Holocene vegetation and climate evolution of Corpus Christi and Trinity bays: Implications on coastal Texas source-to-sink deposition

The Texas coastline stretches 595 km across almost 4° of latitude and is home to diverse coastal vegetation assemblages, yet only a handful of studies have documented the climate and vegetative change of this region through the Holocene. We provide a detailed palynological record of Holocene climate for coastal Texas, based upon three subaqueous sediment cores from Corpus Christi Bay and Trinity Bay. Cluster analysis and correspondence analysis were used to investigate changes in palynological assemblages through time within each core. Common to both bays are nonarboreal taxa including Asteraceae (mainly Ambrosia and Helianthus), Chenopodium, Poaceae, and arboreal taxa such as Carya, Pinus, and Quercus. Our record shows that the coastal environments of central Texas began a transition from herbaceous (nonarboreal) dominated vegetation to arboreal vegetation as early as 8.4 ka within Corpus Christi Bay, and 3.8 ka within Trinity Bay. We note flooding events at 8.2, 5.4, and 3.6 ka in Corpus Christi Bay, and at 1.7, 1.2, and 0.8 ka in Trinity Bay. These events were caused by storms, sea level changes including flooding of relict river terraces, and changes in sediment delivery to the bays. The pollen record also shows evidence for changes in fluvial discharge to Corpus Christi Bay at 4.1 and 2.2 ka, and at 1.8 ka in Trinity Bay. We also see Zea mays in Trinity Bay, indicating local Native American agriculture. We observe no significant changes during the middle Holocene Climatic Optimum, and subtle but not statistically significant evidence of more variable climate oscillations than other records from more interior sites in Texas available for the late Holocene. This indicates that coastal Texas’ climate has operated semi-independently from central Texas regions, and was primarily driven by a coast-wise gradient of precipitation and evapotranspiration.     

Responses of Benthic Infauna to Large-Scale Sediment Disturbance in Corpus Christi Bay, Texas

Responses of benthic infauna to large scale disturbance by dredged material placement were studied at eight paired (placement and reference) areas in Corpus Christi Bay, Texas in 1995 and 1996. Total infaunal abundance, taxa richness, and the biomass of annelids and molluscs in placement areas no longer differed from that of reference areas approximately one year after placement. Annual secondary production for annelids and molluscs did not differ between placement and reference areas, however mean (± standard error) total annual secondary production at reference areas (53.6 ± 5.8 g AFDW/m²/yr) was greater than that of placement areas (26.2 ± 2.5 g AFDW/m²/yr) due to higher brittle star densities in reference areas. Differences in community structure between placement and reference areas returned to pre-placement levels one year after disturbance. The magnitude of changes in sediment grain size related to disturbance was positively correlated with the degree of convergence of placement area communities with pre-placement and reference communities. Sediment compaction was consistently associated with infaunal taxonomic composition (BIOENV) and increased linearly with time after disturbance. The use of the term “recovery” with reference to recolonization of dredging-related disturbance implies a return to pre-placement ecological conditions that are frequently neither a reality nor a practical expectation for areas that are subject to repeated disturbances. Our characterization of biological responses to dredged material disturbance targeted benchmarks that were linked to both pre-disturbance conditions and differences between disturbed and neighboring undisturbed areas and indicate that impacts persisted less than one year.     

Direct and indirect effects of hypoxia on benthos in Corpus Christi Bay, Texas, U.S.A.

Hypoxia (low oxygen conditions) has been found in the southeastern region of Corpus Christi Bay, Texas, U.S.A. every summer since 1988. The objectives of the current study were to determine direct and indirect effects of hypoxia on macrofauna. Direct physiological effects of hypoxia include reduction of benthic abundance, biomass, diversity, species richness and species evenness because of physiological intolerance. Indirect ecological effects of hypoxia include predation of emerging benthic fauna from the sediment. Macrofaunal community characteristics were compared vertically within sediments in caged and uncaged sediment samples in hypoxic and normoxic areas. Cage effects were determined with partial cages, which had reduced flow and no predator exclusion. Dissolved oxygen concentrations during the experiment was monitored in water column profiles and continuous measurement of bottom water in the hypoxic and normoxic areas. Hypoxia in Corpus Christi Bay in 1999 occurred as transient events, many of which were of short duration (less than 1 h) and moderate intensity (around 2 mg l^− 1). The macrobenthic community characteristics (i.e., abundance, biomass, species richness, diversity, and evenness) were directly affected by hypoxia as indicated by depressed levels and few deeper-dwelling organisms in the hypoxic area. Community structure was also different between the hypoxic and normoxic areas because of loss of species (presumably due to intolerance to low oxygen) in the hypoxic areas. Benthic invertebrates were found primarily in the surface in the hypoxic area, but there was no significant indication of indirect effects, i.e., increased predation pressure in the hypoxic area. The increased exposure to predation risk may be mitigated by predator avoidance of hypoxic areas. In conclusion, hypoxia in Corpus Christi Bay has negative direct effects on benthic organisms, but no indirect effects, such as increased predation pressure. The most significant finding is the interaction between hypoxia and vertical distributions of infauna, which drive hypoxia intolerant organisms to the surface and out of sediments.     

Trend of herbaceous pollen diffusion and allergic sensitisation in Genoa, Italy

In order to investigate the relationship betweenallergenic load and allergic sensitisation prevalenceon a long period, we analysed the annual data ofherbaceous pollen airborne diffusion in Genoa(NW-Italy) for 17 years (1981–1997), with particularregard to the most important allergenic species:Poaceae, Parietaria, Artemisia, Ambrosia. Weevaluated the relative trend and compared it with theprevalence data of patients sensitisation to thesepollens in the same period.The analysis of annual pollen amount revealed asignificant rising trend (r = 0.73, p < 0.05) of Parietaria pollen (average 14.324 grains/m³/year),whereas Poaceae (2048/year) and Artemisia(170/year) pollen count did not show any significantchange. Ambrosia (average 70/year) has been rising since 1989 (r = 0.87, p < 0.05) and reached themaximum pollen count in the last three years.The prevalence of pollen sensitisation resulted to bevery high (about 75%) in our atopic patients withrespiratory symptoms and did not change significantlyin the years: Parietaria pollen allergy waspresent in about 70% of patients with at least oneSPT positive to pollens (and 55% of atopicsubjects), and this frequency, much higher than theone found in North Italy, showed low year-to-year variability.Among pollinotics patients, Poaceae cutaneoussensitisation was found at a quite stable rate in theabove mentioned period (about 51%), as well as thatto Artemisia pollen (8%). Ambrosia skinprick test positivity is very rare (about 0.5%),without any evident increase.The present study shows that, for some of theherbaceous species, we cannot demonstrate astraightforward relationship between the trend ofairborne pollen and the frequency of sensitisation inexposed people. However, in the case of Parietaria, the high level of pollen amount in theair is clearly related with the high rate of cutaneous positivity in patients, but it seems tosuggest a ``plateau' that is not modified by anyfurther increase in airborne pollen (perhaps forgenetic limiting factors). On the other hand, Ambrosia pollen count, even if increasing in Genoa'satmosphere, could still be too low, and it would takesome more time to cause allergic sensitisation in exposed people.This kind of study, pointing out the influence ofairborne allergen exposure on hypersensitivitymechanisms, should be extended in time and world-wideto obtain general conclusions.     

Quantification of cyanamide contents in herbaceous plants

Cyanamide (NH2CN) is found in nature, although it has long been recognized as an industrial product. Distribution of cyanamide in the plant kingdom was investigated using a direct quantitative determination method to detect and measure cyanamide by stable isotope dilution gas chromatography-mass spectrometry (the SID-GC-MS method). The SID-GC-MS method proved to be a robust way to quantify cyanamide contents in the extracts of 101 species of herbaceous plants. The average recovery of cyanamide from all plants tested was 55.6+/-20.3%. Vicia villosa and V. cracca contained cyanamide at 369-498 microg/gFW and 3,460-3,579 microg/gFW respectively, while the other 99 species contained no detectable cyanamide (<1 microg/gFW). This result suggests that distribution of cyanamide in the plant kingdom is limited and uneven.     

Seasonality of macroalgae and epilithic diatoms in spring-fed streams in Texas, USA

A seasonal study of two spring-fed stream systems in south-central Texas was undertaken over a 15-month period from June 1996 to September 1997. Relative abundance of the epilithic diatom flora, percent cover of macroalgae, and several physical and chemical conditions were monitored in one 20-m stretch in each of the streams at approximately two-month intervals. Six additional spring-fed stream segments were sampled in May 1996 for macroalgae and measured for the same conditions, in order to determine how representative the macroalgal floras of the study sites were of south-central and western Texas. Conditions in the two stream segments were relatively constant over the 15 months, except for maximum depth; this finding is similar those reported for other spring-fed systems worldwide. Sixty-eight diatom taxa and nine macroalgae taxa were identified from the San Marcos River, which compares to 46 diatom taxa and six macroalgae taxa from the Comal River. Several diatom and macroalgae species were significantly correlated to stream conditions (e.g. Dichotomosiphon tuberosus and Hildenbrandia angolensis with daylength, and Amphora pediculus with maximum depth). Twenty-one macroalgal taxa were identified from the six additional spring-fed steam segments. Conditions in these streams were very similar to those measured in the San Marcos River and Comal River, except that they had a higher average pH _x= 8.1 versus _x= 7.6). The epilithic diatom flora of the San Marcos River and the Comal River contains many of the diatom and some macroalgal taxa commonly reported from springs globally. This revised version was published online in July 2006 with corrections to the Cover Date.     

Resource capture, biomass allocation and growth in herbaceous plants

Plant species differ widely in their rate of biomass production, even when grown under optimal conditions. A key question concerns the extent to which these growth rates correlate with the uptake of carbon and nitrogen and with the biomass allocation between leaves and roots. Recent data show that the answer to this question differs for mono- and dicotyledons, and that more than biomass allocation, it is the ratio between the activities of leaves and roots that correlates with the growth rate of a plant.     

Photosynthesis of herbaceous plants from nutrient-poor tropical forests

Photosynthetic characteristics, specific leaf mass, chlorophyll and total leaf nitrogen concentrations of four herbaceous plants (Dicranopteris linearis, Hanguana malayana, Pentaphragma ellipticum, Tacca integrifolia) from nutrient-poor tropical forests showed that all these plants were well-adapted to their natural growth environments. No photoinhibition was observed even in the understorey plants.     

Photosynthesis of herbaceous plants from nutrient-poor tropical forests

Photosynthetic characteristics, specific leaf mass, chlorophyll and total leaf nitrogen concentrations of four herbaceous plants (Dicranopteris linearis, Hanguana malayana, Pentaphragma ellipticum, Tacca integrifolia) from nutrient-poor tropical forests showed that all these plants were well-adapted to their natural growth environments. No photoinhibition was observed even in the understorey plants. This revised version was published online in June 2006 with corrections to the Cover Date.     

New records of aquatic Oligochaeta from Texas,with observations on their ecological characteristics

Twenty-six species of aquatic oligochaetes are reported from Texas, including 18 Naididae, seven Tubificidae, and one Glossoscolecidae. Illustrations are provided for ten species recorded for the first time from the state: Chaetogaster cristallinus, Nais elinguis, Nais pardalis, Pristina acuminata, Pristina sima, Stylaria lacustris, Aulodrilus limnobius, Ilyodrilus templetoni, Limnodrilus claparedianus, and Sparganophilus tamesis. Species accounts include presently known distributions in Texas and ecological and morphological characteristics.     

Early herbaceous succession along a topographical gradient on forest clear-felling sites in mountainous terrain,central Japan

Early successional patterns of herbaceous communities in forest clear-felling sites were investigated along a topographical gradient, which included ridge, slope and valley habitat types, in warm-temperate evergreen forest regions of central Japan for 5 years. Three dominant species with wind-dispersed seeds played a major role in the succession: an annual,Crassocephalum crepidioides, a biennial,Erigeron canadensis, and a perennial,Miscanthus sinensis. Pioneer herbs that have a seed-bank strategy, which are common in old field succession, were not found in the mountainous sites. The persistence of the annual or biennial dominants during the very early stages of secondary succession was different in the three topographical habitat types. In the ridge habitat,M. sinensis dominated from the first year state, andC. crepidioides andE. canadensis were less prominent.Crassocephalum crepidioides andE. canadensis became dominant as one moved down the slope. In the valley habitat,C. crepidioides dominated in the first year stage, was succeeded byE. canadensis in the second year, and thenM. sinensis gradually replaced it in later years. As all three wind-dispersed dominants simultaneously invaded in all the habitat types after clear-felling, the different successional patterns along the topographical gradient might have resulted from differences in the establishment ability and the growth rate of the three dominants depending on the three habitat types.     

Allergy to pollen of urban cultivated plants

Pollens of many plants located in public or privategardens may cause pollinosis in predisposedindividuals. There is evidence that the prevalence ofsensitization to ``new' tree pollens (Betulaceae,Corylaceae, Cupressaceae, Taxodiaceae, and otherfamilies) is increasing in the recent years in Italy.Allergenic plants are often imported from foreigncountries, therefore low-allergenic species must berecognized in order to prevent new pollensensitizations. In this study we suggest a list ofrecommended and notrecommended plants for public andprivate green.     

The accumulation and storage of nitrogen by herbaceous plants

Abstract Accumulation of nitrogen (N) by plants in response to N supply outstripping demand is contrasted with storage of N, which implies that N in one tissue can be reused for the growth or maintenance of another. Storage can, therefore, occur in N-deficient plants; accumulation can not. The consequence of accumulation and storage of N is considered, particularly in relation to the reproductive growth of annual plants, which can often use a great deal of stored N. Nitrate and proteins are the forms of N most often stored in vegetative tissues and, quantitatively, ribulose 1,5-bisphosphate carboxylase/oxygenase is often the most important protein store. While storing nitrate will be less costly to the plant in terms of energy, protein stores offer several possible advantages. These advantages are (i) maximizing the potential for carbon assimilation, (ii) avoiding problems with the regulation of leaf turgor and (iii) allowing the reduction on nitrate to occur in the young, fully illuminated leaf.     

Social class,admixture, and skin color variation in Mexican-Americans and Anglo-Americans living in San Antonio,Texas

Social class may act in different ways as a barrier to gene flow in urban populations, depending on ethnicity. We test the hypothesis that biological variation is affected by social class subdivision using skin reflectance data collected for 393 Anglo-American and 930 Mexican-American adults in the major urban population of San Antonio, Texas. Two socioeconomic groups were sampled for the Anglo-American population: a middle-income transitional group and a high-income suburban group. In addition, we sampled a third socioeconomic group for Mexican-Americans: a low income barrio. Sex and age effects on skin color are minimal. Social class has no effect on skin color variation for Anglo-Americans, whereas there is a highly significant effect on social class subdivision for Mexican-Americans. Admixture estimates were derived from skin reflectance data and show that the proportion of native American ancestry decreases as social class increases.     

Key to the shallow water Mysidacea of the Texas coast with notes on their ecology

An illustrated key is presented for the shallow water mysid shrimp of the Texas coast. Six genera and 10 species are included. Information concerning the distribution, ecology, reproductive biology, and morphology of the species in Texas waters is given.