Marine Lagoon Research Articles

Effects of host habitat quality on the viability of Cryptocotyle lingua (Trematoda: Digenea) cercariae

In an earlier study it was shown that Cryptocotyle lingua cercariae, matured in Littorina littorea from a polluted marine lagoon, displayed slower horizontal swimming rates, and reduced longevity compared to cercariae released by periwinkles from a cleaner environment. This work investigated whether the pollution-induced reduction in swimming rates was due to an inefficient swimming action or the adoption of a less direct swimming path. In addition, cercariae from L. littorea that had been transferred from an 'unpolluted' to a 'polluted' site for 1 month provided information on the speed with which pollutants affect cercariae through their intermediate hosts. Results indicated that, in general, horizontal swimming rates were reduced due to slower swimming rather than disorientation and longer swimming pathways. Effects of host transplantation to a polluted site were clearly evident after 1 month. Evidence suggested that the pollutants accumulated by the cercariae via their first intermediate host affected the neuromusculature associated with swimming performance rather than sensory structures. Bearing in mind the reduced viability of C. lingua cercariae in polluted sites it is assumed that high prevalence of this digenean in gastropods (at such sites) must be due to their continual introduction by infected birds attracted to these habitats from other areas.

DISSECTING THE SPATIAL STRUCTURE OF ECOLOGICAL DATA AT MULTIPLE SCALES

Spatial structures may not only result from ecological interactions, they may also play an essential functional role in organizing the interactions. Modeling spatial patterns at multiple spatial and temporal scales is thus a crucial step to understand the functioning of ecological communities. PCNM (principal coordinates of neighbor matrices) analysis achieves a spectral decomposition of the spatial relationships among the sampling sites, creating variables that correspond to all the spatial scales that can be perceived in a given data set. The analysis then finds the scales to which a data table of interest responds. The significant PCNM variables can be directly interpreted in terms of spatial scales, or included in a procedure of variation decomposition with respect to spatial and environmental components. This paper presents four applications of PCNM analysis to ecological data representing combinations of: transect or surface data, regular or irregular sampling schemes, univariate or multivariate data. The data sets include Amazonian ferns, tropical marine zooplankton, chlorophyll in a marine lagoon, and oribatid mites in a peat bog. In each case, new ecological knowledge was obtained through PCNM analysis.

Recent evolution of the fishing exploitation in the Thau lagoon, France

Fisheries activity in the Thau marine lagoon (Mediterranean coast of France) has an old tradition and involves different types of gears (set nets, traps and lines) that are used seasonally with varying frequencies in different areas. A survey of fishing activity, main fishing methods and main commercial species composition in the lagoon was carried out to assess the current fishing effort and seasonal yield. Many important changes in fishing effort and in the most important target species occurred during the last 10 years. A gradual decline in eel, Anguilla anguilla (L.), catches followed by an increase of other commercially-exploited species, particularly the gilthead sea-bream, Sparus aurata L., was observed.

Site-specific and density-dependent extinction of prey by schooling rays: generation of a population sink in top-quality habitat for bay scallops.

Bay scallops (Argopecten irradians concentricus) are patchily distributed on two dominant spatial scales: (1) geographically restricted to highly saline marine lagoons, and (2) locally abundant within such lagoons only in relatively discrete beds of seagrass habitat. In the Cape Lookout lagoonal system of North Carolina, adult bay scallop abundance in the most densely occupied seagrass bed (Oscar Shoal) exhibits repeatable declines from up to 70m-2 to near zero in a 2- to 4-week period during late summer. This crash is completed before fall spawning can be initiated, thereby creating a population sink in what is the singly most productive patch of habitat. Field experiments conducted in the summers of 1996 and 1998 demonstrated that the seasonal extinction of bay scallops on Oscar Shoal can be prevented by the erection of 1-m2 stockades, made of 50-cm-high vertical poles, spaced every 25cm, which inhibit access by cownose rays. Because these stockades were porous to emigration and physical transport, and open to access by all other predators of adult scallops, predation by migrating cownose rays is the only viable explanation for the crash. Consequently, the natural predation process in this system achieves the reproductive extinction of prey in the habitat patch of highest productivity. Over 7years of observation, the mortality rate in this patch increased with summer density, reaching the asymptote of 100% at 10m-2. The site-specific habitat selection by schools of rays may be based on prey density, which could render this example representative of a widespread generator of population sinks in habitat patches of high quality. The virtual extinction of scallops within Oscar Shoal despite nearby patches with relatively high density may be related to the highly efficient feeding behavior of schools and the high vulnerability of bay scallops in a context of multiple alternative prey types.

Biogeochemical changes in the sediments of Lake Cantara South, a saline lake in South Australia

Biogeochemical studies were undertaken of a 65-cm long sediment core from Lake Cantara South, South Australia. 14C determinations indicated that the sediments had been deposited over 2000 years. Changes with sediment depth in the concentration or ratio of the following were determined: (i) total organic carbon, total carbonate (inorganic) carbon, total sulfur, total carbon, total inorganic and organic sulfur, atomic C/N, and sulfate/chloride; (ii) n-alkanes; (iii) a highly branched isoprenoid alkane, and (iv) steroids. Interpretation of the changes with sediment depth indicated the nature of changes that took place when the system changed from a protected marine lagoon to an isolated (athalassic) saline lake. This change took place about 1000 years ago.

Abstract: Integrated Paleoecology and Marine Vertebrate Fauna of the Stone City Formation (Middle Eocene), Brazos River Section, Texas 

ABSTRACT Abundant marine vertebrate faunas, including sharks, rays, teleosts, and reptiles, have been collected from two horizons in the Middle Eocene (Claiborne) Stone City Formation of southeast Texas. Extensive collecting, both surface and bulk, and recent advances, especially in the study of otoliths and foraminifera, provide for additional evaluation of paleoecological parameters. Otolith-based teleosts are dominated by neritic taxa such as sciaenids and ophidiids, while skeletal-based teleosts include catfish, barracuda, mackerel, and gar. Selachians include sand, tiger, and catsharks as well as rays and sawfish. Least common are reptiles, represented by crocodiles and turtles. Vertebrate diversity is 50 taxa, the richest marine fauna yet recorded from the Gulf Coast Middle Eocene. Vertebrates were collected from the top of the Main Glauconite bed and a thin lag zone three m below. The lower fauna (Assemblage A) is rich in tiger and sand sharks, eagle rays, plus estuarine elements, such as catfish, sawfish, and softshell turtle. The mixture of estuarine vertebrates with abundant marine mollusks suggests a possible tidal channel emptying into nearshore marine. The upper fauna (Assemblage B) is dominated by a rich, moderately diverse fish fauna with scarce rays and sharks. An assemblage with sciaenids, ophidiids, and myripristids with abundant, diverse mollusks, especially infaunal pelecypods, suggests a fully marine but nearshore setting of 25 m or less. Microfauna includes 33 benthic foraminifera and 15 ostracode species. The shallow nature of this assemblage, plus the lack of planktonic foraminifera, indicatesan absence of open ocean currents. Macrofaunal and microfaunal paleoecology supports the shallow neritic to estuarine conditions indicated by vertebrate parameters. The Main Glauconite bed was deposited in an open marine bay or lagoon which was separated from ocean currents by some barrier, possibly an offshore marine sandbar complex.

Development of a diatom-based specific conductivity model for the glacio-isostatic lakes of Truelove Lowland: implications for paleoconductivity and paleoenvironmental reconstructions in Devon Island lakes, N.W.T., Canada

Diatoms are identified and enumerated from the surface sediments of 100 lakes of Truelove Lowland, Devon Island, N.W.T., Canada. These lakes range from large oligotrophic lakes, to small tundra ponds, to coastal marine lagoons which are diverse in terms of ionic concentration and composition. The relationship between diatoms and 15 limnological variables is examined using Canonical Correspondence Analysis (CCA). Specific conductivity is identified as the most important variable influencing the distribution of diatoms in the Truelove lakes. A Weighted Averaging (WA) calibration model is developed to predict diatom-inferred specific conductivity. The reliability of the model is tested by evaluating the correlation between observed and diatom-inferred values and determining the error of prediction by bootstrapping. The applicability of the predictive conductivity equation is demonstrated by reconstructing the paleoconductivity history of Fish Lake.

New perceptions of the chronology and development of Aboriginal fishing in South‐Western Australia

Aboriginal fishing in south‐western Australia was significantly affected by Late Holocene physical and biological changes along this region's l,600km‐long littoral. About 4000 BP sedimentological processes, in part generated by climatic factors, altered coastal configurations and estuarine hydrologies, blocking marine lagoons from the sea and causing partial filling and seasonal barring of estuary floors and entrances. These geomorphological changes affected most of the region's estuaries, and intensified seasonal differences in their salinity levels, which, combined with seasonal barring, restricted movements of school fish populations, thus compelling shifts in fishing strategies. Review of palaeogeographical and palaeontological data and investigation of former tidal weirs, on the shores of now nearly tideless estuaries and relict marine bodies, gives insight into the chronology of fishing and into the ways this key subsistence activity may have been adapted to changes in estuarine and coastal conditions. The Late Holocene may be the period when south‐western Aboriginal fishing gained the economic and socio‐political importance that it had regionally during the period of European settlement.

Impact of shellfish farming eutrophication on benthic macrophyte communities in the Thau lagoon, France

In a large marine lagoon (Thau lagoon, southern France) with a shellfish farming dominant eutrophication, the macrophyte communities were sampled by six transects of three depths (1.5, 2.5 and 5 m) and their characteristics (species composition, diversity and biomass) were described in relation to environmental and sediment parameters. With increasing eutrophication (total inorganic nitrogen, 0.140-0.295 mg l-1; dissolved reactive phosphorus, 0.045-0.110 mg l-1; and N/P atomic ratio, 3-22), silt fraction and shell fragments in sediments increased (12-93 and 0-65% dry wt respectively). Different types of macrophytic communities could be defined in the shallow zone (1.5-2.5 m) corresponding to four main and successive stages of degradation. A pure eelgrass stand (Zostera marina and Z. noltii) and an eelgrass community colonized by macroalgae were observed in SW sites and could be distinguished by their sedimentary features. In sites (NE) more affected by eutrophication (fine-textured sediment), available incident light determined two main seaweed communities: an Ulva rigida community, outside the shellfish tables, and a Gracilaria bursa-pastoris community in the shellfish tables (lower incident light).

The biogeochemistry of two eutrophic marine lagoons and its effect on microphytobenthic communities

This paper summarizes the results of a study on the biogeochemistry of two eutrophic marine lagoons. The lagoons investigated were the Bassin d'Arcachon situated on the Atlantic coast, and Etang du Prevost on the Mediterranean coast. The sites chosen for this study were characterized by the presence of dense communities of microphytobenthos. Both lagoons receive a large input of nutrients but they differ in several aspects. The Bassin d'Arcachon receives a large amount of iron. Iron is of great importance in reducing the effects of eutrophication. Ferric iron is an efficient scavenger of phosphate and it has been proposed that this is one of the mechanisms that controls primary productivity and algal growth in this lagoon. The mechanisms of phosphate mobilization were studied by using sediment slurries. These experiments demonstrated that not only ferric iron but presumably also calcium was responsible for phosphate binding. Another effect of the high iron content in the Bassin d'Arcachon was the precipitation of sulfide as iron sulfide or pyrite. In the Etang du Prevost sulfate reduction resulted in the accumulation of free sulfide. The relative low content of iron in Etang du Prevost not only allowed the formation of free sulfide but may also have limited the binding capacity of phosphate in the sediment. On the other hand sulfate reduction was not important for the release of phosphate from the sediment. In Etang du Prevost primary productivity is nitrogen rather than phosphorus limited. In contrast in the Bassin d'Arcachon primary productivity was presumably mostly phosphate limited. In Etang du Prevost the non-heterocystous cyanobacterium Oscillatoria sp. was the dominant nitrogen-fixing species. Heterocystous species were excluded from this lagoon as a result of the presence of free sulfide. It was demonstrated that heterocystous cyanobacteria are more sensitive towards sulfide than non-heterocystous species. The absence of free sulfide explained the presence of the heterocystous cyanobacterium Anabaena sp. in Bassin d'Arcachon.

Virological quality of the Ria de Aveiro: Validity of potential microbial indicators

The summer occurrence of human enteroviruses and rotaviruses in the bacteriologically clean area of the Ria de Aveiro, a coastal marine lagoon, prompted the question of the assessment of the virological quality of recreational waters and shellfish raising beds. Enteroviruses were present in surface water at a density of 3 pfu 10 l−1 and were accumulated in sediments and, especially, in cockles where they reached concentrations 2 to 310log units greater. Rotaviruses were detected at one10log unit below the density of enteroviruses in sediments and cockles and were not detected in water. Four bacteriophage systems were assayed as indicators of human enteric viruses: somatic coliphages ofE.coli C, sexual and sexual-RNA coliphages plated onSalmonella WG49 and phages againstBacteroides fragilis HSP40. The results obtained from 2 lagoon stations sampled in summer, autumn and winter showed that the four systems failed to indicate the presence of enteroviruses and rotaviruses in water, sediment and shellfish samples. The absence of phages ofB. fragilis HSP40 in all types of samples taken from the lagoon, but not from the residual waters of the treatment station, suggests that they may suffer a strong negative pressure in this ecosystem as their proportion to the coliphages in the cockles deviated strongly from the ratio of 1∶100 to 1∶1000 observed at the sewage outfall. In fact, no correlation was observed between these phages and enteric viruses or coliphages. Alternatively, it is possible that the importance of diffuse faecal pollution and the interference of faecal pollutants of animal origin, including migratory sea birds which are abundant in winter, can alter the proportions of the faecal bacteriophages beyond recognition. It is apparent that bacteriophage monitoring of the health risk linked to the occurrence of viruses in the marine environment is not yet fully resolved, what may leave viral quality assessment dependent on direct detection of human enteric virus.

Factors affecting the distribution of benthic and littoral rotifers in a large marine lagoon, together with the description of a new species

Factors affecting the distribution of benthic and littoral rotifers in a large marine lagoon, together with the description of a new species

Ecological observations on juvenile flatfish in a tropical coastal system, Puerto Rico

Juvenile flatfish were sampled in Puerto Rico in a number of different habitat types: river mouths, beach systems, estuarine lagoons and marine lagoons. Out of 16 species occurring around Puerto Rico, seven were found, of the family Bothidae: the bay whiff Citharichthys spilopterus, the sand whiff C. arenaceus, the fringed flounder Etropus crossotus and the channel flounder Syacium micrurum, of the family Solidae: the lined sole Achirus lineatus and the scrawled sole Trinectes inscriptus, and of the family Cynoglossidae: the blackcheek tonguefish Symphurus plagiusa. Species composition varied among areas and appeared to be related to habitat requirements. Depending on species, settlement was prolonged over a period from 1 to at least 6 months. Abundances of 0-group were low, in general less than 10 ind·100 m −2. Preliminary growth estimates in Citharichthys spilopterus were within the range of those observed in subtropical waters at the same temperatures.

Seasonal Variations in Benthic Community Metabolism and Nitrogen Dynamics in a Shallow, Organic-Poor Danish Lagoon

The dynamics of benthic primary production and community respiration in a shallow oligotrophic, marine lagoon (Fællestrand, Denmark) was followed for 1·5 years. The shape of the annual primary production cycle was explained primarily by seasonal changes in temperature ( r 2 = 0·67-0·72) and daylength ( r 2 = 0·63), whereas temperature almost explained all variation in benthic community respiration ( r 2 = 0·83-0·87). On a daily basis the benthic system was autotrophic during spring and summer supplied by 'new' and 'regenerated' nitrogen and predominantly heterotrophic during fall and winter caused by light and nutrient limitation. The linear depth-relationship between porewater alkalinity and ammonium indicated that the C:N ratio of mineralized organic matter is low in spring and summer (3-6) and high in fall and winter (9-16). This is inversely related to net primary production and thus the input of labile, nitrogen-rich algal cells. Accordingly, mineralization occurred predominantly in the upper 2-5 cm of the sediment. The pool of reactive material (microalgal cells) was estimated to account for 12% of total organic carbon in the upper 3 cm, and had an average turnover time of less than 1 month in summer. Assimilation of organic carbon by benthic animals was equivalent to about 30% of the annual gross primary production. Grazing reduced chlorophyll a concentration in the sediment during summer and spring to values 30-40% lower than in winter, but maintained a 3-4 times higher specific microalgal productivity. The rapid turnover of organic carbon and nitrogen, and important role of benthic microalgae showed that the benthic community in this oligotrophic lagoon is of a very dynamic nature.

Strategy of eel ( Anguilla anguilla L.) exploitation in the Thau lagoon

Fisheries activity in the Thau marine lagoon (Mediterranean coast of France) rests mainly upon the eel, Anguilla anguilla L. It involves several types of gears: nets, traps and lines, that are used with varying frequencies in different areas at different parts of the year. We showed that the various types of gear select for different fish size classes, with each method focusing on a particular part of the eel stock; that lives at a particular depth. Data was collected weekly during 28 months. Time series analysis (contingency periodogram) made it possible to reveal significant periods of 6 and 12 months in the landings and in the fishing effort data series. Hypotheses about the influence of environmental determinants on the behaviour of fish and fishermen and on the interactions between them, and effects on landings, were tested using the method of path analysis; we found that effort is the most important determinant of landings, while temperature and lunar coefficient also have an effect. The resulting models differ depending on the type of gear under study: ‘capechades’ on the one hand, used mostly by occasional fishermen, and ‘triangles’, ‘brandines’ and longlines on the other, used mostly by resident fishermen.

Diel vertical migration in zooplankton: field evidence in support of the predator avoidance hypothesis

We report results of a field test of the predator avoidance hypothesis as an explanation of the adaptive significance of diel vertical migration in zooplankton. We determined the vertical distribution and diel migration of the planktonic copepod Acartia hudsonica, concurrently with the abundance of pelagic fish, transparency and thermal stratification of the water column, on six cruises over a one year period in a temperate marine lagoon (Jakles Lagoon, San Juan Island, Washington, USA). Striking seasonal variability was observed in all biological and environmental variables. Linear regressions of the strength of diel vertical migration in A. hudsonica on these environmental variables resulted in only one statistically significant relationship, that between copepod diel vertical migration and predator abundance. These results, together with those of previous studies, point to diel vertical migration as a widespread behavioral response of planktonic prey to the presence of their predators.

Marginal Erg Facies: A Trial Approach toward a Descriptive Classification

During the late 1970s and early 1980s, sedimentologists began recognizing the margins of eolian sand seas as separate, components which differed from interior sand seas in geometry, extent, and facies. Stratigraphers have now observed these differences in eolian rocks. Erg margins may be grouped in five ways: (1) by associations with extradunal environments-coastal plain, lacustrine, periglacial, marine (tidal flat, coastal sabkha, beach, and lagoon), and arid alluvial (alluvial fan, fluvial, playa, inland sabkha); (2) by allocyclic controls-eustasy, plate tectonism, and climate; (3) by autocyclic controls-local tectonism, topography, vegetation, hydrology, structure, sediment source and supply, and wind regime; (4) by geographic position-upwind, downwind, and along-wind margins; and (5) by sedimentary facies-texture and architecture. In contrast with erg interiors, erg margins are characterized by smaller, less complex dune-forms related to thinner sand accumulation; elementary dune architecture; more vegetation and bioturbation; high occurrence of sand sheet, zibar, and serir facies; expansive, low-relief interdunes with widely distributed dunes; and a greater proportion of interbedded extradunal deposits. Some of the published studies on ancient eolian systems have identified erg margin facies that have been influences by marine and arid alluvial processes. Few reports have described lacustrine-eolian and periglacial-eolian interactions. This study is an attempt tomore » organize known features of modern and ancient erg margins into a scheme based on erg margin controls.« less

In situphotosynthetic physiology and chlorophyll-protein biochemistry of two dinoflagellate blooms

Photophysiological and biochemical characteristics were defined for a 1981 red-tide of Gonyaulax polyedra along the Santa Barbara coast and a 1980 Exuviella sp. bloom in a marine lagoon. Pigmentation and photosynthesis-irradiance data suggested the G. polyedra population was low-light adapted and nutrient-limited at the time of collection. Analyses of detergent-solubilized chloroplast components indicated that the vast majority of red tide chlorophyll a (Chl a) was organized into four distinct Chl-protein complexes which were biochemically similar to those previously described for a low light clonal isolate of G. polyedra. Differences between laboratory and field populations suggest that Chl c distribution among chromoproteins is regulated by the spectral characteristics of growth irradiance. The Exuviella sp. bloom appeared to be a high-light adapted and nutrient-replete unialgal population at the time of collection. The pigment-protein analysis of Exuviella sp. showed the cellular pigment organization to be also characterized by four major Chl a-containing protein-complexes which were similar to those of other dinoflagellates. Results indicate that the generalized view of chlorophyll organization in dinoflagellates first developed for laboratory clones is applicable to natural red tide populations.

Characterization of biogenic organic matter by stepwise thermogravimetry (STG)

The STG method presented here is a simple approach facilitating the characterization of biogenic organic materials. Pre-dried (130°C and grounded (< 0.5 mm) samples were heated in a muffle furnace at 280 °C for 6 h and subsequently at 520 °C for 6 h. The weight loss in the temperature range, 130–280°C (PI) and 280–520 °C (PII), provided an index (Rp) defined as, Rp = PII/(PI + PII). Plant materials rich in structural carbohydrates generally showed a Rp index around 0.3, whereas Rp for animal tissues rich in proteins usually were around 0.6. A general relationship between Rp and C:N for living biogenic organic matter, ranging from leaves of terrestrial origin to marine invertebrate tissue, was described by the equation: Rp = 0.791 x (C:N)-0.246 (n = 13, r2 = 0.946). During biological decomposition of composting barley straw, Rp increased from 0.17 to 0.37 and C:N decreased from 87 to 16. A similar Rp-C:N pattern was observed with depth in the upper 2 cm of an organic poor marine lagoon sediment (Rp increased from 0.43 to 0.47; C:N decreased from 8.4 to 7.7); indicating that microbial protein synthesis may have occurred with depth in this layer. The observed increase in both Rp and C:N with depth from 2 to 8 cm (Rp increased from 0.47 to 0.52; C:N increased from 7.7 to 10.3) suggested that humification may predominate in this zone. Accordingly, humic acids are found to have a Rp as high as 0.64. The Rp-C:N relationship appears to be a powerful two-dimensional tool applicable to characterize the bulk composition of various biogenic organic materials at different stages of decomposition.

Design for Simultaneous Sampling of Ecological Variables: From Concepts to Numerical Solutions

A multidisciplinary ecological study is in progress in the Thau marine lagoon, on the Mediterranean coast of France. Sampling is being conducted in two phases. Phase 1 is a pre-sampling program (pilot study), spaceand time-intensive, bearing on 10 variables only; it was conducted in 1986 and 1987. During phase 2, that began in 1988, more variables will be studied at fewer stations, and at the most appropriate time scales; the purpose is to increase our understanding of ecological processes through modelling. This paper examines the results of the pre-sampling program and attempts to determine how to distribute samples through space, and through time, in order to best sample the variability of the system. Through space, four methods are proposed to select 20 stations among 63. It is shown that none of the methods always performs better than all others, their power of reproducing the best part of the original variable's variability depending upon the shape of the spatial structure (gradient, patches, hole, etc.). It is also shown that all four methods are far more efficient at rendering the system's variability than either random or systematic sampling designs. Along the time axis, the hourly, daily and monthly sampling scales were compared as to their coefficients of variation for each variable, and the daily and monthly scales were selected as being, overall, the most informative for the processes under study.