STRUCTURE AND DYNAMICS OF A POPULATION OF PALMARIA PALMATA (RHODOPHYTA) IN NORTHERN SPAIN1

Palmaria palmata (Linnaeus) O. Kuntze (Rhodophyta, Palmariaceae) is a seaweed commercially harvested for human consumption. Its population density, size structure, and frond dynamics were investigated from May 1999 to May 2001 at one intertidal locality in the northern coast of Spain, which is within the southern distributional boundary of the species in the eastern Atlantic coasts. The effect of size, age, and the life‐history phase (haploid vs. diploid) on frond growth and mortality were also evaluated. The study was carried out by mapping and monitoring fronds in the field. New fronds (macroscopic recruits or sprouts) appeared in spring, but subsequent mortality of these young fronds and detachment of the host plant led to lower density values in January. Palmaria palmata exhibited a distinctive seasonal growth cycle, with positive net growth from March to August and breakage from August to March. Interannual differences were also detected, with higher net growth in 2000 than in 1999. Net growth was apparently independent of age, reproductive status (fertile vs. reproductive), and life‐history phase (haploid vs. diploid) but was dependent on size, as longer fronds showed minor growth or greater breakage than small ones. Mortality, on the other hand, was more dependent on age than on size in the period analyzed (March–May 2000). Results of the study indicate that both size and age should be included as state variables and temporal changes in transition probabilities considered in the development of demographic models of the species.     

IS THERE AN ECOPHYSIOLOGICAL EXPLANATION FOR THE GAMETOPHYTE–TETRASPOROPHYTE RATIO IN GELIDIUM SESQUIPEDALE (RHODOPHYTA)?1

In the fall, when 61% of the fronds of the Gelidium sesquipedale (Clem.) Born. et Thur. population located in Albufeira (southern Portugal) were reproductive, about 90% of these fronds were tetrasporophytes, whereas an equal percentage of female and male gametophytes was found (5%). The comparison of physiological performances of the reproductive phases (males, females and tetrasporophytes) did not reveal a physiological advantage of tetrasporic fronds. There were no significant differences either in the photosynthesis, nitrogen uptake, nitrate reductase activity, or biochemical composition of adult fronds. On the other hand, vegetative recruitment and spore production in the laboratory were significantly different. The re‐attachment to calcareous substrate and the subsequent rhizoidal growth were faster in tetrasporophytes. Particular levels of temperature, rather than irradiance, had an important effect on the phase differences in the spore release, attachment, and germination rates. Significant results were the higher release of carpospores at all irradiances at 17°C, and the higher attachment percentage of carpospores at 13°C versus tetraspores. Under higher temperatures (21°C), tetraspores showed higher attachment rates while carpospores germinated more. G. sesquipedale cystocarps released carpospores for 2 months, while tetrasporangia stopped shedding tetraspores after 1 month, resulting in a 3‐fold higher production of carpospores than tetraspores. Results showed that vegetative and spore recruitment may explain the low gametophyte–tetrasporophyte ratio of the studied population of G. sesquipedale as opposed to the physiological performance of phases.     

Chondracanthus chamissoi (Rhodophyta, Gigartinales) in northern Chile: ecological aspects for management of wild populations

Abiotic and biotic factors affecting seasonal variations in the biomass andreproductive condition of Chondracanthus chamissoi were evaluatedin a population at La Herradura Bay, northern Chile. During spring,increase in temperature, light, and photoperiod favored the reproductiveactivity of C. chamissoi, contributing to its growth and production ofreproductive biomass. During summer, extremes of temperature and lightavailability were accompanied by bleaching of the thalli, followed bydecomposition and biomass loss, significantly lowering production.Epiphytism and herbivory showed were then at their maximum. Analysis offertility showed that C. chamissoi was in reproductive conditionthroughout the year, with maximum for cystocarpic and tetrasporic plantsduring spring, significantly correlated with total biomass production.Production and liberation of spores and other values for reproductivecapacity showed the highest values in spring. The results of the study,coupled with information from the literature, recommend two commercialharvests during spring, at a time when standing crops are the highest, andvalues for reproductive condition predict adequate expression of the sexualphase. The time of the year suggested as adequate for commercial harvestof this alga probably coincides with the highest quality of its carrageenans,and would precede the phase of local growth cycle, where its biomassbegins to deteriorate due to bleaching, epiphytism and herbivory.     

In vitro recruitment of Ulva sp. and Enteromorpha sp. on gametophytic and tetrasporophytic thalli of four populations of Chondracanthuschamissoi from Chile

Chondracanthus chamissoi is a red alga which is acquiring an increasing economic importance in Chile and becoming a target species for cultivation. Because epiphytism is a major problem in the mariculture of seaweeds, the recruitment of Ulva sp. and Enteromorpha sp. on gametophytic (cystocarpic) and tetrasporophytic thalli of C. chamissoi was tested in vitro on four populations from different locations in Chile. For Ulva sp., the density, cover and length of the recruits varied between the reproductive phases of the host and among the studied populations of C. chamissoi. In most experiments, a larger number of epiphytic thalli was observed on gametophytic plants of C. chamissoi; populations from Calderilla and Lechagua had a higher resistance to epiphytism. For Enteromorpha sp., its ability to grow epiphytically on both phases of the host showed a greater variability, but was inferior to that of Ulva sp. The differential resistance to epiphytism in both reproductive phases and in plant origin indicates the possibility of obtaining selected strains of C. chamissoi with lower susceptibility to epiphytism that could be utilized in planning maricultural programs.     

Factors that affect the re-attachment of Chondracanthus chamissoi (Rhodophyta, Gigartinales) thalli

Vegetative reproduction of Chondracanthus chamissoi by means of fragmentation and re-attachment of thalli is considered an effective strategy for maintaining natural populations of this species. Here, we evaluate the effects of (1) time of drifting thallus, (2) type of substratum, and (3) photon flux density, on the re-attachment capacity of thallus fragments of C. chamissoi. The results show that re-attachment decreases with the time after detachment, and was higher at the lower photon flux densities tested (10 and 40 μmol photons m⁻²s⁻¹), and on calcareous substratum. Secondary attachment discs are formed along the entire surface of the fragment.     

Variation in gametophyte dominance in populations of Chondrus verrucosus (Gigartinaceae,Rhodophyta)

We describe the abundance, including spatial and temporal variability, of phases of the isomorphic Chondrus verrucosus Mikami from Japan. Chondrus verrucosus occurred in a dense (～90% cover) and temporally stable bed on a small, isolated rocky outcrop (Oyakoiwa) in Shizuoka Prefecture. Small vegetative fronds were always much more abundant than large vegetative and fertile fronds over the spring to late summer periods in 1999 and 2000. Over the same period, fertile carposporophytic fronds were generally more abundant than fertile tetrasporophytic fronds, and fertile male fronds appeared infrequently at low densities. Using the resorcinol‐acetal test, we determined the proportion of gametophytes and tetrasporophytes in three populations of C. verrucosus: Oyakoiwa and Noroshi (Shizuoka) in the summers of 1999 and 2000 and Kamehana Point (Miyagi) in autumn 2000. All populations had a significantly higher proportion of gametophytes than tetrasporophytes in both years, although gametophytic proportions were lower at Noroshi (～70%) than at Oyakoiwa (～80%) and Kamehana Point (～97%). However, examination of all isolated individuals sampled on Noroshi showed equal proportions of each phase in 1999, but gametophyte dominance (74%) in 2000. Differences in dispersal and spore production between phases are discussed as mechanisms potentially contributing to variation in gametophyte dominance.     

Spring-Summer Succession of Planktonic Rotifers in a South Andes Lake

The dynamics of planktonic rotifer in Laguna Ezquerra (Rio Negro, Argentina) was studied from October 1988 to March 1989, in relation to food resources and cladoceran populations. During the spring and summer period, total rotifer density differed markedly. In spring rotifer populations remained at low density and an inverse relationship with cladoceran biomass was found. In contrast, in summer, the rotifer densities increased greatly and a positive relationship with cladoceran biomass was observed. Food resources decreased during mid January and this seemed to give rotifers a competitive advantage over cladocerans. Bosmina longirostris and Ceriodaphnia dubia were both present during the spring, but only Bosmina prevailed in summer. The composition of cladoceran assemblages together with food resources seem to be an important factor in rotifer dynamics.     

Plant and frond dynamics of the giant kelp,Macrocystis pyrifera,forming a fringing zone in the Falkland Islands

Fluctuations in plant and frond characteristics are described for Macrocystis pyrifera (L.) C. Agardh (Laminariales, Phaeophyta) forming a fringing zone in the Falkland Islands. Giant kelp plants were sampled along a transect in the austral autumn (May 1986) and late spring (December 1986) which, according to previous frond weight analysis, were the times when extremes in population parameters were expected. Plant density and holdfast wet weights were similar for both seasons, but plants had more fronds and the fronds weighed more in spring than in autumn. Consequently, in autumn the frond biomass (1·1 wet kg m^?2) and productivity (34·1 wet g m^?2 d^?1) were lower than in spring, when a biomass of 5·0 wet kg m^?2 and a productivity of 72·4 wet g m^?2 d^?1 were recorded. Production of new fronds and loss of old fronds were determined at monthly intervals between April 1986 and March 1987. New frond production rates followed fluctuations in the quantity of light and varied between 0·08 and 0·48 fronds per plant per day. Frond loss rates did not show a seasonal pattern and fluctuated between 0·05 and 0·42 fronds per plant per day. It is suggested that the Falkland Islands Macrocystis population is more stable than most other giant kelp beds at high latitudes, because of the absence of winter storms.     

A SHORT-TERM DEMOGRAPHIC STUDY OF CYSTOSEIRA OSMUNDACEA (FUCALES: CYSTOSEIRACEAE) IN CENTRAL CALIFORNIA1

Several demographic features were examined in the field over a period of eleven months for the subtidal alga Cystoseira osmundacea (Turner) C. Agardh at two localities near Monterey, California. This species showed a restricted distribution with depth, with peak average numbers of 3–4 plants per m² occurring at 6–8 m and forming a dense canopy on the surface of the sea. Below 10 m depth, there was a decline in the abundance of plants and also in the proportion of plants which bore seasonal fronds and reproductive tissue. Macrocystis pyrifera (L.) C. Agardh plants were also common at both localities. There was a negative correlation between the presence of this species and C. osmundacea at a scale of 1 m², but no correlation at 4, 9, and 25 m². Cohorts of C. osmundacea were mapped and tagged at one locality. The plants had markedly seasonal growth, with the greatest elongation of fronds occurring between March and June. Dense surface canopies and reproductive tissue were present during the summer months of June–August. These seasonal fronds were shed during September, leaving small perennial holdfasts and fronds. Plants were strictly dioecious, and there was a one-to-one ratio of male to female plants at both localities. Length-dry weight relationships showed that the largest plants had over 80% of their weight invested in seasonal fronds (vegetative plus reproductive tissue). Recruits of C. osmundacea at one locality appeared during September–November only in areas cleared to bare substratum. There was 15% survival of recruits between November and the following May, while 98% of the original mapped cohort survived for the 11 months of the study.     

DEMOGRAPHY OF FRONDS OF SARGASSUM LAPAZEANUM FROM SOUTHERN BAJA CALIFORNIA, MEXICO, DURING EARLY STAGES

In terms of biomass, Sargassum lapazeanum (Phaeophyceae, Fucales) is one of the most important seaweeds in La Paz Bay, on the southeastern coast of the Baja California Peninsula, Mexico. This species can be found year-round in shallow subtidal sites. Standing biomass is lowest between fall and winter and highest between spring and summer. We are currently studying the annual demography of fronds as a necessary step to understanding the mechanisms of population regulation. Work is being done on a bed of about 90 m in length and three m in width. At this stage of abstract submission, we can report results for winter only. Random samples were collected in February and in March 2000 to estimate stand biomass, frond density, and size (frond length) structure. In addition, we labeled fronds with numbered plastic tags to estimate their rates of growth and of mortality during this period. Rates of recruitment were estimated from a combined analysis of the above. In February, fronds were all shorter than 6.5 cm. Between February and March, mean total frond density increased from 122 to 776 fronds m⁻² (n = 30 quadrats). The mean recruitment rate was 667 fronds m⁻², the mean growth rate was 0.5 cm day⁻¹ (n = 60 fronds), and the mean mortality rate was 43 fronds m⁻². From last year's preliminary observations, we expect to observe peaks of biomass and of reproduction in late spring, followed by negative growth rates and high mortality rates during summer.     

Improvement of Process Stability of Microbiological Quinoline Degradation in a Three‐Phase Fluidized Bed Reactor

The biological degradation of quinoline by suspended and immobilized Comamonas acidovorans was studied under continuous and discontinuous operating conditions in a three‐phase fluidized bed reactor. C. acidovorans degrades quinoline into biomass and carbon dioxide. Quinoline and the intermediates of its metabolic pathway are found only by quinoline shockloads. The continuous degradation of quinoline by suspended biomass was only possible, if the dilution rate was less than the growth rate (μ_max =0.42 h^–1) and the concentration of a shockload was less than 1 kg/m³. A concentration greater than 1 kg/m³ led to an irreversible damage of the cells. Hence, two different carrier materials were used for immobilization by attachment, to increase the stability of the process. Using immobilization of biomass on carriers decouples the hydrodynamic retention time and the growth rate of the microorganisms. A comparison of the carrier material showed no differences with respect of activity and stability of the biofilm. The process stability of a three‐phase fluidized bed reactor was increased by immobilized biomass. The degradation of toxic shockloads was only possible with immobilized biomass. A dynamic model has been developed to describe the concentration profile of quinoline, 2‐hydroxyquinoline as metabolite and the suspended biomass. A comparison of the measured and calculated values showed good agreement.     

Attachment strength differs amongst life‐history stages of an intertidal,isomorphic red alga

Complex haploid‐diploid life cycles amongst marine organisms may be maintained by ecological differences in life‐history phases. For red algal species within the Gigartinaceae, such differences may be driven, in part, by different cell wall composition and resultant biomechanical strengths of haploid and diploid phases. A field experiment tested the attachment strengths of gametophytes and tetrasporophytes of the isomorphic red alga, Chondrus verrucosus (with comparisons of fertile and vegetative fronds, with and without natural tissue damage across three wave‐exposed sites). Seventy‐nine percent of all fronds broke at the stipe‐holdfast junction. There were significant differences in attachment strength (break force and break stress), but not gross morphology (frond length, number of branch axes, wet weight and cross‐sectional area of fronds that dislodged at the stipe‐holdfast junction) of life‐history phases, with tetrasporophytes exhibiting weaker tissue strength and attachment, and therefore greater susceptibility to dislodgement by waves. However, fertility and tissue damage did not consistently influence dislodgement in pull‐to‐break tests simulating the effects of single waves. The ecological and evolutionary consequences of greater susceptibility to dislodgement of tetrasporophytes (relative to gametophytes) warrant further investigation.     

A field study on the growth and development ofDumontia contorta

Young, crustose plants ofDumontia contorta grown in the laboratory from carpospores were transferred in September 1983 to their natural habitat in Lake Grevelingen (SW Netherlands). The number of upright fronds per crust, length of upright fronds, and diameter of crusts were determined monthly until October 1984 and the presence of tetrasporangia was noted. Although fronds were initiated from crusts throughout the period of short daylengths (<13 h light per day, i.e. from September to March), the majority of the fronds was initiated in October and November when short daylengths coincided with optimum temperatures for frond initiation (ca 10–20°C). By April, i.e. within 5–6 months, these plants had reached maximum sizes and had become fertile; subsequently, the plants decayed. The successively smaller numbers of fronds that were formed in December and January also reached maximum sizes after ca 5–6 months, i.e. by May and June, but these fronds remained much smaller than the fronds initiated in October–November, possibly because of lower temperatures and light levels at the start of their growth. It is suggested that the fronds have a fixed maturation period (ca 5–6 months) irrespective of their size and the moment of their initiation. Crusts were shown to “oversummer” and to produce new fronds at the onset of shortday conditions in September 1984. Dedicated to Dr. Dr. h. c. Peter Kornmann on the occasion of his eightieth birthday.     

Prediction model for cabbage stem weevil Ceutorhynchus pallidactylus Mrsh. occurrence on winter rape based on an artificial neural network

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Morphological variability in a red seaweed: confirmation of co-occurring f. lessonii and f. chauvinii in Chondracanthus chamissoi (Rhodophyta,Gigartinales)

Variability in thallus morphology is common in red seaweeds. Two co-occurring forms have been described for Chondracanthus chamissoi based mainly on blade width. To determine whether two distinct forms or a range of intermediate morphologies occur in C. chamissoi, thalli were collected from three localities in southern Chile in autumn–winter, repeating the sampling in one locality in spring and in summer. In each occasion, individual sporophytic and male and female gametophytic clumps were collected, and the longest blade with intact apex from each clump was evaluated. Blade length, width, density of spines, axis curvature and thickness, and pinnule length and width were evaluated in each blade. Principal components analyses separated two groups of thalli, one group with narrow, thick, and curved (concavo-convex) blades, with few spines consistent with f. lessonii, and another with broad, thin, and flat blades, with many spines consistent with f. chauvinii. These variables also had bimodal frequency distributions. Pinnule measurements were mainly associated with differences among sporophytes and gametophytes. Age (length), phase of the life cycle, and sex were not related to the forms. Furthermore, thalli of both forms were collected side by side in the study sites and throughout the year so the occurrence of the two forms was not attributable to local environmental conditions. In this species, secondary basal disks are produced after attachment of apexes to the substratum. These disks may produce blades with a modified morphology in a way similar to proliferations and regenerations described for Schottera nicaeensis.     

A sixth‐level habitat cascade increases biodiversity in an intertidal estuary

Many studies have documented habitat cascades where two co‐occurring habitat‐forming species control biodiversity. However, more than two habitat‐formers could theoretically co‐occur. We here documented a sixth‐level habitat cascade from the Avon‐Heathcote Estuary, New Zealand, by correlating counts of attached inhabitants to the size and accumulated biomass of their biogenic hosts. These data revealed predictable sequences of habitat‐formation (=attachment space). First, the bivalve Austrovenus provided habitat for green seaweeds (Ulva) that provided habitat for trochid snails in a typical estuarine habitat cascade. However, the trochids also provided habitat for the nonnative bryozoan Conopeum that provided habitat for the red seaweed Gigartina that provided habitat for more trochids, thereby resetting the sequence of the habitat cascade, theoretically in perpetuity. Austrovenus is here the basal habitat‐former that controls this “long” cascade. The strength of facilitation increased with seaweed frond size, accumulated seaweed biomass, accumulated shell biomass but less with shell size. We also found that Ulva attached to all habitat‐formers, trochids attached to Ulva and Gigartina, and Conopeum and Gigartina predominately attached to trochids. These “affinities” for different habitat‐forming species probably reflect species‐specific traits of juveniles and adults. Finally, manipulative experiments confirmed that the amount of seaweed and trochids was important and consistent regulators of the habitat cascade in different estuarine environments. We also interpreted this cascade as a habitat‐formation network that describes the likelihood of an inhabitant being found attached to a specific habitat‐former. We conclude that the strength of the cascade increased with the amount of higher‐order habitat‐formers, with differences in form and function between higher and lower‐order habitat‐formers, and with the affinity of inhabitants for higher‐order habitat‐formers. We suggest that long habitat cascades are common where species traits allow for physical attachment to other species, such as in marine benthic systems and old forest.     

Extreme climatic events reduce ocean productivity and larval supply in a tropical reef ecosystem

Increasing ocean temperatures due to global warming are predicted to have negative effects on coral reef fishes. El Niño events are associated with elevated water temperatures at large spatial (1000s of km) and temporal (annual) scales, providing environmental conditions that enable temperature effects on reef fishes to be tested directly. We compared remote sensing data of sea surface temperature (SST) anomalies, surface current flow and chlorophyll‐a (Chl‐a) concentration with monthly patterns in larval supply of coral reef fishes in nearshore waters around Rangiroa Atoll (French Polynesia) from January 1996 to March 2000. This time included an intense El Niño (April 1997–May 1998) event between two periods of La Niña (January–March 1996 and August 1998–March 2000) conditions. There was a strong relationship between the timing of the El Niño event, current flow, ocean productivity (as measured by Chl‐a) and larval supply. In the warm conditions of the event, there was an increase in the SST anomaly index up to 3.5 °C above mean values and a decrease in the strength of the westward surface current toward the reef. These conditions coincided with low concentrations of Chl‐a (mean: 0.06 mg m^?3, SE ± 0.004) and a 51% decline in larval supply from mean values. Conversely, during strong La Niña conditions when SST anomalies were almost 2 °C below mean values and there was a strong westward surface current, Chl‐a concentration was 150% greater than mean values and larval supply was 249% greater. A lag in larval supply suggested that productivity maybe affecting both the production of larvae by adults and larval survival. Our results suggest that warming temperatures in the world's oceans will have negative effects on the reproduction of reef fishes and survival of their larvae within the plankton, ultimately impacting on the replenishment of benthic populations.     

Yeast entrapment in Duckweeds: Immobilization performance and biomass localization within the support particles

Cell structured support material (CSM) prepared from Wolffia arrhiza fronds were loaded with Saccharomyces cereevisiae by the propagation of yeast cells introduced in the aerenchyma. The loading process could be strongly accelerated by preventing the growth of freely suspended yeasts in the fermenter. The pathway of the inoculation through the stomata could be visualized by transparent light microscopy of amylase and protease treated CSM. Slices of the loaded CSM clearly showed that the framework of the inner chlorenchyma cells remains intact during the propagation of the included yeast cells. Most of the yeast cells were found to be localized as a dense suspension within unbroken cells. During long-term treatment of the loaded CSM at high convection, about one third of the yeasts was released into water with a constant rate greater than 0.34 h^?1. The residual amount of yeast cells remained in a stable compartment from which further loss did not occur for the period tested (20–48 h). It is assumed that the stable compartment is identical with the interior of chlorenchyma cells. The results are discussed in relationship to the possible use of the immobilized biomass in fermentation.     

Plant cell suspension culture in a bench-scale fermenter with a newly designed membrane stirrer for bubble-free aeration

In this paper, tests of an optimized membrane-stirrer geometry for bubble-free aeration of a plant cell suspension culture are described. Cell attachment and clogging of a previously described system [Piehl et al. (1988) Appl Microbiol Biotechnol 29:456–461] led to the development of a new stirrer. The volumetric oxygen transfer capacity has been measured in aqueous medium. The mass transfer coefficient, k _l a, was 3.75 h⁻¹ at 25 °C and at a stirrer speed of 34 rpm. The overall oxygen transfer capacity was investigated with a suspension culture of Aesculus hippocastanum. It was shown that the oxygen mass transfer was sufficient even at the maximum biomass of 10–12 g dry weight/l, which was obtained by using this system. Furthermore, special attention was given to medium components like C and N sources, to avoid growth limitation due to a shortage of nutrients. Received: 22 October 1996 / Revised version: 11 March 1997 / Accepted: 14 March 1997     

Enhancement of Lead(II) Biosorption by Microalgal Biomass Immobilized onto Loofa (Luffa cylindrica) Sponge

A unicellular green microalga, Chlorella sorokiniana, was immobilized on loofa (Luffa cylindrica) sponge and successfully used as a new biosorption system for the removal of lead(II) ions from aqueous solutions. The biosorption of lead(II) ions on both free and immobilized biomass of C. sorokiniana was investigated using aqueous solutions in the concentration range of 10–300 mg/L. The biosorption of lead(II) ions by C. sorokiniana biomass increased as the initial concentration of lead(II) ions increased in the medium. The maximum biosorption capacity for free and immobilized biomass of C. sorokiniana was found to be 108.04 and 123.67 mg lead(II)/g biomass, respectively. The biosorption kinetics were found to be fast, with 96 % of adsorption within the first 5 min and equilibrium reached at 15 min. The adsorption of lead(II) both by free and immobilized C. sorokiniana biomass followed the Langmuir isotherm. The biosorption capacities were detected to be dependent on the pH of the solution; and the maximum adsorption was obtained at a solution pH of about 5. The effect of light metal ions on lead(II) uptake was also studied and it was shown that the presence of light metal ions did not significantly affect lead(II) uptake. The loofa sponge‐immobilized C. sorokiniana biomass could be regenerated using 0.1 M HCl, with up to 99 % recovery. The desorbed biomass was used in five biosorption‐desorption cycles, and no noticeable loss in the biosorption capacity was observed. In addition, fixed bed breakthrough curves for lead(II) removal were presented. These studies demonstrated that loofa sponge‐immobilized biomass of C. sorokiniana could be used as an efficient biosorbent for the treatment of lead(II) containing wastewater.