Antifungal defenses of seagrasses from the Indian River Lagoon,Florida

We investigated the antifungal chemical defenses and physiological responses of five seagrasses collected from nearshore seagrass beds from the Indian River Lagoon, Florida, against a panel of co-occurring marine fungi isolated from nearby coastal communities. Whole plant tissues from Thalassia testudinum, Halodule wrightii and Syringodium filiforme prevented overgrowth by three of the seven fungi used in this study. Organic extracts from four of the five seagrasses inhibited the growth of at least one fungal strain. The extract from Ruppia maritima exhibited the highest antifungal activity, inhibiting the growth of three fungi including the pathogen Lindra thalassiae. Among the fungal panel, Fusarium sp. 2 was the most susceptible to seagrass extracts, whereas none of the extracts disrupted the growth of Dendryphiella salina and Fusarium sp. 3. Under laboratory conditions fungal inoculation elicited hydrogen peroxide production in all specimens within 25 min post-inoculation as measured with a redox sensitive dichlorodihydrofluorescein diacetate (DCFH-DA) assay. The concentration of H₂O₂ released into the immediate vicinity of infected seagrasses varied between 0.10 and 0.85 μmol g⁻¹ FW min⁻¹ depending on seagrass species and pathogen combination. Longer term incubation (days) of T. testudinum with homogenates of D. salina or L. thallasiae resulted in the induction of caspase activity, a known proteolytic activator of apoptotic and inflammatory activities. The application of micromolar concentrations of H₂O₂ to blades of T. testudinum induced caspase activity suggesting that fungal detection, H₂O₂ production, and caspase activation occur in a consecutive order. The seagrasses examined in this study appear to use a combined strategy to combat fungal infection, including microbial chemical defenses and signaling pathways observed in terrestrial plants.     

Rehabilitation of impounded estuarine wetlands by hydrologic reconnection to the Indian River Lagoon, Florida (USA)

Salt marshes of the Indian River Lagoon, Florida (USA) were once prolific producers of mosquitoes. Mosquitoes lay their eggs on the infrequently-flooded high marsh surface when the soil surface is exposed. The eggs hatch when the high marsh is flooded by the infrequent high tides or summer rains. To control mosquito production, most of the salt marshes (over 16.200 ha) were impounded by the early 1970s. Flooding, usually by pumping water from the Lagoon, effectively controlled mosquitoes.However, impounding had a profoundly negative impact on the wetland plant, fish, and invertebrate communities. Isolation from the Lagoon cut off aquatic access by transient estuarine species that used the wetlands for feeding or as nursery area. In one study, the number of fish species dropped from 16 to 5 after impounding. Wetland vegetation within some impoundments was totally eliminated; other impoundments developed into freshwater systems.When tidal exchange is restored through hydrologic connection, usually by culverts installed through the perimeter dike, recovery to more natural conditions is often rapid. In one impoundment where wetland vegetation was totally eliminated, recovery of salt-tolerant plants began almost immediately. In another, cover of salt-tolerant plants increased 1,056% in less than 3 years. Fisheries species that benefitted the most were snook, ladyfish, and striped mullet. Over 1,500 juvenile snook were captured in a single 3-hr flood-tide culvert trap as they attempted to migrate into an impoundment. The zooplankton community rapidly returned to the more typical marsh-Lagoon community. Water quality and sediment sulfides returned to typical marsh values. Overall, reconnection enhances natural productivity and diversity, although water quality in the perimeter ditch, an artifact of dike construction, remains problematic.Earlier experiments demonstrated that flooding only during the summer mosquito breeding season provided as effective mosquito control as year-round flooding. In standard management, the impoundment is flooded in summer, then left open to the Lagoon through culverts the rest of the year. Culverts are typically opened when the fall sea level rise first floods the high marsh.Impoundment reconnection is being implemented by a multi-agency partnership. The total reconnected area is expected to reach 9,454 ha by the end of 1998, representing 60% of the impounded wetlands in the entire IRL system. One stumbling block is private ownership of many of the remaining isolated impoundments.University of Florida, IFAS, Journal Series No. R-05201.Harbor Branch Contribution Number 1152.Corresponding editor: R.E. Turner     

Spatial and temporal patterns of phytoplankton composition in subtropical coastal lagoon, the Indian River Lagoon, Florida, USA

A 2 year study of the phytoplankton community was carried outin the Indian River Lagoon, USA. In terms of biovolume, thephytoplankton community was generally dominated by dinoflagellates,diatoms or cyanobacteria. Mean phytoplankton standing cropswere highest in the most flow-restricted regions of the lagoon,which had the lowest mean salinity values and comparativelyhigh total nitrogen:total phosphorus ratios. In this region,blooms of dinoflagellates were common in the first year of thestudy, which was characterized by an El Niño event thatyielded exceptionally high rainfall levels and freshwater outflow.Picoplanktonic cyanobacteria blooms became more prominent inthe second year of the study, which was characterized by belowaverage rainfall conditions. In unrestricted flow regions ofthe lagoon, located near inlets to the Atlantic Ocean, diatomswere most often the dominant taxa. Regions of intermediate waterturnover rates and high external loading of phosphorus had aprevalence of diatom blooms. However, the average phytoplanktonstanding crops in the latter regions did not reach the levelsexperienced in the flow-restricted parts of the lagoon. In termsof individual phytoplankton taxa, the most common bloom-formingdiatoms in the Indian River Lagoon system included: Skeletonemacostatum, Dactyliosolen fragilissimus, Skeletonema menzelii,Cerataulina pelagica, Odontella regia, Chaetoceros lorenzianus,Rhizosolenia setigera and Thalassionema nitzschioides. The majorbloom-forming dinoflagellate species included: Pheopolykrikoshartmannii, Akashiwo sanguinea, Prorocentrum micans, the potentiallytoxic species Pyrodinium bahamense var. bahamense and Prorocentrumminimum. Several picoplanktonic cyanobacteria were also prominentmembers of the phytoplankton community, including Synechococcuselongates. The spatial and temporal patterns observed in someof these dominant species were attributable to patterns in keyenvironmental variables, including salinity, temperature andnutrient concentrations.     

Distribution and seasonal biomass of drift macroalgae in the Indian River Lagoon (Florida, USA) estimated with acoustic seafloor classification (QTCView, Echoplus)

Three areas of the Indian River Lagoon, Florida (USA) were surveyed to show seasonal changes in the distribution and biomass of macroalgae and seagrass. Acoustic seafloor discrimination based on first and second echo returns of a 50 kHz and 200 kHz signal, and two different survey systems (QTCView and ECHOplus) were used. System verification in both the field and a controlled environment showed it was possible to distinguish acoustically between seagrass, sparse algae, and dense algae. Accuracy of distinction of three classes (algae, seagrass, bare substratum) was around 60%. Maps were produced by regridding the survey area to a regular grid and using a nearest-neighbor interpolation to provide filled polygons. Biomass was calculated by counting pixels assigned to substratum classes with known wet-weight biomass values (sparse algae 250 g m^− 2, dense algae 2000 g m^− 2, seagrass 100 g m^− 2) that were measured in the field. In three study areas (Melbourne, Sebastian Inlet, and Cocoa Beach), a dependence of algal biomass on depth and season was observed. Seagrass most frequently occurred in water less than 1 m deep, and in November, seagrass beds tended to be covered by dense algae that also extended up- and downstream of shoals in the Lagoon. In March, the pattern was similar, with the exception that some areas of previously dense algae had started thinning into sparse algae. Macrophyte biomass was lowest in May in the Melbourne and Cocoa Beach study areas, with the opposite situation in the Sebastian Inlet study area. In May, seagrass areas were largely devoid of dense algae and most algae accumulations were sparse. In August, dense algae covered large areas of the deep Lagoon floor while shoals were largely free of algae or had only sparse cover. We suggest this summer pattern to reflect moribund algae being washed from the shallows to deeper channels and from there being removed from the lagoonal ecosystem either through tidal passages into the open ocean or by degradation and breakdown in situ. The differences between the study areas indicate high spatial and temporal variability in biomass and distribution of macrophyte biomass in the Indian River Lagoon.     

A revised checklist of planktonic diatoms and dinoflagellates from Helgoland (North Sea,German Bight)

A checklist based on net samples taken twice weekly from 2001 until May 2003 is presented. Identification is based on observations under direct light microscopy and after taking some organisms in culture. The checklist includes 227 taxa observed at the Helgoland Reede sampling station. One hundred and thirty-two species of diatoms from 53 genera and 95 species of dinoflagellates from 35 genera have been recorded from net samples and cultures. Thirty-five diatom and 28 dinoflagellate taxa were documented in the Helgoland phytoplankton for the first time. The list does not claim to be complete, but provides an updated list of the taxa found at Helgoland and, for convenience, also includes data published for different adjacent areas.Communicated by K. Wiltshire     

Home Ranges of Bottlenose Dolphins (<Emphasis Type="Italic">Tursiops truncatus</Emphasis>) in the Indian River Lagoon,Florida: Environmental Correlates and Implications for Management Strategies

Photo-identification surveys conducted between 2002 and 2005 were used to determine dolphin home ranges and site fidelity within the Indian River Lagoon (IRL), Florida. The IRL was divided into six segments based on hydrodynamics and geographic features for purposes of characterization. Among the 615 dolphins with identifiable dorsal fins, 339 had ≥6 sightings and were used in segment and linear range analyses. The majority (98%) of dolphins were seen in ≤3 consecutive segments (331/339); of these, 44% (144/331) occurred in two segments, and 33% (109/331) in one segment. No dolphins were observed in all six segments. The largest number of dolphins was sighted in segment 1C (North Indian River). However, the highest density of dolphins was found in segment 2 (North-Central Indian River). Re-sighting rates for dolphins with ≥6 sightings ranged from 2.8 to 8.7 times observed. The mean linear home range varied from 22 to 54 km. Distributional analyses indicated that at least three different dolphin communities exist within the IRL: Mosquito Lagoon, and the North and South Indian River. No statistically significant correlations were found between the total number or density per km² of dolphins and surface water area, salinity, or contaminant loads within segments of the lagoon. These results suggest that dolphins do not selectively avoid areas with relatively unfavorable water quality. IRL dolphins should be studied on smaller spatial scales than currently practiced, and potential anthropogenic impacts should be evaluated based on geographic partitioning.     

Reproduction of Blackchin Tilapia, Sarotherodon melanotheron, Within an Impounded Mangrove Ecosystem in East-central Florida

I investigated the reproductive biology of introduced blackchin tilapia, Sarotherodon melanotheron, over a twelve month period within a seasonally impounded mangrove ecosystem in east-central Florida, and compared the data to published accounts from native African habitats. Eggs and free embryos were collected from the buccal cavity of adult males from April to October indicating a protracted spawning season, however gonadosomatic indices suggested that most spawning occurred in April and May. The timing of reproduction was adjusted to occur immediately before temperatures reached optimal levels for juvenile growth and when increasing rainfall produced abundant food and shelter for the young. Temperatures below 24°C inhibited reproduction from November to March. The overall sex ratio was essentially 1:1. The minimum and maximum size at maturity were much larger in this study than those reported from Africa; the smallest mature male was 128mm standard length and 0.47 of the maximum size, while the smallest mature female was 145mm standard length and 0.54 the maximum size. However, because of the difficulty in aging this species and a lack of published information, it could not be determined whether the population in this study possessed a relatively early or delayed maturation compared to African populations.     

Rehabilitation of impounded estuarine wetlands by hydrologic reconnection to the Indian River Lagoon,Florida (USA)

Salt marshes of the Indian River Lagoon, Florida (USA) were once prolific producers of mosquitoes. Mosquitoes lay their eggs on the infrequently-flooded high marsh surface when the soil surface is exposed. The eggs hatch when the high marsh is flooded by the infrequent high tides or summer rains. To control mosquito production, most of the salt marshes (over 16.200 ha) were impounded by the early 1970s. Flooding, usually by pumping water from the Lagoon, effectively controlled mosquitoes. However, impounding had a profoundly negative impact on the wetland plant, fish, and invertebrate communities. Isolation from the Lagoon cut off aquatic access by transient estuarine species that used the wetlands for feeding or as nursery area. In one study, the number of fish species dropped from 16 to 5 after impounding. Wetland vegetation within some impoundments was totally eliminated; other impoundments developed into freshwater systems. When tidal exchange is restored through hydrologic connection, usually by culverts installed through the perimeter dike, recovery to more natural conditions is often rapid. In one impoundment where wetland vegetation was totally eliminated, recovery of salt-tolerant plants began almost immediately. In another, cover of salt-tolerant plants increased 1,056% in less than 3 years. Fisheries species that benefitted the most were snook, ladyfish, and striped mullet. Over 1,500 juvenile snook were captured in a single 3-hr flood-tide culvert trap as they attempted to migrate into an impoundment. The zooplankton community rapidly returned to the more typical marsh-Lagoon community. Water quality and sediment sulfides returned to typical marsh values. Overall, reconnection enhances natural productivity and diversity, although water quality in the perimeter ditch, an artifact of dike construction, remains problematic. Earlier experiments demonstrated that flooding only during the summer mosquito breeding season provided as effective mosquito control as year-round flooding. In standard management, the impoundment is flooded in summer, then left open to the Lagoon through culverts the rest of the year. Culverts are typically opened when the fall sea level rise first floods the high marsh. Impoundment reconnection is being implemented by a multi-agency partnership. The total reconnected area is expected to reach 9,454 ha by the end of 1998, representing 60% of the impounded wetlands in the entire IRL system. One stumbling block is private ownership of many of the remaining isolated impoundments.     

Nitrogen limitation of growth and nutrient dynamics in a disturbed mangrove forest,Indian River Lagoon,Florida

The objectives of this study were to determine effects of nutrient enrichment on plant growth, nutrient dynamics, and photosynthesis in a disturbed mangrove forest in an abandoned mosquito impoundment in Florida. Impounding altered the hydrology and soil chemistry of the site. In 1997, we established a factorial experiment along a tree-height gradient with three zones, i.e., fringe, transition, dwarf, and three fertilizer treatment levels, i.e., nitrogen (N), phosphorus (P), control, in Mosquito Impoundment 23 on the eastern side of Indian River. Transects traversed the forest perpendicular to the shoreline, from a Rhizophora mangle-dominated fringe through an Avicennia germinans stand of intermediate height, and into a scrub or dwarf stand of A. germinans in the hinterland. Growth rates increased significantly in response to N fertilization. Our growth data indicated that this site is N-limited along the tree-height gradient. After 2 years of N addition, dwarf trees resembled vigorously growing saplings. Addition of N also affected internal dynamics of N and P and caused increases in rates of photosynthesis. These findings contrast with results for a R. mangle-dominated forest in Belize where the fringe is N-limited, but the dwarf zone is P-limited and the transition zone is co-limited by N and P. This study demonstrated that patterns of nutrient limitation in mangrove ecosystems are complex, that not all processes respond similarly to the same nutrient, and that similar habitats are not limited by the same nutrient when different mangrove forests are compared.     

Habitat use by fishes after tidal reconnection of an impounded estuarine wetland in the Indian River Lagoon,Florida (USA)

Most of the wetlands located along the Indian River Lagoon (IRL) ineast-central Florida (USA) have been impounded since the 1950's and1960's to reduce mosquito reproduction. Impounded marsh (i.e.,impoundment) dikes physically separate the wetlands from the estuary toallow artificial flooding of the impoundments during the mosquito breedingperiod (May to October). Presently, Rotational ImpoundmentManagement (RIM) is the preferred impoundment management techniquein the IRL. Impoundments maintained under RIM have culverts installedthrough the dikes which are kept closed during the mosquito breedingseason (to control mosquitos) and are allowed to remain open for theremainder of the year (to allow tidal flow). A 24.3 ha impoundment8 km north of Sebastian Inlet that had been isolated from the IRL for over39 years was studied for 12 months to determine habitat use by fishes aftertidal reconnection and the implementation of RIM. Fish sampling wasconducted with a seine in the perimeter ditch and with clover and minnowtraps in the upper marsh and tidal creek areas of the impoundment. Waterlevel, impoundment bottom topography, and the seasonal nursery functionof the impoundment were factors that contributed to observed patterns offish habitat use during the study. Within the first 15 weeks of perimeterditch sampling, an increase from 9 to 40 species was observed. Transientspecies used the perimeter ditch almost exclusively and entered theimpoundment primarily during the spring open period. Juvenile Pogonias cromis (Linnaeus), Elops saurus Linnaeus, Centropomusundecimalis (Bloch), and Megalops atlanticus Valenciennes were themost abundant recreationally important species, respectively. Habitat useby the most abundant resident species (Gambusia holbrooki Girard,Poecilia latipinna (Lesueur), Cyprinodon variegatus Lacepède, andFundulus confluentus Goode & Bean) was influenced primarily bywater level fluctuations. Resident species used the upper marsh and tidalcreek habitats during summer flooded periods and the cyprinodontids leftthe interior surface of the impoundment last as water levels decreased. Thisstudy is the first to document the recovery of fish populations in areconnected impoundment north of Sebastian Inlet using both active andpassive sampling techniques.     

An ecological study of three freshwater ponds of hyderabad-India IV. the phytoplankton (diatoms,euglenineae and myxophyceae)

Data on the ecology of Diatoms, Euglenineae and Myxophyceae in three freshwater ponds, differing in chemical composition and algal flora, situated in the vicinity of Hyderabad-India are presented. An attempt has been made to isolate various genera into groups, as their multiplication depended on particular ranges of a single chemical factor or set of factors. Several species could be separated into seasonal forms as they occur in particular periods of the year. Others could be grouped under indifferent forms as these are neither influenced by fluctuations in chemical factors nor by seasonal changes.     

Northern range extension of the seagrasses Halophila johnsonii and Halophila decipiens along the east coast of Florida,USA

The northern geographic limit for Halophila johnsonii and Halophila decipiens has been reported as Sebastian Inlet, within the Indian River Lagoon, Florida. Surveys conducted in August 2007 determined the new northern limit to be 21.5 km north of the previously known limit. This new northern limit is a 10% range extension for H. johnsonii, a federally threatened species. We conclude that these range extensions are recent, based on (1) the small size of patches; (2) unusually good water clarity conditions due to a recent drought; (3) recent mild/warmer winters; and (4) a recent mechanism for transporting propagules, the numerous hurricanes of 2004. Although this recent range extension is considered ephemeral, similar range extensions may have occurred in the past and may occur again in the future under favorable conditions given the high capacity of these two species for dispersal to favorable sites. The northern limits of these species should not be viewed as static locations; rather, they must be considered dynamic features.     

Patterns of Fish Use and Piscivore Abundance within a Reconnected Saltmarsh Impoundment in the Northern Indian River Lagoon, Florida

Nearly all saltmarshes in east-central, Florida were impounded for mosquito control during the 1960s. The majority of these marshes have since been reconnected to the estuary by culverts, providing an opportunity to effectively measure exchange of aquatic organisms. A multi-gear approach was used monthly to simultaneously estimate fish standing stock (cast net), fish exchange with the estuary (culvert traps), and piscivore abundance (gill nets and bird counts) to document patterns of fish use in a reconnected saltmarsh impoundment. Changes in saltmarsh fish abundance, and exchange of fish with the estuary reflected the seasonal pattern of marsh flooding in the northern Indian River Lagoon system. During a 6-month period of marsh flooding, resident fish had continuous access to the marsh surface. Large piscivorous fish regularly entered the impoundment via creeks and ditches to prey upon small resident fish, and piscivorous birds aggregated following major fish movements to the marsh surface or to deep habitats. As water levels receded in winter, saltmarsh fish concentrated into deep habitats and emigration to the estuary ensued (200% greater biomass left the impoundment than entered). Fish abundance and community structure along the estuary shoreline (although fringed with marsh vegetation) were not analogous to marsh creeks and ditches. Perimeter ditches provided deep-water habitat for large estuarine predators, and shallow creeks served as an alternative habitat for resident fish when the marsh surface was dry. Use of the impoundment as nursery by transients was limited to Mugil cephalus Linnaeus, but large juvenile and adult piscivorous fish used the impoundment for feeding. In conclusion, the saltmarsh impoundment was a feeding site for piscivorous fish and birds, and functioned as a net exporter of forage fish to adjacent estuarine waters.     

Toxic blooms of cyanobacteria in the Patos Lagoon Estuary,southern Brazil

The Patos Lagoon is the largest lagoonal system in South America. Its waters are formed by a huge drainage basin (201,600 km²) situated in the most industrialized areas of the Southern state of Rio Grande do Sul. On its margins more than 3 million inhabitants live in several cities and towns. The lagoon waters are used for leisure, drinking, industry, fisheries, agriculture and navigation. A monitoring and sampling program was developed from February 1994 to January 1996 with emphasis on the estuarine area, aiming to evaluate the occurrence of algal blooms. In the last 15 years, several cyanobacterial (blue-green algal) blooms of theMicrocystis aeruginosa have been registered in the lagoon estuary. HighM. aeruginosa biomass (50 to 9,000 g chla l^–1) was observed in the whole region in late summer and autumn 1994, and early summer 1995. The LD50 of toxic bloom samples tested in mice varied from 22 to 250 mg dry weight kg body weight^–1 while levels of toxicity (LC50) in the brine shrimp varied from 0.47 to 2.44 mg ml^–1. Toxicity varied in different blooms, in the distances along the scum and with time, within the same bloom. The hepatotoxin microcystin-LR was identified in almost all samples.     

Hematologic, biochemical, and cytologic findings from apparently healthy atlantic bottlenose dolphins (Tursiops truncatus) inhabiting the Indian River Lagoon, Florida, USA

The objective of this study was to establish reference baseline data for hematologic, biochemical, and cytologic findings in apparently healthy Atlantic bottlenose dolphins (Tursiops truncatus) inhabiting the Indian River Lagoon, Florida, USA. Sixty-two dolphins were captured, examined, and released during June 2003 and June 2004. Mean, standard deviation, and range were calculated for each parameter, and values for which published data were available, were close to or within the ranges previously reported for free-ranging bottlenose dolphins. No pathologic abnormalities were found in fecal and blowhole cytologic specimens. However, 24% (7/29) of the dolphins examined in 2003 had evidence of gastritis, which was graded as severe in 14% (4/29) of the cases. In 2004, only 4% (1/24) of dolphins sampled had evidence of mild or moderate gastritis; no severe inflammation was present. Dolphins with evidence of gastritis were 8 yr of age or older and predominantly male. Several statistically significant differences were found between males and females, between pregnant and nonpregnant animals, and between juveniles (<6 yr) and adults (> or =6 yr). However, the values remained within the established ranges for this species, and the differences were not likely to be of clinical significance.     

Ecophysiological characteristics of Avicennia germinans and Laguncularia racemosa coexisting in a scrub mangrove forest at the Indian River Lagoon, Florida

The purpose of this work is to increase ecological understanding of Avicennia germinans L. and Laguncularia racemosa (L.) Gaertn. F. growing in hypersaline habitats with a seasonal climate. The area has a dry season (DS) with low temperature and vapour pressure deficit (vpd), and a wet season (WS) with high temperature and slightly higher vpd. Seasonal patterns in interstitial soil water salinity suggested a lack of tidal flushing in this area to remove salt along the soil profile. The soil solution sodium/potassium (Na⁺/K⁺) ratio differed slightly along the soil profile during the DS, but during the WS it was significantly higher at the soil surface. Diurnal changes in xylem osmolality between predawn (higher) and midday (lower) were observed in both species. However, A. germinans had higher xylem osmolality compared to L. racemosa. Xylem Na⁺/K⁺ suggested higher selectivity of K⁺ over Na⁺ in both species and seasons. The water relations parameters derived from pressure–volume P–V curves were relatively stable between seasons for each species. The range of water potentials (Ψ), measured in the field, was within estimated values for turgor maintenance from P–V curves. Thus the leaves of both species were osmotically adapted to maintain continued water uptake in this hypersaline mangrove environment.     

Influence of freshwater and terrigenous material on nutrients,bacteria and phytoplankton in a high island lagoon: Mayotte,Comoro Archipelago,Indian Ocean

Freshwater and terrigenous suspended material inputs were studied in Longoni Bay, an area of the lagoon of Mayotte (Comoro, Indian Ocean) that is unaffected by the influence of the most populated area of the island. The influence of terrigenous material on the lagoon waters was limited to the coastal zone and resulted in the increase of inorganic nitrogen and silica. The response of the bacteria was an increase of their cell volume; that of the phytoplankton was an increase of cyanobacteria numbers and chlorophyll a related to ammonia. Ammonification was apparently enhanced in freshwater whereas nitrification was enhanced in seawater. The high nitrate and silicate content of the reef zone were explained neither by river or rainfall inputs nor by enrichments by ocean waters. The hypothesis of the participation of marine groundwater discharges to this enrichment was examined and found to be supported by the range of concentrations in the reef zone and because enrichment did not concern ammonia and nitrite but only nitrate and silicate and occurred during the wet period when the aquifer is fed by abundant rainfall. The response of bacteria to the characteristics of the reef zone was an increase in biomass and a lower level of heterotrophic activity related to nitrate concentration. The changes observed during the wet period confirmed that the nitrogen increase was linked to the terrigenous material, and possibly to discharge of groundwater, and yielded a lower number of bacteria but increased biomass, and despite a drop in large phytoplankton numbers, a strong increase in chlorophyll a related in part to small cyanobacteria. This enrichment is high enough to place the Mayotte Lagoon among the richest high island lagoons, with regard to nitrogen and chlorophyll a. This revised version was published online in July 2006 with corrections to the Cover Date.     

The impact of regulation and salinisation on floodplain lakes: the lower River Murray,Australia

Floodplain lakes along the lower River Murray are subject to a wide range of human impacts including regulation, abstraction, elevated saline groundwater tables, increased nutrient and sediment fluxes and introduced biota. These perturbations are superimposed on those arising from high inter-annual rainfall variability, driven, at least in part, by variations in the southern oscillation. Sediment-based archives from two lakes within a complex of wetlands, situated near to the first site of irrigation development in the lower River Murray, reveal substantial changes over the last 800 years. While high levels of salinity are not foreign to the sites, the recent trend is towards sustained high salinity levels. As a result of European impact, freshwater diatom plankton now dominates Loch Luna, whilst Loveday Wetland is both more saline and nutrient rich than in the pre-European period. In Loveday Wetland, the post-1960 increase in Haslea spicula (Hickie) Lange-Bertalot, may be driven by increases in sulphur salt concentrations that are believed to be a cause of recent acidification episodes. A recent increase in more salt tolerant diatoms in Loch Luna suggests that this site, which has been largely buffered from substantial change, is becoming more vulnerable to perturbation. Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users.     

Occurrence of thick Ethmodiscus oozes associated with a terminal Mid-Pleistocene Transition event in the oligotrophic subtropical South Atlantic

Within generally calcareous sediment sequences, layers of variable thickness of the giant diatom Ethmodiscus were found in five cores recovered in the Subtropical South Atlantic between 23° and 33°S from both sides of the Mid-Atlantic Ridge. Two types of oozes occur: (almost) monospecific layers of Ethmodiscus and layers dominated by Ethmodiscus, with several accompanying tropical/subtropical, oligotrophic-water diatoms. The two thickest Ethmodiscus layers occur in GeoB3801-6 around 29°S, and accumulated during late MIS 14 and MIS 12, respectively. Downcore concentrations of Ethmodiscus valves range between 3.4 ? 10⁴ and 2.3 ? 10⁷ valves g^− 1. We discuss the ooze formation in the context of migration of frontal systems and changes in the thermohaline circulation. The occurrence of Ethmodiscus oozes in sediments underlying the present-day pelagic, low-nutrient waters is associated with a terminal event of the Mid-Pleistocene Transition at around 530 ka, when the ocean circulation rearranged after a period of reduced NADW production.