Abstract
In this study, gamete release by Caulerpa cylindracea was investigated for the first time in the Tyrrhenian Sea (Sardinia, Western Mediterranean), focusing on the main environmental factors triggering gametogenesis and spawning of the species. For this purpose, a combination of field and laboratory experiments was conducted. First, a 2-year mensurative experiment was performed in the field during summer to individuate and quantify the occurrence of C. cylindracea gametogenesis and spawning events, linking them to environmental conditions. Then, based on the results of the field work, a laboratory experiment was performed to directly test, under controlled conditions, the effect on the above-mentioned processes of two abiotic factors that appeared to play a key role in species gamete release processes in the area: sea water temperature and water movement. During the 2 years of field research, several gametogenesis events were recorded in the study area and two spawning events also occurred. Significant differences were observed between the ratio of fertile and total thalli and between releasing thalli (RT) and fertile thalli (FT), among sites with different hydrodynamic conditions and sampling periods with different sea water temperatures. Overall, these results suggest that C. cylindracea sexual reproduction also occurs in the Tyrrhenian Sea, and that, therefore, new genotypes that favor the invasive profile of the species could be produced in the basin, where both its gametogenesis and spawning seem to be mainly regulated by water movement and sea water temperature.
Highlights
Over the last decades, an increasing number of studies have considered the patterns of gametogenesis, sexual reproduction, and fertilization of seaweeds by means of an integrated biological and ecological approach (e.g., Brawley and Johnson, 1992; Santelices, 2002)
Mean values appeared to be significantly higher in July and in the first part of August (25.1◦C), while they were lower in the second part of August and in September (24.3◦C) (Figure 4 and Supplementary Tables 1A,B)
This study presents the first report of gametogenesis and spawning by C. cylindracea in the Thyrrenian Sea and provides useful information on the environmental factors triggering such processes
Summary
An increasing number of studies have considered the patterns of gametogenesis, sexual reproduction, and fertilization of seaweeds by means of an integrated biological and ecological approach (e.g., Brawley and Johnson, 1992; Santelices, 2002). Studies that simultaneously examine the effects of several environmental factors on sexual reproduction, in particular on gametogenesis and spawning, appear to be quite difficult. They are necessary to delineate the conditions that must be simultaneously met for successful sexual reproduction, especially for alien species (Brawley and Johnson, 1992). Focusing on alien invasive species, knowledge of life cycle progression transcends pure academic interest (Liu et al, 2017), as establishing the occurrence of their sexual reproduction events has important environmental management implications, both for gametes and zygote dispersal and the potential to generate more invasive genotypes (Ellstrand and Schierenbeck, 2000, 2006)
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