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Pufferfish represent a serious threat to the marine ecosystem in the Mediterranean Sea. To better understand the population dynamics of pufferfish and their relation with ecological parameters, six pufferfish species were studied in two fishing and one non-fishing zone in one of the most oligotrophic regions of the Mediterranean Sea during 2014 and 2015, including different habitats of vegetated and non-vegetated and seasons. The results provide information on pufferfish ecological status compared with more eutrophic zones in which these species could potentially worsen their impact. Four species were common in the study area and two were rare. The dominant species was Lagocephalus suezensis, reaching abundances of 11,000 ind/km2 at 25 m in October, followed by Lagocephalus sceleratus, Lagocephalus guentheri, and Torquigener flavimaculosus. The rarest species, Tylerius spinosissimus and Sphoeroides pachygaster, reached higher abundance and biomass in October and February than the other sampling months. The riverine and meadow habitats played a crucial role for nursing and reproduction in the population dynamics of Lagocephalus species, while T. flavimaculosus was absent in these areas. Sex ratios changed depending on season and location. The occurrence of larger individuals of Lagocephalus spp. and T. flavimaculosus at greater depths evidenced an ontogenetic migration. Overall, length-weight (L-W) relationships indicate isometric growth for each of the species studied. Pufferfish populations were primarily a function of habitat and depth of seafloor and secondarily with water productivity.

In the present study, we investigated the different ecological characteristics of native and non-native demersal fish collected in 2014–2015 on the shelf of the Antalya Gulf in the Eastern Mediterranean Sea. Lessepsian migrants originating from the Indo-Pacific Ocean were classified as non-indigenous species (NIS) and the other species, which were mostly Atlanto-Mediterranean, were classified as indigenous species (IS). The results showed that the faunistic characteristics of IS and NIS differed significantly in space but only partly over time. The density and species diversity of the IS increased with the seafloor depth, while the opposite pattern was observed for the NIS, which were found mostly in shallow waters. Proximity to rivers and Posidonia oceanica meadows and the presence of a marine protected area (MPA) were also important factors determining the differences in the ecological characteristics of IS and NIS. The ecological ordination of the fish assemblages in the canonical correspondence analysis (CCA) space was V-shaped for the IS and =-shaped for the NIS, and it was mainly determined by bottom depth. Altogether, the ordination took the shape of a double strikethrough (V) due to the NIS filling an available niche. Hierarchically, the NIS (“occupiers”) and IS (“resisters”) shared the shallowest waters, while the middle-shelf waters were occupied by NIS (“gapers”) and IS (“escapers”) separately. The upper shelf was occupied only by IS (“homekeepers”) and “minorities” of NIS. Finally, we identified eight factors as ecological indicators of NIS and IS: bottom depth, bottom vegetation status, fish hierarchy, key species, water productivity, fish trophic level, life strategy and morphometry.

Since 2008 spatiotemporal and ecological distributions of porgies (sparid, all indigenous fish) were examined in the presence or absence of Randall's threadfin bream, Nemipterus randalli in the present study area. Seasonal fish and environmental parameters samplings were conducted at three transects of the fishing (nMPA) or non-fishing (MPA) regions on an oligotrophic shelf (Levantine Sea) in 2014-2015 for understanding management and ecology of the porgies’ catches. Of 13 sparid fish determined during the present study, five species are rarely found. There were no seasonal significant differences in densities of the sparid fish with or without the alien nemipterid fish. However, there were differences in the densities by the bottom depths, the regions, and soft and hard bottoms vegetated by Caulerpa spp and meadow, respectively. Ecologically, fish assemblages and faunistic characters of the sparid fish were highly variable when excluding the N. randalli as highlighted and follows; i) seasonal variation occurred and ii) the depthwise community assemblages became irregular. N. randalli seemed to balance the sparid catch attributed to the biomass-abundance ratio in the ecosystem or vice versa in this trophically sensitive gulf (ultra-oligotrophic) of the eastern Mediterranean Sea.

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