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All parasitoid apostome ciliates infecting krill in the northeastern Pacific are currently assigned to the genus Pseudocollinia. Each krill specimen is apparently infected by only 1 Pseudocollinia species. We describe Pseudocollinia similis sp. nov., discovered infecting the krill Thysanoessa spinifera off Oregon, USA. Its protomite-tomite stage resembles that of P. beringensis, which infects T. inermis (type host species), T. longipes, and T. raschii females in the Bering Sea. These ciliates have similar numbers of somatic kineties (18-21 vs. 16-20) and typically have 3 oral kineties. Furthermore, these 2 apostomes are sister species on gene trees based on sequences of small subunit rRNA (0.06% difference) and cytochrome c oxidase subunit 1 (cox1; 30% difference). P. brintoni and P. oregonensis are closely related as a separate group from P. similis and P. beringensis. The similar tree topologies based on the cox1 sequences of 21 host krill individuals representing 6 krill species (Euphausia pacifica, Nyctiphanes simplex, T. inermis, T. longipes, T. raschii, and T. spinifera) and the apostomes isolated from these krill suggest host-parasitoid codiversification. However, this hypothesis was statistically rejected by an approximately unbiased test in which the host tree topology was used to model parasitoid evolution (p ≤ 0.05).

The effect of wind-induced coastal upwellings on tropical euphausiid abundance and community structure was investigated in the Mexican central Pacific (19°N, 105°W) during a monthly time series (1996−1998). Eight species were identified, of which Euphausia distinguenda contributed between 88 and 90% of the total euphausiid abundance, and E. lamelligera con tributed ~7%. The hydrographic structure (< 200 m depth) and euphausiid species composition had strong seasonality patterns associated with the upwelling (February to May) and downwelling (July to November) periods. Redundancy analysis of euphausiid abundance and community structure as a function of the environmental variables revealed that coastal upwelling index, salinity at 10 m depth, and temperature explained most of the euphausiid abundance variability. Stations sampled during intense upwelling periods had the highest abundance of E. distinguenda and E. lamelligera juveniles and adults. Their abundance was strongly and positively correlated with salinity and abundance of nano-and microphytoplankton, but was negatively correlated with surface temperature. Larvae of E. distinguenda and the oceanic species Nematoscelis gracilis (downwelling ensemble) were strongly associated with warm waters of low phytoplankton abundance. The hepato-somatic index (ratio of hepatopancreas length to carapace length) of E. distinguenda and E. lamelligera adults was significantly larger during mixed and semi-mixed than during stratified periods, providing a useful proxy for euphausiid health and trophic condition. Wind-induced upwelling−downwelling are significant coastal processes that influenced seasonal euphausiid abundance and species composition in this tropical ecosystem, while the strong and brief El Niño event of 1997−98 had only a relatively moderate effect in comparison with that observed on euphausiids from transitional (northwest of Mexico) and temperate (Pacific USA) ecosystems.

The diversity of parasites found on Nyctiphanes simplex and Nematoscelis difficilis (Order Euphausiacea) was compared during 10 oceanographic cruises made off both coasts of the Baja California peninsula, Mexico. We tested the hypothesis that N. simplex has a more diverse parasitic assemblage than N. difficilis because it is a neritic species, has larger population abundance, and tends to form denser and more compact swarms than N. difficilis. These biological and behavioral features may enhance parasite transmission within swarms. We detected 6 types of ectoparasites: (1) epibiotic diatoms Licmophora sp.; (2) Ephelotidae suctorian ciliates; (3) Foettingeriidae exuviotrophic apostome ciliates; (4) an unidentified epicaridean cryptoniscus larvae (isopoda); and 2 castrators: (5) the ectoparasitic Dajidae isopod Notophryxus lateralis and (6) the ellobiopsid mesoparasite Thalassomyces fagei. We also detected 7 types of endoparasites: (1) an undescribed Collinia ciliate (Apostomatida); 3 types of Cestoda: (2) a Tetrarhynchobothruium sp. (Trypanorhyncha), (3) Echinobothrium sp. (Diphyllidea: Echinobothyriidae), and (4) unidentified metacestode; (5) a Trematoda Paronatrema-like metacercaria (Syncoeliidae); (6) the nematode Anisakis simplex (L3); and (7) Polymorphidae acantocephalan larvae (acanthor, acanthella, and cystacanth larval stages). N. simplex is affected by all types of parasites, except the isopod N. lateralis, having a considerably larger parasitic diversity and prevalence rates than N. difficilis, which is only infested with 3 types of ectoparasites and T. fagei. Euphausiid swarming is an adaptive behavior for reproduction, protection against predators, and increased efficiency in food searching, but has a negative effect due to parasitism. Although the advantages of aggregation must overcome the reduction of population and individual fitness induced by parasites, we demonstrated that all types of parasites can affect ~14% of N. simplex individuals. Collinia spp. endoparasitoids must occasionally have a significant influence on population mortality with potential epizootic events.KEY WORDS: Parasites · Parasitoids · Euphausiids · Nyctiphanes simplex · Nematoscelis difficilis · Bahía Magdalena · Gulf of California Resale or republication not permitted without written consent of the publisherDis Aquat Org 88: [249][250][251][252][253][254][255][256][257][258][259][260][261][262][263][264][265][266] 2010 increasing number of parasites and parasitoids have been discovered. The parasites of euphausiids include an array of interspecific associations that ranges from almost innocuous parenthetic epibiotic organisms such as diatoms (McClatchie et al. 1990), suctorians (Nicol 1984, Tarling & Cuzin-Roudy 2008, and apostome exuviotrophic ciliates (Lindley 1978, Rakusa-Suszczewski & Filcek 1988, Landers et al. 2006, to castrators (Field 1969) and parasitoids (Capriulo & Small 1986, Gómez-Gutiérrez et al. 2003, 2006, 2009. It is now apparent that each euphausiid species has a complex interspecific parasite...

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Table S1. List of 157 Operational Taxonomic Units (OTU) found from ichthyoplankton collections taken in 2014 from Cabo Pulmo National Park. The results from NCBI's GenBank, including accession numbers, and the Barcode of Life Database, including sample ID, are shown as well as the percentage of identical sites (% Iden) that matched for each sequence. OTU NCBI Result Accession # % Iden Barcode of Life result Sample ID % Iden Acanthemblemaria macrospilus Acanthemblemaria macrospilus Calamus brachysomus Calamus brachysomus KJ012304 100.0 NO MATCH Carangoides orthogrammus Carangoides orthogrammus KU943780 99.0 NO MATCH Carangoides otrynter Caranx latus JQ841100 90.3 Carangoides otrynter Co-29-IMARPE 100.0 Caranx caninus Caranx caninus EU752066 99.8 NO MATCH Caranx sexfasciatus Caranx sexfasciatus KU199209 100.0 NO MATCH Carapus dubius Halichoeres pictus JQ839789 82.2 Carapus dubius 100.0 Cephalopholis panamensis Cephalopholis cruentata GU225173 94.8 Cephalopholis panamensis 99.8 Chanos chanos Chanos chanos LT669927 100.0 NO MATCH

Vertical distribution and abundance of three numerically dominant krill species (Nyctiphanes simplex, Nematoscelis difficilis, and Euphausia eximia) were surveyed in the Gulf of California to understand the role of oxidative stress in their daily vertical migration (DVM) and zoogeographic patterns. Superoxide radical production, lipid peroxidation, and antioxidant enzyme activities were analyzed from krill collected with stratified nets from the surface down to 200 m during January, July, and October 2007. The upper boundary of the oxygen minimum zone (OMZ) was significantly shallower during October than during January. N. simplex was always distributed above the hypoxic layers, mostly in coastal upwelling areas. Ne. difficilis and E. eximia were relatively abundant during January, but detected mostly during their ascending migration. N. simplex was the most sensitive species to high temperatures and low oxygen concentrations, showing evidence of oxidative stress during summer (100 times more lipid peroxidation and 30 times more antioxidant enzyme activities than in winter). Ne. difficilis had higher glutathione peroxidase activity than N. simplex, which could facilitate its larger DVM. Low abundance of Ne. difficilis at 100 m during summer suggests that high temperature was also an environmental limiting factor. Oxidative stress indicators could explain the absence of N. simplex and Ne. difficilis in the eastern tropical Pacific and the ability of E. eximia to live in the OMZ and the eastern tropical Pacific. The latter had higher superoxide radical production and smaller lipid peroxidation during October. This suggests that E. eximia antioxidant enzyme activities are enough to avoid oxidative damage when exposed to hypoxic conditions during DVM.

A novel parasitoid ciliate, Pseudocollinia brintoni gen. nov., sp. nov. was discovered infecting the subtropical sac-spawning euphausiid Nyctiphanes simplex off both coasts of the Baja California peninsula, Mexico. We used microscopic, and genetic information to describe this species throughout most of its life cycle. Pseudocollinia is distinguished from other Colliniidae genera because it exclusively infects euphausiids, has a polymorphic life cycle, and has a small cone-shaped oral cavity whose left wall has a field of ciliated kinetosomes and whose opening is surrounded on the left and right by 2 'oral' kineties (or ciliary rows) that terminate at its anterior border. Two related species that infect different euphausiid species from higher latitudes in the northeastern Pacific Ocean, Collinia beringensis Capriulo and Small, 1986, briefly redescribed herein, and Collinia oregonensis Gómez-Gutiérrez, Peterson, and Morado, 2006, are transferred to the genus Pseudocollinia. P. brintoni has between 12 and 18 somatic kineties, and its oral cavity has only 2 oral kineties, while P. beringensis comb. nov. has more somatic kineties, including 3 oral kineties. P. oregonensis comb. nov. has an intermediate number of somatic kineties. P. beringensis comb. nov. also infects Thysanoessa raschi (a new host species). SSU rRNA and cox1 gene sequences demonstrated that Pseudocollinia ciliates are apostome ciliates and that P. brintoni is different from P. beringensis comb. nov. High densities of rod-shaped bacteria (1.7 µm length, 0.2 to 0.5 µm diameter) were associated with P. brintoni. After euphausiid rupture, high concentrations of P. brintoni and bacteria cluster to form 3 to 6 cm long filaments where tomites encyst and transform to the phoront stage; this is a novel place for encystation. P. brintoni may complete its life cycle when the euphausiids feed on these filaments.KEY WORDS: Euphausiids · Ciliates · Apostomatidae · Collinia · cox1 · SSU rRNA · MexicoResale or republication not permitted without written consent of the publisher