Green Algae Blooms Research Articles

Assessment of water quality based on Landsat 8 operational land imager associated with human activities in Korea.

Water pollution such as green algae blooms and eutrophication in freshwater fatally influences both water quality and human society. Water quality issues in the 4 major rivers in Korea, including the Nakdong, have recently become a major concern. For this reason, it is essential to monitor water quality parameters (WQPs) that have a widespread characteristic to ensure maintenance of an effective water management system. The possibility of utilizing remote sensing technology for monitoring water quality on a regional scale has been recently investigated. The main objective of this study is to evaluate potential applications of the Landsat 8 Operational Land Imager (OLI) for estimating water quality in the Nakdong River, Korea. Correlations between Landsat 8 bands and in situ measurements are determined, and water quality models are established for estimating suspended solids (SS), total nitrogen (TN), chlorophyll-a (Chl-a), and total phosphorus (TP). The results demonstrate that WQPs correlated well with band reflectance values from Landsat 8. Band 5 was reasonably correlated with all WQPs, particularly with SS (R = -0.74) and Chl-a (R = -0.71). This study constructed multiple regression equations for WQPs based on correlation analysis through band combination and band ratio. The spatial distribution of WQPs in the Nakdong River on October 27, 2013 and May 16, 2014 indicate that the river was nearly eutrophic from human activities. Based on the results, the Landsat 8 OLI may be an appropriate data for estimating and monitoring water quality parameters on a regional scale. However, further validation is required to support the findings of this study.

Harvesting green algae from eutrophic reservoir by electroflocculation and post-use for biodiesel production

Each year there are more frequent blooms of green algae and cyanobacteria, representing a serious environmental problem of eutrophication. Electroflocculation (EF) was studied to harvest the algae which are present in reservoirs, as well as different factors which may influence on the effectiveness of the process: the voltage applied to the culture medium, run times, electrodes separation and natural sedimentation. Finally, the viability of its use to obtain biodiesel was studied by direct transesterification. The EF process carried out at 10V for 1min, with an electrode separation of 5.5cm and a height of 4cm in culture vessel, obtained a recovery efficiency greater than 95%, and octadecenoic and palmitic acids were obtained as the fatty acid methyl esters (FAMEs). EF is an effective method to harvest green algae during the blooms, obtaining the greatest amount of biomass for subsequent use as a source of biodiesel.

Tracing floating green algae blooms in the Yellow Sea and the East China Sea using GOCI satellite data and Lagrangian transport simulations

In an image from the Geostationary Ocean Color Imager (GOCI) taken on 13 June 2011, a recurrent floating green algae bloom was detected around Qingdao. To detect the bloom an index based on multi-spectral band ratios using three wavelengths (555, 660, 745nm) was utilized. One month later, the GOCI images detected widespread floating green algae patches (east–west elongated) across the Yellow Sea and East China Sea (YS, ECS). The presence of the patches was confirmed from various oceanic observation cruises.Lagrangian particle tracking experiments were conducted to understand the pathway of the floating green algae patches and interpret the physical forcing factors that affect the distribution and advection of the floating green algae. The numerical simulation results indicated that dominant southerly winds during June and July 2011 were related to offshore movement of the floating green algae, especially their eastward extension in the YS/ECS. An infrequent and unusual event occurred in June 2011: a typhoon MEARI, caused the green algae to detach from the coast and initiated movement to the east. After the typhoon event, sea surface temperature recovered rapidly enough to grow the floating green algae, and wind and local current controlled the movement of the massive floating algae patches (coastal accumulation or offshore advection in the YS/ECS). Analysis of the floating green algae pixels' movement during passage of Typhoon MAON in July 2011 revealed that the floating green algae patches were significantly controlled by both ocean currents and enhanced winds. These findings suggest that the floating green algae bloom off Qingdao and in the middle of the YS and ECS in the summer of 2011 occurred due to the combined effects of recent rapid expansion of seaweed aquaculture, strong winds, and the wind patterns in blooming regions. Our combined approach, using satellite data and numerical simulations, provides a robust estimate for tracing and monitoring changes in green algae blooms on a regional scale.

Abundance and distribution of Ulva microscopic propagules associated with a green tide in the southern coast of the Yellow Sea

The presence of Ulva microscopic propagules may play an important role in the rapid development of high-biomass blooms of green algae in the Yellow Sea. Six cruises were conducted, to determine the abundance and distribution of Ulva microscopic propagules associated with a green tide that developed in the southern coastal waters of the Yellow Sea from April to August, 2012. Results indicated that Ulva microscopic propagules were widespread in these waters, with the highest density being up to 4800ind.L−1, prior to the appearance of the green tide in April. High densities were also widely distributed along the coast during May and June, after the appearance of the floating green tide. The quantity of Ulva microscopic propagules significantly decreased when the floating green tide declined in July, reaching densities of up to 162ind.L−1, following the disappearance of the floating green tide in August. Quantitative studies on the distribution patterns of Ulva microscopic propagules along the southern coast of the Yellow Sea indicated a significant correlation between density and salinity, turbidity and nutrient concentrations. Temporal and geographical distribution patterns of Ulva microscopic propagules were also significantly affected by the presence of a large biomass of attached, or floating, Ulva species algae.

Non-pollen palynomorphs show human- and livestock-induced eutrophication of Lake Nussbaumersee (Thurgau, Switzerland) since Neolithic times (3840 bc)

Lake Nussbaumersee, located SW of Lake Constance (Switzerland/Germany), was studied at high temporal resolution for non-pollen palynomorphs (NPPs) within a calcareous gyttja sediment core from the deepest part of the lake. At the Nussbaumersee lakeshore, three pile-dwelling settlements have been excavated and dendrochronologically dated (to the Neolithic, 3840–3695 bc; late Early Bronze Age, 1580–1538 bc; and Late Bronze Age, 850–780 bc). The NPP study revealed three peaks of cyanobacteria, likely related to three settlement phases causing phosphate eutrophication of the lake water. The fast decline in cyanobacteria and reduction in green algae blooms after the abandonment of the Neolithic village and the quick recovery of the lake water back to oligotrophic conditions indicate a high prehistoric resilience of the lake ecosystem. After the second eutrophication phase starting around 2500 bc, the density of NPP eutrophication indicators remained at much higher levels, probably showing a loss of resilience of the lake ecosystem due to repeated human disturbance.

Small-scale early aggregation of green tide macroalgae observed on the Subei Bank, Yellow Sea

Massive green algae blooms became an environmental disaster in the Yellow Sea from 2008 to 2013. Recent studies suggested that recurrences of early aggregates of macroalgae were found over the Subei Bank, a unique shallow radial sand ridge system off the Jiangsu coast, China. Yearly field surveys have been carried out over this bank during the past five years (2009–2013), with an aim at identifying and qualifying the physical–biological mechanism for the early aggregation of algae. Data synthesis showed that early aggregation of macroalgae usually occurred from April–May as small-scale patches either over the intertidal mudflat of the Subei Bank or along local isobaths in the northern coastal area north of the bank. Both hydrographic and current measurements were performed by tracking a narrow patchy area of floating macroalgae (nearly 4km in length and 5–10m in width) on April 26, 2013, and the results showed that the algae aggregation was mainly caused by tide-induced convergence. This convergence was produced by the local geometrically controlled interaction of tidal currents with mudflats, which is believed to be a key physical mechanism for the early development of algal blooms in addition to marine ecosystem responses and human aquaculture activities.

Palaeoenvironments and palaeoceanography changes across the Jurassic/Cretaceous boundary in the Arctic realm: case study of the Nordvik section (north Siberia, Russia)

The Jurassic/Cretaceous transition was accompanied by significant changes in palaeoceanography and palaeoenvironments in the Tethyan Realm, but outside the Tethys such data are very scarce. Here we present results of a study of the most complete section in the Panboreal Superrealm, the Nordvik section. Belemnite δ 18 O data show an irregular decrease from values reaching up to +1.6‰ in the Middle Oxfordian and from +0.8 to −1.7‰ in the basal Ryazanian, indicating a prolonged warming. The biodiversity changes were strongly related to sea-level oscillations, showing a relatively low belemnite and high ammonite diversity during sea-level rise, accompanied by a decrease of the macrobenthos taxonomical richness. The most prominent sea-level rise is marked by the occurrence of open sea ammonites with Pacific affinities. Peak abundances of spores and prasinophytes correlate with a negative excursion in organic carbon δ 13 C near the J/K boundary and could reflect blooms of green algae caused by disturbance of the marine ecosystem. Keywords: Biodiversity; stable isotopes; J/K boundary; Arctic Realm; palaeoceanography (Published: 25 March 2014) Citation: Polar Research 2014, 33 , 19714, http://dx.doi.org/10.3402/polar.v33.19714

Green algae blooms caused by Ulva prolifera in the southern Yellow Sea: Identification of the original bloom location and evaluation of biological processes occurring during the early northward floating period

Over the past 6 yr, green algae blooms mainly caused by Ulva prolifera have been recorded in the Yellow Sea. Although satellite images provide a clear picture of the formation of these macroalgal blooms, the location of the original bloom area and the biological processes that occur during the early northward floating period remain poorly understood. Results obtained from more than 50 cruises conducted along coastal areas of the southwest Yellow Sea showed that the blooms originated along the coast of the Rudong area, where oceanographic conditions were favorable for accumulation of floating green algae. The dominant Ulva species changed during the period of northward drift. Massive floating Ulva blooms dominated by U. prolifera occurred mainly from June until the bloom disappeared. U. prolifera dominated the assemblage due to its rapid growth and production under suitable environmental conditions and its apparent competitive advantages over other Ulva species. Phylogenetic analysis of 5S spacer sequences showed that U. prolifera blooms in the Yellow Sea were not from a single genetic source and likely originated from or were supplemented with a number of different genetic sources.

Discrimination of the common macroalgae (Ulva and Blidingia) in coastal waters of Yellow Sea, northern China, based on restriction fragment-length polymorphism (RFLP) analysis

Since 2007, reoccurring large-scale green algae blooms have caused deleterious effects to the estuarine ecosystem of Yellow Sea, northern China and subsequent economical losses. Previous surveys indicated the green tides were initiated in the coastal water of southern Jiangsu province where Porphyra farming was intensively conducted; however, the main ‘seed source’ of floating green algae is still under debate. Ulva prolifera was confirmed to be the major causative species of green tides. The multiple sympatric ulvoid species in the natural environment has complicated species identification in both field surveys and laboratory studies due to their morphological plasticity. Thus, we developed a genetic identification key based on restriction fragment length polymorphism (RFLP) analysis of the ITS nuclear marker to discriminate the common Ulva and Blidingia species in the Yellow Sea. Ten genetic lineages (1 in Blidingia, 9 in Ulva) were detected along the coast of China through phylogenetic analysis of ITS sequences. They can be separated by virtual restriction digestion using the four selected restriction enzymes (BspT107 I, EcoO109 I, Hin1 I and VpaK11B I). With additional PCR amplification of the 5S spacer region, we were able to discriminate U. prolifera from Ulva linza. Using this genetic key, we screened macroalgal samples collected from the coast of the Yellow Sea, and the results indicated 6 common lineages (U. prolifera, U. linza, Ulva compressa, Ulva pertusa, Clade 6 and Blidingia sp.) in this region, which could be explicitly distinguished by a single enzyme (BspT107 I) coupled with 5S spacer polymorphism. U. prolifera was confirmed to be present on the Porphyra aquaculture rafts with seasonal variation in the species composition. This genetic key will facilitate our long-term field surveys to investigate the origin of the floating U. prolifera and furthermore to explore its bloom dynamics along the coast of the Yellow Sea. It also provided a framework for the future inclusion of more Ulva species, which will expand the usage of this key.

Detecting massive green algae (Ulva prolifera) blooms in the Yellow Sea and East China Sea using Geostationary Ocean Color Imager (GOCI) data

The historically massive bloom of the green macroalgae Ulva prolifera reported in June–August 2008 around the Qingdao, Yellow Sea, East China Sea and Japan coasts has recurred in a similar season and region. On June 13, 2011, around Qingdao, China, the world’s first Geostationary Ocean Color Imager (GOCI) detected an enormous bloom of floating green algae, which originated from the nearshore Subei Bank, China. The large floating green algae patches were observed along and across the Yellow Sea and in the East China Sea during 2011 summer by various oceanic cruises. To detect the massive macroalgae blooms from space, we analyzed their spectral characteristics from in situ optical measurements and satellite-derived green algae spectra. An “Index of floating Green Algae for GOCI” (IGAG) was developed from the multiple spectral band ratios using three wavelengths (555, 660, 745 nm), which the spectral response of green algae reflected at 555, 745, and 865 nm and absorbed at 660 and 680 nm. The results were compared with those obtained by the normalized difference vegetation index (NDVI), enhanced vegetation index (EVI), and Korea Ocean Satellite Center (KOSC) approaches. An advantage of the IGAG method was that muted or subtle signals of floating green algae were enhanced and separated from surrounding complex water signals. Although maps of floating green algae derived by the other approaches delineated dense green algae, they were less sensitive to subtle (less dense) features and in cases of nearby cloudy or complex water conditions. The floating green algae maps from IGAG provided a more robust estimate of wide floating green algae blooms than those derived using NDVI, EVI, or KOSC approaches. The IGAG approach should be useful for tracing and monitoring changes in green algae blooms on regional and global scales.

The response of microalgal biomass and community composition to environmental factors in the Sundays Estuary

The Sundays Estuary is permanently open to the sea and experiences regular freshwater inflow in the form of agricultural return flows with large supplies of nutrients. The objectives of this study were to measure microalgal biomass and community composition and relate these to freshwater inflow, water quality and other environmental variables. These data can then be used in setting the ecological water requirements of the estuary. Surveys in August 2006, March 2007, February, June and August 2008 showed that salinity less than 10, expressed in practical salinity units, mostly occurred from 12.5 km from the mouth in the middle reaches of the estuary, which was also where the highest water column chlorophyll a (>20 ƒEgE.-1) was found. The study showed that different groups of microalgae formed phytoplankton blooms during individual sampling sessions. These included blooms of green algae (August 2006), flagellates (March 2007), dinoflagellates (June 2008) and diatom species (February and August 2008). The estuary was then sampled over 5 consecutive weeks from March to April 2009 to identify environmental factors that support different microalgal bloom species. Phytoplankton blooms were found during Weeks 1, 4 and 5 from the middle to the upper reaches of the estuary. It was shown that diatoms occurred in blooms during warm, calm conditions whereas wind-mixing and reduced temperature, as a result of a cold front during 17 to 19 March 2009, promoted the dominance of flagellates throughout the estuary although they were present at all times. Dominant diatom species (Cylindrotheca closterium, Cyclotella atomus and Cyclostephanus dubius) indicated brackish, nutrient-rich water. Nanoplankton (2.7 - 20 ƒEm) was dominant during each week sampled and contributed 55 - 79% to the phytoplankton biomass. Maximum benthic chlorophyll a was found 12.5 km from the mouth. This study is the first to show successive chlorophyll a blooms consisting of different phytoplankton groups in an estuary, an indication of the eutrophic state of the system.

Lentibacter algarum gen. nov., sp. nov., isolated from coastal water during a massive green algae bloom

Two novel Gram-stain-negative, aerobic strains (ZXM100(T) and ZXM098) were isolated from seawater in the coastal region of Qingdao (36.027° N 120.184° E), China, during a massive green algae bloom. Cells were ovoid to irregular short rods and lacked flagella. Poly-β-hydroxybutyrate was accumulated. Cells did not contain bacteriochlorophyll a. The isolates grew at NaCl concentrations of 3-9 % and 22-28 °C. C(18 : 1)ω7c, C(18 : 0) and C(16 : 0) were the major fatty acid components. The polar lipids of ZXM100(T) were phosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine, a single lipid and an unidentified aminolipid. The predominant isoprenoid quinone of ZXM100(T) was Q-10. Phylogenetic analysis based on 16S rRNA gene sequences showed that strains belonged to the family Rhodobacteraceae. Based on the results obtained in this study, strain ZXM100(T) was considered to represent a novel species in a new genus, for which the name Lentibacter algarum gen. nov., sp. nov. is proposed. The type strain is ZXM100(T) ( = LMG 24861(T) = CGMCC 1.10234(T)); the DNA G+C content of the type strain is 54.6 mol%.

Acute toxicity of live and decomposing green alga Ulva (Enteromorpha) prolifera to abalone Haliotis discus hannai

From 2007 to 2009, large-scale blooms of green algae (the so-called "green tides") occurred every summer in the Yellow Sea, China. In June 2008, huge amounts of floating green algae accumulated along the coast of Qingdao and led to mass mortality of cultured abalone and sea cucumber. However, the mechanism for the mass mortality of cultured animals remains undetermined. This study examined the toxic effects of Ulva (Enteromorpha) prolifera, the causative species of green tides in the Yellow Sea during the last three years. The acute toxicity of fresh culture medium and decomposing algal effluent of U. prolifera to the cultured abalone Haliotis discus hannai were tested. It was found that both fresh culture medium and decomposing algal effluent had toxic effects to abalone, and decomposing algal effluent was more toxic than fresh culture medium. The aucte toxicity of decomposing algal effluent could be attributed to the ammonia and sulfide presented in the effluent, as well as the hypoxia caused by the decomposition process.

Salinicoccus qingdaonensis sp. nov., isolated from coastal seawater during a bloom of green algae

A novel Gram-stain-positive, white-pigmented, non-motile, non-sporulating, catalase- and oxidase-positive, strictly aerobic coccus, designated strain ZXM223(T), was isolated from a seawater sample collected from the coast of Qingdao, PR China, during a green algal bloom. It grew at pH 6.0-10.5 and 0-25.0% (w/v) NaCl, with optimum growth at pH 8.5 and 3.0% (w/v) NaCl. Growth occurred at 16-42 °C (optimum at 28 °C). The major fatty acids were anteiso-C(15:0) and iso-C(15:0). Menaquinone 6 (MK-6) was the major respiratory quinone. The polar lipids were phosphatidylglycerol, three unidentified phospholipids and two unknown glycolipids. The peptidoglycan type was L-Lys-Gly(5-6.) The genomic DNA G+C content was 43.5 mol%. Phylogenetic analysis of the 16S rRNA gene sequence placed strain ZXM223(T) within the genus Salinicoccus, with sequence similarity of 92.2-97.1% between ZXM223(T) and the type strains of this genus. The closest relatives were Salinicoccus kunmingensis YIM Y15(T), 'S. salitudinis' YIM-C678 and S. alkaliphilus T8(T). The DNA-DNA relatedness between strain ZXM223(T) and S. kunmingensis CGMCC 1.6302(T) and 'S. salitudinis' CGMCC 1.6299 (=YIM-C678) was 37±3 and 30±2%, respectively. The phenotypic, chemotaxonomic and phylogenetic characteristics and low DNA-DNA relatedness support the proposal of a novel species of the genus Salinicoccus, Salinicoccus qingdaonensis sp. nov., with the type strain ZXM223(T) (=LMG 24855(T) =CGMCC 1.8895(T)).

Huaishuia halophila gen. nov., sp. nov., isolated from coastal seawater

A novel Gram-negative, non-motile bacterium, designated ZXM137(T), was isolated from seawater collected from a coastal region of Qingdao, China, during a massive green algae (Enteromorpha prolifera) bloom. Strain ZXM137(T) was strictly aerobic and did not accumulate poly-β-hydroxybutyrate. Growth occurred with 0.5-11.0% (w/v) NaCl, at pH 6-9 (optimum of pH 7) and at 4-45 °C (optimum at 28 °C). It contained Q-10 as the predominant ubiquinone and the major polar lipids were phosphatidylglycerol, phospholipids, and an unidentified aminolipid and lipid. The major cellular fatty acids of strain ZXM137(T) were C(18:1)ω7c, C(18:1)ω6c and 11-methyl C(18:1)ω7c. The DNA G+C content was 60.1 mol%. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain ZXM137(T) formed a distinct evolutionary lineage within the Roseobacter group in the class Alphaproteobacteria. On the basis of phenotypic, chemotaxonomic and phylogenetic evidence, strain ZXM137(T) represents a novel species in a new genus, for which the name Huaishuia halophila gen. nov., sp. nov. is proposed; the type strain is ZXM137(T) (=CGMCC 1.8891(T)=LMG 24854(T)).

Changes in the aquatic moss Sphagnum denticulatum Brid. population abundance in a softwater lake over a period of three years

Changes in population abundance of submerged <em>Sphagnum denticulatum</em> Brid. were studied in an acidic and oligotrophic lake in NW Poland over three years. Individuals were counted in a moss carpet at a depth of 2.5 m on 4 experimental plots, 1 × 1 m each, every 30 days for 36 months using the SCUBA method. PAR intensity was seasonally variable (in winter higher than in summer). Changes in water pH, conductivity, HCO<sub>3</sub><sup>-</sup> concentration, hydration and sediment pH were statistically insignificant (p > 0.05). In the summer of the second study year the moss carpet disappeared almost completely due to a massive bloom of filamentous green algae. Periods of growth, regression and regeneration were observed in the population. The stabilisation of population size took 24 months and followed the pattern: slight fluctuations, then rapid growth and repetition of slight fluctuations. The first stage lasted nine, the second four and the third nine months. These stages took place irrespective of seasons, temperature or PAR intensity. Each rapid increase in abundance lasted about 30 days, at PAR intensity >20% and water temperature ranging from 11 to 16<sup>o</sup>C (in winter, spring or autumn). The regression stage brought about by the algal bloom started in the second year (in summer) and lasted six months (until the end of January in the third year). The population regeneration began in winter (in February, water temperature 3.0<sup>o</sup>C, PAR about 20%, ice cover 0.15 m) and finished with the end of spring. The population of <em>S. denticulatum</em> shows a repetitive pattern of abundance variations, which is seriously disturbed in summer, especially after a warm spring, by a massive bloom of filamentous green algae.

Development of polypropylene coated hollow fiber membranes as passive sampler for field equilibrium sampling of odorous compounds in environmental waters.

A new passive sampling device was developed for field equilibrium sampling of geosmin (GSM) and 2-methylisoborneol (MIB) in surface water. The sampling device was prepared by coating a 50 cm length polypropylene hollow fiber tubing (50 μm wall thickness, 280 μm inner diameter) with polypropylene glycol 4000. The sampler was brought into equilibrium with the sample in the field, and then transferred and immersed into 100 μL of methanol held in a little desorption device for room temperature desorption and preservation of the sampled analytes. After being transported to the laboratory, the analytes were determined by headspace solid-phase microextraction-GC-MS. The large surface area-to-volume ratio of the developed sampler facilitated the reaching of sampling equilibrium in 1 h, while the equilibrium sampling minimized the effects of environmentally relevant sampling conditions. Variation of sample pH (4.0-9.0) and salinity (0-100 mM NaCl) had no significant effects on the distribution coefficients of analytes to the sampler. The desorption device, constructed with a 200 μL glass insert, and a 2 mL brown glass vial with PTFE sealed screw cap, has no loss of analytes during the storage of the sampler. The proposed procedure had detection limits of 4 and 9 ng L-1 for GSM and MIB, respectively. This developed sampler was successfully applied to field sampling in Taihu Lake (China), with MIB and GSM detected in the range of 0.11-0.61 μg L-1 during a medium out-break of blue-green algae bloom.

Heterogeneous preferences for water quality attributes: The Case of eutrophication in the Gulf of Finland, the Baltic Sea

Abstract This paper examines the preference heterogeneity of the general public regarding water quality attributes and provides welfare estimates (WTP) for three nutrient-reduction scenarios that would improve the water quality in the Gulf of Finland, part of the Baltic Sea. In the choice experiment (CE), the improvement is described in terms of four water quality attributes: water clarity, abundance of coarse (non-attractive) fish, status of bladder wrack (a type of seaweed), and mass occurrences of blue–green algae blooms. The data are analysed with multinomial logit (MNL), random parameters logit (RPL), and latent class (LCM) models. The results from MNL and RPL show that, on average for Finns, clear water is, relatively speaking, the most important water quality characteristics followed by desire for fewer occurrences of blue–green algae. The results also show that the probability of expressing willingness to contribute to improvement of the water quality increases with residential or recreational contact with the Gulf of Finland, a higher income than average, a younger than average age, and lack of dependent children in the household. The LCM reveals that opinions about the order of relative importance of attributes depend on age, household income, coastal residence, and vacation home ownership. The present values for three nutrient reduction scenarios of different intensities ranging from 28,000 million euro to 54,000 million euro were calculated using mean welfare estimates, discounted for perpetuity with a 2% rate.

Benthic algal communities: recovery from experimental acidificationThis paper is part of the series “Forty Years of Aquatic Research at the Experimental Lakes Area”.

Chemical recovery is hypothesized to promote rapid recovery of benthic algal communities in formerly acidified lakes; this expectation needs modification. We evaluated the hypothesis in a small lake (L302S) in the boreal forest of northwestern Ontario, Canada, during a decade of pH recovery following a prior decade of experimental acidification from pH 6.7 to 4.5. To account for regional changes during the study, we also studied a nearby reference lake (L239). Taxonomic changes in the epilithon (biofilm on rock surfaces) included persistently lower cyanobacterial biomass following its acidification-related decline and increases in both diatoms and greens. Epilithic metabolic recovery was incomplete because the acidification-induced increase in respiration continued, although the prior decline in photosynthesis was reversed. Unexpectedly, blooms of metaphytic filamentous green algae occurred at higher pH during recovery than during acidification. Although several community attributes recovered fully, recovery of many aggregate functional and taxonomic properties lagged improvements in pH. Divergence was greater at the taxonomic than at the functional level. Despite pH recovery, potential causes of incomplete algal recovery include incomplete chemical recovery and the persistent absence of functionally important biota. Our findings counter the assumption that ecological recovery mirrors the pathway of damage caused by a human stressor.

The role of the amphipod Gammarus locusta as a grazer on macroalgae in Swedish seagrass meadows

Mesograzers are thought to play a critical role in seagrass beds by preventing overgrowth of ephemeral algae. On the Swedish west coast, eelgrass Zostera marina has decreased in recent decades as a result of eutrophication and increased growth of macroalgal mats (mainly filamentous Ulva spp. and Ectocarpales), with no indication of grazer control of the algae. The aim of this study was to investigate the ability of the amphipod Gammarus locusta to control algal blooms during nutrient-enriched and ambient conditions, using a combination of laboratory, field and model studies. Laboratory experiments demonstrated that juvenile and adult G. locusta could consume both Ulva spp. and Ectocarpales, but that consumption of Ulva spp. was significantly higher. Cannibalism was common in individual treatments involving multiple size-classes of G. locusta, but only large, male gammarids consumed smaller juveniles in the presence of Ulva spp. as an alternative food source. However, no negative effects of cannibalism were found on total grazing impact. A model using size-specific grazing rates and growth rates of G. locusta and of Ulva spp. suggests that approximately 62 young juvenile, or 27 adult G. locusta are needed per gram DW of Ulva spp. to control the algal growth during ambient nutrient conditions, and approximately 2.6 times as many gammarids during enhanced nutrient conditions. On the Swedish west coast, densities and mean sizes of G. locusta in eelgrass beds are below these critical values, suggesting that the gammarids will not be able to control the growth of the filamentous macroalgae. However, in the field cage experiment, immigration of juveniles and reproduction of encaged adult G. locusta resulted in unexpectedly high densities of G. locusta (>4,000 individual m−2), and very low biomass of Ulva spp. in both ambient and nutrient-enriched treatments. Although the high numbers of juveniles in all cages precluded any significant treatment effects, this suggests that in the absent of predators, the population of G. locusta can grow significantly and control the biomass of Ulva spp. Furthermore, low grazing of Ectocarpales in the laboratory and high biomass of these filamentous brown algae in the field indicate a preference for the more palatable green algae Ulva spp. This study indicates that the high grazing capacity of G. locusta, in combination with high reproduction and growth rates, would allow the amphipod to play a key role in Z. marina ecosystems by controlling destructive blooms of filamentous green algae. However, high predation pressure appears to prevent large populations of G. locusta in eelgrass beds on the Swedish west coast today.