Halpern B.S.,University of California at Santa Barbara |
Halpern B.S.,Imperial College London |
Fujita R.,Oceans Program
Ecosphere | Year: 2013
Efforts to underst and and map cumulative impacts of human activities on ecosystems have gained new interest and relevance as management moves towards ecosystem-based approaches that require such assessments. The last five years have seen a proliferation of efforts to characterize and map cumulative impacts, providing insight into the strengths and limitations of these efforts and where opportunities lie for progress. Here we provide a review of the key assumptions that underlie most cumulative impact mapping efforts, describing the implications and rationales for the assumptions, and highlight the many challenges cumulative impact mapping efforts face. We end with a brief summary of several future research directions that will help greatly improve application of cumulative impact mapping to resource management and conservation planning efforts. © 2013 Halpern and Fujita.
Fitzgerald T.P.,Oceans Program |
Gohlke J.M.,University of Alabama at Birmingham
Environmental Science and Technology | Year: 2014
The BP oil disaster posed a significant threat to the U.S. seafood industry. Invertebrates (shrimp, oyster, crab) and other nearshore species comprised the majority of postspill testing by federal and state agencies. Deeper water finfish were sampled less frequently, despite population ranges that overlapped with affected waters. We report on a voluntary testing program with Gulf of Mexico commercial fishermen to ensure the safety of their catch. Seven species of reef fish were tested for polycyclic aromatic hydrocarbons, several metals, and a constituent of Corexit 9500A and 9527A dispersants. Only two of 92 samples had detectable levels of benzo(a)pyrene-equivalents (a combined measure of carcinogenic potency across 7 different PAHs), which were still below federal safety thresholds. PAH ratios for these samples suggest pyrogenic (not petrogenic) contamination - indicating potential sources other than Deepwater Horizon. Metals were largely absent (cadmium, lead) or consistent with levels previously reported (mercury, arsenic). One notable exception was tilefish, which showed mercury concentrations lower than expected. We did not detect dispersant in any of our samples, indicating that it was not present in these species during the study period. Our findings suggest minimal risk to public health from these seafoods as a result of the disaster; however, the most contaminated areas were not sampled through this program. © 2014 American Chemical Society.
Karr K.A.,Oceans Program |
Karr K.A.,University of California at Santa Cruz |
Fujita R.,Oceans Program |
Fujita R.,Stanford University |
And 9 more authors.
Journal of Applied Ecology | Year: 2015
Ecosystem-based management of coral reef fisheries aims to sustainably deliver a diverse portfolio of ecosystem services. This goal can be undermined if the ecosystem shifts into a different state, with altered ecosystem functions and benefits to people. If levels of drivers that cause transitions between states are identified, management measures could be aimed at maintaining drivers below these levels to avoid ecosystem shifts. Analysing data from a large number of Caribbean coral reefs (N = 2001), suites of nonlinear thresholds were identified between metrics of coral reef processes and structure along a gradient of total fish biomass (a proxy for fishing pressure). Several metrics (macroalgal cover, invertivorous fishes and fish species richness) associated with coral-dominated reefs exhibited thresholds at relatively high fish biomass levels (50-88% of unfished biomass). Other metrics (urchin biomass, ratio of macroalgal to coral cover, herbivorous fishes and coral cover) showed thresholds at lower fish biomass levels (28-37% of unfished biomass). Ratios of total fish biomass in fishing areas to closed areas (unfished biomass) in the Caribbean indicate that reefs may generally be at risk for change at ratios between 0·5 (coral dominated) and 0·3 (macroalgal dominated). Similar relationships were found for coral reefs in the Indian Ocean. While these results illustrate thresholds at the scale of the entire Caribbean, assessing local reefs is advisable because biomass levels vary within the region, and reef trajectories depend on past, present and future local conditions. Synthesis and applications. If the thresholds in this study are generalizable to scales relevant to management, it may be possible to produce sustainable yield while simultaneously maintaining coral-dominated reefs by restricting fishing mortality to levels that result in biomass ratios near 0·5. Fishing down to biomass ratios near 0·3 may increase the risk of overfishing (resulting in lower long-term yields) and transition to macroalgal-dominated reefs. Thresholds offer a simple and powerful way for managers to operationalize precautionary ecosystem-based fishery management by adaptively limiting fishing pressure in order to (i) maintain desirable coral reef conditions, (ii) establish a system-specific target for generating pretty good yield and (iii) maintain sustainable multi-species fishery yields. © 2014 The Authors.