Elsevier

Ocean & Coastal Management

Volume 182, 1 December 2019, 104926
Ocean & Coastal Management

On the effects of recreational SCUBA diving on fragile benthic species: The Portofino MPA (NW Mediterranean Sea) case study

https://doi.org/10.1016/j.ocecoaman.2019.104926Get rights and content

Highlights

  • Evaluation of SCUBA diving effects on calcified, fragile species.

  • Comparison among two frequented and two pristine sites in the Portofino MPA.

  • Impact assessed comparing specimens' abundance on cliff and in underlying sediment.

  • Target species fragments in sediments 10 times higher in highly frequented dive spots.

  • MPA management urges to find a balance between fruition and mitigation of impacts.

Abstract

The main aims of Marine Protected Areas (MPAs) are the conservation of natural habitats and their biological resources, together with the promotion of an eco-compatible economic fruition. In Mediterranean MPAs, the main threats for hard bottom benthic communities come from fishing and mass tourism, in terms of boating and SCUBA diving.

The Portofino MPA (Ligurian Sea, North-western Mediterranean Sea) is one of the top diving destinations in Europe and currently hosts an average of 40,000 dives per year, which are mainly carried out along coralligenous cliffs, a habitat of European Community interest, particularly vulnerable to mechanical damages due to the fragility of its numerous calcified species.

The aim of this paper is to evaluate the effects of recreational SCUBA diving on benthic ecosystems characterised by the presence of red coral and other associated fragile species. The impact was assessed through the analysis of the biomasses of target organisms (Corallium rubrum, Leptopsammia pruvoti, Madracis pharensis, and six species of bryozoans) whose fragments were found in the sediments at the base of the cliff. The amounts of these fragments inside the detritus in highly frequented sites were significantly higher than those measured in undisturbed sites, of up to 10 times. Our data suggested a recurrent mechanical action, with also very recent breakages, as demonstrated by the occurrence of living, freshly detached organisms.

Red coral and other calcified species may be sensitive also to natural (heavy storms) and human (fishing) mechanical pressures other than diving: the characterization of these impacts in the study sites, however, indicates divers frequentation as the major contributor to the damages inflicted and suggests the need for specific management measures.

Introduction

The major goals of Marine Protected Areas (MPAs) are the preservation of the local ecosystems and their biological resources as well as the promotion and the enhancement of the anthropic activities related to the sea fruition, whenever they are compatible with the conservation purposes. Within the borders of coastal MPAs, the integrity and composition of the benthic communities are threatened by a number of natural and anthropic impacts, whose intensity can be locally different (Milazzo et al., 2004; Di Franco et al., 2009; Venturini et al., 2017, 2019).

The health status of Mediterranean shallow-water benthic communities in the MPAs, generally located away from major sources of pollution, may suffer the effects of climate change, not only in terms of mass mortalities (Cerrano et al., 2000; Garrabou et al., 2009), but also as appearance and disappearance of species, determining long-term changes in structure and composition of benthic communities (Bertolino et al., 2016; Betti et al., 2017; Longobardi et al., 2017; Parravicini et al., 2013). Another natural impact is represented by the occasional storms that might change the structure of the benthic community as a whole (Teixidó et al., 2013). On the other hand, among the main anthropic threats are recognized artisanal (Lloret and Font, 2013; Bo et al., 2014) and recreational fishing activities (Font and Lloret, 2011; Venturini et al., 2017, 2019), as well as mass tourism in terms of boating (Milazzo et al., 2002) and SCUBA diving (Lucrezi et al., 2017). Since all these impacts might act together, often synergically, it is very difficult to disentangle the importance of each of them in a given situation (Di Franco et al., 2009).

In the Mediterranean Sea, the establishment of several MPAs in the last quarter of the past century, and their consequent positive effects on the naturality recovery of the habitat, favoured a strong increase of SCUBA diving activities (Cattaneo-Vietti and Bava, 2007; Cattaneo-Vietti and Tunesi, 2007; D'Anna et al., 2016; Milazzo et al., 2002). This activity, if well planned and controlled, is certainly compatible with habitat conservation goals and can reach also an important value for local economies (Badalamenti et al., 2000; Rodríguez-Rodríguez et al., 2015; Rees et al., 2015; Lucrezi et al., 2017). Everywhere, diving centres have arisen to cope with this flow, being divers willing to pay a ticket to dive inside the borders of marine reserves, and, in turn, convincing stakeholders of the need to maintain a pristine environment (Jentoft et al., 2012).

SCUBA diving, though, is no immune to some side-effects, the most evident of whom are easily detectable, in the Mediterranean Sea, in the hard substrate communities formed by sessile erected, calcified organisms, particularly within the coralligenous habitat (Ballesteros, 2006). A deterioration of these assemblages has been observed in different locations subjected to intense diving activities (Coma et al., 2004; Calvisi et al., 2003; Casoli et al., 2017; Garrabou et al., 1998; Linares et al., 2010; Luna-Pérez et al., 2009; Ros et al., 1985; Sala et al., 1996). These studies have been mainly focused on bryozoan populations, comparing diver-frequented and unfrequented sites, since these fragile organisms are particularly prone to mechanical injuries, also of slight entity. More recently, also other organisms, such as gorgonians and the ascidian Halocynthia papillosa (Linnaeus, 1767), have demonstrated to be very sensitive to diving impact (Luna-Pérez et al., 2010). These species are now considered reliable bioindicators to evaluate the status of coralligenous communities before the damages become not mitigatable (Coma et al., 2004).

Within the Mediterranean context, the Portofino Promontory (Ligurian Sea) and neighbouring towns (Santa Margherita Ligure, Camogli and Portofino) are target destinations for a worldwide international tourism, thanks to an optimal combination of historical, geographical and environmental features. Since the 1970s, the protection of these localities appeared to be necessary, due to various anthropic activities insisting in the area (Melegari, 1973; Sarà and Tortonese, 1974), and in 1999, the Portofino MPA was established, covering about 346 ha and 13 km of coastline. Three zones, characterized by a different accessibility and use, were defined and human activities, including yachting, boating, artisanal and recreational fisheries, and SCUBA diving, have been regulated and monitored ever since (Cappanera et al., 2012; Cattaneo-Vietti, 2006; Lucrezi et al., 2017; Molina-Canovas et al., 2016; Venturini et al., 2016, 2017; 2018; 2019).

Among others, Portofino MPA is one of the top SCUBA diving destinations in Europe (Cappanera et al., 2012; Cattaneo-Vietti, 2006). Currently, Portofino MPA hosts on average 40,000 dives per year, with a touristic flow not limited to summer season (Lucrezi et al., 2017).

Here, recreational dives are mainly carried out on coralligenous cliffs (Molina-Canovas et al., 2016), a habitat showing a great diversity and complexity, and listed as of European Community interest (Flora Fauna Habitat Directive 92/43/EC, 1170-1114 Code: reefs), being particularly vulnerable to mechanical damages, due to the fragility and low resilience of its calcified species (Ballesteros, 2006; Ingrosso et al., 2018).

The restrains currently carried out to manage the flow of divers in the Portofino MPA waters include only the limitation of the number of diving centres and boats and the interdictions of training divers in the sites characterized by coralligenous habitats. So, despite the high number of people involved in underwater activities, a limited attention has been given so far to their impact on benthic communities in the Portofino MPA, although this information is necessary to develop adequate management measures (Cattaneo-Vietti, 2006; Cattaneo-Vietti and Tunesi, 2007; Lucrezi et al., 2017).

The aim of this paper was to evaluate, by means of an indirect, innovative quantitative approach, the effects of diving frequentation on sites characterised by the presence of the precious red coral Corallium rubrum (Linnaeus, 1758) and other associated fragile, erect and calcified species. Indeed, being the selected dive sites of the Portofino MPA characterized by vertical cliffs, the gently sloping bottoms immediately at their base can be considered good natural collectors of the debris rolling-down the overhanging wall. Therefore, the impact was assessed through the quantification of the biomasses of broken organisms present in the sediments at the base of the cliffs at depths ranging between 35 and 45 m in sites subjected to different diving effort.

Section snippets

Sites description and anthropic impacts

To assess the possible sources of mechanical damages on the red coral assemblages of the Portofino MPA, attention has been addressed on four sites, 35–45 m deep, located along the southern cliffs of the Promontory, characterised by a wide presence of Corallium rubrum. The considered sites share both comparable S-SW exposure to the local wind regime, and main geomorphological features, with vertical walls overhanging a gently sloping detritic bottom; in this situation, it is possible to

Anthropogenic impacts

In the Portofino MPA, anchoring is forbidden everywhere in the B zone (Fig. 1A) and mooring is allowed only for buoys set up in defined points. Nets have to be placed away from the cliff and perpendicularly to it. Furthermore, recreational fishing impact can be considered negligible in the study sites: the B zone is practically inaccessible from land and fishing from boat is permitted only at depths greater than 40 m, off the studied zones. Additionally, spearfishing is totally forbidden inside

Discussion

The carbonatic species thriving in the Portofino MPA appear to be only moderately impacted by fishing and other potentially impacting human activities; nevertheless, some species, such as the red coral Corallium rubrum, which is the main constituent of the assemblages of 2 of the 4 studied sites, are of particular interest for diving activities, and as so they might face an impact derived from relevant and regular frequentation by SCUBA divers. The other principal constituent of the studied

Conclusions and management recommendations

Several sessile erected species can be a suitable proxy to assess the human impact site-to-site on the Mediterranean coralligenous communities. Among them, red coral, appeared to be a valid tool to quantify and monitor the protection effects inside the Portofino MPA. However, the use of these species as indicators must be coupled with a good evaluation of all the possible sources of impact, such as natural stochastic disturbance events, fisheries and anchoring impacts, trying to disentangle the

Declarations of interest

None.

Acknowledgements

This study was carried out thanks to the support of the direction and staff of the Portofino Marine Protected Area; their help was greatly appreciated. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

References (49)

  • M. Milazzo et al.

    Boat anchoring on Posidonia oceanica beds in a marine protected area (Italy, western Mediterranean): effect of anchor types in different anchoring stages

    J. Exp. Mar. Biol. Ecol.

    (2004)
  • S.E. Rees et al.

    The socio-economic effects of a Marine Protected Area on the ecosystem service of leisure and recreation

    Mar. Policy

    (2015)
  • D. Rodríguez-Rodríguez et al.

    Assessing the socioeconomic effects of multiple-use MPAs in a European setting: a national stakeholder perspective

    Environ. Sci. Policy

    (2015)
  • F. Badalamenti et al.

    Cultural and socio-economic impacts of Mediterranean marine protected areas

    Environ. Conserv.

    (2000)
  • E. Ballesteros

    Mediterranean coralligenous assemblages: a synthesis of present knowledge

    Oceanogr. Mar. Biol. Annu. Rev.

    (2006)
  • G. Bavestrello et al.

    Detritus rolling down a vertical cliff of the Ligurian Sea (Italy): the ecological role in hard bottom communities

    Mar. Ecol.

    (1991)
  • G. Bavestrello et al.

    Damage by fishing activities to the gorgonian coral Paramuricea clavata in the Ligurian Sea

    Aquat. Conserv.

    (1997)
  • G. Bavestrello et al.

    Long-term comparison of structure and dynamics of the red coral metapopulation of the Portofino promontory (Ligurian Sea): a case-study for a marine protected area in the Mediterranean Sea

    Mar. Ecol.

    (2014)
  • M. Bertolino et al.

    Changes and stability of a Mediterranean hard bottom benthic community over 25 years

    J. Mar. Biol. Assoc. U. K.

    (2016)
  • F. Betti et al.

    Over 10 years of variation in Mediterranean reef benthic communities

    Mar. Ecol.

    (2017)
  • L. Bramanti et al.

    Involvement of recreational scuba divers in emblematic species monitoring: the case of Mediterranean red coral (Corallium rubrum)

    J. Nat. Conserv.

    (2011)
  • G. Calvisi et al.

    Un metodo di valutazione dell’impatto dell’attività subacquea in un’area marina protetta sarda

    Biol. Mar. Mediterr.

    (2003)
  • V. Cappanera et al.

    Valutazione dell’impatto antropico legato alle attività svolte nell'Area Marina Protetta Portofino. Le attività di fruizione 2010-2011. Santa Margherita Ligure, Rapporto annuale AMP Portofino

    (2012)
  • R. Cattaneo-Vietti

    Stratégie de développement durable du tourisme sous-marin en Méditerranée. Etude sur le tourisme sous-marin dans l'Aire Marine Protégée de Portofino. Interreg III - B – SUBMED

    (2006)
  • Cited by (18)

    • Variability between observers does not hamper detecting change over time in a temperate reef

      2022, Marine Environmental Research
      Citation Excerpt :

      Both inhabitants and tourists also showed a significant increasing trend between 2000 and 2020. On the contrary, recreational diving, which can represent a threat to reef species (Betti et al., 2019), has not shown a substantial increase. Marine protected areas represent one of the most effective tools for conserving biodiversity and mitigating the effects of climate change (Scianna et al., 2018, 2019; Maestro et al., 2019), even if the impacts of sea water warming cannot be kept outside the boundaries of MPAs (Bruno et al., 2018).

    • Quotas regulation is necessary but not sufficient to mitigate the impact of SCUBA diving in a highly visited marine protected area

      2022, Journal of Environmental Management
      Citation Excerpt :

      This, in turn, can potentially jeopardize the socio-ecological wellbeing of the area. The occurrence of these negative effects means that it is crucial for managers and MPA practitioners to identify and monitor the possible sources of anthropogenic impacts for coastal habitats under protection, in order to develop and adopt measures that can minimize a further worsening of the socio-ecological status of the MPA (Betti et al., 2019). In this respect, the adoption in the CPMR of a new regulation based on quotas and the redistribution of the diving pressure to newly opened sites showed promising results for the mitigation of diving impacts, potentially representing a positive example for other tourism hotspots, especially if protected.

    • Tourist carrying capacity as a sustainability management tool for coral reefs in Caño Island Biological Reserve, Costa Rica

      2021, Ocean and Coastal Management
      Citation Excerpt :

      Therefore, the quantification and application of the CC in Caño Island becomes key in increasing the corals’ resiliency to bleaching events as well as incrementing their reproduction success (Strain et al., 2019; Alvarado et al., 2020). Furthermore, it helps turn tourism into a major conservation tool given that it allows visitors to see directly the protection effects of a MPA (Betti et al., 2019) and convinces stakeholders of the need to properly manage and protect these environments (Jentoft et al., 2012). Lastly, the CC calculated for Caño Island will serve as an active management tool for the balanced use of resources, aid in marine spatial planning, and support initiatives such as coral restoration and monitoring.

    • Fate of lost fishing gears: Experimental evidence of biofouling colonization patterns from the northwestern Mediterranean Sea

      2021, Environmental Pollution
      Citation Excerpt :

      Overall, erect bryozoans are a good proxy for ALDFGs age estimation. However, this group is considered fragile and growth rates may be affected by mechanical issues, such as detachment or breakage (Casoli et al., 2017; Betti et al., 2019). In addition, at these depths, summer temperature anomalies may lead to severe mortality events as frequently reported in the Ligurian Sea in the past 20 years (Cerrano et al., 2000; Schiaparelli et al., 2007; Garrabou et al., 2009; Rivetti et al., 2014).

    • Reteporella spp. success in the re-colonization of bare coralligenous reefs impacted by Costa Concordia shipwreck: The pioneer species you did not expect

      2020, Marine Pollution Bulletin
      Citation Excerpt :

      Erect bryozoans are sensitive to nutrients, sediment depositions, and mechanical pressures: these disturbance factors reduce colony size increasing partial mortality (Garrabou et al., 1998; Deter et al., 2012; Casoli et al., 2017b;). Results from control sites are consistent with Reteporella demographic structure described in other studies (Casoli et al., 2017b, 2020): the size distribution may indicate both continuous recruitment episodes and a control of scuba diving activities, that through mechanical disturbance affect population structure (Betti et al., 2019) and do not allow the colonies to reach bigger size. Bare surfaces revealed after the sediment and debris removal represent unique substrates to study the natural recovery of coralligenous assemblages and comprehend the community succession patterns.

    View all citing articles on Scopus
    View full text