Pattern formation at multiple spatial scales drives the resilience of mussel bed ecosystems

Abstract

Self-organized complexity at multiple spatial scales is a distinctive characteristic of biological systems. Yet, little is known about how different self-organizing processes operating at different spatial scales interact to determine ecosystem functioning. Here we show that the interplay between self-organizing processes at individual and ecosystem level is a key determinant of the functioning and resilience of mussel beds. In mussel beds, self-organization generates spatial patterns at two characteristic spatial scales: small-scale net-shaped patterns due to behavioural aggregation of individuals, and large-scale banded patterns due to the interplay of between-mussel facilitation and resource depletion. Model analysis reveals that the interaction between these behavioural and ecosystem-level mechanisms increases mussel bed resilience, enables persistence under deteriorating conditions and makes them less prone to catastrophic collapse. Our analysis highlights that interactions between different forms of self-organization at multiple spatial scales may enhance the intrinsic ability of ecosystems to withstand both natural and human-induced disturbances.

Facilitation shifts paradigms and can amplify coastal restoration efforts

“…However, given that clumping, on average, doubled growth and yields in our experiments and in low elevations in Florida marshes increased it by ∼3×, we expect that a well tuned design can significantly reduce the number of outplants needed per site to still achieve whole marsh restoration over the same time period. Moreover, aggregated designs may more closely follow the observed, natural patchiness that is apparent in many emerging estuarine ecosystems, which in turn improves ecosystem resilience (55).…”

Production efficiency of mussel bottom culture

“…At smaller scale (<1 m), mussels organise in interconnected net-like structures at high densities or in small mussel patches at low densities, that elevate from the sediment, (hummocks) due to the mud build-up underneath the mussel assemblages, which subsequently increases food supply (Liu et al 2012). Aggregation within the <1 m scale can be explained by density-dependent processes, where mussels actively organise in small clusters and move away from higher density spots (Liu et al 2014). When mussel beds get older, patterns may break up due to…”

“…Competition forces mussels to move away from crowded situations and is a driver to self-organise in small-scale patterns (Liu et al 2014). At high densities, however, mussels cannot avoid crowding and competition will result in high losses (up to 75% within four weeks after relaying in Chapter 3).…”

“…The banded patterns result from an interplay of negative feedbacks by food competition when mussels are homogeneously distributed and positive feedback by enhanced food delivery when mussels are heterogeneously distributed (Gascoigne et al 2005, Van de Koppel et al 2005, Van De Koppel et al 2008. At a smaller (centimetre) scale within the banded structure, competition between mussels drives organisation in net-like structures (Liu et al 2014). When mussel beds get older and density decreases, or at low-energy sites, mussels may organise in patches that develop in a fractal power-law pattern (Snover & Commito 1998, Commito et al 2014.…”

“…Patterning promotes food delivery by increasing near bed turbulence and in an environment with strong tidal currents, growth and survival is higher in patterned mussel beds compared to homogeneous beds (Van De Koppel et al 2008, Saurel et al 2013). Models show that patterned mussel beds that are organised on small and large scales can survive at lower algal concentrations and are able to persist in lower mussel densities because of more efficient food uptake (Liu et al 2014).…”