Assassins and apples: the environmental constraints of two snails that threaten Australian aquatic systems

Context: Alien freshwater snails pose a substantial risk to Australian native aquatic biota.Aims: This study aims to determine the thermal and salinity ranges of two introduced species within Australia, Pomacea sp. and Anentome sp., to facilitate predictions of their potential geographic range should they become widely established.Methods: Laboratory tests were conducted to assess behavioural responses of snails to altered temperature or salinity after different acclimation regimes.Key results: After acclimation at 25°C, Pomacea sp. had a median activity range of 13.5–38°C and Anentome sp. of 12–38.5°C. Higher acclimation temperatures produced observable effects, whereas lower acclimation temperatures did not. Salinity tolerances differed, with Pomacea sp. remaining active at up to 8 parts per thousand (ppt) (after acclimation at 25°C), with acclimation at 20°C resulting in a lower salinity tolerance. By contrast, Anentome sp. snails were active at up to 5 ppt after low salinity acclimation, demonstrating enhanced salinity tolerance compared with non-salinity acclimations.Conclusions: These results showed that both snails are capable of surviving temperatures and salinities that would allow invasion into subtropical and warm-temperate Australian aquatic systems.Implications: Free from the constraints of natural predators, competitors, and parasites, these snails should be of great concern to biosecurity agencies in Australia

Water temperature and benthic light levels drive horizontal expansion of Caulerpa taxifolia in native and invasive locations

Caulerpa taxifolia is a marine alga native to tropical and subtropical regions, and invasive in temperate regions worldwide. The aim of this study was to quantify the impacts of water temperature, benthic light and nutrient enrichment on horizontal expansion of C. taxifolia, in the absence of competition from other benthic flora. Field experiments were undertaken in 1 native C. taxifolia population (Moreton Bay, Australia) and 2 invasive C. taxifolia populations (Pittwater and Port River Estuary, Australia). Manipulative experiments were conducted across a range of seasons and different shading and nutrient treatments to determine the effects of water temperature, benthic light dose and nutrient enrichment on horizontal expansion (stolon extension rate). Nitrogen and phosphorus enrichment had negligible effects on stolon extension rate at all locations, suggesting that nutrient conditions at the study sites were saturating for C. taxifolia. Shading significantly reduced stolon extension in Pittwater, and season/water temperature significantly affected stolon extension in Port River Estuary; only in Moreton Bay were both shading and season/water temperature significant. When all data were pooled in a general linear model, water temperature and average daily benthic light dose (log-transformed) significantly affected stolon extension, but nutrient enrichment did not. Site, season and the interaction between water temperature and benthic light dose also improved model performance, indicating that site-specific factors which varied between seasons also affected the measured stolon extension. Overall, our results indicate that C. taxifolia growth increased with light disproportionately at higher temperatures

A sand goby realizes its niche both at high population densities and in the presence of the half bridled goby

To test theories of resource segregation and coexistence, we studied 2 goby species: the eastern sand goby Favonigobius lentiginosus (which typically occupies soft sediment tidepools) and the half-bridled goby Arenigobius frenatus (typically found in nearby subtidal seagrass beds). We used mesocosm experiments to test the hypotheses that (1) occupation of tidepools by F. lentiginosus is a function of exclusion (i.e. realized niche) from subtidal habitats by A. frenatus rather than habitat preference (i.e. fundamental niche) and (2) intraspecific competition among F. lentiginosus may also play a role in their occupation of intertidal pools. In single-species experiments, single specimens of both A. frenatus and F. lentiginosus spent significantly more time in the seagrass habitat. When together in the same mesocosm, F. lentiginosus significantly altered its habitat use to sand, while A. frenatus used more detritus habitat. At higher densities in single-species experiments with F. lentiginosus, a significantly greater number of individuals used the apparently less desirable sand habitat. Habitat preferences displayed by gobies in the laboratory setting did not directly reflect their distribution in their natural habitat, suggesting that the use of soft sediment tidepools by F. lentiginosus may be a consequence of competition with A. frenatus for space in seagrass beds, causing the former to occupy their realized niche of sandy habitat

Better red than dead? Potential aposematism in a harpacticoid copepod, Metis holothuriae

The conspicuous, red harpacticoid Metis holothuriae grows to a large size (similar to 600 mu m length) and accounts for 29.51% of the numerical meiofaunal abundance within blooms of the toxic, benthic cyanobacterium Lyngbya majuscula. Despite this, the meiobenthic juvenile trumpeter whiting, Sillago maculata, consume M. holothuriae at only 2.16% of numerical meiofaunal biomass within simulated blooms, despite their apparent ease of predation. We compared the predation rates of copepods that had been dyed red (primarily Canuellidae and not known to be toxic) to M. holothuriae by S. maculata, to assess whether avoidance by predators is possibly a response to an aposematic signal conveyed by the colouration of the copepods and reinforced by their potential toxicity from exposure to L. majuscula. M. holothuriae were again strongly avoided, with only 6.25% of M. holothuriae consumed, whereas dyed copepods were consumed with relative alacrity, indicating that predation was not deterred by colouration alone. M. holothuriae copepodites were consumed in preference to adult individuals, supporting the idea that toxin accumulation or other factors relating to maturation might explain avoidance by benthivorous fishes. (C) 2011 Elsevier Ltd. All rights reserved

The effect of boat propeller scarring intensity on genetic variation in a subtropical seagrass species

We report here the effect of one form of disturbance, boat propeller scarring, on genetic variation in the subtropical seagrass Halodule wrightii. We developed an amplified fragment length polymorphism assay to measure genetic variation in plots representing four levels of scarring intensity: reference (0% scarring), low (1-5%), moderate (5-15%) and severe (>15%). Although we found severely scarred plots to have the lowest, and moderately scarred plots to have the highest, mean genetic diversity estimates (H, P), differences among scarring levels were found to be non-significant (α=0.05). Analysis of molecular variance also showed no significant effect of scarring intensity. While propeller scarring can cause significant habitat loss, scarring intensities of up to 20% may not yet have seriously affected those factors (population size, flowering density, recruitment, gene flow) that strongly influence population genetic variation. The relatively recent occurrence of this type of disturbance, however, could mean that any long-term effects have yet to be detected

Herbivory in a subtropical seagrass ecosystem: separating the functional role of different grazers

Seagrass meadows provide many important ecosystem services, but they are threatened by human activities and are in decline globally. In particular, eutrophication arising from human activities promotes algal growth, which negatively affects seagrass. Herbivores consume algae and can, therefore, reduce eutrophication effects, but they may also consume seagrass. Little is known, however, about grazer-epiphyte-seagrass interactions in subtropical seagrass in the Indo-Pacific. We used a 5 wk exclusion experiment to quantify the influence of different grazers in seagrass (dominated by Zostera muelleri) in Moreton Bay, eastern Australia. Our results show that herbivory does indeed affect seagrass-epiphyte dynamics in this region and that different grazers can exert different effects in seagrass ecosystems. In particular, exclusion of small mesograzers (i.e. amphipods and juvenile shrimp) caused epiphyte biomass to increase by up to 233%. Exclusion of medium mesograzers (i.e. small fish and prawns) resulted in increases of up to 10% in seagrass cover, 53% in shoot height and 29% in shoot density. Large mesograzers (i.e. adult fish) and macrograzers (i.e. turtles and dugong) did not appear to play a role in the study system. These results demonstrate that mesograzers can be important in controlling epiphytic algae in subtropical Indo-Pacific seagrass, and show that different mesograzers can affect seagrass-epiphyte dynamics in different ways. It is critical that the functional effects of different herbivores be considered when implementing programs for seagrass conservation and restoration

Assassins and apples : the environmental constraints of two snails that threaten Australian aquatic systems

Context : Alien freshwater snails pose a substantial risk to Australian native aquatic biota.  Aims : This study aims to determine the thermal and salinity ranges of two introduced species within Australia, Pomacea sp. and Anentome sp., to facilitate predictions of their potential geographic range should they become widely established.  Methods : Laboratory tests were conducted to assess behavioural responses of snails to altered temperature or salinity after different acclimation regimes.  Key results : After acclimation at 25°C, Pomacea sp. had a median activity range of 13.5-38°C and Anentome sp. of 12-38.5°C. Higher acclimation temperatures produced observable effects, whereas lower acclimation temperatures did not. Salinity tolerances differed, with Pomacea sp. remaining active at up to 8 parts per thousand (ppt) (after acclimation at 25°C), with acclimation at 20°C resulting in a lower salinity tolerance. By contrast, Anentome sp. snails were active at up to 5 ppt after low salinity acclimation, demonstrating enhanced salinity tolerance compared with non-salinity acclimations.  Conclusions : These results showed that both snails are capable of surviving temperatures and salinities that would allow invasion into subtropical and warm-temperate Australian aquatic systems.  Implications : Free from the constraints of natural predators, competitors, and parasites, these snails should be of great concern to biosecurity agencies in Australia.Publisher PDFPeer reviewe

Description of a new marine diatom, Cocconeis caulerpacola sp. nov. (Bacillariophyceae), epiphytic on invasive Caulerpa species

A new species of Cocconeis has been found growing on thalli of the invasive green alga Caulerpa taxifolia collected from the Croatian Adriatic Sea (Bay of Stari Grad, the Island of Hvar, Central Adriatic, Croatia), the coasts of the Mediterranean (Saint Raphaël, west of Cannes, France) and the eastern coast of Australia (Moreton Bay, southeast Queensland). Additionally, it was observed on samples of Caulerpa racemosa, another invasive alga in the Mediterranean. Preserved thalli of Caulerpa and cleaned material of the new diatom were studied by light and electron microscopy (SEM and TEM). The morphology and fine structure of the new marine epiphytic diatom, for which we propose the name Cocconeis caulerpacola Witkowski, Car &amp; Dobosz, was determined, including the internal and external structure of the raphe and sternum valve, and the cingulum. Comparison between the new species and three closely related species, C. borbonica, C. diruptoides and C. pseudodiruptoides, was made using material from our samples, as well as material from Vis (Adriatic Sea) obtained from the Hustedt collection. Surprisingly, C. caulerpacola is able to colonize Caulerpa taxifolia in very high abundance, but its occurrence seems to be strongly patchy. Indeed, it seems that C. taxifolia is a suitable host for epiphytic diatoms, in particular this tiny Cocconeis, despite its reputation as a 'killer seaweed'. Cocconeis caulerpacola was observed on Caulerpa species in varying abundance over a wide geographical range.</p

Human impacts on connectivity in marine and freshwater ecosystems assessed using graph theory: A review

Human activities are altering the processes that connect organisms within and among habitats and populations in marine and freshwater (aquatic) ecosystems. Connectivity can be quantified using graph theory, where habitats or populations are represented by \u27nodes\u27 and dispersal is represented by \u27links\u27. This approach spans discipline and systemic divides, facilitating identification of generalities in human impacts. We conducted a review of studies that have used graph theory to quantify spatial functional connectivity in aquatic ecosystems. The search identified 42 studies published in 2000-14. We assessed whether each study quantified the impacts of (1) habitat alteration (loss, alteration to links, and gain), (2) human movements causing species introductions, (3) overharvesting and (4) climate change (warming temperatures, altered circulation or hydrology, sea-level rise) and ocean acidification. In freshwater systems habitat alteration was the most commonly studied stressor, whereas in marine systems overharvesting, in terms of larval dispersal among protected areas, was most commonly addressed. Few studies have directly assessed effects of climate change, suggesting an important area of future research. Graph representations of connectivity revealed similarities across different impacts and systems, suggesting common strategies for conservation management. We suggest future research directions for studies of aquatic connectivity to inform conservation management of aquatic ecosystems. Journal compilatio