Frond Length Research Articles

Competition between the invasive macrophyte Caulerpa taxifolia and the seagrass Posidonia oceanica: contrasting strategies.

BackgroundPlant defense strategy is usually a result of trade-offs between growth and differentiation (i.e. Optimal Defense Theory – ODT, Growth Differentiation Balance hypothesis – GDB, Plant Apparency Theory – PAT). Interaction between the introduced green alga Caulerpa taxifolia and the endemic seagrass Posidonia oceanica in the Mediterranean Sea offers the opportunity to investigate the plausibility of these theories. We have accordingly investigated defense metabolite content and growth year-round, on the basis of an interaction gradient.ResultsWhen in competition with P. oceanica, C. taxifolia exhibits increased frond length and decreased Caulerpenyne – CYN content (major terpene compound). In contrast, the length of P. oceanica leaves decreases when in competition with C. taxifolia. However, the turnover is faster, resulting in a reduction of leaf longevity and an increase on the number of leaves produced per year. The primary production is therefore enhanced by the presence of C. taxifolia. While the overall concentration of phenolic compounds does not decline, there is an increase in some phenolic compounds (including ferulic acid and a methyl 12-acetoxyricinoleate) and the density of tannin cells.ConclusionInterference between these two species determines the reaction of both, confirming that they compete for space and/or resources. C. taxifolia invests in growth rather than in chemical defense, more or less matching the assumptions of the ODT and/or PAT theories. In contrast, P. oceanica apparently invests in defense rather than growth, as predicted by the GDB hypothesis. However, on the basis of closer scrutiny of our results, the possibility that P. oceanica is successful in finding a compromise between more growth and more defense cannot be ruled out.

A multi‐site assessment of the effectiveness ofPteridium aquilinumcontrol in Great Britain

AbstractQuestions:The objectives of this study were to assess the effect ofPteridium aquilinum(bracken) control treatments, at the national scale, and the impact of restoration practices, at the local scale, onP. aquilinumperformance.Hypotheses:1. Geographical location (locally between and within sites) affects the control ofP. aquilinumthrough time. 2. Are theP. aquilinumcontrol treatments successful at all sites, and if so which ones? 3. The treatments applied at the individual site level to restore vegetation influences the performance ofP. aquilinumthrough time.Location:Four geographically distinct acid grassland and heathland sites infested withP. aquilinumacross Great Britain.Methods:Six main‐plot, bracken control treatments were applied to all sites with site‐specific vegetation restoration treatments. Response variables (P. aquilinumcover, frond length and density) were monitored twice yearly, in June and August between 1993 and 2003.Results:Between‐ and within‐site spatial variation was found, although impact is perhaps less than suggested from shorter‐term data. Despite local variation all sites responded similarly to bracken control treatments; asulam treatment resulted in a rapid reduction in frond performance followed by a continued recovery taking approximately ten years to return to untreated values. Cutting treatments tended to have a slower impact at the start but an increasing one over time, especially cutting twice per year. Restoration treatments had a limited impact; the only significant effect in August was grass seeding on frond length at Sourhope. In June only, the plots where sheep were fenced out showed a significant reduction inP. aquilinumcover at Peak.Conclusions:Long‐term control ofPteridium aquilinumat all sites and on all measures was best achieved using a continuous cutting treatment, preferably twice per year.

Spatial variation in molluscan assemblages from coralline turfs of Argentinean Patagonia

Patterns of spatial variation of molluscan communities associated with coralline algal turfs were evaluated over 1,000 km of the coast of Argentinean Patagonia. A hierarchically-nested experimental design was used to determine the relative importance of molluscan assemblage variation at three different spatial scales (shores, sites and cores). Hypotheses were also tested about the potential role of habitat variables (frond density, frond length, sediment and epiphytes) for determining molluscan community structure. In total, 38 molluscan species were found comprising 16, 18 and 4 species of bivalves, gastropods and polyplacophorans, respectively. Densities of molluscs in coralline turfs reached ca 77,000 individuals per m 2 and were dominated by mussels, especially Perumytilus purpuratus. Multivariate and univariate analyses of assemblage structure consistently showed that variation at scales of metres and hundreds of kilometres dominated, with sites 20 – 50 m apart always contributing less than 24% of the total. Significant associations between molluscan community structure and both frond density and frond length demonstrated the potential importance of habitat structure in determining community structure at local scales. Variation in molluscan assemblages at the scale of shores, however, did not appear to correlate with latitudinal, temperature or wave exposure gradients, indicating that other processes must be operating. The compositions of molluscan assemblages in coralline turfs on the coast of Argentina were similar to those reported for central Chile. Comparisons of the richness of these South American assemblages to other parts of the world revealed some striking biogeographical patterns that warrant further investigation. Overall, this work highlights the general importance of small-scale variation in molluscan assemblages on rocky shores and the consistent influence of habitat complexity in determining the structure of diverse molluscan communities associated with mat-like habitats.

Limited evidence for increased cold-tolerance of invasive versus native Caulerpa taxifolia

Growth characteristics of native and invasive Caulerpa taxifolia from coastal eastern Australia were compared in warm (22–25°C) and cool (15–18°C) water in two laboratory experiments. Measurements of biomass, stolon length, mean frond length and numbers of fronds and stolon meristems, demonstrated that the growth of native and invasive C. taxifolia in warm water was up to ten times greater than in cool water. Growth rates differed substantially among locations over 9 weeks, but for most variables, the growth of native C. taxifolia was greater than the growth of invasive C. taxifolia in warm water. In cool water, there was little difference in growth of invasive versus native C. taxifolia. The morphology of C. taxifolia changed considerably in response to temperature, such that native and invasive samples that were morphologically distinct at the start of the experiment became indistinguishable after 69 days in warm water. We concluded there was little evidence that the C. taxifolia which recently invaded temperate estuaries in New South Wales could spread faster in cool water than could native C. taxifolia from Queensland. Native tropical C. taxifolia appears tolerant of a wide range of environmental conditions and seems capable of surviving and becoming invasive in temperate estuaries.

REPRODUCTIVE LONGEVITY OF DRIFTING KELP MACROCYSTIS PYRIFERA (PHAEOPHYCEAE) IN MONTEREY BAY, USA1

Drifting Macrocystis pyrifera (L.) C. Agardh sporophytes have long been viewed as the primary long‐distance dispersal vector; yet, few data exist that support the ability of reproductive viable sporophytes to actually travel the presumed hundreds to thousands of kilometers. This study addressed the reproductive longevity of experimental and naturally occurring M. pyrifera drifters. Temporal variability in sporophyte size and reproduction was estimated for experimental drifting sporophytes that were tethered to surface buoys and compared with attached plants (controls). Reproductive viability was also studied for beach‐cast drifters (BCD), and naturally drifting sporophytes observed during field surveys in Monterey Bay. Detached drifting sporophytes were tracked with radio transmitters to follow drifter trajectories and to measure drifting speed. Experimental drifters (ED) experienced a 74% reduction in frond length after 35 days, a 76% reduction in average frond number after 70 days, and a reduction in average sorus area by 83% after 28 days. Although zoospore production was reduced following detachment, sporophytes remained fertile with high zoospore germination success as long as sori were present (125 days). Zoospore production and germination success for natural and BCD was similar to ED. The average displacement of radio‐tagged drifters was 7.12 km·day−1, suggesting that a sporophyte adrift for 125 days disperses viable propagules (zoospores) over 890 km (±363). Dispersal of propagules is important for population restoration, distribution, and genetic diversity. Such dispersal distances are long enough to connect potentially all Northern Hemisphere Macrocystis populations across a generational timescale and may facilitate inter‐hemispheric gene flow.

Spatial and temporal variation in density and thallus morphology of Turbinaria ornata in Thailand

Turbinara ornata (Turner) J. Agardh, is a common brown alga, which occurs on tropical shores worldwide. We studied the effects of wave action and seasonal variation on T. ornata populations at Koh Pling, Sirinart Marine National Park, Thailand. Density, length of thallus, length of blade, number of blades, number of reproductive organs, and dry weights were investigated. The algae were collected bimonthly during August 2003–May 2004, at three different areas of wave exposure: sheltered, semi-exposed, and exposed. There were variations in all factors at sites and seasons ( P < 0.05). We found that T. ornata populations were denser on the semi-exposed shore and their biological characteristics reached their peaks during October 2003. The highest density of T. ornata was 27 ± 10 fronds/m 2 (mean ± S.E.). While the average frond length, for example, was 24 ± 1.5 cm, 4 times greater than the minimum; and the number of blades on the thallus were 329 ± 47 blades, 15 times greater than the minimum. Surprisingly, the population disappeared at the beginning of May 2004, and returned in July 2004. In this work, we attempt to explain the differences in various characteristics of T. ornata in relation to the degree of wave exposure, nutrient concentration and other physical factors. We also discuss how our results may provide some insight into the current rapid expansion of T. ornata populations.

Control of Hay-Scented Fern by Mowing

Abstract Hay-scented fern (Dennstaedtia punctilobula) is a native species that can invade and dominate the forest understory, after thinning and intensive deer browsing. Fern colonies form a dense cover 60 to 80 cm high that intercepts light and inhibits tree seedling regeneration. Hay-scented fern can be controlled with herbicides, but some landowners (both public and private) seek alternative methods. We investigated mowing as a possible method of fern control. We tested different mowing schedules and measured the response of ferns (frond length and density) and of natural regeneration and planted seedlings. Mowing the ferns twice in one growing season (first in June when the fern fronds had reached their full height and again in August) led to a significant reduction in frond length during the next two growing seasons compared to untreated controls. Mowing four times over 2 years reduced both length and density of ferns. Mean density of naturally established tree seedlings was four times greater on these treatment plots compared to controls, but with great variability among plots. Red oak (Quercus rubra) and sugar maple (Acer saccharum) seedlings planted the year after mowing showed greater survival and height growth compared to controls.

Germination of spores and growth of gametophytes and sporophytes of Rumohra adiantiformis (Forst.) Ching (Dryopteridaceae) after spore cryogenic storage

Rumohra adiantiformis (Forst.) Ching is a fern (Dryopteridaceae) used in floral arrangements. Spores sterilized in 15% (v/v) solution of commercial sodium hypochlorite for 10 minutes and unsterilized spores were plunged in liquid nitrogen and held for 15 minutes and for 90 days. After the cryogenic treatments, spores were taken out of liquid nitrogen and rapidly thawed out in a water bath or slowly at room temperature and were cultured in Mohr's mineral solution as modified by Dyer, kept at 25 ± 2 oC and a 16-hours photoperiod. Statistical differences were not observed in the germination of unsterilized spores immersed or not immersed in liquid nitrogen, but when the spores were previously sterilized, a severe inhibition of germination was observed in cryopreserved spores. Faster mean germination time was observed for unsterilized spores cryopreserved in liquid nitrogen for 15 minutes. The germination of spores stored in liquid nitrogen for 90 days reached the maximum percentage after 12 days, while control spores reached their maximum percentage after 16 days. Levels of soluble sugars did not vary among treatments in gametophytes cultivated for 10 weeks after spore inoculation. The number of fronds and the length of the longest frond on sporophytes did not differ statistically among treatments. The relative growth rate of sporophytes grown from cryopreserved and control spores were not statistically different among treatments. Spores of R. adiantiformis immersed in liquid nitrogen for 15 minutes apparently produced phenotypically normal plants.

Vegetation patterns and spontaneous regression of Caulerpa taxifolia (Vahl) C. Agardh in Malinska (Northern Adriatic, Croatia)

The green alga Caulerpa taxifolia was recorded at Malinska in 1994 and this actually represents the highest northern latitude (45°7′30″N) at which this invasive alga has been found in the world. The alga was widespread at four sites from which it was eradicated by suction pumps during 1996 and 1997. However, it immediately and intensively recolonized all but one site. Throughout 1998 and 1999 the renewed vegetation showed consistent seasonal patterns. The alga nearly disappeared in April and May while regenerating from over-wintering parts of the thalli in summer. The maximum development occurred in autumn and winter with values of biomass (around 200 g dry weight m −2) and frond number (around 2000 m −2) generally lower than those reported for the north-western Mediterranean. Values for the frond length (10–18 cm) were in the same range as those in the north-western basin. Throughout 1998 and 1999 the biomass was closely correlated to frond number and length (adjusted R 2 = 0.90). During the following years C. taxifolia entered a phase of regression. The total colonized area, which amounted to several thousands of square metres in 1998, spontaneously declined in 2000 and 2001 so that only several thalli were found in 2004 during a detailed survey of the settlement. No major changes in winter seawater temperatures, ranging from 9.5 to 10.5 °C, were observed in the area from 1994 to 2004. Thus, other unknown processes could likely play a role on specific vegetation patterns of C. taxifolia in Malinska. Accordingly, it is difficult to explain why the still surviving thalli did not proliferate during the favourable summer–autumn period.

HERBICIDE USE IN HARDY FERNS

Hardy ferns are widely grown for use in the landscape. Studies were conducted to evaluate the tolerance of variegated leatherleaf fern (Arachniodes simplicor `Variegata'), tassel fern (Polystichum polyblepharum), autumn fern (Dryopteris erythrosora), holly fern (Cyrtomium falcatum `Rochfordii'), and southern shield fern (Dryopteris ludoviciana), to applications of selected preemergence applied herbicides. Liquid applied herbicides were pendamethalin (LPM) at 3.36 or 6.73 kg·ha–1, prodiamine (LPD) at 1.12 or 2.24 kg·ha–1, isoxaben (LIB) at 1.12 or 2.24 kg·ha–1, and the combination of prodiamine plus isoxaben (LPI) at 1.12 plus 1.12 kg·ha–1. Granular applied herbicides were pendamethalin (GPM) at 3.36 or 6.73 kg·ha–1, prodiamine (GPD)1.12 or 2.24 kg·ha–1, oxadiazon plus prodiamine (GOP) at 1.12 + 0.22 or 2.24 + 0.44 kg·ha–1, oxyfuorfen plus oryzalin (GOO) at 2.24 + 1.12 or 4.48 + 2.24 kg·ha–1, trifluralin plus isoxaben (GTI) at 2.24 + 0.56 or 4.48 + 1.12 kg·ha–1, oxadiazon (GO) at 4.48 or 8.97 kg·ha–1, and oxadiazon plus pendamethalin (GOPD) at 2.24 + 1.4 or 4.48 + 2.8 kg·ha–1. The greatest reduction in growth of autumn fern was observed with GOPD, GO, and GOP; all three containing oxadiazon as an active ingredient. Reductions in holly fern growth were most severe when plants were treated with GTI resulting in a 42% and 54% decrease in frond length and frond number, respectively. There were also reductions in number of fronds when treated with LPM, GPM, GOP, GOO, and GOPD. There were no reductions in frond numbers on tassel fern with any herbicides tested. However, there were reductions in frond length from 6 of the 10 herbicides evaluated. The most sensitive fern to herbicides evaluated in 2004 was leatherleaf with reductions in frond length and number of fronds with 6 of the 10 herbicides tested. While all herbicides tested on southern shield fern appeared to be safe, especially in the 2004 study, tassel fern and holly fern appear to be more sensitive. GPD proved to be a safe herbicide for all species tested in both 2004 and 2005. In 2005 all plants from all treatments were considered marketable by the end of the study. However there was significant visual injury observed on the holly fern treated with LIB at 60 and 90 days after treatment which might reduce their early marketability.

Population dynamics of Sargassum lapazeanum (Fucales, Phaeophyta) from the Gulf of California, Mexico

M. Rivera and R. Scrosati. 2006. Population dynamics of Sargassum lapazeanum (Fucales, Phaeophyta) from the Gulf of California, Mexico. Phycologia 45: 178–189. DOI: 10.2216/05-47.1We studied the population dynamics of Sargassum lapazeanum from the southwestern Gulf of California, Mexico, between February 2000 and February 2001. We qua.gified the seasonal changes in frond density, stand biomass, frond size structure and inequality, presence of reproductive structures, and rates of recruitment, growth, and mortality. Fronds were present during the entire year, although with a marked seasonality: mean frond density, frond length, and stand biomass were highest in spring and lowest in winter. The strong increase in frond density between winter and spring resulted from the combination of high recruitment and low mortality rates. Growth rates were highest in spring; the highest absolute value (3.6 cm d−1) is among the highest found for brown seaweeds. The frond size structure became best developed in late spring. Reproductive structures peaked in abundance in late spring and became mostly lost by late summer. Senescence started in late spring and increased dramatically during the summer. The strong decrease in frond density between summer and autumn resulted from the combination of low recruitment and high mortality rates. In early autumn, primarily only small fronds remained in the population, including new recruits and remnants of previously large fronds. The seasonal pattern in the temporal abundance changes for S. lapazeanum agrees with a general model proposed for subtropical species of this genus.

Tolerance of Hardy Ferns to Selected Preemergence Herbicides

Hardy ferns are widely grown for use in the landscape. The 1998 National Agricultural Statistics Services census of horticulture reported production of hardy/garden ferns at 3,107,000 containers from over 1200 nurseries. There is little research on herbicide use in hardy ferns, and herbicides that are labeled for container production are not labeled for use on hardy ferns. Studies were conducted to evaluate the tolerance of variegated east indian holly fern (Arachniodes simplicior `Variegata'), tassel fern (Polystichum polyblepharum), autumn fern (Dryopteris erythrosora), rochford's japanese holly fern (Cyrtomium falcatum `Rochfordianum'), and southern wood fern (Dryopteris ludoviciana), to applications of selected preemergence applied herbicides. Herbicides evaluated included selected granular or liquid applied preemergence herbicides. Spray-applied herbicides were pendimethalin at 3.0 or 6.0 lb/acre, prodiamine at 1.0 or 2.0 lb/acre, isoxaben at 1.0 or 2.0 lb/acre, and prodiamine + isoxaben at 1.0 + 1.0 lb/acre. Granular-applied herbicides were pendimethalin at 3.0 or 6.0 lb/acre, prodiamine at 1.0 or 2.0 lb/acre, oxadiazon + prodiamine at 1.0 + 0.2 or 2.0 + 0.4 lb/acre, oxyfluorfen + oryzalin at 2.0 + 1.0 or 4.0 + 2.0 lb/acre, trifluralin + isoxaben at 2.0 + 0.5 or 4.0 + 1.0 lb/acre, oxadiazon at 4.0 or 8.0 lb/acre, and oxadiazon + pendimethalin at 2.0 + 1.25 or 4.0 + 2.5 lb/acre. The greatest reduction in growth of autumn fern was observed with the high rates of oxadiazon, oxadiazon + pendimethalin, and oxadiazon + prodiamine. Reductions in rochford's japanese holly fern growth were most severe when plants were treated with the high rate of trifluralin + isoxaben resulting in a 66% and 72% decrease in frond length and frond number, respectively. There were also reductions in frond length and number of fronds when treated with the high rate of oxadiazon + pendimethalin. There were no reductions in frond numbers on tassel fern with any herbicides tested. However, there were reductions in frond length from four of the 10 herbicides evaluated. The most sensitive fern to herbicides evaluated in 2004 was variegated east indian holly fern with reductions in frond length and number of fronds with four of the 10 herbicides tested. Southern wood fern appeared to be quite tolerant of the herbicides tested with the exception of the high rate of oxadiazon. Granular prodiamine proved to be a safe herbicide for all species tested in both 2004 and 2005. In 2005 all plants from all treatments were considered marketable by the end of the study. The durations of both studies were over 120 days giving adequate time for any visual injury to be masked by new growth. However, there was significant visual injury observed on the rochford's japanese holly fern treated with isoxaben at 60 and 90 days after treatment, which might reduce their early marketability.

Growth of the Brown Alga Laminaria japonica in a Laboratory Environment

The growth of an individual thallus of the brown alga Laminaria japonica was studied in a laboratory environment. It was found that daily accretion of the Laminaria thallus can remain constant for a long time. The blade grew in length at a distance from 0 to 15–25 cm from the stipe-blade border, which makes up 60% of the blade length. In width, the blade grew both in the central and in the lateral parts of the blade, 0 to 7–10 cm from the stipe-blade border, which makes up 30% of the frond length. The transposition of a perforation hole mark from the stipe-blade border toward the blade tip evidenced the formation of new tissue in the growth zone even when the thallus diminished in size due to destruction of the blade tip. Based on the results of this observation, it was concluded that both restraint of accumulation and even reduction of the algal thallus in biomass and size cannot be taken as an indication of algal growth cessation.

Cultivation of Laminaria japonica (Laminariales, Phaeophyta) in Udo Coast, Jeju, Korea

【In order to produce Laminaria japonica in Jeju as feed for abalone, a transplant experiment was performed with the Baekryungdo and the Wando cultivar stocks at the Udo aquafarm from January to July 2003. Eight water conditions at the aquafarm and eleven traits of the two cultivar stocks were measured once a month. The water temperature ranged from 12.9 $^{\circ}C$ to 23.5 $^{\circ}C$ . The salinity was 31.3-36.8‰ the DO was 5.40-9.86 mg ${\cdot}$ $l^{-1}$ the pH was 7.82-9.61. Concentrations of $NO_2-N,\;NO_3-N,\;NH_4-N\;and\;PO_4-P$ were 0.02-0.15 $\mu$ M, 2.27-3.49 $\mu$ M, 0.16-0.56 $\mu$ M and 0.07-0.99 $\mu$ M, respectively. The whole frond length of the Baekryungdo and the Wando specimens were 173.84 and 153.67 cm. The blade width, stipe length, blade length, fascia length, blade thickness, total weight and substantiality of the Baekryungdo and the Wando specimens were 14.61 and 13.05 cm, 3.94 and 3.02 cm, 169.88 and 150.65 cm, 155.81 and 137.10 cm, 1.01 and 0.96 cm, 258.04 and 200.96 cm, and 101.56 and 94.62, respectively at the conclusion of the experiment in July. The measurements of the Baekryungdo specimens were slightly higher than those of Wando specimens. The fascia width, stipe thickness and fascia thickness of the Wando specimens were slightly higher than those of the Baekryungdo specimens. The relative growth rates of these traits of two cultivar stocks during the growth test were very similar. Generally, the performance of the Baekryungdo cultivar stock seems to be better than that of the Wando samples. Further study of the physiological ecology for cultivation and breeding is needed in the future.】

Habitat characteristics influence macrofaunal communities in coralline turf more than mesoscale coastal upwelling on the coast of Northern Chile

Rocky shore communities are often influenced by near-shore coastal upwelling. For macrofauna in algal turf, these effects may be caused directly by well-studied bottom-up mechanisms or indirectly via changes in habitat structure provided by algal turf associated high nutrient loads. Here, we investigated possible interactions between upwelling and habitat structure by sampling diverse faunal assemblages in coralline algal turf on seven rocky intertidal shores in northern Chile, ranging from El Cobre [23°17′1″S, 70°31′40″W] to La Lobería [23°03′40″S, 70°33′14″W]. Some of these shores were located adjacent to strong upwelling centers, while others were in areas rarely affected. On each shore, we sampled four (2 × 2 m) sites separated by 15–50 m. In each site, we collected three replicate cores (80 mm in diameter) from which we measured macrofauna greater than 850 μm, biomass of sediment and epiphytes, frond density and average frond length. We used mean water temperature and its variation at 1–1.5 m water depth (below Extreme Low Water Spring, ELWS) to represent local upwelling intensity because long-term data have shown that these variables make excellent indicators for this region. In total, we found 94 macrofaunal taxa in coralline turf, which is almost three times higher than has previously been reported in Chile. Although macrofaunal assemblages varied significantly among shores, there were no patterns to suggest mesoscale variation in upwelling intensity affected either faunal assemblages or local habitat characteristics. In contrast, multivariate and univariate correlations highlighted sediment and frond density as strong determinants of community structure. We therefore conclude that traditionally studied habitat characteristics, such as structural complexity and habitat heterogeneity, have greater influence on faunal assemblages in mat-like habitats on rocky shores than environmental variables associated with mesoscale coastal upwelling.

Effects of chlorine and potassium mineral nutrition on the leaf morphology of the PB 121 hybrid coconut palm (Malayan Yellow Dwarf x West African Tall)

The effects of chlorine and potassium on the leaf morphology of 6-year-old PB 121 hybrid coconut palms were studied in 1995 and 1996 in southern Lampung (South Sumatra, Indonesia). The parameters considered were frond and leaflet size (length, maximum width, area) and their number. Chlorine and potassium had an exclusive effect on leaflet size, increasing their area. Potassium primarily affected petiole length, hence total frond length. Synergy between these two ions only occurred for the number of leaflets. Chlorine and potassium acted independently on stem diameter and synergistically on height. Coconut palms receiving potassium or chlorine had significantly more voluminous leaf crowns. As time went by, this phenomenon increased despite constant monthly leaf emission. In a situation of equilibrium, the much larger mean crown area and leaf area index of coconuts receiving chlorine and potassium augured well for an earlier start to bearing and higher nut yields.

Morphology, seasonal phenology and observations on some aspects of the life history in culture of Porphyra dioica (Bangiales, Rhodophyta) from Devon, UK

A seasonal study of the blade phase of Porphyra dioica at its type locality, Sidmouth, Devon, UK, undertaken between June 1999 and May 2000 revealed that individuals were present in the middle and lower littoral zones all year. Field-collected specimens were vegetative (8%), or possessed male (40%) or female (47%) reproductive structures, or had both on the same blade (6%) but totally segregated by a distinct line. Mean wet mass of individuals was greatest in June and least in February. There were no significant differences between the wet mass of individuals with male or female gametangia. Mean frond length was greatest in June and least in February. Mean frond width was greatest in May and least in February. Reproductive sori were marginal and pale straw-yellow for male gametangia, cream to pale green in unfertilized female gametangia, and bright red to dark red-brown once fertilization had taken place. Male gametangia were found in packets of 64 [2 X 4 in surface view (SV)]. Individuals with female reproductive structures were distinguished by one or more of the following: gametangial mother cells, trichogynes, spindle-shaped cells or divided zygotosporangia in packets of 16 (2 X 2 in SV). The ratio of male to female reproductive structures on individual thalli throughout the 12 months was approximately 1:1. In culture, spores were released from blades with female reproductive structures in every month tested. Of those individuals that released spores, the percentage that germinated into a conchocelis phase ranged from 15 % in August to 78 % in April. Conchosporangia or neutral conchosporangia formed at 5°C short days (SD = 8:16 h light-dark cycle), 5°C long days (LD = 16:8 h light-dark cycle), 10°C SD, 10°C LD, 12°C day neutral (DN = 12:12 h light-dark cycle), 15°C SD, 15°C LD, 20°C DN, and 20°C LD, but the completion of the life history was not observed.

해중림 조성을 위한 괭생이모자반(Sargassum horneri) 유체의 이식

Transplantation of Sargassum horneri to natural substrate using the rope seeding method was undertaken. Seeding of S. horneri was grown on net in an indoor tank up to 0.2-0.3 cm in frond length for 2 months, and then transplanted to an architecture tile <TEX>$(10\times10\;cm)$</TEX> with underwater glue and an iron pipe. After two months, number of S. horneri on the tile decreased because of grazing by herbivores. However, S. horneri on the iron pipe grew up to 0.5-2.0 cm in frond length. After 7 months, they rapidly grew up to a frond length of 11.0-203.0 cm with a mean frond length of 122.6 cm. S. horneri grew up to a maximum frond length of 313.0 cm, and mean frond length of 228.0 cm, after 10 months. The artificial S. hornevi beds can be used to clean the seawater and also be utilized as a source of marine biomass as well as for supplying habitat, shelter and spawning beds for fish and invertebrates.

Patterns of association between algae, fishes and grey herons Ardea cinerea in the rocky littoral zone of a Scottish sea loch

The distribution of dominant algae, Fucus vesiculosus and Ascophyllum nodosum, the associated fish community, and the spatial and temporal distributions of the main piscivorous predator, the grey heron Ardea cinerea, were studied on the rocky intertidal zone of Loch Etive, a sea loch on the Scottish west coast. Fucus- and Ascophyllum-dominated shores were not distributed randomly around the shore: the latter was especially common along the more sheltered shores and bays and on the finer substratum types. Coverage and frond length of Ascophyllum were greater than for Fucus. Fourteen fish species were caught in the intertidal zone. Numerically, the catch was dominated by four species caught in Fucus- and Ascophyllum-dominated habitats in both winter and summer: Spinachia spinachia, Pholis gunnellus, Taurulus bubalis and Zoarces viviparus. A higher species richness and fish abundance were recorded on Ascophyllum shores than on Fucus ones in both seasons. On Loch Etive, grey herons foraged exclusively in the intertidal zone usually as solitary, well-spaced individuals. The models suggest the number of foraging birds tended to increase with increasing total algal area (i.e. the two dominant species plus Fucus serratus) and with area of Ascophyllum and decreased with increasing area of Fucus and distance from the breeding colony. Adult grey herons showed a preference for foraging in Ascophyllum habitat and first-years showed no preference, suggesting that Ascophyllum-dominated areas are optimal foraging habitats for coastal-living grey herons. One section of shore was particularly important in establishing these habitat relationships: an Ascophyllum-dominated section with the largest intertidal area and where the highest number of foraging adults but no first-years were recorded. Future conservation and management considerations for the rocky intertidal zone should include associated fish communities and their predators, for which this habitat, and Ascophyllum-dominated areas especially, are of particular importance.

Changes in habitat complexity negatively affect diverse gastropod assemblages in coralline algal turf.

The physical structure of a habitat generally has a strong influence on the diversity and abundance of associated organisms. I investigated the role of coralline algal turf structure in determining spatial variation of gastropod assemblages at different tidal heights of a rocky shore near Sydney, Australia. The structural characteristics of algal turf tested were frond density (or structural complexity) and frond length (the vertical scale over which structural complexity was measured). This definition of structural complexity assumes that complexity of the habitat increases with increasing frond density. While frond length was unrelated to gastropod community structure, I found significant correlations between density of fronds and multivariate and univariate measures of gastropod assemblages, indicating the importance of structural complexity. In contrast to previous studies, here there were negative relationships between the density of fronds and the richness and abundance of gastropods. Artificial habitat mimics were used to manipulate the density of fronds to test the hypothesis that increasing algal structural complexity decreases the richness and abundance of gastropods. As predicted, there were significantly more species of gastropods in loosely packed than in tightly packed turf at both low- and mid-shore levels. Despite large differences between gastropod assemblages at different tidal heights, the direction and magnitude of these negative effects were similar at low- and mid-shore levels and, therefore, relatively independent of local environmental conditions. These novel results extend our previous understanding of the ecological effects of habitat structure because they demonstrate possible limitations of commonly used definitions of structural complexity, as well as distinct upper thresholds in the relationship between structural complexity and faunal species richness.