Competitive ranks of three<Emphasis Type="Italic"> Fucus</Emphasis> spp. (Phaeophyta) in laboratory experiments—testing of Keddy's competitive hierarchy model

Keddy's competitive hierarchy model describes species distribution patterns along gradients under equilibrium conditions and can potentially serve as an explanation for zonation patterns of intertidal seaweeds on rocky shores. One of the assumptions of the model is a competitive hierarchy with the top competitor occupying the benign end of the gradient. Another assumption is the consistency of competitive ranks of species in all environmental conditions included in the shared parts of species' fundamental niches. In laboratory replacement series experiments, the competitive ranks of pairs of Fucus species that occupy adjacent zones in the field were analysed and compared to ranks found in previous field experiments. Unattached thalli of Fucus serratus versus F. vesiculosus or F. vesiculosus versus F. spiralis, respectively, were held in aerated beakers to establish the competitive ranking of the three congeners. Each replacement series was conducted at three total densities. F. vesiculosus was clearly competitively dominant over F. serratus. In competition with F. spiralis, F. vesiculosus was only dominant at its lowest absolute input frequencies, but at higher frequencies dominance was reversed. At high densities, the total ranking was F. spiralis > F. vesiculosus > F. serratus, which is the opposite order to that which would be expected from Keddy's model. Although all three species thrived well under the laboratory conditions, the results did not reflect in situ competitive dominances, which may be an effect of nutrient competition in the laboratory. Keddy's assumption that competitive ranks are consistent over the whole range of fundamental niches cannot be supported for Fucus spp. Communicated by K. Lüning     

Interactions of Patella and macroalgae with settling Semibalanus balanoides (L.)

Biological interactions affecting densities of settling and newly-settled Semibalanus balanoides (L.) have been investigated by manipulative field experiments on the Isle of Man.The effects of sweeping by fucoid clumps of different species and Patella browsing have been compared on moderately-exposed shores. Patella allowed barnacle settlement by preventing growth of competing green algae, but reduced post-settlement densities. Small clumps of Fucus spiralis L., F. vesiculosus L, and F. serratus L. all reduced settlement considerably more so than limpets. F. serratus had the greatest sweeping effect.Interactions between macroalgae and Semibalanus balanoides have been investigated at all levels on sheltered shores and low down on more exposed shores. In the Fucus spiralis and F. vesiculosus zones, post-settlement numbers were higher than in adjacent areas where the canopy was removed. Barnacles did not settle readily in the Ascophyllum zone in either experimental or control areas. Settlement occurred in the upper part of the Fucus serratus zone in experimental areas where the canopy was removed but not in control areas. No settlement occurred in either treatment or control areas lower in the F. serratus zone. At all levels on the shore fucoid canopies seemed to reduce cyprid settlement, but the effect was greatest amongst F. serratus where there was total prevention. High on the shore the effect of enhanced post-settlement survival under the canopy outweighs reduction of cyprid settlement thus there are greater numbers in the controls. Competition with red algal turfs was shown to set the lower limit of the barnacle zone on a vertical pier face.     

Numerical taxonomy of some taxa of the genus Fucus in the Iberian Peninsula

A study of morphological variation patterns in three Iberian Fucus species has been carried out. Data on 36 features from 113 specimens have been studied by numerical methods (PCA, discriminant analysis and ANOVA).The PCA ordination displayed a continuous trend of variation in the following Fucus species: F. ceranoides, F. vesiculosus and F. spiralis. However, no obvious morphological discontinuities have been observed. In addition, three varieties of F. spiralis and five of F. vesiculosus have been identified.At the varietal level discriminant functions could be used for identifying 93–100% of the individuals within F. vesiculosus and 72–91% of F. spiralis.The most discriminating diagnostic character appeared to be the midrib size, as detected by ANOVA procedures.Some qualitative characters, such as presence of vesicles, dioecious-monoecious character and receptacle edge shape, frond and receptacle shape, have been also important for discriminating specific and infraspecific taxa.A nomenclatural discussion of varietal taxa is also included.     

DETERMINING THE AFFINITIES OF SALT MARSH FUCOIDS USING MICROSATELLITE MARKERS: EVIDENCE OF HYBRIDIZATION AND INTROGRESSION BETWEEN TWO SPECIES OF FUCUS (PHAEOPHYTA) IN A MAINE ESTUARY1

The high degree of morphological plasticity displayed by species of the brown algal genus Fucus L. is well documented. Such variation is especially pronounced for those estuarine taxa lacking holdfasts (termed ecads) that often bear little resemblance to the attached species from which they are derived. To better understand the systematics of salt marsh fucoids, we developed a suite of four microsatellite‐containing loci capable of distinguishing between F. vesiculosus L. and F. spiralis L. The genetic markers were used to determine the relationships of the fucoid ecads F. vesiculosus ecad volubilis (Hudson) Turner and a muscoides‐like Fucus in the Brave Boat Harbor (ME, USA) estuary. Ecad populations had 2‐ to 3‐fold higher levels of heterozygosity than attached populations of F. vesiculosus and F. spiralis. Further, ecads were “intermediate” between F. vesiculosus and F. spiralis in their allele frequencies and genotype composition. Our data indicate that populations of muscoides‐like Fucus in Brave Boat Harbor mainly consist of F₁ hybrids between F. vesiculosus and F. spiralis, whereas F. vesiculosus ecad volubilis may arise through backcrosses between F. vesiculosus and other fertile hybrids. Finally, our data support the hypothesis that introgression has occurred between attached populations of F. vesiculosus and F. spiralis.     

Unravelling the complexity of salt marsh ‘Fucus cottonii’ forms (Phaeophyceae,Fucales)

Genetic affiliation, nuclear DNA content, and gamete functioning were examined in small salt marsh Fucus from three localities in western Ireland. Individuals with small and dioecious receptacles were found at all localities, but production of germlings was only evident at Locality 1. Here, the Fucus vegetation formed a morphological cline from F. vesiculosus with bladders in the mid-intertidal to small Fucus individuals lacking bladders in the salt marsh of the upper intertidal. Measurements of nuclear DNA content ranged from 1–1.8 pg at this locality, with F. vesiculosus individuals in the lower range. At the two other localities, the small salt marsh Fucus consisted of distinct morphological entities. Microsatellite analyses revealed that individuals at Locality 2 were derived mainly from F. vesiculosus, whereas those from Locality 3 were hybrids between F. vesiculosus and F. spiralis with greatest affiliation to F. spiralis. While the small salt marsh Fucus forms from Locality 2 had high nuclear DNA content (c. 4 pg) and were probably octoploids, the small salt marsh Fucus from Locality 3 formed two groups: one with high (3.9–4.6 pg) and one with low (1.5–1.9 pg) nuclear DNA content. Nuclear DNA content measured in individuals from Locality 3 varied between 1.1–2.8 pg in F. vesiculosus and 2–3.5 pg in F. spiralis, and showed a more or less stepwise increase in both species, consistent with polyploidy. We hypothesize that the small salt marsh Fucus forms originate from genome size changes in the parental taxa.     

Isolation and cross‐species amplification of microsatellite loci from the fucoid seaweeds Fucus vesiculosus,F. serratus and Ascophyllum nodosum (Heterokontophyta,Fucaceae)

The Fucaceae is a family of brown seaweeds that dominate and frequently co‐occur on North Atlantic rocky shores. We developed nine polymorphic microsatellite markers for the fucoid seaweeds Fucus vesiculosus, F. serratus and Ascophyllum nodosum using a combined, enriched library. Six of these loci were polymorphic in at least two species, showing from two to eight alleles with heterozygosities ranging from 0.41 to 0.85. Loci were also tested on F. spiralis, revealing five polymorphic microsatellite loci in this species.     

Density dependent grazing effects of the isopod Idotea baltica Pallas on Fucus vesiculosus L in the Baltic Sea

In the Baltic Sea, abiotic factors are often supposed to explain the distribution of the key species Fucus vesiculosus. Still, in many areas, decline of F. vesiculosus has coincided with mass occurrence of the herbivorous isopod Idotea baltica. The aim of this work was to examine whether, how and at what densities I. baltica can affect the distribution of F. vesiculosus in the central Baltic proper. Both large-scale field surveys and a two-week grazing experiment have been performed.In the field survey there was a correlation between density of I. baltica and reduction in depth penetration of F. vesiculosus. At 80 animals per 100 g F. vesiculosus wet weight, the depth penetration of the F. vesiculosus belt was reduced by 2.5 m within a year. In the grazing experiment there was a correlation between density of I. baltica and loss of F. vesiculosus biomass and meristems. In the controls biomass and number of meristems increased by 50%, while at 20 animals per 100 g of F. vesiculosus there was no net growth of F. vesiculosus. Intensity of grazing did not differ between isopod densities of 20, 40 and 60/100 g. At isopod densities of 80 and 100/100 g though, biomass and meristems decreased by 50%, indicating a threshold for the survival of F. vesiculosus in the experiment. At all densities the isopods preferred younger tissue to older.Our results indicate that grazing by Idotea baltica is an important structuring factor in the Baltic Fucus vesiculosus populations.     

PROTEINS IMMUNOLOGICALLY RELATED TO DEHYDRINS IN FUCOID ALGAE

Adult fucoid algae on Atlantic shores have well-characterized, species-specific tolerances to the varying levels of desiccation that occur from the low to high intertidal zones; however, less is known about embryonic tolerances and their mechanistic basis. We investigated this by 1) exposing embryos of Fucus evanescens C. Agardh, F. spiralis L., and F. vesiculosus L. from the Maine shore to osmotic desiccation in hypersaline seawater and 2) examining whether these embryos contain species-specific dehydrins, proteins first identified in higher plants that are hypothesized to confer tolerance to dehydration. Embryonic survival when cultured in hypersaline seawater >100 practical salinity units (psu) correlated with the position of these species in the intertidal zone (F. spiralis > F. vesiculosus > F. evanescens), but all 1-day-old embryos of these species tolerated treatment with 100 psu or lower seawater. Proteins (17–105 kDa) immunologically related to dehydrins were detected on western blots with dehydrin antibodies raised against a synthetic peptide representing the conserved motif of dehydrins in higher plants. These proteins were constitutive and unstable when subjected to prolonged (>15 min) temperatures above 55° C, unlike most higher plant dehydrins, which are inducible and remain soluble at 75°–100° C. The presence of these proteins was species- and stage-specific. Sperm of F. vesiculosus had a characteristic protein of 76 kDa, whereas eggs and embryos (6 h to 3 days old) had a 92-kDa protein. By 1 week of age, expression of the 92-kDa protein decreased, and the 35-kDa protein of adults was present. Embryos of A. nodosum L. and Pelvetia compressa J. Agardh DeToni contained an 85-kDa protein rather than the 92-kDa protein of Fucus embryos (F. distichus L., F. evanescens, F. spiralis, and F. vesiculosus). The 92-kDa protein became more abundant in embryos exposed to hyperosmotic seawater at 50 psu (F. evanescens and F. vesiculosus) or 150 psu (F. spiralis); however, dehydrin-like proteins of some molecular masses decreased in abundance simultaneously. Further characterization of these proteins is required to establish whether they protect embryos against intertidal desiccation.     

GENETIC ISOLATION BETWEEN THREE CLOSELY RELATED TAXA: FUCUS VESICULOSUS,F. SPIRALIS,AND F. CERANOIDES (PHAOPHYCEAE)1

All traditional markers, both phenotypic and phylogenetic, have failed to discriminate between the taxa composing the Fucus vesiculosus L., F. spiralis L., and F. ceranoides L. species complex, particularly in Brittany (France), so we used five microsatellite markers to compare the allelic frequencies of populations of the three taxa in this region. The aim of this study was to assess whether the different populations were grouped according to their geographical location, their habitat (open coast versus estuary), or their a priori taxonomic assignment. Species‐specific alleles were identified at one locus, demonstrating the utility of microsatellite markers for recognizing the three taxa in Brittany. Moreover, our results clearly support the separation of F. vesiculosus, F. spiralis, and F. ceranoides into distinct species, independently of geography. We also identified genetic differentiation between estuarine and coastal populations of F. vesiculosus.     

Factors controlling the upper limits of fucoid algae on the shore

Year-round observations on the condition of intertidal seaweeds growing in situ on the shore, show that the upper limits of the zones characterized by Pelvetia canaliculata (L.) Done et Thur., Fucus spiralis L. and Ascophyllum nodosum (L.) Le Jol. were periodically pruned back by environmental conditions. The uppermost plants of each species showed clear signs of tissue damage 21 to 28 days after a time when drying conditions coincided with neap tides which exposed the plant to aerial conditions for long periods. High air temperatures aggravated the damage, but neither frost nor prolonged rain had any obvious adverse effects. On spring tides the plants were wetted every day and no damage resulted regardless of the weather.These species clearly all reach up to their physiological limits on the shore investigated, but presumably Fucus vesiculosus L. and F. serratus L. do not, for they were never observed to show signs of tissue damage attributable to exposure to air. Transplant experiments did, however, prove that F. serratus cannot survive in the F. spiralis zone and nor can F. spiralis persist in the Pelvetia canaliculata zone.Laboratory experiments also demonstrated that the ability to tolerate desiccation and then to resume photosynthesis and growth when re-submerged was greatest in P. canaliculata, the species found highest on the shore, and was progressively less in species inhabiting successively lower levels.     

Factors controlling the lower limits of fucoid algae on the shore

Field and culture studies on fucoid alga of the upper shore showed that their lower limits of distribution were determined largely by interspecific competition. Pelvetia canaliculata (L.) Dcne. et Thur., which is strictly confined to the highest algal zone, grew much more slowly, both in culture and on the shore, than did Fucus spiralis L., which occupies the zone immediately below Pelvetia. When transplanted to the Fucus spiralis zone, macroscopic Pelvetia thalli grew normally, but Pelvetia zygotes which germinated within this zone reached macroscopic size only when competing Fucus spiralis was repeatedly removed.Both species required high light levels to grow in culture, yet their embryos remained viable for long periods in total darkness. Thus, Pelvetia cannot grow in the shade of Fucus spiralis, but actual removal of the Pelvetia germlings from the Fucus spiralis zone must be affected by some other factor.F. spiralis grew vigorously when transplanted to M.T.L., a level at which it is normally rare. In culture, its embryos grew more slowly than those of the species found lower on the shore such as F. vesiculosus L. and F. serratus L.; hence interspecific competition may again be involvedYoung Ascophyltum nodosum (L.) Le Jol. plants grew almost as slowly as those of Pelvetia, yet Ascophyllum dominates the middle shore. In culture it showed only slightly greater tolerance of low light intensity than other fucoids but, unlike Pelvetia, persisted and grew beneath a Fucus canopy in the field. The possibility that differences in life history and palatibility to grazing molluscs contribute to the disparate competitive abilities of Pelvetia and Ascophyllum is discussed.     

Maintenance of zonation patterns in two species of flat periwinkle,Littorina obtusata and L. mariae

The zonation patterns of Littorina obtusata (L.) and Littorina mariae Sacchi et Rastelli were shown to be quite distinct on a sheltered rocky shore. L. obtusata was found at all the heights sampled; it reached peak numbers at mid shore on the alga Ascophyllum nodosum L. (Le Jol). There was no difference in the tidal height occupied by adults or juveniles; or in the mean size of L. obtusata along the vertical gradient of the shore. In contrast L. mariae occurred exclusively low on the shore, on Fucus serratus L. Translocation of the two species within their respective levels resulted in random movement after 4 days, although initial movements after 1 and 2 days were sometimes directional. Animals transplanted to the normal level of the other species showed directional movement towards their home zone; this was most pronounced after 4 days. There was no difference in the distance moved by the two species, although the distance moved did vary with tidal height, both species moving further at mid shore than low shore. Distances moved by littorinids at replicate areas in the low shore were similar but those at mid shore did vary. There was an interaction between the species and the different tidal heights which revealed that transplanted species moved further than translocated species at the same tidal level. However, this was only significant in the case of L. mariae. It is suggested that the close relationship between the winkles and their host algae may direct the homing behaviour of displaced individuals.     

Effects of filamentous algae and deposited matter on the survival of Fucus vesiculosus L. germlings in the Baltic Sea

As a result of increased nutrient levels in the Baltic Sea during thepast 50 years, mass developments of filamentous algae have become a commonfeature along the Swedish east coast and deposition of organic matter has alsoincreased. To test whether these two factors have any effects on the early lifestages of Fucus vesiculosus a number of laboratory andfield studies were conducted. The amount of epilithic and epiphytic filamentousalgae on F. vesiculosus and the amount of deposited matterin the littoral zone were quantified during the two reproductive periods ofF. vesiculosus, early summer (May–June) and lateautumn (September–October). Both filamentous algae (Cladophoraglomerata) and deposited matter (introduced either before or aftersettlement of fertilized eggs) were shown to significantly decrease the numberof surviving germlings. The survival of germlings seeded on stones withfilamentous algae, or seeded on culture dishes concurrently with the lowestconcentration of deposited matter (0.1 g dm^–2),was 5% or less. In the field, the amount of filamentous algae was significantlyhigher during F. vesiculosus summer reproduction, whereasthe amount of deposited matter collected in traps was significantly higherduring the period of autumn reproduction. The greatest biomass of filamentousalgae was observed at sheltered sites. Based on the negative effects offilamentous algae and deposited matter on Fucusrecruitmentand the observation of local and seasonal differences in abundance offilamentous algae and deposition, we suggest that the prerequisites for thesurvival of either summer or autumn-reproducing populations of F.vesiculosus in the Baltic Sea may differ locally.     

Influence of abiotic factors on the structure of the population of the brown alga <Emphasis Type="Italic">Fucus vesiculosus</Emphasis> in East Murman (Barents Sea)

The peculiarities of the structure of the population of the brown alga Fucus vesiculosus in East Murman at different combinations of abiotic factors were studied. Salinity below 10‰ and high surf activity reduced the average life span of the plants (to 1 year) and caused a significant predominance of female specimens (60–90% of the fertile specimens). The proportion of female specimens increased with age. The greatest average age (3 branchings) and the highest survival of F. vesiculosus occurred in the wave-protected parts of bays. The distribution of F. vesiculosus was related to water movement intensity, salinity, and substrate type. The size-weight characteristics of F. vesiculosus thalli were decreased during maximum salinity fluctuations. The optimal conditions for this species were those existing on a weakly protected shore with short-term fluctuations of salinity (24–25‰).     

Interspecific interactions under fertilization among Elymus nutans,Festuca sinensis and Festuca ovina on the eastern Qinghai‐Tibetan plateau

A field replacement experiment was used to study the interspecific interaction among three perennial grasses (Elymus nutans, Festuca sinensis and Festuca ovina) that are distributed widely on the east Qinghai‐Tibetan plateau. The experiment consisted of four different species mixtures at four seeding densities and two fertilizer levels. Above‐ground biomass, relative yield and complementary effect were determined from harvested shoot dry weights. The results showed that above‐ground biomass was greater in all species mixtures than in monocultures. The difference between the observed and expected relative yield was greater than zero in all mixtures for E. nutans and was greater than zero in the F. sinensis/F. ovina mixture, but was below zero in all other mixtures for F. sinensis, and was below zero in all mixtures for F. ovina. The complementary effect was more negative across all seeding densities except at a seeding density of 400 seeds/m², and was negative across all mixtures except the F. sinensis/F. ovina mixture. In addition, fertilization had an insignificant impact on the relative yield, but a significant impact on the complementary effect. Fertilization enhanced negative interspecific interaction among the species.     

Nitrate uptake varies with tide height and nutrient availability in the intertidal seaweed Fucus vesiculosus

Intertidal seaweeds must cope with a suite of stressors imposed by aerial exposure at low tide, including nutrient limitation due to emersion. Seaweeds can access nutrients only when submerged, so individuals living higher compared to lower on the shore may have adaptations allowing them to acquire sufficient amounts of nutrients to survive and maintain growth. Using a combination of observations and experiments, we aimed to identify intraspecific variation in nitrate uptake rates across the intertidal distribution of F. vesiculosus, as well as test for acclimation in response to a change in tide height. We replicated our study at sites spanning nearly the entire Gulf of Maine coastline, to examine how local environmental variability may alter intraspecific variation in nitrate uptake. We found that average nitrate uptake rates were ~18% higher in upper compared to lower intertidal Fucus vesiculosus. Furthermore, we found evidence for both acclimation and adaptation to tide height during a transplant experiment. F. vesiculosus transplanted from the lower to the upper intertidal zone was characterized by increased nitrate uptake, but individuals transplanted from the upper to the lower intertidal zone retained high uptake rates. Our observations differed among Gulf of Maine regions and among time points of our study. Importantly, these differences may reflect associations between nitrate uptake rates and abiotic environmental conditions and seaweed nutrient status. Our study highlights the importance of long‐term variation in ambient nutrient supply in driving intraspecific variation of seaweeds across the intertidal gradient and local and seasonal variation in ambient nutrient levels in mediating intraspecific differences.     

The vertical distribution of Chthamalus montagui and Chthamalus stellatus (Crustacea,Cirripedia) in two areas of the NW Mediterranean Sea

The Mediterranean Sea is characterised by a small tidal range (0.3–1 m). Despite this, intertidal communities are well established and their upper limits often extend above mean high water level. Organisms living in the intertidal region and in the supralittoral zone rely on both tides and wave action to perform their biological functions. Lack of food, desiccation and predation are common stresses in such a harsh environment. The present study deals with the vertical distribution of two species of intertidal barnacles, Chthamalus montagui Southward and Chthamalus stellatus (Poli), which are the main constituents of the barnacle belt along Mediterranean rocky shores. Previous work, carried out in the Atlantic, showed that where the distribution ranges of the two Chthamalus species overlap, C. montagui is more common in the upper barnacle zone while C. stellatus is dominant lower down. The main aims of our study are: (1) to establish if there is a relationship between position and extension of the barnacle belt on the shore and tidal range and/or wave exposure, (2) to test the hypothesis that in the study areas C. montagui is more abundant than C. stellatus high on the shore, and that the pattern is reversed lower down. Barnacle populations were monitored in summer 1998 in the Gulf of Genoa (Ligurian Sea) and in the Gulf of Trieste (North-Adriatic Sea). The two areas differ in tidal range and hydrodynamism, the former presenting quite strong wave action and a tidal range of 30 cm, the latter having limited wave action and 1 m tidal range. Three shores were randomly selected in each gulf and two transects on each shore. Counts of barnacles in 10 ^* 10 cm quadrats were done at different shore heights along each transect. The data was subjected to analysis of variance. Results showed that a more pronounced hydrodynamic regime corresponded to a shift of the barnacle belt towards the higher shore (Gulf of Genoa), while in more sheltered areas (Gulf of Trieste), the barnacle distribution was confined to the intertidal region. The relative spatial distribution of C. montagui and C. stellatus within the barnacle belt varied locally, even between transects on the same shore, and this obscured the distribution pattern along the vertical gradient. Nevertheless, it was still possible to conclude that at mid and high shore in Genoa, C. stellatus was more abundant than C. montagui, while in Trieste the pattern was reversed.     

Characterization of microsatellite loci in the marine seaweeds,Fucus serratus and F. evanescens (Heterokontophyta; Fucaceae)

Fucus serratus and F. evanescens commonly occur on Northern European shores. Nine microsatellite loci were developed for F. serratus (8–22 alleles, observed heterozygosities = 0.367–0.850) and one for F. evanescens (seven alleles, observed heterozygosity = 0.804). Cross‐amplification was apparent, as five F. serratus loci were polymorphic in F. evanescens and 2–5 were polymorphic in F. vesiculosus, F. distichus, and F. spiralis.     

Distinct patterns of nitrate reductase activity in brown algae: light and ammonium sensitivity in Laminaria digitata is absent in Fucus species1

Fucus and Laminaria species, dominant seaweeds in the intertidal and subtidal zones of the temperate North Atlantic, experience tidal cycles that are not synchronized with light:dark (L:D) cycles. To investigate how nutrient assimilation is affected by light cycles, the activity of nitrate reductase (NR) was examined in thalli incubated in outdoor tanks with flowing seawater and natural L:D cycles. NR activity in Laminaria digitata (Huds.) Lamour. showed strong diel patterns with low activities in darkness and peak activities near midday. This diel pattern was controlled by light but not by a circadian rhythm. In contrast, there was no diel variation in NR activity in Fucus serratus L., F. vesiculosus (L.) Lamour., and F. spiralis L. either collected directly from the shore or maintained in the outdoor tanks. In laboratory cultures, transfer to continuous darkness suppressed NR activity in L. digitata, but not in F. vesiculosus; continuous light increased NR activity in L. digitata but decreased activity in F. vesiculosus. Furthermore, 4 d enrichment with ammonium (50 μmol · L^?1 pulses), resulted in NR activity declining by >80% in L. digitata, but no significant changes in F. serratus. Seasonal differences in maximum NR activity were present in both genera with activities highest in late winter and lowest in summer. This is the first report of NR activity in any alga that is not strongly regulated by light and ammonium. Because light and tidal emersion do not always coincide, Fucus species may have lost the regulation of NR by light that has been observed in other algae and higher plants.     

An ecological study of fucus spiralis L.

An ecological study of Fucus spiralis L. has been made at Jaffrey Point, Newcastle, New Hampshire and the adjacent Great Bay Estuary System from 1972–1975. The distribution, growth, reproductive periodicity, attrition and longevity of the plants are described in relation to a variety of environmental factors. F. spiralis shows a broad but discontinuous estuarine distribution within the Great Bay Estuary System. The presence or absence of appropriate substrata is considered to be a factor determining its discontinuous distribution, since it is usually associated with metasedimentary or metavolcanic rock outcrops. The maximum growth and reproduction of F. spiralis are during the summer. The summer growth rates ranged from 1.9 to 2.8 cm/month while the average growth rate throughout the year was 1.2 cm/month.F. spiralis populations showed two periods of major attrition, namely, during the winter and summer. The average longevity of F. spiralis plants is ≈ 2 yr. The F. spiralis zone lies in the uppermost intertidal area between +2.12 and +2.31 m above M.L.W. There is a micro-stratification of biomass, stature, and reproductive activity within this zone. Average plant weight, length, and fertility tend to decrease with increasing elevation.