The effect of localised eutrophication on competition between Ulva lactuca (Ulvaceae,Chlorophyta) and a commercial resource of Gracilaria verrucosa (Gracilariaceae,Rhodophyta)

In spring (August) 1993 a bloom of Ulva lactuca appeared for the first time in Saldanha Bay, South Africa, and persisted through summer. Ulva wash-ups contaminated the beach and part of the commercial Gracilaria beach-cast had to be discarded. The biomass and distribution of Gracilaria and Ulva are described in relation to the seasonal water chemistry of the bay. Gracilaria survives in deeper water in summer by the pulsing of nutrients on an approximately 6-day cycle of movement of the thermocline that separates nutrient-rich bottom water from warm oligotrophic surface water. Ammonium-rich fish-factory discharge into this surface layer in a sector of the bay provided localised conditions for Ulva to out-compete Gracilaria at depths of 2–5m, demonstrating the powerful disruptive effect of eutrophication in this strongly stratified system.     

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.     

Ecological significance and commercial harvesting of drifting and beach-cast macro-algae and seagrasses in Australia: a review

This review provides an overview of aspects of the ecology of drifting and beach-cast macroalgae and marine angiosperms in respect to present and potential commercial use of that resource in Australia. It sets the scene with sections on industries that utilise macro-algae and seagrasses, the ecology of littoral and nearshore sublittoral ecosystems and the processes of deposition of beach-cast macro-algae and seagrasses on beaches. It then describes the major economic macro-algae and seagrasses that occur as beach-cast wrack, with an emphasis on known information on habitat distribution, geographical range, and harvesting issues. Gaps in scientific knowledge are pointed out. The priority areas of future research were found to be: • The importance of beach accumulations of macro-algae and seagrasses on feeding and nesting shorebirds; • Whether available resource allows for ecologically and economically sustainable harvesting; • A survey of present and potential commercial macro-algae and seagrasses: studying biomass, density and annual production rates, interannual variability of recruitment into living stands, the effect of harvesting on trophodynamics and community structure and the stability of the resource base for economically sustainable harvesting; • An assessment of the importance of wrack in recycling nutrients and detritus to nearshore coastal ecosystems at wider geographical scales than previous work. This research should assess the dependence of offshore production on nutrients and detritus that are broken down in beachwracks. This revised version was published online in August 2006 with corrections to the Cover Date.     

The Invasive Kelp Undaria Pinnatifida (Phaeophyceae, Laminariales) Reduces Native Seaweed Diversity in Nuevo Gulf (Patagonia, Argentina)

The kelp Undaria pinnatifida(Phaeophyceae) is a seaweed native to northeast Asia, but during the last two decades, it has been accidentally or intentionally introduced in several temperate coasts worldwide. In central Patagonia (Argentina), this species was first detected in late 1992, and it is progressively spreading from the point of introduction. Through a manipulative experiment involving Undaria removal in 2001, we found that its presence is associated with a dramatic decrease in species richness and diversity of native seaweeds in Nuevo Gulf. Future prospects are worrisome, as, in addition to the negative impact from a biodiversity viewpoint, native commercial macroalgae and invertebrates might also be affected.     

Surveys of Undaria pinnatifida (Laminariales,Phaeophyta) in Golfo Nuevo,Argentina

In December 1992, some sporophytes of the Asian kelp Undaria pinnatiftda were found growing subtidally at 6 m depth below A. Storni Port, Puerto Madryn, Argentina. During the winter of 1994, the species expanded significantly from its original location. Sporelings appear in early autumn and attain their maximum size (1.65 ± 0.10 m) during winter and early spring, when most of them become fertile. The fronds are lost in summer, with only some holdfasts and sporophylls surviving, and these disappear by the end of summer. The occurrence of U. pinnatida in Golfo Nuevo is reportedly due to an accidental introduction by cargo ships or fishing vessels arriving from Asian ports.     

Coupling between macroalgal inputs and nutrients outcrop in exposed sandy beaches

Fluxes of nutrients across habitats are of paramount relevance in ecological studies due to the implication in primary production, trophic structure and biodiversity. This study analyses the role of sandy beaches in the processing of organic matter. Three beaches with different macroalgal inputs were sampled throughout the annual cycle. The standing stock of wrack macroalgae on the beach surface and the nutrient concentration in the intertidal pore water (IPW) and in the surf zone water were measured monthly. Mean concentration of dissolved inorganic nitrogen and phosphate in the IPW increased from the low to the very high subsidized beach. Seasonal coupling was observed between the wrack biomass and the nutrient concentration throughout the year. Among the nutrient species, a variable relationship was found between the NH₄ ⁺/NO _x ^? ratio and the biomass of macroalgae deposited. These results provide evidences of the active role of sandy beaches in the processing of organic matter and in the nutrient cycling, remarking the feedback connectivity between sandy beaches and their neighbour ecosystems.     

Low fish predation pressure in London reservoirs: II. Consequences to zooplankton community structure

The 1992 survey of zooplankton structure in fourteen London supply reservoirs showed the overall dominance of large-bodied zooplankton, mainly species of Daphnia. These reservoirs can be considered as ‘anti-fish’ by virtue of their steeply sloping concrete or brick sides. The average biomass of large Daphnia spp (retained on a 710 μm sieve) in the total zooplankton biomass was higher than 20% for twelve out of fourteen reservoirs. The cladoceran-copepod ratio was inversely correlated with both dominance of large-bodied Daphnia magna and cladoceran body-size structure. Parallelly, there were tendency of more efficient utilization of lowered algal crops in reservoirs dominated by large-bodied Daphnia spp. A graphical model is presented which relates daphnid species composition and zooplankton size structure to a presumed gradient of fish biomass in these reservoirs.     

Age and preservation of Amphistegina (foraminifera) in Hawaiian beach sand: implication for sand turnover rate and resource renewal

Radiocarbon dating of tests of Amphistegina spp. from the surface sand of Hawaiian beaches has revealed ages up to 1500 years or more. Preservation is related to age: the residual umbos are older than the intact tests. The antiquity of some of the tests suggests that predictions of a sand turnover rate of less than 100 years time based on Amphistegina productivity studies are in error and that the majority of tests produced in nearshore environments of Hawaii do not accumulate on the beach.     

The effect of wrack composition and diversity on macrofaunal assemblages in intertidal marine sediments

Wrack (dead, washed-up seaweed and seagrass) buried in soft substrata may increase the organic content and alter the physical structure of sediments. These effects may influence the composition and structure of macrofaunal assemblages in the sediment. Such influences can be expected to vary according to the type and amount of wrack as well as the presence of invasive seaweeds in the wrack. In this study, we deliberately buried different amounts of the invasive species Sargassum muticum in isolation or mixed to the native species Ulva sp. and Fucus vesiculosus, in two intertidal sandflats to test some hypotheses about the response of macrofaunal assemblages. We tested whether (1) diversity of detritus (i.e. different mixtures), and (2) the amount of detritus of S. muticum influenced the composition and the relative abundance of macrofaunal assemblages. We also assessed whether the sediment organic carbon and the biomass of benthic microalgae varied depending on the diversity of detritus and the amount of detritus of S. muticum. Finally, we tested if these effects of wrack were consistent across sites. Results indicated that buried wrack affected the composition and structure of macrofaunal assemblages in short-term (i.e. 4 weeks), but there were no differences depending on detritus diversity or the amount of S. muticum. In addition, sediment organic matter and microalgal biomass were not affected by the addition of wrack. They instead varied greatly among small spatial scales (i.e. plots). Wrack composition or abundance of the invasive species S. muticum played thus a small role in shaping the structure of macrofaunal assemblages or the biomass of benthic microalgae in these intertidal sediments, probably because these sediments are frequently affected by various inputs of organic matter and benthic assemblages are already adapted to organically enriched sediments.     

Ocean color observations of a surface water transport event: Implications for Pseudo-nitzschia on the Washington coast

A persistent patch of high biomass water, associated with the Juan de Fuca Eddy, is often observed in surface chlorophyll a images off the southwest coast of Vancouver Island, Canada. Outbreaks of toxic Pseudo-nitzschia spp. along the Washington, USA, coast are believed to correlate with the transport of waters from Juan de Fuca Eddy southward to Washington beaches. A time series of Sea-viewing Wide Field-of-view Sensor (SeaWiFS) satellite ocean color images from late May 1999 of coastal waters off Washington and Vancouver Island, processed for surface chlorophyll a concentration and spectral remote sensing reflectance, captured a transport event where water from the Juan de Fuca Eddy was transported onto the Washington shelf. Strong upwelling-favorable winds appeared to deform the patch over an 8-day period and move it southward into Washington coastal waters with surface velocities of approximately 8–16 km d⁻¹. SeaWiFS and sea surface temperature imagery showed the local phytoplankton response to wind-driven coastal upwelling restricted to a narrow (10–15 km) region along the Washington coast. Although we did not observe transport of high biomass water originating in the Juan de Fuca Eddy to Washington beaches in May 1999, transport of Pseudo-nitzschia cells could occur following a rapid shift to downwelling-favorable conditions. Tracking the trajectory of surface waters from the Juan de Fuca Eddy by remote sensing could be used to trigger conditional sampling for domoic acid along the Washington coast.     

Differential effects of native and invasive algal wrack on macrofaunal assemblages inhabiting exposed sandy beaches

Many sandy beaches worldwide receive large amounts of drift seaweed, known as wrack, from offshore algal beds and closer rocky intertidal shores. Despite the important influence of algal wrack on macrofaunal assemblages from different coastal systems, relatively little attention has been paid to the macrofaunal responses in sandy beaches to macrophyte wrack supplies. Algal wrack is a key resource, i.e. for food and/or refuge, for beach invertebrates while its availability can affect diversity and abundance of intertidal animals including shorebirds, but the role of certain types of wrack and its location on the shore has not been examined experimentally to date. In this paper, we use experimental manipulation of two species of brown seaweeds, i.e. artificial wrack patches made up of the native macroalgae Saccorhiza polyschides and the invasive species Sargassum muticum, to test hypotheses about influences on macrofaunal assemblages inhabiting the drift line and supratidal levels of exposed beaches. Results pointed out that different types of wrack deposits were not used uniformly by invertebrates. Nutritional value differed between the two species of wrack. In most cases, the carbohydrates, lipids and organic carbon content were greater in patches of S. muticum than in patches of S. polyschides. Data also provided evidences that nutritional content and microclimatic conditions of wrack deposits, i.e. temperature and humidity, might affect macrofaunal assemblages.     

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.     

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.     

Status of biological control by egg parasitoids of Diaprepes abbreviatus (Coleoptera: Curculionidae) in citrus in Florida and Puerto Rico

Eggs of Diaprepes abbreviatus (L.) were routinely monitored in citrus groves at ten locations in Florida during 1997 and 1998 to study egg parasitism. One citrus location was studied in Puerto Rico. No native parasitoids were recovered from 1,337 D. abbreviatus egg masses studied in Florida citrus. In contrast, an average of 35.5% (range 12.5 to 68.8%) parasitism of egg masses was reported in Puerto Rico. The parasitoids Aprostocetus gala, Horismenus spp, and Quadrastichus haitiensis were recovered from the eggs of D. abbreviatusfstudied in Puerto Rico. The Horismenus parasitoids were suspected hyperparasitoids. Releases of the parasitoid Ceratogramma etiennei from Guadeloupe were initiated during 1998 at each of the Florida research sites. By the end of 1998, C. etiennei had been recovered from D. abbreviatus eggs at two of nine locations in Florida citrus. The parasitoid was recovered from 1 of 34 egg masses at one of these locations during the month of September and from 3 of 34 egg masses at the other location during the month of November. Whether or not C. etiennei establishes itself at one or more locations in Florida remains to be seen.     

DISPERSAL OF HORMOSIRA BANKSII (PHAEOPHYCEAE) VIA DETACHED FRAGMENTS: REPRODUCTIVE VIABILITY AND LONGEVITY1

Drifting, fertile thalli are well documented to be the primary long‐distance dispersal vector for many marine macroalgae, but little information about reproductive viability of drift is known. This study examined the reproductive viability and longevity of floating fragments of the intertidal Australasian fucoid Hormosira banksii (Turner) Decne. Beach wrack surveys and field experiments were conducted to test the model that long‐distance dispersal is achieved in H. banksii via floating, fertile fronds. High densities of beach wrack fragments were evident during summer compared to autumn. The majority of beach wrack occurred on sandy beaches rather than rocky shores. Both male and female fragments were present in the beach wrack. Detached fronds were capable of releasing gametes up to 8 weeks after detachment. Beach wrack produced high fertilization rates and recruited successfully onto artificial panels. Results suggest that detached fragments are reproductively viable and that floating, fertile fronds may be an important mechanism for facilitating long‐distance dispersal in this species. Nevertheless, the frequency of fronds reaching a suitable habitat and contributing to gene flow between populations, or colonizing new populations, may not be proportional to the total density of beach wrack.     

Regulation of spatial and seasonal variation of macroalgal biomass in a brackish, eutrophic lake

Processes leading to biomass variation of Ulva were investigated at two contrasting sites in the eutrophic Veerse Meer (The Netherlands). Ulva species dominated at the Middelplaten site, while at the Kwistenburg site a mixture of Ulva spp. and Chaetomorpha linum dominated. Total summer macroalgal biomass was higher at Middelplaten than at Kwistenburg (282 and 79 g DW m^–2, respectively). Growth rates of Ulva spp. were high at both sites in May 1992 (cage mean 0.28–0.30 day^–1), but quickly dropped to lower values (0.05–0.10 day^–1). In May, growth rates were significantly highest at Kwistenburg, while during the rest of the season growth rates were similar for both sites. Temperature, pH, dissolved oxygen, salinity, light attenuation, phytoplankton and nutrient concentrations did not differ between sites. The relation between variation in Ulva spp. growth rates and environmental parameters was analysed using stepwise multiple regression, showing that light and temperature were the main variables regulating Ulva spp. growth rates. As Ulva growth rates were similar for both sites but biomass was much lower at Kwistenburg it was concluded that a large amount of produced biomass was lost at Kwistenburg. Although the exact reason for this remains unclear, it seems most likely that transport of macroalgae by wind and waves is a very important factor. This study shows the importance of simultaneously measuring growth rates and biomass at a high temporal resolution to reveal the mechanisms responsible for spatial variation in macroalgal biomass in shallow coastal areas. Electronic Publication     

Dominance of Lysobacter sp. in the rhizosphere of two coastal sand dune plant species, Calystegia soldanella and Elymus mollis

Bacterial diversity in the rhizosphere of beach morning glory (Calystegia soldanella) and wild rye (Elymus mollis), two of the major plant species inhabiting the coastal sane dune in Tae-An, Korea, was studied by the analysis of community 16S rRNA gene clones. The amplified rDNA restriction analysis (ARDRA) of the clones using HaeIII exhibited significant differences in the community composition between the two plant species as well as regional differences, but also identified a specific ARDRA pattern that was most common among the clones regardless of plant species. Subsequent sequence analysis indicated that the pattern was that of Lysobacter spp., which is a member of the family Xanthomonadaceae, class Gamma proteobacteria. The Lysobacter clones comprised 50.6% of the clones derived from C. soldanella and 62.5% of those from E. mollis. Other minor patterns included those of Pseudomonas spp., species of Rhizobium, Chryseobacterium spp. and Pantoea spp. among C. soldanella clones, and Pseudomonas sp. and Aeromonas hydrophila among E. mollis clones. It is not yet clear what kind of roles Lysobacter plays in association with sand dune plants, but its universal presence in the rhizosphere, together with the potential of this taxon for antagonistic activity against plant pathogens, suggests that Lysobacter might form a symbiotic relationship with its host plants.     

Management of natural <Emphasis Type="Italic">Ulva</Emphasis> spp. blooms in San Quintin Bay,Baja California: Is it justified?

According to Zertuche-González et al. (2009), Ulva spp. blooms, favored by oyster cultivation, are likely displacing subtidal meadows of Zostera marina in San Quintin Bay, Baja California. The authors propose a partial removal of the seaweed to reduce the risk of eutrophication and eelgrass displacement in the bay. We warn about the removal of Ulva spp. biomass by raising six arguments that emphasize the necessity of a historical and ecosystem-based management for San Quintin Bay. First, processes other than competitive exclusion by Ulva spp. blooms more likely explain changes of Z. marina subtidal meadows in the past decade. Second, there is no consistent evidence that oyster cultivation is promoting blooms of Ulva spp. and the loss of eelgrass. Third, the removal of Ulva spp. biomass is based on experiences of heavily anthropogenically eutrophic systems, while San Quintin Bay is not. Fourth, the proposed course of actions to restore eelgrass meadows ignores general historical baselines of estuarine and coastal systems by confusing what it means to be “pristine.” Fifth, despite the important experimental evidence indicating strong top–down control in temperate seagrass meadows, Zertuche-González et al. (2009) underestimated the capacity of consumers in structuring dynamics of vegetated soft-bottom communities in San Quintin Bay. Sixth, Ulva expansa may exert positive effects on seagrass ecosystem properties and functions. Instead, we propose protection against the propagation of unsustainable practices in the bay, and the reintroduction of large consumers that are now absent in this ecosystem. An ecosystem-based analysis of the role of Ulva spp. on eelgrass dynamics is needed.     

Distribution and population characteristics of the alien talitrid amphipod Orchestia cavimana in relation to environmental conditions in the Northeastern Baltic Sea

The talitrid amphipods were found for the first time in the Northeastern Baltic Sea in 1999. Orchestia cavimana inhabited damp wracks cast up on shore within a 200 m area of Saaremaa Island. In the following year, the species expanded its range to a few kilometres. In 2002, six additional locations of O. cavimana were found in Saaremaa Island and two locations in the Northwestern part of Estonia. Abundances and biomasses were highest in the first year of the invasion. In the following years, the values stabilized on remarkably lower levels. Population characteristics of the species varied significantly between locations. The average biomass and abundance were 9 g dw m⁻² and 1975 ind m⁻², respectively. Wrack biomass and interaction between wrack biomass and exposure were the best predictors of the abundances and biomasses of O. cavimana. Humidity explained additional variability in biomasses. The size structure of the population of O. cavimana was mostly related to humidity and wrack biomass. The Southern coast of the Baltic Sea may be regarded as the initial donor region for the Estonian populations of O. cavimana. The vector of this invasion is most likely related to the natural dispersal of the drifting algae but human activities as a transport vector can not be excluded. The incredible speed of the invasion of O. cavimana and its high biomasses indicate that the species will very likely extend its distribution along the coast of the Northeastern Baltic Sea in the following years.     

Wrack promotes the persistence of fecal indicator bacteria in marine sands and seawater

Algae on freshwater beaches can serve as reservoirs for fecal indicator bacteria (FIB). Wrack (especially kelp) at marine beaches might sustain FIB as well. This study examines the relationship between beach wrack, FIB, and surrounding water and sediment at marine beaches along the California coast. Surveys of southern and central California beaches were conducted to observe environmental wrack-associated FIB concentrations. FIB concentrations normalized to dry weight were the highest in stranded dry wrack, followed by stranded wet and suspended 'surf' wrack. Laboratory microcosms were conducted to examine the effect of wrack on FIB persistence in seawater and sediment. Indigenous enterococci and Escherichia coli incubated in a seawater microcosm containing wrack showed increased persistence relative to those incubated in a microcosm without wrack. FIB concentrations in microcosms containing wrack-covered sand were significantly higher than those in uncovered sand after several days. These findings implicate beach wrack as an important FIB reservoir. The presence of wrack may increase water and sediment FIB levels, altering the relationship between FIB levels and actual health risk while possibly leading to beach closures. Further work will need to investigate the possibility of FIB growth on wrack and the potential for pathogen presence.