Dinâmica temporal de Halodule wrightii Ascherson e suas interações ecológicas com macroalgas e herbívoros

Abstract

The seagrasses are the only group of plants adapted to life in the marine environment. Globally, they are being destroyed by human activities. Unfortunately, little is known about the dynamics and ecology of seagrasses in Brazil, despite its great ecological and economic importance. This work has as main objectives try to understand more about the dynamics of Halodule wrightii meadow and watch as the competition and herbivory affect and modulate this meadow. The study was made at two points, in the entrance channel Itajuru, near Japanese Island (RJ) (22°52,951'S 42°00,168'W) and on the north side of the Santa Barbara Island (BA) (17°57,703'S 38°41,834'W), within the National Marine Park of Abrolhos. Monitoring was carried out following the international protocol SeagrassNet, which uses three fixed transects of 50m to detect temporal changes in the meadow. To observe the dynamics that mediate the distribution of macrophytes in Abrolhos transplants replicates were used for the different areas of distribution of organisms (zone without vegetation, zone dominated by H. wrightii and zone dominated by rizophytic algae), within the addition of rizophytic algae and exclusion of herbivores. Measurements were also made of water flow, sedimentation and herbivory intensity in different zones. Monitoring conducted in Abrolhos showed that a monospecific meadow of H. wrightii may present different characteristics according to the season. The average percentage cover of H. wrightii in transects ranged from 34% in april and 25% in october. The maximum height of the shoots was found in july (12,4 cm). A correlation indicated a negative relationship between algae and H. wrightii. The total dry weight average was higher in the months of april and july. The intensity of herbivory is significantly higher near the coral reef which areas of occurrence of macrophytes (F(1,16)=11,72; p≤0,001). No variation in water flow. The rate of sedimentation is greater at the edges of the distribution zones of macrophytes. The replicates of the zone dominated by algae where algae were removed showed a significant increase in density after 75 days of the experiment, from only 46 shoots.400cm-2 to 94 shoots.400cm-2 (F(1,8)=5,71; p=0,04). The average percentage cover of H. wrightii was significantly higher in replicates where there was no addition of rizophytic algae (F(35)=1.93; p=0,161). The shoot density was higher in replicates where there was no addition of seaweeds. The shoot height was 4 cm higher in replicates with total exclusion of herbivores. It was concluded that there are not the abiotic factors and yes the competition and herbivory responsible for the zonation of macrophytes. The results show the effectiveness of the methodology of fixed point monitoring for the detection and comparison of different seagrass meadows, and provide us a greater understanding of the dynamics that mediates the Brazilians seagrass meadows