Aegean Bath Sponges: Historical Data and Current Status

Abstract

This study attempts to evaluate the status of the populations of bath sponges (species of the genera Spongia and Hippospongia) in the Aegean, combining historical sources dated before a series of disease outbreaks that occurred from 1986 on, unpublished data obtained during the recovery phase after the first incident, as well as a current survey of the main spongiferous beds in the area. The latter was implemented through an extensive sampling trip assisted by professional sponge fishermen, including 55 stations distributed in 17 Aegean islands. Our analysis of population and morphometric data exhibits regeneration potential for bath sponge stocks, yet highlights the contrast between their present status and that of historical times. Uniformity is not evident, as several populations retain high abundances, while simultaneously areas purportedly rich in bath sponges appear deprived. Small-scale environmental regimes in the Aegean are proposed as the shaping factors of this situation; however, the importance of additional elaborate studies and the implementation of an effective regulation scheme regarding their fisheries are stressed.

Full text

Reviews in Fisheries Science
,19(1):34–51,2011
Copyright C
!! Taylor and Francis Group, LLC
ISSN: 1064-1262 print
DOI: 10.1080/10641262.2010.531794
Aegean Bath Sponges: Historical
Data and Current Status
E. VOULTSIADOU,1T. DAILIANIS,1,2C. ANTONIADOU,1D. VAFIDIS,3
C. DOUNAS,2and C. C. CHINTIROGLOU1
1Aristotle University of Thessaloniki, School of Biology, Department of Zoology, Thessaloniki, Greece
2Hellenic Centre for Marine Research, Institute of Marine Biology and Genetics, Heraklion, Crete, Greece
3University of Thessaly, School of Agricultural Sciences, Department of Ichthyology and Aquatic Environment, Nea Ionia,
Magnesia, Greece
This study attempts to evaluate the status of the populations of bath sponges (species of the genera Spongia and Hippospongia)
in the Aegean, combining historical sources dated before a series of disease outbreaksthat occurred from 1986 on, unpublished
data obtained during the recovery phase after the first incident, as well as a current survey of the main spongiferous beds in the
area. The latter was implemented through an extensive sampling trip assisted by professional sponge fishermen, including 55
stations distributed in 17 Aegean islands. Our analysis of population and morphometric data exhibits regeneration potential
for bath sponge stocks, yet highlights the contrast between their present status and that of historical times. Uniformity is
not evident, as several populations retain high abundances, while simultaneously areas purportedly rich in bath sponges
appear deprived. Small-scale environmental regimes in the Aegean are proposed as the shaping factors of this situation;
however, the importance of additional elaborate studies and the implementation of an effective regulation scheme regarding
their fisheries are stressed.
Keywords Eastern Mediterranean, sponge fishing grounds, sponge harvesting, sponge disease, production, Porifera
INTRODUCTION
The sponges of the family Spongiidae (Porifera: Dictyocer-
atida) are known for their softness, elasticity, and water retention
capacity. These characteristics are derived from the structure of
their skeleton, which consists of a dense network of resilient
fibers. The above qualities were noticed very early and appreci-
ated by humans rendering sponges one of the first marine animal
groups exploited in the western civilization (see Voultsiadou and
Tatolas, 2005).
Bath sponges have been collected and used in the Mediter-
ranean Sea since prehistoric times. Depictions of sponges on
frescoes and vases dating back to the Late Bronze Age have
been found in the Aegean islands, Crete and Melos (Figure 1),
while plenty of records on sponges occur in the Classical Greek
literature. Oppian (2nd c. BC) in his Halieutica (5.612) gives
adetaileddescriptionofthespongeharvestingprocedureby
Address correspondence to Eleni Voultsiadou, Department of Zoology,
School of Biology, Aristotle University of Thessaloniki, P.O. Box 134, Thessa-
loniki 54124, Greece. E-mail: elvoults@bio.auth.gr
sponge fishermen: their prayers to Apollo before they dived, the
thick rope around their waist, the heavy lead weight for staying
underwater, the sickle for cutting sponges, and their struggle
to emerge as soon as possible after having harvested the black
sponges growing on the rocks. Dioscorides (1st c. AD) in Mate-
ria Medica (5.120) describes the process of cleansing, bleach-
ing, and drying the collected sponges to make them suitable for
usage. The use of sponges in Greek antiquity has been surveyed
in detail by Voultsiadou (2007). During the late 19th century
and the first half of the 20th century, with the development of
diving equipment and the use of dredging methods, intensive
sponge fishing has been practiced in the Eastern basin of the
Mediterranean, mainly along the Aegean, Tunisian, south Ital-
ian, Libyan, and Egyptian coasts; the peculiarities of this activity
have brought about a remarkable cultural heritage in involved
coastal communities (see Pronzato and Manconi, 2008).
Bath sponges represent a small proportion of the whole range
of sponge species recorded in the Mediterranean. Three species
of the genus Spongia, i.e., S. officinallis Linnaeus, 1759; S.
lamella Schulze, 1879 (previously known as S. agaricina); S. zi-
mocca Schmidt, 1862; and the species Hippospongia communis
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AEGEAN BATH SPONGES: HISTORICAL DATA AND CURRENT STATUS 35
Figure 1 Depiction of sponges in Aegean prehistoric localities. (A) Sponges
on the upper and lower border of the “Dolphin fresco” in Knossos, Crete,
1700 BC, according to Evans (1930); (B) Part of the “Flying fish fresco” in
Phylakopi Cave, Melos Island, 2000–1550 BC, showing a bath sponge on the
floor; (C) Clay vase from Kamares Cave in central Crete, 1900–1700 BC. The
last representation was made by Evans (1921), who claimed that the depicted
objects were fossil sponges, while according to Arndt (1935) they are more
likely recent bath sponges. (Figure is available in color online)
(Lamarck, 1814) have been actively harvested for their com-
mercial value. S. officinalis occurs in two morphotypes, namely
“adriatica” (the common Mediterranean type) and “mollissima,”
amorphconfinedtothespecies’southeastdistributionrange.
The latter was recently considered a separate species under the
name S. mollissima by Pronzato and Manconi (2008), but this
is not adopted in our study as explained in the Discussion.
Despite the economic and cultural importance of bath
sponges, little effort has been devoted in research regarding
their fishery (Becerro, 2008), while surprisingly little is known
on their populations along the Mediterranean coastline. The
interest in their status was triggered after a series of disease out-
breaks during the last three decades (Webster, 2007). An early
estimation of the impact the first large-scale epidemics had on
Mediterranean bath sponges was given by Vacelet (1991). This
was followed by a few preliminary evaluations of local commer-
cial sponge populations for Tunisia (Ben Mustapha and Vacelet,
1991), Apulian Ionian coasts (Pronzato et al., 1996), Egypt
(Castritsi-Catharios et al., 2005), Libya (Milanese et al., 2008)
and the South Aegean Sea (Voultsiadou et al., 2008), as well as
information regarding the sponge beds of the Aegean, presented
in a book (Castritsi-Catharios, 1998) aiming at the broader au-
dience. In all the above works a gradual decline of bath sponge
beds after 1986 is ascertained, attributed to the synergetic ac-
tion of harvesting and the disease. The condition became even
worse during the last decade due to some new mortality events;
it is claimed that anomalous increases in the sea temperature
in the years 2003 and 2006–2007 played a key role therein
(Pronzato and Manconi, 2008; Garrabou et al., 2009). The in-
tensity and frequency of such incidents led to the inclusion of
all bath sponge species in the Barcelona Declaration (Annex II)
and the Bern Convention (Appendices II and III) as justified for
regulation of their exploitation regime.
In the Aegean Sea, bath sponge species have been tradition-
ally harvested by qualified sponge fishermen. Although popula-
tions of the four Mediterranean bath sponge species have been
recorded (Castritsi-Catharios, 1998; Voultsiadou, 2005; Kefalas
et al., 2003), the sponge beds in this archetypal sponge-fishing
area have not been surveyed in detail and few data on bath
sponge abundance and biometry have been published, as was
previously pointed out by Voultsiadou et al. (2008). Limited
and fragmented information on the exploitation of the Aegean
sponge grounds exists in a small number of old (Arndt, 1937)
or more recent (Bernard, 1987) publications. After the first out-
break of the sponge disease in Greek waters in 1986, a rough
estimation of sponge production in different areas of the Aegean
and the Ionian Sea (Castritsi-Catharios, 1998) revealed a com-
plicated situation: in some previously known fisheries beds the
sponge populations were totally extinct; in others they appeared
recovered or were in a process of recovery. Voultsiadou et al.
(2008) also recorded some recovery signs in certain areas of the
south Aegean.
Due to the evident decrease of Mediterranean bath sponge
production, an increase in the price of natural sponges has been
observed, reaching high rates for bath sponges of Mediterranean
origin (see Milanese et al., 2008). The latter are highly valued
in the international trade compared to species of Caribbean or
Indo-Pacific origin, due to intrinsic quality characteristics as
they are empirically evaluated by sponge fihermen and mer-
chants (Hyatt, 1877; Moore, 1910; Josupeit, 1990). This ongo-
ing demand, resulting in intense harvesting, calls for research
towards the sustainable exploitation of sponge stocks, which, in
turn, requires the comprehensive knowledge of their status.
Considering all of the above, the present work aims to give
an assessment of current bath sponges stocks in the Aegean Sea
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36 E. VOULTSIADOU ET AL.
by providing information on the diversity, population density,
biometry, and health status of the exploited species. This infor-
mation will form the basis for creating a time-series data base,
which, in turn, will be valuable for constructing a consistent
framework of recursive monitoring of bath sponges’ popula-
tions; this action seems imperative to effectively manage the ex-
ploited resources. Moreover, an attempt to describe the situation
of Aegean sponge harvesting over the years is made by com-
piling published data from the literature and unpublished data.
The essential advances and practices required for the preser-
vation and future sustainability of this valuable marine natural
product are also discussed.
MATERIALS AND METHODS
Historical Data Collection and Treatment
Two separate activities were carried out in order to assess
the earlier status of sponge populations in the Aegean Sea.
On the one hand, a critical review of recent and old sources
was accomplished, in search of information on sponge fishing
process and production in different areas of the Aegean Sea
(Anonymous, 1877; Flegel, 1908; Moore, 1910; Panagiotopou-
los, 1916; Arndt, 1937; Serbetis, 1947; Bernard, 1987; Pecos,
1983; Anonymous, 1991, 1995, 1996, 1998). Data on sponge
production in recent years were acquired from the Fisheries De-
partment of the Ministry of Rural Development and Food. The
harvest estimates published in the FAO sponge fisheries statis-
tics (FAO, 2010), extending over a 60-year time period, were
consulted as well.
On the other hand, an assemblage of raw, unpublished data
on bath sponge production collected by three of the authors dur-
ing the years 1988–1989, immediately after the first outbreak
of the sponge disease, was analyzed in order to estimate the
impact this epidemic had on Aegean sponge populations by that
time. These data were collected in the framework of a research
project funded by the Fisheries Department of the Ministry of
Agriculture, designed primarily as a financial support for the
economically affected sponge fishermen. The detailed informa-
tion kept by the sponge fishermen on board (expressed as the
total weight of processed sponge product collected by the Ka-
lymnian fishing fleet from distinct geographic regions) became a
unique opportunity for recording the sponge fishing fleet at that
period as well as the sponge production over the Aegean Sea.
Current Stock Assessment Methodology
Sampling Design and Data Collection
For the purposes of the study, 17 islands of the Aegean Sea
were surveyed (Figure 2) following the SE gradient, which has
been recognized in the distribution of the Aegean and Mediter-
ranean sponges (Voultsiadou, 2005, 2009). These islands were
distributed in three sectors of the Aegean Sea: (1) the Spo-
rades plateau at the northern part, (2) the Cyclades–Dodecanese
plateau at the central part, and (3) the Crete–Karpathos arch,
at the southern part; these sub-regions can be distinguished
according to their geomorphologic (Sakellariou et al., 2005),
physico-chemical (Zervakis et al., 2005), and biological char-
acteristics (Gotsis-Skretas and Ignatiades, 2005; Voultsiadou,
2005).
The selection of islands in each sector was based on previ-
ous information regarding the distribution of bath sponges in
the Aegean (Castritsi-Catharios, 1998; Voultsiadou et al., 2008;
interviews with sponge fishermen conducted by the authors),
including also the area of the National Marine Park of Alon-
nisos and Northern Sporades (NMPANS). Covering an area of
2,220 km2,the NMPANS was assigned as Marine Park since
1992, constituting the largest Marine Protected Area (MPA)
in the Mediterranean Sea (Badalamenti et al., 2000). At the
coastline of each island two stations were set; in cases where
extended spongiferous beds were detected, additional stations
were assigned. Thus, overall, 55 stations were surveyed (Figure
2). Sampling was carried out during summer 2007 and summer–
autumn 2008 in depths down to 50 m by one scientist and one
sponge fisherman using the surface air supply diving method
currently used in Greek sponge fisheries (see Results section).
Sampling at each station involved in situ measurements in or-
der to estimate bath sponge diversity and abundance as well
as specimen size. For this purpose, each dive was led by the
professional fisherman according to standard commercial fish-
ing practices (at sponge beds with sparse individuals the diver
swims freely at a depth of two or three meters above the sea bot-
tom, thus investigating a broader area, approaching the bottom
occasionally to harvest spotted specimens; at rich sponge beds,
the diver usually stays close to the bottom, harvesting specimens
and then moving towards the next most closely visible one), and
each specimen encountered along the diving route was mea-
sured. To keep the fishing effort equal among stations, each dive
lasted for 90 min. The route for each dive was tracked by GPS
on board and distance was calculated to estimate length of in-
vestigated area; from these data the abundance of bath sponges
was estimated as number of individuals per km of investigated
area, in order to ensure comparability among analyzed data.
All sponges encountered at each station were measured in situ
for their dimensions in three axes (maximum length L, maxi-
mum width D, and maximum height H) and the product of these
values was used to approximate sponge size as volume (V) in
liters (L). In certain cases, due to harsh weather conditions,
dimensions were not recorded. During the dives, 30 randomly
chosen individuals of S. officinalis and 20 of H. communis were
collected from each geographic sector. They were processed (re-
moval of living tissue) on board, and measured for dry weight
(Wd), i.e., processed product weight (10 g accuracy), in order
to describe length-weight relationships. This procedure was fol-
lowed in order to minimize the number of specimens collected
at each location, taking into account the abundance of each bath
sponge species. Notes on the health status of the encountered
sponges were kept.
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AEGEAN BATH SPONGES: HISTORICAL DATA AND CURRENT STATUS 37
Figure 2 Map of the Aegean Sea showing in detail the sampling areas. (A) Islands Patmos (Pt), Leros (L), Pserimos (Ps), Kos (Ko), Symi (Sy), Chalki (X),
Telos (T), and Astypalea (As) in Dodecanese; (B) Islands Skiathos (S), Skopelos (Sk), Adelphi (Ad), and Piperi (P) in Northern Sporades; (C) Karpathos Island;
(D) Islands Antiparos (A), Paros (Pa), and Naxos (N) in Cyclades; (E) Western coast of Crete Island (C); (F) Eastern coast of Crete Island.
Statistical Analyses
Multivariate analyses were used to compare the spatial sim-
ilarity of bath sponge assemblages. Non-metric multidimen-
sional scaling ordination (nMDS) via Bray-Curtis distances on
log-transformed numerical abundance data (stations devoid of
bath sponge species omitted for reasons of clarity and accuracy)
was used to visualize changes in composition of bath sponge
fauna across sampling sites. One-way ANOSIM was used to
examine spatial effects on the distribution of bath sponges. The
BIOENV procedure was used to examine whether substratum
type is related to the observed biotic pattern and the degree
of this relation. Multivariate analyses were performed with the
Primer package (Clarke and Gorley, 2006).
Analysis of variance (GLM ANOVA) was used to exam-
ine differences in population density among geographic sectors
(3-level fixed factor) and islands (random factor nested in geo-
graphic sectors). The same model of ANOVA, also considering
the variability among surveyed stations (random factor nested
in islands), was used to test for spatial differences in the es-
timated biometric characters of each sponge species. Prior to
the analyses, data were tested for normality with the Anderson-
Darling test, while the homogeneity of variances was tested with
Cohran’s test and, when necessary, data were log-transformed
(Underwood, 1997). The Fisher LSD test was used for post hoc
comparisons where appropriate.
Size-frequency distributions for each sponge species and
each island separately were constructed using sponge size data.
Morphometric relationships of sponges, i.e., length-weight,
width-weight, height-weight, and volume-weight were esti-
mated using power function (Y =aXbor LogY =loga +
bLogX), applying a linear regression analysis (Sokal and Rohlf,
1987). The degree of association between variables was calcu-
lated by the determination coefficient (R2), while a t-test with a
confidence level of 95% was applied to detect whether the rela-
tive growth rates of sponge biometric characters were isometric
or allometric.
RESULTS
Historical Data on Bath Sponge Stocks and Fisheries
in the Aegean Sea
The analysis of historical data showed that documentation
on the exploitation of the sponge fishing grounds, albeit frag-
mented, exists for the past two centuries. During the greatest part
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38 E. VOULTSIADOU ET AL.
Figure 3 Evolution of breathing equipment used in sponge fishing in the Aegean Sea. (A) Scaphander and diving suit; (B) Fernez diving system; (C) Modern
surface air supply method (narghile). The first two are exhibited in the Nautical Museum of Kalymnos (Photos by T. Dailianis). (Figure is available in color online)
of the 19th century, collection of bath sponges was performed
mostly by means of free diving without breathing assistance, as
well as harpooning from boats. At the end of the 1850s, approx-
imately 4,500 sponge fishermen from the Dodecanese islands
were harvesting sponges on 600 boats, with a mean annual pro-
duction of about 120 tons (bath sponge dry weight). The first
diving apparatus in the form of the diving dress was introduced
in 1866; it consisted of an air pump located on board, a diving
helmet (or “scaphander”), a diving suit made of canvas, as well
as boots and lead weights (Figure 3A). This innovation resulted
in a dramatic rise in sponge production, which by the end of the
century reached approximately 250–300 tons per year.
In the beginning of the 20th century, a fleet of more than
300 vessels under the Greek flag employing around 2,400 men
were active in the sponge fisheries. Out of them, 130 had diving
equipment and employed around 600 divers plus a crew of 1,200,
36 had dredging equipment (“gangava”) and a crew of 160, while
120 were boats engaged in harpooning manned by 440 persons.
Sponge fishery at that time yielded more than 150 tons per year.
The principal areas traditionally harvested in the Aegean were
the islands of the Cyclades and the Dodecanese clusters, Crete,
and some islands in Argo-Saronikos Gulf (Aegina, Hydra).
In the 1920s, two major novelties, the Fernez system, i.e.,
an early version of the modern diving apparatus (Figure 3B),
and the marine engine, contributed to the increase of sponge
yield. For the period 1920–1940, the total Greek production
exceeded 130 tons per year. At that time, around 6,400 people
were employed in the sponge fisheries sector.
After the Second World War, the Fernez system was replaced
by the modern regulator, the apparatus utilized in SCUBA (Self-
Contained Underwater Breathing Apparatus) diving, though
implemented through a surface air supply system. This sys-
tem, called “narghile” by the Greek fishermen (also known as
“hookah”), consists of an air compressor and a medium-pressure
air tank, both housed on board, which provide air to the diver
through an umbilical ending at a diving regulator’s second stage
(Figure 3C). The diver is also aided by modern accessories, such
as the diving mask, fins, and various types of wet or dry diving
suits. For this period, we have a clearer picture of the status
of sponge harvesting in the Aegean, revealing a continuous de-
cline in annual production (Figure 4A) and also a decrease in
the contribution of Greece to the total Mediterranean sponge
production (Figure 4B).
By the middle 1980s, when the first massive mortality inci-
dent occurred in the Aegean Sea, Kalymnos had remained the
sole sponge fishing center in the area. In 1988, according to our
data collected immediately after this disease outbreak, it had a
sponge fishing fleet of around 60 vessels with a crew of about
150 persons. A total of 5.3 tons of bath sponges were harvested
during the two fishing seasons of 1988–1989 in the Aegean
Sea. Specifically, 38 vessels harvested 4.72 tons in 1988, while
22 vessels harvested 0.61 tons in 1989. The combined sponge
production during these two successive years after the first dis-
ease outbreak showed that healthy sponge populations were
unevenly distributed in the different Aegean areas (Figure 5).
Evoia and Skyros Islands (Area B), the Cyclades Islands Paros,
Melos (Area D), and Karpathos Island (Area H) were the most
prolific in bath sponges. In all areas, sponges affected by the
disease were observed in 1988 and to a lesser extent in 1989.
Exceptions were Skyros Island (Area B) in which no infected
sponges existed and the islands of Chios, Lesvos, Psara (Area
C), and Evoia (Area B), the northern coasts of which had not
been affected by the disease. The Ionian Sea was reported as
heavily affected by all fishermen. It is worth mentioning that in
most areas, young sponges were observed in both fishing years,
while in some only during 1989.
Nowadays, according to the Sponge Fishermen Association
of Kalymnos, 100–120 qualified divers are active, working oc-
casionally on 17 sponge fishing boats with an annual produc-
tion of approximately 4 tons (bath sponge dry weight). Their
main fishing grounds are the Dodecanese, the Cyclades, Crete
and Karpathos, the North Aegean coastline, and the SE coast of
Italy. However, bath sponges are not the exclusive catch of these
boats, since some of them periodically carry out bivalve fishing.
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AEGEAN BATH SPONGES: HISTORICAL DATA AND CURRENT STATUS 39
Figure 4 (A) Bath sponge production in Greece and other Mediterranean
countries during the last six decades, presenting a general decrease trend.
Syria, Libya, Egypt, Lebanon, Croatia, Cyprus, Spain, Italy, and former
Yug o s l a v i a S F R , w hi c h d i d n ot h a v e a p e r m a n en t s p o n ge p r o d u c ti o n t h r ou g h
the years, are presented collectively as “Others.” (B) Greek production as a
percentage of the total Mediterranean bath sponge production at the same time
period. Greek production values resulted from a compilation of data derived
from different sources, i.e., Pecos (1983), Bernard (1987), FAO (2010), while
all the other only from the latter source.
Current Population Status of Bath Sponges
Diversity, Abundance, and Habitat Preferences of Bath
Sponges over the Aegean Sea
Four bath sponge species were found in the study area: Spon-
gia officinalis (Figures 6A,B,C,D), S. lamella,S. zimocca, and
Hippospongia communis (Figures 6E,F). The first and the last
were recorded in most of the surveyed islands (54.6% and
36.4% of the sampled stations, respectively) in the three ge-
ographic sectors, and in different substrate types (see Table
1). H. communis was commonly found in Po s i d o n i a o c e a n i c a
meadows and biogenic detritic bottoms, while S. officinalis on
various rocky bottom types (i.e., boulders, platforms, vertical
and moderately inclined walls), with or without vegetation. On
the contrary, S. lamella and S. zimocca were scarcely detected
exclusively in the area of the Dodecanese: the former on verti-
cal rocky walls at depths greater than 40 m and the latter also
on inclined cliffs and in Posidonia meadows at smaller depths
(<30 m).
S. officinalis was the most abundant species, followed by H.
communis;theformershowedincreasedabundanceinSporades
plateau and the latter in Cyclades-Dodecanese (see Table 2).
The species S. lamella and S. zimocca were encountered only
at three and six stations respectively, with very low abundances
(Table 1), and were accordingly excluded from further analyses.
The abundance of S. officinalis showed significant differences
among the studied islands (F =3.54; p <0.01), but not among
geographic sectors (F =0.56; p =0.58); the species appeared
with dense populations in Piperi Island inside the core area
of NMPANS, at one station of Naxos Island, and one station
of Crete Island (Figure 7A). The abundance of H. communis
did not show significant differences between geographic sectors
and islands (F =0.58; p =0.58 and F =1.05; p =0.42,
respectively); this species had sparse populations in most islands
with the exception of the Dodecanese island Kos and a number
of distinct stations on the islands of Crete (C8), Paros (Pa1), and
Piperi (P2) (Figure 7B).
Spatial Similarity of Bath Sponge Assemblages
The non-metric multidimensional scaling ordination used
to check homogeneity of sponge assemblages among the sur-
veyed areas (Figure 8) showed that sampling stations were
grouped according to their geographic dispersion: most stations
of Karpathos and Crete were grouped together, while an as-
semblage consisting of the Northern Sporades stations was also
formed. The stations belonging to the Cyclades and the Dode-
canese archipelagos were scattered, with the exception of Kos
stations, which formed a distinct group due to the prevalence of
H. communis.Thefewexceptionsreflecteithertheoccurrence
of a very dense population of a species or its exclusive presence.
One way ANOSIM showed that geographic sector significantly
affected bath sponges distribution (R =0.25, p <0.01), whereas
the BIOENV procedure showed that substrate type was very
weakly related with the observed pattern (Sr <0.11).
Spatial Size Variability
Overall, 1,352 bath sponges were measured in situ:1,062
specimens of S. officinalis at 20 stations from six islands and
290 specimens of H. communis at 13 stations from five islands
(see Table 2 and Table 3 for biometry data). Significant differ-
ences in the biometric characters of both species were recorded
among the sampling stations, whereas the relevant differences
among surveyed islands and sectors were not significant (Ta-
ble 4). Large-sized sponge specimens were recorded in Piperi
(P1), Antiparos (A1), Karpathos (K6), and Crete (C9) for S. of-
ficinalis and in Piperi (P2), Kos (Ko1, Ko4), and Naxos (N2) for
H. communis (Figure 7). The largest specimens of S. officinalis
and H. communis were observed at C9 and Ko4 respectively and
the smallest at C11 and C9.
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40 E. VOULTSIADOU ET AL.
Figure 5 Distribution of bath sponge production in the Aegean areas in the years 1988–1989, following the first major disease incidence. (A) North Aegean
Sea; (B) Sporades archipelago, Evoia and Skyros islands; (C) Islands Lesvos Chios and Psara; (D) Cyclades archipelago; (E) Dodecanese islands; (F) Peloponnese
(Aegean coasts); (G) Crete; (H) Karpathos and Kassos; (I) Greek Ionian coasts. Numbers represent weight of processed dry sponges in kilograms (Kg).
Size frequency distributions, constructed per surveyed island
for each species separately, were left-skewed in all cases (Fig-
ures 9A,B). Populations of both species consisted mostly of
small- and medium-sized individuals (up to approximately 3 L
for S. officinalis and 6 L for H. communis). The mode of size
distributions was at 0.84 L for S. officinalis and 2.24 L for H.
communis.
Morphometric Relationships
The estimated morphometric relationships, i.e., length-
weight, width-weight, height-weight, and volume-weight, fol-
lowed negative allometry and had a rather strong determina-
tion coefficient, in most cases between 70–80% (Table 5). The
strongest relationship was volume-weight (correlation coeffi-
cient r >0.80) for both species indicating faster volumetric
growth than mass growth; thus, volume appeared to be the best
predictor of the processed product weight. Width and length
were also strongly correlated with dry weight, while in both
species, sponge height had the weakest correlation with sponge
dry weight (r <60).
Present Health Status of Bath Sponges
Considering the health status of bath sponges, affected in-
dividuals were detected in Karpathos and Kos Islands; they
belonged to S. officinalis and H. communis,respectively,and
represented approximately 13% of the studied population at
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AEGEAN BATH SPONGES: HISTORICAL DATA AND CURRENT STATUS 41
Figure 6 The main bath sponges of the Aegean Sea in their habitat (upper row) and after processing, i.e., removal of living tissue (lower row). (A, B) Spongia
officinalis morphotype adriatica; (C, D) Spongia officinalis morphotype mollissima; (E, F) Hippospongia communis (Photos by T. Dailianis). (Figure is available
in color online)
Karpathos and 8% at Kos (in total 1.5% of the surveyed Aegean
population). The unhealthy status of individuals was evidenced
as a partial necrosis of the sponge tissue, with ectoderm missing
and the fibers of the skeleton exposed; this appeared either in a
patchy pattern, scattered throughout the sponge surface (Figure
10A), or affecting a portion of the sponge body with the rest
in seemingly healthy condition (Figure 10B). In some circum-
stances, the sponge seemed to be in a recovery phase, exhibiting
signs of necrosis (exposed skeleton fibers) superficially, but hav-
ing developed new ectoderm underneath, thus, preventing the
progress of necrosis (Figure 10C). Other unhealthy keratose
sponges were also observed, e.g., some Ircinia variabilis (Fig-
ure 10D) and Scalarispongia scalaris specimens in the area of
Sporades.
DISCUSSION
It is fairly difficult to evaluate the progress of bath sponge
population status in the Mediterranean over the years, since very
scarce published data exist for different areas and time periods.
Most of the available fragmentary information concerns bath
sponge production (see Pronzato and Manconi, 2008; Milanese
et al., 2008), and in most cases all commercial types are treated
uniformly, inhibiting any further estimation at the species level.
Yet , i n v a r io us M e di t er ra n ea n ar e as o v e r- e x pl o it a ti on a n d di s-
ease incidences have led to a decreasing trend in sponge abun-
dance and size (Pronzato and Manconi, 2008).
The Aegean Sea has been the archetypal center of sponge
fisheries, and Greece is the second major Mediterranean sponge
producer and traditionally the center of the Mediterranean
sponge fishing industry (Josupeit, 1990). The present work is
practically the first comprehensive study of bath sponge natural
populations in the Aegean Sea, on the basis of both historical
and original research data.
Recent History of Sponge Harvesting and Status of Bath
Sponge Production in the Aegean
As illustrated in the Results section, the bath sponge popula-
tions of the Aegean have been intensively harvested in the past
two centuries. The development of technologies, such as the
marine engine and diving equipment, and the use of the destruc-
tive dredging devices, facilitated sponge harvesting and severely
influenced the structure of sponge populations (Anonymous,
1877; Arndt, 1937). Sponge collection by harpooning before
the 1860s indicates abundant populations in shallow waters; the
extensive use of both the diving dress and dredging equipment
induced the first signs of decline in shallow sponge grounds in
certain Aegean areas, such as the coasts of Crete (Panagiotopou-
los, 1916) and led to the expansion of sponge harvesting to
greater depths in the beginning of the 20th century (Moore,
1910). Still, high annual rates of sponge biomass were produced
in various areas of the Aegean Sea until the Second World War,
which, however, cannot be accurately estimated. This is because
production was supplemented with sponges from the northern
coasts of Africa, where the Greek sponge fishermen extended
their activities (Serbetis, 1947). It should be taken into account,
however, that a certain amount of the Aegean bath sponge pro-
duction was harvested on the Aegean coasts of Turkey (from
Bodrum to the Dardanelles) by Turkish divers (Kata ˘
gan et
al., 1991). While by 1946 sponges were a major Greek ex-
port, fourth after the tobacco, olives, and raisins (Serbetis,
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42 E. VOULTSIADOU ET AL.
Tab l e 1 Distribution of bath sponges among habitat types in the Aegean Sea1
Habitat Types and Stations
Bath Sponge
Species Ns Fa Ab Sp Rv, M Rv, B Rv, B, M Rc M M, B Rw Rlv
Spongia officinalis 30 54.6 38.77 1,062 P1, P2, P3, P4,
As2
A2, N1, N2 Pa1, Pa2,
As3, X1
As1, T1, T2, Sy1 K1, K2,
K3, K4,
K5, K6,
K7, C5
C11, C6
C2, C3,
C9, C10
Spongia lamella 3 5.5 0.07 — As1, T1, T2
Spongia zimocca 6 10.9 0.17 — As2 As3, X1 T2, Sy1 Ko2
Hippospongia
communis
20 36.4 4.43 290 P1, P2, P3, P4,
As2, Pt1, C8
N1, N2 A1, Pa1,
Pa2, X1
T2, Sy1, Ko1, Ko4 Ko2, Ko3 C2
1Ns =number of stations where the species is found, Fa =frequency of appearance, estimated as the percentage of Ns to the overall number of surveyed stations,
Ab =mean abundance over all stations, estimated as the number of specimens encountered per Km during a 90-min dive, Sp =total number of specimens counted
in situ for their dimensions, M =meadows, Rv =boulders or platforms covered with vegetation, Rc =vertical or moderately inclined walls, Rw =boulders or
platforms without vegetation, Rlv =boulders or platforms sparsely covered with vegetation, B =biogenic bottoms. Assignment of sampling stations to habitat
types (for nomenclature see Figure 2).
1947), a gradual decline in bath sponge production started there-
after. The smaller quantities of harvested sponges reflected the
industrial production of inexpensive synthetic sponges intro-
duced in the 1950s (Bernard, 1987) but also the decrease in
their natural populations (Pecos, 1983). It should be noticed,
however, that the Greek sponge production declined also be-
cause other Mediterranean countries, such as Libya, Egypt, and
Tunisia, su ccessively prohibit ed access to Gr eek trawlers and
divers in the 1960s and 1970s (Kavalakis, 2001). In spite of
this, Greece had a very high contribution to the Mediterranean
sponge production (almost 50%) in the late 1960s and 1970s,
which is probably due to the very restricted contribution of Syria
and Turkey, since both countries presented a strong decline in
their sponge production in that period.
Tab l e 2 Distribution of S. officinalis and H. communis in the surveyed islands of the Aegean Sea1
S. officinalis H. communis
Sampling Location Ns Fa Ab Sp Cs Ns Fa Ab Sp Cs
Sporades plateau 4 40.076.94 749 30 3 30.03.93 31 20
Piperi (P1-4) 4 100.0307.79 749 30 3 66.615.72 31 20
Adelphi (Ad1-2) 0 0.00.00 0 0 0 0.00.00 0 0
Skopelos (Sk1-2) 0 0.00.00 0 0 0 0.00.00 0 0
Skiathos (S1-2) 0 0.00.00 0 0 0 0.00.00 0 0
Cyclades–Dodecanese plateau 12 46.112.80 67 30 14 53.87.01 210 20
Antiparos (A1-3) 1 33.33.23 3 0 1 33.32.63 0 0
Paros (Pa1-4) 2 50.020.54 28 15 2 50.011.04 51 5
Naxos (N1-2) 2 100.0108.65 36 15 2 100.07.21 81 10
Astypalea (As1-3) 3 100.03.34 0 0 1 34.02.38 0 0
Chalki (X1) 1 100.02.44 0 0 1 100.06.09 0 0
Tel os (T 1 -2 ) 2 10 0.02.65 0 0 1 50.03.42 0 0
Symi (Sy1-2) 1 50.00.71 0 0 1 50.01.41 0 0
Kos (Ko1-4 ) 0 0.00.00 0 0 4 100.042.00 78 5
Pserimos (Ps1) 0 0.00.00 0 0 0 0.00.00 0 0
Leros (L1-2) 0 0.00.00 0 0 0 0.00.00 0 0
Patmos (Pt1-2) 0 0.00.00 0 0 1 50.00.96 0 0
Karpathos-Crete arch 14 73.726.57 246 30 3 15.82.35 49 20
Karpathos (K1-8) 7 87.521.15 149 15 0 0.00.00 0 0
Crete (C1-11) 7 63.632.00 97 15 3 27.34.74920
Aegean Sea 30 54.6 38.77 1062 90 20 36.4 4.43 290 60
1Ns =number of stations where the species is found at each island or location, Fa =frequency of appearance, estimated as the percentage of Ns to the overall
number of surveyed stations at each island or location, Ab =mean abundance, estimated as the number of specimens encountered per Km during a 90-min dive,
Sp =number of specimens counted in situ for their dimensions, pooled over stations and locations, Cs =number of specimens collected for dry weight estimation.
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AEGEAN BATH SPONGES: HISTORICAL DATA AND CURRENT STATUS 43
Figure 7 Numerical abundance and spatial size variability of the dominant bath sponges, Spongia officinalis (A) and Hippospongia communis (B) at the sampling
stations in the Aegean Sea. Error bars represent standard deviation. For sampling station nomenclature see Figure 2.
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44 E. VOULTSIADOU ET AL.
Figure 8 Spatial similarity of bath sponge assemblages in the Aegean Sea
as illustrated by MDS scaling ordination. Stations without bath sponges were
omitted from the graph. For sampling station nomenclature see Figure 2.
The low contribution of Greece in the Mediterranean sponge
production during the last two decades is a result of both the
detrimental effects of the disease on the Aegean sponge grounds
and the recent entry of other countries, such as Egypt and Croa-
tia, in sponge fisheries, yet with low production (FAO, 2010).
Nowadays, a considerable amount of sponges is harvested by
Greek sponge fishermen in the international waters off the Ital-
ian coasts.
An inherent difficulty in the estimation of actual Aegean
sponge production comes from the active role Greece, and es-
pecially Kalymnos, traditionally has played in the international
sponge market. The central part in this scene is the sponge
merchants (see Bernard, 1976), who buy the sponges from the
fishing boat captains or crews, process and refine them, and for-
ward them to the world trade. Inevitably, merchants have access
to catches from different sponge beds, being of Aegean, North
African, Adriatic, Western Mediterranean, or Levantine origin.
Although merchants scrutinize carefully the origin along with
the quality of the raw product in order to estimate its price, this
information is practically lost afterwards, as the product leaves
the warehouses unlabeled, distinguished only by species or type,
size, and quality. This practice imposes cautiousness, while ana-
lyzing statistical data regarding Aegean sponge production, and
is also enhanced by the occasional mislabeling of product of
extra-Mediterranean origin as Mediterranean. The mentioned
practices regarding sponge trade remained active with minor
modifications until today according to our experience and the
literature (Pronzato and Manconi, 2008; Milanese et al., 2008).
The above authors also stress the necessity to develop suitable
protocols for accurate labeling of trade sponges origin and ob-
jective evaluation of their quality characteristics. Efforts towards
the latter have been implemented by estimating certain charac-
teristics of the spongin fibers or their network that can be related
to the perceived quality of the sponge (Castritsi-Catharios et al.,
2007; Louden et al., 2007).
Current Diversity and Abundance of Bath Sponges over the
Aegean Sea
Our results showed that over the shallow waters (0–50 m)
of the Aegean Sea two of the four Mediterranean bath sponges,
“fino” or “mantapas” (Spongia officinalis)and“kapadiko”(Hip-
pospongia communis), appeared with fairly dense populations.
The former was recorded at about half of the surveyed stations
and the latter at one third; the failure of finding sponges in sev-
eral stations, previously known for their spongiferous beds, is
most probably indicative of the detrimental effects of epidemics
and overfishing on their populations. These two species have al-
ways been the main target for sponge fishermen over the Aegean
Sea, not only because of their denser populations, but also for
their suitability for general use in comparison to the species S.
zimocca and S. lamella.Thesametwospeciesweresimilarly
recorded as the most abundant bath sponges during an earlier
project held in 1993–1994, which checked the Aegean sponge
fishing grounds status after the devastating disease in 1986, as
briefly stated in the relevant project report (Castritsi-Catharios,
1998). The fact that H. communis was then found in somewhat
higher abundances than S. officinalis is possibly due to the ex-
tensive use of the “gangava” dredge, which works on non rocky
bottoms, where the former thrives.
S. officinalis was the dominant bath sponge in the studied area
(83% of the total sponge specimens collected), showing higher
population abundances in the Sporades and the Crete-Carpathos
arch, both characterized as lower-mesotrophic (Gotsis-Skretas
and Ignatiades, 2005). On the other hand, H. communis was
more abundant in the oligotrophic environment of the Cyclades
Archipelago. Such differences in diversity and abundance deter-
mined the pattern of similarity among sampling stations, which
were generally grouped according to their geographic position,
as described in the Results section. This geographic pattern is
in accordance with the different conditions prevailing in these
three distinct regions of the Aegean, namely the northern, cen-
tral, and southern part, as has been demonstrated by several
authors (e.g., Voultsiadou, 2005). The extremely long but dis-
continuous and variable coastline (Anagnostou et al., 2005) and
the distinct geomorphologic, physical, chemical, and biological
characteristics in the sub-areas of the Aegean Sea (Sakellariou
et al., 2005) obviously affect larval dispersal and settlement, as
well as adult survival and growth rates, resulting in local sponge
populations of variable abundance. The variation in abundance
of keratose sponge species among islands or sites around islands
has been recently demonstrated in Australian marine areas as
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AEGEAN BATH SPONGES: HISTORICAL DATA AND CURRENT STATUS 45
Tab l e 3 Biometric characters of S. officinalis and H. communis
L (cm) D (cm) H (cm) V (l)
Species x±sd min max x±sd min max x±sd min max x±sd min max
Spongia officinalis 15.0 ±4.75 4 38 11.3 ±3.69 4 28 6.8 ±2.25 2 18 1.4 ±1.37 0.05 11.25
Hippospongia communis 19.0 ±7.73 7 49 16.0 ±7.17 5 39 11.0 ±4.17 3 23 4.8 ±5.95 0.13 36.71
1L=maximum length, D =maximum width, H =maximum height, V =volume, x=mean value, sd =standard variation, min =minimum value, max =
maximum value. Length values in cm; volume values in liters. Values represent pooled data from all sampled locations.
a result of a combination of physical, biological, and stochas-
tic factors (Duckworth and Wolff, 2007). Besides, in our case,
sponge fishery is a decisive factor that obviously affects natural
population characteristics since the majority of areas rich in bath
sponges are frequently harvested by sponge fishermen.
AgeneraltrendofS. officinalis towards forming larger pop-
ulations in northern Mediterranean areas, such as the Adriatic
and the Aegean, has been previously reported, while the fish-
ing grounds of H. communis extend mostly in the oligotrophic
northern coasts of Africa and southern areas of the Aegean
Sea (see R¨
utzler, 1975; Pronzato and Manconi, 2008; Milanese
et al., 2008). H. communis was the major commercial sponge of
the Mediterranean Sea before the first epidemic of 1986, its main
production coming from Tunisia (Verdenal and Verdenal, 1987).
The production of “tsimoucha” (S. zimocca)and“lagophyto”or
“elephant ear” (S. lamella)hasbeenmuchlowerovertheyears
and this is probably a result of naturally lower abundances, as
has been suggested by our data as well. Only a few specimens of
these two species have been found during our extensive survey.
Regarding S. lamella, this might be attributed to its preference
for deeper waters (Castritsi-Catharios, 1998), which did not al-
low its collection during our research. Nowadays, this species
is harvested by Greek divers in the international waters off the
southeast coast of Italy.
The high abundance of bath sponges inside the surveyed
MPA suggests that protection measures may be in favor of the
viability of sponge populations, in contradiction with other un-
protected or open to uncontrolled sponge fishery Aegean ar-
eas surveyed during this study. It should be taken into account
that before the imposition of the protective measures (earlier
than 1992) the area was regularly exploited by sponge fish-
ermen, while afterwards sporadic, unauthorized harvesting of
bath sponges occurred mostly outside the core of protection.
In other Mediterranean areas, recovery of bath sponge popu-
lations was observed in protected areas, such as the National
Park of Port-Cros on the Mediterranean French coasts (P´
erez
and Capo, 2001). The systematic comparison of sponge com-
munities between protected and unregulated areas will further
elucidate the reasons of these findings. However, the distinc-
tive physico-chemical and biological characteristics of this area
might have played a particular role in the development of robust
sponge populations as discussed in the next section.
Populatio n Cha rac ter ist ics and Morphomet ry of B ath
Sponge Species
The estimated biometric variables of both species showed
spatial variations. Biometric features were different at the study
sites, possibly due to environmental differences linked to their
trophic status. Size patterns in Dictyoceratida can vary greatly
over small spatial scales and those patterns are species specific
(Duckworth and Wolff, 2007). In our case, however, since the
populations of the two species are subjected to exploitation,
these findings might be connected to the intensity of harvesting
exercised in each area as well.
Aminimumdiameterof5cmforS. officinalis and 10 cm
for H. communis has been designated by Greek legislation
Tab l e 4 ANOVA results for the effects of spatial scale on the analyzed biometric characters of S. officinalis and H. communis1
LDHV
Source of Variation df MS F p MS F p MS F p MS F p
Spongia officinalis
Sector 2 177.19 2.67 0.09 72.50 1.98 0.16 0.519 0.02 0.98 50.14 0.08 0.92
Islands (nested in sector) 3 45.21 1.13 0.35 12.80 0.56 0.64 9.11 0.75 0.53 450.25 1.20 0.32
Stations (nested in island) 15 124.40 5.91 0.00267.32 5.29 0.00 46.81 10.81 0.00 1286.38 7.59 0.00
Hippospongia communis
Sector 2 95.95 1.72 0.18 117.48 2.54 0.08 1.66 0.13 0.87 10.19 0.32 0.73
Islands (nested in sector) 2 5.83 0.10 0.91 84.83 1.84 0.16 196.29 4.52 0.06 79.23 2.48 0.08
Stations (nested in island) 9 111.44 2.00 0.03 118.19 2.56 0.00 72.58 5.74 0.00 81.58 2.55 0.00
1L=maximum length, D =maximum width, H =maximum height, V =volume. Values represent pooled data from all sampled locations.
2Significant differences are in bold.
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46 E. VOULTSIADOU ET AL.
Figure 9 Size frequency distribution of Spongia officinalis (A) and Hippospongia communis (B) in each island (sampling stations pooled over islands).
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AEGEAN BATH SPONGES: HISTORICAL DATA AND CURRENT STATUS 47
Tab l e 5 Morphometric relationships of S. officinalis and H. communis
populations in the Aegean Sea
Relation logabrR2
Spongia officinalis (N=90)
Wd =aLb−1.14 ±0.17 1.88 ±0.06 0.73 52.94 (−)allometry(b<3)
Wd =aDb−0.56 ±0.14 1.87 ±0.05 0.77 58.87 (−)allometry(b<3)
Wd =aHb1.21 ±0.14 1.46 ±0.07 0.58 33.95 (−)allometry(b<3)
Wd =aVb3.91 ±0.01 0.81 ±0.02 0.83 67.49 (−)allometry(b<1)
Hippospongia communis (N=60)
Wd =aLb−2.75 ±0.37 2.20 ±0.12 0.87 75.93 (−)allometry(b<3)
Wd =aDb−2.08 ±0.29 2.14 ±0.11 0.88 79.63 (−)allometry(b<3)
Wd =aHb−0.10 ±0.44 1.66 ±0.19 0.65 43.29 (−)allometry(b<3)
Wd =aVb2.89 ±0.05 0.82 ±0.04 0.89 80.43 (−)allometry(b<1)
a=intercept, b =slope, r =correlation coefficient, R2=determination
coefficient, Wd =dry weight, L =length, D =width, H =height, V =
volume, N =number of specimens.
(Fisheries Code, Decree 420, Official Government Gazette
A27/31.1.1970) as the legal harvest size. The mode of size dis-
tributions estimated for S. officinalis equals a sponge of about
13 cm in length, which is much larger than the minimum le-
gal size. Considering H. communis,thesizedistributionmode
equals a sponge of 14 cm in length. This size is also larger
than the minimum legal size. Thus, both species populations
consist mostly of medium-sized individuals constituting these
populations highly suitable for commercial purposes.
Morphometric relationships are practical condition indices
and may vary temporally according to factors, such as food
availability, feeding rate, and reproductive activity (Bagenal
and Tesch, 1978). Yet, the parameter b is characteristic for
aspeciesanddoesnotvarysignificantlyoveryears(Mayrat,
1970). In all cases examined, i.e., length-weight, width-weight,
height-weight, and volume-weight, b values indicated negative
allometry for the morphometric relationships in both species,
suggesting a relatively faster growth in dimensions than mass
growth. The strongest negative allometric relationship for both
species was the relationship volume-weight and, accordingly,
volume appeared to be the better predictor of the processed
product weight.
The estimated relationships were less strong for the species
S. officinalis (r <0.8 with the exception of width-volume re-
lationship). This can be attributed to its increased phenotypic
variability as manifested by the presence of two distinct mor-
photypes, “mollissima” and “adriatica.” As mentioned in the
Introduction, the recent recognition of the former morphotype
as a separate species by Pronzato & Manconi (2008) was not
adopted in this study. Our observations confirmed the extremely
high morphological diversity of this species (see also Pronzato
et al., 2003), since both morphotypes and several intermediate
phenotypes were found among our specimens. A thorough ex-
amination of the genus Spongia in the Mediterranean is needed
before safe taxonomic decisions are established. For the time
being, we endorse the generally accepted classification (see
Vac e le t, 19 8 7; C oo k a n d Be rg qui s t, 2 001 ) a nd t rea t Spongia
officinalis specimens as belonging to one single species.
Bath Sponge Disease Progression and Recovery in the
Aegean Sea
The diseases of marine invertebrates, and specifically
sponges, lately are a global phenomenon (Webster, 2007) and
Figure 10 Unhealthy sponge specimens, in different stages of recovery, collected in the Aegean Sea. (A, B) Spongia officinalis from Karpathos; (C) Hippospongia
communis from Kos; (D) Ircinia variabilis from the Northern Sporades (Photos by T. Dailianis and E. Voultsiadou). (Figure is available in color online)
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48 E. VOULTSIADOU ET AL.
the most recent incidences in the Mediterranean have been at-
tributed to the climatic change and abnormal warming of sea-
water (P´
erez et al., 2000; Garrabou et al., 2009; Maldonado
et al., 2010). Records of sponge diseases exist for the Caribbean
as well, as early as the second half of the 19th century, but also
in the 1930s and 1990s (Witzell, 1998; Cropper and DiResta,
1999); such records motivated Webster (2007) to claim that the
recent frequency of reports of sponge disease episodes might be
an artefact of increased awareness and detection.
During the present field research, several of the traditionally
harvested sponge grounds in which extended populations pur-
portedly existed (according to the sponge fishermen), e.g., on the
north coasts of Crete, were extremely poor or completely devoid
of bath sponges. This is probably due to insufficient recovering
of sponge populations after the repeated disease incidences, but
can also be attributed to the intensive unregulated harvesting of
sponge grounds that remained intact.
Unhealthy bath sponge specimens were observed in only a
few cases during the present research, in the southern sampling
areas. Thus, the signs of recovery of bath sponge populations
revealed for the Dodecanese area by Voultsiadou et al. (2008)
can be documented for extended areas of the northern, central,
and southern Aegean Sea. Besides bath sponges, other unhealthy
Dictyoceratida were observed during our research, although at
its first outburst in 1986, the disease had been restricted to
bath sponges (Vacelet, 1989). This is in accordance to more
recent reports on mortality incidences in the Mediterranean (e.g.,
Garrabou et al., 2009), where disturbances appear to impact an
array of sessile invertebrates.
The effects of the disease during the late 1980s have been
illustrated in the Results section through the data contributed
by sponge fishermen. It is remarkable that the central Aegean
(Figure 5, zones B and C) was the less affected area. This is
most probably due to the beneficial influence of the cold and
brackish Black Sea Water entering the Aegean through Dard-
anelles, flowing southwestwards, and strongly affecting these
areas (Zervakis et al., 2005). Voultsiadou (2005) has discussed
the favorable effects of the conditions prevailing in this part
of the Aegean on the diversity and distribution of sponges. The
lower temperatures and the higher phytoplankton and zooplank-
ton abundances induced by this current seem to be unfavorable
for the persistence of disturbances, such as high temperatures,
associated with the sponge disease in other Mediterranean areas
(Maldonado et al., 2010) and the Caribbean (Vicente, 1989). The
warm waters of the saline Levantine Intermediate Water flowing
northwards and affecting the southern Aegean areas (Zervakis
et al., 2005) may contribute to making local bath sponge popu-
lations more susceptible to the disease. The lower temperatures
are considered to have inhibited the rapid spread of the dis-
ease to the western Mediterranean and greater depths (Vacelet,
1991). Of course, as mentioned above, protection measures in
the area of the Marine Park might have corroborated the benefi-
cial effect of the lower temperatures. It has been noticed that in
sponge fishing grounds the sensitivity of sponges to infections
by microorganisms increases (Gaino et al., 1992).
The young sponges observed in most areas during the 1988–
1989 survey and during the present field research, the latter
shown by the left skewed size frequency distributions, are
evidence of the recovery capability exhibited by bath sponge
populations. The same was observed for the coasts of Egypt in
1995, where young individuals were abundant in shallow wa-
ters: the repopulation of H. communis showed a gradient from
deeper to shallower waters, while the populations located deeper
than 40 m of depth were less affected by the disease (Castritsi-
Catharios et al., 2005). Repopulation records for S. officinalis
exist also from Sicily, where new specimens, settled 5 years after
the epidemics, resulted in complete restoration of a population
within 8 years of the extinction event (Pronzato, 1999).
CONCLUSIVE REMARKS AND FUTURE
PERSPECTIVES
Fairly abundant and healthy local populations of bath sponges
were recorded in several areas of the Aegean Sea. The tradi-
tionally harvested species Spongia officinalis and Hippospon-
gia communis were mainly structuring the sponge grounds. The
studied bath sponge assemblages displayed diversity, abundance
and size patterns reflecting the physical and biological factors
prevailing in the surveyed areas, as shown for other dictyoceratid
sponges.
Due to the long-term intensive harvesting over the past two
centuries and the repeated sponge disease outbreaks during the
last two decades, bath sponge populations in the shallow waters
of the Aegean Sea appear considerably reduced in comparison
with past time periods. This is shown through both the his-
torical review of their harvesting and production data and the
examination of their present status in the main sponge grounds
of the Aegean. An irreversible damage, however, was not wit-
nessed as recruitment has been observed over the Aegean since
1988–1989, confirmed also by the present survey: young indi-
viduals occurred in most areas manifesting the inherent viability
potential of bath sponge population despite their sensitivity to
disease epidemics. Less affected were the areas subjected to
the influence of the Black Sea water flow, indicating that lower
temperatures are probably in favor of bath sponge population
health. This beneficial effect seems to be corroborated by the
protection measures in the area of the Marine Park. All of the
above stress the need for an effective management strategy of
the partially degraded Aegean sponge populations. This is espe-
cially urgent in view of presumed future mass mortality events
as an effect of the global warming trend (Coma et al., 2009).
The first step towards this approach should be the prolif-
eration of our knowledge regarding bath sponge biology and
population dynamics. Spatio-temporal studies of reproduction
should be performed for all species in representative geographic
sectors of the Mediterranean, since reproduction parameters
are influenced by environmental factors, especially temperature
(Kaye and Reiswig, 1991). Gamete and larval dispersal
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AEGEAN BATH SPONGES: HISTORICAL DATA AND CURRENT STATUS 49
should also be experimentally evaluated in order to estimate
interconnection between populations and possible regeneration
sources for diminished stocks. The recent development of
highly informative molecular markers, specific for Mediter-
ranean bath sponge species (Noyer et al., 2009; Dailianis and
Tsigenopoulos, 2010), can prove extremely useful towards this
direction. Data on the current distribution pattern for all species
in the Aegean (and, generally, throughout the Mediterranean)
should be collected. Surveying of depths greater than 50 m
could be of substantial importance, as these habitats are less
exposed to temperature fluctuations; moreover, since they
undergo less pressure by harvesting, they probably host robust
populations that could provide recruitment for shallower ones.
The second step towards an effective management strategy
should be the monitoring of bath sponge populations in recursive
temporal scales, following specific protocols to create a time-
series data base. Parameters putatively affecting their survival,
such as temperature, salinity, and current speed and direction,
should be also recorded temporally in strategically selected ge-
ographic areas. Anomalous shifts in those key environmental
parameters, as well as mortality events, should be recorded and
communicated in short time scale, in order to maximize the
research benefit and propose direct protection measures.
Assuming an adequate level of knowledge acquired through
the above actions, an essential issue towards the sustainable
exploitation of bath sponge populations is the establishment
of a regulation regime in order to actively control sponge har-
vesting and trade. Although Mediterranean bath sponges are
protected under current international schemes and national leg-
islation includes measures towards stocks protection (i.e., max-
imum harvested size), the authors’ experience evidence that
the sponge fishery in the Aegean is essentially uncontrolled
by the state. The small-scale character of sponge fishery, as
well as the lack of organized trading facilities (equivalent to
landing ports) and the personal nature of transaction between
the producers and the merchant, account for the difficulties in
implementing regulation measures. An effective management
scheme would, thus, require the establishment of a controlling
body, which would effectively monitor and regulate production
according to specific guidelines. Additional management mea-
sures, such as the encouragement of cutting the sponge speci-
mens instead of scraping them off (see Stevely and Sweat, 1985)
and the periodical ban of harvesting in selected areas for sev-
eral years in order to help populations regenerate, in a similar
manner as is implemented in the Aegean for harvested red coral
Corallium rubrum (Presidential Decree 420, Official Govern-
ment Gazette A174/24.10.94), would be of further assistance.
Sponge aquaculture has been suggested as a sustainable alter-
native to harvesting of natural populations (Duckworth, 2009).
In the Aegean, sponge farming units were established twice
(Chatzinikolaou et al., 1990; Pronzato et al., 1998) but both at-
tempts were soon abandoned. Recently, Baldacconi et al. (2010)
proposed transplanting of bath sponges from robust populations
to degraded areas for restocking purposes. This method could
further promote sustainable exploitation.
Development of regulating measures, supported by thorough
research on the biology of bath sponges, emerges as a crucial
need if sponge fisheries in the Aegean are to remain viable in the
years to come. The adoption of sustainable and environmental-
friendly practices can assist towards the availability of this
highly appreciated natural product, the support of coastal arti-
sanal communities and the preservation of this traditional craft.
Our results clearly show that Aegean bath sponge populations,
though fragmented and obviously partially degraded, exhibit the
potential for regulated exploitation.
ACK N OWLEDG E MENT S
This research was financially supported by the Greek Min-
istry of Rural Development and Food (EPAL 2006–2008) and
substantially assisted by the Coastal Fishing Society of Kalym-
nos “Panagia Ypapanti.” We are grateful to the crews of the
sponge fishing vessels “Captain Giorgos” and “Themelis” for
sharing their experience and providing precious help on board.
Thanks are due to the Management Body of the NMPANS for
facilitating our field work in the Northern Sporades, Alexis Lo-
las and Apostolis Krystalas for helping with the field work, and
Spyros Gkelis for his contribution in graph preparation. The con-
tribution of Athanasios Koukouras to the collection of sponge
production data should also be acknowledged.
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