, with sediment transfer from depth to surface) by the intertidal burrowing crab Neohelice (Chasmagnatus) granulata on MPB. We compared sediment properties and MPB attributes between natural burrowed and non-burrowed areas. Moreover, we experimentally manipulated regenerative bioturbation to evaluate if MPB composition and primary production are altered by crab burrowing activity. Field sampling showed that MPB and sediment properties differed between natural burrowed and non-burrowed areas. Experimental results indicated that regenerative bioturbation by N. granulata increased sediment oxygen concentration at each measured depth and also changed MPB composition (due to the reduced total abundance of cyanobacteria), but nearly doubled primary production in comparison with plots without bioturbation. Thus, the net effects of regenerative bioturbation were positive for MPB productivity, reinforcing the idea that this kind of bioturbation is an important biological force that enhances primary production in intertidal systems.