Reproductive biology and population parameters of Petrolisthes

J. Mar. Biol. Ass. U.K. (2007), 87, 729^734
Printed in the United Kingdom
doi: 10.1017/S0025315407055282
Reproductive biology and population parameters
of Petrolisthes laevigatus (Anomura: Porcellanidae)
in southern Chile: consequences on recruitment
P. Gebauer*$, K. PaschkeO and C.A. MorenoP
*Centro de Investigaciones I-MAR, Universidad de Los Lagos, Casilla 557, Puerto Montt, Chile.
O
Instituto de Acuicultura, Universidad Austral de Chile, Casilla 1327, Puerto Montt, Chile.
P
Instituto de Ecolog|¤ a y Evolucio¤n, Universidad Austral de Chile, Casilla 567, Valdivia, Chile.
$
Corresponding author, e-mail: [email protected]
The present study describes the reproductive cycle and population structure of the intertidal crab Petrolisthes
laevigatus, an abundant inhabitant of the upper rocky intertidal zone, as well as the relationship between
seasonal patterns in the release of its planktonic larvae and recruiting. A total of 22 900 individuals was
collected along the coast of southern Chile between May 2001 and March 2003. The structure and density of
the adult population (males and females) was relatively constant throughout the study period, although
seasonal variations were observed in these two parameters of the benthic population (males, females, juveniles
and megalopae), principally due to the incorporation of new individuals (recruitment) into the intertidal zone.
Petrolisthes laevigatus presented a prolonged reproductive period. Females with initial eggs were present from the
end of summer through to the middle of the following summer (11 months) and the breeding season lasted
seven months (from August to February), as re£ected in the six months of intertidal settlement (October^
March). The interannual patterns and variations observed in the settlement along the southern Chilean coastline were related to the patterns in the abundance of potential released planktonic larvae. Petrolisthes laevigatus,
unlike most temperate species, has a broad reproductive and settlement period in the south of Chile, which
allows a highly stable structure and population abundance in this intertidal zone.
INTRODUCTION
The reproductive patterns in marine invertebrates are
assumed as adaptive in order to maximize the survival of
their o¡spring and, therefore, population stability (Ro¡,
1992). These patterns have been related to environmental
characteristics, which are responsible for the length and
season of the reproductive period. Species that inhabit
tropical environments reproduce continuously due to the
relatively stable environmental conditions of temperature
and food. Species in temperate regions, on the other
hand, have marked seasonal reproduction coupled with
the cyclic nature of water temperature, day length and
food availability in the pelagic environment (Sastry,
1983). For the majority of temperate crab species, the
peak of larval release is in spring or summer, when the
planktonic food supply is su⁄cient (Anger, 2001). Nonetheless, some temperate species (Cancer magister and Hyas
araneus) release their larvae at the end of winter (Anger,
2001), whereas others (Crangon crangon) have a long reproductive period, producing eggs and larvae with di¡erent
energetic characteristics that allow the success of larvae
in both winter and summer conditions (Paschke et al.,
2004).
Numerous studies have been carried out on the life
history of anomurans. However, information on the population characteristics and reproductive cycle of porcellanid
crabs in the South Paci¢c is scarce. Speci¢cally, information regarding the 16 species that inhabit the Chilean
Journal of the Marine Biological Association of the United Kingdom (2007)
coastline has been limited to zoogeographical reports
(Carvacho, 1980), scant background on the reproductive
biology (Lardies & Wehrtmann, 1996; Lardies et al.,
2004) and larval descriptions (Albornoz & Wehrtmann,
1996).
Petrolisthes laevigatus (Gue¤rin) is a typical inhabitant of
the upper rocky intertidal zone from northern Peru to
southern Chile (Carvacho, 1980). In spite of its extensive
distribution and high abundance in the southern Chile
intertidal zone, its life history is largely unknown with the
exception of the studies carried out in central-southern
Chile (Lardies & Wehrtmann, 1996; Lardies et al., 2004).
The present study describes the reproductive cycle,
population parameters, and intra- and interannual variability in the release of planktonic larvae and recruitment of
the intertidal crab P. laevigatus in Seno de Reloncav|¤ ,
southern Chile.
MATERIALS AND METHODS
The crabs (Petrolisthes laevigatus) were sampled monthly
from May 2001 to March 2003 during the low tide in the
rocky intertidal zone of Pelluhu|¤ n, Seno de Reloncav|¤ ,
near Puerto Montt (41845’S 72870’W). A 50650 cm
quadrat was used for sampling and each sample comprised
15 replicates. All the crabs were removed from the
quadrats and stored in independent recipients for later
analysis in the laboratory. After taking the measurements,
the animals were returned to their natural habitat.
730
P. Gebauer et al.
Reproduction and recruitment of Petrolisthes laevigatus
Figure 1. Seasonal variation of density (average + SD) of the benthic population of Petrolisthes laevigatus from Seno de Reloncav|¤ .
The crabs collected in the intertidal zone were counted.
Those over 3.5 mm (carapace length; CL) were measured
with a Vernier calliper and those smaller than that with a
stereo microscope. Distinctions were made between ¢rst
juveniles (JI) and megalopae (Albornoz & Whertmann,
1996). Individuals were also sexed during this process
and, in the case of the females, classi¢ed as ovigerous or
not. Those females that were carrying embryos were classi¢ed according to the degree of egg development. Eggs
were examined under a stereo microscope.
Egg development was classi¢ed in three categories: (I)
initial: red-purple colour, homogenous yolk, and no visible
ocular spot; (II) intermediate: having between 1/4 and 1/2
of the yolk consumed and slightly visible ocular spot; and
(III) ¢nal: 3/4 of the yolk consumed and a well-developed
ocular spot of prezoea, following Wehrtmann (1990) and
Lardies et al. (2004).
In order to quantify the number of embryos carried by
females of di¡erent sizes, 106 ovigerous females with
complete eggs were selected at random for size measurement and egg quanti¢cation. Later the data were adjusted
to a predictive equation for the number of eggs according
to the size of the female.
From March 2002 to March 2003, the temperature was
recorded in the intertidal zone every 16 min with a TidBit
Temp Logger (precision: 0.28C).
The seasonal variation in the sex ratio of the population
was evaluated by the deviation between the observed and
expected ratios (1:1) using the G test (Sokal & Rohlf,
1995). Size di¡erences between crabs were established
during the sampling period for each of the population
categories (males, females, juveniles and megalopae) with
a non-parametric ANOVA (Kruskal ^Wallis). In order to
compare the sizes of the males and females in a given
period (month), the Mann ^Whitney statistical test was
applied.
RESULTS
During the sampling period (from May 2001 to March
2003), a total of 22 900 individuals was caught. Abundance peaks were mainly observed in the autumn and
Figure 2. Percentage of ovigerous Petrolisthes laevigatus females with di¡erent stages of embryonic development (Stages I^III) and
monthly temperature (average SD) in the intertidal zone of Seno de Reloncav|¤ .
Journal of the Marine Biological Association of the United Kingdom (2007)
Reproduction and recruitment of Petrolisthes laevigatus
P. Gebauer et al. 731
Figure 3. Relationship between female Petrolisthes laevigatus size and number of eggs in Seno de Reloncav|¤ .
spring^ summer for both monitored reproductive periods
(Figure 1). The population density £uctuated between 219
(March 2002) and 1321 individuals m72 (November
2002). Abundance peaks of the Petrolisthes laevigatus population in Seno de Reloncav|¤ were principally found in the
spring^ summer months (October ^ March) due to the
incorporation of new organisms (megalopae and juveniles)
to the benthic population (the ¢rst benthic stages represented between 1.4 and 36% of the benthic population),
and in autumn due to the increased number of juveniles,
resulting from the settlement period of the previous
months. The adult population (males and females)
remained relatively constant throughout the study period,
while the variations in the density of the benthic population (males, females, juveniles and megalopae) of
P. laevigatus in Seno de Reloncav|¤ were caused by smallersized individuals (Figure 1).
In general, during the study period, the ratio between
the sexes did not deviate from 1:1 (P40.05), with the
exception of May, July and December 2001 and March
2003, when females were signi¢cantly more represented
(P50.05). Only in June 2002 males were more abundant
than females (P50.05).
The size of individuals in the population was between
19.5 (males) and 1.5 mm CL (megalopae). Throughout
most of the study period, signi¢cant di¡erences were not
detected in average male and female sizes with the exception of May, June and September 2001, December 2002,
and January 2003. The maximum size of the females was
greater than that of the males only in November 2003, and
the minimum size observed for both sexes was similar,
£uctuating between 3.8 and 4.5 mm CL. Signi¢cant di¡erences were detected in juvenile sizes (P50.0001) as well as
in settled megalopae (P50.001) during the study period.
Figure 4. Final egg density (Stage III) (average + SD) in (A) 2001^2002 and (B) 2002^2003. Petrolisthes laevigatus recruitment
(megalopa + juvenile I) in Seno de Reloncav|¤ for (C) 2001^2002 and (D) 2002^2003.
Journal of the Marine Biological Association of the United Kingdom (2007)
Journal of the Marine Biological Association of the United Kingdom (2007)
6.6 2.7
6.3 2.6
7.2 3.0
7.5 3.1
7.3 3.1
7.5 3.1
7.8 1.1
8.3 3.3
7.9 2.7
7.5 2.3
8.8 2.6
8.0 2.4
7.9 2.6
8.1 2.8
7.5 2.5
7.5 2.7
8.7 2.9
8.1 2.8
7.4 2.2
8.0 2.8
9.1 2.9
7.4 2.4
8.3 2.8
Mean SD
18.6
17.4
19.5
19.0
18.6
17.1
19.5
19.4
17.0
15.0
16.1
15.6
17.2
16.8
16.0
16.8
18.1
16.0
14.2
19.8
17.0
16.8
16.4
Max
4.0
3.8
4.1
3.8
4.1
4.1
4.1
4.2
4.1
3.8
4.4
4.5
4.2
4.1
4.4
4.0
4.4
4.3
4.4
4.5
3.9
4.2
4.5
Min
SD, standard deviation; Max, maximum; Min, minimum.
May 2001
June
July
August
September
October
November
December
January 2002
February
March
April
May
June
July
August
September
October
November
December
January 2003
February
March
Date
7.2 2.6
6.9 2.5
7.3 3.0
7.6 3.1
8.0 3.1
7.3 3.1
7.4 2.3
8.0 2.5
7.7 2.3
7.0 1.9
8.2 2.5
7.4 1.9
7.8 2.2
8.1 2.3
7.1 2.0
7.1 2.1
8.4 2.5
8.0 2.2
7.2 1.9
8.5 2.3
8.0 2.3
7.6 2.0
7.9 2.3
Mean SD
16.1
15.3
16.2
18.7
17.8
16.7
17.3
16.1
14.8
13.0
15.5
14.7
15.1
14.9
14.0
14.8
17.2
14.0
16.0
17.0
14.2
12.4
15.0
Max
Females
4.0
3.8
4.3
4.0
4.2
4.1
4.0
4.3
4.1
3.8
4.5
4.4
4.3
4.1
4.5
4.2
4.5
4.5
4.2
4.4
4.2
4.4
4.5
Min
16.1
14.7
16.2
15.6
17.8
15.1
17.3
16.1
14.8
12.8
12.1
14.5
14.9
14.0
13.1
17.2
13.8
16.0
15.4
13.4
9.2
12.1
12.8
11.1 1.5
11.6 1.7
12.0 1.8
10.0 1.7
10.6 1.3
10.9 1.5
10.0 1.1
9.3 1.9
9.9 1.7
10.4 2.8
9.2
10.2 1.2
Max
10.9 2.5
10.8 1.6
11.7 2.3
11.3 1.9
12.3 2.2
10.5 1.8
10.5 1.8
10.4 1.9
11.5 4.7
Mean SD
12.8
10.0
8.2
9.9
7.2
8.0
8.0
7.2
6.9
7.1
5.7
9.2
8.4
5.7
8.4
7.7
8.0
7.4
7.5
7.6
7.2
8.1
Min
Ovigerous Females
2.9 0.7
2.8 0.8
2.9 0.8
2.9 0.6
3.1 0.7
3.2 0.7
3.4 0.6
3.4 0.7
2.7 0.8
3.1 0.8
2.8 0.7
3.1 0.7
3.2 0.8
3.1 0.7
3.1 0.7
3.1 0.6
3.2 0.6
3.1 0.6
3.1 0.7
2.9 0.7
2.9 0.8
3.1 0.7
2.9 0.8
Mean SD
4.1
4.0
4.0
3.9
4.0
4.2
4.0
4.2
4.0
4.1
4.2
4.0
4.2
4.0
4.1
4.2
4.2
4.0
4.0
4.1
4.0
4.0
4.0
Max
Juveniles
1.7
1.7
1.9
1.8
1.9
2.0
2.0
1.8
1.7
1.8
1.9
1.9
1.9
2.0
2.0
2.0
2.0
1.7
1.8
1.8
1.8
1.8
1.7
Min
1.9
1.9
1.9
1.9
1.8
1.9
1.7
1.9
1.9
1.9
1.9
1.9
1.8
1.7 0.1
1.7 0.1
1.7 0.1
1.7 0.1
1.7 0.1
1.7 0.1
Max
1.9
1.9 0.2
1.7 0.1
1.7 0.04
1.7 0.04
1.9 0.01
1.6 0.05
Mean SD
Megalopae
1.5
1.6
1.6
1.6
1.5
1.5
1.9
1.6
1.5
1.6
1.6
1.9
1.6
Min
P. Gebauer et al.
Males
Table 1. Temporal variation of Petrolisthes laevigatus size (mm carapace length) for males, females, ovigerous females, juveniles and megalopae observed during the study period (2001^2003)
in Seno de Reloncav|¤.
732
Reproduction and recruitment of Petrolisthes laevigatus
Reproduction and recruitment of Petrolisthes laevigatus
The size of megalopae £uctuated between 1.9 and 1.5 mm
(Table 1). During the two studied reproductive seasons, the
sizes of ovigerous females showed no signi¢cant di¡erences
between months (P40.05) and £uctuated between 17.8
and 5.7 mm (Table 1).
Ovigerous females were present throughout the year,
with low frequency between January and April (less than
3% of total females) and high values between July and
December (over 11%). The maximum of ovigerous
females was concentrated from July to September (20%
approximately) and from September to November (25%
approximately) in the 2001^2002 and 2002^2003
seasons, respectively (Figure 2).
The presence of females with initial embryos was observed
nearly all year round (March to January) although no direct
relationship could be veri¢ed between the temperature of the
intertidal zone and the presence of initial eggs (Figure 2). In
the case of the 2001^2002 season, just one mode of initial
eggs was observed (in July). In contrast, the 2002^2003
season was bimodal: one mode occurred when the
temperature was descending (summer ^ winter) and
another when the temperature was ascending (winter^
summer). The in£ection point coincided with the lowest
recorded temperature in the intertidal zone (August 2002).
The second stage of embryonic development was
observed from June to January. Final eggs (Stage III)
were present from August to February, indicating a
prolonged reproductive period and a period of seven
months during which P. laevigatus release planktonic
larvae into Seno de Reloncav|¤ (Figure 2).
The number of ¢nal eggs was quanti¢ed in relation to
the female size in a single month (October; representative
of the peak of ovigerous females), revealing a potential
relationship between these variables (Figure 3; R2: 0.87,
P50.05). The number of eggs per female £uctuated
between 130 and 1250 for specimens between 8 and
16 mm CL. Throughout the reproductive season, the
maximum contribution of ovigerous females in the population was made by the 10^12 mm size-range, with 300 to
600 eggs per female (Table 1; Figure 3).
The above mentioned relationship allowed the calculation
of the monthly average of potential released planktonic
larvae in the study area, expressed as the number of ¢nal
eggs with regard to the size of the female. The studied reproductive seasons presented no signi¢cant di¡erences, neither
in the average release of planktonic larvae (P40.05; Figure
4A,B) nor in the number of settled megalopa + juvenile I
(recruitment) in the intertidal zone (Figure 4C,D).
Although no di¡erences were observed in the interannual averages of potential released planktonic larvae
and intertidal recruitment, the seasonal abundance
pattern of larval release and settlement varied interannually. During the ¢rst reproductive season, a relatively
constant pattern of planktonic larvae release was observed,
with the exception of January, when the contribution
decreased to approximately half, indicating the end of the
period. Recruitment, in turn, was measured monthly
(based on the analysis of megalopae and ¢rst juveniles)
and showed a maximum recruitment rate in December
2001, followed by a progressive decline until the end of
the season (March 2002). The beginning and the end of
the settlement season (November and March) had an
arrival rate of 20 individuals m72 (Figure 4C).
Journal of the Marine Biological Association of the United Kingdom (2007)
P. Gebauer et al. 733
During the 2002^2003 season, the planktonic larvae
release extended from August to February, with an
evident increase in density in September (3641 Stage III
eggs m72). The following months showed a progressive
decline in density, but with a moderate increase in
January (Figure 4B). Recruitment during this season was
characterized by two clear events incorporating new individuals into the benthic population in November and
February and a drop between December and January
(Figure 4D). This season showed greater intra-annual
variability and greater rates of recruiting than the
previous season, with 751 recruits m72 in November 2002
versus 302 recruits m72 in December 2001.
DISCUSSION
The density of the adult Petrolisthes laevigatus population
in southern Chile (Seno de Reloncav|¤ ) presents low intraand interannual variability but high spatial variability
within the study site, principally due to the size and shape
of the stones (P. Gebauer, personal observation). This is
similar to that reported for P. cinctipes (Donahue, 2004).
The seasonal £uctuations of the observed density of the
benthic P. laevigatus population of southern Chile are
caused by settlement events, with the incorporation of
new individuals to the intertidal population.
The size structure was relatively constant during the
sampling period and similar to the reports of this species
in central-southern Chile (Lardies et al., 2004), most
specimens are juveniles of 3^4 mm CL, regardless of the
season. Sizes smaller than 3 mm CL are highly represented only during settlement months (October ^ March)
and no displacement of the mode toward larger sizes (4^
5 mm CL) is observed during the year. This suggests high
post-settlement mortality of individuals between 4^5 mm
CL probably by predation of coastal ¢sh as Eleginus
maclovinus (Pequen‹o, 1979).
The1:1sex ratio of the intertidal population is maintained
nearly throughout the entire sampling period and no
seasonal migration (summer) of the females to the subtidal
zone was detected, as suggested by Lardies et al. (2004).
Petrolisthes laevigatus has a long reproductive period,
stretching from the end of summer to the middle of the
following summer (11 months), in the south of Chile. In
general, this situation does not agree with the pattern
described for other marine invertebrates inhabiting temperate zones and, in particular, for crabs along the southern
coast of Chile, where the reproductive period is restricted
principally to the spring months (Rodriguez & Bahamonde,
1986; Wol¡ & Cerda, 1992). A comparison of the breeding
period of P. laevigatus with other species of the same genus,
reveals also long reproductive periods: seven months for
P. eriomerus (Knudsen, 1964) and ten months for P. cinctipes
(Boolootian et al., 1959). Speci¢cally, the results obtained
in the present study show a dissimilar pattern from that
reported by Lardies et al. (2004) for the same species
along the coast of Valdivia, approximately 200 km north
of the study area, where reproduction is concentrated in
spring (¢ve months) as compared to the 11 months
reported in Seno de Reloncav|¤ . Nevertheless, a similar
tendency can be seen in both study areas regarding the
period in which females with Stage I eggs are most
abundant. The di¡erences in the reproductive season of
734
P. Gebauer et al.
Reproduction and recruitment of Petrolisthes laevigatus
this species in nearby sites and the presence of initial eggs
during nearly the entire year in the southernmost site
suggests that this population has adapted to the particular
conditions of Seno de Reloncav|¤ , a more protected environment than the exposed rocky, intertidal zone of the
Valdivia coast. Although temperature is one of the factors
a¡ecting gonad growth and development in marine organisms (Nelson et al., 1988), in this case, this factor cannot
explain the di¡erences in the length of the reproductive
cycle at these two southern sites since the temperatures
reported for the Seno de Reloncav|¤ intertidal zone are
similar and, in some cases, lower than those of the Valdivia
coast (Lardies et al., 2004). Therefore, other variables
such as food availability could directly and/or indirectly
through increased competition for food a¡ect the reproductive cycle (Donahue, 2004). Nevertheless, comparisons
with Lardies et al. (2004) should be made carefully, due to
di¡erences in the sampling methods.
The prolonged reproductive period for this species11
months for females with initial eggs in the intertidal
zoneimplied embryonic development between one and
¢ve months (see frequency of initial and ¢nal embryonic
stages in Figure 2), seven months of planktonic larvae
release as compared to four months in central-southern
Chile (Lardies et al., 2004), and ¢ve to six months of
settlement in the intertidal zone. Therefore P. laegivatus
should present a high plasticity allowing that the di¡erent
intra-annual embryonic and larval cohorts face di¡erent
environmental conditions (principally temperature, salinity and food) during their development.
The settlement of marine invertebrates is a¡ected by
exogenous (oceanographic and meteorological) (Shanks et
al., 2000) and endogenous factors (for instance, the availability pattern of ¢nal eggs over time could mould the organisms’settlement patterns, Levitan et al.,1992, as well as factors
such as temperature, food, on others, also a¡ect the ovarian
development and ¢nal egg availability). An evaluation of the
seasonal settlement pattern of P.laevigatus revealed interannual
variations that can be explained not only by abiotic factors
(Gebauer, 2004) but also by the release of planktonic larvae.
Thus we suggest that the settlement patterns observed in Seno
de Reloncav|¤ re£ect the interannual di¡erences in the release
of planktonic larvae, while the abiotic factors related to the
larval transport involved in the settlement magnify or minimize these £uctuations.
The prolonged reproductive period, with the release of
planktonic larvae and settlement, is proposed to be one of
the causes of the low variability in the structure and abundance of the P. laevigatus population in Seno de Reloncav|¤ ,
southern Chile.
The ¢rst author thanks CONICYT for a doctoral scholarship,
the Universidad Austral de Chile for a research scholarship (DID
D2001-12), and the Programa Bicentenario de Ciencia y Tecnolog|¤ a CONICYT-World Bank. We are grateful to two anonymous
referees who helped to improve this paper.
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Submitted 20 July 2006. Accepted 25 January 2007.