Maldives Archipelago Research Articles

Microplastics as a threat to coral reef environments: Detection of phthalate esters in neuston and scleractinian corals from the Faafu Atoll, Maldives

The impact of microplastics (MPs) on reef-building corals are still largely unknown. The scientific literature provides evidence from lab feeding trials that coral may ingest MPs. Several adverse effects, i.e., necrosis and bleaching, have also been highlighted. However, field studies are limited. Here, we investigated for the first time the possible correlation between MP seawater contamination and the presence of phthalic acid esters (PAEs), a class of MP-associated contaminants, in scleractinian corals. The survey was carried out in a remote coral reef atoll in the Indian Ocean located in the Maldivian archipelago, considered as a case study. MPs and PAEs were monitored in subsurface neustonic tow samples and scleractinian corals across twelve sampling sites. The results showed widespread MP contamination and the presence of appreciable levels of PAEs in the scleractinian corals sampled inside the atoll rim near an inhabited island, which correlated with the highest MP concentration.

Upwelling as the major source of nitrogen for shallow and deep reef‐building corals across an oceanic atoll system

AbstractOceanographic processes shape coral reefs worldwide by redistributing inorganic nutrients and particulate resources over depth. Deep‐water upwelling occurs frequently in coral reef ecosystems, but its impact on coral nutrition remains unclear.This study investigated the influence of upwelling on the trophic ecology of three common reef‐building corals (Galaxea fascicularis,Pachyseris speciosaandPocillopora verrucosa) from different reef depths (shallow reef, 10 m, vs. deep reef, 30 m) and reef exposures (oceanic rim vs. Inner Sea) across > 250 km of the Maldives archipelago, Indian Ocean. Carbon and nitrogen stable isotope ratios (δ13C and δ15N) of coral hosts, their symbionts and particulate organic matter (POM) were used to characterize coral trophic strategies.Across the Maldives, consistent mean δ15N values were recorded in hosts (5.5‰) and symbionts (5.2‰) of the three coral species from shallow and deep reefs of oceanic and Inner Sea reef exposures. Coral hosts, symbionts and POM from both depths had δ15N values that were consistent with the isotopic signature of a deep‐water nitrate source transported to surface waters via upwelling.In contrast, a wide range of δ13C values (~10‰) revealed different trophic strategies and isotopic niches among the coral species. Different mean δ13C values ofG. fascicularisindicated greater symbiont autotrophy in corals from shallow (‐15.5‰) compared to deep reefs (‐17.6‰). Conversely, the mean δ13C values ofP. speciosa(‐15.1‰) andP. verrucosa(‐17.7‰) were not affected by reef depth. These corals maintained consistent trophic strategies over depth, withP. speciosarelying more on autotrophy compared toP. verrucosa.Despite different reef exposure to oceanic waters, coral host and POM δ15N and δ13C values did not differ between oceanic and Inner Sea reef exposures. Nutritional resources appear to be homogenous in the central Maldives due to atoll‐wide water circulation. However, species‐specific trophic strategies resulted in diverse patterns of δ13C values over depth. Because heterotrophic feeding has been linked to coral host survival through coral bleaching events, understanding the trophic ecology of corals within the reef assemblage can provide insight into species resilience under ocean warming conditions. As a member of the typically competitive Pocilloporidae family, the dependence ofP. verrucosaon heterotrophy may help this coral be a future “winner” under sustained ocean warming.Aplain language summaryis available for this article.

A NEW SPECIES OF MALDIVEA GERLACH, 1962 (NEMATODA, OXYSTOMINIDAE) FROM FELIDHOO ATOLL (MALDIVES, INDIAN OCEAN) AND AN EMENDED DIAGNOSIS OF THE SUB-FAMILY AND GENUS

Maldivea Gerlach, 1962 is a possible endemic genus of the Maldivian archipelago for which only M. xarifae Gerlach, 1962 has been described so far. A new species of this genus, M. complexa n.sp., was recently found in Felidhoo atoll. It reveals a more complex structure of gubernaculum than in type species which appears to be divided into two pieces: one is a sort of long wing in the ventral part of the spicule and the other one, more complex, is characterized by several curved stripes which envelop the dorsal side of the spicule distal part. According to the present considerations, diagnoses of Paroxystomininae and Maldivea are emended.

Untangling the origin of ghost gear within the Maldivian archipelago and its impact on olive ridley (Lepidochelys olivacea) populations

Untangling the origin of ghost gear within the Maldivian archipelago and its impact on olive ridley (Lepidochelys olivacea) populations

FRACTALS, NATURAL DISASTERS AND ECOLOGICAL PROBLEMS OF MALDIVES

A new idea about the fractal nature of Maldives archipelago is under investigation. The origin of this famous Maldivian islands’ country is still questionable from geodynamic point of view. The present study is focused to the assessment of the fractal properties and the coefficients of the nonlinearity (fractal dimensions) of the areal spatial distribution of the major atolls of the Maldives. This is the most vulnerable area in the world from point of view of the global warming and the possible negative consequences to the country and population from the ocean level increase. From another side the natural hazards (tsunamis, storms, etc.) are common negative phenomena attacking the country. The strongly developed tourism – more than 30% of the GDP and the increased urbanization is another factor creating ecological problems to the local population. The relationships between the fractal nature and the possible ways to avoid the pollution are also in the focus of this research.

Submerged reef terraces in the Maldivian Archipelago (Indian Ocean)

Sea-level changes have shaped the world's carbonate platform margins and continental shelves, leaving typical geomorphic imprints, such as drowned reef terraces. In this paper, we present the results of 112 scuba diving transects across seven different Maldivian atolls and one multibeam survey around Malé Island, the capital of Maldives. We report on the occurrence of drowned reef terraces down to 120 m depth. In total, we identified six levels of submerged terraces that we consider as indicative of periods of time with stable or slowly rising sea level that can be attributed either to deceleration of the last deglacial sea-level rise or to Late Quaternary sea-level highstands. We compare our dataset to the depth of reef terraces reported globally, and we discuss the reasons why common global submerged terrace levels are difficult to identify in the field record.

Biodiversity and distribution of the meiofaunal community in the reef slopes of the Maldivian archipelago (Indian Ocean)

Marine biologists have progressively increased their consciousness of the importance of meiofauna for the benthic domain in both temperate and tropical regions. After the 1998 bleaching, Maldivian reefs (Indian Ocean) have been regarded as a vulnerable ecosystem that must be carefully monitored. Accordingly, an extensive investigation of meiofaunal distribution in the reef slopes of the Maldivian archipelago has been carried out, taking into account geographical position, type of habitat (inner vs. outer slope), inclination and depth gradient. Twenty-four taxa revealed the highest meiofaunal richness ever found in Maldivian reefs. Interestingly, Thermosbenacea and Syncarida were identified, which are two taxa that have only recently been documented in the marine ecosystem. Chaetognatha were also present, which is a group that was only considered to be planktonic until 2000, when they were also discovered in the benthos. The type of habitat, affected by different hydrodynamic conditions, was the main factor influencing the meiofaunal community's structure and diversity. In detail, the outer reefs were characterized by the highest level of diversity, confirming previous observations on the rate of coral reef growth and vitality and underlining the greater vulnerability of the inner slopes. In contrast, depth only significantly affected the community structure, but not its density or diversity. Accordingly, community structure seems to be more sensitive than abundance and diversity indices when it comes to detecting depth gradients. The 10° inclination of the inner slopes revealed the most different community structure and the greatest dominance of nematodes, leading to the lowest diversity levels.

Recent Arborescent Dendrophryid Foraminifera Found On Upper Pleistocene Cold-water Corals from the Inner Sea of the Maldives

Abstract Recent specimens of Spiculidendron were found on Late Pleistocene (21,400–22,500 BP) cold-water corals from the sea floor at 457 m depth of the inter-atoll Kardiva Channel of the eastern row of the Maldives archipelago. Spiculidendron and other dendrophryid foraminifera (Rhizammina-like forms) exclusively colonized specimens of the genus Enallopsammia, which was characterized by a phosphatic-stain surface. The Spiculidendron wall was composed of sponge spicules, elongated diatom frustules, tests of juvenile benthic and planktic foraminifera, and calcareous nannoplankton, among other materials. Sponge spicules and elongated diatom frustules were arranged longitudinally, with foraminiferal tests and other bioclasts packed in between, indicating that the agglutination process of Spiculidendron is selective with respect to the manner of growth. In the most distal parts of the branches, only sponge spicules and elongated diatom frustules were present, working as guides for the test construction, prior to the agglutination of juvenile foraminiferal tests and other bioclasts. Moreover, in the sediment associated with the coral fragments, 94 species of benthic foraminifera were identified, an assemblage distinct from the taxa incorporated into the agglutinated Spiculidendron tests. The process of wall growth is complex and ordered. This foraminifer, as well as the Rhizammina-like specimens, tolerates dysoxic conditions (0.896 ml/l) and low temperature (12°C). This observation represents a new record of Spiculidendron from the Indian Ocean and from deeper (aphotic) environments than previously reported from the shallow waters of the Caribbean. A cryptobiontic habitat is interpreted for Spiculidendron.

What in the World Is North? Translating Cardinal Directions across Languages, Cultures and Environments

What in the World Is North? Translating Cardinal Directions across Languages, Cultures and Environments

A re-description of Longicyatholaimus maldivarum Gerlach, 1964 (Nematoda, Cyatholamidae) with an emended identification key of the genus

Longicyatholaimus maldivarum was a species erected by Gerlach in 1964 from specimens found in the Maldivian archipelago. Due to the finding of additional representatives of this species, L. maldivarum is re-described with the addition of new morphological details mainly about males, because the information about female in the original description are very scarce. The newly found specimens showed a total body length higher than in the type specimens (1936–2063 µm vs. 1330 µm long) as well as the ratio of the total body length divided by maximum body diameter (22–28 vs. 27). The multispiral amphideal fovea showed 5 turns vs. 4 turns and Gerlach did not notice the presence of sub-ventral teeth that were clearly observed in the present specimens. The copulatory apparatus that perfectly matched the Gerlach description showed a central lamella mainly visible under confocal microscopy. A slightly lower ratio of the spicule length divided by anal body diameter (1 vs. 1.4) and longer gubernaculum (25–32 vs. 25 µm long) were noticed as well. Pre-cloacal supplements appeared very interesting for the presence of stout and conical setae protruding from cup-shaped structures. Supplements were more than in type species (8–9 vs. 7). Also the tail revealed some differences with a lower ratio of its total length divided by anal body diameter 6 vs. 7–8. The current list of 15 valid species of the genus was reduced to 10 species. In detail, we considered Longicyatholaimus heterurus and Longicyatholaimus sp. 3 species inquirendae for the absence of male specimens in the original description. We also excluded L. filicaudatus and L. tenuicaudatus because they were considered species inquirendae by Wieser & Hopper (1967) and L. zosterae because it was transferred by Lorenzen (1972) to the genus Paralongicyatholaimus. The new morphological details observed for Longicyatholaimus maldivarum and the modified number of valid species of the genus required also a revision of the identification key.

Land use and land cover (LULC) of the Republic of the Maldives: first national map and LULC change analysis using remote-sensing data.

The Maldives islands in recent decades have experienced dramatic land-use change. Uninhabited islands were turned into new resort islands; evergreen tropical forests were cut, to be replaced by fields and new built-up areas. All these changes happened without a proper monitoring and urban planning strategy from the Maldivian government due to the lack of national land-use and land-cover (LULC) data. This study aimed to realize the first land-use map of the entire Maldives archipelago and to detect land-use and land-cover change (LULCC) using high-resolution satellite images and socioeconomic data. Due to the peculiar geographic and environmental features of the archipelago, the land-use map was obtained by visual interpretation and manual digitization of land-use patches. The images used, dated 2011, were obtained from Digital Globe's WorldView 1 and WorldView 2 satellites. Nine land-use classes and 18 subclasses were identified and mapped. During a field survey, ground control points were collected to test the geographic and thematic accuracy of the land-use map. The final product's overall accuracy was 85%. Once the accuracy of the map had been checked, LULCC maps were created using images from the early 2000s derived from Google Earth historical imagery. Post-classification comparison of the classified maps showed that growth of built-up and agricultural areas resulted in decreases in forest land and shrubland. The LULCC maps also revealed an increase in land reclamation inside lagoons near inhabited islands, resulting in environmental impacts on fragile reef habitat. The LULC map of the Republic of the Maldives produced in this study can be used by government authorities to make sustainable land-use planning decisions and to provide better management of land use and land cover.

Some epibiont suctorian ciliates from meiofaunal organisms of Maldivian archipelago with description of a new ciliate species.

Five species of suctorian ciliates belonging to four different genera attached to meiofaunal organisms of Maldivian archipelago (Suvadiva Atoll) were documented. Three rare species (Acineta sp., Thecacineta urceolata Liao & Dovgal, 2015 and Limnoricus ceter Jankowski, 1981) and one common suctorian ciliate Thecacineta calix (Schröder, 1907) are re-described from nematodes (Croconema cinctum Cobb, 1920, Desmodorella tenuispiculum Allgén, 1928 and Desmodora sp.) and harpacticoid copepod basibionts. In addition, Trophogemma colantonii n. sp. colonizing the abdomen and legs of the harpacticoid copepod Stenhelia sp. is described. The new species differs from the relative species for the less flattened cell body, the absence of both lateral bundles of tentacles and separate lateral tentacles as well as for the presence of longitudinal ribs along the cuticle. The data obtained in this survey give not only new important information on the taxonomy and distribution of Suctorea, but also new insights on their relationship with meiofaunal organisms in one of the most diverse and productive marine micro-habitat of carbonate sediments.

Assessing coral reef health in the North Ari Atoll (Maldives) using the FoRAM Index

Abstract Tropical marine ecosystems are richly diverse, but are experiencing growing pressure from coastal development and tourism. Assessing the status of coral reef communities along gradients of human pressure is necessary to predict recovery capacity of reefs exposed to acute events such as mass bleaching or storm destruction. Islands in the central Maldives Archipelago, which experience three different management regimes (four for each category: local community, uninhabited, and resort islands), were sampled during the International Union for Conservation of Nature (IUCN)-REGENERATE Cruise in 2015. Assessments were carried out using the FoRAM Index (FI), based on relative abundances of larger foraminiferal shells in reef sediments. Overall, FI values (> 5) indicate that water quality currently should support active accretion by reef-building corals and larger benthic foraminifers. The highest median FI values (5.9) were recorded from sites associated with the uninhabited islands. Slightly, but significantly lower medians were recorded at sites near community and resort islands (FI = 5.3 and 5.1, respectively) that host permanent human settlement, indicating possible local deterioration of water quality by disposal of domestic wastes. Note that the FI was designed to assess suitability of local water quality and not to assess responses to regional to global changes associated with temperature stress or ocean acidification.

Upper Pleistocene cold-water corals from the Inner Sea of the Maldives: taphonomy and environment

Cold-water corals of the Late Pleistocene (21,400–22,500 BP) are recorded from the sea-bottom of two inter-atoll channels (Kardiva Channel at 457-m depth and Male Vaadhoo Channel at 443-m depth) of the eastern row of the Maldives archipelago. Coral assemblages are composed mainly by Lophelia pertusa and secondarily by Madrepora oculata and Enallopsammia rostrata. These cold-water coral patches are places where the benthic life, mainly sessile, is concentrated, which is clearly absent off-rubble patches. The main epibionts are tube-dwelling polychaetes (mainly Spirorbis and Serpula), bryozoans, siliceous sponges, barnacles, gorgonids, solitary corals, encrusting foraminifera, and microbial mats. The analysis of epibionts assemblages shows different biocoenoses between both studied sites as well as a dependency of the epibiont coverage with regard to the coral genus. Some living benthic organisms such as brachiopods, bivalves, gastropods, barnacles, and ophiuroids find refuge among coral branches. The common record of juvenile specimens of vagile organisms such as small ophiuroids, is probably related to the nursery function of the cold-water corals in spite they are fossils. Environmental requirements of Recent cold-water corals (Lophelia, Madrepora and Enallopsammia) differ of conditions at both sampling sites with sensibly lower oxygenation degree and density of waters than needed for cold-water corals. Therefore, it is proposed that the present-day oxygen and density conditions are the factors which inhibit modern cold-water coral growth in the inter-atoll channels.

Thinking Architecture with an Indian Ocean Aquapelago

This article takes up the charge of thinking architecture with one of the Indian Ocean’s central coral atoll formations, the Maldives archipelago. It is undertaken as a critique of the concept of the archipelago as deployed in architecture since the 1970s. Architects have used the archipelago as a metaphoric metageographical concept based on a land–sea binary, to conceive of architecture as autonomous from its environments. This permits the discipline exemption from its contexts and frames its engagement with the diverse mobilities of contemporary globalization. To counter this, the article draws from a broad body of literature familiar to readers of GeoHumanities, namely island studies, urban island studies, political ecology, and thinking with water, to undertake a reading of the Maldives as an oceanic aquapelago, as an alternative metageographical concept for architecture in today’s globalized world.

Widespread occurrence of coral diseases in the central Maldives

Coral diseases are one of the most important causes of coral reef decline worldwide. Although they are well investigated in some areas of the Caribbean and the Great Barrier Reef, they have been poorly studied in the Indian Ocean, and particularly in the Maldives, where the presence of coral pathologies has been reported only recently. In order to fill this gap, we investigated the prevalence, local host range and distribution of five coral diseases, namely brown band disease, skeleton eroding band, black band disease (BBD), ulcerative white spot and white syndrome (WS), in the central part of the Maldivian Archipelago, focussing, in particular, on the dominant coral genus Acropora. We estimated an overall disease prevalence of approximately 1.51%. Malè North Atoll was the most affected area; however, coral diseases were present at all study sites. WS was the most widespread disease, whereas BBD affected the highest number of scleractinian genera. We found symptoms of disease on 18 genera belonging to eight families. Acropora was the most affected genus in terms of pathogen diversity. These results provide baseline disease levels for the Maldives and can therefore serve as gauge for monitoring future change.

Stranding and mortality of pelagic crustaceans in the western Indian Ocean

Recent observations of unusual mass stranding and mortality of two Indian Ocean crustacean species, the swimming crabCharybdis smithiiand the mantis shrimpNatosquilla investigatoris, are documented and analysed. Strandings ofC. smithiiwere observed for the first time in the equatorial Indian Ocean, the main area of its pelagic distribution. Strandings of mantis shrimps are reported from throughout the western Indian Ocean; occurrences of mass stranding in the Maldives Archipelago mark an extension of the known range ofN. investigatorisinto the central Indian Ocean. Mortality of crabs probably represents a ‘catastrophic event’. In contrast, mantis shrimp strandings, which were always associated with a sudden increase of its biomass (‘blooms’), are apparently post-reproduction mortalities indicating potential semelparity for this species.

Re-description of Craspodema reflectans (Nematoda, Cyatholaimidae)using confocal laser scanning microscopy.

Craspodema reflectans, erected by Gerlach 1964, is here re-described from some specimens recently found in the Maldivian archipelago and the implication of the new findings for the taxonomy of the Craspodema genus is discussed. Accordingly, an emended diagnosis of Craspodema genus and C. reflectans species are proposed. New data are also provided with the aid of the confocal laser scanning microscopy, using the natural fluorescence of the nematodes. The approach described here lays new foundations for the study of Museum collection material and it may be decisive for capture of new morphological details.

The leaking bucket of a Maldives atoll: Implications for the understanding of carbonate platform drowning

Abstract Seismic and multibeam data, as well as sediment samples were acquired in the South Male Atoll in the Maldives archipelago in 2011 to unravel the stratigraphy and facies of the lagoonal deposits. Multichannel seismic lines show that the sedimentary succession locally reaches a maximum thickness of 15–20 m above an unconformity interpreted as the emersion surface which developed during the last glacial sea-level lowstand. Such depocenters are located in current-protected areas flanking the reef rim of the atoll or in infillings of karst dolinas. Much of the 50 m deep sea floor in the lagoon interior is current swept, and has no or very minor sediment cover. Erosive current moats line drowned patch reefs, whereas other areas are characterized by nondeposition. Karst sink holes, blue holes and karst valleys occur throughout the lagoon, from its rim to its center. Lagoonal sediments are mostly carbonate rubble and coarse-grained carbonate sands with frequent large benthic foraminifers, Halimeda flakes, red algal nodules, mollusks, bioclasts, and intraclasts, some of them glauconitic, as well as very minor ooids. Finer-grained deposits locally are deposited in current-protected areas behind elongated faros, i.e., small atolls which are part of the rim of South Male Atoll. The South Male Atoll is a current-flushed atoll, where water and sediment export with the open sea is facilitated by the multiple passes dissecting the atoll rim. With an elevated reef rim and tower-like reefs in the atoll interior it is an example of a leaky bucket atoll which shares characteristics of incipiently drowned carbonate banks or drowning sequences as known from the geological record.

Taxonomic and functional biodiversity variations of meiobenthic and nematode assemblages across an extreme environment: a study case in a Blue Hole cave

In this paper we have explored for the first time the biodiversity pattern of the meiobenthic assemblage in a Blue Hole of the Maldivian Archipelago. The cave is characterised by a marked change of the chemical water parameters below 50 m of depth, with a relevant increase in hydrogen sulfide, carbon dioxide, and sulfates (H2S, CO2 and SO42–). Thus, three stations were selected above and two below the chemo-thermocline in order to test the possible effects of the chemical variations on the meiobenthos. The difficulty of adaptation to these environmental conditions is clearly suggested by the presence of only a few dominant meiobenthic taxa in the bottom of the cave. However, meiobenthic organisms seemed more resistant than macrobenthos, which disappeared completely below this depth. The nematode assemblage was mainly represented by Xyalidae, Desmodoridae, Comesomatidae and Linhomoeidae. A high level of confinement of nematode genera at the different depths has been documented. In the upper part, their structure and biodiversity were comparable to those of the Maldivian subtidal habitats characterised by fine coralline sediments, while a notable dominance was detected in the bottom. The Blue Hole features also influenced the functional traits of the nematode assemblage with a documented increasing number of general opportunists and decrease of Maturity Index. The dominance of non-selective deposit feeders supports the hypothesis of a high amount of organic matter accumulated on the sea bottom of the cave.