Marco Seminara

Factors Affecting Macroinvertebrate Communities in Astatic Ponds in Central Italy

ABSTRACT Twenty astatic ponds near Rome were studied in order to define the relationships between physicochemical variables and macroinvertebrate communities. The main abiotic factor differentiating the ponds was the annual hydrologic cycle. Depth, surface area, and sand percentages in the sediment were higher in permanent ponds, whereas silt+clay content was higher in temporary ones. No difference was recorded in pH, conductivity and oxygen content in the water or organic matter in the sediments between the two pond types. Three main ecological assemblages were distinguished: a) generalist taxa common to both pond types; b) taxa associated with and adapted to temporary ponds; and c) taxa which seemed to prefer permanent ponds. Overall, there was no relationship between number of taxa and surface area, except for Odonata and aquatic macrophytes. A positive correlation was observed between number of macrophyte species and macroinvertebrate taxa richness, and particularly of odonates and chironomids, suggesting that an increase in aquatic vegetation species leads to an increase in microhabitats and suitable food, substrate, and/or refuge from predators. Odonata seemed also to prefer more stable and sunny ponds.

Chironomids (Diptera: Chironomidae) from Three Temporary Ponds of Different Wet Phase Duration in Central Italy

ABSTRACT A one year-study on three temporary ponds in Central Italy examined relationships between the composition and structure of chironomid communities and some environmental variables. The three ponds showed differences in wet phase duration, dissolved oxygen content, and sediment organic matter. In the pond with longer aquatic phase and lower oxygen content a dominance of Chironominae (mainly Chironomus thummi gr. and C. plumosus gr.) and Tanypodinae (mainly Psectrotanypus varius) was recorded, whereas in the pool with shorter habitat duration and higher oxygen content, Orthocladiinae [mainly Psectrocladius (Allopsectrocladius) spp. and Cricotopus sylvestris] were dominant. The pond with an intermediate wet phase length showed some characteristics common to the other two ponds. The preferences of chironomids for ponds of different habitat duration can probably be ascribed to their larval size and strategies to survive in ephemeral waters. A more detailed analysis of chironomids of the pond with longe...

Profundal macrobenthos structure as a measure of long-term environmental stress in a polluted lake

Profundal macrobenthic community in a polluted lake (Lake Nemi, Italy) was analyzed in three distinct surveys from 1976 to 1984, in order to define long-term changes in environmental conditions of sediments. Profundal macrobenthos was mainly composed of Oligochaeta. Only a few Chironomidae and a few other taxa were characteristically found in the superior zone. The long-term stress, due to persistent hypolimnetic O2 deficit, caused progressive simplification of the total community structure. This leads to a high faunal similarity among stations at different depths. The temporal trend of the community structure parameters and the significant role of some taxa (Potamothrix heuscheri, Procladius and Chaoborus flavicans) in the eutrophication process of the lake are also discussed.

Macroinvertebrates and environmental factors of some temporary and permanent ponds in Italy

Temporary and permanent ponds provide suitable habitats for a very wide range of aquatic plant and invertebrate species, often including endangered and/or nationally rare ones (BIGGS er al. 1994). However, these types of freshwaters have tended to disappear due to changes in land use and building development, with a serious loss of local biological diversity. In particular, species having specific biotope preferences are threatened by increasing landscape disturbance and fragmentation. For these reasons, scientific interese in these small freshwater bodies has increased over the past decade, with an increasing focus on their classification, conservation and management (GROWNS er al. 1992, VERDONSCHOT 1992, BIGGS et al. 1994, COLLINSON et al. 1995).

Differential responses of zooplankton assemblages to environmental variation in temporary and permanent ponds

Permanent and temporary wetlands in Mediterranean shrublands represent unique repositories of biodiversity, which are increasingly threatened by human-induced habitat loss. The zooplankton of a permanent (P1) and a temporary pond (T35) in the Natural Reserve of Castelporziano, a rare residual stretch of such a shrubland in Central Italy (Latium), was investigated to: (1) expand and deepen knowledge of these endangered freshwater habitats, which represent a crucial component of Mediterranean biodiversity; (2) identify environmental controls regulating the development of zooplankton communities of each environment; and (3) highlight differences in the adaptive responses of the zooplankton community in relation to the different ecological conditions experienced by permanent and temporary habitats. Despite summer desiccation in T35, the two ponds exhibited a relative homogeneity in hydrological and physico-chemical dynamics. Zooplankton assemblages contained 41 total taxa, of which 32 were found in P1 and 28 in T35. Out of the 41 taxa identified, 22 (>50%) were exclusively present in one of the two ponds. On a yearly basis, the community dynamics of P1 seemed to be conditioned by physical and chemical factors and by hydrological cycle characteristics, while the community of T35 responded to algal blooms, food competition and predator/prey equilibria rather than correlating to abiotic factors. The main differences amongst zooplankton assemblages were observed over short time scales and occurred both within and between seasons, highlighting the role of some structural taxa that dominated the average composition of the community throughout the year, and the importance of “quick-response” taxa in determining the short-term composition and structure variation of pond zooplankton. A year-round cyclic community succession peculiar to each pond is described.

Seasonal changes of the profundal macrobenthic community in a polluted lake

Late summer and winter structures of the profundal macrobenthos in a polluted lake (Lake Nemi, Central Italy) were compared to verify the relative differences in the faunal structure and the magnitude of the winter recovery of this community. Densities of Oligochaetes and Chironomids did not vary significantly from summer to winter, the latter not showing any recolonization of the profundal zone. Structure and diversity of the total fauna, and Oligochaete/Chironomid ratio were very similar in the two periods. Our results suggest that in a severely polluted lake, with a strong and lasting oxygen deficit in the hypolimnic zone, a lack of recovery of profundal macrobenthos may be expected in improved environmental winter conditions.

Assessing Hypolimnetic Stress in a Monomictic, Eutrophic Lake Using Profundal Sediment and Macrobenthic Characteristics

ABSTRACT Summer-winter variations of the physico-chemical features of profundal sediments and of the characteristics of the profundal benthic community in a small, monomictic and eutrophic lake were analyzed in order to define their relations to environmental stress in the hypolimnion. The sediments were rich in P and N compounds. The benthic fauna exhibited a very poor taxa richness and diversity in summer, probably due to reduced oxygen in the hypolimnion, and there was only slight improvement of these community parameters in winter when reoxygenation occurred. The macrofauna was influenced by both sediments and overlying waters.

A note on chironomids (diptera) of temporary pools in the National Park of Circeo, Central Italy

Preliminary observations on chironomid assemblages in 9 temporary pools of the National Park of Circeo (Central Italy) are reported. A total of 15 genera or species groups (6 Orthocladiinae, 3 Tanypodinae, 1 Tanytarsini and 5 Chironomini) were recorded during March and April, 1986.Psectrotanypus varius, Polypedilum nubeculosum gr.,Chironomus thummi gr. andC. plumosus gr. were the most abundant and frequent taxa in the nine pools. Almost all chironomids collected are eurytopic and widely distributed in Europe, including Italian waters. Only the finding ofGymnometriocnemus is reported in this paper as a new record for Central Italy. Similarity among pools and among taxa (coefficient of Jaccard) shows a major occurrence of aquatic Orthocladiinae in smaller pools and of Chironomini in larger pools. This relationship between chironomid assemblages and pool sizes can be partly related to the duration of the wet phase which affects chironomid species according to their survival strategies.

Environmental stress in a regulated eutrophic lake indicated by the profundal macrobenthic community

Abstract The profundal macrobenthos of a regulated lake (Lake Canterno, Central Italy) was investigated to provide information on the structure and composition of this community in a lake long subject to wide fluctuations of the water level and to the influence of domestic sewage. Pollution‐tolerant forms constituted most of the total macrobenthos. It is suggested that large water movements (water level drawdown and hypolimnical drawoff), by producing a marked environmental instability, and eutrophication phenomena (e.g. deoxygenation), account for: a) high abundances of mobile fauna (Dero digitata, Procladius and Chaoborus flavicans), especially at the station close to the water outlet; and b) high abundances of mud‐dwelling fauna (Tubificidae and Chironomus plumosus) in the stations far from the water outlet. Diversity was negatively affected by mobile form percentages, and positively influenced by mud‐dwelling fauna percentages. Lastly, behavioural indicators are suggested to be useful markers with whi...

Zooplankton Communities in Two Astatic Basins in the Natural Reserve of Castelporziano (Central Italy): Composition and Temporal Succession

ABSTRACT The composition and temporal succession of the zooplankton communities in two neighboring biotopes (a permanent pond, P17; and a temporary pond, T17) in the natural reserve of Castelporziano (Central Italy) were investigated for one year. Along with some physicochemical parameters (pH, dissolved oxygen, conductivity), the relative abundance of major zooplankton groups, species composition, and community structure (i.e., species richness, Shannon diversity, and evenness) of both ponds were compared. Almost all the parameters considered showed greater variations in T17 than in P17; the latter exhibited more stable environmental conditions. A total number of 52 taxa was collected, of which only 20 were shared by both ponds. In spite of its harshness, T17 had a richer and more diversified zooplankton than P17, suggesting an important role of the dry phase in determining such conditions. Substantial differences in temporal succession of zooplankton were apparent for T17, in which distinct successional phases were identified on the basis of diversity and exclusiveness of the taxa present. This composition and structure seemed to be strongly linked to the long-lasting wet phase.