GROWTH AND NITROGEN FIXATION OF THE DIAZOTROPHIC FILAMENTOUS NONHETEROCYSTOUS CYANOBACTERIUM TRICHODESMIUM SP. IMS 101 IN DEFINED MEDIA: EVIDENCE FOR A CIRCADIAN RHYTHM1

Trichodesmium sp. IMS 101, originally isolated from coastal western Atlantic waters by Prufert-Bebout and colleagues and maintained in seawater-based media, was successfully cultivated in two artificial media. Its characteristics of growth, nitrogen fixation, and regulation of nitrogen fixation were compared to those of natural populations and Trichodesmium sp. NIBB 1067. Results indicate that the culture grown in artificial media had nitrogen fixation characteristics similar to those when the culture is grown in seawater-based medium and to those of Trichodesmium sp. in the natural habitat. The study provides practical artificial media to facilitate the physiological studies of these important diazotrophic cyanobacteria, as well as the cultivation of other Trichodesmium species in future studies. Manipulations of the light/dark cycle were performed to determine whether or not the daily cycle of nitrogen fixation is a circadian rhythm. Cultures grown under continuous light maintained the cycle for up to 6 days. We demonstrated that the daily cycle of nitrogen fixation in Trichodesmium sp. IMS 101 was at least partially under the control of a circardian rhythm.     

AMPHIDINIUM CRYOPHILUM SP. NOV. (DINOPHYCEAE) A NEW FRESHWATER DINOFLAGELLATE. II. ULTRASTRUCTURE1

The dinoflagellate Amphidinium cryophilum sp. nov. is one of the few gymnodinians to be studied at the ultrastructural level. It resembles other dinoflagellates in the structure of the nucleus, trichocysts, storage materials, flagella, mitochondria, and microbodies. Other features of A. cryophilum less commonly observed in related organisms include a network of small interconnected vesicles, a system of large, peripheral vacuoles, chloroplasts bound by two rather than three membranes, an accumulation body, thylakoid-associated plastoglobuli, a vesiculated nuclear envelope, a complex tubular pusule, striated flagellar collars, collared pits, and a peduncle. The occurrence of a peduncle, a structure implicated in phagotrophy, in this autotrophic organism is noteworthy. The ultrastructure of the peduncle of A. cryophilum differs significantly from that reported in another dinoflagellate.     

KINETICS OF CELL DEATH IN THE CYANOBACTERIUM ANABAENA FLOS-AQUAE AND THE PRODUCTION OF DISSOLVED ORGANIC CARBON1

Kinetics of cell death and the production of dissolved organic carbon (DOC) were investigated in Anabaena flos-aquae (Lyngb.) Bréb grown on three different N sources (N₂nitrate, and ammonium) in a phosphorus (P)-limited chemostat. The fraction of live cells in the total population increased as growth rate increased with decreasing P limitation. Cell death was less in nitrate and ammonium media than in N₂. The specific death rate (γ), when calculated as the slope ofv^?1_x vs. D^?1, where v_xand D are live cell fraction (or cell viability) and dilution rate, respectively, was 0. 0082 day^?1 in N₂and 0.0042 day^?1 in nitrate. The slope of the plot in ammonium culture was not significant; however, the value of the live cell fraction was within the range for the NO^?₃culture. The fraction of live vegetative cells in N₂ culture was constant at all growth rates and the increase in the overall live cell fraction with growth rate was due entirely to an increase in live heterocysts. Live heterocysts comprised 3.5% of the total cells at a growth rate of 0.25 day^?1 and increased to 6.3% at 0.75 day^?1 with the ratio of live heterocysts to live vegetative cells linearly increasing with growth rate. The fraction of live vegetative cells was invariant in nitrate cultures us in N₂cultures. The live heterocysts fraction also increased with growth rate in nitrate cultures, along with the live heterocysts : live vegetative cells ratio, but the level was lower than in N₂cultures. DOC released from dead cells increased inversely with growth rate in N₂from 36.4% of the total DOC at a growth rate of 0.75 day^?1 to 54.15% at 0.25 day^?1. The contribution of cell death to the total DOC production in nitrate and ammonium media was significantly less than that under N₂DOC from dead cells consisted mainly of high-molecular-weight compounds, whereas DOC excreted from live cells was largely of low molecular weight.     

UPTAKE,EFFLUX, AND PHOTOSYNTHETIC UTILIZATION OF INORGANIC CARBON BY THE MARINE EUSTIGMATOPHYTE NANNOCHLOROPSIS SP.1

Uptake, efflux and utilization of inorganic carbon were investigated in the marine eustigmatophyte Nannochloropsis sp. grown under an air level of CO₂. Maximal photosynthetic rate was hardly affected by raising the pH porn 5.0 to 9.0. The apparent photosynthetic affinity for dissolved inorganic carbon (DIC) was 35 μM DIC between pH 6.5 to 9.0, but increased approximately threefold at pH 5.0 suggesting that HCO₃- was the main DIC species used from the medium. No external carbonic anhydrase (CA) activity could be detected by the pH drift method. However, application of ethoxyzolamide (an inhibitor of CA) resulted an a significant inhibition of photosynthetic O₂ evolution and carbon utilization, suggesting involvement of internal CA or CA-like activity in DIC utilization. Under high light conditions, the rate of HCO₃^? uptake and its internal conversion to CO₂ apparently exceeded the rate of carbon fixation, resulting in a large leak of CO₂ from the cells to the external medium. When the cells were exposed to low DIC concentrations, the ratio of internal to external DIC concentration was about eight. On the other hand, in the presence of 2 mM DIC, conditions prevailing in the marine environment, the internal concentration of DIC was only 50% higher than the external one.     

OCCURRENCE OF PHYIWATED CHLOROPHYLL c IN ISOCHRYSIS GALBANA AND ISOCHRYSIS SP. (CLONE T-ISO) (PRYMNESIOPHYCEAE)1

The pigment composition of two clones of Isochrysis galbana Parke (CCMP 1323 and CCAP 927/1), and Isochrysis sp. (clone T-ISO) was analyzed by high-performance liquid chromatography using a polymeric octadecylsilica column. Fluorescent peaks with retention times higher than chlorophyll a were detected for all three clones. The corresponding pigments were isolated and characterized in terms of their visible absorbance and fluorescence spectra. The pigments were similar to phytol-substituted chlorophyll c, previously isolated from Emiliania huxleyi (Lohm.) Hay and Mohler and other species containing chlmophyll c₃. The presence of phytol-substituted chlorophyll c in I. galbana which lacked chlorophyll c₃, increases the diversity of chlorophyll patterns for the Haptophyta, which can be grouped, at present, into six different pigment types. This is the jrst observation of a haptophyte containing the apolar phytylated chlorophyll c-like pigment but lacking chlorophyll c₃.     

EFFECTS OF ULTRAVIOLET RADIATION ON PHOTOSYNTHESIS IN THE SUBTROPICAL MARINE DIATOM,CHAETOCEROS GRACILIS (BACILLARIOPHYCEAE)1

Acclimation to ambient ultraviolet radiation (UVR) was examined in a subtropical marine diatom, Chaetoceros gracilis Schutt. Short-term exposure to UVR (<24 h) reduced the efficiency of photosynthetic energy conversion, carbon fixation, activity of 1,5-bisphosphate carboxylase-loxygenase (RUBISCO), and the rapid turnover of the putative Dl reaction center (32 kda) protein, whereas longer-term exposure to ambient UVR (24–48 h) revealed a steady-state acclimation, defined as recovery of carbon fixation and RUBISCO activity to rates equivalent to treatments without exposure to UVR. The turnover of D1 and chlorophyll a (Chl a) remained high during exposure to UVR. Efficiency of energy conversion by photosystem II, measured with double flash (pump and probe) fluorometry, increased by 24% in cells acclimated to UVR. Acclimation to UVR had no detectable effect on the functional absorption cross-section or cellular concentrations of Chl a, Chl c, or total carotenoids. However, the maximum rate of carbon fixation was reduced by UVR on a Chl a basis but remained unaffected on a per-cell basis. Response to UVR exposure in this subtropical diatom has two components: a short-term inhibitory response and a longer-term acclimation process that ameliorates the inhibition of carbon fixation.     

LATITUDINAL TRENDS IN THE GROWTH AND REPRODUCTIVE SEASONALITY OF DELESSERIA SANGUINEA,MEMBRANOPTERA ALATA,AND PHYCODRYS RUBENS (RHODOPHYTA)1

The seasonality of Delesseria sanguinea, Membranoptera alata, and Phycodrys rubens (Rhodophyta) was studied at Helgoland (North Sea, Germany) and Roscoff (Brittany, France). Plants were collected at bimonthly intervals, and growth and reproduction were monitored. Growth of blades was observed mainly in spring, although small blades were found on plants of M. alata and P. rubens all year round. In summer, plants started to degenerate and in autumn they became fertile. The reproductive season of D. sanguinea lasted from October to February/April at both locations, whereas reproductive plants of M. alata and P. rubens were found until April at Helgoland and until June and August, respectively, in Roscoff_: Lower winter temperatures at Helgoland than at Rascoff may have caused these differences in the duration of the reproductive season. Using published data, the seasonal patterns at Helgoland and Roscoff were compared to those found at other locations (e.g. Barents Sea; Maine, USA; Isle of Man, UK) and local temperature/daylength conditions. Blade growth was synchronized across all populations and occurred in spring, when temperatures were usually still suboptimal for growth. Maximum reproduction was generally found in the colder half of the year but started earlier in autumn in the Barents Sea. Adaptive strategies in the seasonal control of growth and reproduction are discussed. Adequate timing of the history events (e.g. appearance of juveniles in spring) appears more important than maximal growth and reproduction of adults during the season with the most favorable temperatures.     

REGULATION OF A GLUCOSE TRANSPORT SYSTEM IN STICHOCOCCUS BACILLARIS1

Glucose and related non-metabolizable analogs were transported into cells of Stichococcus bacillaris Naeg. By a specific and active transport system. Glucose transport capacity was stimulated eight-fold by incubation in medium of low osmotic potential (0.09 osM). Stimulation occurred over 24 h in the dark and over 72 h in low osmotic medium. Inhibition of protein synthesis prevented any transport, stimulation from occurring. Kinetic studies revealed that the stimulation caused an increase in Ike maximal velocity of transport and did not affect the half-saturation constant for transport. It was concluded that incubation of cells in the dark or in low osmolar medium induces a synthesis of the transport system. The glucose analog 2-deoxy-D-glucose was only phosphorylated to a limited extent upon entry into the cells, and the free sugar accumulated linearly in dark pre-incubated tells for a period of at least six minutes to reach an intracellular/extracellular concentration ratio of almost 300. Glucose, in contrast, was rapid h converted to sucrose and other cell constituents. Cells incubated 24 h with, glucose or 6-deoxy-D-glucose did not exhibit any altered transport system activity. Cells incubated 24 h with 7 mM dibutyryl cAMP exhibited a 2.5-fold stimulation of transport activity. No stimulation was observed in cells treated only 30 min with dibutyryl cAMP.     

INFECTIOUS DISEASES OF MAZZAELLA LAMINARIOIDES (RHODOPHYTA): CHANGES IN INFECTION PREVALENCE AND DISEASE EXPRESSION ASSOCIATED WITH SEASON,LOCALITY, AND WITHIN-SITE LOCATION1

This study addresses the issues of infection prevalence and disease expression in two wild populations of the red algal host Mazzaella laminarioides and their variability associated with locality, season, and spatial location of the host in the intertidal zone. Our results demonstrated that Endophyton ramosum is the most frequent infective pathogen affecting M. laminarioides in Matanzas and Pucatrihue. This situation prevailed through the year and across the high-to-low intertidal gradient. Although there was a general trend for lower levels of infection in late winter and early spring, only in a few, cases was well-defined seasonality detected. Furthermore, clear seasonal patterns, as displayed by deformative disease in the high intertidal zone of Pucatrihue, were attenuated in the middle and lower intertidal zones. Differences in levels of infection in M. laminarioides between the high intertidal zones of Matanzas and Pucatrihue diminished toward the low intertidal zone. Thus, effects of seasonality and locality on infection prevalence may be influenced, at least in part, by the position of the hosts an the intertidal zone. Spatial distribution of the diseased individuals also varied along the beach. This pattern was consistent between the two sites and seemed related to wave exposure and the specific pathogen. Comparisons of the size distribution of noninfected fronds with their infected counterparts showed that infections by Endophyton ramosum and Pleurocapsa sp. more frequently affected medium-and large-sized fronds. This pattern was consistent temporally and similar in the two localities. Finally, a clear association between maturity and prevalence of infection was detected. This association resulted in most fronds of the noninfected segment of the host population being immature, whereas most mature fronds were infected. In conclusion, infectious diseases affecting the red alga Mazzaella laminarioides are a persistent phenomenon in wild populations of the host, although only a small segment of the infected populations displays the full expression of the disease. In spite of the suggested role of factors such as season, latitude, and spatial location of the host on disease prevalence and expression, additional studies are needed to understand fully the dynamics of infectious diseases in wild populations of algal hosts.     

SEASONAL PATTERNS OF PHOTOSYNTHESIS AND LIGHT-INDEPENDENT CARBON FIXATION IN MARINE MACROPHYTES1

The contribution of light-independent carbon fixation (LICF) to the overall carbon gain and the seasonal patterns of maximum photosynthesis (P_max and LICF were characterized in a broad taxonomic range of macrophytes from Monterey Bay, California. P_max and LICF rates (nmol C.g filtered seawater^?1.min^?1) varied among species and taxonomic groups examined, and as a function of tissue type in the phaeophyte Laminaria setchellii Silva (Phaeophyceae). On average, P_max values were higher in the Rhodophyta, whereas LICF rates were greater in the Phaeophyceae. LICF rates were generally less than 5% of P_max in the marine macrophytes studied and, as a consequence, cannot fully compensate for respiratory carbon losses, which usually are greater than 10% of P_max. All species studied possessed the highest P_max and LICF rates when irradiance levels were highest and decreased during periods of low incident irradiance. Seasonal patterns of P_max and LICF in most of the macrophytes from the stenothermal environment of Monterey Bay were strongly correlated with photosynthetic photon flux rather than seawater temperature. The concomitant decrease of LICF and P_max rates in all species examined argues against LICF playing a major role in carbon acquisition under light-limiting conditions as suggested previously. Rather, the strong positive correlation of P_max and LICF indicates the direct coupling of photosynthate (e.g. 3-phosphoglyceric acid) generation with production of substrates for LICF reactions. Our results also suggest that LICF might be a useful indicator of photosynthetic metabolism in marine macrophytes.     

EFFECTS OF PHOTON FLUENCE RATE AND LIGHT SPECTRUM COMPOSITION ON GROWTH,PHOTOSYNTHESIS AND PIGMENT RELATIONS IN GRACILARIA SP.1

The optimal photon fluence rate for growth of tha llus tips of Gracilaria sp. was low (about 100 μE·^–2·¹); higher photon fluence rates inhibited growth. Both phycoerythrin (PE) and chlorophyll (chl) contents decreased with increasing photon fluence rates (up to 100 μE·–m^–2s^–1) in a fashion inverse to the growth response. Chl/PE ratios varied directly as the growth response over a larger photon fluence rate range. The peak chl/PE ratios were obtained at a photon fluence rate optimal for growth, suggesting that this parameter may be used to estimate in situ growth rates. A low compensation point (about 7 μE·^–2s^–1) was observed for low light (15 μE·^–2s^–1) grown plants. This compensation point was also obtained for growth in the long–term (5–6 weeks) experiments. Plants grown at 60 and 140 μE·^–2s^–1 showed higher light compensation and saturation points, suggesting that the variations in pigment composition found between the different treatments determine the photosynthetic responses at sub–optimal photon fluence rates. Photosynthetic rates at light saturation were the same, on a biomass basis, for plants grown at the various photon fluence rates. Thus, the photosynthetic dark reactions were not influenced by previous light regimes. It is suggested that maximal photosynthetic rates expressed on a biomass basis better reflect the potential productivity at tight saturation than if expressed on a pigment basis. Gracilaria sp. grew better under non–filtered fluorescent and greenish than under reddish and blue–enriched light of equal and sub–optimal photon, fluence rate. However, the pigment relations of the algae did not change in a direction complementary to the light composition at which they grew. This, together with the relatively higher photosynthetic rates under reddish and blueish light for plants previously grown under reddish and blueish light, suggests that adaptations to variouslight spectra are based on mechanisms different from complementary chromatic adaptation of the pigments.     

INTERACTIONS AMONG PHOSPHATE UPTAKE,PHOTOSYNTHESIS, AND CHLOROPHYLL FLUORESCENCE IN NUTRIENT‐LIMITED CULTURES OF THE CHLOROPHYTE MICROALGA DUNALIELLA TERTIOLECTA1

Phosphate‐limited and phosphate‐sufficient continuous cultures of the marine chlorophyte microalga Dunaliella tertiolecta Butcher were examined for their responses to the addition of phosphate. Phosphate‐limited cultures showed a marked quenching of chl fluorescence following a pulse of phosphate. This response was absent from cells growing under phosphate‐sufficient conditions. Both the extent of fluorescence quenching (where present) and the initial rate of change in quenching were dependent on the concentration of phosphate added to cell suspensions and on the degree of limitation (growth rate in continuous culture). The addition of phosphate also brought about a transient decrease in photosynthetic oxygen evolution and a stimulation in respiration, which were relaxed as the added phosphate was depleted from the external medium. The applicability of using nutrient‐induced fluorescence transients as a tool to identify the nutrient status of phytoplankton populations is discussed.     

PHOTOAUTOTROPHIC GROWTH OF A RECENTLY ISOLATED N2-FIXING MARINE NON-HETEROCYSTOUS FILAMENTOUS CYANOBACTERIUM, SYMPLOCA SP. (CYANOBACTERIA)

Photoautotrophic growth of a marine non-heterocystous filamentous cyanobacterium, Symploca sp. strain S84, was examined under nitrate-assimilating and N₂-fixing conditions. Under continuous light, photon flux density of 55 μmol photons·m⁻² ·s⁻¹ was at a saturating level for growth, and light did not inhibit the growth rate under N₂-fixing conditions even when the photon flux density was doubled (110 μmol photons·m⁻² ·s⁻¹). Doubling times of the N₂-fixing cultures under 55 and 110 μmol photons·m⁻² ·s⁻¹ were about 30 and 31 h, respectively. Under 110 μmol photons·m⁻² ·s⁻¹ during the light phase of an alternating 12:12-h light:dark (L:D) cycle, the doubling time of the N₂-fixing culture was also about 30 h. When grown diazotrophically under a 12:12-h L:D regime, C₂H₂ reduction activity was observed mainly during darkness. In continuous light, relatively large cyclic fluctuations in C₂H₂ reduction were observed during growth. The short-term (<4 h) effect of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU; 5 μM) indicated that C₂H₂ reduction activity was not influenced by photosynthetic O₂ evolution. Long-term (24 h) effects of DCMU indicated that photosynthesis and C₂H₂ reduction activity occur simultaneously. These results indicate that strain S84 grows well under diazotrophic conditions when saturating light is supplied either continuously or under a 12:12-h L:D diel light regime.     

EXCYSTMENT AND GROWTH OF CHRYSOPHYTES AND DINOFLAGELLATES AT LOW TEMPERATURES AND HIGH SALINITIES IN ANTARCTIC SEA-ICE1

Extreme environmental conditions have been thought to limit algal growth in the upper sea-ice. In McMurdo Sound, Antarctica, chrysophyte statocysts (stomatocysts) and dinoflagellate hypnozygotes (resting cysts) overwinter in first- and second-year land-fast sea-ice exposed to temperatures of -20° C or lower. In early November, when temperatures in the upper ice are < ?8°C and brine salinities are >126 psu, dinoflagellate cysts activate and shortly thereafter excyst. During early November, chrysophyte statocysts also begin to excyst. Net daily primary production occurs in the sea-ice brine at temperatures as low as ?7.1° C, at brine salinities as high as 129 psu, and at average photon flux densities as low as 5 μmol photons.m^?2.s^?1. Dinoflagellate densities were >10⁶ vegetative cells.L^?1 of ice while temperatures in the upper ice were between ?6.8 and ?5.8° C and brine salinities were ～100 psu. Chrysophyte densities reached >10⁶.L^?1 of ice by early December. High densities of physiologically active clyo- and halotolerant algae can occur in the upper land-fast sea-ice under extreme conditions of temperature and salinity.     

THE EFFECT OF GROWTH TEMPERATURE AND CULTURE DENSITY ON THE MOLECULAR SPECIES COMPOSITION OF THE GALACTOLIPIDS IN THE RED MICROALGA PORPHYHDIUM CRUENTUM (RHODOPHYTA)1

The effects of biomass concentration and growth temperature on the molecular species composition of the major galactolipids of the red microalga Porphyridium cruentum Nag. were detmined. At lower biomass concentrations, the Δ17 desaturation of arachidonic acid to eicosapentaenoic acid (20:5) was enhanced in both prokaryotic-type and eukalyotic-type molecular species of monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol. We suggest that chloroplastic Δ17 desaturation is correlated with the availability of light. A reduction in the growth temperature led to an increase in the proportion of the eukalyotic molecular species of MGDG, especially for 20:5/ 20:5 MGDG, These results suggest that this molecular species, and perhaps eukaryotic molecular species in general, may play a role in the adaptation of cells to low growth temperatures.     

THE KINETICS OF THE PHOTOACCLIMATION RESPONSE OF NANNOCHLOROPSIS SP. (EUSTIGMATOPHYCEAE): A STUDY OF CHANGES IN ULTRASTRUCTURE AND PSU DENSITY

In this study we report the kinetics of photoacclimation of the unicellular alga Nannochloropsis sp. grown under high light (HL), and subsequently transferred to low light (LL). We examined the changes in ultrastructural features, pigmentation, and photosynthetic parameters over short intervals until the LL steady state was reached. The ultrastructural changes were followed by quantitative morphometric measurements of transmission electron micrographs. We found that the increase in the relative volume of the chloroplast during acclimation to LL (twofold) was accompanied by an increase in number of stacks (twofold) and in the surface area of thylakoids per cell (2.5-fold). The increase in photosynthetic unit (PSU) density was about 2.15-fold. Maximal density was about 84 PSU·μm⁻² in LL cells, and minimal density was 39 PSU·μm⁻² in HL cells. The HL/LL ratio of the in vivo optical absorption cross-section of PSU (σ_PSU) was 2.8, whereas in the in vivo optical absorption cross-section of the cell (σ_cell), the trend of change was in the opposite direction: 1.7-fold higher in LL-acclimated cells than in HL-acclimated cells. We propose a partial sequence of the photoacclimation processes based on our data and the derived rate constants.     

IDENTIFICATION OF CYLINDROSPERMOPSIN IN APHANIZOMENON OVALISPORUM (CYANOPHYCEAE) ISOLATED FROM LAKE KINNERET,ISRAEL1

Aphanizomenon ovalisporum (Forti) was identified and isolated from Lake Kinneret upon its first appearance as a dominant bloom in late 1994. This cyanobacterial species, not previously known to be toxic, was evaluated by a commonly used mouse bioassay and was demonstrated to induce toxic symptoms that were distinguishable from the typical symptoms of the neurotoxins previously reported in Aphanizomenon flos-aquae (L.) Ralfs. Mice died 5–24 h after crude extracts were injected intraperitoneally, and the LD₅₀ value was estimated as 465 mg dry wt biomass · kg^?1 mouse. A toxicity-guided fractionation of the active extract indicated that the potent substance is polar an nature. The structure of the active compound was determined by its mass spectrometry and NMR data. The compound was found to be the sulfate-guanidinium zwitterion, cylindrospermopsin, previously isolated from the cyanobacterium Cylindrospermopsis raciborskii (Woloszynska) and recently also reported in Umezakia natans (Watanabe). This is the first time that Aphanizomenon ovalisporum has been reported to contain a toxic compound.     

A CONTINUOUS CULTURE STUDY OF PHOSPHATE UPTAKE,GROWTH RATE AND POLYPHOSPHATE IN SCENEDESMUS SP.1

The kinetics of phosphate uptake and growth in Scenedesmus sp. have been studied in continuous culture with particular reference to the shifts in the cellular P compounds as a function of growth rate. Uptake velocity is a function of both internal and external substrate concentrations and can be described by the kinetics of noncompetitive enzyme inhibition. The concentrations of polyphosphates (alkali-extractable or 7-min) can he substituted as inhibitors in the kinetic equation. The apparent half-saturation constant of uptake. K_m, is 0.6 μM. The apparent half-saturation concentration for growth is less than K_m, by 1 order of magnitude. Growth is a function of cellular P concentrations, and the polyphosphates (alkali-extractable or 7-min) appear to regulate growth rate directly or indirectly. To understand P limitation, therefore, it is necessary to measure both external P and internal polyphosphate levels. Evidence indicates that alkali-extractable polyphosphates, which can be quantitatively determined by a simple method of measuring surplus P, are involved in cell division process find that a maintenance concentration of functional phosphate exists in the form of poly phosphates. Alkaline phosphatase activity has an inversely linear relationship to growth rate and to the reciprocals of both polyphosphates and surplus P. Changes in lipid P, RNA P, and presumably all other forms except DNA are related to changes in growth rate.     

POPULATION GENETICS AND TAXONOMY OF CAULERPA (CHLOROPHYTA) FROM THE GREAT BARRIER REEF,AUSTRALIA1

Allozyme variation was examined in seven species and four varieties of Caulerpa sampled from the Great Barrier Reef (GBR) region, Australia. Differences between species were greater than those between populations of the same taxon sampled from different geographical locations, and typically included fixed gene differences (no alleles found in one taxon shared by the other taxon) at two or more loci. Three varieties of C. racemosa, vars imbricata, laetevirens, and racemosa, and a peltate morph of C. racemosa were as strongly distinguished genetically as the six other species examined: C. cupressoides, C. lentillifera, C. peltata, C. serrulata, C. sertularioides, and C. taxifolia. Cluster analysis did not place all of the C. racemosa varieties together and linked them with other species, but cladistic analyses showed the allozyme data gave little useful phylogenetic information. Eight of 13 plants identified initially as C. serrulata were distinguished at several loci, indicating the presence of an undetermined cryptic taxon. Population genetic analysis of polymorphism, which occurred in some taxa, demonstrated strong spatial differentiation among populations of C. cupressoides, C. racemosa vars laetevirens and racemosa, C. serrulata, and C. taxifolia and significant but variable degrees of clonality and/or inbreeding within these populations. Allozymes proved to be a useful tool for defining species boundaries and investigating population structure in Caulerpa, but not for determining phylogenetic relationships within the genus.