Abelló, Pere

Revistes Catalanes amb Accés Obert

FEEDING HABITS OF MACROPIPUS TUBERCULATUS (BRACHYURA, 
PORTUNIDAE) OFF THE CATALAN COAST (NW MEDITERRANEAN) 
P. ABELLO 
Abelló, P., 1989. Feeding habits of Macropipus tuberculatus (Brachyura, Portunidae) off the 
Catalan coast (NW Mediterranean). Misc. Zool., 13: 45-50. 
Feeding habits of Macropipus tuberculatus (Brachyura, Portunidae) off the Catalan coast (NW 
Mediterranean).- Macropipus tuberculatus predates opportunistically upon epifaunal crustaceans 
and smali fish. Infaunal organisms such as echinoderms, polychaetes and bivalves constitute a 
smaller part of the diet. Pelagic shrimps are preyed upon during day-time hours while they 
are on the bottom. No significant differences in diet composition were found between the 
sexes. Recent post-moult individuals sbowed the highest proportion of empty foreguts. Ad- 
vanced post-moult individuals showed the highest proportion of full foreguts. Seasonal diffe- 
rences in diet composition are attributed to parallel vanation in prey availability, especially 
with respect to juvenile fish. 
Key words: Macropipus tuberculatus, Brachyura, Portunidae, Feeding habits, Mediterranean. 
(Rebut: 2 V 89) 
Pere Abelló, Institut de Ciincies del Mar, Passeig Nacional, 08039 Barcelona, Espanya. 
INTRODUCTION 
Macropipus tuberculatus (Roux) is a portunid 
crab that inhabits muddy areas on the deep- 
est part of the continental shelf and on the 
upper slope dong the eastern North Atlantic, 
from West Nonvay (CHRISTIANSEN, 1969) to 
Morocco and the Azores (MANNING & HOL- 
THUIS, 1981), including the Mediterranean 
(ZARIQUIEY-ÁLVAREZ, 1968). In the area of 
study (north-western Mediterranean), the spe- 
cies occurs at low densities at depths between 
150 and 400 m (ABELL~ et al., 1988), where it 
is often captured as a minor by-catch of the 
demersai fishery. 
Feeding ecology in portunid crabs has been 
studied mainly u1 commercially important spe- 
cies (CAINE, 1974; HILL, 1976; GONZÁLEZ- 
GURRIARAN, 1978; PAUL, 1981; WILLIAMS, 
1982; LAUGHLIN, 1982). The study of the food 
habits of non-comercial crabs however is re- 
cently increasing, since some of them constit- 
ute important by-catches of demersal and ben- 
thic fisheries and are predators of comercial  
species (ROPES, 1969; CHOY, 1986; ABELL~ &
CARTES, 1987; MORI, 1987). Foregut contents 
of M. tuberculatus have so far only been stu- 
died in the Ligurian Sea (MORI, 1987). 
The present work was undertaken to study 
the feeding ecology of M. tuberculatus in the 
trawling grounds off the Catalan coasts (NW 
Mediterranean), in order to examine its role 
within the demersal ecosystem of the area. 
MATERIAL AND METHODS 
Crabs were collected monthly from February 
to December 1984 using a bottom trawl of 18 
mm cod end mesh size near Barcelona (NE 
Spain) within the depth range 146-420 m. Al1 
trawls were taken during daylight. Crabs were 
placed on ice immediately after collection and 
were deep-frozen within 1-3 h. Sex, size (ca- 
rapace length in mm measured between the 
right frontal sinus and the posterior edge of 
the carapace: c.1.) and moult stage of each in- 
dividual were recorded later. 
Misc. Zool. 13. 1989 
The foregut was dissected and preserved in 
70° ethanol. An estimate of foregut fullness 
was assigned to each foregut: (1) empty os 
near empty (< 25 OIo full); (2) partially full (25- 
49%); (3) full (50-74%), and (4) very full 
75 010). Five moult stages were assigned: (1) 
immediate post-moult, (2) post-moult, (3) ad- 
vanced post-moult, (4) intermoult, and (5) pre- 
mouit (ABELLO, 1989). 
A total of 130 crabs in degrees 3 and 4 of 
foregut fullness (i.e. with full or very full fore- 
guts) were examined for prey contents (83 
males and 47 females). Sizes ranged between 
14 and 31 mm c.1. in males, and between 17 
and 27 mm c.1. in females. Foregut contents 
were examined with a binocular microscope, 
and the different prey items were identified 
to the lowest possible taxonomic level. The 
occurrence of many of the prey types in fore- 
gut contents could very often be established 
only from body fragments, limiting the quan- 
titative expression of the contents. Hence, 
broad taxonomic groups were categorized and 
the results were expressed using the frequen- 
cy of occurrence method, this being most ap- 
propriate for the description of natural diet in 
portunid crabs (WILLIAMS, 1981). Data were 
collected on moult stage and degree of fore- 
gut fullness in 1403 individuals. 
To test for differences in the proportional 
constitution of foregut contents of males and 
females, a chi-squared test was performed on 
the frequency of occurrence of the different 
prey categories (WEAR & HADDON, 1987; STE- 
GEL & CASTELLAN, 1988). Low densities of 
crabs in the area limited the number of crabs 
with full foreguts that could be examined. 
Samples were therefore analysed by season to 
look for differences in diet composition. 
RESULTS 
A) Effect of moult stage on foregut fullness 
Crabs having very recently moulted accoun- 
ted for the highest proportion of empty fore- 
guts (fig. 1); no individuals were found with 
full foreguts (degrees 3 and 4). The highest 
proportion of degree 4 (i.e. very fuíí) foreguts 
was found in post-moult individuals when cal- 
cification begins (moult stage 2). The highest 
proportion of degree 3 and 4 foreguts (i.e. full 
and very full) was found in advanced post- 
moult individuals. Around 23 % of crabs in 
intermoult had full or very full foreguts (de- 
gree of fullness 3 and 4). No evidence of a 
decrease in the proportion of foregut fullness 
degrees 3 and 4 was detected in pre-moult in- 
dividual~. 
B) Diet analysis 
It was not always possible to identifi foregut 
material to the species leve1 because of their 
fragmented and partly digested nature. Since 
soft-bodied animals may be underrepresented, 
broad taxonomic groups were used for al1 ana- 
lyses. No significant difTerence in diet compo- 
sition between the sexes was found ( x 2  = 8.32; 
p > 0.05); data were therefore combined for 
both sexes (table 1). 
Crustaceans constituted the most important 
prey of M. tuberculatus, based on presencelab- 
sence data. They were found in over 72 010 of 
the foreguts examined. Severa1 species were 
identified among prey: the pelagic sergestid 
shrimps Sergia robusta (Smith) and Sergestes 
arcticus Kroyer, the pelagic shrimp Pasiphaea 
sivado (Risso), the nektobenthic shrimp Pro- 
cessa canaliculata Leach, and the benthic bu- 
rrowing shrimp Alpheus glaber (Olivi). Uniden- 
tified euphausiids, decapods and amphipods 
also constituted part of the diet. 
Echinoderms and fish were also commonly 
observed, but not in the numbers found for 
crustaceans (over 18 010 and 10 %, respectively). 
Foraminiferans were quite often found in fore- 
guts (over 24%). However, their role in the 
diet remains unclear. Polychaetes and bival- 
ves were poorly represented (around 9 010 and 
2 010, respectively). Arnong the fish, Calbonl- 
mus maculatus Rafinesque (family Callyonimi- 
dae), a small-sized common ínhabitant of the 
muddy bottoms in the area, was the only spe- 
cies that could be identified. Most fish re- 
mains in the foregut contents were of small- 
sized individuals, as stated by the size of the 
vertebrae and other bones and by the size and 
shape of the otoliths. Other prey groups (in- 
cluding unidentified items) occurred occasio- 
nally . 
Crustaceans were the most important type 
of prey throughout the year, according to pre- 
sencelabsence data (table 2). The proportion 
of crustaceans ingested decreased in autumn, 
with fish accounting for a greater proportion. 
However, fish did not constitute an important 
prey in the remainder of the year. Polychaetes 
were scarce in spring and summer samples. 
The proportion of echinoderms ingested was 
low and did not vary substantially throughout 
the year. 
DISCUSSION 
The present study shows that M. tuberculatus 
probably behaves as an opportunistic preda- 
tor especially on epifaunal mobile organisms, 
such as decapod and euphausiid crustaceans 
Fig. 1. Degree of foregut 
fullness in relation to 
moult stage in the por- 
tunid crab. Macrooious 
and small fish, with infaunal or slow-moving 
organisms (e.g. echinoderms, polychaetes or 
bivalves) accounting for only a smaii percen- 
tage of prey occurrences. 
Cessation of feeding in recently moulted 
crabs and its increase over intermoult values 
when the crab begins to harden the carapace 
has also been detected in other portunid crabs 
(ROPES, 1969; WILLIAMS, 1982; ABELLO & 
CARTES, 1987), and may be a consequence of 
the crabs' need to quickly reconstitute mus- 
cle tissue degenerated prior to ecdysis, as weii 
as to properly harden the carapace. Feeding 
must also cease in advanced premoult indi- 
vidual~, as foreguts, being of ectodermic tissue, 
are also shed during ecdysis. However, this 
fact could not be clearly observed in the pre- 
sent study, probably due to the duration of 
the pre-moult stage, which made it difficult to 
accurately differentiate advanced pre-rnoult in- 
dividual~ ready to ecdysis from the rest of pre- 
moult individuals. 
Foregut fullness estimates may reflect the 
foraging activity of M. tuberculatus during day- 
Foregut fullness 
0 1  0 2  m3 1 4  
tuberculatus. ~ o u l t  1 00 
stages: l .  Immediate 
post-moult (n = 7); 2. 
Post-moult (n = 37); 3. 80 Advanced post-moult 
(n = 140); 4. Intermoult 
(n = 1197); 5. Pre-moult 
(n = 22). Degree of fore- 60 
gut fullness: 1. Empty; 2. H! 
Partially full; 3. Full; 4. 
Very full. 40 
Grado de repleción es- 
tomacal en relación con el 
estado de muda en el 20 
braqztiuro portúnido Ma- 
cropipus tuberculatus. 
Estado de muda: l .  Inme- o 
diata post-muda (n = 7); 1 2 3 4 5 
2. Post-muda (n = 37); 3. Moult stage 
Post-tnuda avanzada 
(n = 140); 4. Itztermuda (n = 1197); 5. Pre-muda (n =22). Grado de repleción estomacal: 1. Vacío, 2. Parcial- 
mente Ileno, 3. Lleno, y 4. Muy Ileno. 
Misc. Zool. 13, 1989 
Table l .  Number and percentage of occurrence of different prey groups in male and female Macropipus tu- 
berculatus. 
Número y porcentaje del numero de presencias de los distintos grupos de presas en machos y hembras de 
Macropipus tuberculatus. 
Males Females Total 
No. 010 No. 010 No. "lo 
Crustaceans 54 65.1 40 85.1 94 72.3 
Foraminiferans 19 22.9 13 27.7 32 24.6 
Echinoderms 18 21.7 6 12.8 24 18.5 
Fishes 10 12.0 4 8.5 14 10.8 
Polychaetes 11 13.3 1 2.1 12 9.2 
Cephalopods 2 2.4 1 2.1 3 2.3 
Bivalves 3 3.6 O 0.0 3 2.3 
Others 14 16.9 5 10.6 19 14.6 
Number of crabs 83 47 130 
time hours. No data on activity patterns of M. 
tuberculatus are available. However, activity 
may increase during the night, as has been 
shown for related infralittoral crab species 
(PATTERSON, 1984). Low densities of M. tuber- 
culatus in the area (ABELLO et al., 1988), and 
the time samples were taken, may affect the 
number of individuals found with fuil foreguts. 
Most crustaceans identified as M. tubercul- 
atus prey were pelagic species showing vertic- 
al migratoñy day-night movements, such as 
Sergia robusta, Sergestes arcticus, Pasiphaea 
sivado and euphausiids. M. tuberculatus is 
accordingly involved to some degree in the 
mechanisms of energy transfer from the pela- 
gic to the benthic system. Quantification is 
however dificult and may be too speculative 
based on the actual data collected (prey pre- 
sences and absences). 
Diets of temperate marine crabs change 
markedly according to different seasonal avai- 
labilities of prey (LAUGHLIN, 1982; CHOY, 1986; 
&ELLO & CARTES, 1987). The clear increase 
in occurrence of small fish in foregut contents 
in autumn samples may be attributed to the 
settlement of demersal juvenile fish, as most 
Table 2. Seasonal percentage occurrence of different prey groups in Macropipus tuberculatus. 
Distribución estaciona1 de los distintos grupos de presas (en porcentaje del número de presencias) en Ma- 
cropipus tuberculatus. 
Winter Spring Summer Autumn 
Crustaceans 68.1 70.0 85.0 53.8 
Foraminiferans 31.9 20.0 22.5 15.4 
Echinoderms 17.0 13.3 22.5 23.1 
Fishes 8.5 10.0 7.5 30.8 
Polychaetes 17.0 3.3 0.0 23.1 
Cephalopods 0.0 3.3 5.0 0.0 
Bivalves 6.4 0.0 0.0 0.0 
Others 21.3 16.6 5.0 15.4 
Number of crabs 47 30 40 13 
sheif and upper slope fish in the western Me- 
diterranean spawn in spring or summer (MA- 
R I N A R ~ ,  1971). Thus, recruitment in some 
demersal fish species may be highly affected 
by crab predation. 
Percentage occurrence of crustaceans in this 
study showed similar values to those obser- 
ved in the Ligurian Sea (MORI, 1987). The dii- 
ferences in diet composition between the two 
Mediterranean populations may well reflect 
djfferences in prey species availability in the 
two areas, especially for echinoderms and 
other benthic organisms. This agrees with 
other data on portunid crabs suggesting they 
are not specialised organisms, but mainly op- 
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Alimerztacion de Macropipus tuberculatus (Brachyu- 
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NO). 
El estudio de contenidos estomacales del braquiu- 
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Feeding habits of Macropipus tuberculatus (Brachyura, Portunidae) off the Catalan coast (NW Mediterranean)

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