Distribuição sazonal e interanual de hidroides (Cnidaria, Hydrozoa) epifíticos em gramas marinhas do Atlântico sudoeste tropical (6°S)

Abstract

Hydroids are important epifaunal components of seagrass communities, where they take part of the benthic-pelagic coupling and may also be used as bioindicators. However, little attention has been given to the epiphytic hydroid assemblage structure and their seasonal and interannual variations, particularly from tropical environments. In this study, the monthly occurrence and abundance of epiphytic hydroids on seagrass beds of Halodule wrightii at Northeast Brazilian coast (6°S) was investigated between March 2016 and February 2019. It was analyzed 23,560 leaves of H. wrightii of which 5,308 (22.5%) had epiphytic hydroids of seven species (total of 165,056 polyps). Monthly averages of polyp density and percentage of leaves with hydroids ranged from 0.7±0.6 and 3,659±2,215 polyps/100 cm2 and 0.1±0.3 and 78.4±7.9%, respectively. Seasonal and interannual differences of these variables were found. Higher values typically occurred between March and August (rainy season) in the three years, when higher species richness and reproductive effort also occurred. Orthopyxis sp. (probably an undescribed species) and Tridentata marginata predominated and were the main species responsible by the observed trends. The results found here corroborate the few available data on tropical hydroid, suggesting higher richness, abundance, and investment in sexual reproduction during the rainy season when food availability is higher. On the other hand, the decline of the population during the dry season (September-February) observed here, possibly is related to the lower food availability and increase in algae coverage that compete directly with the hydroids for space. This study draws attention to a possible undescribed Orthopyxis, in addition to provide important and previously inexistent data on temporal dynamics of hydroids from tropical Southwest Atlantic.