Patrick D. Biber

Seasonal Dynamics of Macroalgal Communities of the Northern Florida Reef Tract

Abstract Coral communities worldwide are undergoing intense degradation in response to natural and human disturbances, and many reef systems have already experienced significant declines in live coral cover associated with an increase in macroalgal abundance. Here, we document the seasonal dynamics of the macroalgal communities of the Northern Florida Reef Tract, providing a baseline for long-term studies of coral-algal competition in the area. Both macroalgal biomass and percent cover on reefs showed an increasing trend from January to July, when both light and temperature conditions were favorable for growth. Maximum percent cover (56.7 %) was found in July and minimum levels in December (25.8 %). During these peaks in algal cover, many corals were completely covered by dense mats of algae. Two genera, Halimeda and Dictyota, represented the largest proportion (77–99 %) of the total algal biomass. In the summer, Dictyota spp. dominated the algal community, occupying up to 40% of the reef bottom with a dry biomass of up to 20 g.m−2. In addition, two species, Stypopodium zonale and Trichogloea requienii, showed a significant bloom in April 1998, covering a significant percentage of the bottom (up to 25 %) at an inshore reef. Species that exhibited rapid space monopolization on Florida reefs, such as Dictyota spp. and Stypopodium zonale, also showed rapid growth in microcosm and field growth studies. No correlations were found between fish grazer abundance and algal biomass or percent cover, indicating that present grazer population abundance and composition are not adequate to prevent space monopolization and coral overgrowth by algae such as Dictyota spp. and Halimeda spp. Only a continued monitoring effort will determine whether the seasonal dynamics of the algal community may result in the decline of coral populations in the Northern Florida Reef Tract.

The influence of freshwater runoff on biomass, morphometrics, and production of Thalassia testudinum

Efforts to restore more natural freshwater flows in South Florida will impact Biscayne Bay. In order to evaluate possible effects of decreased freshwater discharge on the seagrass Thalassia testudinum, we determined the biomass, density, morphometrics (width, length, number of blades per shoot) and production of T. testudinum twice a year for 2 year at sites exposed to varying degrees of freshwater runoff. Responses to freshwater discharge varied between the sampling years. The only morphometric variable to be influenced by freshwater runoff in both years was blade width with width of seagrass blades being less at sites influenced by freshwater runoff than at sites with limited influence of freshwater runoff. In 1996, no other parameters differed among the three freshwater conditions considered; canal discharge, sheet-flow runoff, and limited freshwater runoff. In addition, all measured parameters were greater in summer (wet season) than in winter (dry season) in 1996. In 1997, biomass, shoot weight, shoot production, and areal shoot production all were greater at sites on the eastern side of the bay that experience limited influence from freshwater runoff compared to sites on the western side of the bay that experience large amounts of freshwater runoff from sheet-flow and canal discharge. In 1997, only length of seagrass showed a significant increase from winter to summer. Factors thought to be responsible for these interannual differences are winter temperatures and seasonal rainfall amounts. The winter of 1996 was much colder than the winter of 1997, and 1997 experienced an unusually rainy dry season thus increasing the amount of time during the year that freshwater runoff would be influencing sites on the western side of the bay. Based on these results, reduced freshwater inflow to Biscayne Bay should have a positive effect on T. testudinum provided detrimental hypersaline conditions do not occur.

Modeling photosynthesis of Spartina alterniflora (smooth cordgrass) impacted by the Deepwater Horizon oil spill using Bayesian inference

To study the impact of the Deepwater Horizon oil spill on photosynthesis of coastal salt marsh plants in Mississippi, we developed a hierarchical Bayesian (HB) model based on field measurements collected from July 2010 to November 2011. We sampled three locations in Davis Bayou, Mississippi (30.375 N, 88.790 W) representative of a range of oil spill impacts. Measured photosynthesis was negative (respiration only) at the heavily oiled location in July 2010 only, and rates started to increase by August 2010. Photosynthesis at the medium oiling location was lower than at the control location in July 2010 and it continued to decrease in September 2010. During winter 2010‐2011, the contrast between the control and the two impacted locations was not as obvious as in the growing season of 2010. Photosynthesis increased through spring 2011 at the three locations and decreased starting with October at the control location and a month earlier (September) at the impacted locations. Using the field data, we developed an HB model. The model simulations agreed well with the measured photosynthesis, capturing most of the variability of the measured data. On the basis of the posteriors of the parameters, we found that air temperature and photosynthetic active radiation positively influenced photosynthesis whereas the leaf stress level negatively affected photosynthesis. The photosynthesis rates at the heavily impacted location had recovered to the status of the control location about 140 days after the initial impact, while the impact at the medium impact location was never severe enough to make photosynthesis significantly lower than that at the control location over the study period. The uncertainty in modeling photosynthesis rates mainly came from the individual and micro-site scales, and to a lesser extent from the leaf scale.

Historical changes in seagrass coverage on the Mississippi barrier islands, northern Gulf of Mexico, determined from vertical aerial imagery (1940–2007)

Vertical aerial image data were used with an edge-detection procedure and visual image interpretation to determine yearly to decadal changes in seagrass (predominantly Halodule wrightii Ascherson) coverage on the Mississippi barrier islands. On Horn Island, seagrass coverage declined from 77 ha in 1940 to 19 ha in 1971, but returned to its 1940 value by 2006. Coverage on Petit Bois declined from 54 ha in 1940 to 8–19 ha from 1952 through 2007. On East Ship, seagrass coverage varied at 2–19 ha from 1963 to 2007. On West Ship, coverage dropped to zero in 2003, but by 2007 it had increased to approximate its 1975 value of 1.8 ha. On Cat Island, coverage increased from 22 ha in 2003 to 71 ha in 2007. There was no apparent negative impact of Hurricane Camille or Hurricane Katrina on seagrass coverage, which could vary annually by a factor of two or more.

Litter Decomposition of Spartina alterniflora and Juncus roemerianus: Implications of Climate Change in Salt Marshes

ABSTRACT Wu, W.; Huang, H.; Biber, P., and Bethel, M., 2017. Litter decomposition of Spartina alterniflora and Juncus roemerianus: Implications of climate change in salt marshes. Decomposition of plant litter in salt marshes plays an important role in coastal trophodynamics, nutrient cycling, sediment trapping, and short-term carbon storage, all of which are likely to be affected by climate change and accelerated sea-level rise. Warmer temperatures, altered precipitation patterns, longer and more frequent inundation, and saltwater intrusion will all interact to affect decomposition of plant litter in a complex way. A combination of field experiments and model selection techniques was applied to study how these environmental factors affected litter decomposition of two dominant salt marsh species, Spartina alterniflora and Juncus roemerianus, along the northern Gulf of Mexico. The results from summer field experiments conducted between June and August of 2013 showed that S. alterniflora in the low marsh had higher litter losses (0.286 ± 0.0883 g d−1, mean ± standard deviation) and decomposition coefficients (0.0115 ± 0.00416 d−1) than J. roemerianus in the midmarsh locations (0.0963 ± 0.0480 g d−1, 0.00416 ± 0.00223 d−1). Modeling results showed that the interaction between temperature and salinity significantly affected decomposition coefficients of both species positively during this experiment. This study suggests that accelerated leaf litter decomposition due to rising temperature and increased salinity will occur under climate change and sea-level rise, and this will potentially lead to important ecological consequences for salt marshes.

Thresholds of Sea-Level Rise Rate and Sea-Level Rise Acceleration Rate In a Vulnerable Coastal Wetland

Abstract Feedbacks among inundation, sediment trapping, and vegetation productivity help maintain coastal wetlands facing sea‐level rise (SLR). However, when the SLR rate exceeds a threshold, coastal wetlands can collapse. Understanding the threshold helps address key challenges in ecology—nonlinear response of ecosystems to environmental change, promotes communication between ecologists and resource managers, and facilitates decision‐making in climate change policies. We studied the threshold of SLR rate and developed a new threshold of SLR acceleration rate on sustainability of coastal wetlands as SLR is likely to accelerate due to enhanced anthropogenic forces. Deriving these two thresholds depends on the temporal scale, the interaction of SLR with other environmental factors, and landscape metrics, which have not been fully accounted for before this study. We chose a representative marine‐dominated estuary in the northern Gulf of Mexico, Grand Bay in Mississippi, to test the concept of SLR thresholds. We developed a mechanistic model to simulate wetland change and then derived the SLR thresholds for Grand Bay. The model results show that the threshold of SLR rate in Grand Bay is 11.9 mm/year for 2050, and it drops to 8.4 mm/year for 2100 using total wetland area as a landscape metric. The corresponding SLR acceleration rate thresholds are 3.02 × 10−4 m/year2 and 9.62 × 10−5 m/year2 for 2050 and 2100, respectively. The newly developed SLR acceleration rate threshold can help quantify the temporal lag before the rapid decline in wetland area becomes evident after the SLR rate threshold is exceeded, and cumulative SLR a wetland can adapt to under the SLR acceleration scenarios. Based on the thresholds, SLR that will adversely impact the coastal wetlands in Grand Bay by 2100 will fall within the likely range of SLR under a high warming scenario (RCP8.5), highlighting the need to avoid RCP8.5 to preserve these marshes.

Habitat Characterization for Submerged and Floating-Leaved Aquatic Vegetation in Coastal River Deltas of Mississippi and Alabama

Habitat attributes of submerged aquatic vegetation and floating-leaved aquatic vegetation were analyzed from survey data collected in estuaries and coastal river systems of Mississippi and Mobile Bay, Alabama. The objectives were to: locate aquatic plant beds along tidally influenced areas and characterize landscape parameters of the sites; group the plant species into a manageable number of logical clusters; and characterize the landscape attributes indicative of the plant communities through Classification and Regression Tree (CART) analysis. Based on the cluster analyses, aquatic vegetation was categorized into three groups: (1) downstream estuarine/saline group, (2) brackish tolerant freshwater species group, and (3) upstream freshwater only group. Landscape features used for habitat characterization and plant classification were defined by long-term environmental conditions which would shape plant communities, rather than water quality parameters, such as water transparency and salinity, that exhibit higher variability and reflect the discrete conditions at time of sampling. The CART results suggest that salinity and “energy” (relative exposure to waves/currents) are the two most important abiotic factors that structure plant communities in the river deltas studied. Atributos del hábitat de vegetación acuática sumergida y vegetación acuática con hojas flotantes fueron analizados a partir de los datos de encuestas recogidas en los estuarios y sistemas fluviales costeras de Mississippi y la bahía de Mobile, Alabama. Los objetivos fueron: localizar camas de plantas acuáticas a lo largo de las zonas influidas por las mareas y caracterizar los parámetros del paisaje de los sitios; Agrupar las especies de plantas en un número manejable de agrupaciones lógicos; y caracterizar los atributos paisajísticos indicativos de las comunidades de plantas a través del análisis de árboles de clasificación y regresión (CART). Con base en los análisis de agrupaciones, la vegetación acuática se clasificó en tres grupos: (1) Grupo de aguas abajo del estuario / solución salina, (2) Grupo de especies de agua dulce tolerantes salobres, y (3) grupo de aguas arriba solamente agua dulce. Las características del paisaje utilizadas para la caracterización del hábitat y la clasificación de plantas fueron definidas por las condiciones ambientales a largo plazo, que darían forma a las comunidades de plantas, en lugar de parámetros de calidad del agua, tales como la transparencia del agua y la salinidad, que presentan una mayor variabilidad y reflejan las condiciones discretas en el momento del muestreo. Los resultados del CART análisis sugieren que la salinidad y “energía” (exposición relativa a las ondas/corrientes) son los dos factores abióticos más importantes que estructuran comunidades vegetales en los deltas de los ríos estudiados.

Autotrophic net productivity patterns at four artificial reef sites in the Mississippi Sound

Nearshore artificial reefs are common coastal features, for instance the Mississippi Sound has 67 inshore artificial reefs, the goal of which is to increase fisheries production. The success of artificial reefs depends in part on the primary production potential available to support the reef-based food web. In this study, we used settlement plates to estimate periphyton community net productivity, chlorophyll-a (chl-a), and biomass at sites adjacent to four artificial reefs in the Mississippi Sound in order to evaluate the potential of these artificial reefs to enhance local primary production. Water column primary productivity, chl-a, and biomass were also measured to assess the contribution of phytoplankton to total net primary production at these four sites. The largely negative net productivity measurements obtained for the periphyton community suggest that artificial structures deployed in the Mississippi Sound are potentially net heterotrophic and that the autotrophic component of the periphyton is not likely to be a major source of primary production to the reef food web for much of the year except in winter. The higher water column productivity measurements suggest that phytoplankton is a more important source of primary production to the reef food web than the benthic periphyton community especially during the summer.

Testa imposed dormancy in Vallisneria americana seeds from the Mississippi Gulf Coast1

Abstract In response to hurricane and oil-spill environmental impacts along the northern Gulf of Mexico, coastal and marine habitat restoration has become a priority. In particular, restoration of submerged aquatic plants is vital for ecosystem health. To facilitate restoration, developing propagation protocols for Gulf coast plants is necessary, but challenging due to the lack of information on many species. Previous seed germination research of Vallisneria americana, a submerged aquatic species with declining abundance in coastal habitats, from northern latitudinal populations reported germination percentages between 80–90%. Germination experiments using Mississippi Gulf coast plants revealed unexpected outcomes. Less than 8% germination occurred when seeds were germinated in a 16 hr photoperiod or 24 hr dark period at 10, 20, 30 or 40 °C. To enhance germination, cold stratification and gibberellic acid soak treatments were conducted, but germination was below 10%. A subsequent seed scarification experiment was conducted that resulted in 90% germination when incubated at 30 °C. In addition, an imbibition experiment revealed that both scarified and non-scarified seeds imbibed water. Due to this imbibition, V. americana seeds used in this study were considered to be physiologically dormant. Refining existing seed-based propagation protocols is recommended to ensure the success of revegetation in restoration projects.

Seed propagation protocol for wigeongrass (Ruppia maritima) (Mississippi).

potassium concentration in the outside medium increases, potassium absorption rate into root cells increases proportionately, but only to a certain point owing to saturation kinetics caused by the limited number of K+ binding sites for potassium carrier enzymes on the plant cell plasma membrane. Another unlikely possibility is an allelopathic response of brome to wheat straw. Recommendations for growing brome as a forage crop include using wheat as a cover crop during seeding, precluding a negative reaction to wheat straw. Moreover, demonstrated allelopathic relationships tend to be between forbs and grasses (e.g., Hicks et al. 1989) rather than between different grasses. Our results indicate a negative relationship between wheat straw application and early growth of brome. This may be due to potassium leached from straw or ammonium produced during initial decomposition, or possibly some other factor generated by wheat straw. Applying wheat straw to new grassland disturbances may provide some protection against brome invasion; however, more research is required to determine the mechanisms involved, the amount of straw needed, and whether the effect continues beyond the first year. Research into the tolerance limits to potassium and ammonium would be useful, as they could be applied directly as a controlling amendment if found effective. Brome has moved from farmland and roadsides into native grasslands in many parts of North America. Study into the effects of wheat straw, potassium, and ammonium on existing smooth brome stands and in new native prairie restoration sites could determine if these could aid in removing or controlling brome.