Quantification of the foraging activity of Patella caerulea and P. rustica under simulated tides using photographic analysis of radula scratches
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1
Department of Zoology, Faculty of Biology. University of Seville, Spain
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2
Department of Zoology, Faculty of Biology. University of Seville, Spain
Introduction
Limpets are one of the most important herbivorous grazers of temperate rocky shores. Their feeding activity promotes diversity and influences the structure and functioning of intertidal communities. In the current context of global change, harvesting pressures on accessible intertidal and habitat modifications caused by coastal urbanization are threatening these organisms in many coastal areas. In this regard, the improvement of ex situ maintenance techniques, combined with the understanding of limpets’ behavioural traits, would help to improve the effectiveness of conservation strategies and mitigation efforts.
The behaviour ecology of limpets in the natural environment is well understood (i.e. Patella caerulea activity is higher during spring tides and when splashed by moderate waves while P. rustica is more active when splashed during high-wave episodes) and the laboratory microcosm should reflect what we know about limpets in their natural environment. However, there are many issues in limpet aquaculture (either for commercial or conservational purposes), due to their sensitivity and ecological requirements, that remain unknown in laboratory conditions.
The aims of this study are to study the feeding activity of P. rustica and P. caerulea under simulated tides (spring and neap) and to describe a quick photographic method to quantify radulae marks, which would expedite samples treatment.
Methodology
Patella caerulea and P. rustica individuals of 2-3 cm length were obtained within a rip-rap structure in Algeciras, Spain (36°07'02.2"N, 5°26'07.6"W). After 10 days acclimation, limpets were placed in groups of five over 40 35 cm limestone plates (replicates) and introduced into the tanks with a 45º inclination for a period of 10 days (Fig. 1-A). For each species, four replicates were carried out under spring tides (24 cm tidal oscillations) and four under neap tides (8 cm tidal oscillations – Fig. 1-B). To record grazing activity, each replicate had 16 wax discs of 3 cm diameter (Fig. 1-C).
After the experiment, grazed wax discs were primed with black water-based paint (Fig. 1-D). After it dried, discs were re-painted using the dry brush technique with a second white primer to enhance the contrast of radula marks (Fig. 1-E). Then, discs were photographed and the images’ RGB layers, brightness and contrast were modified using Adobe© Photoshop to obtain monochromatic images representing radulae marks (Fig. 1-F). Marks that were not made by limpets were manually deleted from images. To obtain radula marks coverage, black area on images was measured using the “Analyze particles” tool of ImageJ© software. To erase small particles and pixels errors, a minimal particle size was set up and optimized for each image.
A two-way ANOVA was carried out using radula marks coverage data to test orthogonal factors Species (fixed, two levels: P. caerulea and P. rustica) and Tide (fixed, two levels: Spring and Neap). IBM® SPSS® Statistics 22 software was used to perform these analyses.
Results
During the experimental phase, three home-scar marks were found and two different radula scratch patterns observed over wax surfaces (Fig. 1-G). The first pattern was thick and highly covered with marks and the second was scattered and sinuous. Overall, the grazed area as coverage mean was 2.24% (SD: ± 1.41) of wax discs surface, being higher for P. caerulea (3.41%; ± 1.65) than for P. rustica (1.07%; ± 0.87 - Table 1). Intra-specific differences in feeding behaviour were detected only for P. caerulea, which grazed more actively during Spring than Neap tides. On the contrary, P. rustica grazing behaviour was not influenced by tide amplitude.
Discussion
The radula patterns found over wax surfaces match those described for the displacement and intensive grazing phases of limpets’ feeding excursions. In previous studies, P. caerulea showed circa-tidal rhythms under a scenario of simulated tides, which may reduce stress when compared with aquariums without tidal simulation. In this study, grazing activity of P. caerulea was also affected by tidal amplitude in a similar way as it occurs in natural areas. Therefore, tidal range should be taken into consideration when specimens of limpets are maintained in aquarium tanks.
Regarding the methodology used, wax discs were originally processed by identifying the mark patterns and estimating their coverage using a binocular microscope. In this regard, the proposed digitalization of the processing method would simplify the obtention of mark coverage, a heavy task avoided in subsequent studies after the original method proposed in 1997.
Acknowledgements
Acknowledgements
We want to express our greetings to the Aquarium of Seville and the Port of Seville, which helpfully granted the use of their facilities.
Keywords:
Patella,
Aquariums,
artificial tides,
photographic method,
Grazing activity
Conference:
XX Iberian Symposium on Marine Biology Studies (SIEBM XX) , Braga, Portugal, 9 Sep - 12 Sep, 2019.
Presentation Type:
Oral Presentation
Topic:
Ecology, Biodiversity and Vulnerable Ecosystems
Citation:
Sempere-Valverde
J,
Sedano
F,
Megina
C,
García-Gómez
JC and
Espinosa
F
(2019). Quantification of the foraging activity of Patella caerulea and P. rustica under simulated tides using photographic analysis of radula scratches.
Front. Mar. Sci.
Conference Abstract:
XX Iberian Symposium on Marine Biology Studies (SIEBM XX) .
doi: 10.3389/conf.fmars.2019.08.00164
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Received:
31 May 2019;
Published Online:
27 Sep 2019.
*
Correspondence:
Mr. Juan Sempere-Valverde, Department of Zoology, Faculty of Biology. University of Seville, Sevilla, Spain, juan.semperevalverde@kaust.edu.sa