Host Sea Anemones Research Articles

Effects of anemonefish on giant sea anemones: Ammonium uptake, zooxanthella content and tissue regeneration

Zooxanthellae symbiotic with stony corals utilise ammonium excreted by resident fish populations. However, the contribution of ammonium produced by anemonefishes to host sea anemones has not been examined. In split-pair laboratory experiments with the giant sea anemone Entacmaea quadricolor, one half of each sea anemone was maintained with two individuals of the endemic anemonefish Amphiprion bicinctus, and the other half was maintained without anemonefish. Sea anemone fragments maintained with anemonefish regenerated significantly faster than those without anemonefish. After 8 weeks of regeneration, there were more endosymbiotic algae (zooxanthellae) in the tentacles of sea anemones with anemonefish than in those lacking fish. Adult anemonefish (8 cm total length) each excreted ammonium at a rate of about 0.97 µM h−1. Sea anemones that had been maintained without anemonefish for 4 weeks took up ammonia from enriched water at a faster rate than those that had been maintained with anemonefish, which absorbed very little ammonium. We conclude that anemonefishes provide ammonia for their host anemones and zooxanthellae, enhancing rates of tissue growth and regeneration.

Why is group size correlated with the size of the host sea anemone in the false clown anemonefish?

When social groups monopolize discrete habitat patches, group size may be positively correlated with patch size. The correlation can be a direct consequence of limited resources. Alternatively, it can be an indirect consequence of patch-size effects on a dominant group member. We asked which of these two mechanisms was responsible for a positive correlation between the group size of false clown anemonefish (Amphiprion ocellaris Cuvier in Cuvier and Valenciennes, 1830) and that of the host sea anemone Stichodactyla gigantea (Forskål, 1775). We argue that some false clown anemonefish groups may have reached the carrying capacities of their hosts, but that the group size : patch size correlation in the population as a whole is best interpreted as an indirect consequence of a positive relationship between anemone size and the length of the dominant group member. The dominant's length in turn limits group size because dominant group members inhibit the growth of their subordinates. Thus, a correlation between group size and patch size need not imply resource limitation of subordinate group members.

Mutualism can mediate competition and promote coexistence

AbstractMutualistic interactions are not believed to promote coexistence of competitors because mutualisms produce positive feedbacks on abundances whereas coexistence requires negative feedbacks. Here we show that a mutualism between an anemonefish (Amphiprion) and its sea anemone host mediates the effect of asymmetrical competition for space between the anemonefish and another damselfish (Dascyllus) in a manner that fosters their coexistence. Amphiprion stimulates increases in host area, the shared resource, but social interactions cap the number of anemonefish to two adults per host. Space generated by the mutualism becomes differentially available to Dascyllus because the effectiveness of an anemonefish in excluding its competitor declines with increases in the area it defends. This alters Amphiprion's ratio of per capita intra‐ to interspecific effects and thus facilitates coexistence of the fishes. This mechanism may be prevalent in nature, adding another major pathway by which mutualism can enhance diversity.

Sea anemone host selection by the symbiotic saddled cleaner shrimp Periclimenes holthuisi

A preliminary field survey was conducted to determine the distribution of ectosymbiotic shrimp Periclimenes holthuisi on the sea anemone Stichodactyla haddoni in Moreton Bay (Queensland, Australia). Laboratory experiments were also carried out to verify whether the shrimp show a preference for one anemone host. In the field, 45 individuals of P. holthuisi were found to be associated with 70% of the specimens of S. haddoni (n�=�20). We inferred this shrimp population was not space-limited because not all anemones were colonized. After having been isolated from their natural host for 2 weeks, when placed between individuals of S. haddoni and Macrodactyla doreensis (an anemone that is sympatric with S. haddoni), shrimp overwhelmingly selected S.�haddoni (92%). To establish whether M. doreensis may serve as an alternative host for P. holthuisi, unacclimated shrimp were forced to associate with this anemone. Macrodactyla doreensis showed little tentacle reaction during this association; shrimp were found on the anemone's tentacles and the column. The finding that M. doreensis can serve as an alternative host for P. holthuisi demonstrates that this anemoneshrimp is adaptable to another anemone host and thus may not be highly host specific.

Host-use and selection of differently colored sea anemones by the symbiotic crab Allopetrolisthes spinifrons

Adults of the reddish green symbiotic crab Allopetrolisthes spinifrons obtain different degrees of camouflage from the red, green, reddish green, and blue sea anemones Phymactis clematis, and the orange Phymanthea pluvia on which they are commonly found. Previous studies have indicated that the distribution of the crab on sea anemones may be influenced by the host's coloration. During the present study, we tested whether adult crabs dwell more commonly on those sea anemones that offer a higher degree of camouflage, and whether “behavioral preferences” can explain crab distribution on sea anemone species and color morphs in the field. We examined the frequency of occurrence of adult crabs on 200 sea anemones of each color morph, and crab distribution was compared to that expected by the relative abundance of different anemone hosts in the field. Adult crabs occurred more frequently than expected by chance on sea anemones most similar to their own color (reddish green), and occurred less frequently than expected by chance on sea anemones where homochromy was reduced (e.g. blue). Multiple host selection experiments conducted under laboratory conditions demonstrated that adult crabs avoid blue sea anemones compared to other host color morphs offered for colonization, but no preference was observed among red, green, reddish green, and orange sea anemones. These results suggest that “behavioral preference” play a role in determining the field distribution of A. spinifrons adult crabs in the field. The lack of preference for reddish green sea anemones in the laboratory, but its high frequency of occupancy by adult crabs in the intertidal, further suggests that factors other than homochromy-related preferences (e.g. sea anemones habitat) might affect crab distribution in the field. Alternative host selection experiments revealed that the specific host from which crabs were collected (source host) affected the host-choice behavior of crabs, indicating that previous experience is important in choice of sea anemone hosts.

Agonistic Behaviour and Development of Territoriality During Ontogeny of the Sea Anemone Dwelling Crab Allopetrolisthes Spinifrons (H. Milne Edwards, 1837) (Decapoda: Anomura: Porcellanidae)

Allopetrolisthes spinifrons is an ectosymbiotic crab of the sea anemone Phymactis clematis. As a consequence of low host abundance, these represent a scarce and limited resource for the crab. Additionally, the relatively small size of the sea anemone host suggests that few symbiotic crabs can cohabit on one host individual, forcing crabs to adopt a territorial behaviour. In order to examine the potential presence and ontogenetic development of territoriality, the agonistic behaviour between crabs of various ontogenetic stages (adults, juveniles, and recruits) was studied in the laboratory. Laboratory experiments demonstrated that adult or juvenile crabs aggressively defended their sea anemone hosts against adult or juvenile intruders, respectively, but both adult and juvenile crabs tolerated recruits. Adult crabs behaved indifferently towards juvenile crabs, sometimes tolerating them, sometimes expelling them. Recruits never showed agonistic behaviour among themselves. The agonistic interactions observed in the laboratory and the uniform population distribution pattern on sea anemones recently described for A. spinifrons indicate that this species exhibits territorial behaviour, which develops during ontogeny. Territoriality in this species and other symbiotic decapods may function as a density-dependent mechanism of population regulation, being mediated by the availability of hosts. Resource monopolisation behaviours may be common among other symbiotic and free-living marine invertebrates inhabiting discrete habitats that represent a limiting resource.

Ecology of a parasitic barnacle, Koleolepas avis: relationship to the hosts, distribution, left–right asymmetry and reproduction

The pedunculate barnacle Koleolepas avis is a symbiont of the sea anemone Calliactis japonica, which lives on gastropod shells carried by large hermit crabs, usually Dardanus arrosor. Relationships with the host sea anemone, distribution on the gastropod shell, left–right asymmetry and reproduction of the barnacle were investigated. A larger number of barnacles occurred on shells with greater ‘cylindroid dimensions’ of sea anemones. Distribution of barnacles on shells was not random: assuming the in situ position of the shell carried by the hermit crab (∼45° inclination), there were more barnacles along the lower part of the anemone disk than the upper part. Large barnacles lie on either the left or right sides of their capitula, and those lying on the left side (Type L individuals) tended to occur along the left side of the host, and those on the right side (Type R) along the right side. Barnacles [ges ]0·016 g in wet weight had egg masses, and there was a positive relationship between body weight and number of eggs. Koleolepas avis has both hermaphrodites and dwarf (complementary) males attached to them. Large hermaphrodites tended to have larger dwarf males than smaller hermaphrodites.

Social and mating systems of the protandrous anemonefish Amphiprion perideraion under the influence of a larger congener

AbstractThe effect of a larger anemonefish Amphiprion clarkii (Bennett) on the social and mating system of a smaller congener Amphiprion perideraion (Bleeker) was investigated on a coral reef at Okinawa, Japan, where both species use the same host sea anemone Heteractis crispa (Ehrenberg). The population of A. perideraion consisted of adult, subadult and juvenile groups. Adult groups, which consisted of one or two adults and a varying number of subadults and juveniles, usually did not share the host with A. clarkii. In contrast, subadult and juvenile groups, which included no adults, always cohabited with A. clarkii. In the heterospecific groups, subadult A. perideraion were able to mature histologically, and changed to female when they were the largest among conspecific members, although their reproduction was suppressed by A. clarkii. After all members of A. clarkii emigrated or disappeared from a heterospecific group, adult A. perideraion could begin breeding. I suggest that A. perideraion in both heterospecific and conspecific groups adopt a mating strategy that involves waiting for vacated breeding posts because of their low mobility and a low host density.

Cropping of sea anemone tentacles by a symbiotic barnacle

As sessile animals, barnacles (Cirripedia: Thoracica) are generally suspension feeders, extending their cirri into the surrounding water to collect food particles (1). Although it has been suggested that some symbiotic barnacles obtain nutrients directly from their hosts, either by absorbing body fluids (2-4) or by rasping the host's tissue (4-6), most of these cases are inferred from their morphology. Direct evidence, such as gut content analysis, has been limited (for an exception, see ref. 5), and no actual feeding on their hosts has been observed. Koleolepas avis (Hiro, 1931) is a pedunculate barnacle symbiotic with the sea anemone Calliactis japonica, which lives on gastropod shells occupied by large hermit crabs (7), mainly Dardanus arrosor. Symbiotic relationships between various hermit crabs and sea anemones have been well documented (8), but the relationship between the barnacle and its host sea anemone has been virtually unknown. From February to April 1996, we collected living individuals of K. avis from lobster nets landed at Minabe Fishery Port, southwestern Japan (33{deg} 44' N, 135{deg} 20' E). On the basis of behavioral observations in the laboratory and analyses offecalpellets and gut contents, we concluded that this barnacle feeds actively on its host's tentacles.

Correlates of Environmental Variables with Patterns in the Distribution and Abundance of Two Anemonefishes (Pomacentridae: Amphiprion) on an Eastern Australian Sub-tropical Reef System

The relationship between characteristics of the reef environment and variations in the distribution and abundance of the anemonefishes Amphiprion akindynos and A. latezonatus was investigated at North Solitary Island, a sub-tropical rocky reef system on the east coast of Australia. During the summers of 1994 and 1995, fish densities and host sea-anemone cover were assessed on replicate 25 m transects at sites where host sea-anemones form semi-contiguous mats throughout the 6–21 m depth range. Multiple regression analyses indicated that environmental variables accounted for 65–71% and 61–80% of the variations in the number of A. akindynos and A. latezonatus among-sites, respectively. Among-habitat comparisons indicated that A. latezonatus densities were positively correlated with depth (r=0.45–0.90), whereas A. akindynos showed no consistent depth-related abundance patterns. Poor correlations (p>0.05) between the densities of each species on transect lines suggested that present-day competition was unlikely to determine the preference of A. latezonatus for deeper depths. Correlations between host sea-anemone cover and fish densities at the within-habitat (depth) scale were comparatively stronger than correlations at among-habitats in both species. These results suggest that among-habitat comparisons can confound finer scale fish-habitat associations within habitat (depth) zones. Evidence suggests that while sea-anemone cover does, to an extent, regulate the local ecology of anemonefishes, other factors are also likely to interact to limit their densities.

Host recognition and possible imprinting in the anemonefish Amphiprion melanopus (Pisces:Pomacentridae)

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 188:207-218 (1999) - doi:10.3354/meps188207 Host recognition and possible imprinting in the anemonefish Amphiprion melanopus (Pisces: Pomacentridae) Michael Arvedlund1,*, Mark I. McCormick1, Daphne G. Fautin2, Mogens Bildsøe3 1Department of Marine Biology, James Cook University, Townsville, Queensland, Australia 2University of Kansas, Biological Sciences and Natural History Museum, Lawrence, Kansas 66045-2106, USA 3Department of Animal Behaviour, Zoological Institute, University of Copenhagen, 2100 Copenhagen OE, Denmark *Present address: Raadhusvaenget 14, 1. Floor, 3600 Frederikssund, Denmark. E-mail: michaelarvedlund@hotmail.com ABSTRACT: Many reef fish have strong microhabitat preferences when they settle to the juvenile population, and choices at this time may influence fish survival. This is exemplified in anemonefishes (Family: Pomacentridae) that exhibit obligate symbiotic relationships with a restricted range of sea anemone species. This study examined how juvenile anemonefish Amphiprion melanopus select their host, and whether recognition and selection are mediated by an imprinting-like mechanism. Specifically, we experimentally examined the host-selection made by A. melanopus that had been reared under constant conditions, but whose embryos had received 1 of 3 treatments: (1) in contact with a known natural host sea anemone, Entacmaea quadricolor; (2) in contact with the sea anemone Heteractis malu, which is not a host for A. melanopus in nature, but is a host for anemonefish of other species; and (3) without a sea anemone (or chemical cues released from sea anemones) at any life stage. Our study shows that olfaction, not vision, is used by juvenile A. melanopus to recognize host anemones. Furthermore, the choice of a settlement site for juvenile A. melanopus is strongly influenced by events that occur early in development, prior to the dispersal of larvae from their natal site. We suggest that juvenile A. melanopus possess an innate preference for E. quadricolor, a preference that is enhanced by imprinting. Interestingly, it was not possible to imprint A. melanopus larvae to the non-host sea anemone H. malu, which suggests that anemonefish host-imprinting may be rather restricted. KEY WORDS: Chemotaxis · Host-imprinting · Fish larvae settlement · Habitat recognition · Sea anemones · Symbiosis Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 188. Publication date: November 03, 1999 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1999 Inter-Research.

Host selection by shrimps symbiotic with sea anemones: A field survey and experimental laboratory analysis

In three coastal areas of the Republic of China, we found six species of anemoneshrimps and five of host sea anemones in 13 symbiotic combinations; four of the 13 combinations were previously documented. In the laboratory, we tested host preference of the three common shrimps, Periclimenes ornatus Bruce, P. brevicarpalis (Schenkel), and Thor amboinensis (De Man), for anemones of three species. Periclimenes ornatus unequivocally preferred Entacmaea quadricolor (Rüppell and Leuckart), the only anemone with which it occurs in northern Taiwan and from which the experimental specimens had been collected. We therefore consider P. ornatus a specialist on E. quadricolor. Results of experiments with P. brevicarpalis and T. amboinensis were ambiguous: for both, outcome of some experiments was affected by identity of the anemone from which the shrimp had been collected, and in other experiments, T. amboinensis exhibited no preference. We therefore consider Thor a generalist symbiont, and P. brevicarpalis intermediate in specificity. In experiments to determine sensory cue(s) used by the shrimps to locate hosts, none could locate an anemone by vision alone. A significant proportion of shrimp of all three species was chemically attracted to anemones of at least one species; as in the preference experiments, source of the shrimp affected the results for P. brevicarpalis and T. amboinensis. The proportion of shrimp chemically attracted to an anemone in the experiments on sensory cues was lower than the proportion attracted in the host preference experiments. We, therefore, infer that shrimp use more than one sensory modality to locate a host anemone.

Do the Anemonefish Amphiprion ocellaris (Pisces: Pomacentridae) Imprint Themselves to Their Host Sea Anemone Heteractis magnifica (Anthozoa: Actinidae)?

AbstractJuvenile anemonefishes detect their host sea anemone by olfactory stimuli; in order to investigate whether this behaviour is innate or acquired, the anemonefish species Amphiprion ocellaris was bred in two different ways: 1. With no host sea anemone present at all (–A); and 2. With the specific host sea anemone Heteractis magnifica present in the hatching aquarium, so that these eggs were laid and hatched close to the sea anemone, as in nature (+A).The two different types of juvenile A. ocellaris were presented to the odours of the host sea anemone H. magnifica in two sets of short‐term experiments with the host (a) visually hidden in a net cage, and (b) visible but physically separated from the anemonefishes. In both cases, a water flow was established between fishes and host. The +A‐fishes found their host by olfactory and not by visual stimuli. In both series, the –A‐fishes showed a significantly lower affinity behaviour towards the odour compounds from the host sea anemone than the +A‐fishes did.A third type of experiment was a direct confrontation between fishes and host; here, the –A‐fishes were indifferent towards the host sea anemone for almost 48 h, while the +A‐fishes acclimated to the host sea anemone within the first 5 min of the direct confrontation.The results of this study suggest that Amphiprion ocellaris imprints itself olfactorily to its species‐specific host sea anemone Heteractis magnifica, and, furthermore, may be genetically disposed towards olfactory recognition of the host sea anemone.

Patterns of pair formation in protandrous anemonefishes,Amphiprion clarkii, A. frenatus andA. perideraion, on coral reefs of Okinawa, Japan

At Sesoko Island, stocks of anemonefishes were observed for 2 years in a 350 m × 150 m area where host sea anemones were sparse. About 40% of the pairs separated, mostly due to typhoon attacks or displacement. Widowed mates remained and acquired new mates on the same sea anemone, except for one case. New mates were immigrant adults inAmphiprion clarkii and A.frenatus, but resident juveniles inA. perideraion. A. clarkii andA. frenatus moved between sea anemones and sometimes displaced smaller consexuals, butA. perideraion rarely moved. The difference in mobility among the 3 species was related to the mean difference in standard length between the largest juveniles in breeding groups and the minimum size of breeding males in each species, and that between breeding males and the minimum size of breeding females. InA. perideraion both of these differences were small, so pairs could be formed quickly by residents after mate loss. On the contrary, inA. clarkii andA. frenatus, either or both differences were large and it would take a longer time to form a pair after mate loss. Differences in mobility affected the patterns of pair formation, and then the size composition of members in breeding groups.

Co-existence of subadult males and females as alternative tactics of breeding post acquisition in a monogamous and protandrous anemonefish

The monogamous and protandrous anemonefish,Amphiprion clarkii, utilizes only large host sea anemones as breeding sites. Under conditions of breeding site shortage, an important strategy for unmated fish may be to prepare themselves to enter quickly a breeding site from which a breeding male or female has recently disappeared. There are two types of subadults. Some juveniles become subadult males, which can change either to male or female afterwards, but others become subadult females, which can change only to female. Subadult females seem to acquire female posts more easily than subadult males. We develop an ESS model which evaluates the future reproductive success of subadult females and subadult males and test whether coexistence of subadult males and females can be interpreted as adaptive alternative tactics, using field data from two populations. The model predicts that if mortality does not differ between adult males and females the frequency for juveniles to become subadult females should be equal to the proportion of breeding post acquisition by subadult females among that by all subadults. The model also predicts that if mortality does not differ between subadult males and females, nor in adults, the frequency of subadult females among all subadults should be equal to the proportion of post acquisition. The model, with data from two study sites, suggests that alternative life-history pathways found inA. clarkii have evolved through adaptive tactics of breeding post acquisition.

Coexistence of two anemonefishes, Amphiprion clarkii and A. perideraion, which utilize the same host sea anemone

Social structure and interactions between the anemonefishes, Amphiprion clarkii and A. perideraion, which utilize the same host sea anemone Radianthus kuekenthali, were investigated on a coral reef of Okinawa Islands, Japan. In an 87 × 373 m2 study area, 98 sea anemones were inhabited by both species (32.5%), by only A. clarkii (48.9%), or by only A. perideraion (18.6%). A group of A. clarkii often occupied two or more individual hosts, and group members often interchanged. However, a group of A. perideraion usually used only one host and migration between groups was rare. The larger A. clarkii suppressed reproduction of A. perideraion in cohabiting groups, while A. perideraion suppressed settlement of Juvenile A. clarkii to its own hosts. Juvenile A. clarkii settled on small hosts as well as on large hosts, whereas juvenile A. perideraion settled only on large hosts. Coexistence appears to be possible in part by differences in settlement patterns between juveniles of the two anemonefishes.

Do anemonefishes use molecular mimicry to avoid being stung by host anemones?

Anemonefishes are known to have a protective mucous coat that allows them to contact the tentacles of their host anemone without being stung. There are two conflicting hypotheses as to the source and biochemical properties of this mucous coating. One hypothesis proposes that anemonefishes acquire anemone substances from their hosts during the behavioral process of acclimation, that protect the fish from being stung. Anemonefishes are considered to use anemone mucus as “chemical camouflage” or “macromolecular mimicry” to avoid recognition as “not-self” by the anemone, and possible subsequent stinging. Another hypothesis is that anemonefishes produce their own protective mucus coat, which lacks substances that elicit cnida (nematocyst and spirocyst) discharge by their hosts. The present study used immunological techniques to test whether the anemonefish Amphiprion clarkii (Bennett) (which was innately protected from two of the anemones used in the present study) has a mucous coat that resembles the external mucus of anemones. Polyclonal antibodies were prepared to the mucus of four species of anemones [ Heteractis crispa, (Ehrenberg) Stichodactyla haddoni (Saville-Kent), Macrodactyla doreenensis (Quoy and Gaimard), and Condylactis gigantea (Weinland)]. Ouchterlony (double immunodiffusion) tests showed that different antigens were present in the mucus of the four anemone species. Anemone antigens were not detected in the mucous coating of either naive (fish that had never before encountered sea anemones) or associated (those living with sea anemones) anemonefishes in Ouchterlony tests. However, more sensitive ELISA (enzyme-linked immunosorbent assay) tests showed that anemone mucus antigens were present in the mucous coating of associated anemonefish, but not naive fish. This showed that an innately protected A. clarkii does not produce a mucus coat that is biochemically similar to that of anemones, but that the same fish does acquire anemone substances in its mucus coat when it associates with anemones in aquaria. It remains to be shown whether these anemone substances actually provide the initial protection for those anemonefishes that must undergo acclimation behavior in order to keep from being stung by their host sea anemones, or additional protection for innately protected fishes.

On the feeding and comparative biology of iron in coelenterate-associated gammaridean Amphipoda (Crustacea) from N. Norway

Data are presented on the morphology of the mandible, morphometry of the stomach, composition of stomach contents, fine structure of the ventral caeca, and concentration of trace metals (Fe, Cu, Zn, Cd, Mn) in three species of coelenterophagous amphipod: Andaniexis sp. L (Stegocephalidae), Stenothoe brevicornis G.O. Sars (Stenothoidae) and Onisimus normani G.O. Sars (Lysianassidae) collected from sites off Tromsø, N. Norway. Andaniexis sp.L. has a blade-like incisor and highly distensible stomach compatible with functioning ecologically as a gluttonous batch processor of soft food. Stomachs in animals of this species from one site contained nematocyst-bearing soft tissue of coelenterate origin (identity not established) and sand grains, together with occasional polychaete remains. Andaniexis sp. L. from two sites differed in terms of their gut fullness and contribution of coelenterate material to the diet. Octahedral crystals of ferritin were variably present in cells of the ventral caeca; these crystals being a typical feature of the Fe detoxification system of stegocephalid amphipods. The Fe, Cu and Zn concentrations of Andaniexis sp. L., however, did not differ between sites. Stenothoe brevicomis also has a well developed, cutting incisor. This species, though, has a small stomach, compatible with its continuous association with its host sea anemone [ Actinostola callosa (Verrill)]. Analysis of stomach contents showed that it can consume the tentacular tissue of Actinostola callosa. Onisimus normani, also has a blade-like incisor. It lives within the enteron of sea anemones ( Actinostola callosa, Bolocera tuediae) and consumes mesenterial tissue. Although both Stenothoe brevicomis and Onisimus normani proved to have Fe concentrations which were no different from those in Andaniexis sp. L., only the last-mentioned species exhibited ferritin crystals. The reason for this difference in Fe handling strategy is presently unclear and may require knowledge of the Fe challenge posed by the unknown food organism of Andaniexis sp. L. in explanation. This stegocephalid genus is proving to be a less specific feeder on coelenterates than related genera which have been the subject of previous investigations. Calcium phosphate granules detoxify a range of potentially toxic trace metals including Fe in Andaniexis sp. L., Stenothoe brevicornis and Onisimus normani.

The symbiotic interface in an alga—invertebrate symbiosis

Both the cell membranes of the symbiotic alga Symbiodinium and the surrounding membranes of the sea anemone host Anemonia viridis have ATPase activity, as determined by enzyme cytochemistry. The interface between Symbiodinium and Anemonia also bears phosphatase activity, with substrate specificity for B glycerophosphate and a-naphthylphosphate. An immunocytochemical analysis of the distribution of the weak base -N-(3-[2,4-dinitrophenyl-amino]propyl)-N-(3-aminopropyl)methylamine dihydrochloride (DAMP) suggests that the membrane-bound compartment surrounding Symbiodinium cells is not markedly acidic. These data suggest that the symbiosome membrane of A. viridis may control the availability of phosphorous compounds and other nutrients to Symbiodinium . They are not readily compatible with the diffusion-depletion hypothesis, by which symbiont demand is hypothesized to be the primary determinant of the nutrient supply to the symbiont cells.

The role of sea anemones as refuges and feeding habitats for the temperate fish Oxylebius pictus

This study describes an association between the temperate zone fish Oxylebius pictus and sea anemones in Barkley Sound, Vancouver Island, British Columbia, Canada. Fish were observed swimming and resting unharmed among the tentacles, or next to a column of Urticina lofotensis (98% of all observations) and U. piscivora (2% of all observations). These associations were most commonly observed at moderately exposed sites where there were relatively high densities of O. pictus and anemones. Most associations occurred at night when the fish were inactive. Small young-of-year fish ( 12 cm total length) sheltered in rock holes and crevices. Experiments demonstrated that small O. pictus were more vulnerable to predators than large individuals. Urticina lofotensis and U. piscivora were large, persistent structures in the study habitats that provided effective refuge for O. pictus from predators. Anemone size, shape, tentacular adhesive force, and presence of copepod associates influenced patterns of host specificity. Oxylebius pictus fed on copepods and other crustaceans that associated with U. lofotensis and host sea anemones served as both refuges and feeding habitats for the fish. The sea anemones did not appear to receive any significant benefit from the relationship and the fish was considered to be a facultative commensal.