The Impact of Diving on Rocky Sublittoral Communities: A Case Study of a Bryozoan Population

Abstract

In 1992 a diving buoy was installed within a marine reserve off the northeastern coast of Spain, where diving had not previously been permitted. We monitored the effects of diving on a colonial bryozoan ( Pentapora fascialis ) and carried out the study on two distinct benthic habitats, boulders and vertical walls. We used a "beyond before-after/control-impact" sampling design in which one potentially affected and several control locations were sampled simultaneously before and after the installation of the diving buoy. We hypothesized that diving has three major impacts: (1) it decreases the density of P. fascialis , (2) it reduces the mean size of P. fascialis colonies, and (3) it restricts P. fascialis colonies to cryptic positions. Surveys of diving activity conducted from 1992 to 1995 showed that diving increased 60-fold at the impact location. Analysis revealed a significant decrease in density of colonies of P. fascialis ( ‫ف‬ 50% from 1992 to 1993) in both communites at the impact location 1 year after the start of the diving disturbance. The effect of diving on the size of colonies was not clear. The analysis revealed no general pattern of significant impact, although the impact location suffered a general loss of large colonies. P. fascialis colonies on boulders were more numerous in more cryptic positions once diving activity began at the impact location. On walls, although there was a reduction of more exposed colonies after the start of the disturbance (from 1992 to 1993), the changes over time were not significant. The control locations showed no significant changes in the distribution of the degree of exposure of colonies over time on either community. The effects of diving differed in the two communities studied. The impact on boulders was stronger than that on the walls. This may be explained by the protection provided by the dense canopy of gorgonian ( Paramuricea clavata ), the largest organism on vertical walls. On boulders erosion was continuous and cumulative. On walls, however, once the divers had eliminated the most exposed colonies-mainly the epibionts-the arboreal structure of the gorgonians prevented divers from coming into direct contact with the communities and reduced the risk of erosion. Sublittoral benthic communities in the northwestern Mediterranean constituted by sessile organisms with fragile calcareous or corneous skeletons are not adapted to the severe disturbances caused by continuous and intense diving. Recovery after such a disturbance appears to be slow and difficult. Current diving activity may not allow disturbed communities at diving sites to recover. The results of this experiment should be considered by managers and the data used to evaluate the models on which management decisions are based. El Impacto del Buceo en Comunidades Sublitorales sobre Sustrato Rocoso: El Caso de una Población de BriozoosResumen: En 1992 se instaló una boya para el buceo en un lugar previamente no frecuentado por los buceadores, dentro de una reserva marina en el nordeste de España donde el...

STAR: An integrated and standardized procedure to evaluate the ecological status of coralligenous reefs

“…Correlative and experimental studies highlighted severe shifts in the structure of coralligenous assemblages subjected to several kinds of stressors (Balata et al, ; Balata, Piazzi, & Benedetti‐Cecchi, ; Balata et al, ; Gatti et al, ; Gatti, Bianchi, Parravicini, et al, ; Piazzi et al, ; Piazzi, Gennaro, & Balata, ). Indicators used to assess the ecological quality of coralligenous reefs are different, and include erect bryozoans (de la Nuez‐Hernández, Valle, Forcada, González Correa, & Fernández Torquemada, ; Deter, Descamp, Ballesta, et al, ; Garrabou, Sala, Arcas, & Zabala, ; Gatti et al, ; Gatti, Bianchi, Morri, et al, ; Sala, Garrabou, & Zabala, ), erect anthozoans (Cerrano et al, ; Deter, Descamp, Ballesta, et al, ; Gatti, Bianchi, Morri, et al, ; Kipson et al, ) and sensitive macroalgae, such as Udoteaceae, Fucales and erect Rhodophyta (Balata et al, ; Cecchi et al, ; Piazzi, Gennaro, et al, ), as the most effective indicators of good environmental conditions. On the other hand, the dominance of algal turfs, hydroids and encrusting sponges seems to indicate degraded conditions (Gatti, Bianchi, Parravicini, et al, ; Piazzi, Cecchi, et al, ; Piazzi, Gennaro, et al, ).…”

Thirty year ecosystem trajectories in a submerged marine cave under changing pressure regime

“…Tourism and recreational activities, related to the establishment of the Bergeggi Island MPA (in 2007), when intensive may represent a source of impact on coastal marine communities (Garrabou et al, 1998;Milazzo et al, 2002;Bianchi et al, 2018). Major thermal events, along with an increase of about 0.5°C of the surface seawater temperature compared to 1986, took place in almost the same period and so did the time trajectories of the cave sessile communities, thus providing suggestive evidence of an ecosystem phase shift in response to a regime shift in external drivers (Montefalcone et al, 2011), consistently with previous studies in other Mediterranean habitats and sites (Bianchi et al, 2014(Bianchi et al, , 2017Gatti et al, 2015Gatti et al, , 2017.…”

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

“…Highly structurally complex benthic communities, in fact, provide a variety of food and refuge resources to different species, sustaining the presence, abundance and diversity of fishes and other mobile organisms (García-Charton et al, 2004;Carminatto et al, 2020, Di Franco et al, 2021. A reduced biotic complexity can determine a negative change in the characteristics and dynamics of the community, and leave space for the invasion of opportunistic, often nonindigenous organisms, potentially causing a complete ecological phase-shift toward a less resilient costal community, with an increased susceptibility to other direct and indirect anthropogenic impacts (and, in particular, to climate change) (Garrabou et al, 1998;Lyons et al, 2015).…”

“…Specifically, the first campaign (winter 2013-2014) was conducted before the implementation of the diving quotas, and the other three campaigns in the following winters after the introduction of the new regulation (officially in June 2014). The choice to carry out only one sampling campaign each year was motivated by two reasons: (1) the false coral has a long life-span without considerable seasonal fluctuations, as so often for other coralligenous builders (Garrabou et al, 1998); (2) diving impact takes place as a constant disturbance during the high season, thus within-year sampling was considered unnecessary (Garrabou et al, 1998). In order to investigate the potential impact of SCUBA diving on M. truncata and the eventual mitigation of this impact due to the implementation of new diving quotas, two zones associated with opposite SCUBA diving pressure were considered: the no-take zone (NTZ), in which recreational SCUBA diving is prohibited, and the buffer zone (or partially protected area, PPA), in which such activity is allowed (Fig.…”

“…The model design represented a before-after/controlimpact design with one time before and several times after the change in the number of dives, and multiple impacted and multiple control locations (multiple before-after/control-impact -MBACI design) (Underwood, 1992;1994;Keough and Mapstone 1997;Roberts et al, 2007). The rationale of the MBACI design is that the impact (in our case the potential positive impact caused by the reduction of diving pressure) in several diving spots should cause a reduction in the dead/total ratio of M. truncata colonies from before to after greater than the one observed for false coral populations in the multiple control locations where diving is forbidden (Garrabou et al, 1998), causing a significant interaction between sampling year and protection (Y × P). To this aim, a binomial generalized linear mixed model (glmm) was run testing for the significant interactions (Y × P) considering the year before (2013) and the three years after the change of diving quotas (2014, 2015 and 2016).…”