Demography and phenology of the intertidal green algaCodium setchellii: The enigma of local scarcity on sand-influenced rocky shores

Demographic and phenological attributes that characterize rare and scarce species have not been extensively investigated for marine benthic organisms. From 1984 to 1987, 1 investigated the population ecology of the low intertidal, psammophytic green algaCodium setchellii Gardner that forms low-density populations on sand-influenced rocky benches on N.E. Pacific shores. To address why the alga is not more common in the habitat in which it is most abundant, I quantified sand fluctuations and population dynamics ofC. setchellii at several sites along the central coast of Oregon, USA. Sand movement was highly unpredictable both spatially and temporally on a local scale. AlthoughC. setchellii became fertile in late autumn to winter, the alga and rocky surfaces were often deeply buried by sand in these seasons. Algal recruitment was also spatially and temporally variable, and mortality of small thalli was high. Thallus growth was generally slow, and the alga had the capacity to persist at a given size for long periods. On sand-influenced rocky shores, mortality of largethalli was low, with some thalli persisting for several years. In laboratory experiments,C. setchellii lost substantial biomass during 4 to 5 wk sand burials, whereas two sympatric species of psammophytic algae lost little to no biomass. The within-site scarcity ofC. setchellii may be a consequence of (1) largely unpredictable environmental conditions that reduce algal recruitment and survival, and (2) apparent lack of specialized anatomical or reproductive adaptations to persist on sand-scoured rocky shores. The alga's persistence may be due to its slow growth and long lifespan.     

Photosynthetic performance,oxidative damage and antioxidants in <Emphasis Type="Italic">Cylindrotheca closterium</Emphasis> in response to high irradiance,UVB radiation and salinity

Cylindrotheca closterium is a common marine diatom living in intertidal environments where it can be present both in the water column and on sediments, depending on the tidal regime. In the present work this diatom was employed to investigate the responses to desiccation and to increase in PAR and UVB intensity, as occurs during emersion. Under these circumstances, the production of active oxygen species (AOS) may be enhanced resulting in an oxidative stress. Stress responses in this species were measured by exposing it to normal (30) and double salinity (60), supplying light of low or high intensity for 12 h, in the latter case either without or with moderate dose rates of UVB. Pulse amplitude modulated fluorometry was used to measure Chl a autofluorescence (F ₀), an index of photosynthetic efficiency of PSII (F _v/F _m) and the relative electron transfer rate (rETR). The oxidative stress was evaluated by analysing GSH pools and SOD activity. It was observed that at double salinity and under low light, intracellular pools of reduced glutathione (GSH) were higher than under the two conditions of high light without and with UVB at both salinities. The antioxidative defence activity of superoxide dismutase (SOD) was far higher under hypersaline conditions. The oxidative damage was evaluated as protein and lipid damage. The results showed that it expressed itself mainly through protein peroxidation: at normal salinity relative protein carbonyl content was (a) twice as high as in cells grown at double salinity, and (b) three times as high under UVB. Total unsaturated lipid contents doubled under hypersalinity conditions. The lipid peroxidation marker malondialdehyde showed the strongest response to low light and UVB at salinity value of 60. Lipid peroxide content was significantly higher at salinity of 60 compared to normal salinity and was the highest under low light and high light with UVB. The simulated emersion condition of the diatom seems to lead to the establishment of a balance between damage and repair, expressed mainly as (a) oxidative protein damage at normal salinity, in particular due to UV radiation, (b) sufficient protection by SOD activity mainly under hypersaline conditions.     

Introduced versus native subspecies of Codium fragile: how distinctive is the invasive subspecies tomentosoides?

After its introduction, the green alga Codium fragile (Sur.) Hariot ssp. tomentosoides (van Goor) Silva has spread widely on several temperate-zone, rocky shores where non-weedy conspecific subspecies occur (N.E. Atlantic, N.E. Pacific, S. Pacific). To determine how phenologically and morphologically distinctive the invasive alga was relative to native subspecies, I compared marine intertidal populations of C. fragile ssp. tomentosoides and the native C. fragile ssp. novaezelandiae (J. Ag.) Silva (hereafter referred to as ssp. tomentosoides and ssp. novae-zelandiae respectively on New Zealand shores in 1992, 1993 and 1995. On the North Island, the invasive ssp. tomentosoides is sparsely distributed on low intertidal benches on wave-protected shores in the Hauraki Gulf (east coast) in spring and summer, and thalli die back to the perennial holdfast in autumn. In contrast, the native ssp. novaezelandiae forms dense beds within the low intertidal mussel zone on wave-swept shores of Maori Bay (west coast), and fronds are perennial. Whereas ssp. tomentosoides has only a few fronds arising from the spongy basal hold-fast, ssp. novae-zelandiae thalli are composed of many fronds. The ssp. tomentosoides from the Hauraki Gulf is significantly more branched than comparably sized native conspecifics from Maori Bay. These phenological and morphological differences were used to predict the subspecific identity of C. fragile from three other locations on the North Island, two locations on the South Island, and four locations on S.E. Australian shores; microscopic examination of utricles was used to check the predictions. Seasonality and number of fronds per thallus are the most reliable characters for field identification of native vs invasive subspecies: perennial intertidal thalli with large numbers of fronds are indicative of native subspecies for different geographic regions.     

Improved survival under heat stress in intertidal embryos (<Emphasis Type="Italic">Fucus</Emphasis> spp.) simultaneously exposed to hypersalinity and the effect of parental thermal history

Intertidal organisms exposed to thermal stress normally experience other stresses simultaneously, but how these combined stresses modify tolerance to heat, especially for embryos, is poorly understood. Tolerance of fucoid algal embryos to heat, with and without acclimation to a sublethal temperature and with simultaneous exposure to hypersaline media, was examined. Embryos of Fucus vesiculosus L. (mid-intertidal zone) were less tolerant than embryos of Fucus spiralis L. (upper intertidal zone); without acclimation and with a growth temperature of 14°C, about half of the embryos survived 3 h exposure to 33°C in F. vesiculosus and of 35°C in F. spiralis. Conditions experienced by parental thalli (4°C versus 14°C storage) significantly affected the heat tolerance of embryos grown for 24 h post-fertilization at 14°C in F. vesiculosus, a result that is important for biologists using fucoid algae as model systems. Acclimation to a sublethal temperature (29°C) or exposure to the LT₅₀ (33°C, F. vesiculosus; 35°C, F. spiralis) in 100 psu seawater (2850 mmol kg^–1 osmolality) resulted in 30–50% higher levels of embryonic survival. Higher levels of HSP60s were found in embryos exposed to 29–33°C than to 14°C; lower levels of HSP60s were present in embryos exposed to the LT₅₀ under hypersaline conditions than in normal seawater. Contemporaneous studies in 1995–1996 of substratum temperature and desiccation levels were made at Schoodic Point, Maine (USA) underneath F. spiralis and F. vesiculosus canopies and in Semibalanus balanoides patches. This study extends the bioindicator utility of heat-shock proteins in studies of intertidal organisms and demonstrates the importance of integrated stress responses in survival of a single stress factor (e.g. temperature).Electronic Supplementary Material Supplementary material is available in the online version of this article at     

Characterization of in vivo absorption features of chlorophyte,phaeophyte and rhodophyte algal species

Despite the plentiful diversity of macroalgae in coastal environments, few studies have examined the in vivo absorption features of common marine macrophytes. Here we report on results of a survey of 12 central California common intertidal and subtidal taxa, representing Chlorophyta, Phaeophyta and Rhodophyta carried out in the summer of 1988. Computer-assisted analyses were used to obtain fourth-derivative spectra from in vivo absorption spectra determined at room temperature to obtain spectral diagnostics for the different algal divisions and to provide a means to determine whether spectral features could be used to identify stress responses among these plants. Among the Chlorophyta, characteristic maxima for chlorophylls a and b were resolved in all species examined, and a spectral component attributable to siphonaxanthin-like carotenoid(s) was observed in two Ulva species and the coenocytic alga Derbesia marina. Representatives of the Phaeophyta were characterized by similar maxima for chlorophyll a and c, and for fucoxanthin. Among the Rhodophyta, maxima for chlorophyll a, as well as B- and R-type phycoerythrin were resolved. Differences in in vivo absorption features were detected for two tidal populations of Porphyra perforata and Mastocarpus papillatus. High-tidal thalli absorb less green light in regions characterized by phycoerythrin, but have enhanced carotenoid absorption compared with lowtidal thalli. Resolution of spectra by fourth-derivative analysis revealed significant differences in phycoerythrin and carotenoid contents. The spectral changes observed appear to reflect environmental and possibly populational characteristics of these algae. The spectral analyses described here provide robust, non-invasive means to characterize subtle responses of macroalgae to environment in ways not possible previously. Additional merits of these fourth-derivative analyses for use in environmental studies are discussed.This contribution is dedicated to the memory of Professor L. R. Blinks, a pioneer in photosynthesis research and algal physiology     

Tolerance of Mediterranean seagrasses (<Emphasis Type="Italic">Posidonia oceanica</Emphasis> and <Emphasis Type="Italic">Cymodocea nodosa</Emphasis>) to hypersaline stress: water relations and osmolyte concentrations

The present study examines for the first time the effects of increased salinity on water relations and osmolyte (carbohydrates and amino acids) concentrations in two Mediterranean seagrass species, Posidonia oceanica and Cymodocea nodosa, which are adapted to growth in environments with contrasting salinity and have a known differential sensitivity to alterations in ambient salinity. The specific aim was to obtain insights into their respective capacities to cope with natural or anthropogenically induced (e.g. desalination plants) hypersaline stress and its ecological implications. To this end, large plant fragments of both seagrass species were maintained for 47 days in a laboratory mesocosm system under ambient salinity (37 psu; control) and three chronic hypersaline conditions (39, 41 and 43 psu). Analyses of leaf-tissue osmolality indicated that both species followed a dehydration avoidance strategy, decreasing their leaf water potential (Ψ_w) as the external salinity increased, but using different physiological mechanisms: whereas P. oceanica leaves exhibited a reduction in osmotic potential (Ψ_π), C. nodosa leaves maintained osmotic stability through a decrease in turgor pressure (Ψ_p) probably mediated through cell-hardening processes. Accordingly, the concentrations of soluble sugars and some amino acids (mainly Pro and Gly) suggested the activation of osmoregulatory processes in P. oceanica leaves, but not in C. nodosa leaves. Osmotic adjustments probably interfered with leaf growth and shoot survival of P. oceanica under hypersaline stress, whereas C. nodosa showed a more efficient physiological capacity to maintain plant performance under the same experimental conditions. These results are consistent with the more euryhaline ecological behaviour of C. nodosa and contribute to understanding the high vulnerability shown by P. oceanica to even mild increments in seawater salinity.     

No zone is always greener: variation in the performance of<Emphasis Type="Italic"> Fucus gardneri</Emphasis> embryos,juveniles and adults across tidal zone and season

The responses of the different stages of an organisms life-cycle to different environments can have important implications for their persistence in those habitats. The marine intertidal zone is considered among the most stressful of all marine environments, because daily exposure at low tide results in daily fluctuations in a range of important environmental factors. In this study we examined the link between daytime exposure and the performance of embryos, juveniles and adults of the seaweed Fucus gardneri across zones and seasons on San Juan Island, Washington, USA. Specifically we asked: (1) whether three measures of performance for F. gardneri: growth rates, surface area of reproductive tissue and survivorship differed between high- and mid-intertidal zones, and among months throughout the year and, then, (2) whether total daytime exposure within each zone each month was a good predictor of variation in these measures of performance. At our study site, seasonal differences in the timing of low tides result in long periods each day during summer of very harsh conditions (exposure to the air, high temperatures and low humidity) compared to winter when exposure to the air during the day is virtually absent. Contrary to the expectation of lower performance in the high zone, we found no consistent differences between zones over the entire year in any measure of performance for any stage. For nearly all traits, there were significant differences among months and, importantly, significant interactions between zone and month. Thus, for each stage there were some months when thalli in the high zone performed better and some months when thalli in the mid-zone performed better. Regressions between total daytime exposure and performance each month indicated some stage-specific effects. Larger thalli appeared more strongly affected by the amount of exposure per month; there were significant negative relationships between total daytime exposure and (1) growth rates of medium and large adults in the high zone and (2) the surface area of reproductive tissue of medium adults in the high zone and small adults in the mid-zone. The lowest survivorship for all stages occurred in the 2–3 months that followed summer, suggesting a cumulative effect of long daytime exposure in summer on survivorship. Post-settlement survivorship of embryos was very low throughout the year, with only 2 out of 5395 seeded zygotes surviving to a visible size. One-month post-settlement survivorship ranged from 0% to 16.7%, and there were no differences in the survivorship curves between high- and mid-intertidal zones for each cohort. Although it is often assumed that the performance of intertidal species is lower in high-intertidal zones because of exposure to environmental extremes for longer, our results do not support this paradigm. Instead, they indicate a complex and fluctuating pattern of variation in the performance of different stages of the F. gardneri life-cycle throughout the year in different intertidal zones.Communicated by M.S. Johnson, Crawley     

Algal “gardening” behavior by nereid polychaetes: Effects on soft-bottom community structure

Nereid polychaetes (Nereis vexillosa and Platynereis bicanaliculata) attach pieces of drift algae to their tube surfaces. The presence of permanent algal cover increases the predictability of the food supply for at least the herbivores (including the nereids) and the deposit feeders, and modulates the temperature and salinity stresses of the marine intertidal soft-bottom environment. However, it may affect the access of organisms to the oxygenated water layers above the sediment surface. This is true for polychaetes that live head downwards in vertical tubes. It is suggested that the attachment behavior of the nereid polychaetes increases the ability of the plant to colonize habitats both temporally and spatially.     

Photosynthesis in air and in water of Acanthophora najadiformis growing within a narrow zone of the intertidal

In this work, we investigated photosynthetic gas exchange responses of the red alga Acanthophora najadiformis (collected in 1991 from a shore near Netanya, Israel) to heating, light, inorganic carbon and desiccation of the thalli. This was done to elucidate some of the contributing causes for its particular restricted vertical distribution within the lower intertidal zone of the Israeli Mediterranean rocky shore. In contrast to other common intertidal species, the photosynthetic performance of A. najadiformis was very sensitive to desiccation and to high temperature, and these factors may thus prevent the alga from growing above the surge zone. On the other hand, this species photosynthesized five times faster in air than in water (provided it was kept highly hydrated), and this may be the reason why it does not succeed in competing with other algae in the subtidal which use HCO ₃ ^- more efficiently.This paper is in partial fulfillment of a Ph.D. study by R. Einav in cooperation with the Department of Ecology, University of Bielefeld (under supervision of Prof. Dr. S. W. Breckle), under a cooperative arrangement between Tel Aviv and Bielefeld Universities     

Seasonal stresses shift optimal intertidal algal habitats

We studied how the growth, reproduction, and survival of a common intertidal rockweed (Fucus distichus) varied across its tidal elevation at 14 sites around San Juan Island, Washington, USA in spring–summer and fall-winter seasons. We also measured a suite of environmental factors including temperature, light, emersion time, slope, fetch, and herbivory. To interpret the response of Fucus we included measurements of phlorotannins and carbon storage compounds (mannitol, laminarin). Growth and reproduction exhibited parallel patterns across tidal zones and sites. Tidal zone was a significant source of variation for many Fucus response variables, whereas variation between sites was high but not generally a significant factor explaining Fucus growth and physiology. Unexpectedly, the tidal zone in which Fucus achieved its highest growth and reproduction switched between seasons. High zone thalli grew and reproduced better than Mid zone thalli in fall but not in spring. This result can be explained by different combinations of factors influencing Fucus in each season. In spring, longer emersion times due to daytime low tides resulted in lower growth rates higher on the shore, likely due to carbon limitation. In fall during nighttime low tides, emersion and carbon limitation stresses were minimal. Overall, fall growth was lower than spring growth, but low fall light was not responsible. Instead, warmer average fall temperatures in the High zone apparently favored growth and reproduction relative to the Mid zone. In contrast, Mid zone thalli were subjected to more intense herbivory and hydrodynamic stress associated with wave exposure and steep substrata during the fall. At least for some seaweeds, living in the presumably more stressful high zone can actually confer higher integrated performance.     

The marine bacterium Leucothrix mucor as an algal epiphyte

Leucothrix mucor, a filamentous marine heterotrophic bacterium, is found in nature primarily as an algal epiphyte. Its distinctive characteristics make it easily recognizable by dir ect light-microscopic examination, and a method was develop ed to quantify natural populations of L. mucor on algae by direct microscopic counts. L. mucor was found to be widely distributed in the intertidal environment, especially in the mid-to-upper intertidal regions. Populations were most abundant on members of Rhodophyta, particularly on the alga Bangia juscopurpurea. The nature of the L. mucor-algal relationship was investigated by choosing an artificial plastic substrate to which L. mucor would attach. The use of the plastic substrate, both alone, and in conjunction with a natural algal host, gave results supporting the conclusion that L. mucor obtains its nutrients for growth from the alga rather than from seawater. Algae in the upper intertidal region may also protect attached L. mucor from desiccation.     

Callus formation in seven species of agarophyte marine algae

Callus formation of seven species of the agarophyte marine algae Phyllophora nervosa, Gracilaria verrucosa, Furcellaria fastigiata, ceramium kondoi, Gelidium vagum, Laurencia paniculata, Rhodymenia pertusa was obtained from 1984 to 1986. A new sterile agent, chlorhexidin bigluconate, was used to get axenic explants from the algae thalli. The formation of callus from axenic explants depended on temperature of cultivation. In the case of F. fastigiata and G. vagum it occurred at 12° to 20°C, and with P. nervosa at 18° to 26°C. The exchange of sucrose with mannitol in the culture medium and the addition of some growth regulators stimulated the formation of callus. Mass formation of lumpy and warty extensions was observed in the explants from leaf blades of P. nervosa. The results might be useful for improving the aquaculture of agarophyte marine algae.     

Photosynthesis in Codium fragile (Chlorophyta) from a Nova Scotia estuary: responses to desiccation and hyposalinity

Codium fragile ssp. tomentosoides from Caribou Harbour, an estuarine site in the southern Gulf of St. Lawrence, was extremely tolerant to stresses from desiccation and reduced salinity. Photosynthetic responses of both rhizomatous and erect growth forms were measured using pulse amplitude modulation (PAM) fluorometry of chlorophyll a fluorescence to determine effective quantum yield (Φ_PSII) and relative electron transport rate (rETR). After 5 h of desiccation, thalli lost 20% of their mass, but still showed high levels of Φ_PSII. Thalli survived for at least 6 h in freshwater, and showed virtually complete recovery of photosynthetic capacity within a few hours of return to full seawater. Immersion in 8 psu showed virtually complete recovery until the 24 h treatment period. Combining desiccation and salinity stresses produced a synergistic effect, but plants still showed strong recovery even after 86% dehydration and reimmersion in 16 psu. These results suggest that the photosynthetic physiology of Codium fragile is highly adapted to growth in estuarine conditions.     

Adaptations of Gracilaria pacifica (Rhodophyta) to nitrogen procurement at different intertidal locations

Nitrogen uptake, assimilation and accumulation were studied in three populations of Gracilaria pacifica Abbott in Bamfield Inlet, British Columbia, Canada, over three summers, 1979–1981. Two of these populations were in the intertidal one high and one low, and the third was a subtidal cultured population. Nitrate uptake rates, internal nitrate content and nitrate reductase activities were highest in the low intertidal population. Time-courses of uptake and uptake kinetics were studied. Both nitrate and ammonium were taken up simultaneously. Thalli from the high-intertidal population showed enhanced nitrate and ammonium uptake following mild desiccation, and greater tolerance to desiccation in terms of maintaining nitrogen uptake after severe desiccation. Transplants were made to determine the effect of intertidal height and geographic location on responses to desiccation, nitrogen uptake, assimilation and accumulation. Nitrate and ammonium uptake rates were dependent on intertidal height and geographic location. Transplanting up the intertidal increased nitrate uptake and nitrate reductase activity, but decreased the nitrate content of the thalli. There were few significant differences in ammonium uptake rates, and ammonium, amino acid, and soluble-protein content of the various populations. All high-intertidal populations, transplanted or natural, showed enhanced nitrate uptake rates following desiccation. Enhanced ammonium uptake rates following desiccation were restricted to the high-intertidal thalli in only one geographic location. Tolerance to higher levels of desiccation also appeared to be intertidal height-dependent, but required more than five weeks to fully develop or disappear.     

Salinity stress and hydrogen peroxide regulation of antioxidant defense system in Ulva fasciata

The regulation of antioxidant defense system in macroalgae exposed to salinity stress was examined in Ulva fasciata Delile. As compared to the 30‰ control, a long-term (4 days) exposure to hyposaline (5, 15‰) and hypersaline (60, 90, 120, 150‰) conditions inhibited growth rate and TTC reduction ability. A decrease in maximum quantum efficiency (F _v/F _m ratio) and the maintenance of superoxide dismutase activity under salinity stress indicate the potential generation of reactive oxygen species in chloroplasts. An exposure to 15, 60, and 90‰ decreased seawater H₂O₂ contents but increased thallus H₂O₂ contents that are positively correlated with TBARS and peroxide contents. Alleviation of oxidative damage and H₂O₂ accumulation at 15 and 90‰ by a H₂O₂ scavenger, dimethylthiourea, suggests that oxidative damage occurring under moderate hyposaline and hypersaline conditions is ascribed to accumulated H₂O₂. Increased glutathione reductase activity and glutathione content and decreased ascorbate content are responsible for accumulated H₂O₂ at 15, 60, and 90‰, while ascorbate peroxidase activity increased only at salinity ≥ 90‰. Catalase and peroxidase activities also increased at 60 and 90‰ for H₂O₂ removal, but only catalase showed activity increase at 15‰. For the regeneration of ascorbate, the activities of both dehydroascorbate reductase and monodehydroascorbate reductase were increased at 5 and 15‰ while only monodehydroascorbate reductase activity increased at 60 and 90‰. It is hypothesized that the availability of antioxidants and the activities of antioxidant enzymes are increased in U. fasciata to cope with the oxidative stress occurring in hyposaline and hypersaline conditions.     

Photosynthesis and amelioration of desiccation in the intertidal saccate alga Colpomenia peregrina

Rates of gross photosynthesis for the intertidal saccate alga Colpomenia peregrina (Sauv.) Hamel were determined under submersed and emersed conditions. Maximal photosynthetic rates were lower than for most seaweeds but comparable with other saccate members of the genus. By fitting the data to a hyperbolic tangent function, maximal photosynthetic rates were estimated to be 5.29 mmol CO₂ m^-2 h^-1 under submersed conditions and 2.06 mmol CO₂ m^-2 h^-1 under emersed conditions. I_k for submersed thalli was 69.1 E m^-2 s^-1, wherea for emersed thalli it was 149.0 E m^-2 s^-1, or 2.2 times higher. At low tide in the field and under saturating irradiance, carbon from seawater retained within the thallus cavity was assimilated at 0.9 mmol CO₂ m^-2 h^-1. In the laboratory under emersed conditions, carbon from this source was taken up at 0.6 mmol CO₂ m^-2 h^-1 at 20°C and at 0.34 mmol CO₂ m^-2 h^-1. Retained seawater also greatly reduced drying under desiccating conditions. Experimental thalli from which seawater had been removed lost thallus water continuously throughout the drying period (120 min). On the other hand, control, thalli lost water for the first 15 min, after which no further water loss occurred. At the termination of the experiment, control thalli had lost 7.2% of their water, whereas experimental thalli had lost 39.2%. Desiccation affected the emersed photosynthetic rate of experimental and control thalli. Emersed photosynthetic rates for thalli dried for 15 min were higher than for fullyhydrated thalli. However, emersed photosynthesis of thalli dried for longer than 15 min was lower than fully-hydrated rates and was directly related to percent water loss. Utilizing data from this study, a model was constructed to determine total photosynthetic production of C. peregrina over a single daylight period. From these calculations it was determined that emersed photosynthesis can increase daily photosynthetic production of C. peregrina by 50%.     

Biotic and abiotic stress effects on nitrogen chemistry in the salt marsh cordgrassSpartina alterniflora (Poaceae)

Summary Planthopper (Insecta: Homoptera) feeding stress induces a senesence-like response in the leaves ofSpartina alterniflora characterized by decreased soluble protein, an increased total amino acid pool, and elevated levels of 10 individual amino acids. Increased proline and tryptophan in response to planthopper feeding could not be fully explained by protein degradation. Low degrees of soil salinity stress resulted in an increased total free amino acid pool and elevated levels of 7 amino acids. Anaerobic soil stress resulted in decreased glutamic acid and increased asparagine. Low salinity and anaerobic stress had no effect on soluble protein levels. Glycinebetaine was not affected by the stresses examined in this study.     

Some observations on the influence of salinity on growth and photosynthesis inPorphyra umbilicalis

Notwithstanding the great importance of the salinity factor in the marine environment, the knowledge of influence of salinity on growth of marine benthic algae is very limited. Rate of growth (mg, cm²) and O₂ output of the intertidal red algaPorphyra umbilicalis from Helgoland, North Sea, were measured during a 3 week culture in 3 different salinities (1/2-, 1- and 2-concentrated artificial sea water; Table 1). Under hypertonic conditions (2-concentrated sea water) growth rate and photosynthesis rate were depressed, compared to values obtained in normal concentrated sea water. Under hypotonic conditions (1/2-concentrated sea water), growth expressed in mg was the same as in normal concentrated sea water, or higher when expressed in cm³. Rate of O₂ output was almost unaltered in one of the two experiments, lowered in the other. Cell size increased at higher salinity, while swelling of cell walls and intercellular substances as well as the intensity of colouring decreased with salinity. The discrepancies between growth and photosynthesis under hypotonic conditions cannot be completely explained by the observed influences of salinity on morphological structures (cell size, swelling of cell substances). Detailed studies on the time course of photosynthesis and respiration rates, and preparation of a metabolic balance for the algae are necessary.     

Evaluation of chlorophyll fluorescence, in vivo spectrophotometric pigment absorption and ion leakage as biomarkers of UV-B exposure in marine macroalgae

The photosynthetic fluorescence ratio F_v:F_m, in vivo absorption spectra and ion leakage were evaluated as biomarkers of ambient and elevated UV-B (280 to 320 nm) exposure of the intertidal alga Enteromorpha intestinalis (Chlorophyta) and the sublittoral alga Palmaria palmata (Rhodophyta). Measurements of thallus growth were also used to assess adverse biological effects. Ambient and elevated UV-B significantly inhibited photosynthesis in both species. It was shown that the F_v:F_m ratio is a sensitive, non-specific general biomarker of UV-B exposure in both species. Moreover, the in vivo absorption of what was tentatively identified as chlorophylls a and b as well as phycoerythrin and/or carotenoids, phycoerythrobilin and phycocyanin decreased in a dose-response dependent manner and was associated with a decrease in growth rate in P. palmata. The intertidal alga E. intestinalis showed a greater degree of tolerance to UV-B exposure. These results indicate that changes in the F_v:F_m ratio together with reductions in in vivo pigment absorption could provide an early quantitative warning of the detrimental effects of UV-B in marine macroalgae. Received: 16 May 1997 / Accepted: 16 July 1997     

Impact of UV-B radiation on uptake of 15N-ammonia and 15N-nitrate by phytoplankton of the Wadden Sea

Natural marine phytoplankton populations from the German Wadden Sea and unialgal cultures of the haptophycean Phaeocystis pouchetii were tested in 1989 under controlled UV-B stress conditions. Assimilation of ¹⁵N-nitrate in phytoplankton consisting mainly of P. pouchetii, or in pure cultures of this alga, was found to be very sensitive to enhanced UV-B dosage in comparison ¹⁵N-ammonia uptake. In contrast, in phytoplankton samples containing Ceratium spp., Coscinodiscus sp., Noctiluca sp. or others, rate of ¹⁵NO₃ ^- uptake was higher and only slightly affected by UV-B irradiance compared to the P. pouchetii sample. UV-B inhibitory effect on uptake of inorganic nitrogen by P. pouchetii was more pronounced under strong white-light conditions and after a UV-B pre-illumination period of several hours than under low white light. Pools of glutamine and alanine decreased after UV-B exposure. Results are discussed with reference to the damaging effects of white light and UV-B on nitrogen metabolism.