Benthic Production Research Articles

A generic approach to develop a trait-based indicator of trawling-induced disturbance

Biological trait analysis has become a popular tool to infer the vulnerability of benthic species to trawling-induced disturbance. Approaches using multiple traits are being developed, but their generic relevance across faunal components and geographic locations remains poorly tested, and the importance of confounding effects are poorly recognised. This study integrates biological traits of benthic species that are responsive to instantaneous effects of trawling (i.e. sensitivity) and traits expressing recoverability over the longer term (i.e. years). We highlight the functional independence between these 2 components in response to trawling, test the behaviours of single and combined traits and account for potential confounding effects of environment and trawling intensity on benthic communities through variation partitioning. Two case studies are considered: epibenthos from the Bay of Biscay and endobenthos of the Dutch sector of the North Sea. The response to trawling is most pronounced when multiple traits covering different aspects that determine population dynamics (i.e. sensitivity and recoverability) are combined, despite confounding effects between gradients of benthic production and trawling intensity, especially for endobenthos. The integration of traits reflecting both sensitivity and recoverability provides complementary information on the faunal response to trawling, bridging the gap between fishing impact assessments and benthic community status assessments.

Large Pelagic Fish Are Most Sensitive to Climate Change Despite Pelagification of Ocean Food Webs

Global climate change is expected to impact ocean ecosystems through increases in temperature, decreases in pH and oxygen, increased stratification, with subsequent declines in primary productivity. These impacts propagate through the food chain leading to amplified effects on secondary producers and higher trophic levels. Similarly, climate change may disproportionately affect different species, with impacts depending on their ecological niche. To investigate how global environmental change will alter fish assemblages and productivity, we used a spatially explicit mechanistic model of the three main fish functional types reflected in fisheries catches (FEISTY) coupled to an Earth system model (GFDL-ESM2M) to make projections out to 2100. We additionally explored the sensitivity of projections to uncertainties in widely used metabolic allometries and their temperature dependence. When integrated globally, the biomass and production of all types of fish decreased under a high emissions scenario (RCP 8.5) compared to mean contemporary conditions. Projections also revealed strong increases in the ratio of pelagic zooplankton production to benthic production, a dominant driver of the abundance of large pelagic fish vs. demersal fish under historical conditions. Increases in this ratio led to a “pelagification” of ecosystems exemplified by shifts from benthic-based food webs toward pelagic-based ones. The resulting pelagic systems, however, were dominated by forage fish, as large pelagic fish suffered from increasing metabolic demands in a warming ocean and from declines in zooplankton productivity that were amplified at higher trophic levels. Patterns of relative change between functional types were robust to uncertainty in metabolic allometries and temperature dependence, though projections of the large pelagic fish had the greatest uncertainty. The same accumulation of trophic impacts that underlies the amplification of productivity trends at higher trophic levels propagates to the projection spread, creating an acutely uncertain future for the ocean’s largest predatory fish.

Benthic cyanobacteria of the genus Nostoc are a source of microcystins in Greenlandic lakes and ponds

Abstract Benthic primary producers are recognised for their important role in contributing to ecosystem productivity and nutrient cycling in lake and stream ecosystems, particularly in polar environments. In Arctic lakes, benthic producers often comprise mats or colonies of cyanobacteria capable of producing cyanotoxins. However, the extent to which benthic communities contribute cyanotoxins in polar regions remains poorly described. We evaluated the potential for benthic colonies of the cyanobacterium Nostoc pruniforme from lakes in Kangerlussuaq, Greenland, to contribute microcystins (MCs) to lake water using three approaches. First, we dissected field‐collected Nostoc colonies and measured MCs within multiple layers of fresh colony tissue. Second, we conducted a laboratory experiment to evaluate the temporal dynamics of MC release by incubated, intact colonies. Finally, we quantified whether MC concentrations in water and sediment samples in the field were higher in and above dense bands of benthic Nostoc as compared to bare sediment. Field‐collected Nostoc colonies contained MCs throughout the colony tissue, suggesting that damage to colonies from grazers or physical disturbance could facilitate the release of toxins into the water. Undamaged Nostoc colonies incubated in high‐nutrient conditions in the laboratory leaked MCs into the surrounding water at a steady mass‐specific rate over the course of 7 days. Microcystin concentrations in water and sediment from two Greenlandic lakes were highly variable, but slightly higher in lake water immediately above dense bands of Nostoc than in water immediately above bare sediments, suggesting that benthic Nostoc colonies contribute cyanotoxins to lake water and that MCs vary at very fine, 1–2 m spatial scales. Benthic cyanobacteria may be important in releasing MCs into aquatic ecosystems, especially in systems where benthic producers dominate, such as polar environments.

Nematode responses to an Arctic sea-ice regime: morphometric characteristics and biomass size spectra

Body size is one of the most important traits of organisms that affects their behavioral life histories, physiologies, and energy requirements. For sediment-dwelling organisms, such as free-living nematodes, body size is a direct adaptation for living in sediments with a particular particle size, but other environmental factors, e.g., water depth and food availability, directly or indirectly shape nematode morphology. Nevertheless, our knowledge of meiofaunal organisms sizes still lags far behind that of other aquatic fauna, particularly for high-latitude fauna. Therefore, to gain insight into the nematode community size structure, we investigated eight stations located in the seasonal sea-ice zone north of Svalbard (Yermak Plateau, Nansen Basin, and Northern Svalbard shelf) during Arctic spring. Sample locations covered a wide depth gradient, different sea-ice concentrations and subsequent bloom stages. Our study provides previously unavailable data on nematode morphometry for this Arctic region during ecologically important spring to summer transition times. We analyzed nematode biomass, body shape and morphometric attributes, along with respective feeding types and life stage information. Our results show that differences in nematode densities, biomass and allometric attributes most likely reflect differences in the flux of organic material to the seafloor and in the biogeochemical properties of the sediments. Nematode assemblages appeared to respond to spatial gradients in ice cover duration and therefore pelagic productivity from the northern Svalbard shelf to the Yermak Plateau as evidenced by decreasing density, biomass and body size. Considering the entire community, as well as different life stages, average individual body weight decreased northward. Biomass dominance in the lower weight classes and the significantly lower abundance of long and thick morphotype nematodes observed on the Yermak Plateau than in the two other regions were striking. This was in contrast with the assemblage observed on the shelf, where prevailing environmental conditions influenced the presence of other morphotypes - markedly longer and wider organisms. Ongoing changes in sea-ice cover and primary production in the Arctic may significantly affect nematode functioning, as they are expected to have pronounced impacts on nematode morphological characteristics. In this regard, the size-based approach becomes a useful tool for detecting changes in the community and has important implications for predicting the direction of change with regard to benthic productivity.

Effects of changing phytoplankton species composition on carbon and nitrogen uptake in benthic invertebrates

AbstractPelagic primary production is the main input of organic energy for benthic production below the photic zone. In the Baltic Sea, spring phytoplankton blooms are dominated by diatoms that sink out rapidly and export nutritionally favorable matter to benthic secondary production, while the summer blooms have more variable sedimentation rates and nutritional profile. Changes in phytoplankton species composition and bloom dynamics, as a consequence of climate change and eutrophication are reducing high quality diatoms reaching the benthic fauna, while promoting cyanobacteria. Here, we test uptake and assimilation of changing phytoplankton composition for three common benthic invertebrates, a clam, an amphipod and a polychaete under varying degrees of spring‐bloom associated diatoms (Skeletonema costatum) and summer‐bloom associated cyanobacteria (Nodularia spumigena). The phytoplankton were labeled with stable isotopes (15N and 13C, respectively) in order to trace assimilation in consumers' tissues. We found that all three macrofauna species fed on both diatoms and cyanobacteria. A linear pattern was found for all three species in assimilation of carbon and nitrogen from diatoms, with increasing assimilation associated with higher proportion of diatoms. There was no clear pattern found between proportion of cyanobacteria and assimilation of carbon and nitrogen for any of the species. This study shows that the investigated macrofaunal species display a selective feeding behavior with preference for spring‐bloom associated diatoms. Thus, changes in phytoplankton bloom composition are likely affecting benthic species composition and production.

Do diatoms dominate benthic production in shallow systems? A case study from a mixed seagrass bed

AbstractWe report an assessment for determining the contribution by diatoms to community productivity and respiration within a coastal benthic ecosystem with multiple autotrophs. During summer, cores of open sediment and seagrass habitat were collected from a lagoon within the Northern Gulf of Mexico. Cores were maintained in an outdoor mesocosm. Germanic acid, an inhibitor of diatom cell division, was added to half the cores and quantification of production and respiration was done. Inhibition of diatoms reduced benthic productivity within the seagrass habitat. 71–83% production was attributable to diatoms and this contribution moved the benthic system into net autotrophy. Diatom contribution to production in other habitat‐community components was more variable (varied from 0% to 86%). Findings underscore the ecological importance of diatoms as producers in seagrass beds, the role of seagrasses in maintaining productivity, and infer that diatoms may have similar contributions in other aquatic vegetated habitats.

Water Column Turbidity Not Sediment Nutrient Enrichment Moderates Microphytobenthic Primary Production

Soft sediment intertidal habitats are under intense anthropogenic pressure resulting from increased land derived sediment and nutrient delivery. Long term, this can cause high water column turbidity and nutrient enrichment of sediment porewaters, which has cascading effects on coastal ecosystem functionality. However, how these stressors may interact and influence benthic productivity over alternating periods of submergence and emergence is largely unknown. This study investigates the effects of sediment nutrient enrichment (at three levels for 20 months) on benthic primary production at six sites in four New Zealand estuaries that spanned a gradient in water column turbidity. While nutrient enrichment had no detectable effect on microphytobenthic primary production, water column turbidity had a significant influence, explaining up to 40% of variability during tidal submergence, followed by temperature and sediment characteristics. In addition, negative net primary production (NPP) estimates and therefore net heterotrophy for the most turbid estuaries during tidal submergence resulted in an increased reliance on production during emerged periods, where NPP was positive across all sites. This study highlights the prominent role of water column turbidity over nutrient enrichment in moderating microphytobenthic production, and the increasing importance of emerged periods to maintain the health and functioning of coastal habitats.

Species-specific biomass drives macroalgal benthic primary production on temperate rocky reefs

Temperate rocky reefs dominated by the giant kelp, Macrocystis pyrifera, support diverse assemblages of benthic macroalgae that provide a suite of ecosystem services, including high rates of primary production in aquatic ecosystems. These forests and the benthic macroalgae that inhabit them are facing both short-term losses and long-term declines throughout much of their range in the eastern Pacific Ocean. Here, we quantified patterns of benthic macroalgal biomass and irradiance on rocky reefs that had intact kelp forests and nearby reefs where the benthic macroalgae had been lost due to deforestation at three sites along the California, USA and Baja California, MEX coasts during the springs and summers of 2017 and 2018. We then modeled how the loss of macroalgae from these reefs impacted net benthic productivity using species-specific, mass-dependent rates of photosynthesis and respiration that we measured in the laboratory. Our results show that the macroalgal assemblages at these sites were dominated by a few species of stipitate kelps and fleshy red algae whose relative abundances were spatially and temporally variable, and which exhibited variable rates of photosynthesis and respiration. Together, our model estimates that the dominant macroalgae on these reefs contribute 15 to 4,300 mg C m−2 d−1 to net benthic primary production, and that this is driven primarily by a few dominant taxa that have large biomasses and high rates of photosynthesis and / or respiration. Consequently, we propose that the loss of these macroalgae results in the loss of an important contribution to primary production and overall ecosystem function. Key words: benthic production; ecosystem function; kelp forest; macroalgae; primary production

Food web responses to eutrophication control in a coastal area of the Baltic Sea

With successful mitigation of eutrophication and the reductions in nutrient concentrations and productivity of coastal waters, the targets set in nature protection legislation in the EU and the United States may no longer be achievable in regions where key ecological functions are coupled to benthic productivity. Yet, due to both the patchiness of invertebrate distribution and the fragmented and non-integrated nature of monitoring data direct coupling between nutrients, productivity and predators has proven difficult to achieve. As a result, assessments of the status of food webs based solely on monitoring data remains an almost impossible task. The aim of this modelling study was to test the application of fine-scale ecosystem models for assessing cost-benefits or food-web consequences of management decisions in relation to water quality of coastal waters. We applied a fine-scale ecosystem model calibrated against measurements in a coastal area in the Baltic Sea to quantify responses in higher trophic levels to changes in eutrophication over a 18-year period, 1990-2007. The resulting spatio-temporal trends reveal a number of characteristic responses and spatial dimensions in coastal food webs. The coupled hydrodynamic, bio-geochemical and waterbird energetics modules indicated nutrient-related changes and fine-scale covariance patterns across all trophic levels. A 50 % decline in bivalve biomass was predicted in a zone characterised by the overall highest biomass of bivalves and highest densities of bivalve-feeding waterbirds. The nutrient-driven local decline in productivity affected the entire food web with a predicted annual mortality of 72,000 Long-tailed Ducks Clangula hyemalis. This model-based study suggests a strong nutrient control of the available food supply to bivalve-feeding birds in coastal areas. Our results also show that high-resolution ecosystem models are required to resolve the heterogeneous distribution of effects.

High throughput shotgun sequencing of eRNA reveals taxonomic and derived functional shifts across a benthic productivity gradient.

Benthic macrofauna is regularly used in monitoring programmes, however the vast majority of benthic eukaryotic biodiversity lies mostly in microscopic organisms, such as meiofauna (invertebrates<1mm) and protists, that rapidly responds to environmental change. These communities have traditionally been hard to sample and handle in the laboratory, but DNA sequencing has made such work less time consuming. While DNA sequencing captures both alive and dead organisms, environmental RNA (eRNA) better targets living organisms or organisms of recent origin in the environment. Here, we assessed the biodiversity of three known bioindicator microeukaryote groups (nematodes, foraminifera, and ciliates) in sediment samples collected at seven coastal sites along an organic carbon (OC) gradient. We aimed to investigate if eRNA shotgun sequencing can be used to simultaneously detect differences in (i) biodiversity of multiple microeukaryotic communities; and (ii) functional feeding traits of nematodes. Results showed that biodiversity was lower for nematodes and foraminifera in high OC (6.2%-6.9%), when compared to low OC sediments (1.2%-2.8%). Dissimilarity in community composition increased for all three groups between Low OC and High OC, as well as the classified feeding type of nematode genera (with more nonselective deposit feeders in high OC sediment). High relative abundant genera included nematode Sabatieria and foraminifera Elphidium in high OC, and Cryptocaryon-like ciliates in low OC sediments. Considering that future sequencing technologies are likely to decrease in cost, the use of eRNA shotgun sequencing to assess biodiversity of benthic microeukaryotes could be a powerful tool in recurring monitoring programmes.

Interannual changes in δ15N baseline in a lake–swamp–river food web: effects of summer precipitation in West Siberian forest steppe

Frequency and intensity of precipitation events can alter hydrological conditions of lotic systems and material inflow from the catchment. In this study, interannual changes in food web structure were investigated in a lake–swamp–river system in the semi-arid West Siberian forest-steppe region using carbon and nitrogen stable isotope ratios (δ13C and δ15N). The δ15N signatures of aquatic producers and consumers including zooplankton, benthic invertebrates, and fish sharply increased (up to 7.2‰ in range) in 2009 under high summer precipitation. This would reflect the inflow of 15N-rich nutrients accumulated in the catchment through natural and anthropogenic activities, e.g., sewage, livestock farming, evaporation, and/or microbial denitrification. In 2010, benthic producers including epiphytes and macrophytes were more 13C-enriched, which is likely due to limited supply of dissolved inorganic carbon (DIC) under water stagnation, leading to a large isotopic fractionation during photosynthesis. However, 13C-enrichments in the benthic producers were not reflected to those of aquatic consumers in the habitat. Interannual changes in δ13C of particulate organic matter (POM; a proxy of phytoplankton) were reflected to those of zooplankton, benthic invertebrates, and fish fry, suggesting the trophic importance of autochthonous phytoplankton in the system. These findings suggest that occasional precipitation events in semi-arid forest-steppe regions can modify nutrient flux from the catchment, leading to changes in δ15N baseline in the lotic food web.

High rates of carbon and dinitrogen fixation suggest a critical role of benthic pioneer communities in the energy and nutrient dynamics of coral reefs

Abstract Following coral mortality in tropical reefs, pioneer communities dominated by filamentous and crustose algae efficiently colonize substrates previously occupied by coral tissue. This phenomenon is particularly common after mass coral mortality following prolonged bleaching events associated with marine heatwaves. Pioneer communities play an important role for the biological succession and reorganization of reefs after disturbance. However, their significance for critical ecosystem functions previously mediated by corals, such as the efficient cycling of carbon (C) and nitrogen (N) within the reef, remains uncertain. We used 96 carbonate tiles to simulate the occurrence of bare substrates after disturbance in a coral reef of the central Red Sea. We measured rates of C and dinitrogen (N2) fixation of pioneer communities on these tiles monthly over an entire year. Coupled with elemental and stable isotope analyses, these measurements provide insights into macronutrient acquisition, export and the influence of seasonality. Pioneer communities exhibited high rates of C and N2 fixation within 4–8 weeks after the introduction of experimental bare substrates. Ranging from 13 to 25 μmol C cm−2 day−1 and 8 to 54 nmol N cm−2 day−1, respectively, C and N2 fixation rates were comparable to reported values for established Red Sea coral reefs. This similarity indicates that pioneer communities may quickly compensate for the loss of benthic productivity by corals. Notably, between 40% and 85% of fixed organic C was exported into the environment, constituting a vital source of energy for the coral reef food web. Our findings suggest that benthic pioneer communities may play a crucial, yet overlooked role in the C and N dynamics of oligotrophic coral reefs by contributing to the input of new C and N after coral mortality. While not substituting other critical ecosystem functions provided by corals (e.g. structural habitat complexity and coastal protection), pioneer communities likely contribute to maintaining coral reef nutrient cycling through the accumulation of biomass and import of macronutrients following coral loss. A free Plain Language Summary can be found within the Supporting Information of this article.

Spatiotemporal variability of light attenuation and net ecosystem metabolism in a back-barrier estuary

Abstract. Quantifying system-wide biogeochemical dynamics and ecosystem metabolism in estuaries is often attempted using a long-term continuous record at a single site or short-term records at multiple sites due to sampling limitations that preclude long-term monitoring. However, differences in the dominant primary producer at a given location (e.g., phytoplankton versus benthic producers) control diel variations in dissolved oxygen and associated ecosystem metabolism, and they may confound metabolic estimates that do not account for this variability. We hypothesize that even in shallow, well-mixed estuaries there is strong spatiotemporal variability in ecosystem metabolism due to benthic and water-column properties, as well as ensuing feedbacks to sediment resuspension, light attenuation, and primary production. We tested this hypothesis by measuring hydrodynamic properties, biogeochemical variables (fluorescent dissolved organic matter – fDOM, turbidity, chlorophyll a fluorescence, dissolved oxygen), and photosynthetically active radiation (PAR) over 1 year at 15 min intervals at paired channel (unvegetated) and shoal (vegetated by eelgrass) sites in Chincoteague Bay, Maryland–Virginia, USA, a shallow back-barrier estuary. Light attenuation (KdPAR) at all sites was dominated by turbidity from suspended sediment, with lower contributions from fDOM and chlorophyll a. However, there was significant seasonal variability in the resuspension–shear stress relationship on the vegetated shoals, but not in adjacent unvegetated channels. This indicated that KdPAR on the shoals was mediated by submerged aquatic vegetation (SAV) and possibly microphytobenthos presence in the summer, which reduced resuspension and therefore KdPAR. We also found that gross primary production (Pg) and KdPAR were significantly negatively correlated on the shoals and uncorrelated in the channels, indicating that Pg over the vegetated shoals is controlled by a feedback loop between benthic stabilization by SAV and/or microphytobenthos, sediment resuspension, and light availability. Metabolic estimates indicated substantial differences in net ecosystem metabolism between vegetated and unvegetated sites, with the former tending towards net autotrophy in the summer. Ongoing trends of SAV loss in this and other back-barrier estuaries suggest that these systems may also shift towards net heterotrophy, reducing their effectiveness as long-term carbon sinks. With regards to temporal variability, we found that varying sampling frequency between 15 min and 1 d resulted in comparable mean values of biogeochemical variables, but extreme values were missed by daily sampling. In fact, daily resampling minimized the variability between sites and falsely suggested spatial homogeneity in biogeochemistry, emphasizing the need for high-frequency sampling. This study confirms that properly quantifying ecosystem metabolism and associated biogeochemical variability requires characterization of the diverse estuarine environments, even in well-mixed systems, and demonstrates the deficiencies introduced by infrequent sampling to the interpretation of spatial variability.

ASLO 2020 Award Winners

<scp>ASLO</scp> 2020 Award Winners

Putting the lake back together 20 years later: what in the benthos have we learned about habitat linkages in lakes?

ABSTRACT Our understanding of lake ecosystems has undergone a paradigm shift over the past few decades. While the classic tradition in limnology has been the study of planktonic, open-water habitats, a shift toward integrative and cross-habitat watershed and whole-lake perspectives has occurred. This change in perspective integrates the role of terrestrial organic matter and littoral/benthic productivity into a general recognition of multiple basal resources and consumer-mediated habitat coupling in lakes. In light of this evolving paradigm, we address 4 broad questions relating to the role of benthic productivity and food web pathways in lakes. Specifically we ask: (1) What is the contribution of attached algae to whole-lake primary production? (2) Are attached algae an important basal resource for consumers? (3) What are the roles of benthic habitats and resources in supporting lake biodiversity? (4) What is the role of lake benthic pathways in aquatic–terrestrial linkages? While this paper focuses on the role of benthic productivity in lake food webs, it reflects a larger movement toward a more integrated and holistic understanding of lake ecosystems. Recognizing the magnitude and implications of aquatic habitat coupling is necessary to understand and conserve these globally important ecosystems in our current era of unprecedented global environmental change.

Unravelling the metabolism black-box in a dynamic wetland environment using a hybrid model framework: Storm driven changes in oxygen budgets

Estimating gross primary production and ecosystem respiration from oxygen data is performed widely in aquatic systems, yet these estimates can be challenged by high advective fluxes of oxygen. In this study, we develop a hybrid framework linking data-driven and process-based modelling to examine the effect of storm events on oxygen budgets in a constructed wetland. After calibration against measured flow and water temperature data over a two-month period with three storm events, the model was successfully validated against high frequency dissolved oxygen (DO) data exhibiting large diurnal fluctuations. The results demonstrated that pulses of high-DO water injected into the wetland during storm events were able to dramatically change the wetland oxygen budget. A shift was observed in the dominant oxygen inputs, from benthic net production during non-storm periods, to inflows of oxygen during storm events, which served to dampen the classical diurnal oxygen signature. The model also demonstrated the changing balance of pelagic versus benthic production and hypoxia extent in response to storm events, which has implications for the nutrient attenuation performance of constructed wetlands. The study highlights the benefit of linking analysis of high-frequency oxygen data with process-based modelling tools to unravel the varied responses of components of the oxygen budget to storm events.

Restored freshwater flow and estuarine benthic communities in the northern Gulf of Mexico: research trends and future needs.

Restoring river connectivity to rebuild and sustain land is a promising restoration strategy in coastal areas experiencing rapid land loss, such as the Mississippi river delta. Results of these large-scale hydrologic changes are preliminary, and there exists limited empirical evidence regarding how benthic communities will respond, specifically in Barataria Bay and Breton Sound in southeast Louisiana. In this review, the body of existing research in this geographic region pertaining to the drivers of benthic community response that are related to restored freshwater flow and sediment deposition is examined. Overall trends include (1) potential displacement of some species down-estuary due to reduced salinities; (2) temporary lower diversity in areas closest to the inflow; (3) increased benthic production along the marsh edge, and in tidal bayous, as a result of nutrient loading; (4) more habitat coverage in the form of submerged aquatic vegetation; and (5) reduced predation pressure from large and/or salinity-restricted predators. These trends highlight opportunities for future research that should be conducted before large-scale hydrologic changes take place.

Microbenthic Net Metabolism Along Intertidal Gradients (Cadiz Bay, SW Spain): Spatio-Temporal Patterns and Environmental Factors

The changes in the annual biomass distribution of microphytobenthos (MPB) have been addressed by different studies, although this information is scarce in southern European coastal systems when compared to Northern European estuaries. Moreover, there is little information regarding annual changes in the primary production of MPB related with those in the annual biomass. For this reason, we followed the net production in light, dark respiration rates (determined by oxygen microelectrodes) and MPB abundance (estimated by sediment chlorophyll a) along an intertidal gradient of the inner Cadiz Bay during an annual cycle. Sediment cores were collected seasonally along two transects (5 sampling stations per transect) with contrasting sediment granulometry: muddy (Puerto Real, PR) and muddy-sandy (San Fernando, SF). Our results show that MPB biomass and net production increased seawards reaching maxima in winter. The seasonal maximum of daily solar irradiance and high temperature reached in summer in southern Spain likely inhibits MPB production. Spatial patterns of MPB biomass and net production depend on season and environmental heterogeneity. Environmental variables, analyzed by principal component analyses, were used to explain the variability of MPB metabolism by multiple regression. The principal component axes explained up to 60 % of the microphytobenthic net production and 41 % of the respiration rates in the PR transect while they only explained about 25 % of the same rates in SF. The variability in the environmental variables contributing to the observed patterns implies that no single set of variables can be used to predict net production patterns in the entire system. The different patterns of net production observed between transects highlight the importance of considering the spatial heterogeneity of our system to estimate the contribution of MPB to the inner Cadiz Bay productivity. This production is of major importance since our data showed that microphytobenthic production can contribute up to 49 % of the total benthic production of intertidal sediments of the inner Cadiz Bay.

Sediments ratchet-down coral reef algal turf productivity

Coral reefs are highly productive ecosystems, with much of this productivity arising from the algal turfs which cover the hard reef substratum. This productivity can flow up the food chain through herbivorous fishes, to be harvested by humans as fishable biomass. However, algal turfs exist on a spectrum of forms from short productive algal turfs (SPATs), to long sediment-laden algal turfs (LSATs). The latter are increasingly likely to typify Anthropocene coral reefs, however, we have a limited understanding of their nature and potential productivity. We assessed the nature of algal turfs in terms of length, biomass, relative detritus content, and productivity across a sediment load gradient, from SPATs to LSATs, at two reefs separated by >450 km along Australia's Great Barrier Reef (GBR). Furthermore, to assess the capacity of sediments to shape productivity, we modelled algal turf productivity, as a function of sediment load, across multiple spatial scales in a Bayesian framework. We recorded precipitous declines in both the productivity of algal turfs, and the relative nutritional value of particulates, up to sediment loads of ~100 g m−2. However, algal turf biomass did not change with sediment loads. This appears to reflect a shift in algal community composition from short, high-biomass, highly-productive algae at low sediment loads, to longer, low-biomass, less productive algae at high sediment loads. Importantly, these relationships provide a robust framework for estimating algal turf productivity on coral reefs. Indeed, when we applied our models to known sediment loads, we reveal that sediment loads alone can explain observed algal turf productivity gradients across multiple spatial scales. In an era of global climate change and coral reef reconfiguration, algal turf sediments may hold the key to maintaining benthic productivity on coral reefs in the Anthropocene.

Hyporheic secondary production and life history of a common Ozark stonefly

The hyporheic zone plays a key role in stream ecosystem function, but the quantity of biomass produced in this unique and rarely sampled habitat remains underappreciated. We measured hyporheic secondary production and life history characteristics of a stonefly, Leuctra tenuis (Pictet, 1841), in two Ozark streams with extensive gravel beds: a mainstem perennial stream and a tributary with ephemeral surface flow. L. tenuis nymphs were collected 30–45 cm below the streambed surface in both locations monthly for a year (2017–2018). Annual hyporheic secondary production of L. tenuis was 15.23 mg m−2 of streambed (95% CI 12.00–20.41) in the mainstem and 2.61 mg m−2 (95% CI 0.95–4.83) in the tributary. Annual benthic production of L. tenuis collected concurrently from the mainstem was 12.06 mg m−2 (95% CI 6.77–17.73). L. tenuis was univoltine and completed nymphal development in 8 months and approximately 3900 degree days (starting 20 January). This study is the first to measure hyporheic secondary production in the Ozarks, where many streams have deep hyporheic zones that could contribute substantial biomass to stream and riparian food webs. Our results, based on just one species of a diverse hyporheos, indicate the need for more ecological research in this habitat.