Inorganic chemicals in domestic water of the United Arab Emirates

The concentration of selected inorganic chemicals was determined for 396 samples of bottled water, desalinated water, and groundwater used for drinking and domestic purposes in the United Arab Emirates (UAE). The objective of this study was to compare the concentrations of inorganic chemicals in different domestic water types used in the UAE with the World Health Organization (WHO) limits for drinking water. Results of the present study revealed a wide variation in the concentrations of major, minor, and trace inorganic chemicals in domestic water of the UAE. For example, the bottled water sold for drinking is depleted in major ions and the total dissolved solids (TDS) in some brands do not exceed 100 mg/l. On the other hand, some of the domestic water used may contain as much as 3,000 mg/l TDS, which is above the WHO recommended limit for drinking water (500–1,500 mg/l TDS). Similarly, while bottled water is almost free of trace ions and minor constituents, some natural groundwater may have concentrations higher than the WHO recommended limits for drinking water. The cause of this variation is related to the different water sources and the large number of companies producing and distributing drinking and domestic water. Moreover, it is clear that the current controls on domestic water quality in some areas, namely conformance of pH and electrical conductivity measurements with prescribed ranges of values, are currently inadequate. These two parameters are not enough to judge if water is suitable for drinking or not and some consumers may receive domestic water of uncertain quality.     

Cyst formation of the noxious red tide flagellate Chattonella marina (Raphidophyceae) in culture

Cyst formation of the noxious red tide flagellate Chattonella marina (Raphidophyceae), cultured from a cyst in sediments of Suo-nada, Japan in 1986, was investigated by culture experiments. Nitrogen limitation was effective in inducing cyst formation. After incubation in N-limited medium at 25°C with 10000 lux on a 14 h light, 10 h dark photo-cycle, cultures were subjected to six different light intensities (0 10000 lux) in order to determine effects of light intensity on cyst formation. Cysts were formed under light intensities of 1000 lux or below, but not at 10000 lux. Cysts formed in culture displayed morphological characteristics quite similar to those natural cysts observed in sediments collected from the Inland Sea of Japan. Observations on nucleus, using diaminidinophenylindole (DAPI)-staining and epifluorescence microscopy, indicated that the majority of cysts formed in culture were uninucleate, a few were binucleate. Germination of cysts was observed under adequate conditions for germination (22°C, 3500 lux with a 14 h light, 10 h dark photo-cycle) even after storage at 11°C in the dark for more than 4 mo.     

Importance of cysts in the population dynamics of the red tide flagellate Heterosigma akashiwo (Raphidophyceae)

To elucidate roles of cysts in occurrences of Heterosigma akashiwo blooms, cyst dynamics were studied in northern Hiroshima Bay, the Seto Inland Sea of Japan, where H. akashiwo regularly forms red tide in June. Monthly measurements of seasonal changes in the densities of vegetative cells of H. akashiwo and their germinable cysts in surface sediments (top 1-cm layer) were made for 2 years at three stations. Vegetative cells of H. akashiwo could be detected from April through December throughout the water column, and the existence of vegetative cells was confirmed in surface waters even in winter after incubation of sampled seawater in culture medium. Germinable cysts, enumerated by the extinction dilution method, existed in sediments in all seasons, even before and after the seasonal bloom. The effects of incubation temperature on the germination of natural cysts of H. akashiwo in sediments were examined. Germination was not observed at 5 °C, was low at 10 °C, while it increased at 15 °C, and maintained a high level to 25 °C. The bottom water temperature reached 15 °C (suitable for the germination of cysts) and the surface about 18 °C or more (suitable for the growth of vegetative cells) 2 to 3 weeks before the blooms. The dark survival of H. akashiwo cysts was tested, and it was found that the cysts were viable for at least 650 d at 11 °C, and for 165 d at 25 °C, indicating a significant role of cysts in the survival during winter and summer seasons. The cysts presumably also play an important role in seeding primary populations into water columns when the bottom water reaches a suitable temperature (around 15 °C); thereafter the populations develop with great annual regularity to bloom in June. These results suggest that initiation of H. akashiwo red tides in the Seto Inland Sea could be triggered by bottom water temperature. Received: 3 July 1998 / Accepted: 12 January 1999     

The distribution of molluscan assemblages and their postmortem fate on coral reefs in the Gulf of Aqaba (northern Red Sea)

Molluscan assemblages were studied on fringing reefs (reef flats, Millepora-fringing reefs, fringing reefs with massive corals) and fore-reef hard substrata (coral patches, coral carpets and small patch reefs) in the Gulf of Aqaba at water depths ranging from the intertidal to 26 m. A total of 1,665 molluscan individuals from 51 taxa was counted on 44 transects, which covered 220 m2 at eight diving sites. The most important molluscs in the assemblage were the parasitic gastropod Coralliophila neritoidea, the encrusting gastropod Dendropoma maxima and the coral-associated bivalve Pedum spondyloideum. The dead assemblage, in contrast, was dominated by encrusting bivalves (Ostreoidea, Chamoidea, Spondylidae) and the coral-predating gastropod Drupella cornus. Distinct molluscan assemblages inhabit each of the three fringing reef-habitats and most of the important depth-related community changes occurred within the uppermost 5 m. In contrast, the three deeper fore-reef habitats are characterized by a more uniform molluscan composition. Molluscan assemblages were more dependent on substrata and their coral associations than on water depth. Comparisons with other published studies indicate that reefoidal hard substrata in the northern Red Sea are largely characterized by similar species-abundance patterns. The minor differences to other Red Sea studies probably reflect the northern, isolated position of the Gulf of Aqaba, the lack of certain molluscan habitats, and the differential impact of anthropogenic influences. Strong differences between living and dead assemblages in Aqaba are similar to those observed in other regions and are due to distinct biases in the dead assemblage. Molluscs closely associated with living corals (mostly bivalves and Dendropoma) can easily be overgrown after death and are thus undetectable in visual censuses. Some gastropod taxa are preferentially transported into surrounding soft-substrata postmortem or redistributed by hermit crabs. Such complex relationships between ecology and taphonomy are crucial in evaluating the quality of the molluscan fossil record in coral reef environments. The comparison of our results with literature data documents an increase in coral predators during the last two decades in the northern Red Sea. Due to the greater mollusc biodiversity in the shallower Aqaba reef habitats, damage to this coral reef zone would have the greatest impact on the overall mollusc community.     

Some aspects of recolonization of coral rocks in Eilat (Gulf of Aqaba) by fish populations after poisoning

As a result of an accident, a limited strip of the coast of Eilat (Gulf of Aqaba, Red-Sea) was affected by poison that killed all fishes. The area was observed monthly for the following year, to study the recovery of fish populations. The study also included observations on growth rate of fish and size of populations. Recovery of fish populations was complete 10 to 12 months after the poisoning. It is believed that this is due to the relatively small size of the contaminated area and the survival of most invertebrates that constitute an important part of the biotope of the fish.     

Aspects of iron and nitrogen nutrition in the red tide dinoflagellateGymnodinium sanguineum

Iron-stress-mediated effects on biochemical constituents of the red tide dinoflagellateGymnodinium sanguineum Hirasaka were examined in 1988 by comparing Fe-replete and Fe-deplete batch cultures. The influence of nitrogen source (NO₃ or NH₄) on characteristics of Fe-deplete cells was also studied [i.e., Fe-deplete/NO₃-grown (= — Fe/NO₃) vs Fe-deplete/NH₄-grown (= — Fe/NH₄)]. Common to both N sources were reductions of chlorophylla (chla) and Fe quotas (per cell volume) by 75% and ca. 1.5 orders of magnitude, respectively, under Fe depletion. The Fe requirement ofG. sanguineum exceeded those of certain neritic diatoms by one to two orders of magnitude. — Fe/NH₄ cells exhibited 30 to 50% greater N quotas and free amino acid:protein ratios than did Fe-deplete cells grown on NO₃. In vivo fluorescence:chla increased with Fe deficiency particularly in — Fe/NO₃ cultures, surpassing — Fe/NH₄ values by ca. two-fold. Effects of Fe depletion were consistent with this element's essential role in the biosynthesis of chla and components of the photosynthetic electron transport (PET) system, and also in NO₃ utilization. Fe:N ratios were larger (1.5-fold) for iron-deficient NO₃-grown than NH₄-grown cells, likely reflecting the Fe content of NO₃ assimilatory enzymes [nitrate (NR) and nitrite (NiR) reductase] and of electron transport components needed to provide reductant, coupled with a diminished capacity of — Fe/NO₃ cells to acquire and assimilate nitrogen. Indicators of PET efficiency suggested that under iron stress, supply of Fe for NR and NiR is partly at the expense of iron-containing PET components. Utilization of nitrate by NO₃-grown cells was inhibited sufficiently by Fe depletion to yield symptoms bordering on N deficiency. In an ecological context, the most important effect mediated by nitrogen source may be the determination of critical Q_Fe (i.e., Fe required to just sustain maximal growth), thereby regulating the degree of growth limitation for a given subsaturating iron concentration.     

Mitochondrial DNA differentiation and population structure in red drum (Sciaenops ocellatus) from the Gulf of Mexico and Atlantic Ocean

Variation in mitochondrial (mt)DNA was examined among 473 red drum (Sciaenops ocellatus) sampled in 1988 and 1989 from nearshore localities in the northern Gulf of Mexico (Gulf) and the Atlantic coast of the southeastern United States (Atlantic). Data were combined with those from a previous study to generate a total of 871 individuals sampled from 11 localities in the Gulf and 5 localities in the Atlantic. Individuals assayed were from the 1986 and 1987 year-classes. A total of 118 composite mtDNA genotypes (haplotypes) was found. The percentage nucleotide sequence divergence among the 118 haplotypes ranged from 0.184 to 1.913, with a mean (±SE) of 0.878±0.004. MtDNA nucleon diversities and intrapopulational nucleotide-sequence divergence values were similar over all Gulf and Atlantic localities, and were high relative to most fish species surveyed to date. These data indicate that the perceived decline in red drum abundance appears not to have affected the genetic variability base of the species. Significant heterogeneity in the frequencies of at least four haplotypes was detected between pooled samples from the Gulf vs pooled samples from the Atlantic. No heterogeneity was found among localities from the Gulf or localities from the Atlantic. High levels of gene flow among all localities were inferred from F _ST values (a measure of the variance in mtDNA haplotype frequencies) and from Slatkin's qualitative and quantitative analyses. Parsimony and phenetic analyses revealed no strong evidence for phylogeographic cohesion of localities, although there was weak support for cohesion of four of five localities from the Atlantic. These data indicate that the red drum population is subdivided, with weakly differentiated subpopulations (stocks) occurring in the northern Gulf and along the Atlantic coast of southeastern USA. Spatial autocor-relation analysis and heterogeneity tests of haplotype frequencies among regions within the Gulf supported the hypothesis of increased gene flow among neighboring localities; i.e., migration of individuals within the Gulf may be inversely related to geographic distance from an estuary or bay of natal origin. Estimates of evolutionary effective female-population size indicate that the red drum subpopulations may be large.     

Demographic parameters of two populations of red coral (Corallium rubrum L. 1758) in the North Western Mediterranean

The demographic and reproductive structure of populations represents the main data set needed for conservation and management plans. Mediterranean red coral Corallium rubrum has been exploited for 2,000 years, but only recently management plans have been solicited by the international community. We examined and compared the demographic features of two red coral shallow populations located in distinct geographic locations: Portofino (Italy) and Cap de Creus (Spain). Adults and juveniles density, growth rates, population size and age structure, fecundity and fertility were examined. Juveniles were the dominant class (33 %) in both populations. The analysis of the gamete content of 653 colonies revealed that the populations have balanced sex ratios and similar fertility and polyp fecundity. The average annual growth rate, determined on 119 colonies by annual growth rings count, was similar in both populations (0.24 mm year^?1), decreasing with colony age. Maximum life span of 99 % of the colonies was 60 and 40 years at Portofino and Cap de Creus, respectively. Minimum harvestable size (7 mm basal diameter) was reached in 30–35 years, and the percentage of colonies above it was 6.7 % at Portofino and 2.1 % at Cap de Creus, where juvenile and adult colony densities were significantly lower and the percentage of commercial-sized colonies reduced by 25 % in just a few years. Notwithstanding similar growth and fecundity, the two populations showed different densities and size/age structures suggesting local factors, together with different fishing pressures, have to be taken into account in the management plans for this species.     

Diet and seasonal prey capture rates in the Mediterranean red coral (Corallium rubrum L.)

Gorgonians are passive suspension feeders, contributing significantly to the energy flow of littoral ecosystems. More than in active suspension feeders (such as bivalves, ascidians and sponges) their prey capture is affected by spatial and temporal prey distribution and water movement. Corallium rubrum is a characteristic gorgonian of Mediterranean sublittoral hard bottom communities. This study found a high variability in the annual cycle of prey capture rate, prey size and ingested biomass, compared to other Mediterranean gorgonians. Detrital particulate organic matter (POM) was found throughout the year in the polyp guts and constituted the main proportion of the diet (25–44%). Crustacean fragments and copepods (14–46%) accounted for the second major proportion, while invertebrate eggs (9–15%) and phytoplankton (8–11%) constituted the smallest part of the diet. To verify the importance of detrital POM in the energy input of this precious octocoral species, in situ experiments were carried out during the winter–spring period. The results confirm the importance of detrital POM as the main source of food for C. rubrum [0.13±0.04 μg C polyp⁻¹ h⁻¹ (mean±SD)]. This study also compares the prey capture rates of two colony size classes and two depth strata: Within the same patch, small colonies (<6 cm height) captured significantly more prey per polyp (0.038±0.09 prey polyp⁻¹ h⁻¹) than larger colonies (>10 cm high) (0.026±0.097 prey polyp⁻¹ h⁻¹) and showed a higher proportion of polyps containing prey (17% compared to 10%). Comparing colonies of similar size (<6 cm height) revealed that the colonies situated at 40 m depth captured significantly more prey (0.038±0.09 prey polyp⁻¹ h⁻¹) than the ones at 20 m (0.025±0.11 prey polyp⁻¹ h⁻¹). One pulse of copepods was recorded that constituted 16% of all captured prey during the 15-month period studied in one of the sampled populations. The data suggest that the variability of hydrodynamic processes may have a higher influence on the feeding rate than seasonal changes in the seston composition. The carbon ingestion combined with data on the density of the exploited population results in 0.4–9.6 mg C m⁻² day⁻¹. The grazing impact of current, heavily exploited and small-sized populations is comparable to that of larger Mediterranean gorgonians, suggesting that unexploited red coral populations may have a high impact compared with other passive suspension feeders.     

Effects of the 1996 and 1998 positive sea-surface temperature anomalies on corals,coral diseases and fish in the Arabian Gulf (Dubai,UAE)

Two positive sea-surface temperature anomalies occurred in the Arabian Gulf in short sequence. Between May and August 1996 and 1998, sea-surface temperatures in the southern Arabian Gulf were elevated by 2°C above average. The consequences for coral fauna, coral diseases and coral regeneration were studied in Dubai (United Arab Emirates) between Jebel Ali and Ras Hasyan. In 1996, coral death was widespread, affecting primarily the genus Acropora. In Acropora-dominated areas, live coral cover was reduced from 90% to about 26% in 1996, while in 1998 only a reduction from 26% to 22% of the remaining coral cover occurred. In the study area, all six Acropora species suffered total mortality in 1996, thus the coral fauna was reduced from 34 species to 27. The nearest areas with surviving Acropora were 30 km to the east (Deira) and 20 km to the west (Al Jazira). Massive coral species suffered negligible mortality, and slowly increased in space cover. The Acropora overkill turned 7.9 km² (19.7% of total coral-covered area) of previously lush coral gardens into a dead framework that was increasingly bioeroded. Acropora recruitment only started in 1998, average recruit size in 1999 was 7Dž cm, and recruits were rare. Prior to the mass mortality event, coral diseases were common and seasonal (14LJ% of corals, mainly Acropora, affected in summer, in winter 7Lj%, mainly massives), after the mortality event seasonality was lost and infection remained below winter levels (6LJ%, only massives infected). In fish, overall species richness decreased from 95 to 64 species in point counts, but frequency only decreased in one species (Pseudochromis persicus). Guild structure changed inasmuch as herbivores and planktivores increased, and invertivores decreased, although differences were not statistically significant. The most abundant family, both prior to and after the coral mass mortality, was Lutjanidae. It appears that even though much of the coral was dead, the maintenance of structural complexity allowed the fish assemblage to avoid a similar catastrophic change to that experienced by the coral assemblage.     

On the potential use of magnesium and strontium concentrations as ecological indicators in the calcite skeleton of the red coral (Corallium rubrum)

 The variability of magnesium, strontium and calcium concentrations in the two skeleton types (sclerites and axis) of the red coral (Corallium rubrum) was assessed by using X-ray fluorescence spectroscopy and microprobe analysis as a prerequisite for their use as ecological indicators. Axis cross sections showed light and dark circular growth bands corresponding to fast and slow growth, respectively. Using microprobe analyses the Mg and Sr concentrations ranged from 2.8 to 3.0% and from 0.21 to 0.29%, respectively, in the sclerites and from 2.4 to 3.0% and from 0.1 to 0.28%, respectively, in the axis. Mg/Ca and Sr/Ca ratios varied within sclerites (average, 12% for both ratios) and within the axis of single colonies (average, 20% for Mg/Ca and 48% for Sr/Ca). Sr/Ca ratios in the axis were lower in fast-growing branch tips than in older, more basal parts of the colonies, whereas the Mg/Ca ratio did not differ significantly between colony regions. Mg/Ca and Sr/Ca ratios in the axis decreased significantly with depth, and we estimated an increase of the Mg/Ca ratio of 0.004–0.006 per degree Celsius. In all depth layers, Sr/Ca ratios showed a significant direct relationship with skeleton density in axis cross sections, whereas there was no significant relationship for Mg/Ca. Overall, our data indicate that temperature promotes the incorporation of Mg in C. rubrum as in other calcite skeletons, whereas Sr concentrations are inversely related to growth rate. This preliminary study suggests that Mg and Sr concentrations in the axis of the red coral have a strong potential as ecological indicator for temperature and growth rate. Received: 3 March 2000 / Accepted: 30 August 2000     

海洋赤潮藻球形棕囊藻在氮磷富营养下的细胞增殖

利用常见海洋赤潮微藻球形棕囊藻(Phaeocystis globosa)为试验研究材料,以舵海洋微藻营养液为对照(1P1N:磷质量浓度为5×10-3g·L-1.氮质量浓度为75×10-3g·L-1),设置3组富磷和富氮营养处理(3P1N:磷质量浓度为15×10-3 g·L-1,氮质量浓度为75×10-3 g·L-1;1P3N:磷质量浓度为5××10-3 g·L-1,氮质量浓度为225×10-3 g·L-1;3P3N:磷质量浓度为15××10-3 g·L-1,氮质量浓度为225×10-3 g·L-1),利用细胞记数和叶绿素荧光测定等方法研究了藻细胞在不同富磷和富氮条件的增殖情况.结果显示,不同浓度磷和氮营养下的藻体荧光值变化在试验周期内均呈现"S"型曲线,表明藻细胞的生长经历缓慢期,快速期和平缓期3个阶段;同时,不同的富磷和富氮营养条件对球形棕囊藻的叶绿素荧光值有一定的影响,其中在对照1P1N下的藻体荧光值最低,在试验结束时(第10天)只有850 μg·L-1,而在3P1N,1P3N和3P3N条件下的藻体荧光值均达到900 μg·L-1以上,显著高于1P1N下的藻体荧光值,表明富磷和富氮营养可以促进藻细胞的生长增殖,但在试验设置的不同富磷和富氮营养下的藻体荧光值之间没有显著的差异.就不同磷和氮营养条件下的藻最大比生长速率而言,3P3N和3P1N条件下的最大,均达到0.77 d-1,明显高于1P1N和1P3N条件下的藻最大比生长速率(分别只有0.70 d-1和0.69 d-1).此外,试验结束时细胞密度的变化趋势与藻体荧光值相似,富磷和富氮营养条件下的细胞密度显著高于1P1N下的细胞密度,而富磷和富氮营养条件下的细胞密度间也不存在显著的差异.研究结果揭示,水体中的高磷和高氮营养浓度是导致藻细胞大量快速增殖的一个主要因素,而利用叶绿素荧光来测定藻细胞增殖是一种快速、简便,灵敏和可靠的方法,可在今后赤潮监测过程中多加利用,以能及时、准确地预测预报赤潮爆发.从而减少其对环境和经济的影响.     

Surface zooplankton dynamics and community structure in the Gulf of Aqaba (Eilat), Red Sea

Winter and summer zooplankton maxima were observed on both near-reef and offshore sampling sites in the northern part of the Gulf of Aqaba, with summer maxima smaller than those of winter and more characterized by larval forms. Near-reef zooplankton biomass was generally several times greater than that observed 2 km offshore. During 1987, a near-reef maximum of 155 ind. or 12.2 g wet biomass m^–3 was observed in March, while 103 ind. or 8.5 g wet biomass m^–3 was observed in July. In the same year, 2 km offshore a maximum of 53 ind. or 2.5 g wet biomass m^–3 was observed in February, while a maximum of 33 ind. or 0.5 g wet biomass m^–3 was noted in July. The following year, 1988, the near-reef zooplankton abundances were little changed, but offshore zooplankton abundances were much higher (317 m^–3). During 1987, the dominant winter (March) forms near the reef were gammarid amphipods, at maximum concentrations of 100 ind. m^–3, where the summer (July) maximum was composed primarily of mysids (34 m^–3), gammarid amphipods (30 m^–3), and fish eggs (24 m^–3). The offshore winter zooplankton fauna was characterized by copepods and appendicularians, each at a maximum concentrations of ca 13 ind. m^–3, while the summer maximum was dominated by brachyuran zoea (31 m^–3). Though the 1988, winter near-reef zooplankton community compositions were similar to those of 1987, the offshore zooplankton fauna was dominated by ostracods, which were relatively rare in previous years. Preliminary data suggests that holoplanktonic forms like chaetognaths, copepods and appendicularians, at an offshore site exhibit different patterns of vertical migration than those near the reef. This different behavior may result from different species compositions of these taxa or from high concentrations of pseudoplanktonic bentho-neritic peracarid crustaceans.Please address correspondence and reprint requests to T. Echelman, Marine Science Research Center, State University of New York, Stony Brook, New York 11794-5000, USA     

Distribution,abundance and survival of juvenile hermatypic corals (Scleractinia) and the importance of life history strategies in the parent coral community

The distribution and abundance of juvenile corals were examined at depths from 3 to 37 m on the reefs of Curaçao and Bonaire (Netherlands Antilles). Juveniles of Agaricia agaricites were most abundant (60.6%), followed by Helioseris cucullata (8.3%). The large massive corals such as Montastrea annularis, M. cavernosa and branched species such as Madracis mirabilis and Acropora palmata had few juveniles. This, combined with species characteristics, shows that these species employ very different life history strategies. In some species the abundance of juveniles over the reef paralleled that of larger colonies, but not for example in Agaricia agaricites. The composition of the coral community was apparently no direct function of juvenile abundance. A change in angle of settlement of A. agaricites juveniles with increasing depth, from vertical to horizontal surfaces, seems to reflect the preferred light intensity. We studied the survival of juvenile corals during a half-year period. One-third remained unharmed, one-third died or disappeared, and one-third was limited in growth by factors such as spatial competition. This was the same for all depths, but factors influencing survival varied with depth.     

Fluctuations of the red tide flagellates Chattonella spp. (Raphidophyceae) and the algicidal bacterium Cytophaga sp. in the Seto Inland Sea, Japan

A marine algicidal gliding bacterium Cytophaga sp. strain J18/M01 was isolated in 1990 from a station in northern Harima-Nada, the Seto Inland Sea, Japan, using the harmful red tide alga Chattonella antiqua (Hada) Ono as a susceptible organism. The bacterium can prey upon various species of microalgae. Temporal fluctuations of this bacterium and Chattonella spp. [C. antiqua and C. marina (Subrahmanyan) Hara et Chihara] were investigated weekly at the above station in the summer of 1997 and 1998, using immunofluorescence assay employing highly specific polyclonal antibodies for the bacterium. In the summer of 1997, the cell density of Chattonella spp. showed a maximum value (70 cells ml⁻¹) on 8 July, and decreased thereafter. The bacterium Cytophaga sp. J18/M01 was commonly detected around a few hundreds of cells per milliliter or less. The number of Cytophaga sp. J18/M01 increased after the peak of Chattonella spp., and the maximum cell number of the bacterium was 1350 ml⁻¹. This algicidal bacterium also followed the changes of total amounts of microalgal biomass (chlorophyll a+pheophytin) when Chattonella spp. were absent. In the summer of 1998, Chattonella spp. were relatively less abundant (maximum 21 cells ml⁻¹), and the algicidal bacterium Cytophaga sp. J18/M01 showed a close relationship with the change of total microalgal biomass. The present study suggests that the algicidal bacterium Cytophaga sp. J18/M01 preyed upon, not only harmful red tide microalgae, but also other common microalgae such as diatoms, and the bacterium presumably plays an important role in regulating microalgal biomass in natural marine environments. Received: 20 April 2000 / Accepted: 1 December 2000     

Zooplankton standing stock and community size structure within the epipelagic zone: a comparison between the central Red Sea and the Gulf of Aden

Standing stock and size composition of the zooplankton comunity (>100 m) were studied in four depth strata of the upper 200 m of the water column during a Meteor cruise to the central Red Sea and Gulf of Aden in spring 1987. The central Red Sea was divided into a northern area of higher salinity and a less saline southern part. Both areas exhibited significant differences in zooplankton abundance and standing stock. The latter increased by the ratio 1:2:3 from the northern central Red Sea to its southern part and further south to the Gulf of Aden. For size structure analysis samples were fractionated into three size classes (100 to 300, 300 to 500, 500 to 5000 m). In the central Red Sea the smallest size was dominant whereas in the Gulf of Aden the largest size fraction played a greater relative role than in the central Red Sea. This shift in size structure of the zooplankton community from the Red Sea to the Gulf of Aden is apparently primarily related to ecosystem difference between both areas, leading to a change in species composition. In addition, size reduction of individual species common to both seas may be of some significance in the extreme environment of the Red Sea.     

Population structure of red drum (Sciaenops ocellatus) in the northern Gulf of Mexico, as inferred from variation in nuclear-encoded microsatellites

Allelic variation at eight nuclear-encoded microsatellites was assayed among 967 red drum (Sciaenops ocellatus) sampled from four consecutive cohorts at seven geographic localities (=28 samples total) in the northern Gulf of Mexico (Gulf). Number of alleles per microsatellite ranged from 6 to 21; average direct-count heterozygosity values per sample (-SE) ranged from 0.560ǂ.018 to 0.903ǂ.009. Tests of Hardy-Weinberg equilibrium revealed significant departures from expected genotype proportions at one microsatellite, which was omitted from further analysis. Tests of genotypic equilibrium indicated that genotypes between pairs of microsatellites were randomly associated. Homogeneity tests of allele distributions across cohorts within localities were non-significant following correction for multiple tests executed simultaneously, and results from molecular analysis of variance indicated that the genetic variance component attributable to variation among cohorts did not differ significantly from zero. Homogeneity tests of allele distributions among localities (cohorts pooled) revealed significant differences both before and after correction for multiple tests. Neighbor-joining clustering of a pairwise matrix of Š values (an unbiased estimator of F_ST), spatial autocorrelations, and regression analysis revealed a pattern of isolation by distance, where genetic divergence among geographic samples increases with geographic distance between sample localities. The pattern and degree of temporal and spatial divergence in the nuclear-encoded microsatellites paralleled almost exactly those of mitochondrial (mt) DNA, as determined in a prior study. Stability of both microsatellite and mtDNA allele distributions within localities indicates that the small but significant genetic divergence among geographic samples represents true signal and that overlapping populations of red drum in the northern Gulf may be influenced by independent population dynamics. The degree of genetic divergence in microsatellites and mtDNA is virtually identical, indicating that genetic effective size of microsatellites and mtDNA in red drum are the same. This, in turn, suggests either that gene flow in red drum in the northern Gulf could be biased sexually or that red drum populations may not be in equilibrium between genetic drift and migration. If a sexual bias exists, the observation that divergence in mtDNA is considerably less than 4 times that of microsatellites could suggest female-mediated dispersal and/or male philopatry. The observed isolation-by-distance effect indicates a practical limit to dispersal. Approximate estimates of geographic neighborhood size suggest the limit is in the range 700-900 km. Although the genetic studies of red drum indicate significant genetic divergence across the northern Gulf, the genetic differences do not delimit specific populations or stocks with fixed geographic boundaries.     

Succession and growth limitation of phytoplankton in the Gulf of Bothnia (Baltic Sea)

A one year field study of four stations in the Gulf of Bothnia during 1991 showed that the biomass was ca. two times, and primary productivity ca. four times, lower in the north (Bothnian Bay) than in the south (Bothnian Sea) during the summer. Nutrient addition experiments indicated phosphorus limitation of phytoplankton in the Bothanian Bay and the coastal areas in the northern Bothnian Sea, but nitrogen limitation in the open Bothanian Sea. A positive correlation between the phosphate concentration and the production/biomass ratio of phytoplankton was demonstrated, which partly explained the differences in the specific growth rate of the phytoplankton during the summer. Differences in photosynthetic active radiation between the stations also showed a covariation with the primary productivity. The relative importance of nutrient or light limitation for photosynthetic carbon fixation could not, however, the conclusively determined from this study. Marked differences in phytoplankton species composition from north to south were also observed. The number of dominating species was higher in the Bothnian Sea than in the Bothnian Bay. The distribution of some species could be explained as due to nutrient availability (e.g. Nodularia spumigena, Aphanizomenon sp.), while salinity probably limits the distribution of some limnic as well as marine species. The potentially toxic phytoplankton N. spumigena, Dinophysis acuminata and Chrysochromulina spp. were common in the Bothnian Sea but not in the Bothnian Bay. The pico- and nanoplankton biomass during late summer was higher than previously reported due to a revised carbon/volume ratio.     

Temporal stability and spatial divergence of mitochondrial DNA haplotype frequencies in red drum (Sciaenops ocellatus) from coastal regions of the western Atlantic Ocean and Gulf of Mexico

Restriction-site variation in mitochondrial (mt) DNA was assayed among 1675 red drum (Sciaenops ocellatus Linnaeus) sampled from 20 localities along the southeastern coast of the USA (western Atlantic) and the Gulf of Mexico (Gulf). Up to four consecutive year-classes (cohorts) were sampled at most localities. Nucleotide-sequence divergence among 170 mtDNA haplotypes identified ranged (in percentage) from 0.184 to 1.913, with a mean (±SD) of 0.887 ± 0.300. Comparisons of mtDNA haplotype frequencies across year-classes within localities were non-significant, indicating temporal stability of breeding components within localities. Significant heterogeneity in mtDNA haplotype frequencies was found across all localities, between (pooled) samples from the western Atlantic and the Gulf, and among geographically spaced, regional groupings in the Gulf. Genetic divergence between subpopulations of red drum in the western Atlantic and Gulf follows a pattern exhibited in other marine fishes, and probably stems from physical (historical environmental heterogeneity, absence of suitable habitat, and current patterns) and, perhaps, behavioral factors. Genetic differences among red drum in the Gulf appear to be due largely to an isolation-by-distance effect that is attributable to behavioral factors. The latter may include female philopatry to natal bays or estuaries, limited offshore (coastwise) movement of females relative to their natal bay or estuary, or both. Genetic divergence among red drum in the Gulf occurs despite high gene flow (estimated as the number of genetic effective migrants in an island mode). Conservation and management of red drum should be based on the premise that strategies for a given bay or estuary will impact geographically proximal bays or estuaries more than distal ones. Trajectories of correlograms in spatial autocorrelation analysis suggest a geographic neighborhood size, relative to genetic migration of red drum from a bay or estuary, of roughly 500 to 600 km. Received: 22 July 1998 / Accepted: 19 November 1998