| 1. |
- Lindgren, Annelie, 1966, et al.
(författare)
-
Proportion of life cycle stages of Chondrus crispus and its population structure: A comparison between a marine and an estuarine environment
- 1996
-
Ingår i: Botanica Marina. - : Walter de Gruyter GmbH. - 0006-8055 .- 1437-4323. ; 39:3, s. 263-268
-
Tidskriftsartikel (refereegranskat)abstract
- The spatial variation in the proportion of gametophytes to tetrasporophytes of the red alga Chondrus crispus Stackhouse was investigated in two areas, Tjarno and Idefjorden, on the Swedish west coast. Tjarno represents a marine environment and Idefjorden an estuarine, polluted environment, where C. crispus on the regional scale is close to the limits of its distribution. The life-cycle stages were identified by the use of the resorcinol method. The ratio of gametophytes to tetrasporophytes significantly differed from I : I in both areas. The proportion of gametophytes was significantly larger at Idefjorden, the population consisting of 79% gametophytes, compared to Tjarno where it was 62%. This is in contrast to theory and earlier work on red algae which suggest that the proportion of tetrasporophytes should increase in marginal populations. There were no significant differences in the proportion of gametophytes between sites within areas on a spatial scale of 0.5 to 2 km, but partitioning the variation into its components suggested large variation between replicates on a scale of 1 to 50 m. There were also significant differences between the two areas in dry mass per individual and density, the estuarine individuals being larger but fewer. Within patches with C. crispus, the standing crop was not different between the two areas but the distribution was more patchy in the estuary resulting in a much lower standing crop when sampling was done over the whole shore. Fertile individuals were rare at Idefjorden, and in both areas individuals with tetrasporangia were more common than those with carposporangia. The result suggests that differences between the areas are due to differences in survival of spores and/or juvenile stages.
|
|
| 2. |
- Lindgren, Annelie, 1966, et al.
(författare)
-
Spatial and temporal variation in distribution of Gelidium canariensis (Rhodophyta) from natural populations of the Canary Islands
- 1998
-
Ingår i: Journal of Applied Phycology. - : Springer Science and Business Media LLC. - 0921-8971. ; 10:3, s. 273-278
-
Tidskriftsartikel (refereegranskat)abstract
- This study was designed to investigate spatial and temporal variation in Gelidium canariensis populations at two shores in northern Gran Canaria during two years. Spatial scales ranged from some hundred meters (distance between shores), 10 to 30 m (distance between pilots) to less than 3 m (distance between quadrats). Gelidium individuals were defined as distinct Gelidium clumps. The results show a significant difference in size of clumps between shores, but not on the smaller spatial scales. No significant temporal variation was found. There was no significant temporal or spatial variation in standing crop or density (counts made in quadrats where Gelidium was present, rather than counts for the total shore). Sporophytic and gametophytic clumps were also distinguished by identifying reproductive structures in the field. The total proportion of sporophytes was larger than the proportion of gametophytes, but at a smaller scale there could be a shift in dominance. The survival rate of clumps was similar between shores with a mean survival rate of 85%, but there eras a significant difference in recruitment between shores. The results indicate a stable population structure.
|
|
| 3. |
|
|
| 4. |
- Lindgren, Annelie, 1966, et al.
(författare)
-
Susceptibility to grazing in different life cycle stages of the red alga Chondrus crispus
- 2003
-
Ingår i: Proceedings of the 17th International Seaweed Symposium. - 0 19 850742 9 ; , s. 349-356
-
Konferensbidrag (refereegranskat)abstract
- Grazing susceptibilities of gametophytic and tetrasporophytic fronds of Chondrus crispus Stack. from the Swedish west coast were examined in laboratory experiments. The overall consumption, irrespective of stage, as well as the feeding preference was tested on both adult and juvenile fronds. The mesoherbivores used in the experiments were the gastropods Littorina littorea, Lacuna vincta and the crustaceans Idotea granulosa and Gammarus locusta, since they are among the most abundant herbivore species within and among C. crispus stands in the study area. The results showed that all four mesoherbivore species were capable of consuming both adult and juvenile tissue. However, none of the herbivores showed a significant pref erence for a specific stage of adult fronds. For juvenile fronds, it was found that I. granulosa significantly preferred gametophytes to tetrasporophytes and there was a tendency for L. littorea to consume more of juvenile tetrasporophytes than gametophytes. This suggests that grazing could have an influence on the ploidy ratio of C. crispus.
|
|
| 5. |
- Pavia, Henrik, 1964, et al.
(författare)
-
Effects of UV-B radiation and simulated herbivory on phlorotannins in the brown alga Ascophyllum nodosum
- 1997
-
Ingår i: Marine Ecology Progress Series. - : Inter-Research Science Center. - 0171-8630 .- 1616-1599. ; 157, s. 139-146
-
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.
|
|
| 6. |
- Pavia, Henrik, 1964, et al.
(författare)
-
Intraspecific variation in the phlorotannin content of the brown alga Ascophyllum nodosum
- 2003
-
Ingår i: Phycologia. - 0031-8884. ; 42:4, s. 378-383
-
Tidskriftsartikel (refereegranskat)abstract
- Many brown macroalgae contain substantial concentrations of polyphenolic compounds, known as phlorotannins. Previous studies have shown that much of the variation in phlorotannin concentration is correlated with taxonomy and biogeography, but little is known about patterns of variation within species and populations. In this study, we examined intraspecific variation in the phlorotannin content of the intertidal seaweed Ascophyllum nodosum, by testing for differences within as well as between genetic individuals (genets) and populations, and between algal tissues of similar age from juveniles and adults. The results show that variation in the phlorotannin content of annual shoots within primary shoots and genets contributes substantially to the total intraspecific variation. This pattern probably indicates that the phlorotannin content is a highly plastic trait that can be significantly influenced by small-scale variation in extrinsic factors. There were also significant differences in mean phlorotannin content among study sites, and these differences varied significantly between the two study years. The extensive variation within and among genetic individuals and populations shows that it is crucial to use proper sampling designs in field studies comparing phlorotannin levels between different populations, taxa, or experimental treatments, in order to avoid false conclusions. Phlorotannin levels were significantly higher in adult annual tissue than in juveniles in five of six sites, with an overall mean phlorotannin content of 7.8% of dry mass for adult tissue and 5.9% of dry mass for juveniles. This result may be explained by a trade-off between growth and phlorotannin production and a lower mortality risk for larger individuals, leading to a strategy where it is more advantageous for a juvenile to invest in growth than to allocate resources to chemical defence.
|
|
