Genetic diversity and connectivity remain high in eelgrass Zostera marina populations in the Wadden Sea, despite major impacts

Abstract

Beginning in the 1930s, eelgrass meadows declined throughout the Wadden Sea, leaving populations susceptible to extinction through patchiness, low density and isolation. Additional anthropogenic impacts have altered current regimes, nutrients and turbidity -al l of which affect eelgrass. Recent abiotic modeling studies suggest that poor recovery is the result of a regime shift caused by the loss of positive feedbacks between seagrass meadows and their capacity to mediate turbidity. Additionally, it is hypothesized that genetic and demographic factors -in particular, the loss of genetic diversity and patch connectivity -have contributed to lower fitness of eelgrass, thereby further diminishing recovery potential. We assessed genetic diversity and connectivity of Zostera marina among 19 locations, covering some 950 km of coastline between Zeeland, Netherlands and Langhölmen, Sweden. Both allelic and genotypic diversity were high. A Bayesian analysis of population structure revealed 6 significant clusters of subpopulations that are connected by varying degrees of dispersal. Although population divergence was significant at as little as 5 km, isolation by distance was very weak, indicating high connectivity at scales of 150 km. A demographic interpretation of these data suggests that realized gene flow is strong and predominantly northward, leaving the western Wadden Sea relatively isolated. The failure of eelgrass to recover in the western Wadden Sea is, therefore, due to both unsuitable physical conditions and low incoming gene flow. Nonetheless, the greater Wadden Sea can be considered a seed transfer zone providing source material for restoration efforts in any areas where abiotic conditions are more favorable.KEY WORDS: Eelgrass · Zostera marina · Genetic diversity · Connectivity · Fragmentation · Dispersal rate · Wadden Sea Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 372: [87][88][89][90][91][92][93][94][95][96] 2008 dynamics and geomorphology) and the genetic potential of the populations (genetic variation, population structure and connectivity in relation to mating systems and demography). Integration of these 2 factors is a major goal in a management context (Ouborg et al. 2006), and the power of this integration in eelgrass conservation and biodiversity is exemplified in studies that have modeled the importance of positive feedbacks between eelgrass and turbidity in the Wadden Sea (van der Heide et al. 2007) and manipulative experiments documenting the importance of genetic diversity to enhanced ecosystem function in response to disturbance (Reusch 2006) and to global warming (Reusch et al. 2005).Over the past decade, population genetic studies of eelgrass have been greatly facilitated by the development of neutral microsatellite loci. Eelgrass reproduces both sexually and vegetatively with the consequence that the many shoots (ramets) produced in a particular area may or may not correspond to individual genotypes (genets). Thus, one of the f...

Spatio-temporal distribution of floating objects in the German Bight (North Sea)

“…Similarly, Kornmann and Sahling (1977) also inferred that H. elongata, stranded on Helgoland in late summer, probably comes from sources in the British Channel because this seaweed often harbors algal epiphytes that are common in Brittany and southern England. The import of floating seaweed from the British Channel is likely supported by a strong coastal current that is also responsible for intensive gene flow among populations of eelgrass Zostera marina along the Wadden Sea coast (Ferber et al, 2008). The seasonal variations of floating seaweed abundances in the German Bight were similar to those reported from other regions (Thiel and Gutow, 2005a).…”

Restoring Resiliency: Case Studies from Pacific Northwest Estuarine Eelgrass (Zostera marina L.) Ecosystems

“…However, recent information strongly suggests that resilience is linked with genetic diversity (Reusch 2001;Williams 2001;Hufford and Mazer 2003;Reusch et al 2005;Ehlers et al 2008;Ferber et al 2008), and the potential for gene flow among eelgrass populations should be a consideration in planning for the long-term success of eelgrass restoration efforts. In the systems that we studied, low levels of flowering may constrain gene flow even within a discrete patch.…”

High levels of gene flow and low population genetic structure related to high dispersal potential of a tropical marine angiosperm

“…However, the relationship between high or low drifting potential and genetic connectivity between the seagrass populations is not always straightforward (Waycott et al 2006). For example, Zostera marina has been shown to disperse on the order of 100 km by dislodged fruit-bearing rhipidia (Harwell & Orth 2002, Källström et al 2008, and populations showed high genetic connectivity at an oceanic scale (Reusch 2002, Muñiz-Salazar et al 2005, Ferber et al 2008), a phenomenon also found for Zostera noltii ). Contrary to this, Posidonia oceanica has low genetic migration rates, and a clear E-W genetic division was found in the Mediterranean ).…”