Sexual reproduction and settlement of the coral reef spongeChalinula sp. from the Red Sea

Characteristics of the sexual reproduction and larval settlement of the haplosclerid spongeChalinula sp., which inhabits the shallow waters (1 to 6 m) of Eilat, Red Sea, were investigated from September 1985 through to November 1987. This species was found to be a simultaneous hermaphroditic brooder, hence gonochorism is not the rule in the order Haplosclerida. Brooding always takes place in special brooding chambers. While the oocytes in the brooding chambers are among the largest known in sponges (355±37µm), the spermatic cysts distributed in the choanosome are among the smallest known for this phylum (average 26±7µm).Chalinula sp. breeds throughout the year and in experiments most larvae (74%) settled within 1 to 8 h post-release, generally within 4.5 h. Metamorphosis from larval shape to a sessile sponge lasts 1 to 6 h. Thus, larvae had a short swimming period, settled fast, and metamorphosed rapidly (within 1 to 6 h). The large size of the larvae may contribute to their ability to rapidly reorganize their body shape into that of a sessile sponge. In addition, the existence of already differentiated choanocyte chambers in the larvae, facilitates fast construction of the water filtration system in the newly settled sponges. The reproductive and larval characteristics ofChalinula sp. enable the larvae to settle on any vacant space in the reef, which may explain its abundance in the Red Sea.     

Glycohistochemistry of a marine sponge, Chondrilla nucula (Porifera, Desmospongiae), with remarks on a possibly related antimicrobial defense strategy and a note on exopinacoderm function

Based on carbohydrate histochemistry, including the use of lectins, and TEM, the study describes the distribution of terminal sugars in different structures of the demosponge Chondrilla nucula. The results of the general and specific carbohydrate histochemical approaches confirmed the presence of acidic and neutral glycoconjugates in the cells, and, with declining amounts from the ectosome to the mesohyl, in the extracellular matrix (ECM). AB-PAS staining indicated acidic complex carbohydrates particularly in the exopinacoderm, and more neutral ones in the cells and the ECM of the mesohyl. The PO-lectins applied demonstrated a general spectrum of free saccharide residues (α-d-mannose, α-/β-d-N-acetylglucosamine, α-d-N-acetylgalactosamine, α-d-galactose, β-d-galactose) in both sponge parts; α-l-fucose was only distinct in the ectosome. Sialic acids [siaα(2,3)-galactose, siaα(2,6)-N-acetylgalactosamine] were dominant in the very thin exopinacoderm, indicating O-linked high molecular weight glycoproteins. In this way a glycophysiologically ‘rigid’ outer mucus cover is developed as protection against mechanical hazards. Some of the free sugars (α-d-mannose, N-acetylglucosamine, N-acetylgalactosamine β-d-galactose, α-l-fucose) are known to prevent the adherence of different bacteria and fungi to cellular surfaces. Thus a high concentration of such sugars, may impede massive attacks of micro-inhabitants on mobile sponge cells, pinacocytes, and the exopinacoderm layer.     

Rapid tissue reduction and recovery in the sponge Aplysinella sp.

We observed a pronounced, yet reversible tissue reduction in the tropical sponge Aplysinella sp. under non-experimental conditions in its natural habitat, after transfer into seawater tanks, as well as after transplantation from deep to shallow water in the field. Tissue reduction resulted in the formation of small “reduction bodies” tightly attached to the sponge skeleton. Although volume loss and gain were substantial, both tissue reduction and regeneration were often remarkably rapid, occurring within few hours. Microscopic analysis of the reduction bodies revealed morphological similarities to previously described sponge primmorphs, with densely packed archaeocytes and spherulous cells enclosed by a thin layer of epithelial-like cells. Denaturing gradient gel electrophoresis (DGGE) revealed pronounced changes in the sponge-associated microbial community upon tissue reduction during laboratory and field experiments and following changes in ambient conditions after transplantation in the field. Generally, the microbial community associated with this sponge proved less stable, less abundant, and less diverse than those of other, previously investigated Verongid sponges. However, one single phylotype was consistently present in DGGE profiles of Aplysinella sp. This phylotype clustered with γ-proteobacterial sequences found previously in other sponge species of different taxonomic affiliations and geographic provenances, as well as in sponge larvae. No apparent changes in the total secondary metabolite content (per dry weight) occurred in Aplysinella sp. upon tissue reduction; however, comparative analysis of intact and reduced tissue suggested changes in the concentrations of two minor compounds. Besides being ecologically interesting, the tissue reduction phenomenon in Aplysinella sp. provides an experimentally manipulable system for studies on sponge/microbe symbioses. Moreover, it may prove useful as a model system to investigate molecular mechanisms of basic Metazoan traits in vivo, complementing the in vitro sponge primmorph system currently used in this context.     

Rapid tissue reduction and recovery in the sponge <Emphasis Type="Italic">Aplysinella</Emphasis> sp.

We observed a pronounced, yet reversible tissue reduction in the tropical sponge Aplysinella sp. under non-experimental conditions in its natural habitat, after transfer into seawater tanks, as well as after transplantation from deep to shallow water in the field. Tissue reduction resulted in the formation of small “reduction bodies” tightly attached to the sponge skeleton. Although volume loss and gain were substantial, both tissue reduction and regeneration were often remarkably rapid, occurring within few hours. Microscopic analysis of the reduction bodies revealed morphological similarities to previously described sponge primmorphs, with densely packed archaeocytes and spherulous cells enclosed by a thin layer of epithelial-like cells. Denaturing gradient gel electrophoresis (DGGE) revealed pronounced changes in the sponge-associated microbial community upon tissue reduction during laboratory and field experiments and following changes in ambient conditions after transplantation in the field. Generally, the microbial community associated with this sponge proved less stable, less abundant, and less diverse than those of other, previously investigated Verongid sponges. However, one single phylotype was consistently present in DGGE profiles of Aplysinella sp. This phylotype clustered with γ-proteobacterial sequences found previously in other sponge species of different taxonomic affiliations and geographic provenances, as well as in sponge larvae. No apparent changes in the total secondary metabolite content (per dry weight) occurred in Aplysinella sp. upon tissue reduction; however, comparative analysis of intact and reduced tissue suggested changes in the concentrations of two minor compounds. Besides being ecologically interesting, the tissue reduction phenomenon in Aplysinella sp. provides an experimentally manipulable system for studies on sponge/microbe symbioses. Moreover, it may prove useful as a model system to investigate molecular mechanisms of basic Metazoan traits in vivo, complementing the in vitro sponge primmorph system currently used in this context.     

Recurrent disease outbreaks in corneous demosponges of the genus Ircinia: epidemic incidence and defense mechanisms

During 2008 and 2009, an epidemic affected sponges of the genus Ircinia in the Western Mediterranean. Investigations at a site on the European coast (6o43′08.80′′N; 3o43′52.20′′W) and another on the African coast (35o10′51.00′′N; 2o25′33.00′′W) revealed healthier African populations. The disease started with small pustules on the sponge surface, which subsequently coalesced forming larger, extensive lesions. An ultrastructural study suggested that a twisted rod is the etiological agent. It infected the sponges from the outside, initially killing the cells below the ectosome and then penetrating deeper into the body. The sponges responded to the bacterial progression by secreting concentric barriers of collagen and concentrating phagocytic cells at the diseased zones. This primitive immune system successfully resisted the disease in many instances, although mortality reached 27% in the studied populations. Epidemic outbreaks recur each year in September through November, arguably favored by abnormally high seawater temperatures in August.     

Trends in space occupation by the encrusting sponge Crambe crambe: variation in shape as a function of size and environment

The relationship between sponge size, habitat and shape was studied in the encrusting sponge Crambe crambe (Schmidt, 1862), which is distributed widely throughout the shallow Mediterranean littoral. Examination of sponge patches in shaded and well-illuminated habitats showed that the degree of peripheral irregularity of the edges of a patch is directly related to patch size. This relationship is valid only for sponges of >100 mm² in area. Photophilic and sciaphilous sponges display different growth forms. The pattern of growth is interpreted in terms of competition for space. The directional growth of sciaphilous sponges may be due to the presence of dominant neighbours that are good space competitors, and the irregular growth of photophilic sponges to the absence of such neighbours.     

Changes in morphology and physiology of an East Mediterranean sponge in different habitats

The sponge Tetilla sp. (Tetractinomorpha: Tetillidae) is a common species in the eastern Mediterranean. This sponge inhabits four different habitat types differing in wave impact and irradiance levels. Two of these habitats (a shallow cave and deep water) are characterized by relatively calm water, whereas the other two (shallow exposed site and tide pools) are in turbulent water with high energy flow. The present study examined the influence of physical (depth, illumination and water motion) and biotic factors on morphology, skeletal plasticity and reproductive traits among the four spatially separated populations. Sponges from tidal pools had significantly larger body volume than sponges from deep water and from shallow caves (ANOVA: tidal-deep P<0.0001; tidal-shallow caves P<0.05). Sponges from exposed habitats were significantly larger than deep-water sponges (ANOVA: P=0.01). In addition, individuals from tide pools and from the exposed habitat had a significantly higher proportion of structural silica than sponges from the calmer deep water and from the cave sites. Oxea spicules in sponges from the calm habitats were significantly shorter than in those from the tidal pools and the exposed habitats. The percentage of spicules out of a sponges dry weight in individuals transplanted from deep (calm) to shallow (turbulent) water significantly increased by 21.9±12.9%. The new spicule percentage did not differ significantly from that of sponges originally from shallow water. Oocyte diameter differed significantly between habitats. The maximal size of mature eggs was found in deep-water sponges in June (97±5 m). In the shallow habitats, a smaller maximal oocyte diameter was found in the cave, in May (56.5±3 m). Furthermore, oocyte density in shallow-water sponges was highest in May and decreased in June (with 88.2±9 and 19.3±9 oocytes mm^–2, respectively). At the same time (June), oocyte density of deep-water sponges had just reached its maximum (155±33.7 oocytes mm^–2). The difference in oocyte size and density between deep- and shallow-water individuals indicates an earlier gamete release in the shallow sponge population. The results suggest that plasticity in skeletal design of this sponge indicates a trade off between spicule production and investment in reproduction.Communicated by O. Kinne, Oldendorf/Luhe     

Investigation of the relationship between invertebrate predation and biochemical composition,energy content,spicule armament and toxicity of benthic sponges at McMurdo Sound,Antarctica

The biochemical and energetic composition, spicule content, and toxicity of benthic sponges was investigated in McMurdo Sound, Antarctica from October through December 1984. The predominant organic constituent of sponges was soluble and insoluble protein. Levels of total protein ranged from 17.0 to 55.9% dr. wt. Levels of lipid and carbohydrate were low, ranging from 2.1 to 9.6 and 0.6 to 3.5% dr. wt, respectively. Levels of ash were high and variable (32 t0 79% dr. wt), reflecting species-specific differences in spicule contents. Calculated energy contents of sponges were low, with a mean of 9.8±3.5 kJ g^-1 dr. wt; ranging from 5.1 kJ g^-1 dr. wt in Sphaerotylus antarcticus to 17.4 kJ g^-1 dr. wt in Dendrilla membranosa. Insoluble protein accounted for the greatest contribution to the energetic composition of the sponges, while lipid and carbohydrate combined contributed to less than 25% of the overall energy. Normalized spicule volumes of sponges ranged from 0.15 to 0.38 cm³ g^-1 dr. wt. Ichthyotoxicity assays indicated that 9 (56%) of 16 antarctic sponge species were toxic. The most highly toxic species were Mycale acerata and Leucetta leptorhapsis. The high incidence of toxicity in antarctic sponges indicates that the current hypothesis suggesting a simple inverse relationship between toxicity and latitude in marine sponges is invalid. There was little correspondence between the energetic composition or spicule contents of the sponges and feeding patterns (electivity indices) of sponge-eating predators. Although the asteroid Perknaster fuscus antarcticus specializes on the highly toxic, fast-growing M. acerata, most antarctic sponge-eating predators appear to be generalists which feed on the more abundant, non- to mildly-toxic, sponge species. This feeding strategy is based on exploitation of low energy, sedentary prey, which require a minimal energy output to harvest.     

Protein binding of iron in blood plasma of the ascidian Herdmania momus

Blood of the ascidian Herdmania momus var. grandii (Kott, 1952) has typically a low cell haematocrit volume, <1% with a cell density of 12 000 to 15 000 cells mm^-3. Non-dialysable solids in the plasma are 105±10 mg%. Iron-binding in the plasma has been investigated by fractionation of ⁵⁹Fe-labelled plasma, using gel chromatography and electrophoretic procedures. Three fractions, identified as I, II and III in the order of their elution from a G-150 column, bind ⁵⁹Fe in the ratio 60:15:15. The dominant fraction, I, was shown by electrophoresis on polyacrylamide gels to consist of two components in the ratio of ca. 80:20 and with similar electrophoretic mobilities. Dissociation of Fraction I by mercaptoethanol and sodium dodecyl sulfate gave on electrophoresis three components of molecular weights 17 000; 32 000 and 66 000. Fraction 1 contained 10% carbohydrate by weight as determined by the -cysteine/sulphuric acid assay. These data are compared with other iron-binding systems such as transferrin and the siderophores. Phylogenetic aspects of the study are also discussed.     

Evidence for a symbiosis between bacteria of the genus Rhodobacter and the marine sponge Halichondria panicea : harbor also for putatively toxic bacteria?

Halichondria panicea (Pallas) is a marine sponge, abundantly occurring in the Adriatic Sea, North Sea, and Baltic Sea. It was the aim of the present study to investigate if this sponge species harbors bacteria. Cross sections through H. panicea were taken and inspected by electron microscopy. The micrographs showed that this sponge species is colonized by bacteria in its mesohyl compartment. To identify the bacteria, polymerase chain reaction (PCR) analysis of the 16S rRNA gene segment, typical for bacteria, was performed. DNA was isolated from sponge material that had been collected near Rovinj (Adriatic Sea), Helgoland (North Sea), and Kiel (Baltic Sea) and was amplified with bacterial primers by PCR. The data gathered indicate that in all samples bacteria belonging to the genus Rhodobacter (Proteobacteria, subdivision α) are dominant, suggesting that these bacteria live in symbiotic relationship with the sponge. In addition, the results show that the different samples taken contain further bacterial species, some of them belonging to the same genus even though found in sponges from different locations. The possibility of the presence of toxic bacteria was supported by the finding that organic extracts prepared from sponge samples displayed toxicity, when analyzed in vitro using leukemia cells. Received: 7 March 1997 / Accepted: 2 October 1997     

Ecology of toxicity in marine sponges

An investigation of the ecology of toxicity in marine sponges from different latitudes on the North American continent was made. Results indicated that toxicity in sponges increased with decreasing latitude. Three of the 34 species (9%) of sponges from San Juan Island, Washington, USA (48°N), were toxic to fishes. Nine of the 44 species (20%) of sponges from Santa Catalina Island, California, USA (33°N), were toxic. Seven of the 11 species (64%) of sponges from Zihuatanejo Bay, Guerrero, México (17°N), were toxic. Twenty-seven of the 36 species (75%) of sponges from La Blanquilla, Veracruz, México (19°N), were toxic. Most of these toxic sponges are openly exposed to fishes. The most common exposed sponges proved to be highly toxic to fishes. Force-feeding experiments conducted with wrasses demonstrated the effectiveness of the toxin of sponges. A hypothesis is proposed which explains the relationship between species diversity of fishes and sponge toxicity with latitude.     

Low levels of genetic variation in mtDNA sequences over the western Mediterranean and Atlantic range of the sponge<Emphasis Type="Italic"> Crambe crambe</Emphasis> (Poecilosclerida)

Crambe crambe is a common encrusting sponge found in the Mediterranean and Atlantic littoral. An analysis of a partial sequence (535 bp) of the mitochondrial DNA (mtDNA) gene cytochrome oxidase subunit I (COI) was conducted in an attempt to determine population structure in this species. This is the first study of population genetics using this kind of marker in the phylum. Samples (N=86) were taken in eight populations separated by distances from 20 to 3,000 km, spanning from the western Mediterranean to the Atlantic. Low variability of this gene was found, as only two haplotypes were identified, along with low nucleotide diversity (=0.0006). However, the different frequencies found among populations revealed genetic structure and low gene flow between close populations, as expected from the dispersal biology of the species. The low variability found in sponges is in agreement with reports on cnidarians and points to a high conservation of mtDNA in diploblastic phyla.     

Superoxide production by marine microalgae

This study investigated the possible roles of superoxide produced by raphidophyte and prymnesiophyte microalgae as an ichthyotoxic agent to damselfish and an allelopathic agent to bacteria. We found that the rate of superoxide production varied with algal cell density, with cell densities of the raphidophyte Chattonella marina >10,000 cells ml^–1 producing less environmental levels of superoxide per cell (94±14 chemiluminescence units) than cell densities <10,000 cells=">^–1 (390±54 units per cell). Microalgal cells have the capacity to change their superoxide production rate over a period of 1 h, dependent on cell density and metabolic activity. We also examined the effect of superoxide on suppression of bioluminescence of the marine bacterium Vibrio fischeri as a model for bacterial alleopathy and found that both superoxide and free fatty acids such as eicosapentaenoic acid (EPA; 20:53) present in raphidophyte microalgal cells cause suppression of bacterial bioluminescence. The combination of superoxide in the presence of EPA further enhanced bioluminescence suppression. Superoxide was also found to enhance the toxicity of free fatty acid EPA to damselfish (Acanthochromis polycanthus) at concentrations as low as 0.2 mg l^–1. In conclusion, consideration should be given to density dependent and/or metabolic variations of toxicity when publishing minimum alert levels for superoxide producing ichthyotoxic microalgal species. A secondary role of superoxide production may be to enhance the toxicity of algal exudates or serve as an allelopathic agent against bacterial fouling.     

Microbial associations in sponges. III. Ultrastructure of the in situ associations in coral reef sponges

Symbiotic cyanobacteria are associated with marine sponges in three ways: the majority are free-living in the mesohyl; large aggregates occur in cyanocytes (specialized, vacuolated archeocytes); and few are present in digestive vacuoles. The cyanobacteria in Jaspis stellifera and Neofibularia irata are morphologically similar to those described in Mediterranean sponges, whereas those in Pericharax heteroraphis are different. The freeliving bacterial populations are morphologically similar, although the number of bacteria varies between the species. The fourth sponge Ircinia wistarii contains a mixed bacterial population unlike those in the other sponges. Sponge digestion of microbial associates is rare and not considered to contribute significant nutrients.     

Leatherback turtles as oceanographic indicators: stable isotope analyses reveal a trophic dichotomy between ocean basins

Oceanographic sampling is often limited to local and temporally concise assessments of complex, transient, and widespread phenomena. However, long-lived, migratory pelagic vertebrates such as leatherback turtles (Dermochelys coriacea, Vandelli 1761) can provide important integrated information about broad-scale oceanographic processes. Therefore, the present study analyzed stable carbon and nitrogen isotope ratios (δ¹³C and δ¹⁵N) of egg yolk and red blood cells from nesting leatherback populations from Costa Rica in the eastern Pacific in 2003–2004 and 2004–2005 and from St. Croix in the North Atlantic in 2004 and 2005 to establish differences between nutrient sourcing and its influence on higher trophic level consumers in both ocean basins. Whereas δ¹³C signatures were similar between Costa Rica (−19.1±0.7‰) and St. Croix (−19.4±1.0‰) leatherbacks, reflecting the pelagic foraging strategy of the species, Costa Rica leatherback δ¹⁵N signatures (15.4±1.8‰) were significantly enriched relative to St. Croix leatherback δ¹⁵N signatures (9.8±1.5‰). This δ¹⁵N difference likely reflects inter-basin differences in nitrogen cycling regimes and their influence on primary productivity being transferred through several trophic levels. Thus, high-order marine consumer movements, habitat preferences, and stable isotope signatures can be combined with ocean sampling to elucidate interactions between oceanographic processes and marine megafauna.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Effects of sediment on the survival of asexually produced sponge recruits

Sediment deposition is known to affect the structure of marine rocky-bottom communities, but its specific effects on some key organisms, such as sponges, remain poorly investigated. In a 125-day field experiment involving different treatments of exposure to sediment deposition, we investigated survival of asexually produced recruits of the sublittoral demosponge Scopalina lophyropoda, a model organism suitable to understand similar processes in other sponges. A total of 660 explants obtained from 11 non-clonal sponges (explant donors) were distributed on 30 experimental plates. Each donor sponge contributed two clonal explants per plate, one settled under a roof at a silt-protected position and the other at a silt-exposed position. Plates were installed at the rocky walls of the natural community, also at the pillars of a local harbor where the sponge does not occur naturally. A 3-way ANOVA testing for differences in explant longevity as a function of explant donor, exposure to sediment, and habitat detected that longevity was affected by both an undetermined genetic condition of the explant donor and exposure to silt. Silt-protected explants lived longer than silt-exposed explants. A significant “Silt-exposure × Habitat” interaction detected that silt-exposed explants lived shorter within the harbor than in the natural community, suggesting that harbor silt, which was notably finer, is more deleterious. Inspection of daily mortality rates revealed that the detrimental effects of silt were very evident during the first 20 days in treatments and irrespective of habitat. Then, mortality rates progressively decreased, reaching negligible values in all 4 sponge groups by day 65. At this stage, an undetermined mortality factor other than purely sediment deposition reactivated mortality in all 4 sponge groups, but it affected more intensely the sponges in the harbor, irrespective of being protected from or exposed to sediment deposition. All together, the results of our field experiment suggest that sediment loads are a major mortality factor among small sponge individuals in sublittoral rocky communities. Because a significant “donor factor” suggests an unidentified “genetic component” to be involved in the ability to cope with sediment, natural or man-driven processes increasing coastal sediment deposition are susceptible to induce changes not only in the abundance but also the genetic structure of the sponge populations in the long term.     

Temperature influences muscle differentiation and the relative timing of organogenesis in herring (Clupea harengus) larvae

Eggs from spring spawning stocks of herring (Clupea harengus L.) were fertilized and reared at either 5, 8 or 12°C in 1991 and 1992. The differentiation of myotomal muscle fibres was investigated in relation to the development of other organs and tissues using light and electron microscopy. The gut, notochord, eyes and haemocoel appeared at the same relative point in development between fertilization and hatching at all temperatures. In contrast, the formation of the spinal cord, pronephros, pectoral fin buds and muscle fibres was relatively retarded at 5°C compared with 8 and 12°C. Myogenesis in the presumptive inner muscle mass occurred after 12 to 16 d at 5°C, 7 to 10 d at 8°C and 3.5 to 6 d at 12°C. Myoblasts aligned in orderly rows running from myosept to myosept prior to fusion to form myotubes. Actin and myosin filaments were synthesised throughout the cytoplasm in associated with presumptive Z-lines at the periphery of myotubes and immature muscle fibres. Differentiation of the superficial and inner muscle fibres types of larvae occurred at around the same time. Following this initial period of myogenesis, the number of myotomal muscle fibres remained constant until after hatching, so that increases in muscle bulk in the late embryo were entirely due to fibre hypertrophy. At hatching, the number of superficial muscle fibres present in myotomes just posterior to the yolk-sac was significantly less at 5°C (108±12) than at either 8°C (132±10) or 12°C (140±10) (mean±SD, 12 fish/temperature). In contrast, there were around 280 inner muscle fibres/myotome, comprising 90% of the trunk cross-sectional area, at all three temperatures. Myofibrillargenesis occurred relatively slowly at low temperatures, so that the volume density of myofibrils in the inner muscle fibres of larvae at hatching was significantly less at 5°C (39.2±9.0) than at either 8°C (49.6±8.8) or 12°C (50.2±9.8) (mean ±SD, 20 fibres/temperature from total of 5 fish). Undifferentiated myoblasts remained at hatching to form a population of presumptive myosatellite cells. The number of presumptive myosatellite cells per mm² cross-sectional area of muscle fibre was more than two times higher at 8°C (1493±335) than at either 5°C (478±102) or 12°C (924±233) (mean±SD, 5 fish/temperature). The results suggest that temperature can influence the commitment of myoblasts to differentiation at a critical stage in embryogenesis, thereby providing a potential mechanism for influencing future growth characteristics. Correspondence to: I.A. Johnston at Gatty Marine Laboratory     

Distribution of tetrodotoxin in various organs of the starfish Astropecten polyacanthus

Tissues of various organs of the starfish Astropecten polyacanthus collected in the Hiroshima Prefecture from April 1985 to June 1986 were analyzed for lethal potency by the assay method for tetrodotoxin. The ovary showed the highest potency (47 to 1 450 MU g^-1), followed by the digestive organs (<10 to 960 MU g^-1) and the exoskeleton including spines and tube-feet (<10 to 170 MU g^-1). The pyloric caecum and testis were less toxic. Overall toxicity was remarkably higher in females (2 060±382 MU, mean±SE) than in males (1 106±214 MU).     

Incidental capture,direct mortality and delayed mortality of sea turtles in Australia's Northern Prawn Fishery

The species composition, catch and mortality rates of sea turtles captured incidentally by the tiger prawn fishery on Australia's northern coast in 1989 and 1990 were estimated by monitoring the fishery's catch. In 1990, the delayed rate of mortality from damage was estimated and the size composition was measured. Five species of turtles were captured: the flatback (Natator depressa, 59% of the total), loggerhead (Caretta caretta, 10%), olive ridley (Lepidochelys olivacea, 12%), green turtle (Chelonia mydas, 8%) and hawksbill (Eretmochelys imbricata, 5%). The turtle catches varied with water depth: the highest catch rates (0.068±0.006 turtles per trawl) were from trawls in water between 20 and 30 m deep, relatively few turtles (10%) were captured in water deeper than 40 m (25% of trawls). Catch rates varied with time of year: the highest catch rates were 0.098 (±0.013) turtles per trawl in winter. There was no significant difference in the overall catch rate (²= 0.047; p=0.8111; df=1) but a significant difference in mortality rate (²= 3.99; p<0.05; df=1) between the two years. The incidence of capture in the commercial fishery was 0.051 (±0.003) turtles per trawl towed for about 180 min, with 0.007 (±0.001) turtles per trawl drowning in the nets. There were no significant differences in the catch and mortality rates between the two years for any of the turtle species except the loggerhead, which had a significantly (² = 11.029; p=0.0013; df=1) lower catch rate in 1990 (0.002±0.001 turtles per trawl) than in 1989 (0.008±0.002 turtles per trawl), and a significantly higher mortality in 1990 (33%) than in 1989 (19%). Catch rates and mortality varied between the species: the flatback had the highest catch rate (0.030±0.002 turtles per trawl) but the lowest mortality (10.9%); the loggerhead had a catch rate of 0.005±0.001 turtles per trawl, and high mortality (21.9%); the olive ridley had a catch rate of 0.006±0.001 turtles per trawl and a low mortality (12.5%); the green turtle's catch rate was 0.004±0.001 per trawl and mortality 12.0%; the hawksbill had the lowest catch rate (0.002±0.001 turtles per trawl) but highest mortality (26.4%). Based on the fishing effort (27 049 d for 1989 and 25 746 d for 1990), we estimate that 5 503 (±424) turtles were caught and returned to the sea in 1989 and 5 238 (±404) in 1990, of which 567±140 drowned in 1989 and 943±187 in 1990. In 1990, an estimated 25% of all captured turtles suffered some non-lethal damage; an estimated 21% of turltes were captured comatose and 4% were injured. We conclude that, considering other threats, trawl-induced drowning is not the major impact on turtle populations in northern Australia, but that measures to reduce drowning and delayed mortality would be desirable.     

Innovative substrate tiles to spatially control larval settlement in coral culture

We designed settlement tiles for coral culture with the aims: (1) to attract and (2) to spatially control settlement and (3) to produce substrate units for further handling in mariculture. Ceramic tiles with vertical (i.e. pyramid tile; truncated pyramid shape, 22.0×22.0, ±1.0 mm, L×W) and horizontal surfaces (i.e. flat tile; 17.0×17.0, ±1.0 mm, L×W) were temporarily arranged chessboard-like in a polystyrene grid. Surfaces of both types were structured with grooves (width and depth 2.0±0.1 mm). Material analysis by ICP and photospectrometry showed negative influences on water chemistry when new tiles were directly used; high contents of heavy metals could be detected depending on the production process. Planulae of Acropora tenuis (16.3±3.1% settlement) preferred to settle in the grooves of pyramid tiles with a density of 0.19±0.03 to 0.44±0.06 settlers cm^–2, whereas those of Favia fragum (60.7±13.3% settlement) showed high preferences for the grooves of flat tiles (0.48±0.22 to 1.05±0.44 settlers cm^–2). Settlement occurred exclusively on surfaces with a biofilm (turf and crustose coralline algae) and was independent of available substrate surface area, whereas the number of tiles per set-up influenced the density of settlers per unit. Spatial control of settlement was achieved through tile design and arrangement. Tiles with settlers could be easily separated for further use in coral culture.Communicated by O. Kinne, Oldendorf/Luhe