Physical legacy of freshwater bivalves: Effects of habitat complexity on the taxonomical and functional diversity of invertebrates

Abstract

Bivalves may play a major role in structuring aquatic communities. This may be especially relevant in aquatic communities dominated by non-native invasive bivalves, which can contribute to the increase of habitat homogenization. In this study, we assess how habitat homogenization, through the reduction of empty bivalve shells identities, influences the macroinvertebrate assemblages. Towards this end, a manipulative experiment with the empty shells of two native (Potomida littoralis and Unio delphinus) and one non-native (Corbicula fluminea) species was performed. Seven treatments were prepared, three of them consisting of homogeneous substrates using shells of one species, and four of them consisting in heterogeneous substrates using more than one species. The associated fauna colonizing different treatments was analyzed through taxonomic and trait-based approaches. Our results showed that the substrate complexity influenced the density of macroinvertebrates, with the heterogeneous treatments significantly yielding more dense assemblages. Also, the trait patterns differed among the levels of habitat heterogeneity, influencing mainly organisms that feed on microphytes of both small and big sizes, that inhabit areas with slow to moderate water flow, and that have short and long live cycles. Further, the functional diversity was not influenced by the substrate heterogeneity. Therefore, the habitat homogenization, through the accumulation of non-native C. fluminea empty shells in the river bottom, did not affect the functional diversity of the macroinvertebrate assemblages.

Decay and persistence of empty bivalve shells in a temperate riverine system

“…Shells can have many positive influences from an ecological perspective. They provide suitable substrate for attachment and refuge for many species, reduction of the physical and/or physiological stress, and also as reservoirs of nutrients to the benthic compartment (Gutiérrez et al, 2003;Ilarri et al, 2012Ilarri et al, , 2015bIlarri et al, , 2018Wenger et al, 2019). In fact, in previous studies performed in the Minho River it was possible to observe that the shells of the selected species attracted a relevant and similar macrozoobenthic community (Ilarri et al, 2015b).…”

“…However, the water flow differs between sites, with L1 located in the main canal of the Minho River and being characterized by a fastflowing (lotic) water regime during the entire year with the exception of summer and early autumn and L2 located in a side arm of the Minho River and being characterized by a slow-flowing (lentic) water regime throughout the entire year. The classification of sites according to the water flow conditions was done qualitatively, based on previous studies performed in the study area (Sousa et al, 2007(Sousa et al, , 2008Ilarri et al, 2015aIlarri et al, , 2015bIlarri et al, , 2018Novais et al, 2017) and on empirical evidence of the water regime throughout the study period (authors personal observations).…”

Drought-Induced, Punctuated Loss of Freshwater Mussels Alters Ecosystem Function Across Temporal Scales

“…While bivalve soft tissue decomposes quickly, shells persist for many decades (5-30 years), providing habitat for other stream biota (Strayer and Malcom, 2007;Ilarri et al, 2015;Atkinson et al, 2018). Over time, the benthos will be more homogenous as old shells dissolve and new relic shells are produced by a less diverse mussel assemblage ultimately altering benthic microhabitat characteristics and macroinvertebrate community structure ( Figure 1E; Ilarri et al, 2018).…”

Mass Mortality Events of Invasive Freshwater Bivalves: Current Understanding and Potential Directions for Future Research

“…Other studies have shown that shell density of C. fluminea is positively associated with biomass, diversity, and density of macroinvertebrates (Ilarri et al, 2012). Shells resulting from die-offs can also have significant effects on estuarine and freshwater macroinvertebrates than can use them as substrate or as refuge from predators (e.g., Ilarri et al, 2012Ilarri et al, , 2014Ilarri et al, , 2018Bódis et al, 2014b;Novais et al, 2015).…”