Interactions between polyps of Aurelia aurita and planktonic larvae of scyphozoans: an experimental study

Abstract

Predation by polyps of the scyphozoan Aurelia aurita (L.) on planula larvae of their own species and on planulae of the scyphozoan Cjfanea capillata (L.) was studied in laboratory experiments.Transplant experiments in the field tested whether high densities of established A. aurita polyps could affect the recruitment of planktonic larvae and if Interactions between the polyps occur. More planula larvae of C. caplllata than of A. aurita were eaten by the polyps. The transplant experiments showed that dense covers of A. aurita polyps can affect recruitment of planulae and other planktonic larvae to hard-bottom communities. The most likely explanation is predation on the larvae. Interactions indicating competition for space or food between already established polyps and settling planulae were observed. Mortality among established polyps was greater at high than at low densities. Planula larvae of both A. aurita and C. capillata showed an increased rate of metamorphosis in the presence of A. aurita polyps in the laboratory experiments.

Evidence of gregarious settlement of planula larvae of the scyphozoan Aurelia aurita: an experimental study

“…2). These results contradict a previous study (Grondahl 1988b) which showed that even a low density of 100 established polyps (10-d old) can reduce the settling of new planula larvae (Fig. 3).…”

“…The difference between the 2 studies is the duration of the transplant experiments. In the present study 4-d old established polyps were transplanted to the field for 4 d, while in Grondahl (1988b) polyps were transplanted to the field for 10 d. In the latter study, competition for food or space may have developed among the established polyps and they were also more than twice as large as in the present study (0.62 mm and 0.28 mm, respectively). In Grondahl (1988b) the established polyps also had welldeveloped feeding devices (tentacles), whereas this was not the case with the 4-d old polyps used in the present study (Fig.…”

“…Glass slides were glued to plastic supports, leaving an area 2.5 X 6.5 cm (16.25 cm2) free for larval settlement. Thirty glass slides, 6 for each treatment, were attached in rows by nylon bolts to 5 grey, opaque PVC plates (10 x 4 5 c m ) , Grondahl 1988b). The glass slides were conditioned in running seawater for 3 d before use.…”

“…Planula larvae metamorphosed and settled mainly on the bottom of beakers. Ca 20 % of introduced larvae were eaten by established polyps (Grondahl 1988b). …”

A Simple Temperature Dependent Model to Predict the Bloom of Aurelia Aurita Polyps

“…The reproduction and mortality of A.aurita in the polyp stage may have considerable influence on the population size of the medusa [1,8]. Gröndahl suggested that planula and polyp mortality rates influence the medusa population more than ephyra and medusa mortality rates [9]. Biological methods to preserve the environment such as eutrophication treatment are suggested [10].…”