The reproductive biology of the isopod Excirolana braziliensis in upwelling areas off northern Chile
José M. Riascos1, Daniel Carstensen2, Daniela Delgado1, Olaf Heilmayer2, Jürgen Laudien2
1Instituto de Investigaciones Oceanológicas-Universidad de Antofagasta, Antofagasta, Chile. 2Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany
Acknowlegement
This study was conducted in the frame of the EU-project Climate variability and El Niño Southern Oscillation: Impacts for Natural Resources and Management.
References
[1] Dexter, D.M. 1977. Natural history of the Pan-American sand beach isopod Excirolana braziliensis (Crustacea: Malacostraca). Journal of Zoology, London 183, 103–109.
[2] Cardoso, R.S. & Defeo, O. 2003. Geographical patterns in reproductive biology of the Pan-American sandy beach isopod Excirolana braziliensis.
Marine Biology 143:573-581
Material & Methods
Samples were taken at Chipana and Hornitos, between June 2005 and May 2006. Three replicated sediment samples (0.16 m2) were taken along an across-shore transect every four meters using an open ended push-corer.
Retained E. braziliensis(1mm mesh) were counted, measured and classified as juveniles (< 4mm), adult male, adult ovigerous and non-ovigerous female (Fig. 1). Duration of breeding and recruitment season, maximum sizes of ovigerous females and juveniles and female : male ratio were estimated and compared with those reported in the literature for other locations (Fig. 2) [2].
Fig. 1: Excirolana braziliensis.
Length from the cephalon to the end of the telson and sexual differences between males and females are indicated.
Introduction
The pan-American isopod Excirolana braziliensis (Isopoda: Cirolanidae) numerically dominates the macrofauna of tropical, subtropical and temperate Pacific and Atlantic sandy beaches [1]. The present study evaluates if upwelling conditions in northern Chile give rise to deviations from large-scale patterns of the reproductive biology reported for this species [2].
Length
Male ventral view Female ventral view
Paired penes
Results and Discussion
No consistent differences were observed in the reproductive parameters of E. braziliensis between locations at the Pacific coast (i.e. upwelling zones) and Atlantic coast. Minimal size of juveniles was the only parameter lying outside the expected latitudinal pattern; juveniles from the Pacific coast are larger than their counterparts in the Atlantic (Fig. 3). The similarity of strategies at comparable latitudes for populations inhabiting both oceans suggests a comparable efficiency in the rates of conversion of food into somatic tissue. Beach morphodynamics could explain the observed local differences in reproductive parameters.
Fig. 2: Study area (green and yellow) and geographic locations at the Pacific (filled circles) and Atlantic coast (empty circles) from literature [2].
Fig. 3: Regression line (±95% confidence interval) between latitude and a) annual occurrence of ovigerous females; b) annual occurrence of juveniles, c) sex ratio, d-e) extreme length of ovigerous females; f) maximal length of juveniles for the study area (green and yellow), Atlantic (open circles) and Pacific (filled circles) beaches [2].
Latitude 12
10
8
6
4
2 Ovigerousfemales(moyr-1)
12
10
8
6
4
2 Juveniles (moyr-1)
2.0
1.5
1.0
0.5
Sex ratio (females:males)
8
6
4
2
Smalestovigerous female(mm)
10
8
6
4 12
Largestovigerousfemale (mm)
2.0
1.6
1.2
0.8
5 10 15 20 25 30 35 40
2.4
Smalestjuvenile(mm)
2.8
South America
50°
60°
70°
80° 40°
10°
0°
10°
20°
30°
40°
50°
Prainha - 23° 2´
Grumari - 23° 3´
Restringa - 23°3´
Chipana - 21°18´
Hornitos - 22°54´
Errazuriz - 23°27´
Taquaras - 26°59´
Barra del Chuy - 33°45´
Arachnia - 34°36´
Mehuin - 39°26´
Las Delicias - 8°11´
Huanchaquito - 8°6´
Naos Island - 8°55´
50°
