The role of the physical structure of Spartina densiflora Brong. in structuring macroinvertebrate assemblages

MARÍA C. SUEIRO; BORTOLUS, A.; SCHWINDT, E.

AQUATIC ECOLOGY

SPRINGER

Año: 2012

1386-2588

In Patagonian rocky salt marshes, thepresence of the austral cordgrass Spartina densifloraprovide habitat for diverse faunal assemblages. Twodifferentmechanismsmay influence the distribution andabundance patterns of these associated organisms: thosegenerated by the biological properties of cordgrassesand those caused or mediated by the physical structuresupplied by the plants.The aims of this studywere: (1) todetermine the effect of cordgrasses on macroinvertebrateassemblages dominating a rocky marsh and (2) todetermine how much of this effect is caused by thephysical structure supply by the plants. In order toachieve these objectives, we conducted two fieldmanipulative experiments. In the first one, we manipulatedthe presence of defaunated transplants of cordgrass,and in the second one,wedid the samewith plasticcordgrass mimics simulating the architecture of Spartinadensiflora. In both experiments, sessile and mobileassemblages were separately examined to evaluatewhether they respond in the same way or not. Abundanceand richness ofmobile and sessile organismswerehigher in transplant and mimic cordgrass plots comparedto the controls, indicating that the presence ofcordgrasses, either transplanted or artificial, has apositive effect on sessile and mobile assemblages.Furthermore, we found that the composition of mobileand sessile macroinvertebrates assemblages did notdiffer between transplants and mimics. Therefore, thephysical structure of cordgrass was found to be themajor factor influencing macroinvertebrates assemblagesin the studied Patagonia rocky salt marshes.Within the period of 1 year, mobile and sessile faunacolonized several times more abundantly transplant andartificial cordgrass than the control unvegetated plots,highlighting the key role of cordgrasses in optimizingthe colonization rate ofmacroinvertebrate communitiesin this rocky bottom environment. Since Spartinadensiflora is invading different regions worldwide, ourstudy may help to predict its potential effect on theinvaded communities.