Amount Of Periphyton Research Articles

Effects of an invasive crayfish on the littoral macroinvertebrates of large boreal lakes are habitat specific

Summary Invasive crayfish are widely acknowledged to have negative effects on benthic food webs in lakes, but few studies have investigated such effects at wider spatial scales and in varying habitats under natural conditions. We examined the effects of introduced signal crayfish (Pacifastacus leniusculus) on the macroinvertebrate assemblages of different habitats in two large boreal lakes. We evaluated whether the density, taxon richness and species composition are altered by the non‐native crayfish and whether the responses are similar for stony and vegetated habitats and across a depth gradient. We also studied the influence of crayfish on periphyton biomass at stony sites, as a potential link to changes in macroinvertebrate communities. In both lakes, macroinvertebrate density was similar between crayfish and non‐crayfish sites across the habitats and depths studied. However, macroinvertebrate taxon richness was significantly lower, and community composition was altered in the presence of crayfish at stony sites. No similar pattern was detected at vegetated sites or in deeper sublittoral areas. The amount of periphyton was similar regardless of the presence of crayfish, and no clear direct or indirect crayfish–periphyton interaction was detected. Our results suggest that introduced signal crayfish can have negative effects on the littoral macroinvertebrates of large boreal lakes, but that these effects are habitat specific. Our findings highlight how the evaluation of possible effects of invasive species needs to be carried out comprehensively across different habitats and spatial scales if conclusions are to be robust.

Evaluating the Effectiveness of Grassbed Treatments as Habitat for Juvenile Black Bass in a Drawdown Reservoir

AbstractMany reservoirs in arid regions experience highly variable water levels caused by seasonal inflow fluctuations and designated outflow requirements. At Shasta Lake, California, managers plant cereal‐grain grassbeds on exposed drawdown shorelines to increase juvenile fish habitat, localize productivity, and increase invertebrate fish prey. To determine the efficacy of these plantings, the abundance of juvenile black basses Micropterus spp. (20–55 mm standard length) and the amount of periphyton and macroinvertebrate prey were compared among three treatment types: (1) planted grassbeds of cereal barley Hordeum vulgare; (2) artificial rope grassbeds, which eliminated physical deterioration and nutrient release; and (3) nonplanted control sites with predominately sand and gravel substrates. In comparison with control areas, juvenile black bass abundance averaged 54 times higher in planted grassbeds and 230 times higher in artificial grassbeds. Periphyton (chlorophyll a) and benthic invertebrate biomass did not differ significantly between planted grassbeds and control sites. In artificial grassbeds, periphyton was more than two times the control levels, and benthic invertebrate biomass was more than 12 times the control levels. We conclude that the long‐term availability of physical structure, rather than nutrient release associated with decomposition of grassbed materials, drives use and effectiveness of grassbed treatments. Future management decisions in drawdown reservoirs should emphasize increasing long‐term availability and integrity of physical habitat for juvenile fishes in the littoral zone.

STUDY ON PRODUCTION AND DETACHMENT OF PERIPHYTON GROWING ON FLAT CHANNEL BED

Laboratory experiments for the kinetics of periphyton growth were conducted to find out the effect of hydraulic characteristics on the production and the detachment of periphyton, in which the amount of periphyton and the rate of detachment were measured. The results of the experiments show that the growth rate of periphyton becomes large in the case turbulence near the channel bed becomes large. It was also found that the detachment of periphyton mainly depends on the physiological action of periphyton.A numerical simulation model of the growth of periphyton was presented to describe the production and detachment in details. The result of the calculation shows that the biomass of the filament type periphyton is mainly determined by the balance between production rate and respiration rate.

Do submerged aquatic plants influence their periphyton to enhance the growth and reproduction of invertebrate mutualists?

It has been suggested that submerged aquatic plants can influence the nutritional quality of the periphyton which grows on their surfaces, making it more nutritious for grazing invertebrates, particularly snails. In return, these grazers might preferentially feed on the periphyton and clear the plants of a potential competitor, with the plants and grazers both gaining from this mutualistic relationship. A highly replicated experiment was conducted, in which the nature of the plant (isoetid and elodeid types compared with similar-shaped inert substrata), the nutrient loading, and the influence of periphyton grazers (the bladder snail, Physa fontinalis) of similar size and history were controlled. Plant growth and survival significantly increased in the presence of the periphyton grazer. Whilst the presence of the grazers had the largest influence on periphyton abundance, nutrient availability and plant type also had effects. Plant type had little influence on the nutritional quality of the periphyton measured as carbohydrate, protein and C:N. Effects of treatment on snail growth, and the timing and extent of snail reproduction disappeared when they were compared with the quantity of periphyton available. There was no evidence of enhanced grazer success in the presence of the live plants compared with inert substrata. Although submerged plants affect the growth and reproduction of the grazers which feed on their surfaces, through differences in the amount of periphyton which grows there, we found no evidence that they manipulate the periphyton to encourage such grazers.

Patterns in benthic food webs: a role for omnivorous crayfish?

1. The biomass and species richness of macrophytes and invertebrates in artificial ponds at two sites in southern Sweden (twenty‐one ponds at each site) were investigated. Alkalinity was high at one site (H ponds) and low at the other site (L ponds). The ponds chosen had different densities of signal crayfish (Pacifastacus leniusculus), with mean crayfish abundance (estimated by trapping and expressed as catch per unit effort) significantly higher in the L ponds (10.7) than in the H ponds (4.9). Macrophytes, invertebrates, the amount of periphyton on stones and the organic content of the sediment were determined in each pond.2. Macrophyte biomass, cover and species richness declined with increasing crayfish density. Macrophyte species composition differed between ponds and was related to crayfish abundance.3. The total biomass of invertebrates and the biomass of herbivorous/detritivorous invertebrates declined with increasing crayfish abundance, but the biomass of predatory invertebrates declined only in the L ponds. The relative biomass of Gastropoda and Odonata declined in ponds where crayfish were abundant. In ponds where crayfish were abundant the invertebrate fauna was dominated by sediment‐dwelling taxa (Sialis (H and L ponds) and Chironomidae (H ponds)).4. The number of invertebrate taxa in macrophytes declined with increasing crayfish abundance. The percentage of macrophyte‐associated invertebrate taxa differed between ponds, but also between sites. The relative biomass of Gastropoda declined in H ponds where crayfish were abundant. In H ponds Trichoptera or Gammarus sp. and Heteroptera dominated where crayfish were abundant, whereas Odonata dominated in L ponds with abundant crayfish.5. The organic content of the sediment decreased in ponds with high crayfish densities, while the amount of periphyton on stones was not related to crayfish density.6. We conclude that the signal crayfish may play an important role as a keystone consumer in pond ecosystems, but lower trophic levels did not respond to changes in the abundance of the crayfish according to the trophic cascade model. Omnivorous crayfish may decouple the cascading effect.

Sampling techniques for reliable determination of trace metals in macrophytes and periphyton

Sampling techniques were developed to measure trace-metal concentrations reliably in the shoots of a submerged macrophyte, Najas tenuifolia, and its attached periphyton growing in the Magela Creek flood plain in monsoonal northern Australia. At each site, 30 samples were collected within an 8-m by 8-m quadrat in a pattern of five samples from each of six irregularly spaced points. Samples were collected underwater to include all periphyton present, and precautions were taken at all stages of processing to avoid contamination. Periphyton was dislodged for separate chemical analysis by sonication followed by vigorous shaking. A significant aspect was the large amount of periphyton, up to 35% of the total sample dry weight, associated with the Najas sp. Only a proportion, up to 43%, of this periphyton could be dislodged by the physical procedures used. Trace metals were generally not present in the same concentrations in both the Najas sp. and the periphyton. The average trace-metal concentrations (μg g-1 dry weight) and standard errors measured in the Najas sp. (and periphyton) were cadmium 0.24 � 0.013 (0.093 � 0.012), copper 5.2� 0.25 (12 � 0.74), lead 0.93 � 0.084 (6.5 � 0.43), manganese 2500 � 110 (1500 � 110), uranium 0.24 � 0.023 (0.27 � 0.030), and zinc 38 � 1.0 (23 � 1.5). The significant differences in Najas sp. and periphyton trace-metal concentrations show the need to consider the effect of periphyton when sampling and reporting trace-metal concentrations in submerged macrophytes.