Temperature, desiccation, and species performance trends along an intertidal elevation gradient

This study investigated the effects of intertidal elevation on ecologically relevant temperature traits and the intensity of organism desiccation during low tides on a subpolar NW Atlantic shore. The goal was to relate those descriptors of environmental stress to elevational changes in the growth of dominant sessile species (algae and mussels) that influence overall community structure. In-situ measurements taken at the low, middle, and high intertidal zones revealed that daily temperature maxima, daily temperature range, and desiccation rate increased significantly from low to high elevations. Conditions were especially stressful at the high zone, as the highest temperature (47 °C, recorded during aerial exposure at low tide) more than doubled seawater temperature and desiccation rate surpassed 90 %. Transplant experiments showed that seaweed (Ascophyllum nodosum) and mussel (Mytilus edulis) growth rate decreased dramatically from low to high elevations. Therefore, although subpolar shores are mostly known for their harsh winter conditions, the pronounced vertical stress gradient that characterizes the intertidal zone during ice-free months also plays a major role in determining spatial changes in benthic species performance. Our study also suggests that inferring stress differences between habitats based on growth data from transplanted specimens may be a useful field method to further develop stress ecological theory.

Modelling desiccation crack geometry evolution in clayey soils by analytical and numerical approaches

In the present work, the development and geometry of desiccation cracks are studied by using a finite element code including cohesive joints elements. The numerical results show that cracking occurs sequentially to form different crack families. The propagation of each crack at the onset suddenly reaches an ultimate depth. The cracks in each family appear simultaneously and reach an identical ultimate depth. From the numerical results and additional analytical analysis, empirical correlations are proposed to predict the spacing and crack depth as a function of suction applied on the top surface, the soil parameters, and the desiccation rate. The proposed model shows that higher suction is required to initiate cracks at a higher value of soil tensile strength. In addition, there is a general trend of larger spacing and deeper cracks for a slower desiccation rate. Finally, empirical relations are evaluated by comparing them with in situ experimental observations published previously.

Population biology of the sea star Anasterias minuta (Forcipulatida: Asteriidae) threatened by anthropogenic activities in rocky intertidal shores of San Matías Gulf, Patagonia, Argentina

In Patagonian coastal areas, intertidal benthic communities are exposed to extreme physical conditions. The interaction between harsh environment and anthropogenic pressure can generate changes in population biology of marine invertebrates, like density and reproduction. The oral brooding sea star Anasterias minuta is a key organism in food chains of Atlantic Patagonian rocky intertidals, hence changes on its population structure can negatively affect shore communities. We studied the population biology of A. minuta and assess the effect of environmental parameters and anthropogenic activities on its population on rocky intertidal shores of San Matías Gulf, Patagonia, Argentina. Seasonal sea surface temperature, pH, salinity, water velocity, desiccation rate, boulders density, and anthropogenic influence (tourists and octopus fishermen) were recorded. In sites with less tourist influence and high refuge, an increase in density was recorded, especially during the summer. Brooding individuals were found in fall and winter, while feeding individuals were observed in all seasons (12 different prey, mainly the molluscs Tegula patagonica and Perumytilus purpuratus). Environmental variables such as boulders density and water velocity were the most important predictor of variation in population structure. Tourism and pH were the most important variables negatively correlated with density. Rev. Biol. Trop. 65(Suppl. 1): S73-S84. Epub 2017 November 01.

Viability of Aquatic Plant Fragments following Desiccation

Desiccation following prolonged air exposure challenges survival of aquatic plants during droughts, water drawdowns, and overland dispersal. To improve predictions of plant response to air exposure, we observed the viability of vegetative fragments of 10 aquatic plant species (Cabomba caroliniana, Ceratophyllum demersum, Elodea canadensis, Egeria densa, Myriophyllum aquaticum, Myriophyllum heterophyllum, Myriophyllum spicatum, Potamogeton crispus, Potamogeton richardsonii, and Hydrilla verticillata) following desiccation. We recorded mass loss, desiccation rate, and plant fragment survival across a range of air exposures. Mass loss accurately predicted viability of aquatic plant fragments upon reintroduction to water. However, similar periods of air exposure differentially affected viability between species. Understanding viability following desiccation can contribute to predicting dispersal, improving eradication protocols, and disposing of aquatic plants following removal from invaded lakes or contaminated equipment.

Some factors that contribute to poor survival of rhizobia on preinoculated legume seed

Preinoculation of seed is a convenient alternative method to inoculating seed on-farm. With preinoculation, a range of plant-growth and protection agents, polymer adhesives, colour pigments or dyes, and powder materials may be incorporated into an inoculant adhesive-slurry prior to seed coating. However, our recent point-of-sale surveys support findings of previous studies that survival of rhizobia on preinoculated seed is variable and can be poor. We focussed our research, both in the laboratory and at commercial facilities, on some of the factors that may contribute to poor survival of rhizobia on preinoculated seed. We found that rhizobial survival was affected by water quality; filtration improved cell survival but was not equal to distilled water. We also found that polymers affected cell survival differently for each rhizobial strain, and that slowing the desiccation rate reduced the cell rate of decline. Although fewer in cell number, older inoculant afforded more protection for survival of rhizobial cells. There is a need to test each ingredient and stage in the seed-coating process for compatibility to determine the best practices to promote rhizobial survival on seed. Failure to act on these factors prolongs the status quo of the findings from recent retail surveys.

The importance of feeding status and desiccation rate in successful anhydrobiosis of Panagrolaimus detritophagus

We examined the effect of nutritional status and desiccation rate on the ability of Panagrolaimus detritophagus to undergo anhydrobiosis, as well as to survive high temperatures in the dried state. Both nutrition and drying rate were found to be important, with starvation and slow drying providing better success at anhydrobiosis. The upper temperature for survival of dried animals in laboratory studies was 80°C. Starved worms recovered from drying more successfully when the starvation period was followed by a smooth, gradual dry period prior to undergoing desiccation. Thus, the ability of these worms to enter and leave anhydrobiosis is dependent on critical stress signals.

How long does it take for different seeds to dry?

Reduction in rainfall and intensification of dry season moisture deficit threaten to expose desiccation-sensitive seeds in the seasonal tropics to greater potential negative effects of desiccation. A determinate affecting the recruitment of species under increased aridity is how quickly desiccation-sensitive seeds dehydrate. We investigated the rate of seed moisture loss in 24 species that produce desiccation-sensitive seeds in a seasonal tropical forest and tested the common hypothesis that seeds conform to a simple negative exponential model of moisture loss with time. A negative exponential model described moisture loss in 14 species, but was not the best model for the remaining 10 species. Moisture loss in eight species was best described by a double-negative exponential model and by a double-linear model in the remaining two species. We then tested the hypothesis that seed mass could predict the rate of desiccation between and within species. Within species the time to a given state of desiccation could be predicted by seed mass for eight species. Between species there was no relationship between desiccation rate and seed mass. We conclude that different modes of water loss and seed structural features may be more important than seed mass in prolonging desiccation.