Evidence of Halodule wrightii flower and seed production at its northern range extent in the western North Atlantic (USA)

Halodule wrightii is a tropical, euryhaline, dioecious seagrass found in marine waters of the western Atlantic Ocean, ranging from Brazil and the Gulf of Mexico to its northern limit in North Carolina. For seagrasses, sexual reproduction can serve as a resilience mechanism, with seed banks supporting re-establishment and recovery following a stress event. However, environmental stress may limit sexual reproduction due to high energetic costs. H. wrightii in North Carolina was previously thought to rely exclusively on asexual reproduction, with no confirmed reports of fully developed seeds and only a single historical account of flowering. Here, we report field observations of female and male flowers, fruits, and fully developed seeds in the sediment confirming that H. wrightii is capable of successful sexual reproduction at its northern range limit. These findings challenge prior assumptions and highlight the need for future research into the ecological and environmental factors influencing sexual reproduction (e.g. flower formation, timing of pollination, fruit development) and the role it plays in shaping genetic diversity in edge-of-range H. wrigthii populations.