Eutrophication and macroalgal blooms in temperate and tropical coastal waters: nutrient enrichment experiments with Ulva spp.

Receiving coastal waters and estuaries are among the most nutrient‐enriched environments on earth, and one of the symptoms of the resulting eutrophication is the proliferation of opportunistic, fast‐growing marine seaweeds. Here, we used a widespread macroalga often involved in blooms, Ulva spp., to investigate how supply of nitrogen (N) and phosphorus (P), the two main potential growth‐limiting nutrients, influence macroalgal growth in temperate and tropical coastal waters ranging from low‐ to high‐nutrient supplies. We carried out N and P enrichment field experiments on Ulva spp. in seven coastal systems, with one of these systems represented by three different subestuaries, for a total of nine sites. We showed that rate of growth of Ulva spp. was directly correlated to annual dissolved inorganic nitrogen (DIN) concentrations, where growth increased with increasing DIN concentration. Internal N pools of macroalgal fronds were also linked to increased DIN supply, and algal growth rates were tightly coupled to these internal N pools. The increases in DIN appeared to be related to greater inputs of wastewater to these coastal waters as indicated by high δ¹⁵N signatures of the algae as DIN increased. N and P enrichment experiments showed that rate of macroalgal growth was controlled by supply of DIN where ambient DIN concentrations were low, and by P where DIN concentrations were higher, regardless of latitude or geographic setting. These results suggest that understanding the basis for macroalgal blooms, and management of these harmful phenomena, will require information as to nutrient sources, and actions to reduce supply of N and P in coastal waters concerned.     

GRACILARIA EDULIS (RHODOPHYTA) AS A BIOLOGICAL INDICATOR OF PULSED NUTRIENTS IN OLIGOTROPHIC WATERS

The response of the marine macroalga Gracilaria edulis (Gmelin) Silva to nutrient pulses of varying magnitude was investigated to test its applicability as a marine bioindicator at two oligotrophic locations. After exposure to nutrient pulses, algal amino acid, tissue nitrogen, and chlorophyll a content were assessed relative to algae incubated under control conditions (no nutrient enrichment). The smallest nutrient pulse involved a nutrient enrichment experiment conducted within a coral atoll, whereas two larger pulses resulted from sewage discharge to a tropical coastal bay. After exposure to the smallest nutrient pulse (10 × ambient), only changes in macroalgal amino acid concentration and composition were detected (mainly as increases in citrulline). At 100 × ambient concentrations, increases in tissue % nitrogen of the macroalgae were detected, in addition to responses in amino acids. Macroalgae exposed to the highest nutrient pulse (1000 × ambient) responded with increased chlorophyll a , tissue nitrogen, and amino acids within the three day incubation period. In contrast to these algal responses, analytical water sampling techniques failed to detect elevated nutrients when nutrient pulses were not occurring. The responses of this algal bioindicator to variable nutrient pulses may provide a useful tool for investigating the source and geographical extent of nutrients entering oligotrophic coastal waters.     

Rapid physiological assays for nutrient demand by the plankton. I. Nitrogen

Three assays for nitrogen demand were compared on samples ofnatural plankton and on green and blue-green algal species inculture. The most reliable guide was selective luxury uptakeof nitrogen by the plankton after enrichment with a 10-to-1(wt/wt) mixture of inorganic N and P. Ammonium transport capacity,measured either directly (cultures) or by V_max for uptake ofthe NH₄⁺ analogue methylammonium (lakewaters), was generallyhigh in lakewaters with low dissolved inorganic N-to-P ratiosand in N-deficient cultures of green algae. By contrast, transportcapacity was much reduced in both natural and cultured populationsof heterocystous blue-green algae growing under conditions oflow combined inorganic nitrogen. Ammonium enhancement assays(heterotrophic CO₂, fixation after NH₄⁺ enrichment) were conductedat monthly intervals on eutrophic Lake Rotorua. There was astrong, negative correlation between this indicator of N deficiencyand dissolved inorganic N-to-P ratios below a threshold of 6:1.Ammonium enhancement was not, however, a reliable indicatorof combined inorganic N-demand by populations of heterocystousblue-green algae. All three assays provided strong evidenceof a persistent shortage of nitrogen relative to phosphorusfor algal production in Lake Rotorua.     

The effects of nutrients and their ratios on phytoplankton abundance in Junk Bay,Hong Kong

Eutrophication has been considered to be undoubtedly one of the key factors stimulating phytoplankton growth, since it involves the enrichment of a water mass with both inorganic and organic nutrients supporting plant growth. Nutrient enrichment as a result of anthropogenic activity occurs in estuaries and coastal waters as well as in lakes and freshwater impoundments, and blooms of phytoplankton are one of the effects of such an accelerated process of nutrient enrichment. This paper presents the results of a two-year survey of the nutrients and phytoplankton at 3 stations in Junk Bay, Hong Kong, carried out from 1997 to 1998. The relationships between nitrogen, phosphorus, and their ratio, with phytoplankton abundance have been studied. The results show that the highest nitrogen concentration was in Station 2 which is close to a sewage input, whereas the highest phosphorus concentration was in Station 1 which is close to a landfill area. The mean N:P ratios at the three stations were between 8 and 14. The diatoms were the dominant group during most of the year but it seems that diatoms were more sensitive than dinoflagellates and other algal groups to the increase in nutrients.     

Bioassays with Stigeoclonium Kütz. (Chlorophyceae) to identify nitrogen and phosphorus limitations

Eleven strains of the filamentous algae genus Stigeoclonium Kütz. (Chlorophyceae) were tested as bioassay organisms to identify nitrogen and phosphorus limitations to growth in a variety of waters. The assay results were related to the nutrient status of the waters during the year. Optimal growth was obtained at an inorganic phosphorus concentration of 0.65 mg P 1^?1 and an inorganic nitrogen concentration of 3.75 mg N 1^?1. The algal growth potentials were generally higher in November and February than in August. In summer, nitrogen became important as a limiting nutrient. When ratios of inorganic nitrogen to inorganic phosphorus (N/P) were above 6.2, phosphorus was primarily limiting and at lower N/P ratios nitrogen became the important limiting factor. Stigeoclonium proved to be a suitable bioassay organism to identify nutrient limitation in freshwaters.     

Is the invasion of Prorocentrum minimum (Dinophyceae) related to the nitrogen enrichment of the Baltic Sea?

The abundance of the invasive, bloom-forming dinoflagellate Prorocentrum minimum (Pavillard) Schiller and triangular, oval, and oval-round cell shapes were examined relative to salinity, temperature, and nutrient concentrations at the selected sites in the Baltic Sea. Based on the multiple regression and multivariate statistical analysis, all cell shapes of P. minimum had highly similar distribution relative to these environmental parameters as well as chlorophyll-a, nitrite + nitrate, ammonium, total nitrogen, phosphate, total phosphorus, and silicate. The species was related positively to total nitrogen, and negatively to salinity, temperature, nitrite + nitrate, and silicate:total nitrogen ratio. The results suggest that P. minimum could well adapt to low salinity and temperature and occurred particularly in coastal waters, rich in total nitrogen relative to silicate or other inorganic nutrients. These results indicate that the recent invasion of P. minimum into the Baltic Sea could have been enhanced by the DON enrichment. The results also support the suggestion that P. minimum is one morphospecies with no distinct subtaxa.     

New insights into carbon acquisition and exchanges within the coral–dinoflagellate symbiosis under NH4+ and NO3? supply

Anthropogenic nutrient enrichment affects the biogeochemical cycles and nutrient stoichiometry of coastal ecosystems and is often associated with coral reef decline. However, the mechanisms by which dissolved inorganic nutrients, and especially nitrogen forms (ammonium versus nitrate) can disturb the association between corals and their symbiotic algae are subject to controversial debate. Here, we investigated the coral response to varying N : P ratios, with nitrate or ammonium as a nitrogen source. We showed significant differences in the carbon acquisition by the symbionts and its allocation within the symbiosis according to nutrient abundance, type and stoichiometry. In particular, under low phosphate concentration (0.05 µM), a 3 µM nitrate enrichment induced a significant decrease in carbon fixation rate and low values of carbon translocation, compared with control conditions (N : P = 0.5 : 0.05), while these processes were significantly enhanced when nitrate was replaced by ammonium. A combined enrichment in ammonium and phosphorus (N : P = 3 : 1) induced a shift in nutrient allocation to the symbionts, at the detriment of the host. Altogether, these results shed light into the effect of nutrient enrichment on reef corals. More broadly, they improve our understanding of the consequences of nutrient loading on reef ecosystems, which is urgently required to refine risk management strategies.     

Phytoplankton nutrient deficiency in lakes of the McMurdo dry valleys, Antarctica

1. The influence of inorganic nitrogen and phosphorus enrichment on phytoplankton photosynthesis was investigated in Lakes Bonney (east and west lobes), Hoare, Fryxell and Vanda, which lie in the ablation valleys adjacent to McMurdo Sound, Antarctica. Bioassay experiments were conducted during the austral summer on phytoplankton populations just beneath the permanent ice cover in all lakes and on populations forming deep-chlorophyll maxima in the east and west lobes of Lake Bonney. 2. Phytoplankton photosynthesis in surface and mid-depth (13 m) samples from both lobes of Lake Bonney were stimulated significantly (P < 0.01) by phosphorus enrichment (2 μM) with further stimulation by simultaneous phosphorus plus NH₄⁺ (20 μM) enrichment. Similar trends were observed in deeper waters (18 m) from the east lobe of Lake Bonney, although they were not statistically significant at P < 0.05. Photosynthesis in this lake was never enhanced by the addition of 20 μM NH₄⁺ alone. Simultaneous addition of phosphorus plus nitrogen stimulated photosynthesis significantly (P < 0.01) in both Lake Hoare and Lake Fryxell. No nutrient response occurred in Lake Vanda, where activity in nutrient-enriched samples was below unamended controls; results from Lake Vanda are suspect owing to excessively long sample storage in the field resulting from logistic constraints. 3. Ambient dissolved inorganic nitrogen (DIN) (NH4⁺+ NO₂^?+ NO₃^?): soluble reactive phosphorus (SRP) ratios partially support results from bioassay experiments indicating strong phosphorus deficiency in Lake Bonney and nitrogen deficiency in Lakes Hoare and Fryxell. DIN : SRP ratios also imply phosphorus deficiency in Lake Vanda, although not as strong as in Lake Bonney. Particulate carbon (PC): particulate nitrogen (PN) ratios all exceed published ratios for balanced phytoplankton growth, indicative of nitrogen deficiency. 4. Vertical nutrient profiles in concert with low advective flux, indicate that new (sensu Dugdale & Goering, 1967) phytoplankton production in these lakes is supported by upward diffusion of nutrients from deep nutrient pools. This contention was tested by computing upward DIN : SRP flux ratios across horizontal planes located immediately beneath each chlorophyll maximum and about 2 m beneath the ice (to examine flux to the phytoplankton immediately below the ice cover). These flux ratios further corroborated nutrient bioassay results and bulk DIN : SRP ratios indicating phosphorus deficiency in Lakes Bonney and Vanda and potential nitrogen deficiency in Lakes Hoare and Fryxell. 5. Neither biochemical reactions nor physical processes appear to be responsible for differences in nutrient deficiency among the study lakes. The differences may instead be related to conditions which existed before or during the evolution of the lakes.     

CULTIVATION STUDIES OF GIGARTINA SKOTTSBERGII IN SOUTHERN CHILE

Increases in population and agriculture in coastal areas can result in increased nutrient inputs and alterations in the ratios of organic to inorganic nutrients in coastal waters. Such changes in coastal nutrient regimes can affect phytoplankton community structure by creating conditions favorable for growth and dominance of algae that were not dominant before. The effect that changes in ratios and concentrations of nutrients have on toxicity of harmful algal species is not well known. There seems to be a relationship; however, between nutrient stress and toxin production among harmful phytoplankton producing low-N toxins, e.g. Diarrhetic Shellfish Poisoning (DSP) toxins. Even less is known about the relationship between organic nutrient uptake and toxin production. Benthic species and species in coastal areas are probably exposed to greater fluxes of dissolved organic nitrogen (DON). In this study, benthic and planktonic species of Prorocentrum were grown on L1 media with the sole N-source varying among treatments as nitrate, ammonium, urea, L-glutamic acid, and high molecular weight natural DON. An ELISA specific to the DSP toxins, okadaic acid and 35-methylokadaic acid, was used to determine toxin production by each species when grown on the different N sources. Preliminary results indicate that some organic forms of N support growth as well as inorganic forms for Prorocentrum minimum , P. mexicanum , and P. hoffmannianum.     

THE EFFECT OF NITROGEN SOURCE ON THE GROWTH AND TOXICITY OF THREE POTENTIALLY HARMFUL DINOFLAGELLATES

Increases in population and agriculture in coastal areas can result in increased nutrient inputs and alterations in the ratios of organic to inorganic nutrients in coastal waters. Such changes in coastal nutrient regimes can affect phytoplankton community structure by creating conditions favorable for growth and dominance of algae that were not dominant before. The effect that changes in ratios and concentrations of nutrients have on toxicity of harmful algal species is not well known. There seems to be a relationship; however, between nutrient stress and toxin production among harmful phytoplankton producing low‐N toxins, e.g. Diarrhetic Shellfish Poisoning (DSP) toxins. Even less is known about the relationship between organic nutrient uptake and toxin production. Benthic species and species in coastal areas are probably exposed to greater fluxes of dissolved organic nitrogen (DON). In this study, benthic and planktonic species of Prorocentrum were grown on L1 media with the sole N‐source varying among treatments as nitrate, ammonium, urea, L‐glutamic acid, and high molecular weight natural DON. An ELISA specific to the DSP toxins, okadaic acid and 35‐methylokadaic acid, was used to determine toxin production by each species when grown on the different N sources. Preliminary results indicate that some organic forms of N support growth as well as inorganic forms for Prorocentrum minimum, P. mexicanum, and P. hoffmannianum.     

Responses of periphyton to artificial nutrient enrichment in freshwater kettle ponds of Cape Cod National Seashore

Nutrient enrichment bioassays, in conjunction with sampling and analysis of surface water chemistry, were conducted in freshwater lakes (kettle ponds) of Cape Cod National Seashore (Massachusetts, USA) to ascertain the importance of nitrogen (N) and phosphorus (P) in regulating the growth of periphyton. Arrays of nutrient diffusing substrata (NDS) were suspended 0.5 m below the water surface in a total of 12 ponds in July and August 2005. Algal biomass developing on each NDS after ~3 weeks of exposure in each month was assessed by quantifying chlorophyll a + phaeophyton pigments. In both July and August, strong responses to N + P and N enrichments were observed in the majority of ponds, while P had no stimulatory effect. These responses correspond well with low atomic ratios (1–18) of dissolved inorganic nitrogen (DIN) to total phosphorus (TP) in ambient surface waters. The results suggest that conditions in the kettle ponds develop whereby nitrogen is the primary limiting nutrient to periphyton growth. While this may be a seasonal phenomenon, it has implications for nutrient management in individual ponds and within the larger watershed.     

Low ratios of silica to dissolved nitrogen supplied to rivers arise from agriculture not reservoirs

Coastal marine systems are greatly altered by toxic marine algae, eutrophication and hypoxia. These problems have been linked to decreased ratios of dissolved silica to inorganic nitrogen (Si : DIN) delivered from land. Two mechanisms for this decline under consideration are enhanced nitrogen (N) fertiliser losses from agricultural lands or Si sequestration in reservoirs. Here we examine these mechanisms via nutrient concentrations in impoundments receiving water from 130 watersheds in a landscape representative of the agriculture that often dominates coastal nutrient inputs. Decreased Si : DIN was correlated with agriculture, not impoundment. Watersheds with > 60% agricultural land yielded highest DIN, whereas Si was uncorrelated with agricultural intensity. Furthermore, eutrophic lakes were dominated by Cyanobacteria that use little Si, so reservoirs did not diminish Si : DIN. Instead, Si : DIN increased slightly as reservoir residence time increased. These data suggest that impoundments in agricultural watersheds may enhance the water quality of coastal ecosystems, whereas fertiliser losses are detrimental.     

Nitrogen limitation of phytoplankton in a Spanish karst lake with a deep chlorophyll maximum: a nutrient enrichment bioassay approach

An in vitro nutrient addition bioassay was performed to testthe relative inorganic nitrogen (N) and phosphorus (P) limitationof phytoplankton in a Spanish karst lake (El Tejo) during thelast part of the stratification period, when nutrient limitationis most pronounced. Nutrient deficiency was tested in samplesfrom three different layers of the lake: the epilimnion, metalimnionand oxic hypolimnion. Nitrogen additions, either without orcombined with P, increased phytoplankton growth in all threestrata, compared with controls or P treatments. This showedthat N was the nutrient limiting phytoplankton growth in latesummer–early fall. Since both hypolimnetic diffusion andgroundwater fluxes of N-rich waters into the lake are much reducedduring summer, N becomes the limiting nutrient as stratificationadvances. We suggest that in this Mediterranean area with lowatmospheric deposition of anthropogenic N and in lakes relativelyfree of surface run-off, nutrient supply by atmospheric depositionmight be a key factor in controlling nutrient deficiency forphytoplankton growth.     

In-Situ Effects of Simulated Overfishing and Eutrophication on Benthic Coral Reef Algae Growth,Succession, and Composition in the Central Red Sea

Overfishing and land-derived eutrophication are major local threats to coral reefs and may affect benthic communities, moving them from coral dominated reefs to algal dominated ones. The Central Red Sea is a highly under-investigated area, where healthy coral reefs are contending against intense coastal development. This in-situ study investigated both the independent and combined effects of manipulated inorganic nutrient enrichment (simulation of eutrophication) and herbivore exclosure (simulation of overfishing) on benthic algae development. Light-exposed and shaded terracotta tiles were positioned at an offshore patch reef close to Thuwal, Saudi Arabia and sampled over a period of 4 months. Findings revealed that nutrient enrichment alone affected neither algal dry mass nor algae-derived C or N production. In contrast, herbivore exclusion significantly increased algal dry mass up to 300-fold, and in conjunction with nutrient enrichment, this total increased to 500-fold. Though the increase in dry mass led to a 7 and 8-fold increase in organic C and N content, respectively, the algal C/N ratio (18±1) was significantly lowered in the combined treatment relative to controls (26±2). Furthermore, exclusion of herbivores significantly increased the relative abundance of filamentous algae on the light-exposed tiles and reduced crustose coralline algae and non-coralline red crusts on the shaded tiles. The combination of the herbivore exclusion and nutrient enrichment treatments pronounced these effects. The results of our study suggest that herbivore reduction, particularly when coupled with nutrient enrichment, favors non-calcifying, filamentous algae growth with high biomass production, which thoroughly outcompetes the encrusting (calcifying) algae that dominates in undisturbed conditions. These results suggest that the healthy reefs of the Central Red Sea may experience rapid shifts in benthic community composition with ensuing effects for biogeochemical cycles if anthropogenic impacts, particularly overfishing, are not controlled.     

Mixotrophic nanoplankton in oligotrophic surface waters of the Sargasso Sea may employ phagotrophy to obtain major nutrients

The vertical distribution and abundance of mixotrophic nanoplanktonwas examined during two cruises to the Sargasso Sea south ofBermuda. Fluorescently labeled bacteria and cyanobacteria wereused as tracers of ingestion in experiments designed to determineabundances of mixotrophic nanoplankton. Phagotrophic nanoplanktonic(2–20 µm) algae ranged from undetectable to >100ml^–1, and were more abundant near the surface (up to 140ml^–1) than in the deeper euphotic zone. On two occasions,50% of the phototrophic nanoplankton in surface waters wereobserved with ingested fluorescent tracers. The contributionof mixotrophic algae to the total phototrophic nanoplanktonassemblage in the deep chlorophyll maximum, however, did notexceed 0.5%. It is possible that mixotrophic algae were moreabundant in the deep chlorophyll maximum, but were not phagotrophicallyactive. Two 4 day experimental incubations were subsequentlycarried out to examine the adaptive significance of phagotrophicbehavior for algae in surface waters of the Sargasso Sea. Greatermixotrophic nanoplankton abundances were observed in treatmentsthat received no nutrient inputs and were limited by the availabilityof inorganic nutrients during the experiments. A decrease inthe abundance of mixotrophic algae or a decrease in their phagotrophicactivity occurred with nutrient enrichment. Based on the experimentalresults, we suggest that phagotrophy was a mechanism by whichthese algae supplemented nutrient acquisition during periodsof low dissolved nutrient concentrations. Higher abundancesof mixotrophic nanoplankton observed in the upper 50 m of theSargasso Sea may have been due to the generally low nutrientconcentrations in these waters.     

Nitrogen limitation of the phytobenthos in Alpine lakes: results from nutrient‐diffusing substrata

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Top-down and bottom-up control in an eelgrass–epiphyte system

Nutrient supply and the presence of grazers can control primary producers in aquatic ecosystems, but the relative importance of bottom-up and top-down effects remains inconclusive. We conducted a mesocosm experiment and a field study to investigate the independent and interactive effects of nutrient enrichment and grazing on primary producers in an eelgrass bed Zostera marina . Nutrient treatments consisted of ambient or enriched (2× and 4× ambient) concentrations of inorganic nitrogen and phosphate. Grazer treatments consisted of presence or absence of field densities of the common isopod Idotea baltica . We found strong and interacting effects of nutrients and grazing on epiphytes. Epiphyte biomass and productivity were enhanced by nutrient enrichment and decreased in the presence of grazers. The absolute amount of epiphyte biomass consumed by grazers increased under high nutrient supply, and thus, nutrient effects were stronger in the absence of grazing. The effects of grazers and fertilisation on epiphyte composition were antagonistic: chain-forming diatoms and filamentous algae profited from nutrient enrichment, but their proportions were reduced by grazing. Eelgrass growth was positively affected by grazing and by nutrient enrichment at moderate nutrient concentrations. High nutrient supply reduced eelgrass productivity compared to moderate nutrient conditions. The monthly measured field data showed a nitrogen limitation for epiphytes and eelgrass in summer, which may explain the positive effect of nutrient enrichment on both primary producers. Generally, the field data suggested the possibility of seasonally varying importance of bottom-up and top-down control on primary producers in this eelgrass system.     

Morphometry and sedimentation as regulating factors for nutrient recycling and trophic state in coastal waters

The aim of this work is to quantify the importance of morphometry and sedimentation/resuspension on nutrient recycling and trophic characteristics in coastal waters. Extensive field work has been carried out in 23 coastal areas in the Swedish and Finnish part of the Baltic Proper. Sediment traps were deployed for two one-week periods in all areas. On average, 56% of the total sedimentation in sediment traps 3 m below the water surface (SedS) and 62% of the total sedimentation on sediment traps 1 m above the bottom (SedB) was resuspended material. Coastal morphometric parameters, surface water retention time and bottom dynamic conditions were determined for all areas. There is a marked relationship between SedS and inorganic-N concentration in the surface water. The relationship was improved significantly by using sedimentation of the resuspended fraction at 3 m water depth (SedR) instead of SedS.This led to the hypothesis that increased concentration of inorganic nitrogen in the surface water results from increased mineralisation of resuspended organic particles. A model describing SedS is presented where inorganic nitrogen concentration, the water surface area and the surface water retention time can explain 82% of the variation in SedS. In another model inorganic nitrogen and water surface area can explain as much as 93% of the variation in SedR.These results emphasise the importance of resuspension for nutrient recycling and trophic state in coastal waters. The importance of coastal morphometry and surface water retention time on total sedimentation and nutrient recycling makes it possible to classify coastal areas in terms of potential nutrient recycling capacity/trophic state from these simple sensitivity parameters.     

珠江口及毗邻海域营养盐对浮游植物生长的影响

基于2006年7月(夏季),10月(秋季)和2007年3月(春季)的现场调查数据,对珠江口及毗邻海域中的营养盐和叶绿素a等环境生态因子的时空分布特性进行了对比分析,研究了氮磷比与叶绿素a含量和种群多样性之间的联系,探讨了该海域营养盐对于浮游植物生长的影响。结果表明:(1)研究海域营养盐表现出较强的季节和空间差异性,总氮(TN)和总磷(TP)浓度均值春季(1.545 mg/L、0.056 mg/L)和夏季(1.570 mg/L、0.058 mg/L)均大于秋季(1.442 mg/L、0.034 mg/L),且春夏季浓度空间差异更明显。(2)调查期间海域营养盐含量超标现象突出,夏季尤为明显。无机氮(DIN)总体均值0.99 mg/L,超四类海水标准限值1倍,活性磷酸盐(PO4-P)总体均值0.021 mg/L,DIN∶PO4-P平均值为130;叶绿素a浓度与营养盐、p H、温度有较显著的相关性。(3)叶绿素a浓度较高的站位,具有较高的DIN∶PO4-P值,但浮游植物多样性指数偏低,优势种明显,主要为中肋骨条藻。氮磷比的改变会影响不同生长特性的浮游植物间的竞争和种群结构的改变;今后海洋污染治理中,在控制氮、磷污染时要注意氮磷比的改变可能造成的浮游生态影响。