Hopkins Marine Station Student Paper

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Title: Observations of the oval form of Tectura (Notoacmea) depicta (Hinds, 1842): Nocturnal cycle on eelgrass observed in the field and in the lab.
Student Author(s): Dominik, Clare
Faculty Advisor(s): Pearse, John
Pages: 20
Location: Senior Thesis UC Santa Cruz
Abstract: The sudden apperance of a rare oval form of Tectura depicta at Del Monte Beach, Monterey Bay, California has ecologically alarming significance for eelgrass beds (Zostera marina) in the bay. Not only has this limpet appreared in densities never recorded before, but it has reduced the seagrass bed to less than 10% of original coverage since its settlement (Zimmerman, In Press). Examination of the feeding pattern of T. depicta both in the lab and in the field began July, 1995 until March, 1996. Z. marina shoots were collected, planted and placed in a tank at University of California at Santa Cruz's Long Marine Lab. Limpets were observed both during the day and at night. The activity of the limpets was measured by counting how many had traveled above a designated level from the base of the plant at night (5cm above the base of shoot=critical level). The same procedure was done in the field on March 2, 1997 at Del Monte Beach on both day and night dives. Results clearly suggested that T. depicta had a nocturnal feeding cycle (chi-squared test of independence p<<0.001 for both trials in lab, p<<0.001 in the field). The null hypothesis, that limpet position on the plant was independent of time of day, was rejected. Though there is a lack of information on this species it can be postulaed that these limpets are most active at night to avoid diurnal predators that are visually cued (Little et al., 1991), (Franz, 1990).