Lighthouse Reef Research Articles

Cover Image

COVER PHOTO: Lighthouse Reef, Palau, Micronesia, in a healthy state in 2012 prior to a super typhoon which reduced coral cover to zero percent. In their study published in The Scientific Naturalist section of this issue, Doropoulos et al. (Article e3621; doi:10.1002/ecy.3621) document the recovery of corals at Lighthouse Reef over a seven-year period through the growth of cryptic recruits that were dormant in the reef matrix. Photo credit: George Roff.

Movements and residency of Caribbean reef sharks at a remote atoll in Belize, Central America.

We investigated spatial use patterns of 77 Caribbean reef sharks (Carcharhinus perezi) at Lighthouse Reef Atoll, Belize over 7 years using residency patterns, kernel density (KD) estimation and network analysis. We found a high degree individual variation in spatial use of the atoll, but there were significant differences in residency and activity space between sexes, with females being overall more resident. Ontogenetic shifts in movement and residency were largely limited to females, as the residency index increased and activity space estimates decreased as females matured, while for males there was no relationship between space use or residency and size. KD analysis revealed many mature females were highly resident to discrete locations, and average activity space of the intermediate-sized sharks was significantly larger than that of the adults, but not the smallest sharks. Markov chain analyses indicated that the southwestern portion of the atoll was the most important movement corridor for all sharks. Both the Blue Hole and Half Moon Caye Natural Monuments provide some protection for larger Caribbean reef sharks; however, a gear ban on longlines on the southwestern forereef between Long Caye and the channel entrance to the Blue Hole would maximize the benefits for all sharks.

Holocene sediments of an inundated sinkhole: facies analysis of the “Great Blue Hole”, Lighthouse Reef, Belize

Anoxic sinkholes are unique geomorphological features of modern reef systems and in terms of “lake-like” sediment successions very special marine depositional environments. This study presents results of a sedimentological survey, which focuses on the “Great Blue Hole”, a circular Pleistocene karst cavity, situated in the shallow eastern lagoon of Lighthouse Reef Atoll (Belize, Central America). The investigated Blue Hole is located within the tropical cyclone belt and acts as consequence of its unique geomorphology as a giant sediment trap for both fair weather and storm sedimentation. As an important innovation step, we applied a multi-proxy approach based on textural, compositional and geochemical data to ensure a more reliable differentiation between sediments with fair weather and storm condition affiliation. Sediments having formed under both conditions were texturally categorized by determination of classical sedimentary parameters such as mean grain size and sorting. Sediment composition has been quantified in thin sections based on 40 samples discretely taken along a core from the bottom of the 125 m deep and 320 m wide cavern. Classification of sedimentary facies follows a modified scheme for unconsolidated carbonate sediments based on the Dunham nomenclature. Fair-weather sediments are generally finer than 20 μm and consist on average of 81% carbonate fine material, 12% Halimeda platelets, 3% coral fragments, 2% organic material, 1% mollusc shells, 1% foraminifer tests, and minor portions of coralline red algae and echinoderm plates (0–1%). Intercalated event bed sediments are coarse-silt to sand-sized (> 20 μm) and differ in terms of generally lower fine carbonate material amounts (50%) and increased abundances of over-washed Halimeda platelets (28%) and coral fragments (6%). Combined analyses of this study have revealed four primary sedimentary facies with affiliation either to the background (mudstone) or cyclonic event sedimentation (Halimeda wackestone, algae-rich packstone, coralgal rudstone) as well as a transitional sub-facies indicating storm-induced background overprinting (background wackestone). The striking compositional and textural differences of the Halimeda wackestone, algae-rich packstone and coralgal rudstone facies are considered to be another helpful (semi)-quantitative proxy to identify event beds of tropical cyclones in unconsolidated sinkhole sediment successions.

Great Blue Hole (Lighthouse Reef, Belize): A continuous, annually-resolved record of Common Era sea surface temperature, Atlantic Multidecadal Oscillation and cyclone-controlled run-off

The Holocene (<11.7 kyr BP) is characterized by several periods of distinct climate changes. Some of these climate variations had extensive effects on mankind and coincided with demises of extinct high civilizations. Annually-resolved climate reconstructions will certainly play an increasingly important role in public perception, when applying these past patterns to the recent climate debate. The future consequences of the ongoing climate crisis are still challenging to predict, due to the lack of comprehensive, annually-resolved and continuous sea-surface temperature (SST) data. Our 8.55 m long sediment core from the bottom of the Great Blue Hole (Lighthouse Reef, Belize) provides an annually-resolved, continuous and unique south-western Caribbean climate record for the last 1885 years. The varved, “lake-like” sinkhole successions of marine carbonates encompass approximately the entire Common Era (0 CE-modern), a time window, which is key for studying climatic variations and their effects on human society. Our SST record is based on stable isotopes (δ18O) and molecular proxy applications (TEX86). Throughout the Common Era, oxygen isotopes (δ18O) and TEX86 data imply a general SST rise of 0.5 °C and 1.3 °C, respectively, within the south-western Caribbean. The modulation of SST within the Common Era time series likely operated on two different time levels: (1) Solar (e.g., “Gleissberg Cycles”) and volcanic activity triggered climate changes, which in turn induced responses of the Atlantic Multidecadal Oscillation (AMO), the North Atlantic Oscillation (NAO) and the El-Niño-Southern Oscillation (ENSO). Their changing mode of action has been identified as a likely origin of the primary, i.e., centennially scaled SST variability. We suspect long-term positive AMO and NAO modes as the primary key control mechanisms of the Dark Ages Cold and Medieval Warm Period SST patterns. ENSO mode modulation likely exerted primary control on regional SST variability during the Little Ice Age and the Modern Global Warming. (2) Our δ18O data further indicate a striking secondary control on multi-decadal time scales: δ18O variations occur with 32–64 years periodicity. This signal is clearly evidence of SST modulation controlled by AMO phase changes (50–70 years) over almost the entire Common Era. Our carbon isotope record (δ13C) exhibits two remarkable negative anomalies and a long-term up-core decreasing trend. The first excursion (drop of 0.5‰) occurred with the onset of the Medieval Warm Period, which is reconstructed to be a peak time in south-western Caribbean tropical cyclone (TC) activity. This overlap is stressing a potential context between TC activity, enhanced coastal run-off and increased soil-erosion reflected by 13C-depleted carbon isotopes. A second anomaly (>1900 CE) is more likely the result of the “Suess Effect” (anthropogenic impact of the Industrial Revolution on carbon isotopes composition) than another reflection of a TC peak activity interval.

Caribbean cyclone activity: an annually-resolved Common Era record

Tropical cyclones (TC) represent a substantial threat to life and property for Caribbean and adjacent populations. The prospective increase of TC magnitudes, expressed in the 15th chapter of the IPCC AR5 report, entails a rising probability of ecological and social disasters, which were tragically exemplified by several severe Caribbean TC strikes during the past 20 years. Modern IPCC-grade climate models, however, still lack the required spatial and temporal resolution to accurately consider the underlying boundary conditions that modulate long-time TC patterns beyond the Instrumental Era. It is thus necessary to provide a synoptic mechanistic understanding regarding the origin of such long-time patterns, in order to predict reliable changes of TC magnitude and frequency under future climate scenarios. Caribbean TC records are still rare and often lack the necessary continuity and resolution to overcome these limitations. Here, we report on an annually-resolved sedimentary archive from the bottom of the Great Blue Hole (Lighthouse Reef, Belize). The TC record encompasses 1885 years and extends all existing site-specific TC archives both in terms of resolution and duration. We identified a likely connection between long-term TC patterns and climate phenomena responses to Common Era climate variations and offer a conceptual and comparative view considering several involved tropospheric and oceanographic control mechanisms such as the El-Niño-Southern-Oscillation, the North Atlantic Oscillation and the Atlantic Multidecadal Oscillation. These basin-scaled climate modes exercise internal control on TC activity by modulating the thermodynamic environment (sea-surface temperature and vertical wind shear stress dynamics) for enhanced/suppressed TC formation both on millennial (primary) and multi-decadal (secondary) time scales. We interpret the beginning of the Medieval Warm Period (MWP) as an important time interval of the Common Era record and suspect that the southward migration of the intertropical convergence zone (ITCZ) caused, in combination with extensive hydro-climate changes, a shift in the tropical Atlantic TC regime. The TC activity in the south-western Caribbean changed in general from a stable and less active stage (100–900 CE) to a more active and variable state (1,100 CE-modern).

Contrasting patterns in the abundance of fish communities targeted by fishers on two coral reefs in southern Mozambique

Coastal populations of maritime countries in eastern Africa rely on fish as a primary source of protein, but baseline information on the abundance of fish communities on these coastlines is often lacking. We used baited remote underwater video stations to compare the abundance and diversity of reef fishes targeted by fishing at two sites in southern Mozambique, one at Lighthouse Reef within the Bazaruto Archipelago National Park and the other to the south at San Sebastian Reef on the San Sebastian Peninsula. Fish that are known targets of fisheries (mostly small-scale and artisanal) had an abundance that was almost three-times greater at San Sebastian Reef (80.22 ind. h–1 [SE 18.00]) than at Lighthouse Reef (29.70 ind. h–1 [SE 8.91]). Similarly, there was greater mean species richness at San Sebastian Reef (38.74 species h–1 [SE 2.79]) than at Lighthouse Reef (25.37 species h–1 [SE 3.66]). The main drivers of targeted fish abundance were habitat and depth, with shallow (<15 m) and mixed reef areas having the greatest abundance and richness. More sampling was done over sand habitat at Lighthouse Reef, which likely led to the lower abundance and species richness observed at this site; however, that finding could also be attributable to the fact that protection is provided to only a section of available coral reef habitat in a small area. Nevertheless, fish community structure was comparable between the sites, with similar proportions of carnivores (78–81%), herbivores (12–14%) and omnivores (7–8%). Our findings highlight the variation in species abundance and assemblages of coral-reef fish targeted by fishing in Mozambique and emphasise the importance of localised environmental variables as a driver of these patterns. To ensure maximum protection of Lighthouse Reef fish communities, we recommend an extension of the no-take zone to include the entire reef complex.

Adaptive bathymetry estimation for shallow coastal waters using Planet Dove satellites

Accurate bathymetric mapping of shallow waters (above 15 m) is essential for a wide range of scientific research, government, transport, and industry globally. Satellite-based bathymetry estimation approaches offer an alternative to traditional shipborne measurements, especially given advancements in their spatial and temporal resolution of satellite imagery, including the new Planet Dove constellation of >150 satellites providing daily coastal coverage. Dove satellites provide abundant cloud-free images even over cloudy tropical coastal environment, offering an opportunity to generate frequent bathymetry maps at high spatial resolution (4 m). We developed a new adaptive bathymetry estimation algorithm for Planet Dove and similar satellites. The algorithm adaptively tunes a depth estimator according to water column attenuation conditions. The algorithm was tested at five diverse reef sites globally (Lighthouse Reef, Belize; Saona Island, Dominican Republic; St. Croix, U.S. Virgin Islands; Heron Island, Australia; Hawaii Island, U.S.) using 31 satellite images from six Dove satellites. Derived water depth was validated (RMSE = 1.22 to 1.86 m) with field-measured sampling points (61,025) ranging in depth from 1 to 15 m. Algorithm performance was best at depths of 4–10 m. This new adaptive algorithm can be effectively applied to derive high spatial resolution bathymetric maps from Planet Dove satellite imagery across a wide range of conditions.

A Giant Underwater, Encrusted Stalactite from the Blue Hole, Lighthouse Reef, Belize, Revisited: a Complex History of Biologically Induced Carbonate Accretion Under Changing Meteoric and Marine Conditions

A late Pleistocene to Holocene submerged and encrusted speleothem exhibits a complex history including a meteoric phase and two marine phases. A combined study using petrography, mineralogy, and inorganic and organic geochemistry, as well as geochronology has shown that phototrophic and heterotrophic biological activity impacted carbonate precipitation during all phases of carbonate accretion. The stalactite formed ca. 30 m below modern sea level at a marginal overhang in the Blue Hole of Lighthouse Reef Atoll. Unlike purely meteoric speleothems, the Belize example consists of a meteoric core, a marine aragonite crust, and a serpulid-micrite-rich outer crust as a result of postglacial flooding of the karst cave. The core of the stalactite has a tufaceous texture, containing algal or microbial remains, and consists entirely of low-magnesium calcite, formed 19.55-10.68 kyr BP. The texture suggests that the stalactite formed at the cave entrance, and, hence, the former cave ceiling had apparently collapsed earlier during the Pleistocene. Oxygen (δ18O) and carbon (δ13C) isotopes across the core suggest a trend towards drier conditions and reduced soil and plant cover after the last glacial maximum. The marine aragonite crust consists of stacked botryoids in which individual crystals up to 700 lm have dark terminations enriched in high-magnesium calcite. This crust accreted from 10.82 to 9.95 kyr BP in warm shallow water during the early Holocene thermal optimum. Carbonate accretion rates were considerable and averaged 125 μm/yr. The crust has a dense, laminated texture on one side and a porous, shrubby texture on the other. The presence of n-C16:1ω5, n-C17:1ω6, and 10Me-C16 fatty acids in the laminated crust suggests that sulfate-reducing bacteria contributed to aragonite formation in an environment that was less open than the formation environment of the porous crust, where these biomarkers are lacking (n-C16:1ω5,n-C17:1ω6) or are less abundant (10Me-C16). Enrichment of 34S and 18O in carbonate-associated sulfate (CAS) relative to seawater sulfate also suggests sulfate reduction during carbonate formation. The greater contribution of heterotrophic processes to aragonite precipitation in the laminated crust is also reflected in δ13C values as low as -1.3%, whereas no such depletion is observed in the aragonite of the porous crust (δ13C values as low as 0.0%). A pronounced isotopic variability and excursions to positive δ13C values as high as +3.5%0 in the inner half of the laminated crust indicate an episodic, local impact of photosynthesis on aragonite precipitation, whereas the lack of such excursions in the porous crust (δ13C values as high as +1.5%0) is again best explained by a more open environment of formation. After a ca. 5 kyr hiatus, from 4.39 kyr BP, a biogenic crust of abundant serpulids and finely crystalline, microbial and detrital carbonate, consisting of high-magnesium calcite and aragonite, accreted on the outer surface of the stalactite. Outermost crust accretion was probably influenced by the inundation of the Lighthouse Reef lagoon that started to shed abundant fine-grained carbonate sediment into the Blue Hole. The stalactite broke off the cave ceiling either before or after the formation of the outermost crust, likely due to seismic movements along the nearby plate boundary. The study demonstrates that like speleothems from the terrestrial realm, submerged stalactites may have had complex histories with great potential as paleoenvironmental archives.

Movement patterns of juvenile hawksbill turtles Eretmochelys imbricata at a Caribbean coral atoll: long-term tracking using passive acoustic telemetry

ESR Endangered Species Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials ESR 32:309-319 (2017) - DOI: https://doi.org/10.3354/esr00812 Movement patterns of juvenile hawksbill turtles Eretmochelys imbricata at a Caribbean coral atoll: long-term tracking using passive acoustic telemetry Megan G. Chevis1,2, Brendan J. Godley1, James P. Lewis3, Julie Jackson Lewis2, Kylie L. Scales4,5, Rachel T. Graham2,* 1Centre for Ecology and Conservation, University of Exeter, Penryn Campus, TR10 9EZ, UK 2MarAlliance, 32 Coconut Drive/PO Box 283, San Pedro, Ambergris Caye, Belize 3Amphibian Survival Alliance, International Conservation House, 7078 Airlie Road, Warrenton, VA 20187, USA 4Institute of Marine Sciences, University of California, Santa Cruz, CA 95064, USA 5NOAA Southwest Fisheries Center, Environmental Research Division, 99 Pacific Street, Suite #255A, Monterey, CA 93950, USA *Corresponding author: rachel@maralliance.org ABSTRACT: Understanding the ecological interactions that underlie marine ecosystem functioning requires sufficient data describing habitat use by mobile species. Hawksbill turtles Eretmochelys imbricata are considered a key species in coral reef-associated communities, owing to their specific foraging preferences, yet new information is still revealing details of the spatial and temporal aspects of habitat use. We used passive acoustic telemetry to monitor the movements of 18 juvenile hawksbills (minimum curved carapace length: 32.0-59.7 cm, mean ± SD = 43.9 ± 6.7 cm) at a developmental foraging site in a Mesoamerican barrier reef, Lighthouse Reef Atoll in Belize (tracking duration 10-1414 d, mean ± SD = 570 ± 484 d). Although specific home ranges were difficult to quantify, several turtles showed high site fidelity over timescales of months to years, with occasional wide-ranging use of the atoll. Diel variation in the number of detections received strongly suggest nocturnal resting. Long-term tracking data reveal 3 degrees of site fidelity across the atoll, based on the number of detection days near individual stations: high residency (n = 4 turtles), sequential residency (n = 5), and transient behavior (n = 4). These variations in movement raise questions about the differentiation of foraging habitats and degree of individual specialization within this population, as well as the influences of microhabitats and human disturbance. KEY WORDS: Spatial ecology · Home range · Belize · Habitat use · Site fidelity · Marine megafauna · World Heritage Site Full text in pdf format Supplementary material PreviousNextCite this article as: Chevis MG, Godley BJ, Lewis JP, Jackson Lewis J, Scales KL, Graham RT (2017) Movement patterns of juvenile hawksbill turtles Eretmochelys imbricata at a Caribbean coral atoll: long-term tracking using passive acoustic telemetry. Endang Species Res 32:309-319. https://doi.org/10.3354/esr00812 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in ESR Vol. 32. Online publication date: March 28, 2017 Print ISSN: 1863-5407; Online ISSN: 1613-4796 Copyright © 2017 Inter-Research.

Turf algae-mediated coral damage in coastal reefs of Belize, Central America.

Many coral reefs in the Caribbean experienced substantial changes in their benthic community composition during the last decades. This often resulted in phase shifts from scleractinian coral dominance to that by other benthic invertebrate or algae. However, knowledge about how the related role of coral-algae contacts may negatively affect corals is scarce. Therefore, benthic community composition, abundance of algae grazers, and the abundance and character of coral-algae contacts were assessed in situ at 13 Belizean reef sites distributed along a distance gradient to the Belizean mainland (12–70 km): Mesoamerican Barrier Reef (inshore), Turneffe Atoll (inner and outer midshore), and Lighthouse Reef (offshore). In situ surveys revealed significantly higher benthic cover by scleractinian corals at the remote Lighthouse Reef (26–29%) when compared to the other sites (4–19%). The abundance of herbivorous fish and the sea urchin Diadema antillarum significantly increased towards the offshore reef sites, while the occurrence of direct coral-algae contacts consequently increased significantly with decreasing distance to shore. About 60% of these algae contacts were harmful (exhibiting coral tissue damage, pigmentation change, or overgrowth) for corals (mainly genera Orbicella and Agaricia), particularly when filamentous turf algae were involved. These findings provide support to the hypothesis that (turf) algae-mediated coral damage occurs in Belizean coastal, near-shore coral reefs.

Climatic controls on hurricane patterns: a 1200-y near-annual record from Lighthouse Reef, Belize

Tropical cyclones (TCs) are powerful agents of destruction, and understanding climatic controls on TC patterns is of great importance. Over timescales of seasons to several decades, relationships among TC track, frequency, intensity and basin-scale climate changes are well documented by instrumental records. Over centuries to millennia, climate-shift influence on TC regimes remains poorly constrained. To better understand these relationships, records from multiple locations of TC strikes spanning millennia with high temporal resolution are required, but such records are rare. Here we report on a highly detailed sedimentary proxy record of paleo-TC strikes from the Blue Hole of Lighthouse Reef, Belize. Our findings provide an important addition to other high-resolution records, which collectively demonstrate that shifts between active and inactive TC regimes have occurred contemporaneously with shifts hemispheric-scale oceanic and atmospheric circulation patterns such as MDR SSTs and NAO mode, rather than with changes in local climate phenomena as has previously been suggested.

Seismic stratigraphy of the Blue Hole (Lighthouse Reef, Belize), a late Holocene climate and storm archive

Abstract Five seismic units may be identified in the ~ 8 m thick Holocene sediment package at the bottom of the Blue Hole, a 120 m deep sinkhole located in the atoll lagoon of Lighthouse Reef, Belize. These units may be correlated with the succession of an existing 5.85-m-long sediment core that reaches back to 1.385 kyrs BP. The identification of seismic units is based on the fact that uniform, fine-grained background sediments show weak reflections while alternating background and coarser-grained event (storm) beds exhibit strong reflections in the seismic profiles. The main source of sediments is the marginal atoll reef and adjacent lagoon area to the east and north. Northeasterly winds and storms transport sediment into the Blue Hole, as seen in the eastward increase in sediment thickness, i.e., the eastward shallowing of the Blue Hole. Previous assumptions of much thicker Holocene sediment packages in the Blue Hole could not be confirmed. So far, close to 6-m-long cores were retrieved from the Blue Hole but the base of the sedimentary succession remains to be recovered. The nature of the basal sediments is unknown but mid-Holocene and possibly older, Pleistocene sinkhole deposits can be expected. The number of event beds identified in the Blue Hole (n = 37) during a 1.385 kyr-long period and the number of cyclones listed in historical databases suggest that only strong hurricanes (categories 4 and 5) left event beds in the Blue Hole sedimentary succession. Storm beds are numerous during 1.3–0.9 kyrs BP and 0.8–0.5 kyrs BP.

Insights into habitat utilisation of the hawksbill turtle, Eretmochelys imbricata (Linnaeus, 1766), using acoustic telemetry

Patterns of distribution, key biometric parameters and home range extent were determined for hawksbill turtles at Lighthouse Reef Atoll (LRA), Belize over two field seasons (16days, 2009; 30days, 2010). Relative abundance was determined using 49 sightings transects (≈1km) distributed across the atoll and of all turtles encountered (n=68), 91% were immature (CCLmin≤65cm). Habitat type was significantly correlated with abundance, with more turtles encountered on the coral reef than in the lagoon (GzLMM, χ22=6.85, p<0.05; CPUE reef=1.41turtlesh−1, CPUE lagoon=0.62turtlesh−1). Hawksbills were also significantly more abundant within protected areas (GzLMM, χ21=8.69, p<0.05; CPUE Blue Hole Natural Monument (BHNM)=2.96turtlesperson−1h−1; CPUE Half Moon Caye Natural Monument (HMCNM)=2.34turtlesh−1; outside boundaries=0.88 turtlesh−1). Of 26 captures, 19 focal individuals were equipped with ultrasonic transmitters for active acoustic telemetry, and tracked for 6–25days (n=10, 2009; n=9, 2010). Spatial habitat utilisation was found to be highly variable, with large areas of overlap between distinct home ranges. Home range averaged 31.2ha±32.6 (range 5.1–111.3ha) for the juveniles that were successfully tracked (n=15), with maximum displacement in the order of 1.8km±1.0 (range 0.5–4.0km) and net displacement at 1.2km±0.9. This offshore atoll constitutes an important developmental habitat for the regional population and although our tracking durations were limited, home range of juvenile hawksbills at this site is significantly more expansive than that documented elsewhere.

Biology and Status of the Black Catbird (Melanoptila glabrirostris) in Belize

We studied the poorly understood Black Catbird (Melanoptila glabrirostris), a near threatened mimid, at Lighthouse Reef in northeastern Belize. A resident of coastal lowlands and offshore islands, this endemic species of the Yucatan Peninsula has been reported as extirpated from several localities and has declined in numbers at other sites. We found it relatively common on the larger of two islands that comprise Northern Two Cayes from 18 to 25 June 2005. It had not been reported there since first discovered at Lighthouse Reef in 1862 and was considered extirpated until we rediscovered it. The Black Catbird at Northern Two Cayes displayed fierce intraspecific territoriality and both males and females defended against aggressors. However, it exhibited no interspecific territoriality toward its nearest avian associate, the Mangrove Warbler (Dendroica petechia bryanti). It used wing-flashing in territorial defense, mating rituals, and while foraging on the ground. We estimated ∼10 pairs of Black Catbirds in a 3-ha study area in the buttonwood-coconut (Conocarpus-Cocos) ecosystem but made no attempt to estimate the size of an apparently larger population in the more extensive area of coastal scrub on the remainder of the island. The defended territory of the pair studied most extensively was 100 × 25 m, centering on a buttonwood (Conocarpus erectus) grove and included numerous coconut (Cocos nucifera) trees.

Holocene trends in distribution and diversity of benthic foraminifera assemblages in atoll lagoons, Belize, Central America

Seven benthic foraminiferal assemblages were identified in vibracores through Holocene lagoons of three Belize atoll lagoons (Glovers Reef, Lighthouse Reef, Turneffe Islands). These include (1) the low-diversity Cribroelphidium assemblage (2) the Cribroelphidium-Elphidium assemblage (3) the Quinqueloculina-Triloculina-Peneroplis assemblage (4) the high-diversity miliolid assemblage (5) the Archaias-miliolid assemblage (6) the low-diversity miliolid assemblage, and (7) the mixed assemblage. Altogether, 109 species and 56 genera were identified. The highest diversities are observed in the largest lagoon (Turneffe Islands), whereas one of the smaller lagoons (Glovers Reef) exhibits the lowest diversities during the Holocene. No significant changes in diversity over time occur, however, a slight trend to higher diversity may be observed through the Holocene, suggesting that the foraminiferal faunas in the atolls are in a diversification stage. Faunal diversity in atoll lagoons appears to be controlled largely by habitat size, habitat heterogeneity, and water circulation. Habitat age and water depth only play minor roles. Substrate texture, water depth, and turbidity influence the predominant modes of life of benthic foraminifera encountered in the lagoons (epifaunal versus infaunal versus symbiont-bearing). Time-averaging effects were not observed, even though lagoonal sedimentation rates fluctuate in individual cores and the three lagoons, and despite the fact that sediments are modified through bioturbation by callianassid shrimps. This finding underlines the potential of benthic foraminifera for paleoecological studies in the fossil record of reefs and carbonate platforms.

Taphonomic Signatures On Modern Caribbean Bivalve Shells As Indicators Of Environmental Conditions (Belize, Central America)

Taphonomic signatures on modern bivalve shells, such as traces of drilling organisms, encrusters, fragmentation, and abrasion function as indicators of environmental differences on Belize atoll reefs. Glovers Reef, Lighthouse Reef, and Turneffe Islands are three adjacent Caribbean atolls showing variations in geomorphology, lagoonal depth, sedimentation, mangrove growth, sea-grass cover, and exposure to winds and currents, as well as differences in their lagoonal development and age. A variety of bivalve assemblages characterize lagoonal subenvironments and also mirror the above-mentioned environmental variations. Taphonomic signatures, such as shell-size distribution, disarticulation, sorting, boring traces, encrustations, fragmentation, and abrasion, were identified on bivalve shells from a total of 111 surface sediment samples. Shell-size distribution and sorting of right and left valves indicate in situ deposition of populations on each atoll. Increasing residence times of shells on the sediment surface due to decreasing sedimentation rates from Turneffe Islands to Lighthouse Reef to Glovers Reef cause an increase in taphonomic shell signatures.

A 1500-Year Holocene Caribbean Climate Archive from the Blue Hole, Lighthouse Reef, Belize

Abstract Sediment cores (up to 6 m in length) from the bottom of the Blue Hole, a 125 m deep Pleistocene sinkhole located in the lagoon of Lighthouse Reef Atoll, Belize, consist of undisturbed, annually layered biogenic carbonate muds and silts with intercalated coarser grained storm beds. The sedimentation rate of the layered sections is 2.5 mm/y on average, and the long cores span the past 1500 years. Oxygen isotopes of laminated sediment provide a late Holocene climate proxy: A high-resolution δ18O time series traces the final Migration Period Pessimum, the Medieval Warm Period, the Little Ice Age, and the subsequent temperature rise. Carbon isotopes (δ13C) decrease up core and show the impacts of the decline of the Mayan culture and the Suess effect. Time series analyses of δ18O and δ13C content reveal 88-, 60-, 52-, and 32-year cyclicities, and suggest solar forcing. Storm event beds are most common during AD 650–850, around AD 1000, during AD 1200–1300, and AD 1450–1550. Major storm beds are rare du...

Modern bivalve shell assemblages on three atolls offshore Belize (Central America, Caribbean Sea)

The Belize atolls—Glovers Reef, Lighthouse Reef and Turneffe Islands—show differences in geomorphology, lagoonal depth, bottom sediment, growth of mangroves and sea-grass, exposure to waves and currents as well as in their sedimentation rates and their age. Bivalve shell assemblages in lagoonal areas reflect these geomorphological differences. On each atoll, 32 to 44 recent sediment samples were taken (total number of samples 111) and bivalve shells subsequently identified. The resulting database (32,122 bivalve shells in total) was analysed using Q-mode cluster analyses. Both the distribution of species characteristic of different lagoonal habitats and the distribution of bivalves with different life and feeding habits were investigated. Epifaunal suspension feeders were found particularly on hard-bottom along the reef-crests or clinging to mangrove roots. Infaunal suspension feeders show a more diverse distribution. Deeper lagoonal parts and areas with mangrove growth are often inhabited by chemosymbiont-carrying bivalves, indicating locations of reduced sediment. Deep burrowing detritus feeders are very abundant in shallow-water areas with moderate to high water agitation and were seldom found in Halimeda-rich sediments.

Marine Reserve Design and Evaluation Using Automated Acoustic Telemetry: A Case-study Involving Coral Reef-associated Sharks in the Mesoamerican Caribbean

A non-overlapping acoustic receiver array was used to track the movements of two common shark species, nurse Ginglymostoma cirratum (n=25) and Caribbean reef Carcharhinus perezi (n=5), in and around Glover's Reef Marine Reserve (GRMR), off the coast of Belize, between May and October, 2004. Although both species exhibited partial site fidelity in that they were most likely to be detected near the area of original capture, both species also moved widely throughout the 10 by 30 km atoll. One Caribbean reef shark was detected by a monitor at Lighthouse Reef, 30 km from Glover's Reef across deep (&gt;400m) open water. The mean minimum linear dispersal (MLD) was 10.5 km for Caribbean reef sharks and 7.7 km for nurse sharks, with many individuals traveling more than the 10 km width of the no-take "conservation zone" of the marine reserve. Although most sharks were tagged within the conservation zone, individuals were detected outside this part of GRMR on average 48 days out of the 150 days of observations. However, of 7 nurse sharks tagged near the center of the conservation zone, 4 were never detected outside of this part of the reserve. In general, this study suggests that effective conservation of these large roving predators requires an ecosystem-based management approach including a zoned management plan, similar to that used at GRMR, in which a fairly large no-take reserve, incorporating diverse habitats and the connections between them, is surrounded by a larger area in which fishing is regulated.

Characterization of Depositional Environments in Isolated Carbonate Platforms Based on Benthic Foraminifera, Belize, Central America

Abstract Tests of benthic foraminifera were analyzed quantitatively in 43 surface sediment samples collected along E–W traverses across the modern isolated carbonate platforms of Glovers Reef (N=14), Lighthouse Reef (N=14), and Turneffe Islands (N=15), offshore Belize, Central America. Water depths of sample stations range from 0 m (beach) to 40 m (fore reef). Each sample was sieved in the size classes 2–1, 1–0.5, 0.5–0.25, and 0.25–0.125 mm (ϕ=1–0, 0–1, 1–2, and 2–3, respectively) and 300 foraminiferal identifications were attempted for each sieve fraction (i.e., 1,200 individuals per sample, totaling 46,003 specimens). Cluster analyses of samples characterized platform environments and distinguished four benthic foraminifera associations. Fore reef samples were characterized by abundant Amphistegina gibbosa and the occurrence of Asterigerina carinata, both rotaliids. In high-energy, marginal-reef areas the encrusting rotaliid Homotrema rubrum predominated. Platform-interior environments were marked by a...