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Ecosystem change in the southern Benguela and the underlying processes
journal contribution
posted on 2015-04-01, 00:00 authored by L K Blamey, L J Shannon, J J Bolton, R J M Crawford, F Dufois, H Evers-King, C L Griffiths, L Hutchings, A Jarre, M Rouault, Kate WatermeyerKate Watermeyer, H WinkerOverfishing and human-induced climate change are putting severe pressure on marine ecosystems. In the southern
Benguela, most of South Africa's commercial fisheries have a long history of exploitation and this, coupled
with spatio-temporal changes in key species over the last three decades has severely impacted some of South
Africa's fisheries and ecosystems. This review summarizes these spatio-temporal changes and investigates possible
drivers thereof. It incorporates both past and current research, with a large portion of the latter having formed
part of the University of Cape Town's Ma-Re BASICS (Marine Research in the Benguela and Agulhas Systems for
supporting Interdisciplinary Climate-change Science) 2010–2013 program. Almost all described changes involve
a temporal decline or a spatial shift in species. Fishing seems to have played a role in many of the observed stock
declines, for example through geographically disproportionate catches in relation to stock distribution. In some
cases, changes in the physical environment seem to have played an additional role, e.g., rock lobsters on the
west coast have been affected by fishing as well as changes in the physical environment. In almost all cases
these changes have taken place since the 1980s/1990s, except for one or two resources, which have experienced
declines since at least the mid 20th century. Spatial shifts in species have either involved an eastward expansion of
cool-water species, including kelps, rock lobster and pelagic fish, or a retraction of warm-water species such as the
brown mussel, suggesting a cooling of inshore waters along the south-west coast since the 1980s. This suggested
cooling is revealed in ocean temperature (SST Pathfinder), wind and upwelling data for the Cape Peninsula and
south-west coast region during the same period. The absence or inconsistency of long-term data is problematic
when trying to identify drivers of ecosystem change, and actual ecosystem change itself. We discuss this using
ocean temperature in the southern Benguela as an example. In addition, the complex interplay between climate
and anthropogenic (notably fishing) drivers makes identification of drivers difficult and disentangling these
combined effects will require interdisciplinary collaboration, co-ordinated ecosystem projects, increased modelling
effort and the continuation, but also establishment, of new, long-term monitoring studies.
Benguela, most of South Africa's commercial fisheries have a long history of exploitation and this, coupled
with spatio-temporal changes in key species over the last three decades has severely impacted some of South
Africa's fisheries and ecosystems. This review summarizes these spatio-temporal changes and investigates possible
drivers thereof. It incorporates both past and current research, with a large portion of the latter having formed
part of the University of Cape Town's Ma-Re BASICS (Marine Research in the Benguela and Agulhas Systems for
supporting Interdisciplinary Climate-change Science) 2010–2013 program. Almost all described changes involve
a temporal decline or a spatial shift in species. Fishing seems to have played a role in many of the observed stock
declines, for example through geographically disproportionate catches in relation to stock distribution. In some
cases, changes in the physical environment seem to have played an additional role, e.g., rock lobsters on the
west coast have been affected by fishing as well as changes in the physical environment. In almost all cases
these changes have taken place since the 1980s/1990s, except for one or two resources, which have experienced
declines since at least the mid 20th century. Spatial shifts in species have either involved an eastward expansion of
cool-water species, including kelps, rock lobster and pelagic fish, or a retraction of warm-water species such as the
brown mussel, suggesting a cooling of inshore waters along the south-west coast since the 1980s. This suggested
cooling is revealed in ocean temperature (SST Pathfinder), wind and upwelling data for the Cape Peninsula and
south-west coast region during the same period. The absence or inconsistency of long-term data is problematic
when trying to identify drivers of ecosystem change, and actual ecosystem change itself. We discuss this using
ocean temperature in the southern Benguela as an example. In addition, the complex interplay between climate
and anthropogenic (notably fishing) drivers makes identification of drivers difficult and disentangling these
combined effects will require interdisciplinary collaboration, co-ordinated ecosystem projects, increased modelling
effort and the continuation, but also establishment, of new, long-term monitoring studies.
