Coastal food webs greatly impacted by ecosystem engineers

6 April 2016

A new international study reveals that ecosystem engineers, such as sea-grass, cordgrass and mussels, can create the perfect habitat for themselves and other species, making them an invaluable tool for the preservation of endangered coastal ecosystems, such as the Wadden Sea. Peter de Ruiter, Professor of Soil Systems Ecology at the University of Amsterdam's (UvA) Institute for Biodiversity and Ecosystem Dynamics, was involved in the study, which was published in academic journal Proceedings of the Royal Society B.

Species capable of significantly modifying their habitats are referred to as 'ecosystem engineers'. Organisms such as sea-grass, cordgrass and mussels form structures which provide shelter to many other plants and animals and surfaces for them to attach to, often greatly promoting species richness. In addition, ecosystem engineers also appear to alter these species' feeding connections by affecting the food web structure in its entirety (food chain). This was demonstrated by an international consortium under the Dutch leadership of the NIOZ Royal Netherlands Institute for Sea Research, University of Groningen (RUG), Radboud University (RU) and the UvA.

Food web

The researchers examined the effects of ecosystem engineers on the food web of two coastal ecosystems. The first consisted of species-poor pebble beaches along the North American coast (Rhode Island) capable of being colonised by cordgrass. During high tide, plants and wildlife washing up on theses stark beaches are crushed between the large pebbles. During low tide, the organisms are desiccated by the sun. However, a variety of species can suddenly survive once the pebbles are stabilised with cordgrass stalks, which also develop leaves that provide shelter from the sun. If mussels colonise the area, the soil continues to stabilise and the number of species further increases, until the habitat supports approximately 2.5 more species, on average, than pebbled or sandy surfaces. In addition to numbers of species, the number of feeding connections also grows (by an average of around 1.7 times the original number), thereby increasing the complexity of the food web.

Bare sandbanks

The researchers repeated their study on the opposite side of the Atlantic. Along the coast of West Africa (Banc d’Arguin, Mauritania), bare sandbanks are being colonised by sea-grass, which traps fine sediment, forming a thick layer of sludge in which a variety of species can thrive. Crustaceans then burrow into the sludge, creating large pools that become nursery areas for dozens of species of fish. This in turn increases biodiversity, as well as food web complexity, even further.

Profound impact

So in both regions the effects of ecosystem engineering, which occur in two stages, have a profound impact on the food web. It was also found that while almost none of the species depended on sea-grass, cordgrass, mussels or crustaceans as a food source, a great many did rely on their ecosystem engineering effects. Therefore, the development of the food web is determined not only by the food chain, but also on the effects of ecosystem engineering. This makes it important to analyse these effects in particular, in order to learn more about endangered coastal areas.

Scource: Nature Today, Els van der Zee, Altenburg & Wymenga, Han Olff, Groningen University and Tjisse van der Heide, Radboud University

Publication

Van der Zee EM et al.:'How habitat-modifying organisms structure the food web of two coastal ecosystems' in Proceeding of the Royal Society B (9 March 2016). Proc. R. Soc. B 283: 20152326 

Published by  Faculty of Science