Biserka Primc

Meiofauna constitute a considerable portion of invertebrate drift among moss-rich patches within a karst hydrosystem

Aiming to establish the most frequent invertebrate taxa in drift at the small spatial scale within a moss-rich karst tufa-precipitating hydrosystem, we sampled drift among microhabitats differing in substratum type and flow conditions along a tufa barrier-cascading lotic reach. Additionally, we addressed the question of the contribution and the potential significance of meiofauna within the overall invertebrate drift at the small spatial scale. During the study period, a total of 60 invertebrate taxa were recorded in the drift. Six of these taxa belonged to the annelid/arthropod meiofauna and they represented 35% of total drift density. Macroinvertebrates found in drift were represented mainly by larval insects. The composition of the most abundant taxa in total drift was as follows: Alona spp. (Cladocera 26.7%), Riolus spp. (Coleoptera: Elmidae 13.2%), Simulium spp. (Diptera: Simuliidae 12.2%), Enchytraeidae (Oligochaeta 10.4%), Hydrachnidia (6.3%), Orthocladinae (Diptera: Chironomidae 3.9%) and Naididae (Oligochaeta 3.6%). Faunal drift densities and amounts of transported particulate matter (PM) were highest at the fast-flowing sites located at the barriers and lowest at the slow-flowing sites within pools. Similarly to the seasonal amounts of transported PM, faunal drift was lowest in winter, and peaked in autumn and in late spring/early summer. Correlation between flow velocity and PM-faunal drift densities suggested a significant effect of the dislodged PM, though a minor influence of discharge and flow velocity on faunal drift. We suggest that the small-scale habitat heterogeneity and the respective feeding and refugial strategies of the fauna, as well as faunal passive dislodgement initiated by the shear forces of the flow were the most important drivers of observed drift patterns.

Seasonal drift-benthos trends on a moss-covered tufa barrier within a karst barrage hydrosystem (Plitvice Lakes, Croatia)

macroinvrtebrate drift and streambed material transport are very important for the redistribution of energy sources and habitat-building elements within lotic ecosystems. the objective of the present study was to examine seasonal drift-benthos trends of macroinvertebrates and organic/inorganic matter particles between barrier and pool habitats at a small spatial scale within a karst barrage hydrosystem (Plitvice lakes). benthos and drift were sampled seasonally between November 2006 and July 2007 at four sampling sampling sites representing barrier (b; fast-flow velocity) and pool (P; slow-flow velocity) habitats. During the entire study period, amounts of drifting macroinvertebrates, and organic and inorganic particles were significantly higher at barriers than in pools. In benthos, such barrier trend was found for moss only. Considering seasonal differences, benthos showed no significant trends, whereas in drift we found significantly higher loads of all measured items in autumn and winter than in other two seasons, but such trend was observed at barriers only. the quantities of organisms in benthos and drift greatly followed the respective trends of particulate organic and inorganic matter, especially moss. at both habitat types macroinvertebrate drift mostly presented a smaller proportion of total benthos faunal composition, although there were some taxa that occurred in drift or benthos only. In total (including benthos and drift samples), we found 63 taxa during the study 5 of them were found only within pools, 38 only at barriers and 20 of them were found at both habitat types. the most dominant in both benthos and drift, were Oligochaeta, cladoceran Alona spp., Copepoda, and larval stages of coleopteran Riolus spp. and dipteran Simulium spp. most of them belong to mobile, epiphytic and/or interstitial detritivores that most likely originated from the submerged aquatic vegetation (i.e., moss), floating leaf litter and/or sediments along our study reach, whereas cladoceran and copepod taxa likely originated from the upstream lake. the observed seasonality in the faunal drift-benthos composition (e.g., Cladocera increase in summer and autumn, ephemeroptera decrease/absence in winter and spring), was likely a consequence of the seasonal food sourcing for individual taxa, and their particular life history traits. Our findings suggest that within the tufa-precipitating Plitvice lakes hydrosystem: a) drift has a very important role in maintaining benthos structure and stability within the barrier and pool habitats; b) tufa barriers are highly dynamic habitats, characterized by pronounced season-specific dislodgement of the benthic organisms and particulate matter, and effective moss-mediated macroinvertebrate dispersal; c) the abundance of macroinvertebrates and the amounts of organic/inorganic particles in drift are influenced not only by flow velocity and the seasonal lake discharges/biocommunity dynamics, but also by the initial distribution of particles/organisms within benthos as well as by the life history traits of the individual benthic organisms.

Distribution of rotifers and other meiofauna in the bryophytes and hyporheic zone of a karst hydrosystem – an example of a nested community

The meiofauna assemblages inhabiting the bryophyte-covered tufa barriers were investigated in the barrage system of Plitvice Lakes (Croatia). The main aims of the present study were: (1) to analyse the structure of the rotifer community and other meiofaunal communities in the bryophytes and the hyporheic tufa zone; and (2) to determine the influence of food sources on the meiofauna. Our results indicate that meiofauna were a constant and abundant component in bryophytes and tufa. Of the nine identified groups (Catenulida, Gastrotricha, Nematoda, Rotifera, Hydrachnidia, Oligochaeta, Copepoda, Tardigrada and Chironomidae (Diptera)), rotifers (50%) and nematodes (40%) were most abundant. Rotifers were the most diverse meiofaunal group and reached their highest numbers within the bryophytes. Also, the highest amount of ultrafine particulate organic matter, as a potential food source for rotifers, was recorded in this layer. Nematodes were the dominant meiofaunal group in deeper tufa layers. They are an omnivorous trophic group and different food sources (such as phytal remains or other meiofauna) were available in tufa layers. Meiofaunal assemblages were significantly nested and their composition was under the influence of community established in surface bryophyte mats. Information on these often overlooked faunal groups is essential for estimates of overall abundance, species richness and productivity in freshwater ecosystems.