Hamamelis Research Articles

Unravelling winter diatom blooms in temperate lakes using high frequency data and ecological modeling

In temperate lakes, it is generally assumed that light rather than temperature constrains phytoplankton growth in winter. Rapid winter warming and increasing observations of winter blooms warrant more investigation of these controls. We investigated the mechanisms regulating a massive winter diatom bloom in a temperate lake. High frequency data and process-based lake modeling demonstrated that phytoplankton growth in winter was dually controlled by light and temperature, rather than by light alone. Water temperature played a further indirect role in initiating the bloom through ice-thaw, which increased light exposure. The bloom was ultimately terminated by silicon limitation and sedimentation. These mechanisms differ from those typically responsible for spring diatom blooms and contributed to the high peak biomass. Our findings show that phytoplankton growth in winter is more sensitive to temperature, and consequently to climate change, than previously assumed. This has implications for nutrient cycling and seasonal succession of lake phytoplankton communities. The present study exemplifies the strength in integrating data analysis with different temporal resolutions and lake modeling. The new lake ecological model serves as an effective tool in analyzing and predicting winter phytoplankton dynamics for temperate lakes.

Enhanced Winter Carbon Export Observed by BGC‐Argo in the Northwest Pacific Ocean

Key Points Synoptic‐scale winter blooms and mixed‐layer pump events were observed by a BGC‐Argo float in the midlatitude Northwest Pacific Ocean The repetitive mixed‐layer pump episodes generated a very high particulate organic carbon export of ~110 mg C m−2 day−1 in wintertime The current BGC‐Argo protocols captured only 20%, or entirely missed, substantial pulsed carbon export driven by mixed‐layer pump events

Seasonal and Inter-Annual Variability of the Phytoplankton Dynamics in the Black Sea Inner Basin

We explore the patterns of Black Sea phytoplankton growth as driven by the thermohaline structure and circulation system and the freshwater nutrient loads. Seasonal and inter-annual variability of the phytoplankton blooms is examined using hydrodynamic simulations that resolve mesoscale eddies and online coupled bio-geochemical model. This study suggests that the bloom seasonality is homogeneous across geographic locations of the Black Sea inner basin, with the strongest bloom occurring in winter (February–March), followed by weaker bloom in spring (April–May), summer deep biomass maximum (DBM) (June–September) and a final bloom in autumn (October–November). The winter phytoplankton bloom relies on vertical mixing of nitrate from the intermediate layers, where nitrate is abundant. The winter bloom is highly dependent on the strength of the cold intermediate layers (CIL), while spring/summer blooms take advantage of the CIL weakness. The maximum phytoplankton transport across the North Western Shelf (NWS) break occurs in September, prior to the basin interior autumn bloom. Bloom initiation in early autumn is associated with the spreading of NWS waters, which in turn is caused by an increase in mesoscale eddy activity in late summer months. In summary, the intrusion of low salinity and nitrate-rich water into the basin interior triggers erosion of the thermocline, resulting in vertical nitrate uplifting. The seasonal phytoplankton succession is strongly influenced by the recent CIL disintegration and amplification of the Black Sea circulation, which may alter the natural Black Sea nitrate dynamics, with subsequent effects on phytoplankton and in turn on all marine life.

Winter coccolithophore blooms in the Black Sea: Interannual variability and driving factors

The spatial and temporal variability of winter coccolithophore blooms in the Black Sea is studied using satellite measurements for 2003–2017 and Bio-Argo buoys data. Analysis shows that such blooms can occupy the entire upper 60-m layer with satellite-derived estimates of surface cell concentration reaching in some years 3.0·106 cells l−1. On average, winter coccolithophore blooms start in November–December, peak in the first decade of January, and terminate in February. They are characterized by significant interannual variability. Blooms in different years can be “basin-wide” covering most of the sea (2004–2005, 2005–2006, 2006–2007, 2012–2013) and “local” when they are observed only in certain areas of the Black Sea, most often in its southern part. A detailed analysis of the evolution of winter blooms has shown that they are usually triggered by intense storms, which are followed after 1–2 weeks by the initial growth of coccolithophores in the zone of storm-driven upwelling. Cross-shelf nutrients exchange may contribute to the coccolithophore growth over the continental slope. Intense winter coccolithophore blooms are observed in years with low autumn concentrations of chlorophyll-a, i.e., during periods of weakening of the typical diatom blooming autumn-winter. The strongest correlation on annual time scales is found between bloom intensity and decrease of the autumn-winter wind curl. We suggest that low wind curl causes a weakening of the basin-scale cyclonic circulation and intensifies the cross-shelf exchange, impacting the Black Sea trophic structure in the preceding summer period and may promote the winter bloom of coccolithophores in such years.

Particulate trace metal fluxes in the center of an oceanic desert: Northeast Atlantic subtropical gyre

For this study particle flux material collected over 13 years period starting in February 2002 until summer 2015 with the long-term mooring Kiel 276 (33°N, 22°W) in the subtropical Northeast Atlantic was analyzed. Our focus was set on the elemental composition and trace element fluxes which we analyzed with the help of ICP-OES and ICP-MS. The particle flux has a mean of 60 mg m −2 d −1 (range: 1–365 mg m −2 d −1 ) with peak fluxes during February and April shortly after the winter bloom. Especially in 2004 high fluxes occurred through the year when the Azores Front was located south of the mooring. In this year enhanced nutrient supply and high dust concentration in the atmosphere were measured. The analyzed trace elements of Cd, Co, Cr, Cu, Ni, V, Zn, Zr, and Mn have mean fluxes of 43.4 μg Cd m −2 d −1 , 205.7 μg Co m −2 d −1 , 1.4 μg Cr m −2 d −1 , 3.2 μg Cu m −2 d −1 , 1.6 μg Ni m −2 d −1 , 1.0 μg V m −2 d −1 , 5.1 μg Zn m −2 d −1 , 1.3 μg Zr m −2 d −1 , and 7.8 μg Mn m −2 d −1 . Biogenic trace elements (Cd, Zn, Ni) show maximum fluxes in winter and spring while no seasonality was present for refractory (Zr) and redox-sensitive elements (V, Mn, Co). Fe, Ti, Co, Mn, V, Mn, and Zr are only little enriched towards the upper continental crust (EF < 2) as these elements originate from a lithogenic source and are little prone to dissolution or scavenging while Cd, Cu, Cr, Ni, and Zn are more enriched with EF of 3.0, 9.6, 2.4, 6.2, and 5.0, respectively. • 13 years long particle flux time series from the subtropical NE Atlantic • Atmospheric pathways and Azores Front modulate particle and trace elemental fluxes. • Deep ocean particulate trace elemental fluxes depend on the biogenic matter cycle.

The phytoplankton variability in the Pearl River estuary based on VIIRS imagery

A support vector machine (SVM) regression algorithm was developed for estimating the chlorophyll-a concentration (Cchla) in the turbid estuarine waters of the Pearl River estuary (PRE) based on visible infrared imaging radiometer suite (VIIRS) ocean color data. The proposed SVM algorithm outperformed the OC3 algorithm in the turbid waters. The temporal variation and spatial distribution of SVM-based monthly Cchla products were determined during 2012 and 2018. By analyzing the monthly average Cchla products and ancillary data, the underlying mechanisms of the Cchla coastal summer plume jet and winter bloom were revealed. The Cchla coastal plume jet was often observed in June, when the zonal wind direction changed from westward to eastward and the river runoff reached its maximum value of the year. The winter bloom in the ocean area was attributed to strong mixing in the upper layer, which resulted from cooling-induced buoyancy changes.

Distinct oxygen environments shape picoeukaryote assemblages thriving oxygen minimum zone waters off central Chile

AbstractOxygen minimum zones (OMZs) support ocean biogeochemical cycles of global importance. The OMZ off central Chile is characterized by seasonally variable oxygen concentrations due to upwelling events. Bacterial and archaeal communities from this area have been previously described; however, picoeukaryote communities remain largely unexplored. In order to improve our knowledge on picoeukaryote ecology and the effect of controlling factors on its community structure, environmental parameters and 18S rRNA metabarcoding analyses were performed in water samples collected at several depths at a time series station on the continental shelf in March, May and August. Our results showed that oxygen, nitrate, silicate and temperature are relevant factors shaping the picoeukaryote community structure. Overall, according to our sequence dataset, the OMZ was dominated by Dinophyceae members including marine parasitic dinoflagellates. Moreover, dysoxic and suboxic conditions were enriched by fungi and phagotrophic protists from Ustilaginomycetes, Bicoecea and Choanoflagellatea. The latter is particularly relevant in the understanding of metazoan evolution and the origins of multicellularity in low-oxygen environments. Picoeukaryote communities changed significantly over the 3 months sampled with variations in water column stratification, including the occurrence of a winter bloom of Mamiellales. Altogether, this study reveals a great diversity and dynamics of picoeukaryotes inhabiting a coastal OMZ.

Plankton Community Changes From Warm to Cold Winters in the Oligotrophic Subtropical Ocean

Subtropical gyres are large areas of the ocean characterized by high stratification, low nutrients, and low primary production. The Canary Current System (CanCS) shows a rather strong seasonal thermocline during most of the annual cycle, which erodes from January to March promoting the so-called Late Winter Bloom (LWB). Atmospheric deposition from the Sahara desert is also another key feature of the CanCS providing additional nutrients to the euphotic zone. As a consequence of global warming, these oligotrophic regimes systems are expanding and the temperature increase affects phytoplankton, and reverberate on the food web structure and biogeochemical cycles. In this sense, the effect of warming and dust deposition on the planktonic community remains poorly know in the CanCS. Here, we show the effects of a 0.5ºC increase in ocean temperature during two consecutive years. During 2011, winter temperature allowed the development of the LWB, promoting the increase of autotrophic cells and the coexistence of the microbial loop and the “classic” trophic web. The former predominated before and after the LWB, while the latter prevailed during the LWB. The high temperature during 2010 prevented the LWB development, causing highly oligotrophic conditions and Saharan dust being the only nutrient input into the environment. During this warm year, we found a dominance of small cells such as nanoflagellates and dinoflagellates, and surprisingly high biomass of mesozooplankton, hinting at the “tunneling effect” as an alternative trophic pathway. These changes show the impact of a slight increase in temperature in this oligotrophic system and how future scenarios in the context of global warming could promote considerable shifts in the trophic web structure.

Evaluating the impacts of white-tailed deer (Odocoileus virginianus) browsing on vegetation in fenced and unfenced timber harvests

Ensuring the recruitment of desired tree species is a primary goal when considering successful regeneration of timber harvests. Deer populations that are overabundant relative to forage availability within their local landscapes pose a considerable challenge to successful forest regeneration. We evaluated the short-term (<10 years) impact of white-tailed deer browsing on woody structure and composition in northcentral Pennsylvania. Specifically, we compared woody plant species density, height, and cover within 10 pairs of fenced and unfenced regenerating timber harvests. Percent of browsed stems was higher in unfenced harvests for red maple (Acer rubrum), oaks (Quercus spp.), Rubus spp., sassafras (Sassafras albidum), and witch hazel (Hamamelis virginiana). Stem density did not differ between fenced and unfenced harvests for any species except Rubus spp., which was greater in the former. However, height of serviceberry (Amalanchier spp.), sassafras, northern red oak (Quercus rubra), Rubus spp., and red maple was taller in fenced harvests. Both vertical and horizontal vegetation density were greater in fenced harvests, suggesting a more structurally complex understory in fenced harvests. Rubus spp. and tall (>1.5 m) sapling cover were greater in fenced harvests, while unfenced harvests had greater forb, fern, and blueberry/huckleberry (Vaccinium spp./Gaylussacia spp.) cover. Our results suggest that browsing by deer in the years initially (<10 years) following timber harvest may not immediately impact woody species density, but can considerably reduce seedling height, overall horizontal and vertical structure, and composition of vegetation strata. Reduced sapling height and greater prevalence of blueberry/huckleberry, forbs, and ferns in unfenced harvests threaten the successful recruitment of desired species into the future overstory. Our results from large, operational-scale timber harvests combined with those from previous small-scale studies stress the potential value of deer exclusion fencing to achieve successful forest regeneration. Future research should examine the timing of fence removal to achieve forest regeneration success, while also providing deer access to available foraging opportunities during the later portion of stand initiation.

WhISOBAXTM Inhibits Bacterial Pathogenesis and Enhances the Effect of Antibiotics.

As bacteria are becoming more resistant to commonly used antibiotics, alternative therapies are being sought. whISOBAX (WH) is a witch hazel extract that is highly stable (tested up to 2 months in 37 °C) and contains a high phenolic content, where 75% of it is hamamelitannin and traces of gallic acid. Phenolic compounds like gallic acid are known to inhibit bacterial growth, while hamamelitannin is known to inhibit staphylococcal pathogenesis (biofilm formation and toxin production). WH was tested in vitro for its antibacterial activity against clinically relevant Gram-positive and Gram-negative bacteria, and its synergy with antibiotics determined using checkerboard assays followed by isobologram analysis. WH was also tested for its ability to suppress staphylococcal pathogenesis, which is the cause of a myriad of resistant infections. Here we show that WH inhibits the growth of all bacteria tested, with variable efficacy levels. The most WH-sensitive bacteria tested were Staphylococcus epidermidis, Staphylococcus aureus, Enterococcus faecium and Enterococcus faecalis, followed by Acinetobacter baumannii, Klebsiella pneumoniae, Escherichia coli, Pseudomonas aeruginosa, Streptococcus agalactiae and Streptococcus pneumoniae. Furthermore, WH was shown on S. aureus to be synergistic to linezolid and chloramphenicol and cumulative to vancomycin and amikacin. The effect of WH was tested on staphylococcal pathogenesis and shown here to inhibit biofilm formation (tested on S. epidermidis) and toxin production (tested on S. aureus Enterotoxin A (SEA)). Toxin inhibition was also evident in the presence of subinhibitory concentrations of ciprofloxacin that induces pathogenesis. Put together, our study indicates that WH is very effective in inhibiting the growth of multiple types of bacteria, is synergistic to antibiotics, and is also effective against staphylococcal pathogenesis, often the cause of persistent infections. Our study thus suggests the benefits of using WH to combat various types of bacterial infections, especially those that involve resistant persistent bacterial pathogens.

Evidence of Eddy‐Enhanced Winter Chlorophyll‐a Blooms in Northern Arabian Sea: 2017 Cruise Expedition

AbstractThe temperature, salinity, and chlorophyll‐a (Chl‐a) profiles of the upper ocean (0–200 m) were measured during the China‐Pakistan Joint Expedition, 2017. The cruise track passed through an identified cyclonic eddy, and the multi‐disciplinary records thus verify the eddy contributions to winter blooms in the northern Arabian Sea (AS). The records show that the strength of upper blooms within the mixed layer is mainly dominated by surface phytoplankton biomass (the Chl‐a concentration), which increases simultaneously with the shallow mixed layer and uplifted thermocline. A composite analysis of eddy‐tracked sea level anomalies (SLA) and Chl‐a reveals the pumping and stirring effects that cyclonic eddies make to the ocean surface nutrient supply. Based on the high‐resolution Ocean General Circulation Model for the Earth Simulator (OFES) outputs, a mixed layer nitrogen budget calculation was subsequently conducted to quantify the contributions of mesoscale eddies to 10‐year climatological winter blooms. The results indicate that eddy flows are primary contributors to the increased nutrients in the coastal north AS during the mature period (usually in January and February) of the winter blooms, with a concentration histogram double that of convective mixing. The concentration decreases from the north to south, agreeing well with the seasonal northward nutrition gradient. This confirms that (i) the growth of nutrients over the northern AS, which is known to be triggered by convective mixing, would be further maintained by eddy‐induced advection; and (ii) higher concentration of nutrients would facilitate an easier response of Chl‐a to eddy dynamics.

Traction and Hot Fomentations for Osteo-Arthritis.

Editor's note: From its first issue in 1900 through to the present day, AJN has unparalleled archives detailing nurses' work and lives over more than a century. These articles not only chronicle nursing's growth as a profession within the context of the events of the day, but they also reveal prevailing societal attitudes about women, health care, and human rights. Today's nursing school curricula rarely include nursing's history, but it's a history worth knowing. To this end, From the AJN Archives highlights articles selected to fit today's topics and times.In this month's article, from the May 1925 issue, nurse Ellen G. Dawson from Evanston Hospital in Illinois presents three case studies as evidence for a new use for immobilizing traction: the treatment of osteoarthritis. The protocol includes the use of traction for days or weeks, hot fomentations (poultices) applied to the skin over the painful joint, and a body cast (for back pain) or leg cast (for knee pain) worn for an extended period afterward. If the joint pain was severe, a lotion made from tinctures of opium and arnica, witch hazel, and lead water was also applied. The author notes, "We could cite case after case, with varying lengths of time, where the results have been equally gratifying."Today, nurses are involved in more formal arthritis research. In this issue, So-Hyun Park and Shiela M. Strauss examine the impact of arthritis on recommended physical activity in their original research article, "Arthritis-Related Functional Limitations and Inadequate Physical Activity Among Female Adult Cancer Survivors."

An anomalous bi-macroalgal bloom caused by Ulva and Sargassum seaweeds during spring to summer of 2017 in the western Yellow Sea, China

An unprecedented bi-macroalgal bloom caused by Ulva prolifera and Sargassum horneri occurred from spring to summer of 2017 in the western Yellow Sea (YS) of China, where annual large-scale green tides have prevailed for a decade. The distinct genesis and blooming dynamics of the two seaweed species were detected and described. Unlike the consistent raft-origin of the floating Ulva biomass, the massive pelagic S. horneri was derived from multiple sources (residual seaweeds from the previous winter bloom and those drifting from offshore water in the south). The scale of the green tide in 2017 was found smaller than the previous four years. We then discussed a number of hypotheses attributing to this reduction, including reduced epiphytic green algae from aquaculture rafts and the influences of the massive pelagic S. horneri. However, further research is needed to identify the origin of the pelagic S. horneri in the western YS and any affiliations with the benthic populations, and to elucidate the interactions of this species with the annual green tides and the ensuing consequences.

Witch Hazel Significantly Improves the Efficacy of Commercially Available Teat Dips

Bovine intramammary infections (IMIs) are the main cause of economic loss in milk production. Antibiotics are often ineffective in treating infections due to antimicrobial resistance and the formation of bacterial biofilms that enhance bacterial survival and persistence. Teat dips containing germicides are recommended to prevent new IMIs and improve udder health and milk quality. IMIs are often caused by staphylococci, which are Gram-positive bacteria that become pathogenic by forming biofilms and producing toxins. As a model for a teat dip (DIP), the BacStop iodine-based teat dip (DIP) was used. Witch hazel extract (whISOBAX (WH)) was tested because it contains a high concentration of the anti-biofilm/anti-toxin phenolic compound hamamelitannin. We found that the minimal inhibitory or bactericidal concentrations of DIP against planktonic S. epidermidis cells increased up to 160-fold in the presence of WH, and that DIP was 10-fold less effective against biofilm cells. While both DIP and WH are effective in inhibiting the growth of S. aureus, only WH inhibits toxin production (tested for enterotoxin-A). Importantly, WH also significantly enhances the antibacterial effect of DIP against Gram-negative bacteria that can cause IMIs, like Escherichia coli and Pseudomonas aeruginosa. Put together, these results suggest that the antibacterial activity of DIP combined with WH is significantly higher, and thus have potential in eradicating bacterial infections, both in acute (planktonic-associated) and in chronic (biofilm-associated) conditions.

Seasonal vertical stratification and the potential impacts of its fading on algal blooms in winter: Cases of Lake Chenghai and Lake Yangzonghai, Yunnan Plateau

基于2014年10月-2016年7月在云南程海和阳宗海开展了4个季度（秋季，10月；冬季，1月；春季，4月；夏季，7月）的调查，研究了两个湖泊的水体分层特征，探讨了热力分层及其变化与其他环境因子对浮游植物生物量的潜在影响，结果显示：程海和阳宗海水体分层的特征均为冬季混合、春季形成分层、夏秋季分层稳定，两湖均属暖单次混合型湖泊；程海分层期温跃层的平均深度（顶界）、厚度和强度分别为17.70±3.89 m、5.54±4.44 m和0.67±0.43℃/m，阳宗海的分别为12.53±3.35 m、8.25±4.85 m和0.53±0.43℃/m.在热力分层稳定期，两湖底层达到缺氧甚至厌氧状态，底层的电导率总体较表层高.调查期间，两个湖泊水柱表层浮游植物生物量（以叶绿素a浓度表征）均在冬季出现峰值，程海和阳宗海的分别为19.22±11.08和45.82±9.41 μg/L；进一步分析发现，热力分层的消退可能是导致水体表层无机营养盐升高（底层供给）的重要原因，加之适宜的光热条件可诱导两湖冬季水华的发生；在其他季节转化期间，浮游植物生物量变化的主要影响因子亦具有一定的共性及湖泊与季节异质性.;The thermal stratification and its potential impacts on the phytoplankton biomass were studied through the four seasonal field investigations (October 2014-July 2016) in Lake Chenghai and Lake Yangzonghai, two mesotrophic deep lakes on the Yunnan Plateau, southwest China. The results revealed that these two lakes are both warm monomictic lakes, where the vertical stratification was occurred in spring, stabilized in summer and autumn, and disappeared in winter. The mean values of thermocline depth (the upper boundary), thickness and strength during the stratification periods (spring, summer and autumn) were 17.70±3.89 m, 5.54±4.44 m and 0.67±0.43℃/m in Lake Chenghai and were 12.53±3.35 m, 8.25±4.85 m and 0.53±0.43℃/m in Lake Yangzonghai, respectively. During the stabilized thermal stratification periods, the dissolved oxygen in the bottom of the water column reached less than 3 mg/L even 1 mg/L, and the specific conductance in the bottom was generally larger than that in the surface water column. In these two lakes, the maximum values of the seasonal-average algal biomass (represented by chlorophyll-a concentration) were both in winter, which was 19.22±11.08 μg/L in Lake Chenghai and 45.82±9.41 μg/L in Lake Yangzonghai. Moreover, the fading of thermal stratification may be an important factor that increases the inorganic nutrients in the surface of water column (from the bottom of water column). Thereafter, higher nutrients combined with suitable light conditions and water temperature could promote the occurrence of algal blooms in winter. Besides a certain similarity, the major influencing factors of seasonal phytoplankton biomass also had inter-lake and seasonal heterogeneity during the other periods of season changes.

Antibacterial activity and medical properties of Witch Hazel Hamamelis virginiana

Antibacterial activity and medical properties of Witch Hazel Hamamelis virginiana

박노해 시의 생태적 전환의 이유와 지향성—『겨울이 꽃핀다』를 중심으로 -

박노해 시의 생태적 전환의 이유와 지향성—『겨울이 꽃핀다』를 중심으로 -

The Role of EjSPL3, EjSPL4, EjSPL5, and EjSPL9 in Regulating Flowering in Loquat (Eriobotrya japonica Lindl.).

The age pathway is important for regulating flower bud initiation in flowering plants. The major regulators in this pathway are miR156 and SPL transcription factors. To date, SPL genes have been identified in many species of plants. Loquat, as a woody fruit tree of Rosaceae, is unique in flowering time as it blooms in winter. However, the study of its SPL homologous genes on the regulation mechanism of flowering time is still limited. In this study, four SPL homologs—EjSPL3, EjSPL4, EjSPL5, and EjSPL9—are cloned from loquat, and phylogenetic analysis showed that they share a high sequence similarity with the homologues from other plants, including a highly conserved SQUAMOSA promoter binding protein (SBP)-box domain. EjSPL3, EjSPL4, EjSPL5 are localized in the cytoplasm and nucleus, and EjSPL9 is localized only in the nucleus. EjSPL4, EjSPL5, and EjSPL9 can significantly activate the promoters of EjSOC1-1, EjLFY-1, and EjAP1-1; overexpression of EjSPL3, EjSPL4, EjSPL5, and EjSPL9 in wild-type Arabidopsis thaliana can promote flowering obviously, and downstream flowering genes expression were upregulated. Our work indicated that the EjSPL3, EjSPL4, EjSPL5, and EjSPL9 transcription factors are speculated to likely participate in flower bud differentiation and other developmental processes in loquat. These findings are helpful to analyze the flowering regulation mechanism of loquat and provide reference for the study of the flowering mechanism of other woody fruit trees.

Bottom-Up and Top-Down Effects of Forest Fragmentation Differ Between Dietary Generalist and Specialist Caterpillars

Ecological interactions increasingly occur in the context of anthropogenic landscape alteration, such as landscape fragmentation, which engenders numerous changes to abiotic and biotic processes. Theory and empirical evidence suggest that species that are ecologically specialized or positioned at higher trophic levels are most sensitive to the effects of landscape fragmentation, yet the mechanisms underlying this sensitivity remain hypothetical. Here we present an initial test of the hypothesis that landscape fragmentation affects tri-trophic interactions more severely for dietary specialist than for generalist insect herbivores. We specifically tested a bottom-up hypothesis, that fragmentation reduces hostplant food quality to herbivores, with the most pronounced effects for dietary specialists. We also tested a top-down hypothesis, that fragmentation reduces parasitism of caterpillars, with the most pronounced effects on dietary specialists. We studied interactions among trees, caterpillars, and parasitoids in forest fragments (3 – 1013 ha) in Connecticut, U.S.A. in 2017 and 2018. To address the bottom-up hypothesis, we measured the growth performance of multiple dietary specialist and generalist caterpillar species fed leaves from red maple and witch hazel trees sampled from large or small forest patches. We assessed the top-down hypothesis by quantifying mortality from insect parasitoids of many of the same caterpillar species on these tree species sampled from a range of forest patch sizes. Fragmentation did not reduce herbivore growth performance for either dietary specialist or generalist caterpillars even though it accelerated desiccation rates of leaves of both tree species over the growing season. However, dietary specialization increased herbivore sensitivity to yearly variation in food quality, as the growth efficiency of specialist caterpillars varied between 2017 and 2018, while that of generalist caterpillars did not. As predicted, parasitism rates of dietary specialist caterpillars declined as forest fragment size declined, whereas parasitism of generalists was independent of fragment size. Therefore, interactions involving dietary specialist herbivores were most sensitive to top-down environmental variation. Assuming that dietary specialist caterpillars are primarily attacked by host-specific parasitoids, this top-down effect is consistent with the trophic theory of island biogeography, which predicts the sharpest declines of ecologically specialized predators and parasites in small habitat patches.

On the role of physical processes on the surface chlorophyll variability in the Northern Mozambique Channel

In the Indian Ocean regions under the influence of monsoons, two phytoplankton blooms characterize the seasonal cycle of surface chlorophyll, one during summer, and the other during winter. In the Northern Mozambique Channel, however, where the wind regime is an extension of the northern Indian Ocean monsoons, the annual cycle of chlorophyll concentrations is characterized by a single winter bloom. Wind stress and surface net heat flux modulate the seasonal cycle of the mixed layer depth with impacts on the surface chlorophyll. In order to evaluate the importance of these forcing fields on the seasonality of the mixed layer depth, and consequently, the surface chlorophyll variability, we used a suite of physical-biogeochemical model sensitivity experiments. Our results show that the seasonal cycle of surface chlorophyll is primarily modulated by the net heat flux while the wind field controls the amplitude. The winter bloom is triggered by negative surface heat fluxes, where cooling at the surface induces mixing and entrainment of nutrients at the base of the nutricline and light is not limiting. Winds enhance the winter bloom by uplifting additional nutrients and diluting subsurface chlorophyll into the surface layer. In the summertime, weaker wind stress and positive heat flux inhibit vertical mixing. As a consequence, the surface layer is depleted in nutrients and a deep chlorophyll maximum is formed. Analysis of top-down control on phytoplankton biomass reveals that zooplankton abundance increases in a near-linear proportion with phytoplankton biomass despite the deepening of the mixed layer depth. This suggests that the phytoplankton stock in the Northern Mozambique Channel is also controlled by grazing, given that zooplankton biomass is not directly affected by the deepening of the mixed layer during wintertime.