The annual cycle of primary productivity in a tropical estuary: the inner regions of the Golfo de Nicoya, Costa Rica

A one year cycle of primary productivity (PP) was studied using the "light and dark bottle" technique in the Golfo de Nicoya, located at 10 degrees N and 85 degrees W at the Pacific coast of Costa Rica. Samples were always incubated at 0, 1, 2, 3 and 4 m depth for 5 hrs from 8:30 till 13:30. The measurements were performed twice per month, first around high tide and one week later at low tide to account for tidal influences. This routine study was supplemented by special measurements about regional and short-term variations of primary productivity using the 14C-method, which mainly served to account for the shortcomings of the routinely employed incubation technique. The upper Golfo de Nicoya is an extremely productive, phytoplankton dominated estuarine system with an annual gross PP of 1037, a net PP of 610 and a community respiration of 427 g C m(-2) a(-1). Highest monthly PP values occurred during the dry season and at the beginning of the rainy season. Peaks in primary productivity coincided with massive blooms of red tide forming algae. Internal biological dynamics, estuarine circulation and land run-off are the most important nutrient sources. High water turbidity reduces the euphotic layer to 4-5 m depth, making the underwater light regime the rate limiting factor. On an annual basis, 41% of the organic carbon produced in the system is already consumed in the euphotic layer. Considering the entire water column (mean depth at mean tidal water level is around 7.7 m) 79% is consumed in the pelagial. Taking into account the organic material consumed and stored in the sediments the carbon budget of the upper gulf is probably balanced. Since, however, the system receives a considerable amount of organic material from its terrestrial surroundings (especially from the mangrove forests), a surplus of organic carbon is exported from the upper Golfo de Nicoya, which enhances the overall water productivity of the lower gulf and the adjacent area.     

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.     

Characteristics of floor litter and soil arthropod community in different types ot subtropical forest in Ailao Mountain of Yunnan, Southwest China

By using line transect method, an investigation was conducted on the floor litter and soil arthropod community in a mid mountain wet evergreen broad-leaved forest, a mossy dwarf forest, and a Populus bonatii forest in Ailao Mountain of Yunnan in April (dry and hot season), June (rainy season), and December (dry and cold season), 2005. In both dry and rainy seasons, the existing floor litter mass, C storage, and C/N ratio in the three forests all increased in the order of mossy dwarf forest > P. bonatii forest > evergreen broad-leaved forest, but the N storage had less difference. In the floor litter layer of the forests, Acari and Collembola were the dominant groups of soil arthropod community, while Diptera larvae, Coleoptera, ants, and Homoptera were the common groups. The Sorenson coefficients of soil arthropod community in the three forests were extremely great. No significant differences were observed in the soil arthropod density (ind x m(-2)) in the floor litter layer among the three forests, but the relative density (ind x g(-1)) of soil arthropods was higher in the evergreen broad-leaved forest and P. bonatii forest than in the mossy dwarf forest. In the three forests, the density of soil arthropods was significantly higher in dry season than in rainy season, but the Shannon diversity index had less difference. There were significant positive correlations between the existing floor litter mass and the individual density (ind x m(-2)) and dominant groups of soil arthropod communities in dry and hot season (April), but negative correlations between the existing floor litter mass and the relative density (ind x g(-1)) of soil arthropod communities and Acari in dry and cold season (December). The individual densities of Collembola and Coleoptera also had positive correlations with the N storage of the existing floor litter mass in the three forests. It was considered that the floor litter and the development of soil arthropod community in the litter layer of the subtropical forests in Ailao Mountain had a close relation with the vegetation structure of the forests, and the individual density and the diversity of the soil arthropod community were controlled by the floor litter, whereas the environmental factors such as temperature and moisture in the forests also had obvious effects on the seasonal dynamics of the individual density of the soil arthropods.     

El Niño 1997-1998 impact on the plankton dynamics in the Gulf of Nicoya, Pacific coast of Costa Rica

The impact of the El Ni?o 1997-1998 phenomenom on plankton dynamics was studied during 1997 at the Punta Morales estuary, Gulf of Nicoya, Pacific coast of Costa Rica. The study covered dry season/transition and the rainy season. Phytoplankton (microphytoplankton > 30 microm and nanophytoplankton) were collected at two depths (50 and 10% light incidence) using a 5 L Niskin bottle, and samples taken to determine chlorophyll a. Temperature, salinity, oxygen, and Secchi depth were measured. Horizontal sub-surface zooplankton hauls were conducted with a conic zooplankton net of 0.49 m diameter and 280 microm mesh width, supplied with a flowmeter. Surface sea water temperature average was 29.9 +/- 0.9 degrees C, with a maximum of 31.5 degrees C in April and a minimun of 28 degrees C in March and October. Chlorophyll a concentration (phytoplankton net) averaged 3.1 +/- 1.7 mg/m3, with higher values during the rainy season and lower values during the transition. Nanophytoplankton chlorophyll a concentration averaged 2.5 +/- 1.2 mg/m3, with a maximum during the transition season. For both fractions there were significant differences between transition and rainy seasons, and for nanophytoplankton between dry and transition seasons (p < 0.05). In the last case, differences were explained by temperature. Herbivorous copepods dominated the abundance and biomass of zooplankton, with a biomass maximun of 167.3 in October and a minimun of 7.1 mg DW/m3 in December. These values are higher than those found some years ago in the same zone and those reported for some places in the Caribbean. The El Ni?o 1997-1998 phenomenon in the plankton dynamics appears to have produced a change in the phytoplankton structure. This is the first attempt to evaluate the possible impact of El Ni?o on the plankton dynamics of the Pacific coast of Central America.     

Population characteristics of the sea urchin Diadema antillarum in La Parguera, Puerto Rico, 17 years after the mass mortality event

Recent reports indicate that populations of the black sea urchin Diadema antillarum are slowly coming back in several localities in the Caribbean after 15 years of absence. In La Parguera, Puerto Rico, urchins were totally absent from reef localities until 1996, when isolated, medium size individuals were observed in shallow reef habitats. To assess the status (distribution, densities and size structure) of populations of D. antillarum 17 years after the die-off, twelve 20 m2 (10 x 2 m) band transects in each of four depth interval (0-3, 3-7, 7-11 and >11 m) in each of four fringing coral reefs, and six-eight band-transects in each of two depth intervals (0-3 and >3 m) in three lagoonal mounds were surveyed in 2001. All urchins present in the band transects in two depth intervals (0-3 and 3-8 m) were collected and measured (test diameter) in situ to determine the average size and size (age) structure of populations. Overall, average densities were low and not significantly different (F = 1.29, p = 0.125) across reef sites (0.83-1.39 ind/m2) and the seagrass mounds (1.09 +/- 0.6-1.30 +/- 0.6 ind/m2). Urchins were only found in the shallow areas (<3 m) on the seagrass mounds where they formed tight aggregations during daytime. Densities decreased significantly with increasing depth (r2 = -0.60) in reef sites and were significantly higher (F = 5.97, p < 0.001) in shallow reef platforms (0.89 +/- 0.69 - 1.98 +/- 0.65 ind/m2) (0-3 m), and the upper fore-reef (0.56 +/- 0.14 - 2.33 +/- 1.1 ind/m2) habitats (3-7m), compared to deeper (> 7 m) habitats (0.01 +/- 0.02 - 0.88 +/- 1.06 ind/m2). Enrique reef had a significantly higher (K-W, H = 165.19, p < 0.001) population average size (Median = 7.7) compared to all other sites. Populations in the sea grass mounds were dominated by midsize to large individuals. Within reefs, the average size did not vary significantly across depth intervals with medium to large size urchins dominating. Higher number of aggregations and higher number of urchins per aggregation were correlated with low complexity (rugosity) habitats (Pearson's r = -0.772, p < 0.001 and r = -0.778, p < 0.001 respectively), which supports the idea that this behavior provides protection. Although average densities were well below pre-mass-mortality densities in Puerto Rico, results of this study indicate that Diadema seem to be making a slow come back in La Parguera.     

Temporal and spatial distribution of the crab Callinectes sapidus (Decapoda: Portunidae) in Chetumal Bay, Quintana Roo, Mexico

In order to determine temporal and spatial distribution patterns of Callinectes sapidus, samplings were carried out during the cold-front (January-February), dry (May-June) and rainy (August-September, 2002) climatic seasons, in 30 sampling stations of Chetumal Bay, grouped in sectors A (14 stations), B (eight stations) and C (eight stations). In each sampling station crabs were collected from two transects parallel to the coast, each with three traps, separated by 30 m. Sediments were calcareous coarse and medium sand, white or lightly gray. A total of 1 031 specimens were collected. CPEU (Capture Per Effort Unit) differed spatially and temporally. Highest CPEU was found in sector C with 1.3 ind.trap(-1), and in the rainy season with 1.1 ind.trap(-1). Population was predominantly composed of male individuals. The male:female ratio was 15:1. Males and adults (group II) CPEU was significant different between sectors and climatic seasons. Both males and adults (group II) had a greater CPEU in sector C (1.2 ind.trap-) and in the rainy season (1.1 ind.trap(-1)). Abundance of female and juvenile individuals (group I) was low during the sampling period whereas group 0 juvenile individuals were not found. A greater relative frequency between sectors and climatic seasons were observed in 130-139 mm and 140-149 mm size interval (CW). C. sapidus occurred on sandy sediments in Chetumal Bay. Pearson product moment correlations exhibited significant relationships between CPEU and temperature, salinity and dissolved oxygen. In Chetumal Bay, the spatial and temporal distribution of C. sapidus can be related to salinity, temperature, habitat quality, food availability, recruitment and reproduction events of individuals.     

Seasonal emission of seminal coagulum and in vivo sperm dynamics in the black-handed spider monkey (Ateles geoffroyi)

The ejaculate of diverse primate species consists of two portions, liquid and solid; the latter, known as the seminal coagulum, is thought to sequester large numbers of sperm. In the black-handed spider monkey (Ateles geoffroyi), ejaculates collected by electroejaculation did not always contain seminal coagulum. The objective of the present study was to determine seasonal emission of seminal coagulum and in vivo sperm dynamics in the black-handed spider monkey. Seminal coagulum emission was related to season; it was more frequent in the dry season, coincident with maximal female fertility. Sperm concentration was higher (P = 0.02) in the dry season (dry vs. rainy season: 137.9 +/- 15.7 sperm/mL vs. 82.56 +/- 14.7 x1 0(6) sperm/mL; mean +/- S.E.M.) but also in ejaculates (collected during the rainy season) that had seminal coagulum (coagulum vs. no coagulum: 140.0 +/- 29.3 sperm/mL vs. 31.2+/-0.1 x 10(6) sperm/mL, P<0.001). In semen samples collected from the uterus after AI, the percentage of linearly motile sperm was higher during the dry season (dry vs. rainy: 9.1+/-2.1% vs. 5.9+/-2.5%), as well as whenever coagulum was present (coagulum vs. no coagulum: 13.0+/-3.2% vs. 2.0+/-0.9%, P<0.001).     

Asteroidea, Echinoidea y Holothuroidea in shallow bottoms of Bahía de Loreto, Baja California Sur, Mexico

To evaluate echinoderm distribution, abundance and density a double 50 m transect, with a side observation range of 2.5 m was used at each of 11 stations (bimonthly samplings, Aug. 1997-Febr. 1998). In Bahía de Loreto the Phylum Echinodermata consists of 26 taxa. The greatest mean abundance by transect and mean densities in order of importance for Echinoidea were: Echinometra vanbrunti (94.1 +/- 52.9 ind, 0.25 ind/m2), Centrostephanus coronatus (38.15 +/- 9.15 ind, 0.06 ind/m2), Tripneustes depressus (28.68 +/- 6.86 ind, 0.039 ind/m2), Eucidaris thouarsii (10.66 +/- 3.37 ind, 0.025 ind/m2) and Diadema mexicanum (11.75 +/- 4.92 ind, 0.023 ind/m2); for Asteroidea were: Phataria unifascialis, Mithrodia bradleyi and Acanthaster planci. Asteroidea was the dominant class with 12 species, followed by Echinoidea with ten and Holothuroidea was represented by four species.     

Seed bank dynamics and tree‐fall gaps in a northwestern Mexican Quercus‐Pinus forest

Questions: How does the seed bank respond to different types of tree‐fall gaps and seasonal variations? How does the soil seed bank influence recovery of the standing vegetation in the mature forest and tree‐fall gaps? Location: 1800 — 2020 m a.s.l., Quercus‐Pinus forest, Baja California Sur, Mexico. Methods: Seed size, species composition and germination were estimated under different environmental conditions during dry and rainy seasons: a mature forest plot and gaps created by dead standing trees, snapped‐of f trees and uprooted trees. The soil seed bank was investigated using direct propagule emergence under laboratory conditions, from soil cores obtained during both seasons. Results: 21 species, 20 genera and 14 families constitute the seed bank of this forest community. Fabaceae, Asteraceae, Euphorbiaceae and Lamiaceae were the most frequently represented families in the seed bank. Floristic composition and species richness varied according to the different modes of tree death. Species composition of seed banks and standing vegetation had very low similarity coefficients and were statistically different. Seed bank sizes varied between 164 and 362 ind.m^‐2 in the mature forest plot for the dry and rainy seasons, respectively, while soil seed bank sizes for gaps ranged between 23–208 ind.m^‐2 forthe dry season and between 81–282 ind.m^‐2 for the rainy season. Conclusions: Seed bank sizes and germination response were always higher in the rainy season under all the environmental conditions analysed. Results suggest that timing responses to gap formation of the soil seed bank could be more delayed in this temperate forest than expected.     

Airborne pollen grains in Nsukka,Nigeria

A study of the airborne pollen grains in Nsukka, Nigeria, has been carried out at two different sampling heights (1.8?m and 15?m) from February 1993 to January 1994. Twenty‐six plant families (40 genera) were identified at the lower sampling height, whilst thirty‐eight families (58 genera) were identified at the height of 15?m. A total of nine and eighteen fern spore types were observed at 1.80?m and 15?m, respectively. The quantitative results indicate that the number of pollen observed at 15?m sampling height was statistically different (p<0.05) from that observed at the height of 1.80?m. The analysis of airborne pollen grains indicates three different periods: (1) dry season, (2) rainy season, and (3) late rainy season to early dry season/Harmattan. The highest pollen abundance was recorded during the late rainy season – early dry season/Harmattan followed by that of the dry season. The predominant pollen grains and fern spores trapped at both heights include Poaceae, Casuarina equisetifolia, Milicia excelsa, Elaeis guineensis, Celtis integrifolia, Alchornea cordifolia, Amaranthaceae/Chenopodiaceae, Combretaceae/Melastomataceae, Nephrolepis biserrata, Thelypteris totta, and Dryopteris spp.     

Spatial distribution of heavy metals in sediments from the Gulf of Paria, Trinidad

The Gulf of Paria receives heavy metal input from urban runoff, industrial and agricultural activity, sewage and domestic wastes: both from the west coast and from inland areas of Trinidad. Non-residual concentrations of nine metals, as well as total mercury concentrations, were used to determine spatial distributions of heavy metals in sediments in the Gulf of Paria. Surficial sediment samples were collected at 37 stations, which included the mouths of 11 major rivers that flow into the Gulf of Paria. Stations were sampled twice during the wet season (July 1998 and November/ December 1998) and twice during the dry season (March 1999 and April 1999). Sediments were analyzed for aluminium (Al), cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), lead (Pb), manganese (Mn), nickel (Ni), zinc (Zn) and mercury (Hg). Total Organic Carbon (TOC) and grain size analyses were also performed on the sediments. Principal component analysis showed that sediments from river mouths subject to greatest land use and anthropogenic input, were distinct from other sediments in the Gulf of Paria. This was due to higher Pb, Zn, Cu and Hg concentrations (3.53-73.30 microg g(-1), 45.8-313.9 microg g(-1), 8.43-39.71 microg g(-1) and 0.03-0.10 microg g(-1), respectively). Sediments further from the coast were also distinct due to their higher Al, Fe, Cr and Mn concentrations (1.37-3.16 mg g(-1), 9.51-18.91 mg g(-1) , 17.22-28.41 microg g(-1) and 323.6-1,564.2 microg g(-1), respectively). Cd and Pb were higher in the wet season while Ni was higher in the dry season. Pb, Zn, Cu and Hg were correlated with each other and with TOC. Correlation was also observed between Al, Fe, Cr, Mn and Ni. Al, Fe, Cr and Mn were correlated with percentage clay in sediments. The results suggest that Pb, Zn, Cu and Hg are preferentially removed by organic matter, which settles at the river-mouths, while Al, Fe, Cr, Mn, and Ni become associated with clay minerals and are transported away from the coast.     

Seasonal patterns of gas exchange,water relations and growth of it Roupala montana,an evergreen savanna species

Roupala montana is an evergreen species widespread in the seasonal savannas of the central plains of Brazil. I examined the degree of coupling of photosynthetic gas-exchange characteristics, water relations and growth responses of R. montana with regard to seasonal changes in soil water availability. Despite a rainless period of over three months soil water potential at 60 cm depth reached values of only about -1.0 MPa, while pre-dawn leaf water potential (^l) reached about -0.4 MPa by the end of the three-month drought. Thus, R. montana had access to deep soil water in the dry period, but pre-dawn ^l did not reach the high wet season values of -0.2 MPa. Most of the shoot growth was concluded in the onset of the rainy season. Although some individual branches might have shown some extension thereafter, most of them remained inactive during the rest of the rainy season and the subsequent dry season. New leaf production was also restricted to the first part of the wet period. R. montana remained evergreen in the dry season, but there was a 27% decrease in the number of leaves and herbivory removed about 16% of the leaf area still present in the plant. CO₂-exchange rates of these leaves reached only ca. 55% of the maximum rainy season values of 14 µmol m^-2 s^-1. Thus, the estimated potential daily carbon gain was about 34% of the maximum by the end of the dry period. These values will be even lower, if we considered the decrease in photosynthetic rates that occurred around midday. These reductions in photosynthetic rates as a result of partial stomatal closure were measured both in the wet and dry season and they were related to increases in the evaporative demand of the atmosphere. In conclusion, the combined effect of herbivory, leaf loss and reductions in photosynthetic rates limited plant productivity in the dry season.     

Seawater temperature measured at the surface and at two depths (7 and 12 m) in one coral reef at Culebra Bay, Gulf of Papagayo, Costa Rica

Superficial seawater temperature (SST) and at two depths (7 and 12 m) were measured non-continuously during the study of the corals and coral reefs of Culebra Bay (1993-1996). SST showed seasonal variations of approximately 4 degrees C. The highest average temperatures (27.0 +/- 0.1, range 23-29 degrees C) were during the rainy season from May to November and the lowest (22.9 +/- 0.3 degrees C, 15.5-29 degrees C) during the dry season from December to April. Cold fronts with 2-3 degrees C differences in SST frequently pass into the bay and remain there for several hours according to the tidal cycles. Differences of approximately 3 degrees C between SST and the bottom (5-10 m depth) were usually found, particularly at locations where bottom topography and tidal circulation produced tidal bores. The average temperatures recorded by data loggers placed at 7 and 12 m depth on a coral reef at the outer shores of Culebra Bay, were 27.1 +/- 0.02 degrees C (20.5-31.6 degrees C) and 25.8 +/- 0.04 (9.9-31.5 degrees C) respectively. The seasonal pattern of higher and lower temperatures corresponds respectively to the rainy and dry season of the northern Pacific coast of Costa Rica. Water temperature at 12 m was < 14 degrees C for some hours during an upwelling event whilst minimum temperatures at 7 m were > or = 22 degrees C. Negative temperature anomalies coincided with an increase of the NE-E winds intensity and there is a lunar and tidal component which influence diumal variations of temperature. These results suggest that coral reefs built by branching species (e.g. Pocillopora spp.) in Culebra Bay could be limited by both the influence of cold fronts and by seasonal upwellings which affect negatively those coral species, as reported for other locations in the tropical eastern Pacific.     

Monitoring coral reefs, seagrasses and mangroves in Costa Rica (CARICOMP)

The coral reefs, seagrasses and mangroves from the Costa Rican Caribbean coast have been monitored since 1999 using the CARICOMP protocol. Live coral cover at Meager Shoal reef bank (7 to 10 m depth) at the Parque Nacional Cahuita (National Park), increased from 13.3% in 1999, to 28.2% in 2003, but decreased during the next 5 years to around 17.5%. Algal cover increased significantly since 2003 from 36.6% to 61.3% in 2008. The density of Diadema antillarum oscillated between 2 and 7ind/m2, while Echinometra viridis decreased significantly from 20 to 0.6ind/m2. Compared to other CARICOMP sites, live coral cover, fish diversity and density, and sea urchin density were low, and algal cover was intermediate. The seagrass site, also in the Parque Nacional Cahuita, is dominated by Thalassia testudinum and showed an intermediate productivity (2.7 +/- 1.15 g/m2/d) and biomass (822.8 +/- 391.84 g/m2) compared to other CARICOMP sites. Coral reefs and seagrasses at the Parque Nacional Cahuita continue to be impacted by high sediment loads from terrestrial origin. The mangrove forest at Gandoca, within the Refugio Nacional de Vida Silvestre Gandoca-Manzanillo (National Wildlife Refuge), surrounds a lagoon and it is dominated by the red mangrove, Rhizophora mangle. Productivity and flower production peak was in July. Biomass (14 kg/m2) and density (9.0 +/- 0.58 trees/100 m2) in Gandoca were relatively low compared to other CARICOMP sites, while productivity in July in Costa Rica (4 g/m2/d) was intermediate, similar to most CARICOMP sites. This mangrove is expanding and has low human impact thus far. Management actions should be taken to protect and preserve these important coastal ecosystems.     

Temporal fluctuation and reproduction of Thermocyclops decipiens (Copepoda,Cyclopoida) in an eutrophic lake of central Brazil

Lake Paranoá is an eutrophic reservoir situated in the urban region of Brasília. This study was carried out in a fixed collection station located in the Riacho Fundo branch of the reservoir. Zooplankton samples were collected at intervals of 3-5 d at 9:00 a.m. during two months in the dry and rainy seasons for two years (dry-1996, rainy-1997, dry-1997 and rainy-1998), using a 64 microns-mesh plankton net. The most predominant species was Thermocyclops decipiens (about 50% of the total zooplankton community), which during the whole period had a high reproductive rate. The highest densities were found in the dry-1996 season (1700 ind/l for nauplii), and also fluctuated widely overtime. Nauplii stages dominated during the four periods, comprising 50-75% of the total population density. Ovigerous females peaked in the dry-1996 and rainy-1997 seasons, with 20-30% of the total females. The largest peak in egg production occurred during the dry-1996 season, and the total egg production was 2.0 x 10(3) eggs/l. Mesocyclops longisetus is a first record for Lake Paranoá. The ecological factors that determine the success of T. decipiens in eutrophic systems are related to omnivorous feeding habits and prey-predator interactions.     

Density, growth and survival of Lyropecten (Nodipecten) nodosus (Pteroida: Pectinidae) juveniles in suspended-frame culture in Golfo de Cariaco, Venezuela

The effect of culture density on growth and survival of juveniles was studied in the scallop Lyropecten nodosus with intermediate hanging cultures in Golfo de Cariaco, Sucre state, Venezuela, from December 1993 to July 1994. Six spat-densities (7, 15, 30, 60, 125 and 250 scallops/nets) were evaluated. The initial shell height and dry mass tissue were 9.4 +/- 0.18 mm and 0.007 +/- 0.0026 g, respectively. The specimens were placed into pearl nets and suspended in a long line at 8 m depth. Growth patterns of somatic tissue were similar, but with different magnitudes and inverse proportionality to culture density. No effect of density was observed on survival. These results suggest that intraspecific competition of cultivated scallops cause stress, which affects growth but not survival. We suggest as strategy for the management of culture density, successive density reductions, to obtain in a six months culture (intermediate culture) specimens of 50 mm in shell height in order to start the final culture period.     

Phylogenetic analysis of partial bacterial 16S rDNA sequences of tropical grass pasture soil under Acacia tortilis subsp. raddiana in Senegal

We used direct recovery of bacterial 16S rRNA gene sequences to investigate the bacterial diversity under Acacia tortilis subsp. raddiana, a legume tree naturally growing in the dry land part of Senegal (West Africa). Microbial DNA was purified directly from soil samples and subjected to PCR with primers specific for bacterial 16S rRNA gene sequences. 16S rDNA clone libraries were constructed from two soil samples taken at two dates, i.e. June 25th 1999 (dry season) and August 28th 1999 (rainy season) at depths of 0.25-0.50 m and at 3 m distance from the stem. The 16S rDNA of 117 clones was partially sequenced. Phylogenetic analysis of these sequences revealed extensive diversity (100 phylotypes). Comparative sequence analysis of these clones identified members of the Gammaproteobacteria (35% of the phylotypes) as the most important group, followed by the Firmicutes division with 24%. Alphaproteobacteria, Betaproteobacteria, Acidobacteria and Actinobacteria were found to be less represented. Our data suggest that bacterial communities under Acacia tortilis subsp. raddiana might differ according to the season. The relative compositions of the populations is different in both samples: the Acidobacteria are present in a much higher percentage in the dry season than in the rainy season sample while the inverse effect is observed for the members of the other groups. Within the Gammaproteobacteria we found a shift between the dry season and the rainy season from pseudomonads to Acinetobacter and Escherichia related organisms.     

嘉陵江四川段藻类植物群落结构及水质评价

为了揭示嘉陵江四川段藻类植物的群落结构特征和水质现状,分别于枯水期(1月)和丰水期(9月)沿江段至上而下分析了12个样点藻类群落的种类组成、Shannon多样性指数（H′）、Pielou均匀度指数（E）和Margalef丰富度指数（d).结果表明: 嘉陵江四川段共采集到藻类植物8门42科95属171种(包括变种),其中硅藻、绿藻和蓝藻为各样点的优势类群.整个江段枯水期藻类植物的平均细胞密度为14.71×10⁴ ind·L^-1,金溪和红岩子样点的密度最高,分别为28.33×10⁴和25.40×10⁴ ind·L^-1;群落中以硅藻的物种数量最为丰富.丰水期藻类植物的平均细胞密度为10.78×10⁴ ind·L^-1,以青居样点的密度最低,仅3.31×10⁴ind·L^-1,绿藻和蓝藻物种数量有所增加.整个江段12个样点枯水期和丰水期的平均d、平均H′和平均E分别为2.35、1.60、0.31和2.57、2.09和0.39.嘉陵江四川段的藻类植物群落结构、细胞密度、多样性指数和均匀度指数的时空分布格局差异显著.水质整体为中污染型,其中金溪和沙溪样点为寡污型或β中污型,水质较好;苍溪、红岩子、新政和青居样点水质较差,属α中-污型.     

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.     

Photosynthesis and Optimal Light Microhabitats for a Rare Cactus, Mammillaria gaumeri, in Two Tropical Ecosystems

Mammillaria gaumeri , an endemic cactus from Yucatan, is threatened due to human-mediated habitat fragmentation but knowledge regarding factors that would inform management plans is limited, including information on optimal microhabitats and growth. We studied seasonal patterns of microclimate, net CO₂ uptake and growth of adult individuals during the dry, rainy and northwind (late fall to winter) seasons in separate populations located in a coastal dune and in a dry forest. To provide an assay of primary productivity, we measured the production of new axillary buds (areoles) from the apex. We found that patterns of net CO₂ uptake in the three seasons were consistent with obligate crassulacean acid metabolism. The reduction in soil water potential and the increase in water vapor pressure deficit led to a reduction in 24-h net CO₂ uptake from 18.0 to 1.3 mmol CO₂/m², after 30 d of drought. Dry-weight gain was maximal during the rainy season and there was no growth during the dry season, thus seasonal patterns of net CO₂ uptake and growth for M. gaumeri reflected soil and atmospheric water contents. Annual dry-weight gain increased linearly with plant size and with total daily photosynthetic photon flux density (PPFD) up to 80 percent of ambient. Maximal growth was in exposed microhabitats receiving 60–80 percent of total ambient PPFD. We hypothesize that low-magnitude disturbances, resulting in more exposed microhabitats, might be beneficial for growth and conservation of adult individuals of this rare species.