Abstract
The eastern Atlantic and Mediterranean marine Cephalaspidea gastropod Haminoea orbignyana was collected from Lake Qarun (Fayoum, Egypt), a landlocked lake that has undergone a shift from freshwater to estuarine conditions in the past 100 years. Species identity was confirmed by both morphological (anatomical dissection and scanning electron microscopy) and molecular methods (COI gene phylogeny). Observations suggested a robust population of H. orbignyana in the lake with a density of ca. 64 individuals/m2 and ca. 105 egg masses/m2 during surveys conducted in the summer of 2013. The vast majority of snails and egg masses were found under rocks. Observations of egg masses in the lab showed a gradual change from whitish to yellow-green as the eggs matured and the release of veliger larvae alone after about a week. Although adult cephalaspideans readily consumed filamentous red and green algae, and cyanobacteria, laboratory trials showed that they consumed significantly more of the red alga Ceramium sp., than of the green alga Cladophora glomerata, with consumption of Oscillatoria margaritifera being similar to those on the two algae. When grown on these resources for 16 days, H. orbignyana maintained their mass on the rhodophyte and cyanobacterium, but not in starvation controls. No cephalaspideans grew over the course of this experiment. Lake Qarun has been periodically restocked with Mediterranean fishes and prawns since the 1920s to maintain local fisheries, which represents a possible route of colonization for H. orbignyana. Yet, based on literature records, it seems more likely that invasion of the lake by this gastropod species has occurred only within the last 20 years. As human activities redistribute species through direct and indirect means, the structure of the community of this inland lake has become unpredictable and the long-term effects of these recent introductions are unknown.
Highlights
The literature on species invasions is largely focused on organisms that have altered significantly the structure of the communities in which they have been introduced [1,2,3,4]
Egg masses which resembled those of haminoids came with the samples
It was noted that recently laid egg masses were milky white but turned yellow-green as they developed (Fig 2C, 2D and 2E)
Summary
The literature on species invasions is largely focused on organisms that have altered significantly the structure of the communities in which they have been introduced [1,2,3,4]. For many small marine invertebrates that require microdissection or DNA data for positive identification, species introductions may not be noticed, sometimes until almost complete replacement of natives has occurred [2, 6,7,8]. It is such organisms that are often carried inadvertently by human activities to new habitats as adults or larvae. A lack of expert taxonomists for many of these animals, a phenomenon known as the taxonomic impediment, has compounded the problem of identifying small introduced species even in instances where they become locally dominant [5, 8]
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