Ecotypic differentiation in light-related traits of the kelp Laminaria saccharina

Light-related traits were compared for Laminaria saccharina Lamour. collected from three habitats in Maine and New York, USA, with different ambient light regimes. Light-level, expressed as a proportion of surface irradiance (I₀), ranged from 0.04 to 0.32 I₀ in the shallow habitat, but rarely exceeded 0.04 I₀ in the deep and turbid habitats. Juvenile sporophytes collected from each habitat in April, 1985, were grown at four acclimation light-levels (0.065, 0.12, 0.26, and 0.54 I₀) in a common-garden, laboratory experiment. Photosynthesis vs irradiance (PI) parameters, light-harvesting characteristics, and rates of carbon-assimilation and growth were determined for each group of plants. The results indicated that ecotypic differentiation had occurred among the three kelp populations. Photosynthetic capacity (P_max) and photosynthetic efficiency () were generally highest for plants from the turbid habitat, lowest for deep plants, and intermediate for shallow plants. These differences were largely attributable to variations in light-harvesting characteristics. The nature and magnitude of photoacclimation responses also differed among populations. Population differences in photosynthetic parameters resulted in different rates of C-assimilation and growth by plants from shallow, deep, and turbid habitats. Predictions of in situ growth rates indicated that the severity of light-limitation and, therefore, the adaptive significance of efficient light-utilization vary among the three populations. It is concluded that ecotypic differentiation in light-related traits is important to the broad environmetal range of L. saccharina.     

Photoinhibition and recovery of the kelp Laminaria saccharina at optimal and superoptimal temperatures

Effects of high irradiance on photosynthetic characteristics were examined in sporophytes of the kelp Laminaria saccharina Lamour. from 1992 to 1994. Exposure to high irradiance (700 mol photons m^-2s^-1) for 1 h at optimal temperature (12°C) caused a 40 to 60% decline in photosynthetic efficiency (alpha), quantum yield, and the ratio of variable to maximum chlorophyll fluorescence (F_v/F_m), an indicator of Photosystem II efficiency. Although the photoinhibition effects were partly attributable to protective mechanisms, a concurrent increase in minimal fluorescence (F_o) indicated damage to Photosystem II reaction centers. The magnitude of photoinhibition was proportional to irradiance and duration; however, F_v/F_m was significantly reduced after exposure to irradiances as low as 40 to 50 mol photons m^-2s^-1 for 1 h, or to 700 mol photons m^-2s^-1 for only 5 min. In contrast, photosynthetic capacity (P_max) was affected only at much higher irradiance. Superoptimal temperatures up to 24°C did not exacerbate high-light effects. At 25°C, however, alpha and P_max were more susceptible to photoinhibition than at lower temperatures. Recovery from photoinhibition was examined by following F_v/F_m and F_o for 24 h after exposure to high light. Recovery of F_v/F_m was fastest during the first 1 to 3 h, and slowed or ceased after 6 to 12 h, while recovery of F_o was relatively constant over 12 h. Dithiothreitol, which blocks formation of energy-dissipating xanthophylls, reduced both the initial rate and extent of recovery. Chloramphenicol, which blocks chloroplast-encoded protein synthesis, had little effect on initial rates of recovery, but stopped recovery after 3 h. Thus, L. saccharina appears to rely on the xanthophyll cycle to protect the photosynthetic apparatus, and reversal of this protective mechanism causes the rapid initial recovery in F_v/F_m. Longterm recovery depends on repair of damaged reaction centers. Both the rate and extent of recovery were temperature-dependent. The initial rate was higher at 18 to 22°C than at 12°C, but the extent of recovery over 24 h declined with increasing temperature. High temperatures, therefore, appear to enhance protective mechanisms, but disrupt repair processes. L. saccharina from Long Island Sound, an ecotype adapted to low light and high temperature, showed slightly but consistently greater effects of photoinhibition than plants from the Atlantic coast of Maine, but exhibited faster recovery at superoptimal temperatures.     

An annual carbon budget for the kelp Laminaria longicruris

Oxygen evolution and uptake by whole thalli of the large marine alga Laminaria longicruris de la Pylaie were measured for 24 h, once every 2 weeks for a year, using large chambers to incubate the plants on the sea bed. Diel rates of photosynthesis and respiration were calculated from these measurements and continuous light measurements were used to extrapolate the data between observation dates. The resulting estimates were combined with measurements of growth and carbon content to give an annual carbon budget for a typical mature plant. Annual net assimilation was 6.8 mgC per cm² of frond surface (71 cal cm^-2). Approximately 45% of this appeared in the production of new frond tissue, and a further 12% was accounted for by storage of carbon in mature frond tissue. About 8% was needed for stipe growth, and the remaining 35% was assumed to be lost as dissolved organic carbon. Diel net photosynthetic rates reached a maximum in June and July and were negative only in November, indicating an ability to produce a photosynthetic surplus throughout winter. In early winter the plants drew on stored reserves to supplement photosynthesis in providing carbon for growth, but from January onwards photosynthesis provided more than enough carbon for growth.     

“Free space-photosynthesis” in the algae Fucus virsoides and Laminaria saccharina

This paper deals with the role of bicarbonates in the apparent free space (AFS) and their importance for the photosynthetic process. Both the littoral alga Fucus virsoides (Mediterranean Sea) and the sublittoral alga Laminaria saccharina (Baltic Sea) show the same response. Unloading of Clions and subsequent reloading of HCO₃-ions result in a positive photosynthetic rate in distilled water (free of CO₂). Time of exposure of an algal thallus to bicarbonate solutions, as well as the concentration of these solutions, influences AFS-assimilation of the ions.     

Biomass, photosynthesis and growth of Laminaria saccharina in a high-arctic fjord, NE Greenland

Biomass, photosynthesis and growth of the large, perennial brown alga Laminaria saccharina (L.) Lamour. were examined along a depth gradient in a high-arctic fjord, Young Sound, NE Greenland (74°18'N; 20°14'W), in order to evaluate how well the species is adapted to the extreme climatic conditions. The area is covered by up to 1.6-m-thick ice during 10 months of the year, and bottom water temperature is <0°C all year round. L. saccharina occurred from 2.5 m depth to a lower depth limit of about 20 m receiving 0.7% of surface irradiance. Specimen density and biomass were low, likely, because of heavy ice scouring in shallow water and intensive feeding activity from walruses in deeper areas. The largest specimens were >4 m long and older than 4 years. In contrast to temperate stands of L. saccharina, old leaf blades (2-3 years old) remained attached to the new blades. The old tissues maintained their photosynthetic capacity thereby contributing importantly to algal carbon balance. The photosynthetic characteristics of new tissues reflected a high capacity for adaptation to different light regimes. At low light under ice, or in deep water, the chlorophyll a content and photosynthetic efficiency (!) were high, while light compensation (E_c) and saturation (E_k) points were low. An E_c of 2.0 µmol photons m^-2 s^-1 under ice allowed photosynthesis to almost balance, and sometimes exceed, respiratory costs during the period with thick ice cover but high surface irradiance, from April through July. Rates of respiration were lower than usually found for macroalgae. Annual elongation rates of leaf blades (70-90 cm) were only slightly lower than for temperate L. saccharina, but specific growth rates (0.48-0.58 year^-1) were substantially lower, because the old blades remained attached. L. saccharina comprised between 5% and 10% of total macroalgal biomass in the area, and the annual contribution to primary production was only between 0.1 and 1.6 g C m^-2 year^-1.     

Reproduction,growth and photosynthesis of gametophytes of Laminaria saccharina grown in blue and red light

The induction of reproductive activity by blue light in female gametophytes of the brown alga Lamnaria saccharina has been investigated and related to other effects of red and blue light on these plants. Although germination of zoo-spores is slightly delayed in red light, female gametophytes grow at similar rates in blue and red light of the same quantum irradiance up to an age of 8 to 10 days, when plants in blue light begin to form eggs. The percentage of plants forming eggs is proportional to the total quanta of blue wavelengths received up to a saturating value of about 400 μE·cm^-2; a 50% response is induced by 200 μE·cm^-2. The action spectrum for the induction of fertility has a main peak at 430 to 450 nm, with two subsidiary peaks in the blue and one in the near-ultraviolet light, but the action spectrum for photosynthesis is quite different, with peaks in the red, green and blue regions. These results indicate that egg formation in female gametophytes occurs as a specific morphogenetic response to blue light, which is independent of photosynthesis and growth, and trial experiments with male gametophytes of L. saccharina and gametophytes of other species of Laminariales indicate that these plants react similarly.     

Temperature acclimation of respiration and photosynthesis in the brown algaLaminaria saccharina

Sporophytes of the brown algaLaminaria saccharina (L.) Lamour grown at 15°C contained significantly more chlorophylla (chla) than did similar plants grown at 5°C. The increase in chla in 15°C plants was due to increased numbers of photosystem II reaction centes, and possibly to increased photosynthetic unit size, compared with 5°C plants. These changes were associated with increased values (photosynthetic efficiencies) in 15°C-grownL. saccharina relative to 5°C-grown plants. The changes in together with reduced respiration rates allowed 15°C-grownL. saccharina to achieve net photosynthesis and light-saturated photosynthesis at a lower photon fluence rate (PFR) than 5°C plants when both groups were assayed at the same temperature (15°C). The photon fluence rates necessary to reach the compensation point and achieve light-saturated photosynthesis (I _c andI _k , respectively) increased with increasing incubation temperature inL. saccharina grown at both 5 and 15°C. However, acclimation responses to growth temperature compensated for the short-term effect of temperature onI _c andI _k . Consequently, plants grown at 5 and 15°C were able to achieve similar rates of light-limited photosynthesis, and similarI _c andI _k values at their respective growth temperatures. These responses are undoubtedly important for perennial seaweeds such asL. saccharina, which frequently grow in light-limited habitats and experience pronounced seasonal changes in water temperature.Please address all correspondence and requests for reprints to I.R. Davison     

Lack of phlorotannin induction in the kelp Laminaria hyperborea in response to grazing by two gastropod herbivores

Phlorotannins (polyphenolic compounds) are found exclusively in brown algae and are commonly regarded as an important component of algal defense against herbivores. The variation in phlorotannin concentration within and among individual seaweed specimens of the same species can be substantial, and seaweeds may respond to herbivore damage by an increased production of phlorotannins in order to prevent further herbivory. In the present study, we investigated the natural variation of phlorotannins in different parts of the kelp Laminaria hyperborea in an observational field survey. We also performed a manipulative induction experiment in which we studied the effect of natural grazing by the patellid limpet Ansates (=Helcion) pellucida and the littorinid snail Lacuna vincta, as well as artificial damage on the production of phlorotannins in L. hyperborea. There was a large variation in phlorotannin content both among and within L. hyperborea individuals and populations. The control plants in the induction experiment had a higher phlorotannin content compared to plants in natural populations, but grazing by A. pellucida or L. vincta, or artificial damage did not induce a higher phlorotannin concentration in the kelps. Instead, the phlorotannin content in wounded kelps was significantly lower than in the control plants, possibly due to removal of phlorotannin-rich outer layers of the kelp thallus, or to an induced compensatory growth response in the L. hyperborea plants. These results imply that L. hyperborea phlorotannins probably do not function as an inducible chemical defense against A. pellucida and L. vincta, instead grazing by these herbivores decreases the phlorotannin content of the kelps.     

Standing crop and leaf area index of the sublittoral Laminaria species near Helgoland

Standing crop values of Laminaria species sampled between 0 to 2 m depth in the sublittoral of Helgoland, a small rocky island in the southern North Sea, are similar to those reported by other workers from Norwegian or Scottish coasts. Below 2 m water depth, however, standing crop values are found to be reduced to a far greater extent with increasing depth than in the Norwegian or Scottish areas studied. Maximum standing crop values are not found in Laminaria digitata and L. saccharina growing just below the low water mark of spring tides, but in the upper L. hyperborea forest at 2 m depth. Population density and leaf area index (LAI) decrease with increasing depth (but not the average weight of individuals constituting the L. hyperborea forest). It is suggested that the depth at which LAI becomes 1 represents an important ecological threshold, since growth rates of L. hyperborea specimens appear to decrease at greater depths but not to increase above the threshold. Self-shading might equalize, to a certain extent, the quantity of underwater irradiance available to an individual phylloid at all depths at which a close vegetation of Laminaria species occurs.     

Growth of the kelp Ecklonia radiata near the northern limit of its range in Western Australia

The length, growth and survivorship of mature sporophytes of Ecklonia radiata (C.Ag.) J. Agardh were measured on two patch reefs within the lagoon of a high-latitude, coralreef atoll (Easter Group, Houtman Abrolhos; 28° to 29° S; 113°35 to 114°03E) for 1 yr (1982–1983). The sites differed in their proximity to the perimeter reef, but had similar regimes of temperature, light, nutrient concentration and water movement. Kelp length, growth rate and survivorship differed significantly between sites, although plant density was similar (less than l m^-2). At the site near the lagoon perimeter, the central lamina averaged 381 mm in length, grew at an annual mean rate of 1.28 mm d^-1, and 56% of tagged individuals had died after one year. The corresponding values for the site near the centre of the lagoon were: 257 mm, 0.75 mm d^-1 and 92%. Three other sites on the coastal limestone reefs near Perth (400 km to the south) were studied for various intervals over a 5 yr period (April 1979 to August 1984). The kelp from the low-latitude sites were smaller, grew more slowly, and suffered similar or greater mortality than their southern counterparts. Latitudinal comparisons were confounded by differences in kelp density between sites, but there is no evidence for density-dependent effects on the measured parameters across the range of natural densities observed. Growth rates at all sites were negatively correlated with ambient sea temperatures when these were above 20°C. There was no evidence of adaptation to the higher sea temperatures experienced at the Abrolhos, and temperature cannot be dismissed as a factor controlling the growth of the species near the northern limit of its distribution on the Western Australian coast. Other factors however must be involved in determining the latitudinal position of that limit.     

Effect of boundary layer transport on the fixation of carbon by the giant kelp Macrocystis pyrifera

The uptake of inorganic carbon into the thallus of Macrocystis pyrifera (L.) C. Ag. requires first that the inorganic carbon pass through the water medium to the plant surface. This transfer of inorganic carbon to the thallus must take place through a boundary layer. Experiments in water tunnels indicate that the boundary layer adjacent to the M. pyrifera blade may be turbulent in water speeds as low as 1 cm sec^-1. Photosynthetic output of the blade can be increased by a factor of 300% by increasing water speeds over the blade surface from 0 to 4 cm sec^-1. This is consistent with a decrease in the thickness of the boundary layer. Above 4 cm sec^-1, the assimilation of carbon was limiting. The assimilation of carbon is generally known to follow Michaelis-Menten-like kinetics. Combining the two uptake steps into an overall model of carbon uptake agrees well with photosynthetic data obtained from M. pyrifera under varying conditions of water speed and bicarbonate concentrations in the laboratory. The ecological and morphological consequences of these findings are discussed.     

Formation and potential trophic significance of marine foam near kelp beds in the benguela upwelling system

The present study investigates the importance of foam in nearshore waters on the west coast of the Cape Peninsula (South Africa) as a possible food resource for consumer organisms. A bacterial density of 3.45x10⁹ cells ml^-1 foam suspension was recorded. Calorific values of up to 15.39 kJ g^-1 ash-free dry weight were noted, and a biochemical analysis of the drained foam suspension gave a composition of 22.85% protein, 10.76% lipid and 3.07% carbohydrates. Field data showed a correlation between peaks of phytoplankton up to 510 mg C m^-3 water temperatures and days of intense foam formation during periods of strong onshore winds. Experimental foam formation in the laboratory indicates that kelp mucilage and phytoplankton contain surface-active agents. An additional feature of kelp mucilage is its capability to improve foam stability. The comparison of the chemical composition of 12 and 120 h-old foam suspension indicates a loss of easily metabolizable components such as trichloroacetic-acid precipitated protein and neutral lipid with time. It is hypothesised that the losses are due to utilisation of these components by consumers.     

Severe storm disturbances and reversal of community structure in a southern California kelp forest

Regular observations made over a period of 5 yr in four permanent transects provided data on plant, sea urchin, and fish densities which indicate that two unusually severe winter storms in 1980 (Storm I) and 1983 (Storm II) had different effects on a southern California kelp-forest community. Storm I removed all canopies of the giant kelp Macrocystis pyrifera, but spared most understory kelps, mainly Pterygophora californica. Hence, the previously large accumulation of detached drift kelp, mostly M. pyrifera, disappeared. Denied their preferred diet of drift kelp, the sea urchins Strongylocentrotus franciscanus and S. purpuratus then emerged from shelters to find alternative food. Without effective predators, they consumed most living plants, including the surviving understory kelps. This weakened the important detritus-based food chain, as indicated indirectly by declining abundances of algal turf and fish (Embiotocidae) that eat small animals living in turf. In 1983, Storm II reversed the process by eliminating exposed urchins, while clearing rock surfaces for widespread kelp settlement and growth. By summer 1984, the kelp grew to maturity to form extensive canopies despite elevated water temperatures during summer and fall of 1983. Thus, severe storms may have vastly different effects on community structure, depending on the state of the community before the disturbance.     

Dependence of consumers on macroalgal (Laminaria solidungula) carbon in an arctic kelp community: δ13C evidence

Stable carbon isotope measurements (¹³C) were used to assess the importance of kelp carbon (-13.6 to-16.5) versus phytoplankton carbon (-25.5 to-26.5) to resident fauna of an isolated kelp bed community on Alaska's north arctic coast from 1979 to 1983. The predominant kelp, Laminaria solidungula, showed some seasonal variation in ¹³C which was correlated with changes in the carbon content of the tissue. Animals that showed the greatest assimilation of kelp carbon (>=50%) included macroalgal herbivores (gastropods and chitons,-16.9 to-18.2), a nonselective suspension feeder (an ascidian,-19.0) and a predatory gastropod (-17.6). Animals that showed the least incorporation of kelp carbon into body tissues (<=7%) included selective suspension-feeders (hydroids, soft corals and bryozoans,-22.8 to-25.1). Sponges, and polychaete, gastropod and crustacean omnivores exhibited an intermediate dependence on kelp carbon (15 to 40%). Within some taxonomic groups, species exhibited a broad range in isotopic composition which was related to differences in feeding strategies. In the polychaete group alone, ¹³C values identified four major feeding habits: deposit-feeders (-18.0), omnivores (-20.4), predators (-22.2) and microalgal herbivores (-23.0). Distinct seasonal changes in the ¹³C values of several animals indicated an increased dependence on kelp carbon during the dark winter period when phytoplankton were absent. Up to 50% of the body carbon of mysid crustaceans, which are key prey species for birds, fishes and marine mammals, was composed of carbon derived from kelp detritus during the ice-covered period.     

CO2 fixation and translocation in benthic marine algae. III. Rates and ecological significance of translocation in Laminaria hyperborea and L. saccharina

Translocation of ¹⁴C-labelled assimilates in Laminaria hyperborea and L. saccharina is strictly basipetal within the thallus. The lowermost 20 cm of the frond accumulates 71% (L. hyperborea) or 63% (L. saccharina) of the basipetallymoving translocate after a period of 96 h from initial feeding with NaH¹⁴CO₃. Whereas translocation was found to occur at all seasons in L. saccharina, which grows throughout the year, no translocation of newly synthesized photosynthate occurred in L. hyperborea in October, when no frond enlargement takes place, nor in January, when the new fond occurs as a tiny outgrowth. In L. hyperborea, organic material, assimilated by the old frond during the period of rapid growth, is exported at the rate of 0.5 mg C · dm^-2 · h^-1. In L. saccharina, 14 to 18 cm frond length are necessary for an elongation rate of the growing zone, situated in lowermost 10 cm of the frond, of 1 cm per week. The significance of translocation in the two Laminaria species is demonstrated by comparison of export rates with growth rates measured in situ and in the laboratory.Dedicated to Professor Dr. Otto Stocker on his 85th birthday.     

Effects of predators on sea urchin density and habitat use in a southern California kelp forest

Grazing sea urchins can reduce kelp abundance and therefore strongly affect kelp forest community structure. Despite the ecological importance of sea urchins, direct field studies on the role that urchin predators play in shaping urchin populations are rare for southern California. We conducted surveys and manipulative experiments within kelp forests near San Diego, CA, (32–51′28″N, 117–16′00″W) from 2006 to 2009 to determine whether predators such as sheephead (Semicossyphus pulcher) and spiny lobsters (Panulirus interruptus) may be linked to purple urchin (Strongylocentrotus purpuratus) and red urchin (Strongylocentrotus franciscanus) distribution and habitat use, as well as purple urchin density-dependent mortality. Purple urchins were less dense and more cryptic inside a local marine protected area (MPA) that contained high predator abundance than in nearby heavily fished areas, whereas red urchins rarely were found outside the MPA. Urchin proportional mortality was inversely density dependent during the day when sheephead were active, despite fish aggregations in plots of high urchin density, but was density independent during the night when lobsters were active. Urchin mortality was reduced under understory algal cover during the day, but not during the night. Examining whether urchin mortality from predation is density dependent and how habitat complexity influences this relationship is imperative because behavioral changes and increases in urchin populations can have vast ecological and economic consequences in kelp forest communities.     

Quantitative and qualitative observations on Laminaria dentigera and other subtidal kelps of southern Kodiak Island,Alaska

Observations were made and quantitative samples of non-canopy kelps were collected, using SCUBA, at 9 subtidal sites off southern Kodiak Island in May, 1976. At a 10th site, only observations were made. The most abundant species in the quadrats were Laminaria dentigera, L. yezoensis, Pleurophycus gardneri, Agarum cribrosum, and Alaria marginata. We found fertile plants of all these species. L. dentigera dominated at all sampled sites except one within a bed of Nereocystis luetkeana, where P. gardneri was dominant. L. yezoensis was dominant at the site which was visited but not sampled. The average wet weight of non-canopy kelps in the 55 samples was 12 kg m^-2, and the quadrat range was 2 to 35 kg m^-2. The reported ranges of P. gardneri and Alaria marginata are extended westward from Montague Island (147°22W) to Bumble Bay, Kodiak Island (154°43W), where A. marginata was found at a depth of 8.5 m.     

The section Digitatae of the genus Laminaria (Phaeophyta) in the northern and southern Atlantic: crossing experiments and temperature responses

Hybridization experiments between seven north and south Atlantic Laminaria species were carried out. Morphologically normal F₁ sporophytes developed from the following crosses among south Atlantic species: L. pallida x L. schinzii, L. pallida x L. abyssalis and L. schinzii x L. abyssalis. Normal F₁ sporophytes also resulted from the crosses L. digitata (north Atlantic) x L. pallida (south Atlantic) and L. digitata (north Atlantic) x L. abyssalis (south Atlantic). Hybrids between north Atlantic L. ochroleuca and south Atlantic L. pallida, L. schinzii and L. abyssalis and between north Atlantic L. digitata and south Atlantic L. schinzii initially developed as normal sporophytes but became deformed later on and further development was retarded. No hybrids resulted from attempted crosses between northeastern Atlantic L. saccharina and L. abyssalis from Brazil. Temperature tolerance, relative growth rates and temperature demands for gametogenesis revealed the existence of a warm temperate group within the digitate Laminaria species consisting of L. ochroleuca, L. pallida, L. schinzii and L. abyssalis. Hybridization experiments and temperature responses suggest that north Atlantic L. digitata and L. ochroleuca are still similar to south Atlantic Laminaria species, confirming the speculation that a transequatorial migration of a warm-temperate L. ochroleuca-like ancestor may have taken place.     

Nutrient-limited growth of juvenile kelp,Macrocystis pyrifera,during the 1982–1984 “El Niño” in southern California

The relative growth rates of juvenile Macrocystis pyrifera in southern California kelp forests were substantially reduced during the El Niño of 1982–1984. The lower growth rates were correlated with increased temperature and decreased nitrogen availability. Fertilization of juvenile plants with slow-release nitrogen-phosphorus fertilizer increased their growth rates to levels previously observed when temperatures were low and nutrient levels were high. The limitation in growth of M. pyrifera by levels of available nutrients during El Niño was in contrast to the usual limitation of growth by irradiance during non-El Niño years. Thus, there was a shift in the relative importance of factors controlling growth of juvenile M. pyrifera during El Niño.