Saipan, United States
Saipan, United States

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Houk P.,Pacific Marine Resources Institute | Starmer J.,Commonwealth of the Northern Mariana Islands Coastal Resources Management
Coral Reefs | Year: 2010

A central problem for jurisdictional scientists and managers is to reconcile how multiple environmental regimes, encompassing continuous, intermittent and human disturbances, influence pertinent ecological management targets. The presence of heterogeneous environments throughout the volcanic Northern Mariana Islands (NMI), coupled with the availability of descriptive physical data, form the basis examining environmental-ecological relationships. Since 2003, coral abundances and macrobiota (all visibly recognizable taxa greater than 2 cm) occurrences have been estimated at 42 reef slopes along the volcanic archipelago. Analyses showed that reef types acted as surrogates of coral growth capacity and the modern assemblages residing upon them, being highest and most favorable, respectively, where relatively high salinity levels, low-to-moderate wave exposure, and an absence of volcanic activity for ~90 years existed. However, island size was the greatest constraint on species richness overall, but relations with corals were dampened by volcanic activity and increased for sponges and algae where greater connection with the island aquifer existed (i. e., relatively low salinity levels). The number of years since volcanic activity has occurred was positively related to the residuals of species-area relationships and coral cover, with a ~90-year time frame predicted for recovery. Notably, no relationships with watershed characteristics or distance from CNMI's main fishing port and coral-reef assemblages or species richness were found. Further examination of specific management concerns, such as fisheries and feral animal populations, should be designed to account for the inherent differences in driving environmental regimes. Management strategies focused upon conserving biodiversity and ecosystem function should be centered at the island level, matching the operational scale of dominant environmental-ecological relationships. Marine reserves represent a strategy pertinent for the remote NMI; a spatial structure is discussed. © Springer-Verlag 2009.


Houk P.,Pacific Marine Resources Institute | Rhodes K.,University of Hawaii at Hilo | Cuetos-Bueno J.,University of California at San Diego | Lindfield S.,University of Western Australia | And 2 more authors.
Coral Reefs | Year: 2012

A dearth of scientific data surrounding Micronesia's coral-reef fisheries has limited their formal assessment and continues to hinder local and regional management efforts. We approach this problem by comparing catch-based datasets from market landings across Micronesia to evaluate fishery status in the Commonwealth of the Northern Mariana Islands (CNMI), Guam, Yap, and Pohnpei. Initial examinations found that calm weather and low lunar illumination predicted between 6% (Yap) and 30% (CNMI) of the variances in daily commercial landings. Both environmentally driven catch success and daily catch variability increased in accordance with reef-fish demand indices. Subsequent insight from species composition and size-at-capture data supported these findings, highlighting reduced trophic levels and capture sizes where higher human-population-per-reef-area existed. Among the 12-15 target species and/or species complexes that accounted for 70% of the harvest biomass, capture sizes were consistently smallest for CNMI and Guam, often below the reported mean reproductive sizes. Comparatively, Pohnpei has the greatest potential for reef fisheries, with a large reef area (303 km 2) and a moderate human population (34,000 people). However, the estimated harvest volume of 476 mt year -1 was 8-9 times higher than other jurisdictions. Even on Yap where the reef-fish demand index was lowest (67.7 people km -2 reef habitat), many target fish were harvested below their mean reproductive sizes, including the iconic green bumphead parrotfish and humphead wrasse, as well as several other herbivores. We discuss our results with respect to the contemporary doctrine surrounding size-spectra, catch composition, and catch frequencies that afford insight into fishery pressure and status. We posit that regional catch-based policies (initially) instituted at the market level, combined with area and gear-based restrictions, represent plausible vectors for improving Micronesian fisheries. © 2011 Springer-Verlag.


Houk P.,Pacific Marine Resources Institute | Benavente D.,Commonwealth of the Northern Mariana Islands Coastal Resources Management Office | Fread V.,Yap Community Action Program
Biodiversity and Conservation | Year: 2012

This study addresses the coupled themes of science and conservation by characterizing and evaluating the coral reefs around Yap, Federated States of Micronesia. Reef types, and the inherent environmental regimes they constitute, were found to be good predictors of distinct modern assemblages, with minimally overlapping species occurrences. Corals from inner and channel reefs were twice as large and assemblages were half as diverse compared with outer reefs, while food-fish were both larger and more diverse on outer and channel reefs compared with inner. While distinctions were predictable, the magnitude of ecological change along a gradient of inner, channel, to outer reefs was higher than expected, suggesting that human influences are quantifiable. Therefore, an evaluation process was conducted to determine the spatial trends in reef 'condition', defined within by ecological metrics. 'Condition' was highest for reefs associated with a priori defined high conservation value for varying reasons: successful fisheries management, critical habitat determination, and high resiliency potential. Regression analyses highlighted that a two-variable model which interactively incorporated proxies to fishing and pollution, as well as a proxy for hydrodynamic flushing potential, explained 40 % of the variance in 'condition'. Collectively, the results are used to evaluate the current status of reef assemblages, and to point out future conservation priorities. © 2012 Springer Science+Business Media B.V.


Houk P.,Pacific Marine Resources Institute | Musburger C.,Pacific Marine Resources Institute | Musburger C.,University of Hawaii at Manoa | Wiles P.,American Samoa Environmental Protection Agency
PLoS ONE | Year: 2010

Background:Compared with a wealth of information regarding coral-reef recovery patterns following major disturbances, less insight exists to explain the cause(s) of spatial variation in the recovery process. Methodology/Principal Findings: This study quantifies the influence of herbivory and water quality upon coral reef assemblages through space and time in Tutuila, American Samoa, a Pacific high island. Widespread declines in dominant corals (Acropora and Montipora) resulted from cyclone Heta at the end of 2003, shortly after the study began. Four sites that initially had similar coral reef assemblages but differential temporal dynamics four years following the disturbance event were classified by standardized measures of 'recovery status', defined by rates of change in ecological measures that are known to be sensitive to localized stressors. Status was best predicted, interactively, by water quality and herbivory. Expanding upon temporal trends, this study examined if similar dependencies existed through space; building multiple regression models to identify linkages between similar status measures and local stressors for 17 localities around Tutuila. The results highlighted consistent, interactive interdependencies for coral reef assemblages residing upon two unique geological reef types. Finally, the predictive regression models produced at the island scale were graphically interpreted with respect to hypothesized site-specific recovery thresholds. Conclusions/Significance: Cumulatively, our study purports that moving away from describing relatively well-known patterns behind recovery, and focusing upon understanding causes, improves our foundation to predict future ecological dynamics, and thus improves coral reef management. © 2010 Houk et al.


Van Woesik R.,Florida Institute of Technology | Houk P.,Pacific Marine Resources Institute | Isechal A.L.,Palau International Coral Reef Center | Idechong J.W.,Palau International Coral Reef Center | And 2 more authors.
Ecology and Evolution | Year: 2012

Coral bleaching and mortality are predicted to increase as climate changeinduced thermal-stress events become more frequent. Although many studies document coral bleaching and mortality patterns, few studies have examined deviations from the expected positive relationships among thermal stress, coral bleaching, and coral mortality. This study examined the response of >30,000 coral colonies at 80 sites in Palau, during a regional thermal-stress event in 2010. We sought to determine the spatial and taxonomic nature of bleaching and examine whether any habitats were comparatively resistant to thermal stress. Bleaching was most severe in the northwestern lagoon, in accordance with satellite-derived maximum temperatures and anomalous temperatures above the long-term averages. Pocillopora populations suffered the most extensive bleaching and the highest mortality. However, in the bays where temperatures were higher than elsewhere, bleaching and mortality were low. The coral-community composition, constant exposure to high temperatures, and high vertical attenuation of light caused by naturally high suspended particulate matter buffered the corals in bays from the 2010 regional thermal-stress event. Yet, nearshore reefs are also most vulnerable to land-use change. Therefore, nearshore reefs should be given high conservation status because they provide refugia for coral populations as the oceans continue to warm. © 2012 The Authors. Ecology and Evolution published by Blackwell Publishing Ltd.


Houk P.,Pacific Marine Resources Institute | Camacho R.,Commonwealth of the Northern Mariana Islands Coastal Resources Management Office
Botanica Marina | Year: 2010

Despite a wealth of laboratory experiments describing seagrass growth and competitive interactions with macroalgae under varying nutrient concentrations, there is limited information available from field studies conducted in complex natural environments. We examined ecological change over time in the Saipan Lagoon, Western Pacific Ocean. Here, seagrass (Halodule uninervis) canopy cover was quantified monthly at relatively small spatial scales over a 3-year period. Where watershed size and human population were low, there was a significant relationship with seasonal environmental cycles; cooler temperatures correlated with increased drift, red algal abundance and freshwater input increased green algae. Following cyclical macroalgal overgrowth, however, seagrass again became the dominant canopy. Conversely, in the presence of high human population and urbanization, seasonal cycles were absent and a seagrass-to-macroalgal transition was evident. Adjacent to a large watershed with moderate pollution, significant ties were found between seagrass emergence and winter-time disturbance events (large swells), as detached macroalgae that formed during summer months were removed annually. In summary, seagrass systems associated with Saipan Lagoon appear to be hierarchically controlled, following: 1) disturbances, 2) land-based pollution, and 3) seasonal environmental cycles. © 2010 by Walter de Gruyter Berlin New York.


Houk P.,University of Guam | Houk P.,Pacific Marine Resources Institute | Musburger C.,University of Hawaii at Manoa
Marine Ecology Progress Series | Year: 2013

Coral reef assemblages, trophic interactions, and food web stability were examined across a remote and densely populated atoll, in the Republic of the Marshall Islands (RMI). The biomass of sharks, large-bodied piscivores, and secondary invertebrate consumers was expectedly larger in the absence of major human populations. Less intuitively, we report a doubling in the density and biomass of small-bodied acanthurids with significant human presence, whereas large-bodied parrotfishes were halved. These trends provided evidence for prey release of small acanthurids, but also indicated a reduction in grazing function given that power-law relationships govern fish size and physiology. Path analyses supported the conjecture that apex predator biomass enhanced the abundance of large-bodied herbivores, with ensuing benefits to calcifying benthic substrates and coral diversity. Human populations, as low as 40 individuals, had opposing linked interactions. The study next used species abundances to depict food chain interaction strengths, and multivariate measures of heterogeneity to depict food chain diversity. The removal of few strong links along the gradient of investigation (i.e. Acropora corals and sharks), as well as numerous weak links, was associated with fish assemblages and benthic substrates that had reduced grazing and calcification potential, respectively. The results inferred that a reduction in the functional response time of trophic guilds will follow perturbations (i.e. reduce stability), synonymous to food webs with low return rates to their modeled, stable con figuration. This study provides a broader perspective for interpreting how humans and apex predators influence ecological stability across (RMI) coral reef ecosystems. © Inter-Research 2013.


Houk P.,University of Guam | Houk P.,Pacific Marine Resources Institute | Van Woesik R.,Florida Institute of Technology
BioScience | Year: 2013

Despite a steady growth in coral-reef monitoring efforts, the application of the monitoring results to decisionmaking often remains limited, because questions that can be answered are frequently posed after monitoring commences, rather than having the questions define the data to be gathered. We review how hierarchical, question-driven frameworks can improve monitoring designs and how added attention to high-population-variance structures play a central role in this process. Stratification is necessary to avoid the high variance and low power caused by sampling across coral-reef habitats. Yet, knowing when and where to introduce stratification into sampling designs requires information on the environmental and biological processes that drive species abundance patterns. Using case studies, we review some limitations of approaches that back-calculate the effort required to attain desirable statistical power and highlight some approaches to better account for the heterogeneous nature of coral-reef assemblages in monitoring designs. © 2013 by American Institute of Biological Sciences. All rights reserved.


Houk P.,University of Guam | Houk P.,Pacific Marine Resources Institute | Benavente D.,CNMI Bureau of Environmental and Coastal Quality | Iguel J.,CNMI Bureau of Environmental and Coastal Quality | And 2 more authors.
PLoS ONE | Year: 2014

The individual contribution of natural disturbances, localized stressors, and environmental regimes upon longer-term reef dynamics remains poorly resolved for many locales despite its significance for management. This study examined coral reefs in the Commonwealth of the Northern Mariana Islands across a 12-year period that included elevated Crown-of-Thorns Starfish densities (COTS) and tropical storms that were drivers of spatially-inconsistent disturbance and recovery patterns. At the island scale, disturbance impacts were highest on Saipan with reduced fish sizes, grazing urchins, and water quality, despite having a more favorable geological foundation for coral growth compared with Rota. However, individual drivers of reef dynamics were better quantified through site-level investigations that built upon island generalizations. While COTS densities were the strongest predictors of coral decline as expected, interactive terms that included wave exposure and size of the overall fish assemblages improved models (R2 and AIC values). Both wave exposure and fish size diminished disturbance impacts and had negative associations with COTS. However, contrasting findings emerged when examining net ecological change across the 12-year period. Wave exposure had a ubiquitous, positive influence upon the net change in favorable benthic substrates (i.e. corals and other heavily calcifying substrates, R2 = 0.17 for all reeftypes grouped), yet including interactive terms for herbivore size and grazing urchin densities, as well as stratifying by major reeftypes, substantially improved models (R2 = 0.21 to 0.89, lower AIC scores). Net changes in coral assemblages (i.e., coral ordination scores) were more sensitive to herbivore size or the water quality proxy acting independently (R2 = 0.28 to 0.44). We conclude that COTS densities were the strongest drivers of coral decline, however, net ecological change was most influenced by localized stressors, especially herbivore sizes and grazing urchin densities. Interestingly, fish size, rather than biomass, was consistently a better predictor, supporting allometric, size-and-function relationships of fish assemblages. Management implications are discussed. © 2014 Houk et al.


Houk P.,Pacific Marine Resources Institute | Raubani J.,PMB
Journal of Oceanography | Year: 2010

This study identifies linkages between regional ocean productivity and the emergence of large Acanthaster planci starfish populations in Vanuatu. Positive correlations were found between wind stress, chlorophyll-a, and upwelling during January-February 2009, corresponding with coral-eating starfish occurrences. Further, temporal associations have existed between monthly wind stress and upwelling since 2000, and were predictors of past starfish events. Links between starfish emergence and oceanographic features are discussed, drawing upon evidence from other asteroid echinoderms. High regional productivity associated with anomalous oceanographic conditions in Vanuatu, and globally, can be used as early warning indicators of probable, future starfish emergence to aid the foundation and success of local management efforts. © 2010 Springer Science+Business Media B.V.

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