Benthic Microalgae Research Articles

Effects of Sediment Characteristics on Carbon Dioxide Fluxes Based on Interacting Factors in Unvegetated Tidal Flats

The contribution of unvegetated tidal flats to global net primary production is comparable to that of some vegetated coastal habitats. However, compared to carbon flux regulating factors in vegetated habitats, those in unvegetated tidal flats are not well understood, particularly in terms of their cause-effect relationships. Maximum gross primary production (GPPm), net primary production (NPP) and total respiration (TR) during emersion at noon when the irradiance level was at the saturation level for photosynthesis in nine unvegetated tidal flats across the Taiwan Strait in tropical and subtropical regions were determined in winter and summer from 2011 to 2016 to examine the direct and indirect relationships between sediment characteristics and carbon fluxes by using structural equation models (SEM). Most of the GPPm and NPP values were higher in winter than in summer. Conversely, the TR values were higher in summer than in winter. The NPP values at some sites shifted to negative values in summer, indicating the sites were carbon sources. The values of GPPm, TR and NPP for the tidal flats all increased significantly with increasing sediment mud content. The SEM results showed that the sediment mud content directly increased GPPm or indirectly increased GPPm via a compositional shift in benthic microalgae. The sediment mud content also directly increased TR or indirectly increased TR via increased organic matter content. The contribution of benthic microalgal and macrofaunal biomass to TR was relatively minor. This result suggests that primary production was stimulated mainly by the organic matter content rather than by increased microalgal biomass. With the integrated SEM framework, our results showed mechanistic evidence of how sediment mud content acted as a critical factor regulating carbon fluxes in unvegetated tidal flats.

Succession pattern and phylotype analysis of microphytobenthic communities in a simulated oil spill seagrass mesocosm experiment

Microphytobenthic communities play a significant role in nutrient modulation, sediment stabilization, and primary production in seagrass beds, which provide various ecosystem services. We hypothesized that microphytobenthic communities in sediments of chronically oil-exposed seagrass beds will exhibit increased resiliency to stressors associated with oil exposure as opposed to seagrass beds never exposed to oil spills. We prepared 14-liter seawater mesocosms, each containing a submersed macrophyte Ruppia maritima collected from the Chandeleur Islands, Louisiana, and Estero Bay, Florida. Mesocosms were initially exposed to 50% water-accommodated oil fractions (WAF) and subsequently diluted by 50% with daily artificial seawater exchanges over 8 days to simulate tidal dilution. High-throughput amplicon sequencing based on 23S rRNA gene targeting cyanobacteria and chloroplasts of eukaryotic microphytobenthos was conducted to assess the impact of oiling on microphytobenthic communities with additional assessment via microscopy. High-throughput sequencing in combination with traditional microscopic analysis provided a robust examination in which both methods roughly complemented each other. Distinct succession patterns were detected in benthic algal communities of chronically oil-exposed (Louisiana) versus unexposed (Florida) seagrass bed sediments. The impact of oiling in microphytobenthos across all samples showed that benthic diatoms dominated all algal communities with sample percentages ranging from 42 to 97%, followed by cyanobacteria (2 to 50%). It is noteworthy that drastic changes in microphytobenthic community structure in terms of the larger taxonomic level were not observed, rather change occurred at the phylotype level. These results were also confirmed by microscopy. Similarity percentages (SIMPER) analysis identified seven phylotypes (Cyanobacteria, Bacillariophyceae, and Mediophyceae) in the Louisiana samples and one phylotype (Bacillariophyceae) in the Florida samples that increased in relative sequence abundance after oil exposure. The detailed phylotype analysis identifying sentinel microphytobenthic indicators provides a base for future research on benthic microalgae response to ecosystem disturbance.

Assessing the contribution of mangrove carbon and of other basal sources to intertidal flats adjacent to one of the largest West African mangrove forests

Mangrove forests are productive habitats and major potential exporters of organic matter and nutrients to adjacent habitats. Here we examine the extent to which mangrove carbon is transferred to adjacent intertidal food webs in the second largest mangrove-covered area in Africa, in Guinea-Bissau. Applying stable isotope analysis and mixing models, we made comparisons at two spatial scales: (1) a large scale, comparing intertidal flats with (mangrove sites) and without (control sites) adjacent mangrove forests regarding the carbon isotopic signature of macrozoobenthos and sediment organic matter (SOM), and the relative importance of potential primary food sources in sustaining macrozoobenthos, and (2) a fine scale, performing stable carbon isotope measurements along 200 m transects from the coastline out to open intertidal flats, to trace mangrove carbon in macrozoobenthos and in the SOM. We found no evidence that mangrove carbon sustains intertidal food webs, despite SOM being significantly more depleted in 13C in mangrove sites. Mangrove leaves had the lowest relative contribution to the diet of macrozoobenthos, while macroalgae, benthic microalgae and POM showed variable but overall relevant contributions. Yet, at a smaller scale, mangrove carbon was detectable in SOM and in most macrozoobenthos, being strongest within 50 m of the mangrove edge and quickly fading with increasing distance. Our results suggest that there is only a marginal input of mangrove carbon into the food webs of unvegetated intertidal flats. Still, this leaves open the possibility of mangrove forests acting as sources of dissolved inorganic carbon and processed nitrogen, which can be assimilated by the algae and subsequently fuel adjacent food webs.

Benthic Metabolism in Fluvial Sediments with Larvae of Lampetra sp.

Lampreys spend their larval stage within fine sand fluvial sediments, where they burrow and act as filter feeders. Lamprey larvae (ammocoetes) can significantly affect benthic-pelagic coupling and nutrient cycling in rivers, due to high densities. However, their bioturbation, feeding and excretion activities are still poorly explored. These aspects were investigated by means of laboratory incubations of intact sediments added with ammocoetes and of animals alone. Oxygen respiration, nutrient fluxes and excretion rates were determined. Individual ammocoete incubations suggested that biomass-specific oxygen consumption and ammonium, reactive phosphorus and silica excretion were size-dependent, and greater in small compared to large individuals. The comparison of ammocoetes metabolic rates with rates measured in intact sediments revealed that ammocoetes activity decreases significantly when they are burrowed in sediments. Furthermore, results suggest that a major fraction of ammonium excreted by ammocoetes was assimilated by benthic microbes or microalgae to overcome in situ N-limitation. Alternatively, part of the excreted ammonium was oxidized and denitrified within sediments, as nitrate uptake rather increased along with ammocoetes density. Ammocoetes excreted reactive phosphorus and silica but such production was not apparent in bioturbated sediments, likely due to microbial or microalgal uptake or to immobilization in sediments.

In situ characterization of benthic fluxes and denitrification efficiency in a newly re-established mussel farm

Mussel farming has been proposed as a mechanism to mitigate eutrophication in coastal waters. However, localizing the intensive filtration of organic matter by mussels can cause a concomitant enrichment of organic matter in sediments below farms, which may influence biogeochemical processes and fates of nutrients in the system. In the context of mitigating eutrophication, it is important to quantify sedimentary changes induced at early life stages of mussel farms. Accordingly, this study investigated how a newly re-established mussel farm affected sedimentation rates, sediment characteristics, sediment-water solute fluxes and nitrate (NO3−) reduction rates (measured in situ) during the first year of production. Sedimentation rates were enhanced at the farm relative to a reference station, and both organic and inorganic carbon accumulated in the sediment with time. Increased organic matter input likely drove the slightly elevated sedimentary effluxes of ammonium (NH4+) and dissolved inorganic phosphorus (DIP) in the farm. Denitrification was the main NO3− reduction process, however, there was a relative increase in the remobilization of bioavailable nitrogen underneath the farm as dissimilatory nitrate reduction to ammonium (DNRA) rates were enhanced by >200% and the denitrification efficiency was 49% lower compared to the reference station. The sedimentary methane (CH4) release tended to be higher at the farm, but fluxes were not significantly different from reference conditions. Low sedimentary pigment concentrations indicated a reduced presence of benthic microalgae at the farm, which likely influenced sediment-water solute fluxes. Over the production cycle, the release of dissolved inorganic nitrogen (DIN) and DIP underneath the farm were respectively 426% and 510% relative to reference conditions. Impacts of the mussel farm were thus measurable already during the first year of establishment. These immediate changes to the sediment biogeochemistry, as well as long-term effects, should be considered when estimating the environmental impact of mussel aquaculture.

Trophic importance of the seagrass Halophila ovalis in the food web of a Hepu seagrass bed and adjacent waters, Beihai, China

The current paradigm emphasizes the trophic role of epiphytic algae in seagrass-based food webs. However, a growing body of literature demonstrates that grazers would directly cause considerable damage to seagrass rather than targeting epiphytes, perhaps depending on seagrass traits. Here, we analyzed δ13C and δ15N signatures of macrozoobenthos, nekton and their potential organic carbon sources in Halophila ovalis seagrass bed and adjacent waters on the Hepu coast (Beihai, China) to test the hypothesis that Halophila with high nutritive values and fragile leaf-fracture traits may be a key carbon source. The δ13C values of most consumers either fell between H. ovalis (−14.7 ± 0.7‰) and benthic microalgae (microphytobenthos and Halophila’s epiphytes, −19.9 to −19.3‰), or approached the δ13C of H. ovalis, suggesting that H. ovalis and microalgae is basal carbon sources in Halophila-based food web. Further quantification based on a 4-end-member MixSIAR model showed that H. ovalis is the most important basal carbon source, supporting 4 out of 6 trophic groups of macrozoobenthos, and 4 out of 7 nektonic trophic groups (a total of 22 species, accounting for 84.6% in nekton). The mean contribution was 37.2–75.3% for macrozoobenthos and 51.1–64.4% for nekton, respectively. Most macrozoobenthos directly or indirectly assimilated H. ovalis or its detritus and were then mainly utilized by nekton except for bivalves which largely fed on suspended microphytobenthos and particulate organic matter (POM), and porifera filtered POM. Our results re-examined the trophic function of seagrass in seagrass-based food web and emphasize the importance of protecting Halophila resources.

Biofilm formation of benthic diatoms on commercial polyvinylidene fluoride membrane

Marine benthic microalgae always have their own ubiquitous nature to adhere to diverse submerged substrates. Immobilized submerged biofilm system offers huge reduction of liquid culture volume, high biomass production and ease of harvesting of biomass. The studies on the biofilm formation and properties towards membrane surfaces are rare therefore the objectives of this paper were to investigate the relationships between the algal attachment rate onto membranes via biofilm and the compositional changes of the extracellular polymeric substances in the biofilm. To delve further into the biofilm-forming capacity of three benthic diatoms (Amphora coffeaeformis, Cylindrotheca fusiformis and Navicula incerta) onto polyvinylidene fluoride membrane (PVDF), a simple adhesion test was run for 96 h under controlled temperature and light conditions. Attached biomass was carefully scraped for cell count and extracellular polymeric substances (EPS) were extracted for characterization in terms of its biochemical compositions. As a result, A. coffeaeformis and N. incerta were found to adhere well with membrane substrate with equal cell attachment (3 × 108 cells/m2) at the end of the experiment while the lowest was observed for C. fusiformis (1.33 × 108 cells/m2). Biofilm of three diatoms was observed to form as soon as 2 h after inoculation and its development was aided by the high accumulation of TEP amount at 96th hour ranging from 91 mg X eq/m2to 170.61 mg X eq/m2. EPS excreted was found to re-accumulate after 48 h with polysaccharides as major component (>59.87%) for N. incerta and C. fusiformis except A. coffeaeformis which was mainly composed of proteins (>50%). The biofilm formed by A. coffeaeformis was considered the most robust because of its hydrophobic-hydrophobic interaction between the cells and the membrane. Understanding of biofilm physiology will pave the way for describing biofilm systems and membrane-based wastewater treatment systems.

Short term spatio-temporal variabilities of microphytobenthic assemblages in the mangrove ecosystems along the southwest coast of India

Microphytobenthos (MPB) or benthic microalgae are recognized as the dominant flora in shallow neritic ecosystems such as mangroves. The diversity, biomass and community composition of microphytobenthos in selected mangrove ecosystems along the southwest coast of India were assessed. A total of 110 species of microphytobenthos classified under 49 genera were identified during the study. Nine subclasses of MPB were identified—subclass Bacillariophycidae, Fragilariophycidae, Urneidophycidae, Coscinodiscophycidae, Melosirophycidae, Thalassiosirophycidae, Biddulphiophycidae, Oscillatoriophycidae and Nostocophycidae. Division Heterokontophyta (diatoms) was the best-represented division followed by division Cyanophyta. Diatoms comprised 81% of the microphytobenthic community in the selected mangrove ecosystems, and among these, the pennate diatoms (93%) dominated the total diatom population. The major diatom genera observed during the study were Amphora, Navicula, Pleurosigma, Gyrosigma, Mastoglia, Diploneis, Cocconeis, Lyrella, Entomoneis, Caloneis, Bacillaria and Nitzschia. Episammic and epipelic diatoms were observed (Cocconeis sp., Pleurosigma sp.) along Kollam and Kannur, whereas at Kochi, epipelic diatoms were dominant (Nitzschia sp., Navicula sp.). The study also provides a spatial comparison between the microphytobenthic communities within the study area and can act as a baseline data for the trophodynamic studies of the highly diverse ecologically and economically significant mangrove ecosystems.

Glacial melt disturbance shifts community metabolism of an Antarctic seafloor ecosystem from net autotrophy to heterotrophy

Climate change-induced glacial melt affects benthic ecosystems along the West Antarctic Peninsula, but current understanding of the effects on benthic primary production and respiration is limited. Here we demonstrate with a series of in situ community metabolism measurements that climate-related glacial melt disturbance shifts benthic communities from net autotrophy to heterotrophy. With little glacial melt disturbance (during cold El Niño spring 2015), clear waters enabled high benthic microalgal production, resulting in net autotrophic benthic communities. In contrast, water column turbidity caused by increased glacial melt run-off (summer 2015 and warm La Niña spring 2016) limited benthic microalgal production and turned the benthic communities net heterotrophic. Ongoing accelerations in glacial melt and run-off may steer shallow Antarctic seafloor ecosystems towards net heterotrophy, altering the metabolic balance of benthic communities and potentially impacting the carbon balance and food webs at the Antarctic seafloor.

Marine macrophyte composition during summer, southwest and northeast monsoons in Verde Island, Batangas City, Batangas, Philippines

Verde Island Passage is the world’s center of the center of marine shore fish biodiversity, located in southwestern Luzon Island in the Philippines. The passage is named after Verde Island, which is located at its middle. Although the island is located within a key biodiversity area, studies on its marine macrophyte biodiversity are scant. The present study was conducted to determine the composition, distribution, and dominance of marine macrophytes, specifically seaweeds and seagrass, during the northeast monsoon, summer, and southwest monsoon in four coastal areas in Verde Island using the line transect-quadrat method. Results revealed 63 macrophyte species, of which 92% were seaweeds and 8% were seagrass. The majority of the seaweeds were green (41%), followed by red (35%) and brown (16%) seaweeds. In most sites, the brown seaweed Padina sp. was dominant during summer and cover decreased during both monsoons. The green seaweed Neomeris annulata was present in all sites and seasons. The differences in cover across sites may be due to substratum type and topography where a relatively wider intertidal zone with different substratum such as rocky and sandy to muddy provides complex habitat promoting higher macrophyte cover. Temporal differences in marine macrophyte composition were more pronounced in macroalgae-dominated sites than in the seagrass-dominated site. Several important seaweeds that could be studied as bioindicators were recorded, such as Padina sp., which registered high cover especially in sites near populated areas and backyard pig pens. Ulva spp., which are known to form green tide blooms, and Caulerpa verticillata were also noted and should be monitored. Some red seaweeds with potential for cultivation were observed (i.e., Halymenia durvillei and Portieria hornemannii). Claudea sp., an uncommon red seaweed with limited distribution in the Philippines, was recorded and needs verification. This study is the first extensive marine macrophyte assessment at the heart of the Verde Island Passage. KEYWORDS: biodiversity, bioindicator, eutrophication, microbenthic algae, seagrass, Verde Island Passage

A record of diatom community response to catchment land-use change in Moreton Bay, Australia

Embayments and the biota they support are highly susceptible to disturbance within adjacent catchments. Examining the timing and magnitude of impacts arising from human-induced disturbance in these systems is often limited due to the absence of long-term monitoring. Moreton Bay in south-eastern Queensland is a shallow embayment that receives inflows from a 21220-km2 catchment. In this study, diatom abundances, pigment (chlorophyll-a, phaeopigments) and biogenic silica concentrations were evaluated in a composite sediment from central Moreton Bay to explore temporal trends in the photosynthetic community. The record extends from 1200 to 2011, incorporating the period of European settlement (c. 1840s) and rapid population growth and urbanisation of the catchment. The record shows that in central Moreton Bay bloom-forming marine diatoms (Thalassiosira, Thalassiothrix, Thalassionema) have increased in relative abundance since the mid-20th century, whereas the dominant benthic diatom (Paralia fenestrata) has declined. This transition most likely occurred in response to the compounding effects of increased delivery of nitrogen, fine sediments and pollutants to Moreton Bay as a consequence of changes in land use. The inferred historical decline in relative contributions of benthic microalgae to total primary production in central Moreton Bay has likely had wide-ranging ecological effects.

Extraction Improvement of the Bioactive Blue-Green Pigment "Marennine" from Diatom Haslea ostrearia's Blue Water: A Solid-Phase Method Based on Graphitic Matrices.

The compound “marennine” is a blue–green pigment produced by the benthic microalgae Haslea ostrearia, with pathogenicity reduction activities against some bacteria and promising potential as a natural pigment in seafood industries. After decades of research, the chemical family of this compound still remains unclear, mainly because structural studies were impaired by the presence of co-extracted compounds in marennine isolates. To improve the purity of marennine extract, we developed a novel extraction method using a graphitic stationary phase, which provides various advantages over the previous procedure using tandem ultrafiltration. Our method is faster, more versatile, provides a better crude yield (66%, compared to 57% for ultrafiltration) and is amenable to upscaling with continuous photobioreactor cultivation. Our goal was to take advantage of the modulable surface properties of the graphitic matrix by optimizing its interactions with marennine. As such, the effects of organic modifiers, pH and reducing agents were studied. With this improvement on marennine purification, we achieved altogether the isolation of a fucoidan-related, sulfated polysaccharide from blue water. Characterization of the polysaccharides fraction suggests that roughly half of UV-absorbing compounds could be isolated from the marennine crude extracts. The identification of sulfated polysaccharides could be a major breakthrough for marennine purification, providing targeted isolation techniques. Likewise, the added value of Haslea ostrearia and the role of polysaccharides in previous marennine chemical characterization and bioactivity studies remain to be determined.

Controls on diatom biogeography on South Carolina (USA) barrier island beaches

Benthic microalgae are of great significance to coastal productivity and nutrient cycling, yet determinants of their biogeography and community assembly remain unclear. We identified and compared spatial and environmental mechanisms that shape beach diatom biogeography and diversity at regional scales. We sampled at various spatial scales (from 10 cm to 120 km) from 4 barrier island beaches in South Carolina, USA, and characterized diatom assemblages using DNA metabarcoding. Twelve environmental variables from sediments, adjacent waters, and atmosphere were recorded. Despite attempts to sample from similar habitat types, environmental factors varied among islands. Correspondingly, biomass and α-diversity metrics likewise varied and were positively related to sediment nutrient levels. Community composition also varied, with each island dominated by different diatom taxa. Redundancy analysis revealed that spatial influences, in addition to environmental factors (water temperature and porewater nutrients), were significantly related to community dissimilarity (β-diversity). Variation partitioning attributed only ~5% of community variation to geographic distance alone, whereas 22% was explained by combined spatial/environmental factors. A high proportion (73%) of community dissimilarity remained unexplained, which likely implicates stochastic processes, although unmeasured physico-chemical or biological factors cannot be discounted. Weak spatial effects suggest that dispersal limitation was relatively unimportant, likely due to extensive sediment transport between beaches. Instead, spatially structured environmental variables appeared to condition beach diatom biogeography. These findings broaden our understanding of microbial biogeography to less well-studied microorganisms and marine habitats. More practically, results suggest some degree of predictability in diatom community changes in the face of anthropogenic challenges.

Effects of aquatic vegetation cover (Schoenoplectus decipiens) on microalgal biomass and assemblage structure in temporary wetlands of a semi-arid region (Eastern Cape Karoo, South Africa)

Temporary depression wetlands are often overlooked from a conservation and research perspective, despite recent evidence suggesting that their cumulative contribution to biodiversity at the landscape level is substantial. Here, we present observations aimed at understanding the significance of macrophyte cover in relation to the lower trophic levels, more particularly microalgae, within these highly dynamic wetlands. Thirteen such wetlands were sampled during October 2015, December 2015 and March 2016 in the Eastern Cape Karoo region of South Africa, to test the hypotheses that densely vegetated wetlands will have lower microalgal biomass and smaller algal size classes than sparsely vegetated wetlands. PERMANOVA results indicated that neither planktonic nor benthic microalgal biomass differed significantly between macrophyte cover categories (sparse, moderate and extensive cover), although there was a strong difference between the planktonic and benthic biotopes themselves. Planktonic and benthic microalgal assemblages were dominated by cryptophytes and chrysophytes (flagellates) throughout the study, with smaller nanoplankton being more abundant in wetlands with moderate or extensive macrophyte cover and larger microplankton dominating sparsely vegetated sites. Median benthic diatom species richness and diversity were higher under sparse macrophyte cover, but these differences were not significant, and no convincing evidence was found for an effect of macrophyte cover on microalgal biomass and assemblage composition in these temporary wetlands. Using distance-based Redundancy Analysis, dissolved inorganic nitrogen appeared to be the only environmental predictor for which a significant relationship with microalgal assemblage composition was reported. This study adds to the evidence from other assemblages (e.g. invertebrates) suggesting that the generalist nature of species occupying these systems allows them to adapt to the ever-changing conditions typical of ephemeral environments.

Changes in Benthic Microalgae Biomass and Brown Tiger Prawn Penaeus esculentus Body Condition Following a Large Cyclone-Driven Flood in Moreton Bay

Floods are extreme weather events that can rapidly change water quality in receiving estuaries. The delivery of nutrients to the coastal zone via floods may stimulate productivity; however, in urban areas, the degradation of water quality and influx of contaminants can negatively affect inhabiting biota. Determining flood effects on inhabiting biota is important for informing catchment management practices. We investigated the body condition response of a commercially important prawn species, the brown tiger prawn Penaeus esculentus, to a large cyclone-driven flood in an urbanized subtropical coastal bay. Prawns were caught 10 days before the flood, 11 days after the flood, and 53 days after the flood in bare substrate areas of central Moreton Bay in Australia. Stable isotopes (δ15N and δ13C) were determined for prawn muscle tissue, and lipid content and a length-weight (Fulton’s K) index were used to assess prawn body condition. There were two distinct isotope signatures of tiger prawns living in either riverine or marine influenced areas, suggesting different residency areas within the bay. A flood signal (lower δ13C values post-flood) was detected in prawns in the southern area closest to the Logan River. Condition indices showed a short-term increase in condition of prawns in these southern sites, with no apparent condition change in prawns at other sites. A concurrent pulse in benthic primary productivity (chlorophyll a biomass) was measured in this southern area. Our results suggest that nutrients from the flood stimulated benthic primary production that was transferred through the food web, with positive impacts on prawn nutrition at southern sites. With an expected increase in unpredictable weather, including floods, under a changing climate, understanding short- and long-term ecosystem responses in modified catchments is important for mitigating sediment erosion and estuarine and coastal infilling effects, while maintaining productivity benefits to fisheries in receiving estuaries.

Benthic microalgae are more 13C-depleted than phytoplankton in temperate flooded rice fields

We investigated seasonal changes in the δ13C levels of particulate organic matter (POM), which mainly consist of phytoplankton and microphytobenthos from three flooded rice fields treated with different types of fertilizer (chemical NPK, chemical PK, or organic fertilizers) in northeast Japan. Generally, microphytobenthos in lentic freshwater systems show higher levels of δ13C (about− 26‰) than phytoplankton (about− 32‰) due to 13C enrichment under limited resources of dissolved inorganic carbon (DIC) in the benthic boundary layer (BBL). However, our results showed that POM was more 13C-enriched than microphytobenthos regardless of the type of fertilizer applied. Overall mean POM and microphytobenthos δ13C levels in the fields ranged from − 27.5 to − 25.2‰ and − 30.3 to − 27.0‰, respectively. In contrast, δ13C levels in soil organic matter were temporally stable, with means ranging from − 27.6 to − 26.3‰. High δ13C levels in POM were due to limited DIC under conditions of high phytoplanktonic productivity and water stagnation in paddy systems, resulting in DI13C intake during photosynthesis. Conversely, microphytobenthos used more 13C-depleted DIC in the BBL, which was microbially regenerated from the SOM pool. Microphytobenthos in the rice fields showed similar seasonal variations in δ13C, decreasing sharply in late June and then increasing again. This was possibly caused by changes in DIC availability or the growth rates of microphytobenthos during that period. The present results provide basal information about producer-specific δ13C variations in two major microalgal producer groups, phytoplankton and microphytobenthos, in temperate rice paddy wetlands.

Sulfur isotopes (δ34S) in Arctic marine mammals: indicators of benthic vs. pelagic foraging

Consumer tissue stable carbon isotope compositions (δ13C) are well established indicators of benthic and pelagic foraging in marine ecosystems. Stable sulfur isotope compositions (δ34S) are also potentially useful in this regard but have not been widely utilized outside of estuaries and salt marsh ecosystems. To test the ability of δ13C and δ34S to reflect benthic and pelagic foraging, we analyzed the stable carbon, nitrogen (δ15N), and sulfur isotope compositions of bone collagen from walrus (an obligate benthic feeder) and ringed seal (a mixed benthic/pelagic feeder) sampled from across the North American Arctic. Both had relatively low δ34S values compared to those typically observed in marine consumers. These data suggest an important role for benthic microalgae in coastal marine food webs in the Arctic. At all of the 10 locations where both taxa could be sampled, walrus had lower δ34S values than ringed seal, suggesting that this measurement is a useful indicator of benthic and pelagic foraging in nearshore Arctic environments. Contrary to expectations, there were no consistent differences in δ13C between walrus and ringed seal at any of these sites, suggesting that this measurement may not always be best interpreted in light of benthic vs. pelagic foraging, particularly when comparisons are made across trophic levels. When the foraging ecology of a consumer is unknown, our data suggest that δ34S may be a more sensitive indicator of the relative importance of benthic and pelagic prey in the diet than δ13C.

Ecological Engineering for the Optimisation of the Land-Based Marine Aquaculture of Coastal Shellfish.

Whilst the demand for nutritious and sustainable seafood is increasing, fishing yields are declining due to overfishing and climate change. The inshore aquaculture of marine molluscs—e.g., the suspension-feeding cockle Cerastoderma edule for NW Europe—might be an alternative practice if cost-effective and nature-based technology enhances growth and survival. Our inshore experiments revealed that increasing the seawater residence time resulted in improved water quality. The reduction in sediment loads and stimulation of pelagic microalgal growth resulted in enhanced shell growth and meat content of the wild cockles seeded into the system. Shorter residence times resulted also in an increase in benthic microalgae, but the concurrent increase in silt content of the sediment appeared to hamper effective filtration by cockles. The growth conditions (with respect to the water and sediment quality) for the inshore cultivation of cockles can indeed be improved by means of ecological engineering, suggesting that the inshore aquaculture of marine shellfish can provide sustainable food and income for coastal communities, in particular when the shellfish farms are located in low-lying salinized coastal areas where common agriculture practices are no longer profitable. The involvement of the shellfishery industry was and will be crucial for studying and understanding the complex practice of cockle cultivation.

The First Finding of Radiolaria Arachnocorys circumtexta Haeckel, 1860 and the Bottom Microalgae in Brown Alga Cystoseira barbata (Stackhouse) C.A. Agardh Epiphyton (Crimea, Black Sea)

The planktonic species Radiolaria of Arachnocorys circumtexta Haeckel, 1860 (Radiolaria, class Nasseillaria, family Lophophaenidae Haeckel, emend. Petrushevskaya, 1971) in the epiphyton of the brown alga Cystoseira barbata (Stackhouse) C.A. Agardh in August 2002 in Martynov Bay (Sevastopol, Crimea) at a depth of 2.5 m at a water temperature of 24.4°C and a salinity of 18‰ was the first time in the Black Sea. Before, this species was indicated by E. Haeckel in the Mediterranean Sea plankton. For the Black Sea, this species is probably invasive. The sizes of Radiolaria blacksea specimens the correspond to the literature data. In addition to Radiolaria and microalgae have been found in the epiphyton of C. barbata, including 14 species of Bacillariophyta and one species of Dinophyta from the genus Prorocentrum Ehrenb. Marine species predominate (67%) and 53% of all species encountered are β-mesosaprobionts – indicators of moderate organic water pollution. 33% of cosmopolites are found in all geographical zones from the Arctic to the Antarctic waters. The aim of this report is presentation of new information about a rare modern Radiolaria and the taxa of benthic microalgae Cystoseira barbata epiphyton from the Black Sea.

The fiddler crab Minuca pugnax () (Decapoda: Brachyura: Ocypodidae) reduces saltmarsh algae in its expanded range

Abstract It is well known that species across the world are expanding or shifting their ranges because of climate change. Yet, we know little about their impact on the habitats they colonize. In an observational study, we examined the effect of the fiddler crab Minuca pugnax (Smith, 1870) on benthic microalgal biomass in salt marshes in its expanded range (northeastern Massachusetts, USA). We found that plots with M. pugnax had, on average, 74% lower diatom biomass and 77% lower cyanobacteria biomass than plots without M. pugnax. Our results indicate that this climate migrant can impact saltmarsh functioning by limiting benthic microalgal biomass.