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Tracking the indopacific pelagic octopus Tremoctopus gracilis in the Mediterranean
... On the contrary, females are recognized by less precise criteria: T. robsoni for their long and convoluted distal oviducts, while adults of T. violaceus and T. gracilis for the different chromatic patterns of the web surrounding the dorsal arms. However, T. violaceus and T. gracilis are reported to be almost indistinguishable in their juvenile phase [8,9]. ...
... The difficulty in separating these taxa, as well as the paucity of molecular data, could cause several errors in identifications, especially involving T. violaceus and T. gracilis, as exemplified by the records of these two species outside their known geographical limits [7]. For instance, in the Mediterranean Sea, in the past, T. violaceus was the only member of the genus known to live in the area, while nowadays it is reported that two species of the genus Tremoctopus occur in the Mediterranean Sea, i.e., T. violaceus as the native species and T. gracilis as an alien species probably arriving in the Mediterranean due to human-mediated transfer or with Lessepsian migrations [8,10,11]. ...
... However, the occurrence of T. gracilis was reported in the Mediterranean Sea as early as in 1936 in the northern Adriatic Sea [17]; the individual, originally identified as T. violaceus, was later reclassified as T. gracilis based on the color pattern [10]. Recently, in August 2002, a large egg-carrying female of Tremoctopus sp. was observed and photographed in the waters of Ponza Island in the Tyrrhenian Sea [18] and attributed to T. gracilis on the basis of the chromatic pattern of the web [8,9]. This specimen, indeed, exhibited dorsal spots different from the large round spots considered typical of T. violaceus. ...
An integrative approach based on morphological and genetic analyses was undertaken for the first time to confirm the species identification of Mediterranean samples belonging to the genus Tremoctopus. Sequences of two mtDNA genes (cytochrome c oxidase subunit (COI) and 16S) were generated for the first time from Mediterranean samples. Both the similarity-based identifications and tree-based methods indicated that three females can be identified as Tremoctopus violaceus sensu stricto in agreement with their morphological classifications. All Mediterranean sequences clustered with the sequences of Tremoctopus violaceus from the Gulf of Mexico and were clearly differentiated from the sequences attributed to T. gracilis and T. robsoni. The chromatic pattern of the web and some features of gill filaments, arms formula, stylets, radulae, beaks, and stomach contents were given for all the samples; 105,758, 20,140, and 11,237 oocytes were estimated in the mature, immature, and developing samples, respectively. The presence of four spermatangia inside the cavity of the maturing female suggested the ability of this species to mate before reaching full maturity with more partners. Age investigation using beaks, performed for the first time in T. violaceus and within the genus gave results consistent with the different sizes and maturity conditions of the samples.
... The genus Tremoctopus has a worldwide distribution, but at the moment this is mostly based on morphological species identification: T. robsonianus is limited to the south-west Pacific Ocean, T. gelatus inhabits the Indian Ocean, the eastern Pacific Ocean and the western Atlantic Ocean, T. violaceus is widespread through the Atlantic Ocean, Gulf of Mexico, Caribbean Sea and Mediterranean Sea, and T. gracilis is found in the Indo-Pacific waters and the Mediterranean Sea (see references in [1]). Findings of T. gracilis in the Mediterranean waters [5,6] suggest two possibilities: either this Indo-Pacific species is in fact a Lessepsian migrant carried in ballast waters; or it has been misidentified as T. violaceus [7]. ...
... So far, T. gracilis in the Mediterranean was identified exclusively based on morphology and record reports [5,6]. Interestingly, GenBank sequence AF377978, misidentified as T. violaceus, lacks information for a geographical locality, but according to the locale/voucher data in Carlini et al. [39], the specimen originates from the Atlantic Ocean (Key Biscayne, Florida). ...
Tremoctopods are epipelagic argonautoid octopods characterized by their expanded dorsal webs and strong sexual size dimorphism, with dwarfed males. The scarcity of taxonomic features attributed to this genus presents a challenge, and there is growing evidence of species misidentification in Tremoctopus genus on a molecular level. In this study, we investigated four female specimens of blanket octopus Tremoctopus violaceus caught by purse seine fishing in the Central Eastern Adriatic Sea in 2019. Individuals had smooth, firm and muscular bodies, dark bluish purple on the dorsal and iridescent silvery on the ventral side, with dorsal mantle lengths of 113, 82, 80 and 78 mm. The constructed phylogenetic trees based on the 16S ribosomal RNA and cytochrome c oxidase subunit I sequences of investigated Adriatic specimens and publicly available sequences showed strong support for the T. violaceus clade, consisting of individuals collected from the Adriatic Sea, Mediterranean Sea and Atlantic Ocean, with the exclusion of Indo-Pacific clade most probably corresponding to T. gracilis. To fully understand the life-history traits of Tremoctopus species, future research should focus on DNA-based methods for correct species identification combined with morphological characters, geographic distribution and ecological information.
... Most of the reported specimens in the Mediterranean belong to T. violaceus [9,10]. One egg-carrying female was observed and photographed in the coastal waters around Ponza Island [6] and assigned to the species T. gracilis [11]. But the reports of this genus in the Strait of Messina are very old and rare. ...
Reports of rare species are essential for increasing knowledge for biodiversity studies. The Tremoctopodidae is a small family of epipelagic to mesopelagic octopuses with a single genus, Tremoctopus and four recognized species (Diaz et al.,2004). Specimens belonging to Tremoctopus sp. have been rarely found along the Italian coasts (Bello, 2008; Belluscio et al., 2003; Capua, 2004; Mereu et al., 2012). The reports of this genus in the Strait of Messina are very old and rare. In the present study an adult female of Tremoctopus violaceus violaceus (Delle Chiaje, 1830), was recorded from the Strait of Messina. Species of the family Tremoctopodidae are widely distributed in tropical oceans, but rare in coastal waters. It is considered present, but uncommon, in the Mediterranean Sea. A specimen of T. violaceus was found on the shore, in well preserved condition, during a sampling in Mortelle (38°16’28.11”N; 15°36’52.94”E) (Messina, southern Italy).The specimen was preserved on ice and sent to the Centre for Experimental Fish Pathology of Sicily (C.I.S.S.) for identification, measured fresh (HL, ML, TL), weighted (TW) and sex determination. The aim of this study is to report Tremoctopus violaceus int he Strait of Messina, expanding the knowledge in migration behavior regarding this rare mollusc. This record of the uncommon Tremoctopus violaceus from the Strait of Messina, confirms the presence of this genus in the central Mediterranean.
... Most of the reported specimens in the Mediterranean belong to T. violaceus [9,10]. One egg-carrying female was observed and photographed in the coastal waters around Ponza Island [6] and assigned to the species T. gracilis [11]. But the reports of this genus in the Strait of Messina are very old and rare. ...
In the present note an adult female of Tremoctopus violaceus delle Chiaje, 1830, is recorded from the Strait of Messina. Species of the family Tremoctopodidae are widely distributed in tropical oceans, but rare in coastal waters. The morphological characteristics coincide with those described by other authors. Necroscopic examination performed did not reveal any peculiar pathology. Morphometrical characteristics, photos and general information are given, expanding the knowledge about these rare cephalopods in Mediterranean basin.
... According to Bello (2003), seven cephalopods are endemic and quasi-endemic Mediterranean species, which account for 10.4% of its teuthofauna. Four Lessepsian species have been reported during the last decades: Octopus aegina (Salman et al., 1999), Sepioteuthis lessoniana (Salman and Katagan, 2002), Sepia pharaonis (Mienis, 2003) and Tremoctopus gracilis (Orsi-Relini et al., 2004). ...
The water body underlying the photic zone in oceans represents the largest water mass on earth (comprising 1.3×1018 m3), and is also the largest aqueous habitat for various microorganisms. This realm differs distinctly from the photic zone, in terms of its relatively lower temperature (approximately 2~4°C), higher pressure and richer inorganic nutrients. Differences in physical geochemical parameters between uppersea and deep-sea environments create fundamentally different challenges to microbial communities living in these environments. Recent studies found that prokaryotic microbes in deep-sea environments are welladapted to the special dwelling environments after long evolution, carrying genetic features that enable them to live and reproduce in the extreme environmental conditions. Recent progress in sequencing technologies is fueling a rapid increase in the number and scope of deepsea microbial community-targeted studies. While metagenomic analysis can provide information on the taxonomic composition and metabolic potential of microbial communities in the deep sea, metatranscriptomics serves to unveil the actual metabolic activities of the communities at a specific time and location, and how those activities are changing in response to environmental and biotic challenges. Here we provide a summary of recent progress in applying integrated metagenomic and metatranscriptomic analyses to uncover the special genetic features in the well-adapted deep-sea microbial communities.
... According to Bello (2003), seven cephalopods are endemic and quasi-endemic Mediterranean species, which account for 10.4% of its teuthofauna. Four Lessepsian species have been reported during the last decades: Octopus aegina (Salman et al., 1999), Sepioteuthis lessoniana (Salman and Katagan, 2002), Sepia pharaonis (Mienis, 2003) and Tremoctopus gracilis (Orsi-Relini et al., 2004). ...
The Mediterranean Sea is a relatively small but deep basin of 1450 m of mean depth situated between 30° N and 46° N and 5.5° W and 36° E. The only natural connection with the Atlantic Ocean is the Strait of Gibraltar, a narrow and shallow channel of 14 km width and 320 m depth. Given that the high evaporation rates are not compensated by inputs from rainfall and river discharges, the Mediterranean acts as a concentration basin in which water circulation is dominated mainly by salinity and temperature differences (thermohaline forcing). The Mediterranean has been compared with a miniature ocean for studies on oceanographic and biological processes taking place at larger scales. Although representing only 0.8% of the area and less than 0.25% of the volume of the world’s oceans, the Mediterranean includes about 6% of known world marine fauna and 18% of world marine flora of which 28% are endemic. A total of 10000 to 12000 marine species (with 8500 species of macroscopic fauna) have been recorded. Despite its small dimensions, the Mediterranean coastal waters are a hot spot of biodiversity hosting a high percentage of endemic species. However, the diversity of deep megafauna is comparatively low, most probably due to the Gibraltar sill, which would act as a physical barrier for the entrance of larvae and deep-sea benthic organisms from the Atlantic. Although with some exceptions, there is a general decreasing pattern of biodiversity with increasing depth at different extent depending on the taxonomic group. Most megafaunal community studies have focused on fishes, decapod crustaceans and cephalopods and restricted to depths above 800 m. The epibenthic megafaunal communities below 200 m are still fairly unknown, yet cold-water corals communities have been described in recent years. Besides the environmental conditions typical of deep waters, Mediterranean deep-sea organisms must face high homeothermy (12.5-15.5°C), high salinity (38.0-39.5) and high oligotrophy (the eastern basin is one of the most oligotrophic areas of the world). The Mediterranean is among the most impacted seas in the world (e.g. crowding of coastal zones, biodiversity loss, overfishing and pollution). Climate change has been reported to affect deep-sea ecosystems and may have deleterious effects on the biodiversity of such sensitive habitats. In this chapter, we firstly introduce the Mediterranean Sea and describe its main oceanographic conditions. Secondly, we review current knowledge on the biodiversity and life-history strategies of Mediterranean deep-sea megafaunal groups such as fishes, crustaceans, cephalopods and cold-water corals. Finally, we discuss the main threats posed by human impacts on Mediterranean deep-sea ecosystems
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