Micro- and mesozooplankton community response to increasing CO₂ levels in the Baltic Sea: insights from a large-scale mesocosm experiment

Community approaches investigating ocean acidification (OA) effects suggest a high tolerance of micro- and mesozooplankton to carbonate chemistry changes expected to occur within this century. Plankton communities in the coastal areas of the Baltic Sea frequently experience pH variations partly exceeding projections for the near future both on a diurnal and seasonal basis, thus some level of tolerance/adaptation may be expected. We conducted a large-scale mesocosm CO2 enrichment experiment (~ 55 m3) enclosing the natural plankton community in Tvärminne/Storfjärden for eight weeks during June–August 2012 and studied community and species/taxon response of microzooplankton (ciliates) and mesozooplankton to CO2 elevations expected for this century. Besides the response to fCO2 and associate changes in carbonate chemistry speciation, we also considered temperature and chlorophyll a variations in our analyses. Shannon diversity of microzooplankton significantly decreased with fCO2 and temperature with a greater dominance of smaller species. Small sized ciliates (Myrionecta rubra, Balanion comatum, Strombidium cf. epidemum, Strobilidium sp.) showed significant relations with one or more of the factors. The phototrophic Myrionecta rubra seemed to directly benefit from higher CO2 concentrations and showed increased abundance in the pre-bloom phase. With respect to meszooplankton, we neither detected significant effects for total abundance nor for Shannon diversity. The cladocera Bosmina occurred at distinctly higher abundance (more than twice as high compared to the control mesocosms) for a short time period during the second half of the experiment in three of the CO2-enriched mesocosms except for the highest CO2 level. The ratio of Bosmina with empty to embryo/resting egg bearing brood chambers, however, was significantly affected by all three factors. An indirect CO2 effect via increased food availability stimulating Bosmina reproduction is suggested, but too low sampling frequency of this highly flexible organism probably entailed proving a significant relation with fCO2. Filter-feeding cladocerans effectively transfer microbial loop carbon to higher trophic levels. Thus, under increasing OA in cladoceran dominated mesozooplankton communities the importance of the microbial loop in the pelagic zone may be enhanced and carbon transfer to higher trophic levels stimulated.

High-Level Congruence of Myrionecta rubra Prey and Dinophysis Species Plastid Identities as Revealed by Genetic Analyses of Isolates from Japanese Coastal Waters

ABSTRACT We analyzed cryptophyte nucleomorph 18S rRNA gene sequences retained in natural Myrionecta rubra cells and plastid 16S rRNA gene and psbA sequences retained in natural cells of several Dinophysis species collected from Japanese coastal waters. A total of 715 nucleomorph sequences obtained from 134 M. rubra cells and 564 plastid 16S rRNA gene and 355 psbA sequences from 71 Dinophysis cells were determined. Almost all sequences in M. rubra and Dinophysis spp. were identical to those of Teleaulax amphioxeia, suggesting that M. rubra in Japanese coastal waters preferentially ingest T. amphioxeia. The remaining sequences were closely related to those of Geminigera cryophila and Teleaulax acuta. Interestingly, 37 plastid 16S rRNA gene sequences, which were different from T. amphioxeia and amplified from Dinophysis acuminata and Dinophysis norvegica cells, were identical to the sequence of a D. acuminata cell found in the Greenland Sea, suggesting that a widely distributed and unknown cryptophyte species is also preyed upon by M. rubra and subsequently sequestered by Dinophysis. To confirm the reliability of molecular identification of the cryptophyte Teleaulax species detected from M. rubra and Dinophysis cells, the nucleomorph and plastid genes of Teleaulax species isolated from seawaters were also analyzed. Of 19 isolates, 16 and 3 clonal strains were identified as T. amphioxeia and T. acuta, respectively, and no sequence variation was confirmed within species. T. amphioxeia is probably the primary source of prey for M. rubra in Japanese coastal waters. An unknown cryptophyte may serve as an additional source, depending on localities and seasons.

A MULTI-SPECIES MICROALGAE BLOOM IN BAHIA DE LA PAZ, GULF OF CALIFORNIA, MEXICO (JUNE 2008)

Red tide patches were observed in Bahía de La Paz in June 17 and 18 of 2008. According to temperature and wind data this bloom occurred under upwelling-like conditions. Examination of the red tide samples showed the ciliate Myrionecta rubra and the naked dinoflagellates Gyrodinium instriatum and Katodinium glaucum as the main species responsible for this bloom. Total density (microalgae and ciliate) at the sampling stations was similar on both days, varying from 4607 × 103 cells L-1 to 4976 × 103 cells L-1 on the first day, and from 4172 × 103 cells L-1 to 5024 × 103 cells L-1 on the second day. Phytoplankton biomass (chlorophyll a) observed during the first day of the bloom was 1.5 mg m-3. Dinoflagellates and diatoms were the most numerically important phytoplankton groups. The phytoplankton community showed a high species richness, particularly heterotrophic dinoflagellates and ebridians. The ecological importance of the heterotrophic component of naked dinoflagellates and the ebriids for this bay is discussed. Florecimiento multiespecífico de microalgas en la Bahía de La Paz, Golfo de California, México (Junio, 2008) Durante los días 17 y 18 de junio de 2008, se observó una marea roja en la Bahía de La Paz. De acuerdo con los datos de temperatura y de vientos, este florecimiento ocurrió bajo condiciones muy similares a las de una surgencia. El examen de las muestras de marea roja revelaron que el ciliado Myrionecta rubra y los dinoflagelados desnudos Gyrodinium instriatum y Katodinium glaucum fueron las principales especies responsables de esta proliferación. La densidad total (microalgas y ciliado) fue similar en ambos días, variando de 4607 × 103 céls L-1 a 4976 × 103 céls L-1 durante el primero y entre 4172 × 103 céls L-1 y 5024 × 103 céls L-1 el segundo día, respectivamente. La biomasa fitoplanctónica (clorofila a) medida durante el primer día del florecimiento fue de 1.5 mg m3. Los dinoflagelados y las diatomeas fueron los dos grupos del fitoplancton numéricamente más importantes. Se observó una comunidad fitoplanctónica con una alta riqueza de especies, particularmente de dinoflagelados y ebriidos heterotróficos. Se discute la importancia del componente heterotrófico de los dinoflagelados desnudos y ebriidos.

BLOOMS OF Myrionecta rubra IN BAHÍA DE LA PAZ, GULF OF CALIFORNIA, DURING EARLY SUMMER OF 2005

Blooms of the ciliate Myrionecta rubra are quite common in Bahía de La Paz. In June and July 2005 two blooms of this species were sampled to determine abundance, plankton biomass, nutrients, dissolved oxygen, and temperature. During the bloom in June, surface temperature ranged from 19.0 °C to 19.6 °C and dissolved oxygen from 4.2 mg l-1 to 4.7 mg l-1. During the second bloom, surface temperature as 24.2 °C and dissolved oxygen was 6.7 mg l-1. At 25 m depth, conditions were 20.0 °C and 3.5 mg l-1, respectively. At the surface, nutrients were low, except for ammonium (1.14 µM – 2.27 µM). High densities of M. rubra (2.14 × 106 cells l-1), chlorophyll a (55.6 µg l-1), chlorophyll c (6.0 µg l-1), and alloxanthin (8.1 µg l-1) were recorded. This last pigment is characteristic of the cryptophyte group, suggesting an association of the ciliate with this algal group. Winds from the southeast varied from 3 to 4.5 m s-1 in June and 1.7 to 4.8 m s-1 in July. The presence of this bloom under low thermal stratification and with the highest density of the ciliates at the surface during the onset of the bloom suggest that southeastern winds mixed the shallow water column, brought up nutrients from the bottom sediments, and induced high concentrations of the cryptophytes. Proliferaciones de Myrionecta rubra en Bahía de La Paz, Golfo de California, al inicio del verano de 2005 Las proliferaciones del ciliado Myrionecta rubra son frecuentes en Bahía de la Paz. Durante junio y julio de 2005 se registraron dos proliferaciones de esta especie en tres sitios de esta bahía. Durante estos eventos se tomaron muestras para determinar abundancia, biomasa planctónica, nutrientes, oxígeno disuelto y temperatura. En junio, la temperatura osciló entre 19.0 °C y 19.6 °C y el oxígeno entre 4.7 mg l-1 y 4.2 mg l-1. En julio fue de 24.2 °C y 6.7 mg l-1 y disminuyó a 20.0 °C y 3.5 mg l-1 a 25 m de profundidad. Los nutrientes fueron bajos, siendo únicamente altos los de amonio en superficie (1.14-2.27 µM). Se presentaron valores altos de biomasa, expresada como clorofila a (55.6 µg l-1), clorofila c (6.0 µg l-1) y de aloxantina (8.1 µg l-1); este último, es característico de criptofitas asociadas con el ciliado M. rubra, el cual alcanzó densidades máximas de 2.14 x 106 células l-1. Los vientos dominantes de junio fueron del sureste (3.0 m s-1- 4.5 m s-1) y de 1.7 m s-1- 4.8 m s-1 en julio. La débil estratificación y la presencia en superficie de M. rubra durante la tarde, sugieren que los vientos del sureste promueven la mezcla de la columna de agua. Esto propicia la remoción de nutrientes de los sedimentos hacia la superficie, promoviendo el incremento de la abundancia de la criptofita.