South Atlantic cruise on "RV Akademik Ioffe" 2009
8 – 14 November
Author: Stas Kobyliansky (Shirshov Institute of Oceanology)
SA MAR-ECO superstations (SST) 3 and 4 were carried out over the MAR around 4°S and 12°W. This area was likely located off the frontal zone between equatorial and central water masses that most probably resulted in higher biodiversity observed.
Four IKMT hauls were made at SST 3 and 4. Two of them were traditionally focused on study of SSL (sound scattering layer) ichthyofauna over the seafloor in the vicinity of the ridge and over the MAR seamounts. Echo sounders registered similar density, power, and diurnal dynamics of SSLs as compared to previous two SST. However, predominating fish groups differed and richness of species composition was higher. Over deeper depths (3177 m) 24 species belonging to 12 families were encountered in SSL composition during the daytime. According to richness and abundance the leading role belonged to species of the family Myctophidae (88% of number of specimens caught and 48% of number of species). The most abundant were Lampanyctus alatus, Hygophum macrochir and Diogenichthys atlanticus, while Vinciguerria nimbaria (fam. Phosichthyidae) that predominated in catches at previous SSTs was represented in these catches as single specimens only.
The night haul in SSL off the MAR seamounts (over 1900 m depth) composed of 29 species from 11 families. Fishes of Myctophidae family also played predominating role in this catch (77% of total number of specimens caught and 47% of total species number). However, predominating group was composed of higher number of species: Diaphus problematicus, Diogenichthys atlanticus, Hygophum macrochir, Ceratoscopelus warmingii, Diaphus vanhoeffeni (ranked in number of specimens captured). The most abundant species in both catches were mostly those with central equatorial and wide tropical types of the range.Deepwater hauls by depth strata carried out at SST 3 and 4 starting from 1250 and 1800 m respectively allowed us to determine rich species diversity of mesopelagic fishes in this area. About 50 species belonging to 22 families were discovered in the first catch. Rare representatives of deepwater anglers were found: Cryptopsaras couesi (Ceratiidae) and Microlophichthys microlophus (Oneirodidae). There were also several representatives of families have not been captured at previous SSTs, i.e. Cheilodipteridae (Howella sherborni), Eurypharyngidae (Eurypharynx pelecanoides), Giganthuridae (Giganthura chuni) and Opisthoproctidae (Opisthoproctus soleatus, Winteria telescopa, Dolichopteryx sp.). Species of Cyclothone genus (Gonostomatidae) predominated in this catch by number (about 70% of total number of specimens caught).
Second deepwater trawling was conducted in about 100 m off the one of MAR seamount top. This haul allowed us, along with typical mesopelagic species, to catch some bentho-pelagic fishes, such as Maurolicus weitzmani (Sternoptychidae), Diretmus argenteus (Diretmidae), Holtbyrnia anomala (Platytroctidae) and Macrouroides infaticeps (Macrouroididae). Species composition of mesopelagic fishes in this catch also showed high richness (56 species from 22 families). Among them the capture of very rare representative of Megalomycteridae family, Ataxolepis apus, that is known by very limited number of records, seems quite noticeable. Rare deepwater anglers Bufoceratias wedli (Diceratiidae), Gigantactis sp. (Gigantactidae) and Dolopichthys allector (Oneirodidae) were also found in this catch. Cyclothone spp. was the most abundant group as well (47% by number). The high number of new taxa observed within the second polygon allowed us to continue our tissue sampling for further promising work on comparative DNA analysis of deepwater fishes.