Organic Seston Research Articles

Ecological impact of recreational bathing at Las Presillas (Lozoya River, Sierra de Guadarrama National Park, central Spain)

The ecological impacts of recreational uses on the rivers of Sierra de Guadarrama National Park (SGNP) have been scarcely studied. To assess the impacts of these uses at Las Presillas (an area with small dam along a section of the Lozoya River), and in the Lozoya River (upstream and downstream of the dams), the dynamics of the organic seston (FPOM), physicochemical variables (electric conductivity, dissolved oxygen, Temperature, and pH) and biological variables (fecal coliforms, fecal streptococci, and aquatic macroinvertebrates) during the recreational (July to September) and nonrecreational (October) periods were assessed. The variations observed in the physicochemical parameters were associated with autumnal influence. However, at Las Presillas, different values were found than at the rest of the surveyed sites, characterized by an increase in the concentration of FPOM and, human fecal contamination (although they did not reach dangerous levels) and the response of the macroinvertebrate communities, which resulted in a clear decrease in the IBMWP index and other quality metrics, during the recreational period. These findings suggest that the combined effects of the dams and recreational activities at Las Presillas generate functional dynamics in that alter the habitat in summer. The identification and study of these impacts through the application of innovative indices and quality classes that integrate and contextualize Las Presillas in the SGNP monitoring network, have been identified as key management and conservation tools.

The effect of embayment complexity on ecological carrying capacity estimations in bivalve aquaculture sites

Bivalve aquaculture requires the alteration of natural populations of filter-feeders by artificially increasing their density. A bivalve farm could have negative consequences for the ecosystem if the filtration pressure of stocked biomass surpasses the capacity of the system to replenish the depleted resources. The concept of ecological carrying capacity, understood as the magnitude of aquaculture activity in a given area that can be supported without leading to unacceptable changes in the aquatic environment, is commonly used to inform management and regulatory decisions of bivalve aquaculture. In this study, a hydrodynamic model has been coupled to an ecological model that simulates the main dynamics of organic seston to evaluate the effects of bivalve aquaculture on seston supply and assess ecological carrying capacity. The spatially-explicit model allows the identification of areas where organic seston could be reduced beyond precautionary thresholds of ecosystem resilience. The model has been applied to three coastal embayments in Nova Scotia (Canada) that differ in water circulation and inlet/coastal complexity. The outcomes of the model suggest that the current aquaculture operations in Sober Island, Wine Harbour, and Whitehead are within the ecological carrying capacity of the ecosystem for bivalve aquaculture. The simulation of additional hypothetical stocking scenarios had demonstrated the relevance of local water circulation to the ecological carrying capacity of the system, and consequently for aquaculture operations. Accordingly, the placement of leases in areas with optimal circulation should be considered for planning purposes. The capability of the model to explore hypothetical scenarios could be used as a tool to guide management decisions in regard to site selection for new aquaculture sites.

Removal of seston by Crassostrea rhizophorae (Guilding, 1828) in the Vitória bay estuarine system, Brazil

ABSTRACT The clearance of organic suspended particles by bivalve mollusks in estuarine ecosystems has been considered a critical regulating service. In Neotropical estuaries and associated mangrove ecosystems, the mangrove oyster, Crassostrea rhizophorae, is a key species in such process. To evaluate C. rhizophorae clearance rates (CRbd), biodeposit experiments were carried out at dry (2015) and wet (2016) seasons, in three sites of the Vitoria Bay Estuarine System (VBES), southeastern Brazil. The average CRbd was 0.67 L.g−1.h−1, which can be regarded as low CR. Although organic fraction predominates in the particulate matter (>60%), high estuarine salinity caused by low river discharge during prolonged regional drought, impaired oyster feeder rates. When the CRbd take into account the estimate entire mangrove oyster biomass at the VBES (3.77 × 105 kg.km−2) it yields a rate of 6.51 × 106 m3.kg−1.day−1, corresponding to a mean daily capacity of organic seston removal of 26% of the total estuarine volume. Even conservative, this result highlights the importance of mangrove oyster for the estuarine regulation, emphasizing its ecological importance and the need to sustain the critical ecosystem services of regulating estuarine environmental quality.

Disponibilidad de juveniles por captación natural de la ostra Pteria colymbus (Bivalvia: Pterlidae) en el Golfo de Cariaco, Venezuela

We examined the spat availability the oyster Pteria colymbus at 6-8 and 19-21 m depths for 15 months (March 1993-June 1994) in Turpialito, Golfo de Cariaco, Venezuela. Spats were trapped using artificial collectors (plastic filaments in bags, 30 x 60 mm), suspended from a long line. Each collector was replaced by a replica monthly to analyse abundance, shell dimension and mass of P colymbus. Intraweekly, the temperature, salinity, oxygen and food availability (Chlorophylla, total seston, organic and inorganic seston) were determinated. There is juvenile recruitment all year, suggesting continuous reproduction. Spat counts were higher at 6-8 m (generally 50-230 juveniles per collector) with peaks in August and December 1993 (April and June 93 at 19-21 m). The length-weigh mass relation was higher at 19-21 m, suggesting greater food availability because of lower organism density (including P. colymbus) and a greater water flux. Phytoplanktonic abundance and temperature were correlated (r2=0.38) with juvenile abundanc; this relationship and the association of juvenile abundance with higher temperature and Chlorophyll a levels, suggest that spat abundance was higher at the beginning of the water stratification period, when phytoplankton biomass is high.

Ciclo gametogenico de la ostra Pinctada imbricata en cultivo suspendido en el Golfo de Cariaco, Venezuela

The pearl oyster, Pinctada imbricata is an indigenous species that can potentially be used for aquaculture in the Gulf of Cariaco. In this work we examined the monthly gonadal development of a juvenile cohort (27.38 ± 2.70 mm) of the pearl oyster in a hanging culture system. Gonadal development was recorded throughout the study period (April 2012-February 2013), reaching the first maximum sexual maturity within five months of fixation. The females showed a sustained decrease of the gonadal index from December associated to the upwelling period, whereas the males presented oscillations that correspond to partial spawning without completely emptying the gonads. The greater frequency of spawning during upwelling, when there is greater availability of food, suggests that he has an opportunistic reproductive strategy. The sex ratio remained unchanged in the study period with a tendency to have more males (53%) at the beginning of the culture, evidencing that the stage of sexual transition of sex change is experienced by a low proportion of the population. Gametogenic development, in turn, was associated with primary productivity (Chl-a) and the availability of organic particles (organic seston). In culture, the oyster reached a size of 43.85 ± 5.66 mm. The increase in shell size was high during the first five months, stopping associated with a partial spawning with high primary production, from which the increase of the shell decreased in exchange for higher gametes production.

Preliminary model of tunicate infestation impacts on seston availability and organic sedimentation in longline mussel farms

The productivity of a bivalve farm is largely determined by the availability of organic seston and the level of competition for that naturally limited resource. Farm production may also be curtailed by regulatory or certification frameworks concerned with controlling biodeposition, i.e. the sedimentation of organic material. Fouling communities dominated by filter-feeding tunicates which both compete for food resources and increase biodeposition levels thus have the potential to further limit bivalve farm productivity.In the present study a farm-scale modelling approach was used to quantify the effects of the tunicate Ciona intestinalis on longline mussel farms. Both cultured and fouling species were simulated using physiological modules that took into account their interactions with organic seston dynamics in terms of filtration and biodeposition, and also predicted their growth over a typical growing season. Various treatment scenarios for reducing C. intestinalis infestation levels were also analyzed. Model results showed that C. intestinalis populations can rapidly dominate mussel sleeves in terms of their overall biomass and contribution to organic sedimentation. Early treatments during the tunicate reproductive season were the most effective at controlling the level of infestation and its impacts on sestonic food availability, mussel production and organic sedimentation. The proposed generic modelling approach could potentially become an essential aquaculture management tool, especially in the context of biological invasions. Statement of relevanceThe growing importance of bivalve aquaculture combined with its vulnerability to environmental conditions compels to ensure its sustainable development and management. Biofouling can potentially disrupt farm productivity and become a nuisance with profound socio-economic consequences. The numerical tool developed in this study provides valuable information for the management and mitigation of fouling by filter-feeding species on mussel farms.

Histochemistry of the digestive gland of the pearl oyster Pinctada imbricata (Pterioida: Pteriidae) during the gametogenic cycle, Venezuela

Histochemical techniques today allow you to select areas of tissue and generate reliable information on the distribution of energy reserves in bivalve molluscs during their life cycle. The main objective of this study was to describe and relate the gametogenic cycle with the availability of energy reserves and the environmental parameters. For this, we sampled and examined the gonads and digestive glands (DG) of 15 individuals collected monthly during April 2012 and February 2013. We processed and analyzed the samples by standard histological and histochemical light microscopy techniques. Our results showed that for the gametogenic cycle, the monthly proportion of mature organisms was higher for males, between August (40 %) and November (53 %), while the females tend to have a shorter synchronized cycle and release of gametes in September (67 %) and October (60 %). The intense spawning periods in both sexes was the same (October to January). Between the periods April-August 2012 and January-February 2013, we observed the highest values of IGl and glucide index (instead, a decrease was observed in September, reaching minimum values during the period October-December). Besides, the maximum values of IL, lipid index, were observed in April-2012 and February-2013, with an intermediate value in August-2013. The results indicated that the reserves of the GD have a pattern of mobilization inversely related to the proliferation of gametes in both sexes; this was directly linked to the availability of nutrients such as chlorophyll a and the organic seston.

PHYTOPLANKTON COMPOSITION IN COASTAL LAGOONS OF DIFFERENT TROPHIC STATUS IN NORTHERN COLOMBIA DETERMINED BY MICROSCOPE AND HPLC-PIGMENT ANALYSIS

The regional differences in the composition of the phytoplankton assemblages in several coastal lagoons of the “Outer Delta of the Río Magdalena” (Caribbean coast of Colombia) were determined using microscopic counting and HPLC-pigment measurements. The study sites can be classified as 1) a group of limnic lagoons with relatively low (5.5-19 μg/l) chlorophyll a (chl a) concentrations and high inorganic suspension loading, 2) a group of brackish lagoons with high (62-90 μg/l) chl a concentrations and high amounts of organic seston, (two further lagoons form a transition between group 1 and 2, and 3) a fully marine Caribbean bay with very low (0.3 μg/l) chl a and seston concentrations. The regional variations in salinity of the lagoons are due to inflow of water from the Río Magdalena or to inflow of Caribbean Sea water. All lagoons are very shallow (less than 2 m) with small Secchi depths (20 to 30 cm). With the exception of the eutrophic brackish lagoons, where both methods indicated cyanobacteria to be the prevalent algal group, great discrepancies were encountered in all other study sites between the compositions of the algal communities obtained with both approaches. According to the microscopic analysis the phytoplankton of the marine Caribbean bay and the limnic and transient coastal lagoons consisted mainly (in several cases exclusively) of diatoms. The pigment analysis, on the other hand, indicated that cyanobacteria were the dominant algal group in all coastal lagoons, their percentage increased from the limnic over the transient to the brackish lagoons. Fractionated filtration of 14C-labelled phytoplankton revealed that algae of <5μm size in the coastal lagoons contributed 32-88% of the total radioactivity and that algae of >20μm size played only an insignificant role in primary production. Only in the Caribbean bay 14% of the 14CO2 was taken up by organisms >20μm. We assume that the small forms are greatly underrepresented in microscopic observations due to extreme difficulties in identification and counting caused by detritus and/or sediment loadings of the samples. We therefore believe that these small forms (probably mostly picoplanktonic cyanobacteria) are better represented by pigment analysis.

Informing Marine Spatial Planning (MSP) with numerical modelling: A case-study on shellfish aquaculture in Malpeque Bay (Eastern Canada)

A moratorium on further bivalve leasing was established in 1999–2000 in Prince Edward Island (Canada). Recently, a marine spatial planning process was initiated explore potential mussel culture expansion in Malpeque Bay. This study focuses on the effects of a projected expansion scenario on productivity of existing leases and available suspended food resources. The aim is to provide a robust scientific assessment using available datasets and three modelling approaches ranging in complexity: (1) a connectivity analysis among culture areas; (2) a scenario analysis of organic seston dynamics based on a simplified biogeochemical model; and (3) a scenario analysis of phytoplankton dynamics based on an ecosystem model. These complementary approaches suggest (1) new leases can affect existing culture both through direct connectivity and through bay-scale effects driven by the overall increase in mussel biomass, and (2) a net reduction of phytoplankton within the bounds of its natural variation in the area.

The Role of Hydrodynamic Sorting of Seston in the Nutrition of a Benthic Suspension Feeder, Spio setosa (Polychaeta: Spionidae)

AbstractNear-bed gradients in suspended particle quality and material ingested by Spio setosa were studied using an intertidal beach population in Nova Scotia. Spio builds a sand tube that allows it to feed several centimeters above the bed, where hydrodynamic sorting of horizontal transport provides low-density, high-quality organic seston. Characterization and enumeration of particles from both worm guts and ambient sediment in the field demonstrated that guts were enriched in organic mineral aggregates relative to the bed. In a laboratory flume, worms with tubes shortened to bed level received and ingested seston of significantly lower organic quality than worms feeding in intact tubes 4–6 cm above the bed. Because tube building requires ∼2.5 days, winter beach scour which removes tubes may force Spio to feed frequently at suboptimal heights above the sediment surface. The dependence of suspension feeders on organic-mineral aggregates and the tendency for these particles to incorporate estuarine pollut...

Contrasting Growth Patterns of Suspension-Feeding Molluscs (Mercenaria mercenaria, Crassostrea virginica, Argopecten irradians, and Crepidula fornicata) Across a Eutrophication Gradient in the Peconic Estuary, NY, USA

While many coastal ecosystems previously supported dense meadows of seagrass and dense stocks of bivalves, the impacts of overfishing, eutrophication, harmful algal blooms, and habitat loss have contributed to the decline of these important resources. Anthropogenic nutrient loading and subsequent eutrophication has been identified by some researchers as a primary driver of these losses, but others have described potential positive effects of eutrophication on some estuarine resources. The Peconic Estuary, Long Island, NY, USA, offers a naturally occurring nutrient-loading gradient from eutrophic tidal creeks in its western reaches to mesotrophic bays in the eastern region. Over 2 years, we conducted an experiment across this gradient to examine the effects of eutrophication on the growth of estuarine species, including juvenile bivalves (northern quahogs (Mercenaria mercenaria), eastern oysters, (Crassostrea virginica), and bay scallops (Argopecten irradians)) and slipper limpet (Crepidula fornicata). Water quality and phytoplankton community biomass and composition were concurrently monitored at each site, and the effects of these variables on the growth of estuarine species were analyzed with multiple regression model. Eutrophication seemed to impact shellfish through changes in the quality of food and not the quantity since the growth rates of shellfish were more often correlated with densities of specific cell types or quality of seston rather than bulk measures of phytoplankton and organic seston. Northern quahogs and eastern oysters grew maximally within eutrophic locales, and their growth was positively correlated with high densities of autotrophic nanoflagellates and centric diatoms in these regions (p < 0.001). The growth rates of northern quahogs were also positively correlated with relative water motion, suggesting an important role for tidal currents in delivering seston to suspension feeders. Bay scallops and slipper limpets were negatively impacted by eutrophication, growing at the slowest rate at the most eutrophic sites. Furthermore, bay scallop growth was negatively correlated with densities of dinoflagellates, which were more abundant at the most eutrophic site (p < 0.001). These results suggest that nutrient loading can have significant but complex effects on suspension-feeding molluscs with select species (e.g., oysters and clams) benefiting from eutrophication and other species performing poorly (e.g., scallops and slipper limpets). Future management approaches that seek to restore bivalve populations will need to account for the differential effects of nutrient loading as managers target species and regions to be restored.

Macroinvertebrate diets reflect tributary inputs and turbidity-driven changes in food availability in the Colorado River downstream of Glen Canyon Dam

Physical changes to rivers associated with large dams (e.g., water temperature) directly alter macroinvertebrate assemblages. Large dams also may indirectly alter these assemblages by changing the food resources available to support macroinvertebrate production. We examined the diets of the 4 most common macroinvertebrate taxa in the Colorado River through Glen and Grand Canyons, seasonally, at 6 sites for 2.5 y. We compared macroinvertebrate diet composition to the composition of epilithon (rock and cliff faces) communities and suspended organic seston to evaluate the degree to which macroinvertebrate diets tracked downstream changes in resource availability. Diets contained greater proportions of algal resources in the tailwater of Glen Canyon Dam and more terrestrial-based resources at sites downstream of the 1 st major tributary. As predicted, macroinvertebrate diets tracked turbidity-driven changes in resource availability, and river turbidity partially explained variability in macroinvertebrate diets. The relative proportions of resources assimilated by macroinvertebrates ranged from dominance by algae to terrestrial- based resources, despite greater assimilation efficiencies for algal than terrestrial C. Terrestrial resources were most important during high turbidity conditions, which occurred during the late-summer monsoon season (July-October) when tributaries contributed large amounts of organic matter to the mainstem and suspended sediments reduced algal production. Macroinvertebrate diets were influenced by seasonal changes in tributary inputs and turbidity, a result suggesting macroinvertebrate diets in regulated rivers may be temporally dynamic and driven by tributary inputs.

Crecimiento del mejillón verde &lt;i&gt;Perna viridis&lt;/i&gt; (Bivalvia: Mytilidae) bajo sistema de cultivo de fondo en la ensenada de Turpialito, Golfo de Cariaco, Venezuela

Mussels represent one of the most important mollusk species for culture activities around the world, and their growth may depend on the culture system used and locality. In this study, we evaluated the growth of Perna viridis in bottom culture to test its performance when using natural food, and to decide its use as a culture species in the Gulf of Cariaco. For this, mussel seeds (35.81 +/- 1.41 mm in length) were obtained in the locality of Guaca (North coast of Sucre state) and transferred to the Hydrobiological Station of Turpialito, Gulf of Cariaco, Sucre state, Venezuela, where they were planted in "Spanish baskets" to evaluate their growth between July 2007 and February 2008. Monthly survival was determined and the maximum shell length, dry mass of muscle and remains tissues of the gonad. The environmental parameters (water temperature, salinity, dissolved oxygen, chlorophyll a, total seston and organic fraction), in the cultivation area were determined every 15 days. Monthly measurements were made of proteins, lipids and carbohydrates to seston. During the entire study the mussels showed continued growth, ultimately reaching a maximum length of 78.7 +/- 4.43 mm. However, the growth rate of the dry mass of somatic (muscle, other tissue) and reproductive tissues showed variability throughout the study, and observed a significant increase by the end of the experiment. The observed variations in the growth rate of the reproductive tissue mass depended on the reserves accumulated and food offered by the environment. The organic seston throughout the experience showed an independence of temperature and chlorophyll a values; this one maintained values above 1 mg/L, thus forming the main food resource for mussels. The high content of proteins, lipids and carbohydrates observed in the seston at the end of the study, might be mainly associated with coastal upwelling, which provides a great food contribution of phytoplankton and organic type. The high survival rate (>80%), increase in the length of the shell and the high gonad production, suggests an excellent physiological condition of P. viridis, related to the availability and quality of food particularly the organic type present in the medium. We concluded that the bottom culture can provide an alternative aquaculture production in the Gulf of Cariaco.

Annual recruitment, predation rates and biocontrol of Linatella caudata (Mollusca: Gastropoda) in suspended enclosure culture of the pearl oyster Pinctada imbricata

We present data on recruitment of the marine gastropod Linatella caudata (Gmeling, 1791) and their predation rates on the pearl oyster Pinctada imbricata in suspended culture using Spanish baskets. The recruitment rate of juveniles of L. caudata was studied every 30days over a year. The bivalve culture enclosures were suspended in the water column at two sites in the Gulf of Cariaco (northeastern Venezuela) characterized by different oceanographic and environmental conditions; Turpialito and an internal area of Laguna Grande del Obispo (LGO). Environmental variables including temperature, chlorophyll a, total (organic and inorganic) seston and wind intensity were recorded. The sea urchin Echinometra lucunter was placed on culture baskets as a predator (biocontrol). Plastic mesh cultivation bags were also tested as an alternative method to prevent or decrease the recruitment of these predators at Turpialito. The results showed a significantly higher number of predators at Turpialito than in the sheltered LGO site in May, June and July only. During the period of intense predator recruitment, principal component analysis (PCA) revealed that chlorophyll a, organic seston and wind strength were directly related to predator recruitment. During the period of less intense predator recruitment when wind intensity was lower, PCA showed that the same variables were directly related to predator recruitment whereas temperature showed an inverse relationship. In contrast, no relationship between recruitment of predators and environmental variables could be established for the LGO site. However, predator recruitment at LGO was significantly lower in the plastic mesh bags than in Spanish baskets, and in the presence of the sea urchin Echinometra lucunter. Due to high rates of predation observed, L. caudata constitutes a serious problem for the aquaculture industry of marine bivalves.

Role of Transparent Exopolymer Particles on Phytoplankton Dynamics in a Subtropical Estuary, Canan&amp;#233;ia-Iguape (Sp, Brazil)

Transparent Exopolymer Particles (TEP) has a known crucial role in vertical fluxes of carbon in the ocean and has been intensively studied in the last decade. Nevertheless, few studies have considered horizontal fluxes of TEP. These fluxes arise prominently between estuaries and the coast, where its importance is associated to the predominant horizontal transport. This is due both to the low density of the TEP agglomerate generated in low density waters of continental origin, and to the fact that the main component of the advective transport at estuarine regions is the horizontal one. In this study, the significance of TEP in the particulate matter exchange between estuary and coast was analyzed in the estuarine lagoon system of Cananéia-Iguape (southeast coast of Brazil). TEP, total seston (TS), organic seston (OS) and chlorophyll a (Chl.a) were analyzed over complete tidal cycles, during the dry and rainy seasons both at spring and neap tides. Horizontal fluxes and net transport rates of these variables were also calculated. TEP concentrations (max. 4991 μg Xeq/L) were almost one order of magnitude higher during the rainy season. TEP horizontal transport rates as high as 1.8 g Xeq. m/s were observed at the northern inlet of the system. In terms of particulate carbon, it represents 32.7 g TEP-C m/s or 4% of the OS transport rates. Our study quantifies the advective transport of TEP and their importance in particulate matter exchange between a subtropical estuarine system and the adjacent coastal region. Our results contribute to the knowledge of exopolimer particles dynamics in subtropical estuarine systems, and their relationship to phyto-plankton biomass and particulate matter.

In situ effective clearance rate measurement of mangrove oysters (Crassostrea rhizophorae) in a tropical estuary in Brazil

Abstract Anthropogenic nutrient enrichment in estuaries induces high phytoplankton production, contributing to coastal eutrophication. Abundant natural banks of filter feeders, such as bivalves, in downstream areas may contribute to reducing symptoms of eutrophication by decreasing phytoplankton biomass and amount of material subjected to microbial regeneration. The current concern is to what extent bivalves can control water quality and how environmental parameters can influence the filtration process and vice versa. In the present study Crassostrea rhizophorae (Guilding, 1818) grazing ability on suspended particles in their natural environment was determined in situ, using the biodeposition method and uniquely constructed sediment traps. Additionally the effect of body size on effective clearance rate (ECR) was examined using three different size groups. The experiment was conducted in the Piraque-acu/Piraque-mirim estuary system, (Aracruz, ES, Brazil) during the second week of June 2012 (dry season). Environmental parameters were measured together with total particulate matter (TPM, mg L-1) and chlorophyll a analysis (CHL, μg L-1) at the beginning and at the end of the experiment. Average values recorded for TPM and CHL were 5.79 mg L-1 and 2.55 μg L-1 respectively with very high organic seston fraction (80%). The reported effective clearance rate (ECR, in litres per hour) was 17.99 L h-1g-1 dry weight (DW), one of the highest reported in literature and can be associated with a high detritus content and different feeding strategies in comparison to bivalves residing in temperate environments. Weight and length (height) relationship were closely correlated (r = 0.73) however, clearance rate (ECR) standardized to 1 g dry tissue weight did not vary significantly among different size classes. High ECR at high particulate organic matter (POM, %) supports the belief that bivalves can exhibit ECR flexibility according to food quality.

Carbon input, production and turnover in the interstices of a Lake Tegel bank filtration site, Berlin, Germany

The sandy littoral zone of Lake Tegel (Berlin, Germany) was investigated during 2004–2006 down to sediment depths ≥26 cm to derive a scheme of seasonal carbon turnover under induced bank filtration conditions. Carbon turnover processes were quantified regarding external and internal sources of dissolved and particulate organic matter (DOM and POM), primary production, community respiration, redox potential as well as specific loads of soluble chemical compounds such as nitrogen, iron, manganese and DOC. Over the course of the year, infiltrating DOC decreased by about 13–20% within the upper 26 cm sediment of the infiltration stretch. Gradients of all observed soluble compounds that are highly cross-linked to biological activities were highest in the topmost centimetre. In this depth mass balances (output–input) were negative concerning NO3-N (−1 mg dm−2 d−1, summer mean) and DOC (−2 mg dm−2 d−1, winter mean), respectively, while specific loads of cations such as manganese reached up to 0.2 mg dm−2 d−1 during summer. Carbon mineralization ranged between 3 and 7 mg C dm−2 d−1 and was nearly twice as high in summer as in winter. The turnover of the infiltrating DOC contributed maximally 25% in summer to 50% in winter to the entire organic carbon mineralization. Gross and net primary production differed up to a factor of >10, indicating very fast turnover reactions and the predominance of community respiration and mineralization, respectively. The POC in the upper sediment layer (10 cm) temporally varied around 1% sediment d.w.; benthic algae, organic seston input and autumnal leaf fall contributed similar percentages to the POC pool.

Influence of environmental variables and reproduction on the gonadal fatty acid profile of tropical scallop Nodipecten nodosus

We examined the influence of the reproductive cycle and environmental variables on the gonadal fatty acid profile in the tropical scallop Nodipecten nodosus. Individuals from a natural population in north-eastern Venezuela (Caribbean Sea) were sampled monthly during one year. The gonadosomatic index (GSI) and a visual assessment of gonadic status are also reported. The environmental conditions characterized by chlorophyll a, temperature and seston concentration were measured in parallel. The highest reproductive activity, with a GSI of 13-18%, was observed from November 2003 to April 2004, and a decrease in GSI, taken as an indication of three spawning periods, was recorded in October, January and May-June. The GSI was 5-8% outside these intervals. A similar trend was observed in maturity stage frequency. Statistical analysis (MDS-ANOSIM) established two different periods; one dominated by upwelling (January to July) and the other characteristic of non-upwelling conditions (August to December). The fatty acids 16:0, 22:6n-3, 20:5n-3 and 16:1n-7 were responsible for the differences between two periods and explained 50% of the observed variance. Accordingly, during the upwelling period, fatty acids such as 22:6n-3 were positively correlated with temperature, organic seston and bivalves in the spent sexual stage and inversely related to the GSI. Furthermore, individuals in the ripe sexual stage were positively related to 20:5n-3 and 18:3n-3, whereas chlorophyll a was directly related to 18:1n-7 and 16:1n-7. In the non-upwelling period, a significant and positive correlation was obtained between fatty acids such as 20:5n-3 and 22:6n-3 and the GSI and the bivalves in the ripe sexual stage, whereas these acids were inversely correlated with the spent sexual stage. In addition, chlorophyll a was positively related to 18:1n-9 and 18:2n-6. Changes in the gonadal fatty acid profile of N. nodosus were influenced by the environmental variables (exogenous factors) during the upwelling and non-upwelling periods and by reproductions (endogenous factors).

Influence of allochthonous organic matter on bacterioplankton biomass and activity in a eutrophic, sub-tropical estuary

Heterotrophic bacterial and phytoplankton biomass, production, specific growth rates, and growth efficiencies were studied in the Northern region of the Cananéia–Iguape estuarine system, which has recently experienced an intense eutrophication due to anthropogenic causes. Two surveys were carried out during spring and neap tide periods of the dry season of 2005 and the rainy season of 2006. This region receives large freshwater inputs with organic seston and phosphate concentrations that reach as high as 1.0 mg l −1 and 20.0 μM, respectively. Strong decreasing gradients of seston and dissolved inorganic nutrients were observed from the river/estuary boundary to the estuary/coastal interface. Gradients were also observed in phytoplankton and bacterial production rates. The production rates of phytoplankton were 5.6-fold higher (mean 8.5 μg C l −1 h −1) during the dry season. Primary production rates (PP) positively correlated with salinity and euphotic depth, indicating that phytoplankton productivity was light-limited. On the other hand, bacterial biomass (BB) and production rates (BP) were 1.9- and 3.7-fold higher, respectively, during the rainy season, with mean values of up to 40.4 μg C l −1 and 7.9 μg C l −1 h −1, respectively. Despite such a high BP, bacterial abundance remained <2 × 10 6 cells ml −1, indicating that bacterial production and removal were coupled. Mean specific growth rates ranged between 0.9 and 5.5 d −1. BP was inversely correlated with salinity and positively correlated with temperature, organic matter, exopolymer particles, and particulate-attached bacteria; this last accounted for as much as 89.6% of the total abundance. During the rainy season, BP was generally much higher than PP, and values of BP/PP > 20 were registered during high freshwater input, suggesting that under these conditions, bacterial activity was predominantly supported by allochthonous inputs of organic carbon. In addition, BB probably represented the main pathway for the synthesis of high-quality (low C:N) biomass that may have been available to the heterotrophic components of the plankton food web, particularly nanoheterotrophs.

Allochthonous litter inputs, organic matter standing stocks, and organic seston dynamics in upland Panamanian streams: potential effects of larval amphibians on organic matter dynamics

Allochthonous inputs of detritus represent an important energy source for streams in forested regions, but dynamics of these materials are not well studied in neotropical headwater streams. As part of the tropical amphibian declines in streams (TADS) project, we quantified benthic organic matter standing stocks and organic seston dynamics in four Panamanian headwater streams, two with (pre-amphibian decline) and two without (post-decline) healthy amphibian assemblages. We also measured direct litterfall and lateral litter inputs in two of these streams. Continuous litterfall and monthly benthic samples were collected for 1 year, and seston was collected 1–3 times/month for 1 year at or near baseflow. Direct litterfall was similar between the two streams examined, ranging from 934–1,137 g DM m−2 y−1. Lateral inputs were lower, ranging from 140–187 g DM m−1 y−1. Dead leaves (57–60%), wood (24–29%), and green leaves (8–9%) contributed most to inputs, and total inputs were generally higher during the rainy season. Annual habitat-weighted benthic organic matter standing stocks ranged from 101–171 g AFDM m−2 across the four study reaches, with ∼4 × higher values in pools compared to erosional habitats. Total benthic organic matter (BOM) values did not change appreciably with season, but coarse particulate organic matter (CPOM, >1 mm) generally decreased and very fine particulate organic matter (VFPOM, 1.6–250 μm) generally increased during the dry season. Average annual seston concentrations ranged from 0.2–0.6 mg AFDM l−1 (fine seston, 250 μm) and 2.0–4.7 mg AFDM l−1 (very fine, 1.6 μm), with very fine particles composing 85–92% of total seston. Quality of fine seston particles in the two reaches where tadpoles were present was significantly higher (lower C/N) than the two where tadpoles had been severely reduced (P = 0.0028), suggesting that ongoing amphibian declines in this region are negatively influencing the quality of particles exported from headwaters. Compared to forested streams in other regions, these systems receive relatively high amounts of allochthonous litter inputs but have low in-stream storage.