Patterns of Saccharina latissima recruitment.

Guri Sogn Andersen,Tilmann Harder

doi:10.1371/journal.pone.0081092

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.

Highlights

Kelps, seaweeds, and seagrasses provide important ecosystem services in coastal areas, and the loss of these macrophytes is a global concern [1,2,3,4,5]
By December, the spots had grown to larger areas, and the development of visible spore forming tissue continued until February
Recruitment was observed throughout the period when the kelps had visible sori (Figure 1 A), suggesting that spores were released from the adult plant continuously

Summary

Introduction

Seaweeds, and seagrasses provide important ecosystem services in coastal areas, and the loss of these macrophytes is a global concern [1,2,3,4,5]. In Norway, the disappearance of the perennial kelp Saccharina latissima has raised considerable concerns both within and outside the scientific community [6]. Successful kelp recruitment is a prerequisite for recolonization, yet there are few studies of S. latissima recruitment in situ. Kelps exhibit life histories in which large diploid sporophytes (benthic spore producing stages) alternate with microscopic haploid gametophytes (benthic sexual stages) via flagellated spores (planktonic dispersal stages). The production of spores in S. latissima is significant, and kelp spores may disperse over great distances [7,8]. Hartvig Christie] in Norway are consistent with long-distance dispersal of S. latissima, and rapid forest recovery after S. latissima deforestation in the past indicate that natural recolonization was once possible [6]. Turf algae communities loaded with sediments seem persistent in most of the deforested areas, while S. latissima remains absent

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