Macroalgal holdfasts and their interaction with environments from the Neoproterozoic Doushantuo Formation in Guizhou,South China

Numerous macro-organisms of the Doushantuo macrobiota, which were found in the black carbonaceous mudstone of the upper Neoproterozoic Ediacraan Doushan-tuo Formation in Jiangkou County, Guizhou Province, China, are considered to live on sea floor by their holdfasts. The appearance and preserved forms of the macroalgal holdfasts may provide some data to the study of the living and buried environments ofmacrobiota. They lived in the lower energy and clear environment, and fixed on a soupground with rich water (about 79% water). Currents, possibly ocean currents, could pull out the macroalgal holdfasts from the soupground and break off the macroalgal foliations. After such events, the corpses of macro-organisms would be covered in a reduced environment by the deposits. Afterwards, a new community, including regenerating and undying macro-organisms, lived continuously on a new deposit.     

黔东北新元古代陡山沱期宏体藻类的固着器特征及其沉积环境意义

产于贵州江口新元古界陡山沱组上部黑色碳质泥岩和硅质泥岩中的宏体生物群,多数为发育固着器的固着底栖生物。宏体藻类固着器的形态和保存方式可提供生物群生活环境和埋藏环境的信息。黔东北陡山沱期宏体生物群生活于相对平静、较为清澈的水体之中,固着基底为富含水份的粥性基底。可能与洋流有关的水流事件将宏体藻类折断或“连根”拔起;水流事件之后,沉积物将宏体藻类的遗体掩埋于还原性较强的环境之中,新生的和水流事件未致死亡的宏体生物在新的沉积物表面上继续生长。     

Ediacaran macroalgal holdfasts and their evolution: a case study from China

A macroalgal holdfast (root-like structure) anchored or grown into sediments is a key trait of metaphytes and eukaryotic algae. Various patterns and taphonomic variants of congeneric holdfasts are preserved on the bedding planes of black shales of the Ediacaran Wenghui biota in South China. The macroalgal holdfast, which commonly consists of a rhizome, rhizoid and pith (perhaps mechanical tissue), can be morphologically classified into ten types within four groups of rhizomes: bare rhizome holdfasts (Grypania, Tongrenphyton and Sectoralga-type holdfasts), canopy rhizome holdfasts (Gemmaphyton, Gesinella, Discusphyton and Baculiphyca-type holdfasts), pithy rhizome holdfasts (Zhongbaodaophyton and pithy-cone-type holdfasts) and differentiated rhizome holdfasts (Wenghuiphyton-type holdfasts). Analysis of the Precambrian macroalgal record indicates that rhizomes played a more important role in the evolution of macroalgal holdfast than rhizoids. The following evolutionary stages of development of macroalgal holdfasts are proposed: (1) growth of the basal thallus into sediments (Grypania-type holdfast); (2) development of a primitive (indistinct) rhizome from the base of a stipe or thallus (Tongrenphyton-type and Sectoralga-type holdfasts); (3) growth of a distinct rhizome with rhizoid (Gemmaphyton-type, Gesinella-type and Discusphyton-type holdfasts); (4) development of a pith in the stipe (Baculiphyca-type holdfast); (5) pith extension into the rhizome (Zhongbaodaophyton-type and pithy-cone-type holdfasts); and (6) rhizome differentiation and development of a complex holdfast system (Wenghuiphyton-type holdfast).     

New observations on Cucullus Steiner from the Neoproterozoic Doushantuo Formation of Guizhou,South China

Wang, Y & Wang, X. 2011: New observations on Cucullus Steiner from the Neoproterozoic Doushantuo Formation of Guizhou, South China. Lethaia, Vol. 44, pp. 275–286. The Neoproterozoic genus Cucullus is the most abundant and largest organism in the Miaohe biota in China, but has remained poorly understood both in morphology and classification. New material recently obtained from the upper Doushantuo Formation (Ediacaran) of northeastern Guizhou, South China, indicates that Cucullus bears thin organic walls composed of complex spongin fibres forming vertical filaments, which may have given rise to transverse filaments. Filaments, non‐mineralized spongin fibres, which may have served to support body, regularly interweave with each other in a body, and form openings on body sides that may have served as incurrent canals. The top pores may have served as excurrent canals. The overall features, including the organic wall, the complex spongin fibre networks, and the possible canal system of Cucullus, suggest a primitive element of the Demospongea. This benthic organism lived in a low‐energy, calm environment near or below the storm wave‐base with influence of episodic storms. Cucullus’ base nestled into the muddy substrate and its sacciform body floated in seawater. □ Cucullus, Doushantuo Formation, Neoproterozoic, Porifera, South China.     

Herbivory facilitates growth of a key reef‐building Caribbean coral

The decline of reef‐building corals in conjunction with shifts to short‐lived opportunistic species has prompted concerns that Caribbean reef framework‐building capacity has substantially diminished. Restoring herbivore populations may be a potential driver of coral recovery; however, the impact of herbivores on coral calcification has been little studied. We performed an exclusion experiment to evaluate the impact of herbivory on Orbicella faveolata coral growth over 14 months. The experiment consisted of three treatments: full exclusion cages; half cage procedural controls; and uncaged control plates, each with small O. faveolata colonies. We found that herbivorous fish exclusion had a substantial impact on both macroalgal cover and coral growth. Fleshy macroalgae reached 50% cover within some exclusion cages, but were almost absent from uncaged control plates. Critically, O. faveolata calcification rates were suppressed by almost half within exclusion cages, with monthly coral growth negatively related to overgrowth by fleshy macroalgae. These findings highlight the importance of herbivorous fishes for coral growth and the detrimental impact of macroalgal proliferation in the Caribbean. Policy makers and local managers should consider measures to protect herbivorous fishes and reduce macroalgal proliferation to enable coral communities to continue to grow and function.     

Modelling the distribution and growth of ‘problem’ green seaweed in the Medway estuary,UK

The results of a modelling study to investigate the mechanisms controlling macroalgal growth within the Medway estuary, UK, are presented. Intertidal zone bathymetry, tidal dynamics and turbidity control the time available for nutrient uptake and photosynthesis, and were used as a basis for predicting areas where macroalgae will grow. Tidal bed stress was also considered as a controlling factor for the presence of the less robust green macroalgae species. Two approaches to predicting macroalgal distributions were applied: (1) a simple ‘suitability index’ method based on tidal flooding and drying, taking account of the conflict between time available for nutrient uptake and for photosynthesis; and (2) a biological macroalgal growth model that includes a detailed treatment of nutrient uptake and plant growth. The former approach assigns a value between zero and one for the suitability of a location for macroalgal occurrence, while the latter predicts the full macroalgal growth dynamics over an annual cycle. Tidal bed stress was included in both approaches as an independent modifier of macroalgal occurrence/growth. Results were compared with aerial survey maps of observed vegetation cover and time series of measured biomass density. Both approaches gave good predictions of non-species-specific vegetation cover in the intertidal zone of the Medway. Tidal bed stress was found to be a strong predictor of the specific occurrence of Enteromorpha spp. and Ulva spp., with these species favouring areas of low tidal energy. It was concluded that light and a lack of suitable regions with low tidal bed stress, rather than nutrients, were the main factors limiting excessive growth of Enteromorpha spp. and Ulva spp. in the estuary. Although this study was focussed on the Medway, the results are likely to be applicable to a broad range of relatively turbid, meso- and macro-tidal estuaries. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Guest editors: J. H. Andersen & D. J. Conley Eutrophication in Coastal Ecosystems: Selected papers from the Second International Symposium on Research and Management of Eutrophication in Coastal Ecosystems, 20–23 June 2006, Nyborg, Denmark     

Polychaete fauna associated with holdfasts of the large brown alga Himantothallus grandifolius in Admiralty Bay, King George Island, Antarctic

The polychaete community associated with holdfasts of the brown alga Himantothallus grandifolius in Admiralty Bay has been studied. It is the first study of its kind in this area and only the second in the Antarctic. Samples were collected in the summer season of 1979/1980 from a depth range of 10–75 m. Seventy-eight species were found on 19 holdfasts. The community was dominated by Brania rhopalophora and Neanthes kerguelensis. Analysis of similarity showed that polychaete fauna associated with this habitat did not show any partitioning related to depth. Regression analysis showed that densities of both species and individuals decreased with increased holdfast volume. A positive correlation was found between the number of individuals and holdfast volume. Polychaetes from 10 feeding guilds were found with dominance of macrophagous motile herbivores and sessile filter feeders. The complex habitat provided by holdfasts is a shelter for a rich polychaete fauna and may function as important protection from disturbance in the shallow areas of Admiralty Bay.     

The ontogeny of habitat associations in the tropical tiger tail seahorse Hippocampus comes Cantor, 1850

This study examined how habitat associations changed with ontogeny in the tiger tail seahorse Hippocampus comes Cantor, 1850, over four reef zones in a coral reef ecosystem. Hippocampus comes showed ontogenetic differences in their use of habitat at the scale of reef zones (macrohabitat) and holdfasts (microhabitat). Across reef zones, juvenile size classes (25–105 mm standard length, L _S) were most abundant in wild macroalgal beds ( Sargassum spp.) (55·7%), while adults (>105 mm L _S) occupied both coral reefs (39·7%) and macroalgal beds (42·7%). Microhabitat use also varied with ontogeny. Juveniles generally used macroalgal holdfasts, while adults >135 mm L _S used a greater diversity of specialized microhabitats that included branching sponges, branching corals and tall seagrass. Ontogenetic changes in habitat association, as well as size-related shifts in crypsis and aggregation, suggest that H. comes experiences fitness trade-offs that vary with size; juveniles may associate with habitat that reduces predation, while larger individuals may use distinct microhabitat in reef zones to optimize reproductive success. Results are discussed in the context of targeted exploitation, expanding artisanal mariculture, habitat damage from illegal fishing and reserve design.     

In vitro germination and development of western hemlock dwarf mistletoe

A procedure for in vitro culture of the parasitic flowering plant western hemlock dwarf mistletoe, Arceuthobium tsugense (Rosend.) G.N. Jones subsp. tsugense, is described. A factorial experiment evaluated the effects of media (Harvey's medium (HM) and modified White's medium (WM)), temperatures (15 °C and 20 °C), presence or absence of light, and plant growth regulators (the auxin 2,4-dichlorophenoxyacetic acid (2,4-D) and the cytokinin 6-benzylaminopurine (BAP) at varying concentrations (0.001 mg l⁻¹ to 1 mg l⁻¹)). Seed explants germinated in less than one week in culture and produced radicles. Optimal conditions for radicle elongation were WM at 20 °C in the presence of light and without plant growth regulators. Some of the radicles split at the tip to yield callus while others swelled to become spherical holdfasts. Holdfasts were also produced at the tips of radicles, and callus arose from split holdfasts. Factors that promoted holdfast production were Harvey's medium, light, and 2,4-D at 1 mg l⁻¹. Callus development from split radicles and split holdfasts was optimal on WM with 0.5 mg l⁻¹ 2,4-D and 1 mg l⁻¹ BAP at 20 °C in the dark. This revised version was published online in June 2006 with corrections to the Cover Date.     

Production and prey source of juvenile black rockfish <Emphasis Type="Italic">Sebastes cheni</Emphasis> in a seagrass and macroalgal bed in the Seto Inland Sea,Japan: estimation of the economic value of a nursery

The economic value of ecosystem services of vegetated habitats (seagrass and macroalgal beds) has been estimated to be among the highest of the various ecosystems on earth. However, fish production has not been included in the evaluations due to the difficulty of quantitative estimation of fish production in the field. In the present study, annual production and economic value of wild juvenile black rockfish, Sebastes cheni, a dominant fish species in seagrass and macroalgal beds in the central Seto Inland Sea were estimated. Juvenile S. cheni migrated into vegetated habitats at about 20 mm total length (TL) and grew up to about 60 mm TL by late May. Juvenile abundance was highest in April (2007) or March (2008). Eight cohorts with the same extrusion period (each cohort covering a 10-day period) were identified using otolith daily increments. The annual estimates of S. cheni juvenile production were 13,080 g ha⁻¹ year⁻¹ in 2007 and 18,360 g ⁻¹ year⁻¹ in 2008. Based on the unit price of artificially raised S. cheni juveniles, the economic value of the annual wild juvenile production was converted to 654,000 JPY (Japanese yen: 100 JPY = ca. 1 USD) ha⁻¹ year⁻¹ for 2007 and 918,000 JPY ha⁻¹ year⁻¹ for 2008. Analyses of stomach contents and stable isotope (δ¹³C or δ¹⁵N) showed that juvenile S. cheni were highly dependent on copepods. The planktonic trophic pathway originating from phytoplankton supports the majority of the juvenile black rockfish production during the post-migration period (20–60 mm TL) in the seagrass and macroalgal beds through the production of copepod zooplankton. The total economic value of the ecosystem services of the vegetated habitat is suggested to be much higher than estimates in previous studies if the provisioning and regulating services which originate from fish production were included in the estimates.     

Relationships between macroalgal biomass and microbiological quality of water in a phytotreatment pond

The microbiological quality of wastewater in phytotreatment ponds with foliose macroalgae can be influenced by biofilm formation on thallus surface. This hypothesis was tested with an in situ experiment which was carried out in a pond with Ulva spp. receiving wastewater from a land based fish farm at Piombino (Italy). The total bacterial load (TBL) was determined in the inflowing and outflowing waters and a multifactorial design was employed to investigate the effect of different macroalgal biomass. Microbiological analysis revealed a high TBL in the water column (18.4 ± 7.4 × 10⁸ cells ml⁻¹). TBL of inlet water was significantly correlated with quantity and quality of particulate organic matter (POM) of inflowing water, whereas no correlation was found between TBL and POM in the outlet water. A significant decrease in the POM concentration was detected within macroalgal ponds, due to the mechanical action of thalli which favoured POM sedimentation. Nevertheless, great TBLs were found in the outlet water. These findings suggest that TBL probably depended upon macroalgae. Indeed high bacterial density was found on macroalgal thallus surface (~10⁸ cells cm²). Furthermore, high plate counts of faecal bacteria (faecal enterococci) were determined on thallus surface (~ 40 CFU cm²) and outlet water (11 886 ± 3984 CFU 100 ml⁻¹) supporting the evidence that macroalgae negatively affect the microbiological quality of treated water. Bacterial activities in terms of exoenzymatic rates and secondary production were two folds higher in the water within macroalgal beds, than in the open water. These preliminary results suggest that high macroalgal biomass represents a ‚hot spot’ of bacterial density and activity that may affect microbiological quality of the treated water. Bacterial control of inlet water and management of macroalgal biomass through periodic removal are essential for a more efficient treatment of wastewater in phytotreatment ponds.     

Cross-shelf variation in browsing intensity on the Great Barrier Reef

Herbivory is widely accepted as a key process determining the structure and resilience of coral reefs, with regional reductions in herbivores often being related to shifts from dominance by coral to leathery macroalgae. The removal of leathery macroalgae may therefore be viewed as a critical process on coral reefs. However, few studies have examined this process beyond a within-reef scale. Here, browsing activity was examined across the entire Great Barrier Reef shelf using bioassays of the leathery macroalga Sargassum to directly quantify algal removal. The assays revealed marked cross-shelf variation in browsing intensity, with the highest rates recorded on mid-shelf reefs (55.2–79.9% day⁻¹) and decreasing significantly on inner- (10.8–17.0% day⁻¹) and outer-shelf (10.1–10.4% day⁻¹) reefs. Surprisingly, the variation in browsing intensity was not directly related to estimates of macroalgal browser biomass; rather, it appears to be shaped primarily by the local environment and behaviour of the component species. Removal rates across the inner- and mid-shelf reefs appear to be related to the attractiveness of the assays relative to the resident algal communities. Controlling for the influence of the resident algal communities revealed a positive relationship between removal rates and the biomass of a single macroalgal browsing species, Naso unicornis. In contrast, the low removal rates on the outer-shelf reefs displayed no relationship to algal or herbivore communities and appeared to reflect a negative behavioural response by the resident fishes to a novel, or unfamiliar, alga. These findings not only highlight the complexities of the relationship between fish presence and ecological function, but also the value of examining ecological processes across broader spatial scales.     

A common garden experiment with Porphyra umbilicalis (Rhodophyta) evaluates methods to study spatial differences in the macroalgal microbiome

While macroalgal microbiomes are the focus of many recent studies, there is little information about microbial spatial diversity across the thallus. Reliance on field material makes it difficult to discern whether recovered microbiomes belong to the host or its epiphytes, and technical comparisons of macroalgal samples for microbial studies are needed. Here, we use a common garden approach that avoids the problem of epiphytes, particularly at holdfasts, to examine the microbiome of Porphyra umbilicalis (strain Pum1). We used the V6 hypervariable region of the 16S rDNA with Illumina HiSeq sequencing and developed PNA clamps to block recovery of organelle V6 sequences. The common garden approach allowed us to determine differences in the microbiome at the holdfast versus blade margin. We found a notable increase in the relative abundance of Planctomycetes and Alphaproteobacteria at the holdfast, particularly of the possible symbiont Sulfitobacter sp. Nonadjacent 1.5 cm² samples of blade margin had microbiomes that were not statistically different. The most abundant phylum in the overall microbiome was Proteobacteria, followed by Bacteroidetes. Because phycologists often work in remote sites, we compared three stabilization and preparation techniques and found silica gel desiccation/bead‐beating and flash‐freezing/lyophilization/bead‐beating to be interchangeable. Core taxa (≥0.1% of sequences) across treatments were similar and accounted for ≥95% of all sequences. Finally, statistical conclusions for all comparisons were the same, regardless of which microbial community analysis tool was used: mothur or minimum entropy decomposition.     

Phase shifts and the stability of macroalgal communities on Caribbean coral reefs

Caribbean coral reefs are widely thought to exhibit two alternate stable states with one being dominated by coral and the other by macroalgae. However, the observation of linear empirical relationships among grazing, algal cover and coral recruitment has led the existence of alternate stable states to be questioned; are reefs simply exhibiting a continuous phase shift in response to grazing or are the alternate states robust to certain changes in grazing? Here, a model of a Caribbean forereef is used to reconcile the existence of two stable community states with common empirical observations. Coral-depauperate and coral-dominated reef states are predicted to be stable on equilibrial time scales of decades to centuries and their emergence depends on the presence or absence of a bottleneck in coral recruitment, which is determined by threshold levels of grazing intensity and other process variables. Under certain physical and biological conditions, corals can be persistently depleted even while increases in grazing reduce macroalgal cover and enhance coral recruitment; only once levels of recruitment becomes sufficient to overwhelm the population bottleneck will the coral-dominated state begin to emerge. Therefore, modest increases in grazing will not necessarily allow coral populations to recover, whereas large increases, such as those associated with recovery of the urchin Diadema antillarum, are likely to exceed threshold levels of grazing intensity and set a trajectory of coral recovery. The postulated existence of alternate stable states is consistent with field observations of linear relationships between grazing, algal cover and coral recruitment when coral cover is low and algal exclusion when coral cover is high. The term ‘macroalgal dominated’ is potentially misleading because the coral-depauperate state can be associated with various levels of macroalgal cover. The term ‘coral depauperate’ is preferable to ‘macroalgal dominated’ when describing alternate states of Caribbean reefs.     

Cultivation of the brown alga Hizikia fusiformis (Harvey) Okamura: controlled fertilization and early development of seedlings in raceway tanks in ambient light and temperature

Commercial cultivation of the dioecious brown macroalga Hizikia fusiformis (Harvey) Okamura in East Asia depends on the supply of young seedlings from regenerated holdfasts or from wild population. Recent development of synchronized release of male and female gametes in tumble culture provides a possibility of mass production of young seedlings via sexual reproduction. In this paper, we demonstrate that controlled fertilization can be efficiently realized in ambient light and temperature in a specially designed raceway tank in which the sperm-containing water has been recirculated. The effective fertilization time of eggs by sperm was found to be within six hours. Fast growth and development of the young seedlings relied on the presence of water currents. Velocity tests demonstrated that young seedlings of 2–3 mm in length could withstand a water current of 190 cm s⁻¹ without detachment. Culture experiments at 24 h postfertilization showed that elongation of both the seedlings and their rhizoids were not hampered by high irradiance up to 600 μmol photons m⁻² s⁻¹. However, growth was slightly retarded if cultured at a temperature of 16 ^∘C compared to other culture temperatures of 22, 25 and 29 ^°C. No seedling detachment was observed after transfer of the young seedlings to raft cultivation in the sea after one and 1.5 months post-fertilization, indicating the feasibility of obtaining large quantity of seedlings in such a system.     

Varying responses of herbivorous and invertebrate-feeding fishes to macroalgal reduction on a coral reef

 The consequences of macroalgal overgrowth on reef fishes and means to reverse this condition have been little explored. An experimental reduction of macroalgae was conducted at a site in the Watamu Marine National Park in Kenya, where a documented increase in macroalgal cover has occurred over the last nine years. In four experimental 10 m by 10 m plots, macroalgae were greatly reduced (fleshy algal cover reduced by 84%) by scrubbing and shearing, while four similar plots acted as controls. The numerical abundance in all fish groups except wrasses and macroalgal-feeding parrotfishes (species in the genera Calotomus and Leptoscarus) increased in experimental algal reduction plots. Algal (Sargassum) and seagrass (Thalassia) assays, susceptible to scraping and excavating parrotfishes, were bitten more frequently in the algal reduction plots one month after the manipulation. Further, surgeonfish (Acanthurus leucosternon and A. nigrofuscus) foraging intensity increased in these algal reduction plots. The abundance of triggerfishes increased significantly in experimental plots relative to control plots, but densities remained low, and an index of sea urchin predation using tethered juvenile and adult Echinometra mathaei showed no differences between treatments following macroalgal reduction. Dominance of reefs by macrofleshy algae appears to reduce the abundance of fishes, mostly herbivores and their rates of herbivory, but also other groups such as predators of invertebrates (triggerfishes, butterflyfishes and angelfishes). Accepted: 2 February 1999     

Giant kelp vegetative propagation: Adventitious holdfast elements rejuvenate senescent individuals of the Macrocystis pyrifera “integrifolia” ecomorph

Recent findings on holdfast development in the giant kelp highlighted its key importance for Macrocystis vegetative propagation. We report here for the first time the development of adventitious holdfasts from Macrocystis stipes. Swellings emerge spontaneously from different areas of the stipes, especially in senescent or creeping individuals. After being manually fastened to solid substrata, these swellings elongated into haptera, which became strongly attached after 1 month. Within 4 months, new thalli increased in size and vitality, and developed reproductive fronds. Our results suggest the usage of these structures for auxiliary attachment techniques. These could act as a backup, when primary holdfasts are weak, and thus improve the survival rate of the giant kelp in natural beds.     

Patterns of abundance and assemblage structure of epifauna inhabiting two morphologically different kelp holdfasts

The mobile fauna associated with two sympatric kelp species with different holdfast morphology (Saccorhiza polyschides and Laminaria hyperborea) was compared to test for differences in the assemblage structure of holdfast-associated mobile epifauna. A total of 24,140 epifaunal individuals were counted from 30 holdfasts of each kelp species. Overall epifaunal abundances exceeded faunal abundances previously reported from holdfasts of other kelps. Three taxonomic groups, Amphipoda, Mollusca, and Polychaeta, accounted for ca. 85% of all individuals. Total abundances increased with the amount of habitat available, quantified either as the volume or the area provided by the holdfasts. The multivariate structure of the epifaunal assemblage did not differ between holdfasts of the two kelp species. However, epifaunal assemblages responded differentially to the habitat attributes provided by each type of kelp holdfast: multivariate variation in the assemblage structure of epifauna was mostly explained by holdfast area and volume for L. hyperborea, and by the surface-to-volume ratio for S. polyschides holdfasts. Therefore, the physical attributes of biogenic habitats, here kelp holdfasts that better predict patterns in the assemblage structure of associated fauna can differ according to their different physical morphology, even though the overall assemblage structure of associated fauna was similar.     

Use of low-budget monitoring of macroalgae to implement the European Water Framework Directive

Benthic macroalgal communities constitute one of the ecological quality elements needed to implement the Water Framework Directive (2000/60/EC), the legislation targetted at sustainable management of the European aquatic environment. As the Directive foresees the establishment of Ecological Status Class boundaries and Reference Conditions in coastal waters, a study was conducted on the Attica coast of Greece to identify the best method to use macroalgal community data for evaluating ecological quality and at the same time keep the program within a low budget. Six seasonal quantitative and qualitative samples were taken from the upper infralittoral macroalgal communities on the Attica coast of Greece on six occasions between summer 1998 and spring 2002; these sites, which reflect a gradient of anthropogenic perturbation, were used on each occasion. A list of 60 macroalgal taxa was prepared, the cover value of each taxon was measured and the structure of the vegetation was described. The use of four different indices (Shannon-Weaver index, Pielou evenness, Multi-Dimensional Scaling plot of Bray-Curtis similarity, Ecological Evaluation index-EEI) were compared. The multidimensional scaling of Bray-Curtis similarity and the EEI were better at indicating the perturbation pattern of the study area. However, only the EEI succeeded in distinguishing four quality classes (‘low’ to ‘high’). By using EEI, a spatial scale-weighted evaluation of ecological quality was also performed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Biofiltering efficiency, uptake and assimilation rates of Ulva clathrata (Roth) J. Agardh (Clorophyceae) cultivated in shrimp aquaculture waste water

The growth, biofiltering efficiency and uptake rates of Ulva clathrata were studied in a series of outdoor tanks, receiving waste water directly from a shrimp (Litopenaeus vannamei) aquaculture pond, under constant aeration and two different water regimes: (1) continuous flow, with 1 volume exchange a day (VE day^-1) and (2) static regime, with 1 VE after 4 days. Water temperature, salinity, pH, dissolved inorganic nitrogen (DIN), phosphate (PO₄), chlorophyll-a (chl-a), total suspended solids (TSS), macroalgal biomass (fresh weight) and tissue nutrient assimilation were monitored over 12 days. Ulva clathrata was highly efficient in removing the main inorganic nutrients from effluent water, stripping 70–82% of the total ammonium nitrogen (TAN) and 50% PO₄ within 15 h. Reductions in control tanks were much lower (Tukey HSD, P < 0.05). After 3 days, the mean uptake rates by the seaweed biomass under continuous flow were 3.09 mg DIN g DW day⁻¹ (383 mg DIN m⁻² day⁻¹) and 0.13 mg PO₄ g DW day⁻¹ (99 mg PO₄ m⁻² day⁻¹), being significantly higher than in the static regime (Tukey HSD, P < 0.05). The chl-a decreased in seaweed tanks, suggesting that U. clathrata inhibited phytoplankton growth. Correlations between the cumulative values of DIN removed from the water and total nitrogen assimilated into the seaweed biomass (r = 0.7 and 0.8, P < 0.05), suggest that nutrient removal by U. clathrata dominated over other processes such as phytoplankton and bacterial assimilation, ammonia volatilization and nutrient precipitation.