Abstract

A review is presented of literature concerning invertebrate and some vertebrate predators of sea anemones. Several previously unpublished records for New Zealand are given.

Introduction

Invertebrates, particularly the nudibranch Aeolidia papillosa (Boutan, 1898; Fleure and Walton, 1907), pycnogonids (Stephenson, 1928) and starfish (Verwey, 1930), have long been regarded as important or potentially important predators of sea anemones, and actual records are not uncommon for northern hemisphere species (Tables 1, 2).

There appears to be only one previously published record of an invertebrate preying on an anemone in the New Zealand and Australian region, and a few records for vertebrate predators (Table 3). This review therefore aims to encourage more records for these two countries.

Discussion

As predators of sea anemones, Stephenson (1928) cited ‘various fishes, crabs and other crustacea, nudibranchs, starfish, the larger worms [and] pycnogonids’. The relative importance of these predators is still difficult to assess, because of a lack of detailed field studies.

Aeolids have been the most frequently observed predators (Table 1), and Stephenson (1928) thought that these molluscs ‘are no doubt responsible for a good deal of damage’ to actinians in the wild. Fleure and Walton (1907) considered Aeolidia papillosa to be ‘the most formidable enemy sea-anemones possess’, and Harris (1971) suggested that seasonal fluctuations in the numbers of A. papillosa could influence the distribution patterns of its prey, Metridium senile. Certainly, this particular nudibranch exhibits a distinct preference for actinian species such as Actinia equina and Anthopleura elegantissima (Miller, 1961; Waters, 1973; Edmunds, Potts, Swinfen and Waters, 1975), to which it is attracted from some distance (Stehouwer, 1952; Braams and Geelen, 1953), but many more in situ studies, such as Wobber's (1970) observations of Dendronotus iris feeding on Cerianthus sp., are still needed.

Few other molluscs have been reported as predators of anemones (Tables 2, 3). Francis (1973) recorded Calliostoma annulatum and Epitonium sp. as predators of Anthopleura elegantissima, but gave no indication of their effect on populations. Fleure and Walton (1907) ‘once noticed Trochus ziziphinus nibbling at the base of an anemone’, and on two occasions I observed Haustrum haustorium to partially eat juvenile Actinia tenebrosa. The two juveniles died as a consequence of the attacks, but it seems unlikely that predation by Haustrum would have any marked effect on Actinia populations.

The polychaete worm Hermodice carunculata is known to be an active predator of Stoichactis helianthus. After a single Hermodice starts feeding on Stoichactis, other worms are attracted to feed on the same anemone. Although it is not known whether the anemones die following such attacks, Hermodice could still affect the local distribution of Stoichactis (Lizama and Blanquet, 1975). A similar situation might exist for pycnogonids. Even though Fry (1965) considered actinians to be the major food source of Pycnogonum stearnsi, it is not known whether predation by sea-spiders would actually kill adult anemones. Stephenson (1928), however, observed that ‘serious results may ensue from such attacks on young or small anemones’, so there is still the possibility that pycnogonids could influence the distribution of some actinian species.

Some starfish are considered to be omnivorous (Feder and Christensen, 1966) and have been observed to eat anemones in an aquarium (Milligan, 1916) and in the sea (Table 2). Verwey (1930) believed that Acanthaster echinites was ‘probably one of the worst enemies of anemones’; however, the first unequivocal indication that actinians can be a significant part of the diet of some asteroids came from the extensive in situ observations of Mauzey, Birkeland and Dayton (1968). They found that, in some habitats, Dermasterias imbricata fed mainly on Epiactis prolifera, and occasionally on Anthopleura xanthogrammica, A. elegantissima, Tealia coriacea and Metridium senile. Other starfish were also seen to eat anemones (Table 2).

Most known vertebrate predators are fish. Over a century ago Peachia hastata had been discovered in cod stomachs, and ‘swarms’ page 219 of an Edwardsia species in flounder stomachs (McIntosh, 1874). Even within symbiotic relationships, damselfish sometimes eat the tentacles of their host anemone, Stoichactis (Verwey, 1930). Several New Zealand fish species ingest anemones (Table 3), although from the two detailed records it seems likely that the anemones may have been ingested incidentally along with other prey. Webb (1973) found that an Anthopleura species constituted up to 4.8% of the gut contents of the sand flounder Rhombosolea plebeia, but the cockle Chione stutchburyi is a significant part of the diet of this flounder, and where the study was done Anthopleura aureoradiata is commonly found attached to the cockle (Parry, 1951). Similarly, 40 Calliactis conchicola and several Paracalliactis rosea were seen in the gut contents of 12 gummy sharks, Emmissola antarctica (= Mustelus antarcticus), caught in 100m of water offshore from Kaikoura (Ottaway, personal observation). At Kaikoura, both anemones are epizoic on the carapaces of the spider crab, Leptomithrax longipipes, and C. conchicola is also found on living whelks, Austrofusus glans, and whelk shells occupied by hermit crabs (Hand, 1975). Every anemone found eaten by the gummy sharks was attached to Leptomithrax, but there were Leptomithrax present in the stomachs that did not bear anemones. Since there were no whelks or hermit crabs ingested, with or without anemones, it seems that the sharks were preying on Leptomithrax rather than the anemones.

Other vertebrate predators seem to be few. At one time the French collected anemones and sold them in Bordeaux markets (Rondeletius, quoted in Johnstone, 1846, p. 227). Dicquemare (1773) actually carried out cautious experiments on the toxicity of cooked actinians, feeding them to his cat and himself. He apparently satisfied himself that some species, especially Tealia crassicornis, were palatable, because later he wrote (Dicquemare, 1775): ‘De toutes les efpeces d'anémones de mer, celle-ci m'a paru devoir mériter la préférence pour la table. Lorfqu'on les a fait bouillir un peu fermes, et qu'on les fert pour manger à quelle fauffe on juge àpropos, …’ Even so, Johnston (1846) had reservations about Dicquemare's opinion: ‘The mouth waters at the liquorish description, … but I have not been tempted to test its truth.’ More recently, Martin (1960) reported that cooked Rhodactis howesii was commonly eaten by Samoans, although fatal cases of poisoning were known to occur amongst those natives who had eaten the anemone raw.

Acknowledgements

I am indebted to Dr W. C. Clark, Professor G. A. Knox, Professor M. C. Miller and Mr R. C. Willan for their comments and constructive criticisms of the manuscript at various stages of preparation.

This work was supported by a New Zealand Commonwealth Postgraduate Award.

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