Benthic Algal Assemblages Research Articles

Benthic Algal Assemblages Associated with Damselfi sh Territories in The Gulf of Thailand

Territorial damselfi sh are herbivorous fi sh that help maintain algal diversity and abundance by aggressive territorial defense and algal farming. We investigated the effect of territorial damselfi sh on algal diversity and abundance on a reef at Ko Taen, Surat Thani Province, Thailand. Ten permanent patches (20 × 20 cm2) were set up inside and ten outside damselfi sh territory and monitored bimonthly. We found 22 macroalgal species with fi ve dominant species: Polysiphonia sp., Padina minor, Ulva compressa, Gelidium pusillum, and Lobophora variegata. The abundance of Polysiphonia sp. was signifi cantly higher inside damselfi sh territory than outside. In contrast, the abundances of Gelidium pusillum, Padina minor, and Ulva compressa were slightly higher outside the territory. It might be perhaps because their feeding behavior, territorial defense, and farming activities altered the benthic community. These damselfi shes exclude other herbivorous fi shes from their territories and remove unpalatable algae and maintain their algal food crop. For species diversity, there was no signifi cant difference between algal species diversity outside and inside damselfi sh territories. Our results indicated that damselfi shes have a strong effect on algal abundance and composition.

Fatty-acid based assessment of benthic food-web responses to multiple stressors in a large river system

Rivers are often exposed to multiple stressors, such as nutrients and contaminants, whose impacts on the river food webs may not be distinguished by sole assessment of biological community structures. We examined the benthic algal assemblages and the fatty acids (FA) of benthic macroinvertebrates in the lower Athabasca River in Canada, aiming to assess the changes in algal support and nutritional quality of the benthic food web in response to cumulative exposure to natural bitumen, municipal sewage discharge (hereafter, “sewage”), and oil sands mining (“mining”). Data show that the decline in water quality (increases in nutrient concentrations and total suspended solids) was associated with decreases in benthic diatom abundance, and was driven mainly by sewage-induced nutrient enrichment. Responses in nutritional quality of benthic macroinvertebrates, indicated by their polyunsaturated FA (PUFA) concentrations, were taxon- and stressor-specific. Nutritional quality of the larval dragonfly predator, Ophiogomphus, decreased nonlinearly with decreasing benthic diatom abundance and was lowest at the sewage-affected sites, although exposure to natural bitumen also resulted in reduced Ophiogomphus PUFA concentrations. In contrast, the PUFA concentrations of mayfly grazers/collector-gatherers were not affected by natural bitumen exposure, and were higher at the sewage and sewage+mining sites. The PUFA concentrations of the shredder Pteronarcys larvae did not change with cumulative exposure to the stressors. Sediment metal and polycyclic aromatic compound concentrations were not associated with the macroinvertebrate FA changes. Overall, we provide evidence that sewage induced reduction in trophic support by PUFA-rich diatoms, and was the predominant driver of the observed changes in FA composition and nutritional quality of the benthic macroinvertebrates. Fatty-acid metrics are useful to untangle effects of concurrent stressors, but the assessment outcomes depend on the functional feeding guilds used. A food-web perspective using multiple trophic levels and feeding guilds supports a more holistic assessment of the stressor impacts.

Differential responses for stream algal assemblages exposed to factorial N and P enrichment along an in situ DOC gradient

Nitrogen (N) and phosphorus (P) enrichment from the surrounding landscape can enhance the growth and abundance of algal assemblages, both suspended in the water column and occurring as benthic biofilms in the receiving waters of resident stream ecosystems. However, it is unclear how enhanced levels of dissolved organic carbon (DOC) might mediate the response of algae to nutrients. In this study, we aim to understand the relationship between N and P enrichment in stream reaches with varying levels of DOC within a common watershed. Both suspended and benthic algal assemblages were exposed to increasing (low, moderate, high) levels of N and P in an in situ 3 × 3 factorial experimental design. Experiments were carried out simultaneously at three sites of varying DOC concentration, the results of which, showed that both assemblages responded very differently to enrichment. For suspended algae, biomass was enhanced following enrichment with both N and P singularly and in combination, particularly at the highest concentrations levels for both nutrients (3-way ANOVA interactions; p < 0.05). This pattern was consistent at all levels of DOC at the three sites (3-way ANOVA Nutrient-site interaction; F = 1.4, p = 0.228). In contrast, benthic algal biomass progressively increased with enhanced concentration of both N and P, but only at the lowest level of DOC (3-way ANOVA site term; F = 84.2, p = 0.0001). No appreciable biomass accumulation was observed under moderate or high DOC conditions and this pattern was likely attributed to low light penetration at these two sites (ANOVA). Our results indicate that eutrophication is likely to manifest itself in a complex manner throughout watersheds where loading of N and P interacts with DOC.

Compensatory dynamics of lotic algae break down nonlinearly with increasing nutrient enrichment.

One important mechanism governing the temporal maintenance of biodiversity is asynchrony in co-occurring competitors due to fluctuating environments (i.e., compensatory dynamics). Temporal niche partitioning has evolved in response to predictable oscillations in environmental conditions so that species may offset competition, but we do not yet have a clear understanding of how novel anthropogenic stressors alter seasonal patterns of succession. Many primary producers are nutrient limited, and enrichment may decrease the importance of environmental fluctuations that govern which species are effective competitors under naturally low nutrient regimes. Consequently, elevated nutrient concentrations may synchronize species responses to seasonality. By studying benthic algal assemblages over 2 years from 35 streams that spanned a wide gradient of nutrient enrichment, we found that compensatory dynamics characterizing seasonal succession under natural nutrient regimes broke down at relatively low levels of total phosphorus (P) enrichment (~ 25 μg/L). With increasing P more species were able to coexist at any given time, and seasonal variation in assemblage composition was characterized by synchronous swings in species biovolumes. We also observed much higher instability in assemblage biovolumes with declines in compensatory dynamics, which indicates that anthropogenic alteration of nutrient regimes can affect community stability by changing the dominant mode of seasonal succession. Our findings indicate that compensatory fluctuations of stream algae are driven by seasonality and provide insight about how nutrient enrichment alters evolved drivers of species coexistence.

河流着生藻类多样性对城镇化的响应-以深圳市为例

PDF HTML阅读 XML下载 导出引用 引用提醒 河流着生藻类多样性对城镇化的响应——以深圳市为例 DOI: 10.5846/stxb202105271393 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 深圳市主要河流水生态监测与评价项目（NO.2019-07-233） Response of stream benthic algal diversity to urbanization: A case study in Shenzhen Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:着生藻类是河流生态状况的重要指示生物，然而关于城镇化对着生藻类多样性影响的研究还较缺乏。基于深圳市9条主要河流74个样点2020年雨、旱季的调查数据，对比了城区、郊区河流样点的着生藻类α、β多样性。两次调查共鉴定出着生藻类301个分类单元，其中硅藻门种类最多。谷皮菱形藻（Nitzschia palea）、隐头舟形藻（Navicula cryptocephala）、平庸菱形藻（Nitzschia inconspicua）等污染指示种在城区组相对丰度更高，而清洁指示种微小曲丝藻（Achnanthidium minutissimum）在郊区组相对丰度更高。城镇化对着生藻类物种丰富度、香农维纳多样性指数、Pielou均匀度指数等α多样性指数均无显著影响，但对着生藻类群落结构有显著影响。城区组样点的着生藻类β多样性（用主坐标分析质心指示）低于郊区组，城区组与郊区组藻类β多样性差异在旱季更为显著。两组样点的藻类β多样性差异主要来源于物种周转组分。与城区组着生藻类群落显著相关的环境因子包括总氮、高锰酸钾指数、电导率、pH、浊度和水深，而与郊区组着生藻类群落显著相关的是总氮、溶解性无机磷和电导率。研究发现，城市人类活动导致的总氮、溶解性无机磷、高锰酸钾指数、电导率等指标的显著增高导致着生藻类β多样性的降低。为了保护河流生物多样性，建议有效控制城区生产生活污水排放，减少人类活动对河流的干扰。 Abstract:Benthic algae are important indicators for ecological conditions of streams and rivers, but studies on effects of urbanization on benthic algal diversity is still sparse. In this study, we surveyed 74 sites from nine rivers located in Shenzhen City in the wet and dry season of 2020, and compared differences of α- and β- diversity of lotic benthic algal assemblages between urban and suburban groups. A total of 301 algal taxa were identified in the two seasons, among which the most taxa belonging to diatoms. The relative abundance of pollution indicator species such as Nitzschia palea, Navicula cryptocephala and Nitzschia inconspicua was higher in the urban groups, while the suburban groups with higher relative abundance of Achnanthidium minutissimum, which is an indicator species of clean water. We found that urbanization had no significant effects on algal α-diversity indices including richness, Shannon-Wiener's diversity index, and Pielou's index; while, algal community compositions in urban sites were significantly different from that of suburban sites. β-diversity of benthic algae, represented by centroids of the principal coordinate analysis, was lower for the urban sites than that of the suburban sites, with more significant difference in the dry season. The difference of benthic algal assemblages between the two groups mainly came from species turnover components. Total nitrogen, CODMn, conductivity, pH, turbidity and water depth were identified by the Mantel test as the environmental factors that were significantly correlated with algal community compositions in the urban group; while, TN, Dissolved inorganic Phosphorus (PO4-P) and conductivity were significantly correlated with the community compositions of benthic algae in the suburban group. We found that levels of TN, PO4-P, CODMn and conductivity were significantly increased in the urban group, which decreased β-diversity of benthic algae communities in Shenzhen rivers. To protect biodiversity of Shenzhen rivers, we therefore suggest to effectively control domestic and industrial sewage in urban areas to reduce human disturbance to rivers. 参考文献 相似文献 引证文献

Community structure and ecological responses to hydrological changes in benthic algal assemblages in a regulated river: application of algal metrics and multivariate techniques in river management.

The flow regime of the Wimmera River was substantially modified due to the construction of a water supply reservoir. Samples of diatoms and soft algae and measurements of water quality were analysed at ten sampling sites for 3 years (between February 2012 and November 2014) along the MacKenzie River, a tributary of the Wimmera River, in different seasons and under different flow regimes, to understand the spatial and temporal variation in the relationship between algal communities, water quality and stream condition. Baseline information on algal communities and water quality was collected during base flow conditions, while experiments on the effect of water releases on algal communities were based on flow regime variations (manipulated flow regimes), specifically on the algae community structure, water quality and ecosystem function. Algal species composition changed along the river under different flow regimes and different seasons. Under base flow, Bacillariophyta (diatoms) were more abundant upstream, and filamentous green algae were more abundant downstream. The results showed that the algal composition shifted downstream after water release events. Chlorophyta (green algae), Cyanophyta (blue-green algae) and Chrysophyta gradually increased from upstream to downstream under base flow conditions and before water releases, whereas diatoms were greater upstream and increased downstream after water releases. The results are presented to tailor discharge and duration of the river flows by amalgamation of consumptive and environmental flows to improve the condition of the stream thereby supplementing the flows dedicated to environmental outcomes.

Nutrients in sediment regulate benthic algal assemblages in the tropical Tri An reservoir of Vietnam

Nutrients in sediment regulate benthic algal assemblages in the tropical Tri An reservoir of Vietnam

Friends or foes? The ecological relationships between micro- and macroalgae in low-order tropical streams

Streambeds are abundantly colonized by benthic algal assemblages. Environmental factors are the most assessed to find out predictable correlations between algal presence and habitat conditions, but biological interactions can also be important determinant of species composition in stream algae communities. Although there is plenty of information about algal ecology, the mechanisms leading their spatial distribution remain insufficiently clarified. Herein, we contribute to a better understanding regarding this latter issue, carrying out an experimental study to assess possible interactions between micro- and macroalgae during a successional process (75 days) in nine streams, using artificial substrates. The experimental analyses revealed the following main results: (i) streams with higher abundance of macroalgae also registered higher microalgal densities; (ii) the relative interaction index showed values greater than zero for all sampling dates, suggesting positive interaction between micro- and macroalgae during colonization process; and (iii) the multiple partial regression analyses (redundancy, pRDA) showed that environmental variables and microalgae density together explained 25% of macroalgal variation. These results indicate that interactions between stream micro- and macroalgae may contribute to shape the community structure during the successional process on the streambed. As observed previously, microalgae are early successional settlers and macroalgae are late successors, but both community components, besides their inherent competition, seem to cooperate in order to keep their coexistence. Based on this perspective, some typical ecological concepts related to the stream macroalgae, specially from tropical regions, may be expanded. For instance, studies have reported that the highest richness and abundance of lotic macroalgae in tropical/subtropical streams are determined basically by variation in climatic and environmental factors. Our results showed that, in addition to climatic and environmental factors, the increase in richness and abundance of stream macroalgae may also be affected by biotic interactions. In this context, our results suggest that the higher abundance of microalgae on the streambed seems to allow a better development of the benthic algal community, reaching to the later successional stages, in which the relative occurrence of larger and more complex algae (i.e., macroalgae) become more evident.

Characteristics of effluents from trout farms and their impact on water quality and benthic algal assemblages of the receiving stream

In this study, characteristics of effluents from three flow-through rainbow trout farms in Turkey and their impact on water quality and epilithic algal communities of the receiving stream were investigated. Water samples were taken monthly from both inlets and outlets of three fish farms, while both water and epilithic algae samples were collected from two stations (upstream and downstream) in the stream. A significant increase from inlets to outlets was observed for chemical oxygen demand (COD), soluble reactive phosphorus (SRP), total suspended solids (TSS), NH4–N and total phosphorus (TP) (p < 0.05) due to no effluent treatment processes and high FCR at the fish farms. The daily average total nitrogen (TN) and TP fluxes of the fish farms predicted with the nutritional method were found close to those measured with the hydrological method. Although there were significant increases in COD, TSS, NH4–N, TN, NO3–N, NO2–N, TP and SRP concentrations at the downstream station compared to the upstream station of the receiving stream (p < 0.05), water quality of the downstream station remained in Class I in terms of examined parameters. Trophic Diatomic Index and Biological Diatom Index values indicated that the upstream station had a better water quality than the downstream station. Also, filamentous algae such as Cladophora glomerata, Ulothrix zonata and Stigeoclonium lubricum were observed at the downstream station. In view of the above findings, several suggestions were put forward to protect the water quality of the receiving stream.

Colonisation processes in benthic algal communities are well reflected by functional groups

Single-trait analyses are used to select the most appropriate species characteristics for an effective indication of changes in multiple stressors, but they are robust to detect fine-scale functional changes in biofilms. The combination of single traits may appropriately reflect ecological properties of changing benthic assemblages. We studied colonisation processes of benthic algal assemblages focusing on the changes in trait composition using life forms, type of attachments, cell size and mobility as single traits in a small lowland stream. We tested the descriptive power of single-trait groups (STGs) and also combined trait groups (CTGs). We assumed that STGs would be significantly affected by environmental factors, but compositional changes in biofilms would be described more easily by using CTGs rather than STGs. Our hypotheses were confirmed by the results. While some STGs correlated positively to environmental factors indicating disturbances, others correlated to environmental factors indicating the stable conditions. The fast settlement of large-sized groups was also relevant determining the compositional changes in the studied benthic community. Despite the strong correlation between STGs and environmental variables, CTGs analyses revealed important functional relations in the ecosystem, since CTGs display more sophisticated functional features of the organisms, which may provide more realistic responses.

Widespread anatoxin-a detection in benthic cyanobacterial mats throughout a river network.

Benthic algae fuel summer food webs in many sunlit rivers, and are hotspots for primary and secondary production and biogeochemical cycling. Concerningly, riverine benthic algal assemblages can become dominated by toxic cyanobacteria, threatening water quality and public health. In the Eel River in Northern California, over a dozen dog deaths have been attributed to cyanotoxin poisonings since 2000. During the summers of 2013–2015, we documented spatial and temporal patterns of cyanotoxin concentrations in the watershed, showing widespread distribution of anatoxin-a in benthic cyanobacterial mats. Solid phase adsorption toxin tracking (SPATT) samplers were deployed weekly to record dissolved microcystin and anatoxin-a levels at 10 sites throughout the watershed, and 187 Anabaena-dominated or Phormidium-dominated cyanobacterial mat samples were collected from 27 locations to measure intracellular anatoxin-a (ATX) and microcystins (MCY). Anatoxin-a levels were higher than microcystin for both SPATT (mean MCY = 0.8 and ATX = 4.8 ng g resin-1 day-1) and cyanobacterial mat samples (mean MCY = 0.074 and ATX = 1.89 μg g-1 DW). Of the benthic mats sampled, 58.9% had detectable anatoxin-a (max = 70.93 μg g-1 DW), while 37.6% had detectable microcystins (max = 2.29 μg g-1 DW). SPATT cyanotoxin levels peaked in mid-summer in warm mainstem reaches of the watershed. This is one of the first documentations of widespread anatoxin-a occurrence in benthic cyanobacterial mats in a North American watershed.

Recovery of benthic algal assemblages from acidification: how long does it take, and is there a link to eutrophication?

Acidification has adversely affected freshwater ecosystems in many areas, and recovery from acidification is often interrupted by acidic events. We lack detailed information about how benthic algae react to short-term acidic events and long-term recovery from acidification. We sampled 15 stream sites in the Czech Republic to study the effects of (a) water pH, aluminium and lead concentrations, (b) short-term acidic events, (c) 20 years of recovery from acidification and (d) high phosphorus concentrations combined with low pH on soft-bodied benthic algae. Water pH and aluminium concentrations affected benthic algal assemblages, but the acidification index periphyton (AIP) mainly reflected pH. Benthic algal assemblages reflected recent acidic events more closely than maximum or average pH. Our results indicate that the reaction of benthic algae to pH results from a fast effect of pH minima that cause sensitive species to disappear within a few months, and a slower process of dispersal and competition for resources during periods of higher pH. After an acidic event, recolonization of stream sites by sensitive species had started within 2 years, and was largely completed after 9 years. Our data indicate that acidification may mask the effect of enhanced phosphorus concentrations on benthic algal eutrophication indices.

Erratum to: Changes in ecosystem engineers: the effects of kelp forest type on currents and benthic assemblages in Kachemak Bay, Alaska

In many temperate, rocky-reef coastal ecosystems, kelp forests modify alongshore currents, impact invertebrate settlement, and regulate understory algal abundances. Along the southern coasts of Alaska, in particular, two species of canopy-forming kelps with dissimilar morphologies, Nereocystis luetkeana and Eualaria fistulosa, co-occur but vary in their distributions and patterns of abundance, with one species often replacing the other at given sites in subsequent years. As a result, their differences in morphology may affect patterns of current flow through the forests, which could have strong impacts on invertebrate settlement and benthic diversity, particularly in Kachemak Bay, Alaska (59° 36′33ʺN, 151° 20′51ʺW), which experiences large tidal fluctuations resulting in strong alongshore currents. In this study, significant differences in current reductions were observed between the two kelp forest types within Kachemak Bay, but these reductions were small compared to the natural spatiotemporal variability of currents within the bay, and they were primarily limited to the upper few meters of the water column where the two species exhibit their greatest differences in morphology. Consequently, invertebrate settlement and abundance differed between the two kelp forest types as well as among study sites within the bay. In addition, there were differences observed in the composition and abundance of understory algae between the two forest types, which were presumably due to differences in shading abilities of the dominant kelps. Together, our results suggest that future changes in the distribution and abundances of these two kelp forest types may result in corresponding changes in hydrodynamic conditions within the forests, and thereby impact invertebrate and benthic algal assemblages.

Predicting In Situ Responses of Taste- and Odor-Producing Algae in a Southeastern US Reservoir to a Sodium Carbonate Peroxyhydrate Algaecide Using a Laboratory Exposure-Response Model

Efficacy of an in situ algaecide treatment can be predicted prior to an application by physically modeling exposures and responses with laboratory experiments. A sodium carbonate peroxyhydrate (SCP) algaecide was used in a drinking water reservoir (Hartwell Lake, Anderson, SC) to control a benthic algal assemblage putatively producing 2-methylisoboreol (MIB) and geosmin, compounds with adverse taste and odor attributes. These SCP applications provided an opportunity to test hypotheses regarding potential convergence of laboratory and in situ exposures and responses. Objectives of this study were to (1) measure responses of a benthic algal assemblage from Hartwell Lake to 7-day laboratory exposures of SCP [measured as hydrogen peroxide (H2O2) concentrations], (2) to measure the exposure of SCP (as H2O2) applied in a cove of Hartwell Lake and consequent responses of the algal assemblage, and (3) compare exposures and responses measured in the laboratory and in situ. Results demonstrated that in laboratory exposures, H2O2 released by SCP dissipated within 48 h. Significant responses of the algal assemblage in terms of phycocyanin concentrations and cell densities were measured 4 days after treatment (4-DAT) and 7-DAT following exposures of 453, 615, and 812 mg H2O2 m−2. The H2O2 exposure measured in situ was comparable to effective laboratory exposures in terms of initial exposure (619 ± 428 mg H2O2 m−2) and exposure duration (dissipation within 30 h), but the in situ exposure had a large deviation initially (i.e., ±428 mg H2O2 m−2) and was an order of magnitude less than the targeted initial exposure. Therefore, comparison of measured responses was critical to infer comparable exposures and confirm accuracy of the laboratory model. Significant in situ responses were measured 4-DAT and 7-DAT in terms of phycocyanin concentrations and cell densities, and were comparable to responses obtained from effective laboratory exposures (i.e., 453, 615, and 812 mg H2O2 m−2). Decreases in measured concentrations of MIB and geosmin at the intake of the drinking water treatment facility provided additional evidence that algae were sufficiently exposed to H2O2 from SCP. Results of this experiment provide evidence for the design and use of physical laboratory models to predict responses of algae in the field.

Effects of flow regime on benthic algae and macroinvertebrates - A comparison between regulated and unregulated rivers.

Natural fluctuations in flow are important for maintaining the ecological integrity of riverine ecosystems. However, the flow regime of many rivers has been modified. We assessed the impact of water chemistry, habitat and streamflow characteristics on macroinvertebrates and benthic algae, comparing 20 regulated with 20 unregulated sites. Flow regime, calculated from daily averaged discharge over the five years preceding sampling, was generally more stable at regulated sites, with higher relative discharges in winter, lower relative discharges in spring and smaller differences between upper and lower percentiles. However, no consistent differences in benthic algal or macroinvertebrate structural and functional traits occurred between regulated and unregulated sites. When regulated and unregulated sites were pooled, overall flow regime, calculated as principal components of discharge characteristics over the five years preceding sampling, affected macroinvertebrate species assemblages, but not indices used for ecosystem status assessment or functional feeding groups. This indicates that, while species identity shifted with changing flow regime, the exchanged taxa had similar feeding habits. In contrast to macroinvertebrates, overall flow regime did not affect benthic algae. Our results indicate that overall flow regime affected the species pool of macroinvertebrates from which recolonization after extreme events may occur, but not of benthic algae. When individual components of flow regime were analyzed separately, high June (i.e. three months before sampling) flow maxima were associated with low benthic algal taxon richness, presumably due to scouring. Macroinvertebrate taxon richness decreased with lower relative minimum discharges, presumably due to temporary drying of parts of the riverbed. However, recolonization after such extreme events presumably is fast. Generally, macroinvertebrate and benthic algal assemblages were more closely related to water physico-chemical than to hydrological variables. Our results suggest that macroinvertebrate and benthic algal indices commonly used for ecological status assessment are applicable also in regulated rivers.

Effects of in situ phosphorus enrichment on the benthos in a subalpine karst stream and implications for bioassessment in nature reserves

Park managers in nature reserves need scientifically defensible and operationally feasible ecological indicators to better manage protected areas for both nature conservation and tourism. Such needs are much more urgent in karst aquatic ecosystems where spectacular natural scenic wonders attract millions of visitors to natural areas with streams and lakes that are particularly vulnerable to nutrient pollution. To identify a set of biotic indicators of phosphorus (P) pollution in a karst stream, we conducted an in situ P enrichment experiment in a nearly pristine karst stream located at a UNESCO world heritage site in China. Our results show that both benthic algal assemblages and macroinvertebrates were sensitive to P enrichment. Changes in diatoms (e.g., Achnanthidium minutissimum, Delicata delicatula) and macroinvertebrates (e.g., collectors) were indicative of P enrichment. The color change of travertine bryophyte beds from creamy white to green was largely due to increase in filamentous green algae such as Zygnema sp., which may provide a visual cue for P enrichment and pollution. Our findings, in conjunction with further studies that directly link these indicators with human disturbance (e.g., tourist activities) throughout the park, could improve the operation of park managers in minimizing tourist-induced nutrient pollution and in operationalizing these indicators in the current environmental monitoring and assessment program.

Connecting algal taxonomic information to essential fatty acid content in agricultural streams

:Benthic algae comprise a diversity of taxonomic lineages and produce important biochemical compounds required by higher trophic levels. Chief among these compounds are essential fatty acids (EFAs) that aquatic consumers require for their metabolic and reproductive processes. However, habitat changes from anthropogenic activities, namely, agriculture, can affect not only which species of algae may be present but also the quantity and quality of EFAs they produce. This study aims to evaluate how benthic algal taxonomic composition and EFA concentrations vary in streams affected by agriculture and remediation through stream-associated best management practices (BMPs). The study was undertaken in the Upper Delaware River watershed in New York state, in which BMPs have been installed over multiple years (= BMP age). Some results indicate that BMPs were able to reduce effects of agriculture. Changes in benthic algal assemblages, the proportions of algal taxonomic groups, and in specific taxonomic members were not significant. The proportion of diatoms in assemblages decreased with increasing agricultural effects (F = 6.313, P = 0.001). Conversely, the proportion of chlorophytes increased in agriculturally affected streams (F = 9.336, P < 0.001). Changes in taxonomic composition were associated with changes in various EFA compound concentrations. Agricultural streams had higher concentrations of total EFAs along with more chlorophytes (r = −0.268, P = 0.010) and fewer diatoms (r = 0.270, P = 0.009) than did reference or minimally affected streams. Particularly, agricultural streams had greater concentrations of key EFAs such as eicosapentaenoic acid and docosahexaenoic acid. However, there were no differences among assemblage's nutritional quality (Σω3/Σω6). The data presented here suggest that analyzing shifts in algal taxonomic groups in conjunction with measurements of fatty acids in broad EFA groups may provide more information when characterizing algal assemblages than examination of algal taxa or analysis of EFA compounds alone.

Variation of benthic algal assemblages among habitats in subalpine Karstic Lakes and implications for bioassessment

Detecting early warning signs of ecosystem degradation in nature reserves requires ultrasensitive biological indicators. We assessed the potential of using multihabitat assessment of benthic algae (growing on submerged vegetation, rocks, and dead trees) to detect early warning signs of nutrient enrichment in nine karstic lakes in Jiuzhaigou Nature Reserve, a World Natural Heritage site in China. Nonmetric multidimensional scaling analysis showed that variability in benthic diatom assemblages among the major habitats within lakes were generally higher than among lakes. Permutational multivariate analysis of variance indicated that epiphytic diatom assemblages dominated by Achnanthidium minutissimum (Kutzing) Czarnecki differed significantly from both epilithic and epidendric assemblages. Epilithon and epidendron, both dominated by Delicata delicatula (Kutzing) Krammer and Denticula tenuis Kutzing, were not significantly different within lakes. Mean Bray–Curtis dissimilarity index values among the three assemblages in each lake were negatively correlated with the tourism-stress index but the correlation was not statistically significant. Increasing homogeneity in benthic diatom assemblages among habitats within a lake may be due to cumulative nutrient enrichment associated with tourism development. Links among tourisms, nutrient enrichment, and dissimilarity in benthic algae among habitats should be viewed with caution until the cause–effect relationships can be confirmed by in situ manipulative experiments.

Nitrogen limitation of algal biofilms in coastal wetlands of Lakes Michigan and Huron

Coastal wetlands of the Laurentian Great Lakes are critical habitats for many plants and animals of ecological and economic importance and are particularly susceptible to nutrient runoff from the landscape given their proximal location to inflows. We used nutrient diffusing substrata (NDS) to determine whether N, P, or both nutrients limited algal biomass accrual in 54 wetlands of Lakes Michigan and Huron. N was the most common limiting nutrient. Forty-three percent of NDS assays exhibited N limitation, 18% exhibited N+P colimitation, 3% exhibited P limitation, and 36% exhibited neither N nor P limitation. The magnitude of nutrient limitation was negatively correlated with water-column nutrients (dissolved and total N and P) and surrounding agricultural and developed land cover, results suggesting that anthropogenic nutrient loading partially relieved nutrient limitation in many locations. We also analyzed benthic algal assemblages to assess whether N2-fixing taxa were associated with N-limited wetlands. N2-fixing algae were common in our study wetlands, and their abundance was related to nutrient conditions. For example, the percentage of N2-fixing diatoms was significantly higher in N-limited wetlands, positively correlated with the magnitude of N limitation, and negatively correlated with dissolved N concentrations. Our results demonstrate that anthropogenic N loading, which receives considerably less management attention than P in the Great Lakes, can affect coastal wetland algal communities. Benthic algae is an important energy source for much of the food web in Great Lakes coastal wetlands, so effects associated with N loading may have broad implications.

Flood events can reduce key fatty acid content of early-stage benthic algal assemblages in an urban stream

Effects of urbanization on stream chemistry and biota have been widely examined. However, few studies quantify the effect of urban stream characteristics on the biochemical properties of basal food resources, such as benthic algae, which can affect aquatic consumers and food webs. A common feature of urban streams is the high frequency of short floods, which may disrupt aquatic communities and their biotic controls. These disturbances can create algal assemblages low in biomass and which remain in early successional stages. This study examined the effects of frequent flood events and macroinvertebrate grazing on biomass, elemental stoichiometry, and essential fatty acid (EFA) concentration of early colonizing benthic algal assemblages in an urban stream. Over a 3-week period in which two flood events occurred, algal biomass (chlorophyll- a ) and EFA profiles were each affected by floods, but the responses were weakly correlated. Concentrations of EFA molecules essential for aquatic consumers, such as arachidonic acid (ARA) 20:4ω6), eicosapentaenoic acid (EPA) 20:5ω3), and docosahexaenoic acid (DHA) 22:6ω3) were greatly reduced after floods, potentially lessening algal nutritional quality. There were no statistically significant differences in biomass or stoichiometry of benthic algae in assemblages under different grazing regimes, suggesting hydrological factors played a greater role in their production and nutritional quality. This study provides evidence that flood-prone streams in urban landscapes may be susceptible to greatly altered biochemical profiles in early colonizing benthic algal assemblages. Results also suggest that biochemically important compounds, such as EFAs, offer valuable information on the quality of benthic algal assemblages under anthropogenic stress.