Temporal variations in morphology and biomass of vulnerable Halodule wrightii meadows at their southernmost distribution limit in the southwestern Atlantic.

Meadows of the seagrass Halodule wrightii occur on shallow subtidal sandy bottoms of euhaline high-energy sites in Paranaguá Bay, Brazil. Close to their southernmost limit in the South Atlantic, local populations are patchy, unstable and most often do not reproduce sexually. We describe morphological and biomass variations of a local H. wrightii meadow off Rasa da Cotinga Island, which deteriorated from a healthy state to subsequently decline and die-off. Leaf width and length, number of leaves per shoot, leaf sheath length, rhizome width, internodal length and biomass, sediment grain size, CaCO₃ and POM contents were measured on six sampling dates between November 2004 and October 2005. Compared to other Halodule meadows along the southwestern Atlantic coastline, local plants had shorter and narrower leaves, shorter leaf sheaths, thinner rhizomes, fewer leaves per shoot, a larger internodal distance, and lower biomass. Local variations in morphology and plant biomass followed a seasonal pattern, but were affected by stressor, such as the lowering of temperature, precipitation, and high turbidity associated with southwesterly winds that increased meadow vulnerability. Life history traits of H. wrightii, a short-lived species with rapid growth and ability to reproduce vegetatively under stress conditions, promote resilience and rapid recovery of local meadows, which exhibit a typically fugitive behavior. [ABSTRACT FROM AUTHOR]