Andrew Foggo

The future of the northeast Atlantic benthic flora in a high CO2 world

Seaweed and seagrass communities in the northeast Atlantic have been profoundly impacted by humans, and the rate of change is accelerating rapidly due to runaway CO2 emissions and mounting pressures on coastlines associated with human population growth and increased consumption of finite resources. Here, we predict how rapid warming and acidification are likely to affect benthic flora and coastal ecosystems of the northeast Atlantic in this century, based on global evidence from the literature as interpreted by the collective knowledge of the authorship. We predict that warming will kill off kelp forests in the south and that ocean acidification will remove maerl habitat in the north. Seagrasses will proliferate, and associated epiphytes switch from calcified algae to diatoms and filamentous species. Invasive species will thrive in niches liberated by loss of native species and spread via exponential development of artificial marine structures. Combined impacts of seawater warming, ocean acidification, and increased storminess may replace structurally diverse seaweed canopies, with associated calcified and noncalcified flora, with simple habitats dominated by noncalcified, turf-forming seaweeds.

Tri-trophic consequences of UV-B exposure: plants, herbivores and parasitoids

In this paper we demonstrate a UV-B-mediated link between host plants, herbivores and their parasitoids, using a model system consisting of a host plant Brassica oleracea, a herbivore Plutella xylostella and its parasitoid Cotesia plutellae. Ultraviolet-B radiation (UV-B) is a potent elicitor of a variety of changes in the chemistry, morphology and physiology of plants and animals. Recent studies have demonstrated that common signals, such as jasmonic acid (JA), play important roles in the mechanisms by which plants respond to UV-B and to damage by herbivores. Plant responses elicited by UV-B radiation can affect the choices of ovipositing female insects and the fitness of their offspring. This leads to the prediction that, in plants, the changes induced as a consequence of UV damage will be similar to those elicited in response to insect damage, including knock-on effects upon the next trophic level, predators. In our trials female P. xylostella oviposited preferentially on host plants grown in depleted UV-B conditions, while their larvae preferred to feed on tissues from UV-depleted regimes over those from UV-supplemented ones. Larval feeding patterns on UV-supplemented tissues met the predictions of models which propose that induced defences in plants should disperse herbivory; feeding scars were significantly smaller and more numerous – though not significantly so – than those on host plant leaves grown in UV-depleted conditions. Most importantly, female parasitoids also showed a clear pattern of preference when given the choice between host plants and attendant larvae from the different UV regimes; however, in the case of the female parasitoids, the choice was in favour of potential hosts foraging on UV-supplemented tissues. This study demonstrates the potential for UV-B to elicit a variety of interactions between trophic levels, most likely mediated through effects upon host plant chemistry.

Edge effects and tropical forest canopy invertebrates

The term edge effect can be used to encompass a wide range of both biotic and abiotic trends associated with boundaries between adjacent habitat types, whether these be natural or anthropogenic. Edge effects have been shown to represent significant forces affecting both faunal and floral assemblages in fragmented ecosystems. Specific studies of faunal assemblages associated with habitat edges have revealed trends at all levels of biological organisation from individuals to communities. Studies of edge effects on invertebrates in tropical forests have been relatively scarce. In this paper we review the nature and organisation of edge effects, focusing upon the processes which may lead to detrimental consequences for both forest canopy invertebrates and the forests themselves. We present as a case study data illustrating the very large amount of variance (over 50%) in community structure that is predicted simply by abiotic (microclimatic) variables in both a tropical and a temperate forest edge. We summarise major features of edge effects amongst forest invertebrates, stress the inter-relatedness of edge and canopy biology, and present an agenda for study of the canopy as an edge.

Induced resistance in intertidal macroalgae modifies feeding behaviour of herbivorous snails

Herbivory in terrestrial and marine systems can induce changes in plant chemistry affecting the foraging behaviour of herbivores. A model based on terrestrial plant-herbivore interactions predicts herbivory-induced changes in leaf chemistry to be manifested in (1) increased herbivore mobility, (2) increased feeding dispersal and (3) reduced tissue consumption by herbivores. This study is the first to demonstrate that herbivory-induced changes in the tissue chemistry of the brown seaweed Ascophyllum nodosum elicit the same response in the feeding behaviour of the gastropod Littorina obtusata as predicted for herbivorous insects, providing good evidence for the model’s validity across different ecosystems. The potential benefit of increased feeding dispersal to terrestrial plants as suggested by the model is the prevention of concentrated damage to apical tissues thereby preserving the plant’s ability to compete for light; A. nodosum does not conform to these predictions. Increased dispersal of feeding damage on A. nodosum away from primary frond tissues would reduce the likelihood of frond breakage implying a fitness benefit of induced resistance.

HORSE CHESTNUT SCALE (PULVINARIA REGALIS) (HOMOPTERA: COCCIDAE) AND URBAN HOST TREE ENVIRONMENT

The analysis and explanation of the spatial distribution of organisms within a locality are problematic. This study uses a combination of standard analytical methods (Generalized Linear Interactive Modeling [GLIM]) with recently developed spatial statistical techniques (geostatistical analysis), on a model system of insect-plant interactions in an urban setting. Infestations of the horse chestnut scale, Pulvinaria regalis, were mapped on three tree species in Oxford, United Kingdom. Various tree parameters were measured, as were aspects of the site in which each tree was growing. Using general linear modeling and geostatistics, the distribution and intensity of scale populations were investigated in relation to these parameters. The trees were separated into those that showed no symptoms of lack of vigor and those that were clearly unhealthy. In both cases, the only parameter that explained much of the variance in the scale egg densities on trees was the impermeability of the substrate surface under the trees, such that as substrates became more impermeable to water and nutrients (for example, as a result of concrete or roadways), the higher were the pest densities on those trees. For the vigorous trees alone, an extra parameter, that of building distance, was also found to be significant, so that trees very close to buildings also showed high pest densities. The spatial dependence of scale insect eggs on trees was found to be anisotropic through the sample area, in the southwest/northeast direction, attributable to wind speed, direction, and canyon effects.

Insecticidal activity of garlic juice in two dipteran pests

Abstract  1 Botanical products excluding pyrethroids constitute a small, but growing portion of the U.K. pesticides market. With increasing legislative pressure upon chemical pesticides such as organophosphates, interest in this sector is increasing steadily. 2 Garlic Allium sativum L. juices and extracts form the basis of several commercially available pest control products, but the performance of these products is variable, possibly due to lack of quality control upon batches of materials in the manufacturing process. 3 Some garlic products designed for use in the food industry are subjected to rigorous batch‐control to ensure organoleptic consistency. We studied the insecticidal efficacy of a commercially produced food grade garlic juice using two target dipteran pests, Delia radicum (L.) and Musca domestica L. 4 Exposure of the two species to different concentrations of garlic juice revealed variability in insecticidal effect across life stages. LC50 values recorded for D. radicum were: eggs (7‐day exposure) 0.8%; larvae (24‐h exposure) 26.4%; larvae (48‐h exposure) 6.8%; and adults (24‐h exposure) 0.4%. LC50 values recorded for M. domestica were: eggs (7‐day exposure) 1.6%; larvae (24‐h exposure) 10.1%; larvae (24‐h exposure) 4.5%; and adults (24‐h exposure) 2.2%. 5 Mortality rates caused by the garlic juice were comparable with those obtained with the organophosphate pesticide Birlane®, indicating parity of effect at various concentrations depending on life stage. 6 We conclude that this product may provide an effective, naturally‐derived insecticide for use in agricultural systems against dipteran pests.

Edge effects, tropical forests and invertebrates.

The term edge effect can be used to encompass a wide range of both biotic and abiotic trends associated with boundaries between adjacent habitat types, whether these be natural or anthropogenic. Edge effects have been shown to represent significant forces affecting both faunal and floral assemblages in fragmented ecosystems. Specific studies of faunal assemblages associated with habitat edges have revealed trends at all levels of biological organisation from individuals to communities.Studies of edge effects on invertebrates in tropical forests have been relatively scarce. In this paper we review the nature and organisation of edge effects, focusing upon the processes which may lead to detrimental consequences for both forest canopy invertebrates and the forests themselves. We present as a case study data illustrating the very large amount of variance (over 50%) in community structure that is predicted simply by abiotic (microclimatic) variables in both a tropical and a temperate forest edge. We summarise major features of edge effects amongst forest invertebrates, stress the inter-relatedness of edge and canopy biology, and present an agenda for study of the canopy as an edge.

Herbivore-induced infochemicals influence foraging behaviour in two intertidal predators

Herbivore-induced defences appear ubiquitous across most biomes and habitats. Yet the direct correlation between induced changes in host plant chemistry and the population dynamics of the herbivore remain untested in many systems. In plant–herbivore interactions in the terrestrial environment, indirect or tritrophic interactions appear a successful way in which changes in the host plant chemistry induced by prior herbivory can impact on herbivore populations via increased success of natural enemies. This set of interactions remains untested in the marine system. Here, we present work from experiments using orthogonal contrasts of plants with different prior treatments (control, mechanical damage or herbivory) and the presence or absence of herbivores on the foraging behaviour of a crab, Carcinus maenas, and a fish, Lipophrys pholis. These experiments were carried out using a novel flow-through flume, i.e. as a choice chamber supplied by turbulent water from independent cue sources. Our results show that in the Ascophyllum nodosum (plant)–Littorina obtusata (herbivore) system infochemicals from induced plants can directly influence predator foraging behaviour. L. pholis was attracted to the presence of a feeding L. obtusata, but was also more attracted to odours from herbivore-induced tissue than odours from mechanically damaged or naïve A. nodosum. C. maenas was more attracted to odours from herbivore-induced tissue compared to naïve tissue, regardless of the presence of L. obtusata. This is the first demonstration of such behavioural consequences of herbivore-induced changes in plants for marine systems.

Long- and short-term changes in plant growth following simulated herbivory : adaptive responses to damage ?

Much research has been conducted into the impact of defoliating insects on the subsequent growth and development of their host plants, both in terms of the consequences of herbivory for the plant (e.g. Ericsson et al.. 1980 Paige & Whitham, 1987), and also those for the insects (e.g. Haukioja & Niemalti, 1979), as the plant changes as a resource in response to damage. Often, however, these studies are concerned with responses over short time-scales. and may be limited in the facets of plant growth and physiology studied. This limits the scope and applicability of conclusions drawn from them. In contrast with studies of defoliation, those of damage to dormant structures in winter are scarce. Herbivore damage to plants’ dormant structures such as buds, during winter quiescence, differs from most instances of herbivory. The plants are less metabolically active. and the consequences of the damage are to an extent defrayed until the next growing season. In such an instance there is less opportunity for manifestation of short-term responses that influence herbivores, because the transport and synthesis of sap and metabolites may be restricted by climatic constrains and the plant’s pamrns of metabolic activity during dormancy (Essiamah & Escherich. 1985). The effects of damage to buds, however, may be of greater significance to the plant than damage to foliage, as the same buds represent ‘sinks’ of the previous season’s photosynthetic products (sensu Honkanen et al, 1994). and are the source of both foliage and reproductive structures. Buds are also known to be important in determining the growth patterns of trees through the suppressive effects of dominant apical meristems upon other tissues, and so herbivory of buds ofdifferent positions on twigs may have different effects upon both growth, and patterns of resource allocation within the bee (Haukioja et ul., 1990; Karban & Straws. 1993; Haukioja. 1996). Direct studies of the effects of herbivore damage upon the energetics and growth patterns of trees are tractable where herbivores are robust and easily manipulated, and where a degree of latitude in damage levels within treatments is acceptable. Where herbivores cannot be manipulated. or precise treatments are desired however, artificial damage may be substituted (Wright et d., 1989; Welter, 1991). Artificial damage normally takes the

Living in warmer, more acidic oceans retards physiological recovery from tidal emersion in the velvet swimming crab, Necora puber

The distribution patterns of many species in the intertidal zone are partly determined by their ability to survive and recover from tidal emersion. During emersion, most crustaceans experience gill collapse, impairing gas exchange. Such collapse generates a state of hypoxemia and a hypercapnia-induced respiratory acidosis, leading to hyperlactaemia and metabolic acidosis. However, how such physiological responses to emersion are modified by prior exposure to elevated CO2 and temperature combinations, indicative of future climate change scenarios, is not known. We therefore investigated key physiological responses of velvet swimming crabs, Necora puber, kept for 14 days at one of four pCO2/temperature treatments (400 μatm/10°C, 1000 μatm/10°C, 400 μatm/15°C or 1000 μatm/15°C) to experimental emersion and recovery. Pre-exposure to elevated pCO2 and temperature increased pre-emersion bicarbonate ion concentrations [HCO3−], increasing resistance to short periods of emersion (90 min). However, there was still a significant acidosis following 180 min emersion in all treatments. The recovery of extracellular acid–base via the removal of extracellular pCO2 and lactate after emersion was significantly retarded by exposure to both elevated temperature and pCO2. If elevated environmental pCO2 and temperature lead to slower recovery after emersion, then some predominantly subtidal species that also inhabit the low to mid shore, such as N. puber, may have a reduced physiological capacity to retain their presence in the low intertidal zone, ultimately affecting their bathymetric range of distribution, as well as the structure and diversity of intertidal assemblages.