Remarkable size-spectra stability in a marine system undergoing massive invasion

Abstract

The Mediterranean Sea is an invasion hotspot, with non-indigenous species suspected to be a major driver behind community changes. We used size spectra, a reliable index of food web structure, to examine how the influx of Red Sea fishes into the Mediterranean Sea has impacted the indigenous species community. This is the first attempt to use changes in the size spectra to reveal the effect of biological invasions. We used data from trawl catches along Israel's shoreline spanning 20 years to estimate changes in the community size spectra of both indigenous and non-indigenous species. We found that the relative biomass of non-indigenous species increased over the 20 years, especially for small and large species, leading to a convergence with the indigenous species size spectra. Hence, the biomass of indigenous and non-indigenous species has become identical for all size classes, suggesting similar energetic constraints and sensitivities to fishing. However, over this time period the size spectrum of indigenous species has remained remarkably constant. This suggests that the wide-scale invasion of non-indigenous species into the Mediterranean may have had little impact on the community structure of indigenous species.

Alien species stabilize local fisheries catch in a highly invaded ecosystem

“…This latter observation confirms the results of several recent studies demonstrating that competition strength with alien species is not correlated to decreases in indigenous species abundance or richness (Givan et al 2018;Buba and Belmaker 2019). Furthermore, Buba et al (2017) demonstrated that over the same period of increase in alien abundance, indigenous fish size spectra in the eastern Mediterranean did not change. In a system at equilibrium and close to carrying capacity, a strong negative effect of alien species on the food web can be expected (Goren et al 2016;Corrales et al 2017).…”

“…Despite their large abundance and biomass, the effect of alien species on indigenous Mediterranean populations is still unclear. On one hand, the stability of fish size spectra (Buba et al 2017) and a lack of evidence for the competitive exclusion of indigenous species by alien species (Arndt et al 2018;Givan et al 2018; Buba and Belmaker 2019) suggest limited effects. On the other hand, alien species affect the local food-web structure, thus increasing the competition for local resources (Edelist et al 2013a;Goren et al 2016).…”

“…Thus far, studies that quantified the contribution of alien species to local catch have relied primarily on contemporary patterns (Lefkaditou et al 2010;Yemisken et al 2014;Goren et al 2016). Several studies have compared two sampling periods (Edelist et al 2013a;Buba et al 2017;Givan et al 2018), but the lack of continuous sampling throughout these periods prevents the detection of fine-resolution shifts in population sizes (Maunder et al 2006). The detection of such shifts requires high-resolution time series based on standardized sampling.…”

Native biodiversity collapse in the eastern Mediterranean

“…[50,51]). However, recent studies showed that successful non-indigenous fishes preferentially occupy different functional niches than native ones, providing so far little support for active competitive exclusion of functionally similar species [52][53][54][55]. Additionally, the preliminary results of an ongoing functional trait study by our team of the same mollusc assemblages analysed here suggest little potential for active resource competition between native and non-indigenous assemblage components in the shallow subtidal [56].…”

Non‐indigenous molluscs in the Eastern Mediterranean have distinct traits and cannot replace historic ecosystem functioning

“…This suggests that other drivers, particularly regionally rapid seawater warming, might play a more significant role in native species' demise than previously thought (Albano et al, 2021;Givan et al, 2018;Rilov, 2016). Recent studies on Lessepsian fishes further support the secondary role of competitive displacement (Buba & Belmaker, 2019;Buba et al, 2017;Givan et al, 2018) and suggested that NIS indeed tend to occupy 'empty niches' (Azzurro et al, 2014;Givan et al, 2017), but none involved pre-invasion assemblage data.…”