Origin of the antitropical distribution pattern in marine mussels (Mytilus spp.): routes and timing of transequatorial migration

Many marine species, including mussels in the Mytilus edulis species group (i.e. M. edulis L., M. galloprovincialis Lamarck, and M. trossulus Gould), have an antitropical distribution pattern, with closely related taxa occurring in high latitudes of the northern and southern hemispheres but being absent from the tropics. We tested four hypotheses to explain the timing and route of transequatorial migration by species with antitropical distributions. These hypotheses yield different predictions for the phylogenetic relationship of southern hemisphere taxa relative to their northern counter-parts. The three Mytilus species were used to test these hypotheses since they exhibit a typical antitropical distribution and representative taxa occur in both the Pacific and Atlantic. Two types of mtDNA lineages were found among populations of mussels collected from the southern hemisphere between 1988 and 1996; over 90% of the mtDNA lineages formed a distinct subclade which, on average, had 1.4% divergence from haplotypes found exclusively in northern Atlantic populations of M. galloprovincialis. These data indicate that southern hemisphere mussels arose from a migration event from the northern hemisphere during the Pleistocene via an Atlantic route. The remainder of the southern hemisphere lineages (<10%) were very closely related to mtDNA haplotypes found in both M. edulis and M. galloprovincialis in the northern hemisphere, suggesting a second, more recent migration to the southern hemisphere. There was no evidence that southern hemisphere mussels arose from Pacific populations of mussels. Received: 8 December 1998 / Accepted: 8 November 1999     

Spatial segregation amongst goby species within an Australian estuary,with a comparison of the diets and salinity tolerance of the two most abundant species

The present study was undertaken to determine whether the various species of gobies that are found within the large Swan Estuary in south-western Australia are segregated within that system, and to attempt to determine the basis for any differences in their spatial distributions. The Swan Estuary comprises a long entrance channel (lower estuary), two wide basins (middle estuary) and the saline reaches of the tributary rivers (upper estuary). A total of 26232 gobies, representing seven species, was collected using a 3 mm-mesh seine net at 15 sites throughout this estuary on at least one occasion monthly over seven consecutive seasons between September 1983 and March 1985. Favonigobius lateralis and Pseudogobius olorum contributed 47.0 and 47.8%, respectively, to the total catch of gobies at all sites. The densities of each species at each site were used to determine the relative contribution of each species to the gobiid fauna at each of the sites in the lower, middle and upper estuary. Comparisons of these data with those published on the distribution and abundance of gobiid larvae confirmed that F. lateralis, which was found predominantly in the lower estuary, is a marine species that spawns in high salinities near the estuary mouth or in inshore coastal waters. In contrast, the life cycle of P. olorum and Papillogobius punctatus are typically completed within the saline reaches of the upper estuary, and that of Arenigobius bifrenatus within both this region and parts of the middle estuary where the substrate is particularly soft. Afurcagobius suppositus also spawns in this area, as well as in fresh water. Tridentiger trigonocephalus, represented by only eight individuals, is an introduced, marine species that was found mainly in the lower estuary. A single representative of the marine species Callogobius depressus was caught. The relatively low numbers of gobies caught in the middle estuary, where they contributed only about 3.5% to the total number of all gobies at all sites, may represent an aversion to the presence of rougher waters in the large basins. Circumstantial evidence suggests that the sandy substrate and consistently high salinities found in the lower estuary are preferred by F. lateralis, whereas the silty surface to the substrate and lower salinities of the upper estuary are preferred by Pseudogobius olorum. Densities of three of the four most abundant species were higher in either spring or summer than in winter, reflecting the influx of 0 + recruits, and possibly also the tendency for species in estuaries to congregate in the shallows during the warmer periods of the year. F. lateralis fed mainly on polychaetes and crustaceans, whereas P. olorum ingested predominantly algae, reflecting differences in mouth morphology and feeding behaviour, rather than the type of food available.     

Temperature tolerance of embryos and larvae of five bivalve species under simulated power plant entrainment conditions: a synthesis

Upwelling effects of subsurface water on phytoplankton growth were evaluated by 9 simulated culture experiments of coastal upwelling. Particular attention was paid to the effects of nutrient enrichment on the surface phytoplankton by the upwelling of nutrient rich subsurface water and of the exposure of the subsurface phytoplankters to surface radiation. The following are the results obtained: the lag period of phytoplankton growth was inversely related to water temperature; the maximum yield of phytoplankton was proportional to the amounts of available initial nutrients; the specific growth rates of phytoplankton were a function of both the initial nutrient concentrations and water temperature; and the maximum specific growth rate was simply proportional to water temperature. According to the relations found, a simple equation is presented for the estimation of phytoplankton growth in a given upwelling. Succession of species in the phytoplankton assemblage in upwelled water mass was also taken into consideration.     

Interactions between two species of marine diatoms: Effects on their individual copper tolerance

The purpose of this study was to examine the effect of the interaction of two species of marine diatoms,Skeletonema costatum (Cleve) Greville andNitzschia thermalis (Ehrenberg) Auerswald, on their individual copper tolerances. The two species, obtained from stock cultures in 1989, were grown together at three copper concentrations (1, 4 and 5 × 10^–7 M added total copper). In the unialgal cultures that were used as controls, the two species grew as predicted from their tolerance tests. However, in mixed cultures,N. thermalis was the only species that exhibited growth, regardless of the copper concentration in the medium. Growth retardation ofS. costatum in the presence ofN. thermalis was attributed to an inhibitory exudate. The effect of the exudate appeared to have been temporary, as demonstrated by the extended lag phase and subsequent satisfactory exponential growth rate ofS. costatum. It is suggested that the exudate degraded within a period of 5 d (=lag phase) because exponential growth rate was resumed. It thus appears that the interaction between the two diatom species is more important in determining the survival ofS. costatum than its individual copper tolerance. This is not the case forN. thermalis. Such interactions would be unaccounted for in single-species toxicity tests. On the other hand, if they are known, prediction of how a community that includes these two species would respond to copper additions becomes possible.     

Prodigiosin metabolites of a marine Pseudomonas species

The major pigment of a marine micro-organism was identified as prodigiosin on the basis of analytical and spectral data. Two minor pigments were tentatively assigned structures, from thin-layer chromatography (TLC) and mass spectral data, as prodigiosin homologs with 3-n-hexyl and 3-n-heptyl side-chains. The micro-organism was classified as a new Pseudomonas species on the basis of its morphological and biochemical characteristics. It was named Pseudomonas magnesiorubra (ATCC No. 21856).     

Yolk resorption,onset of feeding and survival potential of larvae of three tropical marine fish species reared in the hatchery

This paper provides basic early life-history information on milkfish (Chanos chanos), seabass (Lates calcarifer) and rabbitfish (Siganus guttatus) which may explain in part the observed differences in their survival performance in the hatchery. Egg size, larval size, amount of yolk and oil reserves and mouth size are all greater in milkfish than in seabass, and greater in the latter than in rabbitfish. During the first 24 h after hatching, rabbitfish larvae grow much faster than milkfish and seabass larvae at similar ambient temperatures (range 26°–30°C, mean about 28°C). The eyes become fully pigmented and the mouths open earlier in seabass and rabbitfish (32–36 h from hatching) than in milkfish (54 h). Seabass larvae learn to feed the earliest. Yolk is completely resorbed at 120 h from hatching in milkfish, and yolk plus oil at 120 h in seabass and 72 h in rabbitfish at 26° to 30°C. Milkfish and seabass larvae have more time than rabbitfish to initiate external feeding before the endogenous reserves are completely resorbed. Delayed feeding experiments showed that 50% of unfed milkfish larvae die at 78 h and all die at 150 h from hatching. Milkfish larvae fed within 54 to 78 h after hatching had improved survival times: 50% mortality occurred at 96 to 120 h, and 10 to 13% survived beyond 150 h. Unfed seabass larvae all died at 144 h, while 6 to 13% of those fed within 32 to 56 h after hatching survived beyond 144 h and well into the subsequent weeks. Unfed rabbitfish larvae all died at 88 h, while 7 to 12% of those fed within 32 to 56 h after hatching survived beyond 88 h. A delay in initial feeding of more than 24 h after eye pigmentation and opening of the mouth may be fatal for all three species.Contribution No. 167 from the SEAFDEC Aquaculture Department     

Protected species use of a coastal marine migratory corridor connecting marine protected areas

The establishment of protected corridors linking the breeding and foraging grounds of many migratory species remains deficient, particularly in the world’s oceans. For example, Australia has recently established a network of Commonwealth Marine Reserves, supplementing existing State reserves, to protect a wide range of resident and migratory marine species; however, the routes used by mobile species to access these sites are often unknown. The flatback marine turtle (Natator depressus) is endemic to the continental shelf of Australia, yet information is not available about how this species uses the marine area. We used a geospatial approach to delineate a coastal corridor from 73 adult female flatback postnesting migratory tracks from four rookeries along the north-west coast of Australia. A core corridor of 1,150 km length and 30,800 km² area was defined, of which 52 % fell within 11 reserves, leaving 48 % (of equivalent size to several Commonwealth Reserves) of the corridor outside of the reserve network. Despite limited data being available for other marine wildlife in this region, humpback whale migratory tracks overlapped with 96 % of the core corridor, while the tracks of three other species overlapped by 5–10 % (blue whales, olive ridley turtles, whale sharks). The overlap in the distribution ranges of at least 20 other marine vertebrates (dugong, cetaceans, marine turtles, sea snakes, crocodiles, sharks) with the corridor also imply potential use. In conclusion, this study provides valuable information towards proposing new locations requiring protection, as well as identifying high-priority network linkages between existing marine protected areas.     

Effects of temperature and delayed feeding on growth and survival of larvae of three species of subtropical marine fishes

In larvae of the bay anchovy Anchoa mitchilli (Valenciennes), the sea bream Archosargus rhomboidalis (Linnaeus), and the lined sole Achirus lineatus (Linnaeus), growth, survival, and starvation times were investigated at temperatures of 22° to 32°C. The rate at which hours after hatching until starvation decreased in relation to temperature for unfed larvae did not differ significantly among the 3 species, ranging from-5.4 to-6.3 h per degree increase in temperature. The total number of hours until starvation did differ for all 3 species: lined soles survived longest, bay anchovies were intermediate, and sea bream survived the least time. At 28°C, unfed sea bream could survive 90.1 h, bay anchovy 102.3 h, and lined sole 119.8 h. The eyes pigmented at nearly the same time after hatching for sea bream and bay anchovy, but took about 20 h longer at all temperatures for lined sole. Quadratic equations best described the relationship between hours after hatching when the eyes became pigmented and temperature. Eye-pigmentation times became nearly constant for all 3 species at temperatures above 28°C. At 28°C, eyes pigmented about 27 h after hatching for bay anchovy and sea bream but not until 47 h for lined sole. Hours after eye pigmentation when unfed larvae starved was a measure of the effective time that larvae had to commence feeding. Bay anchovies and lined soles were nearly alike in this respect, but sea bream starved at tewer hours after eye pigmentation. Slopes of regressions representing decrease in times to staration for increasing temperatures ranged from-3.7 to-4.4 h per degree increase in temperature, and were not significantly different among the 3 species. At 28°C, unfed lined soles starved at 70 a after eye pigmentation, bay anchovies starved at 72.5 h, and sea bream at only 62 h. Yolk absorption was most rapid for all species during the first 20 h after hatching, and was faster at higher temperatures. Amounts of yolk remaining at the time eyes became pigmented were less at higher temperatures for bay anchovy and lined sole, but were greater for sea bream, suggesting that sea bream used yolk more efficiently at higher temperatures. Either no yolk or small traces (>0.20%) remained at 24 h after eye pigmentation in all 3 species. Feeding was delayed for periods of 8, 16, 24, 32, 40 and 48 h after eye pigmentation for all species at a series of experimental temperatures from 24° to 32°C. Growth and survival were affected when food was withheld for more than 24 h at 28°C, but survival did not decrease markedly until food was withheld at least 8 h longer. At lower temperatures food could be withheld longer and at higher temperatures for less time. Feeding can be initiated by most larvae for several hours after all visible yolk reserves have been exhausted. All species tested can survive for 24 to 40 h after eye pigmentation at 24° to 28°C without food and still have relatively good growth and survival when food is offered. If the “critical period” is considered relative to time of hatching, lined soles need not find food for 3 to 3.5 days after hatching, but bay anchovy and sea bream must feed within 2.5 days of hatching.     

Marine calanoid resting eggs in Norway: Abundance and distribution of two copepod species in the sediment of an enclosed marine basin

Abundance and distribution of calanoid resting eggs in sediment were examined in 1988–1989 in an enclosed marine basin (Svartatjønn; western Norway). The basin undergoes rotenone treatment and draining every winter. Egg densities were highest in autumn, when up to 2 × 10⁶ eggs m^–2 were found, and lowest in summer. Egg densities were also highest in the deeper parts of the basin and in the upper 1 cm of sediment. Hatching was initiated in late January by pumping warmer deep water from the outside area into the basin. Evidence is given for resting-egg formation inEurytemora affinis Poppe, 1880 andAcartia clausi Gurney, 1931 (present phenotype reclassified asA. teclae by Bradford 1976: N. Z. Jl mar. Freshwat. Res. 10: 159–202). Seasonal differences in inhibition of hatching, together with the longevity and tolerance of these eggs, strongly suggest that they are diapause eggs.     

In situ ontogeny of behaviour in pelagic larvae of three temperate, marine, demersal fishes

The ontogeny of behaviour relevant to dispersal was studied in situ with reared pelagic larvae of three warm temperate, marine, demersal fishes: Argyrosomus japonicus (Sciaenidae), Acanthopagrus australis and Pagrus auratus (both Sparidae). Larvae of 5–14 mm SL were released in the sea, and their swimming speed, depth and direction were observed by divers. Behaviour differed among species, and to some extent, among locations. Swimming speed increased linearly at 0.4–2.0 cm s⁻¹ per mm size, depending on species. The sciaenid was slower than the sparids by 2–6 cm s⁻¹ at any size, but uniquely, it swam faster in a sheltered bay than in the ocean. Mean speeds were 4–10 body lengths s⁻¹. At settlement size, mean speed was 5–10 cm s⁻¹, and the best performing individuals swam up to twice the mean speed. In situ swimming speed was linearly correlated (R ²=0.72) with a laboratory measure of swimming speed (critical speed): the slope of the relationship was 0.32, but due to a non-zero intercept, overall, in situ speed was 25% of critical speed. Ontogenetic vertical migrations of several metres were found in all three species: the sciaenid and one sparid descended, whereas the other sparid ascended to the surface. Overall, 74–84% of individual larvae swam in a non-random way, and the frequency of directional individuals did not change ontogenetically. Indications of ontogenetic change in orientated swimming (i.e. the direction of non-random swimming) were found in all three species, with orientated swimming having developed in the sparids by about 8 mm. One sparid swam W (towards shore) when <10 mm, and changed direction towards NE (parallel to shore) when >10 mm. These results are consistent with limited in situ observations of settlement-stage wild larvae of the two sparids. In situ, larvae of these three species have swimming, depth determination and orientation behaviour sufficiently well developed to substantially influence dispersal trajectories for most of their pelagic period.     

Assessing the extinction risk of insular,understudied marine species

Hydrothermal vents are rare deep-sea oases that house faunal assemblages with a similar density of life as coral reefs. Only approximately 600 of these hotspots are known worldwide, most only one-third of a football field in size. With advancing development of the deep-sea mining industry, there is an urgent need to protect these unique, insular ecosystems and their specialist endemic faunas. We applied the IUCN (International Union for the Conservation of Nature) Red List criteria to assess the extinction risk of vent-endemic molluscs with varying exposure to potential deep-sea mining. We assessed 31 species from three key areas under different regulatory frameworks in the Indian, West Pacific, and Southern Oceans. Three vent mollusc species were also examined as case studies of different threat contexts (protected or not from potential mining) to explore the interaction of local regulatory frameworks and IUCN Red List category assignment. We found that these assessments were robust even when there was some uncertainty in the total range of individual species, allowing assessment of species that have only recently been named and described. For vent-endemic species, regulatory changes to area-based management can have a greater impact on IUCN Red List assessment outcomes than incorporating additional data about species distributions. Our approach revealed the most useful IUCN Red List criteria for vent-endemic species: criteria B and D2. This approach, combining regulatory framework and distribution, has the potential to rapidly gauge assessment outcomes for species in insular systems worldwide.     

The “agitator”: an inexpensive device for culturing large numbers of fragile marine invertebrate larvae

The “agitator”, a device designed for culturing lecithotrophic echinoderm larvae, is described. The unit consists of an open system which is easily constructed and is made up of a base which holds the culturing baskets as well as a lid or manifold carrying a tube which transports fresh seawater into each culture, gently stirring it and eliminating any decaying embryos. The device is scalable and water flow can be adjusted for laminar flow or slow dripping. The method has been used to successfully rear large numbers of lecithotrophic larvae of the starfish Solaster stimpsoni. The agitator could be used to culture any fragile planktonic organisms that require an extended rearing time.     

Population structure,food relations and ecological role of marine oligochaetes,with special reference to meiobenthic species

Data on abundance, biomass and biovolume demonstrate the significant ecological role of oligochaetes in the littoral marine benthos. Their numerical and productive importance is comparable to that of many other common meio-and macrofauna groups from various littoral areas. Oligochaetes often exhibit nutritional specialization (e.g. bacteria or diatoms attached to detritus or sand grains). Consequently, food supply can control their population structure and distribution. Few oligochaetes are, apparently, consumed by predators. Hence, only a small portion of their biomass is transferred to higher trophic levels, while the main part is decomposed directly. Most oligochaetes seem to represent final links of rather short food chains. Ecologically, marine oligochaetes attain major importance only in littoral areas.This investigation was supported by the Sonderforschungsbereich 94 (Meeresforschung) at the University of Hamburg.     

Vertical distribution of fish larvae in the Great Barrier Reef Lagoon,Australia

To investigate the natural defenses of Antarctic marine organisms against exposure to ultraviolet (UV) radiation (280 to 320 nm), 57 species (1 fish, 48 invertebrates, and 8 algae) were collected during austral spring 1988 in the vicinity of Palmer Station (Anvers Island, Antarctic Peninsula) and were analyzed for the presence of mycosporine-like amino acids (MAAs), compounds that absorb UV radiation and may provide shielding from these biologically hazardous wavelengths. Nearly 90% of the 57 species examined contained MAAs, and eight specific MAA compounds were identified. Seven of these (palythine, porphyra-334, shinorine, mycosporineglycine, palythene, asterina-330, and palythinol) have been observed previously in marine organisms from temperate and tropical latitudes. A new MAA, mycosporineglycine: valine, was found in the Antarctic fish and in 38 of the invertebrate species examined. This study confirms widespread occurrence of MAAs in Antarctic marine organisms and suggests that these species have some degree of natural biochemical protection from UV exposure.Contribution No. 502 from the Australian Institute of Marine Science     

Spatial distribution of bacteria associated with the marine sponge Tethya californiana

Microbial diversity and spatial distribution of the diversity within tissue of the marine sponge Tethya californiana was analyzed based on 16S rRNA gene sequences. One candidate division and nine bacterial phyla were detected, including members of all five subdivisions of Proteobacteria. Moreover, chloroplast-derived Stramenopiles- and Rhodophyta-affiliated 16S rRNA gene sequences were found and Stramenopiles represented the most abundant clones (30%) in the clone library. On the phylum-level, the microbial fingerprint of T. californiana showed a similar pattern as its Mediterranean relative T. aurantium. An interesting difference was that Cyanobacteria that were abundantly present in T. aurantium were not found in T. californiana, but that the latter sponges harbored phototrophic Stramenopiles instead. Surprisingly, the phototrophic microorganisms were evenly distributed over the inner and outer parts of the sponge tissue, which implies that they also reside in regions without direct light exposure. The other phyla were also present in both the outer cortex and the mesohyl of the sponges. These results were confirmed by analysis on the operational taxonomic unit level. This leads to the conclusion that from a qualitative point of view, spatial distribution of microorganisms in T. californiana tissue is quite homogeneous. Thirty-two percent of the operational taxonomic units shared less than 95% similarity with any other known sequence. This indicates that marine sponges are a rich source of previously undetected microbial life.     

Mechanisms of copper tolerance in the marine fouling alga Ectocarpus siliculosus — Evidence for an exclusion mechanism

Copper-tolerant strains of the marine fouling alga Ectocarpus siliculosus (Dillw) Lyngb. have been recorded. The mechanisms of tolerance which may operate in a copper-tolerant strain were investigated by comparing the growth characteristics, copper content and extracellular organic production of tolerant and non-tolerant strains. Growth was measured by a wet-weight method. The copper content of dryashed cells was measured spectrophotometrically using tetraethylthiuram disulphide. The extracellular material is ultra-violet absorbing, and the production was measured by recording absorption at 265 nm. Evidence suggests that an exclusion mechanism is operating in the tolerant strain under investigation. The extracellular material, the cell wall or an associated organism make little or no contribution no this exclusion. Membrane and intracellular changes are believed to account for the tolerance in this strain of E. siliculosus.     

Critical swimming speeds of late-stage coral reef fish larvae: variation within species,among species and between locations

The swimming abilities of larval fishes are important for their survival, potentially affecting their ability to avoid predators, obtain food and control dispersal patterns. Near settlement swimming abilities may also influence spatial and temporal patterns of recruitment. We examined Critical speed (U-crit) swimming ability in late stage larvae of 89 species of coral reef fishes from the Great Barrier Reef and the Caribbean. Coefficients of variation in U-crit calculated at the individual level were high (28.4%), and this was not explained by differences in size or condition factor of these same larvae. Among species U-crit ranged from 5.5 cm s⁻¹ to 100.8 cm s⁻¹ (mean=37.3 cm s⁻¹), with 95% of species able to swim faster than the average current speed around Lizard Island, suggesting that most species should be capable of influencing their spatial and temporal patterns of settlement. Inter-specific differences in swimming ability (at both the family and species levels) were significantly correlated with size and larval morphology. Correlations were found between swimming performance and propulsive area, fineness ratio and aspect ratio, and these morphological parameters may prove useful for predicting swimming ability in other taxa. Overall, the swimming speeds of larvae from the same families at the two locations were relatively similar, although the Lutjanidae and Acanthuridae from the Caribbean were significantly slower than those from the great barrier reef. Differences in swimming speed and body form among late stage larvae suggests that they will respond differently to factors influencing survival and transport during their pelagic phase, as well as habitat use following settlement.     

Heavy metals and marine diatoms: Influence of dissolved organic compounds on toxicity and selection for metal tolerance among four species

Experiments were conducted to determine whether diatom clones isolated from waters (Corio Bay or Hobson's Bay, Australia) chronically contaminated with heavy metals were more metal-resistant than clones of the same species isolated from cleaner waters (Bass Strait). Four species (2 clones per species) and 3 metals (Cu, Zn, Cd) were examined. The growth response of each clone to metal additions was assessed in both Corio Bay water and Bass Strait water. Generally, Cu was readily chelated and the most toxic metal and Cd the least chelated and least toxic. Toxicity of Cu to growth was found to be directly related to cellular Cu levels, which in turn were mediated by dissolved organic compounds in seawater. Corio Bay water had a greater metal-complexing capacity than Bass Strait water, and metal additions generally proved more toxic to each clone when in Bass Strait water. Ultraviolet irradiation eliminated differences between the water types. Relative to Bass Strait clones, no trend of enhanced metal tolerance was noted among the Corio Bay and Hobson's Bay clones; on the contrary the Corio Bay and Hobson's Bay cells were generally less to lerant of metals than were their Bass Strait counterparts, being particularly affected when in Bass Strait water. The results suggest that metal additions to waters rich in dissolved organic compounds would likely have less effect (in terms of direct toxicity and as a selective agent for metal tolerance) on resident phytoplankters than similar additions to waters low in organics.Publication No. 274 in the Ministry for Conservation, Environmental Studies Series     

Comparison of laboratory rates of predation of five species of marine fish larvae by three planktonic invertebrates: effects of larval size on vulnerability

Rates of predation by the invertebrates Aurelia aurita, Thysanoessa raschi and Euchaeta norvegica on larval stages of cod (Gadus morhua L.), flunder (Platichthys flesus L.), plaice (Pleuronectes platessa L.), herring (Clupea harengus L.), and turbot (Scophthalmus maximus L.) were determined. Experiments were conducted in late winter and early spring 1982 with predators collected in Loch Etive, Scotland and prey obtained from several locations in Great Britain. Early stages of the smallest species, cod, flounder and turbot, tended to be most vulnerable to all three predators, while the early stages of the larger species, plaice and herring, and older stages of all species, were less vulnerable. For all stages and species of larvae, predation rates by the three predators were most closely related to larval length and escape swimming speed. Larval length itself was closely correlated to indices of larval escape ability. Low predation rates on large larvae by E. norvegica could be due to handling difficulties, whereas for A. aurita and T. raschi these low rates were due to escape abilities of the larger larvae. Prey movement is an important stimulus eliciting predation in E. norvegica but not in A. aurita or T. raschi.