Right Out of The Gate: The Genomics of Lessepsian Invaders in The Vicinity of The Suez Canal

Lessepsian fishes, entering the Mediterranean through the Suez Canal, have showed so far little genetic structure, but notable exceptions suggest the importance of life-history factors that may influence their patterns of spatial genetic variation. In this study, by sampling two invasive fishes with different life histories (the rabbitfish Siganus rivulatus and the filefish Stephanolepis diaspros ), we looked at evidence of population structure and selection at the boundary between the Red Sea and the Mediterranean (the Suez Canal), using thousands of molecular markers. Results illustrate two divergent patterns of genetic patterns, with little genetic structure in S. rivulatus and strong population structure in S. diaspros, even at such small spatial scale. We discuss differences in ecological characteristics between the two species to account for such differences. In addition, we report that in the face of both high ( S. rivulatus ) and low ( S. diaspros ) gene flow, loci under selection were uncovered, and some protein coding genes were identified as being involved with osmoregulation, which seems to be an important feature of individuals crossing the salinity-variable Suez Canal. The presence of genes under selection in populations near the Suez Canal supports the idea that selection may be active and essential for successful invasions right out of the gate.

The update of immigrant Red Sea fish of Egyptian Mediterranean waters during (2013-2021)

Thirty nine immigrant fish species from the Red sea were observed in seven regions of Egyptian Mediterranean waters during 2013- 2021. These were divided according to their importance in the fish markets into economic species (18) and non-economic species (21). Port- Said region (North opening of Suez Canal) constituted high percentage of occurrence (49.1% of all species) followed by Alexandria (41.9%), Abu-Qir (5.2%) and Marsa Matruh (3.7%). Thirteen new species were recorded in the present review whereas fifteen fish species in the checklist given by Halim and Rizkalla (2011) were not encountered in the study area during the study period. Alepes djedaba and Siganus rivulatus were the most important economic species established in Port Said region, whereas Nemipterus randalli and Sargocentrum rubrum were the more dominant in Alexandria region, Also Nemipterus randalli was well established in Abu-Qir area while Upeneus pori was abundant in Marsa Matruh region.

Predation Cues Lead to Reduced Foraging of Invasive Siganus rivulatus in the Mediterranean

Invasive species are one of many anthropogenic challenges to maintaining a healthy marine ecosystem. Two rabbitfish species (Siganus rivulatus and Siganus luridus) are among the more successful migrants from the Red Sea to the Mediterranean, where their intense foraging has caused damage to the algae community, thus reducing primary production and habitat complexity, and impacting nurseries for early life stages. Anecdotal evidence suggests that the impact of rabbitfish on algae is lower in Marine Protected Areas (MPAs) although rabbitfish densities are similar in protected and fished areas. One explanation could be that fear of predators, more often present inside MPAs and an important component of a healthy marine ecosystem, reduces the ecological impacts of rabbitfish. This research aimed to test if such fear effects do occur in rabbitfish. Using controlled mesocosm experiments, we tested S. rivulatus reactions to two chemical predation cues: chemical alarm cues released from a recently killed conspecific fish, and water-borne cues from a tank with a live grouper predator, Epinephelus marginatus. We found that rabbitfish significantly reduce their overall food consumption as well as their bites per minute when exposed to the alarm cue, but not when exposed to the grouper water cue. These results support the idea that MPAs, which effectively increase the density of large piscivores and hence predation, can mitigate the impact of invasive herbivorous species. If the mesocosm results can scale up to natural systems, predation cues may be artificially introduced to other target areas in order to reduce rabbitfish grazing outside reserves. Thus, this study provides information that can be used to manage the ecological impacts caused by invasive rabbitfish, both inside and outside of marine reserves.