Prof. Mark Gibbonshttp://hdl.handle.net/10566/15372024-03-29T11:45:36Z2024-03-29T11:45:36ZJellyfication of marine ecosystems as a likely consequence of overfishing small pelagic fishes: Lessons from the BenguelaRoux, Jean-Paulvan der Lingen, Carl D.Gibbons, Mark J.Moroff, Nadine E.Shannon, Lynne J.Smith, Anthony D.M.Cury, Philippe M.http://hdl.handle.net/10566/33162017-12-12T00:03:43Z2013-01-01T00:00:00ZJellyfication of marine ecosystems as a likely consequence of overfishing small pelagic fishes: Lessons from the Benguela
Roux, Jean-Paul; van der Lingen, Carl D.; Gibbons, Mark J.; Moroff, Nadine E.; Shannon, Lynne J.; Smith, Anthony D.M.; Cury, Philippe M.
Changes in two contrasting ecosystems of the Benguela upwelling region,
one dominated at mid-trophic level by jellyfishes (Namibia, northern Benguela
ecosystem, where small pelagic fish abundance has been severely depleted) and
one still dominated by small pelagic fishes (South Africa, southern Benguela)
were compared in an effort to determine ecosystem trajectories under different
exploitation regimes. The role of small pelagic fishes (clupeoids) was highlighted in
the context of their importance in maintaining interactions in marine ecosystems.
In particular, we examined trophic cascades and possible irreversible changes
that promote the proliferation of jellyfishes in marine systems. We found that
the presence of large populations of small pelagic fishes has a fundamental role
in preserving beneficial trophic interactions in these marine ecosystems. The
implications of trophic cascades, such as those observed in the northern Benguela,
for ecosystem-based management were apparent. In addition, this comparison
provides contrasting case studies to inform the development of management
scenarios that avoid ecosystem shifts that affect predators and reduce the value of
fisheries production.
2013-01-01T00:00:00ZBeyond the jellyfish joyride and global oscillations: advancing jellyfish researchGibbons, Mark J.Richardson, Anthony J.http://hdl.handle.net/10566/32422017-10-20T00:01:53Z2013-01-01T00:00:00ZBeyond the jellyfish joyride and global oscillations: advancing jellyfish research
Gibbons, Mark J.; Richardson, Anthony J.
There has been debate in the literature recently about increases in jellyfish populations in response to anthropogenic change, and this has attracted widespread media interest. Despite an international collaborative initiative [National Center for Ecological Analysis and Synthesis (NCEAS) working group on jellyfish blooms] to investigate trends in global jellyfish numbers, interpretations from the data remain ambiguous. Although this is perhaps to be expected given the diversity of potential drivers, the debate has not been helped by a general lack of rigorous data and loose definitions. There is a need for the community to refocus its attention on understanding the implications of jellyfish blooms and managing them, because regardless of global trends, jellyfish are a problem in some coastal marine ecosystems. Here, we provide recommendations for advancing jellyfish research. These include directing research toward better managing jellyfish impacts, expanding research into socio-economic consequences to grow the money available for research, building more operational and ecosystem models for tactical and strategic management, filling in the gaps in our biological knowledge for supporting models, improving surveillance using observing systems and making jellyfish research more rigorous. Some vehicles to address these recommendations include international standardization of methods, a discipline-specific journal for jellyfish research and an international science program on the global ecology and oceanography of jellyfish.
2013-01-01T00:00:00ZSelf-maintaining or continuously refreshed? The genetic structure of Euphausia lucens populations in the Benguela upwelling ecosystemHarkins, Gordon WilliamD'Amato, Maria EugeniaGibbons, Mark J.http://hdl.handle.net/10566/32412017-10-20T00:01:51Z2013-01-01T00:00:00ZSelf-maintaining or continuously refreshed? The genetic structure of Euphausia lucens populations in the Benguela upwelling ecosystem
Harkins, Gordon William; D'Amato, Maria Eugenia; Gibbons, Mark J.
Populations of Euphausia lucens over the shelf of the southern Benguela upwelling region could be self-maintaining. Alternatively, they could be continually refreshed by expatriates from the SW Atlantic that enter the system via South Atlantic Central Water in the south, before developing and then being lost through advection off Namibia. These two hypotheses are investigated here by examining geographic heterogeneity and molecular variation (cox1 and ND1) of the species across its distributional range in the Southern Hemisphere. Comparisons are made with E. vallentini, which is assumed to show panmixia associated with its circumglobal distribution between 50 and 60°S. Phylogenetic analysis with mitochondrial 16S ribosomal RNA and cytochrome oxidase 1 (cox1) confirmed that E. lucens and E. vallentinirepresent sister taxa. Strong geographic structuring of cox1 and ND1 mtDNA genetic variation by ocean basin was recorded in E. lucens, indicating that neritic populations off South Africa are likely self-maintaining. This contrasts with the results for E. vallentini, which appears to occur as a single panmictic population across its distributional range. These differences are likely related to the habitats (neritic, E. lucens; oceanic, E. vallentini) occupied by each species. The results of the neutrality tests are consistent with demographic processes and suggest growth in E. lucens and equilibrium or shrinkage in E. vallentini. Although purifying selection cannot be ruled out in the former, the very few haplotypes recovered from E. vallentini could indicate that any population expansion following a crash is not yet reflected in the relatively slowly evolving mtDNA markers used here. Further work using other methods is recommended.
2013-01-01T00:00:00ZReviewing evidence of marine ecosystem change off South AfricaMoloney, C. L.Fennessy, S. T.Gibbons, Mark J.Roychoudhury, A.Shillington, F. A.von der Heyden, B. P.Watermeyer, K.http://hdl.handle.net/10566/25602017-02-28T00:01:05Z2013-01-01T00:00:00ZReviewing evidence of marine ecosystem change off South Africa
Moloney, C. L.; Fennessy, S. T.; Gibbons, Mark J.; Roychoudhury, A.; Shillington, F. A.; von der Heyden, B. P.; Watermeyer, K.
Recent changes have been observed in South African marine ecosystems. The main pressures on these
ecosystems are fishing, climate change, pollution, ocean acidification and mining. The best long-term datasets are
for trends in fishing pressures but there are many gaps, especially for non-commercial species. Fishing pressures
have varied over time, depending on the species being caught. Little information exists for trends in other
anthropogenic pressures. Field observations of environmental variables are limited in time and space. Remotely
sensed satellite data have improved spatial and temporal coverage but the time-series are still too short to
distinguish long-term trends from interannual and decadal variability. There are indications of recent cooling on the
West and South coasts and warming on the East Coast over a period of 20 - 30 years. Oxygen concentrations on the
West Coast have decreased over this period. Observed changes in offshore marine communities include southward
and eastward changes in species distributions, changes in abundance of species, and probable alterations in
foodweb dynamics. Causes of observed changes are difficult to attribute. Full understanding of marine ecosystem
change requires ongoing and effective data collection, management and archiving, and coordination in carrying out
ecosystem research.
2013-01-01T00:00:00Z