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Potential of Marine Reserves to Cause Community-Wide Changes beyond Their Boundaries

Abstract and Figures

Fishing and other human activities can alter the abundances, size structure, and behavior of species playing key roles in shaping marine communities (e.g., keystone predators), which may in turn cause ecosystem shifts. Despite extensive evidence that cascading trophic interactions can underlie community-wide recovery inside no-take marine reserves by protecting high-level predators, the spatial extent of these effects into adjacent fished areas is unknown. I examined the potential for community-wide changes (i.e., the transition from overgrazed coralline barrens to macroalgal beds) in temperate rocky reefs within and around a no-take marine reserve. For this purpose I assessed distribution patterns of predatory fishes, sea urchins, and barrens across the reserve boundaries. Predatory fishes were significantly more abundant within the reserve than in adjacent locations, with moderate spillover across the reserve edges. In contrast, community-wide changes of benthic assemblages were apparent well beyond the reserve boundaries, which is consistent with temporary movements of predatory fishes (e.g., foraging migration) from the reserve to surrounding areas. My results suggest that no-take marine reserves can promote community-wide changes beyond their boundaries.
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Potential of Marine Reserves to Cause
Community-Wide Changes beyond Their Boundaries
Laboratory of Zoology and Marine Biology, DiSTeBA, University of Salento, via provinciale Monteroni, 73100 Lecce, Italy, email
Abstract: Fishing and other human activities can alter the abundances, size structure, and behavior of
species playing key roles in shaping marine communities (e.g., keystone predators), which may in turn cause
ecosystem shifts. Despite extensive evidence that cascading trophic interactions can underlie community-wide
recovery inside no-take marine reserves by protecting high-level predators, the spatial extent of these effects into
adjacent fished areas is unknown. I examined the potential for community-wide changes (i.e., the transition
from overgrazed coralline barrens to macroalgal beds) in temperate rocky reefs within and around a no-take
marine reserve. For this purpose I assessed distribution patterns of predatory fishes, sea urchins, and barrens
across the reserve boundaries. Predatory fishes were significantly more abundant within the reserve than in
adjacent locations, with moderate spillover across the reserve edges. In contrast, community-wide changes of
benthic assemblages were apparent well beyond the reserve boundaries, which is consistent with temporary
movements of predatory fishes (e.g., foraging migration) from the reserve to surrounding areas. My results
suggest that no-take marine reserves can promote community-wide changes beyond their boundaries.
Keywords: alternative community states, community-wide changes, marine reserves, overfishing, temperate
rocky reefs, trophic cascades
EL Potencial de Reservas Marinas para Provocar Cambios a Nivel de Comunidad M´as All´adesusL´ımites
Resumen: La pesca y otras actividades humanas pueden alterar la abundancia, tama˜
no, estructura y com-
portamiento de las especies que juegan papeles clave en el modelado de las comunidades marinas (e.g.,
depredadores clave), que a su vez pueden causar cambios en los ecosistemas. No obstante la evidencia ex-
tensiva de que las interacciones tr´
oficas en cascada pueden subyacer en la recuperaci´
on de la comunidad
dentro de reservas marinas que no permiten la pesca mediante la protecci´
on de depredadores de nivel alto,
se desconoce la extensi´
on espacial de estos efectos en ´
areas adyacentes. Examin´
e el potencial de los cambios a
nivel comunidad (i.e., la transici´
on de ´
areas coralinas sobre pastoreadas a lechos de microalgas) en arrecifes
rocosos templados dentro y alrededor de una reserva marina sin pesca. Para este prop´
osito, evalu´
e los patrones
de distribuci´
on de peces depredadores, erizos de mar y ´
areas sobre pastoreadas en los l´
ımites de la reserva.
Los peces depredadores fueron significativamente m´
as abundantes dentro de la reserva que en localidades
adyacentes, con un excedente moderado en los bordes de la reserva. En contraste, los cambios a nivel de comu-
nidad en los ensambles b´
enticos fueron aparentes m´
as all´
a de los l´
ımites de la reserva, lo que es consistente
con los movimientos temporales de los peces depredadores (e.g., migraci´
on de forrajeo) desde la reserva hacia
las ´
areas circundantes. Mis resultados sugieren que las reservas que no permiten la pesca pueden promover
cambios a nivel comunidad m´
as all´
a de sus l´
Palabras Clave: arrecifes rocosos templados, cambios a nivel comunitario, cascadas tr´oficas, estados comuni-
tarios alternativos, exceso de pesca, reservas marinas
Paper submitted February 13, 2006; revised manuscript accepted August 2, 2006.
Conservation Biology Volume 21, No. 2, 540–545
2007 Society for Conservation Biology
DOI: 10.1111/j.1523-1739.2007.00657.x
Guidetti Changes beyond Reserve Boundaries 541
Increasing concern over the consequences of human ex-
ploitation of natural resources at sea has led, in recent
decades, to the proposal of ecosystem-based manage-
ment tools (Pikitch et al. 2004). In coastal areas world-
wide, fishing is one of the most significant human im-
pacts on populations, habitats, and whole communities
(e.g., Tegner & Dayton 2000; Jackson et al. 2001; My-
ers & Worm 2003). No-take marine reserves (i.e., areas
of the ocean protected from extractive uses) have be-
come important tools for management and conservation
of marine communities (Tegner & Dayton 2000). Results
of empirical studies show increased density and/or size
of target species within reserves compared with fished
areas (Halpern & Warner 2002; Halpern 2003), spillover
of fish across reserve boundaries (Roberts et al. 2001;
Abesamis & Russ 2005), and community-wide changes
following fishing bans (Castilla & Dur`an 1985; Sala et al.
1998; Shears & Babcock 2003; Micheli et al. 2004). Such
effects are mostly attributable to protection from fishing,
which directly affects high-level predators and indirectly
affects entire communities (Pinnegar et al. 2000; Jackson
et al. 2001).
In many temperate reefs worldwide, removal of sea
urchin predators has been demonstrated to release sea
urchins from predator control (Breen & Mann 1976; Estes
& Duggins 1995; Sala et al. 1998; Pinnegar et al. 2000;
Witman & Dayton 2001). The related increase in density
of sea urchins (the most important grazers in temperate
regions) can potentially cause the transition of an area
from macroalgal stands and forests to coralline barrens
and loss of ecosystem functions (Tegner & Dayton 2000;
Shears & Babcock 2002). Recovery of predators within
reserves may reverse this community shift (Shears & Bab-
cock 2003).
In Mediterranean subtidal rocky reefs, adult sea urchins
(Paracentrotus lividus and Arbacia lixula) are effec-
tively preyed on by only a few fish species, especially
the sea breams Diplodus sargus and D. vulgaris (Sala et
al. 1998; Hereu et al. 2005; Guidetti 2006), which are
strongly targeted by fishers (Harmelin et al. 1995, Coll et
al. 2004). The relationship between such fish predators
and sea urchins can be affected by a variety of factors,
such as the predator size relative to prey size (Guidetti
2006), availability of shelter (Sala et al. 1998; Hereu et
al. 2005), wave action (Micheli et al. 2005), and the sub-
strate type (Guidetti et al. 2005a). Sea urchins released
from predatory control due to overfishing of predators
can achieve high densities and cause the transition of
the community from macroalgal beds to barrens (Sala et
al. 1998; Guidetti 2006). Recovery of fish predators and
reestablishment of lost trophic interactions within ma-
rine reserves may reverse this community shift (Guidetti
2006). It is important to determine whether these effects
are localized (i.e., occur only within the protected areas)
or whether the potential movements of predatory fishes
beyond the reserve boundaries may cause community-
wide changes in adjacent areas. I sought to provide evi-
dence for possible community-wide changes in sublittoral
rocky reefs by examining distribution patterns of preda-
tory fishes and sea urchins, and the extent of barrens
across the boundaries of a Mediterranean marine reserve.
Torre Guaceto Marine Reserve ( TGMR) is located in
southeastern Italy (southern Adriatic Sea; Fig. 1). The
study area is generally characterized by a rocky plateau
with a gentle-to-medium slope, declining from the water
surface to about 10 m over coarse sand. The TGMR cov-
ers about 2220 ha (entirely a no-take area at the time the
study was done) and was formally established in 1992, al-
though enforcement started being successful some years
later when effective control by local authorities and re-
serve personnel began (Guidetti 2006). Professional and
recreational fishers fish outside the reserve, including ar-
eas close to reserve boundaries (Guidetti et al. 2005b).
Although there has been no quantitative assessment of
the local fishing impact, fewer than 10 small professional
fishing boats are active in the areas outside and surround-
ing the reserve, where trammels, gillnets, traps, and lines
with hooks are used. The impact of spearfishing and recre-
ational fishing from boats is moderate. No diving is done in
or surrounding the reserve. A recent study provided an in-
direct assessment of the fishing impact. The comparison
of fishing yield inside and outside the TGMR showed that
quantities of commercial fishes extracted from the pro-
tected area with trammels were roughly fourfold greater
than those obtained outside the reserve (Vierucci et al.
Figure 1. Study location and sampling sites (arrows)
inside and outside the Torre Guaceto Marine Reserve
Conservation Biology
Volume 21, No. 2, April 2007
542 Changes beyond Reserve Boundaries Guidetti
In the past before the reserve was established and ac-
tually protected, there were large sea urchin barrens in
the area presently included in the reserve and where
rocky reefs are now largely dominated by macroalgae
(Guidetti 2006). This community shift, mediated by the
reestablishment of fish predator pressure on sea urchins
within the reserve (Guidetti 2006), suggests that any dif-
ference detected between the reserve and fished areas at
Torre Guaceto (e.g., fishery yield, fish predator density) is
mostly attributable to effective protection and not to the
fact that the specific areas included in the reserve were
already originally different or special.
In MayJuly 2004 I used scuba to assess the density of
sea breams and sea urchins and the extent of barrens in
rocky reefs 47 m deep. Ungrazed benthic communities
in the area are largely dominated by macroalgae (mainly
turf or erected algae; Guidetti 2006), so cover of barrens
is the variable that may best represent the overgrazed al-
ternate condition. Fish density was evaluated by means of
visual census (along strip transects of 25 ×5 m; Harmelin-
Vivien et al. 1985), whereas sea urchin density and bar-
ren extent were assessed within quadrats (1 ×1 m). Each
fish census and sea urchin and barren quadrat survey was
replicated 160 times. Sea urchin and barren quadrats were
surveyed for densities of sea urchins and the extent of bar-
rens (percentage), respectively, at 20 sites: 8 within the
TGMR (extending from the center to the northern and
southern boundaries) and 12 in adjacent fished areas (6
beyond the northern reserve boundary and 6 beyond the
southern boundary up to a distance of approx. 2 km from
the edges of the reserve; Fig. 1).
I examined correlation between pairs of variables at
each site sampled with Pearson correlation and then used
logistic function (see Kaunda-Arara & Rose 2004 for de-
tails) to describe how fish and sea urchin density and
barren extent changed from the center of the TGMR with
distance across the northern and southern boundaries.
The regression model was tested with the log-transformed
data. Slopes (mean change in the variables per unit change
in distance from the reserve center) and inflexion points
(distance from reserve boundaries at which maximum
values are halved) of the logistic curves were used to in-
vestigate gradients of density or cover across the reserve
Sea bream and sea urchin densities were negatively cor-
related across different sites (R=0.53; p<0.05; n=20).
The correlation between sea urchin density and barren
extent was highly positive (R=0.92; p<0.001; n=20).
The density of predatory fishes declined across the
northern and southern reserve boundaries (northern
boundary: slope =0.003, inflexion point =459.7, F=
32.0, p=0.0005; southern boundary: slope =0.001,
inflexion point =755.8, F=25.3, p=0.001). Nega-
tive values of the inflexion point reveal that maximum
Diplodus density at the center of the TGMR halved in-
side the reserve at approximately 450750 m from the
boundaries (Fig. 2a). In contrast, gradients of sea urchin
density increased from the reserve center to the fished
areas outside the TGMR (north: slope =0.003, inflexion
point =309.6, F=12.6, p=0.007; south: slope =0.005,
inflexion point =305.0, F=10.66, p=0.011). The posi-
tive values of the inflexion point show that maximum sea
urchin density observed in fished areas declined by 50%
at approximately 300 m outside the boundaries of the
TGMR (Fig. 2b). Spatial gradients of barrens were similar
to those of sea urchins (north: slope =0.002, inflexion
point =235.7, F=9.44, p=0.015; south: slope =0.006,
inflexion point =209.9, F=10.52, p=0.012). The max-
imum values measured in fished areas were half that at
approximately 200250 m outside the boundaries of the
TGMR (Fig. 2c).
The density of Diplodus fish was far higher inside the
TGMR than outside. The difference was dramatic and is
likely to be due to protection from fishing (i.e., the so-
called reserve effect; Halpern 2003). Diplodus sargus and
D. vulgaris are targeted by many kinds of fishery (com-
mercial and recreational: lines with hooks, spearfishing),
and the reserve effect is particularly significant for tar-
get species in the Mediterranean Sea (e.g., Guidetti 2006;
Guidetti & Sala 2007) and elsewhere (e.g., Micheli et al.
2004). From this perspective, enforcement at TGMR is ef-
fective (see Methods), and the reserve has been protected
long enough to encompass the life span of Diplodus fish,
which can live up to 10 years (Froese & Pauly 2004). Pro-
tection within the TGMR is thus likely to have allowed
Diplodus populations to recover in terms of both density
and size at levels high enough to effectively control sea
urchin populations and indirectly trigger the transition
from coralline barrens back to macroalgal beds within
the reserve (Guidetti 2006).
Field experiments documented far higher fish preda-
tion rates on sea urchins inside the TGMR than out-
side (Guidetti 2006). The above issues suggest there
may be changes at population and community levels
within marine reserves following a fishing ban. The
community-wide recovery after reestablishment of preda-
tory trophic interactions within reserves could involve
predatory fishes moving from the reserve and feeding on
sea urchins outside the reserve at a rate high enough
to significantly reduce grazing and allow macroalgal
Conservation Biology
Volume 21, No. 2, April 2007
Guidetti Changes beyond Reserve Boundaries 543
Figure 2. (a) Density of Diplodus (a
fish predator of sea urchins), (b)
density of sea urchins, and (c)
extent of barrens across the
boundaries of the Torre Guaceto
Marine Reserve (mean ±SE).
recolonization. Daylight distribution patterns of preda-
tory fishes I observed, nevertheless, suggest a moder-
ate spillover (in terms of passive density-dependent dif-
fusion) from the TGMR and a substantial concentration
of Diplodus within the reserve. Maximum densities of
Diplodus observed at the center of the TGMR were half
that amount well inside the reserve boundaries and de-
creased abruptly within a few hundreds of meters outside
the reserve. Similar declines of fish density around the re-
serve edges seem to be common to many reserves world-
wide (Kaunda-Arara & Rose 2004), although differences
among species may occur depending on the catchability,
mobility, and other traits of species (Rakitin & Kramer
1996; Ashworth & Ormond 2005).
Distribution patterns of target fishes across reserve
boundaries, however, should be interpreted with cau-
tion. At several marine reserves worldwide, fishing ac-
tivities concentrate outside the reserve and close to the
boundaries in order to benefit from the spillover of fish
(Abesamis & Russ 2005). This implies that patterns of
fish density around the reserve boundaries are the result
of the superimposing effects of biomass exportation and
exploitation (Halpern et al. 2004). This is not likely to be
the case, however, at the TGMR, where a relatively small
number of professional and recreational fishers operate
outside the reserve, close to the boundaries. As suggested
by Halpern et al. (2004), the export of increased produc-
tion from within the reserve tends to offset the effects of
displaced fishing effort in conditions of low fishing pres-
sure at the reserve edges. Additionally, visual censuses of
fishes are usually made in daylight (Harmelin-Vivien et
al. 1985), and patterns of Diplodus density observed at
the TGMR showed that fishes tend to concentrate inside
the reserve. Ecological effects of fish predators (i.e., sea
urchin population control and consequent abundance of
macroalgal beds), however, appeared to extend well be-
yond the reserve boundaries (up to 5001000 m from
the edges). Therefore, movements of fishes caused by
processes other than density-dependent spillover, such
as foraging migration of fishes from the reserve toward
and beyond its edges at times when visual censuses are
not done (at dawn, night, or sunset), could explain the
patterns I observed. This hypothesis is supported by data
of fish catches around the TGMR (P.G., unpublished data)
Conservation Biology
Volume 21, No. 2, April 2007
544 Changes beyond Reserve Boundaries Guidetti
that show that Diplodus sargus and D. vulgaris actively
move from sunset to dawn when they forage, as reported
by other authors (Lloret & Planes 2003).
Finally, the patterns I observed were evidently asym-
metric between the northern and southern boundaries.
Although habitat types (e.g., rocky substrates, sands, and
sea grasses) are approximately the same at the two reserve
boundaries, I could not exclude a priori that differences in
the relative cover or patchiness of different habitats may
affect, to some extent, movement patterns of fishes, dis-
tribution of urchins and algae, and consequently their in-
teractions. Ecological interactions within marine reserves
and the haloeffect of marine reserves on community
structure in areas adjacent to a reserve are complex but
central issues that are receiving increasing attention from
conservation ecologists (Langlois et al. 2006).
My results, therefore, highlight the importance of com-
bining static evaluations of effects of marine reserves
(e.g., based on comparisons of patterns between re-
serves and fished areas; e.g., Shears & Babcock 2003;
Guidetti 2006) with experimental and mechanistic stud-
ies of the dispersal and behavior of key species (e.g.,
density-dependent migration and habitat use of preda-
tors) and provides the first evidence that marine reserves
may have the potential to cause ecosystem-wide changes
beyond their boundaries.
This paper represents a contribution toward the aims of
MARBEF (EU Network of Excellence on Marine Biodi-
versity and Ecosystem Functioning under EU-Framework
Programme 6), POR-ECOFISHMOD (funded by Regione
Puglia), and SPILLOVER (funded by MIPAF) projects.
Many thanks are due to F. Micheli, who kindly revised a
previous version of the manuscript and provided invalu-
able suggestions and comments, two anonymous refer-
ees who greatly improved the text, and S. Bussotti and E.
Vierucci, who helped me with field work. This research
was made possible thanks to the permission of A. Cic-
colella, the director of the TGMR.
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Conservation Biology
Volume 21, No. 2, April 2007
... The protection levels of an MPA are expected to change sea urchin predation risk and shape their population structure. Therefore, as a consequence of reserve effectiveness, the sea urchin population structure in fully protected areas should be dominated by a small number of large adult individuals due to a high fish density that increases the predation risk on smaller, young adult sea urchins (Sala & Zabala, 1996;Hereu et al., 2005;Guidetti, 2006b). ...
... In cases where the home range of a species extends beyond the borders of the MPA, effects of protection may spill over to adjacent areas. In fact, the re-establishment of predatory trophic interactions involves predatory fish moving from the fully protected area and feeding on sea urchins beyond the edges (Guidetti, 2006b). However, Dilpodus spp., the most common predatory fish preying on sea urchins in the Western Mediterranean Sea, are strongly habitat associated. ...
... Reserve effect can even influence the surrounding communities due to an increase of predation activity because of the migration of predatory fish from the fully protected area (Guidetti, 2006b). ...
ffective marine protected areas (MPAs) increase top predator density. Accordingly, a large abundance of predatory fish potentially increases predation risk for sea urchins inside an MPA. Intensity of predation was investigated for the sea urchin Paracentrotus lividus at a Mediterranean MPA. Predation rates were estimated for three levels of protection (full, partial, and absent) and two habitats (rocky reefs and Posidonia oceanica meadows). The natural density of sea urchins was correlated with predator biomass (fish sparids Diplodus spp. and Sparus aurata and the gastropod Hexaplex trunculus), and predation risk was evaluated through a tethering experiment. Significantly higher fish predation was found on the rocky reefs of the fully and non-protected areas than in the partially protected area. These findings are consistent with the sparid biomass estimated in the fully and partially protected areas. However, a discrepancy between high predation risk and low sparid biomass was detected outside of the MPA's northern boundary, where marine farms (fish and mussels) are present. Benthic predator biomass also increased significantly across the northern boundary, but its predation activity was negligible. The low predatory fish biomass and low sea urchin density suggest a top-down control by roving predatory fish on the rocky reefs of the non-protected area, in proximity to the fish farms. Similarly, a significant gradient of benthic predator biomass and low sea urchin density suggest potential predation interactions inside the P. oceanica meadows across the northern MPA boundary near the mussel farms. This study highlights deviations from the expected trophic interactions outside the MPA that could be caused by aquaculture activities. Our understanding of the potential synergies between the MPAs and the nearby human activities needs to be broadened to improve the effectiveness of both ecosystem conservation and resource management.
... Examples of this are the top-down control of lower-trophic species by increased predator abundance (Micheli and Halpern., 2005;Mumby et al., 2006) and the unexpected enhancement of other non-commercial species through complex, non-linear mechanism (Watson et al., 2007). Other indirect ecosystem benefits of successful spatial protection may also include prevention of biodiversity loss from anthropogenic disturbance (Pitcher, 2001;Micheli et al., 2004), resiliency to increasing incidences of coral bleaching and diseases (Hughes et al., 2003), and enhanced fisheries production and community recovery outside reserve boundaries (Guidetti, 2007 ...
... In effect, the prohibition of fishing and other damaging activities, such as anchoring, conserves ecosystem integrity by safeguarding all ecological components evident at the scale of the reserve. Specific indirect benefits of such spatial management may also include prevention of biodiversity loss from anthropogenic disturbance (Micheli et al., 2004), resilience to increasing incidences of coral bleaching and diseases (Hughes et al., 2003), and enhanced fisheries production outside reserve boundaries (Guidetti, 2007). In contrast, arrays of single-species fisheries regulations may not preserve the diversity of functional and ecological relationships comprising an ecosystem (Pitcher, 2001). ...
Technical Report
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The aims of this study were twofold. First, we sought to evaluate the effectiveness of current Marine Protected Areas (MPA's hereafter) in promoting the abundance and biomass of fishes. Second, we examined how fish populations are distributed across Bermuda's reef platform, in order to identify regions and habitats of high biodiversity or significance to harvestable and ecologically-important species.
... Επιπρόσθετα έχει παρατηρηθεί αύξηση στη συνολική βιομάζα, την αφθονία, αλλά και στο μέγεθος των ψαριών εντός των ορίων των Θ.Π.Π. σε σχέση με άλλες θαλάσσιες περιοχές (Halpern 2003, Micheli et al. 2004, Guidetti 2007) γεγονός που μπορεί να οδηγήσει σε διάχυση των ιχθυοπληθυσμών και ενίσχυση των γειτονικών αλιευτικών πεδίων (Roberts et al. 2001). Όπως αναφέρεται και από τους Guidetti and Claudet (2010) οι προαναφερθείσες θετικές επιδράσεις, που επιφέρουν οι Θ.Π.Π. ...
... S. salpa seemed to benefit from the low predation pressure to proliferate. This situation can have consequences on the whole ecosystem induced by a possible overgrazing of macroalgae (Pinnegar et al. 2000, Guidetti 2007, Vergés et al. 2009). In contrast, around Port-Cros Island, target species represented a high proportion of the total fish biomass, resulting from an effective management (Astruch et al. 2018). ...
... There is good evidence that ecosanctuary-based birds interact with the surrounding landscape. A 'halo' effect can be created by volant birds dispersing into areas surrounding the ecosanctuary (Brudvig et al., 2009;Guidetti, 2007;Innes et al., 2012); this is analogous to 'spillover' of fish stocks from protected marine areas (e.g. Halpern et al., 2009). ...
Fenced ecosanctuaries are a high-cost method of creating areas of pest predator-free habitat for species or populations for whom predation is a limiting factor. Past research has focused on ‘inside the fence’ habitat and bird populations, overlooking the potential for ecosanctuaries to augment bird populations ‘outside the fence’. We assessed the amount of habitat around both fenced and unfenced ecosanctuaries in New Zealand, how connected the ecosanctuaries were to the wider landscape, and the overall landscape connectivity around ecosanctuaries, for six bird species at 18 sites (15 fenced; 3 unfenced), assuming a predator-free landscape. We found low levels of high-quality habitat around many fenced ecosanctuaries. There was no high-quality habitat at all around some ecosanctuaries for several bird species. Ecosanctuaries on peninsulas (with reduced fencing costs) tended to have a smaller proportion of the surrounding area in habitat and lower functional connectivity than unfenced ecosanctuaries and ring-fenced sites; meaning the reduced fencing costs at peninsular sites needs to be balanced against less habitat, on average, beyond the ecosanctuary. Managers deciding where to locate ecosanctuaries need to consider both the ecosystems within and those surrounding the site, and connectivity between the two. New Zealand is a world leader in fenced ecosanctuaries; lessons learned from this study in New Zealand are likely to apply elsewhere, where the use of fenced ecosanctuaries for predation sensitive species is incipient.
... Tra le diverse problematiche che il Parco si è trovato ad affrontare sin dalla sua istituzione sicuramente una delle maggiori è stata la pesca di frodo. È nota la problematica relativa al conflitto tra la necessità di tutelare le aree marine protette quali strumenti di ripopolamento biologico per la salvaguardia sia dei sistemi ecologici costieri mediterranei che della piccola pesca costiera spesso in crisi proprio a causa della concorrenza della pesca intensiva e della pesca illegale [1,2,3]. In questo contesto la fascia costiera di Posillipo, e la zona della Gaiola in particolare, sono da sempre identificate, nella tradizione popolare, quali aree notevolmente pescose dove da sempre si è concentrata l'attività di pesca. ...
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The 8th International Symposium "Monitoring of Mediterranean Coastal Areas. Problems and Measurements Techniques" was organized by CNR-IBE in collaboration with FCS Foundation, and Natural History Museum of the Mediterranean and under the patronage of University of Florence, Accademia dei Geogofili, Tuscany Region and Livorno Province. It is the occasion in which scholars can illustrate and exchange their activities and innovative proposals, with common aims to promote actions to preserve coastal marine environment. Considering Symposium interdisciplinary nature, the Scientific Committee, underlining this holistic view of Nature, decided to celebrate Alexander von Humboldt; a nature scholar that proposed the organic and inorganic nature’s aspects as a single system. It represents a sign of continuity considering that in-presence Symposium could not be carried out due to the COVID-19 pandemic restrictions. Subjects are related to coastal topics: morphology; flora and fauna; energy production; management and integrated protection; geography and landscape, cultural heritage and environmental assets, legal and economic aspects.
... After recruitment, predation is the second main process regulating sea urchin population structure on a local scale (Guidetti, 2004;Hereu, Zabala & Sala, 2008;Boada et al., 2015). Adult sea urchins are preyed on by few fish species, especially the sea breams which are targeted by artisanal fisheries (Guidetti, 2006). During 2004-2007, there was a negative correlation between the abundances of the sea breams and middle-sized sea urchins. ...
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Sea urchins act as a keystone herbivore in marine coastal ecosystems, regulating macrophyte density, which offers refuge for multiple species. In the Mediterranean Sea, both the sea urchin Paracentrotus lividus and fish preying on it are highly valuable target species for artisanal fisheries. As a consequence of the interactions between fish, sea urchins and macrophyte, fishing leads to trophic disorders with detrimental consequences for biodiversity and fisheries. In Sardinia (Western Mediterranean Sea), regulations for sea urchin harvesting have been in place since the mid 90s. However, given the important ecological role of P. lividus, the single-species fishery management may fail to take into account important ecosystem interactions. Hence, a deeper understanding of population dynamics, their dependance on environmental constraints and multispecies interactions may help to achieve long-term sustainable use of this resource. This work aims to highlight how sea urchin population structure varies spatially in relation to local environmental constraints and species interactions, with implications for their management. The study area (Sinis Peninsula, West Sardinia, Italy) that includes a Marine Reserve was divided into five sectors. These display combinations of the environmental constraints influencing sea urchin population dynamics, namely type of habitat (calcareous rock, granite, basalt, patchy and continuous meadows of Posidonia oceanica), average bottom current speed and predatory fish abundance. Size-frequency distribution of sea urchins under commercial size (
... Partially enforced MPAs fail to achieve sufficient restoration of fish populations, in contrast to adequately enforced no-take marine reserves, which are proved to be effective in the conservation of the fish stocks (Denny & Babcock, 2004;Sala et al., 2012). Moreover, the extent of fish spill-over is related to the amount of fishing pressure being exerted at the MPA boundaries (Guidetti, 2007;Harmelin-Vivien et al., 2008). Still, additional studies are needed to validate the findings of the present study at a greater temporal scale. ...
Technical Report
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This study contributes to a better understanding of the effects of small scale artisanal fisheries on fish stock status and overall marine biodiversity, both within the limits of the MPA of NMPZ, as well as in the North and Eastern coasts of Zakynthos Island. It also provides insights regarding the effectiveness of management measures, fishermen attitudes, preferences and socio-economic profile. Given that fisheries activities and fish stock conservation is a complex issue encompassing both ecological and socioeconomic aspects, we adopted several methodological approaches in order to address all the main parameters involved. The study includes sampling areas located both inside and outside the MPA. We applied underwater visual census to evaluate composition and status of fish assemblages, on board sampling to assess fish stocks and other parameters related to fisheries, fishermen interviews via questionnaires to collect additional ecological information and investigate socioeconomic parameters, as well as fisheries data from local authorities. The observed overexploitation status of fish populations in all studied areas, and the lack of a marine reserve effect, indicate that current management measures are not sufficient in maintaining fish stocks at a sustainable level, whilst compromising ecosystem stability and fishermen profits. The results also suggest that it is of particular importance to maintain the present legal status of recreational fisheries (i.e. total prohibition of recreational fishing within the MPA), and further increase the effectiveness of enforcement. Although the majority of local professional fishermen that fish in the MPA report a significant reduction in fish size and landings over the last years, current opinions and perceptions regarding the existance of an MPA are primarily negative. Based on our findings, a set of additional management actions are being proposed for the sustainable management of fisheries in the MPA of NMPZ.
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A Before–Intermediate–After Multiple Sites (BIAMS) analysis, namely a modified version of the Before–After–Control–Impact (BACI) approach, was used to evaluate the possible effects of fishery management measures implemented in the Pomo/Jabuka Pits area, a historically highly exploited ground for Italian and Croatian fisheries, whose impact may have contributed over the years to the modification of the ecosystem. Since 2015, the area was subject to fishing regulations changing the type of restrictions over time and space, until the definitive establishment in 2018 of a Fishery Restricted Area. These changes in the regulatory regime result in complex signals to be interpreted. The analysis was carried out on abundance indices (i.e., kg/km2 and N/km2) of five commercially or ecologically relevant species, obtained in the period 2012–2019 from two annual trawl surveys. BIAMS was based on the selection of a Closure factor, declined in three levels (i.e., BEFORE/INTERMEDIATE/AFTER) and accounting for regulation changes in time, and on three adjacent strata (i.e. “A”, “B”, and “ext ITA”) a posteriori determined according to the latest regulations. BIAMS allowed us to identify early effects (i.e., changes in abundances), overcoming the unavailability of a proper independent control site; furthermore, the selection of adjacent strata allowed the inference of possible interactions among them.
Consistency in conservation Marine protected areas (MPAs) are now well established globally as tools for conservation, for enhancing marine biodiversity, and for promoting sustainable fisheries. That said, which regions are labeled as MPAs varies substantially, from those that full protect marine species and prohibit human extraction to those that permit everything from intensive fishing to mining. This inconsistency can in some cases inhibit both conservation and quantifying the proportion of the marine environment that is truly protected. Grorud-Colvert et al . review the consistency of MPAs and propose a framework by which levels of protection can be evaluated and improved. —SNV
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Removal of important predators by fishing can result in trophic cascades and indirect effects on marine benthic communities. Indirect effects are especially evident when prey populations released from predation by fishing have the ability to modify entire benthic communities, as do sea urchins. Sea urchins have been shown to dramatically alter the underwater landscape by grazing, by converting stands of large erect algae into coralline barrens. In the western Mediterranean, a recent extension of coralline barrens into areas formerly dominated by erect algal assemblages has been attributed to release of predation on sea urchins by overfishing. Most suggestions concerning the transition from erect algal assemblages to coralline barrens, however, have been speculative, and little descriptive and experimental work has been carried out to verify the hypothesis that fish predation on sea urchins land its subsequent release by overfishing) drives this transition. Here we critically review the literature concerning the effect of fishing on sea urchin populations and its subsequent maintenance of different algal assemblages in the Mediterranean. The extant data cannot refute the "fishes as important predators" model, but we argue that other processes (recruitment, pollution, disease, large-scale oceanographic events, sea urchin harvesting, food subsidies, and availability of shelters) may also be important in regulating the structure of Mediterranean algal assemblages.
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Kelp forests, highly diverse cold water communities organized around the primary productivity and physical structure provided by members of the Laminariales, support a variety of fisheries, and the kelp itself is harvested for alginates. Worldwide, these communities generally share susceptibility to destructive overgrazing by sea urchins. The impact of sea-urchin grazing is governed by the ratio between food availability and grazing pressure, thus factors affecting the abundance of both urchins and kelps are central to ecosystem integrity. Some kelp ecosystems share a second generality, the association of exploitation of various urchin predators with destructive levels of urchin grazing, leading to cascading implications for other species dependent on the productivity and habitat provided by the kelps. Competition between abalones and sea urchins also affects some kelp communities. These ecosystem-structuring processes are complicated by a variety of bottom-up and top-down factors, including variability in ocean climate affecting kelp productivity and recruitment of key species, and echinoid disease, potential ecosystem effects of fisheries for predators, abalones, sea urchins, and kelps are reviewed biogeographically. Given the hundreds to thousands of years that many nearshore marine ecosystems have been exploited, no-take marine reserves may be the only way to determine the true ecosystem effects of fishing. (C) 2000 International Council for the Exploration of the Sea.
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Between 1978 and 1996 benthic communities in the Leigh Marine Reserve shifted from being dominated by sea urchins to being dominated by macroalgae. This was a result of a trophic cascade thought to be an indirect effect of increased predator abundance. We assessed further changes in communities from 1996 to 2000, differences in benthic communities between reserve and adjacent unprotected sites, and the stability of these patterns from 1999 to 2001. Since 1996, densities of sea urchins Evechinus chloroticus have continued to decline in shallow areas of the reserve (< 8 m), and all sites classified as urchin barrens in 1978. are now dominated by large brown algae. Comparisons between reserve and non-reserve sites revealed differences consistent with a trophic cascade at reserve sites. The greatest differences in algal communities between reserve and non-reserve sites occurred at depths where E. chloroticus was most abundant (4 to 6 m). Reserve sites had lower urchin densities and reduced extent of urchin barrens habitat with higher biomass of the 2 dominant algal species (Ecklonia radiata and Caipophyllum maschalocarpum). At reserve sites densities of exposed E. chloroticus (openly grazing the substratum) declined so that urchin barrens were completely absent by 2001. Lower density of the limpet Cellana stellifera and higher densities of the turbinid gastropod Cookia sulcata at reserve sites are thought to be responses to changes in habitat structure, representing additional indirect effects of increased predators. The overall difference in community types between reserve and non-reserve sites remained stab le between 1999 and 2001. Localised urchin mortality events due to an unknown agent were recorded at some sites adjacent to the marine reserve. Only at 1 of these sites did exposed urchins decline below the critical density of 1 m(-2), which resulted in the total replacement of urchin barrens with macroalgae-dominated habitats. At other sites urchin barrens have remained stable. Declines in the limpet C. stellifera occurred across all sites between 1999 and 2001 and may be indirectly associated with urchin declines. Long-term changes in benthic communities in the Leigh reserve and the stability of differences between reserve and non-reserve sites over time are consistent with gradual declines in urchin densities due to increased predation on urchins, thus providing further evidence for a trophic cascade in this system. The rapid declines in urchin numbers at some unprotected sites, however, demonstrate how short-term disturbances, such as disease, may result in shifts in community types over much shorter time frames.
Spillover, the net export of adult fish, is one mechanism by which no-take marine reserves may eventually have a positive influence on adjacent fisheries. Although evidence for spillover has increased recently, mechanisms inducing movement of adult fish from reserve to fished areas are poorly understood. While density-dependent export is a reasonable expectation, given that density of fish targeted by fisheries should increase over time inside well-protected no-take reserves, no study to date has demonstrated development of the process. This study provides evidence consistent with density-dependent export of a planktivorous reef fish, Naso vlamingii, from a small no-take reserve (protected for 20 years) at Apo Island, Philippines. Mean density of N. vlamingii increased threefold inside the reserve between 1983 and 2003. Density approached an asymptote inside the reserve after 15-20 years of protection. Modal size in the reserve increased from 35 to 45 cm total length (TL) over 20 years of protection. In addition, both density and modal size increased outside the reserve close to (200-300 m), but not farther from (300-500 m), the reserve boundary over the 20 years of reserve protection. Movement of adult N. vlamingii across the boundaries of the reserve was rare. Aggressive interactions among adult N. vlamingii were significantly higher (by 3.7 times) inside than outside the reserve. This suggests that density-dependent interactions were more intense inside the reserve. When interacting adults differed in size, the larger individual usually chased away the smaller one. Furthermore, the mean size of adult fish captured by experimental fishing decreased from 35-cm TL 50-100 m outside the boundary, to 32-cm TL 250-300 m outside the boundary. This represents some of the best evidence available for density-dependent home-range relocation of fish from a no-take reserve.
The ecological role played by man as a top predator in a rocky intertidal environment of central Chile was studied. Human exclusion from a rocky intertidal stretch of coast (non-harvested area) at Punta El Lacho, for nearly two years, resulted in a substantial density increase of the economically important high trophic level predator muricid Concholepas concholepas. This was followed by a dramatic decline in the cover of the competitive dominant intertidal mussel Perumytilus purpuratus. According to current ecological theory the removal of the competitively superior primary space dominant species led to a pattern of increasing species diversity. We conclude that in the absence of human interference C. concholepas plays the role of a key species in central Chile rocky intertidal environments. We suggest that the interpretation of the structure and dynamics of intertidal landscapes should include the key role played by man. Comparison of monitoring programs between intertidal areas with and without human interference will prove critical to our understanding of such environments. /// Исследовали экологическую роль человека как высшего хишника в скалистой ли-торальной зоне центрального Чили. Исключение деятельности человека с опреде-ленного отрезка береговой линии (непромысловая территория) в Пунта эль Лахо примерно на 2 года привело к существенному повьшению плотности популяции экономически важного вида мирицид Concholepas concholepas - высшего хищинка. Это сопроваждалось драматическим снижением численности конкурирующего доми-нанта моллюска Perumytilus purpuratus. Согласно современной экологической теории удаление более конкурентоспособного первичного доминирующего вида приводит к повышению видового разнообразия. Мх делаем вывод, что при отсут-ствии антропогенного пресса C. concholepas итрает роль ключевого вида в со-обществах склистой литорали центрального Чили. Мы полагаем, что интерпре-тация структуры и динамики литоральных ландшафтов должна была бы включать и ключевую роль человеческой деятельности. Сравнение программ монторинта разных литоральных зон с антропогенным прессом и без него должно быть кри-тически пересмотрено для нашего понимания таких сообществ.
Multiscale patterns of spatial and temporal variation in density and population structure were used to evaluate the generality of a three-trophic-level cascade among sea otters (Enhydra lutris), invertebrate herbivores, and macroalgae in Alaska. The paradigm holds that where sea otters occur herbivores are rare and plants are abundant, whereas when sea otters are absent herbivores are relatively common and plants are rare. Spatial patterns were based on 20 randomly placed quadrats at 153 randomly selected sites distributed among five locations with and four locations without sea otters. Both sea urchin and kelp abundance differed significantly among locations with vs. without sea otters in the Aleutian Islands and southeast Alaska. There was little (Aleutian Islands) or no (southeast Alaska) overlap between sites with and without sea otters, in plots of kelp density against urchin biomass. Despite intersite variation in the abundance of kelps and herbivores, these analyses demonstrate that sea otter predation has a predictable and broadly generalizable influence on the structure of Alaskan kelp forests. The percent cover of algal turf and suspension feeder assemblages also differed significantly (although less dramatically) between locations with and without sea otters. Temporal variation in community structure was assessed over periods of from 3 to 15 yr at sites in the Aleutian Islands and southeast Alaska where sea otters were 1) continuously present, 2) continuously absent, or 3) becoming reestablished because of natural range expansion. Kelp and sea urchin abundance remained largely unchanged at most sites where sea otters were continuously present or absent, the one exception being at Torch Bay (southeast Alaska), where kelp abundance varied significantly through time and urchin abundance varied significantly among sites because of episodic and patchy disturbances. In contrast, kelp and sea urchin abundances changed significantly, and in the expected directions, at sites that were being recolonized by sea otters. Sea urchin biomass declined by 50% in the Aleutian Islands and by nearly 100% in southeast Alaska following the spread of sea otters into previously unoccupied habitats. In response to these different rates and magnitudes of urchin reduction by sea otter predation, increases in kelp abundance were abrupt and highly significant in southeast Alaska but much smaller and slower over similar time periods in the Aleutian Islands. The different kelp colonization rates between southeast Alaska and the Aleutian Islands appear to be caused by large-scale differences in echinoid recruitment coupled with size-selective predation by sea otters for larger urchins. The length of urchin jaws (correlated with test diameter, r^2 = 0.968) in sea otter scats indicates that sea urchins <15-20 mm test diameter are rarely eaten by foraging sea otters. Sea urchin populations in the Aleutian Islands included high densities of small individuals (<20 mm test diameter) at all sites and during all years sampled, whereas in southeast Alaska similarly sized urchins were absent from most populations during most years. Small (<30-35 mm test diameter) tetracycline-marked urchins in the Aleutian Islands grew at a maximum rate of @?10 mm/yr; thus the population must have significant recruitment annually, or at least every several years. In contrast, echinoid recruitment in southeast Alaska was more episodic, with many years to perhaps decades separating significant events. Our findings help explain regional differences in recovery rates of kelp forests following recolonization by sea otters.
We studied the effect of the abundance of predatory fishes and structural complexity of algal assemblages on the survival of juveniles of the sea urchin Paracentrotus lividus on Mediterranean infralittoral rocky bottoms. Post-settlement juveniles (2–10 mm) were placed on four distinct natural substrates with increasing structural complexity (coralline barren, algal turf, erect fleshy algal assemblages and small crevices) inside and outside the Medes Islands Marine Reserve. Predation on these sea urchins increased at greater abundance of predatory fishes, and decreased with greater structural complexity. The refuge provided by structural complexity, however, decreased with increas-ing size of sea urchin recruits. Predation on the smallest post-settlers was carried out almost exclusively by small fishes (<20 cm), mainly the labrid Coris julis, while the dominant predator of larger juveniles was the sparid Diplodus sargus. Our results demonstrate the cascading effects caused by the prohibition of fishing in marine reserves, and highlight the potential role of small pred-atory fishes in the control of sea urchin populations.
Marine reserves affect areas outside reserve boundaries via the displacement of fishing effort and the export of production. Here we focus on how these key factors interact to influence the results seen once reserves are created. For a settlement-limited fishery, export of increased production from within reserves can offset the effects of dis- placed fishing effort. We develop simple mathematical models that indicate net fisheries benefits can accrue at closures up to and perhaps beyond 50% of total stock area through the export of production, given documented average increases in biomass within reserves. However, reserve monitoring programs face problems identifying independent control sites because the spatial extent of export is unknown. Efforts to monitor reserve impacts on recruitment are further complicated by the fact that large reserve closures are likely nec- essary before significant changes in recruitment can be detected above normal interannual fluctuations. Resolving these limitations requires comprehensive monitoring data before reserves are implemented. Fortunately, studies of reserves that used Before-After, Control- Impact (BACI) experimental designs show that control and reserve sites were equivalent prior to protection, and that control sites improved after reserves were in place. Conse- quently, any bias in our current perception of reserve impacts likely underestimates their effect. Key words: BACI experimental designs of marine reserves; export of fish production; fishing effort; marine protected areas; marine reserves; recruitment; reserve design; reserve monitoring.
High population densities of larger fish within reserves could result in emigration of fish to surrounding non-reserve areas, producing a gradient of abundance and mean size across the reserve boundaries. The difference in fish abundance and size between reserve and non-reserve should be higher for sedentary than for mobile species and for highly catchable than for less catchable species. To test these hypotheses we estimated the abundance and size of fishes by trapping and visual census on fringing reefs in Barbados: 5 reefs within the 2.2 km of the Barbados Marine Reserve (BMR) and 8 reefs in the non-reserve (NR) area within 4 km of the reserve boundaries. The abundance of large, trappable size fish of all species combined was higher in the BMR than in the NR, but abundance of small, nontrappable fish did not differ between BMR and NR. Trap catches decreased gradually with distance from the BMR center, but this gradient of abundance was less evident in visual census counts of trappable size fishes of all species combined, and not apparent in trap or visual census estimates of abundance for individual species. Mean size was larger in the BMR than in the NR for 18 out of 24 species. The relative differences in both abundance and size between BMR and NR did not differ between mobile and sedentary fish taxa. However, for sedentary taxa, the relative differences in abundance and size increased with trappability (the vulnerability to traps, which are the most common fishing method). These patterns suggest that the BMR does protect the fish community from fishing mortality and that emigration rates are generally low. Trappability and mobility depend on complex behavioral characteristics of fishes and are potentially important for the functioning of marine reserves.