Temperate Coastal Lagoon Research Articles

Feeding habits of the deep-snouted pipefish Syngnathus typhle in a temperate coastal lagoon

Feeding habits of Syngnathus typhle were determined based on monthly sampling during experimental fishing in a coastal lagoon (Ria Formosa, South Portugal) from April 2001 to May 2002. The gut contents of 856 individuals were analysed and quantified with numerical and gravimetric methods, as well as with some complementary indices and measures (vacuity, fullness and relative importance). In this study, this species fed mainly on Copepoda, Mysidacea, small caridean grass shrimps (Hippolytidae and Palaemonidae) and small fishes (Gobiidae) and to a lesser degree on other small invertebrates. No significant differences were found between the diets of males and females. However, significant differences in the fullness indexes of both sexes were observed during the reproductive period. Significant differences in the diet among seasons were also verified but no seasonal trends were discovered. Snout length showed a linear increase with growth while mouth area and total length displayed an allometric relation. Mouth shape varied between an ellipse and an almost perfect circle. The increase in mouth area and snout length as S. typhle grows contributed to the observed ontogenic diet shift with specimens smaller than 10 cm feeding almost exclusively on Copepoda, medium sized specimens feeding mainly on Hippolytidae and Mysidacea, while larger specimens preyed on Hippolytidae, Palaemonidae and Gobiidae. Prey size generally increased with size of S. typhle.

Tidal transport and dispersal of marine toxic microalgae in a shallow, temperate coastal lagoon

A numerical model was used to predict toxic microalgal transport and dispersion in Ria de Aveiro in Portugal. A previously developed Lagrangean particle tracking model coupled to a calibrated two-dimensional hydrodynamic model of Ria de Aveiro was used. Microalgae were regarded as passive particles and the methodology used allowed the determination of their trajectories, as induced by the tidal currents predicted by the hydrodynamic model. The model assumes Ria de Aveiro as vertically homogeneous and does not take into account the vertical distribution patterns of microalgae. Simulations were carried out during extreme spring and neap tides, with microalgal released at the mouth of the lagoon at the local flood. The maximum and minimum areas affected during the occurrence of toxic microalgal blooms were estimated to evaluate the suitability of the distribution of the sampling stations included in the local monitoring program. It was found that the tidal currents greatly determine the microalgal horizontal distribution and dispersal in the lagoon. The results confirmed that the locations of water and bivalve shellfish sampling stations, postulated by INIAP/IPIMAR, in the context of the local harmful algal bloom (HAB) program, were appropriate, although some possible refinements were identified.

Long-term and high-resolution measurements of bed level changes in a temperate, microtidal coastal lagoon

This study presents the results of a long-term monitoring program of bed level changes measured during 8 yr at an intertidal mudflat in a microtidal, temperate coastal lagoon. Additionally, bed level measurements obtained at a 10-min temporal resolution at the same tidal flat and at the bed of a nearby tidal channel are presented. Short-term changes in bed level are one or two orders of magnitude larger than the annual net-deposition rate, which shows that the environment is highly dynamic with respect to erosion, transport and deposition of fine-grained sediment. Some seasonality in the bed level changes was observed and there is a tendency for mudflat deposition in spring, summer and early autumn and erosion during the rest of the year, but interannual variations are large and different parts of the mudflat show different seasonal signals. A close coupling between sub- and intertidal deposition and erosion was observed. The time-series showed that some of the material eroded from the mudflat was not exported to the open sea, but instead temporarily deposited in a nearby shallow tidal channel and later returned to the mudflat during calmer weather conditions. These findings support previously published hypothesis and results of modelling studies. Based on the observed abundance of fine-grained sediment at the study sites and the high accretion rates generally found on fine-grained tidal flats in the Danish Wadden Sea area, it is argued that these fine-grained tidal flats are not seriously threatened by the expected sea level rise in the 21st century.

Macroalgae response to a mercury contamination gradient in a temperate coastal lagoon (Ria de Aveiro, Portugal)

Primary producers represent an important pathway for mercury incorporation in aquatic food webs. With eutrophication processes occurring worldwide, macroalgae may represent a substantial pool of mercury, as a result of its high growth rate and capacity to bind trace metals. The main aim of this work was to evaluate the response of the macroalgae to a human-induced environmental mercury gradient in a temperate coastal lagoon, by assessing the total and organic mercury contamination levels of the dominant species ( Enteromorpha, Fucus and Gracilaria). Total mercury in the plant tissues ranged from 0.02 to 2.1 μg g −1 dwt. Fucus was the most contaminated algae, followed by Gracilaria and Enteromorpha. As a whole, organic mercury never exceeded 15% of total mercury content, but tended to increase with distance to metal source on all macroalgae indicating complex physiological responses from these primary producers in areas of high and low mercury concentrations. Sessile macroalgae may be important mercury immobilisation agents, while free-floating algae ( Enteromorpha) play an important role in mercury transport from contaminated areas (±10 g ha −1) to other areas of the lagoon and even to coastal waters. Based on the present results the use of macroalgal biomass from contaminated areas for direct or indirect human use (e.g. agricultural, industrial and food purposes) may result in health risks, due to the high bioaccumulation capacity (as high as 10 4 the dissolved mercury concentrations).

Modelling macroalgae using a 3D hydrodynamic-ecological model in a shallow, temperate estuary

This paper describes an application of MOHID modelling system to a shallow temperate coastal lagoon in Portugal's western coast (Ria de Aveiro), simulating more than one primary producer, for a better understanding of the existing ecological dynamics and creating a useful tool to delineate land activities management practices. MOHID water quality model is driven by a physical transport model and simulates the dynamics and productivity of the two main primary producers (phytoplankton and macroalgae) as well as the cycling of nitrogen, carbon and oxygen in interaction with sediment and hydrodynamics. The integrated model is forced by exchanges with the Atlantic Ocean (tide), atmosphere, and by sediment and nutrient inputs from the upstream rivers and other discharges. Focus is given to the light parameterization of primary production, influence of hydro and sediment dynamics and to the prediction of seaweed beds distribution. The results obtained show that the model is better adjusted to field data with macroalgae's simulation and that macroalgae can have an important role in primary production. Hydrodynamic conditions can be significant in the competition between the two primary producers, determining the predominant groups as well as their limiting factors.

Population biology of the cephalaspidean mollusc Haminoea orbygniana in a temperate coastal lagoon (Ria Formosa, Portugal)

The population ecology of Haminoea orbygniana (Férussac, 1822) has been investigated in the Ria Formosa, a temperate coastal lagoon in southern Portugal by monthly sampling between October 2000 and October 2001. The mean annual density was 341 ind m −2 with highest abundance occurring during winter. An aggregated spatial distribution was observed ( I = 76.4). The species showed continuous reproduction throughout the year with the main breeding period in April. Two recruitment periods were detected, a subsidiary one in June and a major one in September. Growth is continuous throughout life. Growth patterns and life span were deeply influenced by season and recruitment time. The cohort recruited in June, had a higher growth rate from summer until middle autumn (between July and November), decreasing in the autumn and winter (November–March), and rising again in spring (from March to May). The cohort recruited in September had a higher growth rate over autumn and winter (from October to February), a decrease from late winter to spring (February–May), followed by a new growth rate from middle spring onwards (May/June–September). Life spans were 11 months and 19 months for cohorts recruited in June and September, respectively. Biomass was higher during winter and spring, and secondary production between late winter and early summer.

Reproduction of Micropogonias funieri in a shallow temperate coastal lagoon in the southern Atlantic

The white croaker Micropogonias furnieri, in the coastal Rocha Lagoon, spawned during 5 months, in late spring and summer. It was eurythermic (gonad growth at 12·5 to 25·5° C, spawning at 20 to 27° C) and mesoxic (living at 5·2 to 9·1 mg l‐1). The spawning occurred in brackish (8–18 salinity), basic (c. 8 pH) and oxygenated (c. 8·0 mg l‐1) waters. The temperature appeared to be an important environmental factor affecting the timing of reproduction. The size at first maturity (19–20 cm) was 11–12 cm lower than the reported for the Río de la Plata spawning area (Uruguay). Juveniles were observed throughout most of the year suggesting that the lagoon is also a nursery area. In Brazil, M. furnieri spawns in marine areas while in Uruguay it spawns in estuaries. This is the first time that a coastal lagoon of the subtropical and temperate western coast of the South Atlantic Ocean has been shown to be a spawning area of a marine species.

Reproduction of Micropogonias furnieri in a shallow temperate coastal lagoon in the southern Atlantic

Reproduction of Micropogonias furnieri in a shallow temperate coastal lagoon in the southern Atlantic

Reproduction of Micropogonias furnieri in a shallow temperate coastal lagoon in the southern Atlantic

Reproduction of Micropogonias furnieri in a shallow temperate coastal lagoon in the southern Atlantic

Macroalgae Mediation of Dissolved Organic Nitrogen Fluxes in a Temperate Coastal Lagoon

The activity of the benthos, including benthic plants, is important in driving the overall system dynamics in shallow lagoons, due to the high ratio of sediment surface area relative to water volume. In Hog Island Bay, benthic macroalgae appear to be a key regulator of DON dynamics, both while alive and following senescence. We investigated the role of macroalgae in mediating water column concentrations and sediment-water column fluxes of DON across a nutrient gradient in Hog Island Bay, a shallow macroalgal-dominated back-barrier lagoon located on the Virginia Coast. Sediment-water column exchanges of DON, urea and DIN were measured in sediment cores with and without macroalgae (Ulva lactuca) at three subtidal sites from the mainland to the barrier islands in the fall of 1997 and the spring and summer of 1998. The summer sampling dates bracketed a large macroalgal bloom in the mid-lagoon. Dissolved organic nitrogen was an important component (52-98%) of the total dissolved nitrogen pool in Hog Island Bay waters and made up the majority of the sediment N flux to the water column. Macroalgae impacted benthic-pelagic coupling by preventing diffusion of DIN from the water column to the sediments and by intercepting urea fluxes from the sediment to the water column. Closest to the mainland and closest to the barrier islands, at sites with low macroalgal biomass, sediment-water column fluxes of DIN and urea-free DON were negligible or directed into the sediments. Fluxes of urea from the sediment to the water column were significant at both sites, and may play an important role in satisfying macroalgal N demand, especially at the low N island site. Overall, urea was 32% of the mean DON flux from the sediments to the water column. Fluxes of urea-free DON were highest in the mid-lagoon, where macroalgal biomass was highest. The highest overall flux rates of DON (>38mmol m−2d−1) and DIN (>33mmol m−2d−1) were measured following an isolated crash of a large macroalgal mat. These release rates were not sustained for long, however, and we estimated that the majority of the N contained in the decomposing macroalgal tissues disappeared in <2 weeks. In addition to release of organic N following senescence, macroalgae ‘leak’ DON into the water column during active growth; release of DON increased by 250% in cores incubated with U. lactuca relative to cores with sediment only. These algae function as a conduit whereby water-column DIN and sediment urea are taken up and released to the water column as DON over relatively short (hours) time scales. This conversion of bioavailable dissolved N to PON and DON by macroalgae is likely to be important to overall system metabolism and to the retention of N within the lagoon.

Magnitude and variability of benthic and pelagic metabolism in a temperate coastal lagoon

In shallow coastal systems where most of the seafloor lies within the photic zone, ben- thic photoautotrophy is likely to play a key role in regulating carbon and nitrogen cycling. We mea- sured dissolved inorganic carbon exchanges in seasonal microcosm incubations to determine the rel- ative importance of benthic (with and without macroalgae) and water column metabolism at 3 sites located along a nutrient gradient in a coastal barrier-island lagoon on the eastern shore of Virginia. When coupled with data on in situ biomass, the incubations clearly indicated a seasonality in the dominance of primary producers at the sites, with benthic primary producers being the most impor- tant early and late in the growing season and phytoplankton dominating following a mid-summer period of macroalgal decay and the release of algal-bound nutrients to the water column. The ben- thos was always net autotrophic, and differences in community metabolism at the 3 sites appeared to be largely due to variation in macroalgal biomass. Macroalgae accumulated to a greater extent in the mid-lagoon and accounted for up to 96% of benthic production. The water column was net hetero- trophic throughout the lagoon except following the mid-summer macroalgal collapse, when phyto- plankton biomass was highest at the 2 sites closest to the mainland. Benthic microalgal production also increased in importance following the macroalgal decline, suggesting that competition for light and possibly nutrients limited benthic microalgal production when macroalgal densities were high. Overall, there was a distinct seasonality in patterns of total metabolism within the bay, where all sites were net autotrophic in the spring and summer and net heterotrophic in the fall. Up to 8 g N m -2 accu- mulated in macroalgal biomass throughout spring and early summer at the mid-lagoon shoal site, slowing nutrient transport through the lagoon. Nutrient turnover rates were higher during the period when phytoplankton and benthic microalgae were the dominant primary producers. This study illus- trates the functional importance of different primary producer communities to carbon metabolism and to the temporary retention of nutrients in lagoonal land-margin ecosystems.

A high‐resolution pore water sampler for sandy sediments

In this paper, we present a new technique for collecting pore‐water samples in coarse‐to fine‐grained sandy sediments. We have used the technique both for in situ sampling and for pore‐water extraction from sediment cores brought back to the laboratory, in both cases with a depth resolution as fine as 1 cm. The key device is a long, thin (~2 mm) stainless steel tube with a specially designed tip that functions as a filter. Pore‐water samples are collected by inserting the tube into the sediment at the desired depth and applying a light suction from a syringe connected to the tube. The sample is injected immediately into a vial through a syringe filter and stored for later analysis. The technique has some clear advantages over other methods that are used commonly in sandy sediments. In comparison with lysimeters or sippers, it gives pore‐water samples with a much higher depth resolution, which often is needed to accurately estimate fluxes across the sediment‐water interface or transformation rates of solutes within the sediments. In comparison with dialysis cells or peepers, the new technique gives measurements that truly represent the time of collection. This can be crucial when non‐steady‐state systems are studied. Furthermore, disturbance of the sediment is minimal because of the small dimension of the tube. This is especially important in vegetated sediments, in which the deployment of larger conventional samplers is likely to cause significant disturbance. Finally, sample extraction is less laborious than other techniques, requiring only one site visit and typically &lt;1 min of sampling time per sample. In laboratory tests using a dye tracer, we showed that pore water was drawn evenly toward the tube tip from all directions in the surrounding sediment. On the basis of these results, we provide guidelines for choosing the appropriate sampling depth intervals as a function of the sample size. Data from representative pore‐water profiles are presented for PO432 from vegetated coarse‐grained carbonate sediments in the Bahamas and NH4+1 from fine‐grained unvegetated sands in a temperate coastal lagoon in Virginia.

The fish assemblage structure of a hydrologically altered coastal lagoon: the ´ Obidos lagoon (Portugal)

The fish assemblage of the Obidos lagoon was studied between January 1993 and December 1994 based on beach seine catches. Forty-one species were identified, with Gobius niger, Syngnathus acus, Atherina boyeri, Dicentrarchus labrax, Liza aurata, Chelon labrosus and Symphodus bailloni the most common species. The community was dominated by the families Atherinidae, Mugilidae and Gobiidae, which is characteristic of temperate and tropical estuaries and coastal lagoons. Community ordination analysis outlined three major fish assemblages along a longitudinal environmental gradient, determined by salinity, sediment and turbidity. Euryhaline fish species, such as Liza ramada and Mugil cephalus, were particularly abundant in the upper part of the lagoon. The middle area was dominated by estuarine resident species, namely G. niger, A. boyeri, S. acus and S. bailloni, while in the lower part of the lagoon the fish assemblage was composed of inshore marine species. The seasonal pattern was mainly induced by the annual cycle of resident species and by the migration of juveniles moving between coastal areas and the lagoon. If human activities related to keeping the mouth of the lagoon open to the sea ceased, the nursery function of this estuarine system would be affected, with a dominance of euryhaline fish species expected throughout the lagoon.

Responses of Coastal Lagoon Plant Communities to Levels of Nutrient Enrichment: A Mesocosm Study

An experiment was conducted to quantify the effects of different levels of nutrient enrichment on the plant communities of temperate coastal lagoons, specifically the lagoons of the northeast U.S. Ten mesocosms, each containing coastal water, lagoon sediments, and plants and animals found in natural lagoons, were subjected to five levels of enrichment. Two mesocosms served as controls, and received no experimental nutrient additions. The remaining 8 mesocosms were enriched in duplicate with ammonium plus phosphate at 1.0 and 0.11 mmol N or P m−2 d−1, 2.0 and 0.19 mmol N or P m−2 d−1, 4.0 and 0.35 mmol N or P m−2 d−1, and 8.0 and 0.67 N or P mmol m−2 d−1. At all levels of enrichment, and through much of the experiment, water column concentrations of dissolved inorganic nitrogen (DIN) were drawn down to background levels. Despite the efficient drawdown of added DIN even at the highest loadings, differences in plant biomass among the 5 treatments were difficult to detect. Enrichment at the highest loadings increased standing stocks of phytoplankton for one month mid-experiment. No significant effect of loading could be detected for dry biomass of eelgrass (Zostera marina), epiphytic material, drift macroalgae, or for all plant components combined. The experiment has demonstrated that the enrichment responses of coastal lagoons can be diverse, especially at intermediate loadings.

Effects of reduced salinity on juvenile growth of two co-occurring congeneric grapsid crabs

The influence of salinity on the time elapsed between two successive molts and the size reached after each molt were studied at 30, 21, 12 and 3‰S in juveniles of two co-occurring grapsid species, Cyrtograpsus angulatus and C. altimanus, cultured under identical conditions of temperature, photoperiod and food. Juvenile growth patterns were compared between these species (which differ in size-at-maturity and maximum size). C. angulatus grew faster than C. altimanus, reflecting a higher increment per molt and a shorter intermolt period. A significant difference existed between the number of instars preceding the size of maturity in both species: >11 in C. angulatus, 6 in C. altimanus. There was evidence of a differential effect of low salinity on growth. By the end of the experiment, individuals of both species were smaller at the lowest salinity (3‰) tested; the largest crabs developed at 21‰ (C. angulatus) and 30‰ (C. altimanus). The size difference between the “optimal” and the less suitable salinities in the sixth crab instar was 12.4% in C. angulatus and 35% in C. altimanus. During early juvenile development (Crab Instars 1 to 4), there were slight differences in intermolt period among salinities in C. angulatus, but large differences in C. altimanus. The longest intermolt period of C. altimanus was at 3‰S and the shortest at 30‰S. In the following instars (5 to 10 in C. angulatus and 5 to 6 in C. altimanus), the longest intermolt period occurred at 21‰S, the shortest at 3‰S, in both species. Interspecific differences in response to low salinities may explain why C. angulatus occurs throughout a whole temperate coastal lagoon, whereas C. altimanus is restricted to its mouth.

A Comparative Analysis of Eutrophication Patterns in a Temperate Coastal Lagoon

The coastal bays and lagoons of Maryland extend the full length of the state's Atlantic coast and compose a substantial ecosystem at the land-sea margin that is characterized by shallow depth, a well-mixed water column, slow exchange with the coastal ocean, and minimal freshwater input from the land. For at least 25 years, various types of measurements have been made intermittently in these systems, but almost no effort has been made to determine if water quality or habitat conditions have changed over the years or if distinctive spatial gradients in these features have developed in response to changing land uses. The purpose of this work was to examine this fragmented database and determine if such patterns have emerged and how they may be related to land uses. Turbidity, dissolved inorganic phosphate, algal biomass, and primary production rates in most areas of the coastal bays followed a regular seasonal pattern, which was well correlated with water temperature. Nitrate concentrations were low (<5 μM), and only modestly higher in tributary creeks (<20 μM). Additionally, there was little indication of the spring bloom typical of river-dominated systems. There does appear to be a strong spatial gradient in water quality conditions (more eutrophic in the upper bays, especially in tributary creeks). Comparisons of water quality data collected between 1970 and 1991 indicate little temporal change in most areas and some small improvements in a few areas, probably related to decreases in point-source discharges. Seagrass communities were once extensive in these systems but at present are restricted to the eastern portion of the lower bays where water clarity is sufficient to support plant survival. Even in these areas, seagrass densities have recently decreased. Examination of diel dissolved oxygen data collected in the summer indicates progressively larger diel excursions from lower to upper bays and from open bays to tributary subsystems; however, hypoxic conditions (<2 mg 1−1) were rarely observed in any location. Nitrogen input data (point, surface runoff, groundwater and atmospheric deposition to surface waters) were assembled for seven regions of the coastal bay system; annual loading rates ranged from 2.4 g N m−2 yr−1 to 39.7 g N m−2 yr−1. Compared with a sampling of loading rates to other coastal systems, those to the upper and lower bays were low while those to tributaries were moderate to high. Regression analysis indicated significant relationships between annual nitrogen loading rates and average annual total nitrogen and chlorophyll a concentrations in the water column. Similar analyses also indicated significant relationships between chlorophyll a and the magnitude of diel dissolved oxygen changes in the water column. It is concluded that these simple models, which could be improved with a well-designed monitoring program, could be used as quantitative management tools to relate habitat conditions to nutrient loading rates.

Effects of organic enrichment on estuarine macrofaunal benthos: a comparison of sediment profile imaging and traditional methods

Sediment profile imaging (SPI) is a technique that involves collecting data In the field on sedimentary conditions, particularly vertical variations at and below the sed imen tha te r interface SPI approaches were developed nearly 20 yr ago, but have not been widely used in routine pollution monitoring efforts, although their potential for saving time and money is great. The present report is a comparison of SPI and 'traditional' (which involves excising a sediment sample, removing the organisms, and identifying and further processing them in the laboratory) benthic sampling techniques used along an organic enrichment gradient in a temperate coastal lagoon. Twenty-four core samples were taken in summer 1985 along an enrichment gradient mainly resulting from the discharge of sewage effluents, and processed by traditional rnacrofaunal benthic methods. Coincidental with these cores, sediment samples were taken for various physicochemical analyses, and optically clear acrylic box core samples were taken and analyzed in the field for changes in redox potential, dominant benthic taxa and their relative abundances, and sedimentary features. Various univariate and multivariate analyses of the benthic and sedimentary data showed substantial, and expected, changes along the pollution gradient. The changes were similar to those reported from other coastal waters affected by organic wastes: an area nearest the pollution source with lowest taxa numbers (S), abundances (A) and biomass (B); and increased S, A and B with increasing distance from the pollution source. Small near-surface polychaetes (capitellids and Streblospio benedicti) and the amphipod Ampelisca sp , were numerical dominants at all sites, and large, deep-burrowing species (e.g. Asychis elongata) were only found at the least-enriched sites SPI allowed identification of the dominant benthic taxa to useful levels ( e g . 'small near-surface dwelling annelids', 'large deep-burrowing polychaetes'), and location of the apparent color redox potential discontinuity (RPD) layer depth. The RPD ranged from about 1 cm at the site nearest the pollution source to 2 4 cm at the 2 sites farthest away. The SPI data were a s useful a s the traditional data in delimiting the spatial extent of the pollution-impacted benthos. It is suggested that a variety of coring devices presently exist for quickly and efficiently obtaining SPI data, especially in shallow waters.

Effects of organic enrichment on estuarine macrofaunal benthos: a comparison of sediment profile imaging and traditional methods

Sediment profile imaging (SPI) is a technique that involves collecting data In the field on sedimentary conditions, particularly vertical variations at and below the sed imen tha te r interface SPI approaches were developed nearly 20 yr ago, but have not been widely used in routine pollution monitoring efforts, although their potential for saving time and money is great. The present report is a comparison of SPI and 'traditional' (which involves excising a sediment sample, removing the organisms, and identifying and further processing them in the laboratory) benthic sampling techniques used along an organic enrichment gradient in a temperate coastal lagoon. Twenty-four core samples were taken in summer 1985 along an enrichment gradient mainly resulting from the discharge of sewage effluents, and processed by traditional rnacrofaunal benthic methods. Coincidental with these cores, sediment samples were taken for various physicochemical analyses, and optically clear acrylic box core samples were taken and analyzed in the field for changes in redox potential, dominant benthic taxa and their relative abundances, and sedimentary features. Various univariate and multivariate analyses of the benthic and sedimentary data showed substantial, and expected, changes along the pollution gradient. The changes were similar to those reported from other coastal waters affected by organic wastes: an area nearest the pollution source with lowest taxa numbers (S), abundances (A) and biomass (B); and increased S, A and B with increasing distance from the pollution source. Small near-surface polychaetes (capitellids and Streblospio benedicti) and the amphipod Ampelisca sp , were numerical dominants at all sites, and large, deep-burrowing species (e.g. Asychis elongata) were only found at the least-enriched sites SPI allowed identification of the dominant benthic taxa to useful levels ( e g . 'small near-surface dwelling annelids', 'large deep-burrowing polychaetes'), and location of the apparent color redox potential discontinuity (RPD) layer depth. The RPD ranged from about 1 cm at the site nearest the pollution source to 2 4 cm at the 2 sites farthest away. The SPI data were a s useful a s the traditional data in delimiting the spatial extent of the pollution-impacted benthos. It is suggested that a variety of coring devices presently exist for quickly and efficiently obtaining SPI data, especially in shallow waters.

Succession of two Acartia in estuaries : Jefferies H.P., 1962. Limnol. and Oceanogr., 7 (3): 354–364

Coastal lagoons are often exposed to intense short-term environmental changes and strong anthropogenic pressures influencing zooplanktonic communities and production. However, most works focus on long-term temporal scales using monthly or seasonal sampling strategies. The present study analysed the structure of the mesozooplanktonic assemblages, the production (egg production rates) and physiological condition (RNA:DNA ratio) of the copepod Acartia clausi in a temperate coastal lagoon (Ria Formosa) during the summer, using an intensive sampling approach. Salinity was the main factor affecting the short-term variability of mesozooplankton composition, followed by tidal phase (ebb tides) and semilunar cycle (spring tides). There was a positive relationship between the abundance of Appendicularia and the cladoceran Penilia avirostris with the toxic dinoflagellate Gymnodinium catenatum, suggesting no deleterious effects. The egg production rate of A. clausi was influenced by salinity and ammonia concentration, with a positive correlation between the egg productivity and the macronutrient, showing a possible adaptation of this calanoid species. The RNA:DNA index was positively related to egg production rate, suggesting that it is a good proxy for the reproductive output of copepods, even in short-term periods. This study shows that different timescales need to be included in regular monitoring of planktonic assemblages in coastal lagoons in order to understand the influence of environmental and anthropogenic variables on marine organisms.