Population dynamics and production of the seagrass Zostera noltii in colonizing versus established meadows

Abstract

The dynamics of the seagrass Zostera noltii in established and colonizing meadows were assessed in Ria Formosa lagoon, Southern Portugal. Shoot weight, above:belowground biomass ratio, flowering shoot density, meadow production, and biomass–density relationships were investigated. Results indicate that the species population dynamics differ clearly in different development stages of the meadows. The overall mean of flowering shoot density was five times higher in the colonizing (83 flowering shoots m−2) than in the established meadow (16 flowering shoots m−2), revealing a greater contribution of sexual reproduction during the species colonization process. The temporal variation of the biomass–density relationship in the colonizing meadow showed a cyclic seasonal trajectory, a wider range of data, and a simultaneous peak of biomass and density, suggesting no space limitations constraining the internal packing of shoots during the growing season. In the established meadow, density peaked before biomass in agreement to the dominant role of the clonal architecture of seagrasses in the configuration of closed meadows, suggesting the occurrence of self‐thinning and/or regulation of ramet formation. Slope of the biomass–density relationships was similar in the established and colonizing meadows, generally suggesting similar nutritional conditions, regardless of their muddy and sandy sediments. Plants of the colonizing meadow invest mainly on the belowground fraction (above:belowground biomass ratio <1), as meadow expansion is mainly controlled by the elongation of horizontal rhizomes. The annual total production (1163 g C m−2 year−1) and the biomass turnover (34.8 year−1) were also higher in this meadow, corroborating the high investment of the species during the meadow expansion. The faster biomass turnover of the colonizing meadow implies a more limited capacity to accumulate biomass, indicating a greater exportation of organic carbon and nutrients to the coastal area. The different biomass turnover rates suggest different trophic and structural roles of Z. noltii communities in established and colonizing meadows.

Using Temporal Sampling to Improve Attribution of Source Populations for Invasive Species

“…Species accumulation curves were done in Primer v.6 (Primer-E Limited, 2009) where the Chao2 index was compared against observations (S obs ). Due to the occurrence of rare alleles, Chao's Jaccard estimator (Chao-Jacc-Est) of abundance-based similarity index [45]–[47], which accounts for “unseen individuals’ based on rare alleles was used and compared against the Jaccard and Bray-Curtis indices to estimate the similarity between 2006 and 2007 samples, using EstimateS v. 7.5 (Colwell R.K). Finally, using chi-squared analyses we assessed the efficacy of using datasets with and without temporal variation to assign the new incursions.…”

Sediment Characteristics Determine the Flowering Effort of Zostera noltei Meadows Inhabiting a Human-Dominated Lagoon

“…At high latitudes, the flowering of Z. noltei starts in the hottest spring months and ends when the temperatures start to drop, by the end of autumn [ 36 , 39 ]. Although the mechanisms that control sexual reproduction in this seagrass are not yet fully understood, it is known that its flowering effort can vary under different sediment types, colonization stages and vegetative growth capacity [ 28 , 29 , 40 , 41 ]. Therefore, evaluating the flowering of Z. noltei in an environment with great spatial variability and subject to multiple and simultaneous anthropogenic stressors, such as Ria de Aveiro, can help us forecast the future of impacted meadows and understand which factors could influence the stress-induced flowering response of this seagrass.…”

Reproductive Cycle of the Seagrass Zostera noltei in the Ria de Aveiro Lagoon

“…In southern European populations, sexual reproduction usually starts in March/April and lasts until autumn (October/November) [19], whereas at higher latitudes it starts later at the end of June [12]. Sexual reproduction in Z. noltei also differs when exposed to different environmental conditions: flowering is enhanced in areas exposed to environmental stressors such as increased hydrodynamics and organic matter enrichment, whereas stable and sheltered areas lead to reduced flowering effort [20,21]. Thus, flowering seems to be variable in this species and influenced by many environmental factors.…”