Role of infochemical mediated zooplankton grazing in a phytoplankton competition model

Infochemicals released by marine phytoplankton play important roles in food web interactions by influencing the feeding behavior and selectivity of zooplanktonic predators. Recent modeling efforts have focused on the role of such chemicals as toxic grazing deterrents in phytoplankton competition. However, infochemicals may also be utilized as grazing cues, leading predators to profitable foraging patches. Here we investigate the role of infochemical mediated zooplankton grazing in a standard 3-species phytoplankton competition model, with the aim of further elucidating the ecological role of phytoplankton derived infochemicals. We then extend this to consider a more realistic 4-species model. The models produce a range of solutions depending on the strength of competition and microzooplankton grazing selectivity. Our key result is that infochemical chemoattractants, which increase the susceptibility of the producer to grazing, can provide a refuge for both competing phytoplankton species by attracting carnivorous copepods to consume microzooplankton grazers in a multi-trophic interaction. Our results indicate that infochemicals potentially have important consequences for the dynamics of marine food webs. © 2012 Elsevier B.V

The effect of oil sands process-affected water and model naphthenic acids on photosynthesis and growth in Emiliania huxleyi and Chlorella vulgaris

Naphthenic acids (NAs) are among the most toxic organic pollutants present in oil sands process waters (OSPW) and enter marine and freshwater environments through natural and anthropogenic sources. We investigated the effects of the acid extractable organic (AEO) fraction of OSPW and individual surrogate NAs, on maximum photosynthetic efficiency of photosystem II (PSII) (FV/FM) and cell growth in Emiliania huxleyi and Chlorella vulgaris as representative marine and freshwater phytoplankton. Whilst FV/FM in E. huxleyi and C. vulgaris was not inhibited by AEO, exposure to two surrogate NAs: (4'-n-butylphenyl)-4-butanoic acid (n-BPBA) and (4'-tert-butylphenyl)-4-butanoic acid (tert-BPBA), caused complete inhibition of FV/FM in E. huxleyi (≥10 mg L-1 n-BPBA; ≥50 mg L-1 tert-BPBA) but not in C. vulgaris. Growth rates and cell abundances in E. huxleyi were also reduced when exposed to ≥10 mg L-1 n- and tert-BPBA; however, higher concentrations of n- and tert-BPBA (100 mg L-1) were required to reduce cell growth in C. vulgaris. AEO at ≥10 mg L-1 stimulated E. huxleyi growth rate (p ≤ 0.002), yet had no apparent effect on C. vulgaris. In conclusion, E. huxleyi was generally more sensitive to NAs than C. vulgaris. This report provides a better understanding of the physiological responses of phytoplankton to NAs which will enable improved monitoring of NA pollution in aquatic ecosystems in the future

A Comparative Investigation into the Foraging Behaviour of the Intertidal Limpet eel/ana tramoserica on Artificial Seawalls and Natural

Artificial seawalls are becoming increasingly common in marine and estuarine intertidal habitats. These structures are replacing natural habitats at an alarming rate. Previous studies have identified that the species found on artificial seawalls differ from the assemblages found on natural rocky shores. Very few studies have examined if the behaviours exhibited by species living on seawalls differ from the behaviours of species living on natural shores. This study examines the foraging behaviour of the ecologically important grazing limpet Cellana tramoserica in an attempt to determine if the behaviour of this species is consistent between natural rocky shores and seawalls. Limpets were tracked throughout high tide and several components of their behaviour were analysed. Additionally, chlorophyll a concentration and surface rugosity measures were taken to try and identify the underlying causes of any variation in observed behaviour. This study was done within Sydney Harbour, New South Wales, Australia where 50 % of the shore-line is composed of artificial seawalls. Chlorophyll a concentration was shown to have a more patchy distribution at spatial scales of lOs of centimetres on rocky shores and the surface rugosity was also greater on rocky shores in comparison to seawalls. No significant differences in the total distance travelled during foraging excursion or the direction of foraging routes were identified between the two shores. There were, however, differences in rasping behaviour with rocky shore limpets showing far greater variance in the rate of rasping. This study provides further evidence that artificial seawalls can not be regarded as surrogates for natural rocky shores. KEY WORDS: Seawalls . Artificial structures . Intertidal . Foraging Behaviour . Limpet . Cellana tramoserica . Urban ecologySchool of Biological Sciences, The Centre for Research on Ecological Impacts of Coastal Cities, University of Sydney, Australi

An introduction to the special issue: Oxyrrhis marina, a model organism?

Many “model” protists are maintained in culture and used, experimentally, to answer questions associated with planktonic processes. Given the current interest and rapidly increasing amount of literature on the heterotrophic dinoflagellate Oxyrrhis marina, we present in this special issue a series of focused, interlinked research articles. Being written by experts in their respective fields, the authors have included unpublished data and in all cases have offered a synthesis of data and ideas. Furthermore, we have encouraged cross-paper discourse, emphasizing the interdisciplinary nature of our work and the utility of O. marina to this end; we also offer guidance, both practical and intellectual, on how future research related to O. marina might progress. In this introduction, however, we raise the wider issue of which criteria are required to consider a taxon as a “model species”. We then assess the extent to which O. marina can fill this role. In general, we recognize O. marina as a model in three distinct disciplines: ecology, evolution/genomics and biogeography. Of possibly greater importance, we recognize that if O. marina continues to be studied at an escalating rate, there will be a concomitant increase in realized and potential synergies across these fields