Population Biology of the Burrowing Shrimp Callichirus Seilacheri (Decapoda: Callianassidae) in Northern Chile
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Population biology of the burrowing shrimp Callichirus seilacheri (Decapoda: Callianassidae) in northern Chile Patricio Hernáez1 & Ingo S. Wehrtmann2 1 Museo del Mar, Universidad Arturo Prat, Casilla 121, Iquique, Chile; [email protected] 2 Escuela de Biología, Universidad de Costa Rica, 2060 San José, Costa Rica; [email protected] Received 11-X-2005. Corrected 08-VIII-2006. Accepted 16-III-2007. Abstract: The life history of ghost shrimps, known for their role in shaping community structures in shallow water habitats, is poorly studied in species occurring along the coasts of the South American Pacific. Here we present ecological information concerning Callichirus seilacheri based upon individuals collected from January to December 2003 in Las Machas beach, northern Chile. Burrow densities varied between 1.4 and 20.2 burrows / 0.25 m2, and was highest during summer (18.2 burrows / 0.25m2). The sex proportion was 1:1 during most of the study period; however, females outnumbered males in January and September. Males reached a larger maximum size than females (27.1 and 24.0 mm CL, respectively). The presence of juveniles was restricted principally to the time between February and May. Sexual maturity was reached at a size of 20.8 mm (males) and 18.1 mm CL (females). The main breeding period lasted from autumn to winter (May to August, peaking in June), and co-occurred with decreasing water temperatures and the presence of a sediment layer covering the burrows. Rev. Biol. Trop. 55 (Suppl. 1): 141-152. Epub 2007 June, 29. Key words: burrow density, sexual maturity, reproduction, ghost shrimp, South America, Pacific. The infraorder Thalassinidea is com- Berkenbusch and Rowden, 2000a), especially prised by the so-called ghost shrimps, which concerning those populations occurring along typically occupy intertidal and subtidal marine the Chilean coast. and estuarine habitats. They are known to Although the ecology of American thalas- construct burrows of different shapes and sinidean shrimps has received growing atten- depths (Suchanek 1983, Griffis and Chávez tion during the last decade (see Coelho et al. 1988, Lemaitre and Rodrigues 1991), and 2000, Felder 2001, Thatje 2003), the life history play an important role in shaping the com- of these crustaceans along the South American munity structure in shallow water habitats Pacific coast remains mostly unknown, prob- (e.g. Posey 1986, Posey et al. 1991, Nates ably due to their cryptic life style which makes and Felder 1998). Their burrowing activities it difficult to capture and study them (Coelho contribute considerably to perturbation of the et al. 2000). Along the Chilean coast the family sediments, renovation of the nutrient cycle, Callianassidae (Thalassinidea) is represented and increased food availability among the tro- by six species which can be found in soft sedi- phic levels (Ziebis et al. 1996, Berkenbusch ments between 0 and 255 m depth (see Thatje and Rowden 1999, Felder 2001). Despite of and Gerdes 2000, Guzmán and Thatje 2003, their ecological importance, information about Thatje 2003). There are some scattered publi- population and reproductive biology of these cations which mention the presence of dense shrimps is scarce (i.e. Rodrigues and Shimizu populations of ghost shrimps at Chilean beach- 1997, Pezzuto 1998, Nates and Felder 1999, es (Aste and Retamal 1983, Soto et al. 2002). Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 55 (Suppl. 1): 141-152, June 2007 141 In general, however, information concerning and reproductive aspects of C. seilacheri, biology, population dynamics, and ecology of the most conspicuous intertidal callianassid these shrimps is still lacking. shrimp in the northern part of Chile (Soto et Callichirus seilacheri Bott 1955 (synony- al. 2002). We also present data on habitat use my of C. garthi Retamal 1975; see Sakai 1999) and density changes during the year, which is distributed from El Salvador (12ºN) to Chile might facilitate a better understanding of the (37ºS). The species was observed for the first ecological role of this ghost shrimp along the time on beaches in the extreme northern part coastal habitats of Chile. of Chile during the ENSO event of 1982-1983 (Soto et al. 2002). Existing information is lim- ited to larval development (Aste and Retamal MATERIALS AND METHODS 1983), and the interaction between C. seilach- eri and the ectosymbiotic copepod Clausidium Specimens were obtained from the inter- sp. (Marín and George-Nascimento 1993). tidal zone in Las Machas beach, northern The present study aims to provide infor- Chile (Fig. 1) from January to December 2003. mation regarding the population structure The individuals were identified according to Fig. 1. Callichirus seilacheri. Details of the study area, Las Machas beach in northern Chile. 142 Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 55 (Suppl. 1): 141-152, June 2007 the keys for genera and species, published The CL was considered as an independent by Manning and Felder (1991) and Retamal variable; adjustment of each regression was (1975) respectively. In order to get an estimate analyzed by least squares method (Sokal and of the abundance of C. seilacheri, we counted Rohlf 1981). This procedure was applied for all the number of holes in an area of 0.5 x 0.5 categories. Specimens of each category were m, with ten replicates during each monthly grouped into 1 mm size classes; subsequently sampling (typically between day 15 and 20 data were plotted as length-frequency histo- of each month). The entrances of each gallery grams to analyze the population structure of the were easily identifiable due to their diameter; juveniles and adult shrimps. however, shrimps might live in interconnected Morphological maturity in C. seilacheri network tunnels, and each gallery was occu- was estimated from the biometric relation- pied by at least one individual (P. Hernáez, ship between PL x CL in males, and WW pers. obs.). Individuals were collected with a x CL in females. The allometric equation yabby pump (diameter: 77 mm) after inspect- (y= axb) was fitted to each growth phase to ing the area for burrowing holes. However, obtain the allometric growth constant “b” to even when no holes were visible, sediment determine the growth pattern (see Somerton was searched for ghost shrimps. The physi- 1980). Analysis of the allometric growth cal structure of Las Machas beach changed constant (b) gives information about the considerably during the study period making increase of one biometric dimension in rela- it impossible to determine the number of holes tion to another; isometric growth was con- by area between June and August. Therefore, sidered when b was between 0.90 and 1.10, this period was not included when estimating negative allometric growth with b<0.90, and the burrow densities. The following data were positive allometry with b>1.10 (Kuris et also recorded: surface water temperature, al. 1987, Pinheiro and Fransozo 1993). All number of ghost shrimps per yabby pump incomplete individuals were excluded from suck per burrow opening, associated fauna, these analyses and of the determination of and predators present in the burrows. size at first sexual maturity. After extracting the ghost shrimps each Our knowledge about mating in ghost individual was sexed and classified into one of shrimps is scarce, principally because mating the following categories: juvenile (JU), male occurs in cryptic locations (Bilodeau et al. (MA), non-ovigerous female (NOF), and ovi- 2005). To obtain an indirect estimate of the gerous female (OF). The sex determination was mating period of C. seilacheri, we counted the based upon macroscopic features such as the number of burrows occupied by both a female clearly elongated carpus of the major chelipeds with mature gonads and an adult male. The (males) and the presence of colored gonads in percentage of these mature couples (MC) was females; when these criteria did not allow a plotted per month; we considered a month as definitive sex determination, the location of the part of the mating period, when these mature gonopores was revised, too. couples comprised >20 % of all adult individu- The following morphometric measure- als collected per month. ments (+ 0.1 mm) were taken: total length (TL: According to Connell (1985), recruitment from the anterior margin of the rostrum to the is defined as the entry of individuals into the posterior region of the telson), carapace length juvenile and adult benthic population after set- (CL: from the anterior margin of the rostrum tlement from a planktonic larval stage. Since C. to the posterior margin of the carapace), and seilacheri has a larval planktonic development length and width of the propodus of the major (Aste and Retamal 1983), we estimated recruit- chelipeds (PL and PW, respectively). The wet ment through the presence of small individuals weight (WW) of each individual was measured (< 9 mm CL), analyzing the size-frequency with an analytical balance (Sartorius; + 0.1g). histograms of each month. Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 55 (Suppl. 1): 141-152, June 2007 143 Possible monthly differences concerning active in the shafts and tunnels. Burrow densi- the sex proportion were analyzed by means of ties during the year varied between 1.4 and 20.2 a χ2 test (1:1; p<0.05). The time of the repro- burrows/0.25 m2. High monthly mean values ductive period was established by comparing (>19 burrows/0.25 m2) were recorded in spring the percentage of ovigerous females to the total and summer, coinciding with reduced accretion number of females collected during the month intensities in Las Machas beach (Table 1). or the season. The reproduction period was Invertebrates associated to the C. seilach- defined as the months where more than 25 % eri galleries were the carnivorous polychaete of all collected females carried eggs.