Intertidal Sea Anemone Research Articles

Possible cryptic speciationwithin the sea anemone Actinia equina complex detected by AFLP markers

The population genetic profiles of 60 specimens of thecommon intertidal sea anemone Actinia equina taken from foursampling sites (Peroj, Barbariga and the north and south shoresof the Limski Canal), along a 25 km strip of the coastof the Istra Peninsula, Croatia, were evaluated by AFLP markers(144 loci). All populations were characterized by aggregates ofspecimens confined within a few square meters. One of the populations(on the north shore of the canal) contained both large and small-sizedindividuals. Results revealed high within-aggregate genetic heterogeneity(36.1–55.6%). With respect to interpopulationprofiles, geographically remote populations from Peroj, Barbarigaand the south shore of the canal were more closely related geneticallythan those on the north and south shores of the canal. The small-sizedsubpopulation from the north shore exhibits a distinct AFLP pattern,suggesting that it warrants recognition as a cryptic species. © 2002The Linnean Society of London, Zoological Journal of the LinneanSociety, 2002, 136, 315−320

Flow-induced energetic bounds to growth in an intertidal sea anemone

General models exploring patterns of maximal size in indeterminately growing, benthic marine organisms have often focused on potential scaling limits associated with either internal ener- getics or external physical factors such as hydrodynamic force. Rarely, however, have these broad- strokes models considered explicitly the possibility that interactions between physiological energy balances and environmental fluid motion might alter the underlying scaling relationships. Here we examine, using simple principles of allometry, the fundamental energetics of a common intertidal sea anemone Anthopleura elegantissima in the context of the rapid flows that characterize its native habitat. We find that fluid mechanical distortion of the feeding apparatus of this species modifies the scaling of predicted energy intake across size, creating a possible mismatch with its expected meta- bolic requirements, and potentially placing a limit on growth. Such a limit would not be expected from standard metabolic or fluid dynamic arguments applied in isolation, reiterating the often-over- looked importance of an organism's structural design and its associated mechanical response to flow.

Translocation of Photosynthetic Carbon From Two Algal Symbionts to the Sea Anemone Anthopleura elegantissima.

The intertidal sea anemone Anthopleura elegantissima contains two symbiotic algae, zoochlorellae and zooxanthellae, in the Northern Puget Sound region. Possible nutritional advantages to hosting one algal symbiont over the other were explored by comparing the photosynthetic and carbon translocation rates of both symbionts under different environmental conditions. Each alga translocated 30% of photosynthetically fixed carbon in freshly collected anemones, although zoochlorellae fixed and translocated less carbon than zooxanthellae. The total amount of carbon translocated to the host was equivalent because densities of zoochlorellae were two to three times greater than were densities of zooxanthellae. In A. elegantissima maintained under high and low irradiance (100 and 10 {mu}mol photons/m2/s) at 20{deg}C and 13{deg}C for 21 days, both algae fixed and translocated carbon at greater rates at 20{deg}C (translocation rates: 0.38 pg C /zoochlorella/h; 1.12 pg C /zooxanthella/h) than at 13{deg}C (translocation rates: 0.06 pg C /zoochlorella/h; 0.37 pg C /zooxanthella/h). However, zoochlorellate anemones received 3.5 times less carbon at 20{deg}C than at 13{deg}C because the higher temperature caused a significant reduction in the density of zoochlorellae. Environmental variables, like temperature, that influence the densities of the two symbionts will affect their relative nutritional contribution to the host. Whether these differences in carbon translocation rates of the two algal symbionts affect the ecology of their anemone host awaits further investigation.

Sea anemones as secondary consumers on rocky shores in the south-western Cape, South Africa

The species composition, abundance and distribution patterns of intertidal sea anemone assemblages were determined at two sites on the Cape Peninsula, South Africa. A single species, Bunodactis reynaudi (Milne-Edwards) dominated at Bloubergstrand in Table Bay, with a density of 901 m-1 (i.e. per linear metre of coastline). Seven species, with a combined density of 660 m-1, were found at Wooley's Pool in False Bay. Of these Actinia equina Linn. and Anthothoe stimpsoni (Verr.) occurred primarily in the upper intertidal, Anthopleura michaelseni (Pax), Bunodosoma capensis (Less.) and Bunodactis reynaudi in the mid- to low intertidal and Pseudactinia varia Carlgren and P. flagellifera (Hertw.) only in sheltered pools near the sublittoral fringe. Density data are combined with previously reported gut content analyses and digestion rate estimates to calculate total annual consumption rates of natural populations of anemones. At Wooley's Pool the anemones colonizing each linear metre of shore consume an estimated 103 337 isopods, 14 973 amphipods, 21 050 cirripedes, 40 468 pelecypods and 30 102 gastropods annually. At Bloubergstrand the B. reynaudi population consume 38 437 polychaetes, 129 744 pelecypods and 116 229 gastropods m-1y-1. These figures considerably exceed estimated population consumption rates for other major invertebrate predators. However, the bivalves and cirrepedes taken by anemones are dislodged individuals, hence anemones are unlikely to play any significant role in structuring populations of these species. By contrast, consumption of motile prey, such as isopods and gastropods, may impact significantly on these populations. Overall annual consumption by naturally occurring anemone assemblages at Bloubergstrand were calculated to be 182 284 kJ m-2y-1, six times higher than at Wooley's Pool (30 851 kJ m-2y-1). These very high rates suggest that anemones are major secondary consumers in rocky intertidal communities in the south-western Cape.

Benzo[a]pyrene metabolism by the intertidal Sea Anemone, Bunodosoma cavernata

Incubations of Bunodosoma cavernata microsomes with benzo[a]pyrene (B[a]P) and either NAD(P)H or tert-butyl hydroperoxide ( t-BHP) produced several oxidative metabolites including: 3-OH- B[a]P; 4,5-, 7,8-, and 9,10-B[a]P-diols; 1,6-, 3,6-, and 6,12-B[a]P-diones; B[a]P-tetrols; and B[a]P- diol epoxides. NADPH-dependent rates of B[a]P metabolism were approximately 70% greater than with NADH. The t-BHP-dependent reaction proceeded approximately 67-fold faster than the NAD(P)H-dependent reactions and produced primarily dials. Incubation of B[a]P with microsomes from the intertidal sea anemone, Bunodosoma cavernata, results in the production of oxidative metabolites of B[a]P consistent with an active cytochromes P450-mediated microsomal mixed-function oxygenase system.

Extensive genetic divergence between populations of the common intertidal sea anemone Actinia equina from Britain, the Mediterranean and the Cape Verde Islands

Samples of apparently similar red morphs of the common beadlet sea anemone Actinia equina (L.) were collected from rocky shores on the Isle of Man (Irish Sea), on the French Mediterranean coast near Marseille and on the Cape Verde Island of Sal (off West Africa). For additional comparison an orange morph and the green A. prasina were also collected from the Isle of Man. Morphological descriptions were made and the samples were compared by nematocyst analysis and enzyme electrophoresis. The three British samples showed little genetic divergence (I>0.90) but the Mediterranean sample was hugely divergent (I<0.20) from the British ones. The Cape Verde Island anemones were also very different (I<0.60) from all other samples. It is concluded that the red morph samples from the Cape Verde Islands, the Mediterranean and the Isle of Man belong to three different species. For the new species from the Mediterranean and Cape Verde Islands formal descriptions are given, and the names Actinia schmidti sp.n. and Actinia sali sp.n. are proposed.

The effects of temperature and light on two algal populations in the temperate sea anemone Anthopleura elegantissima (Brandt, 1835)

The effects of temperature (13 °C and 20 °C) and irradiance (low light (LL) = 10 μmol/m 2/s; high light (HL) = 137 μmol/m 2/s) on the population density of two symbiotic algae in the tentacle region of the intertidal sea anemone Anthopleura elegantissima (Brandt) were examined in this study. Anemones contained zooxanthellae (brown anemones), zoochlorellae (green anemones), or a mixture of both algae (mixed anemones). Temperature and light have different effects on zooxanthellae and zoochlorellae, resulting in changes in the algal complement of A. elegantissima. High temperature caused a significant decrease in the density of zoochlorellae over 25 days (in green anemones: −32 and −20 algae/μg tentacle protein per day under HL and LL, respectively) and a reduction in algal mitotic index (from 15% to < 5% cells dividing after 6 days). Low light caused a significant increase in the density of zooxanthellae over 25 days (in brown anemones: +15 and +20 algae/μg tentacle protein per day at 13 °C and 20 °C, respectively). Overall, temperature had a greater effect than light on the population density of algae in the tentacles of A. elegantissima; the percent change in zoochlorellae density in tentacles of anemones held at 20 °C was significantly less (in green anemones, −69%) than changes obtained with all other symbiont-temperature interactions. Zooxanthellae and zoochlorellae in mixed anemone tentacles showed the same population density response to the treatments as zooxanthellae and zoochlorellae in brown and green anemones, respectively. Population densities of both algal symbionts are regulated by temperature and light, and the relative abundance of each alga in a host anemone may be shifted with changes in these environmental factors.

Digestion rates of prey eaten by intertidal sea anemones from the south-western Cape, South Africa

Digestion rates were determined for natural prey items offered to each of seven species of sea anemones found at Wooley’s Pool in False Bay and to the single species (Bunodactis reynaudi) recorded at Biouberg on the Atlantic coast of the south-western Cape, South Africa.This was done by examining prey items removed from the coelenterons at regular intervals after feeding and assessing their degree of digestion according to a predetermined scale. There was considerable variation in the gut retention times between different anemone species offered the same prey types, with Actinia equina consistently showing the shortest gut retention times (12 h for amphipods, 15 h for pelecypods and 23 h for isopods). Of the various prey categories tested, amphipods tended to be the most rapidly digested group, while molluscs and echinoderms usually remained in the coelenteron the longest. Mean gut retention times in B. reynaudi, the only species found both in False Bay (17°C) and on the cold west coast (12°C) were markedly longer (72 vs 60 h and 43 vs 30 h for pelecypods and gastropods respectively) at the lower temperature.

Trophic ecology of the intertidal sea anemones Phymactis clematis Dana, 1849, Autactinia marplatensis (Zamponi, 1977) and A. Reynaudi (Milne-Edwards, 1857) (Actiniaria: Actinhdae): relationships between sea anemones and their prey

The feeding ecology of the intertidal sea anemones Phymactis clematis Dana, 1849, Aulactinia marplatensis (Zamponi, 1977) and A. reynaudi (Milne-Edwards, 1857) (Actiniaria: Actiniidae) from Punta Cantera and Santa Clara del Mar (Argentina) was studied using the following relations: available and ingested food, prey and predator size, and prey and predator weight. The food ingested by the three sea anemones clearly reflects the available food, both in quantitative and qualitative terms. In both locations, no correlation was observed between sea anemone size and prey size, or between predator weight and prey weight. These facts suggest that sea anemones feed principally on prey detached by wave action; the mussel Brachydontes rodriguezi d´ Orbigny, 1846 is the principal prey in the study areas.

Sources of nutrition in intertidal sea anemones from the south-western Cape, South Africa

Respiration rates of seven species of intertidal sea anemones from the south-western Cape, South Africa were measured with and without illumination to determine whether zooxanthellae contributed to their nutritional needs. Light had no significant effect on oxygen exchange in any of the species, suggesting that all are azooxanthellate. Diets of anemones from two sites, Wooley’s Pool in False Bay and Blouberg on the Atlantic coast some 20 km north of Cape Town, were examined by gut content analysis. Seven species occurred at Wooley’s Pool, but only one ( Bunodactis reynaudi) at Blouberg. At Wooley’s Pool 39.4% of anemones contained food, while at Blouberg only 7.4% did so. A wide spectrum of prey taxa were consumed by the various anemone species, although considerable dietary overlap occurred. Pelecypods, gastropods and isopods were ingested by all the species examined. Pelecypods dominated the diet of B. reynaudi at Blouberg (91% occurrence), but were recorded in only 42% of the same species at Wooley’s Pool. The frequency of occurrence of pelecypods in the guts of the other species ranged from 9% (Anthothoe stimpsoni) to 28% ( Actinia equina). Gastropods were the main prey items eaten by Anthopleura michaelseni (67% occurrence), Pseudactinia flagellifera (43%) and Pseudactinia varia (42%), while isopods were the most frequently occurring constituent in the diets of A. stimpsoni (62%) and Bunodosoma capensis (16%). A. equina was the only species for which insects were a regular part of the diet (26% occurrence). Platyhelminths were found only in the guts of B. capensis (11%); holothurians only in B. reynaudi at Wooley’s Pool (2%), and crinoids only in P. flagellifera (2%). Large quantities of algal material and indigestible debris were also ingested, indicating that sea anemones are non-selective feeders. Cluster analysis and multi-dimensional scaling techniques revealed four distinct feeding groups among the anemone assemblages. These are characterized as microphagous (A. stimpsoni), generalist ( S. capensis and A. equina), macrophagous (S. reynaudi at Wooley’s Pool, A. michaelseni, P. flagellifera and P. varia) and specialist bivalve- feeder ( B. reynaudi at Blouberg).

The effects of illumination, food and symbionts on growth of the sea anemone Anthopleura elegantissima (Brandt, 1835). II. Clonal growth

The effects of illumination, feeding regime and endosymbiotic algae on the clonal growth via asexual fission of the intertidal sea anemone Anthopleura elegantissima (Brandt, 1835) were examined in a 6 month factorial laboratory experiment. Neither illumination nor symbionts had a significant effect on fission rate, but anemones fed three times a week divided significantly more often than unfed anemones. This result is the opposite of previously published data, and possible explanations for how food may cue divisions in the field are discussed.

The effects of illumination, food and symbionts on growth of the sea anemone Anthopleura elegantissima (Brandt, 1835) I. Ramet growth

The effects of illumination, feeding regime and endosymbiotic algae on the growth of the intertidal sea anemone Anthopleura elegantissima (Brandt, 1835) were examined during a 3 month factorial laboratory experiment. The addition of light (12 h:12 h light:dark), food (fed 3 times per week) and the presence of symbionts each had a significant positive independent effect on percent weight change of anemones, with smaller anemones gaining more weight when fed than larger anemones. There was no difference in percent weight loss between small and large anemones when unfed.

Genetic divergence between colour morphs in populations of the common intertidal sea anemones Actinia equina and A. prasina (Anthozoa: Actiniaria) in the Isle of Man

A distinctive morph ofActinia equina (L.) is found at low frequency among populations on intertidal hard substrata on some shores on the Isle of Man. This morph is red with rows of green oval spots or elongate markings running longitudinally down the column. Starch gel electrophoresis of 21 allozyme loci was used to compare samples of this morph from two localities with other sympatricActinia spp. Collections were made in early summer 1986. For one sampling site the comparison was with redA. equina and greenA. prasina Gosse, whilst at the other site with redA. equina only. At both sites significant genetic differences in allele frequencies at several loci were found between the new morph and sympatricA. equina andA. prasina. The results also confirm the reproductive isolation ofA. prasina. As with much previous work on sea anemones, levels of mean heterozygosity per locus (H) were found to be high (H=0.157 to 0.342). A surprising feature of the results, although bearing out earlier unpublished data, is that high levels of genetic differentiation are found between populations of what appear to be the same morphs collected from shores only a few km apart. Among theActinia spp. studied, differentiation between populations of the same morph on different shores was of the same order as between sympatric, reproductively isolated populations.

Population structure in the sexually reproducing sea anemone Oulactis muscosa

The intertidal sea anemone Oulactis muscosa (Drayton) is dioecious and most individuals are sexually mature throughout the year. Biochemical genetic evidence was used to determine the genetic structure of populations and to infer the relative contributions of sexual and asexual reproduction to recruitment. Data were collected for six enzyme-encoding loci from local populations spread along 735 km of the south east coast of Australia. The genetic structure of each of the nine local populations studied was consistent with recruitment by sexually produced individuals. In almost all cases, the observed single-locus genotypic frequencies closely matched those expected for hardy-Weinberg equilibria, however, consistent deficits of heterozygotes were detected for all loci. No apparent subdivision of the population was detected within the sampling area. Low levels of genetic differentiation were found between local populations and standardised variance (FST) values were similar to those for other species with widespread planktonic dispersal of larvae.

Selective effects of disturbance on populations of sea anemones from northern Baja California, Mexico

Effects of desiccation and sand burial on the surv~val and behavior of intertidal sea anemones Anthopleura elegantissima from northern Baja Califorrua were studied experimentally by comparing: (1) clonal and solitary forms (probably a pair of sibhng species) (Francis 1979); (2) aggregated and 'wandering' (isolated module) configurations of the clonal form; and (3) large and small individuals of the solitary form. We tested the hypothesis that mobility and size are important attributes to avoid desiccation and sand burial. The hypothesis partially explains and predicts the dfferential distribution of the above categories in habitats with different disturbance regimes. Wandering modules were more susceptible to desiccation than were the aggregated clonal anemones, and wandering anemones moved more in response to desiccation than did aggregated ones. Both wandering and aggregated anemones showed little mobility when faced w t h sand burial. Small solitary anemones were more susceptible to desiccation than were large ones. They increased their mobhty when confronted with t h ~ s disturbance; larger specimens did not. Small solitaries reacted to sand burial by increasing their mobility; large ones did not increase their mob~lity but avoided burial by elongating their column. Mobllity and size were important attributes of sol~tary anemones for avoiding sand burial. The clonal form is much less mobile and the individuals tend to be smaller, perhaps because of the aggregated configuration. While the aggregated strategy may reduce the effects of desiccation, the accompanying low mobility may reduce the opportunity to avoid other disturbances. The solitary form is better adapted to sand-influenced habitats. The clonal form is well protected from desiccat~on but only as an aggregated configuration.

β-Glucuronidase activity and detritus utilization in the sea anemones Metridium senile and Anthopleura Elegantissima

1. 1. Activity of β-glucuronidase, an enzyme associated with digestion of detritus, was measured in the intertidal sea anemone Anthopleura elegantissima and the subtidal anemone Metridium senile. The enzyme was present in freshly-collected individuals of both species. 2. 2. β-glucuronidase and chymotrypsin-like potease activities were both similar in high- and low- intertidal individuals of Anthopleura elegantissima. High-shore anemones do not appear to respond to shorter feeding times by increasing digestive capacity for detritus. 3. 3. β-glucuronidase activity increased in individuals of Metridium senile that had been fed detritus compared to starved and Artemia-fed individuals. 4. 4. Metabolic heat dissipation, measured by direct calorimetry, increased in Artemia-fed and detritus-fed individuals of Metridium senile compared to starved individuals. Increased heat dissipation is direct evidence of the potential nutritional importance of organic detritus in this species.

PHOTOBIOLOGY OF THE SYMBIOTIC SEA ANEMONEANTHOPLEURA ELEGANTISSIMA: PHOTOSYNTHESIS, RESPIRATION, AND BEHAVIOR UNDER INTERTIDAL CONDITIONS

Continually immersed specimens of Anthopleura elegantissima freshly collected from the shore receive at least 34—42% of their respiratory carbon requirement from their endosymbiotic zooxanthellae. This value decreases to 17% when intertidal sea anemones are exposed to air for 15 h during daytime spring low tides, primarily owing to a reduction in photosynthesis by the algae, which are shaded when the anemone retracts its tentacles and contracts its marginal sphincter. Contraction of continually immersed anemones during peak irradiance likewise decreases their photosynthesis. This behavior is primarily in response to high levels of intracellular oxygen generated by the symbiotic algae, although ultraviolet radiation also causes contraction, especially in aposymbiotic individuals which have lower concentrations of UV-B absorbing substances than do symbiotic anemones. Although A. elegantissima may vary its photosynthetic capacity according to long-term average light conditions, behavioral adaptations such as...

AGONISTIC BEHAVIOR IN THE INTERTIDAL SEA ANEMONEANTHOPLEURA XANTHOGRAMMICA

The large intertidal sea anemone Anthopleura xanthogrammica (Brandt) forms aggregations of genetically distinct individuals at exposed sites along the west coast of North America. Individuals are often in close tentacle contact and remain that way for several years. However, this species displays the same agonistic behavior, inflation, and application of acrorhagi, as does its smaller clone-forming congener Anthopleura elegantissima. The behavior is frequent and more common among large individuals than small ones. Field transplants were used to show that non-neighbor anemones elicit the full acrorhagial response but that neighbors in close contact fail to behave agonistically towards each other. Microscopic examination of tissue samples revealed that conflicts between opposite sex anemones were as common as those between same sex anemones and that neighbors found in close contact were also as likely to be the same sex as the opposite.Field anemone removal experiments in crowded pools and channels were used to compare subsequent movement of anemones released from crowding to movement of anemones never crowded and of those continuously crowded. Newly released anemones do move away from their neighbors but generally do not move out of tentacle contact. These results support the hypothesis that the application of acrorhagi serves more of a communication function than one of severe intraspecific competition. An anemone that has been attacked receives information on the size and position of its neighbor and can then move or not depending on available space. If movement is not possible, the agonistic behavior of its neighbor probably decreases or disappears altogether as a result of habituation.

Genetic and ecological differentiation between sympatric colour morphs of the common intertidal sea anemone Actinia equine

The abundant intertidal sea anemone Actinia equina occurs in a variety of colour morphs of which 3 (green, red, brown) are investigated in the present work. Green anemones are known to be morphologically and behaviourally different from the other colour morphs and may be ecologically distinct; it is also known that green morphs are differentially selected by certain nudibranch predators. Differences between morphs are investigated in detail using large numbers of anemones and employing enzyme electrophoresis as criterion for genetic differentiation. The green morph has clearly different ecological preferences both with respect to mean tidal position on the shore and choice of microhabitat; it also differs significantly at 4 of the 17 enzyme loci examined. According to biochemical evidence there is little or no gene flow between sympatnc populations of green and other colour morphs It is suggested that the green Actjnia should best be regarded as a separate species, and the name Actinla prasjna is proposed.

The apparent absence of a cortical reaction after fertilization in a sea anemone

Eggs, embryos and larvae of the intertidal sea anemone Actinia fragacea were obtained from spontaneous spawnings in the laboratory and have been examined by scanning and transmission electron microscopy. The eggs average 150 μm in diameter and are covered by tufts of large microvilli known as cytospines, but are not surrounded by a jelly layer or a vitelline coat. The cortical layer of the egg contains large numbers of dense, homogeneous cortical granules. The surface layers of cleavage and blastula stage embryos are similar in composition to those of unfertilized eggs in that the cytospine tufts remain intact and the number of cortical granules remains apparently undiminished. No major discharge of cortical granules indicative of a cortical reaction can have occurred. During gastrulation, many embryos take up large numbers of sperm by a process resembling phagocytosis. These sperm undergo breakdown in the superficial regions of the embryos. The cortical granules persist well into larval life, and their function is unknown.