Unexpected patterns of facilitatory grazing revealed by quantitative imaging

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On artificial surfaces (seawalls) in Sydney Harbour (Australia), local biodiversity of grazers differs between sandstone and concrete constructions because limpets Siphonaria denticulata are more abundant on sandstone, while Patelloida latistrigata are more abundant on concrete walls. Competition between siphonarian and patellid limpets is unstudied on artificial structures, although the limpets are common and are known to compete in natural habitats. We tested hypotheses that the substratum (concrete or sandstone), intra-and/or interspecific competition, or a combination of factors, influence recruitment, survival, rates of grazing, or the quantity and types of algal food to explain the observed patterns. Such analyses enable better understanding of the processes influencing diversity. Both species recruited more to concrete than to sandstone plates. S. denticulata recruited more in the presence of conspecifics and slightly less in the presence of P. latistrigata. Results varied between locations and experiments, but each species survived better on concrete, which had more macro-and micro-algal food. Increased densities of P. latistrigata reduced survival of conspecifics and of S. denticulata. S. denticulata had no effect on survival of P. latistrigata, but reduced amounts of macro-algae. P. latistrigata did not affect macro-algae. Initially, there were more micro-algae on concrete and a minor effect of large densities of S. denticulata. After 95 d, differences between habitats decreased and P. latistrigata were more strongly associated with reduced amounts of micro-algae. Neither substratum, density, nor mix of limpets affected rates of grazing. Thus, interspecific interactions were similar to predictions from knowledge of natural habitats, despite the different characteristics of artificial habitats and the reduced intertidal area available for grazing. Recruitment and competition were important in explaining different densities of these limpets on sandstone and concrete walls. Increasing urbanization requires more experimental tests to identify how well current theories of intertidal ecology and of the processes maintaining local biodiversity can apply to artificial shorelines.

Section: Discussionmentioning

confidence: 99%

Differential patterns of distribution of limpets on intertidal seawalls: experimental investigation of the roles of recruitment, survival and competition

Iveša¹,

Chapman²,

Underwood³

et al. 2010

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“…Recently developed techniques using digital colour-infrared (CIR) imaging for non-destructive quantitative measurements of algae have improved such investigations , Underwood & Murphy 2008. Field spectrometry can also quantify amounts of different pigments in biofilms in situ, providing information on the composition of the algal assemblage (Murphy et al 2005a).…”

Section: Open Pen Access Ccessmentioning

confidence: 99%

Patiriella exigua: grazing by a starfish in an overgrazed intertidal system

Jackson¹,

Murphy²,

Underwood³

2009

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Intertidal rocky shores in south-eastern Australia are dominated by a diverse assemblage of grazing invertebrates that feed on micro-algal biofilms. This resource is spatially variable and frequently over-grazed, causing strong inter-and intra-specific competition among grazers. Most studies on intertidal grazing are about gastropod molluscs. We observed, however, damaged patches in intertidal biofilms that appeared to be associated with the herbivorous asterinid starfish Patiriella exigua (Lamarck). In contrast with predatory starfish, there have been few ecological studies about herbivorous starfish, even though they are often abundant. We demonstrated that these patches were caused by grazing by this starfish. We then used field-based remote-sensing methods to demonstrate that amounts of chlorophyll were reduced inside grazing marks, quantified these changes and measured their longevity. In experiments, starfish could graze up to 60% of the epilithic micro-algae beneath their everted stomach during a single feeding event lasting on average 22 min. Over 5 d, 2 caged starfish could remove nearly half of the available micro-algae from areas of 144 cm 2 . Changes to the amounts of chlorophyll in grazing marks were persistent, remaining visible on sandstone substrata for several weeks. Amounts of chlorophyll on grazed areas of substratum were significantly different from ungrazed areas up to 28 d after being grazed. Recovering areas were demonstrated to be bio-equivalent to ungrazed areas after a similar period. Thus, P. exigua can have a large effect on the temporal and spatial distribution of micro-algal food, with numerous possible consequences for intertidal assemblages. The ecological importance of herbivorous starfish may be greater than previously perceived.KEY WORDS: Herbivore · Intertidal · Echinoderm · Micro-algae · Spatial heterogeneity · Chlorophyll · Food 376: 153-163, 2009 species, persistence of poorer competitors may be dependent on physical heterogeneity in the distribution of resources (Fletcher & Underwood 1987, Fransen et al. 2001. Heterogeneous dispersion of resources can also support greater densities of organisms (Doncaster 2001). Resale or republication not permitted without written consent of the publisher OPEN PEN ACCESS CCESSMar Ecol Prog SerSettlement of the dispersive larvae of many sessile invertebrates (e.g. barnacles, oysters) is also influenced strongly by amounts and types of biofilm (Keough & Raimondi 1995, 1996, Wieczorek & Todd 1998. Thus, grazers altering the amounts, types and distributions of biofilms also affect patterns of settlement and subsequent assemblage structure.Grazing on micro-algae also removes the early stages of development of macro-algae, preventing the growth of foliose macro-algae, which has numerous effects on the diverse assemblages in these habitats (reviewed in Hawkins & Hartnoll 1983). Where the early microscopic phases of life history are not removed by grazing, fleshy, branched algae grow, smothering sessile animals, such as barnacles (B...

“…These studies suggested that plates covered with SWT could be a useful way to manipulate temperature at a single intertidal height on rocky shores and to test for effects on early life history processes. Such an experimental manipulation would also benefit from recently developed infrared imaging techniques used to quantify fine-scale variation in both physical and biological characteristics of rocky intertidal shores (Murphy et al 2006, Underwood & Murphy 2008, Chapperon & Seuront 2011, Cox & Smith 2011. The advantage of such infrared sensing is that temperature variability can be assessed at spatial scales relevant to newly settled benthic marine invertebrates.…”

Section: Introductionmentioning

confidence: 99%

Manipulating thermal stress on rocky shores to predict patterns of recruitment of marine invertebrates under a changing climate

Lathlean¹,

Minchinton²

2012

For rocky intertidal organisms, temperature is often considered the most influential factor governing early survival and growth. Nevertheless, our review of the literature revealed that few studies have manipulated temperatures in the field to test for effects on these critical early life history processes. Here, we present the results from a novel manipulation of substratum temperature using settlement plates of different colour (black, grey and white) and infrared measurements of temperature to test hypotheses that temperature influences the early survival and growth of recent settlers of the intertidal barnacle Tesseropora rosea. Mean surface temperatures of black and grey plates were as great as 5.8°C (on average 2.2°C) and 4.8°C (on average 1.6°C) hotter than white plates across the sampling period, respectively. Cooler, white plates had significantly greater settlement and early growth than hotter, black plates, but differences in plate temperature did not significantly influence early survival or recruitment, though patterns were consistent with thermal variability. Comparisons between grey coloured natural rock and plates indicate that grey plates thermally mimic natural rock. Nevertheless, on average, more than twice as many larvae settled on plates than on natural rock, but early post-settlement survival on natural rock was double that on plates, suggesting that this artificial surface may not adequately capture the natural variability in early life history processes. Regardless, our simple and repeatable thermal manipulation represents a useful tool for experimentally investigating the effects of temperature on recruitment processes and simulating future temperature variability associated with climate change.