Benthic macrofauna associated to Thalassia testudinum in Bahía de Mochima, Sucre, Venezuela

Diversity and abundance of benthic macrofauna associated to Thalassia testudinum were studied at Ensenada de Reyes, Mochima Bay, in the northeastern coast of Venezuela. Samples were taken monthly in six stations, three at 1 m in depth and three at 6 m, between December 1992 and February 1994, using a quadrat of 0.25 m2 for collecting plants and sediment; each sample was washed with seawater through a 1 mm sieve. The specimens were fixed in 6% formaldehyde. A total of 1722 organisms (6 888 ind x m2) and 127 species of macroinvertebrates were collected. Mollusks dominated with 53 species, followed by polychaetes (40), crustaceans (18) and echinoderms (8). Remaining groups were represented by 1-2 species. The highest abundance was in October (214 specimens), and the lowest in December 1993 (79 specimens). Specific richness was between 47 species in October and 18 in May 1993. Mean species diversity was 2.79-1.36 bits/ind. There were differences (ANOVA p<0.01) in number of specimens at the two depths but not throughout the 15 month study period (p>0.05). There were more specimens and species at the lowest depth and in stations with higher Thalassia testudinum biomass.     

Mollusc diversity in an Arca zebra (Mollusca: Bivalvia) community, Chacopata, Sucre, Venezuela

The diversity of a subtidal epifaunal mollusk community was studied from September, 1990 to September, 1991 in Chacopata, Sucre State, Venezuela. There were 40 species (24 bivalves and 16 gastropods). The diversity indexes (H' = 2.087, J' = 0.392, 1/D = 0.528) were low when compared with other tropical zones. Monthly diversity reached its maximum in September, 1990 (1.63 bits/ind.) and July, 1991 (1.60 bits/ind.); minimum diversity occurred in June, 1991 (0.52 bits/ind.). A Log series model applied to species abundance data showed a straight line with a diversity index alpha of 5.56. Of 40 species identified, the turkeywing Arca zebra was dominant (69% in number of individuals and 72% of biomass) followed by Pinctada imbricata, Modiolus squamosus, Chama macerophyla and Anadara notabilis. The predatory snails Phyllonotus pomum, Chicoreus brevifrons and Murex recurvirostris seemed to have trophic relationships with A. zebra. The total mean biomass in wet weight (469.20 +/- 263 g m-2, shell included) was high which indicates that A. zebra, a species with a rapid growth rate, occupies a central role in the assemblage as an efficient filter feeder that converts planktonic food into available biomass, supporting one of the most important fisheries in Venezuela.     

Diversity and abundance of mollusks in the sublittoral epifaunal community of Punta Patilla, Venezuela

The diversity of a sublittoral epifaunal mollusk community of Punta Patilla, Sucre State, Venezuela, was studied from September 1990 to September 1991. We identified 25 species (14 bivalves and 11 gastropods) of mollusks that inhabit gravel, soft sand and bottoms covered by Thalassia testudinum. Total diversity indices were H' = 3.42. J' = 0.74 and 1-D = 0.85. Monthly diversity reached its maximum in March 1991 (3.12 bits/ ind.), June 1991 (2.88 bits/ind.) and September 1991 (2.95 bits/ind.); minimum diversity was recorded in August 1991 (1.20 bits/ind.). A log series model showed a diversity index alpha = 4.56 for species abundance data and alpha = 3.11 for biomass data. The more abundant species were Chione cancellata, Anigona listeri, Chione granulata and Area zebra among the bivalves, and Chicoreus brevifrons, Turritella variegata and Phllonotus pomum among the gastropods (which present maximum biomass). The average total biomass (56.80 g/m2) is low when compared to reports from other tropical zones.     

Polychaeta (Annelida) associated with Thalassia testudinum in the northeastern coastal waters of Venezuela

Seasonal variations of polychaetes in a Thalassia testudinum bed were studied from June 2000 to April 2001 in Chacopata, northeastern Venezuela. Eight replicate samples were taken monthly with a 15 cm diameter core and the sediment was passed through a 0.5 mm mesh sieve. A total of 1,013 specimens, belonging to 35 species, was collected. The monthly density ranged from 387 ind/m2 (September) to 1,735 ind/m2 in May (x = 989+/-449 ind/m2). Species richness was lowest in August and September (8) and highest (25) in April (x = 18.00+/-5.29). The shoot density of Thalassia showed an average of 284+/-77.60 shoots/m2, with extreme values in February (164) and May (422). Species diversity ranged from 1.25 in August and 3.33 bits/ind in December (x = 2.47+/-0.64). Significant positive correlations were detected among the number of Thalassia shoots, polychaete abundance and species richness, as well as among species richness, polychaete abundance and species diversity. Species number and average density were found within the intervals of mean values reported in similar studies. The higher number of species and organisms obtained in March-April and June-July can be attributed to the recruitment correlated with the regional up-welling.     

Community structure of fishes on the east coast of the island of Cabagua, Venezuela

The community structure of fishes on a sandy beach with patch of Thalassia and coral reefs was studied at Punta Las Cabeceras, Cubagua Island, Venezuela. Diurnal monthly samples were obtained from March 1999 to February 2000. Numerical abundance of fish species was recorded to determine the specific diversity. A total of 1 268 individual from 38 species and 20 families were identified: Haemulidae, Scaridae and Gerreidae were the more abundant, with 7, 4 and 3 species, respectively. Nicholsina usta, Eucinostomus argenteus, Halichoeres bivittatus and Tylosurus crocodiles made up 74.38% of the abundance, and present in 50% of the samples. The number of species occasional visitors was 30 (78.94%), indicative of the mobilization from another areas. On a monthly basis, the species number varied between 2 and 12; diversity index between 0.98 and 2.93 bits ind(-1), equitability (J') from 0.44 to 0.98, both indices showing the same tendency. N. usta and E. argenteus had the highest biological index equivalent to 59.1 and 60.0%, respectably, of the maximum possible total and were dominants and characteristics fishes of the community.     

Population of Lytechinus variegatus (Echinoidea: Toxopneustidae) and structural characteristics of seagrass of Thalassia testudinum in Mochima Bay,Venezuela)

To compare the general features of Thalassia testudinum seagrass at Mochima Bay with sea urchin (Lxtechinus variegatus) abundance and distribution, three T. testudinum seagrass beds were selected, from the mouth (strong wave exposure) to the inner bay (calm waters). Each site was surveyed by using 5 line transects (20 m long) parallel to the coast and 1 m2 quadrats. In situ measurements of T. testudinum cover, shoot and leaf density were taken. Estimation of dry biomass for each seagrass fraction (leaves, rhizomes and roots) and leaf length were obtained from 25 vegetation samples extracted per site using cores (15 cm diameter). A multivariate analysis of variance (Manova) and a less significative difference test (LSD) were performed to examine differences between sites and within sites at different depths. A stepwise multiple regression analysis was done, dependent variable was sea urchin density; independent variables: vegetation values at each site. The only seagrass species found in the three sites was T. testudinum, and cover was 56-100%, leaf density 100-1000 leaf/m2, lengths 6-18.8 cm and shoot density 20-475 shoots/m2. The highest sea urchin densities were found at Isla Redonda and Ensenada Toporo (1-3.6 ind/m2), the lowest at Playa Colorada (0.6-0.8 ind/m2). Significant differences in seagrass features between sites were obtained (Manova p < 0.001), but not between depths (Manova p < 0.320). The regression coefficient between sea urchin density and seagrass parameters was statistically significant (r2 = 0.154, p < 0.007), however, total biomass was the only variable with a significant effect on sea urchin distribution (beta = 0.308, p < 0.032). The other variables did not explain satisfactorily L. variegatus abundance and distribution.     

Ichthyofauna from wetlands of San Pedro, Balancán, Tabasco, México

San Pedro River's wetlands sustain trophic nets in the fluvial system, due to the high habitat availability, and space and temporal variations. In order to describe the relationship between environmental parameters and ichthyofauna, this study evaluated fish assemblages composition, distribution, abundance, density, biomass, richness species, diversity and equitability in the wetlands. Sampling considered three different sites and climatic seasons (dry, rainy and cold fronts). The physical and chemical parameters considered were dissolved oxygen, temperature, pH, water transparency and the depth. Fishes were caught with a shrimp net, after six minutes towings and were identified afterwards. A total of 1 049 organisms of 25 fish species were caught, two of which were exotic species: Oreochromis niloticus and Parachromis managuense. A total of 23 species were found at site I (with the highest density 0.23 ind./m2), 17 at site II (0.23 ind./m2) and 14 at site III (0.12 ind./m2). The dry season had the highest species number with 21 species, followed by the rainy season with 17 species, and the cold season with five species. Similarly, the highest biomass (8.30 g/m2) was found in dry season, followed by the rainy (2.16 g/m2) and the cold seasons (0.03 g/m2). Considering seasons, highest density was found during the dry (0.436 ind./m2), followed by the rainy (0.213 ind./m2) and the cold (0.023 ind./m2) seasons. The dominant density species during the study period, according to the quadrants graphic of Olmstead-Tukey were: Petenia splendida, Vieja heterospila, Vieja synspila, Dorosoma petenense and Astyanax aeneus. There were significant differences in the species richness among sites. Temperature, depth and transparency showed differences among the seasons. The canonical correspondence analysis indicated that fish distribution was governed by environmental parameters during all seasons. In terms of fish abundance and composition, environmental parameters play an important role showing spatial and temporal differences in the ecosystem, this could be explained with the fact that most of young fishes have a movement behavior to the wetlands, searching refuge and feed during the dry season. Considering the diversity indexes variation, it may be concluded that San Pedro River's wetlands correspond to a system where the ichthyofauna composition fluctuates spatial and seasonally.     

Abundance of Diadema antillarum (Echinodermata: Echinoidea) in the coasts of Venezuela

Diadema antillarum is a shallow-water sea-urchin from the tropical Atlantic whose populations almost disappeared in 1983-84 because of widespread mortalities which reached 87-100 %. In Venezuela, urchin population densities before the mortality event were comparable to those of other Caribbean regions; however, later abundancies remain unknown. The objectives of this study were to evaluate the recent densities of certain D. antillarum populations along the Venezuelan coasts and compare the densities at the Parque Nacional Mochima before and after the mortality. At each location urchin densities were determined by means of transects using 1 m2-quadrats as sampling units. The highest mean densities were observed at the sites on the central coast: Ensenada de Oricao, 0.28 ind/m2 (2002) and 1.05 ind/m2 (2003), and Chichiriviche de la Costa, 0.84 ind/m2 (2002) and 0.74 ind/m2 (2003). In Mochima, the mean density before the mortality for D. antillarum oscillated between 0.28 and 4 ind/m2, after the mortality event the mean density varied between 0.15 ind/m2 (2000) and 0.47 ind/m2 (2000). The populations of D. antillarum studied at Parque Nacional Morrocoy and Refugio de Fauna Silvestre Cuare showed highest densities at Playuela (0.43 ind/m2) and Cayo Sur (0.95 ind/m2) respectively, whereas other sites showed densities below 0.1 ind/m2. The density registered at Playuela in 2003 is lower than that reported before the mortality event (0.58-3.64 ind/m2). The density for Parque Nacional Archipiélago de Los Roques, specifically for the Arrecife de Herradura remained constant between 2002 and 2003 with values between 0.22-0.23 ind/m2 respectively. To conclude, the sea urchin abundancies observed at most of the Venezuelan coastal sites that we studied were higher than those reported for other areas of the northern Caribbean, even though the values have not yet returned to those preceding the 1984 mass-mortality event, due to the slow recovery of the populations.     

Ichthyofauna associated to Thalassia testudinum at Lobos reef, Veracruz, Mexico: diversity and abundance

The diversity and abundance of ichthyofauna associated with Thalassia testudinum in the Lobos coral reef, Veracruz, Mexico, were studied in September and October 2002. Thirty six visual censuses in four sample sites were made using a 50 x 2 m transect belt. On each census, fish species, abundance and size were recorded. Leaf size and cover of T. testudinum were estimated. The similarity of fish groups was calculated with the Gower coefficient. The most abundant coral reef fishes were: Scarus iseri, Halichoeres bivittatus, Sparisoma radians, Stegastes adustus and Stegastes leucostictus. The highest density (0.04078 ind/m2) and biomass (0.72408 g/m2) of fish species were recorded in site II, where leaf size was greater (30.8 cm). The analysis of variance showed significant differences between sites in leaf size (F = 18.30856; p = 0.00001) and cover (H = 33.8119; p = 0.00001). These differences suggest a relationship between fish diversity and abundance, and T. testudinum leaf size and cover. The Gower similarity index produced two groups of fishes; one of them (site II) showed the highest abundance. In this reef, the fishes associated to sea grasses seem to reflect the characteristics of T. testudinum.     

北部湾海域浮游介形类物种组成、丰度分布及多样性

根据1998年1月～1999年5月北部湾海域4个航次生态环境综合调查资料,对北部湾海域浮游介形类进行分析研究。结果表明,北部湾渔场浮游介形类物种组成较为简单,记录有小型海萤（Cypridina nana）、齿形海萤（Cypridina dentata）、尖尾海萤（Cypridina acuminata）、纳米海萤（Cypridina nami）、针刺真浮萤（Euconchoecia aculeata）、细长真浮萤（Euconchoecia elongata）、后圆真浮萤（Euconchoecia maimai）等18种;隶属于2亚目、2科、4亚科、12属,其中有4种周年出现,9种只在特定的单一季节出现,其余5种季节性出现;夏季和冬季出现的物种数最多,达到11种;春季次之,为9种;秋季最少,只有6种。北部湾浮游介形类可以划分为3个生态类群,即低盐暖水类群、广温广盐类群和高温高盐类群,优势种群主要是近岸低盐暖水类群的针刺真浮萤和尖尾海萤。全海域栖息密度变化范围为0．02～51．58ind．／m^3,年平均1．22ind．／m^3,春季最高,达2．73ind．／m^3,在湾西北部密集有大量的针刺真浮萤;夏季此密集区逐渐向湾中部移动,纳米海萤为其密集种,栖息密度也有所降低;秋、冬季量少,但在湾南、北部各出现一个丰度相对较高的密集区,并由南北向湾中部递减。总生物量具有明显的季节性变化,平面分布趋势与栖息密度相似。生物多样性指数低,以湾口较高、湾顶较低,呈湾口向湾内西北方向递减趋势;全海域年平均多样性阈值为0．329,四季多样性水平皆为Ⅰ级,多样性程度低;多样性程度较高的区域,多出现于受外海水影响较大、水文状况变化较为复杂的海域。对浮游介形类的物种组成、丰度分布及多样性与北部湾的水系、水团、水温及盐度等环境因子的关系进行了探讨。     

福建省主要海湾潮下带大型底栖无脊椎动物组成与分布特征

根据2010年8月对福建省12个主要海湾潮下带大型底栖无脊椎动物的调查资料,分析了大型底栖无脊椎动物的种类组成、生物多样性和群落结构分布特征及其与环境因子的关系.结果表明: 12个海湾共采集到大型底栖动物382种,包括环节动物170种、甲壳动物75种、软体动物78种、棘皮动物19种,以及其他类群40种.物种数、丰度、生物量和生物多样性指数空间差异较大: 罗源湾物种数最高,为92种,旧镇湾最低,为25种,所有海湾平均(55±21)种;所有海湾在物种组成上均为多毛类占优势,其平均物种数百分比为(51.8±5.5)%;诏安湾平均丰度最高,为(1330±1094) ind·m^-2,其次为福清湾、厦门湾、湄洲湾,泉州湾最低;兴化湾平均生物量最高,为(821.2±2387.7) g·m^-2,其次为福清湾、厦门湾,深沪湾最低;丰富度指数和Shannon多样性指数在罗源湾、湄洲湾、深沪湾、厦门湾和东山湾呈现较高值,而在福清湾和旧镇湾呈现较低值,两者的全域均值分别为(0.80±0.09)和(2.73±0.64).以相似度20%为界,可将研究区域的大型底栖无脊椎动物划分为14个群组,其中罗源湾内各站位间群落相似度最高,湾内差异最小,其次为三沙湾、福清湾、深沪湾和诏安湾,而其他海湾不同站位的群落组成差异较大.物种数、多样性指数和环境因子间的相关性分析和主成分分析显示,造成研究区大型底栖动物群落结构组成和分布差异的主要环境因子依次为沉积物铜、水深和底层水体活性磷酸盐.     

莱州湾大型砂壳纤毛虫群落季节变化

为揭示莱州湾砂壳纤毛虫群落季节变化规律, 在莱州湾设置8个站位, 于2011年5-11月及2012年3-4月进行了9个航次的调查, 用浅海III型浮游生物网由底至表垂直拖网采集砂壳纤毛虫。结果表明, 莱州湾3-11月砂壳纤毛虫物种丰富度的变化范围为5-19, 周年变化呈现一峰两谷的趋势。丰度的范围为0-318 ind./L, 丰度较大(> 50 ind./L)的种类有运动类铃虫(Codonellopsis mobilis)和清兰拟铃虫(Tintinnopsis chinglanensis)。各月平均丰度随时间的变化趋势为双峰型, 最大值出现在7月(63 ind./L), 次峰值出现在5月(48 ind./L), 最小值出现在3月(2 ind./L)。黏着壳种类在3-11月均有出现, 透明壳种类仅在温度较高(> 15°C)的6-9月出现。各月的优势种数目为1种(5月)到8种(8月), 其中运动类铃虫在所有月中都是优势种, 对砂壳纤毛虫丰度周年的变化规律产生较大影响。使用各月所有种类的平均丰度对各月砂壳纤毛虫群落进行聚类分析, 得到两个群落(相似度30%): 群落I(7-9月)和群落II(3-6月、10-11月), 说明砂壳纤毛虫群落发生了明显的季节变化。砂壳纤毛虫的物种丰富度、丰度与环境因子(温度、盐度)均没有明显的相关性。     

巨桉凋落叶分解对菊苣生长及光合特性的影响

采用盆栽试验,研究了巨桉凋落叶分解初期对菊苣幼苗生长和光合生理特性的影响.试验设置A₁(30 g·pot^-1)、A₂(60 g·pot^-1)、A₃(90 g·pot^-1)和对照（CK）4个凋落叶水平,将各处理的凋落叶分别与12 kg土壤混合后装盆,播种菊苣.待A₃处理植株的第3片真叶完全展开后测定菊苣光合生理指标及相关生长指标.结果表明：巨桉凋落叶分解初期明显抑制了菊苣生物量积累、叶面积的增加及光合色素的合成,且随着凋落叶施入量的增加抑制作用加大;菊苣叶片胞间CO₂浓度增加,而净光合速率、气孔导度和蒸腾速率均显著低于对照;随土壤中凋落叶含量的增加,除CO₂补偿点呈增加趋势外,其他光响应和CO₂响应的特征参数都呈明显下降趋势,并与对照差异显著.巨桉凋落叶分解过程中,其化感物质逐步释放并作用于受体植物,抑制其光合色素合成和光合作用,降低其环境适应能力,从而抑制菊苣的生长.     

黄河口潮间带大型底栖动物群落特征

2013年2月、5月和8月对黄河入海口附近潮间带的大型底栖动物进行了调查,调查工作涵盖3个季节2条断面的样品,分析了黄河口潮间带大型底栖动物的群落结构特征,包括群落种类组成、丰度和生物量、优势种、多样性,采用CLUSTER聚类分析了大型底栖动物的群落结构,并用AMBI和m-AMBI对底栖群落和环境质量进行了评估。本次调查共鉴定出大型底栖动物52种,其中,多毛纲动物24种,软体动物14种,甲壳动物12种,鱼类1种,纽虫1种。多毛纲动物为该海域底栖群落的主要成分,占据了群落总种数的46.15%。从季节来看,物种数春季最高(38种),夏季则处于最低水平(16种)。群落丰度和生物量均具有明显的季节变化,丰度在春季达到最高,为3 549.33 ind/m2,远高于冬季的256.67 ind/m2和夏季的100.67 ind/m2,其中扁玉螺(Neverita didyma)是丰度的主要贡献者,贡献了全年群落总丰度的75.44%。生物量春季最高,夏季次之,冬季最低。在全年尺度上,甲壳动物的日本大眼蟹(Macrophthalmusjaponicus)是生物量的主要贡献者,占据总生物量的49.86%。群落的季节变化也得到了群落CLUSTER分析与SIMPER分析结果的验证。这与黄河入海口附近底质不稳定,易受侵蚀、环境条件如盐度等具有明显季节差异,以及一定程度的人为扰动密切相关。AMBI和m-AMBI的分析结果显示,该区域环境质量状况较好,仅受到了轻微扰动影响。     

Bathymetric distribution and diversity of deep water polychaetous annelids in the Sigsbee Basin, northwestern Gulf of Mexico

The deep water polychaete fauna is analyzed in this study particularly regarding its composition and variations with depth in the Sigsbee Basin, northwestern region of the Gulf of Mexico. Samples were taken at 10 stations along a bathymetric gradient with depth ranges from 200 to 3760 m with a USNEL (0.25 m²) corer. A total of 287 individuals were identified, from 21 families and 65 species. The most important families, both in terms of abundance and species richness, were: Paraonidae (65.4 ind./0.25 m², 9 spp.), Cirratulidae (28.93 ind./0.25 m², 7 spp.) and Spionidae (18.07 ind./0.25 m², 7 spp.). In general, density tended to decrease with depth with minima at around 2000 m, although two abundance peaks were detected at 3700 and 3760 m, making the pattern seem an inverted parabolic curve. The Shannon-Wiener diversity values varied from 0.54–0.92 at around 2000 m to 3.39 at 3620 m and 3.34 at 3760 m. These results contrast with what is already reported from the North Atlantic and the Tropical Pacific deep benthic communities, where highest diversities are found at 2000 m. Faunal changes evaluated through Beta Diversity (0.08–0.1) and the low similarity found between the stations, emphasized the high variability in the composition of the fauna in the Sigsee Basin, meaning that the faunal composition is practically different at all the sampling stations. Ten species are newly recorded for the Mexican fauna.     

The distribution of zooplankton and bowhead whales, <Emphasis Type="Italic">Balaena mysticetus</Emphasis> Linnaeus, 1758, in Akademiya Bay,Sea of Okhotsk

The modern pattern of distribution and feeding habits of the bowhead whale, Balaena mysticetus, in the Sea of Okhotsk are studied. The existence of a feeding aggregation of this whale species in the southwesternmost portion (apex) of Ulban Bay has been confirmed. There, the animals feed in shallow waters with depths of 3–5 m, which are only slightly larger than their body height. The quantitative composition and species structure of zooplankton at the stations that were set near feeding whales have been analyzed. In the samples taken in the immediate proximity to the feeding whales, the abundance of zooplankton reached 31409 ind./m³, with the average value of 17565 ind./m³. The lowest abundance, from 56 to 1879 ind./m³ (mean 927 ind./m³), was in the samples from western Konstantin Bay, where bowhead whales were not observed. In 16 samples collected in the immediate proximity to the feeding whales in the shallow waters of Ulban Bay, the average zooplankton biomass was 547.9 mg/m³, which is 3.9 times higher than that in the samples from waters where the whales were absent. Copepods dominated quantitatively at all the stations in Akademiya Bay. The proportion of euphausiids in the zooplankton biomass was lower than 1%, both near the feeding whales and in the absence of whales.     

Abundance and richness of mollusks and crustaceans associated to the submerged roots of red mangrove (Rhizophora mangle) at Bocaripo Lagoon, Sucre, Venezuela

Mangrove roots are important habitats for many species. The abundance and richness of mollusks and crustaceans associated with the roots demerged of Rhizophora mangle was studied. The samples were gathered between February 2005 and January 2006, in Bocaripo lagoon, north coast of Sucre state, Venezuela. Five stations were established inside the lagoon; on every station two roots were chosen at random, put in plastic bags and scraped. The associated organisms were separated by taxa and fixed in 10% formaldehyde. One thousand ninety two specimens of mollusks, distributed in two classes: Bivalve and Gastropod were collected. Bivalve was the most abundant with 943 individuals. The most representative family was Mytilidae with 6 species, being Musculus lateralis the dominant species. The crustaceans were represented by 372 organisms, belonging to the class Malacostraca, where Panopeus herbstii (169 ind.) was the most abundant species. The families Panopeidae, Porcellanidae and Majidae had the highest number of species. Maximum abundance was in February (224 ind.), with a richness of 25 species and the minimums in November (45 ind.) and a richness of 12 species. The stations 1 and 5 presented the major abundance and richness of organisms, which could be related to environmental conditions favorable, as the major availability of microhabitats and nourishing offer; on the contrary the station 4, presented a more inhospitable environment, due to the high values in the salinity and temperature, which contributes with the minor abundance and richness of the present species.     

Epibenthic gastropods of the middle Florida keys: the role of habitat and environmental stress on assemblage composition

A survey of epibenthic prosobranch gastropods was undertaken in both seagrass and hard substratum (coral or old reef rock) habitats on opposite sides of the Florida Keys (Florida Bay and Hawk Channel) to compare faunal differences attributable to differences in the above two habitats and environments. Additionally, two data sets (26 continuous months) of daytime dissolved oxygen, surface salinity and water temperature from Florida Bay (Long Key) and Hawk Channel (Key Largo) environments were compared to determine differences that might constitute environmental stresses likely to affect the fauna. The above data were collected to determine if several hypotheses concerning effects of stress on organisms, assemblage, community and faunal composition were consistent with data on assemblage structure. These hypotheses were that: (1) stress should reduce the average size of organisms; (2) shorten food chains; (3) reduce predation intensity; (4) reduce species richness and diversity; and (5) increase the relative abundance of predator-susceptible ancestral species (i.e. Archaegastropoda). Water quality data suggest that the two most likely forms of stress in deeper (>1 m) areas of Florida Bay adjacent to the Keys are cold water temperatures associated with winter cold fronts and low predawn oxygen associated with warm summer temperatures, high salinity, and periodic algal and seagrass drift buildups. Seagrass sites had high population densities and low diversity due to the dominance of Astraea americana Gmelin (American star shell) in Florida Bay and Modulus modulus L. in Hawk Channel seagrass habitats. Florida Bay sites had high species richness on a small spatial scale, but Hawk Channel sites had more species and greater encounter rates of new species on a larger scale. Predawn oxygen measurements taken during July in four habitats were positively correlated with prosobranch species richness and diversity. Faunal data, analysed on a population density basis, fit the above hypotheses of body size, trophic level, and evolutionary age of the species. Attempts to measure predation on an experimental prosobranch (A. americana) were unsuccessful but a tethering experiment with a sea urchin (Echinometra lucunter L.) indicated higher predation in the less stressful Hawk Channel than Florida Bay hard substratum sites. Stress appears to reduce the abundance of higher trophic levels (both prosobranch and finfish predators) resulting in the dominance of ancestral forms not adapted to predation but tolerant of environmental stress. Eutrophication or increased oxygen demands in Florida Bay could result in further species richness and diversity declines.     

Seasonal dynamics and grazing rate of zooplankton in Yueqing Bay,China

The species composition,biomass,abundance,and species diversity of zooplankton were determined for samples collected from August 2002 to May 2003 from 14 stations in Yueqing Bay,China.Phytoplankton growth rate and microzooplankton grazing rate were obtained by using the dilution method developed by Landry and Hassett.The spatial and temporal variations of zooplankton and its relationship with environmental factors were also analyzed.The results showed that the zooplankton in the Yueqing Bay could be divided into four ecotypes,namely coastal low saline species,estuary brackish water species,offshore warm water species,and eurytopic species.A total of 75 species of zooplankton belonging to 56 genera and 17 groups of pelagic larva were identified in the Yueqing Bay.The coastal low saline species was the dominant ecotype in the study area,and the dominant species were Labidocera euchaeta,Acartia pacifica,Acrocalanus gibber,Pseudeuphausia sinica,and Sagitta bedoti among others.There was considerable seasonal variation in zooplankton biomass and abundance in the surveyed areas.The peak biomass appeared in August,descending in November and in May,and the lowest biomass appeared in February.Similarly,the highest abundance of zooplankton was observed in August,with the abundance descending in the following months:May,November,and February.There were similar horizontal distribution patterns for the biomass and the abundance of zooplankton.They both increased from the upper to the lower bay in February and May,but decreased from the upper to the lower bay in August.Biomass and abundance were evenly distributed in the Yueqing Bay in November.Moreover,there was marked seasonal variation in the species diversity of zooplankton,which conformed to the abundance of zooplankton.Results of the dilution experiments indicated that there was grazing pressure of microzooplankton on phytoplankton in the Yueqing Bay throughout the year though the rate of microzooplankton grazing on phytoplankton varied seasonally.Phytoplanktons were growing at 0.26-2.07/d and grazed by microzooplankton at a rate of 0.15--0.48/d in different seasons.     

Composition of a molluscan assemblage associated with macrophytes in Menzel Jemil (Bizerte lagoon,SW Mediterranean Sea)

The molluscan species composition and diversity associated with macrophytes was studied throughout 1 year at Menzel Jemil station (Bizerte lagoon, north‐west of Tunisia). A total of 7,539 individuals belonging to 13 species were collected. The molluscan assemblage was mainly composed of gastropods (98.12%, nine species), followed by bivalves (1.88%, four species). Hydrobia acuta ranked first with 49.97% of total abundance, followed by Bittium reticulatum (17.97%), Tritia mutabilis (11.38%), Haminoea navicula (8.98%), Phorcus articulatus (5.17%) and Cerithium vulgatum (3.94%). The large number of juvenile molluscs collected confirms the importance of macroalgae and seagrass for mollusc recruitment. Significant temporal variations of species richness, density and diversity indices of the mollusc assemblage have been observed during the year. Multivariate analyses applied to our data revealed significant relationships between the macrophyte composition and associated molluscan assemblage. The BIOENV analysis indicated that water temperature, phosphates concentration and macrophyte biomass were environmental variables most closely associated with the temporal variation of molluscan assemblage.