Epiphytic Diatoms Research Articles

Sedimentary multiproxy response to hydroclimatic variability in Lagunillo del Tejo (Spain)

Lagunillo del Tejo is a small groundwater-fed sinkhole lake in the karst region of the Iberian Range (central-eastern Spain), which undergoes significant lake level fluctuation in response to rainfall variability. The aim of this study is to understand the record of water level fluctuations in Lagunillo del Tejo over the last two-and-a-half centuries. This information could be used in future studies to interpret longer sedimentary sequences. We analysed photosynthetic pigments, diatoms and cladoceran remains in sediment sequences recovered from the deepest part of the lake. The paleoecological proxies traced two different communities which have switched their prevalence during the past: (1) a planktonic community of algae, including diatoms, chlorophytes, cryptophytes and cyanobacteria, and phototrophic bacteria associated with higher lake level and water column seasonal stratification; (2) a littoral community with the higher levels of macrophyte pigments and associated epiphytic diatoms and chydorids, all of which indicate lower lake level. The levels of coherence between different proxies, each having an independent mechanistic link to lake-level variability, enhance the reliability of palaeolimnological inferences. The high-resolution stratigraphical data from the upper part of the core was compared with lake-level inferences from instrumental rainfall series (1859–2005) to establish the correspondence between Lagunillo del Tejo sediment sequences and climate record.

Palaeoenvironmental changes during the last 1600 years inferred from the sediment record of a cirque lake in southern Patagonia (Laguna Las Vizcachas, Argentina)

Laguna Las Vizcachas is a cirque lake located at the margin of an extra-Andean volcanic plateau in southern Patagonia, Argentina, within the area of steppe and semi-desert east of the Andes. The number of paleoenvironmental records is still limited in this region. Sediments of this lake were studied in order to obtain multi-proxy information about the paleoenvironmental history of this site for the ‘Medieval Climate Anomaly’ and the ‘Little Ice Age’ chronozones. In combination with results from other sites across southern Patagonia, our data enhance the understanding of spatial patterns of past hydrological changes and contribute to distinguishing between the signals of temperature and precipitation. As Laguna Las Vizcachas is situated at 1100 m a.s.l. in a cool ‘mountain climate’, the lake system is more sensitive to changes of temperature and winter ice cover than other sites from lower elevations in this region. Our interpretation of the multi-proxy dataset is based on signals of clastic sediment input, lake productivity, organic matter sources and preservation, dilution effects and early diagenetic overprint. The record reveals a period of enhanced fluvial runoff resulting from higher precipitation from the 12th until the end of the 14th century as inferred from high concentrations of Ti, Ca, and from magnetic susceptibility. This may coincide with higher wind intensities as suggested by higher proportions of epiphytic diatoms which point to an enhanced lateral transport from their littoral habitat towards the coring position at the center of the lake. In comparison with other records from southern Patagonia, the results from Laguna Las Vizcachas suggest opposite precipitation regimes between the western and eastern parts of Patagonia during that time which corresponds partly to the ‘Medieval Climate Anomaly’ chronozone. However, this proposal is compromised by the chronological uncertainties of the different records under consideration. The diatom record of Laguna Las Vizcachas indicates temperature changes: highest proportions of benthic diatoms point to coldest conditions from the mid-15th until the mid-17th century, followed by relatively warm conditions until the mid-18th century as suggested by a decrease of benthic taxa and a conspicuous rise of the planktonic/non-planktonic diatom ratio that can be used as an indicator for the length or presence/absence of winter ice cover.

Are epiphytes a significant component of intertidal Zostera noltii beds?

The role of epiphytes in an intertidal Zostera noltii seagrass bed in Marennes-Oléron Bay was assessed in comparison with the other main benthic primary producers ( Z. noltii, microphytobenthos) at two bathymetric levels and on a seasonal basis. Assemblage and biomass of epiphytes were studied using scanning electron microscopy (SEM). Z. noltii and its detrital matter followed a typical seasonal pattern: microphytobenthos was present in large quantities throughout the year representing 21% of the total biomass while detrital matter, above-ground parts and below-ground parts accounted for 65, 9 and 5%, respectively. Only two species of epiphytic diatoms, Cocconeis scutellum and Cocconeis placentula, were observed on seagrass leaves. Epiphyte biomass was very low, representing on average less than 0.001% of that of microphytobenthos or leaves. This low epiphyte biomass is linked with the absence of macroalgae and also with the low biovolume of Cocconeis, which formed a monolayer of cells on leaves. This can be explained by the severe conditions of the intertidal and the high leaf turn-over of Z. noltii leaves.

A Stable Isotope Investigation into the Feeding Behavior of Brychius Hungerfordi Spangler (Coleoptera: Haliplidae), a Federally Endangered Crawling Water Beetle

We use carbon and nitrogen isotope data to elucidate the diets of larval and adult Brychius hungerfordi Spangler in streams in Northern Lower Michigan. Diet analysis suggests that feeding behavior during the larval life stage is different from that of the adult. Larvae appear to prefer the alga Dichotomosiphon tuberosus (Braun) Ernst. Adults appear to be generalists, feeding on Dichotomosiphon, Cladophora Kuetzing and Chara Linnaeus as well as the epiphytic diatom Cocconeis Ehrenberg. Dichotomosiphon, although widespread, is not common. Its presence may be an important factor in determining the distribution of the Federally endangered beetle.

Effects of Epiphytic Load on the Photosynthetic Performance of a Seagrass, Zostera marina, Monitored In Vivo by Chlorophyll Fluorescence Imaging

We investigated the effects of epiphytes on photosynthetic activity in a seagrass, Zostera marina. Parameters in our chlorophyll (Chl) fluorescence imaging technique, including Fo, Fm, and Fv/Fm, were monitored from leaf surfaces before and after those epiphytes were removed. Because of the uneven distribution of light intensities, Fm values at the margin of an image were underestimated while those in the central region were overestimated. Chl fluorescence emissions from all leaves except the youngest one were altered by the presence of epiphytes, which predominantly inhabited the surfaces of older leaves. Only a few were found lower on the plant where leaves were very close to each other. Regions where the epiphytes had been loosely bound before their gentle removal showed full restoration of photosynthetic performance to control levels afterward. However, only minor recovery of photosynthesis was found in areas that had been riddled with tightly bound epiphytes and were permanently damaged. In years 2002 and 2003, leaf productivity peaked in May and plummeted in November. More epiphytic diatoms were distributed when the seagrass biomass was larger, with pinnate diatoms dominating.

Impact of secondary salinisation on freshwater ecosystems: effect of experimentally increased salinity on an intermittent floodplain wetland

Intermittent wetlands are particularly at risk from secondary salinisation because salts are concentrated during drawdown. We conducted a field experiment to examine the effect of adding salt at two different concentrations (to achieve nominal conductivities of 1000 μS cm–1 (low salt) and 3000 μS cm–1 (high salt)) on water quality, freshwater plants and epiphytic diatoms in an intermittent wetland during a 3.3-month drawdown. Conductivity increased to 3000 and 8500 μS cm–1 in low-salt and high-salt treatments respectively. Salt was apparently lost to the sediments, causing protons to be released from the sediments and reducing water column pH from 6.9 to 5.5 in the low-salt treatment and to 4.0 in the high-salt treatments. Forty days after adding the salt, biomass, %cover and flower production in Potamogeton cheesmanii were significantly reduced, whereas Amphibromus fluitans was not significantly affected. The salt effect on Triglochin procera was intermediate between the other two macrophytes. Significant reductions in the density, species richness and diversity of epiphytic diatoms occurred in the high-salt, but not in the low-salt, treatments. Our work shows that increases in salinity, and thus conductivity (up to 8500 μS cm–1), in low-alkalinity intermittent wetlands can change water quality, with significant adverse effects on some macrophyte and diatom communities.

Wetland degradation leads to homogenization of the biota at local and landscape scales

Summary1. We examined whether the anthropogenic degradation of wetlands leads to homogenization of the biota at local and/or landscape scales and, if so, what specific factors account for such an effect. We compared 16 isolated wetlands (Michigan, U.S.A.) that varied in surrounding land use: half had developed, and half undeveloped, riparian zones. Samples of macrophytes, epiphytic diatoms, zooplankton, macroinvertebrates and water chemistry were collected along three transects in each wetland.2. Developed wetlands were more nutrient‐rich with higher Cl concentrations. The plant community at developed sites was dominated by Lemnaceae (duckweed), while undeveloped wetlands were dominated by rooted, floating‐leaved vegetation and sensitive plant species. Undeveloped wetlands contained heterogeneous and species‐rich plant communities, greater species richness of zooplankton and diatoms, and heterogeneous zooplankton distributions as compared to developed sites.3. A comparison among wetlands showed that diatom and zooplankton assemblages in developed wetlands were nested subsets of richer biota found in less developed wetlands. Conversely, plant communities were more heterogeneously distributed among developed wetlands at the landscape level. This may be attributable to patchy invasions by exotic species, which were a feature of the degraded wetlands within developed landscapes.4. Our results indicate that several taxonomic groups showed similar, probably inter‐dependent, responses to wetland degradation and habitat homogenization at both the local and landscape scales. This change in community structure from a species‐rich and heterogeneous community dominated by floating‐leaved plants in undeveloped wetlands, to nutrient‐rich wetlands dominated by duckweed may represent a shift to an alternate stable state.

AUXOSPORE FINE STRUCTURE IN A MARINE ARAPHID DIATOM TABULARIA PARVA

Recent studies have led to a rapid increase in our knowledge of auxospore structure in diatoms. However, these studies have been limited to centric and raphid pennate diatoms, and there is still very little information on the sexual reproduction in araphid pennate diatoms. Using LM and SEM, the fine structure of the auxospore of the marine epiphytic diatom Tabularia parva (Kützing) Williams & Round were studied. The auxospores were bipolar, as in many other pennate diatoms. SEM revealed a series of transverse perizonial bands that may all be open hoops. No distinct primary transverse perizonial band was detected. A series of longitudinal perizonial bands was observed beneath the transverse series. The well-developed structures of the longitudinal series observed in T. parva have not been reported before in other araphid pennate diatom taxa. Scales were mainly found on the external surface of the perizonium, but curiously they rarely existed on its inner surface, presumably because the scale formation is not strictly regulated during latter stage of centrifugal perizonium development in the pennate diatoms.

Marine epiphytic diatoms from the shallow sublittoral zone in Potter Cove, King George Island, Antarctica

Abstract Marine epiphytic diatoms in the Antarctic Peninsula have not been studied in detail previously, and information on their distribution and occurrence is scarce. We studied the marine epiphytic diatoms on several species of macroalgae belonging to the Rhodophyta, Phaeophyceae and Chlorophyta. We recorded a total of 50 epiphytic diatoms, with Cocconeis spp., Entopyla australis var. gigantea, Grammatophora arctica, Licmophora antarctica and Pseudogomphonema kamtschaticum the most common taxa. Diatoms appeared to have substratum preferences rather than site preferences. The most frequent hosts for diatom attachment were the rhodophytes Pantoneura plocamioides, Delesseria lancifolia and Georgiella confluens. Phaeophytes were less favourable hosts, and no diatoms were recorded on the chlorophytes.

Temperature, salinity and light duration dependence on the growth and cellular carbon and nitrogen contents of the epiphytic diatom,Achnanthes longipes Agardh

chnanthes longipes Agardh cells were isolated from glass slides submerged in the Eastern Harbour of Alexandria. Addition of D-600 (10 & 25 µM) and EDTA (10 -3 M) was sufficient to prevent adhesion and aggregation of A. longipes cells and get homogenous free cells inocula for culture experiments. The influence of 52 combinations of salinity (5-40 at 5 intervals) and temperature (10 o -25 o C, at 5 o C intervals) under continuous light and 12:12 light/dark cycle on chlorophyll a content, the maximum doubling time, cellular carbon and nitrogen of Achnanthes longipes was examined under constant light intensity (70-80 µE m -2 S -1 ). No growth was detected at 5 salinity levels with all temperatures tested, and under the combination of 15 o C-10 salinity. Maximum Chl. a content during the exponential phase was almost the same at the two light regimes (about 1.2 µg ml -1 ). Based on Chl. a variations by days, A. longipes showed its maximum growth rate and doubling time (1.18 and 0.82 d -1 , respectively) at 20 o C-30 salinity (continuous light) and 1.6 and 1.11 d -1 , respectively at 20 o C-25 salinity (light/dark cycle). A rising in temperature from 15 o C to 20 o C caused about 1.8 fold increases in the doubling time of Chl. a at the two light regimes. The results indicated that Chl. a and carbon proceeded in parallel during the exponential phase under the light regimes, and the increasing in carbon content and Chl. a content accompanied an increasing in temperature. The carbon content was consistently lower in continuous light cultures than in the corresponding light/dark cultures. No definite trend was found between nitrogen and changed temperature and salinity (continuous light), while nitrogen generally increased with increasing temperature under the light/dark cycle. The maximum carbon/nitrogen was measured at 25 o C with salinity range of 35 - 40, it was about two-fold higher at the light/dark (40.03). The carbon: chlorophyll ratio showed a steady increase by days, and varied considerably with changed temperature. However, there was no characteristic relation between temperature, growth rate and carbon: chlorophyll.

Ecological variation within Sellaphora species complexes (Bacillariophyceae): specialists or generalists?

The genus Sellaphora has become a model system for studies of the species concept, speciation and automated identification in diatoms. Three species, S. pupula, S. bacillum and S. laevissima, have proved to be complexes containing several or many species, which are difficult to distinguish morphologically but which are genetically differentiated and (where tested) reproductively isolated. Until now, however, there has been little information about the ecology of the species within this complex, except in relation to parasite sensitivity. In order to test whether semi- and pseudo-cryptic Sellaphora species are ecologically differentiated with respect to trophic status, we used tools recently developed in the UK in response to the EU Water Framework Directive (WFD). Diatom samples from three substrata (plants, rocks, sediment) were taken from 22 lakes in Scotland and England, covering a gradient from oligotrophic mountain lakes to eutrophic lowland ponds. The epilithic and epiphytic diatom assemblages were used to evaluate lake trophic status according to the UK WFD assessment system and showed that there was a strong environmental gradient in the dataset. Sellaphora species occurred in the sediment-derived epipelon and their distributions were analysed in relation to the trophic gradient. A total of 28 Sellaphora phenodemes (putative species) were found, and some of them differed in their environmental demands. Two groups were distinguished: (1) a group indicating rather oligotrophic conditions and containing several demes with linear valves and subcapitate or capitate poles (referred to here as S. [pupula] cap-A, cap-B and cap-C and (2) a group occurring in eutrophic lakes and containing the recently described species S. blackfordensis, S. capitata and S. obesa, as well as S. [pupula] Φ ‘small lanceolate’. The data obtained are also discussed with respect to Finlay’s hypothesis on microalgal cosmopolitanism.

Stable isotope addition reveals dietary importance of phytoplankton and microphytobenthos to saltmarsh infauna

Despite the paradigm that Spartina spp. detritus is the basis for estuarine food webs, other primary producers may contribute to the diets of saltmarsh consumers. To determine the dietary contribution of primary producers to benthic infauna in the Plum Island Estuary, Massachusetts, USA, we examined natural abundance stable isotopes in 4 intertidal saltmarsh habitats and conducted an 15 N enrichment experiment in 2 habitats. Natural abundance isotope data suggested that Spartina spp. detritus was of limited dietary importance to infauna in all habitats (including Spartina spp. understory) and instead benthic algae and phytoplankton were the dominant food sources. 15 N enrichment was used to improve dietary resolution of benthic algae and phytoplankton sources that had similar natural abundance values. To label only benthic algae, 15 N-enriched Na 15 NO3 was applied daily for 14 d to sediment in mudflat and creek-wall habitats. Food-web incorporation of 15 N-labeled benthic algae was found in most species. However, label uptake in the polychaetes Man- ayunkia aestuarina, Fabricia sabella and Streblospio benedicti indicated that phytoplankton was the most important food source for these consumers. Label uptake in the polychaete Nereis diversicolor differed between habitats, suggesting a large dietary contribution of microphytobenthos (MPB) in mudflat and phytoplankton in creek wall. The oligochaete Paranais litoralis consumed both MPB and phytoplankton regardless of habitat. The harpacticoid copepod Heterolaophonte sp. consumed pri- marily epiphytic diatoms. Overall, infauna in this system relied on phytoplankton and benthic algae as dominant food resources, and dietary contributions from primary producers varied among species and habitats.

Epilithic, Epipelic, and Epiphytic Diatoms in the Göksu Stream: Community Relationships and Habitat Preferences

ABSTRACT Community structure of benthic diatom in Góksu Stream was studied over a one year period. The presence of a total of 69 taxa was recorded in the stream. The abundance of diatom taxa recorded varied substantially among the habitat types. The genera Cymbella, Navicula, Nitzschia, and Gomphonema comprised the most species and were numerically dominant in most communities. Frequency, diversity, and similarity of diatoms varied among habitats.

Species Composition of the Epiphytic Diatoms on the Leaf Tissues of Three Zostera Species Distributed on the Southern Coast of Korea

The epiphytic diatom flora living on leaf tissues of Zostera marina, Z. japonica and Z. caespitosa at three study sites (Dadae, Gabae, and Jangmok) located in Geoje Island has been examined from July 2001 to March 2002 bimonthly. Total 81 species in 26 genera of diatoms have been observed on leaf tissues of the 3 Zostera species throughout the present study. Cocconeis spp. were predominant on Z. japonica, whereas Navicula spp. and Nitzschia spp. were predominant on Z. marina and Z. caespitosa. The community structure of the diatom assemblages varied according to the seagrass species. Species compositions of epiphytic diatoms appear to be closely related to morphology and lifespan of seagrasses.

Cooling in down-slope peat ecosystems due to accelerated glacial melting in Higher Himalaya, India

High-resolution paleoclimate data and numerous instrumental records report that, at higher elevations, Himalayan temperatures over the last ca. 100 years have been rising (Liu and Chen 2000, Thompson et al. 2000). However, many instrumental records from various lower elevation localities are reporting cooler temperatures in recent decades (Balling 2001). This recent cooling trend is not only opposite to the global warming trend but also with the accelerated retreat of the Himalayan glaciers. The effect that warming conditions and melting glaciers have on downslope ecosystems has not been fully explored. Here we present compelling evidence that, over the last 200 years, accelerated glacier retreat and increased melt waters have played a central role in changing the ecology (and perhaps local climate) of downslope sites. The Pinder Valley (~30° 50' 30° 52' N, 78° 47' 78° 51’E) of the Kumaon Higher Himalaya, receives precipitation from the Asian monsoon predominantly during the summer but also during winter seasons. The valley climate is also influenced by hanging glaciers (viz. Sunder Dunga, Pindari, and Kaphni), situated along the valley head. An ~ 125-cm thick peat deposit situated in oak dominated mixed evergreen forest 2650-m altitude, was trenched and continuously sampled at 2-cm intervals. Well-dated multi-proxy paleoclimate record (pollen, diatoms, phytoliths, % organic matter, and magnetic susceptibility) from this peat sequence revealed past ca. 3500year high-resolution climate history of the area. At the beginning of the peat sequence (ca. 3500 to ca. 3300 cal yr BP), the pollen assemblage was almost exclusively represented by conifers suggesting that the regional climate was cool and wet. A sudden increase in the dominance of grass, alder (Alnus nepalensis) and brown oak (Quercus semecarpifolia) pollen at ca. 3300 cal yr BP indicates an abrupt climatic shift towards drier conditions that continued until ca 2300 cal yr BP. The increase in silver fir (Abies pindrow) and other conifers [Himalayan spruce (Picea smithiana) and blue pine (Pinus wallichiana)] at the expanse of grasses, and the first appearance of diatoms ca. 2300 cal yr BP mark the end of the dry period. The progressive decrease in grass pollen for the following ~200 years reveals the improved wetness of climate until ca. 2100 cal yr BP. Variations in our proxy indicators throughout the remainder of the peat sequence suggest a stepwise increase in wetness until the present. A major shift in all of the proxy indicators at ca. 680 cal yr BP (~ 1320 AD) indicates an increase in SW monsoon at 1300 AD, evidence of which is widespread throughout the Asian monsoon region (Morrill et al. 2003). Around this time the once dominant Fragilaria diatoms abruptly diminished to trace abundances, Navicula minima appeared for the first time in the record in relatively high abundances, and epiphytic diatom taxa became more prominent. Circa 1580 to 1730 AD, a substantial cooling was inferred with a reduction to trace levels of the epiphytic proportion of the diatom assemblage and the strong re-appearance of Fragilaria species to abundances of 80 – 90%, not seen before or afterwards in the peat profile. A comparison of the last ~400 years of the peat record with reconstructed spring temperature trend derived from a series of 12 Himalayan tree-ring chronologies (Yadav and Singh 2002) is consistent with our proxy-based inferences from ca. 1600 AD onwards. The high rate of glacier melting over the last few centuries in the Himalayan mountains is a clear demonstration of a warming climate. Our data show that increased glacial meltwaters under this warmer climatic scenario has had a substantial impact on down-slope ecosystems. It appears that the glacial retreats are consistent with the global climate scenario but the resulting melt waters are having localized to regional cooling effects at lower elevation sites over the last few decades.

Seasonal assessment of epiphytic diatom distribution and diversity in relation to environmental factors in a karstic lake (Central Turkey)

Seasonal assessment of epiphytic diatom distribution and diversity in relation to environmental factors in a karstic lake (Central Turkey)

Cambios en la estructura de la asociación de diatomeas epifitas de Macrocystis pyrifera (L.) c. ag.

Con el objetivo de determinar la estructura de la asociación de diatomeas que colonizan láminas apicales de Macrocystis pyrifera en las costas de la península de Baja California y detectar sus posibles cambios temporales, se recolectaron mensualmente cuatro frondas de la especie, de febrero a agosto del 2003, en un manto en El Sauzal, Baja California. Las diatomeas de cinco láminas de cada fronda fueron tratadas y montadas en preparaciones permanentes y examinadas en términos de su número y contenido florístico. La distribución de las abundancias de la asociación concordó con el patrón general descrito para asociaciones de diatomeas (pocas especies abundantes y muchas raras). El número de taxa fue alto (171), pero la riqueza por muestra fue heterogénea y en general baja (6 -51 taxa). La diversidad y la equidad fueron bajas: H´ = 2.1 (máx = 3.8, mín = 0.3), y = J’ 0.45. Las diatomeas más abundantes fueron Rhoicosphenia genuflexa (Kützing) Medlin, Gomphonemopsis pseudexigua (Simonsen) Medlin, Tabularia investiens (W.Smith) Williams y Round y Cocconeis costata var. pacifica (Grunow) Grunow, mismas que pueden considerarse constituyentes permanentes de la asociación; R. genuflexa dominó en cinco meses; mientras que en junio prevaleció G. pseudexigua, y en febrero C. costata var. pacifica. La estructura y la composición florística de la asociación de diatomeas epifitas no variaron en láminas de diferente posición (en un intervalo hasta de 2.5 m de longitud de la fronda de Macrocystis). Las diferencias en la estructura y composición de las especies entre frondas de una misma fecha se atribuyen a la edad de las láminas; se sugiere que las más maduras exportan diatomeas que colonizan rápidamente a las láminas jóvenes. Cambios en la estructura y en los taxa de diatomeas que separan a febrero y junio se asocian con periodos de transición.

Extracts of North Sea macroalgae reveal specific activity patterns against attachment and proliferation of benthic diatoms: a laboratory study

A variety of macroalgae (Ceramium rubrum, Corallina officinalis, Palmaria palmata, Mastocarpus stellatus, Fucus vesiculosus, Cladophora rupestris, Ulva sp.) were investigated by scanning electron microscopy to visualize epiphytic colonizers. The macroalgae differed in terms of their epiphytic coverage of bacteria, fungi and diatoms. Macroalgae, largely devoid of epiphytic diatoms, were hypothesized to employ effective antifouling means to reduce epiphytic coverage, whilst heavily fouled macroalgae were proposed to lack antifouling strategies. To test these hypotheses from an allelochemical perspective with regard to fouling diatoms, dichloromethane-methanol (1:1) crude extracts of macroalgae were concentrated in dimethylsulfoxide and investigated in diatom attachment and proliferation assays using four benthic diatoms (Nitzschia sp., Navicula phyllepta, Navicula arenaria and Amphora sp.). Algal extracts exhibited a distinct pattern of activity against the test diatoms, suggesting a targeted and selective effect of macroalgal metabolites on individual fouling diatoms. The main outcome of this study was that visual inspection and quantitative categorization of epiphytic colonizers on macroalgal thalli could not be used to predict reliably whether macroalgae employed a chemical defense mechanism.

HÁBITOS ALIMENTARIOS DE <i>Haliotis</i> spp. Y BASES NUTRICIONALES PARA SU MANEJO

La mayor parte del conocimiento sobre la dieta de abulón emana de bases empí­ricas bajo condiciones de cultivo, sobre todo en las primeras etapas de vida. Así­ mismo la mayorí­a de estos estudios se hacen con adultos y enfocados sobre macroalgas, las cuales albergan un gran número de especies de diatomeas epifitas que podrí­an estar enriqueciendo la dieta del abulón. Sin embargo, al segregarse de los estudios de contenido intestinal éstas podrí­an estar subestimadas. El suministro empí­rico de pocos taxa de diatomeas en la dieta de juveniles de abulón en cultivo no corresponde con el gran número de diatomeas encontradas en contenidos intestinales de organismos del medio natural. De tal forma, su uso como alimento en cultivo requiere de mayor base cientí­fica; observaciones hechas con dietas combinadas a base de macroalga y diatomeas parecen ser mejor opción. Por otro lado, una dieta artificial para abulones adultos que busque sustituir el uso de macroalgas disminuyendo costos de producción, dependerá de la información de los requerimientos nutricionales y del aprovechamiento de la fuente de alimento por las distintas especies de abulón, lo cual se desconoce, sobre todo en relación con su dieta natural. Las dietas mixtas proveen más nutrientes esenciales, a diferencia de dietas monoespecí­ficas en las cuales se puede presentar deficiencia en uno o más nutrientes. Finalmente el sabor del músculo de abulón al ser alimentado con dietas artificiales puede ser diferente al que se obtiene con dietas naturales, reflejándose en una menor aceptación del producto en el mercado. Feeding habits of Haliotis spp. And nutritional basis for its Management Most of the knowledge on abalone diet rises from empirical bases under cultured conditions,especially during its early life stages. Likewise, most of these studies have been made on adults and are focused on macroalgae, which harbor a large number of epiphytic diatom species that could enrich the abalone diet. Nevertheless, when these are segregated its diet contribution could be underestimated. The empiric supply of few diatom taxa on juvenile cultured abalone do not correspond to the large number of diatoms observed in intestinal contents of wild specimens. Likewise, their use as food for cultured abalone needs a larger scientific base; meanwhile combined diets using macroalgae and diatoms seems to be a better alternative. On the other hand, an artificial diet for adult abalones as an alternative for the macroalgal diet with lower production costs, will depend on the information about nutrimental requirements and the use of food sources by different abalone species, which is unknown, especially in relation with their natural diet. On the plus side, mixed diets provide more essential nutrients than the mono-specific diets which can be lacking in one or more nutrients. Also, it has to be taken into account that the flavor of abalone meat fed with artificial diets could be different than that obtained with natural diets and could result in less acceptance of the product in the market

Spatial And Temporal Distribution Of Epiphytic Diatoms On Macroalgae Inhabiting Port Said Coast, Mediterranean Sea, Egypt

The epiphytic diatoms growing on seaweeds inhabiting Port Said coast were investigated seasonally during the period from summer 2004 to spring 2005. A total of 62 species of the epiphytic diatoms were recorded. They comprised fifty nine pennate and three centric forms. The important components in the flora of the epiphytic diatoms were belonging to the genera: Achnanthes, Achnanthidium, Fragilaria, Gyrosigma, Licmophora, Navicula, Pleurosigma, Synedra and Tabellaria. The rest recorded epiphytic diatoms were considered rare and of no significance in defining the epiphytic flora on seaweeds. Summer showed the highest relative abundance of total epiphytes reached to 53%, while the lowest value (5%) was recorded in spring. Site I displayed a maximum relative abundance (64%) of the epiphytes occurrence, while site IV showed a minimum percentage (6%). Of the macroalgal species inhabiting Port Said coast, 14 species were mostly utilized by the epiphytic diatoms. The results revealed that there was a relationship between the architecture of seaweeds and the associated epiphytes. Most of the foliose and flattened macroalgal thallus was nearly not preferred as a substrate. By contrast, the fine and sometimes branched thallus hosted many epiphytic diatoms. Considering the macroalgal species which used as a substrate, the attached epiphytic diatoms observed different patterns of preference. Some epiphytic diatoms showed host specificity giving unialgal epiphytic flora on few hosts. Other epiphytic diatoms did not reflect the previous preference pattern and existed on the majority of the macroalgae indicating the absence of selectivity.New Egyptian Journal of Microbiology Vol. 17 (2) 2007: pp. 285-296