Deviations in the life-history of Gracilaria sp. (Rhodophyta,Gigartinales), from Coquimbo,Chile, under different culture conditions

Cystocarpic branches of a species of Gracilaria from Coquimbo, Chile, were cultured in vitro. A Polysiphonia-like life history was completed in about 6 months, but some abnormalities were observed: i. carpospores gave rise to plants producing either tetrasporangia and spermatangia, or tetrasporangia only; ii. tetraspores cultured without aeration developed into plants bearing spermatangia only; tetraspores cultured with aeration developed into 1:1 female and male gametophytes; iii. plant originated from tetraspore produced spermatangia and tetrasporangia; one of these tetraspores developed into a male gametophyte; iv. some tetraspores gave rise to spherical bodies instead of the ordinary cylindrical branches; one of them bore spermatangia after three months. The results show that environmental factors seem to be interfering with the mechanism of sex determination and induce the development of spermatangia on putative female gametophytes, or on putative tetrasporophytes. Noted added in proof: The Gracilaria sp. studied here was recently described as a new species, G. chilensis by Bird C. J., McLachlan, J & Oliveira, E. C. de, 1986. Can. J. Bot. 64: 2928–2934. Noted added in proof: The Gracilaria sp. studied here was recently described as a new species, G. chilensis by Bird C. J., McLachlan, J & Oliveira, E. C. de, 1986. Can. J. Bot. 64: 2928–2934.     

Cultivation of Gracilaria on the sea-bottom in southern Chile: a review

This review contains information about the cultivation techniques, strategies, problems and new challenges faced as well as an economic analysis of the income-producing capacity of Gracilaria farming, considering the variability of environmental systems where this alga is cultivated in southern Chile. The development of Gracilaria farming in Chile was made possible by an increased market demand, as well as the existence of basic knowledge that permitted the management of wild stocks and the initiation of cultivation practices. Subtidal cultivation systems appear to be more productive than intertidal systems and are less susceptible to wave action than intertidal cultivation areas. In relation to farming practices, this difference implies that planting and harvesting methods and strategies vary between habitats where cultivation is being carried out on a commercial scale. Several problems such as the environmental impact of different cultivation methods adopted by the farmers, the management of contaminating organisms and strain selection appear to be important and new areas for future research. Finally, an analysis of the income-producing capacity indicates that environmental differences also have important consequences for the management strategies of Gracilaria cultivation.     

Gynandromorph analysis of the thoracic disc primordia inDrosophila melanogaster

Summary Cell lineage relationships observable inDrosophila gynandromorphs have been used to locate the primordia of the individual thoracic disc relative to each other in the embryo. Three observations indicate that the borders of the individual disc primordia lie very close to each other, separated by few if any non-disc cells.First, the frequency of mosaicism within each disc indicates large primordia, of similar magnitude to the distances between the centres of adjacent primordia.Second, very few XX/XO-borders cut between adjacent discs without also cutting into one or the other disc.Third, sturt distances between points on adjacent discs are often much smaller than distances measured within individual discs. The proximity of disc primordia suggests that the individual discs might share common precursor cells in the early embryo.     

A review of the life history,reproduction and phenology of Gracilaria

The basic life history of the red alga Gracilaria is of the three-phase Polysiphonia type but a number of species show deviations. Plants can bear both gametangia and tetrasporangia, either on separate parts of the thallus or on the same. Explanations include the in situ germination of tetraspores (allowing gametophytic thalli to be epiphytic on tetrasporophytes), the coalescence of spores or developing discs (resulting in chimaeras), mitotic recombination during cell division in the mature diploid thallus (resulting in patches of diploid male and female cells on the tetrasporophyte), a mutation eliminating the repression of female expression allowing haploid male plants to be bisexual and initial failure of cell walls to form during the development of tetraspores. Polyploids can be produced from plants with diploid gametangia. The sexes and phases are usually morphologically identical but gametophytes or their parts may be smaller. The growth rates of the sexes may differ and diploid juveniles may survive better than haploid. Neither polyploidy nor hybridization results in superior growth. The sex ratio is probably 1:1 but females may appear to be more abundant. Diploid and haploid phases are usually either about equal or diploids predominate, often depending on the type of substratum. At high latitudes reproduction peaks in late summer whereas in the tropics it may be high all year. In temperate regions growth rate is fastest and biomass highest in late summer; in the tropics peak biomass is mainly in the winter. Spermatia are effective for only a few h. Spores vary in size around 25 \m, diploid ones usually being larger. Cystocarps or tetrasporangia in the field may not currently be releasing spores. In the laboratory spore release shows a diurnal rhythm, peaking during the night or day according to the species. All the above attributes are potentially important in planning and executing Gracilaria cultivation.     

The expanding range of Undaria pinnatifida in southern New Zealand: distribution, dispersal mechanisms and the invasion of wave-exposed environments

Very few studies have addressed how the invasive kelp Undaria pinnatifida (Harvey) Suringar spreads beyond initial founding populations in harbours. Surveys of the harbours and accessible areas of open coast throughout southern New Zealand were conducted to determine how far U. pinnatifida populations had extended since initial incursions. Our findings clearly demonstrate that U. pinnatifida is capable of invading native communities and can establish reproductive populations in locations subjected to significant and consistent wave action. The extent of spread from source populations differs between harbours in which it has established. Dispersal is greatest in harbours with long established populations, those where populations have not been strategically managed, harbours with high water exchange with surrounding coastal waters, and where prevailing currents allow establishment of U. pinnatifida on suitable substrata close to harbour entrances. Dispersal along the open coast is primarily achieved by drifting adult sporophytes that are washed up in the rocky intertidal zone. Founding populations are most often found in the intertidal zone, primarily within rockpools. Subtidal transects and observations indicate that U. pinnatifida is well adapted to invade exposed coastlines and can establish within a broad range of niches in wave-exposed areas including rockpools, the low intertidal, shallow subtidal, Macrocystis pyrifera kelp forests, and in low light areas beyond the vertical extent of large native macroalgae. The current range of U. pinnatifida is much greater than expected and appears to be expanding. Due to its ability to grow in a broad range of environments and to form dense monospecific stands, U. pinnatifida has the potential to strongly modify almost all rocky subtidal and intertidal communities in temperate locations.     

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.     

Interaction mechanisms between Gracilaria chilensis (Rhodophyta) and epiphytes

Epiphytes can have a considerable effect on Gracilaria production, and Ulva is one of the commonest algal species identified as an epiphyte, reaching loads of 60% (g of epiphytes per g of Gracilaria) in the intertidal cultures of southern Chile. This study evaluates the relative importance of light reduction, addition of weight to the host thalli and nutrient depletion, as mechanisms determining the interaction effects of Ulva epiphytes on Gracilaria cultivation. Using field experiments undertaken during the main Gracilaria growth season (spring), we evaluate the mechanisms of epiphyte-host algae interaction by manipulating artificial epiphytes. The results indicate that Ulva can significantly depress Gracilaria biomass production and that the addition of weight to the host algae and the consequent dislodgement increase, appear to be the main mechanisms involved in the Ulva-Gracilaria interaction. However, the light reduction caused by the epiphytes can also partially explain the reduction in Gracilaria production. Nutrients depletion would not appear to fully account for the detrimental effects of Ulva over Gracilaria in intertidal farming areas of southern Chile.     

Influence of enhanced CO2 on growth and photosynthesis of the red algaeGracilaria sp. andG. chilensis

The influence of elevated CO₂ concentrations on growth and photosynthesis ofGracilaria sp. andG. chilensis was investigated in order to procure information on the effective utilization of CO₂. Growth of both was enhanced by CO₂ enrichment (air + 650 ppm CO₂, air + 1250 ppm CO₂, the enhancement being greater inGracilaria sp. Both species increased uptake of NO₃ ^– with CO₂ enrichment. Photosynthetic inorganic carbon uptake was depressed inG. chilensis by pre-culture (15 days) with CO₂ enrichment, but little affected inGracilaria sp. Mass spectrometric analysis showed that O₂ uptake was higher in the light than in the dark for both species and in both cases was higher inGracilaria sp. The higher growth enhancement inGracilaria sp. was attributed to greater depression of photorespiration by the enrichment of CO₂ in culture.     

INFECTIOUS DISEASES OF MAZZAELLA LAMINARIOIDES (RHODOPHYTA): CHANGES IN INFECTION PREVALENCE AND DISEASE EXPRESSION ASSOCIATED WITH SEASON,LOCALITY, AND WITHIN-SITE LOCATION1

This study addresses the issues of infection prevalence and disease expression in two wild populations of the red algal host Mazzaella laminarioides and their variability associated with locality, season, and spatial location of the host in the intertidal zone. Our results demonstrated that Endophyton ramosum is the most frequent infective pathogen affecting M. laminarioides in Matanzas and Pucatrihue. This situation prevailed through the year and across the high-to-low intertidal gradient. Although there was a general trend for lower levels of infection in late winter and early spring, only in a few, cases was well-defined seasonality detected. Furthermore, clear seasonal patterns, as displayed by deformative disease in the high intertidal zone of Pucatrihue, were attenuated in the middle and lower intertidal zones. Differences in levels of infection in M. laminarioides between the high intertidal zones of Matanzas and Pucatrihue diminished toward the low intertidal zone. Thus, effects of seasonality and locality on infection prevalence may be influenced, at least in part, by the position of the hosts an the intertidal zone. Spatial distribution of the diseased individuals also varied along the beach. This pattern was consistent between the two sites and seemed related to wave exposure and the specific pathogen. Comparisons of the size distribution of noninfected fronds with their infected counterparts showed that infections by Endophyton ramosum and Pleurocapsa sp. more frequently affected medium-and large-sized fronds. This pattern was consistent temporally and similar in the two localities. Finally, a clear association between maturity and prevalence of infection was detected. This association resulted in most fronds of the noninfected segment of the host population being immature, whereas most mature fronds were infected. In conclusion, infectious diseases affecting the red alga Mazzaella laminarioides are a persistent phenomenon in wild populations of the host, although only a small segment of the infected populations displays the full expression of the disease. In spite of the suggested role of factors such as season, latitude, and spatial location of the host on disease prevalence and expression, additional studies are needed to understand fully the dynamics of infectious diseases in wild populations of algal hosts.     

Gradients of intertidal primary productivity around the coast of South Africa and their relationships with consumer biomass

The structure of rocky intertidal communities may be influenced by large-scale patterns of productivity. In this study we examine the in situ rates of production by intertidal epilithic microalgae (chlorophyll a production per unit area per month), intertidal nutrient concentrations (nitrates, nitrites, phosphates and silicates), and standing stocks of different functional-form groups of macroalgae around the South African coast, and their relationships to consumer biomass. Clear gradients of in situ intertidal primary production and nutrient concentrations were recorded around the South African coast, values being highest on the west coast, intermediate on the south and lowest on the east coast. Primary production by intertidal epilithic microalgae was correlated with nutrient availability and could also be related to nearshore phytoplankton production. The dominance patterns of different functional forms of macroalgae changed around the coast, with foliose algae prevalent on the west coast and coralline algae on the east coast. However, overall macroalgal standing stocks did not reflect the productivity gradient, being equally high on the east and west coasts, and low in the south. Positive relationships existed between the average biomass of intertidal intertebrate consumers (grazers and filter-feeders) and intertidal productivity, although only the grazers were directly connected to in situ production by epilithic intertidal microalgae. The maximum body size of a widely distributed limpet, Patella granularis, was also positively correlated with level of in situ primary production. The maximal values of biomass attained by intertidal filter-feeders were not related to intertidal primary production, and were relatively constant around the coast. At a local scale, filter-feeder biomass is known to be strongly influenced by wave action. This implies that the local-scale water movements over-ride any effects that large-scale gradients of primary production may have on filter-feeders. The large-scale gradient in intertidal productivity around the coast is thus strongly linked with grazer biomass and individual body size, but any effect it has on filter-feeder biomass seems subsidiary to the local effects of wave action.     

Influence of waves and currents on the growth rate of the kelp Laminaria digitata (Phaeophyceae)

The kelp Laminaria digitata growing in the low intertidal region along energetic coastlines are exposed to a range of hydrodynamic environments. Macroalgae in the intertidal zone can experience both waves and currents independently, but it is unknown how they influence growth rate. Relative growth rate of the meristematic region and the entire blade of L. digitata were measured to assess the influence of wave and current motion from three hydrodynamic environments: low current and low wave (LCLW), high current and low wave (HCLW), and high wave and low current (HWLC). Alongside hydrodynamic data, seawater nutrient concentrations and temperature were also collected and analyzed. Results suggest that differences in L. digitata relative growth rates were not attributed to the seawater nutrient concentrations or temperature, but attributed to the hydrodynamic environments. At the high current condition, kelp growth rate of the meristematic region was enhanced by 45% compared to the high wave condition. When including the entire blade growth rate, an average increase of 25% was observed between the high current and high wave condition. Potentially, the division in growth rate observed between the wave and current motion is related to the frequency and magnitude at which the hydrodynamic forces act. These findings highlight the complexity of the hydrodynamic environment and that forces associated with waves and currents may have a significant role on the productivity of kelp.     

The intertidal distribution of the grey mangrove (Avicennia marina) in southeastern Australia: The effects of physical conditions,interspecific competition,and predation on propagule establishment and survival

Abstract The upper and lower limits of the distribution of mature Avicennia marina lie between mean high water and mean sea level in open estuaries in southeastern Australia. Newly established seedlings are highly variable in abundance, but are rarely found in the saltmarsh or on mudflats. Their distribution is unlikely to be limited by dispersal because propagules disperse into the saltmarsh and to intertidal mudflats, but their establishment may be limited by physicochemical conditions, interspecific competition and predation. The model that physicochemical conditions control the intertidal limits of establishment of seedlings was accepted for propagules stranding in the saltmarsh but rejected for those stranding on mudflats. No seedlings established on saltmarsh sediments but similar numbers of seedlings established within light gaps in adult mangrove stands and on intertidal mudflats. The model that interspecific interaction with freeliving macroalgae (Hormosira banksii) reduces the establishment of seedlings on mudflats covered with macroalgae or in stands with a ground cover of macroalgae was accepted. Under controlled conditions five times as many propagules established on cleared ground compared with ground covered with macroalgae. Predators also reduce seedling establishment, but the model that they preferentially act on propagules stranding on the mudflat was rejected. The low number of seedlings found on mudflats without macroalgae appears to relate to wave and current effects on establishment and the effects of waterlogging or fouling on survival.     

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.     

基于孢子粘附功能的大型海藻生态修复技术研究

为实现大型海藻人工移植高效、节约和可持续性,研究基于大型海藻孢子的粘附特性,于2020年4月,初选了几种食品添加剂作为粘附剂,与铜藻(Sargassum horneri)孢子混合后,通过室内外涂覆实验观察孢子附着、萌发和生长情况,筛选出最优的粘附剂,并通过铜藻孢子低温保存实验研究解决延长海藻人工移植周期问题.结果表明:...     

UNUSUAL PHENOMENA IN THE LIFE HISTORIES OF FLORIDEAE IN CULTURE1

Several Florideae grown in natural seawater media under defined laboratory conditions have interesting and unusual life histories. Antithamnion occidentale males of one generation produced tetraspores that gave rise to nonsporangiate males. The functional females of A. pygmaeum developed spermatangia and tetrasporangia; the tetraspores formed new females. Antithamnion defectum tetrasporophytes of one generation bore spermatangia in addition to tetrasporangia; the tetraspores gave rise to typical gametophytes. Tetraspores from successive generations of Callitham-nion sp. developed into tetrasporophytes and males but no females were produced. Functional female gametophytes of Platythamnion sp. bore abortive tetrasporangia. Field-collected plants of two species of Fauchea produced tetraspores that yielded additional sporangiate plants: those of F. pygmaea being bispo-rangiate and tetrasporangiate, and those of F. lacini-ata being strictly tetrasporangiate. Male plants of Pleonosporium vancouverianum from a running seawater table bore spermatangia and polysporangia when collected. The same plants in unialgal culture produced only spermatangia.     

Grazing effects of the periwinkle <Emphasis Type="Italic">Echinolittorina</Emphasis><Emphasis Type="Italic">peruviana</Emphasis> at a central Peruvian high rocky intertidal

Echinolittorina peruviana is the most common gastropod in the high intertidal zone of Peru, representing more than 80% of the individuals present at that zone. Experimental removal of snails was used to evaluate their effects on (a) abundance of epilithic biofilm, (b) barnacle recruitment, and (c) abundance of macroalgae under “normal” conditions of the El Niño Southern Oscillation (ENSO). Experiments were carried out from October 2005 to April 2007 at two intertidal levels of a semi-protected rocky shore of central Peru. Results demonstrated that E. peruviana is able to control biofilm abundance and barnacle recruitment at both heights investigated, with marked effects in the lower zone. Erect macroalgae (Ulva spp. and Gelidium spp.) were less affected by grazing; but negative effects were observed on macroalgal crusts. Season and physical stress seem to play a more important role in the abundance of macroalgae in the high intertidal. Our results are similar to those reported elsewhere for high shore littorinids and represent baseline data to understand how the role of intertidal consumers will vary under the cold (La Niña) and warm (El Niño) phases of ENSO on these shores.     

Kelp versus coralline: cellular basis for mechanical strength in the wave‐swept seaweed Calliarthron (Corallinaceae,Rhodophyta)1

Previous biomechanical studies of wave‐swept macroalgae have revealed a trade‐off in growth strategies to resist breakage in the intertidal zone: growing in girth versus growing strong tissues. Brown macroalgae, such as kelps, grow thick stipes but have weak tissues, while red macroalgae grow slender thalli but have much stronger tissues. For example, genicular tissue in the articulated coralline Calliarthron cheilosporioides Manza is more than an order of magnitude stronger than some kelp tissues, but genicula rarely exceed 1 mm in diameter. The great tissue strength of Calliarthron genicula results, at least in part, from a lifelong strengthening process. Here, a histological analysis is presented to explore the cellular basis for mechanical strengthening in Calliarthron genicula. Genicula are composed of thousands of fiber‐like cells, whose cell walls thicken over time. Thickening of constitutive cell walls likely explains why older genicula have stronger tissues: a mature geniculum may be >50% cell wall. However, the material strength of genicular cell wall is similar to the strength of cell wall from a freshwater green alga, suggesting that it may be the quantity—not the quality—of cell wall material that gives genicular tissue its strength. Apparent differences in tissue strength across algal taxa may be a consequence of tissue construction rather than material composition.     

Seaweeds early development: detrimental effects of desiccation and attenuation by algal extracts

The effects of desiccation on the early development stages of Mazzaella laminarioides, Scytosiphon lomentaria and Lessonia nigrescens, algal species with different patterns of distribution across the intertidal zone, were examined in the laboratory. In addition, the protective effect against desiccation was evaluated using algal extracts, including those from Porphyra columbina, a macroalga tolerant to desiccation that lives in the uppermost part of the intertidal zone. Our results showed that M. laminarioides displayed the highest resistance to daily desiccation, followed by S. lomentaria, whereas L. nigrescens was the most susceptible. Spores from L. nigrescens exposed to desiccation, although being able to germinate, ceased further post-germination development. In addition, our results showed that all species exposed to extracts from desiccated P. columbina successfully completed their development and strongly suggest the occurrence of compounds with protective properties that help in attenuating the stress caused by desiccation. Finally, our results indicate that the magnitude of the effects generated by desiccation on the early algal development is related to the position of the species in the intertidal zone, and that the protective effects of P. columbina extracts reveal an exceptional metabolism of this species under desiccation stress.     

Food and feeding behavior of the nemerteanTortus tokmakovae

The food and feeding behavior of the suctorial nemerteanTortus tokmakovae Chernyshev, 1991, inhabiting the intertidal zone of Peter the Great Bay are studied. Laboratory observations show that this tortus is capable of attacking and consuming 6 species of amphipods, Mysidae gen. sp. mysids andPandalus sp. shrimps. Moreover, the tortuses suck the tissues of various dead crustaceans. Several tortuses may together attack and consume one amphipod. It is suggested thatT. tokmakovae play a significant role in intertidal communities.     

Imaginal disc development in a non-pupariating lethal mutant inDrosophila melanogaster

Summary Imaginal disc development in the non-pupariating lethall(1)npr-1, a mutant that maps to an ecdysone early puff site, is studied in situ, in vitro and in transplanted discs. Disc development is slightly abnormal from the middle of the third instar with severe abnormalities appearing after the rise in 20-hydroxyecdysone that triggers metamorphosis. The mutant discs only partly evaginate and do not undergo any of the detailed morphological changes characteristic of metamorphosis. Treatment of the mutant dises in vitro with colcemid and trypsin facilitates evagination but the appendages remain morphologically abnormal. A number of differentiative processes occur in mutant discs in situ and in discs transplanted into wild type hosts in spite of the absence of normal morphogenesis. Implications of the observations for normal disc development are discussed. Possible modes of action of thel(1)npr-1 gene are also discussed in light of the observation that the mutant gene maps to a locus which is thought to have a regulatory function in development.