The dynamics of meiobenthic community were investigated on sandy sediments of the pilot station of Zoagli (Ligurian Sea) between January 1991 and January 1992. Meiofaunal densities ranged between 447 (April) and 3421 (July) ind./10 cm2. Nematodes were the dominant group comprising on the average 75 % of the total fauna. Harpacticoid copepods were the second most abundant group (from 1.7 to 55.3 %) followed by Turbellaria (on the average 5.5 % of total fauna) and Polychaeta (on average 1.2 % of total fauna). The importance of several environmental parameters (such as total organic matter, grain size and RPD depth) in structuring the meiobenthic community is discussed

Danovaro, R.

Mees, J.

Vincx, M.

Danovaro, R

Mees, Jan

Vincx, Magda

Ghent University Academic Bibliography

Annual dynamics of meiobenthic communities in the Ligurian Sea (Northwestern Mediterranean): preliminary results

Open Marine Archive

 295 
 
 
 
 
 
ANNUAL DYNAMICS OF MEIOBENTHIC COMMUNITIES 
IN THE LIGURIAN SEA (NORTHWESTERN MEDITERRANEAN): 
PRELIMINARY RESULTS 
 
 
Roberto DANOVARO (°), Jan MEES (*) and Magda VINCX (*) 
 
(°) Istituto di Scienze Ambientali Marine, Università di Genova, Corso Rainusso 
14,16038, S. Margherita L., Genova, Italy. 
 
(*) Marine Biology Section, Institute of Zoology, University of Gent, K.L. 
Ledeganckstraat 35, B-9000, Gent, Beigium. 
 
 
 
RIASSUNTO 
 
La struttura e la dinamica di comunità meiobentoniche di una area sabbiosa 
subtidale del Mar Ligure, posta alla profondità di 10 metri, sono state studiate tra il 
Gennaio 1991 ed il Gennaio 1992. La densità della meiofauna era compresa tra 447 
e 3421 ind./lOcm2 (rispettivamente in Aprile e Luglio). I nematodi costituivano il 
gruppo dominante (in media il 75 % della comunità). I copepodi arpacticoidi 
costituivano il secondo gruppo per abbondanza (variando tra l'1.7 ed il 55.3 %) 
seguiti dai turbellari (in media il 5.5 % della meiofauna totale) e policheti (in media 
l'1.2 % del totale). Diversi parametri ambientali (contenuto in materiale organico, 
granulometrìa, profondità dello strato anossico, RPD) sono stati posti in relazione 
alle caratteristiche strutturali della comunità. Viene discussa l'importanza dei   
fattori ambientali nello strutturare la comunità. 
 
 
SUMMARY 
 
The dynamics of meiobenthic community were investigated on sandy sediments 
of the pilot station of Zoagli (Ligurian Sea) between January 1991 and January 
1992. Meiofaunal densities ranged between 447 (April) and 3421 (July) ind./10 cm2. 
Nematodes were the dominant group comprising on the average 75 % of the total 
fauna. Harpacticoid copepods were the second most abundant group (from 1.7 to 
55.3 %) followed by Turbellaria (on the average 5.5 % of total fauna) and 
Polychaeta (on average 1.2 % of total fauna). The importance of several 
environmental parameters (such as total organic matter, grain size and RPD depth) 
in structuring the meiobenthic community is discussed. 
Atti del 10° Congresso A.l.O.L. 
Alassio, 4-6 Novembre 1992 
da pag. 295 a pag. 305 
 
 296 
 
 
 
1. INTRODUCTION 
 
The meiofauna is defined as an assemblage of small benthic metazoans having a 
coherent set of life-history and feeding characteristics which sets them apart as a 
separate evolutionary unit from larger macrofauna (Warwick, 1987). Meiofauna is 
also considered as one of the most important components in marine sediments both 
in terms of abundance and production (Higgins & Thiel, 1988). 
Despite this meiofauna received, untill few years ago, little attention in the 
Mediterranean Sea and very few studies dealt with the distribution of meiobenthos 
in the continental shelf (see Soyer, 1985 for a review) or deeper areas (Soetaert et 
al, 1991). 
The mediterranean basin is considered a semienclosed, oligotrophic System. 
However, meiofaunal densities reported for this area are comparable to those 
recorded in other ocean which are richer in terms of food availability on the sea 
floor (Soyer, 1985). 
Most of the studies suggest that meiofauna populations are related to sediment 
properties (Higgins & Thiel, 1988). However, biological interactions and 
particularly the amount of available food seem to play a significant role in the 
regulation of meiofaunal dynamics. Nevertheless, at the present moment we still 
don't know exactly which are the regulation mechanisms, the factors affecting 
meiofaunal distribution and the importance of meiobenthos in the energetics of 
benthos in the Mediterranean (Gufile & Soyer, 1978). 
In the present study, the observations relative to the annual dynamics of 
meiobenthic communities in a subtidal sandy station of the Ligurian Sea are 
reported. 
 
 
2. MATERIALS AND METHODS 
 
Sediment samples were collected on a monthly basis by SCUBA divers between 
January 1991 and January 1992 in a subtidal sandy station of the Gulf of Marconi 
(Ligurian Sea, Northwestern Mediterranean, Fig. 1). Salinity and temperature were 
recorded using an AANDERAA instrument (mod. 2975). Grain size analysis was 
carried out using dry sieve technique. The depth of the Redox Potential Disconti-
nuity (RPD) was measured on three replicates as depth on which the colour of the 
sediment core turns from grey-brown to black. 
Total organic matter was reported as the difference between the dry weight 
(60°C, 24h) of the sediment and weight of the residue left after combustion at 450°C    
(2 h). Meiofaunal sampling was carried out on two replicate cores (10.7 cm2) after 
division in 3 vertical sections (0-4, 4-8, 8-12 cm). Samples were fixed with a hot 
(60°C), 4 % formaldehyde in prefiltered seawater solution (0.4 µm, Nuclepore 
polycarbonate filters). When sediment was too coarse, a first extraction was based 
 297 
 
 
 
on decantation. The fine 
material (or for the fine 
sediments the whole sample) 
was sieved trough 1000 and 
37 µm mesh sizes. The 
fraction remaining on the 37 
µm sieve was centrifugated 
three times with Ludox TM 
(density 1.18 g cm3 ) in order 
to separate the organisms 
from the sediment grains 
(Heip et al., 1985). All 
meiobenthic animals (of the 
complete core) were counted 
and classified per taxon  
under a stereo microscope 
after staining with Rose 
Bengal. 
 
 
 
 
 
3. DATA ANALYSIS 
 
The whole set of data underwent to least-square regression analysis. Bray-Curtis 
clustering and Two-Ways Indicator Species Analysis (TWINSPAN) was used to 
classify the meiofaunal taxa with replicates kept separately. Analyses were carried 
out on transformed and on non transformed data. When not specified, the results of 
the analyses based on non transformed data are reported. The density values for the 
8 cut levels used for the TWINSPAN analysis are 0,3, 7, 15, 45,150, 750,1500. 
 
 
4. RESULTS AND DISCUSSION 
 
Temperatures recorded during the 13 months investigation showed a typical 
trend characterized by highest temperatures between July and September in 
correspondence to water column stratification (Fig. 2). Lowest temperatures were 
observed in February. As result of the colder air temperature, bottom sediment 
showed temperature higher than at surface waters in March, November and  
January. 
 
 298 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Large seasonal variations were observed both for rain precipitations and for sa-
linity that showed, as consequence of the heavy rainfall during summer, the lowest 
values between May and August remaining quite Constant during the rest of the 
year (Fig. 3). 
 
During the study peri-
od, sediments were always 
characterized by oxic con-
ditions in the top 12 cm. 
Anoxic conditions were 
observed in June (19 cm 
depth), October (16.0 cm 
depth) and January (12 cm 
depth) (Fig. 4). 
Granulometric analysis 
of the sediments in the top 
4 cm is shown in Fig. 5. 
Grain size did not show 
significant variations dur-
ing the year with the only 
exception of May when 
sediments exibited a coar-
ser composition because sampling was carried out after a sea storm. 
Total organic matter content ranged between 0.8 and 2.9 % respectively in June 
and February 91 and January 92. Generally, lowest concentrations were recorded   
in summer (Fig. 6). 
Seasonal variations of total meiofaunal abundance are shown in Fig. 7 and the 
relative  importance  of  the  different  taxa  in  Fig.  8. The  strong  seasonality was 
 
 
 299 
 
 
 
characterised by highest densities during warmest months (3463   247 ind./10 cm2, 
July) while usually lowest densities were recorded in winter. 
The reported densities 
are in good agreement with 
those reported for the 
Mediterranean Sea and 
with those recorded in 
adiacent seas (Table 1 ). 
This is surprising since 
this area is characterized  
by low macrofaunal den-     
sity and biomass when 
compared to other coastal 
areas (Albertelli et al., 
1992). 
Being an usual feature 
of this kind of sediments, 
Nematoda were the domi-
nant group accounting on 
average for 75 % of total 
meiofaunal density (rang-
ing between 30 % in No-
vember and 93 % in 
August, Fig. 9). Copepoda 
harpacticoida were the 
second taxa in terms of 
abundance (ranging be-
tween 1.7 % in April and 
55.3 % in November, Fig. 
9) followed by Turbellaria 
(ranging between 2 %, in 
July and 16 %, in Novem-
ber; Fig. 10) and by Poly-
chaeta (on the average 1.2 % of total meiofaunal abundance, Fig. 10). 
No clear seasonal dynamics can be detected by the result of the cluster analysis 
(Fig. 11). However, a particular feature was observed in November and is the result 
of the temporary copepod recruit. The TWINSPAN analysis allows to identify 
which taxonomic groups are responsible for the observed dynamics (Fig.12). For in-
stance, the bivalve recruit characterised the spring months: March (cut level 1) and 
May-June (cut level 2). Generally low densities were typical of cold months and hig-
hest nematode densities (cut level 8) characterised the warmest months. 
 
 300 
 
 
 
 
 
Few data are available 
on the seasonal cycles of 
abundance of total meio-
fauna (Soyer, 1971, de 
Bovée & Soyer, 1974; 
Hulings, 1974; de Bovée, 
1981; Sandulli & De Ni-
cola, 1990). All of them 
reported strong seasonal 
fluctuations characterised 
by low densities in cold 
months and high peaks in 
summer. In our study we 
found a weak relationship 
between temperature and 
meiofaunal density. Simi-
lar results were observed  
by Soyer (1971) who   
found decreasing seaso-   
nal variations with in-
creasing depth and 
consequently reduced 
temperature variations,   
and indirectly by Bodiou   
& Chardy (1973). How-
ever, no significant rela-
tionships were found    
when the other environ-
mental factors were con-
sidered. 
Another factor usually 
invoked    to    explain    the  
meiofaunal dynamic is the amount of available food. However, in the present study 
we did not find any relationship between total organic matter content and 
meiofaunal densities. Such kind of relationship is usually difficult to establish 
(Coull, 1970; Tietjen, 1977; de Bovée et al, 1979). Khripounoff et al. (1980) 
stressed that the quality of sediment organic matter could not be neglected and 
showed a significant relationship between labile sediment proteins and macrofaunal 
densities. In the deep-sea sediments of the eastern Mediterranean Sea, Danovaro et 
al. (1993) found that microbial biomasses were closely related to the amount of 
labile organic material. In our case, the lack of any relation could be due to the 
largely refractory composition of the total organic matter. 
 
 301 
 
 
5. CONCLUSIONS 
 
The assessment of the meiofauna's role in the sediments of the Mediterranean 
Sea is still based on little evidence. These results confirm the quantitative 
importance of the meiobenthos at shallow depth. Seasonal fluctuations in density 
were only partially due to changes in temperatures but no relationships were found 
with other sedimentary parameters such as grain size and the bulk of sediment 
organic matter. Other factors, such as the amount of labile organic compounds (i.e. 
organic  matter  available  to  benthic  consumers)  should  be probably   taken   into 
 
 302 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
A
c
k
n
o
w
l
e
d
g
m
e
n
t
s 
 
 
Acknowledgements 
 
We would like to thank Prof. Mauro Fabiano (Università di Cagliari) and Prof. 
Giancarlo Albertelli (Università di Messina) for useful criticisms and for providing 
financial support, Dr. Simonetta Fraschetti (Università di Genova) for help during 
sampling and suggestion on the manuscript. Roberto Danovaro was financially 
supported by a grant of the Ministero dell'Università e della Ricerca Scientifica e 
Tecnologica (M. U.R.S. T.) 
 
 
 
 
consideration for understanding 
the factors potentially limiting the 
abundances, trophic strategies   
and dynamics of meiobenthic 
communities in the studied area. 
Further studies are needed for 
identifying the factors related to 
the dynamics of meiofaunal 
communities. 
 
 303 
 
 304 
 
 
 
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Annual dynamics of meiobenthic communities in the Ligurian Sea (northwestern Mediterranean): preliminary results

Annual dynamics of meiobenthic communities in the Ligurian Sea (northwestern Mediterranean): preliminary results

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