J Coast Conserv
DOI 10.1007/s11852-017-0507-7
Anchoring damages to benthic organisms in a subtropical scuba
dive hotspot
Vinicius J. Giglio 1,2 & Maria L. F. Ternes 3 & Thiago C. Mendes 2,4 &
Cesar A. M. M. Cordeiro 2 & Carlos E. L. Ferreira 2
Received: 15 December 2016 / Revised: 26 February 2017 / Accepted: 17 March 2017
# Springer Science+Business Media Dordrecht 2017
Abstract The physical damages to benthic organisms caused
by boat anchorages were assessed in the Arraial do Cabo
Marine Extractive Reserve (ACMER), Brazil. It is one of the
most visited scuba diving sites along the southwestern
Atlantic. Through underwater visual observations, we analyzed if benthic organisms were damaged by anchors and/or
anchor cabling at two dive sites. A total of 112 anchorages
were sampled. Damages to benthic organisms were observed 139 times, mainly affecting epilithic algal matrix,
the zoanthid Palythoa caribaeorum, and the fire coral
Millepora alcicornis. Damages caused by anchor cables
were significantly higher than those caused by anchors
at one site. A significant difference between benthic organisms damaged was observed only for P. caribaeorum, caused
by the anchor’s cable. We present evidence that, at current
visitation levels, anchors are a relevant stressor to benthic
organisms at dive sites in ACMER.
Keywords Subtropical reefs . Scuba diving management .
Recreational diving . Tourism management .
Marine protected area
* Vinicius J. Giglio
[email protected]
1
Programa de Pós-Graduação em Ecologia, Universidade Federal do
Rio de Janeiro, Rio de Janeiro, RJ, Brazil
2
Reef Systems Ecology and Conservation Lab, Universidade Federal
Fluminense, Niterói, RJ, Brazil
3
Programa de Pós-Graduação em Zoologia, Universidade Estadual de
Santa Cruz, Ilhéus, BA, Brazil
4
Departamento de Ecologia, Universidade Federal do Rio de Janeiro,
Rio de Janeiro, RJ, Brazil
Introduction
Impacts of anchoring on benthic organisms have been
widely studied throughout tropical reefs. Mechanical damages have been verified mainly on seagrasses (Creed and
Amado Filho 1999; Milazzo et al. 2004) and coral reefs
(Davis 1977; Jameson et al. 2007), where anchoring activity can break, fragment and overturn several benthic organisms. Not only the anchor itself can be detrimental to
these organisms, but also associated cables and chains can
increase the damaged area by dragging across the substratum or winding around reef organisms and structures
(Dinsdale and Harriott 2004). The loss of benthic organisms due to mechanical damage by anchors causes a considerable reduction in habitat complexity, especially in systems characterized by tridimensionality, such as coral reefs
(Francour et al. 1999). This disturbance may also have an
indirect impact on associated faunal assemblages. For instance, scleractinian corals are important habitat-forming
organisms on coral reefs, providing critical refuge for fish
against predation (Messmer et al. 2011; Coni et al. 2013),
and suitable habitats for small predators to ambush their
prey (Holbrook et al. 2003).
With the increasing pressure of anthropogenic activities,
the physical damage to benthic organisms caused by anchoring activity and divers has become of great concern among
coral reef managers. Scuba diving has become one of the most
popular aquatic recreational activities worldwide (Garrod and
Gossling 2012). By the mid-1980s, the major damage from
recreational diving on corals was related to anchoring
(Harriott et al. 1997; Jameson et al. 1999). To mitigate anchoring impacts, a simple system of mooring buoys has been
widely used and proved to be a successful management approach (Jameson et al. 1999; Tratalos and Austin 2001).
Alongside these mooring buoys, implementation and
V.J. Giglio et al.
enforcement of rigorous carrying capacity programs (Zhang
et al. 2016), and responsible diving practices (Roche et al.
2016), represent management strategies that could be easily
carried out at dive sites but are still inexistent in many destinations, especially in developing countries.
Arraial do Cabo is one of the most visited dive sites on the
Brazilian southeastern coast being known as the country’s
Bdiving capital^. The area represents a transitional zone between
the tropical and subtropical provinces along the Brazilian coast
and is characterized by a relatively high biodiversity in southeastern Brazil (Valentin 2001; Ferreira et al. 2001; Rogers et al.
2014). In 1997, a sustainable use marine protected area named
Arraial do Cabo Marine Extractive Reserve (ACMER) was
created, whereby fishing is allowed exclusively to the local
traditional community, and recreational activities, such as diving
and fishing, are permitted under specific management norms.
Currently, there are 13 dive companies operating within the
boundaries of the ACMER which perform approximately
24,480 dives per year (Giglio, unp. data).
Dive sites of ACMER do not have mooring buoys so diving boats cast their anchors to remain stationary during diving
operations. The main bow anchor of diving boats is placed in the
sand bottom and the secondary anchor, located at the boat stern,
is placed in shallow areas of the rocky reefs. To avoid major
damages to the environment, managers established that secondary anchors should be placed manually in reefs by the dive staff,
avoiding corals or other benthic organisms. However, there have
been no assessments on the effectiveness of this approach to
avoid anchoring damages to the reef biota. In this context, we
assessed the damages caused by anchoring on benthic organisms along rocky reefs at two of the most visited dive sites
within the ACMER. The effects of anchoring are discussed,
and the results of this study are extrapolated to current and
potential future levels of anchoring within the ACMER.
Material and methods
Benthic communities of Arraial do Cabo
The anchors of scuba diving boats were assessed in the dive
sites of Abobrinha and Anequim (Fig. 1). Both areas are
among the most visited by divers in the ACMER and represent small inlets protected from the prevailing NE winds in
Cabo Frio island. The benthic sessile community of
Abobrinha is composed mainly of a conspicuous epilithic algal matrix (EAM) and the zoanthid Palythoa caribaeorum
covering up to 40% of the substratum (Rogers et al. 2014).
Hard corals cover ~13% of the reef, represented by the
branching form Millepora alcicornis, and massive forms
Siderastrea stellata and Mussismilia hispida (Rogers et al.
2014; Lima and Coutinho 2015). At Abobrinha, EAM represents 40 to 60% of benthic cover, with M. alcicornis occurring
down to 4 m deep, while sponges (mainly Aplysina) and the
octocoral Phyllogorgia dilatata are more abundant at lower
depths (ca. 8 m) (Rogers et al. 2014). Likewise, EAM is the
dominant benthic group at Anequim, while M. alcicornis is
restricted to shallow areas, and P. caribaeorum increases its
cover towards deeper areas (ca. 9 m). As indicated by previous
authors cited above, both sites have similar benthic cover
concerning dominant groups. Our aim here in comparing
these two sites was to observe if there were differences in
diving pressure between sites, and if that would lead to similar
effects to benthic fauna.
Prainha
Saco do cherne
Ilha dos Porcos
Brazil
Cardeiros
Ponta Sul
Anequim*
Ponta Leste
Abobrinha*
23°S
0
1500m
42°W
Main dive site
Secondary dive site
* Surveyed site
Fig. 1 Map of the Arraial do Cabo indicating the main dive sites. The main dive sites are those which sustain 90% of total dive annually in the region
(ca. 25,000). A map with all dive sites can be found at www.divepoint.com.br/english/divesites.html
Anchoring damages to benthic organisms
Data collection and analysis
Data was collected between September 2014 and January 2016.
Observers used scuba gear to sample the anchoring underwater.
In order to evaluate possible damages caused by the anchors,
the observer swam along the shallow reefs of the two dive sites,
visually assessing all anchoring along the reef, whilst verifying
if the anchor and its cable were in physical contact with benthic
organisms. Since all physical contact between anchors and benthic organisms resulted in physical damage, dislodgement,
breaks or scratches, we referred to them throughout the text
as ‘damage’. We described whether the damage was caused
by i) the anchor and ii) the cable that connects the anchor to
the boat (see Fig. 2a-d). Some anchors have a meter chain
connected between them and the cable. For analysis purpose,
all were described only as ‘cable’. Damages were assigned
to the following organisms: i) the fire coral Millepora
alcicornis; ii) the massive coral Siderastrea stellata; iii) the
gorgonian Phyllogorgia dilatata; iv) the zoanthid Palythoa
caribaeorum; v) sponges (genus Aplysina); vi) epilithic algal
matrix (EAM); and, vii) sea urchins. Additionally, it was recorded if the anchoring caused damage to more than one organism and if it was damaged in two different areas, for instance, through two parts of the cable.
The differences in the number of damages caused by the
anchor and the cable was verified using Kruskal-Wallis test,
Fig. 2 Damages caused by
anchoring on benthic organisms
in Arraial do Cabo. a Anchor
damaging a colony of the
fire coral M. alcicornis; b anchor
and cable damaging M. alcicornis
and the zoanthid P. caribaeorum;
c cable (chain) damaging
P. caribaeorum; and d suspending
a colony of the massive coral
S. stellata
since data were nonparametric. The number of damages
caused by the anchor and cable according to benthic organism
were compared using the Wilcoxon test. A simple linear model for estimating the number of damages caused by increases
in anchoring, was built to predict damages resulting from increasing diving activity. For instance, anchorages were sampled 112 times, and caused 39 damages on P. caribaeorum.
This value was extrapolated to higher visitation levels by simple multiplication of the results to 2,3,4 and so on.
Results
A total of 112 anchorages were observed, 57 in Abobrinha and
55 in Anequim. Benthic organisms were damaged 139 times,
in which the majority occurred in EAM (n = 53),
P. caribaeorum (n = 39), M. alcicornis (n = 17), sea urchins
(n = 15), sponges (n = 7), S. stellata (n = 6) and P. dilatata
(n = 2). Forty-five percent (n = 52) of anchorages did not
contact any benthic organisms, only the bare rock.
In both sites, EAM and P. caribaeorum were damaged at
higher frequency, followed by M. alcicornis and sea urchins
(Fig. 3a-b). The number of damages caused by the anchor was
not significantly different between sites (Fig. 4a) and the cable
caused significantly more damage to P. caribaeorum at
Abobrinha (χ2 = 12.5, p < 0.001; Fig. 4b). Among the
Fig. 3 Frequency of benthic
organisms damaged by anchoring
in the study sites. a Abobrinha
and b Anequim
(a)
100
Frequency (%)
V.J. Giglio et al.
80
Yes
No
60
40
20
0
Frequency (%)
(b)
100
80
60
40
20
0
Millepora Siderastrea Phyllogorgia Palythoa
alcicornis
stellata
dilatata caribaeorum
sponge
epilithic
algal matrix
sea
urchin
Organism
organisms damaged, a significant difference was verified only
for the cable on zoanthids (Abobrinha mean = 0.33 ± 0.06 (±
SE) damage, Anequim = 0.14 ± 0.05 damage; W = 1862,
p = 0.02; Fig. 4a, b). Extrapolating our results to a conservative estimate of 500 anchorages of scuba diving boats per year
in each dive site surveyed, annually, EAM would be damaged
477 times, P. caribaeorum 351 times, M. alcicornis 153 times,
and S. stellata 54 times (Fig. 5).
Fig. 4 Mean number of damages
to benthic organisms in the
anchorages observed at the dive
sites Abobrinha and Anequim,
caused by: a anchor and b cable,
according to each organism. Error
bars are standard errors. Wilcoxon
test results: *p < 0.05
Discussion
By causing physical breakages, anchor damages are a relevant
stressor to benthic organisms at dive sites in one of the main
scuba diving destinations of the southwestern Atlantic. At
current visitation levels, the fragile corals M. alcicornis and
S. stellata are estimated to be broken 207 times per year in the
surveyed dive sites. Although the size of the damages caused
Fig. 5 Damages caused to
benthic organisms in the two
surveyed dive sites modeled
according to a gradient of
anchorages number. The dashed
line indicates the estimated
anchoring number per year for the
two dive sites surveyed
Number of damages
Anchoring damages to benthic organisms
Epilithic algal matrix
Millepora alcicornis
800
Palythoa caribaeorum
Siderastrea stellata
600
400
200
0
0
500
1000
1500
2000
Number of anchorages
and the recovery rate of organism were not measured, damages were generally severe, causing considerable breakage
and dislodgement. For instance, we observed two entire colonies of S. stellata dislodged from the substrate (see Fig. 2a)
and anchor damage breaking branches of M. alcicornis on
four separate occasions.
The cable was a considerable source of impact to benthic
organisms, being more destructive than the anchor itself, especially when a chain was attached to the anchor (Fig. 2c,d).
Even when the anchor was carefully placed by the dive staff,
the cable stayed in contact with the rocks along the reef at a
horizontal angle and dragged along the bottom. On three occasions, we observed the anchor loosening from the rock,
which resulted in increased damage to the benthic organisms.
Furthermore, this presents a risk to scuba divers, if they are
near the anchor or cable at the time the boat pulls and the
anchor moves. On two occasions, we observed injuries incurred by dive staff while placing the anchor due to collisions
with the reef and sea urchins. Therefore, in addition to potential impacts to the reef, anchoring in ACMER presents a potential risk to diving safety. Mooring buoys would increase the
dive staff’s safety by reducing the risks associated with anchor
placement (e.g. cable entanglement, collision with rocks).
Epilithic algal matrix is an important foraging substrate for
many nominally herbivorous, omnivorous and invertivorous
fishes (Longo et al. 2014). EAM is important functionally
because it is one of the main links between primary production
and higher trophic levels on reefs (Kramer et al. 2013). In our
survey, EAM was the most damaged benthic organism by
anchoring activities. On the other hand, it is expected that
recovery would be fast given the high rates of succession
and replacement (Copertino et al. 2005), minimizing the negative impacts caused by the anchoring in ACMER.
Alternatively, past impact pressure of anchors on more complex reef organisms, likely dislodging corals and sponges,
could facilitate EAM dominance.
In Brazil, the branching coral M. alcicornis is an important
species providing complexity and habitat for reef fishes and a
multitude of invertebrates (Coni et al. 2013; Leal et al. 2013).
At current levels of anchoring in the ACMER, the damages
caused to corals reduce complexity through mechanical damages. These impacts add to a body of multiple stressors that
have markedly reduced the abundance of corals in the region.
In the 1980s, the corals, alongside numerous fishes and invertebrates, suffered a significant decrease in their abundance due
to collection for the aquarium trade (Gasparini et al. 2005).
Additionally, large quantities of lost fishing gear, such as nets
and hooks, are often found entangled on corals, causing damage and increasing the susceptibility of corals to pathogens
(Cassola et al. 2016). In recent decades, the long-term impact
of anchoring on corals and other invertebrates in the
region are unknown. These multiple stressors make the
situation of corals in the ACMER critical. An integrative management approach considering all stakeholders
is urgently required. Corals in the ACMER are almost
at their southernmost distributional limit, and many of them
represent endangered and unique populations (Rogers et al.
2014; Picciani et al. 2016).
Here, we present reasonable evidence that in the rocky
reefs of ACMER, anchoring activity: i) causes significant
impacts on important complexity generators and other benthic organisms; ii) poses a risk to diving safety; and iii) can
reduce the diving potential and revenues may decrease the
aesthetic appeal of reefs. The reduction in both the scenic
beauty of the reefs and the preferred attributes of divers can
lower their satisfaction and their willingness to pay for
diving (Uyarra et al. 2009; Giglio et al. 2015). The local
association of dive companies has requested that ACMER
managers and the coast guard install mooring buoys.
However, bureaucratic barriers and conflicts of interest
among stakeholders have barred their installation. A complete mooring buoy setting program would pose a manageable cost to ACMER of approximately a few thousand in
local currency (~ 4000 US dollars). Mooring buoys appear
to be a low cost-effective tool to reduce physical damage to
the benthic community caused by diving activity, mitigating the ecological impacts on this important reef system of
southwestern Atlantic.
V.J. Giglio et al.
Acknowledgements We thank the diving operators association Associação das Operadoras de Mergulho de Arraial do Cabo and the
Arraial do Cabo marine extractive reserve - ICMBio (through Viviane
Lasmar and Rafaela Farias) for research permits and support. C. Garland
for English editing. The first author was supported by the Brazilian
Ministry of Science and Technology (CNPq). TCM was supported by
FAPERJ (postdoc grant # E-26/202.858/2016). CELF was supported by
grants from CNPq and FAPERJ.
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