5 research outputs found
Human disruption of coral reef trophic structure
The distribution of biomass among trophic levels provides a theoretical basis for understanding energy flow and the hierarchical structure of animal communities. In the absence of energy subsidies [1], bottom-heavy trophic pyramids are expected to predominate, based on energy transfer efficiency [2] and empirical evidence from multiple ecosystems [3]. However, the predicted pyramid of biomass distribution among trophic levels may be disrupted through trophic replacement by alternative organisms in the ecosystem, trophic cascades, and humans preferentially impacting specific trophic levels [4, 5 and 6]. Using empirical data spanning >250 coral reefs, we show how trophic pyramid shape varies given human-mediated gradients along two orders of magnitude in reef fish biomass. Mean trophic level of the assemblage increased modestly with decreasing biomass, contrary to predictions of fishing down the food web [7]. The mean trophic level pattern is explained by trophic replacement of herbivorous fish by sea urchins at low biomass and the accumulation of slow-growing, large-bodied, herbivorous fish at high biomass. Further, at high biomass, particularly where fishers are not selectively removing higher trophic level individuals, a concave trophic distribution emerges. The concave trophic distribution implies a more direct link between lower and upper trophic levels, which may confer greater energy efficiency. This trophic distribution emerges when community biomass exceeds ∼650 kg/ha, suggesting that fisheries for upper trophic level species will only be supported under lightly fished scenarios
Ecological roles and importance of sharks in the Anthropocene Ocean
In ecosystems, sharks can be predators, competitors, facilitators, nutrient transporters, and food. However, overfishing and other threats have greatly reduced shark populations, altering their roles and effects on ecosystems. We review these changes and implications for ecosystem function and management. Macropredatory sharks are often disproportionately affected by humans but can influence prey and coastal ecosystems, including facilitating carbon sequestration. Like terrestrial predators, sharks may be crucial to ecosystem functioning under climate change. However, large ecosystem effects of sharks are not ubiquitous. Increasing human uses of oceans are changing shark roles, necessitating management consideration. Rebuilding key populations and incorporating shark ecological roles, including less obvious ones, into management efforts are critical for retaining sharks’ functional value. Coupled social-ecological frameworks can facilitate these efforts
The role of socioeconomic factors in customary coral reef management in Papua New Guinea
For generations, communities in the Pacific islands have employed a range of resource
management techniques (including reef closures, gear restrictions, limiting entry, and the
protection of spawning aggregations) to limit marine resource use. Because of their
perceived potential to meet both conservation and community goals, these traditional
resource management techniques are being revitalized by communities, governments, and
conservation groups as an integral part of national and regional marine conservation plans
in the Pacific. However, it is uncertain whether traditional management can provide a
solid foundation for the development of these conservation strategies. Little is known
about the social, economic, and cultural processes that enable communities to employ
traditional management and it remains unclear if the traditional management systems will
be resilient to the profound socioeconomic changes sweeping the Pacific region.
Indiscriminate application of “traditional” solutions to present day problems in Pacific
communities without understanding the socioeconomic context in which these systems
can operate effectively may lead to disappointment with results and disenchantment with
the conservation process if results do not meet expectations.
Theoretical and empirical studies have identified a number of specific socioeconomic
factors that may influence the ability of a community to implement or maintain
traditional management, but specific relationships between socioeconomic conditions and
the use of traditional management practices are still not well understood. This thesis aims
to examine the socioeconomic context within which select traditional management
systems operate in Papua New Guinea and further debate on how these systems may be
applicable in the modern conservation context by exploring the following research
questions: Do communities with traditional reef closures have different socioeconomic
characteristics than communities that do not? How do traditional closure systems reflect
the socioeconomic conditions of the communities that implement them? This thesis identified socioeconomic factors that may influence whether a community
employs or maintains traditional management and prioritised 11 that could be collected
within the research timeframe. These factors were population, size of the resource,
distance to market, conflicts, settlement pattern, dependence on marine resources,
modernisation, perceptions about the complexity of human-environment interactions,
perceptions about the condition of the marine environment, social capital and
occupational mobility. These socioeconomic factors were examined in 14 coastal
communities in Papua New Guinea, five of which had traditional closures and nine of
which did not. Data were collected using a combination of quantitative and qualitative
techniques, including household surveys, key informant interviews, participant
observation, and oral histories. A technique called Rasch modelling, commonly used in
psychology and education, was employed to aggregate household-level socioeconomic
indicators into thematic interval-level variables. Then the socioeconomic factors in the
five communities that employ traditional closures of coral reefs were quantitatively
compared with the nine communities that do not. Results showed that the constructs used
to measure modernisation, social capital and occupational mobility had a slight but
significant relationship to the presence of traditional closures, and the construct of
dependence on marine resources was strongly related to the presence of traditional
closures.
Two case studies were used to provide a more detailed examination of how dependence
on marine resources influences whether and how communities can employ a traditional
closure. One case study is from Ahus Island, Manus province where dependence on
marine resources is extremely high. The other is from Muluk village on Karkar Island,
where dependence on marine resources is low. These contrasting case studies help to
provide more detail into the socioeconomic context within which these traditional
practices operate and how a community’s dependence on marine resources may
determine whether and how traditional closures may meet their goals. The thesis
concludes by exploring how traditional closures in Papua New Guinea focus on providing
the communities with benefits rather than biodiversity conservation and examining how
this leads to a fundamentally different resource governance model than we see in western fisheries management and resource conservation. This utilitarian model of conservation
may have a place in the modern conservation context of many developing countries
where the social and economic burdens of Western conservation models are unrealistic
Ecological roles and importance of sharks in the Anthropocene Ocean
In ecosystems, sharks can be predators, competitors, facilitators, nutrient transporters, and food. However, overfishing and other threats have greatly reduced shark populations, altering their roles and effects on ecosystems. We review these changes and implications for ecosystem function and management. Macropredatory sharks are often disproportionately affected by humans but can influence prey and coastal ecosystems, including facilitating carbon sequestration. Like terrestrial predators, sharks may be crucial to ecosystem functioning under climate change. However, large ecosystem effects of sharks are not ubiquitous. Increasing human uses of oceans are changing shark roles, necessitating management consideration. Rebuilding key populations and incorporating shark ecological roles, including less obvious ones, into management efforts are critical for retaining sharks' functional value. Coupled social-ecological frameworks can facilitate these efforts.</p