Eutrophication Of Coastal Waters Research Articles

Assessing water quality and classifying trophic status for scientifically based managing the water resources of the Lake Timsah, the lake with salinity stratification along the Suez Canal.

Lake Timsah is considered as the biggest water body at Ismailia City with a surface area of 14 km2. It is a saline shallow water basin lies approximately mid-way between the south city of Suez and the north city of Port Said at 30o35′46.55“N and 32o19′30.54″E. Because it receives water with high and low salinities, salinity stratification is producing in the Lake Timsah, with values of 14–40‰ for the surface water and over 40‰ for the bottom water. The temperature of the lake water decreased to below 19 °C in the winter and rose to above 29 °C in the summer; the concentration of dissolved oxygen ranged between 6.5 and 12.2 l−1 and the pH fluctuated between 7.9 in its lower value and 8.2 in its higher value. Water transparency was very low as indicated by Secchi disc readings recorded during this study and varied between 0.3 and 2.7 m. The main chemical nutrient (phosphorus) reached its highest levels of 96 µg l−1 in winter and their lowest values of 24 µg l−1 during summer. This nutrient concentration is high especially by comparing with those of unpolluted marine waters, but is typical of the more eutrophic coastal waters worldwide. The composition and abundance of phytoplankton with dominancy of diatoms and increased population density (20,986 cell l−1) reflect the eutrophic condition of the lake. The intensive growth of phytoplankton was enriched by high concentration of chlorophyll a with annual values ranged between 6.5 and 56 µg l−1. The objective of the present work was quantitative assessment of the quality of the water of the Lake Timsah using different approaches. During the present study, three different approaches were applied for the quantitative assessment of Lake Timsah water quality: the trophic state index (TST); trophic level index (TLI) and water quality index (WQI). Application of the trophic state and trophic level indices (TSI & TLI) revealed that the Lake Timsah has trophic indices of 60 and 5.2 for TSI and TLI, respectively. Both indices reflected the eutrophic condition of the lake waters and confirmed that the eutrophication is a major threat in the Lake Timsah. On the other hand, the WQI calculated for the Lake Timsah during the present study with an average of 49 demonstrated that the water of the Lake Timsah is bad and unsuitable for main and/or several uses. Moreover, WQI allows accounting for several water resource uses and can serve a more robust than TSI and/or TLI and can be used effectively as a comprehensive tool for water quality quantification. In conclusion, the three subjective indices used for the assessment process for the lake water are more suitable and effective for needs of the sustainable water resources protection and management of the Lake Timsah.

Stable isotopes demonstrate the effectiveness of a tidally-staged sewage release system

Nutrient loading from sewage wastewater discharge contributes to the eutrophication of coastal waters. Wastewater from the Gold Coast, Australia is discharged into the Gold Coast Seaway (GCS) for 13.5 h d−1 primarily on the ebbing tide to disperse wastewater seawards. Nitrogen stable isotopes were used to assess how effectively the tidally staged release system dispersed wastewater out of the GCS and identified pathways by which sewage-N was incorporated into food webs. Turf algae, limpets and barnacles were sampled at the GCS, at two coastal sites and at the mouth of a control estuary that lacked point-source discharge. In the GCS δ15N values of algae and limpets returned to coastal baseline levels within 250 m of the diffusers. In contrast, δ15N of filter-feeding barnacles did not significantly vary indicating wastewater-N does not dominate the pelagic food web. Nitrogen stable isotopes clearly demonstrated that the tidally-staged wastewater release system effectively disperses wastewater offshore.

An Inventory of Marine Benthic Macroalgae of Hainan Island, China

In this review, the results of the study of marine benthic algal flora of Hainan Island, China, during the period from 1933 to 2015 are considered. It has been found that the local floristic diversity and taxonomic composition are similar to those of macroalgae from other large islands of the Indo-Pacific, where coral reefs are the main ecosystem of the shallow-water zone. An analysis of historical (decadal) changes in the marine benthic flora of Hainan has shown the following pattern of variations in the species diversity of macroalgae since the middle of the 20th century: a decline in low-productive epilithic algae with voluminous forms of thalli and an increase in highly productive opportunistic species with filamentous, fine filamentous, and membranous forms. These historical changes are thought to be caused by human impacts: inappropriate exploitation of coral reefs and eutrophication of coastal waters due to household sewage from large cities and discharge of mariculture wastes.

A modelling approach to assess the effects of atmospheric nitrogen deposition on the marine ecosystem in the Bohai Sea, China

Atmospheric deposited nitrogen (AD-N) approximates or exceeds riverine input in many coastal ecosystems, such as the Bohai Sea (BHS) which is one of the most eutrophic coastal waters in China. We construct a three-dimensional (3D) physical-biogeochemical model to understand the influence of atmospheric dissolved inorganic nitrogen (DIN) on the intra- and inter-annual variations of phytoplankton blooms and nutrient dynamics in the BHS. The biological component, which is coupled to the Regional Ocean Modelling System (ROMS), is a simple but widely used Nutrient-Phytoplankton-Zooplankton-Detritus (NPZD) model with eight state variables. The model simulation successfully reproduces the spatial and temporal variations of observed DIN and dissolved inorganic phosphorus (DIP) and the climatological features of phytoplankton biomasses (chlorophyll a), which confirms the major role of air-transported nutrients in controlling standing stocks and nutrient limitations. The modelling results show that the relative contributions of deposited nitrogen to the total DIN in the seawater for the Bohai, Laizhou and Liaodong Bays and Central Bohai Basin reach 84.8%, 49.3%, 37.4% and 44.4% on average, respectively. The relative contribution ratio is approximately 54% for the entire Bohai region, causing a 56.5% increase in the phytoplankton biomass on average. These results also indicate that the effects of AD-N on nutrient and phytoplankton dynamics vary widely in regional areas because of the uneven spatial distribution of nitrogen deposition fluxes and also partially because of the hydrodynamic conditions, shortwave radiation and water temperatures.

Economic assessment and environmental management of green tides in the Chinese Yellow Sea

Green tides are part of the larger class of harmful algal blooms (HAB), and have developed worldwide at a high rate during the last three decades, favoured by the eutrophication of coastal waters due to human activities. The massive accumulation of seaweeds on the shore resulting from green tides generates a variety of damages to market and non-market activities, and is a potential threat to human health. This work focuses on the green tide phenomenon in the Chinese Yellow Sea, and provides an economic assessment in a cost-benefit perspective. It first investigates the bioeconomic mechanisms of these episodes, their economic consequences, public management policies, and stakeholders' perceptions. Then, it tries to quantify the social cost of green tides, including management costs and residual costs to market and non-market activities. On this basis, alternative management scenarios are compared.

Phytoplankton can bypass nutrient reductions in eutrophic coastal water bodies

The EU-water framework directive aims at nutrient reductions, since anthropogenically induced eutrophication is a major threat for coastal waters. However, phytoplankton biomass in southern Baltic Sea coastal water bodies (CWB) remains high and the underlying mechanisms are not well understood. Therefore, a CWB data set was analysed regarding changes in phytoplankton biomass and nutrient concentration of nitrogen (N) and phosphorus (P) from 2000 to 2014. It was expected to find imbalances between produced phytoplankton biomass and total nutrient concentrations. Inner CWB were cyanobacteria-dominated and showed up to five times higher chlorophyll a-concentrations compared to outer CWB with similar total phosphorus-concentrations. Phytoplankton tended to be P-limited during spring and N-limited during summer. Phytoplankton biomass and nutrient concentrations were even higher during very humid years, which indicated a close coupling of the CWB with their catchment areas. This study suggests that re-mesotrophication efforts need to consider the importance of changed phytoplankton composition and nutrient availabilities.

Correction to Formation of Low-Molecular-Weight Dissolved Organic Nitrogen in Predenitrification Biological Nutrient Removal Systems and Its Impact on Eutrophication in Coastal Waters.

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionNEXTORIGINAL ARTICLEThis notice is a correctionCorrection to Formation of Low-Molecular-Weight Dissolved Organic Nitrogen in Predenitrification Biological Nutrient Removal Systems and Its Impact on Eutrophication in Coastal WatersHeonseop Eom, Douglas Borgatti, Hans W. Paerl, and Chul Park*Cite this: Environ. Sci. Technol. 2017, 51, 22, 13514Publication Date (Web):November 10, 2017Publication History Published online10 November 2017Published inissue 21 November 2017https://doi.org/10.1021/acs.est.7b05408Copyright © 2017 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views833Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (222 KB) Get e-Alerts Get e-Alerts

Aragonite saturation state in a tropical coastal embayment dominated by phytoplankton blooms (Guanabara Bay – Brazil)

The dynamics of the aragonite saturation state (Ωarag) were investigated in the eutrophic coastal waters of Guanabara Bay (RJ-Brazil). Large phytoplankton blooms stimulated by a high nutrient enrichment promoted the production of organic matter with strong uptake of dissolved inorganic carbon (DIC) in surface waters, lowering the concentrations of dissolved carbon dioxide (CO2aq), and increasing the pH, Ωarag and carbonate ion (CO32−), especially during summer. The increase of Ωarag related to biological activity was also evident comparing the negative relationship between the Ωarag and the apparent utilization of oxygen (AOU), with a very close behavior between the slopes of the linear regression and the Redfield ratio. The lowest values of Ωarag were found at low-buffered waters in regions that receive direct discharges from domestic effluents and polluted rivers, with episodic evidences of corrosive waters (Ωarag<1). This study showed that the eutrophication controlled the variations of Ωarag in Guanabara Bay.

Effects of elevated CO2 on phytoplankton during a mesocosm experiment in the southern eutrophicated coastal water of China

There is a growing consensus that the ongoing increase in atmospheric CO2 level will lead to a variety of effects on marine phytoplankton and ecosystems. However, the effects of CO2 enrichment on eutrophic coastal waters are still unclear, as are the complex mechanisms coupled to the development of eutrophication. Here, we report the first mesocosm CO2 perturbation study in a eutrophic subtropical bay during summer by investigating the effect of rising CO2 on a model artificial community consisting of well-characterized cultured diatoms (Phaeodactylum tricornutum and Thalassiosira weissflogii) and prymnesiophytes (Emiliania huxleyi and Gephyrocapsa oceanica). These species were inoculated into triplicate 4 m3 enclosures with equivalent chlorophyll a (Chl-a) under present and higher partial pressures of atmospheric CO2 (pCO2 = 400 and 1000 ppmv). Diatom bloom events were observed in all enclosures, with enhanced organic carbon production and Chl-a concentrations under high CO2 treatments. Relative to the low CO2 treatments, the consumption of the dissolved inorganic nitrogen and uptake ratios of N/P and N/Si increased significantly during the bloom. These observed responses suggest more extensive and complex effects of higher CO2 concentrations on phytoplankton communities in coastal eutrophic environments.

Simplifying Regional Tuning of MODIS Algorithms for Monitoring Chlorophyll-a in Coastal Waters

Monitoring of the phytoplankton pigment chlorophyll-a is often used as an indicator of eutrophication in coastal waters. Improved water quality monitoring using data sourced from MODIS (Moderate Resolution Imaging Spectroradiometer)-sourced data allows for infrequently sampled sites to be interrogated for long-term trends. Despite the wide availability and good spatial and temporal coverage of MODIS data, these data have had little use in operational coastal monitoring of chlorophyll-a in New Zealand. This is in part due to the poor performance of global oceanic algorithms applied in the coastal waters. Accessible algorithm tuning methods that can be validated by in situ measurements may assist the uptake of satellite data for coastal monitoring. This study presents results from regional tuning and validation of two empirical algorithm approaches, including a new simple exponential model, to estimate chlorophyll-a for two coastal locations in New Zealand. A novel method of training chlorophyll-a models using smoothed in situ data to match spatial scales of satellite observations was applied, and shows promise for improving tuned model performance. This approach shows potential for lowering barriers for researchers and coastal managers wishing to make use of the growing satellite data resource in their coastal environments.

Hypoxic Induced Decrease in Oxygen Consumption in Cuttlefish (Sepia officinalis) Is Associated with Minor Increases in Mantle Octopine but No Changes in Markers of Protein Turnover.

The common cuttlefish (Sepia officinalis), a dominant species in the north-east Atlantic ocean and Mediterranean Sea, is potentially subject to hypoxic conditions due to eutrophication of coastal waters and intensive aquaculture. Here we initiate studies on the biochemical response to an anticipated level of hypoxia. Cuttlefish challenged for 1 h at an oxygen level of 50% dissolved oxygen saturation showed a decrease in oxygen consumption of 37% associated with an 85% increase in ventilation rate. Octopine levels were increased to a small but significant level in mantle, whereas there was no change in gill or heart. There were no changes in mantle free glucose or glycogen levels. Similarly, the hypoxic period did not result in changes in HSP70 or polyubiquinated protein levels in mantle, gill, or heart. As such, it appears that although there was a decrease in metabolic rate there was only a minor increase in anaerobic metabolism as evidenced by octopine accumulation and no biochemical changes that are hallmarks of alterations in protein trafficking. Experiments with isolated preparations of mantle, gill, and heart revealed that pharmacological inhibition of protein synthesis could decrease oxygen consumption by 32 to 42% or Na+/K+ ATPase activity by 24 to 54% dependent upon tissue type. We propose that the decrease in whole animal oxygen consumption was potentially the result of controlled decreases in the energy demanding processes of both protein synthesis and Na+/K+ ATPase activity.

Phosphatase activities of a microepiphytic community during a bloom of Ostreopsis cf. ovata in the northern Adriatic Sea

It is becoming more apparent that increased organic nutrient loads deriving from anthropogenic activities and natural processes frequently cause the eutrophication of coastal waters. Concurrently, an increasing number of phototrophs have been shown to make use of organic nutrients, mainly through indirect studies of surface enzyme activities or through direct studies of growth in media containing organic-only nutrients. The potential utilization of dissolved organic phosphorus (DOP) by microepiphytic-mats associated with frequently problematic, toxic dinoflagellate Ostreopsis cf. ovata, was investigated throughout a full cycle of a bloom that occurs annually (over the last few decades) during summer along several stretches of the Mediterranean coast. Measurements of phosphomonoesterase (PMEase) and phosphodiesterase (PDEase) activities of the epiphytic mats (including cells and exopolymeric substances) and a range of chemico-physical parameters were made from late summer to early autumn at a eutrophic site.Analyses of ambient nutrient fractions revealed very high aquatic N:P values (TN:TP = 178 ± 50), very low filterable reactive P (FRP) concentrations (13 out 19 under the limits of detection) and DOP concentrations that were on average 85% of the total dissolved P. We recorded a rapid increase in PMEase and PDEase activities in the epiphytic microalgal community that coincided with the onset of a proliferation of the Ostreopsis population. Chromogenic staining of samples showed that activity was closely associated with the Ostreopsis cells, located both extracellularly (cell surface and within the EPS) and intracellularly (ventral cytoplasm). The increase in both phosphatases indicates that Ostreopsis can utilise a wide range of DOP types. The intense activity in the EPS was suggested to aid in the efficient entrapment and processing of high concentration nutrient pulses, for extracellular processing of larger organic materials and to prevent loss of substrates and products to the surrounding water. Based on the present findings, Ostreopsis seems to have adaptations that allow it to thrive in P-limited environments where organic P is the main source of P.

Effects of eutrophication and benthic respiration on water column carbonate chemistry in a traditional hypoxic zone in the Northern Gulf of Mexico

Abstract A simple river-ocean mixing approach has been frequently used to examine estuarine and coastal carbonate system speciation. Coastal areas receiving significant nutrient inputs, however, can have the carbonate chemistry greatly deviated from this mixing-only scheme because of disparate, but spatially coupled biogeochemical processes, i.e., intense primary production in surface waters and elevated respiration in bottom waters; the latter often leads to bottom-water hypoxia (dissolved oxygen or DO concentration − 1 ) and acidification. As a result of land use change, riverine TA input is known to enhance coastal water buffer capacity, although this effect in eutrophic coastal water has not been systematically studied. The physical disturbances of shallow coastal waters by storms can disrupt bottom hypoxia through overturning the water column. This overturn has been proposed to exacerbate bottom water acidification, because of the different exchange rates of oxygen and CO 2 , which could lead to a ‘reset’ of oxygen concentration but little change in the total dissolved inorganic carbon concentration. We used data from the summer 2010 hypoxia cruise in the northern Gulf of Mexico shelf, during which a tropical depression (Bonnie) perturbed the bottom water. Carbonate buffer capacity in both surface and subsurface waters along the salinity gradient suggested that eutrophication-induced surface production and bottom respiration far outweighed the influence of river TA variation and temperature changes in determining carbonate changes on centennial time scales. We propose, based on literature-based CO 2 flux reported in this area, that the benthic (both aerobic and anaerobic) respiration-produced CO 2 flux (with a lesser flux of alkalinity), instead of bottom water reset by storms, could be responsible for further acidifying hypoxic bottom water in addition to water column aerobic respiration.

Ecological and taphonomical influences on coccoliths in surface sediments in the shelf of the Yellow and East China Seas

Coccoliths, combined with sediment grain size, carbonate calcium and organic matters content, were analyzed to assess the ecological and taphonomical influences on coccolith distribution patterns in surface sediments in the continental shelf of the Yellow and East China Seas. Coccolith abundances ranged from 0 to 2.08×109 coccoliths g−1 sediment. The increasing abundance from the coastal inner shelf to the seaward middle shelf generally reflects the ecological fact that living coccolithophores are more abundant in the mesotrophic shelf waters than in the eutrophic coastal waters, although their deposits are still controlled by taphonomical effects, such as bottom (tidal) currents and calcite preservation conditions. Most abundant coccoliths are found in the fine-grained sediments of southwestern Cheju Island, where both ecology and taphonomy favor coccolith preservation. Still, large densities of coccoliths (>108 coccoliths g−1 sediment) are also found in coarse-grained relict sediments in the middle shelf. Coccolith assemblages were predominated by Gephyrocapsa oceanica and Emiliania huxleyi. The relative abundance of E. huxleyi, in addition to ecological reasons, may relate to selective post-mortem dissolution, since small E. huxleyi coccoliths are more susceptible to dissolution. Coccolith calcite has minor contributions (<1% to 12%) to total sediment CaCO3, and the main parts are attributed to terrigenous CaCO3 debris and relict shell fragments.

Formation of Low-Molecular-Weight Dissolved Organic Nitrogen in Predenitrification Biological Nutrient Removal Systems and Its Impact on Eutrophication in Coastal Waters.

To alleviate eutrophication in coastal waters, reducing nitrogen (N) discharge from wastewater treatment plants (WWTPs) by upgrading conventional activated sludge (CAS) to biological nutrient removal (BNR) processes is commonplace. However, despite numerous upgrades and successful reduction of N discharge from WWTPs, eutrophication problems persist. These unexpected observations raise the possibility that some aspects of BNR yield environmental responses as yet overlooked. Here, we report that one of the most common BNR processes, predenitrification, is prone to the production of low-molecular-weight dissolved organic N (LMW-DON), which is highly bioavailable and stimulates phytoplankton blooms. We found that in predenitrification BNR, LMW-DON is released during the post-aerobic step following the preanoxic step, which does not occur in CAS. Consequently, predenitrification systems produced larger amount of LMW-DON than CAS. In estuarine bioassays, predenitrification BNR effluents produced more phytoplankton biomass than CAS effluents despite lower N concentrations. This was also supported by stronger correlations found between phytoplankton biomass and LMW-DON than other N forms. These findings suggest that WWTPs upgraded to predenitrification BNR reduce inorganic N discharge but introduce larger quantities of potent LMW-DON into coastal systems. We suggest reassessing the N-removal strategy for WWTPs to minimize the eutrophication effects of effluents.

The contrasting effects of nutrient enrichment on growth, biomass allocation and decomposition of plant tissue in coastal wetlands

Eutrophication of coastal waters can have consequences for the growth, function and soil processes of coastal wetlands. Our aims were to assess how nutrient enrichment affects growth, biomass allocation and decomposition of plant tissues of a common and widespread mangrove, Avicennia marina, and how eutrophication drives changes in below-ground carbon sequestration. We assessed this through the measurement of above- and belowground growth and decomposition rates of plants and plant tissue in unenriched or nutrient enriched treatments. Nutrient enrichment increased biomass allocation above-ground compared to below-ground in seedlings but not in fully developed, mature trees where we observed the opposite pattern. Experiments to assess root decomposition found that 40–50% of biomass was lost within six months with little change between 12 and 18 months, indicating a high potential for accumulation of organic matter over time. We estimate root-derived carbon sequestration rates of 53, 250 and 94 g C m−2 year−1 for unenriched control, N and P enriched treatments, respectively. These results show coastal eutrophication can be beneficial and detrimental to ecosystem function of coastal plants. Eutrophication stimulates root growth in fully developed trees, increasing organic matter input to soils. Our data suggests that organic matter accumulation will increase in areas with high nutrient availability where root growth is increased and rates of decomposition are low.

A six thousand‐year record of climate and land‐use change from Mediterranean seagrass mats

Summary The Mediterranean seagrass Posidonia oceanica maintains a biodiverse ecosystem and it is a world‐wide important carbon sink. It grows for millennia, accumulating organic‐rich soils (mats) beneath the meadows. This marine habitat is protected by the European Union; however, it is declining rapidly due to coastal development. Understanding its response to disturbances could inform habitat restoration, but many environmental impacts predate monitoring programs (&lt;50 years). This research explores the palaeoecological potential of Posidonia mats to reconstruct six thousand years of environmental change that could have affected Posidonia meadows and, in turn, left an imprint on the mats. Palynological, microcharcoal, magnetic susceptibility and glomalin‐related soil protein (GRSP) analyses on Posidonia mats enabled us to detect climate‐ and human‐induced environmental processes impacting on the seagrass during the Late Holocene. The pollen and microcharcoal records reconstructed anthropogenic disturbances attributed to agriculture. The record of GRSP shows that agrarian activities affected continental soil quality. Changes in magnetic susceptibility reveal that enhanced soil erosion was caused by both climate (major flooding events in the NW Mediterranean) and humans (cultivation) which impacted on the Posidonia mat. Finally, increased human impact is linked to eutrophication of coastal waters since Roman‐Medieval times. Synthesis. This study shows that climate and land‐use changes in the western Mediterranean resulted in enhanced loadings of terrigenous material to the coastal zone since the Late Holocene, likely disturbing the Posidonia meadows and their mat carbon accumulation dynamics. Under the current global change scenario in which CO2 emissions are projected to increase, restoring carbon sinks is a priority. Seagrass habitat restoration should consider not only the coastal perturbations, but also the continental ones at a catchment scale to preserve the socio‐economic ecosystem services provided by seagrasses.

Formation of Low-Molecular-Weight Dissolved Organic Nitrogen in Predenitrification Biological Nutrient Removal Systems and Its Impact on Eutrophication in Coastal Waters

Formation of Low-Molecular-Weight Dissolved Organic Nitrogen in Predenitrification Biological Nutrient Removal Systems and Its Impact on Eutrophication in Coastal Waters

VARIABILITY IN PHYTOPLANKTON PIGMENT COMPOSITION IN MERSIN BAY

<div><!--block-->Phytoplankton pigment composition and associated biochemical (chlorophyll a, nitrate+nitrite, ammonia, phosphate, silicate) and physical (temperature, salinity) parameters were studied seasonally in the river-fed eutrophic coastal and oligotrophic offshore waters of the Mersin Bay located on NE Mediterranean. Total chlorophyll a concentrations varied seasonally between 0.023 - 7.73 µg/l in the river fed coastal zone (salinity: 36.54-39.68), exhibiting less seasonality in the offshore station (0.01 – 0.91 µg/l). Seven different phytoplankton taxa (namely diatoms, cyanobacteria, prymnesiophytes, dinoflagellates, chlorophytes, chrysophytes, prochlorophytes), determined by High Performance Liquid Chromatography (HPLC), were consistently present in the coastal waters during 2008-2011. The predominant diatom and coccolithophorid taxa in the river-fed coastal waters were replaced by prokaryotic picoplankters (cyanobacteria &amp;amp; prochlorophytes) and prymnesiophytes in the offshore. Contribution of prokaryotic picoplankton and eukaryotic nanoflagellates to total chlorophyll (% 23 to 47 and % 28 to 43, respectively) increased by about 50% from the coastal to the offshore station. Contribution of large cells to total chlorophyll decreased from 49% to 10% towards offshore. Prochlorophytes were observed as the dominant group in relatively colder and darker deep waters.</div>

Growth, feed utilization and energy budgets of the sea cucumber Apostichopus japonicus with different diets containing the green tide macroalgae Chaetomorpha linum and the seagrass Zostera marina

Apostichopus japonicus is one of the main aquaculture species in northern China. The green tide macroalgae Chaetomorpha linum and the seagrass Zostera marina occur in this region. Our previous study has suggested that Z. marina detritus can be a food source for A. japonicus. In the present study, we carried out a laboratory simulation experiment for 60days to understand whether C. linum can also be utilized to fulfill the nutrient demands of A. japonicus. The powdered C. linum and Z. marina detritus, mixed in five ratios (100:0; 75:25; 50:50; 25:75; 0:100), were fed to sea cucumbers along with muddy sediment in a fixed proportion. Sargassum thunbergii (40%) combined with the muddy sediment (60%) was also used as a standard reference/control diet. Results showed that the specific growth rates (SGRs), food utilizing efficiencies and energy budgets of A. japonicus were strongly influenced by the ratio of C. linum and Z. marina in their diets. The growth energy deposited in the bodies of sea cucumbers fed higher proportions of C. linum was significantly higher than those fed higher proportions of Z. marina. Furthermore, sea cucumbers fed on C. linum and S. thunbergii had similar growth performances. This study indicated that C. linum could replace S. thunbergii as a food source for A. japonicus. Statement of relevanceBecause of its high nutritive and medical properties, the sea cucumber Apostichopus japonicus has become a highly valuable fishery and aquaculture species in Asia. Influenced by eutrophication in coastal waters, blooming events of the green tide algae Chaetomorpha linum are increasing around the world, including some natural habitats for A. japonicus in northern China. However, whether C. linum can also be utilized to fulfill the nutrient demands of sea cucumbers, such as A. japonicus, is unknown. We carried out a laboratory simulation experiment for 60days to study this question. Our results showed that sea cucumbers fed on C. linum and Sargassum thunbergii had similar performances. Due to its higher protein and lower cellulose contents, C. linum was easier for A. japonicus to digest and absorb, and more energy per unit of food was converted to growth. This study indicated that C. linum could act as a food source for A. japonicus. The results of this research are also beneficial for promoting the collection and control of C. linum.