Abstract
ABSTRACT This study aimed to establish the reproductive cycle of the mangrove oyster, Crassostrea rhizophorae cultured in the macrotidal estuary of the Paciência River, Maranhão state, on the northeastern coast of Brazil, and its relationship with environmental factors. Oysters were collected monthly throughout 2013 for histological analysis of sex ratio, gonadal development and condition index. The sex ratio was 1:1.39 (M:F) and only 5 specimens presented hermaphroditism. The breeding process was continuous throughout the year and mature (IIIA stage) and spawning oysters (IIIB stage) were present in practically all months. Low variation in temperature seemed to be the main factor for the continuity of the reproductive cycle. Besides temperature, the relationship between rainfall, salinity and primary productivity affected the stimulus and timing of reproductive events. The rainy season, with low values of salinity and high values of chlorophyll a and particulate organic matter, appeared to be the main reproductive period, with release of gametes and production and maturation of new gamete cohorts in the short term. In the tropics, where gamete maturation and release seem to be continuous and concomitant, the condition index does not appear to be the best method to assess reserve accumulation peaks and gonadal repletion.
Highlights
The mangrove oyster, Crassostrea rhizophorae (Guilding 1828) is found mainly in mangroves, bays, and estuarine regions, fixed on rocks and consolidated substrates (Rios 2009)
The gamete release in tropical regions occurs continuously during the year, with evidence of spawning peaks stimulated by environmental variables (Vélez 1977; Lenz and Boehs 2011; Paixão et al 2013)
The condition index in our study presented higher values in the rainy months, between March and May, to Lenz and Boehs (2011), who recorded higher CI values during rainy months, relating to greater food availability
Summary
The mangrove oyster, Crassostrea rhizophorae (Guilding 1828) is found mainly in mangroves, bays, and estuarine regions, fixed on rocks and consolidated substrates (Rios 2009). In mangroves, it is usually found settled on the red mangrove, Rhizophora mangle (Linnaeus 1753) roots in the intertidal region (Bacon 1971). The coastal environments of this region are influenced by the macrotide phenomenon, reaching tidal amplitudes of up to 7 m. This phenomenon, associated with the low slope of the local coastal plains, and two well-defined annual seasons, a rainy season (February to July) and a dry season (August to January), results in a yearly variation in coastal salinity from 0.1 to 49.2 (Sampaio et al 2020)
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