Grazing by manatees excludes both new and established wild celery transplants: Implications for restoration in Kings Bay, FL, USA

We conducted a field experiment between August 2001 and February 2002 in Kings Bay, FL, USA, designed to determine whether the amount of time allowed for wild celery (Vallisneria americana Michx) transplants to establish altered the effect of herbivorous manatees (Trichechus manatus L.)on their survival

Light dependence of Zostera marina annual growth dynamics in estuaries subject to different degrees of eutrophication

Author Posting. © The Authors, 2005. This is the author's version of the work. It is posted here by permission of Elsevier B. V. for personal use, not for redistribution. The definitive version was published in Aquatic Botany 84 (2006): 17-25, doi:10.1016/j.aquabot.2005.05.014.In temperate, shallow systems with clear waters the temporal dynamic of eelgrass (Zostera marina) growth is closely associated with the seasonality of irradiance at the water's surface. It has been recently suggested that increasing eutrophication, via light attenuation by increased algal growth, may disrupt the close temporal association between eelgrass growth and surface irradiance often found in pristine sites. Here, we test this hypothesis by examining the coupling between eelgrass growth dynamics and surface irradiance over an annual cycle in four shallow estuaries of the Waquoit Bay system (Massachusetts, USA) that have similar physical characteristics, but are subject to different land-derived nitrogen loading rates and the intensity of eutrophication sustained. Contrary to our hypothesis, the results show that, in general, most measures of eelgrass demographics were positively correlated with surface irradiance in all four estuaries. Out of the 45 regression models adjusted between irradiance and demographic variables (density, plastochrone intervals, and above- or below-ground biomass, growth, and production, on both a per shoot and areal basis), only 9 of them were non-significant, and only 6 of those corresponded to the eutrophic estuaries. Most notably, we found a lack of correlation between shoot density and irradiance in the eutrophic estuaries, in contrast to the strong coupling exhibited in estuaries receiving the lowest nitrogen loads. Experimental evidence from previous work has demonstrated severe light limitation and other deleterious impacts imposed by macroalgal canopies on newly recruiting shoots in the eutrophic estuaries, likely contributing to the lack of correlation between shoot density and irradiance at the water's surface. Because the range in eutrophication encompassed by this comparison includes the range of conditions at which eelgrass can survive, the relatively consistent temporal coupling between surface irradiance and most eelgrass demographic variables found here may also be a feature of other shallow temperate systems undergoing increasing eutrophication, and indicates a measure of plant recruitment (density) to be one of the first parameters to become uncoupled from light reaching the water's surface.This research was supported by an Environmental Protection Agency STAR Fellowship for Graduate Environmental Study (U-915335-01-0) and a National Estuarine Research Reserve Graduate Research Fellowship from the National Oceanic and Atmospheric Administration (award number NA77OR0228) awarded to JH. We thank the Quebec-Labrador Foundation Atlantic Center for the Environment’s Sounds Conservancy Program and the Boston University Ablon/Bay committee for research funds

Macrophyte abundance in Waquoit Bay : effects of land-derived nitrogen loads on seasonal and multi-year biomass patterns

Author Posting. © The Author(s), 2008. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Estuaries and Coasts 31 (2008): 532-541, doi:10.1007/s12237-008-9039-6.Anthropogenic inputs of nutrients to coastal waters have rapidly restructured coastal ecosystems. To examine the response of macrophyte communities to land-derived nitrogen loading, we measured macrophyte biomass monthly for six years in three estuaries subject to different nitrogen loads owing to different land uses on the watersheds. The set of estuaries sampled had nitrogen loads over the broad range of 12 to 601 kg N ha-1 y-1. Macrophyte biomass increased as nitrogen loads increased, but the response of individual taxa varied. Specifically, biomass of Cladophora vagabunda and Gracilaria tikvahiae increased significantly as nitrogen loads increased. The biomass of other macroalgal taxa tended to decrease with increasing load, and the relative proportion of these taxa to total macrophyte biomass also decreased. The seagrass, Zostera marina, disappeared from the higher loaded estuaries, but remained abundant in the estuary with the lowest load. Seasonal changes in macroalgal standing stock were also affected by nitrogen load, with larger fluctuations in biomass across the year and higher minimum biomass of macroalgae in the higher loaded estuaries. There were no significant changes in macrophyte biomass over the six years of this study, but there was a slight trend of increasing macroalgal biomass in the latter years. Macroalgal biomass was not related to irradiance or temperature, but Z. marina biomass was highest during the summer months when light and temperatures peak. Irradiance might, however, be a secondary limiting factor controlling macroalgal biomass in the higher loaded estuaries by restricting the depth of the macroalgal canopy. The relationship between the bloom-forming macroalgal species, C. vagabunda and G. tikvahiae, and nitrogen loads suggested a strong connection between development on watersheds and macroalgal blooms and loss of seagrasses. The influence of watershed land uses largely overwhelmed seasonal and inter-annual differences in standing stock of macrophytes in these temperate estuaries.This research was supported by the National Oceanic and Atmospheric Administration (NOAA), Cooperative Institute for Coastal and Estuarine Environmental Technologies (CICEET-UNH#99-304, NOAA NA87OR512), NOAA National Estuarine Research Reserve Graduate Research Fellowship NERRS GRF, #NA77OR0228), and an Environmental Protection Agency (EPA) STAR Fellowship for Graduate Environmental Study (U-915335-01-0) awarded to J. Hauxwell. S. Fox was supported by a NOAA NERRS GRF (#NA03NOS4200132) and an EPA STAR Graduate Research Fellowship. We also thank the Quebec-Labrador Foundation Atlantic Center for the Environment's Sounds Conservancy Program and the Boston University Ablon/Bay Committee for their awarding research funds

Earthworm preference: analzying the effects of soil moisture, pH, and calcium levels on the distribution of Lumbricus rubellus.

Studies have shown that the earthworm, Lumbricus rubellus, is often less abundant in soils with lower pH. However, it is not known if earthworms physiologically cannot tolerate low pH or if low pH soils lack nutrients (e.g., calcium) that are necessary for earthworm survival. To determine the effects of pH, moisture, and calcium levels on earthworm distribution, soil samples were taken at four separate sites, and the pH, moisture, and calcium levels of each were recorded. Experiments were run by manipulating the pH, moisture, and calcium levels of these soils and adding worms from each of the sites to test soil preference of worms. The worms preferred soil with relatively high moisture, calcium, and pH levels. The preference by the worms depends upon the original pH, calcium, and moisture levels of the soil from which the worm was taken. Since acid rain affects soil pH and, therefore, calcium levels due to increased nutrient leaching, we conclude that an increase in acid rain could affect earthworm habitat. However, further studies are needed to assess the magnitude to which earthworm habitat would be affected.http://deepblue.lib.umich.edu/bitstream/2027.42/54362/1/2798.pdfDescription of 2798.pdf : Access restricted to on-site users at the U-M Biological Station

Commonly Rare and Rarely Common: Comparing Population Abundance of Invasive and Native Aquatic Species

<div><p>Invasive species are leading drivers of environmental change. Their impacts are often linked to their population size, but surprisingly little is known about how frequently they achieve high abundances. A nearly universal pattern in ecology is that species are rare in most locations and abundant in a few, generating right-skewed abundance distributions. Here, we use abundance data from over 24,000 populations of 17 invasive and 104 native aquatic species to test whether invasive species differ from native counterparts in statistical patterns of abundance across multiple sites. Invasive species on average reached significantly higher densities than native species and exhibited significantly higher variance. However, invasive and native species did not differ in terms of coefficient of variation, skewness, or kurtosis. Abundance distributions of all species were highly right skewed (skewness>0), meaning both invasive and native species occurred at low densities in most locations where they were present. The average abundance of invasive and native species was 6% and 2%, respectively, of the maximum abundance observed within a taxonomic group. The biological significance of the differences between invasive and native species depends on species-specific relationships between abundance and impact. Recognition of cross-site heterogeneity in population densities brings a new dimension to invasive species management, and may help to refine optimal prevention, containment, control, and eradication strategies.</p></div

Abundance distributions for each species used in this analysis.

<p>Labels are coded as follows: taxonomic group abbreviation. Origin. Species ID, where taxonomic group codes are Cr = Crayfish, FHI = Hawaiian fishes, FNA = North American fishes, FSw = Swedish fishes, M = Mussel, Pl = Plant, Pr = Prawn, and S = Snail; origin codes are I = Invasive and N = Native; see Table S3 in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0077415#pone.0077415.s001" target="_blank">File S1</a> for species identities. Colors correspond to taxonomic groups and in every group the darker shade corresponds to invasive species in that group. The x-axis scale shows standardized abundance (proportion of taxonomic group-level maximum abundance) and ranges from 0 to 1; the y-axis scale shows the number of sites falling into each abundance class and varies by species to accommodate different numbers of observations (sites). Note that all abundance values are greater than zero.</p