Shifts in Eastern Mediterranean Fish Communities: Abundance Changes, Trait Overlap, and Possible Competition between Native and Non-Native Species

Abstract

During the last few decades the fish community has changed substantially along the Eastern Mediterranean continental shelf, which is a hotspot of invasion by species that had migrated via the Suez Canal. Trawl data from the Israeli coast spanning two periods (1990-1994 and 2008-2011) were compared to identify species with substantial variation in their relative abundance between the two periods. The aim of this study was to examine if certain ecological traits characterize fish species showing an increase or decrease in relative abundance, and if non-indigenous fishes with strongly increasing populations may have caused the decline of native species with similar habitats and diets. We found that the main predictors of population trends were species length, habitat affinity, and maximum depth, with larger and soft bottom species displaying decreasing abundances. Comparing native and non-indigenous fishes with similar habitat and diet, we found a potential for competitive impact of the Indo-Pacific Plotosus lineatus and two Upeneus spp. on the native Mullus species. However, competition with non-indigenous fishes could not generally explain the dramatic decline of many other native species between the two study periods. Alternative causes, such as fishery pressure and increasing water temperature, are discussed.

Alien species stabilize local fisheries catch in a highly invaded ecosystem

“…and decreasing catches (between 1998 and 2013) of the two indigenous species of the genus Mullus. This finding supports the possibility of competitive exclusion (Arndt et al 2018). Our time-series data captured the establishment of the relatively new arrival Nemipterus randalli (Stern et al 2014) for which habitat selection and trophic properties were found to be very similar to those of the indigenous breams (Chessa et al 2005;Gürlek et al 2010).…”

“…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).…”

Holocene fish assemblages provide baseline data for the rapidly changing eastern Mediterranean

“…Moreover, the post-industrial climate is changing faster and more abruptly than during the Holocene (Burke et al, 2018; Marcott et al, 2013), and human activities are affecting the environment on a larger scale and to a much higher degree. Nonetheless, the most common approach to assessing and predicting the impact of these phenomena on the eastern Mediterranean marine ecosystem is through comparison with time series reaching back the late 20th century at best (Arndt et al, 2018; Belmaker et al, 2013; Corrales et al, 2017a, 2017b; Givan et al, 2017; Goren et al, 2016). However, such short time series capture conditions already strongly modified by human activity.…”

Cold‐water species deepen to escape warm water temperatures

“…Moreover, the fact that we observed a deepening of cold-water species while warm-water species maintained depth hints that alien species are unlikely to cause the observed depth shifts across the Mediterranean. Finally, several studies have found that alien Lessepsian species do not compete strongly with indigenous species (Arndt et al, 2018;Azzurro et al, 2014;Buba & Belmaker, 2019;Givan et al, 2018). Together, these findings provide evidence for climate as the main driver of the deepening pattern observed.…”