| 1. |
- Lindegarth, Mats, 1965, et al.
(författare)
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Analysis of the Spatial Variability in Abundance and Age Structure of 2 Infaunal Bivalves, Cerastoderma-Edule and C-Lamarcki, Using Hierarchical Sampling Programs
- 1995
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Ingår i: Marine Ecology-Progress Series. - 0171-8630. ; 116:1-3, s. 85-97
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Tidskriftsartikel (refereegranskat)abstract
- Spatial variability in abundance and age distribution of 2 infaunal bivalves, Cerastoderma edule (Linnaeus, 1785) and C. lamarcki (Reeve, 1845), were quantified using hierarchical sampling programs. The scales investigated ranged between 100 and 10(5) m. Analyses of variance revealed significant variability in abundance among sites within bays (similar to 100 m apart) for both species and also among bays (similar to 1 km apart) for C. lamarcki. Mean age varied at several spatial scales. For both species, however, the scale contributing most to the variation was bays, which provided about 40 % of the total variation for each species. Randomization procedures were used to test the generality of previous observations of non-random distributions of year classes (namely number of year classes and dominance by single year classes). These analyses showed that for both species a spatial unit contained significantly fewer year classes and the most abundant year class was significantly more abundant than expected by chance. These results were consistent for all spatial scales except among plots (similar to 10(1) m apart) in C. lamarcki. The necessity to assess spatial patterns at a wide range of spatial scales is emphasized. Potentially important processes (focusing on larval supply and recruitment) which generate the observed patterns and general implications of spatial variability are discussed.
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| 2. |
- Loo, Lars-Ove, 1954, et al.
(författare)
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Passive suspension feeding in Amphiura filiformis (Echinodermata: Ophiuroidea): Feeding behaviour in flume flow and potential feeding rate of field populations
- 1996
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Ingår i: Mar Ecol-Progr Ser. - 0171-8630. ; 139:1-3, s. 143-155
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Tidskriftsartikel (refereegranskat)abstract
- Experimental studies in a laboratory flume show that the sediment-living brittle-star Amphiura filiformis captures suspended particles. Feeding activity is a function of now velocity with few animals extending feeding arms in still water. Flow velocity also affects the orientation of feeding arms, and we suggest that this orientation is partly controlled by A. filiformis. By combining field measurements of current velocity and seston concentration with morphometrics and filtration models, a theoretical encounter rate of suspended particles was calculated for A. filiformis. In terms of organic content, A. filiformis can potentially balance growth and respiration with ingested seston although balance will strongly depend on retention efficiency and particle quality. Detailed measurements of flow around feeding arms revealed complex now patterns that will limit the applicability of available models of food encounter for passive suspension feeders, but our sensitivity analysis indicates that suspended aggregates may be especially important in the nutrition of this species.
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| 3. |
- Malinsky-Rushansky, NZ, et al.
(författare)
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Excretion of dissolved organic carbon by phytoplankton of different size and subsequent bacterial uptake
- 1996
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Ingår i: Marine Ecology Progress Series. - : Inter-Research Science Center. - 0171-8630 .- 1616-1599. ; 132:1-3, s. 249-255
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Tidskriftsartikel (refereegranskat)abstract
- Identical techniques and laboratory equipment were used to compare photosynthetic particulate assimilation and excretion of dissolved organic compounds (EOC) by different size classes of phytoplankton from marine and freshwater ecosystems. The subsequent assimilation and respiration of these algal exudates by bacteria were measured. The percentage of extracellular release of dissolved organic compounds was lower (4 to 5 %) for larger algal cells than for picoeukaryotes (29 %). Bacterial assimilation of the EOC released by the algae under these conditions seemed to be related more to algal species than to biovolume, although there may also be an effect on the specific bacterial assemblages. Bacterial uptake and utilization of EOC was 19% for freshwater picoeukaryotes, and 18 to 70 % for marine nanoplankton. Great variations were found in the respiration rates of natural bacteria on EOC released by the freshwater picoalgae (95 %) and nanoplanktonic salt pond algae (20 to 41%).
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| 4. |
- Malm, Torleif, et al.
(författare)
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Grazing effects of two freshwater snails on juvenile Fucus vesiculosus in the Baltic Sea
- 1999
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Ingår i: Marine Ecology Progress Series. - : Inter-Research Science Center. - 0171-8630 .- 1616-1599. ; 188, s. 63-71
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Tidskriftsartikel (refereegranskat)abstract
- The low salinity in the non-tidal Baltic Sea excludes many species, including marine littorinoids. The only large gastropods that occur in substantial quantities in the central Baltic proper are the freshwater snails Lymnaea peregra (O.F. Müller) and Theodoxus fluviatilis (L.); both are known to consume filamentous green and brown algae. The main objective of the present study was to test the hypothesis that freshwater snails can exert substantial grazing pressure on juvenile and regenerating Fucus vesiculosus populations in the Baltic Sea. In laboratory experiments, both snail species were able to graze on F. vesiculosus germlings up to a size of approximately 0.8 to 1.0 mm. During the study period (autumn 1996 and spring and summer 1997), the largest F. vesiculosus germlings of the cohorts settled in September and May reached approximately 1.0 mm at the same time (July). Thus, to reach the 'safe' size and escape grazing requires about 8 mo for germlings settling in autumn but only 1 mo for germlings settling in spring. The survival and growth rate of new fronds from regenerating F. vesiculosus holdfasts in outdoor tank experiments were higher than for sexually recruited juveniles. After 1 yr, 95% of the holdfasts had survived, and the mean length (±SE) of the largest frond on each holdfast was 12 ± 2 mm. Grazing by L. peregra or T. fluviatilis did not affect regeneration or frond growth. During a long-term field study (1991 to 1994), an average of 8.5 ± 0.7 T. fluviatilis ind. dm-2 were found, with a maximum density of 40 ind. dm-2 in September. During a 1 yr study (1996), the average density of L. peregra was comparatively low and varied from 0.5 ind. dm-2 in April to 20 ind. dm-2 in August. The higher density found in August (L. peregra) and in September (T. fluviatilis) suggests that both species may have a grazing impact during this time. We conclude that both T. fluviatilis and L. peregra have the capacity to graze on zygotes and germlings of F. vesiculosus until they reach a safe size of approximately 0.8 to 1.0 mm. Both snail species can occasionally reach abundances high enough to affect the recruitment of F. vesiculosus. Freshwater snails do not affect the regeneration from holdfasts. However, because the time for germlings settled in autumn to reach a safe size is much longer than for germlings settled in spring, it is possible that even a low snail density has an impact on recruitment in the field. This will, however, require verification because levels of grazing activity during different times of the year are unknown.
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| 5. |
- Pavia, Henrik, 1964, et al.
(författare)
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Effects of UV-B radiation and simulated herbivory on phlorotannins in the brown alga Ascophyllum nodosum
- 1997
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Ingår i: Marine Ecology Progress Series. - : Inter-Research Science Center. - 0171-8630 .- 1616-1599. ; 157, s. 139-146
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Tidskriftsartikel (refereegranskat)abstract
- Models and experiments seeking to explain intraspecific variation in brown algal phlorotannins (polyphenolics) have mainly focused on the effect of 2 factors, herbivory and resource availability (carbon/nutrients). The possible importance of other biotic and abiotic factors, e.g. pathogenic micro-organisms, heavy metals and UV radiation, has often been suggested but only rarely experimentally tested. In the present study the effects of increased UV-B irradiance and stimulated grazing (clipping) on phlorotannin production in the brown alga Ascophyllum nodosum were investigated. The 2 treatments were applied simultaneously in a crossed factorial experiment in order to test for interactive, as well as separate, effects. Carbon and nitrogen content of the algae was also determined for each treatment. The effect of the experimental treatments on the feeding selectivity of a natural herbivore was tested in a subsequent feeding preference experiment with the crustacea Idotea granulosa. An increase (similar to 50%) in UV-B radiation during a 2 wk period resulted in a significant increase (similar to 30%) in mean phlorotannin concentration, while no significant changes in phlorotannin levels following simulated grazing were observed. The additional UV light caused a slight increase in the nitrogen content of the algae, indicating that the response in phIorotannin production was not caused by nutrient deficit. Absorption spectra of A. nodosum extracts, before and after removal of phlorotannins with polyvinylpolypyrrolidone, revealed that phlorotannins can contribute to absorption in the UV-B range (280 to 320 nn). The results imply that phlorotannins can function as inducible screens against harmful UV radiation. The grazer I. granulosa showed a clear preference for algae that had been exposed to an addition of UV-B radiation, in spite of their increased phlorotannin levels, supporting the notion that small marine herbivores in general are tolerant to chemical defenses of algae.
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| 6. |
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| 7. |
- Rodhouse, PG, et al.
(författare)
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Cephalopod predation by the king penguin Aptenodytes patagonicus from South Georgia
- 1998
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Ingår i: MARINE ECOLOGY-PROGRESS SERIES. - : INTER-RESEARCH. - 0171-8630. ; 168, s. 13-19
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The king penguin Aptenodytes patagonicus is a sub-Antarctic species that feeds primarily on mesopelagic fish and cephalopods in the vicinity of the Antarctic Polar Front (APF). We examined the cephalopod prey of adult penguins at a breeding colony on Sout
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| 8. |
- Tiselius, Peter, 1958
(författare)
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An in situ video camera for plankton studies: design and preliminary observations
- 1998
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Ingår i: Marine Ecology-Progress Series. - 0171-8630. ; 164, s. 293-299
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Tidskriftsartikel (refereegranskat)abstract
- A design for an in situ video camera for plankton observations is presented. A light weight aluminium rig supports a video camera with an opposing stroboscope which produces dark field images of plankton >0.3 mm. In the present configuration the camera can be used down to 100 m and provides video images of 10 to 40x magnification when viewed on a 14 " (ca 35 cm) monitor. Video recordings from the field show moderate aggregations of small copepods to the subsurface fluorescence maximum and at times indications of horizontal patchiness. The large copepod Calanus finmarchicus was found to aggregate 5 m below the fluorescence maximum at night. In comparisons with a traditional WP-2 plankton net, the video camera provided similar length frequency distributions while abundance estimates from video recordings were 10 to 20% higher than net estimates. II is concluded that the presented video camera offers excellent observations of the pelagic environment at an affordable cost.
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| 9. |
- Tiselius, Peter, 1958
(författare)
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Short term feeding responses to starvation in three species of small calanoid copepods
- 1998
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Ingår i: Marine Ecology-Progress Series. - 0171-8630. ; 168, s. 119-126
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Tidskriftsartikel (refereegranskat)abstract
- Three small, neritic copepods (Acartia tonsa, Acartia clausi, and Centropages hamatus) were exposed to short term (1 to 14 h) periods without food and their clearance over 2 h was measured. Clearance rates in controls consisting of copepods continuously exposed to 3500 cells ml(-1) of the diatom Thalassiosira weissflogii were 1.15 ml mu g(-1) dry wt d(-1) for A. tonsa, 0.65 for A. clausi and 0.35 for C. hamatus. When moved from filtered sea water to a suspension of 3500 T. weissflogii ml(-1), A. tonsa showed elevated (compared to controls) clearance rates after having been deprived of food for 6 h (+77 %) and 14 h (+44%). A. clausi only responded after 14 h of starvation (+60%) whereas C. hamatus showed a moderate response after 6 h without food (+14%). In day-night comparisons with A. tonsa, elevated clearance rates were significantly higher only during the day. Frequent estimates of clearance rates (20 min intervals) showed that the stimulating effect of food deprivation only lasted similar to 1 h in the case of 1 h of starvation but lasted more than 3 h after 14 h without food. Small species like the ones investigated here have more restricted vertical migration and may not leave the food-rich surface layer to avoid predation, as is commonly found in larger copepods. Instead, they have to balance food intake with predator avoidance continuously. The hunger responses observed in the study may allow the copepods to intermittently search for food or avoid predators and still maintain the same overall ingestion rate as constantly feeding animals.
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| 10. |
- Tornblom, E, et al.
(författare)
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Seasonal dynamics of bacterial biomass and production on eelgrass Zostera marina leaves
- 1999
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Ingår i: MARINE ECOLOGY-PROGRESS SERIES. - : INTER-RESEARCH. - 0171-8630. ; 179, s. 231-240
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The seasonal dynamics and distribution of bacteria and bacterial activity on eelgrass leaves were followed at a shallow-water site in the Roskilde Fjord, Denmark. Eelgrass leaves were sites of highly active bacterial communities exhibiting distinct distri
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