Abstract
The cephalopod fauna of the southwestern Atlantic is especially poorly-known because sampling is mostly limited to commercial net-fishing operations that are relatively inefficient at obtaining cephalopods associated with complex benthic substrates. Cephalopods have been identified in the diets of many large marine species but, as few hard structures survive digestion in most cases, the identification of ingested specimens to species level is often impossible. Samples can be identified by molecular techniques like barcoding and for cephalopods, mitochondrial 16S and COI genes have proven to be useful diagnostic markers for this purpose. The Amazon River estuary and continental shelf are known to encompass a range of different substrates with recent mapping highlighting the existence of an extensive reef system, a type of habitat known to support cephalopod diversity. The present study identified samples of the cephalopod fauna of this region obtained from the stomachs of red snappers, Lutjanus purpureus, a large, commercially-important fish harvested by fisheries using traps and hook-and-line gear that are capable of sampling habitats inaccessible to nets. A total of 98 samples were identified using molecular tools, revealing the presence of three squid species and eight MOTUs within the Octopodidae, representing five major clades. These include four known genera, Macrotritopus, Octopus, Scaeurgus and Amphioctopus, and one basal group distinct from all known octopodid genera described here as Lepidoctopus joaquini Haimovici and Sales, new genus and species. Molecular analysis of large predatory fish stomach contents was found to be an incredibly effective extended sampling method for biodiversity surveys where direct sampling is very difficult.
Highlights
The cephalopod fauna of the southwestern Atlantic is especially poorly-known because sampling is mostly limited to commercial net-fishing operations that are relatively inefficient at obtaining cephalopods associated with complex benthic substrates
The majority (N = 12) of the individuals were genetically similar to Doryteuthis plei Blainville, 1823 (0.0–0.5% uncorrected p-distance), a species found on the Atlantic coast of Brazil[9,34] (Supplementary Data 1)
The last individual could only be assigned to the genus Abralia but was distinct from all the 16S sequences of Abralia species available in GenBank, with uncorrected p-distance ranging from 4.6% in relation to Abralia adamanica Goodrich, 1896 to 6.2% in the case of Abralia trigonura Berry, 1913 (Supplementary Data 1)
Summary
The cephalopod fauna of the southwestern Atlantic is especially poorly-known because sampling is mostly limited to commercial net-fishing operations that are relatively inefficient at obtaining cephalopods associated with complex benthic substrates. Www.nature.com/scientificreports commercial fisheries are relatively ineffective at the capture of the majority cephalopod species, and in many cases, cephalopods are found in habitats that are difficult to fish[11,12] To circumvent these limitations, studies of the diets of the predators of cephalopods, including large fishes, marine mammals, seabirds, turtles, and even other cephalopods, can provide useful information on the occurrence of cephalopod species[13,14,15,16]. The identification of species can be achieved by using molecular techniques[19,20,21], which have been used successfully when samples cannot be identified reliably based on their morphological characteristics In this context, DNA barcoding, which uses standardized protocols for the sequencing of a short fragment of the mitochondrial Cytochrome Oxidase I (COI) gene[22], has proven to be very effective for the identification of species in many taxonomic groups including butterflies[23], birds[24], and plants[25], as well as cephalopods[26]. In addition to the COI gene fragment, the large ribosomal subunit (16S rDNA) has proven to be useful for the identification of cephalopod species at the intra-familial level[9,27]
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