Detrimental effects of host anemone bleaching on anemonefish populations

Coral bleaching and related reef degradation have caused significant declines in the abundance of reef-associated fishes. Most attention on the effects of bleaching has focused on corals, but bleaching is also prevalent in other cnidarians, including sea anemones. The consequences of anemone bleaching are unknown, and the demographic effects of bleaching on associated fish recruitment, survival, and reproduction are poorly understood. We examined the effect of habitat degradation including host anemone bleaching on fish abundance, egg production, and recruitment of the panda anemonefish (Amphiprion polymnus) near Port Moresby, Papua New Guinea. Following a high-temperature anomaly in shallow waters of the region, most shallow anemones to a depth of 6 m (approximately 35% of all the anemones in this area) were severely bleached. Anemone mortality was low but bleached anemones underwent a ~34% reduction in body size. Total numbers of A. polymnus were not affected by bleaching and reduction in shelter area. While egg production of females living in bleached anemones was reduced by ~38% in 2009 compared to 2008, egg production of females on unbleached anemones did not differ significantly between years. Total recruitment in 2009 was much lower than in 2008. However, we found no evidence of recruiting larvae avoiding bleached anemones at settlement suggesting that other factors or different chemical cues were more important in determining recruitment than habitat quality. These results provide the first field evidence of detrimental effects of climate-induced bleaching and habitat degradation on reproduction and recruitment of anemonefish.     

The behavior of Dardanus arrosor in association with Cailiactis parasitica in artificial habitat

In the artificial habitat of an aquarium specimens of hermit crabs carrying commensal sea anemones gradually lose their anemones, surprisingly because the crabs frequently damage or eat them.

On the Mediterranean association Dardanus arrosor and Calliactis parasitica, the influence of feeding, of population density, or the activity of Dardanus towards Calliactis, and the presence or absence of a predator, were investigated as possible factors responsible for the disappearance of the anemone and the anomalous behavior of the crabs.

Both lack of food and high population density increased the numbers of anemones that disappeared. It was noted that these artificial conditions probably do not occur in the natural habitat. All freshly collected Dardanus (both sexes), and presumably all Dardanus in their natural habitat, are active in acquiring Calliactis but during 4–5 months in the aquarium most of this activity is lost.

In the presence of a probable predator, the octopus Eledone, these inactive crabs become active again in transferring anemones to their shells. This suggests that predation in the natural habitat is one of the factors responsible for the activity of the crab in acquiring anemones, at least in the association between Dardanus arrosor and Calliactis parasitica.     

Aerial exposure and body temperature of the intertidal sea anemone Anthopleura elegantissima

The sea anemone Anthopleura elegantissima is a common member of intertidal communities along the west coast of North America, and can experience extended periods of increased temperature during summertime low tides. Internal body temperatures of emersed individuals of A. elegantissima were monitored in a laboratory wind tunnel and in the field, and factors influencing the anemones’ thermal experience were examined. Larger body size and aggregation with conspecifics slowed body temperature increases in controlled wind tunnel conditions. In the field, anemones in the interior of an aggregation stayed cooler than those on the edges, and microhabitat features related to light exposure and surface orientation overshadowed any direct effects of body size. In the warmest month only (July), aggregations of A. elegantissima were significantly larger at the upper limit of their distribution than they were at the mid and lower limits, suggesting aggregation in high intertidal zones may be a behavioral response to desiccation and temperature stress. As this sea anemone can host multiple species of symbiotic algae with different thermal tolerances, the ability to slow body heating may affect the type of algae hosted and thus the potential contribution of this abundant anemone to primary production in the intertidal zone.     

Predation risk assessment by larval reef fishes during settlement-site selection

Predation rates of marine species are often highest during the transition from the pelagic to the benthic life stage. Consequently, the ability to assess predation risk when selecting a settlement site can be critical to survival. In this study, pairwise choice trials were used to determine whether larvae of three species of anemonefish (Amphiprion melanopus, A. percula and Premnas biaculeatus) are able to (1) assess the predation risk of potential anemone settlement sites through olfactory cues alone and (2) alter their settlement choices depending on the options available (host or non-host anemone). When predation risk was assessed with host and non-host anemone species independently, all species of anemonefish significantly chose the odor associated with the low-risk settlement option over the high-risk site. Most importantly, all species of anemonefish selected water with olfactory cues from their host anemone regardless of predation risk when paired against non-host anemone odor. These results demonstrate that larval reef fishes can use olfactory cues for complex risk assessment during settlement-site selection; however, locating the correct habitat is the most important factor when selecting a settlement site.     

Growth, reproduction and survival of a tropical sea anemone (Actiniaria): benefits of hosting anemonefish

The ecological performance of the sea anemone Heteractis magnifica was examined during a 36-month experiment with respect to season and the presence and numbers of a mutualist (orange-fin anemonefish Amphiprion chrysopterus). Anemones primarily grew during the autumn, with most asexual reproduction occurring in winter; mortality was not strongly seasonal. Individual growth rates did not differ between anemones harboring one or two anemonefish, but these rates were three times faster than for anemones lacking Amphiprion. Anemones with two anemonefish had the highest fission rate, whereas those without anemonefish had the lowest. By contrast, anemones that were not defended by anemonefish suffered higher-than-expected mortality. As a consequence, anemones with two Amphiprion had the greatest net increase in surface area, and those lacking anemonefish had a negligible gain that was statistically indistinguishable from zero after three years. Anemonefish not only enhanced anemone survivorship as previously believed, they also fostered faster growth and more frequent asexual reproduction.     

Contrasting abundance and contribution of clonal proliferation to the population structure of the corkscrew sea anemone Bartholomea annulata in the tropical Western Atlantic

Clonal propagation is an important life history trait for many sessile organisms, and often leads to the formation of monoclonal aggregations. In the marine environment, sea anemones have been model species for testing theory regarding the evolution of sex and understanding the contribution of sexual versus asexual reproduction to the population structure in facultatively clonal animals. However, little attention has been paid to tropical actiniarians. The corkscrew anemone Bartholomea annulata is common in tropical marine habitats in the western Atlantic and Caribbean; it forms small aggregations (2–4 anemones) on coral reefs and larger aggregations (>10 anemones) in mangrove habitats. We used field surveys and molecular analyses to investigate patterns of distribution, abundance, and genetic structure of aggregations formed by B. annulata on a reef in the US Virgin Islands and in a unique mangrove habitat in the Florida Keys. Abundance was greatest at the abandoned rock quarry mangrove habitat in the Florida Keys, where anemones formed continuously distributed aggregations carpeting the exposed limestone walls. Genetic diversity assessed via intersimple sequence repeats (ISSRs) and six microsatellite loci revealed that asexual reproduction plays only a minor role in the formation of both small and large anemone aggregations. Specifically, ISSR analyses showed that only ~10% of anemone aggregations were clonal in the US Virgin Islands, while microsatellite genotyping identified clonality in only 1 of 35 aggregations. In the Florida Keys, only four clonal genotypes were recovered within aggregations, but eight clones, representing 33% of the total surveyed population, had individuals in multiple aggregations. Thus, population structure of B. annulata appears to rely primarily on sexual reproduction, although asexual reproduction may play a nontrivial role in some environments. Mechanisms that drive the formation of genotypically diverse aggregations remain unknown, but may include attraction toward conspecifics, shared use of preferred habitats, or the local retention of larvae in partially enclosed habitats.     

Ammonia flux,physiological parameters,and <Emphasis Type="Italic">Symbiodinium</Emphasis> diversity in the anemonefish symbiosis on Red Sea coral reefs

Despite the ecological importance of anemonefish symbioses, little is known about how nutritional contributions from anemonefish interact with sea anemone physiology and Symbiodinium (endosymbiotic dinoflagellate) genetic identity under field conditions. On Red Sea coral reefs, we measured variation in ammonia concentrations near anemones, excretion rates of anemonefish, physiological parameters of anemones and Symbiodinium, and genetic identity of Symbiodinium within anemones. Ammonia concentrations among anemone tentacles were up to 49% above background levels, and anemonefish excreted ammonia significantly more rapidly after diurnal feeding than they did after nocturnal rest, similar to their excretion patterns under laboratory conditions. Levels of 4 physiological parameters (anemone protein content, and Symbiodinium abundance, chlorophyll a concentration, and division rate) were similar to those known for laboratory-cultured anemones, and in the field did not depend on the number of anemonefish per anemone or depth below sea surface. Symbiodinium abundance varied significantly with irradiance in the shaded reef microhabitats occupied by anemones. Most anemones at all depths harbored a novel Symbiodinium 18S rDNA variant within internal transcribed spacer region 2 (ITS2) type C1, while the rest hosted known ITS2 type C1. Association with Symbiodinium Clade C is consistent with the symbiotic pattern of these anemones on other Indo-Pacific reefs, but the C1 variant of Symbiodinium identified here has not been described previously. We conclude that in the field, anemonefish excrete ammonia at rapid rates that correlate with elevated concentrations among host anemone tentacles. Limited natural variation in anemonefish abundance may contribute to consistently high levels of physiological parameters in both anemones and Symbiodinium, in contrast to laboratory manipulations where removal of fish causes anemones to shrink and Symbiodinium to become less abundant.     

Territorial Behavior and Ecology of the Anemonefish Amphiprion melanopus on Guam1)

Field observations and experiments on the Indo-Pacific anemonefish Amphiprion melanopus at Guam show that it colonizes the aggregating sea anemone Physobrachia douglasi extensively and nearly exclusively. There are an average of four fish per colony. The total standard length of anemonefish at each aggregation is highly correlated with the total area covered by resident anemones, suggesting both a carrying capacity and some form of social control of growth of anemonefish²). Inter-colony migration of juveniles, as well as larval recruitment, may contribute to maintenance of the optimum colony size. Adults do not migrate. Both juveniles and adults defend territory. Juvenile territories are mutually exclusive areas within the confines of the anemone aggregation, while adult territories are considerably larger than the area covered by the anemone aggregation. Though territories of mated ♀♀ and ♂♂ overlap completely, female emphasis is peripheral relative to the ♂. Adult conspecific intruders are attacked more heavily and at greater distances than are juveniles. Intraspecific territoriality in juveniles probably reflects the limited availability of critical habitat. In adults it may function to protect the pair bond. Interspecific aggression is less intense and appears to protect both the spawn and host anemones from various predators.     

Temperate and tropical algal-sea anemone symbioses

Abstract. In this review, we seek to develop new insights about the nature of algal‐sea anemone symbioses by comparing such associations in temperate and tropical seas. Temperate seas undergo pronounced seasonal cycles in irradiance, temperature, and nutrients, while high irradiance, high temperature, and low nutrients are seasonally far less variable in tropical seas. We compare the nature of symbiosis between sea anemones (= actinians) and zooxanthellae (Symbiodinium spp.) in both regions to test tropical paradigms against temperate examples and to identify directions for future research. Although fewer anemone species are symbiotic in temperate regions, they are locally dominant and ecologically important members of the benthic community compared to the tropics. Zooxanthella densities tend to be lower in temperate anemones, but data are limited to a few species in both temperate and tropical seas. Zooxanthella densities are far more stable over time in temperate anemones than in tropical anemones, suggesting that temperate symbioses are more resistant to fluctuations in environmental parameters such as irradiance and temperature. Light‐saturated photosynthetic rates of temperate and tropical zooxanthellae are similar, but temperate anemone hosts receive severely reduced carbon supplies from zooxanthellae during winter months when light is reduced. Symbiont transmission modes and specificity do not show any trends among anemones in tropical vs. temperate seas. Our review indicates the need for the following: (1) Investigations of other temperate and tropical symbiotic anemone species to assess the generality of trends seen in a few “model’ anemones. (2) Attention to the field ecology of temperate and tropical algal‐anemone symbioses, for example, how symbioses function under seasonally variable environmental factors and how zooxanthellae persist at high densities in darkness and winter. The greater stability of zooxanthella populations in temperate hosts may be useful to understanding tropical symbioses in which bleaching (loss of zooxanthellae) is of major concern. (3) Study of the evolutionary history of symbiosis in both temperate and tropical seas. Continued exploration of the phylogenetic relationships between host anemones and zooxanthella strains may show how and why zooxanthellae differ in anemone hosts in both environments.     

Effects of microhabitat characteristics on the settlement and recruitment of a coral reef fish at two spatial scales

Populations of fishes on coral reefs are replenished by the settlement of pelagic larvae to demersal populations. Recruitment varies spatially and temporally and can exert strong effects on the dynamics of reef fish populations. This study examined the effect of microhabitat characteristics on small-scale and large-scale recruitment variation in the three-spot damselfish, Stegastes planifrons (Cuvier). Comparison of 0.25-m² quadrats occupied by three-spots with randomly sampled null quadrats showed that three-spots quadrats contained a higher percent cover of the coral Montastrea annularis than would be expected at random. Manipulative experiments on three types of 1.0-m² patch reefs (living M. annularis, dead Porites Porites and dead Acropora palmata) patch reefs on showed that this non-random distribution was established by microhabitat choice during settlement and not by differential post-settlement survival. The presence of conspecific juveniles did not affect settlement. Recruitment was monitored at nine sites on three islands over 3 years. Recruitment showed no consistent pattern in the relative levels of recruitment among sites. Similarly, no consistent relationship emerged between recruitment levels and microhabitat characteristics at the nine sites. For example, at this large scale, the percent cover of M. annularis explained variation in recruitment in only 1 out of 3 years. These results suggest that small-scale recruitment patterns are influenced by microhabitat choice during settlement, but that these habitat effects do not scale up to influence large-scale variation in recruitment.     

Marine protected area restricts demographic connectivity: Dissimilarity in a marine environment can function as a biological barrier

The establishment of marine protected areas (MPAs) can often lead to environmental differences between MPAs and fishing zones. To determine the effects on marine dispersal of environmental dissimilarity between an MPA and fishing zone, we examined the abundance and recruitment patterns of two anemonefishes (Amphiprion frenatus and A. perideraion) that inhabit sea anemones in different management zones (i.e., an MPA and two fishing zones) by performing a field survey and a genetic parentage analysis. We found lower levels of abundance per anemone in the MPA compared to the fishing zones for both species (n = 1,525 anemones, p = .032). The parentage analysis also showed that lower numbers of fishes were recruited from the fishing zones and outside of the study area into each anemone in the MPA than into each anemone in the fishing zones (n = 1,525 anemones, p < .017). However, the number of self‐recruit production per female did not differ between the MPA and fishing zones (n = 384 females, p = .516). Because the ocean currents around the study site were unlikely to cause a lower settlement intensity of larvae in the MPA, the ocean circulation was not considered crucial to the observed abundance and recruitment patterns. Instead, stronger top‐down control and/or a lower density of host anemones in the MPA were potential factors for such patterns. Our results highlight the importance of dissimilarity in a marine environment as a factor that affects connectivity.     

The distribution of the orange‐striped green anemone,Diadumene lineata,in relation to environmental factors along coastal British Columbia,Canada

The cosmopolitan nonindigenous sea anemone, Diadumene lineata, has been recorded from the Pacific coast of Canada since 1859. Despite its long historical presence in the region, the factors influencing the distribution of this species in British Columbia, Canada, are poorly understood, as are the factors that may restrict its local abundance. We conducted large‐scale surveys of D. lineata during the winter and summer of 2016, coupled with higher frequency surveys at one focal site. Furthermore, we used laboratory and field experiments to determine the potential importance of a large‐scale driver, salinity, and a small‐scale driver, microhabitat within boulders, in setting distributional limits at various spatial scales. Our results confirm that D. lineata is widely distributed within the Salish Sea. This broad distribution may be facilitated by post‐introduction dispersal; we observed anemones attached to floating substrata, and a few mature specimens contained eggs, suggesting that reproduction is perhaps not limited to asexual fission. We found that D. lineata was abundant throughout the year, although absent from the lowest salinity sites. This corresponded with our laboratory experiments, in which survival of individuals of D. lineata declined at salinities below 10 psu, and no survivors were observed at or below 2 psu. Manipulative experiments in the field demonstrated that survival was high under rocks where D. lineata is commonly found, but was reduced on the tops of rocks, highlighting the importance of microhabitat refugia in buffering temperature and reducing desiccation. A better understanding of the factors that limit the broad‐scale and local distribution of this anemone are an important step in determining potential ecological impacts of this organism and how distributions may shift into the future.     

Incorporating fine-scale seascape composition in an assessment of habitat quality for the giant sea anemone Stichodactyla gigantea in a coral reef shore zone

Habitat loss due to land reclamation often occurs in sandy coral reef shore zones. The giant sea anemone Stichodactyla gigantea, which harbors the false clown anemonefish Amphiprion ocellaris, both of which are potentially flagship species, inhabit these places. To assess habitat quality for S. gigantea, we examined correlative associations between the number and the body size of S. gigantea and the amount of habitat types in fine-scale seascape composition quantified from an enlarged section of a high-resolution (1/2,500) color aerial photograph of the shallow shore zone of Shiraho Reef, Ishigaki Island, Japan. This study confirmed that anemones were most abundant at the edges of dense seagrass beds characterized by shallow sandy bottoms, rock beds, and sparse seagrass beds, while they were less abundant in coral patch reefs. However, anemones inhabiting coral patch reefs were significantly larger and their rate of disappearance over 3 years was lower than those inhabiting other habitats. This suggests that coral patch reefs may be more suitable habitats supporting larger animals and greater persistence of S. gigantea. The visual census techniques applied here, combined with aerial photography and image-analysis software, may be useful as a simple analytical tool for local assessment of suitable habitats for relatively small-bodied marine fauna in shallow-water seascapes.     

Direct attachment of eggs to the body wall in the externally brooding sea anemone <Emphasis Type="Italic">Cnidopus japonicus</Emphasis> (Actiniaria; Actiniidae)

The externally brooding sea anemone Cnidopus japonicus (Verrill) inhabits boulder shores between the mid-intertidal and shallow subtidal zones of Mutsu Bay, northern Japan. The anemones usually adhere to the side and under-surfaces of boulders. These anemones keep offspring on the middle part of their body wall during the breeding season. Our observations of spawning behavior in an aquarium revealed that this anemone lays eggs through an elongated oral margin and directly attaches the eggs to its body wall, while making a circular groove on the column. The anemone rotates its elongated oral margin around its body trunk several times and arranges eggs in the circular brooding groove. This behavior suggests that mother anemones, regardless of their attachment position on substrata, are able to attach their offspring effectively to their body wall. Electronic Publication     

Effects of anemonefish on giant sea anemones: expansion behavior,growth, and survival

The symbiosis between giant sea anemones and anemonefish on coral reefs is well known, but little information exists on impacts of this interaction on the sea anemone host. On a coral reef at Eilat, northern Red Sea, individuals of the sea anemone Entacmaea quadricolor that possessed endemic anemonefish Amphiprion bicinctus expanded their tentacles significantly more frequently than did those lacking anemonefish. When anemonefish were experimentally removed, sea anemone hosts contracted partially. Within 1–4 h in most cases, individuals of the butterflyfish Chaetodon fasciatus arrived and attacked the sea anemones, causing them to contract completely into reef holes. Upon the experimental return of anemonefish, the anemone hosts re-expanded. The long-term growth rate and survival of the sea anemones depended on the size and number of their anemonefish. Over several years, sea anemones possessing small or no fish exhibited negative growth (shrinkage) and eventually disappeared, while those with at least one large fish survived and grew. We conclude that host sea anemones sense the presence of symbiotic anemonefish via chemical and/or mechanical cues, and react by altering their expansion behavior. Host sea anemones that lack anemonefish large enough to defend them against predation may remain contracted in reef holes, unable to feed or expose their tentacles for photosynthesis, resulting in their shrinkage and eventual death.     

The acclimation of anemone fishes to sea anemones: Protection by changes in the fish''s mucous coat

The anemone fish Amphiprion clarkii (Bennett) lives unharmed among the tentacles of sea anemones following acclimation. What occurs during this process is unknown; however, two hypotheses have been formulated recently. One suggests that the fish coats itself with anemone mucus to mask its chemical stimulus for cnida discharge. The second suggests that the fish is protected by some alteration in its own mucous coating.

In order to test these alternative hypotheses, a surrogate anemone was constructed and an Amphiprion allowed to associate with it prior to being placed with a real anemone. If the subsequent acclimation times to a real anemone are reduced significantly after exposure to the surrogate anemone, one would conclude that the fish does not need to coat itself with anemone mucus to become protected.

After association with a surrogate anemone, it was found that the acclimation times of isolated A. clarkii to the sea anemone Macrodactyla doreensis (Quoy & Gaimard) decreased seven-fold. These results support the hypothesis that the fish is responsible for manufacturing its own protection from sea anemones, presumably by independently altering its own mucous coat during acclimation.     

Evaluation of the sea anemone Anthothoe albocincta as an augmentative biocontrol agent for biofouling on artificial structures

Augmentative biocontrol, defined as the use of indigenous natural enemies to control pest populations, has not been explored extensively in marine systems. This study tested the potential of the anemone Anthothoe albocincta as a biocontrol agent for biofouling on submerged artificial structures. Biofouling biomass was negatively related to anemone cover. Treatments with high anemone cover (>35%) led to significant changes in biofouling assemblages compared to controls. Taxa that contributed to these changes differed among sites, but included reductions in cover of problematic fouling organisms, such as solitary ascidians and bryozoans. In laboratory trials, A. albocincta substantially prevented the settlement of larvae of the bryozoan Bugula neritina when exposed to three levels of larval dose, suggesting predation as an important biocontrol mechanism, in addition to space pre-emption. This study demonstrated that augmentative biocontrol using anemones has the potential to reduce biofouling on marine artificial structures, although considerable further work is required to refine this tool before its application.     

The Social Structure of Inachus phalangium,a Spider Crab Associated with the Sea Anemone

The behaviour of the spider crab Inachus phalangium (Fabricius, 1775), which lives in association with the sea anemone Anemonia sulcata (Pennant), was studied in the field. The crab was found in the littoral zone of the Mediterranean Sea near Banyuls sur Mer, France, in the whole depth range studied (0.5–25 m). The crabs had a long-lasting association with individual Anemonia sulcata, occasionally with Aiptasia mutabilis. Most crabs were found in association with the same anemone for several days, some crabs were found in association with the same anemone for longer than one month. In the areas studied, on average 65 Inachus phalangium were found on 100 anemones. Crabs released in the vicinity of anemones moved towards them and entered them. Inachus phalangium could walk between the tentacles of Anemonia sulcata and Aiptasia mutabilis without eliciting feeding reactions of the anemone. The crabs left the anemones for moulting. After moulting masking material was removed from the exuvia and used again. The animals returned into an anemone while still soft. Material used for masking, usually algae, could be picked off the body and eaten. Masking material may be a food reservoir in addition to providing camouflage. Anemones were left only during night-time. The crabs left their anemone to moult, to feed in the vicinity, fleeing from larger conspecifics, and to migrate to a different anemone. Outside the anemone's protection Inachus was eaten by several species of fish. Individuals appeared to avoid each other. 57% of all animals were found alone on an anemone. Large males and females were more frequently found alone than were small males and females. Fights were observed between members of the same and of the opposite sex. During fights, legs and claws could be torn off. Adult males migrated more often between anemones and moved over larger distances when migrating than did adult females. Adult males probably migrated in search of sexually mature females. Such a roving strategy is evolutionarily stable only when the higher costs (in terms of energy expenditure and mortality) are compensated for by a higher number of offspring than produced in the alternative, pair-bonding strategy.     

Produktion oder übernahme von schutzstoffen als ursache des Nesselschutzes von Anemonenfischen?

Investigations concerning the protection of anemone fishes have been conducted on reefs near Shimoni (Kenya). Acclimated Amphiprion xanthurus Cuv. & Val. when placed in perforated plastic boxes in the midst of anemones do not lose their protection against stinging. Unacclimated A. xanthurus became protected in this manner. Protected A. xanthurus lost their protection and unprotected ones could not acquire this protection when they were placed within a distance of 5–7 cm or more from actinians. In order to maintain the protection, the intimacy of anemones is absolutely necessary. The quality of protection acquired by the fishes depends on the species of anemone, being either good against only one species or good against several species simultaneously. The fact that the fishes remain protected only if they live in the midst of anemones or very close to them and that the degree of protection is determined by the anemone indicates the importance of the anemones for the acquisition of this protection. These results confirm the suggested mechanism of protection formulated previously by Schlichter, namely that the fishes acquire anemone-substances (‘protective substances’) during the process of acclimation. After becoming protected they bear the same chemical impregnation on their surface as, e.g., tentacles, which do not sting each other. The transmission of protecting substances to unprotected fishes by incubation with extracts from anemones was found to be impossible. After incubation in pepsin, acclimated fishes lost their protection. It seems as though anemone fishes exploit for their protection a principle which the actinians have for their own use. This mechanism exists quite independently of the symbiosis with fishes. The anemones themselves require such ‘protective substances’ for several purposes.     

Pycnogonid‐cnidarian trophic interactions in the deep Monterey Submarine Canyon

Abstract. Whale carcasses, sunken wood, and cold seeps provide organically enriched oases in the food‐limited deep‐sea benthos. At three such enriched habitats in Monterey Bay, CA, at a depth of nearly 3000 m, we observed pycnogonids (sea spiders) of at least two species, Colossendeis gigas and C. japonica, feeding on sea anemones that were commonly found there. Submersible remotely operated vehicles provided direct observations of feeding, as well as high definition video and photographic images. We recorded the co‐occurrence of both pycnogonids and prey anemones during ten of 12 visits during 2002–2006. Anemones and pycnogonids were conspicuously more abundant at these oases than in the surrounding benthos. The sedentary anemone Anthosactis pearseae was attached directly to whalebones while the pom‐pom anemone, Liponema brevicornis, was found resting on soft sediment, rolling in benthic currents, or accumulating where these currents were disrupted by topography, as at whale falls, wood falls, and clam fields. Both pycnogonid species were observed feeding on these anemones, either as predators or as micropredators.