Life History, Reproduction, Growth, Population Dynamics and Production of Gammarus aequicauda (Crustacea: Amphipoda) at Extremely Low Salinities in a Mediterranean Lagoon

Abstract

Aspects of the biology of Gammarus aequicauda were studied at extremely low salinities (0.3-5.7 psu) in Monolimni Lagoon, N. Aegean Sea. Samples were collected monthly from February 1998 to February 1999. Breeding occurred continuously but peaked in late spring, late summer and autumn and three cohorts were produced. The spring and summer cohorts showed fast growth (0.15 mm d -1 ), accelerated maturity and life span of about three and seven months respectively, while the overwintering cohort showed a life span of about nine months. The largest individual had a body length of 23.6 mm. Mean brood size was 54.5 early embryos, while the intramarsupial loss was 46%. Population density sharply increased in late spring, summer and autumn. Secondary production calculated by Hynes' method gave a mean annual density of 1077.4 ind. m -2 , a mean annual crop (B) of 2.93 g DW m -2 , an annual production (P) of 35.03 g DW m -2 and a P : B ratio of 11.96. Gammarus aequicauda showed a life-history pattern similar to those previously reported for this species at higher salinity environments with comparatively large final body length and high growth rate during summer, brood size and P : B ratio, but with high embryo loss as well.

Life History Traits of the Endangered Endemic Amphipod Echinogammarus cari (Crustacea, Gammaridae) from the Dinaric Karst

“…Furthermore, a higher number of cohorts (12) born during the sampling period could be distinguished at B2 with a life span of 6-7 months, while at D5 only four cohorts occurred with a life span of 7-9 months in cohorts born during winter and early spring and about 12 months in late spring and early summer cohorts. Such a pattern of a longer life span for summer cohorts at D5 is completely different than that observed in other fresh and brackish water gammarids, in which winter cohorts had a longer lifespan (e.g., PÖCKL et al, 2003;SUBIDA et al, 2005;KEVREKIDIS et al, 2009). This can be explained by the negative effect of increasing temperatures on growth and development of spring and early summer cohorts, which thus require a longer time to reach sexual maturity and additionally have a reproductive resting stage that postpones their reproduction and further increases the life span.…”

Effects of Different Salinities on Juvenile Growth ofGammarus aequicauda(Malacostraca: Amphipoda)

“…Kevrekidis et al [14] suggested that the growth and reproductive biology of G. aequicauda are not markedly affected by low salinities. According to the present results, G. aequicauda could well tolerate the salinities that were reported in the study area (4-37 psu) [13].…”

“…aequicauda (Martynov, 1931) is one of the most common and abundant amphipods from lagoons and brackish environments of the Mediterranean and the Black Sea [8][9][10][11][12][13][14][15][16][17]. G. aequicauda is a euryhaline species, being very resistant in isolate habitats from the sea with extensive ranges of salinity.…”

“…This species has an important trophic role in the transport of energy to a higher consumer level, and its feeding activities contribute greatly to macrophyte fragmentation, thus enhancing microbial colonization and macrophyte decomposition [9][10][11][12][18][19][20][21][22]. Although the distribution, life cycle, reproductive biology, and population dynamics of G. aequicauda have been studied in several coastal environments [8,13,14,18,22,23], laboratory studies on the effect of salinity on survival and growth are scarce [24].…”

“…In this habitat, population densities of G. aequicauda vary greatly throughout the year [13], and the most important factors that regulate population density 2 International Journal of Zoology of this amphipod are unknown Prato et al [24] showed that the survival of G. aequicauda was affected by salinity with the optimal range of 15 psu to 36 psu. Kevrekidis et al [14] concluded that life history, growth, and reproduction are not markedly affected by low salinity (0.3-5.7 psu) although low salinity does affect embryo viability. Previous studies on the biology and population dynamics in the Ebro delta showed that abundance is not correlated with changes in salinity [13].…”