The arrival of propagules of marine macroalgae in the intertidal zone

The composition and abundance of macroalgal propagules contained in sea water arriving at intertidal rocky shores was estimated monthly at Pelancura, central Chile, from June to December, 1984. Samples from surface water and from water running off rocky platforms with mixed algal vegetation were cultured in laboratory conditions and examined for development of sporelings. Thirty eight macroalgal entities grew in the cultures, 75% of them with opportunistic life-styles. The total number of sporelings was similar in the surface water of sites separated by 300 m. Marked variability in composition and number of sporelings was, however, observed between samples taken simultaneously at one site and between different months, suggesting patchiness in the dispersal of propagules. Marked differences were established in the ratio run-off water/surface water in the number of sporelings, which could be related to the dispersal shadows of the various taxa. Sporelings of late successional algae showed marked spatial and temporal variations in number. Some taxa of opportunistic algae were characterized by the development of several thousand sporelings per litre of sea water while in others the number of sporelings was two or three orders of magnitude less, suggesting differences in reproductive effort.     

Role of crabs in the natural regeneration of mangroves in the Sundarbans forest of Bangladesh

Abstract A study in the Bangladesh Sundarbans forest observed the impact of crabs on mangrove regeneration. Crabs were not found to cause any damage to the seedlings of experimental plots. In addition, no morphological damage attributable to crabs was observed in Rhizophora propagules collected from the forest floor. Further studies covering other areas of the forests have been suggested.     

Polychaete zonation and its relation to algal distribution down a vertical cliff in the western Mediterranean (Italy): a structural analysis

The zonation of polychaetes down a vertical cliff (0–5 m in depth) at Cape Romito, Leghorn, Italy, was investigated. The structural organization of the community changed with depth. A community typical of photophilic environments was found in the superficial zone (0–2 m), while in the deeper zone (3–5 m), a more diversified community characterized by species typical of sciaphilic environments was present. At the surface (0 m) the community was very poor in species and individuals and thus probably corresponds to the midlittoral fringe. In fact, some species typical of the midlittoral zone were found. This distribution pattern was constant for samples taken in February and August 1985. The distribution of polychaetes was closely related to that found for macroalgae. It is hypothesized that algae condition the substratum and that this is the main factor responsible for the zonation of polychaetes.     

Priority effects, taxonomic resolution, and the prediction of variable patterns of colonisation of algae in littoral rock pools

This study focuses on succession of macroalgae in littoral rock pools on the west coast of Italy. Previous studies in this system indicated that either canopy algae or turf-forming algae may dominate late in succession. Priority effects and non-hierarchical interactions have been proposed as possible explanations for these patterns. From previous knowledge on the timing of reproduction and recruitment of the two groups of algae and their interactions, I predicted that: (1) canopy algae would dominate patches of substratum cleared during their main period of recruitment (between April and July); (2) the turf-forming algae, although initially present, would be replaced by canopies in these patches; (3) turf-forming algae would characterise both the early stages of colonisation and the mature assemblage in patches cleared before or after the main period of recruitment of canopy algae, and (4) succession would be more consistent in space (i.e. canalised) in the presence of canopy algae than when the turf-forming plants achieve dominance. These predictions were tested in a multifactorial experiment where patches of substratum were cleared in three different periods (before, during and after the main period of recruitment of canopy algae), on three dates within each period and in two replicate pools in each date. Univariate and multivariate analyses indicated that variability at early stages of colonisation dictated much of the subsequent dynamics in this system. Predictions 1–3 were supported by the results, but only at a gross level of taxonomic resolution. Patterns of colonisation of individual species of turf-forming algae were unpredictable due to large small-scale spatial and temporal variation in abundance. Prediction 4 was not supported by the results. This study indicated that knowledge of the life-histories and ecology of individual populations is crucial to increase the accuracy and precision of ecological models that attempt to predict succession in variable systems. Received: 4 May 1999 / Accepted: 8 November 1999     

β-d-(1→4), β-d-(1→3) ‘mixed linkage’ xylans from red seaweeds of the order Nemaliales and Palmariales

Xylans from five seaweeds belonging to the order Nemaliales (Galaxaura marginata, Galaxaura obtusata, Tricleocarpacylindrica, Tricleocarpa fragilis, and Scinaia halliae) and one of the order Palmariales (Palmaria palmata) collected on the Brazilian coasts were extracted with hot water and purified from acid xylomannans and/or xylogalactans through Cetavlon precipitation of the acid polysaccharides. The β-d-(1→4), β-d-(1→3) ‘mixed linkage’ structures were determined using methylation analysis and 1D and 2D NMR spectroscopy. The presence of large sequences of β-(1→4)-linked units suggests transient aggregates of ribbon- or helical-ordered structures that would explain the low optical rotations.     

Effect of five chinese traditional medicines on the biological activity of a red-tide causing alga—Alexandrium tamarense

The activity of algal cells plays an important role in the development of a red tide. Thus, when mass sedimentation of algae occurs, the scale of the red tide is reduced to some degree. Using cell suspension ability as an indicator, we studied the inhibitory effect of five Chinese traditional medicines/Chinese herbs on the activity of the red tide causing alga, Alexandrium tamarense, strain DH01. The results showed that among the five herbs, golden thread (Rhizoma coptidis Huang Lian) and areca seed (Semen arecae Bing Lang) had the best inhibitory effect, followed by indigowoad (Isatis tinctoria L.), and the least effect was found in lightyellow sophora (Sophora flavescens Ait.) and chameleon plant (Houttuynia cordata Thunb.). The 1hLC₅₀ of golden thread and areca seed was 0.054% (w/v) and 0.074% (w/v), respectively. Moreover, the higher the concentration of the herbs, the higher the inhibitory rate (IR), and the shorter reaction time needed. Combination of two herbs improved, to some extent, the inhibitory effect on the algae. A mixture of golden thread and areca seed was the most effective treatment against cell mobility of this red tide alga, and the 1 h inhibitory rate was 70.7%. Next most effective was the combination of indigowoad root and lightyellow sophora. The best inhibition results in the experiments using absorbents were golden thread and indigowoad with aloe (Aloe vera L. var. chinensis (Haw.) Berg.); followed by areca seed with aloe, and golden thread and areca seed with kelp (Laminaria japonica). In general, the zeolite based algal inhibitors were less effective. The inhibitory rates of the algal inhibitors LA, LI, KG, KA and KG were all above 90%, and remained high for 72 h. Our research results showed that the red tide inhibitors made with Chinese herbs, such as golden thread and areca seed, had the merits of low concentration, fast reaction time, and demonstrated a promising future for use in the control of red tides.     

Algal polymorphism in high rate wastewater treatment ponds

In the past as well as today there have been two conflicting opinions as to whether changes in the algal species in water bodies indicate polymorphism or the development of separate species. Similar changes were also found in High Rade Algae Pond (HRAP) used for wastewater treatment, effluent reclamation and protein production. To critically examine both opinions, samples of HRAP effluent were taken and the algal species identified and measured continuously, using conventional methods.Two main algal species were identified. These remained stable during all four monitoring sessions over a three-year period. The external changes observed in the algae were a reflection of controlled periods of organic loading and the conditions under which the pond was operated, such as retention time (a dependant of radiation), ambient temperature, effluent depth and aeration methods.Current address: Institute for Desert Research, Ben-Gurion University of the Negev, Sde-Boker, Israel 84990     

Host-finding behaviour and navigation capabilities of symbiotic zooxanthellae

Past studies have shown that the initiation of symbiosis between the Red-Sea soft coral Heteroxenia fuscescens and its symbiotic dinoflagellates occurs due to the chemical attraction of the motile algal cells to substances emanating from the coral polyps. However, the resulting swimming patterns of zooxanthellae have not been previously studied. This work examined algal swimming behaviour, host location and navigation capabilities under four conditions: (1) still water, (2) in still water with waterborne host attractants, (3) in flowing water, and (4) in flow with host attractants. Algae were capable of actively and effectively locating their host in still water as well as in flow. When in water containing host attractants, swimming became slower, motion patterns straighter and the direction of motion was mainly towards the host—even if this meant advancing upstream against flow velocities of up to 0.5 mm s⁻¹. Coral-algae encounter probability decreased the further downstream of the host algae were located, probably due to diffusion of the chemical signal. The results show how the chemoreceptive zooxanthellae modify their swimming pattern, direction, velocity, circuity and turning rate to accommodate efficient navigation in changing environmental conditions.     

An in vitro oxidative stress test for determining pollutant tolerance in algae

An in vitro oxidative stress test has been developed to assess pollutant tolerance in freshwater algae using Euglena gracilis as the test organism and FeSO₄ and NaCl as the pollutants. The test evaluates free radical-mediated oxidative stress through the concomitant application of three biochemical assays: (1) the non-invasive, gas chromatographic-volatile headspace analysis of hydroxyl radicals (OH) using dimethyl-sulphoxide as a radical trap; (2) the spectroscopic determination of total antioxidant activity; (3) a fluorescent microscopy viability test. In vitro pollutant testing was devised to simulate contaminant loadings that impact urban retention ponds. E. gracilis was found to be tolerant to FeSO₄ (2–10% (w/v)) and NaCl (10–5000 ppm) as indicated by high positive viabilities (ca. 100%) and low, or no OH production, as compared to controls. Total antioxidant activity increased with increasing pollutant loading suggesting that the organism has the capacity to enhance antioxidant defence in response to pollutant stress. This in vitro test provides a new approach to monitor the effects of water quality on the biological components of urban and/or polluted aquatic ecosystems. It also has a potential application in the identification of putative algal phytoremediators.