Phenology, sexual reproduction, and the factors affecting sexual reproduction of the marine angiosperm, Thalassia testudinum, in the Florida Keys National Marine Sanctuary (FKNMS)

Kevin M. Cunniff

Department of Biological Sciences, Florida International University, University Park, Miami, FL 33199

Manuscript submitted 5 May 2005; thesis defended 18 July 2005; final manuscript accepted 14 April 2006

Abstract

This study described phenology and investigated the factors affecting sexual reproduction of Thalassia testudinum in the FKNMS. Flowering was assessed at 30 permanent monitoring stations via direct observation with SCUBA in 2002 and through age reconstruction techniques of T. testudinum short shoots previously collected from the same monitoring stations in 2001. The observed mean FKNMS flowering frequency was 1.49%, was spatially variable, and exhibited sex-specific timing in floral anthesis and fruit set. Historical flowering reconstruction demonstrated that mean T. testudinum flowering frequencies are not temporally variable. Observed and reconstructed floral sex ratios in the FKNMS were female-biased, spatially variable, and may be temporally variable.

A total of 25 water quality variables, 13 seagrass vitality variables, and 6 relative nutrient availability variables were used to explore the relationship of environmental factors to observed and historical flowering patterns in the FKNMS. Significant correlative evidence suggests that relative N availability is most important in affecting T. testudinum phenology and flowering patterns, with higher flowering at low N availability and lower flowering at high N availability. Additionally, sexual reproduction (flowering) was negatively correlated with asexual reproduction (rhizome apices per short shoot), and asexual reproduction was positively correlated with N availability.

A 15 month in situ nutrient addition experiment was conducted at 10 sites in the upper Florida Keys to further investigate the relationship between nutrient availability and T. testudinum flowering. N + P were added at ecologically significant loading rates (0.77 g N m^-2 d^-1 and 0.12 g P m^-2 d^-1, respectively) from May 2001 – August 2002. Flowering responses were measured during the 2002 flowering season. Flowering was significantly reduced in the N + P treatment plots relative to control plots at all 10 sites.