Dubravka Čerba

Benthic macroinvertebrates associated with four species of macrophytes

Benthic macroinvertebrates associated with four species of macrophytes (Nymphoides peltata, Ceratophyllum demersum, Polygonum amphibium and Carex sp.) were investigated during two growing seasons (2001 and 2002) in the slow-flowing Čonakut Channel in the Kopački rit Nature Park in Croatia. A total of 31 macroinvertebrate taxa were found. C. demersum, a submerged plant with dissected leaves, supported the highest macroinvertebrate abundance, almost seven times more than N. peltata, a floating plant with undissected leaves, which harboured the lowest abundance during the research period. Chironomidae larvae (50–83%) and Oligochaeta (14–46%) were the most abundant groups recorded on all macrophyte species. Water-level fluctuation, because of its influence on the appearance and growth of aquatic vegetation, and the trophic state of water within the macrophyte stands seemed to be the main factors which affected the taxonomic composition and abundance of macroinvertebrates.

Interactions of weed-bed invertebrates and Ceratophyllum demersum stands in a floodplain lake

This investigation reports on weed-bed invertebrate abundance associated with the submersed macrophyte Ceratophyllum demersum L. in Lake Sakadaš within Kopački rit Nature Park (Croatia). Twenty five taxonomic groups, with the dominance of chironomids (79%), were recorded at three stations during the investigation from July 14 to September 8, 2004. Nematodes and large predatory larvae of Zygoptera with 6% were second in dominance, followed by oligochaetes with 5%. Weed-bed invertebrates on C. demersum were more abundant than on Myriophyllum spicatum L. due to different morphology of the host plants. Environmental parameters within C. demersum stands were found in the same range at all stations, but they changed during the season. They indicated eutrophy with the tendency to hypertrophy which is reflected by the composition of the weed-bed invertebrate community.

Colonisation trends, community and trophic structure of chironomid larvae (Chironomidae: Diptera) in a temporal phytophylous assemblage

Spatial and temporal trends of a phytophylous chironomid community on the submerged plant species Ceratophyllum demersum L. were investigated in a eutrophic lake (Lake Sakadas, Danube floodplain area in Croatia) during summer 2004. The study also included an analysis of functional feeding groups (FFG) and the influence of environmental parameters on the chironomid community. Within macrophyte stands at three sites, the chironomids were very abundant and the recorded larvae belonged to three subfamilies: Chironominae (Chironomini and Tanytarsini), Orthocladiinae and Tanypodinae. Endochironomus albipennis type was the dominant species with high abundance in July and September and lower abundance in August, most likely due to summer emergence. At the beginning of the sampling season, high abundance was recorded for Cricotopus sylvestris type as well. The secondary colonizers, Polypedilum sordens type, Glyptotendipens pallens type and Parachironomus varus type, displayed an increase in abundance towards the end of the season. ANOSIM analysis indicated significant differences in chironomid abundance between samples from July and September as a result of the higher abundance of Chironomini larvae in September. Active filterers, detritovores and predators were more abundant in September as compared to the other two months, while grazer abundance decreased towards the end of the study period. ANOSIM analysis separated August and September based on the abundance of different functional feeding groups (FFG). We found no significant differences between research stations for either chironomid abundance or FFG. BIO-ENV analysis indicated an influence of environmental variables, especially water temperature, Secchi depth and oxygen concentration on chironomid abundance.

Phytophilous fauna of a small and artificial urban lake

Abstract Phytophilous community on Myriophyllum spicatum was studied in a small artificial urban lake in the city of Osijek (eastern Croatia), during the spring and summer season in 2010. In the eutrophic conditions, macrophyte stands were well developed and in the formed periphyton representatives of the following invertebrate taxa were found: Hydrozoa, Nematoda, Gastropoda, Cladocera, Copepoda, Insecta larvae - including families Chironomidae and Coleoptera. They displayed differences in temporal abundance patterns. Two separate phases in macrophyte colonization with differences in invertebrate composition and abundance were recorded. Insect larvae, particularly Chironomidae, were most abundant in the first phase, through the spring period, and Hydra oligactis (brown hydra) was most abundant in the second phase, i.e. summer period. Concurrently, microcrustacean abundance declined towards the end of the summer. Results of the analyses indicated that water temperature and perihyton biomass were the variables exerting the main influence on the invertebrate assemblage, while interestingly, macrophyte size and biomass were negatively correlated with most of the fauna abundance. On the other hand, brown hydra was negatively correlated with all other invertebrate taxa, except gastropods. Larger surface of submersed macrophytes is the main parameter supporting the increase of invertebrate abundance due to providing protection from predators and growth for periphyton, an important food source for these phytophilous organisms. Macrophyte length was positively correlated with Hydra abundance, while Chironomids were more influenced by periphyton biomass. These organisms can indicate water quality conditions and a potential increase in primary and secondary production.

The colonization and succession patterns of the periphytic ciliate community in a temperate floodplain lake

Abstract An in situ experiment to investigate periphytic community development was conducted on an artificial substrate (glass slides) in a Danube floodplain lake in Croatia. The main aim of the research was to analyze the structure of the ciliate community (Ciliophora, Protozoa) in the periphyton. We wanted to investigate how biotic and abiotic factors change and influence the ciliate community, reflecting not only the temporal community dynamics, but also the complex interactions within the periphyton. The experiment lasted from April to December 2009. To monitor the colonization process, the samples were collected on the 1st, 3rd, 5th, 7th and 14th day of exposure. After that, sampling was conducted biweekly, with the aim of studying the successional patterns of the periphytic ciliate community. 116 ciliate taxa were recorded. Non-metric multidimensional scaling indicated that development of the periphytic ciliate community occurred in three phases: initial, intermediate and mature. Water temperature and transparency were the most important parameters influencing the initial and intermediate phases of community development when mainly vagile bacterivorous and algivorous ciliates were present. The mature phase was characterized by higher organic content in the periphyton and an increased concentration of chlorophyll in the water column, indicating the potential food source as the primary factor influencing ciliates. The complex three-dimensional structure of the periphyton also affected the ciliate assemblage throughout the later successional stages. The trophic structure of the ciliates became more diverse during the mature phase, with sessile suspension-feeding and predatory ciliates as dominant groups. The present study shows that the early stages of the periphytic ciliate community are influenced mainly by external abiotic factors, whilst the mature community is characterized by biotic factors.

Trophic State and Water Quality in the Danube Floodplain Lake (Kopački Rit Nature Park, Croatia) in Relation to Hydrological Connectivity

The investigated floodplain lake is located in the marginal part of the Kopacki Rit Nature Park, Croatia, a floodplain area of the Danube. In this chapter, we have assessed the influence of hydrological connectivity with the main channel on the trophic state and water quality in the Lake Sakadas. The evaluation of trophic state combines a number of physical, chemical and biological parameters with the objective to select the relevant indicators for the floodplain lakes. The following environmental parameters have been considered: water temperature, nutrients, dissolved oxygen, water transparency, chlorophyll-a concentration, phytoplankton primary productivity, benthic and periphytic communities and laboratory experiments (nutrient enrichment bioassay). An integrative approach, which includes in situ research and laboratory experiments, indicated strong correlations of abiotic and biotic components with a hydrological regime. Also, during the biological monitoring, occurrence and spread of invasive species was noted as an indication of ecosystem disturbance (hydrological and/or anthropogenic). Therefore, our results contribute to the perception of importance of the hydrological connectivity (by inundation) on the eutrophication process in the investigated floodplain lake.