Kwang Young Kim

Feeding by phototrophic red-tide dinoflagellates on the ubiquitous marine diatom Skeletonema costatum.

ABSTRACT We investigated feeding by phototrophic red‐tide dinoflagellates on the ubiquitous diatom Skeletonema costatum to explore whether dinoflagellates are able to feed on S. costatum, inside the protoplasm of target dinoflagellate cells observed under compound microscope, confocal microscope, epifluorescence microscope, and transmission electron microscope (TEM) after adding living and fluorescently labeled S. costatum (FLSc). To explore effects of dinoflagellate predator size on ingestion rates of S. costatum, we measured ingestion rates of seven dinoflagellates at a single prey concentration. In addition, we measured ingestion rates of the common phototrophic dinoflagellates Prorocentrum micans and Gonyaulax polygramma on S. costatum as a function of prey concentration. We calculated grazing coefficients by combining field data on abundances of P. micans and G. polygramma on co‐occurring S. costatum with laboratory data on ingestion rates obtained in the present study. All phototrophic dinoflagellate predators tested (i.e. Akashiwo sanguinea, Amphidinium carterae, Alexandrium catenella, Alexandrium tamarense, Cochlodinium polykrikoides, G. polygramma, Gymnodinium catenatum, Gymnodinium impudicum, Heterocapsa rotundata, Heterocapsa triquetra, Lingulodinium polyedrum, Prorocentrum donghaiense, P. micans, Prorocentrum minimum, Prorocentrum triestinum, and Scrippsiella trochoidea) were able to ingest S. costatum. When mean prey concentrations were 170–260 ng C/ml (i.e. 6,500–10,000 cells/ml), the ingestion rates of G. polygramma, H. rotundata, H. triquetra, L. polyedrum, P. donghaiense, P. micans, and P. triestinum on S. costatum (0.007–0.081 ng C/dinoflagellate/d [0.2–3.0 cells/dinoflagellate/d]) were positively correlated with predator size. With increasing mean prey concentration of ca 1–3,440 ng C/ml (40–132,200 cells/ml), the ingestion rates of P. micans and G. polygramma on S. costatum continuously increased. At the given prey concentrations, the maximum ingestion rates of P. micans and G. polygramma on S. costatum (0.344–0.345 ng C/grazer/d; 13 cells/grazer/d) were almost the same. The maximum clearance rates of P. micans and G. polygramma on S. costatum were 0.165 and 0.020 μl/grazer/h, respectively. The calculated grazing coefficients of P. micans and G. polygramma on co‐occurring S. costatum were up to 0.100 and 0.222 h, respectively (i.e. up to 10% and 20% of S. costatum populations were removed by P. micans and G. polygramma populations in 1 h, respectively). Our results suggest that P. micans and G. polygramma sometimes have a considerable grazing impact on populations of S. costatum.

Feeding by the newly described mixotrophic dinoflagellate Paragymnodinium shiwhaense: feeding mechanism, prey species, and effect of prey concentration.

ABSTRACT. To investigate the feeding by the newly described mixotrophic dinoflagellate Paragymnodinium shiwhaense (GenBank accession number=AM408889), we explored the feeding process and the kinds of prey species that P. shiwhaense is able to feed on using several different types of microscopes, including a transmission electron microscope and high‐resolution video‐microscopy. In addition, we measured the growth and ingestion rates of P. shiwhaense on its optimal algal prey Amphidinium carterae as a function of prey concentration. We also measured these parameters for edible prey at a single concentration at which the growth and ingestion rates of P. shiwhaense on A. carterae were saturated. Paragymnodinium shiwhaense feed on algal prey using a peduncle after anchoring the prey by a tow filament. Among the algal prey offered, P. shiwhaense ingested small algal species that had equivalent spherical diameters (ESDs) ≤11 μm (e.g. the prymnesiophyte Isochrysis galbana, the cryptophytes Teleaulax sp. and Rhodomonas salina, the raphidophyte Heterosigma akashiwo, and the dinoflagellates Heterocapsa rotundata and A. carterae). However, it did not feed on larger algal species that had ESDs ≥12 μm (e.g. the dinoflagellates Prorocentrum minimum, Heterocapsa triquetra, Scrippsiella trochoidea, Alexandrium tamarense, Prorocentrum micans, Gymnodinium catenatum, Akashiwo sanguinea, and Lingulodinium polyedrum) or the small diatom Skeletonema costatum. The specific growth rates for P. shiwhaense feeding upon A. carterae increased rapidly with increasing mean prey concentration before saturating at concentrations of ca. 350 ng C/ml (5,000 cells/ml). The maximum specific growth rate (i.e. mixotrophic growth) of P. shiwhaense on A. carterae was 1.097/d at 20 °C under a 14:10 h light–dark cycle of 20 μE/m2/s, while its growth rate (i.e. phototrophic growth) under the same light conditions without added prey was −0.224/d. The maximum ingestion and clearance rates of P. shiwhaense on A. carterae were 0.38 ng C/grazer/d (5.4 cells/grazer/d) and 0.7 μl/grazer/h, respectively. The calculated grazing coefficients for P. shiwhaense on co‐occurring Amphidinium spp. was up to 0.07/h (i.e. 6.7% of the population of Amphidinium spp. was removed by P. shiwhaense populations in 1 h). The results of the present study suggest that P. shiwhaense can have a considerable grazing impact on algal populations.

Enhanced Production of Oceanic Dimethylsulfide Resulting from CO2-Induced Grazing Activity in a High CO2 World

Oceanic dimethylsulfide (DMS) released to the atmosphere affects the Earths radiation budget through the production and growth of cloud condensation nuclei over the oceans. However, it is not yet known whether this negative climate feedback mechanism will intensify or weaken in oceans characterized by high CO(2) levels and warm temperatures. To investigate the effects of two emerging environmental threats (ocean acidification and warming) on marine DMS production, we performed a perturbation experiment in a coastal environment. Two sets of CO(2) and temperature conditions (a pCO(2) of ∼900 ppmv at ambient temperature conditions, and a pCO(2) of ∼900 ppmv at a temperature ∼3 °C warmer than ambient) significantly stimulated the grazing rate and the growth rate of heterotrophic dinoflagellates (ubiquitous marine microzooplankton). The increased grazing rate resulted in considerable DMS production. Our results indicate that increased grazing-induced DMS production may occur in high CO(2) oceans in the future.

NaOCl produced by electrolysis of natural seawater as a potential method to control marine red-tide dinoflagellates

Abstract As part of the development of a method to control the outbreak and persistence of red tides using sodium hypochlorite (NaOCl), we investigated the effect of NaOCl on the survival of red-tide dinoflagellates, diatoms, heterotrophic protists, planktonic crustaceans, fin-fish, shellfish, and macroalgae. Because NaOCl introduced into natural waters would be subject to dilution, as well as breakdown in sunlight to NaCl, the survival of organisms was determined after 10 min exposure and 1 h exposure to NaOCl, and again after transfer to fresh seawater for 6 or 24 h. The lethal total residual chlorine (TRC) concentration that killed 50% of the test organisms (LC50) for the red-tide dinoflagellates Gymnodinium catenatum, Cochlodinium polykrikoides, Akashiwo sanguinea, Lingulodinium polyedrum, Prorocentrum micans, Alexandrium affine, and Gymnodinium impudicum ranged from 57 to 157 ppb for 10 min exposure and from 30 to 106 ppb for 1 h exposure. Complete mortality of all red-tide species occurred at TRC concentrations of ~ 500 ppb. The LC50 of the diatoms Skeletonema costatum and Thalassiosira rotula, 3083–3383 ppb for 10 min exposure and 3128–3433 ppb for 1 h exposure, were much higher than for red-tide dinoflagellates. But the LC50s of the heterotrophic dinoflagellates Polykrikos kofoidii and Oxyrrhis marina were similar to those of red-tide dinoflagellates. The ciliate Strombidinopsis sp. had LC50s of 306 ppb for 10 min exposure and 119 ppb for 1 h exposure, which are higher than those for dinoflagellates. The LC50s of the calanoid copepods Acarlia spp. and Pseudodiaptomus sp. were 1397–1493 ppb for 10 min exposure and 744–987 ppb for 1 h exposure, and those for larvae of the brine shrimp Artemia franciscana were 4905 ppb for 10 m exposure and 2814 ppb for 1 h exposure. The LC50s of juvenile gray mullet Mugil cephalus and juvenile black rockfish Sebastes schlegeli were 1234–1883 ppb for 10 min exposure and 1234–1440 ppb for 1 h exposure, whereas those of adult Manila clam Ruditapes philippinarum and spat of the abalone Nordotis discus were> 20,000 ppb. The LC50s of the macroalgae Griffithsia japonica (Rhodophyta) and Ulva pertusa (Chlorophyta) were 1519–12,365 ppb for 10 min exposure and 1085–12,558 ppb for 1 h exposure. The present study therefore suggests that, if NaOCl is introduced into waters containing red-tide organisms at TRC concentrations of 300–500 ppb for 10 min exposure and 200–400 ppb for 1 h exposure, red tides can be effectively controlled without serious harmful effects on other marine organisms, except heterotrophic dinoflagellates.

Physiological ecology and seasonality of Ulva pertusa on a temperate rocky shore

Abstract Green tides, i.e. blooms of Ulva species, occur on rocky intertidal shores over a wide geographic area in Korea. For the first time we report seasonal fluctuations in biomass, photosynthetic performance and chemical composition of the green-tide forming Ulva pertusa on the southern coast of Korea. Water temperature, salinity, inorganic nutrients and precipitation influencing Ulva mat dynamics were also monitored. There was a pronounced seasonality, not only in the biomass of U. pertusa, but also in photosynthetic performance and in variation in tissue pigments and nutrients. In addition to a primary seasonal response, significant variation in biomass was correlated in parts of the year with nutrient inputs from the surrounding watershed, heavy rain events and summer desiccation. There was a unimodal seasonal pattern in which biomass peaked in May (2.2 kg fw m−2) and dropped significantly from June to September. Recovery of Ulva mats, as indicated by recruitment of new plants, began during autumn. Photosynthetic rates, maximum photosynthesis (Pmax) and photosynthetic efficiency (α) were highest during the growth period and were lowest when biomass peaked or declined in May and July. Tissue pigments had a less clear seasonal pattern. Relative amounts of nitrogen and phosphorus bound in U. pertusa also displayed an obscure seasonal trend. Complex interactions among biological and environmental variables precluded strong correlations with any particular environmental factor. Stochastic events also played a major role in seasonality and can override normal physiological adaptations.

Host specificity and growth of kelp gametophytes symbiotic with filamentous red algae (Ceramiales, Rhodophyta)

Kelp gametophytes were previously observed in nature living endophytically in red algal cell walls. Here we examine the interactions of two kelp species and six red algae in culture. Gametophytes of Nereocystis luetkeana (Mertens) Postels et Ruprecht became endophytic in the cell walls of Griffithsia pacifica Kylin and Antithamnion defectum Kylin, and grew epiphytically in high abundance on G. japonica Okamura and Aglaothamnion oosumiense Itono. Alaria esculenta (Linnaeus) Greville from the Atlantic coast of Nova Scotia became endophytic in Aglaothamnion oosumiense, Antithamnion defectum, Callithamnion sp., G. japonica, G. pacifica, and Pleonosporium abysicola Gardner, all from the Pacific Ocean. Some cultures were treated with phloroglucinol before infection to thicken the cell walls. The endophytic gametophytes were smaller and grew more slowly than gametophytes epiphytic on the same host. N. luetkeana failed to become endophytic in some of the potential hosts, and this may reflect host specificity, or culture artifacts. This work improves our understanding of the process of infection of red algae by kelp gametophytes, and broadens our knowledge of host specificity in endophytic symbioses.

Fluorescence and photosynthetic competency in single eggs and embryos of Ascophyllum nodosum (Phaeophyceae)

K.Y. Kim, H.J. Jeong, H.P. Main and D.J. Garbary. 2006. Fluorescence and photosynthetic competency in single eggs and embryos of Ascophyllum nodosum (Phaeophyceae). Phycologia 45: 331–336. DOI: 10.2216/05-40.1 Pulse amplitude modulation (PAM) fluorometry was used in 2004 and 2005 to measure chlorophyll α fluorescence associated with photosystem II in eggs and embryos of Ascophyllum nodosum (Linnaeus) Le Jolis from the Atlantic coast of Nova Scotia. Fucoid eggs and embryos were maintained in the laboratory for 8 days over which fluorescence measurements were taken. Newly released eggs saturated at about 20 μmol photons m−2 s−1 with maximum electron transport rate (rETRmax) declining to <3 after 3 days. Embryos saturated at about 50 μmol photons m−2 s−1 and rETRmax increased to >11 by day 3. Although some egg senescence was apparent by day 3, some eggs continued to generate a strong photosynthetic signal throughout the 8-day experimental period, even though rETRmax was reduced. Differences in photosynthetic responses associated with fertilisation were apparent in Fv/Fm, within 24 h, and in rETRmax after 2 days. Eggs showed relatively stable or declining responses, whereas embryos showed stable or increasing responses. By day 8, quantum yield of embryos was similar to values reported elsewhere for mature fucoids.

Phytoplankton dynamics in Pomquet Harbour, Nova Scotia: a lagoon in the southern Gulf of St Lawrence

Abstract Weekly determination of cell number and cell volume of phytoplankton (excluding picoplankton) was carried out over a 13 month period (August 1996 to August 1997) in Pomquet Harbour, Nova Scotia, Canada, in the southern Gulf of St Lawrence. Eighty-eight species were identified, of which 72 species contributed 0.1% or more to the cell volume from all sampling. Ten to 35 species were present at individual sampling times, and there was a 4–67% turnover in species composition from week to week. This turnover may be a function of low species diversity (H′ = 0.06–2.59), low phytoplankton abundances (mean of 76 cells ml−1) and high flushing rates in Pomquet Harbour. A summer nutrient increase was correlated with a summer phytoplankton bloom in August of two successive years, in which at least 80% of cell volume was contributed by Ceratium fusus (1996) or Gonyaulax spinifera (1997). A fall bloom of Skeletonema costatum contributed 52% of cell counts, but only 3.2% of cell volume. Nutrients and phytoplankton populations were lower than comparable lagoon systems of Cape Cod, but similar to another site from the Gulf of St Lawrence. Multivariate analyses (cluster and principal component analyses) showed four distinct phytoplankton seasons: summer (July, August), fall (September to mid-December), winter (mid-December to April) and spring (May, June).

Anatomical Differentiation and Photosynthetic Adaptation in Brown Algae

The photosynthetic parameters of dark- adapted minimum fluorescence (Fo) and maximum quantum yield of charge separation in PSII (Fv/Fm) were measured in transverse sections of eight species of marine Phaeophyceae (species of Laminariales, Fucales, Desmarestiales, Chordariales) using pulse amplified modulation (PAM) fluorometry. Within each transverse section fluorescence was measured in three regions corresponding to outer cortical and meristoderm cells, inner cortical cells and innermost medullary cells. Minimum fluorescence declined from 19-74% (mean of 39%) from outermost to innermost cells. Maximum quantum yield varied from 0.51-0.59 in outermost cell layers and this was reduced to 0.23-0.40 in innermost cell layers, with an average reduction of 50%. Despite the reduction Fo in medullary cells (inner), medullas of all species showed maximum quantum yields consistent with a photosynthetic role in carbon fixation. These results show that medullary cells of complex brown algae have more than a role in structure, storage or transport, and may also provide an important role in carbon fixation.

Fluorescence responses of photosynthesis to extremes of hyposalinity, freezing and desiccation in the intertidal crust Hildenbrandia rubra (Hildenbrandiales, Rhodophyta)

K.Y. Kim and D.J. Garbary. 2006. Fluorescence responses of photosynthesis to extremes of hyposalinity, freezing and desiccation in the intertidal crust Hildenbrandia rubra (Hildenbrandiales, Rhodophyta). Phycologia 45: 680–686. DOI: 10.2216/05-43.1 A winter collection of the intertidal, red algal crust, Hildenbrandia rubra (Sommerfelt) Meneghini, was examined for tolerance of photosynthesis to extremes of temperature, salinity and desiccation. Pulse amplitude modulation fluorometry of chlorophyll a fluorescence was used to determine various photosynthetic parameters including effective quantum yield (ΦPSII) and relative electron transport rate (rETR). Thalli from the same collection were successively exposed to freezing, desiccation, hyposalinity and high temperature. Thus thalli over 13 days experienced temperature fluctuations from −17 to 27°C, from fully hydrated to extremely desiccated, from full seawater to 4 psu and back, all without any apparent long-term effects to the photosynthetic apparatus. There was no significant difference in ΦPSII between thalli at the beginning and end of the experiments. Algae showed a significant acclimation to low light in that immediately after collection thalli had optimum light intensity, Ik, in terms of rETR at 50 μmol photons m−2 s−1, whereas 24 h later maximal rETR was at about 20 μmol photons m−2 s−1. Hildenbrandia rubra is the most physiologically tolerant of any tested seaweed, and this helps explain its wide geographic and ecological range.