First results of embryonic development, spawning and larval rearing of the Mediterranean spider crab Maja squinado (Herbst ) under laboratory conditions, a candidate species for a

First results of embryonic development, spawning

and larval rearing of the Mediterranean spider crab

Maja squinado (Herbst 1788) under laboratory

conditions, a candidate species for a restocking

program

Juana Duran, Elena Pastor, Amalia Grau & Jose Marıa Valencia

LIMIA, Laboratori d’Investigacions Marines i Aquicultura, Port d’Andratx, Mallorca, Spain

Correspondence: Juana Duran, LIMIA, Laboratori d’Investigacions Marines i Aqüicultura, Avenida Gabriel Roca 69, 07158 Port

d’Andratx, Mallorca (Spain). E-mail: [email protected]

Abstract

The Mediterranean spider crab, Maja squinado, is

depleted due to overfishing. The crab has virtually

disappeared from areas where it was abundant,

such as the Balearic Islands and the Catalan

coast. Maja squinado, is economically and ecologi-

cally very valuable, and it is essential to obtain

information on its biology and rearing conditions

to attempt to repopulate the damaged stocks of

the species in the Mediterranean basin. Herein,

we describe the first successful rearing of M. squi-

nado under laboratory conditions. Our results

show that M. squinado is an excellent candidate

for restocking using cultured juveniles. Two con-

secutive broods with a 1–4 day interbrood period

were observed in the laboratory in wild-caught

females, the maximum observed duration of

embryonic development of the egg mass being

32 days at 18.4 ± 0.9°C, and went through four

different stages. The complete larval and first

juvenile development was studied in laboratory

cultures fed enriched Artemia metanauplius. At

19.6 ± 0.6°C, development from hatching to first

crab moult took 17 days, and it comprised two

zoeae stages and one megalopa stage. The sur-

vival rate at the different stages was monitored,

and 7.13 ± 2.3% was achieved at the first crab

instar.

Keywords: Maja squinado, spider crab, spawn-

ing, embryonic development, larval rearing

Introduction

Programmes for enhancing or improving stocks of

several severely depleted crab and lobster species

have been implemented in Japan, North America

and Europe, using aquaculture techniques as a

tool for producing juveniles. Examples are the

swimming crab, Portunus trituberculatus, in Japan

(Ariyama 2000, 2001; Secor, Hines & Place

2002), the blue crab, Callinectes sapidus, in Chesa-

peake Bay (Davis, Eckert-Mills, Youg-Williams,

Hines & Zohar 2005; Zohar, Hines, Zmora, John-

son, Lipcius, Seitz, Eggleston, Place, Schott, Stub-

blefield & Chung 2008), the European lobster,

Homarus gammarus (Beard, Richards & Wickins

1985; Bannister 1998; Browne & Mercer 1998;

van der Meeren 2000; Beal, Mercer & O’Conghaile

2002), the American lobster, Homarus americanus

(Van Olst, Carlberg & Ford 1977 and Beal, Chap-

man, Irvine & Bayer 1998) and the spiny lobster,

Jasus edwardsii (Svasand, Skilbrei, van der meeren

& holm 1998; van der Meeren 2000; Oliver, Stew-

art, Mills, MacDiarmid & Gardner 2005; Mills,

Gardner & Johnson 2006) among other crusta-

cean species. We studied preliminary data on

embryonic development, spawning and larval rear-

ing to assess whether it is possible to restock the

Maja squinado population around the Balearic

Islands.

Maja squinado (Herbst 1788) was reported to be

widely distributed throughout the Mediterranean

and the NE Atlantic to the southern North Sea

© 2011 Blackwell Publishing Ltd 1

Aquaculture Research, 2011, 1–10 doi:10.1111/j.1365-2109.2011.02983.x

(Clark 1986 and d’Udekem d’Acoz 1999). Based

on certain morphological and biometric charac-

ters, Neumann (1998) suggested that the Atlantic

and Mediterranean spider crabs were in fact

different species: Maja brachydactyla (Balss 1922)

and M. squinado respectively. Recently, Sotelo,

Moran, Fernandez and Posada (2008), who used

molecular techniques to study variation in two

mitochondrial genes, showed that Atlantic and

Mediterranean spider crabs are two distinct spe-

cies, corroborating the classification previously

proposed by Neumann (1996), Neumann (1998).

Therefore, it follows that all the records of M. squi-

nado from the NE Atlantic must be considered as

M. Brachydactyla. The geographical delimitation

should be taken into account for the stock

enhancement of the Spanish Mediterranean spider

crab, M. squinado, using conspecific crabs from the

Mediterranean, and never from the Atlantic coasts

(Sotelo et al. 2008).

Spider crabs are species of great commercial

interest in many European countries, with annual

catches of 5000 tonnes according to FAO (1988),

especially in the English Channel and on the north

coast of Spain. In spite of this, it was not until the

early 90s that the first biological and fishing

research on M. brachydactyla was carried out. It

was then when studies related to reproduction

(Gonzalez-Gurriaran, Fernandez, Freire, Muino &

Parapar 1993; Gonzalez-Gurriaran, Fernandez,

Freire & Muino 1998), growth and moult cycles

(Gonzalez-Gurriaran, Freire, Parapar, Sampedro &

Urcera 1995; Sampedro, Gonzalez-Guarriaran &

Freire 2003), population dynamics (Corgos, Ber-

nardez, Verısimo & Freire 2002) and migratory

movements (Gonzalez-Gurriaran, Freire & Bernar-

dez 2002; Corgos, Verısimo & Freire 2006) began

to be carried out in Galician waters. Others like

Clark (1986), Urcera, Arnaiz, Rua and Coo (1993)

and Iglesias, Sanchez, Moxica, Fuetes, Otero and

Perez (2002), studied some aspects of M. brachy-

dactyla larval development and larval and juvenile

rearing. Andres, Estevez and Rotllant (2007),

Andres, Estevez, Anger and Rotllant (2008)

recently carried out laboratory studies and

obtained data on growth, survival and the bio-

chemical composition of the same species.

However, there are only a few studies on the

Mediterranean spider crab, M. squinado Herbst

1788; and in some cases these are rather impre-

cise. This research was mainly carried out by

Stevcic (1963), Stevcic (1968a), Stevcic (1968b),

Stevcic (1971), Stevcic (1973), Stevcic (1975),

Stevcic (1976), who studied the biological, repro-

ductive and migratory behaviour, as well as

moulting and fishery characters based on wild and

aquarium observations. There are no studies on

the reproductive process, embryonic development,

spawning or larval and juvenile rearing under

intensive culture conditions.

The critical decline of the M. squinado popula-

tion all over the Mediterranean basin, despite its

abundance 50 years ago, makes it difficult to

obtain living specimens to work within the Balea-

ric Islands, where LIMIA is carrying out its

M. squinado projects. In the last 4 years, only a

few specimens have been caught per year around

Formentera Island (comments made by Formenter-

a fishermen). In the rest of the Balearic Islands, M.

squinado has not been observed for over 20 years.

The reasons for this rarefaction remain unclear

and have not been specifically studied (Garcıa

2007).

Maja squinado is one of the invertebrate species

included in the Action Plan for the Mediterranean,

and its exploitation in the Mediterranean is regu-

lated according to UNEP 1996 and ZEPIM 1999

(Annex III). In the particular case of the Balearic

Islands, catching M. squinado in marine reserves is

banned due to its delicate conservation status. The

dramatic decline of this population means that

fisheries management tools need to be used to

recover the stock, and restocking with hatchery-

reared juveniles is one possibility; therefore, the

viability of rearing this species in captivity needs

to be studied. This idea is not new, since Bussani

and Zuder 1977 considered that producing M.

squinado juveniles could be a solution for recover-

ing this species in the Gulf of Trieste after its

decline due to overfishing.

This article describes our experiences in collect-

ing a wild broodstock of M. squinado and its adap-

tation to captivity conditions. Spawning of the

species was achieved for the first time in captivity,

and larval rearing took place under hatchery con-

ditions. We obtained preliminary data on egg mass

development, larval growth parameters, intermoult

period and survival at different larval stages. These

experiences represent the first step towards estab-

lishing a detailed protocol for successful mass-rear-

ing techniques, which will allow us to obtain an

adequate number of juveniles to start a pro-

gramme for enhancing the M. squinado population

around the Balearic Islands.

© 2011 Blackwell Publishing Ltd, Aquaculture Research, 1–102

First results of rearing Maja squinado J Duran et al. Aquaculture Research, 2011, 1–10

Material and methods

Broodstock management and embryonic

development

In April 2007, 15 wild M. squinado breeders, 10

males and 5 ovigerous females, were caught in

the ‘Reserve Naturelle de Scandola, Parc Naturel

Regional de la Corse’ (Corsica) by local fisher-

men using trammel nets. From Corsica to the

‘Laboratori d’Investigacions Marines i Aquicultur-

a’ (LIMIA), in Port d’Andratx, Mallorca, they

were transported in a refrigerated van equipped

with two 0.5 m3 tanks and supported with air

pumps and biological filters. The water tempera-

ture was kept at 16 ± 1°C. The trip took 30 h

and the temperature, oxygen and ammonium

levels were checked every 3–4 h. The oxygen

and temperature parameters did not change sig-

nificantly during the trip; however, the ammo-

nium values increased quickly after 2 h, and it

was necessary to add ammonium neutralizer to

the tank water.

As all females were caught carrying a fertilized

egg mass and according to Stevcic (1976) M. squi-

nado mates before ovulation, once at the labora-

tory, males (1.29 ± 0.35 kg) and females

(1.33 ± 0.22 kg) were kept separately in two

5 m3 fibreglass tanks with a water renewal rate of

50 L min�1. Ammonium levels were checked daily

and maintained at values of 0–0.5 mg L�1. Water

temperature and salinity were 18.36 ± 0.94°Cand 37 g L�1 respectively. The crabs were fed on

fresh mussels ad libitum. The broodstock was kept

in a half-light regime with a natural photoperiod.

After the first spawning, the female crabs pro-

duced a second egg mass without mating, which

indicates that M. Squinado has the ability to store

sperm, similar to M. brachydactyla (Gonzalez-Gurr-

iaran et al. 1998).

Ovigerous females were monitored every 2 days

to check the maturity stages of the egg mass and

macroscopic and microscopic characters. To col-

lect newly hatched larvae, a larval collector with

a 500 lm mesh size was installed, and it received

the water that overflowed from the tank with the

females in it. Estimations of the number of newly

hatched zoeae spawned per female were made

volumetrically by counting five 500 mL aliquots

of well mixed larvae from an aerated 60 L con-

tainer.

Larval rearing

At 0 days post hatch (DPH), 6510 newly hatched

larvae from one single spawning of one female were

individually counted and stocked at an initial den-

sity of 70 larvae L�1 in six 15.5 L spherical upwel-

lings with a 150 lm mesh size bottom. The

spherical upwellings were hung in a 1 m3 cylinder-

conical fibreglass tank. The water renewal rate was

2.4 L min�1 in each upwelling. A recirculation sys-

tem was used to maintain the desired water quality

and temperature (19.66 ± 0.58°C). The recircula-

tion system consisted in a 1000 L fibreglass tank,

from which water was pumped through a biological

filter and then through a refrigerator equipped with

an ultraviolet sterilization lamp. Finally, the water

was returned to the tank. Salinity was 37 g L�1,

and the photophase 24L/0D. The dissolved oxygen

ranged from 7.0 to 7.5 mg L�1.

Phytoplankton (Nannochloropsis gaditana and Is-

ochrysis galbana) was added once a day at a den-

sity of 80 000–100 000 cells mL�1 during the

entire larval period to maintain a green medium.

Zoeae, megalopae and first juveniles were fed 24 h

with enriched EG Artemia metanauplii (Easy DHA

Selco, INVE, Animal Health S.A., Vigo, Ponteve-

dra, Espana) distributed in each upwelling twice a

day at a rate of 4.3 prey mL�1 (60 prey per lar-

vae). Before providing the food, the remaining Art-

emia were counted with volumetric procedures to

determine the appropriate quantity to add to reach

the required concentration.

Growth, dry weight, biometric values and survival

determinations

Biometric determinations were performed to the

nearest 0.01 mm using an Olympus stereomicro-

scope (Olympus, Barcelona, Espana S.A.U) equip-

ped with a calibrated eyepiece micrometre. A

sample of 10 eggs from each female was measured

at each egg mass developmental stage. Egg mass

colour, morphological changes, the duration of the

embryonic period and the interbrood period were

macroscopically and microscopically observed. Lar-

val measurements were taken according to the

guidelines described by Guerao, Pastor, Martin,

Andres, Estevez, Grau, Duran and Rotllant (2008).

Replicates of pre-weighted samples (50 individu-

als) at each developmental stage, zoea I (ZI), zoea

II (ZII), megalopa (MG) and first juvenile (C1),

© 2011 Blackwell Publishing Ltd, Aquaculture Research, 1–10 3

Aquaculture Research, 2011, 1–10 First results of rearing Maja squinado J Duran et al.

were kept at 110°C for 24 h. The dry weights

were determined after cooling in vacuo for 1 h.

The specific growth rate (SGR), moult increment

in carapace length (%CLG) and the percentage of

dry weight gain (%DWG) were used as growth

indices and calculated using the following formu-

las:

SGR ¼ 100� ððln final DW - ln initial DWÞ=days between stages

%CLG ¼ 100� ððfinal CL - initial CLÞ=initial CLÞ

%DWG ¼ 100� ððfinal DW - initial DWÞ=initial DWÞ

where CL: carapace length and DW: dry weight.

Survival values were recorded by counting each

container once all the larvae had moulted to the

following instar, ZII (4-5 DPH), MG (9-10 DPH)

and C1 (16-17 DPH), and were related to the ini-

tial stocking densities (Table 2).

Statistical analysis

The statistical treatment of the data was performed

using SPSS 15.0 for Windows software (IBM Espana

S.A., Santa Hortensia, Madrid, Spain). Data are

presented as means ± SD (standard deviation of

the mean). Statistical analyses to determine differ-

ences in size and growth for each developmental

stage were performed using one-way ANOVA at

P < 0.05. Growth in DW and body size was analy-

sed by means of regression analyses.

Results

Hatched zoeae per female and embryonic

development

The number of zoeae hatched per female was high,

and varied from 150 000 to 194 000 newly

hatched zoeae per wild M. squinado female (n = 5).

Zoeae hatched 4 weeks after the crabs arrived at

LIMIA, and four females developed a second egg

mass in captivity (not valued) with an interbrood

period between 1 and 4 days.

As all the females were carrying a fertilized egg

mass when they were caught in Corsica and it

was not possible to study the second egg mass in

captivity, a maximum duration of the embry-

onic period of 32 days at 18.36 ± 0.94°C was

observed. Four different egg mass developmental

stages were observed in all M. squinado females: an

early stage (A) (Fig. 1a) with non-pigmented yel-

low-orange eggs and 90% yolk, which occurred

approximately 32 days before hatching (DBH); the

second stage (B) occurred 20.5 ± 3.53 DBH, with

red eggs in which eye spots and light pigmentation

could already be seen (Fig. 1b); the third stage (C)

showed 75% pigmented brown eggs in which

some movement could be detected (Fig. 1c) and

occurred about 9.0 ± 0.0 DBH; and finally the

fourth stage (D) prior to hatching with 100% pig-

mented black eggs (Fig. 1d) occurred 4.0 ± 0.0

DBH. During embryonic development from stage A

(741 ± 0.0 lm egg diameter) to stage D (830 ±30.73 lm egg diameter), a slight increase in egg

size, 12% of the initial size, was observed

(Table 1). Egg diameters at stage D were signifi-

cantly larger than at stage A (P � 0.05).

Table 1 shows the results of the macroscopic

and microscopic characters, egg diameter and days

before hatching of each egg mass developmental

stage.

Larval development

During larval rearing, the larval stages zoea I, zoea

II and megalopa were observed at 0 DPH, 4–5

DPH and 9–10 DPH respectively (Fig. 2a–c), and

the moult to first juvenile was observed at 16–17

DPH (Fig. 2d). The CL and CW evolution and the

increase in DW during larval development from

one DPH to first juvenile settlement are shown in

Table 2. The following equations represent

growth, and suggest a linear model for larval cara-

pace length and width and an exponential model

for dry weight (see also Fig. 3):

CL ¼ 0:097DPHþ 0:975ðR2 ¼ 0:903Þ

CW ¼ 0:039DPHþ 0:906ðR2 ¼ 0:570Þ

DW ¼ 0:099e0;101 DPHðR2 ¼ 0:944Þ

where CL: carapace length, CW: carapace width

and DW: dry weight. Each larval stage signifi-

cantly increased in CL in relation to the previous

phase, 2.01 ± 0.11 mm at MG in relation to

1.27 ± 0.10 mm at ZII and to 1.18 ± 0.07 mm at

ZI, but no significant differences were found in CW

until the first juvenile stage, and in DW until the



megalopa larval stage, 0.29 ± 0.05 mg with

respect to 0.14 ± 0.02 mg at zoea II and 0.55 ±0.03 mg at the first crab stage (P � 0.05).

Throughout larval development, the highest relative

growth ratio in DW (107%) and CL (58.2%) and spe-

cific growth rate (14.6%) was observed at the megal-

opa stage. The growth ratios were lower at first

juvenile and especially at the zoea II stage.

The highest mortality occurred during the

megalopa stage, which was the larval rearing

phase in which the majority of individuals were

lost, as even the last ecdysis to first juvenile did

not involve such low survival rates. Carapace

length (CL) and width (CW), dry weight (DW),

survival (S),%CLG,%DWG and%SGR of M. squinado

larvae and first juveniles are shown in Table 2.

Discussion

Our results suggest that M. squinado could be an

excellent candidate for rearing in laboratory

conditions to achieve a hatchery-reared juvenile

population to restock depleted areas, such as the

Balearic Islands: metamorphosis to first juvenile

was achieved with a mean survival rate of 7.13 ±2.33%, which is near the survival rate reported by

other authors with M. brachydactyla (12.9 ±1.44%, Andres et al. 2007; 8–13%, Iglesias et al.

2002), but lower than the one achieved by Urcera

et al. (1993) (46%) and by Phena-Lopes, Rhyne,

Lin and Narciso (2005) for Mithraculus forceps

(60.1 ± 5.1%).

Four egg mass developmental stages with differ-

ent colourations were observed in M. squinado.

Stevcic (1976) noticed a red colour stage during

the incubation period of wild Mediterranean spider

crabs M. squinado from the Adriatic Sea. However,

none of the authors who have studied the Atlantic

spider crab M. brachydactyla have mentioned a red

colour stage. Gonzalez-Gurriaran et al. (1993),

Gonzalez-Gurriaran et al. (1998), Garcıa-Florez

and Fernandez-Rueda (2000) and Iglesias et al.

(2002) only described three egg mass developmen-

tal stages for M. brachydactyla, with colouration

varying from orange to dark orange-grey and

finally dark grey in the descriptions by the first

two authors, and from orange to orange-brown

and brown for the third author.

(a) (b) (c) (d)

Figure 1 Maja squinado egg mass developmental stages: (a) egg mass stage A, microscopically (925) and macro-

scopically. (b) egg mass stage B, microscopically (920) and macroscopically. (c) egg mass stage C, microscopically

(920) and macroscopically. (d) egg mass stage D, microscopically (920) and macroscopically.

Table 1 Macroscopic and microscopic observations of Maja squinado egg mass stages

Stage A Stage B Stage C Stage D

Colour Yellow-orange Red Brown Black

Eggs Ø 741 ± 0.00 785 ± 33.74 812.5 ± 25.00 830 ± 30.73

Dbh 32 ± 0.00 20.5 ± 3.53 9 ± 0.00 4 ± 0.00

Character 90% yolk no pigmentation Eye spots Movements 75% pigmentation 100% pigmentation

Colour, egg diameter (lm), days before hatching (Dbh) and microscopic characteristics (Character). Values are given as mean ± SD.



Egg diameters measured during embryonic

development varied between 0.741 mm at stage A

(eggs containing 90% yolk) and 0.83 mm at stage

D (just before hatching). These measurements are

very similar to those previously described by Stev-

cic (1976) for wild M. squinado caught in the Adri-

(a) (b)

(c) (d)

Figure 2 Maja squinado larval stages and first juvenile: (a) larval stage zoea I, 925. (b) larval stage zoea II, 930.

(c) larval stage megalopa, 930. (d) first juvenile, 915.

Table 2 Results of the larval growth and survival of Maja squinado larvae

ZI ZII MG FJ

Dph 1 5 10 17

Carapace length (mm) 1.18 ± 0.07a 1.27 ± 0.10b 2.01 ± 0.11c 2.65 ± 0.15d

Carapace width (mm) 1.04 ± 0.06a 1.06 ± 0.10a 1.16 ± 0.07a 1.80 ± 0.32b

Dry weight (mg) 0.12 ± 0.01a 0.14 ± 0.02a 0.29 ± 0.05b 0.55 ± 0.03c

Survival (%) 100 ± 0.00 88.26 ± 8.9 13.42 ± 2.25 7.13 ± 2.33

% CLG – 7.6 58.2 31.8

% DWG – 16 107 89.6

SGR (%) 3.5 14.6 9.1

SGR, specific growth ratio; ZI, zoea I; ZII, zoea II; MG, megalopa; FJ, first juvenile; Dph, days post hatch. Values are given as

mean ± SD. Means in the same row with different superscripts are significantly different from each other (P � 0.05).

Figure 3 Larval growth of Maja squinado larvae: carapace length and width (mm) on the left and dry weight (mg)

on the right.



atic Sea (0.76–0.92 mm). However, the eggs of M.

brachydactyla seem to have a smaller diameter,

between 0.5 and 0.7 mm, at temperatures from

15 to 18°C, according to Iglesias, Sanchez, Mox-

ica, Fuetes, Otero and Perez (2001).

Stevcic (1967) considered that the time between

hatching and the following brood, that is, the

interbrood period, was a small unspecified number

of days for M. squinado. In our experience, the four

females that developed a second egg mass during

May, showed an interbrood period of one (three of

them) to 4 days. This is shorter than the inter-

brood period found for M. brachydactyla by differ-

ent authors on the northwest coast of Spain, for

example, the 4–5 day interval described by Iglesias

et al. (2002) at 19–22°C or the average of

3.4 days determined by Gonzalez-Gurriaran et al.

(1998) during a complete breeding period; how-

ever, Garcıa-Florez and Fernandez-Rueda (2000)

found a longer period, a mean of 19 days, for M.

brachydactyla on the north coast of Spain.

The same authors described an embryonic devel-

opment duration for M. brachydactyla from 30 to

40 days (Iglesias et al. 2002), 40 to 58 days (Gon-

zalez-Gurriaran et al. 1998) and 28 to 77 days

(Garcıa-Florez & Fernandez-Rueda 2000) depend-

ing on the season, which is similar to the duration

of the embryonic development we observed

(32 days from stage A to D).

We observed two different egg masses in four of

the five females. Stevcic (1967) found that M.

squinado has three broods a year in the Adriatic

Sea, the first between March and May, the second

from late May to early July and the last brood

from July to August. This agrees with our observa-

tions, as our brood female spider crabs were

caught in early May, and developed a second

brood, but not a third. It is possible then that

there was a previous spawning (March) in the

wild before they were caught.

The duration of larval development is very simi-

lar for all the Majidae species currently described,

and agrees with our results: for M. brachydactyla,

15–20 DPH at 18 ± 1°C (Rotllant & Estevez

2005), 6 DPH until the zoea II stage, 12 DPH to

the megalopa stage, 22 DPH to first crab (Urcera

et al. 1993) at the same temperature, 9 DPH to

the megalopa stage and 16 DPH to the first juve-

nile stage at 19–22°C (Iglesias et al. 2002); and

for the newly metamorphosed crabs of Mithraculus

forceps, 9 DPH at 28°C (Phena-Lopes, Figueiredo &

Narciso 2007).

The preliminary growth data obtained for M.

squinado larvae suggest that carapace length and

width grow linearly, but that there is an exponen-

tial growth pattern for dry weight. Other studies

on M. brachydactyla larvae also determined a lin-

ear growth pattern for CL and CW and an expo-

nential pattern for DW (Andres et al. 2008).

However, Iglesias et al. (2002) determined an

exponential pattern for carapace length.

The feed and feeding schedules are very impor-

tant for the seed production of any aquatic organ-

ism. According to Soundarapandian, Thamizhazh-

agan and Samuel (2007), the advantage of using

Artemia for the last feeding of larval mud crab is

that they can contribute to lipids and energy, and

thus the feeding efficiency is higher. Using

enriched Artemia as live food for rearing, M.

brachydactyla larvae has been shown to reduce the

development time and significantly increase the

viability percentage (Urcera et al. 1993; Iglesias

et al. 2002; Andres et al. 2007). Although we did

not use another prey to feed M. squinado larvae,

our results showed a good increase in dry weight

and carapace length, especially at the megalopa

stage. However, the survival rate was the lowest

at this instar out of the entire larval process.

Andres et al. (2007) found a significant increase

in dry weight at the megalopa stage of M. brachy-

dactyla fed enriched Artemia, and suggested it

could be because Artemia enrichments seem to

influence the progress of larval development,

which is reflected in a higher dry weight rather

than higher survival. In our trial, there was

always the same amount of prey per volume

throughout larval development (4.3 prey mL�1).

Due to the considerable reduction in the number

of larvae at the megalopa stage, a higher prey

number per larva was available at this stage and

the feeding rates of megalopa larvae could have

been higher than in other stages. An increase in

Artemia density has been seen to lead to an

increase in dry weight in other decapod crusta-

ceans (Brick 1974; Bigford 1978; Anger & Nair

1979; Minagawa & Murano 1993; and Barros &

Valenti 2003). However, necrophagous and canni-

balistic behaviour at early developmental stages

has been reported for other crab species (Anger &

Nair 1979 and Hamasaki 2003) and could be a

possible explanation for the high specific growth

ratio found at the megalopa stage in M. squinado,

because not all larvae showed pelagic behaviour

all the time (personal observation), and live larvae



could come into contact with dead larvae at the

bottom of the rearing tank.

A decrease in survival at the megalopa stage

has been observed by several authors in other

decapod crustaceans. Urcera et al. (1993) attrib-

uted the significant mortality that occurred during

the first days of the megalopa stage of M. brachy-

dactyla to the change from predatory pelagic

behaviour to benthic behaviour in the larvae,

because the inability to adapt to this change could

cause high mortalities. Phena-Lopes et al. (2005)

described this for the crab Mithraculus forceps, but

they attributed it to an increase in interaction

(cannibalistic behaviour) between megalopa and

zoea II larvae when unsynchronized larval moult-

ing took place. Our observations are more in

agreement with the last authors, as it is common

to observe the earlier moulted megalopae preying

on zoea II larvae, although agonistic behaviour

would not be the only cause for the large decrease

in survival. More work is required to clarify this

issue.

Conclusion

Our results represent the first successful rearing of

M. squinado under laboratory conditions. We

believe that these results, in terms of the high lar-

val hatching rate, several spawnings during the

reproductive season, short larval development,

rapid larval growth and good survival rates, are

very encouraging and suggest that M. squinado is

as an excellent candidate for aquaculture. This

would allow us to plan, in the medium term,

restocking policies with juveniles in selected zones

and protected marine areas around the Balearic

Islands. Although there is a broodstock limitation

in the Balearic Islands, it is possible to obtain wild

breeders of M. squinado from other areas of the

Mediterranean Sea where the species is not

depleted, or use reared breeders at the laboratory,

as long as genetic diversity is maintained. How-

ever, much work is needed to understand the basic

population dynamics (growth, recruitment, matu-

ration, reproductive behaviour) and to provide the

necessary information (management and optimal

feeding of breeders, optimal stocking larval densi-

ties, feeding regime, prey size, etc.) for designing a

hatchery system in the future. The next step is to

conduct further investigations to determine the

parameters needed to develop a culture protocol

that provides a sufficient number of juveniles to

restock depleted areas, such as the Balearic

Islands.

Acknowledgments

The present work is part of the National Plan for

the culture of spider crabs financially supported by

JACUMAR.

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Documents

First results of embryonic development, spawning and larval rearing of the Mediterranean spider crab Maja squinado (Herbst ) under laboratory conditions, a candidate species for a