L
Journal of Experimental Marine Biology and Ecology 248 2000 207–223
www.elsevier.nl locate jembe
Predicting amphipods’ brood size variation in brackish environments: an empirical model for Corophium
multisetosum Stock, 1952 Corophiidae in Ria de Aveiro NW Portugal
a , a
b
M.R. Cunha , M.H. Moreira , J.C. Sorbe
a
Departamento de Biologia , Universidade de Aveiro, P-3810-193 Aveiro, Portugal
b
´ Laboratoire d
’Oceanographie Biologique, UMR 5805 CNRS-UB1, 2, rue du Prof. Jolyet, F-
33120 Arcachon, France Received 13 September 1999; received in revised form 20 January 2000; accepted 27 January 2000
Abstract
˜ Data on fecundity of Corophium multisetosum from Areao Ria de Aveiro, Portugal are
analysed by non linear regression to quantify the relationship between brood size N and head
e
length L , in mm, water temperature T, in degrees Celsius and salinity S, in psu. The aim of
h
the analysis is to obtain a simple line N 5 a 1 bL , in which the slope b and the y intercept a
e h
are functions of salinity and or temperature on each sampling occasion. The equation N 5
e 2
22.940 2 8.027S 1 289.431 1 18.171S 1 12.904T 2 0.368T L explains 64 of the vari-
h
ability of brood size throughout the breeding period. The model predicts an optimal temperature around 188C and a very low fecundity at low salinities. The graphical comparison of the lines
obtained by the model and by a usual linear regression illustrates its potential usefulness to predict fecundity changes. The authors suggest that the observed variation in the fecundity of other
brackish-water amphipods can be described and predicted using similar models.
2000 Elsevier
Science B.V. All rights reserved.
Keywords : Amphipods; Brackish-water; Fecundity; Model
1. Introduction
Invertebrates that release their offspring at advanced stages of development, or provide some kind of brood protection appear to enjoy ecological advantages where
Corresponding author. Tel.: 1351-234-370-785; fax: 1351-234-426-408. E-mail address
: mcunhabio.ua.pt M.R. Cunha 0022-0981 00 – see front matter
2000 Elsevier Science B.V. All rights reserved.
P I I : S 0 0 2 2 - 0 9 8 1 0 0 0 0 1 6 4 - 7
208 M
.R. Cunha et al. J. Exp. Mar. Biol. Ecol. 248 2000 207 –223
salinity undergoes pronounced changes Kinne, 1970a. Amphipods are thus amongst the most successful animal groups in colonising brackish environments. Their spatial and
temporal patterns of abundance are ultimately the consequences of the schedules of fecundity and survivorship that represent life history strategies. Overall the strategy
adopted by an organism is a compromise allocation of energy to the various aspects of its life history, each of which contributes to total fitness Begon and Mortimer, 1986.
The age of first reproduction, reproductive effort the proportion of the available resource input that is allocated to reproduction and longevity are crucial aspects of life
history schedules. The egg size, brood size and number of broods per female are the main traits that determine reproductive effort in amphipods Sainte-Marie, 1991.
Brood size in gammarideans is often reported as being proportional to body length of incubating females and this relationship is frequently summarised by a linear regression
analysis of the raw or log-transformed data e.g. Fish, 1975; Sheader, 1978; Fish and Mills, 1979; Murdoch et al., 1986. Differences between the mean brood size of two
generations or fluctuations throughout the breeding period are usually ascribed to the variation in body length of the incubating females e.g. Dauvin, 1988a,b; Beare and
Moore, 1998. However, other studies have shown that this is not a rule. The scatter of values for females of the same size is often large, especially if samples over the entire
breeding period are pooled, and sometimes no satisfactory explanation can be found for the variability in the number of embryos per brood, e.g. Echinogammarus obtusatus
Sheader and Chia, 1970.
The slope of the regression line that represents the increase in brood size with increasing body length can be used as an index of fecundity Sheader, 1978. Several
authors have shown that the slope of the regression may change throughout the breeding period, which implies a temporal variation in the size-specific fecundity Sheader, 1978,
1983; Fish and Mills, 1979; Naylor et al., 1988. Environmental factors such as latitude, temperature, photoperiod, oxygen concentration and food availability may be important
in determining brood size, as it has been suggested in studies on several amphipod species Kinne, 1959; Vlasblom, 1969; Fish and Preece, 1970; Nelson, 1980; Van Dolah
and Bird, 1980; Sheader, 1983; Moore, 1986.
In the present work, field data on brood size of Corophium multisetosum are analysed in relation to the body size of incubating females and also to the temperature and salinity
throughout the breeding period. These environmental factors, currently assessed in brackish-water studies, are easy to measure and can be used as simple indices of
seasonal changes. The analysis aims to produce a mathematical equation allowing the prediction of changes in fecundity according to the seasonal variation of temperature and
salinity. The term ‘fecundity’ is used as a synonym for the number of embryos per brood.
2. Material and methods
