Complex Macrophyte Research Articles

Macrophyte complexity influences habitat choices of juvenile fish

The nursery function of littoral habitats for juvenile fish is widely recognized, but data on the specific habitat features that contribute to this function is sparse for many species, in part related to the difficulty of studying juvenile fish in their natural environment. However, this information is required to understand the potential risks of environmental change to the nursery functions of habitats. In this context, the habitat choice behaviour, with respect to differences in structural features, was evaluated for three Mediterranean littoral fish species known to be associated to macrophytes as juveniles. The overarching aim of this experiment was to determine if juveniles actively choose between different macrophyte configurations of varying complexity and height. Juveniles were exposed simultaneously to multiple visual habitat stimuli within an experimental choice arena, and their swimming behaviour was tracked by video recordings to determine the amount of time they spent near each habitat configuration. All three species showed a clear association in their occupancy towards more complex habitat configurations demonstrating that juveniles distinguished and actively selected habitats using visual cues. Subtle differences in species' affinity for complex habitats allowed us to appraise their potential vulnerabilities to habitat loss in the Mediterranean under environmental change scenarios. Furthermore, the results of this study provided evidence that differences in juvenile distribution between habitats found in previous observational studies may indeed be caused by active habitat selection, as well as through differential survivorship rates.

Subtidal macrophyte diversity and potentials in Nha Trang Bay - baseline data for monitoring a rising natural resource

Tropical coastal ecosystems provide a unique complex marine habitat with a high diversity of algal species, Viet Nam being a particular hotspot. These algae may host a variety of potential unknown or underestimated bioactive algal compounds. In parallel the worldwide rising interest in macroalgae-based products leads to increasing activities in seaweed natural harvest and mariculture within coastal waters. With this growing interest, the present work provides baseline data for a systematic and science-based macroalgal monitoring program in Nha Trang Bay, Viet Nam, to keep track of potentially interesting taxa and to identify driving environmental factors which may also naturally influence biodiversity and species abundance. The present study investigated macrophyte diversity and abundance by combining a qualitative and quantitative macroalgal survey approach with environmental sampling (e.g. physicochemical properties of water column, underwater light regime, and sediment characteristics). Surveys were performed in the dry season (May/June) 2019 in different water depths (3, 6 and 10 m) at seven sites within Nha Trang Bay. The study revealed a coastal patchwork of diverse habitats inhabited by complex macrophyte communities, including estuarine dense Sargassum forests and Turbinaria meadows, sheltered sandy seagrass (Halodule spp.) beds with upcoming Lyngbya blooms, low diverse Padina deserts and highly turbid aquaculture (lobster and fish farms) impacted sites with surprisingly high macroalgal diversity. During our study a total of 86 macrophyte species were encountered in the subtidal (>1 m water depth), whereas only 6 species (Padina australis, Sargassum mcclurei, Turbinaria ornata, Halimeda discoidea, Amphiroa fragilissima, Tricleocarpa cylindrical) were frequently found at every survey site. The observed high patchiness and presence of economically important (e.g. Sargassum spp., Gracilaria spp., Caulerpa spp., Gelidiella acerosa, Acanthophora spicifera) and potentially economically interesting (e.g. Padina australis, Turbinaria ornata, Stypopodium zonale, Chondria armata) taxa during the survey underlines the high potential of the present macrophytic bio-resource, which apparently is strongly structured and will be altered by the changing heterogenic environment.

Response of Zooplankton Indices to Anthropogenic Pressure in the Catchment of Field Ponds

As methods for assessing the environmental conditions in ponds are still not well developed, I studied zooplankton to identify a response of community indices to abiotic, biotic, and habitat type in two types of ponds differing in the level of human stress. Ponds of low human alterations (LowHI) harbored generally richer communities and a higher share littoral zooplankton, whose occurrence was associated with higher water transparency and complex macrophyte habitat, particularly the presence of hornworts and charoids. In high human-impact ponds (HighHI) planktonic communities prevailed. Their distribution was mainly related to the open water area and fish presence. Anthropogenic disturbance was also reflected in the frequency of rare species, which were associated with LowHI ponds. Higher diversity of zooplankton increased the chance for rare species to occur. Despite the fact that the majority of rare species are littoral-associated, they had no prevalence towards a certain ecological type of plants, which suggests that any kind of plant cover, even macrophytes typical for eutrophic waters (e.g., Ceratophyllum demersum) will create a valuable habitat for conservation purposes. Thus, it is postulated that a complex and dense cover of submerged macrophytes ought to be maintained in order to improve the ecological value of small water bodies.

Effects of shoreline alteration and habitat heterogeneity on macroinvertebrate community composition across European lakes

Human lake shore alterations often result in a substantial decrease of littoral and riparian habitat diversity and physical complexity, but the intensity at which shore alterations affect biodiversity may differ among European geographical regions. We tested if the response of littoral macroinvertebrate communities to human shoreline alterations is consistent among geographical regions. We compared community composition and diversity of human altered with those of unmodified littoral zones from 51 lakes across seven European countries in four geographical regions based on pooled composite as well as habitat-specific macroinvertebrate samples. Taxon richness and community composition differed among shore types and different habitats in all geographic regions, with morphological alteration having an overall negative effect on macroinvertebrate taxon richness. In addition, habitat heterogeneity also had a strong effect on littoral communities, with highest taxon richness found in the structurally complex macrophyte habitats in all regions. Average proportional densities of Diptera and Oligochaeta taxa generally increased in morphologically altered shores in all geographical regions, while Bivalvia, Crustacea, Ephemeroptera, Gastropoda and Trichoptera showed comparatively lower numbers in many anthropogenically altered sites. Furthermore, taxon richness was positively correlated with habitat diversity. We were able to relate changes in littoral communities to anthropogenic shoreline alterations, and linked the effect to the loss of habitats and habitat complexity. The results of our study demonstrate that littoral macroinvertebrates respond consistently negative to the influence of morphological alterations across European geographical regions in terms of biodiversity. While macroinvertebrates have previously been identified to be useful descriptors of morphological change in single countries/regions, we can now validate that they can be used to assess the ecological status of lakes in terms of morphological alterations across European regions. Our results can be used to further improve ealready existing WFD-compliant multimetric indices, for example by including taxa groups, which show a strong reaction to shoreline alterations. This could be supported by the inclusion of a suit of indicator taxa reflecting the loss of complex habitats such as macrophytes in the lake littoral.

Great Lakes coastal fish habitat classification and assessment

Abstract Basin-scale assessment of fish habitat in Great Lakes coastal ecosystems would increase our ability to prioritize fish habitat management and restoration actions. As a first step in this direction, we identified key habitat factors associated with highest probability of occurrence for several societally and ecologically important coastal fish species as well as community metrics, using data from the Great Lakes Aquatic Habitat Framework (GLAHF), Great Lakes Environmental Indicators (GLEI) and Coastal Wetland Monitoring Program (CWMP). Secondly, we assessed whether species-specific habitat was threatened by watershed-level anthropogenic stressors. In the southern Great Lakes, key habitat factors for determining presence/absence of several species of coastal fish were chlorophyll concentrations, turbidity, and wave height, whereas in the northern ecoprovince temperature was the major habitat driver for most of the species modeled. Habitat factors best explaining fish richness and diversity were bottom slope and chlorophyll a. These models could likely be further improved with addition of high-resolution submerged macrophyte complexity data which are currently unavailable at the basin-wide scale. Proportion of invasive species was correlated primarily with increasing maximum observed inorganic turbidity and chlorophyll a. We also demonstrate that preferred habitat for several coastal species and high-diversity areas overlap with areas of high watershed stress. Great Lakes coastal wetland fish are a large contributor to ecosystem services as well as commercial and recreational fishery harvest, and scalable basin-wide habitat models developed in this study may be useful for informing management actions targeting specific species or overall coastal fish biodiversity.

Disentangling food webs interactions in the littoral of temperate shallow lakes

Elucidation of food web interactions provides better understanding of ecosystem functioning, indicates anthropogenic impacts which often cause alterations in environmental conditions and detoriorations in feeding network in terrestrial and aquatic ecosystems. The importance of microfauna and macroinvertebrates in littoral zones of shallow waters has poorly been studied regarding their trophic interactions. This study compares invertebrate assemblage and food web interactions among epiphyton, zooplankton and benthic macroinvertebrates across structural heterogeneity in the littoral zone of three temperate shallow water bodies. Submerged and structurally-complex stands of Ceratophyllum demersum inhabited higher abundance of cladocerans and supported higher diversity and biomass of epiphytic protozoans and invertebrates in comparison to floating-leaved Nuphar lutea stands. Analysis of the ecosystem functioning illustrated the increased biomass of macroinvertebrate predators and a preference of predation over planktonic crustaceans in more complex macrophyte stands. Food webs displayed higher complexity and size with habitat heterogeneity, while epiphyton and zooplankton shared the important fraction in food resources among the invertebrate trophic network. Results of food web modelling indicated zooplankton and epiphyton as more vulnerable to invertebrate predation in the complex submerged macrophytes than in floating-leaved macrophyte stands. Integrated community, ecosystem and food web approaches in explanation of complex trophic interactions in the littoral zones justified an increase in diversity and food-web functional complexity with structural heterogeneity of microhabitats.

The role of macrophyte structural complexity and water flow velocity in determining the epiphytic macroinvertebrate community composition in a lowland stream

Habitat structural complexity provided by aquatic macrophytes in lowland streams affects the associated epiphytic macroinvertebrate assemblages in both direct (increased microhabitat diversity, refuge against predation) and indirect ways (e.g. current attenuation by physical structures). In a correlative field study carried out in two different years in a Belgian stream, we investigated the effects of the factors macrophyte identity, macrophyte complexity (represented as fractal complexity) and current velocity on the composition of the macroinvertebrate community associated with monospecific macrophyte patches, consisting of plants with differing structural complexity; Sparganium emersum Rehmann (least complex), Potamogeton natans L. (intermediate) and Callitriche obtusangula Le Gall (most complex). In addition to significantly lower within-patch current velocity being observed, vegetation stands consisting of complex macrophytes also harboured significantly richer macroinvertebrate communities than stands of simpler macrophytes. A significant part of the variation in the macroinvertebrate community composition could be explained by plant identity, macrophyte complexity and current velocity. However, it was not possible to determine the relative importance of these three factors, because of their high degree of intercorrelation. Additionally, the explanatory power of these factors was higher under conditions of high current velocity, suggesting a role of macrophyte patches as instream flow refugia for macroinvertebrates.

Analyzing the effects of four submerged macrophytes with two contrasting architectures on zooplankton: A mesocosm experiment

<p>Increases in the structural complexity of submerged macrophytes are often shown to be linked to higher invertebrate abundance and diversity, but a number of studies have demonstrated, however, that this is not always the case. The objective of this study was to analyze the effects of four macrophyte species with two contrasting architectures (simple architecture with broad leaves: <em>Vallisneria spiralis</em> L. and <em>Potamogeton malaianus</em> Miq. and complex architecture with finely dissected leaves: <em>Ceratophyllum demersum</em> L. and <em>Myriophyllum verticillatum </em>L.) on zooplanktons. We hypothesized that structurally more complex macrophytes would support more zooplanktons and higher diversity, species richness, abundance and biomass, and to test our hypotheses, zooplankton samples within the above-mentioned macrophytes were collected to analyze the variances at different times. Contrary to our expectations, we found that the zooplankton’ responses were independent to the macrophyte architecture. Specially, although finely dissected<em> M</em>.<em> verticillatum</em> could significantly increase total zooplanktons, diversity, species richness, rotifers and cladocerans than the other three macrophytes, the effects of finely dissected <em>C</em>.<em> demersum</em> on these parameters exhibited no significant differences compared to two broad leaved macrophytes (<em>V</em>.<em> spiralis</em> and <em>P</em>.<em> malaianus</em>). Moreover, broad leaved macrophytes even increased more abundance zooplanktons than finely dissected <em>C</em>.<em> demersum</em>. In addition, the effects of macrophytes on zooplanktons also varied with zooplankton species. For example, the four tested macrophytes could significantly increase cladoceran abundance and biomass. Yet for copepods, the density was significantly increased<em> </em>in presence of <em>V</em>.<em> spiralis</em> and <em>C</em>.<em> demersum</em>, but<em> P</em>.<em> malaianus </em>and<em> M</em>.<em> verticillatum</em> did not show significant effects on copepod density. Moreover, all the tested macrophytes except for <em>V</em>.<em> spiralis</em> even significantly suppress copepod biomass. Therefore, our results did not support the hypothesis that structurally complex macrophytes harbor more zooplanktons, and showed that the effects of the investigated macrophytes on zooplanktons were not likely to depend on their architectures, but seemed to rely on complex relationships between macrophyte and zooplankton species.</p>

Effects of macrophyte complexity and hydrometric level on fish assemblages in a Neotropical floodplain

Habitat heterogeneity provided by aquatic macrophytes and water level variations (flood pulse) are essential factors in structuring fish assemblages. This study aimed to describe the fish species that prefers macrophytes covered areas and to evaluate how macrophytes complexities and a flood pulse influence the structure of fish assemblages and selected attributes (viz. fish species density, species richness and evenness). Sampling was performed with seining nets in five floodplain lakes associated with the Baia River, before (November to December 2011) and after (February to July 2012) a flood, considering different degrees of macrophyte complexity (Absent, intermediate, and high). A total of 48 fish species was recorded, with Characiformes the most dominant. Eight species were indicators of high complexities (seven before the flood and only one after). Significant differences among the different degrees of macrophyte complexity and before and after the flood were found for assemblage structure, species density and richness. Fish assemblage attributes were high in higher habitat heterogeneity provided by macrophytes, but all before the flood. Nevertheless, macrophyte stands with high and intermediate complexity were less affected by the flood, suggesting that the structure propitiated by macrophytes favors the persistence of the fish assemblage in floodplain lakes. Therefore, any action towards conservation of fish assemblages in macrophytes should consider dam operation upstream, to ensure seasonality of flood pulses.

Local and landscape scale determinants of macroinvertebrate assemblages and their conservation value in ponds across an urban land-use gradient

Urbanisation represents a growing threat to natural communities across the globe. Small aquatic habitats such as ponds are especially vulnerable and are often poorly protected by legislation. Many ponds are threatened by development and pollution from the surrounding landscape, yet their biodiversity and conservation value remain poorly described. Here we report the results of a survey of 30 ponds along an urban land-use gradient in the West Midlands, UK. We outline the environmental conditions of these urban ponds to identify which local and landscape scale environmental variables determine the biodiversity and conservation value of the macroinvertebrate assemblages in the ponds. Cluster analysis identified four groups of ponds with contrasting macroinvertebrate assemblages reflecting differences in macrophyte cover, nutrient status, riparian shading, the nature of the pond edge, surrounding land-use and the availability of other wetland habitats. Pond conservation status varied markedly across the sites. The richest macroinvertebrate assemblages with high conservation value were found in ponds with complex macrophyte stands and floating vegetation with low nutrient concentrations and little surrounding urban land. The most impoverished assemblages were found in highly urban ponds with hard-engineered edges, heavy shading and nutrient rich waters. A random forest classification model revealed that local factors usually had primacy over landscape scale factors in determining pond conservation value, and constitute a priority focus for management.

Distribution and attachment characteristics of Sida crystallina (O.F. Müller, 1776) in lentic freshwater ecosystems of South Korea

Macrophytes are commonly utilised as habitat by epiphytic species; thus, complex macrophyte structures can support high diversities and abundances of epiphytic species. We tested the hypothesis that the presence of aquatic macrophytes is an important factor determining Sida crystallina (O.F. Muller, 1776) distribution. An ecological survey was conducted in 147 lentic freshwater bodies. S. crystallina was frequently observed, and its density was strongly associated with macrophyte abundance. S. crystallina was found on emergent plant species such as Phragmites australis and Paspalum distichum, attached to the stem surfaces by adhesive substances secreted by the nuchal organ. Thus, S. crystallina was more strongly attached to macrophytes than to other epiphytic cladoceran species. We found higher densities of S. crystallina in filtered water with increased macrophyte shaking effort (i.e. 10, 20, 40, or 80 times). S. crystallina attachment was not related to fish predation. Stable isotope analysis showed that S. crystallina utilises epiphytic organic matter (EOM) on macrophytes as a food source. Consequently, S. crystallina seems to have a strong association with species-specific macrophyte biomass than with other cladoceran species, which may contribute to this species’ predominance in various freshwater ecosystems where macrophytes are abundant.

Microbial community diversity and composition varies with habitat characteristics and biofilm function in macrophyte‐rich streams

Biofilms in streams play an integral role in ecosystem processes and function yet few studies have investigated the broad diversity of these complex prokaryotic and eukaryotic microbial communities. Physical habitat characteristics can affect the composition and abundance of microorganisms in these biofilms by creating microhabitats. Here we describe the prokaryotic and eukaryotic microbial diversity of biofilms in sand and macrophyte habitats (i.e. epipsammon and epiphyton, respectively) in five macrophyte‐rich streams in Jutland, Denmark. The macrophyte species varied in growth morphology, C:N stoichiometry, and preferred stream habitat, providing a range in environmental conditions for the epiphyton. Among all habitats and streams, the prokaryotic communities were dominated by common phyla, including Alphaproteobacteria, Bacteriodetes, and Gammaproteobacteria, while the eukaryotic communities were dominated by Stramenopiles (i.e. diatoms). For both the prokaryotes and eukaryotes, the epipsammon were consistently the most diverse communities and the epiphytic communities were generally similar among the four macrophyte species. However, the communities on the least complex macrophyte, Sparganium emersum, had the lowest richness and evenness and fewest unique OTUs, whereas the macrophyte with the most morphological complexity, Callitriche spp., had the highest number of unique OTUs. In general, the microbial taxa were ubiquitously distributed across the relatively homogeneous Danish landscape as determined by measuring the similarity among communities (i.e. Sørensen similarity index). Furthermore, we found significant correlations between microbial diversity (i.e. Chao1 rarefied richness and Pielou's evenness) and biofilm structure and function (i.e. C:N ratio and ammonium uptake efficiency, respectively); communities with higher richness and evenness had higher C:N ratios and lower uptake efficiency. In addition to describing the prokaryotic and eukaryotic community composition in stream biofilms, our study indicates that 1) physical habitat characteristics influence microbial diversity and 2) the variation in microbial diversity may dictate the structural and functional characteristics of stream biofilm communities.

Do the abundance, diversity, and community structure of sediment meiofauna differ among seagrass species?

The structural complexity of macrophytes that provide various microhabitats is related to local infaunal abundance and diversity. Seagrass is considered an ecosystem engineer that alters the benthic environment and enables certain distinct meiofauna to thrive in sediments. The effects of seagrass species in a mixed-species seagrass bed at Haikou, Taiwan were examined. Analysing quantitative samples obtained from patches ofThalassia hemprichii, Halodule uninervis, Halophila ovalisand adjacent unvegetated sediments inspected the community structures of meiofauna and marine nematodes. The abundance and diversity of crustaceans and nematodes were substantially higher in habitats in which seagrass grew than in those comprising unvegetated sediments. Both the compositions of higher meiofaunal taxa and nematode species were distinct between seagrass habitats and unvegetated areas. Several nematode species existed exclusively in patches of individual seagrass species, whereas no nematode specifically occurred in unvegetated areas. Regarding the trophic types of nematodes, non-selective deposit feeders were prevalent in the present study, whereas selective deposit feeders and epistrate feeders were relatively dominant in seagrass habitats. Sediments underneath various patches of seagrass species harbour dissimilar nematode communities, even with similar sediment parameters and at a small-scale distance.

Macrophyte Complexity Controls Nutrient Uptake in Lowland Streams

Macrophytes act as ecosystem engineers in lowland stream ecosystems, enhancing habitat complexity and physical structure. Studies have demonstrated that macrophyte abundance and growth form can dictate the degree to which physical and biological stream characteristics are altered. However, few studies have investigated the influence of macrophytes and their species-specific variation in morphological complexity on functional processes, such as nutrient uptake. We injected 15N-labeled ammonium (15N-NH4 +) into four macrophyte-rich lowland streams in Denmark to quantify the uptake of NH4 + by macrophytes, epiphytic biofilms, benthic biofilms, and suspended particulate organic matter in the water column. Overall, macrophytes and their epiphytic biofilms accounted for 71–98% of the reach-weighted uptake across the study streams. While macrophytes had the highest rates of NH4 + uptake among the compartments we measured, the epiphytic biofilms had the highest uptake efficiency, ranging from 0.06 to 0.6 mg N mg N biomass −1 d−1. Among all compartments, the uptake efficiency was inversely related to the carbon-to-nitrogen ratio. Macrophyte complexity, expressed as leaf perimeter-to-area ratio (P:A), varied among the five species found in the study streams. The uptake rates by macrophyte species with high leaf P:A were, on average, an order of magnitude higher than the rates for species with simple leaf morphology (430 vs. 49 mg N m−2 d−1). In summary, our results indicate that macrophytes regulate stream function both via direct uptake of NH4 + from the water column and by providing a substrate for epiphytic biofilms. Furthermore, the effect of leaf architecture on nutrient uptake rates provides evidence that physical complexity can enhance ecosystem function.

Nonlinear and density-dependent fish habitat selection across physiochemical gradients in an invasive macrophyte habitat

Invasive macrophytes drive substantial changes to freshwater fish habitats. Such changes can influence how fish select for habitats, but fish–habitat relationships in many invasive macrophytes are often poorly understood at micro-scales. Fish habitat use is influenced by dissolved oxygen (DO) and habitat complexity, but this response can be nonlinear and dependent upon fish density. This study tested whether microhabitat use of sunfish (Lepomis spp.) in invasive macrophyte beds was density-dependent. Fish were sampled with underwater video point counts in six 0.405 ha experimental ponds with surface-matted hydrilla Hydrilla verticillata and stocked with varying densities of sunfishes. Regression models were used to evaluate the key drivers for fish habitat selection across DO, complexity and fish densities. Both fish occurrence and fish counts were positively influenced by DO and negatively influenced by habitat complexity, but the fish counts-DO relationship was dome-shaped and both fish occurrence and counts depended upon fish densities. For example, at high fish densities, fish used low and high DO and high macrophyte complexity; at low fish densities, fish avoided such areas. Fish counts peaked at intermediate DO and low macrophyte complexity. Density-dependent fish habitat selection appeared to mitigate detrimental effects of invasive macrophytes on fish habitats, indicating that fish can and do use ‘inhospitable’ habitats with potential positive population growth. Understanding density-dependent habitat selection is needed when evaluating the quality of habitats, as apparently inhospitable habitats can be utilized when fish density is high.

Habitat type as strongest predictor of the body size distribution of Chydorus sphaericus (O. F. Müller) in small water bodies

Chydorus sphaericus, a cladoceran characterized by a wide range of distribution, is often numerous in various water habitats. Its body size is a consequence of environmental characteristics and physiology. The aim of the study focused on the distribution of body size and densities of C. sphaericus in relation to environmental conditions represented by: (i) habitat types (elodeids, helophytes, and the open water); (ii) specific pond types (forest and field); (iii) pond size (surface area); (iv) the presence/lack of fish; and (v) physicochemical factors. Similar to large daphnids, in the case of the examined small water bodies, fish presence was responsible for a reduction of the body size of C. sphaericus in the zone of open water. More abundant crustacean communities and the presence of larger specimens were found among macrophytes, which indicated that aquatic vegetation offered optimal growth conditions as well as an effective refuge against fish predation. These facts reflect the necessity for maintaining a varied mosaic of habitats even in small water bodies such as the examined ponds. We found that not only the abundance of C. sphaericus but also its body size can be used as an bioindicator of environmental conditions as it preferred small and eutrophic ponds, particularly those with complex macrophyte cover (such as elodeids). Furthermore, the abundance pattern of zooplankton dominant species was affected by elodeids and fish presence as well as by the area of the ponds.

Macroinvertebrates select complex macrophytes independently of their body size and fish predation risk in a Pampean stream

Macrophyte complexity has been associated with high abundance and richness of macroinvertebrates. While the effect on richness has been attributed to an increase in the number of niches, the effect on abundance has been explained by a higher availability of space for small individuals, refuge, and/or food. For studying effects of complexity on macroinvertebrates, we used complementary approaches of laboratory choice and field colonization experiments, with macrophytes (Egeria densa and Elodea ernstae) and plastic imitations of contrasting fractal dimension. We investigated whether macroinvertebrates may actively select complex habitats by Hyalella sp. choice experiments. Then, we tested effects of complexity on macroinvertebrate density, biomass, richness, diversity, and body size using colonization experiments. Finally, a caging experiment was performed to study interacting effects of complexity and predation. The active choice of complex substrates by Hyalella sp., and the significant positive relationship between macrophyte fractal dimension and macroinvertebrate density support the existence of a positive effect of complexity on abundance. As macroinvertebrate length was not associated with fractal dimension, such differences could not be attributed to a higher space available for smaller invertebrates in complex plants. Finally, neither macroinvertebrate density nor size was reduced by fish predation in the Las Flores stream.

Effect of habitat complexity attributes on species richness

Habitat destruction is a leading cause of biodiversity loss worldwide. Destruction involving structural simplification tends to be a large contributing factor to this loss as many studies have reported a positive relationship between habitat complexity and taxonomic richness. However, the aspects of complexity that are most important for this relationship are still unclear. We tested whether several attributes of complexity contribute significantly to the effects of habitat complexity on macroinvertebrate richness. We sampled macroinvertebrates associated with several species of macrophytes covering a wide complexity gradient in freshwater coastal wetlands. Macrophyte complexity was quantified by measuring vertical and horizontal interstitial distances. Multiple regression was used to assess the relative importance of complexity attributes including the overall complexity as a space size/frequency index, space‐size heterogeneity as the variation in space sizes, as well as the more commonly used macrophyte biomass, number of stems and the number of macrophyte species. Our results indicate that space‐size heterogeneity is a more important contributor to taxonomic richness than overall complexity and the other complexity attributes examined. The results of this study have implications for the use of this concept in habitat restoration by the enhancement of habitat structures.

Effects of macrophyte architecture and leaf shape complexity on structural parameters of the epiphytic algal community in a Pampean stream

Habitat heterogeneity is one of the main factors determining distribution of organisms, and vegetation is of primary importance in shaping the structural environment in aquatic systems. The effect of macrophyte complexity on macroinvertebrates has been well researched; however, much remains to be revealed about the influence of complexity on epiphytic algae. Here, we used fractal dimension to study the effect of complexity at two scales, macrophyte architecture and leaf shape, on several parameters of the epiphytic algal community (number of individuals, biomass, taxon richness and diversity) in a Pampean stream. Four submerged macrophyte species with different complexities and associated algae were sampled in late spring, summer and autumn. Important differences were found in fractal dimension of the whole plant and leaves among macrophyte species. The particulate organic matter and chlorophyll a associated positively to leaf fractal dimension, but not to plant fractal dimension, partially supporting the hypothesis of a positive effect of macrophyte complexity on periphyton biomass. No association was found in fractal dimension with algal abundance, taxon richness or diversity. Complementary, a mesocosm experiment was performed with plastic imitations of different plant fractal dimensions. After four weeks, there were differences in chlorophyll a and autotrophy index between treatments that suggested a positive effect of complexity on autotrophic periphyton biomass. These results indicate that the well-known positive effect of macrophyte complexity on macroinvertebrates might be partially explained by a positive effect of complexity on periphyton biomass.

Does Nature and Persistence of Substrate at a Mesohabitat Scale Matter for Chironomidae Assemblages? a Study of Two Perennial Mountain Streams in Patagonia, Argentina

Chironomid substrate—specific associations regarding the nature (organic—inorganic) and stability (stable—unstable) of different habitats were investigated at two low order Patagonian streams, during high and low water periods. Nant y Fall and Glyn rivers were visited twice (October 2007 and March 2008) and seven different habitat types were identified. A total of 60 samples were collected using a Surber sampler (0.09 m -2 and 250 µm) and a set of 23 environmental descriptors including physicochemical parameters and different fractions of particulate organic matter were assessed. 35 Chironomidae taxa were recorded with Orthocladiinae (20), Chironominae (7), and Podonominae (4) being the most well—represented subfamilies. Paratrichocladius sp. 1, Parapsectrocladius sp. 2, Parametriocnemus sp. 1, Pseudochironomus sp., and Rheotanytarsus sp. were the most abundant taxa. According to the relative preference index, at least 14 taxa showed strong affinity for a particular substrate. The structurally complex macrophyte Myriophyllum quitense supported 11 taxa compared with only five taxa found on the less complex Isoetes savatieri. Generally, stable substrates (boulders, cobbles, and rooted plants) supported significantly higher chironomids richness, abundance, and diversity than unstable ones (gravel—sand). Canonical correspondence analysis revealed that detritus (leaves, seeds, and biomass), macrophyte biomass, and secondarily hydraulic variables had high explanatory power on chironomids species composition and structure. This work suggests that more complex substrates showing persistence in the temporal dimension supported a diverse array of chironomids, meaning that the maintenance of natural habitat heterogeneity is essential for the community. Land—use practices having significant effects on ecological stream attributes such as increased turbidity, sediment deposition, and runoff patterns will alter assemblages. Understanding environmental associations of the Chironomidae assemblage at the habitat scale is significant for conservation purposes and for the management of low order streams in Patagonia.