Global change and physiological challenges for fish of the Amazon today and in the near future

Abstract

Amazonia is home to 15% (>2700, in 18 orders) of all the freshwater fish species of the world, many endemic to the region, has 65 million years of evolutionary history and accounts for 20% of all freshwater discharge to the oceans. These characteristics make Amazonia a unique region in the world. We review the geological history of the environment, its current biogeochemistry and the evolutionary forces that led to the present endemic fish species that are distributed amongst three very different water types: black waters [acidic, ion-poor, rich in dissolved organic carbon (DOC)], white waters (circumneutral, particle-rich) and clear waters (circumneutral, ion-poor, DOC-poor). The annual flood pulse is the major ecological driver for fish, providing feeding, breeding and migration opportunities, and profoundly affecting O2, CO2 and DOC regimes. Owing to climate change and other anthropogenic pressures such as deforestation, pollution and governmental mismanagement, Amazonia is now in crisis. The environment is becoming hotter and drier, and more intense and frequent flood pulses are now occurring, with greater variation between high and low water levels. Current projections are that Amazon waters of the near future will be even hotter, more acidic, darker (i.e. more DOC, more suspended particles), higher in ions, higher in CO2 and lower in O2, with many synergistic effects. We review current physiological information on Amazon fish, focusing on temperature tolerance and ionoregulatory strategies for dealing with acidic and ion-poor environments. We also discuss the influences of DOC and particles on gill function, the effects of high dissolved CO2 and low dissolved O2, with emphasis on water- versus air-breathing mechanisms, and strategies for pH compensation. We conclude that future elevations in water temperature will be the most critical factor, eliminating many species. Climate change will likely favour predominantly water-breathing species with low routine metabolic rates, low temperature sensitivity of routine metabolic rates, high anaerobic capacity, high hypoxia tolerance and high thermal tolerance.

Caribbean red snapper fishing performance indicators in Brazilian amazon shelf: Is it the beginning of the end of a fishing system?

“…The effects of climate change, which result in the global decline of biomass and changes in distribution patterns, diversity, and reproduction [ 64 , 65 ] of aquatic resources [ 66 , 67 ], are factors that have raised concerns in the Amazon region. The increase in temperature leads to changes in precipitation patterns and prolonged dry periods, reducing water discharge and the consequent productivity of the Amazon River [ 68 ]. These alterations are likely to favor aquatic species with high thermal tolerance [ 68 ].…”

“…The increase in temperature leads to changes in precipitation patterns and prolonged dry periods, reducing water discharge and the consequent productivity of the Amazon River [ 68 ]. These alterations are likely to favor aquatic species with high thermal tolerance [ 68 ]. Recent studies have found that elevated temperatures in coral reef regions can accelerate the growth of Lutjanidae larvae, but survival rates are lower [ 69 ].…”

Climate Change Impact on the Distribution of Forest Species in the Brazilian Amazon

“…The Amazonian ecosystem has an important role in the conservation of biodiversity and the regulation of the global climate because it is home to the largest rainforest, which has been intensively devastated [1,2]. The maintenance and conservation of biodiversity have been the biggest challenges in the last few decades [3][4][5].…”

“…Deforestation in the Amazon promotes environmental degradation and consequently the reduction in species and natural resources in the region [8]. During 2022, the increase in deforestation in the Brazilian Amazon was about 12,480 km 2 , presenting an increase of 2.3% compared to 2021 (12,188 km 2 ) [9]. The rainforest is highly heterogeneous and considered a complex system, which makes it difficult to conduct species monitoring and to obtain more information about mortality, growing and natural regeneration, and climate change impacts [10][11][12].…”

“…Area with environmental suitability for the occurrence of the timber forest species A. desmanthum, C. micranta, C. racemosa, C. oblongifolia, and V. guianensis according to two climate scenarios (SSP2-4.5 and SSP5-8.5) for two periods 2021-2040 and 2041-2060 in km2 and the reduction in these areas in relation to the base period in %.…”