Gracilaria conferta and its epiphytes: (2) Interrelationship between the red seaweed and Ulva cf. lactuca

Ulva cf. lactuca has been a disturbing competitor of experimental Gracilaria conferta outdoor cultures in Israel. The effect of environmental conditions on the competitive ability of Ulva versus Gracilaria, and the main limiting factors for which these seaweeds compete, were studied here. Single and biculture experiments of both seaweeds showed that Ulva outgrew and damaged Gracilaria under all irradiance and temperature combinations. The higher competitive ability of Ulva cf. lactuca in bicultures was not a result of responses to shading or nitrogen shortage, but rather to a shortage of available inorganic carbon, an increase in pH and apparent excretions of Ulva which inhibited the growth of Gracilaria.     

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.     

Gracilaria conferta and its epiphytes: 3. Allelopathic inhibition of the red seaweed byUlva cf.lactuca

In a previous study (Svirski et al., 1993), it was found that growth inhibition ofGracilaria spp., when cultured in the presence ofUlva cf.lactuca, was not due to shading or nutrient depletion, but seemed to be caused by competition for inorganic carbon or some type of allelopathy. In the present study, we attempted to differentiate between these two possible influences by (1) growing the two algae in biculture under various conditions, but keeping inorganic carbon levels constant and measuring net photosynthesis, respiration and growth rates, and by (2) measuring growth rates ofGracilaria spp. in the presence of extracts derived from media previously used to growUlva cf.lactuca.Both net photosynthesis and growth rates ofGracilaria spp. in biculture were inhibited, despite CO₂ (and also HCO₃ ^–) levels being kept constantly high in the culture media. It is likely that these responses were due to markedly enhanced rates of dark respiration inGracilaria spp. when grown together withUlva cf.lactuca. Growth ofGracilaria spp. was also inhibited by extracts derived from seawater in whichUlva cf.lactuca had previously been grown. The strong inhibition by ethyl acetate and chloroform extracts indicate an allelopathic effect onGracilaria spp.     

The effect of cooling seawater effluents of a power plant on growth rate of cultured Gracilaria conferta (Rhodophyta)

The effect of cooling seawater effluents of a power plant on the growth rate of Gracilaria conferta in tanks has been studied, as a possible solution for the decrease in the winter growth rate in ambient seawater tanks. The Gracilaria cultures did not survive more than 2–8 weeks in the power plant effluents during the one-year-long repeated experiments. The major reason was the high accumulation of copper, iron, lead and chromium from the power plant effluents as compared to concentrations in Gracilaria cultured in ambient seawater. The survival increased and the copper accumulation decreased significantly when the effluents were passed through an Ulva biofilter.     

Saldanha Bay,South Africa: recovery of Gracilaria verrucosa (Gracilariales,Rhodophyta)

Since World War II the greater Saldanha Bay lagoon system, South Africa, has been an important Gracilaria producer. Two agar factories, built in the 1960's, used Gracilaria from Saldanha Bay as their raw material. In the early 1970's the industry was destroyed as a result of dredging and marine construction operations to establish a harbor in the bay for loading ore. These environmental changes destroyed stocks and prevented the previously significant beachings of the seaweed from occurring. After a few years of no or very low commercial production, the resource slowly started to recover. The size of Gracilaria drifts increased over the following eight years to approximately one-third of the original output. This trend seems to continue. Although the stocks and resultant drifts are unlikely to recover fully to their original quantity, current production is already sufficient to ensure re-establishment of a seaweed industry in Saldanha Bay. This could have considerable socio-economic impact on the area.     

Experimental tank cultivation of Gracilaria sp. (Gracilariales,Rhodophyta) in Ecuador

This paper describes experiments to grow a local and still unidentified species of Gracilaria in shrimp hatcheries in Ecuador. The experiments used outdoor tanks of 1 and 18 m³ capacity, with continuous aeration and water renewal every two and five days, respectively. The sea water (salinity 34 ppt) was enriched with Guillard's f/2 medium; light and temperature were monitored but not controlled. One kg of fresh seaweed, inoculated into each tank, produced a biomass of ca. 3 kg in a period of 35 days in the 1 m3 tank and 18 kg in 43 days in the 18 m³ tank. We therefore believe that it is technically feasible to use the large infrastructure of existing shrimp hatcheries in Ecuador to produce Gracilaria.     

Characterization of an agar fraction extracted from Gracilaria dura (Gracilariales,Rhodophyta)

The evaluation of biopolymers of biotechnological interest has stressed the importance of renewable sources from the northern Adriatic Sea. In the frame of this research program, the red alga Gracilaria cf. dura, has been studied. Agar was obtained from Gracilaria cf. dura by means of alkali treatment and hot water extraction. In order to purify the extracts, amylase and isopropyl alcohol were used. Analysis of sugars was carried out by means of gas chromatography on alditol acetate derivatives; sulfate content was evaluated by means of infrared spectroscopy. An analysis of molecular weight distribution was carried out by means of high performance gel permeation chromatography coupled with a low angle laser light scattering device as detector. Analytical data were examined in terms of specificity of the algal source utilized, and the agar fractions extracted by means of this procedure were compared with a commercial sample.     

A simple method for mass isolation of protoplasts from species of Monostroma, Enteromorpha and Ulva (Chlorophyta, Ulvales)

A simple enzyme mixture containing 2% Cellulase Onozuka R–10 and1% Macerozyme R–10 prepared in deionised water supplemented with 3% NaCland 1 mM CaCl₂ was developed for isolating rapidlyprotoplasts from different species of Monostroma,Enteromorpha and Ulva. The yield fordifferent species of Monostroma ranged from 9.6 ×10⁶ to 10.2 × 10⁶ cells g^–1f. wt thallus, and forEnteromorpha from 3.48 × 10⁶ to 11.7× 10⁶ cells g^–1 f. wt and forUlva from 4.58 × 10⁶ to 26.8 ×10⁶ cells g^–1 f. wt. The overallregeneration rate of the protoplasts isolated was usually > 90% and showednormal morphogenesis. The method yields rapid mass production of viableprotoplasts with high regeneration rates.     

Spatial and temporal variations of Penilia avirostris and Evadne tergestina (Crustacea,Branchiopoda) in a Tropical Bay,Brazil

We analysed monthly samples collected in Guanabara Bay, with a conical net of 200 m mesh during 1985. The bay was divided into three areas: an outer region (area A), influenced by oceanic waters; an inner region (area C), influenced by fluvial inflow; and a transition region (area B) with intermediate features. Penilia avirostris and Evadne tergestina were observed in the three areas, with greatest densities, however, in the outermost region, which had the highest salinities and lowest temperatures. Penilia avirostris was more abundant in summer (March), a period with the greatest relative densities of nanoplankton. Evadne tergestina was also abundant in summer, but its peak fell in November, a period with a relative increase in microphytoplankton density in the bay. The two species disappeared in winter: Penilia avirostris was absent from May to August, whereas Evadne tergestina disappeared in August and September.     

Utilization of seaweed Ulva sp. in Paracas Bay (Peru): experimenting with compost

In Paracas Bay (Peru), large quantities of Ulva sp. interfere with various important activities of the zone. In this context, the present study was undertaken to evaluate the effect of adding Ulva sp. in compost piles and the quality of the resulting composts. Six compost piles were prepared using, straw, green material mixture, cow manure and Ulva in different quantities (9, 17 and 28% of volume) and forms. Several variables were monitored during the process and the chemical characteristics of the final composts were determined. Aerial biomass achieved by maize plants was also evaluated for each compost at different compost/sand proportions. Results show that the compost pile made with Ulva powder registered the highest temperature and the longest thermophilic phase. Piles prepared with 28% washed Ulvapresented anoxic conditions at the beginning and had higher electrical conductivity values. Carbon/Nitrogen ratio diminished appropriately in all piles and there was no negative effect observed on the pH of the piles. Compost prepared with Ulva had lower contents of Total Kjeldahl Nitrogen, and produced maize plants aerial biomass.     

Ulva rigida (Ulvales,Chlorophyta) tank culture as biofilters for dissolved inorganic nitrogen from fishpond effluents

Ulva rigida was cultivated in 7501 tanks at different densities with direct and continuous inflow (at 2, 4, 8 and 12 volumes d^–1) of the effluents from a commercial marine fishpond (40 metric tonnes, Tm, of Sparus aurata, water exchange rate of 16 m³ Tm^–1) in order to assess the maximum and optimum dissolved inorganic nitrogen (DIN) uptake rate and the annual stability of the Ulva tank biofiltering system. Maximum yields (40 g DW m^–2 d^–1) were obtained at a density of 2.5 g FW 1^–1 and at a DIN inflow rate of 1.7 g DIN m^–2 d^–1. Maximum DIN uptake rates were obtained during summer (2.2 g DIN M^–2 d^–1), and minimum in winter (1.1 g DIN m^–2 d^–1) with a yearly average DIN uptake rate of 1.77 g DIN m^–2 d^–1 At yearly average DIN removal efficiency (2.0 g DIN m^–2 d^–1, if winter period is excluded), 153 m² of Ulva tank surface would be needed to recover 100% of the DIN produced by 1 Tm of fish.Abbreviations DIN= dissolved inorganic nitrogen (NH _inf4 ^sup+ + NO _inf3 ^sup– + NO _inf2 ^sup– ); - FW= fresh weight; - DW= dry weight; - PFD= photon flux density; - V= DIN uptake rate     

A Finding of the Crab Planes marinus Rathbun, 1914 (Decapoda: Grapsidae) in Peter the Great Bay,Sea of Japan

A crab Planes marinus Rathbun, 1914 was found on a drifting buoy in Peter the Great Bay (Sea of Japan). The crab probably arrived in the bay with subtropical waters penetrating into this area during the summer period.     

Effect of grazing by isopods and amphipods on growth of Ulva spp. (Chlorophyta)

Eutrophication of shallow coastal waters often leads to blooms of macroalgae. Grazing by crustaceans, such as amphipods and isopods, can reduce macroalgal biomass accumulation. At the same time, growth of the macroalgae can be stimulated by epiphyte removal. The role of grazing by isopods and amphipods on Ulva spp. biomass development was investigated in the Veerse Meer, a brackish lagoon situated in the southwest Netherlands. Exclusion of grazing in the field did not stimulate Ulva spp. growth. In fact, growth rates were higher in exclosures that allowed grazers to enter. Edibility tests identified the amphipod Gammarus locusta, and the isopods Idotea chelipes and Sphaeroma hookeri as potential grazers on Ulva spp. However, when epiphytic diatoms were present on the Ulva spp. thalli, Gammarus and Sphaeroma grazed on ephiphytes and not on Ulva tissue. Only Idotea continued to graze on Ulva spp. A laboratory growth experiment revealed a positive effect of Gammarus presence on Ulva spp. growth, probably caused by preferential removal of epiphytic diatoms from the Ulva spp. thalli. The growth stimulation by epiphyte removing grazers such as Gammarus may explain the higher growth rates in the presence of grazers observed in the field. When determining the potential role of invertebrate grazers in controlling macroalgal biomass accumulation, it is important to include an assessment of the epiphyte abundance on the macroalgae, as preferential removal of epiphytes may stimulate growth and thus have the opposite effect.     

Assessment of populations ofGracilaria chilensis (Graeilariales,Rhodophyta) utilizing RAPDs

Phenotypic variability and mixing of material due to massive cultivation for commercial purposes has contributed to the taxonomic confusion ofGracilaria in Chile. At least four species with cylindrical thalli and similar morphology have been recorded. However, since establishment ofG. chilensis, most of the collected thalli have been attributed to this species despite the lack of diagnostic features. In an attempt to resolve whetherGracilaria from 3 localities where it grows in natural and artificial populations belongs to the same species, gametophytic samples were compared by applying RAPD-PCR to their total DNA. This was analysed using 25 different 10-mer primers from which 21 revealed polymorphism within and between populations. Similarity matrices and cluster analyses were performed based on the presence/absence of bands representing fragments of DNA generated by random amplification. Similarity values between two of the populations were equivalent to those detected within a third, indicating the mixing of genetic material due to transplant between the two former localities. Similarities between samples of ChileanGracilaria andG. tenuistipitata from Sweden are considerably lower (0.45–0.53) than those between populations from Chile (0.74–0.88), confirming the existence of a single specific taxon,G. chilensis, in these three localities.     

Trophic relationships and seasonal utilization of salt-marsh creeks by zooplanktivorous fishes

Synopsis In a high salinity estuary at North Inlet, South Carolina, co-occurrence and possible competition among adults of four dominant zooplanktivorous fishes were minimized by seasonal adjustments in lateral and vertical distributions as well as in dietary preferences. In winter, Atlantic silversides, Menidia menidia, occupied the entire water column while other planktivores were rare or absent from the estuary, and they consumed large prey such as mysid shrimps and fish larvae. An immigration of bay anchovies, Anchoa mitchilli, in the spring resulted in a redistribution of species with Atlantic silversides shifting to the surface waters and bay anchovies dominating the lower half of the water column. Both fishes consumed mostly copepods in the spring, but each favored a different species. There was little similarity in the large prey items consumed by the two fishes. Striped anchovies, Anchoa hepsetus, arrived in mid-summer and were most abundant at the surface while bay anchovies continued to dominate the bottom waters. Atlantic silversides were rare in all summer collections. The diets of the two anchovies were similar, but vertical separation during the period of maximum zooplankton abundance probably minimized competition. Rough silversides, Membras martinica, which were obligate surface dwellers, shared the upper water column with striped anchovies, but the two species had very different diets during their period of co-occurrence. Although seasonal changes in fish diets reflected shifts in zooplankton composition and all fishes consumed a variety of prey types, preferences for some prey taxa and total avoidance of others were indicated. Electivity indices indicated an especially strong selection for fiddler crab megalopae by all fishes in the summer and fall. All fishes, except rough silversides, which fed almost exclusively on copepods and crab zoeae, consumed large prey items when they were available. Fine scale partitioning of the food resources was apparent in the selection of different copepod and insect species by the fishes. Spatial and temporal separation in the distribution and/or dietary preferences of the zooplanktivores fishes probably reduces the potential for resource competition. Given the high abundances and selectivity of the planktivores, significant impacts on some zooplankton populations probably result.     

The role of herbivores in the collapse of the Gracilaria resource at Saldanha Bay,South Africa

At Saldanha bay on the west coast of South Africa, annual yields of beach-cast Gracilaria often exceeded 1000 metric tons, until the construction of an ore jetty and breakwater in 1974. Yields were then drastically reduced, recovered to 429 tons in 1988, then fell to zero. Diving surveys revealed a steady decline in the biomass of the remaining beds from 50 t in April to less than 1 t in August 1989. The presence of large numbers of herbivores suggested that grazing was the cause. This hypothesis was tested by experimental exclusions of fish and/or invertebrate herbivores (keyhole limpets and sea urchins). Results show that grazing by the fish in shallow water and the keyhole limpets and urchins in deep water prevented recovery of the resource and may have caused the initial decline.     

Can Kelp Extract (KELPAK®) be Useful in Seaweed Mariculture?

The addition of low concentrations of commercial kelp extract (Ecklonia maxima: Kelpak^®) in addition to fertiliser has proven to be beneficial in agriculture. It triggers rooting in field crops, increases yields and has other useful effects, such as parasite reduction. Its efficacy has been attributed to the fact that Kelpak^® is produced by a cold process, and is a high auxin/low cytokinin product. The aim of this study was to investigate if seaweeds (which do not have a root system) grown in culture systems, would benefit from the addition of Kelpak^® or a combination of Kelpak^® and fertilizer. A preliminary laboratory experiment was carried out by growing excised 15 mm tips of the red alga Gracilaria gracilis in culture dishes containing Provasoli Enriched Seawater medium to which various concentrations of Kelpak^® were added. Gracilaria tips in some of the Kelpak^® treatments (1:2500; 1:1000; 1:500) grew significantly better than the control. Further experiments were carried out on a pilot commercial scale at Jacobsbaai Sea Products Ltd. on the South African west coast. Ulva lactuca was grown in effluent from fish (turbot) culture, with additions of 1:5000, 1:2500 and 1:500 concentrations of Kelpak^® once a week. The intermediate Kelpak^® concentration (1:2500) produced the highest growth of Ulva in the turbot water, while the highest Kelpak^® concentration (1:500) inhibited Ulva growth. In another Ulva experiment, various combinations of aquaculture effluent water, commercial fertiliser and Kelpak^® at 1:2500 were used. Best growth of Ulva was obtained in turbot water containing both fertiliser and Kelpak^®. The results suggest that Kelpak^® could be useful in commercial seaweed mariculture operations.     

Agar properties of two species of Gracilariaceae from the Gulf of California,Mexico

Agar properties of two potentially commercial important seaweeds from the Gulf of California were studied. Maximum yield in Gracilaria vermiculophylla (45.7%) occurred during the summer months, coinciding with high water temperatures (31°C) whereas minimum yields (11.6%) were obtained during the coldest months of the year when populations of this species diminish in the bay. Gracilariopsis longissima showed two yield peaks, one in spring and another in fall, before the maximum and minimum seawater temperatures. Gel strength in native agar from the two species was low (<22.5 g cm⁻²) for most of the year. G. vermiculophylla native agar showed a slight increase in gel strength from June to August, which were the hottest months. Maximum value was 85 g cm⁻¹ in August. Maximum gel strength in G. longissima was observed in October (91 g cm⁻¹), and an unusual native agar with no detectable gel strength was observed in March and April samples. Gelling temperatures range from 27.7 to 36.5°C in G. vermiculophyla and from 26.6 to 34.9°C in G. longissima, meanwhile melting points were 73.9 – 53.5°C and 75.5 – 56.6°C, respectively. Sulfate content was high, 6.3–13.9% in G. vermiculophylla and 1.9–11.9% in G. longissima, and on the other hand 3,6 anhydrogalactose content was low 12.1–26.7% and 9.1–23%, respectively compared to other species. Results obtained showed that mean native agar yields of Gracilaria vermiculophylla and Gracilariopsis longissima from the Gulf of California are comparable to other tropical Gracilaria. However, the low gel strength, high sulfate content and low 3,6 anhydrogalactose content observed in the native agar extracted from these species make this an agaroid, thus alternative methods of extraction should be used to evaluate the possibility of commercial utilization of both species.     

The yield,physical and chemical properties of agar gel from Gracilaria species (Gracilariales,Rhodophyta) of the Kenya coast

Six species of Gracilaria, G. corticata J. Agardh, G. crassa Harvey, G. millardetii J. Agardh, G. salicornia (J. Ag.) Dawson, G. verrucosa (Huds.) Papenfuss and Gracilaria sp, collected from different stations along the Kenya coast were studied. The yield of hot water native agar extract ranges from 8.1–30% of dry weight, with G. verrucosa and G. salicornia having the greatest and the least yield, respectively. The gel-strength of 1.5% agar solution was highest in G. verrucosa (220 g cm^–2) and lowest in G. corticata (< 60 g cm – 2) whereas the highest gelling temperature was recorded for Gracilaria sp. (40.4 °C) and the lowest in G. verrucosa (28.9 °C). 3,6 anhydrogalactose content was the highest in G. verrucosa and the lowest in G. corticata while sulphate content was higher in the latter.     

Growth of the seaweed Ulva rigida C. Agardh in relation to biomass densities, internal nutrient pools and external nutrient supply in the Sacca di Goro lagoon (Northern Italy)

Growth of the seaweed Ulva rigida C. Agardh was investigated in relation to biomass densities, internal nutrient pools and external nutrient supply. Research was carried out from 23 March to 5 July 1994 in the Sacca di Goro (Po Delta, Northern Italy), whose south-eastern part was covered by extensive mats of Ulva rigida. Two types of field experiments were conducted by incubating Ulva thalli inside large cages. In the first experiment, beginning on 23 March, 100 g of wet thalli were placed into the cages, allowed to grow for two weeks, then collected and replaced. This procedure was repeated 8 times over the study period. In the second experiment, Ulva thalli were left inside the cages and collected at selected time intervals (14, 27, 41, 64 and 76 days) in order to simulate the effects of increased density on growth and nutrient storage.We recorded specific growth rates (NGR) ranging from 0.025 to 0.081 d^–1 for a period up to two months in the repeated short-term experiments performed at relatively low initial algal densities (300–500 g AFDW m^–3). These NGR resulted significantly related to dissolved inorganic nitrogen (DIN) in the water column. Tissue concentrations of total Kjeldahl nitrogen (TN) were almost constant, while extractable nitrate decreased in a similar manner to DIN in the water column. Total phosphorus showed considerable variation, probably linked to pulsed freshwater inflow.In the long-term incubation experiment, NGR of Ulva was inversely related to density. Internal concentrations of both total P and TN reached maximum values after one month; thereafter P concentration remained almost constant, while TN decreased below 2% w/w (by dry weight). The TN decrease was also accompanied by an abrupt decrease in nitrate tissue concentration. The biomass incubated over the two month period suffered a progressive N limitation as shown by a decreasing NY ratio (49.4 to 14.6). The reciprocal control of Ulva against biogeochemical environment and viceversa is a key factor in explaining both resource competition and successional stages in primary producer communities dominated by Ulva. However, when the biomass exceeds a critical threshold level, approximately 1 kg AFDW m^–3, the macroalgal community switches from active production to rapid decomposition, probably as a result of selfshading, biomass density and development of anaerobic conditions within the macroalgal beds.