Abstract

The deep-sea copepod Megacalanus princeps Wolfenden, 1904 was previously recorded from the northern and southeastern Atlantic, Indian and Pacific oceans, but not previously observed from southwestern Atlantic. Here we report its first occurrence in Brazilian waters. The current record increases the knowledge on the species distribution and on the deep-sea copepod fauna in the south Atlantic.

Key words
Geographic distribution; mesopelagic; northeastern Brazil; Calanoida

The Megacalanidae Sewell, 1947Sewell, R.B.S. 1947. The free-swimming planktonic Copepoda. Systematic account. Scientific Reports of the John Murray Expedition, 8: 1-303. consists of three genera (BathycalanusSars, 1905Sars, G.O. 1905. Liste Preliminaire des Calanoides recueillies pendant les Campagnes de S.A.S. le Prince Albert de Monaco, avec diagnoses des genres et des espèces nouvelles. 1re Partie, Bulletin de Musée Océanographique de Monaco, 26: 1-22., Bradycalanus A. Scott, 1909Scott, A. 1909. The Copepoda of the Siboga Expedition. Part 1. Free-swimming, Littoral and Semi-parasitic Copepoda. Siboga-Expedittie 29a, 323p. and MegacalanusWolfenden, 1904Wolfenden, R.N. 1904. Notes on the Copepoda of the North Atlantic Sea and Faroe Channel. Journal of the Marine Biological Association of the United Kingdom , 7: 112-142. ) with 13 species (Razouls et al., 2005-2016Razouls, C.; De Bovée, F.; Kouwenberg, J. and Desreumaux, N. 2005-2016. Diversity and Geographic distribution of Marine Planktonic Copepods. Available at Available at http://www.copepodes.obs-banyuls.fr/en/ . Accessed on 3 October 2016.
http://www.copepodes.obs-banyuls.fr/en/... ). The Megacalanidae are the largest known species of pelagic copepods, reaching 17 mm (Boxshall and Halsey, 2004Boxshall, G.A. and Halsey, S.H. 2004. An Introduction to Copepod Diversity. The Ray Society, London, 166: 1-966.). The adults of this family are primarily meso-bathypelagic, being widely distributed in deep seas and oceans (Michel, 1994Michel, H.B. 1994. Antarctic Megacalanidae (Copepoda: Calanoida) and the distribution of the family. Journal of the Marine Biological Association of the United Kingdom, 74: 175-192.). The genus Megacalanus currently consists of only one species: Megacalanus princeps Wolfenden, 1904.

This species is absent in the first superficial 300 m depth (Hsiao et al., 2004Hsiao, S.H.; Lee, C.Y.; Shih, C.T. and Hwang, J.S. 2004. Calanoid Copepods of the Kuroshio Current East of Taiwan, with Notes on the Presence of Calanus jashnovi Huslemann, 1994. Zoological Studies, 43: 323-331.), and presents the typical vertical migration behavior, leaving the deeper water masses and reaching 300 m, always at night (Gueredrat, 1969Gueredrat, J.A. 1969. Distribution de quatre espèces de Copepodes bathypelagiques dans l’ouest du Pacifique Equatorial et tropical sud. Deep-Sea Research, 16: 361-375.).

According to Razouls et al. (2005-2016Razouls, C.; De Bovée, F.; Kouwenberg, J. and Desreumaux, N. 2005-2016. Diversity and Geographic distribution of Marine Planktonic Copepods. Available at Available at http://www.copepodes.obs-banyuls.fr/en/ . Accessed on 3 October 2016.
http://www.copepodes.obs-banyuls.fr/en/... ), M. princeps has been recorded in the northern and southeastern Atlantic, Indian, Pacific oceans, and also in the Mediterranean Sea. However, despite the records for the Atlantic Ocean, this species has never been previously registered in the southwestern Atlantic. This paper reports M. princeps for the first time from southwestern Atlantic, off Brazilian northeastern coast.

The zooplankton community was sampled under the framework of the project “ABRACOS” Acoustic along the Brazilian coast, on board of R/V Antea in October 2015, using a Micronekton net (mesh size of 1 mm) through oblique hauls. The samples were collected around the Rocas Atoll (3°51’S 33°49’W), Brazil, simultaneously with the plankton hauls, the sounder TDR: Time Depth Recorders (model: G5, 31 mm length by 8 mm diameter, 3g, CEFAS Technology, UK) was towed, which checked the real depth of each tow.

After collected, the samples were fixed in formalin 4% and the Megacalanidae copepods identified to species level by observing the external morphology according to Miller (2002Miller, C.B. 2002. A variant form of Megacalanus longicornis (Copepoda: Megacalanidae) from deep waters off Southern California. Hydrobiologia, 480: 129-143.). All material was deposited in the carcinological collection of the “Museu de Oceanografia Professor Petrônio Alves Coelho (MOUFPE)” of the Federal University of Pernambuco in Recife, Brazil. In the distribution section the new record is in bold.

Systematics

Order Calanoida Sars, 1903Sars, G.O. 1903. An account of the Crustacea of Norway, with short descriptions and figures of all the species, volume IV: Copepoda Calanoida. Bergen, Bergens Museum, 171p.

Family Megacalanidae Sewell, 1947Sewell, R.B.S. 1947. The free-swimming planktonic Copepoda. Systematic account. Scientific Reports of the John Murray Expedition, 8: 1-303.

Genus MegacalanusWolfenden, 1904Wolfenden, R.N. 1904. Notes on the Copepoda of the North Atlantic Sea and Faroe Channel. Journal of the Marine Biological Association of the United Kingdom , 7: 112-142.

Megacalanus princeps Wolfenden, 1904Wolfenden, R.N. 1904. Notes on the Copepoda of the North Atlantic Sea and Faroe Channel. Journal of the Marine Biological Association of the United Kingdom , 7: 112-142.

(Fig. 1)

Material examined. 1 Male [Total length (TL) 9.9 mm], Rocas Atoll, #ST-14, Leg. 1 water column, 510 m depth, initial coordinate tow: 03°58’S 34°03’W, final coordinate tow: 03°57’S 34°04’W, 6 October 2015, MOUFPE 15581. 1 female (TL 9.21 mm) and 1 male (TL 10.31 mm), Rocas Atoll, #ST-22/Leg. 1 water column, 525 m depth, initial coordinate tow: 04°07’S 33°47’W, final coordinate tow: 4°07’S 33°48’W, 8 October 2015, MOUFPE 15658.

Figure 1
Megacalanus princeps Wolfenden, 1904, female (TL: 9.21 mm; MOUFPE: 15658) from northeastern Brazil. (A) Habitus, dorsal view; (B) lateral view; (C) P1 total view; (D) P1 highlighting the hook-like process followed by an inner seta on anterior surface of basis of leg 1.

Distribution (Fig. 2). West Atlantic Ocean: Greenland, Iceland (W), Canada (Newfoundland), USA (Woods Hole, New Scotia, Carolinas, Florida), Bermudas (32°10'N 64°30'W), Sargasso Sea, Gulf of Mexico, Dominican Republic, Caribbean Sea, Brazil (Rio Grande do Norte: Rocas Atoll), Antarctic (Drake passage). East Atlantic Ocean: Faroe Island, Ireland (S & W), Spain (Bay of Biscay, Cape Finisterre, Canary Island), Portugal (Azores, Madeira Islands), Mediterranean Sea (Ligurian Sea, Tyrrhenian Sea, Gulf of Gabès, Ionian Sea, Alexandria), Ibero-moroccan Bay, Morocco, Mauritania-NW, Cape Verde Island, São Tomé Island, Angola, Saint Helena Island, South Africa. Indian Ocean: Arabian Sea, Bay of Bengal. Indonesia-Malaysia. West Pacific Ocean: Japan (Hokkaido), China, Taiwan, Philippines, New Caledonia, New Zealand, SubAntarctic (SW & SE Pacific). East Pacific Ocean: USA (Gulf of Alaska, Saint Paul Island, California, Hawaii), Canada (British Columbia), Peru (San Lorenzo Island), Chile (Juan Fernandez Island) (Gueredrat, 1969Gueredrat, J.A. 1969. Distribution de quatre espèces de Copepodes bathypelagiques dans l’ouest du Pacifique Equatorial et tropical sud. Deep-Sea Research, 16: 361-375.; Hsiao et al., 2004Hsiao, S.H.; Lee, C.Y.; Shih, C.T. and Hwang, J.S. 2004. Calanoid Copepods of the Kuroshio Current East of Taiwan, with Notes on the Presence of Calanus jashnovi Huslemann, 1994. Zoological Studies, 43: 323-331.; Razouls et al., 2005-2016Razouls, C.; De Bovée, F.; Kouwenberg, J. and Desreumaux, N. 2005-2016. Diversity and Geographic distribution of Marine Planktonic Copepods. Available at Available at http://www.copepodes.obs-banyuls.fr/en/ . Accessed on 3 October 2016.
http://www.copepodes.obs-banyuls.fr/en/... ; this study).

Figure 2
Worldwide geographic distribution of Megacalanus princeps Wolfenden, 1904.

Bathymetric distribution. The specimens examined were found at a depth of 525 m, in accordance with Miller (2002Miller, C.B. 2002. A variant form of Megacalanus longicornis (Copepoda: Megacalanidae) from deep waters off Southern California. Hydrobiologia, 480: 129-143.) and Hsiao et al. (2004Hsiao, S.H.; Lee, C.Y.; Shih, C.T. and Hwang, J.S. 2004. Calanoid Copepods of the Kuroshio Current East of Taiwan, with Notes on the Presence of Calanus jashnovi Huslemann, 1994. Zoological Studies, 43: 323-331.), but their occurrence is usually between 300-2000 m.

Remarks. The specimens examined presented the same characteristics than those reported by Wolfenden (1904Wolfenden, R.N. 1904. Notes on the Copepoda of the North Atlantic Sea and Faroe Channel. Journal of the Marine Biological Association of the United Kingdom , 7: 112-142. ). Segmentation and setation patterns from swimming legs and maxilla were the same of that observed by Bradford-Grieve (1994Bradford-Grieve, J.M. 1994. The marine fauna of New Zealand: pelagic calanoid Copepoda: Megacalanidae, Calanidae, Paracalanidae, Mecynoceridae, Eucalanidae, Spinocalanidae, Clausocalanidae. Wellington, National Institute of Water and Atmospheric Research, 160p.). Also, the proportional length of urosomites and furca was different than the one found by Tanaka (1956Tanaka, O. 1956. The pelagic copepods of the Izu region, Middle Japan. Systematic account I. Families Calanidae and Eucalanidae. Publications of the Seto Marine Biological Laboratory, 2: 119-140.); which found a proportional length from 41:20:15:7:17, while we found 33:23:13:8:23, indicating a small morphological variation, when compared with specimens collected in the Pacific Ocean. The specimens have long rostral filaments as observed by Sars (1924Sars, G.O. 1924. Copépodes particulièrement bathypélagique provenant des campagnes scientifiques du Prince Albert de Monaco. Résultats of Campagnes Scientifiques Prince Albert I, 69: 1-127.) and Tanaka (1956)Tanaka, O. 1956. The pelagic copepods of the Izu region, Middle Japan. Systematic account I. Families Calanidae and Eucalanidae. Publications of the Seto Marine Biological Laboratory, 2: 119-140.. Finally, as observed by Miller (2002Miller, C.B. 2002. A variant form of Megacalanus longicornis (Copepoda: Megacalanidae) from deep waters off Southern California. Hydrobiologia, 480: 129-143.), the specimens found here presented a cephalic crest; this characteristic was only found before in specimens collected in deep waters off Southern California. Probably due to the low sampling effort, scarcity in meso-bathypelagic collections and the increasing of deeper waters studies in Brazil, the spatial distribution of M. princeps was not known in this region. The occurrence of M. princeps in Brazilian waters expands its world distribution and increases the knowledge about zooplankton species from south Atlantic deep waters.

Acknowledgements

The authors (FAA-J; EPC and LGPF) would like to thank the scholarship granted by Capes (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior) for the graduate scholarship on Oceanography. We also acknowledge the French oceanographic fleet for funding the ABRACOS survey (http://dx.doi.org/10.17600/15005600) and the officers and crew of the R/V Antea for their contribution to the success of the operations. We would especially like to thank the anonymous reviewers for the great comments on this paper.

References

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