Invasive ecosystem engineers and biotic indices: Giving a wrong impression of water quality improvement?

Highlights: • We test the effect of an invasive alien species on ecological quality assessment. • We calculate Benthic Quality Index for the coastal lagoon affected by zebra mussel. • Zebra mussel may modify benthic habitats enhancing local biodiversity. • This might bias BQI by showing false improvement of ecological status. • We suggest a framework how the bias in could be minimized. Abstract: Benthic component of an ecosystem is considered in ecological status assessment of the key European Directives. Most of the metrics proposed for the benthic quality assessment are biodiversity based. Their robustness and applicability are widely discussed in many recent studies. However an impact of invasive alien species on biotic indices and environmental quality assessments has been largely overlooked by researchers so far. In the current study we assessed Benthic Quality Index (BQI) in a coastal ecosystem, highly affected by the invasive zebra mussel Dreissena polymorpha. Zebra mussel is able of modifying benthic habitats and enhancing local biodiversity. In the analyzed ecosystem it affected benthic species richness, abundance and community structure. As a result the calculated BQI values were significantly higher in the presence of zebra mussel with evident outliers in samples with particularly high zebra mussel abundances. Therefore we found that BQI determined in our study was artificially elevated providing false signal of the ecological status improvement. Based on the results presented, we suggested data correction framework that has been tested on the current dataset and proved to be effective minimizing zebra mussel impact on BQI assessment. Our experience could be applied for other coastal ecosystems invaded by the zebra mussel or any other aquatic invasive species with resembling biological traits and bioinvasion impacts

Mapping an ecosystem service: A quantitative approach to derive fish feeding ground maps**This study was supported by Norwegian Financial Mechanism (project No. LT0047) and BONUS PREHAB.

AbstractThis study presents a quantitative approach to mapping benthophagous fish feeding grounds. This approach combines the spatial biomass distribution of benthic prey items and their importance for the diets of predators. A point based biomass data of macrozoobenthos together with a set of environmental factors was used to develop Random Forests models that produce continuous biomass distribution layers for individual prey species. Depending on the diet composition and the importance of prey for fish feeding, these layers are overlaid and an integrated GIS map of the seabed showing the quality of feeding grounds is generated. These maps provide a useful basis for conservation and marine spatial planning. In addition, this method could be applied to the mapping of resources used by other benthophagous organisms. The method is presented using the example of three common Baltic fish species: cod, flounder and viviparous eelpout

Drivers of Cyanobacterial Blooms in a Hypertrophic Lagoon

The Curonian Lagoon is Europe's largest lagoon and one of the most seriously impacted by harmful blooms of cyanobacteria. Intensive studies over the past 20 years have allowed us to identify the major drivers determining the composition and spatial extent of hyperblooms in this system. We summarize and discuss the main outcomes of these studies and provide an updated, conceptual scheme of the multiple interactions between climatic and hydrologic factors, and their influence on internal and external processes that promote cyanobacterial blooms. Retrospective analysis of remote sensed images demonstrated the variability of blooms in terms of timing, extension and intensity, suggesting that they occur only under specific circumstances. Monthly analysis of nutrient loads and stoichiometry from the principal tributary (Nemunas River) revealed large interannual differences in the delivery of key elements, but summer months were always characterized by a strong dissolved inorganic N (and Si) limitation, that depresses diatoms and favors the dominance of cyanobacteria. Cyanobacteria blooms occurred during high water temperatures, long water residence time and low-wind conditions. The blooms induce transient (night-time) hypoxia, which stimulates the release of iron-bound P, producing a positive feedback for blooms of N-fixing cyanobacteria. Consumer-mediated nutrient recycling by dreissenid mussels, chironomid larvae, cyprinids and large bird colonies, may also affect P availability, but their role as drivers of cyanobacteria blooms is understudied

Recent distribution and stock assessment of the red alga Furcellaria lumbricalis on an exposed Baltic Sea coast: combined use of field survey and modelling methods

Recent results of field studies on the exposed coast of Lithuania were used to model the area occupied by the red alga Furcellaria lumbricalis using the Natural Neighbor interpolation technique, while linear regression was applied to estimate the species’ standing stock. The area covered by F. lumbricalis extended for 26 km along thecoast between depths of 1 and 15 m. The maximum species cover in the study area ranged between 4 and 10 m depth, which is one of the widest in the Baltic Sea. The modelled area of F. lumbricalis covered 35 ± 11 km2 with a total biomass of 7554 ± 3813 t

Response of long-tailed duck (Clangula hyemalis) to the change in the main prey availability in Its Baltic wintering ground

The long-tailed duck (Clangula hyemalis) is a vulnerable and declining species wintering in the Baltic Sea. The introduction of the invasive fish, the round goby (Neogobius melanostomus), dramatically impacted the benthic macrofauna in hard-bottom habitats, while no significant changes occurred in soft-bottom benthic macrofauna. Therefore, we aimed to assess the extent to which the diet of long-tailed ducks changed in two different bottom types. We analysed the stomach content of 251 long-tailed ducks bycaught in gillnets from 2016 to 2020 in hard-and soft-bottom habitats and compared these results with those published by Žydelis and Ruškyte (2005). The results show that the long-tailed duck experienced a change in diet in hard-bottom habitats, shifting from the blue mussel to Hediste diversicolor, barnacles, and fish. In soft-bottom habitats, their diet remained similar over time and was based on H. diversicolor, a few bivalve species, and Saduria entomon. There was no evidence of significant differences in diet between sex or age. Despite the abovementioned changes in diet, the average body condition of the species did not change over time or between habitats. This confirms that long-tailed ducks have high feeding flexibility and quick species response to changes in prey availability, as they are capable of shifting their diet to new prey

Baltic herring (Clupea harengus membras) spawning grounds on the Lithuanian coast: current status and shaping factors* This study was supported by the Norwegian Financial Mechanism (project No. LT0047).

During the 2009 and 2010 seasons Baltic herring (Clupea harengus membras L.) spawning grounds were investigated by SCUBA divers off the Lithuanian Baltic Sea coast. The most important spawning substrate was a hard bottom overgrown with red algae Furcellaria lumbricalis, but only 32.8% of potentially suitable spawning locations had herring eggs. Bottom geomorphological analysis using multibeam bathymetry revealed that the distribution of spawning beds is not random, but is determined rather by small-scale geomorphological features. The majority of the detected spawning locations were on local elevations characterised by 2.4 ± 1.1 m depth differences and 4.8 ± 1.8 slopes

Sediment-water oxygen, ammonium and soluble reactive phosphorus fluxes in a turbid freshwater estuary (Curonian lagoon, Lithuania): evidences of benthic microalgal activity

Seasonal measurements of total and diffusive benthic fluxes were performed during the ice-free period in the Curonian Lagoon (Lithuania). This mostly freshwater hypertrophic basin exhibits wide seasonal variations of water temperature (1-22°C) and inorganic nitrogen availability and it is subjected to dramatic blooms of diatoms and cyanobacteria (>100 mg chl a L-1). In this shallow lagoon, nutrient exchanges at the sediment-water interface and the regulating factors have been poorly explored. Overall aim of the present work is to demonstrate that the activity of benthic microalgae, generally neglected in turbid systems, can be a relevant regulator of sedimentary processes. To this purpose, light and dark fluxes of oxygen, ammonium and soluble reactive phosphorus were measured seasonally by intact core laboratory incubation and diffusive fluxes were calculated from sediment profiles. We investigated sandy sediments that were collected from the central area lagoon, that is representative of the most of the shallower lagoon area. Oxygen and ammonium fluxes were significantly different under light and dark incubations, suggesting an active role of benthic microalgae at the sediment-water interface. In the light net oxygen production was measured in three out of four samplings, with July as only exception, and ammonium was retained within sediments. In the dark sediment respiration displayed a temperature-dependent pattern while ammonium efflux increased from March to October. Fluxes of reactive phosphorus varied significantly with sampling seasons but were less affected by the incubation condition. Diffusive fluxes peaked in July, where highest concentration gradients at the interface and theoretical efflux of ammonium and reactive phosphorous were calculated. [...

Sediment-water oxygen, ammonium and soluble reactive phosphorus fluxes in a turbid freshwater estuary (Curonian lagoon, Lithuania): evidences of benthic microalgal activity

Seasonal measurements of total and diffusive benthic fluxes were performed during the ice-free period in the Curonian Lagoon (Lithuania). This mostly freshwater hypertrophic basin exhibits wide seasonal variations of water temperature (1-22°C) and inorganic nitrogen availability and it is subjected to dramatic blooms of diatoms and cyanobacteria (>100 μg chl a l-1). In this shallow lagoon, nutrient exchanges at the sediment-water interface and the regulating factors have been poorly explored. Overall aim of the present work is to demonstrate that the activity of benthic microalgae, generally neglected in turbid systems, can be a relevant regulator of sedimentary processes. To this purpose, light and dark fluxes of oxygen, ammonium and soluble reactive phosphorus were measured seasonally by intact core laboratory incubation and diffusive fluxes were calculated from sediment profiles. We investigated sandy sediments that were collected from the central area lagoon, that is representative of the most of the shallower lagoon area. Oxygen and ammonium fluxes were significantly different under light and dark incubations, suggesting an active role of benthic microalgae at the sediment-water interface. In the light net oxygen production was measured in three out of four samplings, with July as only exception, and ammonium was retained within sediments. In the dark sediment respiration displayed a temperature-dependent pattern while ammonium efflux increased from March to October. Fluxes of reactive phosphorus varied significantly with sampling seasons but were less affected by the incubation condition. Diffusive fluxes peaked in July, where highest concentration gradients at the interface and theoretical efflux of ammonium and reactive phosphorous were calculated. The marked differences between diffusive and total nutrient fluxes are probably due to photosynthetic activity by benthic microalgae, and thus oxygen production, enhancement of aerobic processes and net solute uptake at the sediment-water interface. Our findings support the hypothesis that even in highly turbid systems benthic microalgae can have a relevant role as filters for regenerated nutrients and as regulators of benthic processes

Estuarine macrofauna affects benthic biogeochemistry in a hypertrophic lagoon

Coastal lagoons display a wide range of physico-chemical conditions that shape benthic macrofauna communities. In turn, benthic macrofauna affects a wide array of biogeochemical processes as a consequence of feeding, bioirrigation, ventilation, and excretion activities. In this work, we have measured benthic respiration and solute fluxes in intact sediment cores with natural macrofauna communities collected from four distinct areas within the Sacca di Goro Lagoon (NE Adriatic Sea). The macrofauna community was characterized at the end of the incubations. Redundancy analysis (RDA) was used to quantify and test the interactions between the dominant macrofauna species and solute fluxes. Moreover, the relevance of macrofauna as driver of benthic nitrogen (N) redundancy analysis revealed that up to 66% of the benthic fluxes and metabolism variance was explained by macrofauna microbial-mediated N processes. Nitrification was stimulated by the presence of shallow (corophiids) in combination with deep burrowers (spionids, oligochaetes) or ammonium-excreting clams. Deep burrowers and clams increase ammonium availability in burrows actively ventilated by corophiids, which creates optimal conditions to nitrifiers. However, the stimulatory effect of burrowing macrofauna on nitrification does not necessarily result in higher denitrification as processes are spatially separated