Patterns of Saccharina latissima Recruitment

Abstract

The lack of recovery in Norwegian populations of the kelp Saccharina latissima (Linnaeus) C. E. Lane, C. Mayes, Druehl & G. W. Saunders after a large-scale disturbance that occurred sometime between the late 1990s and early 2000s has raised considerable concerns. Kelp forests are areas of high production that serve as habitats for numerous species, and their continued absence may represent the loss of an entire ecosystem. Some S. latissima populations remain as scattered patches within the affected areas, but today, most of the areas are completely devoid of kelp. The question is if natural recolonization by kelp and the reestablishment of the associated ecosystem is possible. Previous studies indicate that a high degree of reproductive synchrony in macrophytes has a positive effect on their potential for dispersal and on the connectivity between populations, but little is known about the patterns of recruitment in Norwegian S. latissima. More is, however, known about the development of fertile tissue (sori) on adult individuals, which is easily observed. The present study investigated the degree of coupling between the appearance of sori and the recruitment on clean artificial substrate beneath adult specimens. The pattern of recruitment was linked to the retreat of visible sori (i.e. spore release) and a seasonal component unrelated to the fertility of the adults. The formation and the retreat of visible sori are processes that seem synchronized along the south coast of Norway, and the link between sori development and recruitment may therefore suggest that the potential for S. latissima dispersal is relatively large. These results support the notion that the production and dispersal of viable spores is unlikely to be the bottleneck preventing recolonization in the south of Norway, but studies over larger temporal and spatial scales are still needed to confirm this hypothesis.

Shifts Between Sugar Kelp and Turf Algae in Norway: Regime Shifts or Fluctuations Between Different Opportunistic Seaweed Species?

“…The seasonal development and demise of visible sori in S. latissima are processes that largely overlap along the south coast of Norway (Andersen et al, 2011;Andersen, 2013). The tight link between the timing of recruitment and these patterns shown by Andersen (2013) support the notion that the potential for connectivity between sugar kelp populations in Norway is high. This may enable forest regeneration by natural recruitment from distant remnant source populations.…”

“…Connectivity between kelp populations is reinforced by reproductive synchrony because higher densities of spores in the currents increase the probability of long-distance dispersal (Reed et al, 1997). The seasonal development and demise of visible sori in S. latissima are processes that largely overlap along the south coast of Norway (Andersen et al, 2011;Andersen, 2013). The tight link between the timing of recruitment and these patterns shown by Andersen (2013) support the notion that the potential for connectivity between sugar kelp populations in Norway is high.…”

“…The study by Andersen (2013) revealed synchronous development of fertile tissue, high concentrations of viable spores, consistent settlement patterns and a relatively steady in situ recruitment on clean substrate throughout the winter FIGURE 4 | Recruitment of sugar kelp (S. latissima) to an isolated island where sea urchins were removed during autumn 1988 and spring 1989 (data from Table 1 in Leinaas and Christie, 1996). months. Connectivity between kelp populations is reinforced by reproductive synchrony because higher densities of spores in the currents increase the probability of long-distance dispersal (Reed et al, 1997).…”

“…As a basis for understanding the recruitment and spreading potential of sugar kelp, we have used the experiments performed by Andersen (2013). This study recorded S. latissima recruitment FIGURE 2 | Substrate coverage of both S. latissima and turf algae was recorded at more than 600 sites on the southern coast of Norway in the period 2005-2008.…”

“…Data from Leinaas and Christie (1996), presented in Figure 4, document a rapid recolonization of S. latissima to a small isolated island after removing sea urchins (Strongylocentrotus droebachiensis). As sugar kelp normally release spores in the winter season (Andersen, 2013) the small sporophytes start to grow in the spring and may be observed in early summer. The average density of small sporophytes was more than 470 per m 2 (Figure 4, see also Leinaas and Christie, 1996).…”