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Journal of Experimental Marine Biology and Ecology, 241 1999 263–284
Effect of the burrowing crab Chasmagnathus granulata Dana on the benthic community of a SW Atlantic coastal
lagoon
Florencia Botto , Oscar Iribarne
´ Departamento de Biologıa
FCEyN, Universidad Nacional de Mar del Plata, CC 573 Correo Central, 7600 Mar del Plata, Argentina
Received 19 March 1999; accepted 23 June 1999
Abstract
This study evaluated the effect of the burrowing crab Chasmagnathus granulata on the benthic community in mudflats of the Mar Chiquita coastal lagoon Argentina, 378 459 S, 578 269 W. A
significantly higher abundance of the polychaete Laeonereis acuta was found inside the C .
granulata crab bed than outside. However, L . acuta abundance decreased in summer probably due
to the greater activity of crabs. A series of exclusion and inclusion field experiments showed a combined effect of the non-burrowing crabs Cyrtograpsus angulatus and C
. granulata on the polychaete L
. acuta inside crab beds, and also, an effect of C. granulata on the polychaetes L. acuta and Heteromastus similis when added outside the crab bed. C
. granulata also affected nematodes, even when experiments were of short duration. The effect of crab burrows on the
small scale distribution of nematodes may be related to passive transport of organisms. Adults of both crab species, Cy
. angulatus and C. granulata, also affected the settlement of Cy. angulatus. The juveniles of C
. granulata showed no effect for any meiofaunal species. The results of this work showed that C
. granulata plays an important role in determining the benthic community in mudflats of the Mar Chiquita coastal lagoon.
1999 Elsevier Science B.V. All rights reserved.
Keywords : Benthos; Bioturbation; Burrowing crabs; Chasmagnathus granulata; Community; Mudflats
1. Introduction
There are several saltmarshes between southern Brazil and northern Patagonia Argentina on estuaries with large discharges and prevailing brackish conditions Adam,
Corresponding author. E-mail address
: fbottomdp.edu.ar F. Botto 0022-0981 99 – see front matter
1999 Elsevier Science B.V. All rights reserved.
P I I : S 0 0 2 2 - 0 9 8 1 9 9 0 0 0 8 9 - 1
264 F
. Botto, O. Iribarne J. Exp. Mar. Biol. Ecol. 241 1999 263 –284
1990. There is no information on the ecological processes within these estuaries appropriate to predict the ecological impact of human alterations. The burrowing crab
Chasmagnathus granulata Dana is one of the most abundant macroinvertebrates up to 40 mm carapace width inhabiting these environments Boschi, 1964. They are
distributed in almost all the zones of the marsh intertidal; in the mudflat and in the
22
Spartina densiflora cordgrass habitats with a mean density of 20 crabs m Spivak et
al., 1994; Iribarne et al., 1997. This crab species is an important bioturbator in mudflats,
22 21
removing and processing up to 5.9 kg m day
of sediment Iribarne et al., 1997. This reworking of the upper sediment layer, probably affects the sedimentary environ-
ment and benthic organisms, especially during spring–autumn when crab activity is intense pers. obs..
Crabs are often important habitat modifiers e.g., Montague, 1980; Bertness, 1985, significantly influencing microtopography e.g., Bertness, 1985; Hall et al., 1991,
sediment chemistry Hoffman et al., 1984; Wolfrath, 1992 and drainage Bertness, 1985. Sediment disturbance resulting from the foraging and burrowing activities of
decapods may have direct and indirect impacts on macroinfauna and or meiofaunal species e.g., Hoffman et al., 1984; Thrush, 1988; DePatra and Levin, 1989; Warwick et
al., 1990. Such sediment-mediated interactions are common in many infaunal com- munities of mudflats and creeks Rhoads and Young, 1970; Aller and Dodge, 1974;
Kneib, 1991; Wilson, 1991.
Burrowing organisms can also affect benthic community composition by altering recruitment patterns, increasing mortality of settling larvae by ingestion or suffocation
Woodin, 1976, or increasing survival by providing refuge e.g., Tamaki and Ingole, 1993. Burrowing animals may also increase sediment transported through bedload
Aller and Dodge, 1974 affecting benthos indirectly by controlling food availability Luckenbach et al., 1988; Miller and Sternberg, 1988, increasing mortality by abrasion
Miller, 1989 or predation Grant, 1981, or directly favoring dispersion through passive transport Palmer, 1988.
C . granulata, in bare mudflats of Mar Chiquita coastal lagoon Argentina, 378 459 S,
578 269 W is a deposit feeder that excavates and maintains semi-permanent open burrows Iribarne et al., 1997. These burrows are funnel shaped, with large entrances
up to 14 cm major axis length and a surface sediment mound which is a product of feeding or burrow maintenance Iribarne et al., 1997. C
. granulata coexists with Cyrtograpsus angulatus Dana, another grapsid crab up to 40 mm carapace width
which is highly mobile and does not make permanent burrows in this environment Spivak et al., 1994. While Cy
. angulatus is mainly a subtidal species, C. granulata inhabits the upper intertidal zones, and the two species overlap only during high tides.
Juveniles of Cy . angulatus are confined to protected microhabitats like areas with
stones, or in crevices of the tube building polychaete Ficopomatus enigmaticus; Spivak et al., 1994, while juveniles of C
. granulata live in bare mudflats with adults Spivak et al., 1994.
The infaunal community of mudflats of Mar Chiquita coastal lagoon and of other northern Argentinean estuaries i.e., Bahia Samborombon and Bahia Blanca have very
low diversity. Macroinfauna has a high dominance of two polychaete species Laeonereis acuta and Heteromastus similis, Ieno and Bastida, 1998; Botto et al., 1998
F . Botto, O. Iribarne J. Exp. Mar. Biol. Ecol. 241 1999 263 –284
265
that fluctuate widely in abundance Ieno and Bastida, 1998. The few studies of meiofauna in these environments showed also low diversity of ostracods two species,
Whatley et al., 1997 and nematodes two species, Mammoli, 1992. No previous studies of other meiofaunal organisms exist for these environments.
Due to their behavior, abundance and extensive distribution C . granulata may play a
determinant role in the intertidal mudflat communities of most SW Atlantic estuaries. Particularly, species that are sensitive to modifications of the structure, composition or
chemistry of the sedimentary environment, may suffer higher mortality rate due to crab activities e.g., Kneib, 1991; Billick and Case, 1994. Also burrows may enhance spatial
heterogeneity, in a small scale affecting meiofauna distribution e.g., Bell, 1980. Thus, the objective of this work is to determine abundance and distribution patterns of benthic
organisms associated with areas inhabited by C
. granulata, and experimentally evaluate the effect of these crabs on benthic organisms.
2. Materials and methods
