Molgula

Abstract: Blue mussel Mytilus edulis aquaculture lines and associated gear provide habitat for sessile and mobile epifaunal fouling organisms. Due to food limitations and substrate space, these species are likely to interact among themselves and with mussels. In some areas of Prince Edward Island and elsewhere in Atlantic Canada, invasive sea squirts such as the vase tunicate, Ciona intestinalis, colonize mussel socks and rapidly become the dominant species in terms of abundance and biomass. A relevant question for these systems is which native epifauna are most affected by the growth of these invasive tunicates. Our study documents local variations in the abundance of vase tunicates and relates this information to the abundance patterns of three groups of native epifauna with distinctive levels of mobility: sessile tunicates of the genus Molgula, sedentary polychaetes and errant polychaetes. Following recruitment, large abundances of vase tunicates created a significant among-site variation pattern that was consistent over time irrespective of the season when the mussel socks were deployed. In contrast, native tunicates of the genus Molgula colonized the mussel socks in lower numbers and in a spatial pattern opposite to that of invasive tunicates. With the exception of one sampling period, sedentary polychaete colonization also displayed a negative relationship with invasive tunicates. Errant polychaetes displayed erratic patterns that were apparently unrelated to the other species studied. Overall, these results suggest that invasive tunicates have negative effects on many epifaunal species, particularly those that are sessile or have limited mobility.

Abstract: 1. The ascidian Molgula arenata produces an anural larva lacking a tail and other structural features of typical urodele larvae in the family Molgulidae, yet its embryos developed a histochemically detectable acetylcholinesterase in the tail muscle rudiment. Development of the myoblasts seemed to fail during the neurula stage.2. Larval enzyme activity occurred at a mean of 5-6% of the level found in the urodele species Molgula occidentalis and Molgula manhattensis, as measured by scanning integrating microdensitometry of the histochemical reaction product. Some anural larvae had as much as 20% of the enzyme activity in urodele larvae.3. This example of vestigial expression in the absence of other urodele larval features further illustrates the autonomy of a histospecific enzyme development thought to be controlled by an egg cytoplasmic determinant. Partial suppression of the determinant might be the cause of this diminished expression.4. Two other anural molgulid species, Molgula occulta and Bostrichobran...