Flávia K. Siqueira-Souza

An initial assessment of drought sensitivity in Amazonian fish communities

The Amazon River Basin encompasses the world’s largest remaining tropical rainforest, and the largest freshwater system with the highest fish species diversity on earth, but global climate change is predicted to cause the loss of 7–12% of fish species by 2070. The severe drought anomaly of 2005, caused by warming of Atlantic surface waters, provided a unique opportunity to examine the impact of a major climatic disturbance on a tropical fish assemblage. We monitored fish species diversity in six Brazilian floodplain lakes along the Solimões River from 2004 to 2007 (before, during, and after drought). Statistical analysis revealed changes in species composition of these lakes following the drought, with both positive and negative responses observed. The response to drought was not uniform among species with regard to trophic guild or migratory behavior. SIMPER analysis showed that planktivores on the average increased in abundance in the years following the drought, carnivores and omnivores decreased, and herbivores and detritivores increased. Some of these changes were transitory, others persisted through monitoring. Migratory species disproportionately increased in abundance post-drought compared to non-migratory species. Interlake (β) diversity of fish declined during the drought year, indicating that lakes were becoming less heterogeneous in species composition, but showed a trend toward recovery of pre-drought level in the following years. According to both global climate change models and recent experience, the intensity and frequency of droughts in this region of the world is increasing. Given the sensitivity of resident fish species to the single, short-term, perturbation reported here, assessment of how tropical freshwater fish populations respond to drought will be crucial to understanding the consequences of this kind of perturbation to these communities and to the human inhabitants who depend upon this important protein source.

Interconnectedness during high water maintains similarity in fish assemblages of island floodplain lakes in the Amazonian Basin

We conducted a study to test the hypothesis that interconnectedness among island floodplain lakes and the adjacent Solimoes River during the flood stage of the hydrologic cycle is enough to maintain similarity in fish species assemblages. Gill net samples were collected during high and low water periods for three consecutive years (July 2004 to July 2006) in four lakes on Paciencia Island. Two lakes, Piranha and Ressaca, are connected to the river all year, and the other two, Preto and Cacau, which are in the center of the island, are isolated during low water periods. The abundance, species richness and evenness of the fish assemblages in these lakes did not differ according to their relative positions or the season of the hydrological cycle, which confirmed our hypothesis. However, fish abundance during the dry season was greater than in the flood season. Apparently, the short period of full connection between the lakes is enough to allow the colonization of all fish species, but not to cause similar abundances. Our study indicates that persistence of the species composition of island floodplain lakes is primarily due to the annual replenishment of fish to the lakes during the flood season.

Intra- and inter-annual changes in the condition factors of three Curimatidae detritivores from Amazonian floodplain lakes

The flood pulse is a key factor that drives the biota of large rivers with adjacent floodplains, but the direction and intensity of its effects are not uniform for all trophic guilds of fish. In this study, we tested the existence of intra- and inter-annual changes in the relative condition factors (kn) of three Curimatidae: Potamorhina altamazonica, Potamorhina latior, and Psectrogaster rutiloides. We used weight and length data from fish that were caught in eight floodplain lakes of the Rio Solimoes. These data were from experimental fisheries during each season of the hydrological cycle: flooding, flood, drying, and dry from 2004, 2005, and 2006. In general, there are similar patterns of intra-annual changes for these three species, with the highest estimates of kn during high water conditions. The lowest values were observed during the drying and dry seasons of 2005, when an extreme drought occurred in the Amazon basin. Higher values were observed during the same seasons in the year post-drought. We hypothesized that these patterns would be explained by the biological characteristics of these species and the effects of intra-annual hydrological changes, mainly the flood pulse effect, and by inter-annual climatic events, which are determined by global climate phenomena.

Amazon floodplain fish diversity at different scales: do time and place really matter?

Amazonian floodplain lakes, which are of different types based on their proximity to the main river channels, are subjected to a strong seasonal hydrologic cycle and have different habitat types within them. We hypothesized that these two spatial scales (lake type, and habitat type within lakes), and the temporal scale associated with hydrological seasons help explain the high fish diversity of the Amazon basin. We sampled three lake types categorized by proximity and connectivity with the Solimões River (island, coastal, and mainland) in 2011 during both high and low water seasons. Within these lakes, we sampled three habitat types (open water, flooded forest, and macrophyte banks). Although comparisons of diversity indices revealed few differences with respect to overall species numbers, actual species composition, which is not included in calculation of diversity indices, differed markedly at all three scales. Although many species (86) were common to all three types of lakes, each type also had many unique species (11–20), as did within-lake habitat type (10–15) and hydrologic season (26 each). Thus, these temporal and spatial scales are important to the detection and understanding of fish species diversity in this region, and will be important to keep in mind when designing preserves.

Ecomorphological correlates of twenty dominant fish species of Amazonian floodplain lakes

Fishes inhabiting Amazonian floodplain lakes exhibits a great variety of body shape, which was a key advantage to colonize the several habitats that compose these areas adjacent to the large Amazon rivers. In this paper, we did an ecomorphological analysis of twenty abundant species, sampled in May and August 2011, into two floodplain lakes of the lower stretch of the Solimões River. The analysis detected differences among species, which could be probably associated with swimming ability and habitat use preferences.

Fish species richness is associated with the availability of landscape components across seasons in the Amazonian floodplain

Understanding environmental biodiversity drivers in freshwater systems continues to be a fundamental challenge in studies of their fish assemblages. The present study seeks to determine the degree to which landscape variables of Amazonian floodplain lakes influences fish assemblages in these environments. Fish species richness was estimated in 15 Amazonian floodplain lakes during the high and low-water phases and correlated with the areas of four inundated wetland classes: (i) open water, (ii) flooded herbaceous, (iii) flooded shrubs and (iv) flooded forest estimated in different radius circular areas around each sampling site. Data were analyzed using generalized linear models with fish species richness, total and guilds as the dependent variable and estimates of buffered landscape areas as explanatory variables. Our analysis identified the significance of landscape variables in determining the diversity of fish assemblages in Amazonian floodplain lakes. Spatial scale was also identified as a significant determinant of fish diversity as landscape effects were more evident at larger spatial scales. In particular, (1) total species richness was more sensitive to variations in the landscape areas than number of species within guilds and (2) the spatial extent of the wetland class of shrubs was consistently the more influential on fish species diversity.

Condition factor variations over time and trophic position among four species of Characidae from Amazonian floodplain lakes: effects of an anomalous drought

The effects of extreme droughts on freshwater fish remain unknown worldwide. In this paper, we estimated the condition factor, a measure of relative fitness based on the relationship of body weight to length, in four fish species representing two trophic levels (omnivores and piscivores) from Amazonian floodplain lakes for three consecutive years: 2004, 2005 (an anomalous drought year), and 2006. The two omnivores, Colossoma macropomum and Mylossoma duriventre, exhibited trends consistent with their life cycles in 2004 and 2006: high values during the hydrologic seasons of high water, receding water, and low water, with a drop following reproduction following the onset of rising water. However during the drought year of 2005 the condition factor was much lower than normal during receding and low water seasons, probably as a result of an abnormal reduction in resource availability in a reduced habitat. The two piscivorous piranhas, Serrasalmus spilopleura and S. elongatus, maintained relatively stable values of condition factor over the hydrologic cycles of all three years, with no apparent effect of the drought, probably because the reduction in habitat is counterbalanced by the resulting increase in relative prey density. We suggest that if predictions of increasing drought in the Amazon are correct, predatory species may benefit, at least in the short run, while omnivores may be negatively affected.

Small dams for aquaculture negatively impact fish diversity in Amazonian streams

Much has been written about the negative impacts of large hydroelectric dams on fish species diversity in the Amazon River Basin; however, less is known about the impacts of small dams in streams that are created for fish aquaculture. Our study of fish assemblages upstream and downstream of fish farm dams in Rondônia State, Brazil, revealed that the dams act as physical barriers to fish movement and that upstream assemblages showed lower measures of diversity and abundance compared to downstream. The greatest impact was the obstruction of upstream movement of a number of fish groups, coupled with isolation and disappearance of relatively rare fish species living upstream. The fish species most affected were from frugivore, herbivore and detritivore trophic levels that are associated with migration and the forming of schools (potamodromous species), although the impact was also evident in piscivorous fish commonly found in lentic habitats. Although stream dams may cause small negative effects relative to huge hydroelectric barriers, the cumulative impact of hundreds of fish farms in stream channels could be considerable. Amelioration of the damage caused by fish farm impoundments will require (1) design of effective fish passage systems around dams to reduce impact on fish diversity and (2) prohibition of the complete stream blocking to build these fish farms, which will require derivative channels to their water supply.