Quality or quantity: small-scale patch structure affects patterns of biodiversity in a sublittoral blue mussel community

Abstract

It is widely accepted that blue mussel Mytilus edulis L. beds support a high macrofaunal diversity. Nonetheless, sublittoral mussel beds on rocky shores have rarely been examined in a patch context to determine the processes creating and maintaining the diversity and assemblages of organisms occupying them. Whereas the species-area relationship is a well-established theory in ecology, less is known about its effect on faunal compositions in aquatic habitats. Also, the effect of patch shape and relative patch edge are poorly studied within a rocky shore mussel framework. The present study examined the effects of blue mussel patch size, patch shape, and the presence of algae and sand in mussel patches on the composition and diversity of associated macrofaunal communities in sublittoral habitats. In line with the species-area relationship, we found that the total number of taxa increased with patch size up to ca. 500 cm 2 , thereafter declining. Small patches largely lacked annelid worms and showed a lower diversity of gastropod species. We also found that the diversity was further enhanced by a high biomass of blue mussels, the presence of algae and the weight of interstitial sand. The shape of the patch had no effect on species richness, but affected the species composition. We conclude that structural components of sublittoral blue mussel habitats, such as patch content and shape, greatly affect the diversity and faunal assemblage. This has important implications in conservation biology, since habitats are becoming more fragmented. Our study demonstrates that not only habitat quantity, but also quality has a large impact on species communities in marine ecosystems.KEY WORDS: Species-area relationship · Patch shape · Edge effect · Ecosystem engineer · Rocky shores · Macrofauna · Baltic Sea Resale or republication not permitted without written consent of the publisherAquat Biol 12: [261][262][263][264][265][266][267][268][269][270] 2011 experimental evidence confirming this in marine ecosystems.Studies in mussel and seagrass beds suggest that patch size affects the number of taxa present (Tsuchiya & Nishihira 1985, Witman 1985, Bell et al. 2001, Bowden et al. 2001, Norling & Kautsky 2008. Nonetheless, few studies have clearly distinguished its role in determining the faunal communities, and the relationship can sometimes be non-linear and scale dependent (Kelaher 2003). For example, there might be distinct thresholds after which the influence of habitat structure changes in direction and/or magnitude, or there might be a minimum amount of structure that is required before positive benefits are implemented (Coull & Wells 1983, Gotceitas & Colgan 1989. Also, upper thresholds, beyond which increased habitat structure no longer has an effect or even negatively affects the associated fauna, may exist (Fonseca et al. 1996, Kelaher 2003. Not only patch size, but also the architectural complexity (e.g. Kostylev et al. 1997, Commito & Rusi gnuolo 2000, as well as the density and size of the habitat-forming sp...

Facilitation Cascades in Marine Ecosystems: A Synthesis and Future Directions

“…Explicit tests that utilize mimics of habitat-formers to resolve whether facilitation occurs via food enhancement versus habitat-provisioning, however, provide mixed results. Communities on habitat mimics can be characterized by different compositions and numbers of taxa compared to a live habitat-former (Hall & Bell 1988, Verweij et al 2006, Koivisto et al 2011, Gartner et al 2013). In addition to mimics, stable isotopes have been used to identify potential trophic linkages among habitat-formers and associated intertidal food webs.…”

“…Studies have generally examined the effects of variation in basal and secondary habitat-former traits on the enactment of the cascade independent of one another (but see Bishop et al 2013). Surveys and experimental manipulations of habitat-formers generally demonstrate positive relationships between increasing habitat-former biomass, cover or density and the associated species' abundance or richness (Mukai & Iijima 1995, Pavia et al 1999, Gribben et al 2009a, Thomsen 2010, Drouin et al 2011, Koivisto et al 2011, Angelini et al 2015. However, such relationships are often nonlinear as they start to plateau at higher abundances of the basal habitat-former (Bishop et al 2013), perhaps indicating a saturation point beyond which structural habitat no longer limits colonization of the secondary habitat-former or the facilitated inhabitants, or a point beyond which increases in density no longer enhance amelioration of abiotic or biotic stress.…”

An introduction to assessments

“…Not surprisingly, thus, in literature different relationships are found between patch size, even within a single study area, although always either positive or not significant (see e.g. Tsuchiya and Nishihira 1986;Norling and Kautsky 2008;Koivisto et al 2011;Jungerstam et al 2014;Sepúlveda et al 2016).…”