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.     

Optimal growth and maximal survival temperatures of Atlantic Laminaria species (Phaeophyta) in culture

The effects of temperature on growth rate of rapidly-growing cultured macrosporophytes of 9 isolates of Atlantic Laminaria comprising 4 species have been investigated. No significant population variation was observed within species despite wide variations in temperature between the original collecting sites. L. saccharina showed a broad temperature optimum in the 10°–15°C range, whereas L. longicruris had a sharp optimum at 10°C. L. digitata and L. hyperborea grew more slowly, with only slightly sub-optimal growth over a wide temperature range, but with peaks at 10°C (L. digitata) and 15°C (L. hyperborea). The maximum survival temperatures of individual male and female vegetatively-growing gametophytes were ascertained for these species plus the Arctic L. solidungula, and were as follows: L. saccharina and L. longicruris, 23°C; L. digitata (male), 23°C; L. digitata (female), 22°C; L. hyperborea, 21°C; L. solidungula, 18°C. The lack of within-species differences demonstrates that the success of the genus in areas with different temperature regimes is brought about by phenotypic plasticity of individuals rather than the selection of temperature races or ecotypes.     

Occurrence and biological role of light-induced chromatophore displacements in seaweeds

The occurrence of light-induced chromatophore displacements and concomitant transmittance changes in marine algae was investigated by microscope and photometrically with an automated recording microphotometer system; 16 brown, 6 green and 20 red algae were studied. In most of the brown algae, both phaeoplast displacements and transmittance changes were found. In some red algae which are frequently exposed to direct sun light during emergence at low tide, light-induced transmittance changes were measured, but they could not unequivocally be correlated with changes in the position of rhodoplasts. Among green algae, only Ulva lactuca shows chloroplast displacements which, however, follow circadian rhythms and are consequently not light-induced in the strict sense. The dose-response curves of light-induced chromatophore displacements were measured in the following Fucus and Laminaria species: F. spiralis, F. vesiculosus, F. serratus, L. digitata, L. saccharina and L. hyperborea. While in Fucus species correlations between light-induced transmittance changes and zonation of the intertidal area seem to exist, no significant differences have been found in the Laminaria species. The physiological role and ecological importance of light-induced chromatophore displacements for seaweeds living in the intertidal belt are discussed.     

Modeling kelp forest distribution and biomass along temperate rocky coastlines

We address the global deficit of data describing kelp forest distribution, relative covers and biomass by testing the ability of species distribution models to predict these attributes at locations where data are currently limited. We integrated biological ground truth data with high-resolution environmental datasets to develop generalized additive models that accurately predict the structure of Laminaria forests within the Bay of Morlaix (48°42′42″N, 3°55′40″W). Forest distribution and proportional covers were predicted using water depth, light availability, wave exposure and sediment dynamics. The biomass of individual kelp species was modeled by supplementing these same variables with measures of seafloor slope and benthic position. Biomass predictions for Laminaria digitata and Laminaria hyperborea contrast the physiological tolerances of these species to light and wave exposure gradients. As a direct management output, we produced high-resolution maps (25 m² grids) that closely match independent field data and provide vital information for marine spatial planning.     

Ecological energetics of the seaweed zone in a marine bay on the Atlantic coast of Canada. I. Zonation and biomass of seaweeds

An intertidal and underwater survey of the zonation of seaweed in St. Margaret's Bay, NovaScotia, Canada showed 8 major zones as one proceeded away from shore: (1) Fucus and Ascophyllum; (2) Chorda with filamentous browns; (3) Chondrus crispus; (4) Zostera marina; (5) Laminaria digitata with L. longicrusis; (6) Laminaria longicruris; (7) L. longicruris with Agarum cribrosum; (8) Agarum cribrosum with Ptilota serrata. Zostera occurred at the same level as O. crispus but replaced it in sheltered water. Ascophyllum was more abundant in sheltered water. L. digitata was confined to the more exposed, steeper shore. The average horizontal extent of the seaweed zone was 369 m, and the greatest depth of significant amounts of seaweed 20 to 30 m. Laminaria longicruris contributed 36% of the total biomass, and Laminaria spp. and Agarum together constituted 83%, while intertidal seaweeds contributed less than 10% of the biomass. The estimated average total biomass per m of shore line was 1,481 kg fresh weight, 326 kg dry weight, 98 kg carbon, or 980x10³ kcal. When averaged over the whole area of the bay, the corresponding figures were 1.38 kg/m² fresh weight, 0.30 kg/m² dry weight, 91 g/m² carbon or 912 kcal/m². Dry matter of Laminaria was 15 to 27% of fresh weight in blades, 10 to 12% in stipes. The dry matter content of blades was least in spring and highest in autumn, but carbon content and calorific value of dry matter showed little difference with species or season.Contribution to the International Biological Programme CCIBP 108.Bedford Institute Contribution BI 249.     

Depth as a factor in abundance and size of juvenile penaeid shrimps in the absence of estuaries and marshes

Triweekly trawling around low tide during daylight at 1, 2, 3, and 4 m depths along north Kuwait Bay's extensive intertidal mudflats from 1 April 1985 through 9 December 1986 showed the catchability ofMetapenaeus affinis (H. Milne-Edwards, 1837),M. stebbingi Nobili, 1904,Parapenaeopsis stylifera (H. Milne-Edwards, 1837), andPenaeus semisulcatus De Haan, 1844 differed significantly with depth and season. All species were significantly more catchable in 1 and 2 m depths than in 3 and 4 m depths.M. affinis showed the clearest and most consistent relationship with depth: catchability in 1 m depths was significantly greater than that in 2 m depths (24.9 vs 5.4 per 5-min tow), and catchability in 1 and 2 m depths was significantly greater than that in 3 and 4 m depths (15.2 vs 1.4 per 5-min tow).M. affinis also showed the clearest relationship of increasing size with depth. Shrimp captured in 1 m depths were significantly smaller (~ 14 mm carapace length, CL) than those captured in 2 m depths in the spring (~23 mm CL) and summer (~ 18 mm CL). In the absence of low-salinity waters and intertidal vegetation, it is believed that the edge of the advancing and receding tide over the mudflats, i.e. the shallowest waters, provides juvenile shrimp, particularlyM. affinis, protection from predation.     

Molecular association of Cu,Zn, Cd and 210Po in the digestive gland of the squid Nototodarus gouldi

In July 1985, very fine burrows extending at least to a sediment depth of 50 cm were found in sediments of the Vöring-Plateau, Norwegian continental slope, at depths of 1 261 to 1 969 m. Such burrows have been described from other areas of the oceans, but until now the producers have been unknown. In the box-cores from Vöring-Plateau sipunculans of the genus Golfingia, subgenus Nephasoma, were identified as inhabitants and producers of these Lebensspuren, which correspond with the fossil ichnogenus Trichichnus.     

Growth and DNA damage in young Laminaria sporophytes exposed to ultraviolet radiation: implication for depth zonation of kelps on Helgoland (North Sea)

Growth as an integrative parameter of all physiological processes was measured in young sporophytes of temperate Laminaria digitata, Laminaria saccharina and Laminaria hyperborea exposed in the laboratory to irradiance consisting of either only photosynthetically active radiation (PAR) or to a spectrum including ultraviolet radiation (UVR) (PAR+UVA+UVB) by use of cut-off glass filters. Size increment was measured every 10 min over a period of 18–21 days using growth chambers with on-line video measuring technique. In the chamber, plants were grown at 10±2°C and 16:8 h light–dark cycles with 6 h additional UVR exposure in the middle of the light period. Tissue morphology and absorption spectra were measured in untreated young sporophytes while chlorophyll a content and DNA damage were measured in treated thalli at the end of the experiment. Sensitivity of growth under UVR was found to be related to the observed upper depth distribution limit of the upper sublittoral L. digitata, upper to mid sublittoral L. saccharina and lower sublittoral L. hyperborea. Tissue DNA damage is, however, dependent on thallus thickness which minimizes UVR effect where outer cell layers shade inner cells and provide longer pathlength for UVR. Exposure to UVR causes cellular, enzymatic and molecular damage. Presence of UV-absorbing compounds further reduces effective UVR from reaching physiological targets. The cost of producing higher amount of UV-absorbing compounds and effective DNA repair mechanism can, however, divert photosynthate at the expense of growth. Tissue chlorophyll a content was not significantly different between treatments suggesting a capacity for acclimation to moderate UVR fluence. Growth acclimation to repeated UVR exposure was observed within a period of 12 days while growth inhibition was observed after a longer UVR exposure period of 21 days. The results give further insight into the effects of UVR on the cellular level and show how ecological parameters such as the upper depth distribution limit are dependent on cellular processes.     

Seasonal distribution of modern coccolithophores in the western North Atlantic Ocean

The seasonal successions of standing crop and floral assemblage were studied for oceanic coccolithophores at 5 weather stations in the western North Atlantic Ocean. The coccolithophores were less populous during winter at the northern stations, whereas they became scarce during summer at the southern stations. The average standing crop in the surface water was quite consistent throughout all climatic regions, being a few tens of thousand cells per liter. The average standing crop at the 100 m level showed a clear trend of increasing southwards. The population at this depth was only one-tenth as large as that of the surface level at the northernmost station, whereas it was almost two-thirds as large as the surface levels at the southernmost station. Many of the major species exhibited seasonally biased occurrences. The trend was mostly repeated in consecutive years, although the magnitude of their abundances fluctuated from year to year in some case. The average species composition was obtained for the 5 weather stations at the surfacewater (surface and 20 m levels combined) and 100 m levels; Emiliania huxleyi dominated the flora at all stations. The relationship between occurrences of major species and ambient water temperature was also studied. Although some species were stenothermal, the majority exhibited eurythermal characteristics; this accounts for the high specific diversity of the coccolithophore community throughout the wide range of waters studied.Contribution No. 2899 of the Lamont-Doherty Geological Observatory of Columbia University.     

Deep-sea caging of the mussel Mytilus galloprovincialis: Potential application in ecotoxicological studies

We experimented with caging the Mediterranean mussel (Mytilus galloprovincialis) at various depths for 69 d to measure basic physiological parameters, histological response and bio-accumulation of contaminants in a deep-sea contaminated area. In preliminary experiments, we demonstrated, under artificial pressure conditions, the ability of mussels Mytilus galloprovincialis to tolerate rapid immersion (at a speed of up to 120 m min^?1). In situ experiments were performed using submerged lines enabling mussels to be maintained at depths ranging of 40–1550 m with survival rates ranging from 80 to 38%, respectively. No significant differences in condition indexes were observed between treated and control specimens. However, histological observations demonstrated a clear reduction in thickness of the digestive epithelium with increasing depth exposure. By determining the contaminants in caged mussels, we found the following values for chromium accumulation: 27.4 μg g^?1 dry weight at 580 m depth and 9.8 μg g^?1 dry weight at 1550 m. Selected stations were located downstream of an industrial effluent at 420 m. The biological and environmental consequences of deep-sea contamination demonstrate the suitability of caged mussels for monitoring contaminant accumulation.     

PIXGRO: A model for simulating the ecosystem CO2 exchange and growth of spring barley

A model, PIXGRO, developed by coupling a canopy flux sub-model (PROXEL_NEE; PROcess-based piXEL Net Ecosystem CO₂ Exchange) to a vegetation structure submodel (CGRO), for simulating both net ecosystem CO₂ exchange (NEE) and growth of spring barley is described. PIXGRO is an extension of the stand-level CO₂ and H₂O-flux model PROXEL_NEE, that simulates the NEE on a process basis, but goes further to include the dry matter production, partitioning, and crop development for spring barley. Dry matter partitioned to the leaf was converted to leaf area index (LAI) using relationships for the specific leaf area (SLA). The canopy flux component, PROXEL_NEE was calibrated using information from the literature on C3 plants and was tested using CO₂ flux data from an eddy-covariance (EC) method in Finland with long-term observations. The growth component (CGRO) was calibrated using data from the literature on spring barley as well as data from the Finland site. It was then validated against field data from two sites in Germany and partly via the use of MODIS remotely sensed LAI from the Finland site.Both the diurnal and the seasonal patterns of gross CO₂ uptake were very well simulated (R² = 0.92). A slight seasonal bias may be attributed to leaf ageing. Crop growth was also well simulated; simulated dry matter agreed with field observed data from Germany (R² = 0.90). For LAI, the agreement between the simulated and observed was good (R² = 0.80), giving an indication that functions describing the conversion of fixed CO₂ to dry matter and the subsequent partitioning leaf dry matter and LAI simulation were robust and provided reliable estimates.The MODIS LAI at a resolution of 1000 m agreed poorly (R² = 0.45) with the PIXGRO simulated LAI and the observed LAI at the Finland site in 2001. We attributed this to the coarse resolution of the image and/or the small size of the barley field (about 17 ha or 0.25 km²) at the Finland site. By deriving a regression relation between the observed LAI and NDVI from a higher resolution MODIS (500 m resolution), the MODIS-recalculated LAI agreed better with the PIXGRO-simulated LAI (R² = 0.86).PIXGRO provides a prototype model bridging the disciplines of plant physiology, crop modeling and remote sensing, for use in a spatial context in evaluating carbon balances and plant growth at stand level, landscape, regional, and with some care, continental scales. Since almost 50% of the European land surface is covered by crops, such a model is needed for the dynamic estimation of LAI and NEE of croplands.     

The distribution and net productivity of sublittoral populations of attached macrophytic algae in an estuary on the Atlantic coast of Spain

A short term study was made on the ecology and the net productivity of sublittoral populations of benthic macrophytes in, and near, the Ria de Aldan on the Atlantic coast of Spain. A preliminary survery was made using SCUBA diving techniques and this revealed that the most extensive sublittoral communities were those dominated by Laminaria ochroleuca and/or Saccorhiza polyschides. The effect of depth and the amount and type of water movement on the distribution and productivity of these two populations was studied at 7 localities. There was found to be a narrow zone of transition between the two populations and the depth of this zone was governed by the amount of water movement. The factors which might control the dynamic equilibrium between these two populations are discussed. The total standing crop and productivity per unit area was found to undergo a decrease with both an increase in depth and wave action whilst the highest values of all were in two localities where there was considerable current surge. The maximum productivity of L. ochroleuca (17 metric tons/hectare/annum) was found in the most sheltered locality studied, whilst the highest value for S. polyschides (39 metric tons/hectare/annum) was found where the current surge was greatest but wave action was only moderate. This maximum value for S. polyschides is the highest yet reported for naturally occurring beds of submerged seaweeds. Figures for the net efficiency of energy fixation are presented and discussed.     

Depth limits of Bermudan scleractinian corals: a submersible survey

Depth distribution, zonation pattern and growth morphology of 17 hermatypic and 4 ahermatypic coral species were investigated at eight different locations along the Bermuda platform with the research submersible GEO and by SCUBA diving in August–September 1983. Hermatypic coral growth occurs to a depth of 50 to 70 m, with a single Montastrea cavernosa growing at 78 m. Dominant forms in shallow-water coral communities are Diploria sp. and Porites astreoides, while M. cavernosa, Agaricia fragilis and Scolymia cubensis occur in deep-water associations below 60 m. Vertical visibilities (up to 178 m) and distribution of the photosynthetically active radiation revealed good light penetration values (1% level at about 100 m depth), which should favour hermatypic coral growth to a much greater depth than it actually occurs. Nor should the prevailing temperatures limit the depth of coral growth. Most deep-water hermatypes observed grow on remnants of Pleistocene reefs down to about 60 m. The vast areas of large massed rhodolith nodules below 50 to 60 m are unsuitable bottom for coral colonisation. Macroalgae growth seems to be the strongest factor controlling coral growth in deep water. Bermuda stony corals have a low growth form diversity. Various intraspecific morphs may occur at the same as well as at different depths, with a general trend towards flatter shapes with depth. Comparison with a similar study on Red Sea corals suggests that annual distribution of radiant energy on the most northern Atlantic reefs of Bermuda may be responsible for the occurrence of flat and cuplike growth forms in relatively shallow water, and for the shallower depth limits of hermatypic growth.     

Temporal and vertical distribution of two ecologically different calanoid copepods (<Emphasis Type="Italic">Calanoides carinatu</Emphasis>s Krøyer 1849 and <Emphasis Type="Italic">Lucicutia grandis</Emphasis> Giesbrecht 1895) in the deep waters of the central Arabian Sea

The full-depth vertical distributions of males, females and juveniles of Lucicutia grandis and Calanoides carinatus are presented from the surface down to depths of 3,900 m in the central Arabian Sea at the end of the NE monsoon and the February and October inter-monsoonal periods. L. grandis is a steady component and C. carinatus is a temporal resident of the central Arabian Sea oxygen minimum zone. Maximum abundances of C. carinatus and L. grandis juveniles were found at depths around 600 m, whereas the center of the distribution of L. grandis adults was somewhat deeper at 950 m. Both copepods are indicator species which can help to understand the functioning of the mesopelagic Arabian Sea ecosystem.     

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.     

Diets of four decapod crustaceans (Linuparus trigonus,Metanephrops andamanicus,M. australiensis and M. boschmai) from the continental shelf around Australia

Linuparus trigonus (Palinuridae) was collected from northeast Australia at depths of 220 to 300 m in the austral summer of 1985–1986 and its diet was analysed for diel feeding-periodicity and composition. The sex and size of the lobsters and the depth at which they were caught were recorded. About 35% of the foreguts were less than 10% full. L. trigonus appears to be a predator of slow-moving or nearsessile benthic invertebrates; its diet is mainly bivalves, gastropods, ophiuroids, crustaceans, polychaetes, and foraminiferans. Most dietary items differed significantly between the size classes of lobster. The frequency of crustacean remains increased with depth and more gastropods were consumed by lobsters caught at 260 m than at other depths. No significant periodicity in feeding was found for L. trigonus. The foreguts of three Metanephrops spp. (Nephropidae) collected from north-west Australia in August 1983 (M. andamanicus) and January/February 1984 (M. australiensis and M. boschmai) were nearly empty, and nearly half were less than 10% full. Fish, crustaceans and squids were the most common food items eaten. The main food items varied between the species: M. andamanicus ate nearly equal amounts of fish and crustaceans; M. australiensis ate chiefly crustaceans; M. boschmai mainly ate fish and seldom fed on squid. Metanephrops spp. appear to feed by attacking mobile animals and tearing off appendages or by scavenging.     

Deep Arabian Sea mesozooplankton distribution. Intermonsoon, October 1995

Mesozooplankton (<5 mm) collected by stratified oblique tows with a 1-m² MOCNESS was examined at four stations in the Arabian Sea, with special reference to the bathypelagic zone. The profiles commenced about 20 m above bottom, at 4430 m as a maximum depth. The highest mesozooplankton biomass concentrations (wet weight per cubic meter) were obtained from the surface layer during night. A secondary maximum was situated between 150 and 450 m, with maximum concentrations at daytime. This layer coincided with the daytime residence depth of the deep scattering layer. The standing crop of the mesozooplankton in the upper 1000 m was highest at station WAST at 16°N; 60°E (ca. 47 000 mg m⁻²); station CAST at 14°N; 65°E ranked second (ca. 22 500 mg m⁻²), followed by station SAST at 10°N; 65°E (11 420 mg m⁻²). The differences can be related to different productivity regimes at the sea surface generated by the Findlater Jet during the SW monsoon. The differences in surface production were also reflected below 1000 m depth, in the bathypelagic zone, with mesozooplankton wet weights of 5330 mg m⁻² at WAST, 3210 mg m⁻² at CAST, 3390 mg m⁻² at EAST (15°N; 65°E) and 2690 mg m⁻² at SAST. The decrease of mesozooplankton concentration with depth in the oxygen minimum zone (OMZ) was stronger than in comparable depths of open-ocean areas where an OMZ is absent. Among the discriminated four size classes of mesozooplankton, the largest fraction (2 to 5 mm) indicated a biomass peak at 1200 m depth, which coincided with the lower boundary layer of the OMZ. The rate of decrease of mesozooplankton biomass with depth in the bathypelagic zone was statistically similar between the sites, even though the absolute zooplankton biomass at the sites was different. There is no evidence that the presumed lower carbon degradation rates in the OMZ of the Arabian Sea caused a larger standing crop and less of a decrease in biomass with depth in the bathypelagic zone in comparison to other seas. Received: 16 May 1997 / Accepted: 5 June 1997     

Stable isotope analysis of two species of anguilliform leptocephali (<Emphasis Type="Italic">Anguilla japonica</Emphasis> and <Emphasis Type="Italic">Ariosoma major</Emphasis>) relative to their feeding depth in the North Equatorial Current region

Anguilla japonica leptocephali are transported from their offshore spawning area to their recruitment areas in East Asia, but their depth distributions, food sources and feeding are still poorly known. This study analyzed carbon and nitrogen stable isotope ratios of leptocephali of A. japonica, Ariosoma major and Ariosoma spp., and of particulate organic matter (POM), their likely food source, at five different depths in 2004–2009. We used mixing models to show that A. japonica appeared to be feeding at depths between 5 and 50 m, but sometimes deeper. A. major appeared to have a tendency of mostly feeding at depths of 50 m or shallower. Although the A. japonica and Ariosoma spp. collected in the same area during the leptocephalus stage appeared to have different feeding ecologies possibly related to different types of POM, their different depth distributions, sizes and transport histories may also help explain these differences.     

Distribution of phytoplankton communities in relation to the large-scale hydrographical regime in the Fram Strait

In June and July 1984 phytoplankton distribution was investigated in the Fram Strait between Greenland and Svalbard. Chlorophylla, particulate organic carbon, nitrate and phytoplankton species composition were determined from six different depths in the upper 200 m of the water column. Multivariate analysis methods were applied to identify phytoplankton communities in relation to different hydrographic regimes. Three main domains could be distinguished in terms of both hydrography and biology: (1) the East Greenland shelf polynya with a high biomass mainly produced by chain-forming diatoms, (2) the ice-covered East Greenland Current with an extremely low standing stock dominated by flagellates and (3) the marginal ice zone with a biomass maximum in 20 to 40 m depth formed by diatoms, dinoflagellates andPhaeocystis pouchetii.     

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.