SwissSed - past, present and future trends in Swiss sedimentology
Distribution of benthic foraminiferal assemblages in the transitional environment of the Djerba lagoon (Tunisia)
Swiss Journal of Geosciences volume 111, pages 589–606 (2018)
The eastern edge of the Djerba Island represents an important tourist pole. However, studies describing the environmental processes affecting this Island are scarce. Although never studied before, the peculiar Djerba lagoon is well known by the local population and by tourists. In July 2014, surface sediment and seawater samples were collected in this lagoon to measure grain size, organic matter content and living foraminiferal assemblages to describe environmental conditions. Seawater samples were also collected and the concentration of 17 chemical elements were measured by ICP-OES. The results show that a salinity gradient along the studied transect clearly impacts seagrass distribution, creating different environmental conditions inside the Djerba lagoon. Biotic and abiotic parameters reflect a transitional environment from hypersaline to normal marine conditions. Living benthic foraminifera show an adaptation to changing conditions within the different parts of the lagoon. In particular, the presence of Ammonia spp. and Haynesina depressula correlates with hypersaline waters, whilst Brizalina striatula characterizes the parts of the lagoon colonized by seagrass. Epifaunal species, such as Rosalina vilardeboana and Amphistegina spp. colonize hard substrata present at the transition between the lagoon and the open sea.
Coastal lagoons are present in all continents and are water bodies, generally parallel to the coast line, and separated from the ocean by barriers and by one to more inlets. Water salinity can vary from very low (fresh water) to high (hypersaline conditions), depending on the hydrological balance (Kjerfve 1994).
A large number of lagoons are present in the Mediterranean Sea. One of the largest and thoroughly studied mainly because of the intense anthropogenic impacts (e.g., tourism) is the Venice lagoon in Italy (e.g. Sfriso et al. 1987, 1992; Livingstone et al. 1995; Bellucci et al. 2002). Additional lagoons along the Italian coast have also been investigated (Bouchet et al. 2018). Other lagoons like Berre and Thau (France) (e.g. Arfi 1989; Point et al. 2007; Chambouvet et al. 2011; Delpy et al. 2012); Mar Menor (Spain) (e.g. García-Pintado et al. 2007); Paradeniz (Turkey) (e.g. Türkmen et al. 2011); and Marina (Egypt) (e.g. El-Gamal et al. 2012) have been studied as a consequence of anthropogenic practices (e.g., tourism, agriculture, sewage) leading to pollution concerns. Along the Tunisian coast, the Bizerte, Ghar El Melh (e.g. Chouba et al. 2007) and El Bibane lagoons (Vela et al. 2008) are known to be impacted by heavy metals, organic pollutants. The most studied is the Bizerte lagoon, located in the northern part of Tunisia (e.g. Mzoughi et al. 2005; Dridi et al. 2007; Louiz et al. 2008; Ben-Ameur et al. 2012; Martin et al. 2015, 2016). The high population density and the industrial activities around this large (over 150 km2) lagoon represent an environmental threat. The lagoon of Bizerte is therefore of major interest to assess its environmental quality (Martins et al. 2015 and references therein). Although a large part of the Tunisian costal environments have been studied, some important areas were neglected or poorly investigated. For example, the Eastern edge of the Djerba Island is one of the least explored regions in Tunisia, where only grain size distribution related to the dynamic of coastal currents has been studied (Brahim et al. 2014).
Located in front of the south-eastern coast of Tunisia, the Djerba Island is the largest island (Fig. 1) and is surrounded by the Gulf of Gabes to the North and by the Boughrara lagoon to the South-east. Approximatively 2 km long and 200 m wide, the Djerba lagoon can be considered as small in comparison to the other Tunisian lagoons. Its northern and western parts are the shallowest whereas the southern part is the deepest. A natural channel connects the lagoon to the sea. Based on the classification of Kjerfve (1986), the Djerba lagoon is a choked lagoon as it connects to the Sea by a single channel. Tidal currents acting along the eastern coast of Djerba modulate the hydrology of the lagoon (Brahim et al. 2014) because tides in this region are some of the highest in the Mediterranean Sea (Sammari et al. 2006). The water depth inside the lagoon varies depending on the tide amplitude although it never exceeds 2 m, following the semidiurnal tide, and the water flows out of the lagoon twice a day.
Most coastal areas in the world are impacted by some level of pollution (Shahidul and Tanaka, 2004) and coastal lagoons are especially vulnerable to anthropogenic activities because they represent ideal environments for different economical activities such as fishing, aquaculture, tourism and agriculture which affect their ecology (Gamito 2008 and references therein). The geographical position of the Djerba lagoon makes it particularly exposed to anthropogenic-related pollution since tourism is very intense especially during summer.
The arid climate in southern Tunisia, has also a strong impact on the environmental setting of the Djerba lagoon. High temperature, low precipitation, changing circulation patterns and the heterogeneity of the sediments in the lagoon may impact and influence environmental conditions of the ecosystems within a few meters.
Benthic foraminifera have been used since the 1960s to describe marine environments (e.g., Schönfeld et al. 2012). Their high density in marine sediments, high species variability, short life cycle and the good preservation of tests in marine sediments make these organisms an ideal tool to describe and monitor marine environments (Gooday 2003; Jorissen et al. 2007; Schönfeld et al. 2012). Coupling investigations on living benthic foraminiferal assemblages with environmental parameters (e.g., physiochemical parameters, grain size, and sedimentary facies) may allow to better understand the environmental and ecological conditions in the Djerba lagoon. Availability of organic matter (OM) in sediments, representing as a food source, can influence the benthic species distribution, including foraminifera (e.g., Martins et al. 2015).
Eutrophication of marine environments can be the result of anthropogenic activity, which is induced by an increasing supply of OM into the ecosystems (Nixon 1995). The eutrophic state of marine environments can be described using OM (and its compounds) as a proxy because it reflects a higher primary productivity due to the increase of nutrient input (Dell’Anno et al. 2002, Martin et al. 2015, 2016).
Heavy metals, although minor elements in seawater, are also good pollution and/or anthropogenic indicators (Callender 2003).
The aim of this study is to describe for the first time the Djerba lagoon by investigating hydrodynamic patterns, seagrass meadow distribution and water physiochemical parameters. This approach will allow to describe the environmental conditions that characterize the different parts of the lagoon and to correlate them with living benthic foraminiferal distributions. This study also provides a preliminary assessment of the anthropogenic impact on this lagoon.
Material and methods
Sampling and station description
Ten stations have been sampled (LA-01 to LA-10) in the Djerba lagoon on July 2014. Stations are located along a transect from the internal to the external part of the lagoon (Table 1 and Fig. 2). Most of the stations are located inside the lagoon, only station LA-10 is located outside the lagoon on the rocky substrate on the eastern side of the lagoon.
For each station, surface grab sediment (the first centimeter) and seawater samples were collected. Two sub-samples were collected: (1) approximatively 15 cm3 of sediment per station were collected in falcon tubes for geochemical analyses (Rock–Eval, stable carbon isotope ratio of OM, C, H, N elemental analysis) and were stored at 4 °C; (2) around 50 cm3 of surface sediment samples were collected for living (stained) foraminiferal assemblage analysis following Schönfeld et al. (2012) protocols. Sediments were placed in a rose Bengal solution (2 g/L in alcohol at 90%) for at least 14 days to stain living foraminifera. At station LA-10 two different sediment samples were taken: (i) sediment layout on the bottom of cavities (LA-10a) (ii) sediment trapped in the algal carpet (LA-10b). Both samples (LA-10a and LA-10b) were also analyzed for living foraminifera, only the sediment trapped in the algae carpet were used for geochemistry.
At each station, 120 mL of surface seawater samples were collected in high density polyethylene Nalgene® bottles. Seawater samples were acidified (pH 1) by adding 5 mL of concentrated nitric acid to avoid precipitation of coordination complexes and were stored at 4 °C.
Sediment and seawater analysis
Surface sediment samples for geochemical analysis were dried in a ventilated oven at 35 °C until reaching a constant weight. Rock–Eval analyses were performed on approximatively 100 mg of bulk surface sediment previously crushed in an agate mortar. Rock–Eval analyses were performed following Rock–Eval6 technology to obtain total organic carbon (TOC) content (wt%), hydrogen index (HI), oxygen index (OI), S1 S2 and S3 peaks, maximal temperature (Tmax) and mineral carbon (MINC) content on approximately 100 mg bulk sediment. HI correspond to the free hydrocarbons present in the sample (mg HC/g TOC, measured on S1 peak) and OI to the amount of hydrocarbons containing oxygen that are produced during the thermal cracking of kerogen (mg CO2/g TOC, measured on S2 and S3 peaks). Tmax is measured at the maximum of S2 peak. High temperatures (up to 850 °C) allow MINC determination through mineral carbon oxidation (Espitalié et al. 1985; Lafargue et al. 1998).
Total carbon, hydrogen and nitrogen (C, H, N) contents (in wt%) were measured in the surface sediment samples using a Thermo Finnigan Flash EA 1112 gas chromatography analyser. Rock-Eval and C, H, N analyses were performed at the laboratory of Sediment Geochemistry at the University of Lausanne on approximately 100 mg bulk sediment.
Carbonate minerals in surface sediment were dissolved using a 10% HCl solution at 50 °C. This process was repeated twice and the sediment was rinsed with milli-Q water. Stable carbon isotope ratio of OM (δ13COM) from surface sediment samples were measured at the Stable Isotopes Laboratory of the University of Lausanne by flash combustion on a Carlo Erba 1108 elemental analyser connected to a Thermo Fisher Scientific Delta V Plus isotope ratio mass spectrometry that was operated in a continuous helium flow mode via a Conflo III split interface.
Major elements (Na, Mg, S, K, Ca and Sr) and trace elements (Li, Al, Si, P, Cr, Mn, Fe, Ni, Cu, As, and Cd) were measured in seawater samples by inductively coupled plasma optical emission spectroscopy (ICP-OES) at ATI Aquaristik lab at Hamm in Germany. Measurements were performed with a Spectro Arcos 2 ICP-OES analyser with four points of calibration for major elements and eight points of calibration for trace elements. For each sample and each chemical element, four measurements were performed and corresponding average values were calculated. Every five measurements, a control sample was measured to check the stability of the plasma torch and to avoid any shift during the set of measurements.
Concentration factors (CF) were calculated from the ICP-OES data set. The concentration of each element and of each sample was divided by the concentration of a reference seawater sample, considered as representing normal seawater conditions. Station LA-10 was chosen as the reference site to represent values of seawater because it is located outside the lagoon.
Grain size analysis was performed on the stained (rose Bengal) surface sediments. The samples were wet sieved through four mesh sieves: 500, 250, 125 and 63 µm. Each fraction (< 63, 63–125; 125–250; 250–500 and > 500 µm) was dried in a ventilated oven at 35 °C and weighed to calculate the proportion (wt%).
Following the FOBIMO protocols (Schönfeld et al. 2012), stained foraminifera were picked from plummer cells for each size fraction. Taxonomy was done to species level following the work of Cimerman and Langer (1991), Hottinger and Halicz (1993), Loeblich and Tappan (1994), Milker and Schmiedl (2012). Quantitative data were treated with the software Primer 6 (Clarke and Gorley 2006). The number of living foraminifera (for each species) per samples was standardize for an equivalent volume of sediment of 100 cm3, then the data set was double square root transformed to limit the contribution of most abundant species (Field et al. 1982). The Bray–Curtis (dis-)similarity was calculated and used to obtain the non-metric MultiDimensional Scaling-nMDS plots. The contribution of each species to the total average similarity and dissimilarity between different groups and within single groups where determined by using the similarity percentage analysis (SIMPER). The density of living foraminifera was calculated for every station by dividing the number of living specimens by the total volume of sediment. To compare the diversity pattern of living (stained) benthic foraminifera, in addition to the number of species per stations, the Shannon-Index (H′) and Fisher’s α Index were calculated with the software Primer 6 (Clarke and Gorley 2006).
Sedimentary and environmental facies
Based on the visual sample description and in situ observation of the sampling sites, five facies were distinguished (Fig. 2):
Facies A groups stations LA-01 and LA-02, it correspond to the inner part of the lagoon. The main characteristic of this facies is the abundance of living Cerithium vulgatum (gastropod).The numerous furrows on the sediments’ surface confirm this observation. The water depth was very shallow in comparison to the other areas of the lagoon (< 10 cm).
Facies B groups stations LA-03 and LA-04. This facies is characterized by the presence of numerous burrows. Unfortunately, the organisms responsible for these burrows were not observed and thus, could not be identified.
Facies C groups station LA-05 and LA-08. This facies does not show any peculiar characteristics, sediments are close to pure sand. However, station LA-05 is located on a country road crossing the lagoon.
Facies D groups stations LA-06, LA-07 and LA-09. This facies is characterized by the seagrass Posidonia oceanica.
Facies E is represented by station LA-10. The bottom is a consolidated sandstone and is probably beachrock. However, numerous cavities present are filled by soft sediments of two types: (i) sediment layout at the bottom of the cavity (i.e. LA-10a). (ii) sediment trapped by a carpet of algae on the wall of these cavities (i.e. LA-10b).
Sediment grain sizes are fairly evenly distributed across all stations. However, sample LA-10a which is relatively coarser (Fig. 3) with the fractions > 500 and 250–500 µm reaching 71 and 19 wt%, respectively. In addition, samples LA-07 and LA-09 are dominated by the fraction 125–250 µm ranging between 31 and 40 wt%, respectively. The finest fraction (< 63 µm) is the least represented and does not exceed 20 wt% except in sample LA-01 with values reaching 27 wt%.
The results of the geochemical analyses are presented in Table 2. TOC values are generally very low for all samples. The maximum TOC content is observed in sample DJB-10 with 0.9 wt%, however, in general, TOC fluctuates from 0.07(LA-04) to 0.5% (LA-01). MINC values are relatively low in the inner part of the lagoon and increase towards the outer part. Minimum and maximum MINC values are reached respectively at station LA-04 and LA-09 with 3.62 and 9.04 wt%. The HI values do not fluctuate significantly among samples varying from 213 (LA-07) to 373 mg HC/g TOC (LA-01), whereas, OI oscillates from 298 (LA-10) to 823 mg CO2/g TOC (LA-06). These data was used in this study to determine the provenance of the sedimentary OM (Fig. 4): (i) HI vs OI plot is widely used to represent the origin of the sedimentary OM, however the plots are out of the different delimited areas for the kerogen type. (ii) HI vs Tmax plot indicates a kerogen type IIb (Delvaux et al. 1990). (iii) S2 vs TOC plot confirms the type II kerogen (Langford and Blanc-Valleron 1990).
Total nitrogen (TN) contents are low and do not exceed 0.088 wt% (LA-10) with some samples being below the detection limit (LA-03, LA-04 and LA-06). Total carbon contents have similar trends as the MINC, with a maximum of 9.074 wt% for sample LA-10 and a minimum of 3.583 wt% for sample LA-04. Total hydrogen content is relatively high in sample LA-01 with 1 wt% but low for all other samples, fluctuating from 0.066% (LA-04) to 0.288% (LA-10). Stable carbon isotopic composition of OM is similar for all samples, ranging between – 16.7‰ (LA-04) to – 14.6‰ (LA-09).
Concentration and CF of major and minor elements in seawater are shown in Tables 3 and 4. In general the lowest concentrations of major elements are found at station LA-10. Sodium and magnesium have respectively concentrations of 11,869 and 1399 mg/L. Sulfur has also a relatively low concentration with 945 mg/L followed by Ca and K with respectively 462 and 442 mg/L. Strontium has the lowest concentration at station LA-10 with only 8.4 mg/L. An almost two-fold increase in major element concentrations was observed from the external (LA-10) to the internal parts of the lagoon (LA-01). However, the concentration of major elements in seawater is relatively similar in stations LA-06 and LA-10 and their CF is equal to 1. For samples between LA-01 to LA-05, the CF did not exceeded 1.8 for all major elements.
Concentration factors of most minor elements in the seawater are different than those of major elements. Generally, the CF of minor elements increased from station LA-10 to LA-01, with the exception of Cd (CF = 1), As (CF slightly decreasing from stations LA-10 and LA-01) and Cr (CF < 1.4, except for station LA-05). Concentration factors of Li have similar trends as major elements. Silicon reaches its highest concentration factor at station LA-01, with a value of 23.6. Concentration factors of P, Al, Fe and Mn fluctuate from station LA-10 to LA-01, they reach maximum factors at station LA-05 and LA-01, respectively.
Living foraminifera and multivariate analyses
Living foraminiferal diversity is relatively high in the lagoon. Ninety-six living species have been identified (Online Resource 1). Fourteen species (> 7% of relative abundance on at least one station) represent at least 60% of all living specimens (LA-10a). The distribution of the 14 most dominant species changes significantly along the transect (Figs. 3, 5). The inner part of the lagoon is dominated by Haynesina depressula and Ammonia spp., although the species Ammonia tepida is only present at stations LA-01 and LA-02. Brizalina striatula, Glabratella altispira, Mychostomina revertens become progressively more abundant from station LA-05 to station LA-10, although in variable amounts. The abundance of Rosalina vilardeboana increases significantly from station LA-05 to LA-06 and is especially abundant at station LA-10b. Abditodentrix rhomboidalis and Amphistegina lessonii are present, but only dominant in station LA-10. Specimen density and number of species per station have similar trends along the transect (Figs. 3, 5). They are relatively low in the inner part of the lagoon, especially at station LA-01 (1.3 specimen/cm3 of sediment and only 4 living species). The density of living foraminifera shows an increasing trend from station LA-01 to LA-10. Some fluctuation in abundances are observed at station LA-02 and LA-09, station LA-10b has a very high living specimen density, with 99 specimens/cm3 of sediment. The number of species shows a continuous increase trend from station LA-01 to LA-10, except samples LA-09 and LA-10a, which show a slight decrease in comparison to station LA-08. Sample LA-10b shows the highest species number with 48 species. Species richness varies from 4 to 48. The Shannon Index (H′) reaches lowest value on station LA-02 with 0.69 and has the highest score of 2.42 on station LA-10 (Fig. 3). The Fisher α Index displays values between 0.58 and 11.86. Both diversity Indexes show similar trends with the number of species per stations (Online Resource 1) and increase from station LA-02 to LA-10 with a marked decrease on station LA-09.
Based on the Bray–Curtis Similarity and n-MDS plots, two clusters are identified in the dendrogram. Cluster 1 groups samples LA-01 to LA-07 with Ammonia parkinsoniana (57.51%), Haynesina depressula (19.45%) and Elphidium incertum (7.31%) as dominant species and is interpreted as representing the internal part of the lagoon. Cluster 2 groups samples LA-08, LA-09, LA-10b and LA-10b representing the external parts of the lagoon with Brizalina striatula (21.09%), Rosalina vilardeboana (18.37%), and Rosalina bradyi (7.12%) as the dominant species.
Impact of water parameters on the marine flora and macrofauna
Water parameters are important factors controlling the distribution of the flora and fauna in the marine environment (Ruivo 1973). In coastal regions, the water parameter that has a major impact on the distribution and density of flora and fauna is salinity (e.g. Bulger et al. 1993; Montague and Ley 1993; Lamptey and Armah 2008). Unfortunately, during the sampling campaign, we were not equipped to record salinity measurements (e.g., with electrical conductivity meter, refractometer for seawater, seawater density meter). Therefore, in the present study, major elements are used to estimate salinity in the Djerba lagoon. A clear increase in the concentration of major chemical elements from the open sea towards the internal part of the lagoon was observed (Fig. 3). Based on CF the lagoon can be divided into two parts: (i) an external part close to the open sea characterized by normal saline seawater with CF ≤ 1. (LA-06, LA-07, LA-08, LA-09 and LA-10). (ii) An internal part that can be considered as hypersaline with a salinity that can be estimated to be around 1.5 times higher than normal seawater conditions (LA-01, LA-02, LA-03, LA-04 and LA-05). However, the seawater sampling was performed during the rising tide and it has to be taken in account that the current probably influences the internal part of the lagoon close to the channel. Stations LA-06 and LA-07 can be regarded as transitional stations where the salinity (i.e. CF) can significantly fluctuate depending to the tide level.
The concentrations of major elements in the internal part of the lagoon are directly linked to the arid climate. This is especially true in the summer, when increased evaporation may increase salinity to hypersaline values (Kjerfve et al. 1996). Reduced seawater exchange between the internal part of the lagoon and the open sea may also be responsible for the hypersaline conditions as this is characteristic of choked lagoons with longer flushing times (Kjerfve 1994). The entrance of the lagoon may act as a dynamic filter significantly reducing the strength of tidal current and thus, seawater flow exchange toward the inside of the lagoon (Kjerfve 1994). In addition, the arched morphology of the channel may contribute to decrease the strength of the tidal current. This difference in the tidal current strength is expressed by the presence of moving sand banks (Fig. 2) between the lagoon entrance and the sharp bend of the lagoon.
A relationship exists between the CF and the P. oceanica seagrass meadow distribution inside the lagoon of Djerba. Posidonia oceanica is present only in areas where the CF does not exceed 1, although P. oceanica is absent in two stations (LA-08 and LA-10). In the case of station LA-10 the rocky sea floor may prevent the roots of P. oceanica from colonizing the substrate, and in case of LA-08 (> 10 cm of the water depth) the very shallow water conditions may prevent the development and vertical growth of P. oceanica leaves.
Several studies demonstrated the sensitivity of P. oceanica to hypersaline conditions (Fernández-Torquemada and Sánchez-Lizaso 2005; Gacia et al. 2007; Sanchez-Lizaso et al. 2008). Brine discharges from desalination plants may increase the salinity of seawater and have a negative impact on P. oceanica meadows (e.g., Platja de Mitjorn on the Island of Formentera; Alicante in Spain) (Fernández-Torquemada et al. 2005; Gacia et al. 2007). Laboratory experiments have demonstrated that when seawater salinity exceeds 39.1 psu, marine vegetation mortality increases, while at 45 psu, 50% of the marine vegetation died within 15 days. However, P. oceanica is able to recover to normal growth when exposed to short hypersaline episodes (Fernández-Torquemada and Sánchez-Lizaso 2005).
Google Earth is an efficient tool to observe landscape evolution through time. Satellite images of Djerba lagoon, dating back to July 10th 2003, are available on Google Earth (https://www.google.com/earth/) where the distribution of Posidonia oceanica is clearly visible on satellite images. The comparison of images from 2003 with the present distribution of P. oceanica suggests no spatial/temporal variation and no seasonal effects. This observation indicates that the salinity of the Djerba Lagoon has not changed since 2003.
If the hypersaline environment is not favorable for P. oceanica, it may possibly provide a suitable ecological niche for other marine macro-organisms, such as C. vulgatum. This marine gastropod is very common along the Mediterranean Sea coast in shallow water marine ecosystems. The diet of this gastropod consists of diatoms and epibenthic microalgae (Nicolaidou and Nott 1999). Hypersaline conditions can be considered as an important stressor on marine organisms leading to a decrease in biodiversity, coupled with a reduced competition among marine organisms. Well-adapted and/or stress-tolerant organisms to natural fluctuations in environmental conditions can thus proliferate and dominate specific ecological niches, as C. vulgatum does in the innermost parts of the lagoon.
Organic matter: origin and trophic state
Organic matter is an essential food resource in marine environments and can also impact faunal and/or microfaunal distribution (e.g., Whitlatch 1981; Mojtahid et al. 2009). The amount and the origin of this food resource allows for better understanding of ecological processes in marine environments (e.g., Whitlatch 1981; Lopez and Levinton 1987) in addition to providing information on trophic resources.
Rock–Eval pyrolysis can be successfully used in environmental studies to determine the type of kerogen which indicates the origin of the OM. Type I kerogen is indicative of lacustrine environments, Type II kerogen of marine environments and type III of terrestrial environments (Espitalié et al. 1985). However, some study differentiate the Type IIa kerogen (marine) and Type IIb (mixed marine/terrestrial) (e.g., Delvaux et al. 1990). Some limitations on Rock–Eval pyrolysis exist due to the low TOC content and where HI and OI should be interpreted with caution. Below 0.3% of TOC, a very limited amount of hydrocarbons can be produced which may induce low S1 and S2 peaks and form a wide gentle hump (Nunez-Betelu and Baceta 1994). In addition, values lower than 0.2 mg HC/g sediment (S2 peak) may influence on Tmax because the S2 peak becomes broad and low and hen the top of the peak cannot be accurately defined (Nunez-Betelu and Baceta 1994). The classical HI versus OI graph prevents a precise determination of the kerogen type (Fig. 4) because of the high OI values. Adsorption of CO2 is possibly induced by low TOC content in the sediments (Table 2) (Nunez-Betelu and Baceta 1994). In addition high carbonate mineral content increases the OI during the heating process of Rock–Eval analysis (Katz 1983) and may therefore represent serious limitations in the interpretation of the OM content.
The graphs S2 vs TOC and HI vs Tmax (Fig. 4) indicate that the OM composition is relatively homogenous along the lagoon of Djerba, and is mainly composed by type II kerogen. This kerogen type reflects a mix marine and terrestrial OM origin (Langford and Blanc-Valleron 1990; Delvaux et al. 1990). The type II kerogen is mostly composed by amorphous kerogen (e.g. planktonic material) and exinite (e.g. pollen, cuticle of leave and herbaceous plants). This mixed provenance of OM can be easily explained: in a coastal environment, planktonic material can be carried inside the lagoon by tidal currents, while the terrestrial OM origin is due to the presence of vegetation such as date palm trees on the western shore of the lagoon of Djerba. Organic matter can also come from the seagrass P. oceanica. This seagrass species presents similarities with land plants as it possesses cuticles and contains a high amount of cellulose (Nunez-Betelu and Baceta 1994; Khiari et al. 2010). Stable carbon isotope composition signal of OM from surface sediment correlates well with land plants and with P. oceanica. Enriched δ13COM values (> – 18.5‰) is typical for C4 land plants (Smith and Epstein 1971; Hedges et al., 1997). The δ13COM of P. oceanica ranges from – 19.7 to – 10.8‰ (Cooper and DeNiro 1989; Vizzini et al. 2002; Lepoint et al. 2003; Vizzini et al. 2003), which corresponds to δ13COM values measured inside the lagoon of Djerba (Table 2).
The relatively high TOC content at station LA-10 (Table 2) can be explained by the algae carpet which traps the sediment, however, we cannot exclude a contribution of OM from the beachrock itself. Strasser et al. (1989) noticed organic compounds (e.g. algae, roots residue) in the beachrock from Bahiret el Biban (southeastern Tunisia). In addition, Vousdoukas et al. (2007) noticed OM associated with microbial structures in the beachrock. Environmental conditions in station LA-01 are extreme (high salinity coupled with high water temperature) and the TN content is relatively high in comparison to the other stations (Table 2). As a nutrient, nitrogen and phosphorus can influence the productivity of microalgae and increase the TOC content in the sediments, hence creating eutrophic conditions (Nixon 1995; Taylor et al. 1995). Following Smith (2003), the concentration in total phosphorus on station LA-01 (Table 4) is indicative of a very high nutrient pollution level (> 31 µg/L of total phosphorus) for a coastal marine ecosystem and thus contribute probably to form eutrophic conditions at this station. High nutrient pollution level together with high sedimentary OM content indicate a high primary productivity which is the definition of eutrophication (Nixon 1995). High primary productivity may explain the high density of C. vulgatum as it provides an ideal food source for this gastropod. In contrast, low TOC content in the rest of the lagoon (LA-03 to LA-09) (Table 2) may possibly be related to the coarse sediment present in the lagoon. Coarse sediment may allow better oxygen diffusion into the sediments, promoting mineralization of OM and leading to the decrease of TOC content (Tyson 1995). Despite these low values (except for stations LA-01 and LA-10), the TOC content shows a consistent gradient in the Djerba lagoon probably due to the constant OM flux from tidal currents. However, we also suggest a possible ecological link between OM content and P. oceanica meadow distribution. During its life cycle, P. oceanica, regenerates its leafs (Ott 1980) and leaf litter represents a significant OM source laying on the surface sediment (Romero et al. 1992; Lepoint et al. 2006).
Benthic foraminifera as bioindicators
Foraminifera are good bioindicators that can provide valuable information about environmental conditions (e.g. Alve 1991; Kaiho 1994; Hallock et al. 2003; Mateu-Vicens et al. 2010; Dimiza et al. 2016). Changes in foraminiferal assemblages can be related to changes of environmental physiochemical parameters (e.g., pH, dissolved oxygen), OM, or substrate type. Living benthic foraminiferal assemblages change significantly within the Djerba lagoon (Fig. 3) based on variations in physiochemical parameters, tidal currents and seagrass distribution. Previous studies demonstrated that some foraminiferal species are sensitive to variations in grain size (e.g., Murray 2006). However in the case of the study area, grain size is fairly homogeneous within the entire lagoon and its possible influence on foraminiferal assemblages can be excluded.
Living benthic foraminiferal assemblages suggest a division of the lagoon into two parts (Fig. 6) separated by the channel, acting as a natural barrier between the internal and the external parts of the lagoon. The channel represents a dynamic environment due to the action of tidal currents that have shaped its present morphology. The channel also acts as a preferential flowing path for the tidal flow, thus reducing tidal energy towards the internal lagoon preventing the transport of foraminifera between internal and external parts of the lagoon.
Ammonia parkinsoniana is one of the most abundant species along a large part of the lagoon and is especially dominant in the internal part. Ammonia parkinsoniana can be considered as stress tolerant because it is a dominant species in the NorthwesternGulf of Mexico under highly variable environmental condition (Gupta et al. 1996 and references therein). In addition, in Puerto Rican bays and lagoons, this species is abundant in fine-grained, polluted and organic-rich sediments (Gupta et al. 1996 and references therein). Ammonia parkinsoniana is also abundant in the Bizerte lagoon and this species is common in transitional environments under seawater influence (Martins et al. 2016) such as Djerba lagoon.
The hypersaline environment directly impacts benthic foraminiferal density in the internal part of the lagoon where species numbers is lower than in its external part. The dominance of Ammonia tepida reflects the extreme hypersaline conditions and high water temperature in the internal edge of the lagoon. In particular, A. tepida was observed in shallow marine environments and lagoons (Frontalini et al. 2009) and is tolerant to thermal pollution. Ammonia spp. is also known to be very tolerant to hypersaline environments (Walton and Sloan 1990; Murray 2006). Another dominant species in the hypersaline internal part of the lagoon is H. depressula. This species is known to colonize sandy substrate in inner shelf environments and is tolerant to brackish water intolerant to salinity higher than 50 psu (Murray 2006). However, this species was identified in several locations along the Gulf of Saros (Turkey) in environments where salinity reached over 50 psu (Bassler-Veit et al. 2013). Based on the concentration factor and the normal seawater salinity in the southern coast of Tunisia (~ 37 psu) (Béranger et al. 2004), the present study suggests that salinity can exceed 55 psu in the part of the lagoon where H. depressula is dominant and confirms the ecological tolerance of this species to high salinity.
Elphidium incertum is relatively abundant in the internal part of the lagoon (Online Resource 1). It is described as uncommon in bays, marshes and in lagoon barriers (Phleger 1965). In the northern Gulf of Mexico, E. incertum is typical for brackish inlet-influenced outer lagoon environments (Otvos 1985). This species is less abundant than Ammonia spp. in the internal part of Djerba lagoon and its presence is probably not directly related to the salinity conditions like H. depressula. Elphidium incertum was also observed in the inner part of Flensburg Fjord (SW Baltic Sea), where high organic matter content in the muddy sediment provides ideal living conditions (Polovodova et al. 2009). Murray (2006), indicates that E. incertum prefers shallow infaunal habitats in sandy substrates, with high oxygen positively impacting on its reproduction. In the Djerba lagoon, the abundances of E. incertum correlate with burrows and seagrass in the internal lagoon. Burrows from macrofaunal activity increase oxygenation in the first centimeters of sediment, and P. oceanica, as a marine plant, supplies oxygen through photosynthesis, providing ideal conditions for E. incertum to develop.
A strong correlation exists between the presence of B. striatula and the distribution of the seagrass P. oceanica. The genus Brizalina has an infaunal mode of life and has specific resistance to oxygen depletion in the environment (Murray 2006). Generally, taxa, which are tolerant to low oxygen conditions are typical of muddy substrates that can accumulate high amounts of organic matter (Van der Zwaan et al. 1999). In the Djerba lagoon, the presence of B. striatula and its preference for oxygen-depleted environments does not match with the observed low OM content and the coarse sediments. However, low oxygen tolerant species and low oxygen conditions can be associated to seagrass decaying in sediments (Mateu-Vicens et al. 2014). In addition, the trophic preference of brizalinids for organic detritus (Murray 2006) suggests that remains of P. oceanica could be a potential food resource.
The abundance of the epifaunal Rosalina vilardeboana and Amphistegina lessonii at station LA-10 can be explained by the hard substratum (Murray 2006). The beachrock located in the eastern part of the lagoon is an ideal environment for their development. The genus Amphistegina is widely used to assess water quality because of its fast response to environmental changes (e.g. water temperature) (e.g. Emrich et al. 2017; de Freitas Prazeres et al. 2012; Hallock et al. 2003). The abundance of Amphistegina spp. and its sensitivity to water quality deviating from normal conditions (e.g., Hallock et al. 2003) confirms the normal marine conditions at the external part of the lagoon. Water quality influencing the development of R. vilardeboana are poorly described in the literature. However this species was described as opportunistic in a benthic foraminiferal culturing system (Hintz et al. 2004). Erginal et al. (2013) describe this species as an indicator of shallow water. However, the present study confirms that R. vilardeboana shows affinity for substrates with more abundant organic carbon and is influenced by the distribution of Posidonia oceanica (Buosi et al. 2012).
The changes in the living foraminiferal assemblages within the lagoon is the consequence of an important environmental zonation due to changes in salinity, water depth, presence/absence of seagrass and type of substrate along a 2 km area. Biotic and abiotic changes reflect the transition from hypersaline conditions from the internal part of the lagoon to normal marine conditions in its external part.
Is there an anthropogenic impact on the lagoon?
The Gulf of Gabes is well known to be severely polluted by one of the main industrial phosphate treatment complex in Tunisia. Many studies have demonstrated a negative impact of this pollution on marine flora such as P. oceanica (e.g. El Zrelli et al. 2017), or on macrofauna like the coral Cladocora caespitosa (El Kateb et al. 2016). The geographic position of the Djerba lagoon, within the center of the touristic area of the Djerba Island, makes it particularly vulnerable to the pollution by tourist activities. Despite of human activities around the Djerba lagoon (e.g., tourism), only few signs of eutrophic conditions were noticed. High nutrient contents on station LA-01 were not clearly defined as anthropogenic origin. Urban sewage close to station LA-01 could be one explanation for high phosphorus content (Gilabert 2001). However, remineralization of OM under warm temperatures carried at the station LA-01 could release phosphorus from the sediment (Nixon 1982) and induce eutrophic conditions. High heavy metal content in marine or terrestrial environments is generally interpreted as a sign of contamination by anthropogenic activities. In the case of the Djerba lagoon, the concentration of metal elements in the seawater is relatively low (Table 4). Concentration factors of minor elements are significantly different depending on the element. Processes can control trace metal concentrations in seawater, such as active biological processes, which can remove trace metals from seawater (Bruland and Lohan 2006). Redox cycling of metals can also influence trace metal concentrations in seawater (Morel and Price 2003). The cause of high CF for silicon (Table 4) on the station LA-01 is not clearly defined. However, the eutrophic state of this station is suspected as a possible factor for quartz solubility. In agreement with the biogeochemical cycle of Si (Basile-Doelsch et al. 2005) siliceous sources in seawater are provide by silicate minerals of endogenous rocks. Quartz is one of the main substrate minerals in the Djerba lagoon. Several studies (Bennett and Siegel 1987; Bennett et al. 1988; Bennett 1991) show the influence of organic acid/compounds on the quartz solubility and quartz dissolution kinetics. Organic matter decay caused by eutrophic conditions probably releases dissolved organic acid/compounds in water and thus increase the solubility of quartz. However, further investigations are needed to confirm this hypothesis. A peculiar behavior of concentrate factors of some minor elements was noticed at station LA-05 (Table 4), corresponding geographically to the country road crossing the Djerba lagoon. This country road is used by tourists to cross the lagoon with vehicles. The increase in seawater of the concentration factors for P, Al, Cr, Fe and Mg at the country road station (LA-05) is probably the result of intense tourist passage on this country road crossing the lagoon. In addition, the lowest living foraminiferal specimen density is reached when in close proximity to this road (Fig. 3). Although the road side site may be slightly impacted by tourism, our preliminary results suggest a minor anthropogenic impact in the Djerba lagoon.
The Djerba lagoon is a transitional environment from hypersaline to normal marine conditions. The high salinity in the inner lagoon is due to the shallow water depth combined with the arid climate (e.g., warm weather and high solar radiation). The variation in salinity has a direct impact on seagrass distribution and creates small-scale ecological niches for macro fauna in the internal part of the lagoon. A clear zonation in the distribution of living foraminiferal assemblages was noticed in the Djerba lagoon. A channel seems to act like a natural barrier, separating the internal and the external part of the lagoon. Based on these observations, the lagoon represents a unique ecosystem in the Djerba Island.
Alve, E. (1991). Benthic foraminifera in sediment cores reflecting heavy metal pollution in Sorfjord, western Norway. Journal of Foraminiferal Research, 21(1), 1–19.
Arfi, R. (1989). Annual cycles and budget of nutrients in Berre Lagoon (Mediterranean Sea, France). International Review of Hydrobiology, 74(1), 29–49.
Basile-Doelsch, I., Meunier, J. D., & Parron, C. (2005). Another continental pool in the terrestrial silicon cycle. Nature, 433(7024), 399–402.
Bassler-Veit, B., Barut, I. F., Meric, E., Avsar, N., Nazik, A., Kapan-Yeşilyurt, S., et al. (2013). Distribution of microflora, meiofauna, and macrofauna assemblages in the hypersaline environment of northeastern Aegean Sea coasts. Journal of Coastal Research, 29(4), 883–898.
Bellucci, L. G., Frignani, M., Paolucci, D., & Ravanelli, M. (2002). Distribution of heavy metals in sediments of the Venice Lagoon: The role of the industrial area. Science of the Total Environment, 295(1), 35–49.
Ben-Ameur, W. B., de Lapuente, J., El Megdiche, Y., Barhoumi, B., Trabelsi, S., Camps, L., et al. (2012). Oxidative stress, genotoxicity and histopathology biomarker responses in mullet (Mugil cephalus) and sea bass (Dicentrarchus labrax) liver from Bizerte Lagoon (Tunisia). Marine Pollution Bulletin, 64(2), 241–251.
Bennett, P. C. (1991). Quartz dissolution in organic-rich aqueous systems. Geochimica et Cosmochimica Acta, 55(7), 1781–1797.
Bennett, P. C., Melcer, M. E., Siegel, D. I., & Hassett, J. P. (1988). The dissolution of quartz in dilute aqueous solutions of organic acids at 25 °C. Geochimica et Cosmochimica Acta, 52(6), 1521–1530.
Bennett, P., & Siegel, D. I. (1987). Increased solubility of quartz in water due to complexing by organic compounds. Nature, 326(6114), 684–686.
Béranger, K., Mortier, L., Gasparini, G. P., Gervasio, L., Astraldi, M., & Crépon, M. (2004). The dynamics of the Sicily Strait: A comprehensive study from observations and models. Deep Sea Research Part II: Topical Studies in Oceanography, 51(4), 411–440.
Bouchet, V. M., Goberville, E., & Frontalini, F. (2018). Benthic foraminifera to assess Ecological Quality Statuses in Italian transitional waters. Ecological Indicators, 84, 130–139.
Brahim, M., Atoui, A., Sammari, C., & Aleya, L. (2014). Surface sediment dynamics along the eastern coast of Djerba Island (Gabes Gulf, Tunisia). Journal of African Earth Sciences, 92, 45–54.
Bruland, K. W., & Lohan, M. C. (2006). Controls of trace metals in seawater. The oceans and marine geochemistry, 6, 23–47.
Bulger, A. J., Hayden, B. P., Monaco, M. E., Nelson, D. M., & McCormick-Ray, M. G. (1993). Biologically-based estuarine salinity zones derived from a multivariate analysis. Estuaries and Coasts, 16(2), 311–322.
Buosi, C., Châtelet, E. A. D., & Cherchi, A. (2012). Benthic foraminiferal assemblages in the current-dominated Strait of Bonifacio (Mediterranean Sea). The Journal of Foraminiferal Research, 42(1), 39–55.
Callender, E. (2003). Heavy metals in the environment—Historical trends. In B.S. Lokkar (Ed.), Environmental geochemistry, H.D. Holland, K.K. Turekian (Eds.), Journal of treatise on geochemistry (pp. 67–106). Elsevier: Pergamon Oxford.
Chambouvet, A., Laabir, M., Sengco, M., Vaquer, A., & Guillou, L. (2011). Genetic diversity of Amoebophryidae (Syndiniales) during Alexandrium catenella/tamarense (Dinophyceae) blooms in the Thau lagoon (Mediterranean Sea, France). Research in Microbiology, 162(9), 959–968.
Chouba, L., Kraiem, M., Njimi, W., Tissaoui, C. H., Thompson, J. R., & Flower, R. J. (2007). Seasonal variation of heavy metals (Cd, Pb and Hg) in sediments and in mullet, Mugil cephalus (Mugilidae), from the Ghar El Melh Lagoon (Tunisia). Transitional Waters Bulletin, 1(4), 45–52.
Cimerman, F., & Langer, M. R. (1991). Mediterranean Foraminifera (Vol. 30, p. 118). Ljubljana, Dela Opera.
Clarke, K. R., & Gorley, R. N. (2006). PRIMER v6: User Manual/Tutorial. Primer-E: Plymouth.
Cooper, L. W., & DeNiro, M. J. (1989). Stable carbon isotope variability in the seagrass Posidonia oceanica: evidence for light intensity effects. Marine Ecology Progress Series, 50(3), 225–229.
de Freitas Prazeres, M., Martins, S. E., & Bianchini, A. (2012). Assessment of water quality in coastal waters of Fernando de Noronha, Brazil: Biomarker analyses in Amphistegina lessonii. Journal of Foraminiferal Research, 42(1), 56–65.
Dell’Anno, A., Mei, M. L., Pusceddu, A., & Danovaro, R. (2002). Assessing the trophic state and eutrophication of coastal marine systems: a new approach based on the biochemical composition of sediment organic matter. Marine Pollution Bulletin, 44(7), 611–622.
Delpy, F., Pagano, M., Blanchot, J., Carlotti, F., & Thibault-Botha, D. (2012). Man-induced hydrological changes, metazooplankton communities and invasive species in the Berre Lagoon (Mediterranean Sea, France). Marine Pollution Bulletin, 64(9), 1921–1932.
Delvaux, D., Martin, H., Leplat, P., & Paulet, J. (1990). Geochemical characterization of sedimentary organic matter by means of pyrolysis kinetic parameters. Organic Geochemistry, 16(1–3), 175–187.
Dimiza, M. D., Triantaphyllou, M. V., Koukousioura, O., Hallock, P., Simboura, N., Karageorgis, A. P., et al. (2016). The Foram Stress Index: A new tool for environmental assessment of soft-bottom environments using benthic foraminifera. A case study from the Saronikos Gulf, Greece. Eastern Mediterranean. Ecological Indicators, 60, 611–621.
Dridi, S., Romdhane, M. S., & Elcafsi, M. H. (2007). Seasonal variation in weight and biochemical composition of the Pacific oyster, Crassostrea gigas in relation to the gametogenic cycle and environmental conditions of the Bizert lagoon, Tunisia. Aquaculture, 263(1), 238–248.
El Kateb, A., Stalder, C., Neururer, C., Pisapia, C., & Spezzaferri, S. (2016). Correlation between pollution and decline of Scleractinian Cladocora caespitosa (Linnaeus, 1758) in the Gulf of Gabes. Heliyon, 2(11), e00195.
El Zrelli, R., Courjeault-Radé, P., Rabaoui, L., Daghbouj, N., Mansour, L., Balti, R., Castet, S., Attia, F., Michel., S., & Bejaoui, N. (2017). Biomonitoring of coastal pollution in the Gulf of Gabes (SE, Tunisia): Use of Posidonia oceanica seagrass as a bioindicator and its mat as an archive of coastal metallic contamination. Environmental Science and Pollution Research. https://doi.org/10.1007/s11356-017-9856-x.
El-Gamal, A. A., Peterson, R. N., & Burnett, W. C. (2012). Detecting freshwater inputs via groundwater discharge to Marina Lagoon, Mediterranean Coast, Egypt. Estuaries and coasts, 35(6), 1486–1499.
Emrich, K., Martinez-Colon, M., & Alegria, H. (2017). Is untreated seawage impacting coral reefs of Caye Caulker, Belize? Journal of Foraminiferal Research, 47(1), 20–33.
Erginal, A. E., Ekinci, Y. L., Demirci, A., Bozcu, M., Ozturk, M. Z., Avcioglu, M., et al. (2013). First record of beachrock on Black Sea coast of Turkey: Implications for Late Holocene sea-level fluctuations. Sedimentary Geology, 294, 294–302.
Espitalié, J., Deroo, G., & Marquis, F. (1985). La pyrolyse Rock-Eval et ses applications. Première partie. Revue de l’Institut français du Pétrole, 40(5), 563–579.
Fernández-Torquemada, Y., & Sánchez-Lizaso, J. L. (2005). Effects of salinity on leaf growth and survival of the Mediterranean seagrass Posidonia oceanica (L.) Delile. Journal of Experimental Marine Biology and Ecology, 320(1), 57–63.
Fernández-Torquemada, Y., Sánchez-Lizaso, J. L., & González-Correa, J. M. (2005). Preliminary results of the monitoring of the brine discharge produced by the SWRO desalination plant of Alicante (SE Spain). Desalination, 182(1–3), 395–402.
Field, J. G., Clarke, K. R., & Warwick, R. M. (1982). A practical strategy for analysing multispecies distribution patterns. Marine ecology progress series, 8(1), 37–52.
Frontalini, F., Buosi, C., Da Pelo, S., Coccioni, R., Cherchi, A., & Bucci, C. (2009). Benthic foraminifera as bio-indicators of trace element pollution in the heavily contaminated Santa Gilla lagoon (Cagliari, Italy). Marine Pollution Bulletin, 58(6), 858–877.
Gacia, E., Invers, O., Manzanera, M., Ballesteros, E., & Romero, J. (2007). Impact of the brine from a desalination plant on a shallow seagrass (Posidonia oceanica) meadow. Estuarine, Coastal and Shelf Science, 72(4), 579–590.
Gamito, S. (2008). Three main stressors acting on the Ria Formosa lagoonal system (Southern Portugal): Physical stress, organic matter pollution and the land–ocean gradient. Estuarine, Coastal and Shelf Science, 77(4), 710–720.
García-Pintado, J., Martínez-Mena, M., Barberá, G. G., Albaladejo, J., & Castillo, V. M. (2007). Anthropogenic nutrient sources and loads from a Mediterranean catchment into a coastal lagoon: Mar Menor, Spain. Science of the Total Environment, 373(1), 220–239.
Gilabert, J. (2001). Seasonal plankton dynamics in a Mediterranean hypersaline coastal lagoon: The Mar Menor. Journal of Plankton Research, 23(2), 207–218.
Gooday, A. J. (2003). Benthic foraminifera (Protista) as tools in deep-water palaeoceanography: Environmental influences on faunal characteristics. Advances in Marine Biology, 46, 1–90.
Gupta, B. K. S., Turner, R. E., & Rabalais, N. N. (1996). Seasonal oxygen depletion in continental-shelf waters of Louisiana: Historical record of benthic foraminifers. Geology, 24(3), 227–230.
Hallock, P., Lidz, B. H., Cockey-Burkhard, E. M., & Donnelly, K. B. (2003). Foraminifera as bioindicators in coral reef assessment and monitoring: The FORAM Index. Environmental Monitoring and Assessment, 81(1–3), 221–238.
Hedges, J. I., Keil, R. G., & Benner, R. (1997). What happens to terrestrial organic matter in the ocean? Organic Geochemistry, 27(5), 195–212.
Hintz, C. J., Chandler, G. T., Bernhard, J. M., McCorkle, D. C., Havach, S. M., Blanks, J. K., et al. (2004). A physicochemically constrained seawater culturing system for production of benthic foraminifera. Limnology and Oceanography: Methods, 2(6), 160–170.
Hottinger, L., & Halicz, E. R. (1993). Recent Foraminiferida from the Gulf of Aqaba, Red Sea (Vol. 33, p. 412) Ljubljana, Dela Opera.
Jorissen, F., Fontanier, C., & Thomas, E. (2007). Paleoceanographical proxies based on deep-sea benthic foraminiferal assemblage characteristics. In C. Hillaire-Marcel & A. de Vernal (Eds.), Proxies in late cenozoic paleoceanography (pp. 227–242). Amsterdam: Elsevier.
Kaiho, K. (1994). Benthic foraminiferal dissolved-oxygen index and dissolved-oxygen levels in the modern ocean. Geology, 22(8), 719–722.
Katz, B. J. (1983). Limitations of ‘Rock-Eval’pyrolysis for typing organic matter. Organic Geochemistry, 4(3–4), 195–199.
Khiari, R., Mhenni, M. F., Belgacem, M. N., & Mauret, E. (2010). Chemical composition and pulping of date palm rachis and Posidonia oceanica–A comparison with other wood and non-wood fibre sources. Bioresource Technology, 101(2), 775–780.
Kjerfve, B. (1986). Comparative oceanography of coastal lagoons. In D. A. Wolfe (Ed.), Estuarine variability (pp. 63–81). New York: Academic.
Kjerfve, B. (1994). Coastal lagoons. In B. Kjerfve (Ed.), Coastal lagoon processes (Vol. 60, pp. 1–8). Amsterdam: Elsevier Oceanographic Series.
Kjerfve, B., Schettini, C. A. F., Knoppers, B., Lessa, G., & Ferreira, H. O. (1996). Hydrology and salt balance in a large, hypersaline coastal lagoon: Lagoa de Araruama, Brazil. Estuarine, Coastal and Shelf Science, 42(6), 701–725.
Lafargue, E., Marquis, F., & Pillot, D. (1998). Rock-Eval 6 applications in hydrocarbon exploration, production, and soil contamination studies. Revue de l’institut français du pétrole, 53(4), 421–437.
Lamptey, E., & Armah, A. K. (2008). Factors affecting macrobenthic fauna in a tropical hypersaline coastal lagoon in Ghana, West Africa. Estuaries and Coasts, 31(5), 1006–1019.
Langford, F. F., & Blanc-Valleron, M. M. (1990). Interpreting Rock-Eval pyrolysis data using graphs of pyrolizable hydrocarbons vs. total organic carbon (1). AAPG Bulletin, 74(6), 799–804.
Lepoint, G., Cox, A. S., Dauby, P., Poulicek, M., & Gobert, S. (2006). Food sources of two detritivore amphipods associated with the seagrass Posidonia oceanica leaf litter. Marine Biology Research, 2(5), 355–365.
Lepoint, G., Dauby, P., Fontaine, M., Bouquegneau, J. M., & Gobert, S. (2003). Carbon and nitrogen isotopic ratios of the seagrass Posidonia oceanica: Depth-related variations. Botanica Marina, 46(6), 555–561.
Livingstone, D. R., Lemaire, P., Matthews, A., Peters, L. D., Porte, C., Fitzpatrick, P. J., et al. (1995). Assessment of the impact of organic pollutants on goby (Zosterisessor ophiocephalus) and mussel (Mytilus galloprovincialis) from the Venice Lagoon, Italy: Biochemical studies. Marine Environmental Research, 39(1–4), 235–240.
Loeblich Jr, A. R. & Tappan, H. (1994). Foraminifera of the Sahul Shelf and Timor Sea (p. 661.) Cushman Foundation for Foraminiferal Research, Special Publication 31.
Lopez, G. R., & Levinton, J. S. (1987). Ecology of deposit-feeding animals in marine sediments. The Quarterly Review of Biology, 62(3), 235–260.
Louiz, I., Kinani, S., Gouze, M. E., Ben-Attia, M., Menif, D., Bouchonnet, S., et al. (2008). Monitoring of dioxin-like, estrogenic and anti-androgenic activities in sediments of the Bizerta lagoon (Tunisia) by means of in vitro cell-based bioassays: Contribution of low concentrations of polynuclear aromatic hydrocarbons (PAHs). Science of the Total Environment, 402(2), 318–329.
Mateu-Vicens, G., Box, A., Deudero, S., & Rodríguez, B. (2010). Comparative analysis of epiphytic foraminifera in sediments colonized by seagrass Posidonia oceanica and invasive macroalgae Caulerpa spp. The Journal of Foraminiferal Research, 40(2), 134–147.
Martins, M. V. A., Helali, M. A., Zaaboub, N., Boukef-BenOmrane, I., Frontalini, F., Reis, D., et al. (2016). Organic matter quantity and quality, metals availability and foraminiferal assemblages as environmental proxy applied to the Bizerte Lagoon (Tunisia). Marine Pollution Bulletin, 105(1), 161–179.
Martins, M. V. A., Zaaboub, N., Aleya, L., Frontalini, F., Pereira, E., Miranda, P., et al. (2015). Environmental quality assessment of Bizerte Lagoon (Tunisia) using living foraminifera assemblages and a multiproxy approach. PLoS One, 10(9), e0137250.
Mateu-Vicens, G., Khokhlova, A., & Sebastián-Pastor, T. (2014). Epiphytic foraminiferal indices as bioindicators in Mediterranean seagrass meadows. Journal of Foraminiferal Research, 44(3), 325–339.
Milker, Y., & Schmiedl, G. (2012). A taxonomic guide to modern benthic shelf foraminifera of the western Mediterranean Sea. Palaeontologia electronica, 15(2), 1–134.
Mojtahid, M., Jorissen, F., Lansard, B., Fontanier, C., Bombled, B., & Rabouille, C. (2009). Spatial distribution of live benthic foraminifera in the Rhône prodelta: Faunal response to a continental–marine organic matter gradient. Marine Micropaleontology, 70(3), 177–200.
Montague, C. L., & Ley, J. A. (1993). A possible effect of salinity fluctuation on abundance of benthic vegetation and associated fauna in northeastern Florida Bay. Estuaries and Coasts, 16(4), 703–717.
Morel, F. M. M., & Price, N. M. (2003). The biogeochemical cycles of trace metals in the oceans. Science, 300(5621), 944–947.
Murray, J. W. (2006). Ecology and applications of benthic foraminifera (p. 426). Cambridge: Cambridge University Press.
Mzoughi, N., Lespes, G., Bravo, M., Dachraoui, M., & Potin-Gautier, M. (2005). Organotin speciation in Bizerte lagoon (Tunisia). Science of the Total Environment, 349(1), 211–222.
Nicolaidou, A., & Nott, J. A. (1999). The role of the marine gastropod Cerithium vulgatum in the biogeochemical cycling of metals. Nato Science Series 2 Environmental Security, 59, 137–146.
Nixon, S. W. (1982). Nutrient dynamics, primary production and fisheries yields of lagoons. Oceanologica Acta, Special Issue, 357–371.
Nixon, S. W. (1995). Coastal marine eutrophication: A definition, social causes, and future concerns. Ophelia, 41(1), 199–219.
Nunez-Betelu, L., & Baceta, J. I. (1994). Basics and application of Rock-Eval/TOC pyrolysis: An example from the uppermost Paleocene/lowermost Eocene in the Basque Basin, Western Pyrenees. Munibe Ciencias naturales, 46, 43–62.
Ott, J. A. (1980). Growth and production in Posidonia oceanica (L.) Delile. Marine Ecology, 1(1), 47–64.
Otvos, E. G. (1985). Barrier platforms: Northern Gulf of Mexico. Marine Geology, 63(1–4), 285–305.
Phleger, F. B. (1965). Patterns of living marsh foraminifera in south Texas coastal lagoons. Boletin de la Sociedad Geologica Mexicana, 28(1), 1–44.
Point, D., Monperrus, M., Tessier, E., Amouroux, D., Chauvaud, L., Thouzeau, G., et al. (2007). Biological control of trace metal and organometal benthic fluxes in a eutrophic lagoon (Thau Lagoon, Mediterranean Sea, France). Estuarine, Coastal and Shelf Science, 72(3), 457–471.
Polovodova, I., Nikulina, A., Schönfeld, J., & Dullo, W. C. (2009). Recent benthic foraminifera in the Flensburg Fjord (western Baltic Sea). Journal of Micropalaeontology, 28(2), 131–142.
Romero, J., Pergent, G., Pergent-Martini, C., Mateo, M. A., & Regnier, C. (1992). The detritic compartment in a Posidonia oceanica meadow: Litter features, decomposition rates, and mineral stocks. Marine Ecology, 13(1), 69–83.
Ruivo, M. (1973). Marine pollution and sea life (p. 664). London: Fishing News.
Sammari, C., Koutitonsky, V. G., & Moussa, M. (2006). Sea level variability and tidal resonance in the Gulf of Gabes, Tunisia. Continental Shelf Research, 26(3), 338–350.
Sanchez-Lizaso, J. L., Romero, J., Ruiz, J., Gacia, E., Buceta, J. L., Invers, O., et al. (2008). Salinity tolerance of the Mediterranean seagrass Posidonia oceanica: Recommendations to minimize the impact of brine discharges from desalination plants. Desalination, 221(1–3), 602–607.
Schönfeld, J., Alve, E., Geslin, E., Jorissen, F., Korsun, S., & Spezzaferri, S. (2012). The FOBIMO (FOraminiferal BIo-MOnitoring) initiative—Towards a standardised protocol for soft-bottom benthic foraminiferal monitoring studies. Marine Micropaleontology, 94, 1–13.
Sfriso, A., Marcomini, A., & Pavoni, B. (1987). Relationships between macroalgal biomass and nutrient concentrations in a hypertrophic area of the Venice Lagoon. Marine Environmental Research, 22(4), 297–312.
Sfriso, A., Pavoni, B., Marcomini, A., & Orio, A. A. (1992). Macroalgae, nutrient cycles, and pollutants in the Lagoon of Venice. Estuaries and Coasts, 15(4), 517–528.
Shahidul, I. M., & Tanaka, M. (2004). Impacts of pollution on coastal and marine ecosystems including coastal and marine fisheries and approach for management: A review and synthesis. Marine Pollution Bulletin, 48(7–8), 624–649.
Smith, V. H. (2003). Eutrophication of freshwater and coastal marine ecosystems a global problem. Environmental Science and Pollution Research, 10(2), 126–139.
Smith, B. N., & Epstein, S. (1971). Two categories of 13C/12C ratios for higher plants. Plant Physiology, 47(3), 380–384.
Strasser, A., Davaud, E. & Jedoui, Y. (1989). Carbonate cements in Holocene beachrock: example from Bahiret el Biban, southeastern Tunisia. Sedimentary Geology, 62, 23–46.
Taylor, D., Nixon, S., Granger, S., & Buckley, B. (1995). Nutrient limitation and the eutrophication of coastal lagoons. Marine Ecology Progress Series, 127(1/3), 235–244.
Türkmen, M., Türkmen, A., & Tepe, Y. (2011). Comparison of metals in tissues of fish from Paradeniz Lagoon in the coastal area of Northern East Mediterranean. Bulletin of Environmental Contamination and Toxicology, 87(4), 381.
Tyson, R. V. (1995). Abundance of organic matter in sediments: TOC, hydrodynamic equivalence, dilution and flux effects. In R. V. Tyson (Ed.), Sedimentary organic matter (pp. 81–118). Dordrecht: Springer.
Van der Zwaan, G. J., Duijnstee, I. A. P., Den Dulk, M., Ernst, S. R., Jannink, N. T., & Kouwenhoven, T. J. (1999). Benthic foraminifers: proxies or problems?: A review of paleocological concepts. Earth-Science Reviews, 46(1), 213–236.
Vela, A., Pasqualini, V., Leoni, V., Djelouli, A., Langar, H., Pergent, G., et al. (2008). Use of SPOT 5 and IKONOS imagery for mapping biocenoses in a Tunisian Coastal Lagoon (Mediterranean Sea). Estuarine, Coastal and Shelf Science, 79(4), 591–598.
Vizzini, S., Sarà, G., Mateo, M. A., & Mazzola, A. (2003). δ13C and δ15N variability in Posidonia oceanica associated with seasonality and plant fraction. Aquatic Botany, 76(3), 195–202.
Vizzini, S., Sara, G., Michener, R. H., & Mazzola, A. (2002). The role and contribution of the seagrass Posidonia oceanica (L.) Delile organic matter for secondary consumers as revealed by carbon and nitrogen stable isotope analysis. Acta Oecologica, 23(4), 277–285.
Vousdoukas, M. I., Velegrakis, A. F., & Plomaritis, T. A. (2007). Beachrock occurrence, characteristics, formation mechanisms and impacts. Earth-Science Reviews, 85(1-2), 23–46.
Walton, W. R., & Sloan, B. J. (1990). The genus Ammonia Bruennich, 1772; Its geographic distribution and morphologic variability. Journal of Foraminiferal Research, 20(2), 128–156.
Whitlatch, R. B. (1981). Animal-sediment relationships in intertidal marine benthic habitats: Some determinants of deposit-feeding species diversity. Journal of Experimental Marine Biology and Ecology, 53(1), 31–45.
Editorial handling: W. Winkler.
Electronic supplementary material
Below is the link to the electronic supplementary material.
Supplementary material 1 (XLSX 30 kb) Online Resource 1: Diversity indexes, counting and contribution (%) of living (stained) foraminifera in surface sediment samples
About this article
Cite this article
El Kateb, A., Stalder, C., Neururer, C. et al. Distribution of benthic foraminiferal assemblages in the transitional environment of the Djerba lagoon (Tunisia). Swiss J Geosci 111, 589–606 (2018). https://doi.org/10.1007/s00015-018-0300-0
- Djerba Island
- Transitional environment


Finally spotted the elusive penguin! They have several species here. The Blue Eyed Penguins are the smallest and only active at night but we’ve seen a few in nesting boxes. Watched 3 Yellow Eyed Penguins along the beach and then made their way to their nests. Most of the penguins are tagged so they can track their travel patterns and monitor population which is declining.


For twenty-nine years, UBC’s Project Seahorse has been bringing awareness to the threats to seahorses, along with innovations in conservation.
Program leader Dr. Sarah Foster has been working with Project Seahorse for over twenty years, originally as a volunteer after finishing her master’s degree in Fish Physiology. “I was looking for a way to contribute more to the world, while still geeking out on fish,” she recalls.
She remembers being out at night with lantern fishers and seeing her first seahorse in the wild – and the wonderment she felt. Seahorses are evolutionary marvels, being the only known species with male pregnancy. We often hear of scientists discovering species in the ocean that we didn’t even know we have. It makes Foster wonder, “Are we negatively impacting species that we don’t even know are in the ocean?”
iSeahorse is one of their projects, ten years in the making. A community of scientists, conservationists, and citizen scientists around the world report sightings on iSeahorse, helping keep tabs on seahorse populations, habitats, and their conservation status. Sightings logged on the platform are validated, and this information can extend known habitat ranges, depth distribution, habitat use, and breeding season.
“If we don’t know what the ocean floors were like before bottom trawling began, how can we say how we’re really doing?”
Of the 44 known species of seahorses, at least 14 species are threatened. Of those, eight are vulnerable to extinction, and 17 are labelled as “Data Deficient” – meaning they are unable to be assessed for The International Union for Conservation of Nature’s Red List. This lack of a designation impedes conservation decisions and policy.
Project Seahorse has developed a way to model threats by estimating cumulative human impact (CHI) at the species level. The researchers are now calling on the United Nations Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) and local managers to use species-level modelling, so that threat-mitigation plans can be tailored to protect species – rather than a broad-stroke approach on ecosystems. This species-specific modelling could estimate conservation status “for thousands of Data Deficient species on the IUCN Red List,” says Project Seahorse website.
Foster spent many years focusing on fisheries and trade, so she has “seen many more dead and dried seahorses than living.” Through trade surveys, the project estimates 25 million seahorses are dried alive for the Traditional Medicine Trade. Project Seahorse mapped the human impact of 12 human-created stressors, and found the most severe pressure to be grossly non-selective bottom trawling.
“A mark of the intensity of such bottom trawling globally,” Project Seahorse researchers found, “is that catches of only one or two seahorses per vessel per night amounted to a total extraction of more than 11 million seahorses annually from just the first 21 countries we surveyed.” A myriad of other species are impacted, from molluscs to sharks and rays. The catch is unmanaged and unreported, says Project Seahorse.
Hundreds of thousands of bottom trawlers operate all over the world, and more than 80% of the seabed is trawled in some regions, “most of it repeatedly.” Trawling generates 25% of global marine catches, and as much as 50% in Asia. Bottom trawlers drop wide-mouth nets with heavy weights that gouge and scrape the ocean floor. The catch is often sold unsorted “for mere pennies,” as feed for fish farms, chicken feed, fish meal, or fish oil. Government subsidies offset the low value, enabling the cycle of going out in search of all marine life indiscriminately – “annihilation fishing,” as Project Seahorse founder Dr. Amanda Vincent has described it.
“People may say some bottom trawl fisheries are well managed,” says Foster, “but you have to ask – to what reference point?” There is no historical pre-trawling data to compare numbers against. “It might be managed if your only goal is to maintain the catches of the targeted species over a short timeframe, but the picture changes when one considers ocean health more broadly.”
Left in the wake of trawlers are ruined habitat: seagrasses, corals, sponges destroyed. As Pacific Wild states on their website, if our unique glass reefs recover at all, it takes “well over 100 years.” Even the chemistry is changed, found another study of shrimp fisheries. The disturbed sediment interferes with carbon sequestration, re-suspending stored carbon into the water where it can more easily break down. One study has calculated this carbon release to equal the aviation industry.
Some people think the problem can be resolved by regulating mesh size, says Foster, but that doesn’t work when the thing you’re trying to catch and the thing you’re trying to protect are the same size – “They’re going to get caught no matter what.”
Part of the problem is being out of sight, out of mind. When people think of the ocean, they think of a blue expanse, explains Foster. Think of your favourite forest, she illustrates. “If we were using bulldozers to go in and catch a few of the animals, and left the rest behind or ground it up for animal feed, you would be pretty upset.” Getting bottom trawling on the radar, and people talking about it, is how it enters policy dialogues at the government level.
Something people can do on a personal level is to consider how their seafood is caught. It’s spot prawn season here in BC, and as Foster says, “they are ridiculously delicious, local, and caught by traps which are far more sustainable than bottom trawls.”
Foster is cautiously optimistic – “It seems we’re moving towards a more holistic sense of management where we need to look at ocean health in general, and make sure that we have oceans that support livelihoods and food security well into the future.” Circling back to the data deficiencies, Foster asks, “If we don’t know what the ocean floors were like before bottom trawling began, how can we say how we’re really doing?”
Through research and advocacy work, Project Seahorse aims to provide solutions and drive conservation interventions. Phasing out bottom trawling is one focus, along with demanding that governments favour selective fisheries, remove harmful subsidies, enforce laws that control trawling, and implement protected areas that explicitly exclude trawling.
“They’re magical ambassadors for the problems facing the ocean,” says Foster. “The solutions that are going to help seahorses are going to help many other species.”
Learn more about how you can help Project Seahorse take action here.
Odette Auger is Sagamok Anishnawbek through her mother. As a freelance journalist, Odette’s bylines include Watershed Sentinel, The Resolve, La Converse, The Tyee, Asparagus Magazine, and APTN National News. Odette lives on Klahoose, Homalco, and Tla’amin territories (Cortes Island). You can follow all her stories in one place here.


Marine Aquarium of the Zoological Survey of India
10:00 am to 6:00 pm (All days of the weak except Tuesday)
No entry fee (Free)
State Highway 57, Old Digha Main Road, Purba Medinipur, West Bengal 721428, India
Marine Aquarium of the Zoological Survey of India Overview
MARC- Marine Aquarium and Regional Centre is located within an area of 6.5 acres on the Foreshore Road of Digha town, this is a major tourist attraction for all Digha visitors. This is one of the 16th regional centres of Zoological Survey of India under Ministry of Environment and Forests, Government of India. And also it has the largest inbuilt aquarium in India.
The museum houses more than 500 marine species, including fishes, sea snakes, molluscs, corals, crabs, prawns, lobsters, echinoderms, horse-shoe crabs etc. It displays various awareness posters related to marine life, marine biodiversity and conservation. It will help the students and public in raising awareness about marine biodiversity conservation’s as well as serve as a platform for the students having interest on marine biology from all over India.


Late- and postglacial geological evolution of the southern Kattegat connection to the Great Belt was investigated from high-resolution seismic data and radiocarbon-dated sediment cores in order to elucidate the Ancylus Lake drainage/Littorina Sea transgression. It was found that glacial deposits form the acoustic basement and are covered by Lateglacial (LG) marine sediments and postglacial (PG; Holocene) material. The LG deposits form a highstand systems tract, whereas the PG deposits cover a full depositional sequence, consisting of a lowstand systems tract (PG I), transgressive systems tract (PG II; subdivided into three parasequences) and finally a highstand systems tract (PG III). PG I sand deposits (11.7–10.8 cal. ka BP) are found in a major western channel and in a secondary eastern channel. PG II (10.8–9.8 cal. ka BP) consists of estuarine and coastal deposits linked to an estuary located at the mouth of the channels. Both channels drained fresh water from south to north. The PG III, that is younger than 9.8 cal. ka BP, represents the threshold marine flooding at the southeastern branch of the palaeo-Great Belt channel. At 9.3 cal. ka BP, fully marine conditions were established, shortly before the flooding of the threshold to the northern part of the Great Belt. These early Holocene spits and sand bars are preserved as features on the present seabed, probably as a result of the rapid sea-level rise that led to back-stepping of the early Holocene palaeo-coast system. This study shows no evidence of major erosion or delta deposition linked to the emptying of the Ancylus Lake, which suggests that continuous water flow from the south characterized the area, without any major drainage event of the Ancylus Lake impacting the southwestern Kattegat.
- Programområde 5: Natur og klima


Shark attacks dropped sharply worldwide in 2016, reverting to average levels after breaking records in 2015.
There were 81 unprovoked attacks last year, well down from 98 the previous year, according to the International Shark Attack File at the University of Florida. There were four fatal attacks — two in Australia and two in the French South Pacific territory of New Caledonia.
Florida again led the United States, with 32 attacks, up from 30 in 2015. Volusia County, the state's shark-attack capital, recorded 15 attacks, the largest number.
The single South Florida bite took place in Palm Beach County, where a 12-year-old boy was bitten on the foot from a suspected blacktip shark at Ocean Reef Park on Singer Island.
The total does not include bites that are considered provoked. For example, a spearfisherman was bitten on the arm by a bull shark off Singer Island while reeling in a cobia trailing blood. And a snorkeler was bitten by a two-foot nurse shark off Boca Raton after people had been teasing and grabbing at the shark.
George Burgess, curator of the International Shark Attack File, said as more people go in the water to swim and dive and surf, the number of attacks will continue to increase.
"A shark attack is a human phenomenon," he said. "Sharks are a natural part of the ecosystem. The ocean is a foreign environment to humans, and when we enter the sea, we're entering a wilderness."
He attributed the decline from 2015 to the end of El Niño, the warm-water phenomenon in the western Pacific. Warmer weather led sharks to roam farther north and more people took to the water, causing an increase in opportunities for the two to interact.
More than half the attacks worldwide involved people on surfboards, boogie boards or paddle boards, activities that involve kicking and splashing.
"Sharks are attracted to irregular activity, especially with the inevitable wipeout and the big splash that follows," he said. "If you have a shark trailing, that's often when it will strike."
While the number of humans in the water is increasing, the number of sharks is not. Targeted for their fins and meat, many shark species have sustained sharp declines over the past few decades.
"Once shark populations are down, recovery takes a long, long time," Burgess said. "They hold a special place in their ecosystem, and a loss at one node in the web of marine life is going to have an effect on the overall system."


ESP T-Kit on Fishery
M A R YA M E S K A N D A R J O U Y
Understand the concept of Fishery in general
Be able to identify different fishery types
Be familiar with the term ―fish‖ in science
Be able to apply fishery technical words to use in real world
Generally, a fishery is an entity engaged in raising or harvesting fish which is determined by some
authority to be a fishery. According to the FAO, a fishery is typically defined in terms of the "people
involved, species or type of fish, area of water or seabed, method of fishing, class of boats, purpose of
the activities or a combination of the foregoing features". The definition often includes a combination
of fish and fishers in a region, the latter fishing for similar species with similar gear types.
A fishery may involve the capture of wild fish or raising fish through fish farming or
aquaculture. Directly or indirectly, the livelihood of over 500 million people in developing countries
depends on fisheries and aquaculture. Overfishing, including the taking of fish beyond sustainable
levels, is reducing fish stocks and employment in many world regions. If fisheries are poorly
managed, environmental impacts go unchecked. Unsustainable fishing practices put seafood resources
and fishing livelihoods at risk – the United Nations FAO estimates that 11 of the world's 15 major
fishing areas, and 69 percent of the world's major fish species, are in decline and in need of urgent
The term “fish”
In biology – the term fish is most strictly used to describe any animal with
a backbone that has gills throughout life and has limbs, if any, in the shape
of fins. Many types of aquatic animals commonly referred to as fish are not fish in
this strict sense; examples include shellfish, cuttlefish, starfish, crayfish and jellyfish.
In earlier times, even biologists did not make a distinction — sixteenth century
natural historians classified also seals, whales, amphibians, crocodiles,
even hippopotamuses, as well as a host of aquatic invertebrates, as fish.
True fish – The strict biological definition of a fish, above, is sometimes called a
true fish. True fish are also referred to as finfish or fin fish to distinguish them from
other aquatic life harvested in fisheries or aquaculture.
Fisheries are harvested for their value. They can be saltwater or freshwater, wild or farmed. Examples are
the salmon fishery of Alaska, the cod fishery off the Lofoten islands, the tuna fishery of the Eastern Pacific, or
the shrimp farm fisheries in China. Capture fisheries can be broadly classified as industrial scale, small-scale or
artisanal, and recreational.
Close to 90% of the world’s fishery catches come from oceans and seas, as opposed to inland waters. These marine
catches have remained relatively stable since the mid-nineties (between 80 and 86 million tons).
Most fisheries are wild fisheries, but farmed fisheries are increasing. Farming can occur in coastal areas, such as
with oyster farms, but more typically occur inland, in lakes, ponds, tanks and other enclosures.
There are species fisheries worldwide for finfish, mollusks, crustaceans and echinoderms, and by
extension, aquatic plants such as kelp. However, a very small number of species support the majority of the
world’s fisheries. Some of these species are herring, cod, anchovy, tuna, flounder, mullet, squid, shrimp,
salmon, crab, lobster, oyster and scallops. All except these last four provided a worldwide catch of well over
a million tons in 1999, with herring and sardines together providing a harvest of over 22 million metric tons in
1999. Many other species are harvested in smaller numbers.
Overfishing is the act whereby fish stocks are depleted to unacceptable levels, regardless of
water body size. Low biological growth rates and critically low biomass levels result from
overfishing. For example, overfishing of sharks has led to the upset of entire marine
The ability of a fishery to recover from overfishing depends on whether the ecosystem’s
conditions are suitable for the recovery. Dramatic changes in species composition can result in
an ecosystem shift, where other equilibrium energy flows involve species compositions
different from those that had been present before the depletion of the original fish stock. For
example, once trout have been overfished, carp might take over in a way that makes it
impossible for the trout to re-establish a breeding population.
the occupation or industry of catching,
processing, or selling fish or shellfish.
The marine fishery is in steep decline
or even collapse.
a limbless cold-blooded vertebrate
animal with gills and fins and living
wholly in water.
The fossils rarely exhibited any traces
of the soft tissues of fish .
A person who catches fish
for a living or for sport.
Earthworms are then moved to the
surface, much to the fisherman 's delight.
Deplete the stock of fish in (a body of
water) by too much fishing.
Years of badly managed and overfishing
has left tuna in a parlous state.
The series of vertebrae extending from
the skull to the pelvis; the spine.
Cut off head and tail and remove fish
from backbone .
The respiratory organ of aquatic animals,
as fish, that breathe oxygen dissolved
Your fish doesn't have lungs, and gills
only work in water.
A flattened appendage on various parts of
the body of many aquatic vertebrates and
some invertebrates, including fish and
cetaceans, used for propelling, steering, and
The two subspecies differ in color
and size of their dorsal fin .
An aquatic animal is an animal, either
vertebrate or invertebrate, which lives in
water for most or all of its life.
Aquatic animals are subject to pressure
A swimming marine mollusk that
resembles a broad squid, having eight
arms and two long tentacles that are
Among the invertebrates the octopus,
squid and cuttlefish are rather brainy.
An aquatic shelled mollusk or a crustacean
esp. one that is edible.
Allergies to peanuts, tree nuts, and
shellfish tend to be lifelong.
A marine echinoderm with five or more
radiating arms. The undersides of the arms
bear tube feet for locomotion and, in
predatory species, for opening the shells of
It seems to me that the outbreak of
crown-of thorns starfish is a natural event.
A nocturnal freshwater crustacean that
resembles a small lobster and inhabits
streams and rivers.
The predators feed on other fish, as well
as small amounts of crab and crayfish .
A free-swimming marine coelenterate
with a jellylike bell- or saucer-shaped
body that is typically transparent and
has stinging tentacles around the edge.
Their nets are trapping jellyfish : giant,
gelatinous,wobbly and worthless.
A diverse group of semi-aquatic
marine mammals many of which are
commonly called seals
Crops will spread north as seal hunters
A very large marine mammal with a
streamlined hairless body, a horizontal tail
fin, and a blowhole on top of the head for
There is no eel so small but it hopes to
become a whale .
A cold-blooded vertebrate animal of a class
that comprises the frogs, toads, newts, and
There is some chemical that can get into
groundwater and it's bad for fish and
A large predatory semi-aquatic reptile with
long jaws, long tail, short legs, and a horny
textured skin, using submersion and stealth
to approach prey unseen.
Among others at risk: wild ginseng,
orchids and the crocodile newt.
A large thick-skinned semi-aquatic African
mammal, with massive jaws and large
They were found among stone tools
and butchered hippopotamus bones.
A large edible fish that is a popular
game fish, much prized for its pink
flesh. Salmon mature in the sea but
Migrate to freshwater streams to spawn.
Salmon in all their varieties are a
great resource for humanity.
Cod is the common name for the genus
Gadus of demersal fishes, belonging to
the family Gadidae.
In the autumn the dried cod was stored
in depots and sometimes used as
A large and active predatory schooling
fish of the mackerel family.
The fishing potential, mostly lobster
and tuna , is not fully exploited.
An invertebrate of a large phylum that
includes snails, slugs, mussels, and
octopuses. They have a soft,
unsegmented body and live in aquatic
or damp habitats.
All cephalopod mollusks with three
hearts are carnivorous.
A n arthropod of the large, mainly
aquatic group Crustacean, such as a
crab, lobster, shrimp, or barnacle.
Flamingoes, for instance, extract
pink pigments from algae and
A marine invertebrate of the
phylum Echinodermata, such as a
starfish, sea urchin, or sea cucumber.
It is an echinoderm which have
radial symmetry because of its
A large brown seaweed that typically
has a long, tough stalk with a broad
frond divided into strips.
Sea otters eat sea urchins and sea
urchins eat kelp .
A silvery fish that is most abundant in
coastal waters and is of great
commercial importance as a food fish in
many parts of the world.
In my view, juxtaposing these two
choices is a red herring.
A small shoaling fish of commercial
importance as a food fish and as bait.
It is strongly flavored and is usually
preserved in salt and oil.
Try the fried artichokes and a spicy
anchovy bread sauce.
Demersal fish found at the
bottom of coastal lagoons and
estuaries of the Northern Atlantic
and Pacific Oceans.
Flounder are a group of
A chiefly marine fish that is widely
caught for food.
Mullet are so profuse they will literally
jump into a fisherman's boat.
An elongated, fast-swimming
cephalopod mollusk with ten arms,
typically able to change color.
Feeding habits cobia feed primarily
on crabs, squid and other fish.
A small free-swimming crustacean
with an elongated body, typically
marine and frequently harvested for
There is also a thriving fishing
industry, providing shrimp
A crustacean with a broad carapace,
stalked eyes, and five pairs of legs, the
first pair of which are modified as
No crab has ever been attacked by a
truck when standing outside its burrow.
A large marine crustacean with a
cylindrical body, stalked eyes, and the
first of its five pairs of limbs modified
There's no better way to enjoy lobster’s
pure flavor than to have it boiled.
Any of a number of bivalve mollusks
with rough irregular shells.
Therefore the first preparation was
made for the oyster .
An edible bivalve mollusk with a
ribbed fan-shaped shell.
Tales of skate wings cut into circles
and sold as scallops are common.
A young pilchard or other young or small
herring like fish.
The looters may have found a few old
sardine cans but not much else.
The total mass of organisms in a
given area or volume.
Conversion of biomass to bio fuel
can be achieved by different
methods which are broadly classified
into: thermal, chemical, and
A biological community of
interacting organisms and their
Wildebeests, also known as gnus,
shape the ecosystem as they move.


Impacts of aquaculture fish cages and their biomass on the local water current field is investigated with extensive, full scale field measurements. This is important for the fish welfare as well as for waste transport from open fish cages. The relationships between the current flow rate at various locations close to fish cages are examined at an aquaculture marine site close to Frøya, Norway. This is an area with a complex current pattern due to the bathymetry, rocks and islands, coast current and strong wind conditions. An array of ADCPs (Acoustic Doppler Current Profilers) measured currents. Moreover, CTD and separate temperature profiler instruments were made in order to analyse flow stratification. Two different measurement periods are analysed with 1) small fish size (0,2–0,4 kg) and 2) large fish size (1 kg–5 kg). The field measurements indicate some impact from the biomass on the measured current flow at distances from 90 to 320 m around it. The results are supported by results from the numerical ocean model SINMOD (SINtef MODel).


Queen's University, Belfast
|Telephone||+44 (0) 2842727803|
|Departments||School of Natural and Built Environment|
|Quadrat Core Themes||Biodiversity, Environmental Management|
|Methods I Use||Bio / Geo / Chemical Analytical, Modelling|
Key Research Interests
- Environmental interactions of wave and tidal energy devices: Sound emission, animal interaction, changes in
hydrodynamics and the influence on the marine environment.
- Coastal processes including larval and spore dispersal both applied and for restoration purposes.
- The influence of hydrodynamics on macroalgal productivity.
Recent Key Papers
- Schmitt P, Pine M, Culloch R, Lieber L, Kregting L. Noise characterisation of a sub-sea kite. Journal of the American Society of Acoustics. Accepted.
- Lieber, L., Nimmo-Smith, W. A. M., Waggitt, J. J., & Kregting, L. (2018). Fine-scale hydrodynamic metrics underlying predator occupancy patterns in tidal stream environments. Ecological Indicators, 94(1), 307-408. DOI: 10.1016/ j.ecolind.2018.06.071
- Mooney, K. M., Beatty, G. E., Elsäßer, B., Follis, E. S., Kregting, L., O’Connor, N. E., … Provan, J. (2018). Hierarchical structuring of genetic variation at differing geographic scales in the cultivated sugar kelp Saccharina latissima. Marine environmental research. DOI: 10.1016/j.marenvres.2018.09.02
Summary Title of Current Studentships
- The influence of currents and waves on the productivity of Laminaria digitata.
- The interplay of hydrodynamics and invasive species around anthropogenic structures in the marine environment.
- Developing a framework for a flexible and detailed marine renewable energy collision risk model.
- How differences in behaviour can influence functional response in invasive and native species.
- Aquatic Invasive Alien Species: Distribution, Impact, Control & Biosecurity
- Behavioural changes of top predators related to tidal-stream energy extraction – using Unmanned Aerial Vehicles (UAVs) to measure animal distribution.
- QUADRAT DTP student, Rosslyn Watret: Fish Spas: The importance of turbulence on stress levels of fish in dynamic environments
- QUADRAT DTP student, Molly Crowe: Quantifying kelp detrital pathways: what is potentially locked away as Blue Carbon?


This week I discover an oceanographer working here in Slovenia on behalf of the Scottish Association for Marine Science. Emily Venables and a colleague was taking samples of water from all around the Mediterranean as the start of a project to examine the water temperatures and other qualities, something she has done all around the world. Perhaps her most interesting work has been carried out in the Arctic and Antarctic regions but I also discovered that as a keen mountaineer she spent some time on Triglav last year.
Za prikaz vsebine morate omogočiti vtičnike za družbena omrežja (Twitter, Facebook, Scribble, ...), ki uporabljajo piškotke za sledenje uporabnikov. S pritiskom se strinjate z uporabo piškotkov!


Since 2011 MVSG's Shell Recovery Partnership has collected shells from restaurants and events for use in their oyster restoration projects in Tisbury and Edgartown Great Ponds. Although they are most often thrown away as trash, shells are a valuable natural resource. They provide substrate for settling oyster larvae and buffer against coastal acidification, which threatens calcifying animals like shellfish. Hear from Biologist and Executive Director, Emma Green-Beach, how shells are being recycled to build oyster habitat and improve the health of the ponds.
Email firstname.lastname@example.org to sign up and get the Zoom invite.
Wednesday, August 5 at 5:00pm to 6:00pmVirtual Event


Observations of density and velocity in a channel in northern San Francisco Bay show that the onset of vertical density stratification during flood tides is controlled by the balance between the cross-channel baroclinic pressure gradient and vertical mixing due to turbulence. Profiles of velocity, salinity, temperature, and suspended sediment concentration were measured in transects across Suisun Cutoff, in northern San Francisco Bay, on two days over the 12.5-hour tidal cycle. During flood tides an axial density front developed between fresher water flowing from the shallows of Grizzly Bay into the northern side of Suisun Cutoff and saltier water flowing up the channel. North of the front, transverse currents were driven by the lateral salinity gradient, with a top-to-bottom velocity difference greater than 30 cm/s. South of the front, the secondary circulation was weak, and along-channel velocities were greater than to the north. The gradient Richardson number shows that stratification was stable north of the front, while the water column was turbulently mixed south of the front. Time-series measurements of velocity and salinity demonstrate that the front develops during each tidal cycle. In estuaries, longitudinal dynamics predict less stratification during flood than ebb tides. These data show that stratification can develop during flood tides due to a lateral baroclinic pressure gradient in estuaries with complex bathymetry.


Do you think sharks are dangerous? Look this barracuda!!
Do you think sharks are the most ferocious sea creatures? May be not. Take a look to this video and see how barracudas are pretty dangerous.
It shows a fast barracuda attack to a giant trevally almost when it was almost at the boat. Al this happened in Alfonse Island, Seychelles.