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M. Angiolillo et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx 9
Table 6
Results of mixed Poisson regression models for the number of dead specimens in each
sampling unit as a function of the debris type detected. The coefficients can be
interpreted as the expected additional number of dead specimens that are due to each 2003), considering that the most heavily encrusted debris is pre-
debris type. For all tests, p < 0.0001.
Debris types Coefficient C.I. 95% 0.024
5.69
(Intercept) 0.016 0.011 6.46
Line 3.13 1.72 26.86
Net 2.76 1.18
Plastic 2.75 0.28
nian colonies were rarely broken but were found to be covered by
epibionts (mainly the fast-growing parasitic alcyonacean A. corallo-
ides). Colonies of P. clavata were recorded as being detached and
buried in the sediment; thus, showing the typical arborescent mor-
phology, and were rarely found with broken branches. The resis-
tant skeleton of black coral allows this taxa to hold out against
mechanical friction that normally only scrapes the soft tissue of
the branches. As a consequence, these corals were frequently
observed partially covered by epibionts, but were rarely found hav-
ing broken branches or being completely overgrown. On the con-
trary, numerous branching fragments of C. verticillata, known as
being very breakable (Bo et al., 2013), were often observed lying
on the sea bottom, as also reported by Fabri et al. (2014).
In this study, 30% of the observed coral colonies in contact with
debris, showed traces of epibiosis of up to nine different taxa of
sessile invertebrates. Opportunistic fast growing species, such as
hydroids, polychaetes, sponges and bryozoans were widely found
on dead coral branches. Corals are capable of rapidly healing small
lesions. But in cases of more extensive damage or under the fre-
quent occurrence of physical stress, recovery may be difficult
(Bavestrello et al., 1997; Yoshikawa and Asoh, 2004) and the devel-
opment of aggregates of epibionts can lead to the death of colony
portions (Mistri, 1994). Then, once caught by a fishing gear, the
probability of death of a colony can be very high (Yoshikawa and
Asoh, 2004). The positive correlation between the number of dead
colonies and the presence of lost gears in the habitat indicates the
destructive effects of fishing activities. This point is particularly
relevant considering the longevity and slow growing rate of these
coral species, which make them more susceptible and vulnerable.
Other ROV surveys in the western Mediterranean (Orejas et al.,
2009; Madurell et al., 2012; Watremez, 2012; Bo et al., 2013, 2014;
Fabri et al., 2014) have highlighted the widespread presence of
how fishing has impacted all the investigated areas, which reduces
the coverage of these habitat-forming taxa and lastly the diversity
and abundance of associated invertebrates and fish. The decline in
these communities may lead to the significant modification in the
structure and functioning of deep ecosystems whose consequences
are still not clear.
Despite debris is harmful to biota altering the seafloor, these
anthropogenic materials can also provide artificial substratum for
sessile organisms (Watters et al., 2010; Miyake et al., 2011). In this
study, the majority of debris (80%) was colonized quite heavily by
encrusting invertebrates. Nets, usually occurring as large agglom-
erates, showed the highest frequency of epibiosis (66%), probably
due to their greater surface with respect to single strands of nylon
or other debris.
Hydroids, as well as encrusting sponges, observed growing on
all types of debris were the most frequent fouling taxa, as already
recorded by De Palma (1983) and Montanari et al. (1990). It is
known that, due to their fast growth rates, they are among the pio-
neering species, capable to completely colonize artificial substrates
and enhance the settlement of other organisms (Ardizzone et al.,
1989), incorporating debris items into the habitat matrix.
Please cite this article in press as: Angiolillo, M., et al. Distribution and assessment of marine debris in the deep Tyrrhenian Sea (NW Mediterranean Sea,
Italy). Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2014.12.044
Few debris, which did not show any sign of colonization, may
have been discarded or lost relatively recently. The fouling extent
may give an indication to the age of lost gear (Saldanha et al.,
sumably of older origin (Donohue et al., 2001). However, debris
may show different species-specific variations in abundance of
fouling organisms, depending on material, geography, depth and/
or season (Saldanha et al., 2003).
The presence of marine litter, used as substratum or as refuge
by organisms, can increase both the number of species and the
total abundance of individuals in a specific habitat (Katsanevakis
et al., 2007) altering the natural community structure, modifying
the spatial heterogeneity (Saldanha et al., 2003) and in some cases
enhancing the settlement of non-indigenous species (Mordecai
et al., 2011). Therefore, although apparently the presence of marine
litter can increase diversity, this alteration contrasts with the prin-
ciple of habitat and biodiversity conservation and sustainability
(Katsanevakis et al., 2007).
The results here presented can provide a baseline for future
monitoring efforts, as well as a quantitative assessment, useful to
motivate adequate managerial actions. Further studies are neces-
sary to reach a more comprehensive and precise understanding
of litter distributions. Moreover, mapping the abundance of coral
communities remains a necessary step in order to quantify the
threats to which these characteristic environments are exposed.
Acknowledgements
The authors would like to thank the crew and researchers of R/V
Astrea for their support during ROV’s operations. We thank Raffa-
ele Proietti for preparing GIS charts and the native English speaker
Tonia Szkurhan for revising the language on the manuscript.
Finally, the authors would like to thank the anonymous reviewer,
whose suggestions and comments greatly improve the manuscript.
This study was carried out within the framework of two pro-
jects focused on red coral deep-dwelling population, financed by
the Italian Ministry for Environment, Land and Sea (MATTM) and
by the Sardinian Regional Council for Agriculture.
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