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Studies on the Paua, Haliotis iris Martyn in the Wellington district, 1945-46

Food and Method of Feeding

page 14

Food and Method of Feeding

H. iris feeds on a large variety of seaweeds. In some fifty specimens examined for gut contents the following seaweeds were identified: Xiphophora chondrophylla var. maxima, Caulerpa sedoides, Pterocladia lucida, Halopteris bordacea, Gigartina sp. and Ulva sp. Most of the animals examined were collected from Chaffer's Passage and The Runaround and they all had crop contents composed almost exclusively of brown seaweeds. Thus it can be said that in these animals which ranged from 10 to 16cm in length, brown seaweeds formed the predominating food. Crofts (1929) states for H. tuberculata that "mature animals show a preference for the delicate Algae, particularly red seaweeds such as Delesseria and Griffithsia, but will eat Chondrus as well as coarser weeds ". From examination of the gut content of H. iris the reverse condition appears to be the case. In small specimens the predominant food consists of small red seaweeds. In one instance a few specimens taken from a large pool just below low water mark, i.e. where the small paua between 1–8cm are found, the green seaweed Ulva was most noticeable but all the crops examined contained principally varieties of red seaweeds. A preference for red seaweed is undoubtedly shown by the New Zealand species but not by the larger specimens, as in H. tuberculata. The areas where the best shell grows generally contain a large amount of Xiphophora chondrophylla var. maxima and sometimes a great deal of Ulva.

Specimens held in aquaria were found to eat blue-green algae and diatoms which were present on the side of the tank. The diatom was Cocconeis sp. or a species very close to it. On a number of occasions Ulva was given to the aquarium specimens when there was very little algal growth on the sides of the tanks, but on only one occasion was a specimen observed eating it. The feeding of small H. iris on the sides and floor of the tanks was observed on many occasions. Each feeding movement of the radula resulted in two minute areas on the side of the tank being cleared of Algae, as can be seen in Fig. 6. As far as could be ascertained the scraping off of the Algae was accomplished by the two lateral sets of teeth in the radula as described by Crofts (1929). Six or seven feeding movements would be taken transversely with the posterior region of the foot hardly moving at all, then the whole animal would move forward sufficiently to be in a position to clean the next area in front. This method results in the feeding tracks having a branched appearance. In Fig. 6 the feeding tracks of two small specimens are shown. The larger set of "tracks" was made by an animal approximately 3cm in length and the smaller (lower left corner) by a specimen approximately 2cm in length. The latter did not make such regular tracks.

The size of the particles of seaweed found in the gut varied with the size of the animal. The largest specimens (13–17cm in length) contained food particles averaging 5mm in length and 1.5mm in width. They may, however, reach up to 10mm in length. The shape of the particles is fairly uniform, generally pointed at both ends and slightly curved towards one side.