Grazing Ability Research Articles

Defense against Paramecium predation via long filament morphology favors the survival of Raphidiopsis raciborskii populations

Raphidiopsis blooms are notorious for cyanotoxin formation and strong invasiveness, threatening the stability of aquatic ecosystems and human health. The protozoa Paramecium can potentially serve as an organism for controlling Raphidiopsis blooms owing to its grazing effect. However, the grazing ability of Paramecium is largely determined by the size of the prey, and the population of Raphidiopsis consists of filaments of varying lengths and sizes. The selective grazing behavior of Paramecium toward short-length or small-sized filaments in the Raphidiopsis population, as opposed to long filaments, remains unclear. Therefore, in this study, we co-cultured the predator Paramecium sp. with different initial abundances and the prey Raphidiopsis raciborskii to explore this knowledge gap. Our results suggested that: (1) the population of R. raciborskii declined under the selective grazing effect of Paramecium sp. on short filaments, whereas R. raciborskii with long filaments survived; (2) the growth of Paramecium sp. feeding on the same abundance of R. raciborskii was reduced at higher initial abundances, whereas its carrying capacity exhibited an opposite trend; (3) under ingestion by Paramecium sp., the morphology of R. raciborskii developed in the direction of becoming larger, and higher initial abundances of Paramecium sp. intensified this process; (4) increasing initial abundance of Paramecium sp. aggravated the decline of R. raciborskii photosynthetic activity. Therefore, the grazing effect of Paramecium sp. on R. raciborskii mainly affects filaments of short length or small size. Collectively, these results clarify the inter-species interaction between the protozoa Paramecium and filamentous cyanobacteria Raphidiopsis, including population dynamics and morphological and physiological changes in the predator and prey. Such insights into the interactions between Paramecium and R. raciborskii may have implications for the biological control of blooms caused by filamentous cyanobacteria.

The behavior of sympatric sea urchin species across an ecosystem state gradient.

In temperate macroalgal forests, sea urchins are considered as a keystone species due to their grazing ability. Given their potential to shape benthic communities, we monitored the habitat use by three sympatric sea urchin species and compared their behaviors in a vegetated habitat (VH) and an adjacent isoyake habitat (IH). We monitored the environmental conditions and sea urchin density along deep and shallow transects of the VH and IH for over a year. The benthic rugosity at both sites were also surveyed. A mark-recapture experiment was conducted on the two most abundant sea urchins, Diadema setosum and Heliocidaris crassispina, to elucidate sea urchin movement patterns and group dynamics. We found that exposure to waves was highest at the VH while the IH was sheltered. The deep IH experienced the least amount of light due to high turbidity. Water temperature patterns were similar across sites. The VH benthic topography was more rugose compared to the smoother and silt-covered IH substate. Peak macroalgal bloom occurred three months earlier in IH, but macroalgae persisted longer at the shallow VH. Among the sympatric sea urchins, H. crassispina was most abundant at the shallow VH and was observed in pits and crevices. The most abundant across IH and in the deep VH was D. setosum, preferring either crevices or free-living, depending on hydrodynamic conditions. The least abundant species was D. savignyi, and most often observed in crevices. Small and medium sea urchins were most often observed at the IH site, whereas larger sea urchins were more likely observed at the VH. The mark-recapture study showed that D. setosum was found to displace further at the IH, and H. crassispina was more sedentary. Additionally, D. setosum was always observed in groups, whereas H. crassispina was always solitary. The behaviors of sympatric urchins, Diadema savignyi, D. setosum and H. crassispina, differed in response to changes in the benthic environment and physical conditions. Sea urchin displacement increased when rugosity and wave action were low. Habitat preference shifted to crevices in seasons with high wave action. In general, the mark-recapture experiment showed that sea urchins displaced further at night.

Kinopus chlorellivorus gen. nov., sp. nov. (Vampyrellida, Rhizaria), a New Algivorous Protist Predator Isolated from Large-Scale Outdoor Cultures of Chlorella sorokiniana.

The large-scale culture of low-cost algal biomass can be significantly affected by microbial grazing on the algae. To minimize the impact, it is necessary to manage the predators. In this study, we describe a new genus and species of vampyrellid amoeba, Kinopus chlorellivorus, which caused the loss of Chlorella sorokiniana in large-scale cultures. We assigned it to the family Leptophryidae (Vampyrellida) based on morphology and small-subunit (SSU) rRNA gene sequence comparisons. Using transmission electron microscopy, we found spherical lucent inclusions, which have not been reported for any leptophryids or other vampyrellids. The gene sequence of SSU rRNA did not match any recognized genera or species and contained four characteristic regions. K. chlorellivorus preys on algae by engulfment. Laboratory feeding experiments confirmed that its grazing rate was as high as 131 Chlorella cells day-1 individual-1. Results of prey-range experiments demonstrated that it could consume other chlorophyte microalgae (e.g., Scenedesmus, Coelastrella, and Haematococcus) but with a strong feeding ability on Chlorella spp., with ingestion rates ranging from 2.67 to 3.15 prey predator-1 h-1 and growth rates of the amoeba ranging from 0.039 to 0.045 h-1. On the basis of its high grazing ability on Chlorella, capacity to form large populations in a short period of time, and capacity to form resistant resting stages, this contaminant has the potential to cause serious problems in large-scale Chlorella culture and should be of concern to operators of algal production facilities. IMPORTANCE The vampyrellids (Vampyrellida, Rhizaria) are a major group of predatory amoebae that have attracted significant attention because of their diversity of feeding strategies. The crucial roles they play in important processes such as suppressing soil disease and controlling aquatic algae, and as microbial contaminants in outdoor large-scale algal cultures, have also received increasing attention. In this study, a new genus and species of algivorous vampyrellid amoeba, Kinopus chlorellivorus, is described as a significant grazer responsible for losses in outdoor industrial Chlorella cultures. We found that the amoeba's detrimental effects on Chlorella cultures may be related to its specific feeding characteristics. This study provides phenotypic and genetic information on a previously unknown vampyrellid, emphasizes the impact of contaminating vampyrellids in commercial microalgal cultures, and will contribute to the development of management strategies for predicting this kind of contaminant in large-scale microalgal cultivation.

Effects of Nutritional Mode on the Physiological and Biochemical Characteristics of the Mixotrophic Flagellate Poterioochromonas malhamensis and the Potential Ecological Implications.

Mixotrophic flagellates play an important role in connecting the classical food chain and microbial food loop. The feeding characteristics of the mixotrophic flagellate Poterioochromonas malhamensis have been well studied, but its role as a food source for other large zooplankton is less studied. This study focuses on the physiological and biochemical changes in P. malhamensis when using autotrophy, chemoheterotrophy, and phagotrophy, and the effect of these changes on the feeding ability of one of its predators, the ciliate Paramecium caudatum. The results showed that chemoheterotrophic P. malhamensis had a higher growth rate and larger cell size than autotrophic and phagotrophic P. malhamensis. The biochemical composition of P. malhamensis also varied greatly between the three nutritional modes. The protein, total absolute amino acid, and fucoxanthin contents were highest for autotrophic P. malhamensis, while chemoheterotrophic P. malhamensis had the highest contents of total sugar and total absolute fatty acid. The contents of most biochemical components in phagotrophic P. malhamensis fell between those in autotrophic and chemoheterotrophic P. malhamensis. A feeding experiment showed that the grazing ability of P. caudatum on chemoheterotrophic P. malhamensis was significantly higher than that on phagotrophic P. malhamensis and autotrophic P. malhamensis. This study showed that the transformation of nutritional modes can alter the biochemical composition of the mixotrophic flagellate P. malhamensis and, as a result, affect the grazing ability of its predator P. caudatum.

Broad phylogenetic and functional diversity among mixotrophic consumers of Prochlorococcus

Small eukaryotic phytoplankton are major contributors to global primary production and marine biogeochemical cycles. Many taxa are thought to be mixotrophic, but quantitative studies of phagotrophy exist for very few. In addition, little is known about consumers of Prochlorococcus, the abundant cyanobacterium at the base of oligotrophic ocean food webs. Here we describe thirty-nine new phytoplankton isolates from the North Pacific Subtropical Gyre (Station ALOHA), all flagellates ~2–5 µm diameter, and we quantify their ability to graze Prochlorococcus. The mixotrophs are from diverse classes (dictyochophytes, haptophytes, chrysophytes, bolidophytes, a dinoflagellate, and a chlorarachniophyte), many from previously uncultured clades. Grazing ability varied substantially, with specific clearance rate (volume cleared per body volume) varying over ten-fold across isolates and six-fold across genera. Slower grazers tended to create more biovolume per prey biovolume consumed. Using qPCR we found that the haptophyte Chrysochromulina was most abundant among the isolated mixotrophs at Station ALOHA, with 76–250 cells mL−1 across depths in the upper euphotic zone (5–100 m). Our results show that within a single ecosystem the phototrophs that ingest bacteria come from many branches of the eukaryotic tree, and are functionally diverse, indicating a broad range of strategies along the spectrum from phototrophy to phagotrophy.

Synergistic reduction of a native key herbivore performance by two non-indigenous invasive algae

Native generalist grazers can control the populations of non-indigenous invasive algae (NIIA). Here, it was found that the simultaneous consumption of two co-occurring NIIA, Caulerpa cylindracea and C. taxifolia var. distichophylla, hinders the grazing ability of the main Mediterranean herbivorous, the native sea urchin Paracentrotus lividus. The ingestion of any of the two NIIA alone did not produce any difference in sea urchin righting time with respect to usual algal diet. In contrast, the simultaneous consumption of both NIIA, which grow intermingled in nature and are consumed by P. lividus, retarded its righting behavior. Such result reveals substantial physiological stress in the sea urchin, which resulted in reduced motility and coordination. The reported findings reveal the potential of NIIA co-occurrence to escape the supposed control exerted by the main native generalist grazer in Mediterranean sublittoral communities, which in turn can be locked in an “invaded” state.

Identification and feeding characteristics of the mixotrophic flagellate Poterioochromonas malhamensis, a microalgal predator isolated from outdoor massive Chlorella culture

Chlorella is a strong candidate as a potential production organism for future biofuels and other algal-derived products, but contamination by grazing protozoa is a major constraint to its commercial production on a large scale. In this study, a mixotrophic flagellate chrysophyte that targeted Chlorella in mass culture was observed in samples from outdoor massive photobioreactor systems. Data from field studies demonstrated that once the predatory flagellate was observed in the algal culture, there was a dramatic reduction in Chlorella cell concentration. The grazer was identified as Poterioochromonas malhamensis, based on both morphology and molecular barcoding employing 18S rDNA gene sequences. Transmission electron microscopy revealed that P. malhamensis digested the ingested Chlorella sorokiniana cells within a food vacuole, with residual cell wall from the prey being observed in the final phase. It was noted that during the process of ingesting and digesting the C. sorokiniana cells, the chloroplast of P. malhamensis reduced in size, whereas the number and volume of mitochondria increased. After the prey had been completely digested, the chloroplast and mitochondria of P. malhamensis returned to their pre-feeding status. Feeding experiments in the laboratory demonstrated that cell concentrations of C. sorokiniana and P. malhamensis were negatively correlated. Furthermore, once P. malhamensis reached 5×105cellsmL−1 and the ratio of C. sorokiniana to P. malhamensis was in the range 15:1 to 30:1, the cell concentration of the C. sorokiniana culture decreased dramatically. The optimal temperature for P. malhamensis grazing on C. sorokiniana was 25°C; the grazing ability of P. malhamensis in light conditions was higher than that in dark conditions; and P. malhamensis preferred weakly acidic conditions. In addition, it was demonstrated that this flagellate could graze on other common microalgae of commercial value. On the basis of its capacity to ingest a wide spectrum of phytoplankton, and its wide environmental range and global distribution, this contaminant has the potential to be a common problem in microalgal mass cultures and warrants further study.

Detection of suitable zooplankton from three taxonomic groups for application in biomanipulation

Many lentic water bodies of the world are under the threat of cultural eutrophication and experience problems associated with algal blooms. Biomanipulation is a useful technique applied to control algal blooms by deliberate alteration of an ecosystem through addition and removal of organisms. The feeding behavior of zooplankton has been applied in biomanipulation in controlling algal densities and to accelerate ecosystem recovery. For this, it is important to select the most efficient filter feeders. The present experiment was carried out to assess the grazing ability of five different zooplankton species belonging to three taxonomic groups, Cladocera, Copepoda and Ostracoda. Filtering efficiency of each algal species by selected zooplankton species were assessed by counting algal cells in each zooplankton introduced systems. Specific growth rate was calculated using the equation (ln N 1 -ln N 0 ) / (t 1 -t 0 ) where, N 0 (cells/µl) and N 1 (cells/µl) are cell counts at times t 0 (day) and t 1 (day) respectively. The results indicated that zooplankton used in the experiment possess varied capacities of grazing on different species of algae. Chlorella sp. was well controlled by Ceriodaphnia cornuta whereas Crucigenia sp. was controlled better with the Stenocypris sp. Although species of Scenedesmus are favored by many zoopklankton as a food, it was better controlled by the members of the group Ostracoda and also by C. cornuta. Even though Monoraphidium sp. was controlled better by all the study species of zooplankton, C. cornuta showed the highest performances followed by ostracods.

Parrotfish grazing ability: interspecific differences in relation to jaw-lever mechanics and relative weight of adductor mandibulae on an Okinawan coral reef.

Parrotfishes (family Labridae: Scarini) are regarded to have important roles for maintaining the ecosystem balance in coral reefs due to their removal of organic matter and calcic substrates by grazing. The purpose of the present study was to clarify the interspecific differences in grazing ability of five parrotfish species (Chlorurus sordidus, C. bowersi, Scarus rivulatus, S. niger and S. forsteni) in relation to interspecific differences in jaw-lever mechanics and the relative weight of the adductor mandibulae (muscles operating jaw closing). The grazing ability was calculated by using stomach contents (CaCO3 weight/organic matter weight) defined as the grazing ability index (GAI). There were significant interspecific differences in GAI (C. sordidus = C. bowersi > S. rivulatus > S. niger = S. forsteni). Teeth of C. sordidus and C. bowersi were protrusive-shape whereas teeth of S. rivulatus, S. niger and S. forsteni were flat-shape. C. sordidus and C. bowersihave jaw-lever mechanics producing a greater biting force and have a larger weight of adductor mandibulae. S. rivulatus has jaw-lever mechanics producing a greater biting force but a smaller weight of adductor mandibulae that produce an intermediate biting force. In contrast, S. niger and S. forsteni have jaw-lever mechanics producing a lesser biting force and have a smaller weight of adductor mandibulae. Feeding rates and foray size of S. rivulatus, S. niger and S. forsteni were greater than C. sordidus and C. bowersi. The degree in bioerosion (GAI × feeding rate) was the largest for S. rivulatusand the smallest for S. forsteni. The degree in bioerosion for C. sordidus was larger than S. niger whereas relatively equal between C. bowersi and S. niger. These results suggest that interspecific difference in GAI was explained by interspecific differences in teeth shape, jaw-lever mechanics and relative weight of adductor mandibulae. The interspecific difference in the degree of bioerosion suggests the importance of various size of parrotfishes with diverse feeding modes to maintain healthy coral reef ecosystems.

The ability of winter grazing to reduce wildfire size and fire-induced plant mortality was not demonstrated: a comment on Davies et al. (2015)

A recent study by Davies et al. sought to test whether winter grazing could reduce wildfire size, fire behaviour and intensity metrics, and fire-induced plant mortality in shrub–grasslands. The authors concluded that ungrazed rangelands may experience fire-induced mortality of native perennial bunchgrasses. The authors also presented several statements regarding the benefits of winter grazing on post-fire plant community responses. However, we contend that the study by Davies et al. has underlying methodological errors, lacks data necessary to support their conclusions, and does not provide a thorough discussion on the effect of grazing on rangeland ecosystems. Importantly, Davies et al. presented no data on the post-fire mortality of the perennial bunchgrasses or on the changes in plant community composition following their experimental fires. Rather, Davies et al. inferred these conclusions based on their observed fire behaviour metrics of maximum temperature and a term described as the ‘heat load’. However, we contend that neither metric is appropriate for describing the heat flux impacts on plants. This lack of post-fire data, several methodological errors and the use of inappropriate thermal metrics limit the authors’ ability to support their stated conclusions.

Altered Host Cell–Bacteria Interaction due to Nanoparticle Interaction with a Bacterial Biofilm

Nanoparticle (NP) use in everyday applications creates the potential for NPs to enter the environment where, in aquatic systems, they are likely to settle on substrates and interact with microbial communities. Legionella pneumophila biofilms are found as part of microbial communities in both natural and man-made environments, especially in man-made cooling systems. The bacterium is the causative agent of Legionnaires' disease. Legionella requires a host cell for replication in the environment, and amoebae commonly serve as this host cell. Our previous work demonstrated significant changes in Legionella biofilm morphology after exposure to 0.7 μg/L gold NPs (AuNPs). Here, we investigate how these morphology changes alter host-bacteria interactions using Acanthamoeba polyphaga as a model. Host-bacteria-NP interactions are affected by NP characteristics. Biofilms exposed to 4- and 18-nm, citrate-capped, spherical AuNPs significantly altered the grazing ability of A. polyphaga, which was not observed in biofilms exposed to 24-nm polystyrene beads. Uptake and replication of NP-exposed planktonic L. pneumophila within A. polyphaga were not altered regardless of NP size or core chemistry. Nanomaterial effects on the interaction of benthic organisms and bacteria may be directly or, as shown here, indirectly dependent on bacterial morphology. NP contamination therefore may alter interactions in a normal ecosystem function.

Predator-Prey Dynamics Driven by Feedback between Functionally Diverse Trophic Levels

Neglecting the naturally existing functional diversity of communities and the resulting potential to respond to altered conditions may strongly reduce the realism and predictive power of ecological models. We therefore propose and study a predator-prey model that describes mutual feedback via species shifts in both predator and prey, using a dynamic trait approach. Species compositions of the two trophic levels were described by mean functional traits—prey edibility and predator food-selectivity—and functional diversities by the variances. Altered edibility triggered shifts in food-selectivity so that consumers continuously respond to the present prey composition, and vice versa. This trait-mediated feedback mechanism resulted in a complex dynamic behavior with ongoing oscillations in the mean trait values, reflecting continuous reorganization of the trophic levels. The feedback was only possible if sufficient functional diversity was present in both trophic levels. Functional diversity was internally maintained on the prey level as no niche existed in our system, which was ideal under any composition of the predator level due to the trade-offs between edibility, growth and carrying capacity. The predators were only subject to one trade-off between food-selectivity and grazing ability and in the absence of immigration, one predator type became abundant, i.e., functional diversity declined to zero. In the lack of functional diversity the system showed the same dynamics as conventional models of predator-prey interactions ignoring the potential for shifts in species composition. This way, our study identified the crucial role of trade-offs and their shape in physiological and ecological traits for preserving diversity.

Short-term grazing of lucerne and chicory increases ovulation rate in synchronised Merino ewes

This study evaluated the ability of short-term grazing of live = green pasture to increase ovulation rate during late summer when annual pasture is generally dead and of low quality. Ovulation rates, measured by the number of corpora lutea, were compared between 4 nutritional treatments: senesced phalaris ( Phalaris aquatica), phalaris plus 500 g lupin grain per day, lucerne ( Medicago sativa) or chicory ( Chicorum intybus) pastures. The study used 100 Merino ewes per treatment, divided between 2 replicates. The experiment was repeated in 3 years; February 2006, and January 2007 and 2008. Oestrus was synchronised and the ewes grazed the pastures for 9 days prior to ovulation at times corresponding to days 8–17 of the cycle in 2006, and days 6–14 in 2007 and 2008. The proportion of ewes producing multiple ovulations was higher ( P < 0.05) in the lucerne and chicory (0.36, 0.38) than the phalaris (0.27), and intermediate in the lupin (0.33) treatment. Regression analysis showed that the proportion of ewes with multiple ovulations increased with the quantity of live herbage ( P < 0.04). Responses were achieved even at low levels of live herbage with 90% of the maximum proportion of multiples occurring at 350 kg DM/ha. It is concluded that providing short-term grazing of live chicory or lucerne to ewes can increase ovulation rates relative to ewes grazing senesced phalaris and to levels similar to those achieved by lupin grain supplementation.

Adaptability of pregnant Merino ewes to the cold desert climate in Nevada1

Grazing ability is difficult to record in animals under free-ranging conditions without sophisticated methods. Alternatively, grazing ability may be indirectly inferred from changes in BW and production characteristics during the grazing period. The present study investigated the effect of grazing on resource-limited rangelands on BW, wool characteristics, and offspring weaning weights in nine hundred five 5/8, 7/8, and fullblood Merino ewes of 2 to 7 yr of age during a grazing period of approximately 2.5 mo (between January and March). A total of 469 ewes gave birth to a single lamb, 248 to twin lambs, and 188 did not give birth. Body weights were measured and wool samples taken before and after the ewes were allowed to graze freely on the rangelands; absolute change in BW and change in BW as a percentage of initial BW were estimated. On average, grazing on resource-poor rangelands resulted in BW loss, a reduction in fiber diameter and its CV, and increased staple length. Animals with finer wool at the start of the grazing period lost phenotypically (r = -0.07, P < 0.05) and genetically (r = -0.23, P < 0.05) less BW during the grazing period and had a greater probability to carry 1 lamb (or 2) to term (P < 0.05). Animals that lost less BW produced more greasy fleece (r = 0.09, P < 0.01). Body weight change did not significantly influence offspring weaning weights. Change in BW was moderately heritable at h(2) = 0.29; fiber diameter was strongly heritable at h(2) = 0.51. Animals with the least inclusion of Merino genetics lost more BW (P < 0.01) during the grazing period and had a more uniform fiber diameter (P < 0.05) but shorter staples (P < 0.05) and less fleece (P < 0.0001) than animals with a greater level of Merino genetics. Our results indicate that animals with finer wool appeared to be better adapted to the cold Nevada desert. Thus, selection for finer wool may positively influence adaptability to resource-limited cold climate conditions; alternatively, BW change may be selected for directly. Because nutritional deficiencies during pregnancy can have adverse consequences for the offspring, indirect selection for grazing ability would foremost result in healthier ewes that can produce lambs and wool without compromising their welfare.

Phenotypic Description And Productive Performance Of Tarime Zebu Cattle In Tanzania

On-farm survey and characterization of Tarime zebu cattle was carried out to describe their phenotypic characteristics, reproductive performance and adaptive qualities. Data on physical characteristics were collected through onsite observation of 626 animals. Data on reproductive and lactation performances were collected through individual interview of 120 farmers from six villages using a structured questionnaire. Body measurements (body weight, wither height, body length and heart girth) were obtained by measuring 84 animals. The coat colour of most animals was brown (14.2%), fawn (13.4%) or brown mixed with other colours (21.4%). In most animals muzzles were brown (71.4%), hooves were grey (73.8%), naval flap was either absent (69%) or small (28.6%) and the dewlap was medium in size (83.3%). The majority of Tarime zebu cattle had small udder size (92.3%), small front quarter size (61.5%) and medium sized teats (80.8%). The estimated average live weights of mature cattle were 292 ± 32, 319 ± 35 and 249 ±.23 kg for entire males, castrates and females, respectively. Average age at first calving and calving interval were 4.3 ± 3.3 years and 17.6 ± 5.1 months, respectively. Average lactation length was 8.2 ± 2.3 months and average daily milk yield for the whole lactation period was 1.4 ± 0.6 litres. Most farmers reported that Tarime zebu cattle were tolerant to diseases (80.5%) and drought (75.8%), had good grazing ability (34.2%) and were better draught animals (24.2%). It is concluded that Tarime zebu cattle are preferred to pure and crossbred dairy breeds because of their ability to withstand diseases and adverse environmental conditions. Tanzania Veterinary Journal Vol. 25 (1) 2008: pp. 60-74

Lacuna vincta (Mollusca, Neotaenioglossa) herbivory on juvenile and adult Nereocystis luetkeana (Heterokontophyta, Laminariales)

Herbivory can be an important factor structuring coastal algal communities. Herbivores may preferentially graze particular algal species or tissue types. Mesograzers, despite their small size, can critically weaken kelp thalli and impact entire kelp beds. We propose that when kelp beds are composed of several kelp cohorts, mesograzers will selectively choose to inhabit younger plants and grazing activities will have a greater impact on younger plants. This study investigated the effects of grazing by the littorinid gastropod, Lacuna vincta, on different age classes of the bull kelp, Nereocystis luetkeana by (1) testing food preference of L. vincta on juvenile, first-year adult, and second-year adult Nereocystis blades in the laboratory, (2) determining substrate (blades of different ages) preference of L. vincta in the laboratory, and by (3) estimating in-situ herbivore abundances and densities on juvenile and adult Nereocystis. Results demonstrated that grazing by L. vincta produced greater damage on juvenile than older Nereocystis tissues. Although L. vincta did not select juvenile versus older kelps as substrate in the laboratory, in situ surveys showed that differences existed between age classes with higher L. vincta densities on juvenile than adult kelp. We conclude that at a local scale, L. vincta can be an important structuring factor in Nereocystis populations due to its high density and grazing ability.

Challenges for establishing a modern reindeer dairy industry (In Norwegian with Summary in English)

To achieve efficient milk ejection has been a recurrent problem in machine milking of reindeer does. The field season 2004 was a breakthrough for an efficient and complete milk let down in reindeer. The proportion of residual milk was reduced as lactation progressed; from around 40-50% at start of the milking in mid June to around 10-15% in late August, suggesting that habituation and training are important factors for triggering the ejection. We performed an experiment including 3 treatments; 1) Calves equipped with a "kjevle" (a wooden stick placed in the mouth of the calves making them unable to suckle but keeping their grazing ability intact) for 8 - 14 hrs dependent of lactation stage, followed by milking of the does, 2) Physically separation of the mothers and their calves for 8 - 14 hrs dependent of lactation stage, followed by milking of the does and 3) Permanent separation of females and calves at start of the milking period and females milked twice per day. The females and calves in group 1 and 2 were rejoined after the "kjevle" and separation period. The females in these two groups were milked every second day. The "kjevle" treatment apparently works better than physical separ¬ation according to welfare parameters and proportion milk ejected in the first part of the milking period. Permanent separation did also work well and permits that the whole production after separation can be utilized. However, in order to keep up the milk production frequent milkings are required during the first days of separation. The growth of the calves was high and did not differ between treatments. This suggests that the calves are able to compensate the reduced milk intake by increasing their intake of forages.

The effects of nutrients and zooplankton community structure on phytoplankton growth in a subtropical Australian reservoir: An enclosure study

Patterns of zooplankton–phytoplankton interactions in subtropical lakes of the Southern Hemisphere may deviate from those established for north-temperate lakes. We tested the responses of phytoplankton growth to different community structures of zooplankton and nutrient enrichment in a subtropical Australian reservoir for the prediction of potential outcomes of lake biomanipulation. Two zooplankton communities were created in lake enclosures over 4 weeks: a rotifer-dominated community developed in the presence of planktivorous fish ( Hypseleotris spp.) and a Ceriodaphnia-dominated community developed in the absence of fish. Biomass gradients of both communities were established in 20 L containers and several separate containers received no additions (controls) or were enriched with nitrogen and/or phosphorus. The growth rate of total phytoplankton significantly increased in response to nutrient enrichment, indicating nutrient limitation. Most phytoplankton taxa were not markedly affected by grazing of either zooplankton community. However, both communities had significant stimulatory effects on the growth of inedible chlorophytes. The ability of zooplankton grazing to negatively affect phytoplankton growth during the summer was counteracted regardless of zooplankton community structure, possibly by nutrients regenerated by zooplankton. We hypothesise that in the subtropical system studied, changes in food web nutrient recycling may be more important for the outcome of biomanipulation than grazing impacts.

Effectiveness of grazing and herbicide treatments for lucerne removal before cropping in southern New South Wales

The difficulty of reliably removing an established lucerne pasture before cropping has been identified as a major problem with phase-farming systems on mixed farms. A series of experiments were undertaken on established lucerne stands at the Ginninderra Experimental Station in the Australian Capital Territory (ACT) and at the Temora Research Station in southern New South Wales (NSW) to compare the ability of grazing, either alone or in combination with herbicides, to remove a lucerne pasture. A pilot study at the Ginninderra Experimental Station in 1998–99 utilised a high stocking rate (30 dry sheep equivalents [dse]/ha), while the main study at the Ginninderra Experimental Station and the Temora Research Station in 1999–2000 used a lower stocking rate (10–12 dse/ha) considered to be closer to farmer practice in the region. Continuous grazing at the high stocking rate removed 73% of the lucerne stand over 3 months. In contrast, the stocking rates applied in the main study proved too low to substantially impact on lucerne survival at both the ACT and NSW sites (13–23% removal) under the good seasonal conditions experienced in 1999–2000 even though the pastures were continuously grazed for 8–9 months. The use of herbicides both alone or in conjunction with grazing greatly improved lucerne removal in both studies. However, herbicide efficacy was variable (53–100% removal), and seemed to be related to the time of year it was applied, the period of lucerne regrowth or the amount of rainfall before herbicide application. An additional on-farm study was undertaken near Junee Reefs in southern NSW between 2001 and 2003 that compared the survival of a range of lucerne cultivars under simulated hay-cutting (mown) and commercial grazing regimes. Dry conditions during 2002–03 resulted in a decline in lucerne frequency at about 50% in mown control plots. Grazing increased the stand decline, particularly for many winter-active cultivars where lucerne frequency was reduced by up to 70–93%. It was concluded that: (i) continuous grazing for prolonged periods can be effective at removing lucerne, but the rate of lucerne loss will be influenced by both stocking rate and rainfall; (ii) the application of herbicides can improve lucerne removal either in association with, or in the absence of grazing; however, herbicide efficacy appeared to be dependent upon the physiological status of the lucerne plants and/or the environmental conditions before application; and (iii) cultivar responses indicated that lucerne types could potentially be developed for phase-farming systems with increased susceptibility to grazing mismanagement.

Grazing ability of European black pine understorey vegetation by goats

Goats’ utilizing ability of spontaneous vegetation, depending on stocking density, grazing season and day period, was studied on a European black pine ( Pinus nigra Arnold subsp. nigra) reforested slope of the Pyrenees with direct observation of the animals’ grazing behaviour. Goats spent about 59% of their time eating in spring versus 85% in autumn. However, the mean grazing time (8.6 h) was not affected either by stocking density or grazing season. While stocking density showed an effect on the time that goats devoted to consuming different groups of plants, it was much affected by the grazing season. Goats spent 50% of their total grazing time on browse species in spring, but this activity decreased to 32% in autumn. Browsing preferences, however, varied markedly among plant species. Buxus sempervirens L. was never consumed by goats, but Genista scorpius (L.) DC. was frequently browsed both in spring (36%) and autumn (20%). The time devoted to consume thorny species, like Rosa spp., declined significantly from spring to autumn showing an opposite tendency to that observed for aromatic species that were almost exclusively consumed in autumn. Goats spent up to 7.1% of their grazing time eating lower pine branches and up to 1.3% on the litter layer of needles. The high proportion of time devoted to consuming these materials suggests that goats’ grazing activity may effectively contribute towards controlling the dead fuel layer build-up in European pine stands. A diurnal pattern of plant utilisation was observed that was characterised by a longer time devoted to browsing species early in the morning than during the rest of the day. The different seasonal and diurnal utilisation ability of the spontaneous vegetation by goats could provide foresters with a useful management tool in sustainable mixed forage systems.