In this study, the ecological and social impact of the invasive pufferfish Lagocephalus sceleratus on the coastal habitats of an area in the eastern Mediterranean Sea (Rhodes Island) was investigated. Seasonal quantitative sampling in two common coastal habitats were used to investigate habitat use by different life-stages. Sandy areas were found to be highly important for the early life stages of L. sceleratus. In contrast, Posidonia oceanica habitats were mainly preferred by larger (>29 cm) reproductive adults, not exceeding 64 cm. Lagocephalus sceleratus was found to feed on invertebrates and fish, while size classification revealed a tendency for a diet shift with increased size. During the early life stages, L. sceleratus inhabits sandy bottoms where it feeds on various invertebrates. The predominant molluscan species found in the diet of larger (> 20 cm) L. sceleratus individuals were the economically important Sepia officinalis and Octopus vulgaris. The size at which 50% of individuals have reached maturity was estimated at 36 cm. With increased size, habitat shift to seagrass meadows most possibly occurs to meet both the increased demand in prey availability and requirement for appropriate spawning ground. The condition factor for L. sceleratus showed significantly higher values during summer than all other seasons and this was attributed to the spawning season and increased feeding. Social impacts were alarming due to increased public attention concerning its lethal effects (presence of tetrodotoxin), if consumed. Its high abundance in coastal fish communities of the studied area combined with ecological and social impacts, clearly classify L. sceleratus as a pest for fisheries and a potential threat for biodiversity.

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Temporal and spatial variation in density, biomass and body size of littoral fish species associated with nearshore Posidonia oceanica meadows was studied over an annual cycle in an area of the eastern Mediterranean Sea. A total of 109,350 littoral fishes were collected, belonging to 34 families and 88 species. Density of fishes peaked during the summer due to high numbers of juveniles. Season was a significant factor determining density, although number of species and biomass did not show any obvious seasonal pattern. Throughout the study, schooling planktivorous fish species such as the picarel Spicara smaris, the bogue Boops boops and the damselfish Chromis chromis were dominant, both in terms of density (80%) and biomass (70%). Temporal variation in density and body size of fishes was used to assess the seasonal and ontogenetic habitat use of each species, with their affinity to seagrass assessed by comparing their respective distribution on sand. Four functional guilds were created (juvenile migrants, seagrass residents, seasonal migrants and occasional visitors) to describe the habitat use of P. oceanica meadows by each species. Several species associated with P. oceanica meadows used this habitat mainly as juveniles during summer, although many others were present concurrently as adults and as juveniles. Among the species encountered, 11 were non-indigenous of Indo-Pacific origin, of which three used seagrasses mainly as juveniles and four as residents. The non-indigenous silverstripe blaasop Lagocephalus sceleratus ranked among the 10 most dominant species in terms of biomass (2%) and was classified as a seagrass resident.

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Standardized tools are needed to identify and prioritize the most harmful non-native species (NNS). A plethora of assessment protocols have been developed to evaluate the current and potential impacts of non-native species, but consistency among them has received limited attention. To estimate the consistency across impact assessment protocols, 89 specialists in biological invasions used 11 protocols to screen 57 NNS (2614 assessments). We tested if the consistency in the impact scoring across assessors, quantified as the coefficient of variation (CV), was dependent on the characteristics of the protocol, the taxonomic group and the expertise of the assessor. Mean CV across assessors was 40%, with a maximum of 223%. CV was lower for protocols with a low number of score levels, which demanded high levels of expertise, and when the assessors had greater expertise on the assessed species. The similarity among protocols with respect to the final scores was higher when the protocols considered the same impact types. We conclude that all protocols led to considerable inconsistency among assessors. In order to improve consistency, we highlight the importance of selecting assessors with high expertise, providing clear guidelines and adequate training but also deriving final decisions collaboratively by consensus.