Showing papers by "Patricia A. Tester published in 2002"

Life cycle of the heterotrophic dinoflagellate pfiesteria piscicida (dinophyceae)1

Abstract: The putatively toxic dinoflagellate Pfiesteria piscicida (Steidinger et Burkholder) has been reported to have an unusual life cycle for a free-living marine dinoflagellate. As many as 24 life cycle stages were originally described for this species. During a recent phylogenetic study in which we used clonal cultures of P. piscicida, we were unable to confirm many reported life cycle stages. To resolve this discrepancy, we undertook a rigorous examination of the life cycle of P. piscicida using nuclear staining techniques combined with traditional light microscopy, high-resolution video microscopy, EM, and in situ hybridization with a suite of fluorescently labeled peptide nucleic acid (PNA) probes. The results showed that P. piscicida had a typical haplontic dinoflagellate life cycle. Asexual division occurred within a division cyst and not by binary fission of motile cells. Sexual reproduction of this homothallic species occurred via the fusion of isogamous gametes. Examination of tanks where P. piscicida was actively feeding on fish showed that amoebae were present; however, they were contaminants introduced with the fish. Whole cell probing using in situ hybridization techniques confirmed that these amoebae were hybridization negative for a P. piscicida-specific PNA probe. Direct observations of clonal P. piscicida cultures revealed no unusual life cycle stages. Furthermore, the results of this study provided no evidence for transformations to amoebae. We therefore conclude that P. piscicida has a life cycle typical of free-living marine dinoflagellates and lacks any amoeboid or other specious stages.

Seasonal niche strategy of the bloom-forming dinoflagellate Heterocapsa triquetra

Abstract: Heterocapsa triquetra is one of the most common bloom-forming dinoflagellates found in estuaries and near shore regions around the world. This work examined the environmental factors associated with 3 separate wintertime H. triquetra blooms in the shallow tidally mixed Newport River estuary, North Carolina, USA. During 2 of the blooms in 1982 and 1983, the estuary was sampled from a fixed, single location every hour for 14 d. During the third study, the estuary was sampled at 9 fixed locations over its entire length each week from late December 1997 through March 1998. This time period included the formation and decline of the H. triquetra bloom. Barometric pressure, precipitation, photosynthetically active radiation, salinity, temperature, nutrient concentrations, and chl a were mea- sured in each study. During the 1997-1998 study, pigments were analyzed using HPLC to characterize the phytoplankton assemblages and the dominant dinoflagellates in each sample were counted. The prevailing environmental conditions associated with the wintertime blooms were largely the result of atmospheric forcing. Low pressure systems moved through the study area at 3 to 4 d intervals and were accompanied by low ambient air temperatures and regular rainfall. Runoff following the rainfall events supplied inorganic nutrients critical for bloom initiation and development. It also created a mesohaline frontal zone in the middle portion of the estuary with salinity and hydrodynamic conditions favorable for H. triquetra growth. Here, the H. triquetra bloom reached its maximal development with chl a levels >100 µg l -1 and cell densities between 1 and 6 × 10 6 l -1 . As the H. triquetra bloom developed, nutrient in- puts from the river became insufficient to meet growth demand and H. triquetra began feeding mixo- trophically, supplementing its nutritional requirements and reducing competition from co-occurring dinoflagellates. Cloud cover associated with the low pressure systems transiently limited H. triquetra growth as did low temperatures. More importantly though, low temperatures limited micro- and macro- zooplankton populations to such an extent that grazing losses were minimal. Hence, in order to bloom, H. triquetra optimizes a suite of factors including low grazing pressure, increased nutrient inputs, alternative nutrient sources, and favorable salinity and hydrodynamic conditions, as well as the nega- tive factors of temperature-limited growth, short day lengths, and periods of transient light limitation.

Effect of diel and interday variations in light on the cell division pattern and in situ growth rates of the bloom-forming dinoflagellate Heterocapsa triquetra

Abstract: Heterocapsa triquetra is an important bloom-forming dinoflagellate found in estuaries and nearshore regions worldwide. In an initial time-intensive study, the shallow, tidally mixed Newport River estuary, North Carolina, USA, was sampled from a fixed point located in the middle of the estuary every 2 h for 2 wk during the development of an H. triquetra bloom. The objective of this study was to investigate how short-term, high-frequency changes in temperature, light and salinity affected diel and interday cell division patterns and in situ growth rates of H. triquetra. During this study, phytoplankton samples were preserved in buffered formaldehyde and mitotic indices determined by acridine orange staining. The diel division pattern showed a nocturnal maximum between 23:00 and 05:00 h with reduced division during the day, a pattern characteristic of most dinoflagellates. The relative proportion of binucleate cells present during the day was influenced by interday variations in total irradiance, increasing during 2 of the 3 periods when there were 3 or more consecutive high light days (>28 E m -2 d -1 ). Approximately 40 % of the overall variation in interday division rates could be accounted for by differences in daily irradiance. The interday light differences were largely due to well-developed atmospheric frontal systems that brought increased cloud cover to the study area at regular 3 to 4 d intervals. The initial study, however, was of insufficient length to determine if the transient day-to-day light limitation could significantly affect seasonal bloom formation. A second longer-term, spatially intensive study was therefore undertaken to assess the relative importance of the incident light levels and nutrient inputs in controlling H. triquetra bloom initiation. During the second study, the estuary was monitored for photosynthetically active radiation (PAR), salinity, temperature, inorganic nutrients and cell densities of H. triquetra at 9 locations every wk from 23 December 1997 to 27 March 1998. Maximal H. triquetra bloom formation occurred during a 2 wk period when daily incident light levels were at or near the annual low. This suggested that H. triquetra is well adapted for utilizing low light levels and that variation in in situ growth rates in response to daily changes in PAR had little effect on bloom development. Instead, bloom initiation began with inputs of nitrogen-rich water following a runoff event, indicating that nutrient inputs are much more important in controlling bloom development than is light.

Skin problems related to noninfectious coastal microorganisms

Abstract: While there are a number of coastal microorganisms that can cause infections of the skin, there are many that can cause skin problems that are noninfectious in nature. From cyanobacterial dermatitis to skin problems related to dinoflagellates, to skin signs of ciguatera or scombroid fish poisonings, to “sea lice”/“seabather's eruption,” to “swimmer's itch,” this article attempts to separate these entities into distinct syndromes caused by a variety of bacteria, phytoplankton and zooplankton. Treatment and prevention of these diseases are also discussed.

Reply to comment on the life cycle and toxicity of pfiesteria piscicida revisited1

Abstract: Free-living, marine dinoflagellates are typified by a well-defined, haplontic life cycle with relatively few stages. The most unusual departure from this life cycle is one reported for the heterotrophic dinoflagellate Pfiesteria piscicida Steidinger et Burkholder. This species is alleged to have at least 24 life cycle stages including amoebae and a chrysophyte-like cyst form (Burkholder et al. 1992, Burkholder and Glasgow 1997a) not previously known in free-living marine dinoflagellates. Litaker et al. (2002) redescribed the life cycle of P. piscicida from single-cell isolates and found only life cycle stages typical of free-living marine dinoflagellates. The discrepancy between these observations and the life cycle reported in the literature prompted a rigorous study to resolve the life cycle of P. piscicida.Burkholder and Glasgow (2002) took exception to this study, arguing that Litaker et al. (2002) misunderstood the life cycle of P. piscicida and ignored recent publications. We present a rebuttal of their criticisms and suggest a simple way to resolve the discrepancies in the P. piscicida life cycle.