Comparison of survival and growth in germlings of six fucoid species (Fucales, Phaeophyceae) at two different temperature and nutrient levels

Abstract

H, Rueness J. 2004. Comparison of survival and growth in germlings of six fucoid species (Fucales, Phaeophyceae) at two different temperature and nutrient levels. Sarsia 89:175-183. SARSIADuring their initial post-settlement period, fucoid germlings will be exposed to large variations in environmental factors such as temperature and nutrient concentration, which may influence survival and growth. Factorially designed culture experiments were used to compare the effects of temperature and nutrient concentration on the survival and growth of germlings in six fucoid species from the Norwegian Skagerrak coast. In four of the species (Ascophyllum nodosum, Fucus evanescens, F. serratus, and F. vesiculosus), survival did not differ between the two temperatures tested (7 and 17°C), whereas survival was reduced at 7°C in F. spiralis and Sargassum muticum. The effect of nutrient enrichment (seawater enriched with 32 mmol N and 2 mmol P per litre) on germling growth depended on the temperature regime, and differed little between species. The relative growth rate of germlings increased with increasing temperature in all six species and was higher in S. muticum ($0.21 day À1 ) than in the other fucoids (0.09-0.14 day À1 ) at 17°C. At 7°C, F. serratus germlings had the highest relative growth rate ($0.13 day À1 ), whereas those of S. muticum and F. spiralis were reduced to $0.05 and $0.03 day À1 , respectively. These results are in accordance with the reproductive season for the species, as germlings of the summer/autumn reproducers, F. spiralis and S. muticum, were less tolerant to low temperatures than the other Skagerrak fucoids whose reproduction occurs earlier in the year. Egg volume varied almost 10-fold across species, from F. vesiculosus (smallest) to S. muticum (largest), and showed no correlation with relative growth rates or survival, wherease the size of germlings was positively related to egg volume after 15 days of cultivation under nutrient-enriched conditions at 17°C. These results suggest that summer reproduction, larger eggs and a higher growth rate of germlings may give the introduced species, S. muticum, a competitive advantage.

Temporal and spatial variation in the early recruitment of fucoid algae: the role of microhabitats and temporal scales

“…), and the asynchronous phenology of the 3 species did allow some temporal separation of their relative contributions. Temperature responses of germlings appear to reflect the temperature range in the species season of reproduction (Steen & Rueness 2004). Ascophyllum nodosum released gametes towards the end of June, followed by an abrupt loss of receptacles.…”

Interspecific competition between Enteromorpha (Ulvales: Chlorophyceae) and Fucus (Fucales: Phaeophyceae) germlings: effects of nutrient concentration, temperature, and settlement density

“…If the success of F. evanescens in eutrophic waters depended solely on a favourable reproductive season to avoid competition from ephemeral algae, then F. serratus, whose reproduction starts earlier in the year and at lower water temperatures than that in F. evanescens (Steen & Rueness 2004), should be facilitated too. There are several factors that might induce such interspecific differences in responses to eutrophication.…”

“…Although the exact mechanisms behind the apparent nutrient-induced changes in the abundance of F. serratus and F. evanescens remain unknown, interspecific differences in autecology and competitive ability of the early post-settlement stages may contribute. F. serratus and F. evanescens reproduce at lower water temperatures than most other north European fucoids (Steen & Rueness 2004), and this has been proposed as a potential mechanism that may protect the most vulnerable initial germling stages from the severest competition pressure by ephemeral algae, whose growth is reduced at low temperatures (Lotze et al 1999, Lotze & Worm 2002). This hypothesis relies on the assumption that competition effects of ephemeral algae on fucoid germlings are positively related to temperature, which has so far not been tested.…”

Grazer-controlled recruitment of the introduced Sargassum muticum (Phaeophyceae, Fucales) in northern Europe

“…Van Alstyne et al (2001) suggested that algae have 2 strategies for surviving the juvenile stage: (1) allocating the majority of resources to growth and less to defence in order to outgrow mesograzers, (2) allocating resources to defence and consequently growing more slowly. Compared with other fucoids, S. muticum germlings grow relatively fast under optimum conditions (Steen & Rueness 2004), and therefore possibly rely on the first strategy. However, this will result in high risk of being grazed when the juveniles grow under suboptimal conditions in an environment with high grazing impact.…”