Seed Reserve Hot Spots for the Sub-Tropical Seagrass Halodule wrightii (Shoal Grass) in the Northern Gulf of Mexico
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SPECIAL ISSUE: SEAGRASSES TRIBUTE TO SUSAN WILLIAMS
Seed Reserve Hot Spots for the Sub-Tropical Seagrass Halodule wrightii (Shoal Grass) in the Northern Gulf of Mexico Kelly M. Darnell 1 & Bradley T. Furman 2 & Kenneth L. Heck Jr. 3 & Dorothy Byron 3 & Laura Reynolds 4 & Kenneth H. Dunton 5 Received: 23 March 2020 / Revised: 8 July 2020 / Accepted: 15 July 2020 # Coastal and Estuarine Research Federation 2020
Abstract Halodule wrightii (shoal grass) is a dioecious seagrass with a widespread tropical and subtropical distribution. Like all seagrass species, H. wrightii has the ability to expand asexually through rhizome elongation and to reproduce sexually through seed. To better understand H. wrightii sexual recruitment dynamics in the northern Gulf of Mexico, we investigated seed bank densities at 815 sites from south Texas to the Florida Panhandle. H. wrightii seed reserves were spatially variable across the region, with seed densities ranging from 0 to 5290 seeds m−2. Spatial analysis revealed clusters of high seed densities (“hot spots”) in Upper Laguna Madre, TX, and Santa Rosa Sound, FL, and clusters of low seed densities (“cold spots”) in Lower Laguna Madre and Aransas Bay, TX. Hot spots were dominated by H. wrightii, whereas cold spots were dominated by Thalassia testudinum (turtle grass). We frequently found intact seed coat halves, suggesting germination; however, we also encountered broken seed coat pieces, characteristic of seed predation. Genotypic surveys within and adjacent to seed hot spots revealed genetically diverse adult populations 6 years post seed bank sampling. Our data show that H. wrightii seed reserves are heterogeneous across the northern Gulf of Mexico and that the factors driving variation in seed bank density, viability, and germination remain poorly understood. Information on the spatial heterogeneity of H. wrightii seed densities has relevance for seagrass management, including targeting meadows with high levels of reproductive effort for protection or designation as marine reserves. Keywords Shoal grass . Reproduction . Dormant seeds . Seed bank . Gulf of Mexico . Genetic diversity
Introduction Communicated by Just Cebrian Electronic supplementary material The online version of this article (https://doi.org/10.1007/s12237-020-00808-y) contains supplementary material, which is available to authorized users. * Kelly M. Darnell [email protected] 1
School of Ocean Science and Engineering, Gulf Coast Research Laboratory, The University of Southern Mississippi, Ocean Springs, MS 39564, USA
2
Florida Fish and Wildlife Conservation Commission, Florida Fish and Wildlife Research Institute, St. Petersburg, FL 33701, USA
3
Dauphin Island Sea Lab, Dauphin Island, AL 36528, USA
4
Soil and Water Sciences Department, University of Florida, Gainesville, FL 32611, USA
5
Marine Science Institute, The University of Texas at Austin, Port Aransas, TX 78373, USA
Many plants produce seeds that remain dormant for some period of time (Baskin and Baskin 2014). This life history strategy is e
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