Saipan Lagoon Research Articles

Evaluation of the Humphead Wrasse, Cheilinus undulatus, in Shallow Water Habitats in Saipan Lagoon, Commonwealth of the Northern Mariana Islands1

Visual census surveys utilizing a distance sampling approach were undertaken in Saipan Lagoon to determine the density of humphead wrasse (HHW) in four shallow water habitats, and compared to observations in the Saipan nighttime commercial spear fishery. Fish observed from the survey ranged in total length from 6.5 to 35 cm total length, generally smaller than the range of fish sampled from the commercial fishery of 16 to 47 cm total length. The majority of survey observations occurred in the central and northern part of Saipan Lagoon, which correlated with capture locations documented in the commercial fishery landings. Analysis of contemporary and historical commercial fishery data showed that HHW could not be considered primary fishery target species. Distance sampling results indicated that coral/hard bottom and Enhalus acroroides seagrass were the habitats most important to HHW, as reflected by higher density estimates. The use of distance sampling was useful in estimating the spatial distribution and density of HHW, and should be considered when assessing other rare marine finfish species.

Microbial Source Tracking of Fecal Indicating Bacteria in Coral Reef Waters, Recreational Waters, and Groundwater of Saipan by Real-Time Quantitative PCR.

The Commonwealth of the Northern Mariana Islands (CNMI) recently identified the need to improve its capacity for detecting and tracking land-based sources of pollution (LBSP) in coastal waters, particularly microbial contaminants like fecal indicator bacteria (FIB). Reported here is a baseline study of a suite of host-specific FIB microbial source tracking (MST) markers in the coastal shoreline and reef waters around the island of Saipan. Three sampling campaigns were conducted in September 2017, March 2018, and August 2018. Samples were collected from the nearshore surface waters of Saipan, the reef waters of Saipan Lagoon, and groundwater from beaches along the Saipan Lagoon shoreline. Measurements of submarine groundwater discharge (SGD) into nearshore waters and isotopic source tracking of nitrogen inputs were conducted concurrently with MST. Environmental DNA was extracted from the samples and analyzed by quantitative polymerase chain reaction (qPCR) for MST gene markers of fecal Bacteroidales specifically associated with humans, dogs, cows, and pigs, and for an MST gene marker of Catellicoccus associated with seabirds. MST assessments were combined with local knowledge, assessments of sanitary infrastructure, and routine watershed surveys. This study identified hotspots of human FIB along the western Saipan Lagoon shoreline in both surface waters and groundwater, plus another hotspot of human FIB at a popular tourist bathing area known as the Grotto. FIB hotspots on the Lagoon shoreline coincided with areas of high SGD and nitrogen isotopic data indicating sewage-derived N inputs. It appears that faulty sanitary infrastructure may be contributing to inputs to Saipan Lagoon, while bather shedding is likely a primary input for the Grotto area. Moderate levels of dog fecal contamination were common and widespread across the island. High levels of seabird fecal contamination were more random, both spatially and temporally, and mostly concentrated along the less developed northeast region of Saipan. No significant levels of cow or pig fecal marker were detected in coastal water samples. This study provides demonstration and establishment of analytical capacity to resource management in CNMI for MST technology to aid in trouble-shooting water quality issues involving land-based sources of microbial contaminants to CNMI coastal waters.

Life history of two data-poor but commercially valuable tropical reef fishes, Parupeneus barberinus and Mulloidichthys flavolineatus, from the Saipan fishery, Northern Mariana Islands

We provide a detailed characterisation of the life histories of two commercially important tropical goatfish species, Parupeneus barberinus and Mulloidichthys flavolineatus, from the Commonwealth of the Northern Marianas Islands (CNMI). Two years of continuous fishery-dependent data were used to assess age, growth, mortality and reproduction. Both species are short-lived, with a maximum age of 5 years and maturation within the first year of life. Female and male P. barberinus reach 50% maturity at 15.4- and 20.2-cm fork length (FL) respectively. The M. flavolineatus females and males reach 50% maturity at 15.8- and 16.1-cm FL. Temporal variation in the reproductive cycle of M. flavolineatus indicated that average monthly gonadosomatic index had a clear reproductive period of May–June and an anomalously high peak in November. The reproductive seasonality of P. barberinus was less clear, owing to the abnormally high proportion of inactive physiologically mature females found throughout the year in the fishery across a wide size range. Migrations of P. barberinus into and out of the main fishing area (Saipan lagoon) may explain why the fishery does not encompass the actively spawning population.

Managers, modelers, and measuring the impact of species distribution model uncertainty on marine zoning decisions.

Marine managers routinely use spatial data to make decisions about their marine environment. Uncertainty associated with this spatial data can have profound impacts on these management decisions and their projected outcomes. Recent advances in modeling techniques, including species distribution models (SDMs), make it easier to generate continuous maps showing the uncertainty associated with spatial predictions and maps. However, SDM predictions and maps can be complex and nuanced. This complexity makes their use challenging for non-technical managers, preventing them from having the best available information to make decisions. To help bridge these communication and information gaps, we developed maps to illustrate how SDMs and associated uncertainty can be translated into readily usable products for managers. We also explicitly described the potential impacts of uncertainty on marine zoning decisions. This approach was applied to a case study in Saipan Lagoon, Commonwealth of the Northern Mariana Islands (CNMI). Managers in Saipan are interested in minimizing the potential impacts of personal watercraft (e.g., jet skis) on staghorn Acropora (i.e., Acropora aspera, A. formosa, and A. pulchra), which is an important coral assemblage in the lagoon. We used a recently completed SDM for staghorn Acropora to develop maps showing the sensitivity of zoning options to three different prediction and three different uncertainty thresholds (nine combinations total). Our analysis showed that the amount of area and geographic location of predicted staghorn Acropora presence changed based on these nine combinations. These dramatically different spatial patterns would have significant zoning implications when considering where to exclude and/or allow jet skis operations inside the lagoon. They also show that different uncertainty thresholds may lead managers to markedly different conclusions and courses of action. Defining acceptable levels of uncertainty upfront is critical for ensuring that managers can make more informed decisions, meet their marine resource goals and generate favorable outcomes for their stakeholders.

Primary Production and Calcification Rates of Algae‐Dominated Reef Flat and Seagrass Communities

AbstractMonitoring variability in coral reef primary production and calcification is needed to understand changes over time and between reef systems, which helps separate differences due to natural and/or anthropogenic factors happening now and in the future. This study measured net productivity and calcification for two reef systems at Shark Bay, Heron Reef in the southern Great Barrier Reef and Saipan Lagoon, Commonwealth of the Northern Mariana Islands. Net primary productivity and calcification were strongly correlated for reef flats with an adjusted R2 = 0.66. Night time dissolution occurred at Shark Bay reef flat with an average of −12.66 mmol CaCO3 · m−2 · hr−1, while calcification increased at night for the Saipan reef flat. For both reef flat sites, net productivity from oxygen flux was much lower than rates calculated from change in dissolved inorganic carbon. This study provided the first baseline estimates of net productivity and calcification for a reef flat and seagrass community in Saipan Lagoon. The seagrass community had the lowest productivity of all sites. However, the high presence of calcareous algae at the site highlights the need for more research on the carbonate chemistry of these habitats. All sites had high net productivity that was most likely associated with the dominant presence of algae.

Evaluation of a Fishery Resource Response to a Net-Use Restriction in Saipan Lagoon, Commonwealth of the Northern Mariana Islands1

Abstract: A wide variety of fishing methods is used to harvest coral-reef fishes worldwide, with increasing concerns regarding long-term sustainability. As such, there is a need to determine the degree to which specific fishing methods influence coral-reef fish resources. In 2004 the Commonwealth of the Northern Mariana Islands instituted restrictions on use of gill, drag, and surround nets, limiting use to special exemption for annual fiestas. Historical creel survey data and data from net-use exemptions were reviewed and underwater visual census surveys conducted in southern Saipan Lagoon to assess changes in abundance and biomass from 2004 to 2011. Generalized linear modeling results showed numerical increases in four reef fish families, including Labridae, Scaridae, Mullidae, and the primary target of exempted net-fishing events, Lethrinidae. In addition, mean increases in total reef fish biomass were observed from 2004 to 2011. Positive changes in abundance and biomass of certain coral-reef fish fami...

Life history characteristics and stock status of the thumbprint emperor (Lethrinus harak) in Saipan Lagoon

Life history characteristics and stock status of the thumbprint emperor (Lethrinus harak) in Saipan Lagoon

Influence of urban runoff, inappropriate waste disposal practices and World War II on the heavy metal status of sediments in the southern half of Saipan Lagoon, Saipan, CNMI

Heavy metals were examined in sediments from the southern half of Saipan Lagoon. These waters provided tactical access for US troops during WWII and were heavily shelled at the time. Mercury profiles in sediments were, to some extent, reflective of this event. Samples from the southern end of the lagoon, where an old post-war dumpsite once existed, were found to be substantially enriched with Pb, Cu and Zn. Further north, the lagoon was primarily impacted by urban runoff. Metal enrichment in sediments from this region was generally highest at storm drain outlets and attenuated seawards. Moderate enrichment was rarely exceeded for any element other than Hg beyond the 50m mark. Sediment quality guidelines used to flag potentially adverse ecological health effects revealed no PEL exceedances. TEL exceedances for Pb and Cu were identified in sediments near the former dumpsite. The public health implications of the data are briefly addressed.

Visualizing lateral anisotropy in modern carbonates

Statistical stationarity is a key assumption for the many modeling techniques based on variograms and transiograms used for geostatistical reconstruction of the subsurface. Stationarity expresses the property that the rules of geometry and neighborhood in the model are translation invariant, that is, no directional change in either mean or variance is observed. These criteria are met when the lateral arrangement of lithologic elements into a facies mosaic is isotropic. The balance between isotropy and anisotropy is a defining statistic in the configuration of both real and modeled carbonate landscapes. Even a cursory look at a satellite image of a modern carbonate platform shows that gradients in environment and hydrodynamics cause radical departures from isotropy. Although reef-forming organisms have changed through time, we do not expect that ancient reef systems behaved any differently than today. Hence, significant anisotropy should also be anticipated in the vertical and lateral arrangements of lithologies in the subsurface. To maintain sufficient geologic realism, it is paramount that process-imitating and pattern-replicating models alike be capable of honoring an expected degree of nonstationarity. Despite this need, few studies exist that provide quantitative information to the reach and location of zones of geometric isotropy and anisotropy in carbonate systems, let alone methods with which this property can be assessed. In an effort to close this disjoint, we develop a method for evaluating a modern Pacific depositional system, the Saipan Lagoon, for which we have created a geographic information system stack consisting of mapped facies distributions and a seabed topographic model, both at meter-scale resolution. By developing a lagged spatial metric based on the Markov property of facies transitions, we demonstrate that the degree of anisotropy is influenced by water depth; the shallowest areas (5 m [16 ft]) of the platform interior tend to be anisotropic whereas areas at greater depth are isotropic. This behavior suggests a possible extension to a genetic rule set that could be imparted to subsurface models based on the environment of deposition. This marks an advance in the understanding and, ultimately, handling of geometric nonstationarity in models of carbonate depositional systems.

Impact of a Medical Waste Incinerator on Mercury Levels in Lagoon Fish from a Small Tropical Island in the Western Pacific

In 2004–2005, several species of marine fish were collected for mercury (Hg) analysis from Saipan Lagoon, Saipan, Commonwealth of the Northern Mariana Islands. Relatively high concentrations were found in representatives from the Hafa Adai Beach area located some distance from known sources of Hg contamination. A follow-up investigation aimed at identifying additional land-based sources of Hg in the area was launched in early 2007. The study identified a medical waste incinerator as the primary source of Hg enrichment. The incinerator was operational for about 20 years before it was closed down by the U.S. Environmental Protection Agency (EPA) in January 2006, for multiple violations of the Clean Air Act. Stormwater runoff from this facility entered a drainage network that discharged into the ocean at the southern end of Hafa Adai Beach, about 1 km away. At the time of this investigation storm drain sediments at the coast were only marginally enriched with mercury although values some 50x above background were detected in drainage deposits a few meters down-gradient of the incinerator site. Mercury concentrations in fish from the Hafa Adai Beach area were also significantly lower than those determined in similar species 3 yr earlier. The implications of the data are briefly discussed.

Dynamics of seagrass and macroalgal assemblages in Saipan Lagoon, Western Pacific Ocean: disturbances, pollution, and seasonal cycles

Abstract 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.

Dynamics of shallow-water assemblages in the Saipan Lagoon

The Saipan Lagoon (Northern Mariana Islands) was first examined for benthic compo- sition and habitat distribution in the late 1940s. Here, we employ a 4-stage approach to evaluate and explain change in the distribution of the 9 habitats previously demarcated. We show that there have been considerable reductions in seagrass, staghorn Acropora, and Acropora palifera dominated habi- tats (-3.72, -1.26, and -1.37 km 2 , respectively) that were replaced by 6.16 km 2 of sand (~20% of the lagoon area). Multiple regressions showed that the spatial extent of Enhalus seagrass was positively related with, and best predicted by, the adjacent watershed area and lagoon width. Although the interaction was not as strong, Enhalus also increased in accordance with human development. The size of the Halodule seagrass and macroalgal habitat was negatively related to water-flow velocities and positively related to human development, while its integrity (i.e. the density of seagrass within a given habitat) decreased with human development. Taken together, the results suggest Enhalus and Halodule respond differently to proxies of watershed pollution, and contradict contemporary doctrine linking pollution with reduced seagrass density. This study found no relationship between offshore habitats and watershed characteristics, but suggests their expansion and contraction on relatively short time scales is a result of large-scale disturbances such as typhoons. We posit that, while habitat integrity can be altered by human disturbances, habitat identity is only altered under extreme condi- tions. In summary, this study advances habitat mapping by increasing resolution and accuracy, which, in turn, improves the texture at which reef ecology is used by management.