Effects of habitat fragmentation on Zostera marina seed distribution

Abstract

Habitat fragmentation is a process which can alter the spatial configuration and reduce the overall area of a habitat. This generally results in a degradation of habitat functioning. Fragmentation of seagrass (Zostera marina) beds has become increasingly common, and it may threaten the valuable ecosystem services they provide. Sexual reproduction through flowering and seed dispersal could contribute to the species’ potential resiliency by reducing its vulnerability to fragmentation. We investigated whether the proportion and density of flowering Z. marina shoots, and subsequently the density and distribution of seeds, differed between fragmented and continuous beds. Our results revealed that while flowering effort did not differ between the two bed types, seed density was significantly reduced in fragmented versus continuous beds. Further, seed distributions were altered in fragmented beds when compared to continuous beds, both within and directly outside the bed’s boundaries. Seagrass patch size positively influenced seed density, with lower seed densities in small patches. Fragmented beds consistently contained fewer seeds per-unit-area than continuous beds, regardless of bed seagrass area and flowering effort. Collectively, these results emphasize the vulnerability of Z. marina to habitat fragmentation by demonstrating a negative effect on seed density and an impact on seed distribution, which likely reduces the potential advantages of sexual reproduction for bed growth and resiliency to perturbations.