THE ASSESSMENT OF FINE SEDIMENT ACCUMULATION IN RIVERS USING MACRO‐INVERTEBRATE COMMUNITY RESPONSE

Increased fine sediment deposition and entrainment in rivers can arise from a combination of factors including low flows, habitat modification and excessive sediment delivery from the catchment. Physical and visual methods have traditionally been used to quantify the volume of deposited fine sediment (<2 mm in size), but here we propose an alternative, the development and utilization of a sediment‐sensitive macro‐invertebrate metric (PSI — Proportion of Sediment‐sensitive Invertebrates) which provides a proxy to describe the extent to which the surface of river beds are composed of, or covered by, fine sediments. Where suitable biomonitoring data exists, the index can be calculated retrospectively to track trends in fine sediment deposition, and its ecological impact, through time. Furthermore, the utilization of reference condition models such as RIVPACS (River InVertebrate Prediction And Classification System), allows site‐specific unimpacted conditions to be defined, opening‐up the possibility of standard classification and assessment systems being developed. In Europe, such systems are vital if the Water Framework Directive is to be implemented. Knowledge regarding spatial differences in sediment/flow interdependencies may provide valuable information on diffuse sources of fine sediment to rivers and we illustrate this with an example from the UK (Laceby Beck). Further UK case studies are presented to show a range of applications, including the demonstration of improvements in habitat heterogeneity following river restoration (rivers Chess and Rib) and the detection of fine sediment impacts downstream of an impoundment (Eye Brook). The PSI metric offers a readily deployable, cost‐effective and hydroecologically relevant methodology for the assessment of fine sediment impacts in rivers. The technique has potential for application outside of the UK and an adaptation of the methodology for use in the Simandou Mountains (Guinea) is used to illustrate this. Copyright © 2011 John Wiley & Sons, Ltd.     

Status of the amphipod Diporeia spp. in Lake Superior, 2006–2016

The amphipod Diporeia spp. has historically been an important component of the benthic food web of the Laurentian Great Lakes. The Great Lakes Water Quality Agreement included its population density as an indicator of ecological condition for Lake Superior, with target values of 220–320 m^?2 in nearshore areas (≤100 m depth) and 30–160 m^?2 in offshore areas (>100 m). To assess the status of Diporeia in Lake Superior, we used a probability-based lake-wide survey design to obtain estimates of Diporeia density and biomass in 2006, 2011 and 2016. A PONAR grab sampler was used to collect Diporeia at 50–53 sites each year, with approximately half in the nearshore (<100 m depth) region of the lake and half in the offshore. The mean area-weighted lake-wide density was 395 ± 56 (SE) m^?2 in 2006, 756 ± 129 m^?2 in 2011, and 502 ± 60 m^?2 in 2016. For all years, both density and biomass were greater in the nearshore than in the offshore stratum. The densities for 2006–2016 were 3–5 times higher than those reported from a lake-wide survey conducted in 1973 by the Canada Centre for Inland Waters. The severe declines in Diporeia populations observed in the other Great Lakes during recent decades have apparently not occurred in Lake Superior. Further research is needed to understand spatial and temporal variability of Diporeia populations in Lake Superior to enhance the utility of Diporeia density as an indicator of benthic condition.     

EFFECTS OF GEOMORPHIC PROCESS DOMAINS ON RIVER ECOSYSTEMS: A COMPARISON OF FLOODPLAIN AND CONFINED VALLEY SEGMENTS

The geomorphic template of streams and rivers exerts strong controls on the structure and function of aquatic ecosystems. However, relationships between stream geomorphology and ecosystem structure and function are not always clear and have not been investigated equally across spatial scales. In montane regions, rivers often alternate between canyon‐confined segments and unconfined floodplain segments. Yet, few studies have evaluated how this pattern influences aquatic ecosystems. Here, we compared five confined river segments to five paired floodplain segments in terms of allochthonous inputs, aquatic primary producer and invertebrate production, stream retentive capacity, and aquatic invertebrate community composition. We found that floodplains had a higher (up to 4×) retentive capacity, a greater richness (58%) of aquatic invertebrates, and a distinctly different invertebrate community, relative to confined segments. Contrary to our expectations, allochthonous inputs were approximately 2× greater for confined segments, and aquatic primary and invertebrate production exhibited no consistent differences between segment types. However, results did indicate that floodplains had greater overall community respiration than confined segments. Together, these findings suggest that floodplain and confined segments do indeed differ in terms of aquatic ecosystem structure and function but not entirely as expected. Confined segments had greater allochthonous inputs but a lower capacity to retain those inputs, whereas floodplains had a high capacity to retain transported organic matter and also a more diverse community of invertebrates and higher overall community respiration to ‘digest’ retained organic matter. If these findings are generalizable, then they would indicate that confined segments are sources for organic matter within river networks, whereas floodplains act as filters, removing and processing organic matter transported from upstream confined segments. Copyright © 2013 John Wiley & Sons, Ltd.     

Physico-chemical and biological parameters determine metal bioavailability in soils

The Netherlands Stimulation program on System-oriented Ecotoxicological Research focused on three study areas, including two floodplains and a peaty grassland. All three areas were polluted with metals, with total soil concentrations often exceeding Dutch Intervention Values. The floodplain areas showed a homogeneous distribution of metal pollution, while pollution in the peaty area was more heterogeneous. This study aimed at establishing possible general trends in metal bioavailability by combining results obtained at the three different study sites. Available metal concentrations, measured as pore water or 0.01 M CaCl₂ extractable concentrations in soil, were lowest in the floodplain soils, probably due to the high pH (> 7.0) and high organic matter (8-30%) and clay contents (13-42%). In the peaty soil, having a lower soil pH (4.5-6.5) but higher organic matter contents (38-60%), in some but not all samples Cu concentrations in pore water and Cu and Pb concentrations in 0.01 CaCl₂ extracts were higher than in non-polluted reference areas. Plants in the floodplain areas had only low metal concentrations in their leaves, but soil invertebrates and small mammals did contain elevated concentrations in their body. Cd showed high levels in earthworms, snails and small mammals, while also Cu levels were sometimes increased in earthworms, millipedes and small mammals from the floodplain areas. Earthworms from the peaty area contained increased levels of Cu and Pb. These results suggest that metal bioavailability cannot be predicted from available concentrations in pore water or 0.01 M CaCl₂ soil extracts, but requires measurement of biota and more insight into the biodynamics of metal uptake.     

Impact of partial removal of the invasive macrophyte Lagarosiphon major (hydrocharitaceae) on invertebrates and fish

Invasive macrophyte species are a threat to native biodiversity and often grow to nuisance levels, therefore, making control options necessary. Macrophyte control can have pronounced impacts on littoral fish by reducing habitat heterogeneity and the loss of profitable (high density of invertebrates) foraging areas. Yet, there is little known about the impacts of macrophyte removal on invertebrates themselves. We conducted a macrophyte removal experiment, that is the cutting of channels into dense macrophyte beds, to investigate the impact of mechanical macrophyte control on invertebrate and fish communities in a littoral zone dominated by the invasive macrophyte Lagarosiphon major. The effect of macrophyte removal had only a temporary effect on macrophyte areal cover (4 months). Nevertheless, the treatment increased light penetration significantly. However, we could not detect any difference in epiphyton biomass. Invertebrate biomass increased in macrophyte stands 4 months after treatment and there was a shift in the invertebrate community composition. Mechanical control had no effect on invertebrate biodiversity. The higher invertebrate biomass did not translate into a higher fish density in the treated areas. The results of this study indicated that partial mechanical removal is a suitable option to control unwanted macrophyte stands. Copyright © 2008 John Wiley & Sons, Ltd.     

Expansion of Dreissena into offshore waters of Lake Michigan and potential impacts on fish populations

Lake Michigan was invaded by zebra mussels (Dreissena polymorpha) in the late 1980s and then followed by quagga mussels (D. bugensis) around 1997. Through 2000, both species (herein Dreissena) were largely restricted to depths less than 50 m. Herein, we provide results of an annual lake-wide bottom trawl survey in Lake Michigan that reveal the relative biomass and depth distribution of Dreissena between 1999 and 2007 (although biomass estimates from a bottom trawl are biased low). Lake-wide mean biomass density (g/m²) and mean depth of collection revealed no trend between 1999 and 2003 (mean = 0.7 g/m² and 37 m, respectively). Between 2004 and 2007, however, mean lake-wide biomass density increased from 0.8 g/m² to 7.0 g/m², because of increased density at depths between 30 and 110 m, and mean depth of collection increased from 42 to 77 m. This pattern was confirmed by a generalized additive model. Coincident with the Dreissena expansion that occurred beginning in 2004, fish biomass density (generally planktivores) declined 71% between 2003 and 2007. Current understanding of fish population dynamics, however, indicates that Dreissena expansion is not the primary explanation for the decline of fish, and we provide a species-specific account for more likely underlying factors. Nonetheless, future sampling and research may reveal a better understanding of the potential negative interactions between Dreissena and fish in Lake Michigan and elsewhere.     

Invertebrate Gonadotropin-Releasing Hormone Receptor Signaling and Its Relevant Biological Actions

Gonadotropin-releasing hormones (GnRHs) play pivotal roles in reproduction via the hypothalamus-pituitary-gonad axis (HPG axis) in vertebrates. GnRHs and their receptors (GnRHRs) are also conserved in invertebrates lacking the HPG axis, indicating that invertebrate GnRHs do not serve as “gonadotropin-releasing factors” but, rather, function as neuropeptides that directly regulate target tissues. All vertebrate and urochordate GnRHs comprise 10 amino acids, whereas amphioxus, echinoderm, and protostome GnRH-like peptides are 11- or 12-residue peptides. Intracellular calcium mobilization is the major second messenger for GnRH signaling in cephalochordates, echinoderms, and protostomes, while urochordate GnRHRs also stimulate cAMP production pathways. Moreover, the ligand-specific modulation of signal transduction via heterodimerization between GnRHR paralogs indicates species-specific evolution in Ciona intestinalis. The characterization of authentic or putative invertebrate GnRHRs in various tissues and their in vitro and in vivo activities indicate that invertebrate GnRHs are responsible for the regulation of both reproductive and nonreproductive functions. In this review, we examine our current understanding of and perspectives on the primary sequences, tissue distribution of mRNA expression, signal transduction, and biological functions of invertebrate GnRHs and their receptors.     

Endemic Caspian Sea mollusks in hotspot and non-hotspot areas differentially affected by anthropogenic pressures

The Caspian Sea is renowned for its endemic mollusk biodiversity. However, over the past decades, increasing anthropogenic pressures have caused decreases in abundances and even extinction of species. Both key pressures and endemic taxa are distributed spatially unevenly across the Caspian Sea, suggesting that ecologically different taxa such as gastropods and bivalves are also affected differentially. In addition, hotspot and non-hotspot areas for these taxa might differ quantitatively in pressure scores and qualitatively in key individual anthropogenic pressures. To test this working hypothesis, hotspot areas for endemic bivalve and gastropod species were identified using stacked species ranges. Cumulative and individual pressure scores were estimated for hotspot and non-hotspot areas of bivalves and gastropods. Differences in cumulative and individual pressure scores were tested for significance using non-parametric MANOVA and Wilcoxon rank sum tests, respectively. We identified various mollusk biodiversity hotspots across locations and depths, which are differentially affected both in terms of cumulative pressure scores and in the composition of the contributing individual pressures. Similarly, hotspot and non-hotspot areas for both bivalves and gastropods are differentially affected by anthropogenic pressures. By defining endemic hotspot areas and the respective anthropogenic pressures, this study provides an important baseline for mollusk-specific conservation strategies.     

Long-term dynamics of Lake Erie benthos: One lake,three distinct communities

Lake Erie has experienced multiple anthropogenic-driven changes in the past century, including cultural eutrophication, phosphorus abatement initiatives, and the introduction of invasive species. The benthos of Lake Erie has been studied infrequently over nine decades and can provide not only insights into the impact of environmental changes but can also be used to examine ecosystem recovery through time. We used multivariate analyses to examine temporal changes in community composition and to assess the major drivers of long-term changes in benthos. Eutrophication, water quality improvement, and dreissenid introduction were the major drivers of changes in benthos in the western basin, while hypoxia was a major factor in the central basin, and dreissenid introduction was most important in the eastern basin. Non-dreissenid community composition of the western basin has changed dramatically over 90 years from benthic species indicative of good water quality in the 1930s, with a diverse community dominated by Hexagenia, to one of low diversity dominated by oligochaetes and other pollution-tolerant species in the 1960s, followed by recovery in the early 2000s to a state similar to that reported in 1930. In contrast, the non-dreissenid benthic community of the central basin over 60 years was consistently dominated by low oxygen-tolerant taxa, signifying the persistence of hypoxia, the major community driver in this basin. The eastern basin community also changed dramatically, including the disappearance of Diporeia after the introduction of Dreissena in the 1990s and more recent declines in oligochaetes, amphipods, gastropods, sphaeriid clams, and leeches.     

Oxidative effects of the harmful algal blooms on primary organisms of the food web

Degraded water quality from nutrient pollution, physical, biological, and other chemical factors contributes to the development and persistence of many harmful algal blooms (HABs). The complex dynamics of the HABs is a challenge to marine ecosystems for the toxic effects reported. The consequences include fish, bird, and mammal mortality, respiratory or digestive tract problems, memory loss, seizures, lesions and skin irritation in many organisms. This review is intended to briefly summarize the recent reported information on harmful marine toxin deleterious effects over the primary organisms of the food web, namely algae, zooplankton and invertebrates. Special focus is made on oxidative stress status of cells and tissues. Even though in situ field research is less controlled than laboratory studies, in which the organisms are directly exposed to the toxins under consideration, both types of approaches are required to fully understand such a complex scenario. On top of that, the contribution of the increasing water temperatures in the sea, as a consequence of the global climate change, will be addressed as a topic for further studies, to evaluate the effect on regulating algal growth, species composition, trophic structure, metabolic stress and function of aquatic ecosystems.