Benthic Primary Production Research Articles

Benthic primary production in emerged intertidal habitats provides resilience to high water column turbidity

Increasing inputs of terrigenous sediments from anthropic land use change elevates water column turbidity, reducing light availability to benthic primary producers that sustain estuarine food webs. For intertidal habitats, photosynthesis during low tide periods of emergence may provide resilience against this temporally displaced stressor, yet the significance of low tide production (PP) has largely been overlooked. Emerged and submerged benthic PP was measured in adjacent seagrass (Zostera muelleri) and microphytobenthos-dominated (sandflat) soft-sediment habitats at three locations encompassing a turbidity gradient. Light and dark benthic incubation chambers were used to measure the flux of CO2 across emerged sediments, and dissolved oxygen across submerged sediments to derive net (NPP) and gross (GPP) PP. Seagrass NPP and GPP exceeded sandflat habitats (by 3–8 times) at low turbidity sites during submergence and at all sites during emergence (p < 0.01), whereas habitat differences were absent (p > 0.1) in turbid locations. Emerged NPP and GPP were higher (2–16 times) than submerged in all habitats and locations (p < 0.01). When standardised by mean incident photosynthetically active radiation (PAR), the difference between emerged and submerged seagrass PP increased with site turbidity, from 2 to 26 times greater. In a global context of increasing inputs of terrigenous sediment to estuaries, emerged PP may be crucial for providing resilience against benthic productivity losses in highly turbid environments.

Intertidal Seaweeds Modulate a Contrasting Response in Understory Seaweed and Microphytobenthic Early Recruitment

Recruitment is a fundamental step upon which all subsequent interactions within a community occur. We explored how the attenuation of physical conditions by seaweed plots comprised of either Chondracanthus canaliculatus, Pyropia perforata, Sylvetia compressa or a mixed aggregation, at varying densities (average 1199, 816 and 408 in. m-2), affected recruitment of seaweeds and microphytobenthic organisms in the understory, and if physical factors modulate their abundance and distribution. We outplanted macroscopic seaweeds in the intertidal and measured changes in understory irradiance, particle retention, and bulk water flow. Both factors influenced physical conditions below the canopy. However, only canopy density had a significant effect on recruitment. The low-density treatments showed greater abundance of seaweeds, with the opposite found for microphytobenthic organisms. The recruitment processes of seaweeds and microphytobenthic organisms, however, appeared to be independent of each other and were not due to competition. We conclude that it is crucial to consider microscale biological interactions, which are rarely addressed when assessing recruitment processes of benthic primary producers.

Shifting south-eastern North Sea macrofauna community structure since 1986: A response to de-eutrophication and regionally decreasing food supply?

Since the second half of the 20th century drastic changes were found within the marine environment, mostly driven by anthropogenic and climatic pressures. Within this study, the long-term variability of south-eastern North Sea macrofauna community structure was analysed on a large spatial extent, to examine effects of increasing sea surface temperature, decreasing pelagic and benthic primary production and phytoplankton biomass, together with de-eutrophication effects since the late 1980s. Macrofauna data from the 1986 North Sea Benthos Survey and the 2000 North Sea Benthos Project were reanalysed and compared with present data from 2010 to 2015. A stable spatial distribution of four main macrofauna communities was found, based on the environmental parameters depth, sediment composition, and tidal parameters. Diversity and taxa numbers remained stable since 1986. However, in 2010–2015, mean abundance and biomass of offshore waters had decreased slightly, while at the coastal nearshore areas and parts of the Oysterground a significant increase was found. Simultaneously, a spatial shift in maximum mean abundance and biomass from the Dogger Bank and Oysterground in 1986 towards the North Frisian coast in 2000 and 2010–2015 was found. Changes were probably driven by de-eutrophication effects in line with food limitation caused by decreasing phytoplankton biomass and pelagic and benthic primary production that strengthen the dominance of opportunistic tube-living taxa such as Phoronis spp. and Spiophanes bombyx. Synergistic effects of increasing sea surface temperature, ongoing seabed degradation, and predation by small non-target fish species caused distinct regionally different changes in characteristic species and dominance structure.

Dynamics of microphytobenthos photosynthetic activity along a depth transect in the sandy northeastern Gulf of Mexico shelf

The temporal and spatial dynamics of microphytobenthos activity in sandy shelf sediments are poorly understood, which limits assessments of the role of the benthic production in the coastal carbon cycle. The goal of this two-year time series study in the northeastern Gulf of Mexico therefore was to determine how benthic primary production rates in the West Florida Shelf change over the seasons and water depth. The study took place in the Big Bend region of Florida and used three stations along a transect starting at 5 m water depth and ending 29 km offshore, at 18 m water depth. Multisensor YSI 6600 probes installed at each station recorded key environmental parameters at the seafloor. Sediment cores, collected by SCUBA divers from each of the 3 stations at near-monthly intervals over a two-year time period were incubated in the laboratory for production and consumption rate measurements. Incubation of the cores at 200 μE m−2 s−1 allowed comparison of potential productivity between stations and seasons. Community light response curves, produced from sediment incubations at different light intensities, were used to calculate benthic productivity for measured in-situ light levels. The benthic production rates calculated from the core incubations and those calculated using the community light response curves agreed within a factor of three. Average sediment gross primary production rates based on in-situ light intensities ranged from 48 ± 60 mg C m−2 d−1 at 5 m and 81 ± 104 mg C m−2 d−1 at 10 m, to 13 ± 18 mg C m−2 d−1 at 18 m water depth. The corresponding average sediment consumption rates were −62 ± 36, −50 ± 55, and −29 ± 46 mg C m−2 d−1 at 5, 10 and 18 m water depth respectively. On average, production and consumption in the benthic system were found to be balanced, and the nearshore Stations A and B may temporarily turn net autotrophic during periods of high light intensity at the bottom. Our results suggest that the benthic production in this region may contribute up to 50% to the shelf primary production.

Allometric scaling of estuarine ecosystem metabolism

There are still significant uncertainties in the magnitude and direction of carbon fluxes through coastal ecosystems. An important component of these biogeochemical budgets is ecosystem metabolism, the net result of organismal metabolic processes within an ecosystem. In this paper, I present a synthesis of published ecosystem metabolism studies from coastal ecosystems and describe an empirical observation that size-dependent patterns in aquatic gross primary production and community respiration exist across a wide range of coastal geomorphologies. Ecosystem metabolism scales to the 3/4 power with volume in deeper estuaries dominated by pelagic primary production and nearly linearly with area in shallow estuaries dominated by benthic primary production. These results can be explained by applying scaling arguments for efficient, directed transport networks developed to explain similar size-dependent patterns in organismal metabolism. The main conclusion from this synthesis is that the residence time of new, nutrient-rich water is a fundamental organizing principle for the observed patterns. Residence time changes allometrically with size in pelagic ecosystems because velocities change by only an order of magnitude across systems that span more than ten orders of magnitude in size. This nonisometric change in velocity with size requires lower specific metabolic rates at larger ecosystem sizes. This change in transport may also explain a shift from predominantly net heterotrophy to net autotrophy with increasing size. The scaling results are applied to the total estuarine area in the continental United States to estimate the contribution of estuarine systems to the overall coastal budget of organic carbon.

Fluorescent organic exudates of corals and algae in tropical reefs are compositionally distinct and increase with nutrient enrichment

AbstractDissolved organic matter (DOM) composition influences microbial community metabolism and benthic primary producers are a source of DOM in coral reefs. As reef benthic communities change, in part due to nutrient pollution, understanding impacts on reef microbial processes requires knowledge of DOM sources and composition. We conducted a multi‐week mesocosm experiment dosing four coral reef benthic constituents with three levels of nitrate and phosphate to contrast exudate composition and quantify the effects of nutrient enrichment on exudate release. Moderate nutrient enrichment enhanced bulk dissolved organic carbon exudation by all producers. Corals exuded rapidly accumulating DOM with a markedly high concentration of aromatic amino acid‐like fluorescent DOM components that clearly distinguishes them from algal exudates, which were dominated by humic‐like fluorescent components and did not accumulate significantly. Our results indicate that corals and algae release DOM of different quality and the quantity of DOM release increases with inorganic nutrient availability.

Macrophytes as bioindicators of heavy metal pollution in estuarine and coastal environments

The Derwent estuary, in Tasmania (Australia), is highly contaminated with heavy metals with significant levels in both sediments and benthic fauna. However, little is known about metal content in benthic primary producers. We characterized metal content (Arsenic, Cadmium, Copper, Lead, Selenium and Zinc) in twelve species of macrophyte, including red, green, and brown algae, and seagrasses, from the Derwent. The metals, arsenic, copper, lead, and Zinc were detected in all of the macrophytes assessed, but the levels differed between species. Seagrasses accumulated the highest concentrations of all metals; with Zn levels being particularly high in the seagrass Ruppia megacarpa (from the upper Estuary) and Pb was detected in Zostera muelleri (from the middle estuary). Ulva australis was ubiquitous throughout the middle-lower estuary and accumulated Zn in relatively high concentrations. The findings suggest that analysis of multiple species may be necessary for a comprehensive understanding of estuary-wide metal pollution.

Different ecological mechanisms lead to similar grazer controls on the functioning of periphyton Antarctic and sub-Antarctic communities

The processes underpinning the differences between Antarctic and sub-Antarctic ecological communities are still unclear. Dispersal, drift, speciation, and abiotic environmental filtering have been considered to explain these differences; biotic interactions, however, have received less attention. Antarctic intertidal assemblages of macrobenthic grazers are characterised by numerically abundant populations of a single species, Nacella concinna. In contrast, sub-Antarctic habitats display a diverse assemblage of herbivores like chitons, keyhole limpets, and several species of Nacella. Thus, it was hypothesised that herbivores would have significant density-dependent effects of a single species on benthic primary productivity in Antarctica, but stronger effects of the whole assemblage in the sub-Antarctic. Field grazer inclusion-exclusion experiments showed that chlorophyll-a (chl-a) concentration was one order of magnitude lower in Fildes Bay (King George Island, Antarctica) than in the Strait of Magellan (Chilean South Patagonia). Still, grazers had significant and negative effects on chl-a accrual, a proxy for productivity, in both sites. In Fildes Bay, these effects were similar between experimental levels or grazer density. Accordingly, evidence for negative density dependence of per capita interaction strength was detected in this region. In the Strait of Magellan, only the open access treatments, exposed to the diverse assemblage of grazers, significantly decreased chl-a accrual. Grazers negatively affected the relative abundance of browns (i.e. diatoms, dinoflagellates, and early stages of brown algae) and cyanobacteria at both sites, but favoured green algae and bare substratum in Fildes Bay and Strait of Magellan, respectively. These results suggest that different mechanisms, such as negative density dependence and resource partitioning, can lead to similar grazing controls of the productivity of Antarctic and sub-Antarctic periphyton communities. Herbivory should be incorporated as a local biotic filter into a comprehensive model of community structure and functioning for these ecosystems.

Effects of CO2 enrichment on benthic primary production and inorganic nitrogen fluxes in two coastal sediments

Ocean acidification may alter the cycling of nitrogen in coastal sediment and so the sediment–seawater nitrogen flux, an important driver of pelagic productivity. To investigate how this perturbation affects the fluxes of NOX− (nitrite/nitrate), NH4+ and O2, we incubated estuarine sand and subtidal silt in recirculating seawater with a CO2-adjusted pH of 8.1 and 7.9. During a 41-day incubation, the seawater kept at pH 8.1 lost 97% of its NOX− content but the seawater kept at pH 7.9 lost only 18%. Excess CO2 increased benthic photosynthesis. In the silt, this was accompanied by a reversal of the initial NOX− efflux into influx. The estuarine sand sustained its initial NOX− influx but, by the end of the incubation, released more NH4+ at pH 7.9 than at pH 8.1. We hypothesise that these effects share a common cause; excess CO2 increased the growth of benthic microalgae and so nutrient competition with ammonia oxidising bacteria (AOB). In the silt, diatoms likely outcompeted AOB for NH4+ and photosynthesis increased the dark/light fluctuations in the pore water oxygenation inhibiting nitrification and coupled nitrification/denitrification. If this is correct, then excess CO2 may lead to retention of inorganic nitrogen adding to the pressures of increasing coastal eutrophication.

Seasonal Partitioning of Primary Production and Biomass between Phytoplankton and Metaphyton in a Shallow Lake Agmon, Hula Valley (Israel)

Agmon is a small, shallow man-made lake (area: 1.1 km2; mean depth 0.45 m), excavated in the peat soils of the Hula Valley in northern Israel, that was filled with water in August 1994. We followed the seasonal variations in phytoplankton and metaphyton biomass, primary production and related environmental conditions between December 1995 and July 1997. Water temperature ranged between 9.5°C - 30.8°C; pH ranged between 7.2 - 8.6. The algae in Lake Agmon were characterized by seasonal alterations between summer-fall phytoplankton blooms and spring proliferation of benthic algal mats, with a winter clear-water phase. Chlorophyll a content in the water, as a measure of planktonic algal biomass, was low in winter (1.75 - 5 μg·L-1) and high in summer (>100 μg·L-1), when planktonic cyanobacteria (Microcystis spp.) bloomed. Metaphyton biomass varied between 3.5 and 970 g·dry·wt·m-2, with chlorophyll a content ranging from 5 - 701 mg·m-2. The dominant benthic algal genera were Spirogyra and Oedogonium in 1996 and Cladophora in 1997. Phytoplankton primary production was high in summer-fall, with a maximum of 1200 mg·O2·m-2·h-1. Benthic primary production was high from March till May, with a peak of 2173 mg·O2·m-2·h-1 in April 1997. The rate of benthic algal primary production was positively correlated to benthic chlorophyll a (r2 = 0.90). Diel measurements of water column dissolved oxygen (DO) concentration, conducted monthly from January to May 1997, revealed that DO concentration ranged from a nighttime minimum of 5.3 to a noon peak of 15.3 mg·L-1. Only during January to February, no significant changes in DO with depth were found, suggesting that at that time the water column was well mixed. The most salient feature of primary production in the lake was the seasonal partitioning between its benthic and planktonic components. This was most evident in the significant inverse relationship between benthic and planktonic primary productivity rates (r2 = 0.78).

富营养化对白洋淀底栖-浮游耦合食物网结构和功能的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 富营养化对白洋淀底栖-浮游耦合食物网结构和功能的影响 DOI: 10.5846/stxb201701060057 作者: 作者单位: 河北科技大学,河北科技大学,河北科技大学,河北科技大学,河北科技大学,河北科技大学 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41601547）；国家重点基础研究发展计划（2015CB458900）；河北省自然科学基金项目（D2017208003）；河北省高等学校青年拔尖人才项目（BJ2017013） Effects of eutrophication on the benthic-pelagic coupling food web in Baiyangdian Lake Author: Affiliation: Hebei University of Science and Technology,,,Hebei University of Science and Technology,,Hebei University of Science and Technology Fund Project: The National Natural Science Foundation of China (41601547) 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:国际湖沼学的长期研究发现，一个完整的湖泊生态系统应包括底栖食物网和浮游食物网，而营养条件变化会显著改变浅水湖泊中底栖-浮游食物网的结构和功能。为了明晰富营养化对浅水湖泊底栖-浮游耦合食物网结构和功能的影响，以浅水草型湖泊——白洋淀为研究区，运用野外监测和ECOSIM与ECOPATH（EwE）模型相结合方法，构建白洋淀底栖-浮游耦合食物网的概念模型，模拟1982-2011年间富营养化对白洋淀底栖路径和浮游路径的结构和功能影响：（1）野外监测的结果表明，从1999年至今白洋淀一直处于富营养化状态；（2）EwE模型模拟结果表明1982-2006年，总生物量呈下降趋势，下降比例达66.38%；能流路径从以底栖路径为主转变为以浮游路径为主；（3）运用Pearson相关分析，结果表明：浮游植物与TN（r=0.67，P < 0.01）和TP（r=0.37，P < 0.05）呈显著正相关，而底栖藻类和大型沉水植物与TN（r=0.77，P < 0.01；r=0.67，P < 0.01）和TP（r=0.54，P < 0.01；r=0.36，P < 0.05）呈显著负相关。富营养化是白洋淀底栖初级和次级生产力向浮游初级和次级生产力转变的主要驱动力。采用科学的方法准确评估富营养化对湖泊底栖-浮游耦合食物网结构和功能的影响，可为湖泊生态系统管理提供技术和方法支持。 Abstract:According to the research finding for the limnology, in the whole lake ecosystem it should be including benthic pathway and pelagic pathway, while the variation of nutrition conditions can significantly change the structure and function of the bethic-pelagic coupling foodweb. In order to certain the effects of eutrophication on the benthic-pelagic coupling foodweb in shallow lake ecosystem, Baiyangdian Lake as the study area. Field samping and ECOSIM with ECOPATH(EwE) model method were applied in this study, the conceptual model for benthic-pelagic coupling foodweb in Baiyangdian Lake was established, the effects of eutrophication on the benthic-pelagic coupling foodweb was monitored during the period of 1982-2011. The research finding was:(1) the result for the filed sampling was showed that the nutrition condition for Baiyangdian Lake was belonged to eutrophication from 1999 to 2011; (2) the result for the EwE model was showed that the total biomass of Baiyangdian Lake was decreased for 66.38%, and the main energy pathway was changed from benthic pathway to pelagic pathway; (3) through Pearson correlation analysis, the phytoplankton was showed significantly positive correlation with TN (r=0.67, P < 0.01) and TP(r=0.37, P < 0.05) while the periphyton and macrophyte were showed significantly negative correlation with TN (r=0.77, P < 0.01; r=0.67, P < 0.01) and TP (r=0.54, P < 0.01; r=0.36, P < 0.05). Therefore, eutrophication is the main driving force for the change from benthic primary and secondary productivity to pelagic primary and secondary productivity. Applying scientific method to evaluate the effects of eutrophication on the pelagic-benthic coupling foodweb is very important, it also can help to provide technology and method to the lake ecosystem management. 参考文献 相似文献 引证文献

Fisheries productivity under progressive coral reef degradation

Abstract In response to multiple stressors, coral reef health has declined in recent decades, with reefs exhibiting reduced living coral and structural complexity, and a concomitant rise in the dominance of algal resources. Reef degradation alters food availability and reduces the diversity and density of refuges for prey. These changes affect predator–prey interactions and can have cascading impacts on food webs and fisheries productivity. We use a size‐based ecosystem model of coral reefs that incorporates the influence of structural complexity, benthic primary production and detrital recycling to explore how predator–prey interactions and fisheries productivity respond to a gradient of reef degradation. We show that fisheries productivity overall may be robust to initial stages of reef degradation because the benefits of increased resources outweigh the costs of moderate refuge decline. However, the assemblage composition and size structure of reef fish will differ on degraded reefs, with herbivores and invertivores contributing relatively more to productivity. More significant losses of refuges associated with the erosion of structural complexity correspond to fisheries productivity losses of at least 35% compared to healthy reefs. Synthesis and applications. Our model provides fisheries managers with quantitative predictions about how fisheries productivity may change in response to the ongoing degradation of coral reefs. We predict an initial increase in productivity at intermediate reef degradation, followed by a drastic decline when structural complexity is lost. We also capture subtle changes to potential catch composition and fish size, including increases in smaller herbivorous and invertivorous fish from degraded reefs, which will undoubtedly impact fisheries value. On the one hand, our results reassure for continued productivity in the short term, but on the other, we warn against complacency. Management must change to capture any potential benefits to fisheries, and long‐term sustainability still depends on the maintenance of complex coral reef habitats.

Food Composition for Blue Mussels (Mytilus edulis) in the Menai Strait, UK, Based on Physical and Biochemical Analyses

To clarify the composition of food ingested by blue mussels (Mytilus edulis) in the Menai Strait, where the largest mussel bed in the United Kingdom lies, hydrodynamic observations with organic carbon and nitrogen biochemical analysis were conducted. This strait is characterized by a narrow channel and wide tidal flats with large tidal mixing that influences the distribution of particulate organic matter (POM), which is food formussels. The maximum velocities of the tidal currents were estimated to be 0.5–1.0 m s-1 during northeastward flow and 0.6–1.3 m s-1 during southwestward flow. The residual current was southwestward and the water flux was estimated to be 510 m3 s-1. Field observations indicate that the inflow of pelagic phytoplankton into the strait mainly occurred in the northern region of the strait. Resuspended benthic primary production, however, also causes higher chlorophyll-a concentration in the central region of the strait near the mussel bed and its contribution to mussel growth was estimated to be 22%–50%. The concentrations of chlorophyll-a and particulate organic carbon indicated that the POM in the strait mainly originated from detritus. Benthic microalgae is, however, an important factor to understand the total primary production in the strait. The consumption of the primary producers was estimated to be approximately 6.3 t C day-1. In the phytoplankton community, pelagic and thycopelagic (living in both pelagic and benthic environments) species comprised 59.3%–77.2% and 12.8%–40.7% of the cells, respectively. The primary production by resuspended benthic species in the Liverpool Bay region was considerably larger than that in the Menai Strait region. As a conclusion, theMenai Strait is an area with complex hydrodynamic conditions causing horizontal advection and resuspension of both pelagic and benthic phytoplankton, and this complex would cause the most suitable condition for mussel production.

The invasive kelp Undaria pinnatifida hosts an epifaunal assemblage similar to native seaweeds with comparable morphologies

Invasive seaweeds have the potential to disrupt ecosystem functioning if they are unsuitable hosts for the small mobile invertebrates (epifauna) that are an important trophic link between benthic primary producers and higher trophic levels. The Asian kelp Undaria pinnatifida has successfully invaded many coastal regions worldwide. We compared the epifaunal assemblage on U. pinnatifida with epifauna of 7 co-occurring, canopy-forming native brown seaweed species in southern New Zealand to help understand the effect of the invasive species on shallow subtidal ecosystems. The density, diversity and composition of epifauna across the 8 seaweeds were much more strongly related to host morphology than to the geographic origin of the host. U. pinnatifida and several native seaweeds with similarly simple morphologies supported relatively depauperate epifaunal assemblages dominated by copepods. More structurally complex native seaweeds supported more abundant and diverse epifaunal assemblages containing lower proportions of copepods and higher proportions of amphipods and other epifaunal groups. Our results indicate that abundances of epifauna at the ecosystem level will be reduced if U. pinnatifida displaces more structurally complex native seaweed species that host more diverse and dense epifaunal assemblages. The findings suggest that morphological complexity may be key to predicting the impacts of invasive seaweeds on epifaunal assemblages, and potentially on food webs, in other geographic regions.

Influence of littoral periphyton on whole-lake metabolism relates to littoral vegetation in humic lakes.

The role of littoral habitats in lake metabolism has been underrated, especially in humic lakes, based on an assumption of low benthic primary production (PP) due to low light penetration into water. This assumption has been challenged by recent recognition of littoral epiphyton dominance of whole-lake PP in a small highly humic lake and of epiphyton as an important basal food source for humic lake biota. However, as these studies have mostly concerned single lakes, there is a need to test their wider generality. We studied the whole-lake PP and community respiration (CR) in eight small humic lakes in southern Finland during July 2015 using 14 C incorporation to measure pelagic PP and the changes in dissolved inorganic carbon in light and dark insitu incubations to measure CR and littoral PP by epiphyton. Changes in O2 concentration in both pelagic and littoral surface water were measured periodically from each lake and, additionally, continuously with a data logger from one lake during the study period. The results revealed that the littoral dominated whole-lake net primary production (NPP) in five of the eight lakes, which was supported by observed O2 supersaturation in the littoral surface water in most of the lakes. Calculated pelagic:littoral ratios by area correlated negatively with both littoral NPP and littoral contribution to whole-lake NPP. Moreover, there was a significant positive relationship between littoral proportion of whole-lake NPP and the fraction of lake surface area covered by littoral aquatic vegetation. This demonstrates that increased aquatic littoral vegetation cover increases the overall importance of the littoral to whole-lake PP in highly humic lakes. Littoral NPP also correlated strongly with littoral O2 saturation, and the continuously measured O2 revealed substantial temporal variation in O2 saturation, particularly in the littoral zone. Whole-lake gross primary production:community respiration (GPP:CR) ratios revealed that accounting for littoral metabolism produced a marked shift towards lake metabolic balance, although all the eight lakes remained net heterotrophic. This study emphasizes that littoral metabolism needs to be accounted for when estimating whole-lake C fluxes in all lakes, even in highly colored humic waters.

Interplay between abiotic factors and species assemblages mediated by the ecosystem engineer Sabellaria alveolata (Annelida: Polychaeta)

Sabellaria alveolata is a gregarious polychaete that uses sand particles to build three-dimensional structures known as reefs, fixed atop rocks or built on soft sediments. These structures are known to modify the local grain-size distribution and to host a highly diversified macrofauna, altered when the reef undergoes disturbances. The goal of this study was to investigate the different sedimentary and biological changes associated with the presence of a S. alveolata reef over two contrasting seasons (late winter and late summer), and how these changes were linked. Three different sediments were considered: the engineered sediment (the actual reef), the associated sediment (the soft sediment surrounding the reef structures) and a control soft sediment (i.e. no reef structures in close proximity). Univariate and multivariate comparisons of grain-size distribution, soft sediment characteristics (organic matter content, chlorophyll a, pheopigments and carbohydrate concentrations) and macrofauna were conducted between the different sediment types at both seasons and between the two seasons for each sediment type. A distance-based redundancy analyses (dbRDA) was used to investigate the link between the different environmental parameters and the macrofauna assemblages. Finally, we focused on a disturbance continuum of the engineered sediments proxied by an increase in the mud present in these sediments. The effects of a continuous and increasing disturbance on the associated fauna were investigated using pairwise beta diversity indices (Sørensen and Bray-Curtis dissimilarities and their decomposition into turnover and nestedness). Results showed a significant effect of the reef on the local sediment distribution (coarser sediments compared to the control) and on the benthic primary production (higher in the associated sediments). At both seasons, S. alveolata biomass and sediment principal mode were the environmental parameters which best differentiated the engineered, associated and control sediment assemblages. These two parameters are under the ecosystem engineer's influence stressing its importance in structuring benthic macrofauna. Furthermore, in late summer but not in late winter, presence/absence and abundance-based beta diversity were positively correlated to our disturbance proxy (mud content) a tendency driven by a species replacement and a rise in the associated fauna density. Our first set of results highlight the importance of S. alveolata reefs as benthic primary production enhancers via their physical structure and their biological activity. The results obtained using beta diversity indices emphasize the importance of recruitment in structuring the reef's macrofauna and – paradoxically – the ecological value of S. alveolata degraded forms as biodiversity and recruitment promoters.

Interactive effects of temperature and habitat complexity on freshwater communities.

Warming can lead to increased growth of plants or algae at the base of the food web, which may increase the overall complexity of habitat available for other organisms. Temperature and habitat complexity have both been shown to alter the structure and functioning of communities, but they may also have interactive effects, for example, if the shade provided by additional habitat negates the positive effect of temperature on understory plant or algal growth. This study explored the interactive effects of these two major environmental factors in a manipulative field experiment, by assessing changes in ecosystem functioning (primary production and decomposition) and community structure in the presence and absence of artificial plants along a natural stream temperature gradient of 5–18°C. There was no effect of temperature or habitat complexity on benthic primary production, but epiphytic production increased with temperature in the more complex habitat. Cellulose decomposition rate increased with temperature, but was unaffected by habitat complexity. Macroinvertebrate communities were less similar to each other as temperature increased, while habitat complexity only altered community composition in the coldest streams. There was also an overall increase in macroinvertebrate abundance, body mass, and biomass in the warmest streams, driven by increasing dominance of snails and blackfly larvae. Presence of habitat complexity, however, dampened the strength of this temperature effect on the abundance of macroinvertebrates in the benthos. The interactive effects that were observed suggest that habitat complexity can modify the effects of temperature on important ecosystem functions and community structure, which may alter energy flow through the food web. Given that warming is likely to increase habitat complexity, particularly at higher latitudes, more studies should investigate these two major environmental factors in combination to improve our ability to predict the impacts of future global change.

Holocene environmental history of the Ångermanälven Estuary, northern Baltic Sea

The Baltic Sea has experienced a complex geological history, with notable swings in salinity driven by changes to its connection with the Atlantic and glacio‐isostatic rebound. Sediments obtained during International Ocean Drilling Program Expedition 347 allow the study of the effects of these changes on the ecology of the Baltic in high resolution through the Holocene in areas where continuous records had not always been available. Sites M0061 and M0062, drilled in the Ångermanälven Estuary (northern Baltic Sea), contain records of Holocene‐aged sediments and microfossils. Here we present detailed records of palaeoecological and palaeoenvironmental changes to the Ångermanälven Estuary inferred from diatom, palynomorph and organic‐geochemical data. Based on diatom assemblages, the record is divided into four zones that comprise the Ancylus Lake, Littorina Sea, Post‐Littorina Sea and Recent Baltic Sea stages. The Ancylus Lake phase is initially characterized as oligotrophic, with the majority of primary productivity in the upper water column. This transition to a eutrophic state continues into the Initial Littorina Sea stage. The Initial Littorina Sea stage contains the most marine phase recorded here, as well as low surface water temperatures. These conditions end before the Littorina Sea stage, which is marked by a return to oligotrophic conditions and warmer waters of the Holocene Thermal Maximum. Glacio‐isostatic rebound leads to a shallowing of the water column, allowing for increased benthic primary productivity and stratification of the water column. The Medieval Climate Anomaly is also identified within Post‐Littorina Sea sediments. Modern Baltic sediments and evidence of human‐induced eutrophication are seen. Human influence upon the Baltic Sea begins c. 1700 cal. a BP and becomes more intense c. 215 cal. a BP.

Decrypting stable‐isotope (δ13C and δ15N) variability in aquatic plants

Abstract Variability in C and N stable isotopes has been acknowledged to hinder their use as tracers of food sources in the study of trophic interactions in ecosystems. This is particularly so whenever benthic primary production is substantial (variability in δ13C) and the ecosystem under study is affected by human impacts (variability in δ15N) in aquatic ecosystems. In this study, we aim to better understand the large and often unexplained variability in the natural abundance of δ13C and δ15N signatures of aquatic plants by analyzing the isotopic composition of plants from 81 lentic systems from NE Spain in relation to extrinsic (alkalinity, pH, nutrient concentrations, water body typology and basin land use) and intrinsic (functional group, carbon assimilation metabolism, elemental composition) predictors. We have encountered significant plasticity in isotopic signatures of aquatic plants associated with the variation in local conditions at the regional scale. The δ13C signature varied from −43.1‰ to −7.5‰ (35.7‰ range) and drivers were both intrinsic and extrinsic. The functional group was the most important factor as it is influenced by different carbon sources. Aquatic plants with leaves in contact with the atmosphere (helophytes, free floating and floating attached; −34.8‰ to −14.6‰) responded in a similar way as terrestrial plants. This contrasted with the enriched mean values of rooted submerged plants (−16.7‰ to −10.5‰) that were more enriched than the described terrestrial C3 range (−34‰ to −22‰) and completely overlapped the terrestrial C4 range (−20‰ to −8‰). Concentration of DIC and pH also emerged as important extrinsic factors driving δ13C variability. The δ15N signature ranged from −5.2‰ to 20.1‰ (25.2‰ range) and the variability was mostly associated with extrinsic factors such as water body type and basin land use, as they influence both the δ15N signature and concentration of the dissolved inorganic nitrogen in the aquatic ecosystems. Only one multifactorial model including the functional group (with the largest contribution), DIC and pH was selected as the best model explaining the variability in δ13C signatures of aquatic plants. The final model had a relatively large explained deviance and was consistent with the previous unifactorial results. Two different models were selected as the best models explaining variability in δ15N signatures of aquatic plants. The models included the geomorphological type of water body as the variable with the largest contribution, and the percentage of either natural or agricultural coverage in the basin. These results are summarized in a conceptual model showing the predictors and their range and direction of variation. This study shows that extrinsic factors are of greater importance in influencing the stable‐isotope signatures of aquatic plants compared to terrestrial plants, because of varied sources and an often limited isotopic discrimination.

Phosphorus scarcity and desiccation stress increase the occurrence of dominant taxa in wetland benthic primary producer communities

A few dominant species of plants often disproportionately contribute to primary production; however, dominance has an underappreciated influence on ecosystem processes and functioning. Cascading impacts of dominant species have been documented in ecosystems undergoing eutrophication, but competitive exclusion may also influence dominance structures when limiting nutrients become scarce (i.e., in lakes experiencing oligotrophication) or with exposure to stressors to which few species are adapted (i.e., desiccation stress in wetlands). To predict impacts of widespread changes in nutrients and hydrology on dominance structures in aquatic ecosystems, we need quantitative assessments of dominance of important primary producers, including algae and cyanobacteria, which can regulate other structural and functional properties of ecosystems. We used a highly spatiotemporally resolved (7 years, 165 sites) dataset from the abundant microbial mats of the Florida Everglades to assess how and why the degree of dominance and the identity of dominant taxa vary across nutrient and desiccation gradients. Using algal counts and the dimensions of algal units (cells, coenobia, colonies, and filaments), we measured dominance as relative biovolume. As hypothesized, the relative biovolume of dominant taxa increased and the number of taxa comprising 95% of the biovolume decreased with lower concentrations of limiting nutrient in the mats (phosphorus; P) and higher desiccation stress. Algal taxa that regulate the structural integrity of mats, such as the filamentous, calcium carbonate precipitating cyanobacterium Scytonema sp., strongly influenced these patterns through their tolerance of P scarcity and desiccation. Our indicators and approach can be used to test whether dominance of microscopic primary producers, and other organisms, increases with nutrient scarcity and desiccation stress in other aquatic ecosystems.