Hranidbene skupine oblića u sedrenim staništima (Plitvička jezera, Hrvatska)

Free-living nematodes are an important group in all benthic habitats. They occur in high abundance and due to the feeding types they have strong influence on bacteria, algae, detritus and meiofauna in periphyton and sediments. The main aims of this study were to determine the vertical distribution of nematodes and their feeding types within the moss-covered tufa barrier over a one year period in Plitvice Lakes National Park. Altogether 23 taxa were identified with a maximum value of 198 ind. 10 cm-2 in spring. Stylet-bearing suction feeders were the dominant nematode feeding type in bryophytes and in the deeper layers of the tufa substrates. The domination of Adenophorea and the high value of the maturity index (MI) confirmed that this was clean, unpolluted water and showed the oligotrophic state of investigated habitat. The results demonstrated that nematodes, due to their high abundance and biomass, play an important role in karst water sediments.Slobodnoživući, nenametnički oblići su važan segment u svim bentičkim staništima. Oni su prisutni u velikoj brojnosti te svojim prehrambenim navikama značajno utječu na bakterije, alge, detritus i meiofaunu u perifitonu i sedimentu. Glavni ciljevi ovog rada su bili utvrditi vertikalnu distribuciju oblića i njihove hranidbene skupine u mahovinom prekrivenim sedernim barijerama Nacionalnog Parka Plitvička jezera tijekom jedne godine. Ukupno smo utvrdili 23 svojte oblića s maksimalnom brojnošću od 198 ind. 10 cm–2 u proljetnom razdoblju. U mahovinama i u sedrenom sedimentu dominantna hranidbena skupina bili su oblići s bodežićem - „isisavači“. Velika brojnost oblića iz skupine Adenophorea i visoke vrijednosti MI indeksa (eng. Maturity index) potvrdile su čisti, nezagađeni vodeni medij i oligotrofno stanje ekosustava. Navedeni rezultati ukazuju da oblići, brojnošću i biomasom, imaju važnu ulogu u sedimentima krških voda

Veličinska struktura ličinki vodenih kukaca tijekom naseljavanja

Colonization of aquatic insect larvae was investigated in a second order woodland stream using trays filled with natural substrate. Patterns of colonization differed significantly between seasons in terms of number of taxa, density and biomass of aquatic insect assemblages. Larvae in the first (out of five) size class made up 35.5% of all colonizers during the spring, highest share of 54.1 % during the summer, 40.8% and 17.5% during the autumn and winter, respectively. Many peak values in density during spring and summer matched with single-species mass colonization of first or second size classes, explained by »distributional drift« of newly-hatched insects, or direct oviposition on substrate. Size structure of the community did not change with time of exposition, although it reflected life histories of the aquatic insects, which led to seasonal changes in colonization patterns.Naseljavanje ličinki vodenih kukaca praćeno je u šumskom potoku drugog reda upotrebom podloga s prirodnim supstratom. Kolonizacija se značajno razlikovala između godišnjih doba s obzirom na broj svojti, brojnost i biomasu zajednica vodenih kukaca. Ličinke prvog (od pet) veličinskog razreda imale su udio od 35,5% među svim kolonizatorima tijekom proljeća, najveći udio od 54,1% tijekom ljeta, 40,8% i 17,5% tijekom jeseni i zime. Mnoge vršne vrijednosti brojnosti tijekom proljeća i ljeta odgovarale su masovnom naseljavanju jedne svojte prvog ili drugog veličinskog razreda, što je objašnjeno »distribucijskim driftom« mladih ličinki, ili direktnim polaganjem jajašaca na podlogu. Veličinska struktura cijele zajednice nije se mijenjala s vremenom ekspozicije, već je odražavala svojstva životnih ciklusa vodenih kukaca što je dovelo do sezonskih promjena u obrascima naseljavanja

Slatkovodni grebeni kao mezostaništa za utvrđivanje dnevnih obrazaca drifta beskralježnjaka

Freshwater reefs (known as tufa barriers) are special karst features recognized for highly heterogeneous habitat structures, complex hydrogeological features, and unique macrozoobenthos drift (downstream dispersal) patterns. Our study objective was to investigate diel and seasonal drift patterns between barriers and pools, both composed of moss-rich and fishless mesohabitat types, aligned on a small spatial scale within the karst, tufa-precipitating Plitvice Lakes hydrosystem. We monthly sampled drift at the two mesohabitat types (barriers and pools) during midday and dusk and examined quantitative and qualitative drift compositions, including drifting invertebrates, moss, and associated particulate organic and inorganic matter (APOIM). Barriers displayed higher invertebrate drift densities than those of pools. The same pattern was observed for moss and APOIM. At both mesohabitat types, invertebrate drift showed peak but highly variable densities during late spring and summer (mean >100 individuals m-3), whereas during late winter and early spring the drift densities were 5-fold lower than those densities. The nonmetric multidimensional scaling analysis revealed that invertebrate drift seasonality was influenced by seasonal drift patterns of aquatic moss and moss-dwelling invertebrate taxa. Adult and/or larval Riolus spp. and larval Hemerodromia spp. were found to be the most significant for the separation of midday and dusk within the NMDS ordination of barriers and pools. At barriers, midday drift densities of invertebrates, moss, and APOIM were higher than the respective dusk records. Within pools, invertebrate drift was largely aperiodic. We suggest that increased midday and/or aperiodic drift are a consequence of the lack of fish between barrier- and pool-mesohabitats. Our results further indicated that aquatic invertebrates inhabiting fast-flowing barriers and slow-flowing pools mostly exhibit “passive drift” mediated by transport agents such as water flow and dislodged aquatic vegetation. The observed spatio-temporal drift patterns are also likely influenced by ontogenetic shifts in drift periodicity (i.e., shifts depending on the development stage and morphological characteristics of the individual taxa) as well as benthic distribution of moss-dwelling invertebrate taxa. We can conclude that biotic (vs. abiotic) controls of drift are likely minimized in the fishless case of the freshwater reefs and associated barrier–pool sequences within Plitvice Lakes hydrosystem.Slatkovodni grebeni (engl. freshwater reefs; poznati kao sedrene barijere) posebnost su krša, a poznati su po jako heterogenim staništima, složenim hidrogeološkim značajkama i jedinstvenim obrascima drifta (nizvodnog rasprostranjivanja) makrozoobentosa. Cilj našeg istraživanja bio je istražiti dnevne i sezonske obrasce drifta između barijera i ujezerenih dijelova toka, koji predstavljaju različite tipove mezostaništa bogatih mahovinom, ali bez riba, na maloj prostornoj skali unutar krškog sedrotvornog hidrosustava Plitvičkih jezera. Mjesečno smo uzorkovali drift na dva tipa mezostaništa (barijere i ujezerenja) tijekom podneva i sumraka, ispitujući kvantitativni i kvalitativni sastav drifta, uključujući beskralježnjake, mahovinu i pridružene čestice organske i anorganske tvari (APOIM). Barijere su bilježile veće gustoće drifta beskralježnjaka nego ujezereni dijelovi toka. Isti obrazac uočen je za mahovinu i APOIM. U oba tipa mezostaništa, beskralježnjaci su pokazali izrazito visoke, ali vrlo promjenjive gustoće drifta tijekom kasnog proljeća i ljeta (u prosjeku > 100 jedinki m-3), dok su tijekom kasne zime i ranog proljeća gustoće drifta bile peterostruko niže. Analiza nemetričkog višedimenzionalnog skaliranja (NMDS) otkrila je da na sezonske obrasce drifta beskralježnjaka utječe sezonsko otplavljivanje vodenih mahovina i pridruženih im beskralježnjaka. NMDS analizom je utvrđeno da su odrasli i/ili ličinački stadiji svojte Riolus spp. te ličinke svojte Hemerodromia spp. najznačajnije utjecale na razlike između podnevnih i sumračnih gustoća drifta na barijerama i u ujezerenim dijelovima toka. Na barijerama su podnevne gustoće drifta makrozoobentosa, mahovina i APOIM bile više od gustoća drifta u uzorcima sakupljenima u sumrak. Unutar ujezerenih dijelova toka, drift beskralježnjaka je u velikoj mjeri bio aperiodičan. Sugeriramo da je porast podnevnog i / ili aperiodičnog drifta posljedica nedostatka riba između barijera i ujezerenih dijelova toka. Naši rezultati nadalje su pokazali da vodeni beskralježnjaci koji nastanjuju barijere (brze dijelove toka) i ujezerenja (spore dijelove toka) uglavnom pokazuju „pasivni drift“ posredovan čimbenicima važnima za transport tvari i organizama unutar vodenih tokova, poput protoka vode i otplavljivanja vodene vegetacije. Na promatrane prostornovremenske obrasce drifta vjerojatno utječu i ontogenetski pomaci u periodičnosti drifta (tj. pomaci koji ovise o stupnju razvoja i morfološkim obilježjima pojedinih svojti), kao i bentoska raspodjela pojedinih svojti beskralježnjaka unutar mahovine. Možemo zaključiti da je u područjima slatkovodnih grebena i pridruženih slijedova barijera i ujezerenih dijelova toka unutar hidrosustava Plitvičkih jezera, utjecaj biotičkih čimbenika na obrasce drifta minimalan u odnosu na snažan utjecaj abiotičkih čimbenika

The Influence of the Lotic and Lentic Stretches on the Zooseston Flux through the Plitvice Lakes (Croatia)

We studied the influence of lotic and lentic stretches on zooseston flux in the karstic barrage Plitvice Lakes (Croatia). Three sampling stretches were selected: 1) a channel with low inclination; 2) water flow through a deep lake (retention), and 3) a channel with cascades and sharp inclination. At all sampling points of the three stretches, zooseston reached maximum abundance in September (up to 147.39 ind/m3). Rotifers dominated in both zooseston abundance (58 to 80%) and diversity (66 taxa), followed by crustaceans (23 taxa), predominantly Cladocera and Copepoda. Kruskal-Wallis test suggest statistically significant differences between the lentic and both lotic stretches in the biomass net flux of euplanktonic organisms. The net flux of benthic organism biomass and changes in the biodiversity index were significantly different between the lentic stretch and lotic stretch with high inclination. Lotic stretches had a greater influence on the increase of abundance and biomass of benthic and semiplanktonic organisms than on the decrease of euplanktonic organisms. Principal Components Analysis of the species environment relationship explained 66% of the variance by the two first axes, where axis 1 accounted for 39% and axis 2 accounted for 27% of the variance. Oligochaets, insect larvae, nematodes and total zooseston were associated with component 1, showing that their biomass was negatively correlated with discharge and dissolved oxygen concentration and positively correlated with temperature. Other taxa showed a similar correlation with component 1. Biomass of Cladocera, Copepoda, T. birostris, Polyarthra spp., K. cochlearis and rotifers was associated with component 2, and positively correlated with food resources such as chl-a, POM and DOM. The inference is that zooseston flux through Plitvice Lakes is a function of the hydrological and physiographical features of the stretches, as well as food resources from the lakes