Establishment Of Macroalgae Research Articles

Determining the post-herbivore-exclusion effect on an intertidal community by the recovery response of a known dominant herbivore

Following a long-term herbivore-exclusion study (2003-2008) in the mid-eulittoral zone at Kalk Bay, Cape Town, South Africa, the post-herbivore-exclusion effect (12 years later) of the limpet Cymbula oculus, the dominant herbivore in the community, was examined after it had recolonised the area. Despite the limpet having recruited into all plots (previous exclusion plots and control plots), the species richness, percentage cover of sessile organisms, invertebrate densities and invertebrate biomass were all significantly higher in previous exclusion plots compared with in control plots. Cymbula oculus density was higher in previous exclusion plots (11.11 [SD 12.54] ind. m−2) than in control plots (9.26 [SD 7.97] ind. m−2) (p = 0.038); however, its biomass was similar between the previous exclusion plots and control plots (366.39 [SD 421.63] vs 367.96 [SD 285.44] g m−2, p = 0.179), indicating that limpets outside exclusion plots were generally larger. This was likely because of younger C. oculus individuals, heightened interspecific competition, or insufficient space in previous exclusion plots. The observed differences might be attributed to a combination of factors, including the persistence of species that have achieved a size refuge from grazing and bulldozing by C. oculus, as well as the establishment of invasive mussels Mytilus galloprovincialis which offer secondary substrates and microhabitats for the establishment of macroalgae and other invertebrates. The recruitment of M. galloprovincialis into the previous exclusion plots is likely to be the cause of the alternative community state observed. Unless some extreme disturbance event occurs, the community from which C. oculus was previously excluded is unlikely to revert to its pre-C. oculus exclusion state.

Patterns in establishment of macroalgae in an artificial channel before and after drainage event

Patterns in establishment of macroalgae in an artificial channel before and after drainage event

Effects of crevice size on the establishment of macroalgae in subtropical streams.

Considering that in previous studies, the surface roughness (micrometric dimension) showed a weak effect on the colonization of stream macroalgae, we investigated the effects of different crevice sizes (milimetric dimension, a scale slightly higher than previous investigations) on the macroalgal abundance in three streams exposed to full sunlight in southern Brazil. We used smooth sterile glass plates with different shapes: P - plane surface without crevices; S - sinuous surface (depth of crevices with 0.159 mm ± 0.03); N - non-unifom surface (0.498 mm ± 0.09); C - surfaces with convex structures (1.190 mm ± 0.12); and three additional surface types with different patterns of heterogeneity with combinations of glass pieces: P + S (H1); P + S + N (H2) and P + S + N + C (H3). The plates were placed into the streams and after 105 days the percent cover of macroalgal community was measured. No significant differences among treatments were recorded. However, we observed a trend of macroalgae occurs within the crevices in all treatments and this suggests that, for stream macroalgae, the crevice sizes used in this study was still not enough to provide an expressive algal growth, even in the treatment with bigger crevices.

The effects of habitat complexity and hydraulic conditions on the establishment of benthic stream macroalgae

Summary Habitat complexity is thought to play an important role in various ecological communities, but its role under variable natural conditions is not well understood, particularly in lotic habitats where the complexity of the substratum influences the diversity and abundance of the benthic community. We investigated the effects of the habitat complexity of the substratum, as represented by fractal structure, on the establishment of stream macroalgae. We also analysed the influence of hydraulic conditions associated with variations in the fractal dimension of the substratum. We hypothesised that habitats with higher surface complexity would have higher macroalgal abundance and that hydraulic conditions would affect macroalgal establishment differently on surfaces of differing complexity. We designed a field experiment to elucidate the role of habitat complexity (represented by the fractal dimension and density of roughness elements) and consequent hydraulic conditions (assessed by the Reynolds number and drag forces) on algal growth. Sterile artificial substrata with five levels of complexity were placed in four unshaded streams. After 60 days of complete submergence, the substrata were removed from the streams, and the per cent cover of macroalgae was measured. We used a principal components analysis (PCA) to reduce the dimensionality and collinearity among our variables (fractal dimension, density of roughness elements, Reynolds number and drag force) and summarise them adequately. Axis 1 (PC1) values were used in a linear model to assess the relationship between the variables and macroalgal cover. PC1 explained 82.2% of the variability in substratum complexity and hydraulic condition. The fractal dimension and density of the roughness elements were negatively related with PC1, whereas the Reynolds number and drag force were related positively. Hydraulic conditions differed among each level of complexity, with the Reynolds number and drag force decreasing with increasing complexity. Macroalgal cover increased on surfaces with lower turbulence and drag force, indicating that less aggressive conditions are suitable for macroalgal colonisation. Additionally, the establishment of macroalgae was greatest on the leading edge of flat‐top ridges, where the water velocity slows and the current changes direction. Habitat complexity and hydraulic conditions play an important role in the establishment of macroalgae in streams and could explain their naturally patchy distribution.

Effects of irradiance and spectral composition on the establishment of macroalgae in streams in southern Brazil

The relative effects of irradiance and spectral composition on the colonization and development of macroalgal communities were examined in four streams exposed to full sunlight in southern Brazil. A set of solar filters surrounded the artificial substrata to provide various quantitative and qualitative light conditions. In addition to the control, the conditions were full sunlight attenuated by 50, 70 and 90%, blue light (filter transmitting 430-500 nm), green light (500-600 nm) and red light (> 600 nm). Macroalgal percent cover was determined three times during the colonization period (15, 39 and 70 days). Significant differences occurred in the mean values for macroalgal community percent cover between treatments at 15 and 39 days, suggesting that early and intermediate stages of the colonization were directly influenced by irradiance. There was an almost complete absence of macroalgae with 90% attentuation, but progressive increases with 70 and 50% attenuation. However, the mean values for macroalgal community percent cover did not differ significantly between color treatments, suggesting that the effects of irradiance on macroalgal colonization were stronger than those of spectral composition at similar intensity. The quantitative responses differed among the taxa.