“Natural” agglutinins against sea urchin sperm in the hemolymph of the crab Cardisoma guanhumi

“Natural” agglutinins against sperm have been considered to be broadly specific. However, the clumping of sperm from one species of sea urchin in hemolymph from the crab Cardisoma guanhumi, revealed a narrowly specific agglutinin. Additional testing could establish the taxonomic distribution of the reacting antigen.     

Seasonal variation in the white muscle biochemical composition of deep-sea macrourids in the North-east Atlantic

The peculiar limpet-like morphology of the genus Colobocentrotus is unique among the regular echinoids. This shape has been interpreted as an adaptation to life in areas of extreme wave exposure. In this study the attachment strength of C. atratus is compared with that of three sympatric species, Echinometra mathaei, Heterocentrotus trigonarius and Stomopneustes variolaris, which have more typical echinoid morphology and live in different microhabitats. For each species, the adhesion of individual sea urchins was measured as well as the tenacity of single tube foot and the mechanical properties of the tube foot stems. Colobocentrotus always presented the highest measured values, although not always significantly different from those of the other species. Of the mechanical properties of the stem measured, the stem extensibility was the only property that was significantly different among species. In general the stems of all the species studied became more extensible and more difficult to break with increasing strain rate, providing an adaptative advantage to the sea urchin when subjected to rapid loads such as waves. In terms of single tube foot tenacity, C. atratus tube feet attached with a tenacity (0.54 MPa) two times higher than the one of E. mathaei, H. trigonarius and S. variolaris (0.21–0.25 MPa). Individual sea urchins of the four species, however, attached with a similar strength (0.2–0.26 MPa). The calculation of safety factors showed that it is the very high number of adoral tube feet of C. atratus and not the overall shape of the animal that allows this species to withstand very high water velocities. However, C. atratus streamlined morphology may be a functional adaptation to reduce the impact of other hydrodynamic forces (such as wave impingement forces) or to cope with other selective environmental stresses (such as dessication), and thus to inhabit extremely exposed areas of the intertidal.     

Ein mimetisches Kollektiv — Beobachtungen an Fischschwärmen,die Seeigel nachahmen

In the Indian Ocean, the fish Siphamia argentea usually lives in small groups within the interradial spaces of the sea urchin Astropyga radiata. The fish has a colouration similar to that of the sea urchin and is thus protected from predators both by camouflage and the physical barrier of the sea urchin's spines. If the fish do not keep to the interradial spaces, the urchin can prick them with its spines. When the fish groups become too large, there is not enough space for them in these protected interradial spaces. Individuals which cannot be accomodated, form a dense group around the sea urchin which resembles a large urchin. Such dense groups are also known to occur in the fish Plotosus anguillaris where the individuals actually touch each other. The relationship between fish and sea urchin is described and discussed as an example of collective mimetic behaviour. This is the first record of collective mimetic behaviour in a marine environment. It is difficult to decide whether this is mimicry or mimese, as detailed research on the predators of both the sea urchin and the fish has not been carried out.     

Effects of sea urchin disease on coastal marine ecosystems

Outbreaks of disease in herbivorous sea urchins have led to ecosystem phase shifts from urchin barrens to kelp beds (forests) on temperate rocky reefs, and from coral to macroalgal-dominated reefs in the tropics. We analyzed temporal patterns in epizootics that cause mass mortality of sea urchins, and consequent phase shifts, based on published records over a 42-year period (1970–2012). We found no evidence for a general increase in disease outbreaks among seven species of ecologically important and intensively studied sea urchins. Periodic waves of recurrent amoebic disease of Strongylocentrotus droebachiensis in Nova Scotia coincide with periods when the system was in a barrens state and appear to have increased in frequency. In contrast, following a major epizootic that decimated Diadema antillarum throughout the Caribbean in 1983, subsequent outbreaks of disease were highly localized and none have been reported since 1991. Epizootics of Strongylocentrotus in the NW Atlantic and NE Pacific, and Paracentrotus and Diadema in the eastern Atlantic, have been linked to climate change and overfishing of sea urchin predators. The spatial extent of recurrent disease outbreaks in these species, and the frequency of phase shifts associated with these epizootics, has decreased over time due to the expansion of the macroalgal state and its stabilization through positive feedback mechanisms. Longitudinal studies to monitor disease outbreaks in sea urchin populations and improved techniques to identify causative agents are needed to assess changes in the frequency and extent of epizootics, which can profoundly affect the structure and functioning of coastal marine ecosystems.     

Eine Fisch-Seeigel-Partnerschaft. Untersuchungen optischer reizparameter beim formenerkennen

The shrimp Tuleariocaris sansibarica and the fish Siphamia permutata live between the spines of the sea urchin Diadema setosum. Visual attration is important in maintaining this association. The spines of the sea urchin act as an optical stimulus for shrimp and fish. The specific optical stimuli which the shrimp (Fricke and Hentschel, 1971) and the fish perceive during their stay with the urchin were investigated and compared. Dummy experiments in the coral reef of the Red Sea (Eilat, Israel) have shown that the fish is able to distinguish between at least 5 different stimuli patterns: color (black or white), diameter, number, distance between spines, and orbital position. Color is less attractive than number and orbital position; the relations between number and orbital position are nearly linear. The different visual systems of shrimp and fish are capable of selecting similar optical parameters. Slight differences in evaluation of single parameters are understood as adaptive processes to an identical environment.     

Trophic cascades result in large-scale coralline algae loss through differential grazer effects

Removal of predators can have strong indirect effects on primary producers through trophic cascades. Crustose coralline algae (CCA) are major primary producers worldwide that may be influenced by predator removal through changes in grazer composition and biomass. CCA have been most widely studied in Caribbean and temperate reefs, where cover increases with increasing grazer biomass due to removal of competitive fleshy algae. However, each of these systems has one dominant grazer type, herbivorous fishes or sea urchins, which may not be functionally equivalent. Where fishes and sea urchins co-occur, fishing can result in a phase shift in the grazing community with subsequent effects on CCA and other substrata. Kenyan reefs have herbivorous fishes and sea urchins, providing an opportunity to determine the relative impacts of each grazer type and evaluate potential human-induced trophic cascades. We hypothesized that fish benefit CCA, abundant sea urchins erode CCA, and that fishing indirectly reduces CCA cover by removing sea urchin predators. We used closures and fished reefs as a large-scale, long-term natural experiment to assess how fishing and resultant changes in communities affect CCA abundance. We used a short-term caging experiment to directly test the effects of grazing on CCA. CCA cover declined with increasing fish and sea urchin abundance, but the negative impact of sea urchin grazing was much stronger than that of fishes. Abundant sea urchins reduced the CCA growth rate to almost zero and prevented CCA accumulation. A warming event (El Ni?o Southern Oscillation, ENSO) occurred during the 18-year study and had a strong but short-term positive effect on CCA cover. However, the effect of the ENSO on CCA was lower in magnitude than the effect of sea urchin grazing. We compare our results with worldwide literature on bioerosion by fishes and sea urchins. Grazer influence depends on whether benefits of fleshy algae removal outweigh costs of grazer-induced bioerosion. However, the cost-benefit ratio for CCA appears to change with grazer type, grazer abundance, and environment. In Kenya, predator removal leads to a trophic cascade that is expected to reduce net calcification of reefs and therefore reduce reef stability, growth, and resilience.     

Effects of artificial eutrophication on the metabolism of the Japanese oyster Crassostrea gigas

The morphology of the primary tube feet in 15 species of comatulid (unstalked) crinoids from coral reefs in the Palau Islands and Lizard Island, Great Barrier Reef, was investigated using close-up underwater photographs of the tube feet taken in the natural habitat. Measurements of length of the tube feet and their spacing along the pinnule were taken from these photographs. Tube feet of species of the family Comasteridae have a mean length of 0.75 mm and a mean spacing of 6 tube feet mm^-1. Tube feet of non-comasterid species occurring in the same environments have a mean length of 0.55 mm and a mean spacing of about 8 tube feet mm^-1. The relationship between spacing and length of the tube feet is highty significant for both the Palau and Lizard Island samples (P<0.01). Species having longer and more widely spaced tube feet live partly concealed within the infrastructure of the reef and hold the arms and pinnules in a multidirectional posture. Species having shorter and more closely spaced tube feet perch on top of reef pinnacles or alcyonarians and form planar filtration fans normal to unidirectional currents or wave oscillations. Longer and more widely spaced tube feet in species dwelling within the reef infrastructure provide more efficient filtration in the slow, meandering flow prevailing there. Closer spacing of the tube feet in species exposed to near-mainstream flow provides a more efficient filtration mechanism at higher flow velocities. Reduced length of the tube feet in these species may be a consequence of closer spacing of the pinnules. Differentiation of these co-occurring species in spacing and length of the tube feet implies differentiation in food particles captured. This may in some cases constitute resource partitioning. Most species which overlap in living habits are significantly different in spacing and length of the tube feet.     

Möglicher einfluß von feinden auf das verhalten von Diadema-seeigeln

The diurnal rhythms of the sea urchin Diadema setosum differ in coral-reef and port populations at Eilat, Israel. In the port basin (built in 1967), predators of D. setosum are not present. The locomotory activity of reef and port sea-urchins was measured in the field, using SCUBA equipment. During the day, reef sea-urchins sit motionless in sheltered areas; at night, they crawl around and search for food. In contrast, port sea-urchins are active during 24 h. The activity pattern of D. setosum seems to depend on the presence or absence of predators. Apparently, the sea urchins which entered the newly-built harbour have adapted to their predatorless environment. It is not known how this fast adaptation came about; possible explanations are discussed.     

Migratory activity by hatchling loggerhead sea turtles (Caretta caretta L.): evidence for divergence between nesting groups

The South Florida subpopulation of loggerhead sea turtles (Caretta caretta L.) nests with great fidelity on either the southeast or the southwest coast of Florida, USA. The hatchlings that emerge from those nests must swim in opposite directions and search for different surface currents to migrate away from continental shelf waters. In this laboratory study, we compared the pattern of swimming activity shown by the hatchlings from each coast over the first 6 days of migration. Turtles from both coasts were equally active during their “frenzy” period (the first 24 h of swimming) and during the daylight hours of the 5 days that followed (the “postfrenzy” period). However, the west coast turtles were significantly more active than the east coast turtles during the nocturnal portion of the postfrenzy period. This difference may be related to the greater distance southwest coast turtles must negotiate to locate surface currents for transport out of the Gulf of Mexico and into the Atlantic Ocean basin. These differing behavioral strategies may be genetically determined, as similar correspondence between activity and distance is well known among migratory populations of birds and fish and is often based upon inherited programs of endogenously driven activity. Alternatively, behavioral differences between the two nesting groups could be a manifestation of phenotypic plasticity that arises as the hatchlings respond to unique environmental cues on each coast.     

Effects of predators on sea urchin density and habitat use in a southern California kelp forest

Grazing sea urchins can reduce kelp abundance and therefore strongly affect kelp forest community structure. Despite the ecological importance of sea urchins, direct field studies on the role that urchin predators play in shaping urchin populations are rare for southern California. We conducted surveys and manipulative experiments within kelp forests near San Diego, CA, (32–51′28″N, 117–16′00″W) from 2006 to 2009 to determine whether predators such as sheephead (Semicossyphus pulcher) and spiny lobsters (Panulirus interruptus) may be linked to purple urchin (Strongylocentrotus purpuratus) and red urchin (Strongylocentrotus franciscanus) distribution and habitat use, as well as purple urchin density-dependent mortality. Purple urchins were less dense and more cryptic inside a local marine protected area (MPA) that contained high predator abundance than in nearby heavily fished areas, whereas red urchins rarely were found outside the MPA. Urchin proportional mortality was inversely density dependent during the day when sheephead were active, despite fish aggregations in plots of high urchin density, but was density independent during the night when lobsters were active. Urchin mortality was reduced under understory algal cover during the day, but not during the night. Examining whether urchin mortality from predation is density dependent and how habitat complexity influences this relationship is imperative because behavioral changes and increases in urchin populations can have vast ecological and economic consequences in kelp forest communities.     

Patterns of distribution and composition of sea urchin assemblages on Brazilian subtropical rocky reefs

Sea urchins are a key group of herbivores in both temperate and tropical food webs because they control macroalgal cover, and consequently influence primary productivity and phase shifts on reefs. Despite being abundant on southwestern Atlantic reefs, sea urchin distributions, and their association with abiotic and biotic variables, are poorly known. In this study, sea urchin assemblages were surveyed in 2011 at multiple depths at eight sites in Arraial do Cabo (Brazil, 22°57′S/41°01′W), with sites split between a colder, more wave-exposed location, and a warmer, more sheltered location. The influence of this large-scale physical gradient, along with changes in depth and substrate complexity, on sea urchin densities was then investigated. Predator biomass was low and did not vary significantly among sites. Among the seven species recorded, Paracentrotus gaimardi, Echinometra lucunter and Arbacia lixula were dominant. Linear mixed-effects models indicated that location was important, with mid-sized P. gaimardi individuals and A. lixula more common at cooler, exposed sites and E. lucunter more abundant at warmer, sheltered sites. Sea urchin densities typically decreased with increasing depth, probably caused by changes in factors such as light, wave exposure, and sedimentation. Substrate complexity had a positive effect on the abundance of all species, presumably because of the increased availability of refuges. Physical gradients have important consequences for urchin distributions and their ecological functions at relatively small spatial scales on these reefs, and should be incorporated into herbivore monitoring programmes. Research is also required to examine how differential sea urchin distributions affect benthic dynamics.     

Chemische tarnung. Die stoffliche grundlage der anpassung von anemonenfischen an riffanemonen

Dissolved amino acids (³H-phenylalanine, ³H-proline) were accumulated and incorporated into proteins and glycoproteins by sea anemones. On objects (glass rods, pipe cleaners or filter paper) which had touched labelled anemones, tritiated substances could be detected. The mucus of labelled anemones was analysed by disc-electrophoresis. Tritium activity was found in the bands (stained by amino black). Anemone fishes adapted to labelled anemones had 4 times more tritium activity on their surface than control fishes. Most radioactivity was found on those regions which made closest contact with the anemones. The mucus of anemone fishes adapted to labelled anemones was also analysed by disc-electrophoresis. The analysis revealed protein-containing fractions in which ³H-amino acids were incorporated. The pattern of tritium activity in disc-electropherograms from labelled anemones corresponds to that of fishes adapted to those anemones. Anemones produce specific substances which influence the discharge of their nematocytes. These substances have special functions in the normal behaviour of the anemones. The substances provide protection against self-nettling and prevent the discharge of nematocytes into nearby objects which the tentacles continuously contact. The production of these substances by anemones is completely separate from the association with anemone fishes. The fishes thus simply exploit a mechanism existing independently in the anemones. Therefore, it is possible to form, in an aquarium, unnatural associations between anemone fishes and anemone species which never live in association with fishes in their natural biotope. On the basis of previous information, as well as on these new data, it is possible to develop a model which explains the control of nematocyte discharge: Substances with inhibitory qualities (protecting substances) are produced by the anemones themselves, and de-sensitize the sensory inputs of the anemones (nematocytes and sensory cells). Sensitization takes place as soon as the anemones come into contact with “stimulating substances”. This happens if anemones are touched by food objects or by anemone fishes which have been previously isolated from anemones. The surfaces of these fishes are not impregnated with protecting substances. Adapted anemone fishes, neighbouring anemones of the same species and other “adapted” objects are coated with the inhibitory substances and thus do not induce nematocyte discharge.     

Der Einfluß physikalischer und chemischer Faktoren auf die Aufnahme in Meerwasser gelöster Aminosäuren durch Aktinien

Changes in abiotic environmental factors do not adversely influence the capacity of Anemonia sulcata (Coelenterata, Anthozoa) to take up dissolved amino acids from sea water; e. g., A. sulcata resorbs also under anaerobic conditions. The influence of temperature on amino acid uptake (Q₁₀=2) indicates that the translocation of the organic molecules through membranes of the ectoderm depends on energy. Uptake of amino acids is possible against a gradient of up to 9×10⁶:1. It can be postulated that L-amino acids (also D-isomers) and glucose are resorbed by different “carrier systems”, since glucose does not influence the uptake of amino acids; however, amino acids can interfere with each other, e. g. phenylalanine/glycine. Blocking of anaerobic glycolysis results in uptake reduction; at the same concentrations “oxidative” blockers have a much smaller effect on amino acid uptake. The possibility of exploiting the surrounding water as an energy source by taking up dissolved organic material is discussed with reference to ecological and evolutionary aspects.     

Profitability and sustainability of edible sea urchin fishery in Sardinia (Italy)

Sea urchin (Paracentrotus lividus) fishery is intensively practiced in several areas of the Mediterranean basin. In Sardinia, as well as other Mediterranean countries, sea urchin is a basic ingredient for several dishes due to the delicacy of its gonads (roe), and demand is constantly increasing. Restrictions have been implemented in order to minimise the risk of overexploitation, however, these measures might jeopardize economic convenience in sea urchin harvesting. This paper estimates economic convenience within the edible sea urchin fishery in Sardinia. It aims to determine whether both profitability and sustainability, in terms of the preservation of sea urchin stock, can be guaranteed by actual policy regulation. We found high variability in terms of captures and profitability among firms, and a considerable degree of this variability is the result of technological differences between fishing methods. Analysis also suggests that a slight increase in allowed captures should generate a more than proportional increase in profits. This evidence gives some useful suggestions for improving the efficacy of policies in affecting the economic and environmental sustainability of the Mediterranean sea urchin fishery.     

Patterns of abundance, population size structure and microhabitat usage of Paracentrotus lividus (Echinodermata: Echinoidea) in SW Portugal and NW Italy

In coastal habitats, wave exposure influences several aspects of the life history of marine organisms. Here, we assess how hydrodynamic conditions can generate variation in density, size structure and microhabitat usage of Paracentrotus lividus and whether these effects are consistent between regions that are markedly different for oceanic climate, such as the coasts of SW Portugal and NW Italy. The abundance of P. lividus was ~4 times higher in SW Portugal than in NW Italy, but within each region, there was no effect of wave exposure. In SW Portugal, higher urchin abundances were found at shallower depths, while no effect of depth on urchin abundance emerged in NW Italy. Most of the variation in urchin abundance occurred at small spatial scales (metres), and our results suggest that habitat complexity, that is, the presence of cracks and crevices, is an important determinant of patterns of distribution of this species. The population in NW Italy was characterized by a unimodal size distribution, with a higher proportion of medium-sized individuals. In contrast, in SW Portugal, smaller individuals represented a large proportion of the populations. Size structure varied between exposed and sheltered habitats in SW Portugal, suggesting that the proportion of individuals from different size cohorts may vary along wave-exposure gradients as a result of direct or indirect effects of hydrodynamic forces. In SW Portugal, most urchins occurred in burrows, while in NW Italy, urchins were mainly observed in crevices. These results suggest that creating/occupying burrows might be an adaptive behaviour that allows sea urchins to better withstand stressful hydrodynamic conditions and, therefore, are more common on exposed Atlantic coasts. Overall, our study suggests that the effects of hydrodynamic forces on sea urchin populations are context dependent and vary according to background oceanic climate.     

Fische als Feinde tropischer Seeigel

The techniques used by 9 species of fish (representing 3 families) to capture Diadema sea urchins were observed under water in the Red Sea at Eilat, Israel. Different species displayed different techniques. Fish belonging to the Lethrinidae and Labridae families devoured the entire urchin after capture; Labridae alone were also capable of breaking up large sea urchins by banging them on rocks. The fish did this by shaking its head while holding the urchin in its mouth. Under experimental conditions, fish can distinguish between large and small urchins, and show a preference for the small urchin. The fish also shun contact with some other species of urchins. The trigger fish Balistes fuscus exposed to a dummy sea urchin responds to optical stimuli (body shape and spines); when exposed to a living sea urchin it responds to both optical and behavioural stimuli (movements of the spines). Morphological and ethological preadaptation of the fish to alter its preference for other food is essential before it can develop differentiated capture techniques. The ecological significance of the behaviour of fish in the coral reef ecosystem and the alternating influences in the predator-prey-relationship are discussed.     

Host preference,site fidelity,and homing behavior of the symbiotically luminous cardinalfish,Siphamia tubifer (Perciformes: Apogonidae)

The sea urchin cardinalfish, Siphamia tubifer (Perciformes: Apogonidae), is unusual among coral reef fishes for its use of bioluminescence, produced by symbiotic bacteria, while foraging at night. As a foundation for understanding the relationship between the symbiosis and the ecology of the fish, this study examined the diel behavior, host urchin preference, site fidelity, and homing of S. tubifer in June and July of 2012 and 2013 at reefs near Sesoko Island, Okinawa, Japan (26°38′N, 127°52′E). After foraging, S. tubifer aggregated in groups among the spines of the longspine sea urchin, Diadema setosum, and the banded sea urchin, Echinothrix calamaris. A preference for D. setosum was evident (P < 0.001), especially by larger individuals (>25 mm standard length, P < 0.01), and choice experiments demonstrated the ability of S. tubifer to recognize and orient to a host urchin and to conspecifics. Tagging studies revealed that S. tubifer exhibits daily fidelity to a host urchin; 43–50 and 26–37 % of tagged individuals were associated with the same urchin after 3 and 7 days. Tagged fish also returned to their site of origin after displacement; by day two, 23–43 and 27–33 % of tagged individuals returned from displacement distances of 1 and 2 km. These results suggest that S. tubifer uses various environmental cues for homing and site fidelity; similar behaviors and cues might be used by larvae for recruitment to settlement sites and for the acquisition of luminous symbiotic bacteria.     

Diet, movement, and covering behavior of the sea urchin Toxopneustes roseus in rhodolith beds in the Gulf of California, México

The density, diet, movement, and covering behavior of Toxopneustes roseus (Agassiz) were investigated in rhodolith beds in the Gulf of California. Densities varied from a mean of 0.4 to 1.8/20 m² with most urchins occurring in aggregations. Spatial patterns of urchins varied with depth, with greatest abundance at intermediate depths (7.5–9.4 m) in the middle of the rhodolith bed. Urchins ate rhodoliths and nongeniculate coralline algal crusts almost exclusively, despite the availability of other algae. The mean amounts ingested were 3.87 and 7.96 g carbonate/individual per day. Even when food was abundant, animals were highly mobile, moving an average of 6.6–11.7 cm/h depending on site and time of day. Diel movement may be a behavioral adaptation to avoid surge, which is greatest during the day. Covering behavior may also be related to surge, as the ratio of covering material:body weight and the percent cover of material held were highest at the site with the most surge. While an urchin consumed rhodoliths, its movement spread the grazing impact over large areas. Bioturbation resulting from urchin feeding, movement, and covering activity probably benefits the rhodoliths by turning them, which maintains rhodolith integrity, prevents fouling, and contributes to bed persistence. Received: 22 February 1999 / Accepted: 3 July 2000     

Quantifying behavioural determinants of the coastal European sea-urchin Paracentrotus lividus

Field observations of covering (placement of objects on upper surface) and migration (movement between upper and lower rock surfaces) by the sea urchin, Paracentrotus lividus (Echinodermata: Echinoidea), were conducted at Lough Hyne, Ireland. Numerous hypotheses have been proposed to explain such behaviour in echinoids but have failed to consider the importance of multiple abiotic and biotic factors. Our study aimed to quantify the influence of interacting variables upon both behaviours in P. lividus using log-linear analysis. Our resultant model ranked the factors influential in covering behaviour as follows: (1) availability of covering item; (2) migratory behaviour; (3) size of P. lividus; (4) time of day; (5) time of year; and (6) predation intensity. The same variables were ranked differently in terms of their importance to the migratory behaviour of P. lividus. Moreover, the model showed, for the first time, an unequivocal relationship between covering and migration . Covering was mostly restricted to upper-rock-surface individuals, and therefore daylight periods, and was most intense in summer. This supports the theory that echinoids may cover to avoid over-exposure to light. We also conclude that rock upper surfaces are important as the principal source of food; lower surfaces may provide refuges from predators, with migration between these surfaces as a result. Certain individuals become too large to fit in boulder interstices and therefore incapable of migration to lower surfaces, whereas small individuals rarely migrate to upper surfaces. Models such as these provide a baseline for understanding the relative importance and interrelationship of factors of complex behaviour.