Distribution, seasonal abundance and shoot size of the seagrass Halodule wrightii near its southern limit at Rio de Janeiro state, Brazil

A search for Halodule wrightii. Aschers. carried out along the most coast o f Rio de Janeiro state revealed 21 populations, Populations were usually sm all, sparsely distributed and essentially monospecific. To quantify the int ensity of seasonal variation within these southerly populations, samples we re collected every 45 days at the site with most seagrass-IIha do Japones, Cabo Frio, Variation in biomass and density, and size distributions of shor t shoot lengths were measured. Short shoots made up between 21 and 44% of H . wrightii biomass. Seasonal changes in seagrass parameters (e.g. biomass f rom 12.1-37.3 g dry weight m(-2), short shoot density from 2080-8482 m(-2) and short shoot size from 28-106 mm), were strongly pronounced in the popul ation between 1995 and 1997, although inter-annual variation in the measure d parameters was also evident. The variation (coefficient of variation) of shoot size distributions also showed seasonal differences but differences i n size skewness (skewness coefficient) were not found. No evidence of sexua l reproduction was found. A comparison of the same variables in ten populat ions distributed along the coast of Rio de Janeiro state revealed substanti al between site variation in shoot density, biomass distribution and short shoot size distributions. Biomass values for H. wrightii were relatively lo w. In the populations at Rio de Janeiro, rhizome biomass was positively cor related with root biomass, while shoot biomass was positively correlated wi th mean shoot length rather than shoot density. (C) 1999 Elsevier Science B .V. All rights reserved.