Lack of exotic hydrilla infestation effects on plant, fish and aquatic bird community measures

The invasion of hydrilla into North American lakes has provoked concern over loss of native flora and fauna and resulted in costly suppression efforts. We used two data sets to determine if common measures of ecosystem health; abundance, species richness, diversity and evenness, were affected by the presence of hydrilla. Data Set 1 consisted of 27 Florida lakes, 11 of which had hydrilla present for approximately 4-8 years in varying abundances, and 16 did not have hydrilla. Given the number of lakes, each was sampled only once in the summers of 1986-1990 for community measures of aquatic plants, birds, and fish. Data Set 2 consisted of 12 lakes, six with abundant hydrilla for over 23 years and six without hydrilla. These lakes were sampled every year in the summer (with a few exceptions due to weather conditions) between 1999 and 2006 for community measures of aquatic plants and fish. The results for both data sets show that presence of hydrilla had no statistically significant effect (P > 0.05) on all community measures tested (i.e., richness, diversity, abundance). Our conclusions support the hypothesis that hydrilla in these Florida lakes has occupied a mostly vacant ecological niche and has not affected the occurrence or relative composition of native species of aquatic plants, birds, and fish. Because pond experiments have found negative effects of hydrilla, further focused research is needed to assist management decisions when considerable resources are to be spent each year on hydrilla suppression.