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Jupiter, FL, United States

Hixon M.A.,Oregon State University | Anderson T.W.,Oregon State University | Anderson T.W.,San Diego State University | Buch K.L.,Perry Institute for Marine Science | And 6 more authors.
Ecological Monographs | Year: 2012

Do small-scale experiments showing spatial density dependence in marine fishes scale-up to temporal density dependence and regulation of relatively large local populations? If so, what are the causative mechanisms and their implications? We conducted an eight-year multigeneration study of population dynamics of bicolor damselfish (Stegastes partitus) inhabiting four large coral reefs in the Bahamas. After a four-year baseline period, it was clear that two populations naturally received very few settlement-stage larvae, so recruitment of recently settled fish was artificially enhanced at one low-settlement reef and reduced at one high-settlement reef to ensure a broad range of population sizes over which to test for regulation. Over all eight years, populations on the two naturally high-settlement reefs experienced temporal density dependence in multiple per capita demographic rates: mortality, survival to adulthood, and fecundity. These local populations also displayed components of regulation: persistence, boundedness, and return tendency. Reefs supporting regulated populations were structurally complex, providing sufficient prey refuges that ensured high survival at low densities. In contrast, populations at low-settlement reefs experienced either density-independent or slightly inversely density-dependent demographic rates, even though recruitment was artificially augmented to high levels at one reef. There was no evidence of regulation at these reefs, and indeed, one local population suffered temporary extirpation. Here, habitat complexity was relatively low, increasing the risk of predation, especially at low population densities when fish would have to travel longer distances when finding mates or home sites inhabited by conspecifics. Among all demographic parameters, density dependence in individual growth (an indicator of within-species competition for food) was least correlated with the presence or absence of local population regulation. We conclude that, for systems like these, the environmental context of a local population, especially predation risk and the distribution and abundance of spatial refuges, is more important than the magnitude of larval supply alone in determining the existence of regulating density dependence. At the broader metapopulation scale, density dependence in both survival and fecundity exogenously caused by predation may provide regulation for the entire stock, even when endogenous withinspecies competition (assumed to be important in most fisheries models) is weak. © 2012 by the Ecological Society of America. Source


Santavy D.L.,U.S. Environmental Protection Agency | Mueller E.M.,Perry Institute for Marine Science | MacLaughlin L.,Florida Keys National Marine Sanctuary | Peters E.C.,George Mason University | And 2 more authors.
Diversity | Year: 2011

The decline of coral reefs in the Caribbean over the last 40 years has been attributed to multiple chronic stressors and episodic large-scale disturbances. This study assessed the resilience of coral communities in two different regions of the Florida Keys reef system between 1998 and 2002 following hurricane impacts and coral bleaching in 1998. Resilience was assessed from changes in coral abundance, diversity, disease, and bleaching prevalence in reefs near the remote off-shore islands of the Dry Tortugas compared to reefs near Key West, a center of high population density and anthropogenic influences. During the first assessment in spring 1998, Key West and Dry Tortugas coral communities had similar abundance, species diversity, and disease prevalence. Bleaching and disease significantly increased in all reef areas during the summer 1998 El Niño event, with Key West reefs exhibiting higher bleaching and disease prevalence and severity compared to Dry Tortugas. Acroporids and total coral abundance significantly declined in both regions during 1998 following mass-coral bleaching and hurricane impact, but remained reduced only on Key West reefs during the 5-year assessment. These results provide additional evidence that coral reef systems distant from anthropogenic influences may have greater resilience to large-scale disturbances. Source


Micheli F.,Stanford University | Mumby P.J.,University of Queensland | Brumbaugh D.R.,CNRS Center for Marine Biodiversity, Exploitation and Conservation | Brumbaugh D.R.,University of California at Santa Cruz | And 7 more authors.
Biological Conservation | Year: 2014

Determining how ecosystem function and services are related to diversity is necessary for predicting the consequences of diversity loss and for setting goals and priorities for marine conservation. The consequences of biodiversity loss for ecosystem functions and services depend on the level of functional redundancy - the number of species with similar ecological functional traits. Using field data on fish assemblages from 199 coral reef and lagoon sites from six islands, and on local fisheries from four islands in The Bahamas, we examined levels of functional diversity and redundancy within these assemblages and determined how fish biomass and local fisheries catches vary with local diversity. A majority of functional groups contain few species, suggesting that these assemblages have limited functional redundancy. Most also include species targeted by local fisheries, thus fishing has the potential to broadly impact food webs. Comparisons between a large marine reserve and fished reefs confirm that fishing significantly reduces functional redundancy and removes whole functional groups. Positive exponential relationships of fish biomass and fisheries catches with species and functional diversity highlight that even small declines in biodiversity may result in large reductions in secondary production and seafood provision. Taken together, these results indicate that Caribbean fish assemblages have low functional redundancy and high vulnerability of ecosystem functions and services to diversity loss, and that protection of multi-species assemblages is needed to maintain functions and services. © 2014 Elsevier Ltd. Source


O'Farrell S.,University of Exeter | O'Farrell S.,University of Queensland | Bearhop S.,University of Exeter | McGill R.A.R.,Scottish Enterprise | And 4 more authors.
Ecosphere | Year: 2014

Species invasions are a significant threat to global biodiversity and ecosystem function, and yet our knowledge of consequences for native species remains poor. The problem is exacerbated in highly speciose ecosystems like coral reefs. The invasion of the wider Caribbean by predatory lionfish (Pterois spp.) is one of the most successful marine colonizations ever documented, and its impact is anticipated to be substantial on native species. However, despite the ecological and commercial importance of iconic Nassau grouper (Epinephelus striatus), the impacts of the invasion on this IUCN Red-Listed species remain unexamined. Using data gathered from two critical habitats in the Bahamas, we investigate isotopic niche space overlap between lionfish, Nassau grouper and putative prey species. Despite their relatively small body size, we find that lionfish occupy the highest isotopic niche position on patch reefs, occupying much of the same space as the native apex predator. Contrary to expectation, lionfish trophic level (δ15C) does not increase with body size, contrasting with confamilials in their native range. However, we find that tissue carbon (δ13C) changes systematically with body size on deep forereef habitats, representing a lengthspecific shift in food resources, with smaller individuals partitioning resources from larger individuals in this habitat but not on shallow patch reefs. We conclude that, despite the difference in body size, lionfish are capable of directly competing for food resources with Nassau grouper, and that impacts on guilds such as planktivores and invertivores may vary systematically by habitat. Our study contributes to the growing body of research aimed at understanding how a species that is relatively rare in its native range achieved the most successful fish invasion ever documented. Copyright: © 2014 O'Farrell et al. Source


Eakin C.M.,National Oceanic and Atmospheric Administration | Morgan J.A.,Systems Watch | Heron S.F.,ReefSense Pty. Ltd | Heron S.F.,James Cook University | And 67 more authors.
PLoS ONE | Year: 2010

Background: The rising temperature of the world's oceans has become a major threat to coral reefs globally as the severity and frequency of mass coral bleaching and mortality events increase. In 2005, high ocean temperatures in the tropical Atlantic and Caribbean resulted in the most severe bleaching event ever recorded in the basin. Methodology/Principal Findings: Satellite-based tools provided warnings for coral reef managers and scientists, guiding both the iming and location of researchers' field observations as anomalously warm conditions developed and spread across the greater Caribbean region from June to October 2005. Field surveys of bleaching and mortality exceeded prior efforts in detail and extent, and provided a new standard for documenting the effects of bleaching and for testing nowcast and forecast products. Collaborators from 22 countries undertook the most comprehensive documentation of basin-scale bleaching to date and found that over 80% of corals bleached and over 40% died at many sites. The most severe bleaching coincided with waters nearest a western Atlantic warm pool that was centered off the northern end of the Lesser Antilles. Conclusions/Significance: Thermal stress during the 2005 event exceeded any observed from the Caribbean in the prior 20 years, and regionally-averaged temperatures were the warmest in over 150 years. Comparison of satellite data against field surveys demonstrated a significant predictive relationship between accumulated heat stress (measured using NOAA Coral Reef Watch's Degree Heating Weeks) and bleaching intensity. This severe, widespread bleaching and mortality will undoubtedly have long-term consequences for reef ecosystems and suggests a troubled future for tropical marine ecosystems under a warming climate. Source

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