Sexual recruitment in Z ostera marina : A patch to landscape-scale investigation

Abstract

Seagrasses are a diverse group of clonal marine macrophytes. Their disappearance in recent decades has been an alarming component of estuarine urbanization, effectively transitioning vast portions of global coverage to disturbed or recovering states. Understanding dispersal and recruitment patterns within and among extant populations is now vitally important to predicting both the form and pace of recovery. Working with a perennial ecotype of Zostera marina within a shallow lagoon in Long Island, New York, U.S.A., we combined high resolution, decade-long seagrass mapping with polymorphic microsatellite analysis to examine the interactive effects of pollination and seed dispersal distance on the dynamics of sexual recruitment across a range of spatial scales (centimeters to decameters). We found clone structure to be restricted to less than three meter across a 56,250-m 2 study site. Pollination distances ranged from 0.57 m to 73.91 m, while seed dispersal varied systematically from 1.85 m to 5.31 m for naked seeds, and randomly throughout the study site (0.17 m to 34.54 m) for seeds deposited by floating reproductive shoots. Pedigree analyses corroborated these findings, with full sibling groups clustering neatly within larger half-sibling kinships at spatial scales of 2-6 m. We successfully demonstrate that over a four-year period sexual reproduction and seedling recruitment played appreciable roles in the colonizing process of Z. marina, configuring the landscape through the deposition of rafted seeds, and contributing to patch expansion via the limited dispersal of naked seeds.

Canopy-Mediated Hydrodynamics Contributes to Greater Allelic Richness in Seeds Produced Higher in Meadows of the Coastal Eelgrass Zostera marina

“…This difference in travel distance implies that pollen released in the lower canopy is more quickly captured by the canopy and thus has a higher probability of self-pollination. Observed selfing rates in our genotyped seeds were low, as has been found in other eelgrass populations with polyclonal patches (Ruckelshaus, 1995;Reusch et al, 2000;Furman et al, 2015). However, more putatively selfed seeds were found on lower infloresences than upper ones, and upper inflorescences showed greater paternal diversity, suggesting greater access to diverse pollen sources higher in the canopy.…”

“…Overall, the simulated pollen travel distances exhibited a wide range, from essentially zero to distances that extended beyond the end of the model domain (x > 200h = 200 m) indicating that both short-and long-distance fatherhood is possible. Furman et al (2015) similarly found genetic evidence of a range of father distances through genotyped single seeds from the tallest rhipidium on flowering shoots in a dynamic and patchy eelgrass meadow. Fathers were identified, with pollination found to occur from fathers located 0.57-74 m upstream.…”

Blue Carbon Storage Capacity of Temperate Eelgrass (Zostera marina) Meadows

“…Mcleod et al (2011) reported that 0.7-7% of the blue carbon ecosystems are lost annually. In the past 130 years,~29% of the global seagrass area has been lost, and in many regions, these rates are accelerating (Bertelli et al, 2017;Furman et al, 2015;Marba et al, 2015;Orth et al, 2006;Waycott et al, 2009). In contrast, salt marsh loss rates have remained relatively stable and loss rates for mangrove forests have slowed from 1.04%/year in the 1980s to 0.66%/year in 2000 (Waycott et al, 2009).…”

Propagule risk in a marine foundation species: Seascape effects on Zostera marina seed predation

“…Similar patterns have been documented in other studies with higher seed consumption within seagrass meadows as compared to adjacent sandy matrix (Darnell & Dunton, ; Orth, Heck, & Tunbridge, ; Orth et al, ). As parental sources of seeds (Furman, Jackson, Bricker, & Peterson, ; Jarvis & Moore, ; Orth, Luckenbach, & Moore, ), seed banks are routinely higher within patches, decreasing with distance from patch edges (Livernois et al, ; Manley et al, ). Seed predators also aggregate in seagrass patches, around parent plants (Eggleston et al, ; Hovel & Lipcius, ).…”

“…In conclusion, our estimates of seed consumption in our system were relatively low, similar to other studies of Zostera marina (Manley et al, ; Wigand & Churchill, ), as well as of other seagrass species (Darnell & Dunton, ; Nakaoka, ) and predation events outside patches were almost nonexistent. Thus, seeds that arrive in unstructured bottom likely have a higher probability of surviving to germination than those that settle within patches, a pattern critical for the persistence and resilience of seagrass patches and meadows, which rely on seed production and seed banks for meadow formation, expansion (Furman et al, ; Kaldy & Dunton, ) and recovery from loss (Jarvis, Brush et al, ; Orth et al, ). Anthropogenic activities have caused dramatic declines in seagrass coverage world‐wide (Burdick & Short, ; Waycott et al, ).…”