Opsonin-like molecule found in coelomic fluid of a sea cucumber, Holothuria leucospilota

Opsonins, a group of serum proteins present in vertebrates, are known to bind to the surface of many kinds of pathogens and tag them as targets for phagocytosis. Opsonin-like molecules have been suggested to exist in several invertebrates. In this paper, we report the discovery of a new opsonin-like molecule in the coelomic fluid of the sea cucumber Holothuria leucospilota. Opsonic activity in cell-free coelomic fluid was characterized by sodium dodecyl sulfate–polyacrylamide gel electrophoresis, two-dimensional electrophoresis and gel filtration. Phagocytic uptake of yeast cells and latex beads by amoebocytes was quantified by microscopic analysis. It was found that a 20 kdalton protein bound to and enhanced phagocytosis of heat-killed yeast cells. The results of Western blot analysis suggest that both amoebocytes and spherule cells produce this opsonin-like molecule. Received: 22 October 1998 / Accepted: 4 March 2000     

Maintenance of coelomic fluid pH in sea urchins exposed to elevated CO2: the role of body cavity epithelia and stereom dissolution

Experimental ocean acidification leads to a shift in resource allocation and to an increased [HCO₃ ^?] within the perivisceral coelomic fluid (PCF) in the Baltic green sea urchin Strongylocentrotus droebachiensis. We investigated putative mechanisms of this pH compensation reaction by evaluating epithelial barrier function and the magnitude of skeleton (stereom) dissolution. In addition, we measured ossicle growth and skeletal stability. Ussing chamber measurements revealed that the intestine formed a barrier for HCO₃ ^? and was selective for cation diffusion. In contrast, the peritoneal epithelium was leaky and only formed a barrier for macromolecules. The ossicles of 6 week high CO₂-acclimatised sea urchins revealed minor carbonate dissolution, reduced growth but unchanged stability. On the other hand, spines dissolved more severely and were more fragile following acclimatisation to high CO₂. Our results indicate that epithelia lining the PCF space contribute to its acid–base regulation. The intestine prevents HCO₃ ^? diffusion and thus buffer leakage. In contrast, the leaky peritoneal epithelium allows buffer generation via carbonate dissolution from the surrounding skeletal ossicles. Long-term extracellular acid–base balance must be mediated by active processes, as sea urchins can maintain relatively high extracellular [HCO₃ ^?]. The intestinal epithelia are good candidate tissues for this active net import of HCO₃ ^? into the PCF. Spines appear to be more vulnerable to ocean acidification which might significantly impact resistance to predation pressure and thus influence fitness of this keystone species.     

Penetration and storage of sponge spicules in tissues and coelom of spongivorous echinoids

When echinoids feed on sponges, silicate spicules of the sponge were found to enter their body either by penetration through the wall of the food canal into coelomic cavities or by penetration into skeletal plates and spines. The spicules, which have penetrated into the coelom, obviously evoke a kind of protective answer. They were found to be entangled by clusters of cell remnants, the so-called brown bodies. The brown bodies contain melanin and gather at special sites of the echinoid body; these are the Stewart Organs, the gills and the inner side of the ambulacral plates. Sometimes the silicate spicule becomes surrounded by a calcareous sheath. The length of the sponge spicules makes their removal impossible, so that they are stored. The spicules penetrating into the plates are partly incorporated into the stereom. The four species examined in this study were Asthenosoma ijimai, Araeosoma owstoni, Diadema setosum (collected in Sagami Bay, Japan in 1991) and Hapalosoma gemmiferum (collected in Suruga Bay, Japan in 1991).     

Differences in relative abundance and size structure of the sea stars Pisaster ochraceus and Evasterias troschelii among habitat types in Puget Sound, Washington, USA

We surveyed patterns in the relative abundance and size structure of the sea stars Pisaster ochraceus and Evasterias troschelii in five habitat types of varying structural complexity and prey availability (sand/cobble, boulder, and rocky intertidal; pilings; and floating docks) in Puget Sound and the San Juan Islands, Washington. For both species, small sea stars were most abundant in the most structurally complex habitat type (boulder), where they occurred almost exclusively under boulders during low tide. Larger individuals became more abundant as structural complexity decreased, occurring more frequently in open habitat types (rocky shores, pilings, and docks) known to have greater abundances of prey resources. Gull foraging observations and experiments demonstrated that exposed small sea stars of both species were highly vulnerable to predation, suggesting that small sea stars require structural complexity (crevice microhabitat) as a predation refuge. Large sea stars, once attaining a size refuge from predation, appear to migrate to more exposed habitat types with more abundant food resources. These results suggest parallel ontogenetic habitat shifts in two co-occurring consumer species related to a shared predation risk at early life stages and demonstrate how the relative importance of top-down and bottom-up processes may differ with ontogeny.     

Time-lapse cinematography of feather stars (Echinodermata: Crinoidea) on the Great Barrier Reef,Australia: demonstrations of posture changes,locomotion, spawning and possible predation by fish

Aspects of feather star behavior and ecology were recorded by time-lapse cinematography approximately 1 frame min^-1 on the Great Barrier Reef, Australia over a 1 mo period in 1983. The current regime influenced body postures of most species studied, whether nocturnal or not. Moreover, feather stars of several species crawled on the substratum with their arms; each crawling episode lasted roughly 10 min, and the maximum speed attained was about 1 arm length min^-1. Nocturnal feather stars crawled to their nighttime feeding perches around dusk and crawled back to their daytime hiding places around dawn. Surprisingly, some species of feather stars living on the reef surface both day and night also crawled around at dawn and dusk for reasons that are not known. In the time-lapse films, and individual of Comanthus bennetti (sex undetermined) spawned for about 2 min just after dark on 5 July 1983. Another film showed possible predation on a feather star (Himerometra robustipinna) by a saddled coralfish (Chaetodon ephippium).     

Functional morphology of the larval tentacles of Phragmatopoma californica (Polychaeta: Sabellariidae): composite larval and adult organs of multifunctional significance

Larvae of the sabellariid polychaete Phragmatopoma californica (Fewkes), which were collected in San Diego, California and were competent to metamorphose after 18 to 30 d of development were observed in vivo by videoequipped light microscopy, and the fine structure of the larval tentacles was examined by transmission and scanning electron microscopy. Each tentacle has tufts of at least two types of immotile cilia arranged in dorsolateral and ventrolateral rows, and a ventral groove covered by two types of motile cilia that beat independently of each other. The epidermis is regionalized into glandular, sensory, locomotory, and support cell types and contains four longitudinal bundles of basiepithelial nerve fibers. A layer of connective tissue separates the epidermis and the nerve tracts from obliquely striated muscles that occur within the peritoneum that lines the central coelomic cavities. The peritoneum forms an intact coelomic epithelium that overlies and interdigitates with the muscle cells, with no intervening basal lamina. The muscle cells are considered to be intraperitoneal because they are located above the basal lamina and they lack intercellular junctions with the peritoneal cells. Specialized peritoneal cells form a striated myoepithelial blood vessel that partitions the coelom into medial and lateral cavities. No neuromuscular junctions were found, but both muscular and ciliary movement seem to be under neuronal control. The basiepithelial nerve terminals appear to synapse into the connective tissue layer toward the intraperitoneal muscle. Several similarities in tissue organization are noted between the larval tentacles of P. californica and the tube feet of echinoderms. Observations on the ontogeny, morphology, and behavior of the tentacles suggest that they are multifunctional organs involved in feeding, construction of the juvenile sand tube, locomotion, attachment, and sensory perception during larval and adult lives.     

Studies on the transport of sugars in the holothurian Holothuria scabra

Experiments using ¹⁴C sugars were carried out on the holothurian Holothuria scabra Jäger, in order to assess the role of its perivisceral fluid in the translocation and transportation of dissolved organic materials. The results obtained indicate that the perivisceral fluid plays a significant part. Rates of ¹⁴C glucose, fructose and sucrose uptake were followed in major tissues such as the alimentary canal, haemal system, respiratory tree and body wall. The monosaccharides are absorbed more intensively by digestive and haemal systems, the disaccharide by respiratory tree and body wall. It is, therefore, presumed that tissues in H. scabra selectively absorb sugars depending on their metabolic activity.     

Die stickstoffhaltigen stoffwechselendprodukte und ihre exkretion bei Paracentrotus lividus

The perivisceral fluid of Paracentrotus lividus (Lamarck) contains, as main end-products of the nitrogenous metabolism, ammonia, urea, creatine, creatinine and traces of uric acid. In the organs analysed, the distribution and abundance of ammonia and urea fluctuate considerably. the intestine was found to have the highest NH₄ ⁺?N and the lowest urea-N contents. The axial organ contained the highest amount of urea-N and the lowest quantity of NH₄ ⁺?N; the perivisceral fluid, including the coelomocytes, contained intermediate amounts. The special relations to hemal system and coelothel, the presence of excretory material, and the analogous conditions to other invertebrates, suggest that the coelomocytes and parts of the intestine and axial organ are excretophoric and able to synthesize urea. From the known distribution of ammonia and urea in echinoid species, it is concluded that the ability to synthesize urea must have developed and improved in efficiency during echinoid evolution. P. lividus is predominantly ureotelic. It excretes approximately 91% of the nitrogenous wastes released into the surrounding sea water as urea-N, and only 9% as ammonia-N. Ammonia, and most of the urea, are excreted via the body surface — probably through respiratory surfaces; however, one third of the urea is excreted through the intestine, since urea excretion decreases by this amount when the anus is sealed artificially.     

The introduction of Littorina littorea to British Columbia, Canada: potential impacts and the importance of biotic resistance by native predators

Although the establishment and spread of non-indigenous species depends upon survival in the face of novel environmental conditions and novel biological interactions, relatively little attention has been focused on the specific role of native predators in limiting invasion success. The European common periwinkle, Littorina littorea, was recently introduced to the Pacific coast of Canada and provides a case study of an introduction into an area with an important predator guild (sea stars) that is functionally minor in the invader’s native habitat. Here, we assess the likelihood of establishment, spread, and negative ecological impact of this introduced gastropod, with an emphasis on the role of native sea stars as agents of biotic resistance. Size frequency distributions and local market availability suggest that L. littorea was most likely introduced via the live seafood trade. Non-native hitchhikers (e.g., the trematode Cryptocotyle lingua) were found on/in both market and field specimens. Laboratory studies and field observations confirmed that L. littorea can survive seasonal low salinity in Vancouver, British Columbia. Periwinkles also readily consumed native Ulva, suggesting that periwinkles could impact native communities via herbivory or resource competition. Unlike native gastropods, however, L. littorea lacked behavioural avoidance responses to Northeast Pacific predatory sea stars (Pisaster ochraceus and Pycnopodia helianthoides), and sea star predation rates on L. littorea were much higher than predation rates on native turban snails (Chlorostoma funebralis) in common garden experiments. We therefore expect periwinkle establishment in British Columbia to be limited to areas with low predator density, as is seen in its field distribution to date. We caution that this conclusion may understate the importance of the L. littorea introduction if it also serves as a vector for additional non-indigenous species such as C. lingua.     

Interactions among sea otters, sea stars, and suspension-feeding invertebrates in the western Aleutian archipelago

The structuring and organizing effects of apex predators on ecosystems are becoming increasingly well documented. The enhancement of kelp forests via sea otter predation on herbivorous sea urchins is among the earliest and best known examples. This study provides evidence for direct and indirect trophic interactions among sea otters, predatory sea stars, and filter-feeding mussels (Mytilus trossulus) and barnacles (Semibalanus cariosis). In western Massacre Bay at Attu Island (173°E, 53°N), subtidal transects showed sea star body size and biomass density declined markedly between 1983 and 1994 as sea otters reinhabited this area. Mussels and barnacles translocated from the rocky intertidal zone to shallow subtidal habitats to assess loss rates from sea star predation showed lower mortality rates after the arrival of sea otters. Prey mortality rates in subtidal caged controls were consistently low and similar to those of intertidal controls in both years. These findings elucidate a trophic pathway by which sea otters can influence ecosystems separate from the well-known sea otter/sea urchin/macroalgae cascade.     

Notes on the ecology of Astropecten aranciacus

In a shallow coastal region of Sardinia (European Mediterranean Sea) the activity pattern and migration habits of the sea star Astropecten aranciacus were studied by means of SCUBA diving. The species is nocturanl, with two modes of abundance. Different size classes revealed different activity schedules. A sample taken at dusk consisted of comparatively large-sized sea stars, while another sample taken at night included small-sized sea stars with the larger individuals. By tagging the sea stars with numbers, their locomotory activity during the night, as well as day, was investigated.     

Digestive mechanics and gluttonous feeding in the feather starOligometra serripinna (Echinodermata: Crinoidea)

The movement and digestion of food in the gut ofOligometra serripinna (Carpenter) were studied at Lizard Island (14°3842S; 145°2710E) in the austral winter of 1986. Feather stars in the laboratory were fed a brief, small meal of brine shrimp nauplii and killed at increasing time intervals thereafter. Histological reconstructions showed that the ingested nauplii progressed along the digestive tract surprisingly quickly. Some nauplii were found in the mid and hind intestine in only 30 min, and all of the nauplii had reached the hind intestine and rectum in 1 h. Digestion of the nauplii had started at 1 h, and only a few fragments of naupliar exoskeleton remained in the hind intestine and rectum 5 h after the start of feeding. Videotape analysis showed that no fecal pellets were released during this experiment. In the natural environment ofO. serripinna, ingested particles may similarly be transported quickly to the hind part of the gut and digested there — when feather stars were fixed in the field, most of the gut contents were found in the hind intestine and rectum.O. serripinna, which efficiently rejects inert particles before they are ingested, usually defecates infrequently (probably not more than once over a span of many hours) and differs from some other feather stars that ingest numerous inert particles and defecate much more frequently. When specimens ofO. serripinna were fed continuously on brine shrimp nauplii,Artemia sp. (San Francisco strain), in the laboratory, the feather stars fed gluttonously, packing their guts with several hundred nauplii in 1 to 2 h. Thereafter, superfluous feeding began (i.e., further ingestions appeared to force undigested nauplii, some of them still living, out of the anus). These observations suggest thatO. serripinna usually feeds at relatively modest rates in its natural habitat, but can feed gluttonously to take advantage of infrequent patches of highly concentrated, nutritious particles (e.g. copepod swarms, migrating demersal zooplankton, and invertebrate gametes from mass spawnings). It is likely that such patches of nutritious particles are usually small enough to drift out of reach of the feather stars before gluttonous feeding proceeds to superfluous feeding. Opportunities for superfluous feeding in nature are probably very infrequent (e.g. ingestion of coral gametes and embryos after a mass spawning), and the feather stars evidently have no behavior that stops further ingestions after the gut becomes filled to capacity.     

Chemical defense in the eggs and embryos of antarctic sea stars (Echinodermata)

Fifteen species of reproductively mature echinoderms (11 sea stars, 3 sea urchins, 1 sea cucumber) were collected from McMurdo Sound, Antarctica, during austral spring and summer of 1985 and 1986; eggs and embryos were obtained, and were tested for ichthyonoxicity using the common marine killifishFundulus grandis as a model predator. Chemical deterrents occurred in the large, yolky eggs of the pelagic lecithotrophic sea starPerknaster fuscus and the planktotrophic sea starPorania antarctica. Brooded embryos of the sea starsDiplasterias brucei andNotasterias armata were also noxious. Significant ichthyonoxicity was not detected in the remaining 7 species of sea stars, 3 sea urchins, and 1 sea cucumber. Chemical deterrents were generally effective at concentrations below a single egg or embryo per agar test-pellet. Although chemicals found in these eggs and embryos are noxious to an allopatric fish, they may not be noxious to sympatric fish.     

Anaerobic and aerobic energy metabolism in ovaries of the sea urchin Strongylocentrotus droebachiensis

The gonads of sea urchins undergo large changes in mass during their gametogenic cycle. In addition, they have relatively low aerobic capacities and are poorly perfused by the circulatory system and thus are continually hypoxic or anoxic. The present study of Strongylocentrotus droebachiensis investigates seasonal changes in the relationships among mass of the ovaries, pH and P_O2 of the perivisceral coelomic fluid which bathes the ovaries, and partitioning of ovary energy metabolism into its anaerobic and aerobic components. S. droebachiensis were collected at Blue Hill Falls, Maine, USA, from August 1982 to March 1984. We found that from 76 to 92% of the heat dissipated by isolated ovaries of the sea urchin S. droebachiensis derives from anaerobic energy metabolism at partial pressures of oxygen prevailing in vivo. Ovaries from S. droebachiensis have the capacity to produce large amounts of lactate under imposed anoxia, but lactate accounts for only 37% of the total anoxic heat dissipation, which suggests that other end products of anaerobiosis are present. Seasonal changes in pH and P_O2 of the perivisceral coelomic fluid can be explained by a complex relationship among changes in temperature, reproductive condition, and anaerobic and aerobic metabolism in the ovaries, gut and body wall. Seasonal changes in the buffering capacity of the perivisceral coelomic fluid must be determined before the effects of respiratory and metabolic acid production on the acid-base status of the coelomic fluid can be fully understood.     

Habitat complexity impacts persistence and species interactions in an intertidal whelk

Although experiments have shown that habitat structure may influence the distribution of species and species interactions, these effects are still not commonly integrated into studies of community dynamics. Since habitat structure often varies within and among communities, this may limit our understanding of how various factors influence communities. Here, we examined how mussel bed complexity (the presence and thickness of mussel layers) influenced the persistence of whelks (Nucella emarginata) and interactions with a top predator (ochre sea stars, Pisaster ochraceus) and prey (mussels, Mytilus californianus). Results from a mark?Crecapture experiment indicate that whelk recapture rates are higher in more complex habitats, and laboratory experiments demonstrate that habitat complexity affects whelk feeding, growth, and nonconsumptive interactions with a keystone predator. Habitat complexity therefore has direct effects on species and also may lead to trade-offs among feeding, refuge, and other factors, potentially influencing the distribution of whelks and the effects of both whelks and sea stars on intertidal communities. These results demonstrate that habitat structure may play an important role in intertidal communities and other habitats and should be further considered in the experimental design of future studies of community dynamics.     

Settlement, recruitment and potential predators and competitors of juvenile echinoderms in the rocky subtidal zone

Recruitment patterns of marine invertebrates are affected both by settlement and early post-settlement events. This study examined the settlement and recruitment patterns of echinoderms at three sites in the rocky subtidal zone of Bocabec Cove, Bay of Fundy, Canada using artificial turf collectors and quadrats on the natural substrate. Potential predators were quantified at two of the sites along transects and in 1-m² quadrats. Both potential predators and competitors were quantified in 0.0625-m² quadrats. Settlement varied across sites (1.5–3 km apart) and two years of sampling (2004, 2005). The site of most potential settlement differed for the three groups of echinoderms: sea urchins (Strongylocentrotus droebachiensis), sea stars (Asterias spp.) and sea cucumber (Psolus fabricii). Settlement densities on the artificial turf collectors tended to be greater than the densities of settlers on the natural substrate. On the natural substrate, the only significant difference between densities of juveniles over time was that newly settled sea stars were found in July and were not found the following October. Large lobsters and carnivorous worms were potential predators with densities that varied between sites. Potential competitors that differed in abundance between sites were herbivorous gastropods and conspecifics for sea urchins; and carnivorous worms for sea stars. This study suggests that patterns of recruitment are either set up by patterns of settlement or by events during the first few weeks/months on the benthic substrate for these echinoderms.     

Interactive accumulation of mercury and selenium in the sea starAsterias rubens

Interactions between mercury and selenium accumulation and subcellular binding inAsterias rubens (L.), collected in 1987 from Lille Bælt at Middelfart, Funen, Denmark, were investigated in laboratory experiments. Sea stars exposed to 10µg Hg l^–1 for 30 d accumulated mercury in body wall, tube feet and stomach linearly with time at 1.2, 1.2 and 0.5µg Hg g^–1 dry wt d^–1, respectively. Mercury was accumulated in pyloric caeca and coelomic fluid initially at 1.4µg Hg g^–1 dry wt d^–1 and 9.4 ng Hg ml^–1 d^–1, respectively; after 10 d uptake rates decreased. Sea stars exposed to 75µg Se-SeO ₃ ^{- -} l^–1 accumulated selenium linearly with time over 30 d in the stomach, pyloric caeca, tube feet and body wall at 2.0, 1.2, 1.2 and 0.6µg Se g^–1 dry wt d^–1. Sea stars exposed to 75µg Se-SeO ₄ ^{- -} l^–1 maintained selenium levels in the coelomic fluid at 75µg Se l^–1 over 30 d. Exposure to selenate did not alter the selenium concentrations in the tissues. Sea stars exposed concurrently to 75µg Se-SeO ₃ ^{- -} and 10µg Hg l^–1 accumulated more mercury and selenium in tube feet and body wall than did sea stars exposed to the two elements alone. In pyloric caeca and stomach concurrent exposure reduced accumulation of both elements. Mercury was bound predominantly in the insoluble fraction of the tissues, and soluble mercury was bound in proteins of high (> 70 kilodaltons) or very low (< 6000 daltons) molecular weight. Ca. half of the selenium recovered was bound in the insoluble fraction, and soluble selenium was bound in proteins of high (> 70 kilodaltons) or very low (< 6000 daltons) molecular weight. Interaction between the two elements was exerted predominantly in the insoluble fraction of the tissues.     

Chemical mediation of invertebrate defensive behaviors and the ability to distinguish between foraging and inactive predators

When the predatory sea star Pycnopodia helianthoides was placed upstream, the sea urchin Strongylocentrotus purpuratus responded defensively by extending and opening its globiferous pedicellariae. No pedicellaria response was given in control seawater or when the sea star was downstream. The snail Tegula funebralis responded by moving up vertical surfaces when Pycnopodia helianthoides or when Pisaster ochraceus were placed upstream. When these sea stars were introduced downstream, the snail's response was not significantly different from that in control seawater. Water collected from an aquarium containing a single sea star was sufficient to trigger the response of S. purpuratus and T. funebralis; the physical presence of the sea star was not essential. This indicated that a chemical stimulus was involved, and the lack of responses when sea stars were downstream argued strongly against the possible additional involvement of visual or vibrational stimuli. S. purpuratus gave stronger pedicellaria responses to water flowing over an active Pycnopodia helianthoides than to water flowing over the same sea star when it was inactive. The significance of the ability to distinguish between actively foraging and inactive predators is discussed, and a mechanism is proposed to explain differences in the amount of stimulatory chemicals released by active and inactive sea stars.     

Mind the gap: a comparative study of migratory behavior in social amoebae

Social amoebae aggregate to form a multicellular slug that migrates some distance. Most species produce a stalk during migration, but some do not. We show that Dictyostelium giganteum, a species that produces stalk during migration, is able to traverse small gaps and utilize bacterial resources following gap traversal by shedding live cells. In contrast, we found that Dictyostelium discoideum, a species that does not produce stalk during migration, can traverse gaps only when in the presence of other species’ stalks or other thin filaments. These findings suggest that production of stalk during migration allows traversal of gaps that commonly occurs in soil and leaf litter. Considering the functional consequences of a stalked migration may be important for explaining the evolutionary maintenance or loss of a stalked migration.     

Photoperiodic regulation of gametogenesis and gonadal growth in the sea star Pisaster ochraceus

A photoperiod regime 6 mo out of phase between December 1978 and August 1980 resulted in gametogenesis, gonadal growth, and spawning in laboratory-maintained sea stars [Pisaster ochraceus (Brandt)] 6 mo out of phase with individuals in the field or laboratory on normal celestial photoperiods at Santa Cruz, California (USA). The seasonal fluctuation of pyloric cecum size also was shifted when the sea stars were held on the out-of-phase photoperiod regime. Phase shift of all these events was evident within 6 to 9 mo. Long daylengths (or short nightlengths) in spring and summer apparently synchronize or entrain the initiaion of gametogenesis and gonadal growth in fall.