Fish on fire: Shifts in Amazonian fish communities after floodplain forest fires

Severe droughts can lead to fires that cause massive tree mortality in
even the wettest and most isolated Amazonian forests. After repeated
fires, blackwater floodplain forests can remain in an open vegetation
state of arrested succession that facilitates a transition towards a
white-sand “savanna-like” vegetation. These vegetation shifts from
closed-canopy floodplain forests to open fire scars, and eventually
white-sand savannas, may have profound implications for fish communities
that depend on floodplain forests for food and recruitment. In turn,
changes in fish communities may contribute to the arrested forest recovery
after fires as fish are important seed dispersal agents for many
floodplain tree species. To explore the impacts of floodplain forest fires
on fish communities, we sampled fish in unburnt forests, fire scars, and
white-sand savannas in the middle Rio Negro basin (Brazil) during two
consecutive flooding seasons. We compared the abundance, species richness,
and the taxonomic and trophic composition of fish assemblages across the
three habitat types.  We found significant shifts in fish
assemblages in fire scars compared to unburnt floodplain forests. Also, as
fire scars increased in size, total fish biomass decreased strongly. Fish
communities in unburnt floodplain forests seem to be characterized by a
higher proportion of smaller and omnivorous fish species than fish
communities in burned floodplain forests and white sand savannas. Fish
assemblages in fire scars and white-sand savanna were not significantly
different. Synthesis and Applications. Amazonian fish communities change
after floodplain forest fires. Unburnt forests have diverse fish
communities, with a large proportion of unique and small omnivorous
species. In contrast, carnivores and detritivores become more common in
fire scars and white-sand savannas formed after forest fires. Less
omnivore fish after forest fires can reduce tree seed dispersal and forest
regeneration, affecting ecosystem functioning and the services provided by
Amazonian forests. Fish are also a primary source of food and income for
people living in Amazonian floodplains. Preventing forest fires is
therefore of fundamental importance for the conservation of Amazonian
aquatic and terrestrial ecological communities as well as for the
livelihood of people.