Roberto Munehisa Shimizu

ESTIMATING THE POPULATION SIZE OF AEGLA FRANCA (DECAPODA: ANOMURA: AEGLIDAE) BY MARK-RECAPTURE TECHNIQUE FROM AN ISOLATED SECTION OF BARRO PRETO STREAM, COUNTY OF CLARAVAL, STATE OF MINAS GERAIS, SOUTHEASTERN BRAZIL

Abstract The Schumacher-Eschmeyer and the Schnabel estimators for closed population were employed to estimate the population size of Aegla franca from an isolated section (30 m long; area: 76.125 m2) of the Barro Preto stream (20°18′47″S; 47°16′37″W) in the summer and winter seasons of the year 2005. These methods involve mark-recapture technique with multiple sampling, and each season estimate was conducted for eight consecutive days. The study area was isolated with a 4 mm mesh net to prevent migration of aeglids into or out of the study area. Traps were randomly set overnight and inspected for captured aeglids in the following morning. Two marking techniques were employed separately: a mixture of silver purpurin powder and fast-drying glue gel (summer estimate) and cauterization by red-hot pin head (winter estimate). All unmarked individuals from each sampling event were sexed, had their carapace length measured and were then marked, and released back in midpoint of the isolated area of the stream along with previously marked (recaptured) specimens. The Schumacher-Eschmeyer estimator provided very close results between the summer (N = 212 and density = 2.8 ind./m2) and the winter (N = 218 and density = 2.9 ind./m2) estimates. The Schnabel estimate results were also very similar to that obtained by the Schumacher-Eschmeyer method for each corresponding season of the year. Regardless of the marking technique employed, the results obtained and field observations from each estimate indicate that none of the assumptions required by both methods were violated. After subtracting the percentage of immature specimens, the projected overall population size of mature Aegla franca for the whole extension of Barro Preto stream varied from approximately 33,200 in the summer and 29,500 adults in the winter (Schumacher-Eschmeyer estimator) for an estimated area of occupancy equivalent to 0.0125 km2.

REPRODUCTIVE BIOLOGY AND FUNCTIONAL MATURITY IN FEMALES OF AEGLA FRANCA (DECAPODA: ANOMURA: AEGLIDAE)

Abstract We describe the reproductive period, fecundity, and average size at the onset of functional maturity of female Aegla franca, the northernmost distributed aeglid species. The reproductive period is markedly seasonal and takes place from May (austral mid-autumn) to August (late winter). Ovigerous females appear quite abruptly in the population by May, and this condition is observed in all adult females sampled regardless of their size. The average size at the onset of functional maturity in females, at which 50% of the females sampled during the reproductive period were considered adults, was 12.75 mm CL. The smallest post-ovigerous female measured 12.06 mm carapace length (CL). Mean fecundity (±S.D.) from 41 females bearing early and intermediate eggs was 129.1 ± 32.2 and corresponded to a mean female CL of 14.11 mm. The elliptical-shaped eggs exhibited significant increase in size along the development stages. The third pair of pleopods bore higher number of eggs than the others. Compiled information regarding the reproductive period reported for aeglids revealed an increase in the breeding period length with latitude. The reproductive period tends to be shorter in localities under larger rainfall variation and smaller temperature variability than in sites with opposite climate conditions. Eggs tend to be fewer in number and larger in size towards lower latitudes. We present an hypothesis that stream water velocity might act as a major selective pressure during the early life history of fluvial aeglids with direct effect on the reproductive pattern.

Life Cycle and Population Structure of Aegla paulensis (Decapoda: Anomura: Aeglidae)

Abstract We describe growth, longevity, sex ratio, reproductive period, and recruitment of Aegla paulensis from Jaraguá State Park, São Paulo, Brazil (23°27′27.9″S; 46°45′32.3″W). The population was sampled monthly (September 2007 through August 2009) with the aid of traps. Over five thousand individuals were captured, sexed, measured (carapace length  =  CL) and inspected for reproductive traits (females only), and then released back to the sampling site. The pattern of the reproductive cycle was strongly seasonal (austral mid autumn through late winter), with a single recruitment pulse per year. The obtained von Bertalanffy growth equations were CL  =  21.25[1-e−0.041(t + 1.250)] and CL  =  16.52[1-e−0.049(t + 1.823)] for males and females, respectively. Males (mean CL ± SD  =  11.86 ± 2.79 mm) attain larger sizes than females (mean CL ± SD  =  10.84 ± 2.36 mm). Aegla paulensis reproduces twice during an estimated life span of 40.2 months for females and 33.9 months for males. Temporal variation of sex ratio showed a distinctive pattern characterized by a sequence of three distinct periods that repeated from one year to another, and which suggested that a behavioral component influence the proportion of sex in adult specimens sampled with traps during reproductive and non-reproductive periods.

Allometric Growth, Sexual Maturity, and Adult Male Chelae Dimorphism in Aegla Franca (Decapoda: Anomura: Aeglidae)

Abstract Allometric growth analysis on chelae dimensions vs. carapace length (CL) was employed to estimate average size at the onset of morphometric maturity (= puberty molt) and sexual dimorphism regarding the pair of chelae in Aegla franca. Males attain morphometric maturity (12.15 mm of CL) at a larger size than females (10.93 mm of CL). After the puberty molt, an additional change in the allometry level regarding chelae dimensions was detected in adult males (average CL = 19.00 mm). As a result, two sequential morphotype groups of adult males, herein designated as morphotype I and morphotype II, were recognized according to the state of development of the pair of claws. We postulate that the second change in this allometry level is related to functional maturity in this sex, based on the following observations: 1) temporal variation in the proportion between the two morphotype groups reveals that morphotype II individuals make up most of adult males in the population at the beginning of the seasonal reproductive period of the species, and 2) morphotype II males show a more robust pair of claws as compared to the predecessor morphotype, which might represent an advantageous trait in reproductive competition. Males and females of Aegla franca are heterochelous with handedness preponderance of the left chela. Claw size is a distinct dimorphic trait in this species, being significantly larger in male specimens.

Bathymetric distribution of the shrimp Rimapenaeus constrictus (Stimpson, 1874) (Decapoda, Penaeidae) in two locations off the southeastern Brazilian coast

Abstract The distribution of benthic organisms is directly or indirectly associated with the physical and chemical properties of the water and sediment. This study analysed the spatial and temporal distribution of Rimapenaeus constrictus in unconsolidated sublittoral sediments of two areas off the northern coast of the state of São Paulo, Brazil. We also analysed the association of environmental factors with the occurrence of this species. Shrimp were collected monthly from July 2001 to June 2003, with a fishing boat equipped with two double-rig nets, in the regions of Ubatuba (UBA) and Caraguatatuba (CA). The collections were made during the day, along five transects with mean depths of 5, 10, 15, 20, 25, 30, and 35 m. We obtained a total of 5478 individuals, 3403 (UBA = 2025 and CA = 1378) during the first year, and 2075 (UBA = 875 and CA = 1200) during the second year. Significant differences in abundance were observed in relation to depth, season of the year, and also in the interaction between region and depth. Higher abundances occurred in fall and winter, independently of the sampling year. The largest numbers of shrimp were caught on the 20-m transect in UBA and the 25-m transect in CA. It is concluded that the distribution pattern of this species is closely related to environmental factors, and the temperature of the bottom water and the sediment texture were the most significant variables affecting the distribution.

Reproductive Biology in Females of Aegla Strinatii (Decapoda: Anomura: Aeglidae)

Abstract Females of Aegla strinatii (n  =  466) were sampled monthly (September 2003 to September 2005) by means of sieves and traps from Rio das Ostras (24°38′16.2″S; 48°24′05.2″W), at Jacupiranga State Park, South of São Paulo State, Brazil. The reproductive period was markedly seasonal (from May to September) encompassing the Austral late autumn through late winter. This is in accordance to the pattern of reproductive period variations in relation to the latitudinal climate variability verified in species of Aegla. The proportion of adult females exhibiting the ovigerous condition was higher in young/small specimens as compared to old/large ones, and suggests the occurrence of senescence in the latter group. Average size at the onset of functional maturity in females was estimated as 16.66 mm of carapace length (rostrum excluded). The number of eggs per ovigerous females ranged from 1 to 325. Eggs are slightly elliptical and average size varied according to embryonic stage. Mean (± standard deviation) carapace length of juveniles (n  =  118) was 1.50 ± 0.05mm (range: 1.40-1.65mm).

FLUCTUATIONS IN THE POPULATION SIZE OF THE HIGHLY ENDEMIC AEGLA PEROBAE (DECAPODA: ANOMURA: AEGLIDAE) CAUSED BY A DISTURBANCE EVENT

During a two-year field study (July 2008-June 2010), we observed a sharp decrease in the number of the freshwater decapods, Aegla perobae, sampled monthly at the type locality. A series of population size estimates by means of the Schumacher and Eschmeyer markrecapture method confirmed the decreasing trend of population size. Density dropped rapidly from 9.05 ind./m 2 in April 2009 to a situation in which a reliable population size estimate was no longer possible due to the difficulty in retrieving marked individuals by February 2010. Results from additional estimations in 2011 and 2012 indicated that a slow and steady recovery phase of the population size has initiated. We present the hypothesis that the observed decrease in population size is due to an extraordinarily high precipitation episode during the 2007 reproductive period, which likely suppressed recruitment of the cohort produced in that year, with impact on the size-class structure and reproductive output of the population in the years that followed.

LONG-TERM PATTERNS OF SPATIAL AND TEMPORAL DISTRIBUTION IN THE SEABOB SHRIMP XIPHOPENAEUS KROYERI (DECAPODA: PENAEIDAE) POPULATION IN SOUTHEASTERN BRAZIL

The effect of some environmental factors on the distribution and abundance of different demographic categories of Xiphopenaeus kroyeri (Heller, 1862) was tested for three 12-month periods over 13 years in Ubatuba Bay, Sao Paulo State, southeastern Brazil. Four sites with different characteristics were sampled monthly from January to December 1998, July 2006 to June 2007 and September 2010 to August 2011. Bottom water temperature and salinity samples were taken monthly, and one sediment sample from each site was taken during each period. Although total abundance, as the number of adult males and non-reproductive females did not differ among periods, in 1998 the abundance of juveniles was greater and reproductive females was lower than the other two periods. The high abundance of juveniles in 1998 was associated with the high frequency of optimal temperatures for juvenile’s metabolism and this environmental variable can influence the abundance of individuals among years. Adult shrimp can be established in sites with variations in sediment grain size composition, whereas juveniles are more abundant in sites with finer sand. We suggest that areas with high juvenile abundance in Ubatuba Bay must have controlled exploitation and that the fishery can be focused on the deepest areas, where adults are predominant.

A Remarkable Anomuran: The Taxon Aegla Leach, 1820. Taxonomic Remarks, Distribution, Biology, Diversity and Conservation

The family Aeglidae comprises three genera, one extant (Aegla) and two extinct genera (Protaegla and Haumuriaegla), the latter two genera are known only from fossils from marine sediments (indicating a marine origin for the group). Aegla contains all extant species and constitutes a monophyletic group within the Anomura. All 78 species and subspecies described so far are entirely adapted to freshwater habitats and are endemic to temperate and subtropical regions of continental South America. While most species are found in epigean habitats, there are a few cave-dwelling species in southeastern Brazil. The reproductive period varies from 8 to 12 months (in species from colder higher latitudes), to 4–7 months (in species from lower latitudes where warm-rainy and cold-dry seasons alternate). The adult males of seasonally breeding species include two morphotypes, one non-reproductive and the other reproductive. Eggs are large and few in number, and post-embryonic development is epimorphic. Juveniles have limited dispersal capacity and recruits tend to remain with the parental population. Aegla is the most severely threatened group among South American freshwater decapods because of habitat degradation, high endemism, a restricted area of occupancy, and a severely fragmented spatial distribution with reproductively isolated subpopulations.

REPRODUCTIVE BIOLOGY AND POPULATION STRUCTURE OF POTIMIRIM BRASILIANA VILLALOBOS, 1959 (DECAPODA, ATYIDAE) FROM A LITTORAL FAST-FLOWING STREAM, SAO PAULO STATE, BRAZIL

The importance of decapod crustaceans has induced scientific studies in various fields of biology. Therefore, structure, reproductive biology and fecundity of a population of Potimirim brasiliana Villalobos, 1959 from Jureia-Itatins Ecological Station in Peruibe, State of Sao Paulo, were studied. Shrimps were captured at 4-month intervals from spring 2000 to summer 2001. Overall sex ratio was skewed towards males (2.2 males : 1 female). Mean ± S.D. total body length was 17.1 ± 2.1 mm (or 4.8 mm carapace length (CL)) for females and 14.0 ± 1.4 mm (or 3.6 mm CL) for males. Ovigerous females comprised 55.4% of all females collected and were present in all samples and at higher proportions in the spring and the summer. The size at onset of maturity (= smallest ovigerous female) was 13.3 mm (CL = 3.7 mm). Fecundity ranged from 171 to 749 eggs (mean ± S.D. = 361.5 ± 119.5 eggs) per female. In addition, there was a positive correlation between the number of eggs and the carapace length of ovigerous females according to the equation NE = 197.99CL − 520.75. Mean ± S.D. size and volume of eggs was 520.1 ± 32.5 × 309.1 ± 17.8 μm and 0.038 ± 0.006 mm3 (early eggs) and 534.2 ± 15.8 × 324.4 ± 12.6 μm and 0.042 ± 0.003 mm3 (late eggs). The increment in size during the embryonic development was marginally significant for the minor axis ( U = 3 ; p < 0 . 047 ), not significant for the major axis ( U = 5 ; p = 0 . 117 ) and significant for volume ( U = 840 ; p = 0 . 0009 ). Compiled data on the reproductive pattern reported for Potimirim Holthuis, 1954 species from Brazil revealed that temporal variation of reproductive activity and fecundity are influenced by environmental limiting factors correlated with latitude.