Marjut Rajasilta

New site formation and colonizing vegetation in primary succession on the western Amazon floodplains.

The major proportion of western Amazon forests grow on fluvial deposits and thus originated in floodplain environments. The fluviodynamic character of the sites initially colonized by plants was studied along different river types, and this information was combined with botanical observations from the same areas. Special emphasis was given to colonizing plant distribution and survival in relation to the abiotic environment. Four frequently occurring landform types, each rich in microforms, were recognized in relation to the colonization process : fluvial bars, swales, abandoned channels and riverbanks (...)

River types, site evolution and successional vegetation patterns in Peruvian Amazonia

Lateral migration of Amazonian lowland rivers causes a vegetation succession on recently deposited fluvial sediments. The forest ground is formed gradually in se- quence, giving rise to age-zonation of the successional stages. Using Landsat MSS maps and field observations, we studied variations in fluvial landform evolution and river character. The widely used characterizations of the rivers ac- cording to their suspension-load character and channel pattern were evaluated in relation to the vegetation succes- sion. Sequential successional forests appear extensively along meandering white-water rivers, which are rich in sus- pended sediments and are characterized by mobile channels. Conversely, vegetation zonation is less pronounced at the margins of slowly eroding suspension-poor rivers. Line transects were established to document meander develop- ment along eight different rivers. The chemical composition of the recently deposited alluvium differs markedly both among rivers and along the transects. Concentrations of organic carbon and nitrogen increase toward the meander neck along with the acid reaction of the soil. The rate of riv- erine forest regeneration in Peruvian lowland Amazonia was extrapolated on the basis of erosion data from four different rivers, and suggests that approximately 130 km2 of forest is annually eroded and replaced by successional vegetation, the equivalent of 0.2% of the present floodplain area of this region.

Selective predation and habitat shift in a copepod species — support for the predation hypothesis

SummaryIn studying the relevance of the predation hypothesis as an explanation for the vertical migration of zooplankton two predictions were tested:1)The egg sacs of Eurytemora are sufficient to cause different predation pressure in food selection experiments with visually hunting planktivores as predators and ovigerous vs. non-ovigerous Eurytemora females as prey.2)If copepods avoid predation by vertical migration, there should occur differences in the vertical distribution pattern of ovigerous and non-ovigerous females according to selective predation. The results showed that, when ovigerous and non-ovigerous females were presented to predators, a significant preference for ovigerous females was found in high densities of prey. No preference was found in experiments with males vs. non-ovigerous females and at low copepod densities. In a field study we found that non-ovigerous females distributed throughout the water column preferred the deeper parts. Ovigerous females were also abundant in deeper waters but almost totally avoided the surface layer above 20 m. Thus our results support the predation hypothesis when the adaptive value of vertical migration is considered.On the basis of our results we deduced testable predictions on the evolutionary effects of predation:1)In heavily foraged communities there is strong coevolution among the prey to resemble each other in terms of which are critical in selective predation.2)If the carrying of an egg sac is considered as parental care, it is likely that parental care occurs more seldom in environments with high predation.

A field study of prey selection in planktivorous fish larvae

SummaryThe food selection of larval fish was studied from field samples collected in two areas that differ in productivity. In the area where planktonic primary and secondary production was high the fish larvae showed a tendency to specialise and they selected the largest prey species available as food; in the area of lower production fish were generalists and they fed equally on all size classes.Abundance of prey was found to be one of the decisive factors in the prey selection of planktivorous fish larvae. Large prey species (calanoids) were selected when their absolute abundance was high but when their abundance was low, small-sized cladocerans were preferred. Visibility and stage of life history were also assumed to affect the mode of selection.

Littoral fish communities in the Archipelago Sea, SW Finland: a preliminary study of changes over 20 years

A collapse of the littoral fish populations was found in the middle archipelago zone near the Island of Seili (northern Baltic Sea) when fish populations were studied in summer 1996 in a comparable way with earlier studies done in the early 1970s and 1980s. A similar comparison was made in the outer archipelago (the islands off the island of Utö), but no evident change was found. Reasons for the decline in littoral fish stocks are discussed, but no single-cause effect can be pointed out. Among possible explanations is a substantial increase of eutrophication in the middle archipelago together with increasing ferry traffic which both cause structural changes in the littoral environment of the study area.

Comparison of lipid and fatty acid composition in vendace (Coregonus albula L.) and available plankton feed

Abstract 1. 1. The food of vendace in Lake Pyhajarvi (SW Finland) consisted mainly of cladocerans and copepods throughout the sampling period from May to October. 2. 2. The content of triacylglycerols and polar lipids of vendace flesh, varied seasonally, in accordance with the total lipids. Triacylglycerols dominated in vendace flesh, while these and polar lipids occurred in nearly equal proportions in composite plankton. In vendace gut, the share of polar lipids decreased markedly. 3. 3. Plankton and vendace flesh total lipids were composed of the same fatty acids. Their relative amounts varied, especially in polyenoic acids and in the ratio of ω-6 and ω-3 polyenoics. 4. 4. The fatty acid composition of fish flesh lipids remained fairly similar throughout the whole sampling period with a slight seasonal variation of some fatty acids occurring in plankton total lipids.

Female Baltic herring Clupea harengus allocate resources from growth to reproduction in poor feeding conditions

The trade-off between somatic growth and reproduction in the female Baltic herring Clupea harengus was investigated from 1984 to 2002. During the study period, growth decreased, as a consequence of decreasing salinity and weakening of feeding conditions. Production of muscle and ovarian tissue decreased in repeat spawners, but investment in reproduction took an increasing amount of the total production of new tissues. This suggested that a shift in allocation to reproduction takes precedence over body growth in the reproductive strategy of C. harengus. The process also indicated one possible mechanism leading to dwarf forms in fish populations.

Corrigendum to “Scenario simulations of future salinity and ecological consequences in the Baltic Sea and adjacent North Sea areas – Implications for environmental monitoring” [Ecol. Indic. 50 (2015) 196–205]

Scenario simulations of future salinity and ecological consequences in the Baltic Sea and adjacent North Sea areas - Implications for environmental monitoring (vol 50, pg 196, 2015)