Zones Of Lagoon Research Articles

Structure of benthic macroinvertebrates and dynamics in the northern lagoon of Tunis

Sampling data on abiotic parameters and benthic communities in the northern lagoon of Tunis were obtained seasonally from November 1999 to November 2000. Abiotic parameters studied revealed evident improvement of water quality compared with previous. Indeed, management has re-established a tidal marine influence (Gulf of Tunis), induced a remarkable change in physico-chemical parameters and as a consequence, a regulation of the lagoon environmental quality. A total of 90 species of benthic macroinvertebrates, belonging to seven different taxa were collected in the northern lagoon of Tunis. A comparison of ecological indices indicate significant variations in the spatial and seasonal distribution and structure of the benthic community and reflect changes that might be related to open marine water and climatic influences as well as effects of discharge of the neighbouring city. Generally, the lagoon macrobenthic community appeared to be better structured, richer and more diverse than the one described before sanitation works began. However, significant disturbance of the benthic communities is detected in the south-eastern lagoon zone (C) and is dominated by disturbance indicator species. In contrast, the Station A2 which is sufficiently influenced by marine currents, is dominated by species of marine affinity and indicates an undisturbed zone. Multivariate analysis indicates heterogeneity in the benthic community structure between stations and suggests that the most significant variations of abundance occur in the groups: Anthozoa, Placophora, Cephalopoda, Ascidia and Echinodermata. The results of correspondence analysis also testify to a gradational distribution of benthic species in relation to hydrological and edaphic (organic matter) factors.

Spatially distributed ecological risk for fish of a coastal food web exposed to dioxins

The ecological risk posed by 2,3,7,8-polychlorodibenzo-p-dioxins and furans (PCDD/Fs) and dioxin-like polychlorobiphenyl (PCB) congeners to five edible fish species of the aquatic food web of Venice Lagoon, Italy, was estimated by applying a state-of the-art kinetic bioaccumulation model. Site-specific data were used to define a representative food web. The experimental data set for model validation and application included PCB and PCDD/F congener concentrations in sediments, in water, and in five organisms (both invertebrates and fish). The spatial distribution of risk was evaluated by dividing the lagoon into six homogeneous areas, and for each area, sediment, water, and organism dioxins concentrations were calculated. The bioaccumulation model was calibrated for both nonmetabolizing and metabolizing congeners, the metabolic elimination rates of which were estimated. The model validation showed an acceptable bioaccumulation estimation, evaluated using the model bias parameter. The calibrated model was applied to the six areas of the lagoon to estimate the fish predicted exposure concentration as 2,3,7,8-tetrachlorodibenzo-p-dioxin toxicity equivalents from sediment concentration. Internal no-effect concentrations were calculated for each fish species from literature data. Risk was estimated by applying the hazard quotient (HQ) approach, obtaining the ecological risk for each fish species on the basis of 90 and 99% protection levels, in each of the six lagoon areas. The sediment dioxins concentration does not pose a significant risk to the selected fish species at the 90% protection target (HQ<1), whereas risk is significant (HQ>1) at the 99% protection target. Risk results were higher near the Porto Marghera industrial district, Italy, and in lagoon zones characterized by a low water-exchange rate and freshwater basin inputs.

Two crab species-Chinese mitten crab (Eriocheir sinensis Edw.) and mud crab (Rhithropanopeus harrisii (Gould) ssp. tridentatus (Maitland) in the Lithuanian coastal waters, Baltic Sea

1 - The main objective of this research was to overview both historical and recent data on two alien crab species-Chinese mitten crab (Eriocheir sinensis Milne-Edwards, 1854) and mud crab (Rhithropanopeus harrisii (Gould) ssp. tridentatus (Maitland) distribution in the Curonian Lagoon and coastal zone of the Baltic sea. 2 - Data collected since 1935 includes interviews with fishermen, popular science publications, museum collections and ichthyological monitoring. 3 - During the last two decades records of the mitten crabs became more frequent, probably representing changes in the commercial fishery regulations. 4 - Several gravid females of the mitten crab were caught in the coastal area of the Baltic Sea, however, larval development is not documented. 5 - Unlike the mitten crab, the mud crab distribution is restricted to the rapidly-changing salinity (0 to 5 - 7 psu) area.

Cladóceros fitófilos (Crustacea, Anomopoda and Ctenopoda) do vale do Rio Paranã, Goiás, Brasil

A rapid assessment survey identified 39 phytophilous cladocerans species from littoral zones of rivers, permanent and temporary lagoons, and swamps of the Parana River Valley, Goias, Brazil, 22 are registered for the first time in Central Brazil. Aspects of the taxonomy of some of these species are discussed. Cluster analysis (UPGMA) revealed two phytophilous cladoceran assemblages, characterized by higher or lower richness and relative abundance of species of the families Daphniidae and Moinidae (filter feeders), in comparison with the dominant families Chydoridae and Macrothricidae (scraper feeders).

Phytophilous cladocerans (Crustacea, Anomopoda and Ctenopoda) from Paranã River Valley, Goiás, Brazil

A rapid assessment survey identified 39 phytophilous cladocerans species from littoral zones of rivers, permanent and temporary lagoons, and swamps of the Paranã River Valley, Goiás, Brazil, 22 are registered for the first time in Central Brazil. Aspects of the taxonomy of some of these species are discussed. Cluster analysis (UPGMA) revealed two phytophilous cladoceran assemblages, characterized by higher or lower richness and relative abundance of species of the families Daphniidae and Moinidae (filter feeders), in comparison with the dominant families Chydoridae and Macrothricidae (scraper feeders).

Fluxes of carbon dioxide, methane and nitrous oxide in two contrastive fringing zones of coastal lagoon, Lake Nakaumi, Japan

We measured fluxes of carbon dioxide (CO(2)), methane (CH(4)), and nitrous oxide (N(2)O) simultaneously in two typical fringing zones, sandy shore and salt marsh, of coastal lagoon, Lake Nakaumi, Japan, in mid-summer 2003. Our aim was to quantify net the greenhouse gases (GHGs) fluxes and examine key factors, which control variation of the GHGs fluxes in the two sites. Net CO(2) and CH(4) fluxes were markedly different between the two sites; magnitudes and variations of the both fluxes in sandy shore were lower than those of salt marsh. Meanwhile, magnitude and variation of net N(2)O flux in the two sites were similar. In sandy shore, temporal and spatial variation of the three GHGs fluxes were highly controlled by water level fluctuation derived from astronomic tide. In salt marsh, spatial variation of the three GHGs fluxes were correlated with aboveground biomass, and temporal variation of CO(2) and CH(4) fluxes were correlated with soil temperature. The sum of global warming potential, which was roughly estimated using the observed GHGs fluxes, was ca. 174-fold higher in salt marsh than in sandy shore.

Phytoplankton production and community respiration in different zones of the Curonian lagoon during the midsummer vegetation period

1 - Phytoplankton structure, primary production, extracellular release of dissolved organic carbon and pelagic community respiration were investigated in different zones of the Curonian Lagoon in July 2002-2004. 2 - Phytoplankton biomass and primary production rates in different zones varied from 10.3 to 30.2 mg 1 -1 and from 530 to 2300 mg C m -3 d -1 , respectively. Photosynthetic activity during the period of investigation on average was 2 times lower in the zone of seawater influence (Klaipeda Strait) than in the central part. 3 - The greatest differences in phytoplankton biomass and the rate of primary production in the investigated areas were registered during an intensive Aphanizomenon bloom. Total phytoplankton exudation ranged from 5 to 24% (on average 12%) of the total organic carbon production. 4 - The rates of production processes exceeded decomposition processes, thus stimulating the accumulation of autochthonic organic matter in the Curonian Lagoon during the midsummer vegetation period.

Blooms of Single Bacterial Species in a Coastal Lagoon of the Southwestern Atlantic Ocean

We investigated seasonal differences in community structure and activity (leucine incorporation) of the planktonic bacterial assemblage in the freshwater and brackish-water zones of a shallow coastal lagoon of the southwestern Atlantic Ocean. Alphaproteobacteria formed the dominant microbial group in both zones throughout the sampling period. After an intrusion of marine water, members of the SAR11 lineage became abundant in the brackish-water zone. These bacteria were apparently distributed over the lagoon during the following months until they constituted almost 30% of all prokaryotic cells at both sampling sites. At the first sampling date (March 2003) a single alphaproteobacterial species unrelated to SAR11, Sphingomonas echinoides, dominated the microbial assemblages in both zones of the lagoon concomitantly with a bloom of filamentous cyanobacteria. Pronounced maxima of leucine incorporation were observed once in each zone of the lagoon. In the freshwater zone, this highly active microbial assemblage was a mix of the typical bacteria lineages expected in aquatic systems. By contrast, a single bacterial genotype with >99% similarity to the facultative pathogen gammaproteobacterial species Stenotrophomonas maltophilia formed >90% of the bacterial assemblage (>10(7) cell ml(-1)) in the brackish-water zone at the time point of highest bacterial leucine incorporation. Moreover, these bacteria were equally dominant, albeit less active, in the freshwater zone. Thus, the pelagic zone of the studied lagoon harbored repeated short-term blooms of single bacterial species. This finding may have consequences for environmental protection.

Assessment of ecological risk from bioaccumulation of PCDD/Fs and dioxin-like PCBs in a coastal lagoon

The ecological risk posed by dioxin-like PCBs and PCDD/Fs congeners mixtures in five organisms representative of the food web of the lagoon of Venice (Italy) was estimated by applying the US-EPA [US-EPA. Guidelines for Ecological Risk Assessment. EPA/630/R-95/002F. Final Report. U.S. Environmental Protection Agency, Washington, DC; 1998.] procedure. Experimental concentrations of dioxin-like PCBs and PCDD/Fs in sediments, water, and organisms in six lagoon zones were used to define the spatial distribution of the pollutant homolog patterns. The Principal Component Analysis of homolog patterns in biota permitted to remark the difference between PCDD/Fs and dioxin-like PCBs bioaccumulation. Dioxin-like PCBs were found almost unaltered in all selected organisms, while PCDD/Fs homologs underwent an enrichment of low chlorinated furans in fish. The ecological risk for the dioxin-like PCBs and PCDD/Fs was estimated in the selected lagoon zones according to the Hazard Quotient approach by comparing the biota experimental concentrations in TEQ with an Internal No Effect Concentration of the 2,3,7,8-TCDD, estimated from both Ambient Quality Criteria and literature toxicity data. A high potential risk was found for benthic biota (i.e. clam and crab) and for mussel, while a negligible risk was estimated for fish. Moreover, the ecological risk resulted higher in the central part of the lagoon, and lower in the northern lagoon. Finally, the comparison between the TEQ concentrations of each homolog in biota and the estimated ecological risk highlighted that the risk was determined essentially by lower chlorinated PCDD/Fs (i.e. pentachloro and hexachloro PCDD/Fs), and by pentachloro-PCBs. These compounds should be regarded as homologs of concern and preferentially investigated in environmental monitoring of sediment, water, and biota.

Deposition and cycling of carbon and nitrogen in carbonate mud of the lagoons of Arlington and Sudbury Reefs, Great Barrier Reef

The dynamics of carbon and nitrogen in carbonate mud were examined in the lagoons of Arlington and Sudbury Reefs, Great Barrier Reef. Most (89–93%) of the organic carbon and total nitrogen depositing to the carbonate mud zones was mineralized over a sediment depth of 1 m, with ∼50% of CO2 produced during microbial decomposition involved in carbonate precipitation/dissolution reactions. There was proportionally little burial of organic carbon (10–11%) or nitrogen (7–10%). Nitrogen budgets suggest rapid turnover of porewater inorganic N pools on the order of hours to a few days. Incubation experiments indicate carbonate dissolution in surface deposits (≤20 cm depth) and carbonate precipitation in deeper sediments. Depth-integrated reaction rates indicate net carbonate precipitation of 7–10 mol CaCO3 m2 year−1 over a depth of 1 m. Budget calculations at the whole-reef scale imply that deposition of CaCO3 in the mud zones of both lagoons may equate to 50–90% of total reef carbonate production, with organic carbon fluxes equating to nearly all net primary production on each reef. These biogeochemical estimates point to the functional importance of carbonate mud zones in the lagoons of the shelf reefs of the Great Barrier Reef.

Structure of a unique inland mangrove forest assemblage in fossil lagoons on the Caribbean Coast of Mexico

Scrub mangrove wetlands colonize the intertidal zone of fossil lagoons located in carbonate continental margins along the Yucatan Peninsula of Mexico. These unique ecological types were investigated in October, 1994, by locating transects in several mangrove forests along the Caribbean coast of the peninsula. Four species of mangrove occurred at these sites including Rhizophora mangle, Avicennia germinans, Laguncularia racemosa, Conocarpus erecta. This is one of the first examples of a species rich scrub forest. The mangroves fell into three height categories: short scrub less than 1.5 m, tall scrub to 3.0 m, and basin forests between 4.5 and 6 m. Average height, diameter (dbh), basal area, and complexity index generally increased from short scrub to basin forests. Basal area, ranged from 0.16 m2 ha−1 in a short scrub forest intermixed with Cladium jamaicense to 12.9 m2 ha−1 in a basin forest. Density ranged from 1520 trees ha−1 to over 25,000 trees ha−1 in a short scrub forest dominated by R. mangle. The complexity index ranged from 0.01 to 8.3. Height, dbh, basal area, and complexity index were positively related. A number of trees were growing as sprouts from larger downed trunks, suggesting that hurricanes, such as Gilbert that occurred in 1988, are important in controlling the structure of these forests. These forests appear isolated from the sea, but are influenced by groundwater exchange occurring at the land-margin zone.

Testate Amoeba (Rhizopoda) Diversity in Plankton of the Upper Paraná River floodplain, Brazil

In this study we examine the influence of environmental variability on the α and β diversity of testate amoeba assemblages from plankton samples. The samples were collected in the littoral and pelagic zones of the rivers and lagoons of the Parana River floodplain, over one hydrological cycle. Seventy-three species were identified. Alpha diversity was similar in both lagoons and rivers. Although the relationship between α diversity and water level was significant, it was not consistent for all environments, i.e. the pelagic and littoral zones of rivers and lagoons. Temporal β diversity was low and unrelated to environmental stability. Despite the high connectivity among floodplain environments and the suggested homogenizing effect of the flood pulse, spatial β diversity was high, mainly between rivers and lagoons. Also, testate amoeba species composition seems to be more predictable than local species richness.

Isoenzyme Analysis of Percids (Stizostedion Lucioperca, Perca Fluviatilis, Gymnocephalus Cernua) in LithuaniaCoastal Zone of the Baltic Sea, the Curonian Lagoon and Kaunas Water Reservoir

The isoenzyme analysis of percids in the Curonian Lagoon and coastal zone of the Baltic Sea was performed during 1999-2000. The liver tissue homogenate was used for the investigations. Isoenzyme analysis was carried out by electrophoresis in polyacrylamide gel (PAA) method. After investigating three populations of percids according to five enzyme systems it has been established that four (MDH, ME, XDH, G-6-PH) were monomorphic and only one (EST) polymorphic. Four loci (EST-1, EST-2, EST-3, EST-4) with 2-7 different alleles were found in esterase polymorphic system. The highest number of alleles and genotypes has been established for the four loci of the Curonian Lagoon populations, and only for ruffe population of EST-4 locus at Kaunas water reservoir. It is evident that the Curonian Lagoon populations distinguish by their high genetic diversity.

Evidence for effects of Spartina anglica invasion on benthic macrofauna in Little Swanport estuary, Tasmania

Abstract Spartina anglica is an exotic perennial grass that can rapidly colonise the intertidal zone of temperate estuaries and lagoons. Consequently, there is considerable concern about its impact on estuarine flora and fauna. This study provides the first investigation of ecological impacts by S. anglica in Australia. The objective was to investigate the impacts of S. anglica on benthic macroinvertebrate communities inhabiting mudflat and native saltmarsh habitats at Little Swanport estuary, Tasmania. The null hypothesis that species richness and species abundance of benthic macroinvertebrates in exotic S. anglica marsh does not differ from adjacent native saltmarsh and mudflat habitats was tested. Eighteen species and 3716 macroinvertebrates were collected from 60 intertidal core samples in three habitats. Species richness, total abundance of invertebrates, crustacean abundance and mollusc abundance of mudflat communities were significantly (P &lt; 0.05) lower when compared to those inhabiting adjacent S. anglica marsh and native saltmarsh. However, species richness and total abundance of invertebrates of native saltmarsh and S. anglica marsh did not differ significantly. Ordination of macroinvertebrate data clearly separated mudflat sites from vegetated sites but showed remarkable similarity between exotic and native vegetated sites.

Effects of anthropogenic disturbances of tropical soft-bottom benthic communities

The benthic ecosystem of the lagoon surrounding Tahiti, the most populated island of French Polynesia, was investigated to assess the impacts of terrestrial runoff on these benthic communities. Five lagoonal zones based on population densities around the coast of Tahiti were identified, and within each zone a transect from the fringing reef to the barrier reef was sampled, a total of 18 stations. Only large macrofauna collected on a 2 mm sieve were considered in this study. Multivariate analysis using total biomass and environmental factors showed that the stations formed 3 main groups which were related to sediment characteristics, including percentage of silt, organic matter and phaeopigment levels. The distribution of the major feeding groups was related to the amounts of terrestrial inputs and distance from the shore. The stations on the barrier reef and those in zones adjacent to low population areas were not impacted by these terrestrial inputs. Deposit-feeding communities of capitel-lid polychaetes were dominant in the channel parts of the lagoon, which acted as decanting ponds. Chaetopterid polychaetes played an important role in recycling sediments of terrigenous origin in the fringing ecosystem. The patterns of diversity, density and biomass of the benthos around the lagoon revealed that some areas were impacted by moderate terrigenous inputs. It appears that the intermediate disturbance hypothesis explains the functioning of the parts of the benthic lagoonal ecosystem which are subjected to human impact. The organic enrichment by terrestrial inputs contrasts with food limitation that appears to occur in the non-disturbed areas. Despite high organic loads, the benthic communities present at the harbour station were not depauperate, as bioturbation by burrowing alpheids and callianassids prevented anoxic conditions from developing.

Carbon flux by suspended and sinking particles around the barrier reef of Palau, western Pacific

Suspended and sinking particles were studied around a barrier reef of the Palau Islands in the western Pacific. Concentrations of particulate organic carbon (POC), particulate organic nitrogen (PON), and chlorophyll a were high in reef waters and decreased toward the open ocean. At the reef edge, concentrations of organic particles in outgoing waters were higher than those in incoming waters, indicating net export of organic matter. Sediment trap observations conducted off the barrier reef showed a larger vertical flux of POC at an inshore station (2.5 km off the reef edge) than that at an offshore station (20 km), attributable to the net export of organic particles. Organic/inorganic carbon ratios of particles trapped at a depth of 45 m in the lagoon were smaller than those of suspended particles in surface water, suggesting a rapid decomposition of organic matter during sedimentation and a resuspension of carbonate‐dominant bottom sediments.We estimate that 7% of the gross community production in the reef is deposited in the lagoon zone, 4% is exported to the open ocean, and 0.6% is transferred below the thermocline (150 m depth) in the ocean.

Isotopic Analysis of Individual Compounds: A Tool to Investigate Fossil Plants Isotopic Signal

where 13R stands for the ratio 13C/12C, standard being PDB (marine carbonate: belemnite from the Pee Dee Formation). Isotopic fractionation of carbon associated with photosynthesis in living terrestrial plants depends upon three main factors (e.g. O'Leary, 1981): (1) the photosynthetic pathway of the plant, C3, C4 or CAM, (2) the inorganic-carbon source and (3) environmental parameters. Such factors can be recorded by fossil plant via 613C values. Carbon isotope ratios were often used to investigate the emergence of C4 photosynthetic pathway in fossil plants. Stable carbon isotopic abundances were also studied to research an isotopic record of palaeoatmospheric condition in terrestrial fossil plants, to reconstruct local palaeoenvironments or as chemostratigraphic tool. However, stable carbon isotope abundances in fossil plants can be diagenetically altered if the carbon lost by degradation has 613C values significantly different of the carbon which is preserved. Hedges et al. (1985) showed that lignin is selectively preserved to the detriment of cellulose in buried wood. Since lignin is 13C-depleted when compared to the whole tissue, that may lead to significant changes in 813C values as demonstrated by Benner et al. in a modern salt marsh (1987). However, several experimental studies on modern plants (e.g. Balesdent and Mariotti 1996) and investigations on fossil ones suggested that fossil plants typically have retained their original isotopic composition. That could be explained by the presence of remnant of carbohydrates in fossil plants. Nevertheless, significance of ~13C values in fossil plants is strongly dependent on the level of diagenesis. The aim of the present study was thus to get a tool allowing for investigation of the isotopic signal in fossil plant whatever the level of preservation of bulk ~13C values. Isotopic analysis of an individual molecular biomarker, present in substantial amounts in fossil plants and stable through geological time, could constitute an adequate methodology. The identification of such a biomarker was first undertaken in leaf lipids since most lipid constituents are stable through geological times, and, were shown not to move into the surrounding sediment during burial (Logan et al., 1995). To validate the use of a given biomarker it was necessary to measure its 513C value in fossil plants in which the bulk isotopic signal is well preserved, and, to compare these values with those obtained in modern counterparts. The Cenomanian lagoonal Member of the 'Argiles du Baugeois' (Anjou, France) yielded a rich and exceptionally well preserved fossil flora. Preliminary studies have shown that the bulk ~13C values were not significantly altered in these fossil plants. 13C/12C ratios thus allowed the reconstruction of the ecological distribution of each species studied, along a decreasing salinity gradient from the lagoonal zones to the flood plain. Leaf lipids from the most abundant species of the deposit, the Ginkgoale Eretmophyllum andegavense, were thus analysed, and compared to the ones of its extant counterpart Ginkgo biloba. GC-MS analyses of leaf lipids from both Ginkgoales reveal the presence of 3 common compounds in E. andegavense and its modern counterpart: long chain n-alkanes, predominantly even n-acids and alkyl, dimethoxycoumarins. They all constitute potential biomarkers of the isotopic signal. Isotopic analyses were first undertaken on n-

Lagoonal to Reefal Ostracod Assemblages from Holocene and Recent Deposits, Chesterfield Islands and Northern New Caledonia (Southwestern Pacific)

Lagoonal to Reefal Ostracod Assemblages from Holocene and Recent Deposits, Chesterfield Islands and Northern New Caledonia (Southwestern Pacific)

Associations d'ostracodes d'un environnement récifal envasé: Le lagon de l'île de Mayotte (Archipel des Comores, Océan Indien occidental)

Ostracode assemblages have been collected from sediments dredged in the lagoon of Mayotte Island in order to study effects of mudflows from land to lagoonal zones due to anthropisation. Two main facies occur: bioclastic sandy bottoms in the external part and muddy deposits which progressively invade the major part of coastal bays and proximal lagoonal zones. Previous geological analyses are available dealing with some micropalaeontological (foraminifera) and sedimentological aspects. A systematic approach of the ostracode content is proposed within the same context; records obtained constitute a preliminary account concerning this area; nevertheless, a few data already given in the selected bibliography may be used. In such sedimentary environments characterized by a high evolutionary rate, the knowledge of present-day assemblages and their qualitative/quantitative composition will be of great interest because they may be considered as reference for the future. One of the prior applications will be to put in a prominent position the effect of occasional variations of physico-chemical parameters related with the development of human activities. The ostracode fauna is composed of thirty-nine recorded species belonging to thirty-five genera (four indetermined) and ranging mainly into the Cytheracea and Bairdiacea; Cypridacea are less common. Poorly local documentation and occurrence of rare and/or badly preserved specimens does not permit an accurate ostracode check-list. Accordingly, many species are left in open nomenclature. Within the two sedimentary type-deposits, ostracode assemblages show many qualitative differences; diversity is maximum in medium mud-content areas (transitional facies between sands and pure muds). From a quantitative point of view, it is noteworthy the more important scarcity of microfaunas on bioclastic (shelly) sands and several well-muddy substrates. An assessment is made of the biogeographic point of view; mahoran microfaunas show strong affinities with those of North Madagascar and Reunion Island. Common species have been described or located in the Western Pacific Ocean, especially Australia. Relationships with South African coasts are not clearly demonstrated.

Chronology of inland shell deposits on the southern coast of Sri Lanka

Extensive patches of fossil shell deposits are found in many places along the rims of emerged coastal embayments and lagoon floors on the southern coast of Sri Lanka. Compositional and depositional sequences of fossil shells (Veneridae, Cerithidae, and Nassaridae) reveal that the bulk of the valves has been accumulated by three processes: (a) the shells have been piled up on the rims of emerged coastal embayments mainly by wave action; (b) following coastal progradation since the late Subboreal the shells possibly gathered on lagoon floors; and (c) the valves on the coastal hilly areas and dune areas were discarded by early human inhabitants in the course of their daily activities. Radiocarbon dates of fossil corals along the southwest and south coasts support this interpretation and indicate that mean sea level was at least 1 m higher than present in the middle Holocene. The fossil species may have lived in an intertidal zone of embayments and lagoons that extended 3 km or more inland form the present shore in the middle Holocene.