TY - JOUR
T1 - Climate warming reduces fish production and benthic habitat in Lake Tanganyika, one of the most biodiverse freshwater ecosystems
AU - Cohen, Andrew S.
AU - Gergurich, Elizabeth L.
AU - Kraemer, Benjamin M.
AU - McGlue, Michael M.
AU - McIntyre, Peter B.
AU - Russell, James M.
AU - Simmons, Jack D.
AU - Swarzenski, Peter W.
N1 - Funding Information:
We thank Ishmael Kimerei, Donatius Chitamwebwa, the Tanzania Fisheries Research Institute staff, Rashid Tamatamah, Kiram Lezzar, Simone Alin, and the students of the Nyanza Project for coring assistance; The Nature Conservancy and its Tuungane Project staff for logistical support; and Colin Apse and two anonymous reviewers for comments on an earlier draft of this paper. Research permits were kindly provided by the Tanzania Council for Science and Technology and the University of Dar es Salaam. Digital bathymetric model data in Fig. 1 are courtesy of tcarta.com. This project was funded by the National Science Foundation [Grants ATM 0223920 (to A.S.C.) and BIO 0353765 (to A.S.C.), The Nyanza Project and Grant DEB 1030242 (to P.B.M.)], the Lake Tanganyika Biodiversity Project (A.S.C.), the USGS Coastal and Marine Geology Program (P.W.S.), Society of Exploration Geophysicists Foundation Geoscientists Without Borders Program [Grant 201401005 (to M.M.M.)], a Packard Foundation Fellowship (P.B.M.), and the Nature Conservancy [Tuungane Project (P.B.M. and M.M.M.)].
Publisher Copyright:
© 2016, National Academy of Sciences. All rights reserved.
PY - 2016/8/23
Y1 - 2016/8/23
N2 - Warming climates are rapidly transforming lake ecosystems worldwide, but the breadth of changes in tropical lakes is poorly documented. Sustainable management of freshwater fisheries and biodiversity requires accounting for historical and ongoing stressors such as climate change and harvest intensity. This is problematic in tropical Africa, where records of ecosystem change are limited and local populations rely heavily on lakes for nutrition. Here, using a ∼1,500-y paleoecological record, we show that declines in fishery species and endemic molluscs began well before commercial fishing in Lake Tanganyika, Africa's deepest and oldest lake. Paleoclimate and instrumental records demonstrate sustained warming in this lake during the last ∼150 y, which affects biota by strengthening and shallowing stratification of the water column. Reductions in lake mixing have depressed algal production and shrunk the oxygenated benthic habitat by 38% in our study areas, yielding fish and mollusc declines. Late-20th century fish fossil abundances at two of three sites were lower than at any other time in the last millennium and fell in concert with reduced diatom abundance and warming water. A negative correlation between lake temperature and fish and mollusc fossils over the last ∼500 y indicates that climate warming and intensifying stratification have almost certainly reduced potential fishery production, helping to explain ongoing declines in fish catches. Long-term declines of both benthic and pelagic species underscore the urgency of strategic efforts to sustain Lake Tanganyika's extraordinary biodiversity and ecosystem services.
AB - Warming climates are rapidly transforming lake ecosystems worldwide, but the breadth of changes in tropical lakes is poorly documented. Sustainable management of freshwater fisheries and biodiversity requires accounting for historical and ongoing stressors such as climate change and harvest intensity. This is problematic in tropical Africa, where records of ecosystem change are limited and local populations rely heavily on lakes for nutrition. Here, using a ∼1,500-y paleoecological record, we show that declines in fishery species and endemic molluscs began well before commercial fishing in Lake Tanganyika, Africa's deepest and oldest lake. Paleoclimate and instrumental records demonstrate sustained warming in this lake during the last ∼150 y, which affects biota by strengthening and shallowing stratification of the water column. Reductions in lake mixing have depressed algal production and shrunk the oxygenated benthic habitat by 38% in our study areas, yielding fish and mollusc declines. Late-20th century fish fossil abundances at two of three sites were lower than at any other time in the last millennium and fell in concert with reduced diatom abundance and warming water. A negative correlation between lake temperature and fish and mollusc fossils over the last ∼500 y indicates that climate warming and intensifying stratification have almost certainly reduced potential fishery production, helping to explain ongoing declines in fish catches. Long-term declines of both benthic and pelagic species underscore the urgency of strategic efforts to sustain Lake Tanganyika's extraordinary biodiversity and ecosystem services.
KW - Climate change
KW - Fisheries
KW - Freshwater biodiversity
KW - Lake Tanganyika
KW - Paleoecology
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U2 - 10.1073/pnas.1603237113
DO - 10.1073/pnas.1603237113
M3 - Article
C2 - 27503877
AN - SCOPUS:84983347783
SN - 0027-8424
VL - 113
SP - 9563
EP - 9568
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
IS - 34
ER -