Torleif Malm

Effects of filamentous algae and deposited matter on the survival of Fucus vesiculosus L. germlings in the Baltic Sea

As a result of increased nutrient levels in the Baltic Sea during thepast 50 years, mass developments of filamentous algae have become a commonfeature along the Swedish east coast and deposition of organic matter has alsoincreased. To test whether these two factors have any effects on the early lifestages of Fucus vesiculosus a number of laboratory andfield studies were conducted. The amount of epilithic and epiphytic filamentousalgae on F. vesiculosus and the amount of deposited matterin the littoral zone were quantified during the two reproductive periods ofF. vesiculosus, early summer (May–June) and lateautumn (September–October). Both filamentous algae (Cladophoraglomerata) and deposited matter (introduced either before or aftersettlement of fertilized eggs) were shown to significantly decrease the numberof surviving germlings. The survival of germlings seeded on stones withfilamentous algae, or seeded on culture dishes concurrently with the lowestconcentration of deposited matter (0.1 g dm−2),was 5% or less. In the field, the amount of filamentous algae was significantlyhigher during F. vesiculosus summer reproduction, whereasthe amount of deposited matter collected in traps was significantly higherduring the period of autumn reproduction. The greatest biomass of filamentousalgae was observed at sheltered sites. Based on the negative effects offilamentous algae and deposited matter on Fucusrecruitmentand the observation of local and seasonal differences in abundance offilamentous algae and deposition, we suggest that the prerequisites for thesurvival of either summer or autumn-reproducing populations of F.vesiculosus in the Baltic Sea may differ locally.

Effects of offshore wind farms on marine wildlife—a generalized impact assessment

Marine management plans over the world express high expectations to the development of offshore wind energy. This would obviously contribute to renewable energy production, but potential conflicts with other usages of the marine landscape, as well as conservation interests, are evident. The present study synthesizes the current state of understanding on the effects of offshore wind farms on marine wildlife, in order to identify general versus local conclusions in published studies. The results were translated into a generalized impact assessment for coastal waters in Sweden, which covers a range of salinity conditions from marine to nearly fresh waters. Hence, the conclusions are potentially applicable to marine planning situations in various aquatic ecosystems. The assessment considered impact with respect to temporal and spatial extent of the pressure, effect within each ecosystem component, and level of certainty. Research on the environmental effects of offshore wind farms has gone through a rapid maturation and learning process, with the bulk of knowledge being developed within the past ten years. The studies showed a high level of consensus with respect to the construction phase, indicating that potential impacts on marine life should be carefully considered in marine spatial planning. Potential impacts during the operational phase were more locally variable, and could be either negative or positive depending on biological conditions as well as prevailing management goals. There was paucity in studies on cumulative impacts and long-term effects on the food web, as well as on combined effects with other human activities, such as the fisheries. These aspects remain key open issues for a sustainable marine spatial planning.

Two reproductive strategies in Baltic Fucus vesiculosus (Phaeophyceae)

Marked seasonal reproduction is a widespread phenomenon in seaweeds in temperate waters strongly influenced by seasonal variations. In the Baltic Sea, however, the perennial brown alga Fucus vesiculosus exhibits two periods of reproduction: early summer (May–June) or late autumn (September–November). In this study, we compared the geographical distribution, the reproductive biology and the recruitment success for F. vesiculosus that reproduce during either of these two periods on the east coast of Sweden. Both monocultures and mixed populations of summer- and autumn-reproducing F. vesiculosus occurred along the mainland coast from the southern parts of the Stockholm archipelago to the southernmost part of Sweden. F. vesiculosus reproduced only during summer around the coasts of the large islands of Oland and Gotland. After reproduction, in July and January respectively, plants that reproduced in summer abscised their receptacles and part of their branches, while plants reproducing in autumn abscised only ...

Effects of filamentous algae and sediment on recruitment and survival of Fucus serratus (Phaeophyceae) juveniles in the eutrophic Baltic Sea

Eutrophication of the Baltic Sea has increased both the growth of annual filamentous algae and the rate of sedimentation. Together these factors may have a detrimental effect on the survival of perennial macroalgal populations. The aim of this research was to study how these factors affect the colonization success of Fucus serratus at the local level. We investigated the settlement and survival of F. serratus germlings through a combination of field studies and laboratory experiments. The study area lay off the east coast of Öland, along the central Baltic Sea, where consistently-submerged, extensive fucoid stands occur at depths of 2 – 10 m, together with turf-forming filamentous algae, mainly Polysiphonia fucoides. Very few F. serratus juveniles were observed outside the sweeping radius of adult F. serratus individuals at a 7-m depth, while abundant recruits were found inside F. serratus stands. Amounts of filamentous algae and sediment were significantly larger outside the F. serratus stands than inside, and the amount of fine sediment (< 0.25 mm) was positively correlated with the amount of filamentous algae, suggesting that fine sediment accumulates in the turf. Experimental studies showed that both filamentous algae and sediment negatively affect the settlement ability of F. serratus eggs and zygotes and the subsequent survival of the germlings, with sediment having the strongest effect. Thus, the prior existence of an adult F. serratus population may allow for continuing recruitment of juveniles, while colonization of new areas unaffected by the sweeping effect of larger individuals seems very difficult under current conditions.

Interaction between isopod grazing and wave action: a structuring force in macroalgal communities in the southern Baltic Sea

The macroalgal belt in the southern Baltic Sea may be partly structured by the interaction of physical and biological factors. A field study, spanning the 1990s, describes a rapid decline of the Fucus spp. stands along the wave-exposed Swedish southeast coast. During this period, a relative dominance of Fucus vesiculosus L. shifted to a relative dominance of Fucus serratus L. The decline of F. vesiculosus coincided with observations of large numbers of the grazing isopods Idotea baltica (Pallas) and Idotea granulosa Rathke, or with field observations of frequent grazing marks on Fucus fronds. I. baltica, but not I. granulosa, tended to aggregate in the declining Fucus spp. stands, indicating a strong preference for Fucus spp. In a mesocosm experiment I. baltica, when given a choice, grazed both Fucus species at weak water motion. At strong water motion grazing was concentrated on F. vesiculosus. It is hypothesized that one of the reasons I. baltica preferred F. vesiculosus to F. serratus at strong water motion may have been differences in habitat quality, like width of thallus, influencing the ability to cling to the plant. Smaller thallus, as in F. vesiculosus, thus is the preferred habitat for grazing of I. blatica. We postulate that the existence of F. serratus in the area may be favoured by strong wave action and moderate but not strong grazing by I. baltica, relaxing the interspecific competition from F. vesiculosus.

Distribution and host plant preference of Idotea baltica (Pallas) (Crustacea:Isopoda) on shallow rocky shores in the central Baltic Sea

Partially due to the mass occurrence of the isopod Idotea baltica, the perennial fucoid vegetation in the Baltic Sea has been destroyed over large areas and replaced by filamentous algae. With a combination of field investigations and laboratory experiments, we tested whether I. baltica preferred Fucus serratus to the dominant red alga Polysiphonia fucoides. In the field, the I. baltica density was higher inside F. serratus than P. fucoides patches when measured per unit area, but the situation was reversed if measured per biomass algae. Diet in the field was well correlated with the distribution of the isopods. A large proportion of the isopod faecal pellets collected in the field contained remnants of microalgae, planktonic animals, and bacteria, but the dominating material was always cells from the actual host plant. In a host plant preference experiment, I. baltica distributed evenly between the two host plant types, but the isopods grazed more heavily on F. serratus. We conclude that although F. serratus is the preferred food item in a choice situation, P. fucoides appears to have the potential to support the I. baltica population with food and shelter. A possible relationship between the weak host plant preference and the low stocks of predatory fish is discussed.

DIFFERENCES IN LIFE‐HISTORY CHARACTERISTICS ARE CONSISTENT WITH THE VERTICAL DISTRIBUTION PATTERN OF FUCUS SERRATUS AND FUCUS VESICULOSUS (FUCALES, PHAEOPHYCEAE) IN THE CENTRAL BALTIC SEA

On the rocky shores of southeast Sweden, in the central Baltic Sea, the brown seaweed species Fucus serratus L. and Fucus vesiculosus L. form dense constantly submerged stands. The relative proportion of the two species in the belt is shifting both vertically and geographically. Our hypothesis is that differences in life‐history characteristics and the tolerance to physical factors such as wave force, freezing, and light may alter the competitive outcome between the two species with increasing wave exposure. This study included a combination of field studies and laboratory experiments. In sheltered locations, F. serratus and F. vesiculosus grow in mixed stands from 0.5 to 3 m deep, whereas at exposed sites F. vesiculosus grow from 0.5 to 2 m deep and F. serratus mainly from 1 to 5 m deep. The two Fucus species differed markedly in their tolerance to physical stress as well as in a number of reproductive and vegetative characteristics. Tolerance to freezing and wave action was higher in F. vesiculosus compared with F. serratus. Fucus vesiculosus also produced 10 times more eggs per receptacle, allocated significantly more tissue per frond for reproduction, and produced more reproductive fronds per individual than did F. serratus. In addition, the survival rate of F. vesiculosus germlings was slightly higher than that of F. serratus germlings during the first year. These differences in life history characteristics are suggested to partly explain the observed distribution patterns of the two Fucus species in the Baltic Sea.

The effects of chlorine-free pulp mill effluents on reproduction and grazing interactions in baltic sea fucus vesiculosus l.

Abstract The effect of ClO2-bleached and chlorine-free pulp mill effluents on different life stages of the brown alga Fucus vesiculosus L. from the Baltic Sea was investigated in a series of laboratory experiments. The ClO2-bleached effluent strongly inhibited germination already at a 5% concentration. In contrast, chlorine-free effluent had little effect on either fertilisation or germination in the species; a slightly negative effect on fertilisation was seen only at 25% concentration. It is concluded that a shift to chlorine-free bleaching improves the potential for survival and re-establishment of F. vesiculosus in pulp mill receiving areas. One week of pre-exposure of F. vesiculosus germlings to chlorine-free pulp-mill discharge with a concentration of 25% did not significantly affect the palatability of the F. vesiculosus germlings to the fresh water snail Lymnaea peregra O. F. Müller. Neither did pre-exposure of adult F. vesiculosus tissue to chlorine-free effluents (25%) affect the grazing rate of the isopod Idotea baltica Pallas. However, when offered a choice, I. baltica significantly preferred feeding at pre-exposed F. vesiculosus. This indicates that the effluent indirectly can contribute to a higher grazing pressure of I. baltica in areas affected by pulp mill effluents.