VARIATIONS IN GROWTH,EROSION, PRODUCTIVITY,AND MORPHOLOGY OF ECKLONIA RADIATA (ALARIACEAE; LAMINARIALES) ALONG A FJORD IN SOUTHERN NEW ZEALAND1

Spatial and temporal patterns of growth, erosion, productivity, and morphology of the dominant habitat‐forming kelp Ecklonia radiata (C. Agardh) J. Agardh were studied bimonthly over 1.5 years in a southern New Zealand fjord characterized by strong gradients in light and wave exposure. Spatial differences in growth were observed with rates at two outer coast, high‐light, wave‐exposed sites reaching 0.42 and 0.45 cm · d^?1, respectively, compared to 0.27 cm · d^?1 at an inner, more homogeneous site. Sporophyte productivity was similar among sites, although population productivity was greater at the outer sites due to population density being 5‐fold greater than at the inner site. It was expected that the inner site would have no pronounced seasonal pattern in growth and productivity due to its homogeneity; however, all three sites displayed maximum rates in late winter/spring and minimal in autumn. Growth rates were 2‐fold greater during the first growth period than the following year. This discrepancy was not correlated to inorganic nitrogen (N) levels, which remained low year‐round (<4 μM), and is likely a result of an interaction between light and temperature, and the photosynthetic capability of E. radiata. Variable pigment content indicated photoacclimation at the inner site. Morphological differences were observed between sites, with E. radiata from the inner site having longer, wider, thinner blades and longer stipes. While E. radiata displayed spatial differences in growth, erosion, productivity, and morphology, populations displayed no temporal differences. These results highlight the need for greater understanding of the mechanisms influencing kelp growth and productivity in a unique marine environment.     

Seasonal growth,erosion rates,and nitrogen and photosynthetic ecophysiology of Undaria pinnatifida (Heterokontophyta) in southern New Zealand1

The goal of this study was to examine growth, erosion rates, and the photosynthetic and nitrogen ecophysiology of the invasive seaweed Undaria pinnatifida (Harv.) Suringar. Sporophytes of U. pinnatifida that appeared in Otago Harbour, southeastern New Zealand, in late autumn (May) 1996 were tagged, and their growth rates followed until the onset of senescence in early summer (November 1996). Blade growth rates were maximal between May and August when they ranged from 0.77 ± 0.05 to 0.93 ± 0.05 cm · d^?1 and declined from September onward. In laboratory experiments, U. pinnatifida took up nitrate and ammonium simultaneously at rates ranging from 21.3 ± 2.1 to 179.3 ± 65.1 μmol · g^?1 dry weight (dwt) · h^?1. When monthly patterns of growth rate, seawater inorganic nitrogen, nitrogen uptake kinetics, soluble tissue nitrate, % tissue carbon (C) and nitrogen (N), and C:N ratio were considered together, there was no evidence that N limited the growth of U. pinnatifida. Furthermore, the photosynthetic parameters P_max, α, E_k, E_c, and R_d derived from P versus E curves indicated that the growth of U. pinnatifida was not light limited, and that the population could potentially grow deeper than its observed location at 4 m depth. Nitrogen and light ecophysiological parameters of U. pinnatifida more closely resemble those of small, ephemeral seaweeds, such as Ulva, than other members of the Laminariales. We suggest that a “plastic” physiology may allow U. pinnatifida sporophytes to match their physiology to a range of environments, which is one reason for its success as an invasive seaweed.     

Plant and frond dynamics of the giant kelp,Macrocystis pyrifera,forming a fringing zone in the Falkland Islands

Fluctuations in plant and frond characteristics are described for Macrocystis pyrifera (L.) C. Agardh (Laminariales, Phaeophyta) forming a fringing zone in the Falkland Islands. Giant kelp plants were sampled along a transect in the austral autumn (May 1986) and late spring (December 1986) which, according to previous frond weight analysis, were the times when extremes in population parameters were expected. Plant density and holdfast wet weights were similar for both seasons, but plants had more fronds and the fronds weighed more in spring than in autumn. Consequently, in autumn the frond biomass (1·1 wet kg m^?2) and productivity (34·1 wet g m^?2 d^?1) were lower than in spring, when a biomass of 5·0 wet kg m^?2 and a productivity of 72·4 wet g m^?2 d^?1 were recorded. Production of new fronds and loss of old fronds were determined at monthly intervals between April 1986 and March 1987. New frond production rates followed fluctuations in the quantity of light and varied between 0·08 and 0·48 fronds per plant per day. Frond loss rates did not show a seasonal pattern and fluctuated between 0·05 and 0·42 fronds per plant per day. It is suggested that the Falkland Islands Macrocystis population is more stable than most other giant kelp beds at high latitudes, because of the absence of winter storms.     

CARBON ALLOCATION IN MACROCYSTIS PYRIFERA (PHAEOPHYTA): INTRINSIC VARIABILITY IN PHOTOSYNTHESIS AND RESPIRATION1

Measurements of net photosynthesis (PS, O₂ evolution), dark respiration (R, O₂ consumption), and light and dark carbon fixation (¹⁴C) were conducted on whole blades, isolated blade discs, sporophylls, apical scimitars and representative portions of stipe and holdfast of the giant kelp Macrocystis pyrifera L.C. Ag. On a dry weight basis, highest net PS rates were observed in apical scimitar segments and whole blades (3.81 and 3.07 mgC · g dry wt^?1· h^?1, respectively), followed by sporophylls (1.42 mgC·g dry wt^?1· h^?1) and stipe segments (0.15 mgC·g dry wt^?1· h^?1). No PS capacity was observed in holdfast material. Respiration rates showed similar ranking ranging from 1.22 mgC·g dry wt^?1·h^?1 for apical scimitar to 0.18–0.22 mgC·g dry wt^?1· h^?1 for holdfast material. Considerable within blade variability in both PS and R was also found. Steepest PS and R gradients on both an areal and weight basis were found within immature blades followed by senescent and mature blade material. Highest net PS rates were associated with the blade tips ranging from 3.08 (mature blades) to 10.3 mgC·dry wt^?1·h^?1 (immature blades). Highest rates of R generally occurred towards the basal portions of blades and ranged from 1.03–1.80 mgC·g dry wt^?1·h^?1 for immature blades. The variability within and between blades was high, with coefficients of variation approaching 50%. The observed patterns can be related to the decreasing proportionment of photosynthetic tissue and increasing proportionment of structural tissue as occurs from the blade tip to the blade base. Rates of light carbon fixation (LCF) revealed longitudinal profiles similar to oxygen measurements for the different blade types, with the absolute rates being slightly lower. Patterns of dark carbon fixation (DCF) were less easily interpreted. Highest rates of DCF (0.04–0.06 mgC·g dry wt^?1·h^?1) occurred at the basal portions of immature and senescent blades. Longitudinal profiles of total chlorophyll (a + c) on both an areal and weight basis were very similar to the profiles of PS. Normalized to chlorophyll a, PS displayed an unusual longitudinal profile in immature tissue; however, such profiles for mature and senescent tissues were similar to those for PS on an areal basis. It was demonstrated that it is difficult, if not impossible, to select single tissue discs that are representative of whole blades. The metabolic longitudinal profiles reveal a characteristic developmental pattern; the previous working definitions of immature, mature, and senescent blades, based on morphology and frond position thus have a physiological basis.     

Nutrient uptake and alkaline phosphatase (ec 3:1:3:1) activity of emiliania huxleyi (PRYMNESIOPHYCEAE) during growth under n and p limitation in continuous cultures

Emiliania huxleyi (strain L) expressed an exceptional P assimilation capability. Under P limitation, the minimum cell P content was 2.6 fmol P·cell^?1, and cell N remained constant at all growth rates at 100 fmol N·cell^?1. Both, calcification of cells and the induction of the phosphate uptake system were inversely correlated with growth rate. The highest (cellular P based) maximum phosphate uptake rate (V_max^P) was 1400 times (i.e. 8.9 h^?1) higher than the actual uptake rate. The affinity of the P‐uptake system (dV/dS) was 19.8 L·μmol^?1·h^?1 at μ = 0.14 d^?1. This is the highest value ever reported for a phytoplankton species. V_max and dV/dS for phosphate uptake were 48% and 15% lower in the dark than in the light at the lowest growth rates. The half‐saturation constant for growth was 1.1 nM. The coefficient for luxury phosphate uptake (Q_maxt/Q_min) was 31. Under P limitation, E. huxleyi expressed two different types of alkaline phosphatase (APase) enzyme kinetics. One type was synthesized constitutively and possessed a V_max and half‐saturation constant of 43 fmol MFP·cell^?1·h^?1 and 1.9 μM, respectively. The other, inducible type of APase expressed its highest activity at the lowest growth rates, with a V_max and half‐saturation constant of 190 fmol MFP·cell^?1·h^?1 and 12.2 μM, respectively. Both APase systems were located in a lipid membrane close to the cell wall. Under N‐limiting growth conditions, the minimum N quotum was 43 fmol N·cell^?1. The highest value for the cell N‐specific maximum nitrate uptake rate (V_max^N) was 0.075 h^?1; for the affinity of nitrate uptake, 0.37 L·μmol^?1·h^?1. The uptake rate of nitrate in the dark was 70% lower than in the light. N‐limited cells were smaller than P‐limited cells and contained 50% less organic and inorganic carbon. In comparison with other algae, E. huxleyi is a poor competitor for nitrate under N limitation. As a consequence of its high affinity for inorganic phosphate, and the presence of two different types of APase in terms of kinetics, E. huxleyi is expected to perform well in P‐controlled ecosystems.     

Growth and shoot:root partitioning of spinach plants as affected by nitrogen supply

Spinach plants (Spinacia oleracea L.) were grown hydroponically in fixed environmental conditions either at full nitrate availability (11·8mol m^-3) or at a suboptimum relative nitrate addition rate of 0·20d^-1, 0·15d^-1 or 0·10d^-1 respectively, the other nutrients being adequately provided. The relative growth rate (RGR) of the plants varied significantly with the nutrition treatment and decreased during development in all treatments. The concentration of reduced nitrogen in the plants grown at full nitrate availability did not change significantly during the experimental growth period and nitrate accumulation was substantial. After an adaptation period, the concentration of reduced nitrogen in the plants at the suboptimum nitrate addition rates increased during growth and was lowest at the lowest relative nitrate addition rate. Nitrate uptake was almost complete in the suboptimum treatments and nitrate accumulation was negligible as long as the concentration of reduced nitrogen was below 2·0 mmol (g dry weight)^-1. The RGR of all plants was proportional to the concentration of reduced nitrogen in the plant minus a minimal tissue concentration required for growth. However, the proportionality factor was inversely related to the plant mass. This relationship was summarized in an empirical model which explained 98·7% of the variance of the dry weight (log scale) data of all treatments at all harvests. The model was compared with other growth models found in the literature. The shoot/root weight ratio increased from 2 to 4 if nitrate provision was not limiting, and initially, this ratio decreased at suboptimum nitrate provision but increased at higher growth stages. Possible explanations of the dynamics of dry matter partitioning are discussed in relation to models.     

PHYSIOLOGICAL RESPONSES OF ANABAENA VARIABILIS (CYANOPHYCEAE) TO INSTANTANEOUS EXPOSURE TO VARIOUS COMBINATIONS OF LIGHT INTENSITY AND TEMPERATURE1

Light intensity and temperature interactions have a complex effect on the physiological process rates of the filamentous bluegreen alga Anabaena variabilis Kütz. The optimum temperature for photosynthesis increased with increasing light intensity from 10°C at 42 μE·m^?2·s^?1 to 35°C at 562 μE·m^?2·s^?1. The light saturation parameter, I_K, increased with increasing temperatures. The maximum photosynthetic rate (2.0 g C·g dry wt.^?1·d^?1) occurred at 35°C and 564 μE·m^?2·s^?1. At 15°C, the maximum rate was 1.25 g C·g dry wt.^?1·d^?1 at 332 μE·m^?2·s^?1. The dark respiration rate increased exponentially with temperature. Under favorable conditions of light intensity and temperature the percent of extracellular release of dissolved organic carbon was less than 5% of the total C fixed. This release increased to nearly 40% under combinations of low light intensity and high temperature. A mathematical model was developed to simulate the interaction of light intensity and temperature on photosynthetic rate. The interactive effects were represented by making the light-saturation parameters a function of temperature.     

PRODUCTION AND NUTRIENT REMOVAL BY PERIPHYTON GROWN UNDER DIFFERENT LOADING RATES OF ANAEROBICALLY DIGESTED FLUSHED DAIRY MANURE1

Growing algae to scrub nutrients from manure presents an alternative to the current practice of land application and provides utilizable algal biomass as an end product. The objective of this study was to assess algal growth, nutrient removal, and nitrification using higher light intensities and manure loading rates than in the previous experiments. Algal turfs, with periphyton mainly composed of green algal species, were grown under two light regimes (270 and 390 μmol photons·m^?2· s^?1) and anaerobically digested flushed dairy manure wastewater (ADFDMW) loading rates ranging from 0.8 to 3.7 g total N and 0.12 to 0.58 g total P·m^?2·d^?1. Filamentous cyanobacteria (Oscillatoria spp.) and diatoms (Navicula, Nitzschia, and Cyclotella sp.) partially replaced the filamentous green algae at relatively high ADFDMW loading rates and more prominently under low incident light. Mean algal production increased with loading rate and irradiance from 7.6±2.71 to 19.1±2.73 g dry weight· m^?2·d^?1. The N and P content of algal biomass generally increased with loading rate and ranged from 2.9%–7.3% and 0.5%–1.3% (by weight), respectively. Carbon content remained relatively constant at all loading rates (42%–47%). The maximum removal rates of N and P per unit algal biomass were 70 and 13 mg·g^?1 dry weight·m^?2·d^?1, respectively. Recovery of nutrients in harvested algal biomass accounted for about 31%–52% for N and 30%–59% for P. Recovery of P appeared to be uncoupled with N at higher loading rates, suggesting that algal potential for accumulation of P may have already been saturated. It appears that higher irradiance level enhancing algal growth was the overriding factor in controlling nitrification in the algal turf scrubber units.     

Effects of wild and farm-grown macroalgae on the growth of juvenile South African abalone Haliotis midae Linnaeus

The effect of various macroalgal diets on the growth of grow-out (>20 mm shell length) South African abalone Haliotis midae was investigated on a commercial abalone farm. The experiment consisted of four treatments: fresh kelp blades (Ecklonia maxima (Osbeck) Papenfuss) (c. 10% protein); farmed, protein-enriched Ulva lactuca Linnaeus (c. 26% protein) grown in aquaculture effluent; wild U. lactuca (c. 20% protein); and a combination diet of kelp blades + farmed U. lactuca. Abalone grew best on the combination diet (0.423 ± 0.02% weight d^?1 SGR [specific growth rate]; 59.593 ± 0.02 ?m d^?1 DISL [daily increment in shell length]; 1.093 final CF [condition factor]) followed by the kelp only diet (0.367 ± 0.02% weight d^?1 SGR; 53.148 ± 0.02 ?m d^?1 DISL; 1.047 final CF), then the farmed, protein-enriched U. lactuca only diet (0.290 ± 0.02% weight d^?1 SGR; 42.988 ± 0.03 um d”¹ DISL; 1.013 final CF) that in turn outperformed the wild U. lactuca only diet (-0.079 ± 0.01% weight d^?1 SGR; 3.745 ± 0.02 ?m d”^?1 DISL; 0.812 final CF). The results suggest that protein alone could not have accounted for the differences produced by the varieties of U. lactuca and that the gross energy content is probably important.     

Root respiration and associated costs in deciduous and evergreen species of Quercus

Root construction and maintenance costs were estimated in four evergreen and three deciduous Quercus species that are typical in the landscape of southern Spain. The cost quantification was based on analysis of the growth–­respiration ratio. Values observed for both construction cost (ranging from 1·17 to 1·29 g glucose g^?1 dry weight) and maintenance cost (ranging from 6·22 to 11·71 mg glucose g^?1 dry weight d^?1) were generally lower than those reported in other studies. The results showed non‐significant differences between deciduous and evergreen species. The lack of significant differences between species appeared to be due to the homogeneity of growth conditions. Hydroponic culture, with unrestricted nutrient and water supply, would lead to low tissue carbon content and low respiration rates, leading to the low costs observed. Furthermore, the fact that root organs are clearly importers of organic molecules inevitably entails some underestimation of the respiration associated with growth and, to a lesser extent, with maintenance respiration. This leads in turn to underestimation of the corresponding construction and maintenance costs. All this raises doubts as to the suitability of this method for studying root systems.     

EXTREMELY HIGH GROWTH RATE OF THE SMALL DIATOM CHAETOCEROS SALSUGINEUM ISOLATED FROM AN ESTUARY IN THE EASTERN SETO INLAND SEA,JAPAN1

Small single‐celled Chaetoceros sp. are often widely distributed, but frequently overlooked. An estuarine diatom with an extremely high growth potential under optimal conditions was isolated from the Shinkawa‐Kasugagawa estuary in the eastern part of the Seto Inland Sea, western Japan. It was identified as Chaetoceros salsugineum based on morphological observations. This strain had a specific growth rate of 0.54 h^?1 at 30°C under 700 μmol · m^?2 · s^?1 (about 30% of natural maximal summer light) with a 14:10 L:D cycle; there was little growth in the dark. However, under continuous light it grew at only 0.35 h^?1 or a daily specific growth rate of 8.4 d^?1. In addition, cell density, chlorophyll a, and particulate organic carbon concentrations increased by about 1000 times in 24 h at 30°C under 700 μmol · m^?2 · s^?1 with a 14:10 L:D cycle, showing a growth rate of close to 7 d^?1. This very rapid growth rate may be the result of adaptation to this estuarine environment with high light and temperature. Thus, C. salsugineum can be an important primary producer in this estuary in summer and also an important organism for further physiological and genetic research.     

The challenge of estimating kelp production in a turbid marine environment

Coastal kelp forests produce substantial marine carbon due to high annual net primary production (NPP) rates, but upscaling of NPP estimates over time and space remains difficult. We investigated the impact of variable underwater photosynthetically active radiation (PAR) and photosynthetic parameters on photosynthetic oxygen production of Laminaria hyperborea, the dominant NE-Atlantic kelp species, throughout summer 2014. Collection depth of kelp had no effect on chlorophyll a content, pointing to a high photoacclimation potential of L. hyperborea towards incident light. However, chlorophyll a and photosynthesis versus irradiance parameters differed significantly along the blade gradient when normalized to fresh mass, potentially introducing large uncertainties in NPP upscaling to whole thalli. Therefore, we recommend a normalization to kelp tissue area, which is stable over the blade gradient. Continuous PAR measurements revealed a highly variable underwater light climate at our study site (Helgoland, North Sea) in summer 2014, reflected by PAR attenuation coefficients (K_d) between 0.28 and 0.87 m⁻¹. Our data highlight the importance of continuous underwater light measurements or representative average values using a weighted K_d to account for large PAR variability in NPP calculations. Strong winds in August increased turbidity, resulting in a negative carbon balance at depths >3–4 m over several weeks, considerably impacting kelp productivity. Estimated daily summer NPP over all four depths was 1.48 ± 0.97 g C · m⁻² seafloor · d⁻¹ for the Helgolandic kelp forest, which is in the range of other kelp forests along European coastlines.     

EFFECT OF LIGHT AND TEMPERATURE INTERACTIONS ON GROWTH OF CRYPTOMONAS EROSA (CRYPTOPHYCEAE)1

Cryptomonas erosa Skuja, a planktonic alga, was grown in batch culture at different combinations of light intensity and temperature, under nutrient saturation. Growth was maximal (1.2 divisions · day^?1) at 23.5 C and 0.043 ly · min^?1, declining sharply with temperature (0.025 divisions-day^?1 at 1 C). With decreasing temperature, the cells showed both light saturation and inhibition at much reduced light intensities. At the same time the compensation light intensity for growth declined towards a minimum of slightly above 0.4 × 10^?4 ly · min^?1 (~1 ft-c) at 1 C or <0.1 ly · day^?1 (PAR). Cell division was more adversely affected by low temperature than carbon uptake, and the resulting excess production of photosynthate was both stored and excreted. Extreme storage of carbohydrates resulted in cell volumes and carbon content ca. 22 and 30 × greater, respectively, than the maxima observed for cells incubated in the dark, whereas, at growth inhibitory light levels, as much as 57% of the total assimilated carbon was excreted. A marked increase in cell pigment was observed at the lowest light levels (<10^?3 ly · min^?1), at high temperature. The growth response of C. erosa in culture provides insight into the abundance and distribution of cryptomonads and other small algal flagellates in nature.     

GROWTH AND CARBON CONTENT OF THREE DIFFERENT‐SIZED DIAZOTROPHIC CYANOBACTERIA OBSERVED IN THE SUBTROPICAL NORTH PACIFIC1

To develop tools for modeling diazotrophic growth in the open ocean, we determined the maximum growth rate and carbon content for three diazotrophic cyanobacteria commonly observed at Station ALOHA (A Long‐term Oligotrophic Habitat Assessment) in the subtropical North Pacific: filamentous nonheterocyst‐forming Trichodesmium and unicellular Groups A and B. Growth‐irradiance responses of Trichodesmium erythraeum Ehrenb. strain IMS101 and Crocosphaera watsonii J. Waterbury strain WH8501 were measured in the laboratory. No significant differences were detected between their fitted parameters (±CI) for maximum growth rate (0.51 ± 0.09 vs. 0.49 ± 0.17 d^?1), half‐light saturation (73 ± 29 vs. 66 ± 37 μmol quanta · m^?2 · s^?1), and photoinhibition (0 and 0.00043 ± 0.00087 [μmol quanta · m^?2 · s^?1]^?1). Maximum growth rates and carbon contents of Trichodesmium and Crocosphaera cultures conformed to published allometric relationships, demonstrating that these relationships apply to oceanic diazotrophic microorganisms. This agreement promoted the use of allometric models to approximate unknown parameters of maximum growth rate (0.77 d^?1) and carbon content (480 fg C · μm^?3) for the uncultivated, unicellular Group A cyanobacteria. The size of Group A was characterized from samples from the North Pacific Ocean using fluorescence‐activated cell sorting and real‐time quantitative PCR techniques. Knowledge of growth and carbon content properties of these organisms facilitates the incorporation of different types of cyanobacteria in modeling efforts aimed at assessing the relative importance of filamentous and unicellular diazotrophs to carbon and nitrogen cycling in the open ocean.     

EFFECTS OF ENVIRONMENTAL VARIATION ON SINKING RATES OF MARINE PHYTOPLANKTON1

The effects of environmental variables, particularly irradiance, on the sinking rates of phytoplankton were investigated using cultures of Chaetoceros gracilis Schütt and C. flexuosum Mangin in laboratory experiments; these data were compared with results from assemblages in the open ocean and marginal ice zone of the Greenland Sea. In culture experiments both the irradiance under which the diatom was grown and culture growth rate were positively correlated with sinking rates. Sinking rates (ψ) in the Greenland Sea were smallest when determined from chlorophyll (mean ψ_chl= 0.14 m · d^?1) and biogenic silica (ψ_si= 0.14 m · d^?1) and greatest when determined from particulate carbon (ψ_c= 0.55 m · d^?1) and nitrogen (ψ_N= 0.64 m · d^?1). Field measurements indicated that variations in sinking may be associated with changes in irradiance and nitrate concentrations. Because these factors do not directly affect water density, they must be inducing physiological changes in the cell which affect buoyancy. Although a direct response to a single environmental variable was not always evident, sinking rates were positively correlated with growth rates in the marginal ice zone, further indicating a connection to physiological processes. Estimats of carbon flux at stations with vertically mixed euphotic zones indicated that approximately 30% of the daily primary production sank from the euphotic zone in the form of small particulates. Calculated carbon flux tended to increase with primary productivity.     

Primary production of the kelp Lessonia corrugata varies with season and water motion: Implications for coastal carbon cycling

Kelp forests provide vital ecosystem services such as carbon storage and cycling, and understanding primary production dynamics regarding seasonal and spatial variations is essential. We conducted surveys at three sites in southeast Tasmania, Australia, that had different levels of water motion, across four seasons to determine seasonal primary production and carbon storage as living biomass for kelp beds of Lessonia corrugata (Order Laminariales). We quantified blade growth, erosion rates, and the variation in population density and estimated both the net biomass accumulation (NBA) per square meter and the carbon standing stock. We observed a significant difference in blade growth and erosion rates between seasons and sites. Spring had the highest growth rate (0.02 g C · blade⁻¹ · d⁻¹) and NBA (1.62 g C · m⁻² · d⁻¹), while summer had the highest blade erosion (0.01 g C · blade⁻¹ · d⁻¹), with a negative NBA (−1.18 g C · m⁻² · d⁻¹). Sites exhibiting lower blade erosion rates demonstrated notably greater NBA than sites with elevated erosion rates. The sites with the highest water motion had the slowest erosion rates. Moreover, the most wave-exposed site had the densest populations, resulting in the highest NBA and a greater standing stock. Our results reveal a strong seasonal and water motion influence on carbon dynamics in L. corrugata populations. This knowledge is important for understanding the dynamics of the carbon cycle in coastal regions.     

BIOCHEMICAL STRATEGIES FOR GROWTH OF GRACILARIA TIKVAHIAE (RHODOPHYTA) IN RELATION TO LIGHT INTENSITY AND NITROGEN AVAILABILITY1

The main effects and interactions between light (I_o, full incident sunlight to 0.07 I_o) and NO₃^? loading (0.4 to 4.3 mmol · g dry weight^?1· d^?1) on growth rate, photosynthesis and biochemical constituents of Gracilaria tikvahiae McLachlan were studied using a factorial design experiment in outdoor, continuous-flow seawater cultures. Incipient nitrogen limitation in the low NO₃^? loading, I_o and 0.57 I_o treatments occurred after 2.5 weeks of growth under the experimental conditions and resulted in decreased tissue NO₃^? and R-phycoerythrin. Tissue NO₃^? and R-phycoerythrin accounted for up to ca. 15 and 20%, respectively, of the total N in G. tikvahiae suggesting a N reserve role for these N pools. Under light and NO₃^? limitation, growth rate was a parabolic function of the C:N ratio. As light limitation increased, growth rate and the C:N ratio decreased as levels of Chl-a, R-phycoerythrin, percent N and percent protein increased. As NO₃^? limitation increased, growth rate and levels of Chl-a, R-phycoerythrin, percent N and percent protein all decreased with parallel increases in the C:N ratio. In contrast to the inverse relationship between pigment content and light, ribulose bisphosphate carboxylase (RuBPCase) activity (on both a protein and dry weight basis) varied directly with light. This biochemical acclimation of G. tikvahiae to light and N availability appears to be a process directed towards maximizing photo synthetic capacity and growth.     

EFFECTS OF VARIATIONS IN LIGHT INTENSITY ON THE EFFICIENCY OF GROWTH OF SKELETONEMA COSTATUM (BACILLARIOPHYCEAE) IN A CYCLOSTAT1

The relative importance of respiration and organic carbon release to the efficiency of carbon specific growth of Skeletonema costatum (Grev.) Clave was evaluated over a light range from 1500–15 μE · m^?2· s^?1. Net growth efficiency ranged from 0.45–0.69 with a maximum at 130 μE · m^?2· s^?1. Respiration was 93% or more of the variations in growth efficiency. Organic carbon release ranged from 0–7% of gross production and increased with light intensity. Carbon specific particulate production was a hyperbolic function of incident light intensity and was related exponentially to particulate carbon production per unit chlorophyll a. Full sunlight conditions, 1500 μE · m^?2· s^?1, did not induce photoinhibition of gross production. Variations in the efficiency of growth of S. costatum were minimized over a wide range of light intensities mainly because of variations in cellular pigments which permitted the efficient utilization of available light energy, and a reduction in the losses of carbon which increases the growth rate, possibly as a consequence of the recycling of respired carbon within the cell.     

Linking light attenuation and suspended sediment loading to benthic productivity within an Arctic kelp‐bed community1

Annual growth and productivity of kelp in the Stefansson Sound Boulder Patch, located along the Arctic coast of Alaska, is regulated almost entirely by PAR received during the summer open‐water period. Increased water turbidity during summer, often in response to storm activity, has been linked to low levels of ambient PAR and measurable decreases in kelp elongation. However, the relationship between PAR and water transparency has not been quantified, which compromises efforts to assess the effects of changing climate and weather conditions on kelp production. During the 2001–2002 summer periods, the inherent optical properties (IOPs) of Stefansson Sound waters were measured in conjunction with total suspended sediments (TSS) concentrations, which differed significantly between the 2 years, for input into a radiative transfer equation (RTE). In both years, the highest TSS levels (24.2 and 18.5 mg · L^?1 in 2001 and 2002, respectively) occurred in nearshore areas and were coincident with increased beam attenuations (13.8 and 8.3 m^?1). Lower TSS concentrations and attenuations were measured offshore. Data input to the RTE provided a TSS‐concentration‐specific attenuation coefficient that was used in a productivity model to estimate annual kelp productivities throughout the Boulder Patch based on modeled irradiance and averaged site‐specific TSS concentrations. Production estimates varied across the Boulder Patch but were lower in 2001 (0.12–0.34 g C · g dwt^?1 · year^?1, where dwt stands for dry weight) compared to 2002 (0.24–0.80 g C · g dwt^?1 · year^?1). Production in both years was greater in offshore locations with lower TSS loads. Results suggest that PAR availability during the summer is heavily influenced by TSS concentrations, and that changes in storm intensity and frequency, associated with current warming trends, may have significant effects on the primary production of these unique benthic algal communities.     

PHYSIOLOGICAL VARIATION AND ELECTROPHORETIC BANDING PATTERNS OF GENETICALLY DIFFERENT SEASONAL POPULATIONS OF SKELETONEMA COSTATUM (BACILLARIOPHYCEAE)1

Clones of Skeletonema costatum (Grev.) Cl. isolated from Narragansett Bay, R.I., during different seasons were grouped according to their electrophoretic banding patterns. The growth rates, pg chlorophyll · cell^?1, carbon uptake · cell^?1· h^?1, and carbon uptake · pg chl^?1· h^?1 were measured at 20°C, in a 14:10 h L:D cycle at 180 μE · m^?2· s^?1. Statistically significant sources of variation were found among groups of clones in growth rate, pg chl · cell^?1, and carbon uptake · pg chl^?1· h^?1. It was concluded that there is a significant relationship between the physiological characteristics of clones isolated from populations in different seasons and patterns of genetic variation inferred from the electrophoretic studies. However, genetic diversity detected by banding patterns tends to underestimate the total genetic diversity in natural populations. The groups of clones most common in summer bloom populations had significantly higher growth rates, lower values of pg chl · cell^?1, and higher rates of carbon uptake · pg chl^?1· h^?1 at 20°C than did the group of clones most common in winter bloom populations. However, differences among groups in these parameters at 20°C alone cannot account for the seasonal cycling of genetically variable populations of Skeletonema in Narragansett Bay. The range of growth rates among clones of this species is 0.1–5.0 divisions · d^?1 under a single set of temperature and light conditions. Chlorophyll concentrations range from 0.2–1.7 pg chl · cell^?1 and carbon uptake · pg chl^?1· h^?1 varies by a factor of 7 among clones. The range of physiological variation in this species means that it is difficult to use laboratory studies of single clones to analyze the responses of natural populations of Skeletonema.