Benthic Primary Production Research Articles

Fish species richness is a key predictor of community biomass and productivity in littoral regions of Severn Sound, an embayment of southern Georgian Bay, Lake Huron

Catches from standardized littoral electrofishing (EF) surveys (1990–2016) at various locales in Severn Sound, Georgian Bay, were analyzed. Catches were adjusted for size-selectivity using published results of laboratory immobilization experiments. Adjusted abundance-mean size relationships were consistent with the metabolic theory of ecology where body size has a central role in structuring community features. Relationships among species richness and areal estimates of biomass and annual production of the adjusted catches were assessed. Richness was the key variable driving other community metrics and was, in turn, largely driven by habitat fetch metrics and sampling time of day. Richness, biomass, and production decreased with increasing maximum effective fetch. Richness increased with time after sunset. Year and locale had smaller roles in variation of community metrics with more vegetated/ less urbanized areas having higher values. Higher fish production is expected in sheltered areas where the contributions of allochthonous and benthic primary production are expected to be greater. Further analyses using additional EF datasets from Great Lakes’ littoral zones should increase understanding of the differences between littoral and offshore fish productivity and help guide management of littoral habitats to ensure healthy fish communities.

Data on phenological changes of benthic primary producers from Lake Saint-Pierre (1982-2019), Lake Müggelsee (2000-2021), Limnotron warming experiments and a literature synthesis

Data on phenological changes of benthic primary producers from Lake Saint-Pierre (1982-2019), Lake Müggelsee (2000-2021), Limnotron warming experiments and a literature synthesis

Going under: The implications of sea‐level rise and reduced light availability on intertidal primary production

AbstractEstuarine intertidal flats are known for high rates of primary production, however, globally these ecosystems are under threat from rising sea‐level and accelerated inputs of terrestrial sediments. These stressors simultaneously alter the duration of submersion/emersion periods and water‐column turbidity impacting seafloor photoperiods. To assess how changes in submergence time and water‐clarity can affect benthic primary production, we derived in situ seasonal photosynthesis‐irradiance (P‐I) curves over 2 yr. These were conducted during submerged and emerged periods in a seagrass meadow (Zostera muelleri) and an unvegetated sandflat (dominated by microphytobenthos). P‐I curves showed strong light responses during submergence in both habitats and seagrass during emergence, but in the exposed sandflat there was little relationship between light availability and photosynthesis. Light‐saturated measures of gross primary production (GPPsat) were 2.1 (submerged) and 4.1 times (emerged) higher in the seagrass than the sandflat habitat. Submerged GPPsat was always higher than emerged GPPsat, but this difference was much more pronounced in the sandflat habitat (2.4 vs. 1.3 times for seagrass). Integrating seasonally averaged P‐I curves for both tidal states into a simple model suggests that increasing submergence time could increase primary production in both habitats. However, reductions in water‐clarity will decrease submerged primary production; an effect that will be exacerbated with sea‐level rise. The sandflat trophic state was more sensitive to these environmental stressors because emerged production could not compensate for reductions during submergence. Collectively, regional management of water‐clarity may be key to providing resilience to intertidal habitats, against the inevitable effects of sea‐level rise.

Primary production modeling identifies restoration targets for shifting shallow, eutrophic lakes to clear-water regimes

Benthic primary production (BPP) plays an important functional role in lakes, improving water quality by stabilizing clear-water regimes. Shallow, eutrophic lakes lacking BPP communities can be difficult to restore because self-stabilizing feedbacks of phytoplankton dominance can impede the establishment of BPP. BPP in lakes is light limited, and ecosystem models can provide guidance for determining the water clarity necessary to re-establish BPP dominance. We developed a multi-tiered framework for the restoration of shallow, eutrophic lakes that incorporates multiple turbidity sources, lake morphometry, and water-level fluctuations to determine water-clarity thresholds above which BPP dominance may be established. We present a case study applying this restoration target framework to a large, shallow lake (Utah Lake, Utah, USA), where water clarity was greatly impeded by sediment resuspension and high algal biomass. Our analysis, which used commonly available lake-monitoring data, indicated that a return to BPP dominance is possible in Utah Lake, particularly if external nutrient loading to its shallow, wind-protected bays is reduced. Our novel framework incorporates regime shift theory to improve shallow, eutrophic lake restoration efforts. By incorporating ecological feedbacks when identifying the restoration targets necessary for returning a lake to a self-stabilizing, clear-water regime, this restoration target framework offers economical and logistical advantages over strategies that focus solely on phytoplankton management or fish biomanipulation.

Sandy seepage faces as bioactive nitrate reactors: Biogeochemistry, microbial ecology and metagenomics

Subterranean estuaries are highly dynamic in processing dissolved inorganic nitrogen (DIN). Here we investigate DIN turnover in surface sediments (0–20 cm depth) at the higher, medium and lower intertidal of a seepage face, i.e., the outer “mouth” of the subterranean estuary, during four consecutive seasons in Sanggou Bay, China. Throughout the studied period, ammonium (NH4+) and nitrite (NO2−) concentrations in the sampled porewaters did not vary significantly with depth or season. In contrast, peaks in porewater nitrate (NO3−) concentration and decreases in δ15N-NO3− and δ18O-NO3− were observed in the 15–20 cm depth (bottom) sediment, particularly during summer and autumn. Coupled with NO3− production, the sediment total nitrogen was also markedly peaking in the bottom layer of the studied seepage face. Together with abundant heterotrophic microbes in the sediment, this NO3− accumulation was linked to a reaction chain including organic matter decomposition, ammonification and nitrification. During winter, porewater enrichment in total nitrogen occurred closer to the surface of the seepage face but triggered also active NO3− production. This pattern reinforced the importance of pelagic organic matter supply on NO3− production. In the shallower depths of the seepage face (<12 cm), active net NO3− removal occurred except in winter. The isotopic fractionation (δ15N-NO3− and δ18O-NO3−) and metagenomic results revealed denitrification as the main pathway for NO3− reduction. Biological assimilation from benthic primary producers may also consume a fraction of NO3− at the sediment water interface. Both NO3− production and removal significantly varied in magnitude with season (−13.6 to 6.2 nmol cm−3 h−1). Substrate supply was the key driver for nitrate cycling, as evidenced by the high NO3− production rate in spring by comparison to autumn. The highest NO3− turnover rates were found in summer, suggesting the combined influence of advection rates and sediment microbiota composition. In spite of active removal (peak NO3− removal capability: 61%), a significant amount of NO3− was still transported from the seepage face into the bay waters. The magnitude of NO3− fluxes ranged from 312 to 476 kg N d−1, accounting for approximately 15% of the total exogenous NO3− loading into the bay. NO3− isotopic fingerprint revealed chemical fertilizer as the main source of terrestrial NO3− in SGD, highlighting the importance of land use to coastal system nitrogen budgets.

Depth and basin shape constrain ecosystem metabolism in lakes dominated by benthic primary producers

AbstractMetabolism is one of the most fundamental ecosystem processes, but the drivers of variation in metabolic rates among lakes dominated by benthic primary producers remain poorly constrained. Here, we report the magnitudes and potential drivers of whole‐lake metabolism across 43 Swedish arctic–alpine lakes, based on the free‐water diel oxygen technique with sondes deployed during the open‐water season near the surface and bottom of the lakes. Gross primary production (GPP) and ecosystem respiration (R) were strongly coupled and ranged from 0.06 to 0.45 mg and 0.05 to 0.43 mg L−1 d−1 among lakes. On average, GPP and R decreased eightfold from relatively shallow to deep lakes (mean depth 0.5–10.9 m) and twofold from concave to convex lakes (mean depth: maximum depth 0.2–0.5). We attribute this to light limitation and shape‐specific sensitivity of benthic GPP to disturbance by lake ice. Net ecosystem production (GPP‐R) ranged from −0.09 to 0.14 mg L−1 d−1 and switched, on average, from positive to negative towards deeper lakes and lakes richer in dissolved organic carbon (DOC; 0.5–7.4 mg DOC L−1). Uncertainties in metabolism estimates were high (around one and three times mean R and GPP), especially in deep lakes with low insulation and diurnally variable wind speed. Our results confirm the role of DOC in stimulating net heterotrophy and highlight novel effects of lake shape on productivity in benthic‐dominated lake ecosystems and its response to changes in lake ice cover.

Landscape determinants of pelagic and benthic primary production in northern lakes.

Global change affects gross primary production (GPP) in benthic and pelagic habitats of northern lakes by influencing catchment characteristics and lake water biogeochemistry. However, how changes in key environmental drivers manifest and impact total (i.e., benthic + pelagic) GPP and the partitioning of total GPP between habitats represented by the benthic share (autotrophic structuring) is unclear. Using a dataset from 26 shallow lakes located across Arctic, subarctic, and boreal northern Sweden, we investigate how catchment properties (air temperature, land cover, hydrology) affect lake physico-chemistry and patterns of total GPP and autotrophic structuring. We find that total GPP was mostly light limited, due to high dissolved organic carbon (DOC) concentrations originating from catchment soils with coniferous vegetation and wetlands, which is further promoted by high catchment runoff. In contrast, autotrophic structuring related mostly to the relative size of the benthic habitat, and was potentially modified by CO2 fertilization in the subarctic, resulting in significantly higher total GPP relative to the other biomes. Across Arctic and subarctic sites, DIC and CO2 were unrelated to DOC, indicating that external inputs of inorganic carbon can influence lake productivity patterns independent of terrestrial DOC supply. By comparison, DOC and CO2 were correlated across boreal lakes, suggesting that DOC mineralization acts as an important CO2 source for these sites. Our results underline that GPP as a resource is regulated by landscape properties, and is sensitive to large-scale global changes (warming, hydrological intensification, recovery of acidification) that promote changes in catchment characteristics and aquatic physico-chemistry. Our findings aid in predicting global change impacts on autotrophic structuring, and thus community structure and resource use of aquatic consumers in general. Given the similarities of global changes across the Northern hemisphere, our findings are likely relevant for northern lakes globally.

Carbon dioxide limitation of benthic primary production in a boreal lake

Abstract Gross primary production (GPP) by benthic microalgae growing on soft sediments is an important contributor to lake productivity in many lakes world‐wide. As benthic microalgae have access to nutrients in the sediment they have been regarded as primarily controlled by light, while the role of CO2 as a limiting factor for benthic GPP in lake ecosystems is largely unknown. In this study, we experimentally tested for CO2 limitation of benthic GPP by collecting littoral surface sediments, with associated benthic microalgae, from a typical boreal lake. Intact sediment cores were incubated at different depths (light conditions) after addition of dissolved inorganic (bicarbonate) or organic (DOC; glucose) carbon as direct and indirect sources of CO2, respectively. Benthic microalgal GPP was stimulated by both dissolved inorganic carbon and DOC additions at high, but not at low, light levels. This study shows that benthic microalgal GPP can be CO2‐limited when light is not limiting and suggests that both direct (e.g., via groundwater inflow) and indirect (via mineralisation of DOC) CO2 supply can stimulate benthic GPP.

The effects of subterranean estuary dynamics on nutrient resource ratio availability to microphytobenthos in a coastal lagoon

Causal links between subterranean estuary (STE) dynamics, their climatological drivers, and the ecology of coastal ecosystems have remained elusive. Yet, establishing these connections is essential for fully integrated management of coastal ecosystems. We test, in a semi-arid climate, whether the composition of submarine groundwater discharge (SGD) to a lagoon can be regulated by the annual oscillation of the local STE, itself driven by groundwater recharge variability. We study STE outflow samples gathered monthly for a year in the Ria Formosa lagoon, examining the temporal dynamics of salinity, EH, pH (Total scale), dissolved oxygen and nutrient (PO43−, NO2−, NO3−, NH4+, and Si(OH)4) concentrations under the local hydrological regime. The objectives were threefold: (1) to determine the annual variability of nutrient content and N:P:Si stoichiometry in SGD into the lagoon; (2) to identify the main drivers of variability in SGD composition and stoichiometry and their interactive effects; (3) to discuss links to, and implications for, ecosystem function that could help define expectations of cause-effect relationships and be useful for environmental management of the lagoon and similar systems elsewhere.We find that the terrestrial groundwater recharge cycle drives the expansion and contraction of the subterranean estuary on annual timescales, causing the pH of SGD to fluctuate in opposition to continental groundwater level. The annual dynamics of the STE and the resulting pH oscillation determine the annual variability of nutrient composition ratio in SGD and shape benthic primary production dynamics. When saltwater intrusion occurs, the pH within SGD increases, enhancing nitrification and desorption of exchangeable phosphorus, while silicate fluxes increase with seawater retreat. The result is that nutrient resource ratio availability for coastal primary production depends on the fresh groundwater level. This implies that ecosystem function in such systems is more tightly related to the dynamics of linked groundwater reservoirs than previously thought.

Filamentous Algae Blooms in a Large, Clear-Water Lake: Potential Drivers and Reduced Benthic Primary Production

An apparent proliferation of filamentous algal blooms (FABs) in pristine lakes around the world is a source of concern. However, little is known about the predominant drivers and effects of such FABs on lake ecosystems. We observed FABs in a large clear-water lake (Bear Lake, UT/ID, USA) and analyzed long-term lake monitoring data and algal stable isotopes for changes in climate, food webs and anthropogenic nutrient loading, respectively, as potential local drivers of FAB formation. Furthermore, we quantified in situ metabolism rates on rocks with and without FABs at two locations. Long-term monitoring data revealed increasing summer water temperatures (2009 to 2020) and decreasing winter ice cover (1923 to 2021). The FABs had δ15N values that were higher than 0 ‰, indicating a potential nutrient influx to Bear Lake from livestock or human waste. Climate change and anthropogenic nutrients may thus have facilitated FAB occurrence. Contrary to expectation, the FABs exhibited significantly lower gross primary production rates compared to low-biomass periphyton communities, indicating potentially negative effects of FAB proliferations on lake food webs. Our results highlight the need for expanding lake monitoring programs to include littoral zones to detect and mitigate changes occurring in lakes.

Organic matter seasonality and ecosystem metabolism in two tropical first-order streams

Dissolved and particulate organic matter are the energy source for secondary production in forested streams. Cycling of or¬ganic matter and stream ecosystem functioning are linked to organic matter input and storage capacity and timing. This study assessed the seasonal variation (dry and rainy seasons) of environmental parameters, organic matter stock and input, and stream metabolism in two first-order tropical streams in the Selva Lacandona, Mexico. We also aimed to identify the drivers of organic matter and stream metabolism seasonality. We found seasonal variation in organic matter stock and input correlated with trop¬ical seasonality. Dissolved organic matter and seston increased in the rainy season, while benthic primary producers and leaf litter stock and input increased in the dry season correlated with lower water discharge. Gross primary production increased in the dry season, while ecosystem respiration did not differ between seasons. Seasonality defined by the rainfall pattern and its effect on stream hydrology is the main driver of organic matter dynamics in tropical streams. However, environmental parameters and organic matter stock and input were not good predictors of stream metabolism.

Benthic-Pelagic Coupling of Marine Primary Producers Under Different Natural and Human-Induced Pressures’ Regimes

Marine primary producers are highly sensitive to environmental deterioration caused by natural and human-induced stressors. Following the Water Framework Directive and the Marine Strategy Framework Directive requirements, the importance of using the different primary producers of the coastal marine ecosystem (pelagic: phytoplankton and benthic: macroalgae and angiosperms) as appropriate tools for an integrated assessment of the ecological status of the coastal environment has been recognized. However, the processes by which water column characteristics and phytobenthic indicators are linked have not been systematically studied. Based on a large dataset from three Mediterranean sub-basins (Adriatic, Ionian and Aegean Seas) with different trophic conditions, this study aims to explore the coupled responses of benthic and pelagic primary producers to eutrophication pressures on a large scale, focusing on the structural and functional traits of benthic macroalgal and angiosperm communities, and to investigate the key drivers among the different eutrophication-related pelagic indicators (such as nutrient and Chl-a concentrations, water transparency, etc.) that can force the benthic system indicators to low ecological quality levels. In addition to the effects of high nutrient loading on phytoplankton biomass, our results also show that increased nutrient concentrations in seawater have a similar effect on macroalgal communities. Indeed, increasing nutrient concentrations lead to increased coverage of opportunistic macroalgal species at the expense of canopy-forming species. Most structural traits ofPosidonia oceanica(expressed either as individual metrics: shoot density, lower limit depth and lower limit type, or in the context of PREI index) show opposite trends to increasing levels of pressure indicators such as ammonium, nitrate, phosphate, Chl-a and light attenuation. Furthermore, our results highlight the regulating effect of light availability on the ecological status of seagrass meadows (Posidonia oceanicaandCymodocea nodosa). Increasing leaf length values ofC. nodosaare closely associated with higher turbidity values linked to higher phytoplankton biomass (expressed as Chl-a). Overall, the coupling of pelagic and benthic primary producers showed consistent patterns across trophic gradients at the subregional scale.

Benthic and Pelagic Contributions to Primary Production: Experimental Insights From the Gulf of Trieste (Northern Adriatic Sea)

Although the 14C-method remains one of the most sensitive measures of primary production in marine ecosystems, few data from coastal sublittoral areas are available. We applied an integrated approach to quantify the benthic (PPs) and pelagic (PPw) contributions to total primary production (PPt) in a 17-m deep coastal site. From March 2015 to March 2019, we carried out 16 in situ experiments on a seasonal basis, at the LTER site C1, whereas benthic rates were estimated in the laboratory. To relate PP to seawater physical features and to the water column stability, the Brunt-Väisälä frequency was calculated. We further related our PP rates to the abundance, biomass, main taxonomic groups and diversity of eukaryotic phytoplankton and microphytobenthos (MPB). In November 2018, the maximum PPw (6.71 ± 0.82 µgC L-1 h-1) was estimated at the surface layer, in correspondence to the highest value of dinoflagellates biomass (29.35 µgC L-1), on the account of small (&amp;lt;20 µm) naked and thecate forms. PPi, integrated over the water column, displayed the highest values in July 2017 and July 2018. In sediments, negative PPs values were estimated in late autumn/winter, when minima of MPB abundance occurred. The highest rates were displayed in January 2018 and October 2016 (28.50 and 17.55 mgC m-2 h-1), due to the presence of dominant diatoms Paralia sulcata and Nitzschia sigma var. sigmatella, respectively. The PPs contribution to PPt was negligible (&amp;lt;2%) in 6 out of 16 experiments, with a mean value of 11.3% (excluding negative PPs values) over the study period, while it reached up to 43% in January 2018. The principal component analyses revealed that nutrients availability affected the seasonal development of pelagic and benthic phototrophs and primary production more than the physical variables, except for the surface layer of the water column where temperature and salinity were the main drivers. Our results add on the limited database on primary production in sublittoral areas and represent one of the few attempts, on a global scale, of integrating pelagic and benthic primary production using the 14C method to quantify the overall ecosystem productivity.

Benthic-Pelagic state changes in the primary trophic level of an ancient tropical lake

Many large, ancient lakes support primarily planktonic-driven food webs. In contrast, the lowest trophic levels of the Malili Lakes of Sulawesi Island, Indonesia are dominated by benthic diatom communities composed mainly of endemic species. Centric diatoms are not observed in the current diatom assemblage and pennate pelagic species are rare. Using two deep drill-cores from Lake Towuti, we investigated whether the lake has always been dominated by benthic primary production. Despite the ultra-oligotrophic conditions observed in the lake today, we observed state changes characterized by productive planktonic communities and less productive, benthic-dominated diatom assemblages. Two periods of planktonic production, each lasting approximately 50 kyr, were dominated by a complex mixture of Aulacoseira spp., with valve densities >1.0 × 10 9 valves/g with a maximum biovolume of 3.5 × 10 12 μm 3 /g. A similar planktonic assemblage was observed at much lower abundances (<10 7 valves/g) in the deeper sediments (>1 Ma), during the earliest stages of lake formation. Two periods of increased benthic primary production of approximately ~11 kyr in duration, originating from the littoral zone of the lake, were also observed, one between the two planktonic phases and one above the last planktonic maxima. The benthic periods were dominated by Cymbopleura spp., with valve densities of approximately 2.0 × 10 8 valves/g and a maximum biovolume of 1.2 × 10 11 μm 3 /g. Nonmetric multidimensional scaling analysis of sediment chemistry revealed that the benthic and pelagic states clustered with distinct chemical environments. The benthic phases were associated with well-mixed conditions in the lake whereas the planktonic phases were related to rapidly reoccurring water column mixing followed by intense stratification that generate nutrient recycling events. We conclude that lake mixing and nutrient cycling regimes regulated, in part, the switch between benthic and pelagic states in Lake Towuti. • Major switches between benthic and pelagic states in lake's diatom fossil record • Long-term planktonic diatom dominance in current benthic Lake Towuti • Planktonic communities established and persisted naturally for ~50 ky each • Both planktonic diatom communities had similar composition and abundance • Switches in state potentially linked to shifts in lake mixing regime

Effects of Habitat-Specific Primary Production on Fish Size, Biomass, and Production in Northern Oligotrophic Lakes

Ecological theory predicts that the relative distribution of primary production across habitats influence fish size structure and biomass production. In this study, we assessed individual, population, and community-level consequences for brown trout (Salmo trutta) and Arctic char (Salvelinus alpinus) of variation in estimated habitat specific (benthic and pelagic) and total whole lake (GPPwhole) gross primary production in 27 northern oligotrophic lakes. We found that higher contribution of benthic primary production to GPPwhole was associated with higher community biomass and larger maximum and mean sizes of fish. At the population level, species-specific responses differed. Increased benthic primary production (GPPBenthic) correlated to higher population biomass of brown trout regardless of being alone or in sympatry, while Arctic char responded positively to pelagic primary production (GPPPelagic) in sympatric populations. In sympatric lakes, the maximum size of both species was positively related to both GPPBenthic and the benthic contribution to GPPWhole. In allopatric lakes, brown trout mean and maximum size and Arctic char mean size were positively related to the benthic proportion of GPPWhole. Our results highlight the importance of light-controlled benthic primary production for fish biomass production in oligotrophic northern lakes. Our results further suggest that consequences of ontogenetic asymmetry and niche shifts may cause the distribution of primary production across habitats to be more important than the total ecosystem primary production for fish size, population biomass, and production. Awareness of the relationships between light availability and asymmetric resource production favoring large fish and fish production may allow for cost-efficient and more informed management actions in northern oligotrophic lakes.

Freshwater snail and shrimp differentially affect water turbidity and benthic primary producers

Benthic macroinvertebrates play key roles in shallow aquatic ecosystems and can contribute substantially to aquatic food webs. However, how macroinvertebrates with different behaviors (for example, pertaining to locomotion, foraging and burrowing) impact water quality and primary producers has not been fully explored. Here, we performed two consecutive microcosm experiments to test the effects of (1) macroinvertebrates with different behaviors (a low mobility scraper aquatic snail Bellamya aeruginosa and a high mobility shredder freshwater shrimp Macrobrachium nipponense) and (2) different shrimp biomasses on water clarity and the composition of benthic primary producers. The results showed that presence of snails significantly increased the biomass of filamentous green algae and decreased the biomass of periphyton. In contrast, presence of shrimp significantly decreased the biomass of filamentous green algae and increased the biomass of periphyton, and these effects were biomass dependent. Filamentous green algae disappeared when shrimp biomass reached 9.8 ​g ​m−2. No interactive effects of snail and shrimp presence were found. This could be attributed to different food preferences by the two consumers, with snails preferring periphyton (mainly diatoms) and shrimp preferring filamentous green algae. The presence of snails decreased water turbidity, while shrimp increased water turbidity, which showed a hump-shaped response to shrimp biomass with a peak at 24.2 ​g ​m−2. These results are likely because the snail is a low mobility grazer and can filter suspended particles, while the shrimp is a high mobility shredder with burrows, which can strongly disturb sediment. The decrease in water disturbance at high shrimp biomass might be due to food limitation, thus reducing burrowing and foraging activities. Neither snail nor shrimp affected the biomass of H. verticillata, while the biomass of V. spinulosa increased with shrimp biomass. The reason for this could be that shrimp increased nutrient availability and decreased the growth of filamentous green algae that compete with macrophytes. Our study demonstrated that different macroinvertebrates have complementary functions in benthic habitats; thus, maintaining macroinvertebrate diversity is important for shallow aquatic ecosystems. Furthermore, the freshwater shrimp M. nipponense could be a potential consumer to control filamentous green algal blooms in its native range, but their biomass should be taken into consideration.

Daily and seasonal population dynamics of Brachynotus sexdentatus (Risso, 1827) (Varunidae: Brachyura: Decapoda) in a temperate coastal lake

The grapsoid Brachynotus sexdentatus (Risso, 1827) is a small sized Mediterranean crab, whose ecology is poorly known despite frequently cited in the scientific literature. High densities occasionally recorded in estuarine habitats suggest this opportunistic species might play a functional role in connecting benthic primary production with consumption at higher trophic levels. The brackish Lake Ganzirri (north-eastern Sicily) hosts a population of this varunid crab, whose differential distribution of juveniles and adults, respectively found on hard and soft substrates, involves different habitat preferences and consequent resource partitioning. Investigation on daily and seasonal dynamics of the soft-bottom dwelling adults showed a male biased population, with size-related differences between sex, station, season and female reproductive phase. Our data, suggesting an annual life span, prolonged spawning and related continuous recruitment, are in agreement with the intrinsic unpredictability of the colonized brackish environment. At last, preliminary in aquaria observations on the characteristic male cheliped vesicles, showed they might involved in agonistic and courtship behaviour.

Seasonal Dietary Shifts of the Gammarid Amphipod Gondogeneia antarctica in a Rapidly Warming Fjord of the West Antarctic Peninsula

The amphipod Gondogeneia antarctica is among the most abundant benthic organisms, and a key food web species along the rapidly warming West Antarctic Peninsula (WAP). However, little is known about its trophic strategy for dealing with the extreme seasonality of Antarctic marine primary production. This study, using trophic markers, for the first time investigated seasonal dietary shifts of G. antarctica in a WAP fjord. We analyzed δ13C and δ15N in G. antarctica and its potential food sources. The isotopic signatures revealed a substantial contribution of red algae to the amphipod diet and also indicated a significant contribution of benthic diatoms. The isotope results were further supported by fatty acid (FA) analysis, which showed high similarities in FA composition (64% spring–summer, 58% fall–winter) between G. antarctica and the red algal species. G. antarctica δ13C showed a small shift seasonally (−18.9 to −21.4‰), suggesting that the main diets do not change much year-round. However, the relatively high δ15N values as for primary consumers indicated additional dietary sources such as animal parts. Interestingly, G. antarctica and its potential food sources were significantly enriched with δ15N during the fall–winter season, presumably through a degradation process, suggesting that G. antarctica consumes a substantial portion of its diets in the form of detritus. Overall, the results revealed that G. antarctica relies primarily on food sources derived from benthic primary producers throughout much of the year. Thus, G. antarctica is unlikely very affected by seasonal Antarctic primary production, and this strategy seems to have allowed them to adapt to shallow Antarctic nearshore waters.

Factors regulating lake periphyton biomass and nutrient limitation status across a large trophic gradient

Abstract Because of the historical focus of limnology on pelagic processes, the factors controlling lake periphyton growth and nutrient limitation are understudied compared to the phytoplankton. We deployed nutrient‐diffusing substrata at 28 sites spanning a wide trophic status gradient in Lakes Superior and Michigan to assess periphyton biomass accrual on control substrata and the response of periphyton to single and combined phosphorus (P) and nitrogen (N) additions. Periphyton growth was unimodally related to a composite metric of site trophic status, with highest biomass at mesotrophic sites and lower growth at oligotrophic and highly eutrophic sites. Contrary to expectations, P limitation was rare. Instead, several lines of evidence pointed to primary N or N + P co‐limitation of periphyton. Limitation extent was negatively related to site trophic status, with stronger nutrient limitation at oligotrophic sites. Our results support the hypothesis that phytoplankton and periphyton biomass respond differently to nutrient enrichment and suggest that different nutrients may limit pelagic and benthic primary production, even in the same system. Our findings also support the use of periphyton as an early warning indicator of nutrient pollution and help explain why large, oligotrophic lakes may be especially susceptible to localised benthic algal blooms.

Benthic nutrients and oxygen fluxes at the water sediment interface in a pearl farming atoll (Ahe, Tuamotu, French Polynesia)

Benthic exchanges of oxygen and nutrient at the sediment-water interface were investigated under light and dark conditions at 5 selected sites in a sub-tropical atoll. Mean oxygen fluxes were - 1316.5 ± 242.0 μmol m−2 h−1 and mean effluxes of oxygen under light conditions were 2231.7 ± 626.4 μmol m−2 h−1, presumably due to microphytobenthos present at the sediment-water interface. The consequences of this high related productivity was a systematic consumption of nutrients (DIN, PO4 and Si(OH)4) during almost all light incubations, contrasting with the effluxes of nutrients during dark incubations. Our results suggest that the sediments were net autotrophic and the oxygen balance in favor of microbenthic production when compared to community demand. Diurnal rates of gross benthic primary productivity were high (3423 ± 1192 μmol m−2 h−1) which emphasize the role of microphytobenthos in maintaining the oxygen reservoir in tropical lagoons.