PHOTOSYNTHESIS OF THE RED ALGA GASTROCLONIUM COULTERI (RHODOPHYTA) IN RESPONSE TO CHANGES IN TEMPERATURE,LIGHT INTENSITY,AND DESICCATION1

Previously reported transplantation experiments in the field showed that Gastroclonium coulteri (Harvey) Kylin could survive above its normal intertidal range (0.0–0.5 m above MLLW), except during periods of daytime low tides in spring. Net photosynthetic rate measurements in the laboratory were performed to determine which physical factors might determine the upper boundary for this species in the intertidal zone. Maximum net photosynthesis occurred between 15 and 20° C, but remained positive between 4 and 35° C. The air temperature extremes observed in the field were 2° C (only seen once) and 26° C. Net photosynthesis increased as expected with light intensity to the highest value obtainable in the laboratory, 1400 μEin m^?2 s^?1. Plants collected from the field under higher light intensity (up to 2000 μEin m^?2 s^?2) also showed high rates of photosynthesis. Neither the temperature nor light levels observed in the field were directly damaging to photosynthesis. Desiccation, however, resulted in a sharp decrease in both photosynthesis and respiration. G. coulteri fully recovered from successive daily treatments of about 35% desiccation, but not from successive treatments of 50% desiccation. One exposure to 70% desiccation allowed no recovery of photosynthetic capacity.     

TAXONOMIC SIGNIFICANCE OF NUCLEUS-MICROBODY ASSOCIATIONS,SEGREGATED NUCLEOLI AND OTHER NUCLEAR FEATURES IN SIPHONOUS GREEN ALGAE1

On the basis of fine-structural features of nuclei the “true” siphonous green algae (Eusiphoniidae) are divided into three groups. In the Codium group nuclei are generally similar to those in most other algae. The Penicillus group is characterized by the association of microbodies with nuclei. In the Avrainvillea group nucleoli are segregated into a granular and a fibrillar component. This condition, known as macrosegregation, persists throughout the vegetative phase of the life history and may indicate a peculiar ribosomal RNA cycle. The Penicillus group corresponds to the order Caulerpales Feldmann. Avrainvillea and Cladocephalus probably constitute a new order. Blastophysa, although having a type of segregated nucleoli, is probably more closely related to Siphonocladales than to any order in Eusiphoniidae.     

Temporal and altitudinal variations in the attached algae of mountain streams in Colorado

Attached algae were examined from eight sites in Central Colorado streams (five sites on St. Vrain Creek and three on the Snake River) between June and November, 1995. The sites ranged in elevation from 1600 m to 3500 m a.s.l.(plains zone to alpine zone). Seasonal variation in algal communities were qualified in forms of species composition and abundance (cell counts and biovolumes). The Ochiai coefficient of similarity was used to estimate degree of similarity between communities at different times, on different streams, and at different locations on the same stream. The composition of communities across streams for alpine and foothills zones was very close, but montane communities differed greatly across streams (similarity < 0.1). Temporal variability of attached algae was almost absent in the alpine zone, but was high in other zones. The composition of the alpine community in August developed downstream with a temporal shift: October in the montane and foothills zones, November in the plains zone. This revised version was published online in July 2006 with corrections to the Cover Date.     

RESPONSE OF ANABAENA FLOS-AQUAE (CYANOPHYTA) NITROGENASE ACTIVITY TO SUDDEN PHOSPHATE DEPRIVATION1

Cultures of Anabaena flos-aquae (Lyng.) Breb. Were used to determine changes in nitrogenase activity (acetylene reduction) after external concentrations of phosphorus were lowered. Two days following immersion in phosphorus-free medium, nitrogenase activity (NA) had doubled and required 8 days to return to time zero levels. Subsequent long-term experiments showed that concentrations of soluble reactive phosphorus (SRP) released from the algae transferred into the –P medium reached maximum levels by day 3 and returned to initial low values by days 7–10. NA was always highest during this SRP release-reassimilation phase but steadily decreased after reassimilation was complete. Day 56 NA was 5–14% of initial activity. The data support the hypothesis that heterocyst and vegetative cell ATP pools are discrete and suggest that the short-term effects of phosphorus removal as an aquatic restoration technique need further study.     

Growth and Grazing Rates of the Heterotrophic Dinoflagellate Polykrikos kofoidii on Red-Tide and Toxic Dinoflagellates

We investigated growth rates, grazing rates, and prey selection of Polykrikos kofoidii when feeding on several species of red-tide and/or toxic dinoflagellates. Polykrikos kofoidii ingested all prey species used in this study, exhibiting positive growth on Lingulodinium polyedrum, Scrippsiella trochoidea, Ceratium furca, Gymnodinium catenatum, Gyrodinium impudicum, Prorocentrum micans, and the toxic dinoflagellate Amphidinium carterae, but not on P. minimum. Specific growth rates of P. kofoidii increased rapidly with increasing density of L. polyedrum, S. trochoidea, C. furca, and G. catenatum before saturating between 500-2,000 ng C ml(-1). Specific growth rates increased continuously when P. kofoidii was fed the other prey species. Maximum specific growth rates of P. kofoidii on G. catenatum (1.12 d(-1)), S. trochoidea (0.97 d(-1)), and L. polyedrum (0.83 d(-1)) were higher than those on C. furca (0.35 d(-1)), A. carterae (0.10 d(-1)), P. micans (0.06 d(-1)), G. impudicum (0.06 d(-1)), and P. minimum (-0.03 d(-1)). Threshold prey concentrations (where net growth = 0) were 54-288 ng C ml(-1). Maximum ingestion and clearance rates of P. kofoidii on these dinoflagellates were 5-24 ng C pseudocolony(-1) d(-1) and 1.0-5.9 microl pseudocolony(-1) h(-1), respectively. Polykrikos kofoidii strongly selected L. polyedrum over S. trochoidea in prey mixtures. Polykrikos kofoidii exhibited higher maximum growth, ingestion, and clearance rates than previously reported for the mixotrophic dinoflagellate Fragilidium cf. mexicanum or the heterotrophic dinoflagellates Protoperidinium cf. divergens and P. crassipes, when grown on the same prey species. Grazing coefficients calculated by combining field data on abundances of Polykrikos spp. and co-occurring red-tide dinoflagellate prey with laboratory data on ingestion rates obtained in the present study suggest that Polykrikos spp. sometimes have a considerable grazing impact on prey populations.     

FURTHER EVIDENCE FOR ANOMALOUS SIZE SCALING OF RESPIRATION IN PHYTOPLANKTON1

Respiration per unit mass decreases as organism size increases among metazoans and heterotrophic unicells. The rate of decrease is described by a power function of organism mass; the exponent of the power function is 0.75 (Three-fourths Rule). Previously unanalyzed respiration rates for 11 species of phytoplankton ranging in size over four orders of magnitude show a size-scaling exponent of 1.13 (SE, ±0.15), which is statistically different from 0.75. This result confirms the result of an earlier study of eight phytoplankton species indicating that size scaling of respiration is absent or minimal in phytoplankton, in contrast to the pattern of heterotrophic unicells. The size-related range of respiration rates per unit mass across the full size spectrum of phytoplankton would be approximately 18–fold if respiration were scaled according to the Three-fourths Rule. If respiration does not scale with size or scales minimally with size, as suggested by present evidence, the size-related range of rates will be much smaller or negligible. The apparent anomaly of size scaling for phytoplankton respiration is potentially of great ecological and adaptive significance in unicellular algae.     

ESTABLISHMENT,PERSISTENCE AND DOMINANCE OF CORALLINA (RHODOPHYTA) IN ALGAL TURF1

The dominance of Corallina thalli in an intertidal algal assemblage was examined by a series of algal removal experiments to test the hypothesis that other tam are competitively excluded from rock substrate. An alternate explanation, that environmental factors seasonally filter out taxa leaving Corallina as the only alga adapted for year to year survival, was considered. Development of vegetation on patches of naturally exposed bare rock was monitored and compared with manipulated surfaces. Thalli of several species were selectively removed from exposed surfaces and intact turf;. changes in tam occupying primary substrate were recorded over more than three years. No significant differences in mean percent cover for Corallina, Lithothrix, bare rock, or algal crusts were found among treatments. Except for initial growth of colonizing species, abundances of other species dad not increase in the absence of Corallina. Large amounts of rock remained bare or intermittently covered by transient populations of short-lived algae. Data from single quad-rats, where individual clumps of Lithothrix were followed from month to month, indicated that the continued presence of this co-occurring and often abundant species depended on turnover of short-lived thalli rather than persistence of the same clumps. No interactions were found among the several categories of species that appeared after rock substrate was cleared. Most species were the same ones that grew, epiphytically in intact turf at the same time. In control quadrats Corallina maintained 59-95% cover while slowly increasing on surfaces earlier exposed. I predict that Corallina species will regain their dominance in the absence of competitors for primary substrate if the slowly spreading basal crusts remain undisturbed. Morphological and life history characteristics are identified that adapt Corallina to its dominant role in this habitat.     

BIOMINERALIZATION OF THE STALKS OF ANTHOPHYSA VEGETANS (CHRYSOPHYCEAE)1

Mineralized stalks of the chryophyte Anthophysa ve-getans (O. F. Müller) Stein were examined by electron microscopy, and the composition of the stalks was determined by energy dispersive x-ray microanalysis. Colonies grown in water from a local lake (Dowdy Lake) had mineralized stalks that were colorless and composed mainly of spherules of calcium phosphate up to 0.7 μm in diameter. The addition of 0.1 mM MnCl₂ to the culture medium resulted in deeply orange-brown stalks mineralized primarily with minute granules of a manganese compound. The addition of 0.1 mM FeCl₃ to the culture media resulted in light yellow stalks mineralized mainly with small granules of an iron compound. The addition of 0.1 mM MgCl₂ or KCl resulted in stalks that were similar in appearance and composition to the colonies grown in culture medium alone. These results show that the composition of the mineralized stalks of A. vegetans is dependent on the elements present in the culture medium. This is also the first time that calcium phosphate has been reported as a mineralization product in the chrysophytes.