Eutrophication Of Coastal Waters Research Articles

Typhoon-induced precipitation impact on nutrient and suspended matter dynamics of a tropical estuary affected by human activities in Hainan, China

Typhoons regularly hit the coasts along the northern South China Sea during summer monsoon. However, little is known on the effects of typhoon-related heavy precipitation on estuarine dynamics and coastal ecosystems. We analyzed physico-chemical characteristics, and concentrations and composition of dissolved and suspended matter in the Wenchang/Wenjiao Estuary (WWE) on the tropical island of Hainan, China, prior to and after typhoon Kammuri in August 2008. Before the typhoon, the estuary displayed vertical and horizontal gradients. High nutrient inputs from agriculture and widespread aquaculture were to a large extent converted into biomass inside the estuarine lagoon resulting in low export of nutrients to coastal waters and a mainly autochthonous origin of total suspended matter (TSM). Heavy typhoon-associated precipitation increased river runoff, which moved the location of the estuarine salinity gradient seaward. It resulted in an export of dissolved and particulate matter to coastal waters one day after the typhoon. Dissolved nutrients increased by up to an order of magnitude and TSM increased approximately twofold compared to pre-typhoon values. Lower δ 13C org and δ 15N and elevated C/N ratios of TSM together with lower chlorophyll a (chl a) concentrations indicated an increased contribution of terrestrial material originating from typhoon-induced soil erosion. Local uptake of excess nutrients inside the lagoon was inhibited because of reduced water transparency and the lack of phytoplankton, which had been washed out by the initial freshwater pulse. Two weeks after the typhoon, TSM concentration and composition had almost returned to pre-typhoon conditions. However, physico-chemical properties and nutrients were still different from pre-typhoon conditions indicating that the estuarine system had not fully recovered. Unusually high chl a concentrations in the coastal zone indicated a phytoplankton bloom resulting from the typhoon-induced nutrient export. The typhoon-induced flushing of the WWE resulted in hyposalinity, reduced water transparency, siltation, as well as temporary eutrophication of coastal waters. These are physiological stressors, which are known to impair the performance of adjacent seagrass meadows and coral reefs. The predicted increase in typhoon frequency and intensity will lead to a frequently recurring exposure of coastal ecosystems to these threats, particularly in the South China Sea region where aquaculture is widespread and tropical cyclone frequency is at a maximum.

Marine ciliate community in relation to eutrophication of coastal waters in the Yellow Sea

We assessed the potential of marine ciliate community as an indicator to coastal water quality using water samples collected from four stations in the Yellow Sea in the summer 2000. The four stations were characterized by different levels of pollution. The ciliate communities consisted primarily of tintinnids and aloricate ciliates that were < 30 mu m. A total of 78 species were classified: 55 species at Station 2, 51 species each at Stations 1 and 4, and 47 species at Station 3. The mean number of species at each site was 29.2 +/- 2.0 (Station 1), 28.5 +/- 2.9 (Station 2), 27.8 +/- 1.7 (Station 3), and 24.5 +/- 2.3 (Station 4). The abundance was highly variable: 19 331 +/- 11 187 ind./L at Station 1, 7 960 +/- 5 639 ind./L at Station 2, 29 015 +/- 12 999 ind./L at Station 3, and 8 190 +/- 4 658 ind./L at Station 4. Our results suggest that neither the simple chemical analysis (e.g. chemical oxygen demand, dissolved inorganic nitrogen, and phosphate) nor the eutrophication/pollution index adequately described the water quality at the four stations. The same was true of the number of species and their abundance, both of which had no correlation with the chemical indices. In contrast, Margalef's diversity index values (3.12 at Station 2, 2.89 at Station 1, and 2.64 at Stations 3 and 4) generally discriminated the water quality status of the four stations. The difference in water quality among the stations was strongly supported by the pattern of species richness (i.e. the total number of species) of ciliates at each station. Our evaluation was consistent with the results of long-term water quality monitoring at the four stations. With increasing eutrophication, we observed also a compositional and functional shift in the ciliate assemblages from algivorous oligotrich/choreotrich to nonselective-omnivorous gymnostomatids to bacterivorous-detrivorous scuticociliatids. Thus, ciliates may be used to indicate the coastal water quality status of a given site.

Impact of biomass burning on ocean water quality in Southeast Asia through atmospheric deposition: eutrophication modeling

Abstract. Atmospheric deposition of nutrients (N and P species) can intensify anthropogenic eutrophication of coastal waters. It was found that the atmospheric wet and dry depositions of nutrients was remarkable in the Southeast Asian region during the course of smoke haze events, as discussed in a companion paper on field observations (Sundarambal et al., 2010b). The importance of atmospheric deposition of nutrients in terms of their biological responses in the coastal waters of the Singapore region was investigated during hazy days in relation to non-hazy days. The influence of atmospherically-derived, bio-available nutrients (both inorganic and organic nitrogen and phosphorus species) on the coastal water quality between hazy and non-hazy days was studied. A numerical modeling approach was employed to provide qualitative and quantitative understanding of the relative importance of atmospheric and ocean nutrient fluxes in this region. A 3-D eutrophication model, NEUTRO, was used with enhanced features to simulate the spatial distribution and temporal variations of nutrients, plankton and dissolved oxygen due to atmospheric nutrient loadings. The percentage increase of the concentration of coastal water nutrients relative to the baseline due to atmospheric deposition was estimated between hazy and non-hazy days. Model computations showed that atmospheric deposition fluxes of nutrients might account for up to 17 to 88% and 4 to 24% of total mass of nitrite + nitrate-nitrogen in the water column, during hazy days and non-hazy days, respectively. The results obtained from the modeling study could be used for a better understanding of the energy flow in the coastal zone system, exploring various possible scenarios concerning the atmospheric deposition of nutrients onto the coastal zone and studying their impacts on water quality.

Community structure of macrozoobenthic feeding guilds in responses to eutrophication in Jakarta Bay

Taurusman AA (2010) Community structure of macrozoobenthic feeding guilds in responses to eutrophication in Jakarta Bay.Biodiversitas 11: 133-138. The group of benthic fauna which feed on the same food sources are classified as a feeding guild. The objective of the present study was to evaluate the distribution and composition of macrozoobenthic feeding guilds along gradient of organic enrichment (trophic states) in Jakarta Bay. The result of the present study was shown that at the hypertrophic stations of the bay dominated by species of surface deposit feeding polychaetes such as, Dodecaceria sp., Cirratulus sp., Capitella sp., and Spionidae. The eutrophic zone of the bay was dominated by suspension feeding bivalves Mactra sp., Chione sp. The offshore area (mesotrophic zone)showed a high diversity of species and feeding guilds compared to other areas. The patterns of feeding guilds in the mesotrophic zone indicated a higher stability of macrozoobenthos community, indicated by the presence of deep-deposit feeder (e.g. Acetes sp.), surface deposit feeders (e.g. Prionospio sp.), suspension feeders (e.g. Chione sp.), and carnivores (e.g. Nephthys sp.) in comparable proportions.The structure of macrozoobenthic feeding guilds in an eutrophic coastal water is positively related to the quantity and quality of organic matters (eutrophic states), and the capability of benthic species in adaptation to such environmental condition.Key words: macrozoobenthos, feeding guild, eutrophication, coastal water, Jakarta Bay.

Mesozooplankton selective feeding in subtropical coastal waters as revealed by HPLC pigment analysis

Phytoplankton community composition and mesozooplankton selective feeding on dif- ferent phytoplankton taxa were studied by HPLC pigment analysis at 2 sites with contrasting hydro- graphy in the coastal areas of Hong Kong. The site (WE) on the western part of Hong Kong is located in the Pearl River estuary, whereas the site (EO) on the eastern part of Hong Kong is influenced by oceanic waters. Despite the strong difference in hydrographic conditions, diatoms were the dominant phytoplankton at both sites throughout most months of the year, contributing on average more than 40% of the total phytoplankton in terms of chlorophyll a (chl a). Cryptophytes were the second most abundant phytoplankton group at both sites, whereas contributions from haptophytes, green algae, cyanobacteria and dinoflagellates were small. Diatoms and cryptophytes, the 2 most dominant phyto- plankton groups, accounted for about 80 and 75% of the diets of mesozooplankton at EO and WE, respectively. One consistent pattern observed throughout the study period was that mesozooplank- ton assemblages strongly preferred dinoflagellates over other types of phytoplankton, especially in estuarine waters, even though dinoflagellates only contributed to a small fraction of total chl a. On the other hand, phytoplankton groups with relative small cell sizes, such as green algae and cyanobacte- ria, were not efficiently ingested. Overall, mesozooplankton feeding selectivity in subtropical eutrophic coastal waters, where planktonic food is sufficient, appears to be influenced by a combina- tion of different factors, including the compositions of predators and the size and quality of the prey.

Modeling of HABs and eutrophication: Status, advances, challenges

Harmful algal blooms (HABs) are often associated with eutrophication of coastal waters and estuaries. However, identifying quantitative relationships between nutrient input and proliferation of specific algal species is very challenging and complex. The complexity arises from the diversity of sources, forms and fluxes of nutrients both exported into and cycled within the system, the diversity of algal mechanisms for acquiring nutrients, and the interaction of the target harmful species with other members of the food web. Even more challenging is the development of forecasts and predictions, both on the short term and on the long term. Short term scales (days to weeks) are necessary for managers to prepare for, and respond to events; longer scales are needed to enable strategic planning to prevent HAB events, mitigate their impacts, or estimate the interactive effects of anthropogenic activities and climate change. To address these needs the HAB modeling community will need to engage with climate scientists (assess climate change scenarios), marine ecologists (describe organism ecophysiology), invasive species experts, watershed modelers and hydrologists (estimate future changes in the land derived inputs), and socio economists, managers and policy makers (define future land use scenarios and to interpret results in a policy context).

Nitrogen interception and export by experimental salt marsh plots exposed to chronic nutrient addition

Mass balance studies conducted in the 1970s in Great Sippewissett Salt Marsh, New England, showed that fertilized plots intercepted 60 to 80% of the nitrogen (N) applied at several treatment levels every year from April to October, where interception mechanisms include plant uptake, denitrification and burial. These results pointed out that salt marshes are able to intercept land-derived N that could otherwise cause eutrophication in coastal waters. To determine the long-term N interception capacity of salt marshes and to assess the effect of different levels of N input, we measured nitrogenous materials in tidal water entering and leaving Great Sippewissett experimental plots in the 2007 growing season. Our results, from sampling over both full tidal cycles and more inten- sively sampled ebb tides, indicate high interception of externally added N. Tidal export of dissolved inorganic N (DIN) was small, although it increased with tide height and at high N input rates. NH4 + export was gen- erally 2 to 3 times NO3 - export, except at the highest N addition, where DIN export was evenly partitioned between NO3 - and NH4 + . Exports of dissolved organic N were not enhanced by N addition. Overall, export of added N was very small, <7% for all treatments, which is less than earlier estimates. Apparent enhanced tidal export of N from N-amended plots ceased when N additions ended in the fall. Nitrogen cycling within the vegetated marsh appears to limit N export, such that interception of added N remains high even after over 3 decades of external N inputs.

Seasonal population dynamics and trophic role of planktonic nanoflagellates in coastal surface waters of the Southern Baltic Sea

We investigated the temporal dynamics and trophic role of different nanoflagellates in surface waters of the Gulf of Gdańsk (Baltic Sea) between April and October 2007. Two 18S rRNA gene clone libraries were constructed from samples collected in spring and summer, and weekly changes in the abundances of five phylogenetic groups were studied by fluorescence in situ hybridization with newly designed probes. Stramenopiles affiliated with MAST-6 and Pedinellales were most numerous in spring but rare in summer. Both groups formed short-lived blooms during a sudden drop of salinity due to riverine influx (from 7.1 to 6.2 practical salinity units). The analysis of food vacuole content suggested that MAST-6 nanoflagellates were herbivorous, whereas bacterivory was found both in plastidic and aplastidic pedinellid populations. Members of an uncultured lineage of aplastidic, bacterivorous cercozoans distantly related to Ebria tripartita were more abundant in summer when water temperatures exceeded 17 degrees C. Multicellular trophonts and/or free-living single cell stages of two lineages of Group 1 parasitic Syndiniales (alveolates) were present in spring and early summer. One of these alveolate populations repeatedly peaked before and after the freshwater influx, but was conspicuously absent throughout the period of decreased salinity. Our results indicate that nanoflagellate populations in coastal surface waters may form short-lived blooms that can only be detected by high-frequency sampling, and that may be related both to seasonal development and to sporadic (e.g. mixing) events. In view of their trophic diversity we moreover suggest that nanoflagellates in eutrophic coastal waters should not be regarded as a single functional unit.

The yield of microphytobenthic chlorophyll from nutrients: Enriched experiments in microcosms

The yield of phytoplankton chlorophyll from nitrogen is a useful parameter in the study of eutrophication of coastal waters, providing the link between chlorophyll formation and nutrient consumption. This parameter has been estimated for microphytobenthos from Ria Formosa lagoon on the south coast of Portugal with a series of three experiments conducted in May and September 2007. Six sediment cores were collected from Ria Formosa in acrylic cylinders and cork stoppers were placed in the bottom. Water samples were collected in large containers and prepared (filtered and enriched) to be pumped to the top of the sediment inside the acrylic cylinders, which are the microcosms of the experiments. Microcosms were isolated to avoid water exchanges and placed in large tanks full of water to maintain temperature stability. Experiments were run for 5 to 9 days in a continuous diluted nutrient enriched system. One of the experiments was carried out with half the microcosms in the dark to evaluate the nutrient fluxes between the sediment and the water column, when no algal growth is expected. Nutrient fluxes of muddy sediments, during the two last days of the experiment in the dark were estimated to be 0.1015 μmol cm − 2 d − 1 for nitrogen, − 0.0015 μmol cm − 2 d − 1 for phosphorus, and 0.1395 μmol cm − 2 d − 1 for silicon. The yield of chlorophyll was determined to be between 3.65 and 4.11 μg chl (μmol N) − 1 from nitrogen and between 4.03 and 4.77 μg chl (μmol Si) − 1 for silicon in muddy sediments. It was not possible to determine the yield from phosphorus. These values are higher than for phytoplankton which may be due to physiological reasons, or due to the presence of a smaller fraction of microheterotrophs, which would divert nutrients. For sand, smaller yields were obtained but it is likely that this was mainly due to the fact that the values of the sediment fluxes used were the ones obtained for mud, which are higher than they should be for sand. This extra input of nutrients is considered to be taken up by algae, thereby decreasing the value of the yield. Therefore, reliable chlorophyll yield estimates for sand could not be obtained.

Phytoplankton biomass size structure and its regulation in the Southern Yellow Sea (China): Seasonal variability

Phytoplankton size structure plays a significant role in controlling the carbon flux of marine pelagic ecosystems. The mesoscale distribution and seasonal variation of total and size-fractionated phytoplankton biomass in surface waters, as measured by chlorophyll a (Chl a), was studied in the Southern Yellow Sea using data from four cruises during 2006–2007. The distribution of Chl a showed a high degree of spatial and temporal variation in the study area. Chl a concentrations were relatively high in the summer and autumn, with a mean of 1.42 and 1.27 mg m −3, respectively. Conversely, in the winter and spring, the average Chl a levels were only 0.98 and 0.99 mg m −3. Total Chl a showed a clear decreasing gradient from coastal areas to the open sea in the summer, autumn and winter cruises. Patches of high Chl a were observed in the central part of the Southern Yellow Sea in the spring due to the onset of the phytoplankton bloom. The eutrophic coastal waters contributed at least 68% of the total phytoplankton biomass in the surface layer. Picophytoplankton showed a consistent and absolute dominance in the central region of the Southern Yellow Sea (>40%) in all of the cruises, while the proportion of microphytoplankton was the highest in coastal waters. The relative proportions of pico- and nanophytoplankton decreased with total biomass, whereas the proportion of the micro-fraction increased with total biomass. Relationships between phytoplankton biomass and environmental factors were also analysed. The results showed that the onset of the spring bloom was highly dependent on water column stability. Phytoplankton growth was limited by nutrient availability in the summer due to the strong thermocline. The combined effects of P-limitation and vertical mixing in the autumn restrained the further increase of phytoplankton biomass in the surface layer. The low phytoplankton biomass in winter was caused by vertical dispersion due to intense mixing. Compared with the availability of nutrients, temperature did not seem to cause direct effects on phytoplankton biomass and its size structure. Although interactions of many different environmental factors affected phytoplankton distributions, hydrodynamic conditions seemed to be the dominant factor. Phytoplankton size structure was determined mainly by the size-differential capacity in acquiring resource. Short time scale events, such as the spring bloom and the extension of Yangtze River plume, can have substantial influences, both on the total Chl a concentration and on the size structure of the phytoplankton.

Offshore advection of particles within the Cape Blanc filament, Mauritania: Results from observational and modelling studies

This article will review major features of the ‘giant’ Cape Blanc filament off Mauritania with regard to the transport of chlorophyll and organic carbon from the shelf to the open ocean. Within the filament, chlorophyll is transported about 400 km offshore. Modelled particle distributions along a zonal transect at 21°N showed that particles with a sinking velocity of 5 m d −1 are advected offshore by up to 600 km in subsurface particle clouds generally located between 400 m and 800 m water depth, forming an Intermediate Nepheloid Layer (INL). It corresponds to the depth of the oxygen minimum zone. Heavier particles with a sinking velocity of 30 m d −1 are transported from the shelf within the Bottom Layer (BL) of more than 1000 m thickness, largely following the topography of the bottom slope. The particles advected within the BL contribute to the enhanced winter–spring mass fluxes collected at the open-ocean mesotrophic sediment trap site CB-13 (∼200 nm offshore), due to a long distance advection in deeper waters. The lateral contribution to the deep sediment trap in winter–spring is estimated to be 63% and 72% for organic carbon and total mass, respectively, whereas the lateral input for both components on an annual basis is estimated to be in the order of 15%. Biogenic opal increases almost fivefold from the upper to the lower mesotrophic CB-13 trap, also pointing to an additional source for biogenic silica from eutrophic coastal waters. Blooms obviously sink in smaller, probably mesoscale-sized patches with variable settling rates, depending on the type of aggregated particles and their ballast content. Generally, particle sinking rates are exceptionally high off NW Africa. Very high chlorophyll values and a large size of the Cape Blanc filament in 1998–1999 are also documented in enhanced total mass and organic carbon fluxes. An increasing trend in satellite chlorophyll concentrations and the size of the Cape Blanc filament between 1997 and 2008 as observed for other coastal upwelling areas is not documented.

Salt marshes and eutrophication: An unsustainable outcome

Most plant production by emergent coastal marshes occurs belowground. This belowground production adds to the accumulation of organic matter sustaining salt marshes as sea level rises, thus preventing excessive flooding, eventual plant death, and habitat loss. The ubiquitous nutrient enrichment of coastal salt marshes stimulating aboveground plant growth may result in higher rates of inorganic matter accumulation that compensates for marsh flooding caused by sea level rise. Results from several short‐term experiments, however, demonstrate that root and rhizome biomass and carbon accumulation is reduced with nutrient enrichment, suggesting that eutrophication of coastal waters may not be a compensatory counterbalance to the effects of global sea level rise on salt marshes. We show that the net effects of 36 yr of nutrient enrichment in replicated field experiments do not lead to higher organic or inorganic accumulation. Enrichment reduces organic matter belowground and may result in a significant loss in marsh elevation equivalent to about half the average global sea level rise rates. Sustaining and restoring coastal emergent marshes is more likely if they receive less, not more, nutrient loading.

Spatial and Temporal Distribution of Zooplankton Communities of Coastal Marine Waters Receiving Different Human Activities (Fish and Pearl Oyster Farmings)

Seasonal changes of zooplankton communities were monitored at two coastal marine areas, Uchiumi and Fukuura Bays located at the Uwa Sea, east side of Bungo Channel. The two sites are close to each other (c.a. 20 km) with similar habitat environments, but receive different environmental stresses from aquaculture activities, pearl oyster farming for Uchiumi Bay and fish farming for Fukuura Bay. Since both bays have no inflowing river and small populations in the catchment, the impacts of different aquaculture activities on meso- and microzooplankton communities were compared. As results, Fukuura Bay showed higher ammonium and phosphate concentrations, suggesting that fish farming could accelerate eutrophication more seriously. The dominant species of mesozooplankton were similar at the two sampling sites with dominance of small coastal calanoid copepod, Paracalanus spp., but the abundances of larger calanoid species, Calanidae, Eucalanidae, Temoridae and Acartiidae, were markedly higher in Uchiumi Bay. Small cyclopoid copepods, Oithona spp. were abundant at both sites, but the densities varied seasonally, and often more abundant at Fukuura Bay. The abundances of microzooplankton including rotifers and small Oithona copepodids were higher at Fukuura Bay. Results suggest that fish farms accompanying discharge of nutrients from additional food supply for fish may seriously modify zooplankton community structure by decreasing the abundance of mesozooplankton through accelerating the eutrophication of coastal waters.

An ecological–economic model for catchment management: The case of Tonameca, Oaxaca, México

Coastal environmental impacts are generally due to both local and remote land uses. Eutrophication of coastal waters, for example, may be due to local urbanization and tourist development, but typically also stems from nutrient flows from agriculture away from coastal areas. To deal with this problem, catchment and coastal management need to be integrated. Management recommendations need to be supported by integrated analysis linking the geographically dispersed drivers of change from an appropriately interdisciplinary perspective. This paper presents an ecological–economic model that embeds existing food web models within fishery and tourism production functions. The aim is to identify optimal management strategies for catchments in which changes in nutrient loads have consequences for the relative abundance of economically important species. The model is calibrated on data for the Tonameca catchment, located on the coast of Oaxaca in Mexico.

Can the EU agri-environmental aid program be extended into the coastal zone to combat eutrophication?

Eutrophication of coastal waters is a serious environmental problem with high costs for society globally. This is a development which demands immediate environmental action along many coastal sites. Since the 1980s, mussel farming has been recognized by Swedish environmental authorities as a possible measure to improve coastal water quality. Concepts and management strategies on how to increase mussel farming and thus combat coastal marine eutrophication has recently been developed in Sweden. The main principle of this development has been the implementation of nutrient trading as a management tool. This imposes demands on those who emit the pollution through the establishment of emission quotas, which are traded and bought by the emitter. The seller is a nutrient harvesting enterprise, e.g., a mussel farmer. This principle is particularly straightforward when the nutrients are discharged from a point source. When examining the nutrient supply from all diffuse sources, the situation is more complex. However, since the major part of the nutrient supply to coastal waters in many areas of Europe has its origin in agricultural operations, we suggest that the EU agro-environmental aid program could be extended into the coastal zone in order to combat eutrophication. In practice, this should involve support paid to mussel farming enterprises through their harvest of mussels (and thus their harvest of nutrients) in the same way as support is paid to agricultural farmers for operations that reduce nutrient leakage from their farmland. This is a simple, cost-effective and straightforward way of improving coastal water quality at many coastal sites that will, at the same time, provide coastal jobs. However, this eutrophication combat method depends on the EU agro-environmental aid program being extended beyond the shoreline.

Global change and eutrophication of coastal waters

AbstractRabalais, N. N., Turner, R. E., Díaz, R. J., and Justić, D. 2009. Global change and eutrophication of coastal waters. – ICES Journal of Marine Science, 66: 1528–1537. The cumulative effects of global change, including climate change, increased population, and more intense industrialization and agribusiness, will likely continue and intensify the course of eutrophication in estuarine and coastal waters. As a result, the symptoms of eutrophication, such as noxious and harmful algal blooms, reduced water quality, loss of habitat and natural resources, and severity of hypoxia (oxygen depletion) and its extent in estuaries and coastal waters will increase. Global climate changes will likely result in higher water temperatures, stronger stratification, and increased inflows of freshwater and nutrients to coastal waters in many areas of the globe. Both past experience and model forecasts suggest that these changes will result in enhanced primary production, higher phytoplankton and macroalgal standing stocks, and more frequent or severe hypoxia. The negative consequences of increased nutrient loading and stratification may be partly, but only temporarily, compensated by stronger or more frequent tropical storm activity in low and mid-latitudes. In anticipation of the negative effects of global change, nutrient loadings to coastal waters need to be reduced now, so that further water quality degradation is prevented.

Development and application of an algorithm for detecting Phaeocystis globosa blooms in the Case 2 Southern North Sea waters

While mapping algal blooms from space is now well-established, mapping undesirable algal blooms in eutrophicated coastal waters raises further challenge in detecting individual phytoplankton species. In this paper, an algorithm is developed and tested for detecting Phaeocystis globosa blooms in the Southern North Sea. For this purpose, we first measured the light absorption properties of two phytoplankton groups, P. globosa and diatoms, in laboratory-controlled experiments. The main spectral difference between both groups was observed at 467 nm due to the absorption of the pigment chlorophyll c3 only present in P. globosa, suggesting that the absorption at 467 nm can be used to detect this alga in the field. A Phaeocystis-detection algorithm is proposed to retrieve chlorophyll c3 using either total absorption or water-leaving reflectance field data. Application of this algorithm to absorption and reflectance data from Phaeocystis-dominated natural communities shows positive results. Comparison with pigment concentrations and cell counts suggests that the algorithm can flag the presence of P. globosa and provide quantitative information above a chlorophyll c3 threshold of 0.3 mg m−3 equivalent to a P. globosa cell density of 3 × 106 cells L−1. Finally, the possibility of extrapolating this information to remote sensing reflectance data in these turbid waters is evaluated.

Nutrients' removal from aquaculture wastewater using the macroalgae Gracilaria birdiae

Intensive aquaculture releases large amount of nutrients into aquatic ecosystems and can lead to eutrophication of coastal waters. Studies conducted in aquaculture systems have demonstrated that the seaweeds are efficient in reducing nutrients and at the same time provides extra income, when species of economic importance are used. This study was conducted to evaluate whether Gracilaria birdiae could be cultivated efficiently for the production of useful algal biomass and removal of nutrients from shrimp pond effluents. The results obtained showed a gradual increase in biomass and relative growth rate (RGR) over the experimental period. Mean RGR between the weeks varied significantly (p < 0.01), reaching a maximum of 3.6 ± 0.35% d−1 and a minimum of 1.6 ± 0.52% d−1. The mean for the whole period was 2.6% d−1. The biofiltration capacity of G. birdiae was confirmed by the significantly reduced concentration of the three nutrients analyzed (PO43−, NH4+ and NO3−) over the study period. The concentration of PO43− decreased by 93.5%, NH4+ by 34% and NO3− by 100% after the 4-week experimental period. The results obtained in this study indicated that G. birdiae can be used in aquaculture systems as a biofilter. In addition, the macroalgae biomass produced offers alternative source of raw material for the extraction of the phycocolloid agar, human food and animal feed.

How well can we forecast high biomass algal bloom events in a eutrophic coastal sea?

High biomass algal bloom events are a characteristic of eutrophic coastal waters; these may result both in ecosystem degradation and economic loss. We present a skill evaluation of a coupled hydrodynamic ecosystem model of the NW European shelf for predicting bloom events based on a comparison with satellite chlorophyll estimates. By setting thresholds to define bloom events we use a binary classification system to generate maps showing the probability a model bloom prediction is correct. Model and satellite data limitations are discussed along with the application of this method to forecasting specific harmful algal species.

EFFECTS OF NUTRIENT ENRICHMENT ON PRIMARY PRODUCTION AND BIOMASS OF SEDIMENT MICROALGAE IN A SUBTROPICAL SEAGRASS BED(1).

Eutrophication of coastal waters often leads to excessive growth of microalgal epiphytes attached to seagrass leaves; however, the effect of increased nutrient levels on sediment microalgae has not been studied within seagrass communities. A slow-release NPK Osmocote fertilizer was added to sediments within and outside beds of the shoal grass Halodule wrightii, in Big Lagoon, Perdido Key, Florida. Gross primary production (GPP) and biomass (HPLC photopigments) of sediment microalgae within and adjacent to fertilized and control H.wrightii beds were measured following two 4-week enrichment periods during June and July 2004. There was no effect of position on sediment microalgal GPP or biomass in control and enriched plots. However, nutrient enrichment significantly increased GPP in both June and July. These results suggest that sediment microalgae could fill some of the void in primary production where seagrass beds disappear due to excessive nutrient enrichment. Sedimentary chl a (proxy of total microalgal biomass) significantly increased only during the June enrichment period, whereas fucoxanthin (proxy of total diatom biomass) was not increased by nutrient enrichment even though its concentration doubled in the enriched plots in June.