三亚岩相潮间带底栖海藻群落结构及其季节变化

为了解三亚潮间带大型海藻生态现状,布设6条岩相断面,于2008年1—11月进行了四季野外的调查,并使用物种多样性指数与聚类分析研究了潮间带大型海藻四季的群落结构和多样性变化。调查共鉴定出大型底栖藻类130种,隶属于4门75属,其中红藻门41属67种、褐藻门16属31种、绿藻门15属29种、蓝藻门3属3种。潮间带海藻种类数季节变化不大,并呈低潮带>中潮带>高潮带的垂直分布特征,且中低潮带有共同分布种,夏季尤为普遍。潮间带海藻夏冬两季平均生物量高于春秋两季,但并无显著差异。优势种季节变化明显:春季有波利团扇藻Padina boryana、日本仙菜Ceramium japonicum、半叶马尾藻Sargassum hemiphyllum、海柏Polyopes polyideoides,夏季有波状软凹藻Chondrophycus undulates、冠叶马尾藻Sargassum cristaefolium、宽扁叉节藻Amphiroa dilatata、石花菜Gelidium amansii,秋季有冠叶马尾藻、波状软凹藻、叶状铁钉菜Ishige foliacea,冬季有瓦氏马尾藻Sargassum vachellianum、苔状鸭毛藻Symphyocladia marchantioides、珊瑚藻Corallina officinalis、波利团扇藻、日本仙菜。群落多样性冬高夏低:Shannon多样性和Margalef丰富度指数最大值出现在冬季,Shannon多样性和Pielou均匀度指数最低值出现在夏季。区域底栖藻类以暖水性热带-亚热带种为主,其次为温水性的暖温带种类,基本符合南海南区暖水区系特点。研究表明,尽管三亚潮间带底栖海藻种类数与生物量上并无显著的季节差异,但群落结构与多样性均显示出一定的季节变化。     

Specific photosynthetic and morphological characteristics allow macroalgae Gloiopeltis furcata (Rhodophyta) to survive in unfavorable conditions

Gloiopeltis furcata (Postels & Ruprecht) J. Agardh, a macroalga, which grows in an upper, intertidal zone, can withstand drastic environmental changes caused by the periodic tides. In this study, the photosynthetic and morphological characteristics of G. furcata were investigated. The photosynthetic performance and electron flows of the thalli showed significant variations in response to desiccation and salinity compared with the control group. Both PSII and PSI activities declined gradually when the thalli were under stress. However, the electron transport rate of PSI showed still a low value during severe conditions, while the rate of PSII approached zero. Furthermore, PSI activity of the treated thalli recovered faster than PSII after being submerged in seawater. Even though the linear electron flow was inhibited by DCMU [3-(3, 4-dichlorophenyl)-1,1-dimethylurea], the cyclic electron flow could still be restored. The rate of cyclic electron flow recovery declined with the increasing time of dark treatment, which suggested that stromal reductants from starch degradation played an important role in the donation of electrons to PSI. This study demonstrated that PSII was more sensitive than PSI to desiccation and salinity in G. furcata and that the cyclic electron flow around PSI played a significant physiological role. In addition, G. furcata had branches, which were hollow inside and contained considerable quantities of funoran. These might be the most important factors in allowing G. furcata to adapt to adverse intertidal environments.     

The importance of shore height and host identity for amphipod assemblages

The spatial distribution of organisms associated with marine intertidal macroalgae may be a direct result of their tolerance to air exposure or an indirect consequence of the distribution of their host. We compared amphipod assemblages from five intertidal macroalgae to investigate their relationship with algal identity. To test the effect of height regardless of algal characteristics, we transplanted coralline algal turfs to three different levels within the intertidal zone and compared amphipod assemblages after 1 and 14 days. Interstitial volume was positively correlated to the abundance of amphipods, suggesting that this attribute may correspond better to the potential space for their occupation when compared to algal biomass, thallus volume or the ratio between thallus and interstitial volume. Algal level determined the structure of the amphipod assemblages. Upper-level (Acanthophora spicifera and Caulerpa racemosa) and intermediate-level (coralline) algae host similar amphipod assemblages dominated by Apohyale media, but different from lower-level algae (Padina gymnospora and Sargassum cymosum), which were dominated by Hyale niger. Ten of the 15 amphipod species reported from natural communities were found in the transplanted plots. Distinct pools of amphipod species colonized coralline transplants at upper and lower levels after 1 day. However, regardless of the position on the shore, transplanted coralline turfs supported similar assemblages after 14 days, indicating that algal identity is also important for species assemblages. Our results suggest that both height on the shore and host identity combine to determine the vertical structure of amphipod assemblages in the rocky intertidal.     

A short-term response of macroalgae to potential competitor removal in a mid-intertidal habitat in Korea

Interspecific interactions among three dominant macroalgae, Pterocladia capillacea (Rhodophyta), Hizikia fusiformis (Heterokontophyta) and Chondracanthus intermedius (Rhodophyta), were experimentally investigated on the rocky mid-intertidal zone of Sungsan, Jeju Island, Korea from March 1998 to June 1999. Each of the potentially competing species was removed in permanent plots (20 × 20 cm), and percent covers of non-manipulated species were measured by an image analyzing method using a digital camera. Pterocladia capillacea was the most abundant during all seasons, except for winter. Its abundance was lowered by the removal of the turf-forming alga C. intermedius, indicating that turf had a positive effect on P. capillacea. Conversely, there was a negative effect of P. capillacea on the abundance of C. intermedius. Interactions between C. intermedius and P. capillacea can probably be explained as a consequence of the water-trapping ability of the former and the canopy-forming ability of the latter. There was, however, no apparent effect related to H. fusiformis since the abundance of this alga remained low. This study supports that both negative and positive effects between same pair of species could be common depending on the morphological differences of algae and particular habitat conditions.     

Patterns of organizations of intertidal and shallow subtidal vegetation in wave exposed habitats of central Chile

Wave-exposed rocky intertidal habitats of central Chile exhibit zonation of algal morphologies rather than strict patterns of species zonation. In low shore areas, there is a vertical sequence of perennial belts of calcareous crusts, kelp-like forms and expanded cushions or non-calcareous crusts. The calcareous crusts are represented by species of Mesophyllum, the kelp-like forms include Lessonia nigrescens and Durvillaea antarctica, while the cushions are represented by Gelidium chilense and G. lingulatum and the noncalcareous, expanded crusts by Codium dimorphum. Thin and thick blades, represented by Iridaea laminarioides, Ulva rigida and Porphyra columbia and filamentous forms including Ceramium rubrum, Centroceras clavulatum and Polysiphonia spp. are more patchy than the lower, perennial belts. They may, however, form distinct temporal monocultures at upper intertidal levels. Upper and lower limits of the various zones are set by interactions of several factors, the relative importance of which can change seasonally. When some of the factors restricting species distribution are experimentally removed, other interactions among factors become limiting.Within each zone, species are morphologically similar, with the abundance of species being regulated by symmetric competitive interactions. Competition is often asymmetric at the boundaries of zones except when adults of small-sized forms interact with morphologically similar juveniles of larger forms. Irrespective of their extremely different morphologies, the permanent, zone-forming algal species generally combine escape from grazers or defensive adaptations with clear competitive abilities. Nevertheless, there is a clear competitive hierarchy which is expressed in vertical displacements and zonation. The lowershore habitats could potentially be occupied by any of the different types of algae. Fast growth and large size allow the kelps to occupy this zone pushing the calcareous crust dominated-zone down into shallow subtidal areas and displacing the cushions and fleshy crusts into the low and middle intertidal regions. In turn, these last forms can displace thick and thin foliose forms and filaments to upper levels on the shore. Displaced forms may exist as patches at various levels of the shore.     

Effects of height on the shore and complexity of habitat on abundances of amphipods on rocky shores in New South Wales, Australia

Patterns of abundance of epifaunal crustaceans were compared between two common brown algae in intertidal rock pools on a shore near Sydney, New South Wales, Australia. Amphipods were significantly more abundant on Sargassum globulariaefolium (which was most common low on the shore) than on Hormosira banksii (more common at mid-shore levels). Experiments tested the hypotheses that height on the shore and structural complexity of the algae were the main factors influencing patterns of abundance of amphipods. Reciprocal transplants using defaunated plants and similar experiments using artificial plants allowed simultaneous tests of these hypotheses. The abundance of a common intertidal amphipod, Sunampithoe graxon was significantly smaller on Sargassum transferred from low to mid-tidal level of the shore than on any other treatments, indicating that height on the shore affects numbers of this species. There were no Sunampithoe on Hormosira even when transplanted to low shore areas, indicating that other factors, apart from the height on the shore, are also important for this amphipod. Another common amphipod, Hyale maroubrae was generally found in greatest abundances on Hormosira transplanted from mid- to low shore and on Sargassum low on the shore, again indicating the importance of height on the shore. There was no difference in abundance of amphipods on ‘complex’ and ‘simple’ artificial plants indicating that structural complexity (as defined in this study) did not influence these amphipods.     

Sur la disparition progressive de Laminaria digitata sur les côtes du Calvados (France)

In comparison with results from 1983–1988, when a cartographic study was made on the distribution of the Laminariales and of Sargassum muticum in Lower Normandy (France), we note, on the Calvados coast, a regression of Laminaria digitata which has almost disappeared on the Grandcamp rocks. On the contrary, the growth of the populations of Sargassum muticum is very spectacular at Grandcamp; in summer, 80 % of the substratum in the lower parts of the intertidal zone and in the subtidal are covered by this species.     

Ecology and dynamics of two intertidal algal communities on the littoral of the island of São Miguel (Azores)

The intertidal benthic algal communities of two sites located on opposite coasts of São Miguel Island (Azores), were studied over a 2-year period (September 1993–September 1995). At both sites (São Roque on the south coast and São Vicente on the north), the littoral region was surveyed from the upper intertidal down to the sublittoral fringe. The survey revealed five distinct zones, with a variable degree of overlapping. The two upper zones were characterized by animals (littorinids and barnacles, respectively). Lower down, algal communities formed three distinct zones: an upper Fucus spiralis/Gelidium microdon association, a more extensive turf zone, and a belt featuring erect or frondose algae. Upper in the eulittoral, the turf was mainly monospecific, and dominated by Caulacanthus ustulatus. The lower eulittoral turf was dominated by articulated coralline algae, the associated species differing between the two sites studied. Mainly erect algae (Pterocladiella, Asparagopsis, etc.) occurred furthest down the shore and extended into the nearby shallow sublittoral. Two intertidal communities were studied at each locality: the upper eulittoral (Caulacanthus turf in São Roque and the Fucus spiralis/Gelidium microdon association at São Vicente), and the lower eulittoral (the coralline turf). The lower littoral communities had a higher algal diversity. A general pattern was observed in the seasonal variation of biomass: the lower levels exhibited the higher values in late summer/early autumn, the period in which the upper levels had the lowest standing crops. Physical factors are proposed to account for this. No significant inter-annual variations could be detected, indicating relatively stable communities, at least on a short-term basis.     

Usefulness of tissue nitrogen content and macroalgal community structure as indicators of water eutrophication

We tested the hypothesis that the community structure and biochemical composition of macroalgae reflect the degree of nutrient concentrations in the water column. Benthic community structure and tissue nitrogen (N) content of macroalgae on intertidal rocky shores at three sites were investigated in relation to sewage effluents on Mireuk Island, Tongyeong city, on the southern coast of Korea. Ulva australis clearly dominated at site 1, which was close to a sewage treatment plant, where higher dissolved inorganic N and dissolved inorganic phosphate concentrations were observed. U. australis-dominated communities also appeared at site 2 (intermediate levels of nutrient enrichment). The macroalgal assemblage at site 3 (unimpacted site) was significantly different from those at sites 1 and 2. Five species (U. australis, Sargassum fusiforme, Grateloupia elliptica, Gelidium amansii, and Sargassum horneri) were dominant at site 3, representing 87 % of the total coverage throughout the study period. Species richness (d), evenness (J'), and diversity index (H') were highest at site 3, intermediate at site 2, and lowest at site 1, showing a negative relationship with nutrient levels. These results indicate that macroalgal community structure can be used as a bioindicator in water quality assessment. The tissue N content of green and red algae was responsive to nutrient availability, while the tissue N content of brown algae was relatively unchanged among the sites. This suggests that tissue N content as a bioindicator for detecting the influence of sewage effluent should be considered to reflect the N storage capacity of macroalgae.     

Inhibition of Taq DNA polymerase by seaweed extracts from British Columbia, Canada and Korea

Fifty-nine species of marine macrophytes from the coasts of British Columbia, Canada and Korea have been screened for the presence of PCR inhibitors, namely inhibitors of Taq DNA polymerase. Eleven of the species displayed some inhibitor activity. At the concentration of 5 μg of methanol extract in 25μL reaction mixture of PCR containing 1.5 unit of Taq DNA polymerase, one (Ulva sp.) of 8 Chlorophyta, eight (Colpomenia bullosa, Ecklonia cava, Endarachne binghamiae, Fucus distichus, Hizikia fusiformis, Sargassum confusum, Sargassum sagamianum, and Sargassum thunbergii) of 28 Phaeophyta, and one (Symphyocladia latiuscula) of 34 Rhodophyta showed inhibition in PCR amplification. In the case of the water extract, two (Cladophora columbiana, Ulva sp.) Chlorophyta, seven (Endarachne binghamiae, Fucus distichus, Hizikia fusiformis, Sargassum confusum, Sargassum sagamianum, Sargassum horneri, Scytosiphon dotyi) Phaeophyta, no Rhodophyta and one (Phyllospadix scouleri) seagrass showed inhibition in PCR amplification. the methanol fraction of Sargassum confusum and the water fraction of Fucus gardneri (mid–intertidal) have been found to inhibit PCR at level as low as 0.5 μg in 25μL of PCR reaction mixture. This revised version was published online in August 2006 with corrections to the Cover Date.     

Single-species versus mixed-species community: which one is better for shore stabilization. A case study of Chongming Island, China

There are five vegetation communities for shore stabilization on the southern coast of Chongming Island: a reed (Phragmites australis) community, a 4-yr-old Salix babylonica-Phragmites australis community (4Sb), an 8-yr-old S. babylonica-P. australis community (8Sb), a 4-yr-old Taxodium ascendens-Phragmites australis community (4Ta), and an 8-yr-old T. ascendens-P. australis community (8Ta). One major question is which is better for shore stabilization: the reed community (a single-species community) or 4Sb, 8Sb, 4Ta and 8Ta (mixed-species communities)? The soil stability index (K) and root length density (RLD) were selected as indicators for evaluating soil stability in response to water erosion. There are two main types of shore facing downward erosion and erosion scarp retreat along the southern coast of Chongming Island, and the erosion period may occur from March to August (scenario 1) or October to December (scenario 2). The assumed erosion period is scenario 1, and 4Sb is the most suitable plant community for preventing erosion scarp failure and mitigating shoreline retreat because it has the greatest K and RLD in the 20-50-cm deep soil layer among all of the vegetation communities within all intertidal zones. Additionally, 4Sb and 8Ta provide the best protection for reducing downward beach face erosion compared to the other vegetation types in the lower intertidal zone (LIT). At the middle intertidal zone (MIT) and higher intertidal zone (HIT), the reed community is optimal for protecting the shore face because it has the greatest K and RLD at 0-20-cm soil among the five vegetation communities in March-April and July-August within the MIT and HIT. Under scenario 2, 4Sb is still the most suitable type for reinforcing the scarp and preventing shoreline retreat. With respect to shore face downward erosion, 8Ta might provide the best protection for beach surfaces within the intertidal zones because it had the greatest K and RLD at 0-20-cm depth among the five vegetation types in November-December within the LIT, MIT and HIT.     

LONG‐TERM CHANGES IN THE STRUCTURE OF INTERTIDAL ASSEMBLAGES AFTER INVASION BY SARGASSUM MUTICUM (PHAEOPHYTA)1

The macroalgal assemblages at the low intertidal zone were studied at three localities on the north coast of Spain between 1977 and 2002. Two of these localities were invaded at the end of the 1980s by the brown seaweed Sargassum muticum (Yendo) Fensholt (Phaeophyta, Sargassaceae), whereas the third locality remained free of the invader. In 2002, distinct algal assemblages were noticed in invaded and noninvaded localities. No major changes were detected in the noninvaded locality. Apart from the obvious presence of S. muticum, the changes observed in the invaded localities included a significant reduction in abundance of the previous dominant species (the red alga Gelidium spinosum (S. G. Gmelin) P. C. Silva) as well as an increased number of species and diversity, increased primary productivity, and variations in the seasonal abundance patterns of some species. We speculate that the arrival of S. muticum had a negative effect on the dominant native G. spinosum, probably related to competition for light. This resulted in indirect positive effects on other species of the assemblage (such as Bifurcaria bifurcata R. Ross). Other small epiphytic opportunistic species might also have been benefited from the presence of S. muticum, because the invader has a rich associated epiphytic assemblage.     

Effects of light and temperature on the attachment and development of <Emphasis Type="BoldItalic">Gloiopeltis tenax</Emphasis> and <Emphasis Type="BoldItalic">Gloiopeltis furcata</Emphasis> tetraspores

Two 60-day experiments were conducted to study the influence of photon flux density (PFD) and temperature on the attachment and development of Gloiopeltis tenax and Gloiopeltis furcata tetraspores. In the first experiment, tetraspores of the two Gloiopeltis species were incubated at five temperature ranges (8°C, 12°C, 16°C, 20°C, 24°C) under a constant PFD of 80 μmol photons m⁻² s⁻¹ with a photoperiod of 12:12. In a second experiment, tetraspores were incubated under five PFD gradients (30, 55, 80, 105, 130 μmol photons m⁻² s⁻¹) at a constant temperature of 16°C with a photoperiod of 12:12. Maximum density of attached tetraspores was observed at 16°C for both species. Maximum per cent of spore germinating into disc was recorded at 12–16°C for G. tenax and 8–12°C for G. furcata. Maximum per cent of discs producing erect axes for G. tenax and G. furcata were recorded at 24°C and 20°C, respectively. Light had no significant effect on tetraspore attachment and developing into disc, but it affected the growth, sprouting and survival of its discs. Under 30–55 μmol photons m⁻² s⁻¹, the discs of the two species of Gloiopeltis did not form thallus until the end of the experiment. Optimum PFD range for G. tenax discs was 80–105 μmol photons m⁻² s⁻¹, whilst it was 80–130 μmol photons m⁻² s⁻¹ for G. furcata. Results presented in this study are expected to assist the progress of artificial seeding of Gloiopeltis.     

Zooplankton and meiobenthos diversity at the intertidal sandy shores of Jizan and Farasan coastal areas of Red Sea

Distinctive studies were conducted for the identification of meiobenthos and zooplankton at Farasan Islands and Jizan sandy shores. The present work compares the meiobenthos and zooplankton communities at Alhsas sandy shore at Farasan Islands and As-Suways sandy shore at Jizan. Population density, species richness and Shannon-Weiner diversity index were determined for meiobenthos and zooplankton inhabiting both the studied sites. Water criteria; surface water temperature, pH and conductivity were determined for each investigated site. Eleven zooplankton species were defined at Alhsas sandy shore Farasan, nine species were identified at the littoral zone at As-Suways sandy shore, Jizan. Ten meiobenthos species were defined at Alhsas site, Farasan. Only eight meiobenthos species were defined at the intertidal zone of As-Suways site, Jizan. The results were discussed to highlight the effect of water criteria on the spatial distribution of zooplankton and meiobenthos at the investigated sites.     

Ecological studies on the community of drifting seaweeds in the south-eastern coastal waters of Izu Peninsula, central Japan. I: Seasonal changes of plants in species composition, appearance, number of species and size

Seasonal patterns of drifting seaweeds in the southeastern coastal waters of Izu Peninsula of central Japan were examined by sampling 966 patches from spring to autumn 1991–1993. In total, 57 plant species appeared, including 10 epiphytic algal species. Monthly totals of the number of species, excluding epiphytic aigae, were highest in May (33) and August (27), though 19–21 species of sargassaceous algae were found from May to August, The number of species, excluding epiphytic algae, in one patch of drifting seaweeds was 1 to 11 (x?= 2.93 ± 2.06) with high richness in May a result of almost entirely sargassaceous species. The wet weight of each patch and maximum stipe length of plants varied from 5 to 6970 g and from 20 to 840 cm (x?= 536.1 ± 782,3 g and 110.6 ± 76.8 cm), respectively, with highs in April and May. Out of 18 species common to all years, 10 species dominated the top or second rank in monthly pooled frequency of appearance. Seasonal changes of these 10 major species were examined, Sargassum horneri (Turner) C. Agardh and Hizikia fusiformis (Harvey) Okamura were abundant in April, but were replaced partly by Sargassum muticum (Yendo) Fensholt in May and largely by Sargassum yamamotoi Yoshida in June. In July, Sargassum nipponicum Yendo and Sargassum piluliferum (Turner) C. Agardh dominated. Subsequently, the major species shifted to Sargassum ringgoldianum Harvey and S. yamamotoi in August, Sargassum micracanthum (Kützing) Endlicher, Sargassum macrocarpum C. Agardh and Zostera marina Linnaeus in September, and S. ringgoldianum and S. micracanthum in October. However, the occurrence of S. yamamotoi, S. nipponicum and S. piluliferum in June or July were particularly heterogeneous compared with other areas of Japan. Dendrogram analysis was done based on frequency of appearance. Pooled monthly samples were divided into three groups characterized from the dominant species, degree of domination, weight, length and number of species of drifting seaweeds as well as the degree of diversity or evenness in appearance. This characterization indicated that the diversity and abundance of drifting seaweeds were higher from April to June than in later months.     

Identification of true Gloiopeltis furcata (Gigartinales,Rhodophyta) and preliminary analysis of its biogeography

In the red algal genus Gloiopeltis, five species (G. complanata, G. dura, G. frutex, G. furcata and G. tenax) are currently recognized, but genetic analyses have suggested considerably greater species diversity. Gloiopeltis specimens formed nine highly supported clades, six of which are morphologically referable to G. furcata. In order to identify the clade corresponding to true G. furcata, we examined the morphology and genetics of the type specimen of Dumontia furcata Postels & Ruprecht, the basionym of G. furcata, housed in the Herbarium of V.L. Komarov Botanical Institute (LE). A clade comprising the type and specimens from the northwestern to northeastern Pacific Ocean was determined to correspond G. furcata. We concluded that the type locality of G. furcata is Sitka, Alaska, based on the identity of haplotypes. We investigated the genetic divergence of populations within this species, using specimens covering most of its distributional range. We confirmed the merger of G. minuta and G. dura with G. furcata.     

The relationship between the lethal freezing temperatures and the amounts of ice formed in the foot muscle of marine snails (Mollusca: Gastropoda).

The differences in the lethal freezing temperatures of the foot muscles of the marine snails used in this study were related to the vertical distributions of the snails on the shore. The muscles of the subtidal species Thais lapillus and Nassarius obsoletus were injured at temperatures that were significantly higher than those of the muscles of the intertidal species Littorina obtusata, Littorina littorea, and Littorina saxatilis. The lethal freezing temperatures also varied among the intertidal species. The foot muscle of the high-intertidal species, L. saxatilis, was injured at a significantly lower temperature than the foot muscles of the low-intertidal species L. obtusata.Calorimetry was used to show that the differences in the lethal freezing temperatures between the subtidal and intertidal snails were related to the amounts of tissue ice formed. The ability of the muscles of the intertidal snails to tolerate lower subfreezing temperatures was associated with an increased tolerance to greater quantities of tissue ice. In contrast, the differences in the lethal freezing temperatures among the intertidal species were independent of the amounts of tissue ice formed. The percentage of water frozen in the muscles of these snails at their respective lethal freezing temperatures were not significantly different and were equal to 82%. Thus, the physiological mechanism responsible for the differences in the lethal freezing temperatures of the muscles of the intertidal snails is associated with an increased tolerance to a factor other than the amounts of tissue ice formed.     

Differential effects of native and invasive algal wrack on macrofaunal assemblages inhabiting exposed sandy beaches

Many sandy beaches worldwide receive large amounts of drift seaweed, known as wrack, from offshore algal beds and closer rocky intertidal shores. Despite the important influence of algal wrack on macrofaunal assemblages from different coastal systems, relatively little attention has been paid to the macrofaunal responses in sandy beaches to macrophyte wrack supplies. Algal wrack is a key resource, i.e. for food and/or refuge, for beach invertebrates while its availability can affect diversity and abundance of intertidal animals including shorebirds, but the role of certain types of wrack and its location on the shore has not been examined experimentally to date. In this paper, we use experimental manipulation of two species of brown seaweeds, i.e. artificial wrack patches made up of the native macroalgae Saccorhiza polyschides and the invasive species Sargassum muticum, to test hypotheses about influences on macrofaunal assemblages inhabiting the drift line and supratidal levels of exposed beaches. Results pointed out that different types of wrack deposits were not used uniformly by invertebrates. Nutritional value differed between the two species of wrack. In most cases, the carbohydrates, lipids and organic carbon content were greater in patches of S. muticum than in patches of S. polyschides. Data also provided evidences that nutritional content and microclimatic conditions of wrack deposits, i.e. temperature and humidity, might affect macrofaunal assemblages.     

Population structure, recruitment, and succession of the brown alga, Padina boryana Thivy (Dictyotales, Heterokontophyta), at an exposed shore of Sirinart National Park and a sheltered area of Tang Khen Bay, Phuket Province, Thailand

The brown algal genus, Padina, has a worldwide distribution in tropical and subtropical climate zones. Padina individuals are common and sometimes dominant in both the intertidal and shallow subtidal regions associated with coral reefs. We investigated the population structure and recruitment of two populations of Padina boryana at an exposed shore in Sirinart National Park (SNP) and a sheltered shore of Tang Khen Bay (TKB), Phuket Province, Thailand. From September 2005 to August 2006, the number of released spores and the height and radius of fronds were measured monthly. New recruits were recorded and monitored on manipulated permanent plots 0.25 m². The experiment was carried out monthly over a year. We found Padina recruits 1 month after the plots were cleared at both sites. There was a significant difference in percentage cover by new individuals between the two locations (P < 0.05) and also at the shore levels within the sites. At SNP, the highest recruitment was found in the uppermost zone, while at TKB high recruitment occurred at all shore levels except at 80-100 m from the shore. The factors influencing recruitment of P. boryana include wave motion, competition with other earlier successional species and sediment. The high availability of reproductive spores throughout the year, the successful recruitment and the Dictyerpa stage promote the successful establishment of Padina populations.     

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.