SEXUALITY AND CYST FORMATION IN PACIFIC STRAINS OF THE TOXIC D1NOFLAGELLATE GONYAULAX TAMARENSIS1,2

Sexuality has been established for a culture of Gonyaulax tarnarensis Lebour (strain NEPCC–71). The addition of a thick inoculum to a nitrogen–deprived medium results in the occurrence of anisogamous sexual fusion within the first three days in the new culture. Planozygotes, large “lumpy” cells recognizable by their four flagella, may persist up to 2 wk before forming a smooth–walled, oval hypnozygote. The latter resembles cysts released asexually by ecdysis but has a slightly thicker wall. Viable cysts resembling hypnozygotes (zygotic cysts), but with reduced photosynthetic pigmentation, have been isolated from natural murine sediments in Hidden Basin, British Columbia, and a culture (strain NEPCC–254) was initiated from excysted individuals. Zygotic cysts of NEPCC–71 remained encysted in the light at 17 C for 8 wk before excysting. The presence of a ventral pen with toxicity in the latter strain indicates that the taxonomy of G. tamarensis-like organisms is still in a stale of flux and the criteria for recognition of G. excavata (Braarud) Balech as a separate species are not satisfactory as presently formulated.     

Studies on woloszynskioid dinoflagellates IX: ultrastructure,cyst formation and phylogeny of the ‘red-snow’ alga Borghiella pascheri (Suchlandt) Moestrup (= Glenodinium pascheri,Woloszynskia pascheri,Gyrodinium nivalis)

Red snow caused by dinoflagellates is a phenomenon rarely reported, described from the European Alps from 1914 onwards, and subsequently observed outside Europe on several occasions in Ontario, Canada. Considerable taxonomic confusion exists regarding the identity of the organism(s) causing red snow, but the most recent occurrence in 2016 in Ontario has now allowed detailed studies, including LM, SEM, TEM and molecular sequencing of the causative species. We conclude that the two species originally described as the cause of red snow, Glenodinium pascheri and Gyrodinium nivale, are synonymous and that the appropriate name for the organism is Borghiella pascheri (syn. Woloszynskia pascheri) as suggested by Moestrup & Calado in the recent volume of the Süsswasserflora. The central part of Borghiella pascheri cells is tomato red and filled with numerous organelles, whose ultrastructure indicates modified chloroplasts. Lack of cultures has prevented chemical characterization of the red pigment. Formation of temporary cysts was common in the samples. Transformation of the motile cells into temporary cysts was followed in detail, and the cysts were shown to be surrounded by the fused inner membranes of the amphiesmal vesicles, which became the cell membrane of the cysts, covered by the fused pellicle precursors. The cell membrane from the motile cell was discarded together with the outer amphiesmal vesicle membrane and the thin thecal plates, and the temporary cysts were therefore not surrounded by any pattern of vesicles. Sexual reproduction resulted in the formation of hypnozygotes. Although the species possessed several unusual features, DNA sequencing showed it to belong to Borghiella. The culture established in 1965 from the Botanical Garden in Göttingen, Germany and generally identified as Woloszynskia pascheri belongs to a separate species of Borghiella, to be described separately.The occurrence of red snow caused by dinoflagellates is discussed.     

Development,morphological characteristics and viability of temporary cysts of Pyrodinium bahamense var. compressum (Dinophyceae) in vitro

Pellicle or temporary cysts of Pyrodinium bahamense var. compressum (Böhm) Steidinger, Tester & F.J.R. Taylor and their role in bloom dynamics have not yet been adequately characterized and understood. We investigated the role of temperature- and nutrient-mediated stress as factors that could induce pellicle formation in batch cultures. Cellular features and their implications for temporary cyst viability were examined using confocal laser scanning microscopy (CLSM). Our data suggest that temperature change is one of the key factors influencing pellicle formation, preserving viability at low temperature (i.e. 13°C). Hypnocysts (resting cysts) were not observed. During pellicle formation, motile cells generally undergo ecdysis, extrusion of cytoplasmic materials and bacteria, compaction of the nucleus and non-motility. The outermost covering of the temporary cysts shows red autofluorescence and it contains lower concentrations of chlorophyll (chl) a and no detectable chl c. The nuclear region is surrounded by transitional red bodies and other unidentified cellular structures. Temporary cysts can immediately revert back to the motile state upon exposure to optimum conditions. This is accompanied by the expansion of the nuclear region, regeneration of the chloroplasts and enlargement of the cell. Developmental changes during reversal of temporary cysts to motile forms were also observed to cause breaks in the cell covering that could serve as sites for bacterial entry. Though observed in vitro, such behaviour may also be occurring in nature especially as a response to drastic short-lived environmental changes. This is the first detailed report on the characteristics of temporary cysts of P. bahamense var. compressum.     

SEXUALITY AND CYST FORMATION IN THE DINOFLAGELLATE GONYAULAX TAMARENSIS: CYST YIELD IN BATCH CULTURES1

Encystment of the toxic dinoflagellate Gonyaulax tamarensis Lebour (var. excavata) was monitored in batch cultures exposed to a variety of nutritional and environmental treatments. Limitation by nitrogen (as ammonium or nitrate) or phosphorus (as phosphate) resulted in cyst formation. When the initial concentration of limiting nutrient was varied, total cyst yield (mL^?1) was directly proportional to the cell yield at all but the highest nutrient concentrations (where encystment was minimal). Encystment efficiency was relatively constant (0.1–0.2 cysts · cell^?1) over a 5-fold range of cell densities, indicating that 20 to 40% of the vegetative populations successfully encysted. Cyst formation was negligible in nutrient-replete medium, even with a significant reduction in growth rate due to non-optimal light, temperature, or to high batch culture cell densities. Low light levels did decrease cyst yield once encystment was initiated by nutrient limitation, but this was probably linked to smaller motile cell yield and not to a specific inhibition of encystment. In contrast, encystment was more sensitive to temperature than was growth rate: optimal cyst production occurred over a relatively narrow temperature range and no cysts were formed at [Page missing]     

RESTING CYST FORMATION OF EUTREPTIELLA GYMNASTICA (EUGLENOPHYCEAE) IN THE NORTHERN COASTAL BALTIC SEA1

Resting cyst formation of Eutreptiella gymnastica Throndsen was observed during a mesocosm experiment, where nutrient enrichment had induced almost a unialgal bloom. Cells and resting cysts of E. gymnastica were examined in scanning (SEM) and transmission electron microscopy (TEM) and light microscopy. Mature cysts were spherical, with a smooth thick mucilaginous cover that appeared layered when observed with the TEM. Intermediate forms were spherical and lacking flagella and a mucilaginous cover; the euglenoid pellicular striation and canal opening were easily visible. The volume of these intermediate spherical cells and mature cysts was estimated to have increased threefold compared to flagellated cells and contained many paramylon grains. When the cells were grazed by zooplankton, the paramylon grains passed the gut intact and were packed into fecal pellets. Intact undigested paramylon grains were observed in SEM after the breaking up of the pellets.     

The toxic dinoflagellate Cochlodinium polykrikoides (Dinophyceae) produces resting cysts

While harmful algal blooms (HABs) caused by the toxic dinoflagellate Cochlodinium polykrikoides have been known to science for more than a century, the past two decades have witnessed an extraordinary expansion of these events across Asia, North America, and even Europe. Although the production of resting cysts and subsequent transport via ships’ ballast water or/and the transfer of shellfish stocks could facilitate this expansion, confirmative evidence for cyst production by C. polykrikoides is not available. Here, we provide visual confirmation of the production of resting cysts by C. polykrikoides in laboratory cultures isolated from North America. Evidence includes sexually mating cell pairs, planozygotes with two longitudinal flagella, formation of both pellicular (temporary) cysts and resting cysts, and a time series of the cyst germination process. Resting cyst germination occurred up to 1 month after cyst formation and 2–40% of resting cysts were successfully germinated in cultures maintained at 18–21 °C. Pellicular cysts with hyaline membranes were generally larger than resting cysts, displayed discernable cingulum and/or sulcus, and reverted to vegetative cells within 24 h to ∼1 week of formation. A putative armored stage of C. polykrikoides was not observed during any life cycle stage in this study. This definitive evidence of resting cyst production by C. polykrikoides provides a mechanism to account for the recurrence of annual blooms in given locales as well as the global expansion of C. polykrikoides blooms during the past two decades.     

POTENTIAL IMPORTANCE OF BENTHIC CYSTS OF GONYAULAX TAMARENSIS AND G. EXCAVATA IN INITIATING TOXIC DINOFLAGELLATE BLOOMS1,2,3

Thick-walled, nonmotile cysts (termed hypnocysts) of two dinoflagellates were isolated from estuarine sediments in Cape Cod, Massachusetts, and germinated to produce their respective motile, thecate stages. Hypnocysts from Orleans district were identified as Gonyaulax excuvata (Braarud) Balech sensu Loeblich & Loeblich. Visually identical hypnocysts from Falmouth district were provisionally identified as Gonyaulax tamarensis Lebour. Both species were toxic. A geographic survey in September detected hypnocysts in only the sediments of locations where toxic blooms developed the preceding and following Spring. Laboratory incubation (16 C) of hypnocysts from sediment samples stored in the dark (5 C) for 6 mo initiated excystment by the temperature increase, with no appreciable effect from light regime, nutrient, or chelator concentrations. Motility of excysted germlings was optimum in highly chelated medium and in the presence of light. We conclude that hypnocysts of both tasa are important in seeding recurrent annual blooms, synchronizing early bloom development with vernal warning of seawater and increasing the geographic range of the species. We suggest that many red tides in New England and eastern Canadian waters are initiated through the displacement of motile estuarine populations into nearshore area by tidal advection and surface runoff, although the potential existence and importance of offshore cyst reservoirs cannot be discounted. Evidence is presented that hypnocysts are probable sexual zygotes whereas the thin-walled cysts readily formed in laboratory cultures (pellicle cyst) are asexual. Pellicle cysts are of limited durability, do not overwinter in nature, and therefore do not play a significant role in initiating toxic blooms.     

SEXUAL REPRODUCTION IN THE TOXIC DINOFLAGELLATE GONYAULAX MONILATA1

The sexual cycle of Gonyaulax monilata Howell was observed in stationary cultures and in nitrogen-deficient medium. The armored, isogamous gametes fuse in a characteristic manner with cingula at oblique angles. Nuclear fusion lags slightly behind cytoplasmic fusion. The zygote enlarges for several days. The dark, double-flagellated planozygote encysts within 1–3 wk. Early hypnozygotes are round to ovoid and contain lipid and one or two large golden-yellow globules. As the hypnozygote matures, the globules become smaller and the cytoplasm darkens and pulls from the wall. All cysts examined contained only one nucleus. A very dark, uninucleate post-hypnozygotic cell escapes through an archeopyle and within 24 h divides into daughter cells which divide in 24–48 h forming a small chain. The production of thick walled zygates in culture implies that such resting stages in marine sediments could serve as a source stock for blooms. This species causes toxic red tides and the existence of benthic “seed beds” consisting of hypnozygotes is now plausible.     

ULTRASTRUCTURAL ASPECTS OF SEXUAL REPRODUCTION IN THE RED TIDE DINOFLAGELLATE GONYAULAX TAMARENSIS1

The marine dinoflagellate Gonyaulax tamarensis Lebour is best known for its propensity to form blooms known as red tides in coastal waters worldwide. This paper examines the sexual cycle of this organism using light and electron microscopy. Sexual reproduction begins with contact between thecate gametes which subsequently shed their thecae to fuse along their pellicular layers. Nuclear fusion occurs well after cytoplasmic fusion and is characterized by several distinctive features: a highly vesiculate nucleoplasm without microtubules; nucleoli and V-shaped chromosomes abut the nuclear envelope distal to the region of nuclear contact; and each chromosome possesses a longitudinal line, the central chromosomal axis. Fusion results in a planozygote with numerous cytoplasmic storage products and a slightly thickened layer beneath the pellicle. Subsequent loss of thecal plates and a thickening of the sub-pellicular layer results in a non-motile hypnozygote. A newly-formed hypnozygote possesses numerous minute papillae along its outer surface, formed by the up-folding of the accumulating wall layer. Maturation of the hypnozygote wall results in a smooth three-layered wall, the outermost layer of which is the pellicular layer. Hypnozygote germination produces a large quadriflagellate plan-omeiocyte with a single nucleus and thecal plates identical to vegetative cells. Two subsequent divisions, presumably meiotic, result in Jour cells morphologically identical to vegetative cells.     

CONTROL OF GERMINATION OF ALEXANDRIUM TAMARENSE (DINOPHYCEAE) CYSTS FROM THE LOWER ST. LAWRENCE ESTUARY (CANADA)

Cysts of the toxic dinoflagellate Alexandrium tamarense (Lebour) Balech 1992 from the lower St. Lawrence estuary were used in a test of the following hypotheses: (1) cyst germination is triggered by a change in temperature, and (2) germination rate varies throughout the year and is controlled by a circannual internal biological clock. Results show that cyst germination was not affected significantly by temperature of incubation over the range 1°–16° C, and light showed no significant stimulation of germination. This is supported by the lack of effect of cyst incubation conditions during evaluation of the seasonal changes in germination rate (two temperatures: 4° and 15° C, and two light conditions: darkness and 150 μmol photons·m^?2·s^?1). Thus, direct environmental control through short-term increases in temperature and exposure to light has no effect on the germination of the cysts tested. The rate of germination, observed monthly over a 16-month period, showed low germination (<20%) over most of the period tested, except for a maximum reaching more than 50% germination in August to October of the second year of the experiment. This pattern was observed for cysts both from monthly field collections and from laboratory-stored cysts kept under constant environmental conditions (4° C, in the dark). The peak in germination observed under constant environmental conditions (in the laboratory), the almost coincidental increase in cyst germination observed for the field-collected cysts, and the absence of effects of temperature and light during incubation could be explained either by a temperature-controlled cyst maturation period (the time-temperature hypothesis of Huber and Nipkow 1923) or by the presence of an internal biological clock. However, the large decline in the rate of germination 2 months after the maximum provides strong support for the biological clock hypothesis. The ca. 12-month maturation (dormancy) period observed for the laboratory-stored cysts is the longest reported for this species to our knowledge; this might be related to the low storage temperature (4° C), which is close to bottom temperatures generally encountered in this environment (0° to 6° C). Similar field and laboratory storage temperatures could explain the coincidental increase in germination rate in the fall of the second year if cyst maturation is controlled by temperature. A fraction of the laboratory-stored cysts did not follow a rhythmic pattern: A rather constant germination rate of about 20% was observed throughout the year. This continuous germination of likely mature cysts may supplement the local blooms of this toxic dinoflagellate, as these often occur earlier than peak germination observed in late summer. It seems that two cyst germination strategies are present in the St. Lawrence: continuous germination after cyst maturation, with temperature controlling the length of the maturation period, and germination controlled by a circannual internal rhythm.     

Life Cycle of the pseudocolonial dinoflagellate Polykrikos kofoidii (Gymnodiniales,Dinoflagellata)

The athecate, pseudocolonial polykrikoid dinoflag‐ellates show a greater morphological complexity than many other dinoflagellate cells and contain not only elaborate extrusomes but sulci, cinguli, flagellar pairs, and nuclei in multiple copies. Among polykrikoids, Polykrikos kofoidii is a common species that plays an important role as a grazer of toxic planktonic algae but whose life cycle is poorly known. In this study, the main life cycle stages of P. kofoidii were examined and documented for the first time. The formation of gametes, 2‐zooid‐1‐nucleus stages very different from vegetative cells, was observed and the process of gamete fusion, isogamy, was recorded. Karyogamy followed shortly after completed plasmogamy. A complex reorganization of furrows (cinguli and sulci) and flagella followed zygote formation, resulting in a 4‐zooid zygote with one nucleus. The fate of zygotes under different nutritional conditions was also investigated; well‐fed zygotes were able to reenter the vegetative cycle via meiotic divisions as indicated by nuclear cyclosis. However, nuclear cyclosis was preceded by a presumably mitotic division of the primary zygote nucleus which by definition would imply that P. kofoidii has a diplohaplontic life cycle. Nuclear cyclosis in germlings hatched from spiny resting cysts indicate that these cysts are of zygote origin (hypnozygotes). Hypnozygote formation, cyst hatching, the morphology of the germling (a 1‐zooid cell), and its development into a normal pseudocolony are documented here for the first time. There is evidence that P. kofoidii has a system of complex heterothallism.     

THE DINOFLAGELLATE PELLICULAR WALL LAYER AND ITS OCCURRENCE IN THE DIVISION PYRRHOPHYTA1

Forty-five species of dinoflagellates were surveyed for the presence of a pellicular layer in the amphiesma or cell covering. Such a layer was found in 15 of the 20 genera studied. Half the pellicles tested were resistant to acetolysis and may contain a sporopollenin-like material similar to that of some dinoflagellate cyst walk. Most organisms which formed pellicles were capable of reinforcing this layer with cellulose. Pellicles of Heterocapsa niei (Loeblich) Morrill & Loeblich and Scrippsiella trochoidea (Stein) Loeblich were studied with the electron microscope. Evidence is presented indicating that dividing cells of S. trochoidea from new walls while still enclosed in the parental pellicular layer.     

The significance of sexual versus asexual cyst formation in the life cycle of the noxious dinoflagellate Alexandrium peruvianum

Alexandrium peruvianum (Balech et Mendiola) is a noxious phototrophic marine dinoflagellate. During the life cycle of this species, two kinds of cysts are produced: resting cysts, which are long-lasting and double-walled, and temporary cysts, which are short-lasting and thin-walled. In addition, short-lasting, but resting-like cysts can also be formed. Although it is crucial to identify sexual events in a dinoflagellate population, sexual and asexual cysts are morphologically very similar in this species. Therefore, we studied the complete life cycle and the nature of the cyst-like stages formed after individual isolation of specimens and crossing of clonal cultures established from germination of wild resting cysts. Asexual division in A. peruvianum takes place either in the motile stage by sharing of the theca (desmoschisis), or inside a vegetative cyst (temporary cyst), from which two, or at times four or six naked daughter cells can originate. The daughter cells completely synthesize new cell walls (eleutheroschisis). Sexuality was confirmed by the presence of fusing gamete pairs and longitudinally biflagellated planozygotes after out-crossing of compatible clonal strains. However, the clonal cultures had low levels of self-compatibility, since a flow cytometry analysis showed that synchronized self-crosses produced few zygotes (<5%). After isolation of individual cells, it was proved that the fate of the planozygotes depended on the nutritional status of the isolation media. Most of the planozygotes isolated to replete medium (L1) divided, whereas in medium lacking nitrates (L-N) or phosphates (L-P) they formed temporary, thin-walled cysts. Temporary cysts formed in L1 were always uninucleated and gave rise to one cell, while those formed in L-N or L-P produced 1–6 small cells. In addition, resting cysts were formed in culture, but never after individual planozygote isolation. Resting cysts were uninucleated and needed maturation time before entering dormancy. The resting cysts were considered sexual products, since longitudinally biflagellate germlings were liberated after germination in all cases studied. Mature resting cysts (52.3 ± 3.0 μm) had a dormancy period of 1–3 months, whereas temporary asexual cysts (32.5 ± 5.4 μm) germinated in less than 7 days.     

Different life cycle strategies of the dinoflagellates Fragilidium duplocampanaeforme and its prey Dinophysis acuminata may explain their different susceptibilities to the infection by the parasite Parvilucifera infectans

Some marine dinoflagellates form ecdysal cyst (=temporary cysts) as part of their life cycle or under unfavorable growth conditions. Whether the dinoflagellates form ecdysal cysts or not may influence susceptibility to parasitism. In this study, parasite prevalence relative to inoculum size of the parasitoid Parvilucifera infectans zoospores for two dinoflagellate hosts (i.e., Fragilidium duplocampanaeforme and Dinophysis acuminata), which have different life cycle strategies, was examined. Further, susceptibility of cysts to parasitism, encystment signal, duration of encystments, and effects of induced encystment on diel periodicity, using ecdysal cyst-forming F. duplocampanaeforme were explored. The percent hosts infected by P. infectans plotted as a function of inoculum size showed a sharp increase to a maximum in D. acuminata, but a gradual linear rise in F. duplocampanaeforme: while the parasite prevalence in D. acuminata increased to a maximum of 78.8 (±2.4%) by a zoospore:host ratio of 20:1, it in F. duplocampanaeforme only reached 8.9 (±0.3%), even at a zoospore:host ratio of 120:1. In F. duplocampanaeforme, infections were observed only in the vegetative cells and not observed in ecdysal cysts. When exposed to live, frozen, and sonicated zoospores and zoospore filtrate, F. duplocampanaeforme formed ecdysal cysts only when exposed to live zoospores, suggesting that temporary cyst formation in the dinoflagellate resulted from direct contact with zoospores. When the Parvilucifera zoospores attacked and struggled to penetrate F. duplocampanaeforme through its flagellar pore, the Fragilidium cell shed all thecal plates, forming a ‘thecal cloud layer’, in which the zoospores were caught and immobilized and thus could not penetrate anymore. The duration (35 ± 1.8 h) of ecdysal cysts induced with addition of zoospores was significantly longer than that (15 ± 0.8 h) of normally formed cysts (i.e., without addition of zoospores), thereby resulting in delayed growth as well as influencing the pattern of diel periodicity. The results from this study suggest that in addition to the classical predator-prey interaction and allelopathic interaction, parasitism and its accompanying defense can make the food web dynamics much more complicated than previously thought.     

PHAGOTROPHIC FEEDING AND ITS IMPORTANCE TO THE LIFE CYCLE OF THE HOLOZOIC DINOFLAGELLATE,GYMNODINIUM FUNGIFORME1

The holozoic dinoflagellate, Gymnodinium fungiforme Anissimova, has been observed in both asexually and sexually reproducing cultures. Asexual reproduction is characterized by zoosporangium formation and subsequent new cell release. Sexuality is gametic, and planozygotes and hypnozygotes are present. The life cycle is highly dependent on feeding, and in food-depleted cultures the swimming cells rapidly disappear. These are replaced with resistant long-term resting cysts. Despite its small size (8.5–19 μm), G. fungiforme can feed on prey as large as the ciliated protozoan, Condylostoma magnum Spiegel (600–1000 μm in length), or small injured metazoans, and has been cultured phagotrophically with the chlorophyte, Dunaliella salina Teodoresco as a food source. Eleven additional species of algae including 1 chlorophyte, 7 chrysophytes and 3 rhodophytes, however, were not suitable as food sources. Feeding is characterized by the formation of ‘dynamic aggregations’ of hundreds of dinoflagellates that attach to the surface of a prey organism by a peduncle. G. fungiforme ingests the cytoplasm or body fluids of its prey and a feeding aggregation can ingest a C. magnum in 20–30 minutes.     

The Cysts of Blastocrithidia triatomae Cerisola et al., 19711

ABSTRACT. Flagellar cysts of Blastocrithidia triatomae form from active flagellates by diminution in size. The pellicular microtubules disappear. The inner layer of the cell membrane thickens progressively as the organism shrinks. The fully formed cyst has an electrondense layer that corresponds to the outer layer of the unit membrane. An electron-lucent layer is approximately twice the thickness of the middle layer of the unit membrane. Inside that is a 92 nm layer that may represent the cytoplasm. The nuclear content is in the form of whorled bundles of 10–15 nm fibrils. The kinetoplast was not seen in electron micrographs of cysts.     

Electron Microscopic Observations of the Bloodstream Form of Cryptobia salmositica Katz, 1951 (Kinetoplastida: Bodonina)1

The ultrastructure of the bloodstream form of Cryptobia salmositica in rainbow trout was examined during the acute phase of experimental infection. The arrangement of the major groupings of cytoplasmic microtubules originating near the basal bodies is similar to that in other bodonids. The cytostome is reinforced both by pellicular microtubules and an electron-dense plaque. Certain microtubules associated with the flagellar pocket serve as nucleating sites for pellicular microtubules. A flagellar rootlet, consisting of two parallel fibers which are bound together intermittently by electron-dense plaques, curves posteriorly from the basal body of the recurrent flagellum towards the kinetoplast. The basal body associated plaque on the kinetoplast membranes is duplicated at the same time as the basal bodies. Cytoplasmic microtubules are found in association with the plaque and the outer kinetoplastic membrane. A pulsatile vacuole, described for the first time in a hemoparasitic cryptobiid, lies adjacent to the post-flagellar pit. Smaller, interconnected vesicles of the spongiome are continuous with the pulsatile vacuole. Since a pulsatile vacuole occurs not only in free-living and ectoparasitic cryptobiids but in the hemoparasitic (=trypanoplasm) forms as well, this is no longer a character by which the genus Trypanoplasma may be separated from the genus Cryptobia. Possession of this osmoregulatory complex may allow the organism to survive outside of a host and fulfill a monoxenous life cycle, in addition to the usual heteroxenous cycle involving a leech as vector.     

Aspects of the population dynamics of Neosarmatium meinerti at Mgazana, a warm temperate mangrove swamp in the East Cape, South Africa, investigated using an indirect method

Encysted embryos (cysts) of the brine shrimp, Artemia provide an excellent model system for the study of biochemical adaptation to environmental extremes. Here, we describe an experiment in which cysts of A. franciscana from the San Francisco Bay (SFB), California, U.S.A., were inoculated into experimental ponds in the Mekong Delta region of Vietnam where water temperatures are much higher than the SFB. Cysts produced in each of three successive growing seasons (1996–1998) were collected and examined in the laboratory for resistance to high temperature and relative contents of three stress proteins (Hsp-70, artemin and p26). Thermal adaptation took place rapidly, during the first growing season. The increase in thermal tolerance was reflected in an overall increase in stress protein content, compared to SFB cysts used for the initial inoculation. Also examined were cysts of A. tibetiana collected from a lake on the high plateau of Tibet, PR China, almost 4.5 km above sea level. These cysts were very sensitive to high temperatures, and contained much lower levels of all stress proteins examined, compared to A. franciscana cysts from SFB and Vietnam. Cysts of A. sinica, collected from a hypersaline lake in Inner Mongolia, PR China, were examined in the same fashion and found to be similar to SFB cysts in terms of thermal resistance and stress protein content. The harsh environments in which Artemia are found, and the great diversity of its habitats, world-wide, provide excellent opportunities to relate the ecological setting of an organism to the underlying physiological and biochemical processes enabling its survival.