Temperate Diatom Research Articles

Growth, photosynthesis and carbon metabolism in the temperate marine diatom Skeletonema costatum adapted to low temperature and low photon-flux density

The temperate diatom Skeletonema costatum (Grev.) Cleve was grown in low temperature and/or low light conditions. The cultures were acclimatized for at least three months before experiments were begun. Our data indicate that the initial slope of the photosynthesis vs irradiance curve (α) is controlled predominantly by light history and the light-saturated photosynthesis (Pmax) by temperature. The number of divisions per day decreased with decreasing light intensity, but was identical for cultures grown at 3° or 18°C. The metabolic pathways of inorganic carbon fixation were not fundamentally affected by low temperature or low light intensity, but both these factors increased labelling of C3 compounds, synthesized by the Calvin-Benson cycle, and decreased that of phosphoenolpyruvate (PEP) and other metabolites. This indicates an enhancement of ribulose-1,5-bisphosphate (RuBP) carboxylase activity, which is the first step in the C3 pathway (3-phosphoglycerate and sugar phosphate synthesis); this may optimize cell functions. At low temperatures, a seven-fold increase in RuBP carboxylase activity per cell was observed. S. costatum is able to adapt to low irradiance by increasing α and decreasing Ik (the ratio of Pmax:α, light intensity at onset of light saturation), and to low temperature by increasing its cellular chlorophyll a and RuBP carboxylase content. However, in the latter case, adaptation is not optimal. This study revealed two main features: (1) there is evidence that RuBP carboxylase has a key function in adjustment to high rates of photosynthesis at suboptimal temperatures or irradiances; (2) adaptive mechanisms are dynamic processes and the role of the time scale in physiological adaptation should be considered.

Observations of the island mass effect in the Prince Edward archipelago

The distribution of diatoms around the sub-Antarctic Prince Edward Island archipelago, as affected by the island mass effect is examined. Collections were made by continuous flow filtration of surface waters interrupted arbitrarily to give individual integrated samples. These were analyzed and the number of each species per cubic meter determined. Chlorophyll a was measured spectrophotometrically. Potential Primary Productivity was measured by the carbon-14 method. The major inorganic nutrients were analyzed by on-board use of an autoanalyzer. In May 1987 a massive bloom of Chaetoceros radicans was encountered in the island waters. The distribution was found to be closely correlated with high Chl a and potential primary productivity values. Of the major inorganic nutrients analyzed silicate was found to be inversely correlated with phytoplankton standing stock. Nitrate and phosphate showed a complex patchiness which was, however, obviously correlated directly with the phytoplankton bloom. The nitrate/phosphate ratio is shown to be variable with time and this may be attributed to the high phosphate content of the island leachate or differential phosphate depletion at time of bloom. A situation is described where, in 1983, the temperate diatom C. radicans and the Antarctic silicoflagellate Dictyocha speculum occurred in bloom stage in adjacent, separate communities. This suggests that separate watermasses of different origin were present at the time.

OCCURRENCE OF AN ISOPRENOID C25 DIUNASATURATED ALKENE AND HIGH NEUTRAL LIPID CONTENT IN ANTRACTIC SEA‐ICE DIATOM COMMUNITIES1

ABSTRACTThe lipid and hydrocarbon composition of natural populations of diatom communities collected during the austral spring bloom of 1985 in the sea‐ice at McMurdo Sound, Antartica was analyzed by TLC‐FID, GC and GC‐MS. Sea‐ice diatom communities were dominated by Amphiprora sp., Nitzschia stellata Manguin and Berkeleya sp. at Cape Armitage; N. stellata, Amphiprora, Pleurosigma, N. kerguelensis (O'Meara) Hasle and some small centric diatoms adjacent to the Erebus Ice Tongue; and Porosira pseudodenticulata (Hustedt) Jouse at Wohlschlag Bay. Lipid distributions of the sea ice diatom communities from the Cape Armitage and Ereus sites were characterized by high concentrations of tracylaglecycerol (triacylglycerolplar lipid = 1.0 to 1.5). The hydrocarbon n‐C21:6, common in temperate diatoms, and an isoprenoid C25 diunsaturated alkene were the dominant hydrocarons detected at these two sites. Hydrogenation of the C25 diene produced the known alkane 2, 6, 10, 14‐tetramethyl‐7‐ (3‐methylpentyl)‐pentadecane. The C25 diene is one of several structurally related hydrocarbons reported in many estuarine, coastal and ocean ic sediments. We propose that certain species of diatoms are a likely source of these alkenes in sediments. The first reported biological occurrence of the C25 diene in the green seaweed Enteromorpha prolifera may have been due to the presence of epiphytic microalgae in the field sample analysed.

Primary Production Potential of Blue-Green Algal Mats on Southern Texas Tidal Flats

Blue-green algal mat biomass, productivity, and nitrogen fixation were determined for two southern Texas tidal flats, and environmental factors affecting productivity rates were assessed. Algal biomass over three seasons ranged from 0.50 to 1.53 g chl a · m-2. The rate of carbon fixation (by '4C technique) ranged from 0.6 g C'm-2 day-' (in fall) to 2.4 g C'm- 2day-' (in spring) on days when flats were flooded. The rate of N2 fixation on the same days varied from 0.09 to 0.5 kg N-ha-'day-'. On days when mats were severely desiccated (mat water 25% but < 60%) were capable of fixing gaseous CO2 in air. Exposure to sunlight equivalent to one-fourth full sunlight (ca. 500 uE'm-2s-') sustained maximum photosynthetic activity. Tidal flats consist of broad, relatively level shorelines of bays, estuaries, or lagoons that are periodically inundated by high tides and storm surges. In the Laguna Madre of southern Texas, this habitat typically comprises the entire leeward barrier island intertidal zone and covers hundreds of km2 (Fig. 1). While an arid, windy climate, high summer temperatures, and subsequent hypersalinity prevent establishment of estuarine salt marsh (Simmons, 1957; Copeland, 1966; Hoese, 1967), these flats are often covered with a 2-4 mm thick blue-green algal mat. Quantitative productivity data for such subtropical Texas mats are unreported. Existing studies of benthic microalgae production have dealt mostly with temperate mudflat diatom communities (Pomeroy, 1959; Pamatmat, 1968; Riznyk et al., 1978) or salt marsh systems containing sparse blue-green mats (Gallagher and Daiber, 1974; Van Raalte et al., 1976). Sage and Sullivan (1978) found very few blue-green mats in a Mississippi salt marsh, and they concluded that mat distribution in eastern Gulf Coast marshes was limited by shading from salt marsh vascular plants. Wanders (1976), as part of a study on tropical coral reefs, found high primary productivity for epilithic blue-green algae, but only over limited areas. Recent work on blue-green mats from southern California marshes (Zedler, 1980) revealed that these subtropical flats had much higher productivity than temperate flats; and blue-green production was equal to the highest values recorded for some mudflat diatoms (Riznyk et al., 1978). Dawes et al. (1978) concluded that intertidal green and red macroalgae were adapted to periodic tidal exposure and were more productive when exposed to air than when continuously submerged. Dawes (1981) emphasized the need for additional studies of production potential of intertidal algae and evaluation of the concept that such algae are under stress due to exposure per se. During the present study, primary

Multivariate statistical analysis of net diatom species distributions in the Southwestern Atlantic and Indian Ocean

Vertical net haul diatom assemblages from near South Georgia, and from between Africa and Antarctica, were examined and compared. Variation among South Georgia stations was examined by principal component, cluster and canonical discriminant analyses. Diatom distributions provide evidence for at least two distinct water masses. The region north of the island is characterized by neritic, temperate diatoms and by an assemblage with low species diversity. The region south of the island is characterized by oceanic, antarctic species and relatively high species diversity. The regions are most distinct to the west of the island, intergrading east of the island. Within the north-south division, five station groupings were detected on the basis of distribution of dominant net diatoms. By comparing classical species ecological categorizations to results of principal component analysis, a “neritic-oceanic” factor was identified from net diatom distributions. This factor was common to both areas in spite of the fact that Biscoe and Agulhas collections were from different seasons.

The effect of Po river discharge on phytoplankton dynamics in the Northern Adriatic Sea

An oceanographic transet,, extending from Yugoslavia across the Northern Adriatic Sea to the Po delta in Italy, was occupied during 1972 and 1973 to establish the effect of Po river discharge on the phytoplankton communities of the region. Density distribution showed distinct seasonal features: a winter-spring period of low stability throughout the water column, and a summer period of stratification. The total water-column plant nutrients (nitrate, nitrite, phosphate, silicate) showed a 1.3 to 4.5-fold decrease eastward, with semi-eutrophic conditions restricted to an area off the Po delta. Nannoplankton usually dominated the phytoplankton community, in terms of cell density, surface chlorophyll a concentrations, and surface primary production rates. However, all significant maxima in these characteristics resulted from increases in the microplankton component. Changes in the frequency of major microplankton groups characterized three periods of the annual cycle: September–December, neritic, temperate diatom flora with some littoral elements (e.g. Nitzschia seriata); January–May, neritic, temperate diatom flora of different composition (e.g. Lauderia borealis, Skeletonema costatum); May–August, dinoflagellates (e.g. Prorocentrum micans) at western stations and dinoflagellates plus neritic, warm-water diatoms at eastern stations. The seasonal cycle was characterized by spring and fall maxima tending to coincide with maximum Po river discharge and/or periods of low water-column stability and vertical mixing. The higher nutrient input at western stations was correlated with the co-dominance of only a few species of microplankton during bloom periods, suggesting that these species (S. costatum, N. seriata, and 5 others) can serve as indicators of eutrophic conditions in this region. Assimilation ratios of both the micro- and nannoplankton suggested borderline nutrient conditions. Phosphate was implicated as the limiting nutrient.

DIATOMS FROM NEASHAM LATE‐GLACIAL DEPOSITS

In the remainder of this note the samples will be referred to by the arabic numerals given to them above. An appreciable number of diatoms was found in sample no. i, and they were present in large numbers in sample no. 2. There were none in samples nos. 3 and 4 and very few in samples nos. 5 and 6. Table 4 sets out the species found in the samples and gives information on the present geographical and ecological distribution of each, where available. This is presented in the same way as in the account of the Aller0d age diatom deposit from Bodmin Moor, Cornwall (appendix to Conolly, Godwin & Megaw, 1950), in which will be found references to the definitions of the terms used and the sources of information. In classifying the species into geographical groups I have also consulted a recent paper by Hustedt (1948) and, because of his opinions, I have here classified Fragilaria leptostauron (Ehrenb.) Hust. as a temperate arctic, instead of a temperate diatom. In Table 4 those species which are present in a gathering in sufficient numbers to be classed as frequent, or as more abundant than that, are designated by f., and those found less often by +. The abbreviations used in this table are: