Ecological aspects of Sargassum muticum (Fucales,Phaeophyta) in Baja California,Mexico: reproductive phenology and epiphytes

The reproductive phenology and epiphytic macroalgae of Sargassum muticum were studied through an annual cycle (September 1987 to November 1988) at two sites on the northwestern coast of Baja California, Mexico, which were subjected to different degrees of wave exposure. Sargassum muticum is a brown alga of Japanese origin, now considered a permanent member of the marine flora of Baja California. A similar reproductive development was observed at both sites, with a maximum percentage of reproductive plants from May to July (spring–summer) and minimum from December to March (winter). Reproductive plants were found throughout the year. A total of 48 species of epiphytes were identified and seasonal variation in their diversity was observed. The greatest diversity was found at the more protected site.     

Isolation of protoplasts from Fucus serratus and F. vesiculosus(Fucales, Phaeophyceae): factors affecting protoplast yield

Protoplasts were isolated enzymatically from meristematic tissues of the brown algae, Fucus serratus, using a combination of 2% cellulase R-10 Onozuka, 0.5% macerozyme and 1% crude extract of gland gut of Aplysia vaccaria. The main factors affecting protoplast yield were identified. Protoplasts were produced in large quantities from apical region of thallus and from plantlets compared to mature explants. Yields were greatly improved by the addition of sodium citrate and bovine serum albumin in the enzymatic solution and could reach 5.8 × 10⁶ protoplasts per gram of fresh wt. The applicability of these optimal parameters to other species Fucus vesiculosus was shown.     

Size-dependence of reproductive allocation of Sargassum thunbergii (Sargassaceae, Phaeophyta) in Bohai Bay, China

Reproductive allocation (the proportion of biomass allocated to reproductive tissue, RA) in Sargassum thunbergii was studied in Yantai, Shandong Peninsula, southern coast of Bohai Bay, China. Annual reproduction initiated in mid-June and peaked in mid-July (90 ± 8% fertile thalli and 75 ± 6% RA mean). Both RA and percentage of fertile thalli exhibited significant temporal variations during reproduction. Sterile thalli were only observed in small length hierarchies at peak reproduction and mean values of RA showed a significantly hierarchical variation, suggesting that the size of thalli played an important role in reproduction and RA were size-dependent. Numerous receptacles were produced along the lateral branches during the reproductive period. A distinct seasonal pattern was observed wherein the presence of lateral branches was followed by the onset of reproduction. RA was positively correlated with the number of lateral branches, as well as the total length of lateral branches. In addition, fertile thalli decayed quickly after peak reproduction. The probability of decay was evidently higher for fertile than for sterile thalli, because all surviving thalli were sterile and short during July–August. So, a trade-off between reproduction and survival may exist at individual levels in S. thunbergii.     

Seasonality of standing crop of a Sargassum (Fucales,Phaeophyta) bed in Bolinao,Pangasinan, Philippines

The seasonality of standing crop of a Sargassum bed was investigated by conducting monthly sampling from February 1988 to July 1989. Environmental parameters of water movement, salinity, number of daytime minus tides, and water temperature were also measured. An intra-annual pattern of variation in standing crop of Sargassum crassifolium, S. cristaefolium, S. oligocystum, and S. polycystum was observed. Standing crop was generally lowest in February, March, April, or May, and highest in November through January. Sargassum accounted for about 35 to 85% of the monthly algal standing crop of the bed, and the observed variation in overall standing crop of the bed generally reflected the standing crop of Sargassum. The seasonality of the standing crops of the associated algal divisions also followed an annual cycle, but their maximum and minimum standing crops did not coincide with those of Sargassum. Individually, as well as collectively, the standing crops of the Sargassum spp. were poorly correlated with the environmental factors observed.     

Canopy characteristics of the brown alga Sargassum muticum (Fucales,Phaeophyta) in Lake Grevelingen,southwest Netherlands

The present distribution of the invasive brown alga Sargassum muticum in the southwest Netherlands is updated. Populations of the alga were found to remain at their 1985 level in Lake Grevelingen, with a small eastward expansion into the Eastern Scheldt estuary. A new population for the brackish, non-tidal Lake Veere is reported. Within Lake Grevelingen S. muticum forms a persistent, extensive canopy of 100% cover (4,442.5 ± 525.6 g fresh wt m^–2, 640.3 ± 75.8 g dry wt m^–2) that has a marked effect upon the penetration of photosynthetically active radiation (PAR) (reduced by 97% at 0.1 m). Surface sea water temperatures can be elevated by 2.7 °C above water not associated with a Sargassum canopy; furthermore, the dense canopy shades and hence reduces water temperatures below 0.1 m depth. Productivity studies indicate that assimilation occurs in the upper levels of the canopy (57.09 µg C mg dry wt^–1 m^–2 at a mean PAR rate of 106.7 J cm^–2 h^–1). Self-shading and a resultant decrease in the rate of assimilation was evident below the canopy.     

Recolonization and restoration of upper intertidal Fucus gardneri (Fucales,Phaeophyta) following the Exxon Valdez oil spill

The Exxon Valdez oil spill in March 1989 and subsequent cleanup caused injury to intertidal Fucus gardneri populations especially in the upper intertidal. A survey in 1994 in Prince William Sound, Alaska showed that the upper boundary of Fucus populations at oiled sites was still an average of 0.4 m lower than the upper boundary at unoiled sites.Restoration of severely damaged Fucus populations was started on a small-scale at a heavily oiled rocky site in Herring Bay, Prince William Sound. Experiments employed mats of biodegradable erosion control fabric to act as a substratum for Fucus germlings and to protect germlings from heat and desiccation stress. A series of plots was covered with mats made from a resilient coconut-fiber fabric in June 1993. Half of the mats were inoculated with Fucus zygotes. A series of uncovered control plots was also monitored. There was no enhancement of Fucus recruitment on the rock surfaces under the mats. Dense populations of Fucus developed on the surface of all of the mats by the summer of 1994. The natural rock surfaces in the control plots, both inoculated and not, were barren of macroscopic algal cover. By September 1994, the juvenile thalli on the mats were approximately 2 cm in length. Inoculating the mats had an effect only in the upper region of the intertidal. It is expected that the thalli will become fertile during the 1995 season. These thalli may serve as a source of embryos to enhance the recovery of new Fucus populations in this high intertidal area.     

The effect of a liquid seaweed extract from Ascophyllum nodosum (Fucales,Phaeophyta) on the two-spotted red spider mite Tetranychus urticae

This paper presents evidence from an initial trial in favor of claims that the liquid seaweed extract of Ascophyllum nodosum, marketed in the UK as Maxicrop, can reduce numbers of the two-spotted red spider mite Tetranychus urticae on crop plants. Seven applications of Maxicrop Triple over 20 days significantly suppressed the population build-up of two-spotted red spider mites on treated strawberry plants (Fragaria sp. var. Redgauntlet) raised under high polythene tunnels as compared to untreated controls.     

Comparison of the structure of populations of Ascophyllum nodosum (Fucales,Phaeophyta) at sites with different harvesting histories

Changes in the structure of the Ascophyllum nodosum population at Pubnico, southwest Nova Scotia, Canada, at an experimental site subjected to mechanical harvest and at two control sites never subjected to mechanical harvest were monitored from 1991 to 1994. A bimodal population structure measured in terms of plant length was characteristic of all these sites before the experiment. The population structure of the experimental site became unimodal immediately after experimental harvest by machine and remained unimodal for the subsequent two years. However, a bimodal population structure began to appear in the third year. A bimodal population structure remained evident at the control site with bedrock as the substratum but was less evident at the other control site where the substratum is made up of boulders and cobbles. Movement of loose rocks with rockweeds still attached may have contributed to the less distinct modal structure of this control site. Other sites with different harvesting histories monitored in the summer of 1992 showed some interesting patterns. A unimodal population structure was evident in Argyle Sound and Pubnico Point South and at Charlesville, which had been harvested one and two years before, respectively. A bimodal population structure was more evident at Frenchman's Point, which had been harvested three years prior. The rate of change from a unimodal to a bimodal population structure may depend on the intensity of harvest. Extensive canopy removal in intensively harvested areas may be conducive to an influx of recruits and to regeneration from the holdfast. Hence, plant length modal structure may be a useful measure of the relative state of recovery of a harvested population.     

On the origin and development of vacuoles in promeristematic cells ofCystoseira stricta sauvageau (Phaeophyta,Fucales)

Summary Promeristematic cells of theCystoseira thallus have been studied by transmission electron microscopy and cytochemistry in order to observe vacuole formation and development.Vacuolation seems to occur by different processes. Those here concerned involve the intervention of provacuolar formations, originating probably from G.E.R.L., in the sequestration of cytoplasmic materials. The sequestrated portion then undergoes a degradation. These observations agree with the processes recently reported in root meristematic cells of two higher plants:Euphorbia characias andHordeum sativum.     

Competitive interactions between Fucus spiralis L. and F. vesiculosus L. (Fucales,Phaeophyta)

Fucus spiralis forms a conspicuous belt in the upper intertidal on rocky shores of the NW Atlantic. The objective of this study was to determine whether competition among congeners plays a role in restricting the distribution of F. spiralis to the upper shore. A replacement series design was used to test the growth performance of F. spiralis and F. vesiculosus in monocultures and in mixtures set up in the mid shore level on an exposed rocky coast. For F. spiralis and F. vesiculosus, all individual and relative crowding coefficients were < 1 and > 1, respectively. Hence, F. vesiculosus succeeded relative to F. spiralis in all mixtures tested. This finding was confirmed by graphical analysis. Ratio diagrams showed that the outcome of long term interaction among the species is extinction of F. spiralis. The results lead to the conclusion that interaction among congeners is a major determinant of the restricted distribution of F. spiralis.     

Cleavage of DNA by brown algal polyphenols

Extracts of marine algae have been tested to determine their ability to cleave DNA. The species producing positive results wereAscophyllum nodosum, Fucus serratus, F. spiralis, F. vesiculosus, Halidrys siliquosa andHimanthalia elongata. Partial purification of each extract by dialysis against water revealed that the active compounds in each species were high molecular weight polyphenols.     

Spatial variation in polyphenolic content of Ascophyllum nodosum (Fucales,Phaeophyta)

Spatial variation in polyphenolic content in annual shoots of the brown alga Ascophyllum nodosum was quantified using a hierarchical sampling design. Three sampling levels, covering distances of 10⁰–10⁶ m, were used. Comparisons were made between two areas, Tjärnö on the Swedish west-coast and the Isle of Man in the Irish Sea, with very different types of environmental conditions. No significant differences in mean polyphenolic levels were found between the two study areas (6.6% of dry mass at Tjärnö and 9.2% at the Isle of Man), whereas significant and substantial differences were found among sites within areas (range 5.7%–11.4%) and among quadrats within sites (range 3.7%–13.1 %). The extensive variation at the smaller spatial scales points out the importance of using thorough sampling procedures at all levels in large-scale studies on algal polyphenolics, e.g. biogeographical comparisons, which have been neglected in several previous studies. Moreover, the results imply that experiments on causal factors of polyphenolic variation should be designed to explain the spatial scales on which the factors are impportant. This study also investigated the relationship between polyphenolic concentration and both plant size and mean area of annual shoots. The mean area was used as an estimate of the mean growth rate of the annual shoots within an individual. No significant relationships were found between shoot growth rate, or plant size, and polyphenolic levels in annual shoots at any of the three spatial scales that were investigated.     

Electron and immunofluorescence microscopy on the fertilization ofFucus distichus (Fucales,Phaeophyceae)

Summary Processes of fertilization and zygote development inFucus distichus were studied by indirect immunofluorescence microscopy using anti- tubulin antibody and electron microscopy. Just after plasmogamy, sperm aster formation occurs during migration of a sperm nucleus toward an egg nucleus at the center of cytoplasm. Only sparse microtubules (MTs) exist around the egg nucleus. The sperm aster can be observed till karyogamy, but afterwards vanishes. Accompanying sperm aster formation, cortical MTs which are reticulately arranged develop further in the zygotes. In 4 h-old zygotes, characteristic structures which are composed of fine granular masses and consist of intermixed dense and lighter staining areas appear around the nucleus. These structures cannot be detected with anti- tubulin immunofluorescence microscopy. The two centrioles derived from the sperm separate and migrate to both poles. In 4 h-and 8 h-old zygotes, there are no defined MT foci around the zygote nucleus and MTs radiate from the circumference of it. In 12 h-old zygotes, each centriole has migrated to the poles and derivative centrioles are generated. The fine granular masses also migrate to both poles and finally disappear accompanying the appearance of numerous MTs radiating from the poles. Therefore, two distinct MT foci appear from 12 h onwards. Progressive stages of nuclear division were also examined with electron and immunofluorescence microscopy in 16 h-old zygotes. The sperm chloroplast with an eyespot and the sperm mitochondria with an intercristal tubular structure, which are distinctive from those of egg, can be detected after plasmogamy and karyogamy. The sperm chloroplast is still present in 16 h-old zygotes.     

Polar acyclic diterpenoids from Bifurcaria bifurcata (Fucales, Phaeophyta)

From the lipophilic extract of the brown alga Bifurcaria bifurcata collected off the Atlantic coast of Southern Brittany (Quiberon, France), five polar linear diterpenoids have been isolated. These metabolites have been identified as hydroxylated derivatives of 13-oxo- and 13-hydroxygeranylgeraniol. Their structures were characterized on the basis of chemical and spectral evidence including two-dimensional NMR experiments and mass spectrometric techniques. The absolute configuration of the 13-position has been determined, for the 13-hydroxygeranylgeraniol derivatives, to be R by means of a modified Mosher's method and therefore that of 13-hydroxygeranylgeraniol (eleganediol) has been revised. Along with these compounds, three related known geranylgeraniol derivatives were also identified, and these data were used for chemotaxonomical purposes.     

Long-term decline and recent recovery of Fucus populations along the rocky shores of southeast Sweden, Baltic Sea

The Fucus populations on rocky shores along 300 km of the coastal waters of southeast Sweden in the Baltic proper have been studied since 1984 at a number of fixed sites as part of monitoring programmes. This paper describes changes in distribution and abundance of F. vesiculosus and F. serratus during the period 1984–2001. Sheltered sites showed a consistent temporal and spatial pattern of Fucus spp. distribution over a coastline of 300 kilometres. The depth penetration and abundance of Fucus spp. increased during the 1980s. Around 1990 the development reversed as a consequence of grazing and in 1997 many sites were almost devoid of Fucus spp. Since 1998 both abundance and depth penetration have increased again, possibly as a result of local measures against eutrophication. Exposed sites, on the other hand, lost their Fucus populations at the beginning of the 1990s, and they have not recovered. Extended field studies lead us to deduce that the fixed sites referred to above were representative of the Fucus populations in the area investigated. Major declines, both at sheltered and exposed sites, are attributed to grazing by the isopod Idotea baltica. The populations of I. baltica may have been favoured by the continuing eutrophication of the Baltic, a series of mild winters in the 1990s, and a contemporary decline in some potential predators.     

Physiological energetics of the zebra musselDreissena polymorpha in lakes I. Growth and reproductive effort

Shell growth of tagged zebra mussels (Dreissena polymorpha) was monitored in lakes at 3 sites over 1 1/2 years. It varied greatly with the season and was almost absent during winter months. Shell growth was significantly correlated with seston concentration, but not with water temperature. The theoretical maximum size (L∞) of the v. Bertalanffy growth equation did not vary seasonally. Tissue weight underwent a pronounced seasonal cycle. In animals of 20 mm shell length, minimum weights recorded in September only corresponded to one quarter to one third of the maxima in late spring. Tissue weight of animals from the 3 sites was distinctly different. Carbohydrate content of the tissue stayed below 10 per cent and tended to be highest in spring. Spring maxima of lipids were very pronounced. These lipids were primarily located in the digestive gland. These data were combined with data of gonad size by Borcherding (1991). Results imply that production of reproductive tissue even continues at a retarded rate during winter months, if food conditions were favourable. With poor food conditions, no production of reproductive tissue was estimated during winter; this, however, was followed by an elevated rate of reproductive tissue production in spring. Weight specific production decreased with a weight exponent of −0.24. Shell and byssus production contributed only in the range of 10 per cent to total production. Reproductive effort showed maxima of 30 to 45%. It increased with shell length at 2 sites and decreased at the other site with the largest animals.     

Restriction enzyme analysis of variation and taxonomy in the kelp genus Laminaria (Laminariales,Phaeophyta)

High levels of phenotypic variation in kelp species necessitate the use of taxonomic markers that are independent of morphology. Restriction fragment length polymorphism (RFLP) analysis of nuclear DNA can provide such markers. In this paper we present the results of an RFLP analysis of cytoplasmic ribosomal DNA (rDNA) in three Laminaria species (L. agardhii, L. digitata, L. groenlandica). Comparison of the restriction maps of the nontranscribed spacer (NTS) in the rDNAs suggests that this method should be useful for the differentiation of these taxa. These results are discussed, as are the applications of RFLP mapping to the identification of field-collected, morphologically variable plants.     

Regeneration from callus of Undaria pinnatifida (Harvey) Suringar (Laminariales,Phaeophyta)

Calli were formed on the explants of midrib, meristem and immature stipe parts from freshly collected Undaria pinnatifida sporophytes. Each part was sterilized by Betadine and ethanol, and was cut into explants. The explants were incubated on an agar medium at 10 hours light and 14 hours dark photoperiod under a photon flux density of 80 µmol m^–2 s^–1. Callus was formed best on the explants of meristem parts at a temperature of 13 °C on PESI medium. Calli were cut off from the explants and were transferred into a sterile liquid PESI medium in flasks. Callus was dark brown in colour and was composed of well-pigmented cells. The cells were loosely bound and were separated by low power sonication, and were easy to attach to vinylon strings. From the calli formed on the explants of meristem parts, entire fronds were regenerated, but from the calli formed on the explants of midrib parts, only thin layered laminae were regenerated. The calli formed on the explants of immature stipe parts did not exhibit any regeneration at all.