Variable and complex food web structures revealed by exploring missing trophic links between birds and biofilm.Ecol.Lett

Abstract Food webs are comprised of a network of trophic interactions and are essential to elucidating ecosystem processes and functions. However, the presence of unknown, but critical networks hampers understanding of complex and dynamic food webs in nature. Here, we empirically demonstrate a missing link, both critical and variable, by revealing that direct predator-prey relationships between shorebirds and biofilm are widespread and mediated by multiple ecological and evolutionary determinants. Food source mixing models and energy budget estimates indicate that the strength of the missing linkage is dependent on predator traits (body mass and foraging action rate) and the environment that determines food density. Morphological analyses, showing that smaller bodied species possess more developed feeding apparatus to consume biofilm, suggest that the linkage is also phylogenetically dependent and affords a compelling re-interpretation of niche differentiation. We contend that exploring missing links is a necessity for revealing true network structure and dynamics

High tolerance of phytoplankton for extremely high ammonium concentrations in the eutrophic coastal water of Dokai Bay (Japan)

The tolerance of phytoplankton in Dokai Bay for an extremely high ammonium concentration in culture media has been studied. Six species of phytoplankton, three diatoms (two clones of Skeletonema sp. and Chaetoceros sp.) and three flagellates (Heterosigma akashiwo, Chattonella antiqua and Karenia mikimotoi) were grown in various concentrations of NH4Cl. The results suggested that high ammonium concentrations had negative effects on phytoplankton growth. Non-indigenous species in Dokai Bay, Japan, C. antiqua and K. mikimotoi, were unable to grow at 200 and 150 μ M, respectively. Growth rates of Skeletonema sp. isolated from Harima Nada (Seto Inland Sea, Japan), Chaetoceros sp. and H. akashiwo were reduced significantly at higher ammonium concentrations compared to the control treatment. However, such a high ammonium concentration of even 1,500 μ M could not produce a significant adverse effect on the growth rate of Skeletonema sp. isolated from Dokai Bay. Furthermore, the maximum chlorophyll fluorescence of tested species was also gradually decreased with an increase in ammonium concentration. The influence of a high ammonium level on phytoplankton growth observed in this study confirmed the phytoplankton species composition observed in Dokai Bay. Our results suggested that such a high ammonium concentration was an important factor in determining the species composition of the phytoplankton assemblage in that bay

Size Fractionations of Phytoplankton Community in Osaka Bay and Kii Channel

大阪湾から紀伊水道にかけての海域において, 1993年10月, 1994年1月, 4月および6月の4回の航海において, 植物プランクトン群集のサイズ組成について調査した. クロロフィルa(Chl a)濃度を三つのプランクトンサイズ(0.2-2.0μm, 2.0-25μm, >25μm)に分画して測定した. 調査海域において全Chl a濃度は, 0.72から105μg l^であった. 大阪湾における平均Chl a濃度は6.41μg l^であり, 紀伊水道における平均Chl a濃度の0.87μg l^に比べて約7倍高かった. 全Chl a濃度に占めるピコ, ナノ, およびマイクロプランクトンサイズの割合は大阪湾でそれぞれ33%, 31%および36%であり, 紀伊水道ではそれぞれ62%, 27%および11%であった, このサイズ分布の結果より, 両海域では明らかにその植物プランクトンのサイズ組成が異なっており, その群集組成も異なることが予想された. 本研究におけるピコサイズのChl a濃度の最大値は6.0μg l^であり, この値は外洋域で報告されている値よりも明らかに高かった. さらに, このピコブランクトンサイズのChl a濃度の最大値は, 過去に報告されているピコ植物プランクトンの細胞当たりのChl a含量を5fg cell^と仮定して算出すると, 10^6cells ml^の細胞密度であると推定された.The phytoplankton community size distribution in Osaka Bay and Kii Channel was investigated, during four cruises in October 1993, and January, April and June 1994. The chlorophyll a (Chl a) concentrations of three size-fractionated samples (0.2-2.0 µm, 2.0-25 µm, > 25 µm) were measured. Total Chl a concentrations varied from 0.72 to 105 µg l^. The average total Chl a concentrations in Osaka Bay was 6.41 µg l^, which was about seven times higher than that of Kii Channel (0. 87 µg l^). Moreover, the average contributions of the pico-, nano- and micro-phytoplankton to the total Chl a in Osaka Bay were 33%, 31% and 36%, respectively, but in Kii Channel were 62%, 27% and 11%, respectively. We concluded that phytoplankton community between Osaka Bay and Kii Channel differs according to size distribution. This phytoplankton community in Osaka Bay and Kii Channel contained picoplankton with a maximum Chl a concentration of 6.0 µg l^, apparently higher than that of open ocean. Also, the Chl a concentration is correlated with an organism density of 10^6 cells ml^, assuming that the picoplankton Chl a content is 5 fg cell^

Dispersion of the small particles in the high turbidity water from sea sand mining boat

海砂利採取船からの高濁度排水中の微粒子の拡散状況を簡単な数値モデルで計算した。高濁度水排出地点では透明度の低下が著しいことが明らかになった。2日に一度の操業を繰り返した場合, 影響範囲は広範囲に拡がることが明らかになった。海砂採取による影響を最小限に抑えるためには, 5日以上の間隔で操業することが必要であることが示唆された。The dispersion situation of the small particles in the high turbidity waters from sea sand mining boat was calculated using a simple numerical model. The transparency (Secchi disk depth) decreased remarkably near the discharge spot of high turbidity waters. When the operation of sea sand mining at intervals of two days was repeated, it was clear that the influence area of high turbidity waters spreaded widely. To suppress influence of sea sand mining in a minimum, it was suggested that the operation of sea sand mining at intervals of five days and above should be done

The elemental composition of particulate matters in Bang Pakong River estuary, Thailand

Biological and chemical conditions were investigated at Bang Pakong River estuary, Thailand, where red tides were often occurred. Chlorophyll a (Chl a) concentration, nutrients, particulate organic carbon (POC), particulate organic nitrogen (PON) and particulate phosphorus (PP) were determined on November 2002, as the preliminary survey, and November 2004. Moreover, the latter observation was conducted including with upper stream (salinity varied from 0-27psu). The average stoichiometric ratios of particulate matter (POC:PON:PP) which derived from the slope of linear regression between each C, N and P concentrations and Chl a concentration was discussed. Our results indicated that the major composition of particulate matter in Bang Pakong River originated from planktonic particulate materials. In Bang Pakong River system, nutrients originated in upper stream and ran toward to estuarine zone. In the cast of particulate organic matter, it was not produced by allochthonous detritus but derived from autochthonous planktonic materials

Diatoms Grow Faster Using Ammonium in Rapidly Flushed Eutrophic Dokai Bay, Japan

The importance of the nitrogen source for phytoplankton growth in a highly eutrophic embayment, Dokai Bay, was investigated. The DIN concentration often exceeded 100 mu M of which 40-70\% was NH4+. During two incubation experiments, the natural assemblage of mainly diatoms took up NH4+ instead of NO3-. The growth of two Skeletonema species isolated in Dokai Bay were significantly faster on NH4+ (1.86 and 1.27 div. d(-1) respectively) than on NO3- (1.55 and 1.04 div. d(-1) respectively). Our re suits indicated that these diatoms could grow faster by using NH4+ compared to NO3- in this eutrophic bay

Effects of temperature and irradiance on growth of strains belonging to seven Skeletonema species isolated from Dokai Bay, southern Japan

The effect of temperature on the growth of Skeletonema ardens, S. costatum sensu stricto, the S. marinoi-dohrnii complex, S. japonicum, S. menzelii, S. pseudocostatum and S. tropicum isolated from Dokai Bay in southern Japan were examined under five to seven different temperatures and an irradiance of 150 mu mol m-2 s-1. The effect of irradiance on the growth of the seven Skeletonema species was also examined under a wide range of irradiances ranging from 7-700 mu mol m-2 s-1 at 20 degrees C. All Skeletonema species were able to grow at temperatures ranging from 15 to 25 degrees C. Intra-species differences in specific growth rates of four strains for S. menzelii, and five strains for S. ardens, the S. marinoi-dohrnii complex, S. japonicum and S. tropicum were not significant (Kruskal-Wallis test, P 0.05). Significant inter-species differences in specific growth rates were observed at 10, 15, 25 and 30 degrees C (Kruskal-Wallis test, P 0.01; Steel-Dwass test, P 0.01). The S. marinoi-dohrnii complex and S. japonicum grew faster than other species at the lower temperatures of 10 and 15 degrees C, and S. ardens and S. menzelii grew at the highest temperature of 35 degrees C. The maximum specific growth rates (max) from growth-irradiance curves ranged from 1.50 to 3.44 d-1. Threshold values of irradiance (I0) and saturation irradiance (S) for growth ranged from 3.9 to 7.6 mu mol m-2 s-1, and from 250 to 740 mu mol m-2 s-1, respectively. In Dokai Bay, our results suggested that the occurrence of Skeletonema species should be affected mainly by temperature and less by irradiance. In particular, only two species, the S. marinoi-dohrnii complex and S. japonicum could maintain their populations in the surface water during the cold season, whereas during other periods, all seven species could maintain their population under the strong influence of estuarine circulation, which rapidly flushed the surface water out of Dokai Bay. Temperature and irradiance dependent growth values were in good agreement with their geographical distributions. The S. marinoi-dohrnii complex and S. japonicum were capable of growing in cold regions, but our results suggested that S. ardens and S. menzelii will tend to prefer tropical regions