Eutrophication-induced changes in benthic algae affect the behaviour and fitness of the marine amphipod Gammarus locusta

This study, conducted in mesocosms, natural field sites, and in laboratory aquaria, showed that eutrophication altered the nutrient status and dominance patterns among marine macroalgae, which in turn, stimulated gammaridean density. Gammaridean abundance correlated positively with both nutrient addition and the amount of green algae (also stimulated by nutrient enrichment). Path analysis indicated that the direct effect of nutrients on gammaridean density was of less importance than the indirect effect through increased production of green algae. In cage colonisation experiments, either in the field or in a control mesocosm kept under ambient nutrient conditions, more gammarids colonised nutrient enriched algae (E-algae) than algae with ambient nutrient levels (A-algae). Gammarus locusta generally grew faster on nutrient enriched algal specimens and when reared on green rather than on brown algae (fucoids). The nutrient status of periphytic algae did not affect gammaridean growth significantly, but the number of egg-carrying females (and thus egg production) was significantly higher among gammarids reared on E-periphyton. The gammaridean habitat preference order (red > green > brown > periphyton) was almost the reverse of their growth rate in feeding assays (periphyton > green > brown). This implies that macroalgae may be more important as a habitat than as a food source for these animals, which then have to become mobile in search of optimal food items. In this process, algal nutrient content was important as the gammarids in our study actively chose high quality nutrient-rich food, which, in addition, increased their fitness. Stimulated growth rates and egg production may ultimately lead to population increase, which, combined with the preference for high nutrient food items may dampen the initial effect of nutrient enrichment (i.e. blooms of green macroalgae) in shallow coastal waters.     

Population dynamics of alien gammarid species in the River Odra estuary

During the period of 1988–2000, three alien gammarid species, i.e. Gammarus tigrinus Sexton, 1939, Pontogammarus robustoides G. O. Sars, 1894, and Dikerogammarus haemobaphes (Eichwald, 1841) were recorded in the Odra estuary. This study, the first record of G. tigrinus and P. robustoides in Poland, focuses on the distribution, abundance, and biomass as well as on population structure of the three new species found in the coastal zone of the estuary. G. tigrinus and P. robustoides were first sampled in the Szczecin Lagoon (mid-part of the estuary) in 1988. The densities of both species were high from the time they were first recorded and exceeded 10 000 ind. m^–2, while the biomass was 25 and 140 g m^–2, respectively. G.tigrinus occurred at higher densities in northern and eastern parts of the Lagoon, while P. robustoides was particularly abundant in the south-eastern part, most heavily affected by River Odra discharge. In 1999, the third gammarid, D. haemobaphes, was recorded in the southern part of the estuary. Both in 1999 and 2000, the species was found in qualitative samples (dredge collections of Dreissena polymorpha) taken from the western branch of the river. As estimated from quantitative samples, densities and biomass in the eastern branch were rather low and did not exceed 150 ind. m^–2 and 2.7 g m^–2, respectively. The Szczecin Lagoon population of G. tigrinus produces at least two generations within a year: a summer one and an overwintering one. The latter is dominated by older and larger specimens. The species may reproduce in the Lagoon from April until November.     

δ15N values of macroalgae as an indicator of the potential presence of waste disposal from land-based marine fish farms

The nitrogen isotope ratio (δ¹⁵N) in tissues of native macroalgae was evaluated as a means of indicating the intensity and spatial extent of organic contamination due to disposal of waste from land-based marine fish farms (LBMFFs). Three species of macroalgae from the genus Fucus and the green macroalgae Codium tomentosum were selected for study. The study was carried out at seven flat marine fish farms located in Galicia (NW Spain). Tests were carried out to determine the intra-annual variation in δ¹⁵N values and any differences between selected macroalgae. The δ¹⁵N values enrichment was observed close to the disposal point, and δ¹⁵N values varied more widely throughout the year (±5.57 ‰) at sites affected by the marine fish farm effluent compared to natural conditions (±2 ‰). No significant differences in the isotopic signals were observed in the different species studied (standard major axis). The δ¹⁵N values of macroalgae may be an ideal means of detecting the presence of LBMFFs effluents.     

Dispersal and development ofMarenzelleria spp. (Polychaeta, Spionidae) populations in NW Europe and The Netherlands

The North American spionid polychaeteMarenzelleria cf.wireni was first recorded in the North Sea by Scotland in 1982.Marenzelleria cf.viridis was first found in the Baltic Sea in 1985. Tentative routes of dispersal since then are presented in this paper. In the Netherlands, a biological monitoring programme has revealed populations ofM. cf.wireni in the Ems estuary, Wadden Sea, and in the SW Netherlands. In the Dollard (Ems estuary) a large population has developed (2000–3000 individuals m^?2; 8–16 g ash-free dry weight m^?2). Since the introduction, the macrozoobenthic community has changed from being dominated (by biomass) by bivalves, to domination by polychaetes. Recently, a similar population started to develop at Balgzand (western Dutch Wadden Sea).     

Tracing estuarine organic matter sources into the southern North Sea using C and N isotopic signatures

Sources and distribution of particulate organic matter in surface waters of the Humber and Thames estuaries and in the East Anglian plume in the southern North Sea were investigated in winter 2006/2007. Carbon (C) and nitrogen (N) stable isotopes provided evidence for the presence of three particulate organic matter sources; riverine plankton (δ¹³C ?30 ‰ and δ¹⁵N 7.9 ‰) identified in the Thames estuary only, marine plankton (average δ¹³C ?21.4 ‰ and δ¹⁵N 4.5 ‰) and a third source with an enriched ¹³C signature (>?16.7 ‰) and elevated C:N ratio (>12.7). Particulate organic matter with enriched ¹³C values were observed throughout the Humber estuary and at the marine end-member of the Thames estuary. While bacterial cycling of organic carbon undoubtedly takes place within these estuaries, these processes on their own are unlikely to account for the isotopic signatures seen. The ¹³C enriched organic matter source is suggested to be due to particulate organic matter input from marsh plants and seagrasses such as Spartina spp. and Zostera on the adjacent salt marshes and mudflats and/or macroalgae along the banks of the estuaries. This ¹³C enriched signal was also identified approximately 50 km offshore within the southern North Sea, in the East Anglian plume, which transports UK riverine water off-shore in a discrete plume. This plume therefore provides a mechanism to transport this estuarine derived organic matter pool offshore out of the estuaries. These results indicate that estuarine derived organic matter from marsh plants, seagrasses and/or macroalgae contributes to the southern North Sea organic matter pool and is therefore likely to contribute to winter-time shelf sea carbon and nitrogen cycles.     

Coastal zone use and migratory behaviour of the southern population of Mugil liza in Brazil

We analysed the ratios Sr:Ca and Ba:Ca in the otoliths of 55 adults of the southern population of Mugil liza in Brazil (Paraná to Rio Grande do Sul) to investigate its coastal zone use and migratory behaviour. All individual M. liza analysed had Sr:Ca and Ba:Ca values indicating that their birth was in the marine environment, which is consistent with the southern population migration to spawn in the ocean,. Juveniles exhibited at least three coastal use and recruitment strategies (contingents): the majority (89%) of M. liza juveniles migrated toward brackish water. They entered the estuary before completing the first year of life (64%) or after (25%) their first year of life. The remaining 11% did not appear to enter brackish or freshwater water as a nursery or at any point in their life cycle. Some adults returned to the estuary after spawning in the ocean but others (of both sexes) never returned to the estuary after spawning, remaining in the marine environment. The pattern of juvenile habitat use in the Brazilian southern population of M. liza seems to be recurrent throughout the extent of its distribution as a consequence of the reproductive spawning aggregation behaviour, which mixes all contingents (with marine or estuarine preferences).     

Observations on the life history of the belted sandfish,Serranus subligarius (Serranidae)

Synopsis The biology of Serranus subligarius, a typical inhabitant of low limestone reef outcroppings and artificial reefs from North Carolina to Florida and in the northern Gulf of Mexico, was studied on inshore jetties in the northeastern Gulf of Mexico from February 1974 to April 1975. The length-weight relationship was expressed by the equation W = 0.000006L^3.431. Growth was greatest in the first year (43.5 mm SL) and declined in the remaining three years of life (17.3, 10.5, and 7.1, respectively). In individuals larger than 40 mm SL, gammaridean and caprellid amphipods were the most numerous food items but crabs, shrimp, and fishes were the most important food items by weight. In individuals less than 40 mm SL, copepods were the most numerous food item, but gammaridean amphipods and shrimp were the most important items by weight. Two incidents of cannibalism were recorded. The ovotestis of the belted sandfish is composed of two lobes which are broadly united posteriorly, with the testicular tissue restricted to a broad band encircling the posterior region of the gonad. Age-group 1 fish are functional synchronous hermaphrodites. Testicular tissue matures in the fall or winter of a fish's first year (all specimens examined histologically, including those from the nonspawning season, contained flagellated spermatozoa) while ovarian tissue matures in the following spring. Spawning season in 1974 extended from late April or early May to September. Crossfertilization is the usual reproductive mode, although individuals are capable of selffertilization.     

Restoration flows for the Colorado River estuary, México: estimates from oxygen isotopes in the bivalve mollusk Mulinia coloradoensis (Mactridae: Bivalvia)

Because of competing demands for freshwater, restoration of estuaries requires estimates of inflows to sustain key species. In this study we estimated the pre-dam salinities of the Colorado River estuary by using oxygen isotopes in subfossil shells of the bivalve mollusk Mulinia coloradoensis. Since the construction of upstream dams and water diversions, average salinity in the estuary has increased to 38 practical salinity units (psu) and the population of M. coloradoensis has decreased by ~90%. In the pre-dam estuary, specimens grew when salinity ranged from 22 to 33?psu at the mouth of the river while populations 40?km distant grew at salinities from 30 to 38?psu. The river flow needed to reduce salinities at the mouth of the river to those recorded in the most distant localities (40?km from river??s mouth) ranges from 120 to 290?m³?s^?1. If these flows were sustained for a year, they would total 7?C16?% of the river??s annual average historical flow (~1.8?×?10¹⁰?m³).     

Epiphytes of the St. Lucia Estuary and their response to water level and salinity changes during a severe drought

St. Lucia is the largest estuary in South Africa with extensive areas of submerged macrophytes that fluctuate rapidly in response to water level and salinity changes. Epiphytes associated with submerged macrophytes were sampled during a severe drought between November 2004 and October 2005 when very low water level and high, variable salinity characterised the estuary. Potamogeton pectinatus and Ruppia cirrhosa were the dominant submerged macrophytes throughout the estuary, with P. pectinatus occurring at relatively low salinity (∼10 ppt) and R. cirrhosa at higher salinity (9–33 ppt). Zostera capensis, normally the other dominant submerged macrophyte, was conspicuously absent under the prevailing conditions. Epiphytic biomass, estimated as chlorophyll a, varied greatly between sites and over the 12 month sampling period, ranging from 10.9 to 71.7 mg Chl a m⁻² leaf area for P. pectinatus and 16.9–165.0 mg Chl a m⁻² leaf area for R. cirrhosa. Epiphytic biomass was twice as high in the Southern Lake where R. cirrhosa occurred, probably because the dominant epiphytes were macroalgae. An assessment of the diatom species composition of the epiphytic community indicated the dominance of only six species throughout the estuary. Neither epiphytic biomass nor diatom species composition showed strong statistical relationships with the environmental variables measured and it is believed that biological factors may be more important than the physico-chemical environment in determining epiphyte biomass distribution. Because epiphyte biomass is dependent on the presence of host surface area it will only contribute substantially to overall system biomass and productivity when submerged macrophyte area cover is high. In the St. Lucia Estuary this will occur when the water level is high and the upper level of the salinity gradient does not increase above that of seawater.     

Population traits and colonization success of non-native Eurasian perch (<Emphasis Type="Italic">Perca fluviatilis</Emphasis>) 35 years after its first appearance in the Mediterranean Lake Skadar

Abundance, spatial distribution, population structure and growth of non-native Eurasian perch (Perca fluviatilis) were examined in the Lake Skadar, a large, unstratified lake in the Mediterranean region inhabited by several endemic, rare and threatened fish species. Fish were caught in the infra-littoral and littoral habitats of the northern and central parts of the lake using multi-mesh gill nets over three consecutive years. Eurasian perch was among the most dominant species in both habitats. The mean relative abundance is - NPUE (0.556 individuals m^?2) and relative biomass is - WPUE (23.56 g m^?2) (years and habitats combined). Its population consisted primarily of individuals in first, second and third year of life span (0+???2+ age classes). The youngest fish in first and second year showed low mortality rates, older fish in third, fourth, fifth and sixth year of life span (age classes 2+???5+) experienced great losses, with mortality rates ranging from 0.6–1.0. The von Bertalanffy growth curve formula, expressing the expected total length L _t ?=?36.98 (1-e^{-0.23 (t?+?1.018)}) with growth performance value Φ ^’ ?=?2.50, revealed fast growth-in-length. Length-to-weight relationship was W_t?=?6.2?×?10^?3 L _t ^3.27, indicating positive growth-in-weight. It has been concluded that 35 years after the first finding in the Lake Skadar, Eurasian perch adapted well to local conditions in this Mediterranean environment, with the life span changed in favor of fast growth and early maturation.     

Population biology of the intertidal kelp, Alaria marginata Postels and Ruprecht: A non-fugitive annual

Persistence of annual plant populations requires sufficient seeds and suitable habitat for development and growth each year. Competition with perennials may prevent within site persistence and result in “fugitive” annual populations. Comparisons have been made between the population biology of annual macroalgae and terrestrial plants, but demographic information necessary to make strong comparisons is lacking for most of these algae, and life history differences may make such comparisons questionable. We studied population dynamics of the kelp Alaria marginata to determine if it was an annual and, if so, how populations persisted. This kelp is the dominant macroalga on exposed mid to low rocky intertidal shores along the Big Sur coast of California. Experimental clearings at two sites were used to assess recruitment timing and survivorship. Sporophytes were collected monthly to determine growth and fecundity. Recruitment occurred in late winter to early spring, primarily on geniculate corallines and residual A. marginata holdfasts. Thinning was inversely related to density, and occurred during the February through July growing season as larger thalli rapidly increased in length (up to 1.4 m month^− 1) and formed a thick canopy. Sorus development was positively related to size, began as early as March, peaked in late August-October, and decreased as adults were removed by winter surf. Spore release was generally highest (10⁸-10⁹ spores individual^− 11 h^− 1) between October and January and associated with high water motion. Survivorship of sporophytes beyond one year was < 1%, showing the populations were annual.Field observations and experiments on effects of canopy clearing, season of clearing, and influence of substrate type on recruitment were done to assess how these annual populations persist. Massive spore production at the onset of fall storms, survival of microscopic stages for 3-4 months facilitated by microhabitat refuges, rapid growth, large size and rapid maturation of sporophytes contributed to persistence. Furthermore, the dense stands with thick canopies may suppress potential competitors via shading and abrasion. Rather than being a fugitive, this combination of growth and life history features enables A. marginata and perhaps other large, annual kelps to maintain perennial populations.     

The green tide-forming macroalga Ulva linza outcompetes the red macroalga Gracilaria lemaneiformis via allelopathy and fast nutrients uptake

The objective of this study was to evaluate the interactions between green tide-forming macroalgae Ulva linza and red macroalgae Gracilaria lemaneiformis in the laboratory. The results demonstrated that the presence of U. linza can restrict growth (9–31 %) and photosynthesis (25–85 %) of G. lemaneiformis. In contrast, G. lemaneiformis had little apparent effect on the growth of U. linza. Culture medium experiments confirmed that allelochemicals may be released by both the tested macroalgae. The causative mechanism for the growth and photosynthesis inhibition of G. lemaneiformis was not light limitation nor increase of pH, but a combination of allelopathic effects of U. linza and nutrient competition between the two macroalgae. Moreover, the “green tide” macroalga U. linza was a stronger competitor for nutrient than G. lemaneiformis. The results from this study provide evidence for the mechanisms of “green tide” formation by U. linza: potent allelopathic effects on G. lemaneiformis and faster nutrients uptake than its competitors.     

The effect of salinity on the growth rate of the macroalgae Enteromorpha intestinalis (Chlorophyta) in the Mondego estuary (west Portugal)

The excessive growth of opportunistic macroalgae in estuaries and other coastal areas, characterised by enormous values of vegetal biomass in the form of dense mats, is a common and widespread picture nowadays. In such conditions, macroalgae completely dominate the nutrient dynamics in the ecosystem and function as high quality food for the microbial, meio- and macrofaunal communities. Due to their important role in the nutrient pathways of the ecosystems, it becomes essential to obtain new information on variables and processes that regulate the bloom formation of these primary producers. The Mondego estuary (west Portugal) is a eutrophic estuary, where usually macroalgae of the genera Enteromorpha seasonally bloom. Nevertheless, in years with high precipitation characterised by a significant increase of the freshwater runoff to the system, no Enteromorpha blooms are observed. Possible explanations for this are related to the reduction of light in the water column, high water speed, high sediment turbulence and low salinity values. Thus, because the decrease in salinity seemed an important feature during such periods, a set of experiments were conducted, to evaluate to what extent the growth of Enteromorpha intestinalis (the most abundant species in the Mondego estuary) is affected by fluctuations in salinity and, particularly, by low salinity values. In the laboratory, the growth rate of E. intestinalis was tested against a range of salinity, from 0 to 32 psu. E. intestinalis showed the lowest growth rates at extreme low salinity values (≤ 3 psu) and for salinity ≤ 1 psu, the algae died. Growth rates at salinity lower than 5 psu and higher than 25 psu were also low, when compared with growth between salinity of 15 and 20 psu, where E. intestinalis showed the highest growth rates. These results agree with the field observations and suggest that, in the Mondego estuary, salinity is an important external parameter to control the growth of E. intestinalis, which has important ecological implications for the system.     

Origin here,impact there—The need of integrated management for river basins and coastal areas

This study highlights the effect that estuarine polluted waters may have on adjacent coastal waters and the need of an integrated management of the coastal area. Pollution of land-to-sea water plumes varies spatially and temporally, being difficult, costly and time consuming to determine. However, the reduction in water quality of both estuarine and coastal environments and the consequent degradation of its biological communities is at issue. Chlorophyll-a analysis from water and stable nitrogen isotopic analysis (δ¹⁵N) from opportunistic macroalgae Ulva species were respectively used as proxies to detect phytoplankton proliferation and nitrogen related nutrient fluxes in the water. These analytical techniques were combined with the use of three-dimensional hydrodynamic models, and revealed to constitute reliable early warning instruments, able to identify coastal areas at risk, and supporting an integrated management of coastal and river basin areas. The approach detected synchronized δ¹⁵N signal variations along time between estuarine sites (Mondego estuary, Portugal) and nearby adjacent coastal shore sites (NE Atlantic coast). The higher values recorded by macroalgal tissues’ δ¹⁵N signals, which occurred simultaneously to higher chlorophyll-a values, were linked to the anthropogenic contamination of the water, probably related with the Mondego valley land use patterns throughout the year (reflecting the opening of sluices that drain agriculture fields). Modeling scenarios point to a Mondego’s influence that is able to reach its adjacent coastal shores in about 7 km from its river mouth. The methodology used here is replicable elsewhere and allowed to track nutrients from the source, inside the estuary, until the final area of impact, where primary producers may use those for growth, and to define vulnerable areas on adjacent coastal zones.     

Reproduction, population dynamics, growth and production ofScrobicularia plana da costa (pelecypoda) in the Bidasoa estuary, Spain

The breeding cycle, recruitment, population dynamics, growth and production ofScrobicularia plana were studied at one station in the Bidasoa estuary (SE of the Biscay Bay, Spain) during a period of 3 or 4 years. To complete this study, the reproduction for a period of 1 year was analysed at two other sites of the estuary. At none of the stations important differences in spawning activity were observed between the different years. The animals reproduced for the first time when they reached the age of two years. The histological data and the recruitment analysis showed only one spawning period between June and mid-September, with a peak in July-August. This breeding pattern differs from those shown by other southern European populations. The recruitment of spat (0.25–0.50 mm) occurred from June–July to October–December in different years. The population showed different annual patterns of density and population structure, depending on recruitment success. Growth was most rapid in spring and summer. The bivalves reached a mean length of 21.8 mm at the age of approximately 16 months; in the following year they grew to 30 mm. The growth during the life span fitted the theoretical growth equation of Von Bertalanffy. Annual production was in the range of 59.0–83.4 g AFDW m^–2 year^–1. The P/B ratios of the population varied between 0.84 and 1.48 (1.06 ± 1.36; ¯x ± 95% C.I.).     

Biology,abundance, and life cycle of big-head Far East goby <Emphasis Type="Italic">Gymnogobius urotaenia</Emphasis> (Gobiidae) from the Serebryanka River (Central Primor’e)

Biology and seasonal (from May to November) population dynamics of big-head Far East goby Gymnogobius urotaenia from the Kolkhoznaya channel is analyzed (the estuary part of the Serebryanka River). This species attains length 145 mm, weight 23.9 g, and age 5+. Males live one year longer than females. In both sexes, the highest growth rate is observed in the first and second years of life, and that of weight growth is observed in the third and fourth years. It spawns from the end of May until the end of June. The absolute fecundity does not exceed 4000 eggs. The base of the diet consists of mysids. This is an abundant species. The annual life cycle of G. urotaenia comprises spawning migration, spawning, embryonic development, pelagic larval stage, the phase of transition to bottom mode of life, feeding, and wintering migration.     

Macroalgal-mediated transfers of water column nitrogen to intertidal sediments and salt marsh plants

In many temperate estuaries, mats of opportunistic macroalgae accumulate on intertidal flats and in lower elevations of salt marshes, perhaps playing a role in linking water column nitrogen (N) supply to these benthic habitats. Using a flow-through seawater system and tidal simulator, we varied densities (equivalent to 0, 1, 2, or 3 kg m⁻² wet mass) of ¹⁵N-labelled macroalgae (Enteromorpha intestinalis) on estuarine sediments in microcosms with/without pickleweed (Salicornia virginica) to assess N transfers from algae. In the 6-week experiment, macroalgal biomass increased from initial levels in the lower density treatments but all algae lost N mass, probably through both leakage and decomposition. With all densities of algae added, sediments and pickleweed became enriched in ¹⁵N. With increasing mat density, losses of algal N mass increased, resulting in stepwise increases in ¹⁵N labeling of the deeper sediments and pickleweed. While we did not detect a growth response in pickleweed with macroalgal addition during the experiment, N losses from algal mats that persist over many months and/or recur each year could be important to the mineral nutrition of N-limited marsh plants. We conclude that N dynamics of intertidal sediments and lower salt marsh vegetation are linked to the N pools of co-occurring macroalgae and that further study is needed to assess the magnitude and importance of N transfers.     

The effect of different primary producers on Hydrobia ulvae population dynamics: a case study in a temperate intertidal estuary

The effect of macroalgal blooms and the consequent disappearance of Zostera noltii meadows on Hydrobia ulvae population dynamics and production was studied in the Mondego estuary based on data obtained from January 1993 to September 1995. Sampling was carried out at a non-eutrophicated area, covered with Z. noltii, and also at an eutrophicated area, where seasonal Enteromorpha spp. blooms occur.Stable populations represented by individuals of all age classes were found only at the Z. noltii meadows throughout the study period. On the contrary, at the eutrophicated area, during most of the time, solely juveniles were present, with adults appearing only during the macroalgal bloom (>1.5 mm width).During the algal bloom (e.g. 1993), H. ulvae population density was clearly higher in the eutrophicated area due to the combined effect of stronger benthic recruitments (99% of veliger larvae newly recruited) and dispersion of juveniles proceeding from the Z. noltii meadows to this area. On the other hand, in the absence of macroalgae (spring of 1994), 98.9% of veliger larvae was recruited in the Z. noltii meadows. Therefore, H. ulvae seems to respond rapidly to macroalgal dynamics and its presence at the eutrophicated area depends on the existence of green macroalgae.H. ulvae presented the same benthic recruitment pattern at the two sampling areas, with new cohorts being produced in March, June, July and September. Depending on the time of the year in which the recruitment took place, cohorts showed different growth rhythms. However, after 12 months they reached a similar size.A three-generation life cycle involving a short-lived (16 months), fast growing spring generation, a medium growing (17-19 months) summer generation and a longer-lived (20 months) slower growing generation that overwinters is identified.As a general trend, productivity and mean population standing biomass were higher at the Z. noltii meadows, during the entire study, except for a short period, during the macroalgal bloom, when production was higher at the eutrophicated area. On the contrary, P/B? ratios were higher at the eutrophicated area. According to our results, H. ulvae population structure and yearly productivity are clearly affected by eutrophication, namely by the dynamics of macroalgal blooms.In the long run, we may infer that, following the disappearance of the Z. noltii meadows, due to eutrophication, H. ulvae would also tend to disappear, since reproductive adults were almost exclusively found in this area.     

Copepod biomass in an estuarine and a stagnant brackish environment of the S. W. Netherlands

In the mesohaline zone of the Westerschelde estuaryEurytemora affinis is the dominant copepod, demonstrating large biomass values nearly throughout the year. In the meso-polyhaline Lake VeereAcartia tonsa is abundant, mainly during summer. In spring a small population ofEurytemora americana is found. The tidal estuary harboured far denser copepod populations throughout the year than the stagnant brackish lake water. The average yearly copepodid+adult biomass in the Westerschelde estuary was approx. 850 mg/m³ (wet weight), in Lake Veere approx. 130 mg/m³. Temporarily low oxygen values did not influence negatively the copepod populations in the Westerschelde estuary. The seasonal distribution of the dominant copepods in both areas is explained in the light of recent litterature data. PerennialEurytemora affinis abundance in the Westerschelde estuary must be mainly caused by large concentrations of nannodetritus particles, bacteria included, throughout the year.Acartia tonsa in Lake Veere has to thrive mainly on nannophytoplankton. Communication no. 141 of the Delta Institute for Hydrobiological Research, Yerseke, The Netherland.     

Comparison of macroalgal (Ulva and Grateloupia spp.) and formulated terrestrial feed on the growth and condition of juvenile abalone

The culture of abalone is a growth industry in Australia that primarily utilises terrestrial crops to produce formulated pellet feeds. The use of cultivated macroalgae in place of such feeds could provide for better environmental, nutritional and/or economic outcomes for this industry. However, direct comparison trials using macroalgae and formulated crop feeds are rare, and it is therefore difficult to ascertain the benefits and costs of each feed type. This study compares the benefits to growth and performance of the cultivated hybrid abalone cross (Haliotis rubra 1814 Leach and Haliotis laevigata 1808 Donovan) which was fed one of eight dietary treatments, including two commercially formulated pellet feeds and six mixed macroalgae dietary treatments. Macroalgae dietary treatments comprised the three macroalgae species Grateloupia turuturu Yamada, Ulva australis Areschoug and/or Ulva laetevirens Areschoug. Four replicate tubs, each containing 40 juvenile abalone (10–15 mm), were used to test each dietary treatment over a 12-week period. Macroalgae dietary treatments provided for significantly higher specific growth rates of abalone compared to formulated feeds, by orders of magnitude, for both length (>0.2 % compared to <0.1 %?day^?1, F _{7, 31}?=?22.3, p?<?0.0001) and weight (from <0.4 to >0.8 %?day^?1, F _{7, 31}?=?24.4, p?<?0.0001). In addition, abalone health and condition increased, and the proximate composition of abalone tissue had a higher carbohydrate/protein ratio, higher ash content and lower lipid content. These findings suggest that the juvenile abalone may benefit from macroalgae diets in comparison to two formulated feeds as a result of optimal proximate composition of the algae biomass and improved condition of the abalone.