Effects of Pilayella littoralis on Fucus vesiculosus recruitment: implications for community composition

Abstract

With increasing eutrophication in coastal areas, mass developments of annual filamentous algae, such as Pilayella littoralis and Enteromorpha spp., have increased. Simultaneously, the perennial macroalga Fucus vesiculosus has declined in many areas in the Baltic Sea. To test the effects of P. littoralis on F. vesiculosus we performed a number of laboratory and field studies. The most severe negative effect observed was the reduced number of settled germlings (95%) when P. littoralis was present on the substrate prior to seeding of F. vesiculosus eggs. A low concentration (0.1%) of exudates from P. littoralis reduced the attachment rate of F. vesiculosus during the initial 12 h, while higher concentrations of exudates (5 to 10%) negatively affected germination and rhizoid development. These results could explain for the negative correlations that have been observed between F. vesiculosus and annual filamentous algae in the Baltic Sea. Our field data showed that the biomass of filamentous algae was higher in the summer than in the autumn, suggesting that recruits from the summer-reproducing F. vesiculosus may encounter more competition from P. littoralis and other filamentous algae than do recruits from the autumn-reproducing populations. The summerand autumn-reproducing F. vesiculosus host similar abundance and biomass of their associated flora and fauna; hence, a potential shift from summer-to autumn-reproducing F. vesiculosus would not change the overall community composition in this ecosystem.

First Record of the Alien Macroalgae, Rivularia Atra and Polysiphonia Opaca, on the Libyan Coastline With Special Reference to Their Bionomics

“…In addition, the high tolerance of R. atra to wide variations in salinity and temperature in the upper intertidal zone compared with the other macroalgal species such as Laurencia optusa and the probable ability of P. opaca in lower intertidal zone to secrete allellopathic compounds might contribute to the marked competing activity of the two species. This agrees with Råberg et al (2005) who reported that, the exudates from Polysiphonia species appear to exert a negative effect on the reproduction of Fucus vesiculosus. These alien species might represent greater threat to native biodiversity than do pollution in the study area since…”

Benthic communities in relation to wave exposure and spatial positions on sublittoral boulders in the Baltic Sea

“…Furthermore, surface siltation has been found to be stressful to both filter feeders (Seed & Suchanek 1992, Dame 1996 and macroalgae (Wallentinus 1976, Eriksson 2002, Berger et al 2003. Also, filamentous macroalgae may overgrow and negatively influence the underlying community by shading (Rohde et al 2008), causing anoxic conditions while decaying (Paalme et al 2002) and impairing settling, recruitment and early survival of other species (Berger et al 2003, Råberg et al 2005, Qvarfordt 2006). Water movement keeps the substrate clean (Kautsky 1988) and more efficiently removes loosely attached macroalgae from the substrate at wave-exposed compared to sheltered locations, and may thereby influence the recruitment and growth of different benthic species.…”

Macroalgal Chemical Defenses and Their Roles in Structuring Temperate Marine Communities

“…When P. littoralis is present on the substrate prior to seeding of F. vesiculosus eggs, the recruitment of F. vesiculosus germlings is reduced (Råberg et al 2005). Allelopathy may be involved as exudates from P. littoralis affect F. vesiculosus negatively: a low concentration of exudates reduce the attachment rate, while higher concentrations hamper germination and rhizoid development (Råberg et al 2005).…”

“…Allelopathy may be involved in competitive success of bloom-forming macroalgae (Nelson et al 2003;Råberg et al 2005). Nelson et al (2003) studied toxic properties of two common "green tide" seaweeds Ulva fenestrata and Ulvaria obscura.…”

“…Such detrimental exudates may have ample community level effects through their release during the bloom and later during decomposition. For example, in addition to lowering recruit survival of canopy-forming macroalgae (Eklund et al 2005;Råberg et al 2005), intact and/or degrading filamentous algae may decrease survival of fish eggs (Aneer 1987) and reduce the abundance of benthic animals (Norkko and Bonsdorff 1996).…”