Page 3 - Preprint_2014

45° Congresso della Società Italiana di Biologia Marina
Venezia, 19-23 maggio 2014
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Two linear regressions analyses were performed, the first between the average density
of all limpets in each site and the rank of accessibility of the site itself, a second
analisys was run between the density of the individuals with a diameter greater than
18.1 mm and the rank of accessibility of the site.
Results - The average density of Patella in the examined localities was 10.08±7.11
2
individuals per 400 cm . The lowest value was recorded in Barcarello (1.3±1.42),
within the “Capo Gallo – Isola delle Femmine” Marine Protected Area, and the highest
one in Monte Cofano Coastal Reserve (24.2±10.98). Considering all the individuals
into the plots, no relation was shown by regression analysis between limpet density and
2
accessibility (R =0,00004; p>0,05). Considering only larger individuals, the relation
2
between density and accessibility was significant (R =0,381; p<0,05), with again the
lowest density recorded in Barcarello (0) and the highest one in Monte Cofano (8.6 ±
1.82).
Conclusions - A non exploited population of Patella ulyssiponensis can be considered
well structured when the relation between males, females and undifferentiated follow
the ratio 2.3:1.3:1 (McCarthy et al., 2008), so 51% should be males, 28% should be
females and 21% should be undifferentiated. Our populations showed an imbalance of
sex ratio, with 61.5% of males, 0% of females and 38.5% of undifferentiated
individuals in Barcarello, and with 91% of males, 2.5% of female and 6.5% of
undifferentiated in Monte Cofano. The only location that showed a quite-balanced sex
ratio was Favignana, with 61.6% of males, 34.2% of females and 4.2% of
undifferentiated.
The results of this study show that all the examined limpet populations are impacted by
size-selective harvesting, becoming susceptible to “recruitment overfishing” (Santos et al.
1995) due to distortion of the sex ratio by removal of the larger females, especially during
Summer, when the coasts are more frequented. Then harvest pressure is able to change
population structure and, consequently, it alters ecosystem functions.

References
MARTINS G.M., JENKINS S.R., HAWKINS S.J., NETO A.I., THOMPSON R.C. (2008) -
Exploitation of rocky intertidal grazers: population status and potential impacts on community
structure and functioning. Aquatic Biology, 3: 1–10.
MCCARTHY M., WOOSNAM P., CULLOTY S.C. (2008) - Histological investigation of the
reproductive cycles of the limpets Patella vulgata and Patella ulyssiponensis. Marine Biology, 153:
871–877.
THOMPSON G.B. (1979) - Distribution and population dynamics of the limpet Patella aspera
(Lamarck) in Bantry Bay. Journal of Experimental Marine Biology and Ecology. 40: 115-135.
SANTOS R.S., HAWKINS S.J., MONTEIRO L.R., ALVES M., ISIDRO E.J. (1995) - Marine
research, resources and conservation in the Azores. Aquatic Conservation: Marine and Freshwater
Ecosystems, 5: 311-354.

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