Environmental conditions influencing the larval fish assemblage during summer in the Gulf of Gabes (Tunisia: South central Mediterranean)

Abstract

An oceanographic survey was carried out during the summer of 2009, from June 25 to July 3 in the Gulf of Gabes. The study area was characterised by a wide continental shelf.A plankton sampling scheme was carried out to study the structure of the larval fish assemblages that characterised the surface mixed layer, and to assess the influence of the environmental parameters on their spatial distribution.A total of 36 taxa were identified, three classified to the level of genus, five to the family and 28 to the species. The majority of identified fish larvae belonged to the demersal species, mainly picarel Spicara smaris (23.76% of the total larval fish abundance), followed by red mullet Mullus barbatus (14.92%) and several species of the Sparidae family (9.15%). Small pelagic species such as Sardinella Sardinella aurita and European anchovy Engraulis encrasicolus were also abundant (27.75%) and dominated the fish larvae community in offshore stations. Five large pelagic species were found among the larvae, including bullet tuna Auxis rochei, Atlantic black skipjack Euthynnus alletteratus, albacore Thunnus alalunga, swordfish Xiphias gladius and the highly migratory Atlantic bluefin tuna Thunnus thynnus. All these apex predator species appear in 38.5% of the sampling stations and contributed to about 7.9% of the total larval catches.The larval fish assemblage of the Gulf of Gabes is predominantly composed of the neritic species in correspondence with the shallow depths of the study area. Canonical Correspondence Analysis (CCA) showed that larval distributions were mainly conditioned by depth. However, other factors, such as, hydrographic processes, also play a very significant role in shaping the spatial pattern of larval fish distribution.

Characterization of the spawning area of tuna species on the northern Tunisian coasts

“…The high concentrations of Atlantic bluefin tuna larvae at the offshore stations may be clear evidence that this species tends to avoid the productive coastal waters and prefers the offshore oligotrophic waters, in agreement with earlier ichthyoplankton studies carried out in Tunisia (Koched et al 2012(Koched et al , 2015 and in other areas of the Mediterranean (Oray andKarakulak 2005, Alemany et al 2010).…”

“…Larvae of the same species, except the Atlantic bonito, have also been collected in other areas of Tunisian waters (Koched et al 2012, 2013, 2015, Zarrad et al 2013) and in the central and eastern part of the Mediterranean (Garcia et al 2005, Tsuji et al 1997, Oray and Karakulak 2005.…”

Jellyfish diversity, trends and patterns in Southwestern Mediterranean Sea: a citizen science and field monitoring alliance

“…The area has been recognized as a phytoplankton blooms ecoregion (Ayata et al, 2018), leading to a small-copepod-dominated-zooplankton density higher than in the TWM (Annabi-Trabelsi et al, 2005;Ben Ltaief et al, 2015;Gueroun et al, 2020). The area is also an essential nursery for several fish species (Koched et al, 2015), contributing to ≈40% of the national fish production. R. pulmo outbreaks might therefore represent, in the first stage, a threat to zooplanktivorous fish larvae recruitment through competition and/or its top-down control of the plankton community, and in the second stage, affect higher trophic levels.…”

Zooplankton abundance and community structure driven by tidal currents in a Mediterranean coastal lagoon (Boughrara, Tunisia, SW Mediterranean Sea)

“…Based on complementary biogeochemical and plankton criteria synthesized from recent regionalization analyses by Ayata et al (2018), the Gulf of Gabès was recently identified as one of the eleven consensus ecoregions of the Mediterranean and classified as a shallow and phytoplankton bloom region. Linked to this planktonic richness, this area is an important nursery for several fish species (Koched et al, 2015;Enajjar et al, 2015) and contributes approximately 40% of the national fish production in Tunisia (DGPA, 2015). However, this singular and economically important region was recently identified as a 'hotspot' of anthropogenic pressures (Reygondeau et al, 2017), strongly threatened by industrialization, particularly discharges from large-scale phosphate production plants, and overfishing, both potentially causing ecosystem disequilibrium and the decline of fish resources (Bejaoui et al, 2019).…”