Impact of the zebra mussel Dreissena polymorpha invasion on the budget of suspended material in a shallow lagoon ecosystem

The role of the zebra mussel Dreissena polymorpha in redistribution of total particulate material (TPM) between the water column and bottom sediment was estimated using the TPM budget for a mussel bed in the Curonian lagoon, the Baltic Sea. Seasonal clearance rates were derived from the TPM budget assuming two resuspension scenarios: no resuspension and full resuspension of biodeposits. Estimated clearance rates for both scenarios were compared with the rates calculated from the population clearance rate model. Seasonal clearance rates estimated using the population model (1.1 and 11.8 l g⁻¹ SFDW day⁻¹) fitted well into the interval of seasonal clearance rates calculated from TPM budgets assuming no resuspension of biodeposits (3.2 and 21.4 l g SFDW⁻¹ day⁻¹). In the scenario with biodeposits resuspension clearance rates were much higher (57.4 and 148.9 g SFDW⁻¹ day⁻¹). The ratio of clearance to residence time was highly dependent on the fate of biodeposits. Therefore its use in interpretation of the species impact on TPM was limited. An alternative measure based on the ratio of the amount of TPM biodeposited to TPM transported into the bed was used. It was found that zebra mussels are able to deposit between 10 and 30% of the incoming TPM, and the amount of biodeposited material was correlated with water residence time. Results indicate that the impact of zebra mussels on TPM in the lagoon is small relative to the high transport rates of TPM over the bed. However, annual biosedimentation rate (~590 g m⁻²) in the mussel bed was higher than physical deposition rate (~380 g m⁻²) in accumulation areas devoid of large suspension feeders. We suggest that a local impact due to enhanced availability of organic material to other trophic groups of associated benthic organisms may be more significant than effects on TPM pathways at an ecosystem scale.     

Factors Influencing the Growth Rates of Three Commercial Eucheumoids at Coastal Sites in Southern Kenya

As a possible means of improving the livelihoods of local villagers, off-bottom rope cultivation of commercial eucheumoids was investigated on the southern Kenyan coast at three sites, representative of the variety of environments. The morphotypes used were brown Eucheuma denticulatum and green and brown Kappaphycus alvarezii. The study was carried out over a 15 month period from August 2001 until October 2002. Relative growth rates were highest at a sandy flat in a mangrove system (Gazi; 5.6% d⁻¹), and lowest in an intertidal reef flat (Kibuyuni; 3.2% d⁻¹) with a lagoon being intermediate (Mkwiro; 4.8% d⁻¹). The brown E. denticulatum had the highest growth rate of 4.7% d⁻¹ compared to the green and brown K. alvarezii which were 4.3% d⁻¹ and 4.2% d⁻¹, respectively. Growth was more variable at Kibuyuni and Mkwiro. The growth was higher during the southeast monsoon (4.7% d⁻¹) than during the northeast monsoon (4.0% d⁻¹). This is part of a larger study and the effects of water motion, salinity, temperature, thallus nitrogen, and ‘ice-ice’ syndrome on growth of morphotypes is discussed. The water motion was observed to increase thallus nitrogen and hence the growth of eucheumoids. The ‘ice-ice’ condition affected both brown E. denticulatum and brown K. alvarezii but not green K. alvarezii. The results suggest that commercial cultivation of eucheumoids in Kenya will be feasible.     

The influence of diet on the growth of Stenonema vicarium (Walker) (Ephemeroptera: Heptageniidae)

Laboratory studies compared the growth rate of Stenonema vicarium (Walker) nymphs on diets of detritus and natural stream periphyton. In three consecutive runs of the experiment, growth rates were consistently higher on periphyton (mean growth rate = 2.1% wet wt. d⁻¹) than detritus (mean = 1.8% wet wt. d⁻¹). The starting date of each run also significantly influenced growth rates. In each treatment growth rates generally decreased over the course of the 3 runs, and ca. one-half of the nymphs in the last run did not molt or grow. It appeared that growth of S. vicarium may be partially controlled by seasonal factors.     

Seasonal changes in abundance and spatial distribution of the soil arthropods in a Japanese cedar (Cryptomeria japonica D.Don) plantation,with special reference to collembola and acarina

Seasonal changes in abundance and distribution pattern of soil micro-arthropods were studied in connection with a few environmental factors in a Japanese cedar (Cryptomeria japonica D. Don) plantation. The soil arthropods were sampled from three different depths at intervals of two months for two years. Of the collected animals (total 51000–155000 m⁻²), Collembola (20000–76000 m⁻²), oribatid mites (19000–55000 m⁻²) and carnivorous mites (6200–21000 m⁻²) were the numerically dominant animal groups. Low seasonal variations in abundance indicated their seasonal stability in population levels. The trends in seasonal fluctuation were similar among these groups and between the two years, showing bimodal pattern with little peaks in early summer and winter. The pattern of seasonal fluctuation in abundance of carnivorous mites (P _d) was significantly synchronized with that in the total abundance of Collembola and oribatid mites (P _τ). Thus, the number-ratios (P _d/P _τ) were fairly constant, ranging from 0.10 to 0.25. Seasonal changes in vertical distribution of the three animal groups showed a similar pattern for both years. The downward migrations were shown to be more affected by low temperatures in winter accompanied by snow coverage rather than by the desiccation of the surface soil in summer. All the three groups demonstrated as a whole slightly aggregated patterns of horizontal distribution throughout the two years. Temporal increases in the patchiness indices were observed from summer to autumn when the moisture content of the surface soil was low.     

The Role of Surface and Subsurface Processes in Keeping Pace with Sea Level Rise in Intertidal Wetlands of Moreton Bay,Queensland, Australia

Increases in the elevation of the soil surfaces of mangroves and salt marshes are key to the maintenance of these habitats with accelerating sea level rise. Understanding the processes that give rise to increases in soil surface elevation provides science for management of landscapes for sustainable coastal wetlands. Here, we tested whether the soil surface elevation of mangroves and salt marshes in Moreton Bay is keeping up with local rates of sea level rise (2.358 mm y⁻¹) and whether accretion on the soil surface was the most important process for keeping up with sea level rise. We found variability in surface elevation gains, with sandy areas in the eastern bay having the highest surface elevation gains in both mangrove and salt marsh (5.9 and 1.9 mm y⁻¹) whereas in the muddier western bay rates of surface elevation gain were lower (1.4 and −0.3 mm y⁻¹ in mangrove and salt marsh, respectively). Both sides of the bay had similar rates of surface accretion (~7–9 mm y⁻¹ in the mangrove and 1–3 mm y⁻¹ in the salt marsh), but mangrove soils in the western bay were subsiding at a rate of approximately 8 mm y⁻¹, possibly due to compaction of organic sediments. Over the study surface elevation increments were sensitive to position in the intertidal zone (higher when lower in the intertidal) and also to variation in mean sea level (higher at high sea level). Although surface accretion was the most important process for keeping up with sea level rise in the eastern bay, subsidence largely negated gains made through surface accretion in the western bay indicating a high vulnerability to sea level rise in these forests.     

Photolithotrophic cultivation of <Emphasis Type="Italic">Laminaria japonica</Emphasis> gametophyte cells in a silicone tubular membrane-aerated photobioreactor

Gametophyte cells of brown algae Laminaria japonica were employed both in a modified silicone tubular membrane-aerated photobioreactor (bubble-less cultivation mode) and a bubble-column photobioreactor (bubbling cultivation mode), to study different gas–liquid mixing modes on cell growth rate and cell physiological status. With an inoculum density of 50 mg DCW l⁻¹, in modified artificial Pacific seawater (APSW) medium at 13°C, light intensity of 60 μE m⁻² s⁻¹, light cycle of 16/8 h L/D, and aeration rate of 60 ml min⁻¹, the specific growth rates were 0.082 d⁻¹ for bubble-less mode and 0.070 d⁻¹ for bubbling mode with biomass, in the form of dry cell density, increasing 10.9 and 6.8 times, respectively, during the 36 days’ photolithotrophic cultivation. The specific oxygen evolution rate under bubble-less mode was 39.6% higher than under bubbling mode on the 18th day. The gametophyte cells grew in cell aggregates with clump sizes, at day 36, of 1.5 mm and 0.5 mm diameter under bubble-less and bubbling mode respectively and cell injury percentages of 5.1% and 21.1%, respectively. The silicone tubular membrane-aerated photobioreactor was better suited for the cultivation of fragile macroalgal gametophyte cells due to the absence of hydrodynamic shear stress caused by fluid turbulence and the presence of a bubble-less gas supply.     

Carbonate production by scleractinian corals at Aqaba,Gulf of Aqaba,Red Sea

Summary In a fringing reef at Aqaba at the northern end of the Gulf of Aqaba (29°26′N) growth rates, density, and the calcification rate ofPorites were investigated in order to establish calculations of gross carbonate production for the reefs in this area. Colony accretion ofPorites decreases with depth as a function of decreasing growth rates. The calcification rate ofPorites is highest in shallow water (0–5 m depth) with 0.9 g·cm⁻²·yr⁻¹ and falls down to 0.5 g·cm⁻²·yr⁻¹ below 30 m. Scleractinian coral gross production is calculated from potential productivity and coral coverage. It is mainly dependent on living coral cover and to a lesser extent on potential productivity. Total carbonate production on the reef ranged from 0 to 2.7 kg/m² per year, with a reef-wide average of 1.6 kg/m² perycar. Maximum gross carbonate production by corals at Aqaba occurs at the reef crest and in the middle fore-reef from 10 to 15 m water depth. Production is low in sandy reef parts. Below 30 m depth values still reach ca. 50% of shallow water values. Mean potential production of colonies and gross carbonate production of the whole reef community at Aqaba is lower than in tropical reefs. However, carbonate production is higher than in reef areas at the same latitude in the Pacific, indicating a northward shift of reef production in the Red Sea.     

Effect of temperature and irradiance on the uptake of ammonium and nitrate by <Emphasis Type="Italic">Laurencia brongniartii</Emphasis> (Rhodophyta,Ceramiales)

The effects of temperature (20, 24 and 28 °C) and irradiance (15 and 40 μmol photon m⁻² s⁻¹) on the nitrate and ammonium uptake rates of the subtropical red alga, Laurencia brongniartii, were investigated to prepare for tank cultivation. Nitrate uptake followed saturation kinetics and was faster at higher irradiances and temperatures. In contrast, ammonium uptake was linear over the experimental range and was not affected by an increase in temperature. A parameter, β, was calculated to compare substrate uptake rates of nitrate along the linear portion of the uptake curve with that of ammonium. For nitrate, β was lower at low irradiance and higher at high irradiance (β = 0.007 ± 0.003 and 0.030 ± 0.002 [μmol N L⁻¹ (μmol N g_ww⁻¹ d⁻)⁻¹], respectively). However, β was 0.023 ± 0.002 and 0.034 ± 0.002 [μmol N L⁻¹ (μmol N g_ww⁻¹ d⁻¹)⁻¹] for ammonium, suggesting a preference for ammonium over nitrate.     

Multiple Scales of Temporal Variability in Ecosystem Metabolism Rates: Results from 2 Years of Continuous Monitoring in a Forested Headwater Stream

Headwater streams are key sites of nutrient and organic matter processing and retention, but little is known about temporal variability in gross primary production (GPP) and ecosystem respiration (ER) rates as a result of the short duration of most metabolism measurements in lotic ecosystems. We examined temporal variability and controls on ecosystem metabolism by measuring daily rates continuously for 2 years in Walker Branch, a first-order deciduous forest stream. Four important scales of temporal variability in ecosystem metabolism rates were identified: (1) seasonal, (2) day-to-day, (3) episodic (storm-related), and (4) inter-annual. Seasonal patterns were largely controlled by the leaf phenology and productivity of the deciduous riparian forest. Walker Branch was strongly net heterotrophic throughout the year with the exception of the open-canopy spring when GPP and ER rates were co-equal. Day-to-day variability in weather conditions influenced light reaching the streambed, resulting in high day-to-day variability in GPP particularly during spring (daily light levels explained 84% of the variance in daily GPP in April). Episodic storms depressed GPP for several days in spring, but increased GPP in autumn by removing leaves shading the streambed. Storms depressed ER initially, but then stimulated ER to 2–3 times pre-storm levels for several days. Walker Branch was strongly net heterotrophic in both years of the study, with annual GPP being similar (488 and 519 g O₂ m⁻² y⁻¹ or 183 and 195 g C m⁻² y⁻¹) but annual ER being higher in 2004 than 2005 (−1,645 vs. −1,292 g O₂ m⁻² y⁻¹ or −617 and −485 g C m⁻² y⁻¹). Inter-annual variability in ecosystem metabolism (assessed by comparing 2004 and 2005 rates with previous measurements) was the result of the storm frequency and timing and the size of the spring macroalgal bloom. Changes in local climate can have substantial impacts on stream ecosystem metabolism rates and ultimately influence the carbon source and sink properties of these important ecosystems.     

Varying growth rates in bamboo corals: sclerochronology and radiocarbon dating of a mid-Holocene deep-water gorgonian skeleton (<Emphasis Type="Italic">Keratoisis</Emphasis> sp<Emphasis Type="Italic">.</Emphasis>: Octocorallia) from Chatham Rise (New Zealand)

A branched mid-Holocene bamboo coral skeleton of the isidid gorgonian genus Keratoisis (Octocorallia) recovered at southwestern Chatham Rise (New Zealand) from an average water depth of 680 m is described with respect to sclerochronology and age determination. Growth rates of the Mg-calcitic internodal increments were investigated by the counting of colour bands and radiocarbon dating. Growth banding is produced by varying orientations of crystal fan bundles towards the image plane. The skeleton shows three growth interruptions, which are documented in all branches. AMS ¹⁴C ages decrease from base to top of the trunk and from the central axes to the margins of the branches, documenting a simultaneous vertical and lateral growth. The data provide a maximum age of 3,975 ± 35 years BP, and a record spanning 240 ± 35 years. While calculated longitudinal growth rates amount to an average of 5 mm year⁻¹ during a 55-year record, average lateral linear extension rates of 0.4 mm year⁻¹ are an order of magnitude lower, still allowing for a seasonal to annual resolution of colour bands on a macroscopic scale and for a daily to monthly resolution on microscales of individual crystal generations to fascicle bundles. Hence, the isidid skeleton provides a high-resolution archive of paleoceanographic dynamics in deeper water masses. Concentric incremental accretion around the central axis in the early growth stages changed into a unilaterally asymmetric growth during late-stage evolution, probably triggered by the establishment of a stable system of unidirectional currents and nutrient flux. While colour band counts, related to the AMS ¹⁴C ages, support a seasonal to annual accretion of macroscopic growth bands in the inner concentric and complete outer parts of the skeleton, incremental growth rates at the condensed side are highly variable, as documented by hiatuses and unconformities. Thus the specimen proves that growth rates of bamboo corals may vary within individual skeletons and strongly deviate from the annual mode, hence showing implications on paleoceanographic proxy analyses.     

Cruoriella rhodoliths from shallow-water back reef environments in La Parguera, Puerto Rico (Caribbean Sea)

The occurrence of shallow-water (0.9 to 1.3 m) rhodoliths in back reef environments in southwest Puerto Rico is reported. The rhodoliths were generally cylindrical, discoidal or irregular in shape with an average longest dimension of 7.2 cm. They occurred at a maximum density of 524 m⁻². The rhodoliths were composed of mostly coral nuclei with concentric laminations of aragonite-producing Cruoriella armorica (Peyssonneliaceae, Rhodophyta). Maximum Cruoriella accretion around coral nuclei was 30 mm although accretions of 1 to 20 mm were more common. Based on measurements of Cruoriella accretion, these shallow water rhodoliths are estimated to have minimum ages of 12 to 24 years. It is further estimated that approximately 2% of the rhodoliths are turned over daily. Accepted: 1 October 1999     

Production Ecology of the Non-indigenous Seagrass, Dwarf Eelgrass (Zostera japonica Ascher. & Graeb.), in a Pacific Northwest Estuary, USA

The non-indigenous seagrass Zostera japonica Ascher. & Graeb. (dwarf eelgrass) was first identified in central Oregon (USA) estuaries about 30 years ago. The autecology of this species is poorly described at the southern end of its non-native range although several process oriented studies have been conducted. I examined the production ecology of Z. japonica in the Yaquina Bay estuary. Strong seasonal patterns in light and temperature appeared to control the seasonal variations in biomass and growth. Above- and below-ground biomass ranged between 40–100 and 70–170 gdw m⁻² respectively and seasonal changes in the root:shoot ratio were controlled by above-ground biomass dynamics. Shoot density ranged between 4000 and 11 000 shts m⁻². Areal leaf growth ranged between 0.1 and 1.7 gdw m⁻² d⁻¹ and annual production was about 314 ± 60 gdw m⁻² y⁻¹ (mean ± SD). Nutrients were not limiting in this system as a result of coastal upwelling and watershed inputs. The Z. japonica population studied in Oregon exhibited different patterns of persistence, phenology and flowering intensity relative to other populations along its native and non-native range. These differences suggest that management policies developed for one site may not be appropriate for other sites. The data presented here greatly expands our knowledge base on Z. japonica and provides insight to the processes controlling the dynamics and spread of this non-indigenous seagrass. An erratum to this article is available at .     

Salinity effect on plant growth and leaf demography of the mangrove, Avicennia germinans L.

We assessed the effect of salinity on plant growth and leaf expansion rates, as well as the leaf life span and the dynamics of leaf production and mortality in seedlings of Avicennia germinans L. grown at 0, 170, 430, 680, and 940 mol m⁻³ NaCl. The relative growth rates (RGR) after 27 weeks reached a maximum (10.4 mg g⁻¹ d⁻¹) in 170 mol m⁻³ NaCl and decreased by 47 and 44% in plants grown at 680 and 940 mol m⁻³ NaCl. The relative leaf expansion rate (RLER) was maximal at 170 mol m⁻³ NaCl (120 cm m⁻² d⁻¹) and decreased by 57 and 52% in plants grown at 680 and 940 mol m⁻³ NaCl, respectively. In the same manner as RGR and RLER, the leaf production (P) and leaf death (D) decreased in 81 and 67% when salinity increased from 170 to 940 mol m⁻³ NaCl, respectively. Since the decrease in P with salinity was more pronounced than the decrease in D, the net accumulation of leaves per plant decreased with salinity. Additionally, an evident increase in annual mortality rates (λ) and death probability was observed with salinity. Leaf half-life (t _0.5) was 425 days in plants grown at 0 mol m⁻³ NaCl, and decreased to 75 days at 940 mol m⁻³ NaCl. Thus, increasing salinity caused an increase in mortality rate whereas production of new leaves and leaf longevity decreased and, finally, the leaf area was reduced.     

Effect of seawater temperature on the productivity of <Emphasis Type="Italic">Laminaria japonica</Emphasis> in the Uwa Sea,southern Japan

Recent studies on global climate change report that increase in seawater temperature leads to coastal ecosystem change, including coral bleaching in the tropic. In order to assess the effect of increased seawater temperature on a temperate coastal ecosystem, we studied the inter-annual variation in productivity of Laminaria japonica using long-term oceanographic observations for the Uwa Sea, southern Japan. The annual productivity estimates for L. japonica were 2.7 ± 2.5 (mean ± SD) kg wet wt. m⁻¹ (length of rope) (2003/2004), 1.0 ± 0.6 kg wet wt. m⁻¹ (2004/2005) and 12.1 ± 12.5 kg wet wt. m⁻¹ (2005/2006). Our previous study using the same methodology at the same locality reported that the productivity was estimated for the 2001/2002 (33.3 ± 15.2 kg wet wt. m⁻¹) and 2002/2003 (34.0 ± 8.7 kg wet wt. m⁻¹) seasons. Productivity in 2003/2004 and 2004/2005 was significantly lower than in years 2001/2002, 2002/2003 and 2005/2006. A comparison of oceanographic conditions among the 5 years revealed the presence of threshold seawater temperature effects. When the average seawater temperature during the first 45 days of each experiment exceeded 15.5°C, productivity was reduced to about 10 % of that in cooler years. Moreover the analysis of growth and erosion rates indicates that when the seawater temperature was over 17.5°C, erosion rate exceeded growth rate. Thus, an increase of seawater temperature of just 1°C during winter drastically reduces the productivity of L. japonica in the Uwa Sea.     

Treatment of swine manure effluent using freshwater algae: Production, nutrient recovery, and elemental composition of algal biomass at four effluent loading rates

Cultivating algae on nitrogen (N) and phosphorus (P) in animal manure effluents presents an alternative to the current practice of land application. The objective of this study was to determine how algal productivity, nutrient removal efficiency, and elemental composition of turf algae change in response to different loading rates of raw swine manure effluent. Algal biomass was harvested weekly from laboratory scale algal turf scrubber units using four manure effluent loading rates (0.24, 0.40, 0.62 and 1.2 L m⁻² d⁻¹) corresponding to daily loading rates of 0.3–1.4 g total N and 0.08–0.42 g total P. Mean algal productivity values increased from 7.1 g DW m⁻² d⁻¹ at the lowest loading rate (0.24 L m⁻² d⁻¹) to 9.4 g DW m⁻² d⁻¹ at the second loading rate (0.40 L m⁻² d⁻¹). At these loading rates, algal N and P accounted for> 90% of input N and 68–76% of input P, respectively. However, at higher loading rates algal productivity did not increase and was unstable at the highest loading rate. Mean N and P contents in the dried biomass increased 1.5 to 2.0-fold with increasing loading rate up to maximums of 5.7% N and 1.8% P at 1.2 L m⁻² d⁻¹. Biomass concentrations of Al, Ca, Cd, Fe, K, Mg, Mn, Mo, Si, and Zn increased 1.2 to 2.6-fold over the 5-fold range of loading rate. Biomass concentrations of Cd, K, Pb, and Si did not increase significantly with loading rate. At the loading rate of 0.40 L m⁻² d⁻¹ (corresponding to peak productivity) the mean concentrations of individual components in the algal biomass were (in mg kg⁻¹): 250 (Al), 4900 (Ca), 0.30 (Cd), 1050 (Fe), 3.4 (Pb), 2500 (Mg), 105 (Mn), 6.0 (Mo), 7,500 (K), and 510 (Zn). At these concentrations, heavy metals in the algal biomass would not be expected to reduce its value as a soil or feed amendment.     

Phenotypic plasticity for skeletal growth,density and calcification of <Emphasis Type="Italic">Porites lobata</Emphasis> in response to habitat type

A reciprocal transplant experiment (RTE) of the reef-building coral Porites lobata between shallow (1.5 m at low tide) back reef and forereef habitats on Ofu and Olosega Islands, American Samoa, resulted in phenotypic plasticity for skeletal characteristics. Transplants from each source population (back reef and forereef) had higher skeletal growth rates, lower bulk densities, and higher calcification rates on the back reef than on the forereef. Mean annual skeletal extension rates, mean bulk densities, and mean annual calcification rates of RTE groups were 2.6–9.8 mm year⁻¹, 1.41–1.44 g cm⁻³, and 0.37–1.39 g cm⁻² year⁻¹ on the back reef, and 1.2–4.2 mm year⁻¹, 1.49–1.53 g cm⁻³, and 0.19–0.63 g cm⁻² year⁻¹ on the forereef, respectively. Bulk densities were especially responsive to habitat type, with densities of transplants increasing on the high energy forereef, and decreasing on the low energy back reef. Skeletal growth and calcification rates were also influenced by source population, even though zooxanthella genotype of source colonies did not vary between sites, and there was a transplant site x source population interaction for upward linear extension. Genetic differentiation may explain the source population effects, or the experiment may have been too brief for phenotypic plasticity of all skeletal characteristics to be fully expressed. Phenotypic plasticity for skeletal characteristics likely enables P. lobata colonies to assume the most suitable shape and density for a wide range of coral reef habitats.     

The response of the early developmental stages of Laminaria japonica to enhanced ultraviolet-B radiation

The responses of the early development of Laminaria japonica collected from Kiaochow Bay in China to enhanced ultraviolet-B radiation (UV-B, 280–320 nm) were studied in the laboratory. The low UV-B radiations (11.7–23.4 J·m⁻²·d⁻¹) had no significant effects on zoospores attachment, but when the UV-B dose > 35.1 J·m⁻²·d⁻¹ the attachment decreased significantly compared with the control. Germination of embryospores was >93% under the low (11.7–35.1 J·m⁻²·d⁻¹) doses, and in the range of 78.5%–88.5% under the high (46.8–70.2 J·m⁻²·d⁻¹) UV-B doses, indicating a significant radiation effect. Under the higher UV-B exposure (35.1–70.2 J·m⁻²·d⁻¹), all of the few gametophytes formed from embryospores died 120 h post-release. After exposure to the low UV-B radiation (11.7–23.4 J·m⁻²·d⁻¹), the formation of sporophytes decreased and the female gametophyte clones increased compared with the control. However, the sex ratio and the relative growth of female gametophytes/sporophytes had not significantly changed. According to the results, enhanced UV-B radiation has a significant effect on the early development of L. japonica under laboratory conditions, suggesting that the UV-B radiation could not be overlooked as one of the important environmental factors influencing the ontogeny of macroalgae living in marine ecosystems. Supported by the Program for New Century Excellent Talents in University (Grant No. NCET-05-0597) and National Natural Science Foundation of China (Grant No. 30270258)     

Impact of Microzooplankton and Copepods on the Growth of Phytoplankton in the Yellow Sea and East China Sea

Dilution and copepod addition incubations were conducted in the Yellow Sea (June) and the East China Sea (September) in 2003. Microzooplankton grazing rates were in the range of 0.37–0.83 d⁻¹ in most of the experiments (except at Station A3). Correspondingly, 31–50% of the chlorophyll a (Chl a) stock and 81–179% of the Chl a production was grazed by microzooplankton. At the end of 24 h copepod addition incubations, Chl a concentrations were higher in the copepod-added bottles than in the control bottles. The Chl a growth rate in the bottles showed good linear relationship with added copepod abundance. The presence of copepods could enhance the Chl a growth at a rate (Z) of 0.03–0.25 (on average 0.0691) d⁻¹ ind⁻¹ l. This study, therefore parallels many others, which show that microzooplankton are the main grazers of primary production in the sea, whereas copepods appear to have little direct role in controlling phytoplankton.     

Effects of ants on water and soil losses from organically-managed citrus orchards in eastern Spain

Ants can play a key role in the erosion processes on agriculture land by modifying soil properties and increasing macropore flow. Ants are abundant in organically-managed orchards in the Mediterranean region due to climate conditions, no-till practices, no pesticide use, and the resulting vegetation cover. In order to determine the effect of ants on soil and water losses from these orchards growing on moderately-sloped land (4–8%), forty 1.0 m² plots (20 with ants mounts and 20 without ants — controls) were established during the summer of 2007. A rainfall simulator was used to apply 78 mm of water to each plot over a one-hour period, equivalent to a 20-year return-period thunderstorm. Runoff was collected at 1-minute intervals and sediment concentration measured every 10 minutes. Sediment concentrations were 300% higher on plots with ant mounds, but runoff rates were similar to the plots without ants. Average soil erosion rates averaged 41 kg ha⁻¹ h⁻¹ on the ant plots and 13 kg ha⁻¹ h⁻¹ on the control plots. The low erosion rates are due to the effect of the vegetation and litter cover in this organically-managed soil, which were little impacted by ant activity at the pedon scale.     

Effect of high temperature on photosynthesis and transpiration of sweet corn (<Emphasis Type="Italic">Zea mays</Emphasis> L. var. <Emphasis Type="Italic">rugosa</Emphasis>)

Four temperature treatments were studied in the climate controlled growth chambers of the Georgia Envirotron: 25/20, 30/25, 35/30, and 40/35 °C during 14/10 h light/dark cycle. For the first growth stage (V3-5), the highest net photosynthetic rate (P _N) of sweet corn was found for the lowest temperature of 28–34 μmol m⁻² s⁻¹ while the P _N for the highest temperature treatment was 50–60 % lower. We detected a gradual decline of about 1 P _N unit per 1 °C increase in temperature. Maximum transpiration rate (E) fluctuated between 0.36 and 0.54 mm h⁻¹ (≈5.0–6.5 mm d⁻¹) for the high temperature treatment and the minimum E fluctuated between 0.25 and 0.36 mm h⁻¹ (≈3.5–5.0 mm d⁻¹) for the low temperature treatment. Cumulative CO₂ fixation of the 40/35 °C treatment was 33.7 g m⁻² d⁻¹ and it increased by about 50 % as temperature declined. The corresponding water use efficiency (WUE) decreased from 14 to 5 g(CO₂) kg⁻¹(H₂O) for the lowest and highest temperature treatments, respectively. Three main factors affected WUE, P _N, and E of Zea: the high temperature which reduced P _N, vapor pressure deficit (VPD) that was directly related to E but did not affect P _N, and quasi stem conductance (QC) that was directly related to P _N but did not affect E. As a result, WUE of the 25/20 °C temperature treatment was almost three times larger than that of 40/35 °C temperature treatment.