On the Ecology and Conservation of Marine Endangered Species, Pinna nobilis (Linnaeus, 1758) and Patella ferruginea (Gmelin, 1791), in the Marine Protected Area of Penisola del Sinis - Isola di Mal di Ventre (western Sardinia, Italy)
Author(s)
Coppa, Stefania
Date Issued
March 20, 2012
Type
Doctoral Thesis
Abstract
Marine Protected Areas (MPAs) have been established to protect vulnerable species and habitats, to conserve biodiversity, to restore ecosystem integrity, to avoid user conflicts and to enhance the productivity of fish and invertebrate populations in the neighbouring zones. Often the lack of information on the species ecology can limit or make void the existing management measures. One of such cases is the Penisola del Sinis - Isola di Mal di Ventre MPA (hereafter Sinis MPA) which was instituted in 1997 in order to protect the local marine resources. This thesis, carried out in the Sinis MPA, was aimed at increasing the knowledge on the distribution, abundance and ecological traits of two endangered species, the molluscs Pinna nobilis and Patella ferruginea, as fundamental prerequisites for their management and conservation. These species were considered both for their conservation priority and because molluscs are commonly considered good indicators of MPA effectiveness.
The fan mussel P. nobilis is the largest bivalve of the Mediterranean Sea (it can exceed one meter in length). P. nobilis is a sessile suspension feeder endemic of this basin which lives in coastal areas, mainly on soft sediments colonized by seagrass meadows. In the last few decades, P. nobilis populations have declined drastically due to increasing anthropogenic pressure. Thus, P. nobilis has been declared a protected species since 1992. This study considered a population living within a Posidonia oceanica meadow in the Gulf of Oristano, a partially protected Zone of the Sinis MPA. Based on field surveys conducted in the summer of 2007 and 2009, differences in density, percentage of dead individuals, population structure, shell burial level and orientation of P. nobilis were investigated in relation to sites features (e.g. seabed compactness) and habitat type (P. oceanica, dead matte, sand, P. oceanica edge). Moreover, it was tested if spatial differences in density and orientation of P. nobilis were related to hydrological features such as wave height, wave direction, bottom current direction and speed. Although fairly widespread in the whole Sinis MPA, this species showed a remarkable density only within the Gulf of Oristano with mean value of 1 ind.100 m-2, in line with the majority of the Mediterranean populations. The substrate type resulted a considerable factor in defining P. nobilis distribution with significant higher density values on the meadow edge which was considered the most suitable habitat for P. nobilis. The substrate type and particularly its compactness influences also the shell stability; in fact, the burial level of individuals decreases with increasing fine sediments. A specimen not sufficiently deeply buried can be more susceptible to predation and hydrodynamics. In addition, it was demonstrated that bottom current direction and speed are the main factors influencing shell orientation. In contrast, the effect of wave action was found to be negligible. Where bottom current speed exceeded 0.07 m/s specimens resulted in line with the prevalent current direction with the ventral side exposed to incoming flow. This feature suggests that feeding strategy is an important factor in determining shell orientation, possibly in addition to drag. Moreover, it was assumed that the lagoon waters (Cabras and Mistras lagoon) and the sedimentation areas (e.g. gyre located in the site of Tharros) play a key role in determining high density of P. nobilis. Indeed, the food availability seem to be a driving force in determining the patchiness distribution of P. nobilis population with higher values in those sites close to the mouth of the lagoons, in sedimentation area or in the meadow channels where the water flow is conveyed. The second endangered species considered in this thesis is P. ferruginea, an endemic limpet of the Mediterranean Sea. P. ferruginea, the biggest limpet of the Mediterranean Sea (up to 10 cm), is mostly affected by human exploitation. Moreover, considering that P. ferruginea is a protandrous species, human predation directly affects the sex ratio and, consequently, the reproductive population success. Due to the severe contraction of its geographic range and to the high vulnerability of the remaining populations, this invertebrate is actually considered the most threatened with extinction of the Mediterranean basin. Sardinia is one of the few areas where specimens of Patella ferruginea can still be observed. Despite the importance of this region for its protection, the available information on the distribution and conservation of Sardinian populations was substantially absent prior to this study. To fill this lack of information the population of P. ferruginea living within the Sinis MPA was examined. In particular, during the summer 2009, a systematic census of P. ferruginea was carried out along a 8114 m georeferenced perimeter of coast in the no take-no entry zone of the Mal di Ventre Island. The aim was to provide a detailed map of the distribution of P. ferruginea (and of its morphotypes i.e. Rouxi and Lamarki form) and to investigate the effects of accessibility, exposure and slope of the coast on its occurrence. The studied population showed the lowest average density (0.02 ind./m) ever reported for this species, confirming the highly endangered status of P. ferruginea on Sardinia rocky shores. Moreover the lack of largest females (>80 mm) indicate a low reproductive potential supported by the limited presence of small specimens (<30 mm). These results constitute the first evidence of the extinction threat of P. ferruginea in the Sinis MPA and, probably, along the whole western Sardinian coast where no other large breeding population has been described. This study also demonstrated that the main constraint affecting the population success in the Mal di Ventre Island is human exploitation in relation to the accessibility of the coast. Illegal catches cause the low population density and the absence of largest individuals (>80 mm) which constitute the common fishing target, even though the study area is a no take-no entry zone. Also the exposure of the coast resulted a noteworthy factor in influencing the density and mean size of P. ferruginea as well as the distribution of its two morphotypes. Higher density and mean size were recorded on north-western exposed coast were Lamarki form is significantly confined. These findings suggest that a strong wave motion can support a higher percentage of the existing population including the less adaptable morphotype (Lamarki). However, this pattern could be largely influenced by the human exploitation which is lower at the exposed site. Overall, this thesis contributed to increase the knowledge of population ecology of P. nobilis and P. ferruginea. In particular, new information on the P. nobilis-P. oceanica association and the conservation status of the local population of P. ferruginea was described, providing useful advices for the management and conservation of these species and their habitat. This work also showed how an inadequate surveillance, combined with a lack of environmental awareness, can lead to limit the effectiveness of a MPA as a flagship tool of marine conservation. This issue is particularly noticeable for P. ferruginea whereas P. nobilis population appears to be less vulnerable to the local anthropogenic impact. Our results are in line with previous studies conducted in other MPAs showing that a large proportion of Italian Marine Protected Areas receive ineffective enforcement. A new strategy for the national MPAs, where major efforts are invested in public information and participation promotion on the decision making process, is needed. Thus, Italy should concentrate more on enforcing regulations within the MPAs equipping them with surveillance staff than in establishing of new marine reserves. Finally, the findings of this study provided scientific-based recommendations to the local authorities in order to reinforce the management of biological resources in the Sinis MPA. This has prompted the issue of a ministerial decree (M.D. 20/07/2011) for the enlargement of the Sinis MPA in the area colonized by P. nobilis. Specific awareness campaigns have also been conducted on the conservation of the studied species and a regional network, aimed at defining a common conservation strategy for both species, has been established.
The fan mussel P. nobilis is the largest bivalve of the Mediterranean Sea (it can exceed one meter in length). P. nobilis is a sessile suspension feeder endemic of this basin which lives in coastal areas, mainly on soft sediments colonized by seagrass meadows. In the last few decades, P. nobilis populations have declined drastically due to increasing anthropogenic pressure. Thus, P. nobilis has been declared a protected species since 1992. This study considered a population living within a Posidonia oceanica meadow in the Gulf of Oristano, a partially protected Zone of the Sinis MPA. Based on field surveys conducted in the summer of 2007 and 2009, differences in density, percentage of dead individuals, population structure, shell burial level and orientation of P. nobilis were investigated in relation to sites features (e.g. seabed compactness) and habitat type (P. oceanica, dead matte, sand, P. oceanica edge). Moreover, it was tested if spatial differences in density and orientation of P. nobilis were related to hydrological features such as wave height, wave direction, bottom current direction and speed. Although fairly widespread in the whole Sinis MPA, this species showed a remarkable density only within the Gulf of Oristano with mean value of 1 ind.100 m-2, in line with the majority of the Mediterranean populations. The substrate type resulted a considerable factor in defining P. nobilis distribution with significant higher density values on the meadow edge which was considered the most suitable habitat for P. nobilis. The substrate type and particularly its compactness influences also the shell stability; in fact, the burial level of individuals decreases with increasing fine sediments. A specimen not sufficiently deeply buried can be more susceptible to predation and hydrodynamics. In addition, it was demonstrated that bottom current direction and speed are the main factors influencing shell orientation. In contrast, the effect of wave action was found to be negligible. Where bottom current speed exceeded 0.07 m/s specimens resulted in line with the prevalent current direction with the ventral side exposed to incoming flow. This feature suggests that feeding strategy is an important factor in determining shell orientation, possibly in addition to drag. Moreover, it was assumed that the lagoon waters (Cabras and Mistras lagoon) and the sedimentation areas (e.g. gyre located in the site of Tharros) play a key role in determining high density of P. nobilis. Indeed, the food availability seem to be a driving force in determining the patchiness distribution of P. nobilis population with higher values in those sites close to the mouth of the lagoons, in sedimentation area or in the meadow channels where the water flow is conveyed. The second endangered species considered in this thesis is P. ferruginea, an endemic limpet of the Mediterranean Sea. P. ferruginea, the biggest limpet of the Mediterranean Sea (up to 10 cm), is mostly affected by human exploitation. Moreover, considering that P. ferruginea is a protandrous species, human predation directly affects the sex ratio and, consequently, the reproductive population success. Due to the severe contraction of its geographic range and to the high vulnerability of the remaining populations, this invertebrate is actually considered the most threatened with extinction of the Mediterranean basin. Sardinia is one of the few areas where specimens of Patella ferruginea can still be observed. Despite the importance of this region for its protection, the available information on the distribution and conservation of Sardinian populations was substantially absent prior to this study. To fill this lack of information the population of P. ferruginea living within the Sinis MPA was examined. In particular, during the summer 2009, a systematic census of P. ferruginea was carried out along a 8114 m georeferenced perimeter of coast in the no take-no entry zone of the Mal di Ventre Island. The aim was to provide a detailed map of the distribution of P. ferruginea (and of its morphotypes i.e. Rouxi and Lamarki form) and to investigate the effects of accessibility, exposure and slope of the coast on its occurrence. The studied population showed the lowest average density (0.02 ind./m) ever reported for this species, confirming the highly endangered status of P. ferruginea on Sardinia rocky shores. Moreover the lack of largest females (>80 mm) indicate a low reproductive potential supported by the limited presence of small specimens (<30 mm). These results constitute the first evidence of the extinction threat of P. ferruginea in the Sinis MPA and, probably, along the whole western Sardinian coast where no other large breeding population has been described. This study also demonstrated that the main constraint affecting the population success in the Mal di Ventre Island is human exploitation in relation to the accessibility of the coast. Illegal catches cause the low population density and the absence of largest individuals (>80 mm) which constitute the common fishing target, even though the study area is a no take-no entry zone. Also the exposure of the coast resulted a noteworthy factor in influencing the density and mean size of P. ferruginea as well as the distribution of its two morphotypes. Higher density and mean size were recorded on north-western exposed coast were Lamarki form is significantly confined. These findings suggest that a strong wave motion can support a higher percentage of the existing population including the less adaptable morphotype (Lamarki). However, this pattern could be largely influenced by the human exploitation which is lower at the exposed site. Overall, this thesis contributed to increase the knowledge of population ecology of P. nobilis and P. ferruginea. In particular, new information on the P. nobilis-P. oceanica association and the conservation status of the local population of P. ferruginea was described, providing useful advices for the management and conservation of these species and their habitat. This work also showed how an inadequate surveillance, combined with a lack of environmental awareness, can lead to limit the effectiveness of a MPA as a flagship tool of marine conservation. This issue is particularly noticeable for P. ferruginea whereas P. nobilis population appears to be less vulnerable to the local anthropogenic impact. Our results are in line with previous studies conducted in other MPAs showing that a large proportion of Italian Marine Protected Areas receive ineffective enforcement. A new strategy for the national MPAs, where major efforts are invested in public information and participation promotion on the decision making process, is needed. Thus, Italy should concentrate more on enforcing regulations within the MPAs equipping them with surveillance staff than in establishing of new marine reserves. Finally, the findings of this study provided scientific-based recommendations to the local authorities in order to reinforce the management of biological resources in the Sinis MPA. This has prompted the issue of a ministerial decree (M.D. 20/07/2011) for the enlargement of the Sinis MPA in the area colonized by P. nobilis. Specific awareness campaigns have also been conducted on the conservation of the studied species and a regional network, aimed at defining a common conservation strategy for both species, has been established.
Additional information
Dottorato di ricerca in Ecologia e gestione delle risorse biologiche
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