First record of Oithona attenuata Farran , 1913 ( Crustacea : Copepoda ) from Brazil

Here, we report the first record of the marine copepod Oithona attenuata Farran, 1913, in Brazil, from a costal station near Cabo Frio Island, Arraial do Cabo Municipality, Rio de Janeiro State. Specimens were found during March and May 2011 in zooplankton samples obtained from horizontal hauls using a plankton-net with a 100μm mesh size, and mouth opening of 40 cm diameter.


Oithona attenuata from Brazil
Nauplius, 27: e2019001 Fonseca and Björnberg, 1976, Oithona linearis Giesbrecht, 1891, Oithona nana Giesbrecht, 1893, Oithona plumifera Baird, 1843, Oithona pseudofrigida Rosendorn, 1917, Oithona robusta Giesbrecht, 1891, Oithona sapucaiae Oliveira, 1945, Oithona setigera (Dana, 1849), Oithona similis Claus, 1866, Oithona simplex Farran, 1913, andOithona tenuis Rosendorn, 1917.Different species of Oithona show different levels of adaptability to physical and hydrological parameters (Nishida, 1985) and include cosmopolitan species as well as those with narrower distribution ranges.They comprise both neritic and oceanic species that feed on smaller-sized organisms, such as heterotrophic and autotrophic protists and copepod nauplii (Yahia et al., 2004).In turn, they are the more important food for fish larvae and other zooplanktivorous.Oithonids, therefore, may play a more important role in the transfer of both bacterial and algal carbon to higher trophic levels than previously thought (Hwang et al., 2010).The species Oithona attenuata Farran, 1913 occurs only in the Southern Hemisphere, but has not yet been recorded on the Brazilian coast.However, this species has already been recorded in places of resurgence such as South Africa (Razouls et al., 2018).In this present work we report the first record of O. attenuata in regions of upwelling currents in Brazil.
Weekly zooplankton samples were obtained for over three years (2010)(2011)(2012) in Arraial do Cabo Municipality, Rio de Janeiro State, Brazil in a horizontal haul (3 min, ~1 m depth) using a 100 μm mesh 40 cm diameter WP2 plankton net in water of about 10 m deep (Fig. 1).Immediately after collection, samples were fixed in a 4% formalin solution diluted with seawater and previously buffered with sodium tetraborate.Copepod abundance (ind.m -3 ) was estimated from three sub-samples taken with a modified Stempel pipette (2.68 ml) to a lower limit of 100 individuals (Frontier, 1981).Immediately after the hauls, water temperature (SST) was measured using a reverse thermometer mounted on the Nansen bottle and salinity using a Guildline salinometer.
Copepods sorted from samples were identified and measured under a Zeiss Stemi SV6 stereo microscope.Measurements were taken with Zeiss Zen  software from pictures taken in petri dishes.The World Register of Marine Species -WoRMS website (http://www.marinespecies.org) was used to confirm the current species names.The entire field and laboratory procedure was performed with the assistance of the Instituto de Estudos do Mar Almirante Moreira (IEAPM).More details of the copepod assemblage can be found in the work by Rosa et al. (2016).

Oithona attenuata from Brazil
Nauplius, 27: e2019001 The temperature and salinity at the sampling site off Cabo Frio Island (22°59'86"S, 42°00'28"W) were approximately 24.4°С and 35.9 psu, respectively, at the end of the austral summer (March) and approximately 24.5°С and 34.5 psu in autumn (May).The mean copepod abundance ranged between 92 and 125 ind.m -3 with higher densities found in more saline waters.In contrast, lower densities of copepods were found in less saline waters and constituted 17% of the Oithonidae collected over the two days of sampling.Over three years of monitoring, 6 individuals of O. attenuata were found in only two months: March and May 2011 (Fig. 2).Oithonidae species registered over the years include O. simplex, O. oligohalina, O. plumifera, and O. setigera.The size of O. attenuata females varied between 0.63 and 0.62 mm (prosoma 0.28 and 0.29 mm; depth the prosoma 0.12-0.14;urosoma 0.32-0.34mm).

Oithona attenuata from Brazil
Nauplius, 27: e2019001 Oithona attenuata is an epipelagic species most commonly found in the Mediterranean Sea (Lebanon Basin), Red Sea, Gulf of Oman, Arabian Sea and Arabian Gulf.It is also found throughout the Indian and tropical Pacific (W & central) oceans.More specifically, this includes: out off South Africa (Cape of Good Hope, Eastern side), the Maldives, Madagascar (Nosy Bé), Seychelles, Nicobar Is., Christmas Is., Straits of Malacca, Indonesia-Malaysia, Samoa (Pago Pago Harbour), China (Yellow Sea, East China Sea, South China Sea), Pa-Li, Taiwan (E, S, SW, W, NE, Tapong Bay, Danshuei Estuary), South Korea, Japan, Palau, W Baja California (Bahia Magdalena), Australia (Melbourne, Great Barrier, Exmouth Gulf, North West Cape, G. of Carpentaria) and Chile (Razouls et al., 2018).
Oithona attenuata is recorded here for the first time off Brazil, even though several studies had previously been conducted in the same place (Valentin, 1984;Dias and Araujo, 2006;Dias et al., 2010;Rosa and Monteiro-Ribas, 2012;Rosa et al., 2016).Its absence in plankton samples over the last 30 years leads us to suggest that this species was brought to Brazilian waters as an exotic species.The study site is close (less than two miles) to the Arraial do Cabo harbor, where foreign ships rarely discharge ballast water.The potential of O. attenuata to become an introduced species depends upon its resilience and ability to adapt to the new environment (Villac et al., 2009).In other words, it'd have to be some advantage in feeding or reproduction over native species that have similar environmental requirements, namely Dioithona oculata (Farran, 1913), O. nana, O. oligohalina and Oithona simplex quinquesetosa Früchtl, 1923 among others (Razouls et al., 2018), to be successfully introduced.Exotic copepods that have been successfully introduced off the Brazilian coast include: Temora turbinata (Dana, 1849), Pseudodiaptomus trihamatus Wright, 1937, Apocyclops borneoensis Lindberg, 1954, Paracyclopina longifurca (Sewell, 1924), Phyllopodopsyllus setouchiensis Kitazima, 1981. Furthermore, another exotic species, Pontella marplatensis Ramirez, 1966 (Pontellidae), was also recorded for the first time in the same region off Arraial do Cabo in September 2010 (Rosa and Monteiro-Ribas, 2012).It was described from the Argentine Sea (Mar del Plata) by Ramirez (1966) and had since also been found off Texas (Gulf of Mexico) (Waggett and Buskey, 2008).There is a hypothesis that O. attenuata may have come from the Indian Ocean from a whirlwind and arriving in Brazil, because according to Villar et al. (2015) plankton can be transported in this way.The absence of more individuals in samples collected during ongoing monitoring in the following months lead us to conclude that O. attenuata did not successfully reach the status of an introduced species.Since little is known about the rate of introduction, as more exotic species are recorded in the literature, the more confident our results in addressing the risk of unintended introductions off the Brazilian Coast will be.

Figure 1 .
Figure 1.Map of the geographic location of Arraial do Cabo, state of Rio de Janeiro, Brazil.