Infestation dynamics of gnathiid isopod juveniles parasitic on the coral-reef fish Hemigymnus melapterus (Labridae)

The dynamics of infestation by parasitic juveniles of gnathiid isopods were investigated at Lizard Island in the summer of 1997/1998 to determine when, and at what rate, they infest fishes. Variation in gnathiid abundance on wild-caught fish (Hemigymnus melapterus) between dawn and sunset was examined, and unparasitized H. melapterus in cages were exposed to gnathiids in the field for 4 h (8 h for fish sampled at 06:00 h) at five different times of the day and night (10:00, 14:00, 18:00, 22:00, 06:00 hrs) on three reefs. To control for any potential effect of the cleaner-fish Labroides dimidiatus, which consumes large numbers of gnathiids each day, sampling was carried out on reefs from which all cleaner-fish had been removed. Gnathiid abundance decreased during the day. Standardized abundance per wild-caught fish was 1.9 times higher at dawn than at sunset. Gnathiids successfully infested fish in cages. Sixty-one percent of the fish in cages were infested with ≥1 gnathiids, with 51% of the fish having between 1 and 4 gnathiids after 4 h exposure. Gnathiids infested fish both day and night. The log₁₀ (abundance +1) of gnathiids per caged fish varied significantly between time periods, with higher gnathiid numbers on fish sampled at 18:00, 22:00, and 06:00 hrs than on fish sampled at 10:00 and 14:00 hrs. In contrast to gnathiid abundance on wild-caught fish, the number of gnathiids on caged fish sampled at sunset was as high as that at dawn. The estimated mean (SE) cumulative number of gnathiids per caged fish [mean size = 13.7 cm (±0.25)] per day was 7.8 (1.1); this is similar to the estimated mean number of 7.3 gnathiids on similar-sized wild-caught fish at 6:00 hrs. The high infestation rate of gnathiids on caged fish in the late afternoon contrasted with the low numbers on wild-caught fish at this time, suggesting that factors other than infestation behaviour may be responsible for the low numbers of gnathiids on wild-caught fish in the afternoon. Received: 19 August 1998 / Accepted: 1 June 1999     

Variation in emergence of parasitic and predatory isopods among habitats at Lizard Island, Great Barrier Reef

Gnathiid isopods are one of the most abundant groups of ectoparasites on coral reef fishes. They, and other isopods, have been shown to significantly affect the health and behaviour of many reef fish. Whether isopod emergence differs among habitats on coral reefs is not known. In this study, we measured emergence rates of parasitic isopods (Gnathiidea and Flabellifera) in six habitats at two sites at Lizard Island during new moon periods in March and December 2004. Isopods were collected from the periphery and centres of micro-reefs, patch reefs, continuous reefs, and from inter-reefal habitats (sand or rubble) with 1 m² emergence traps. Sites (Casuarina and Coconut Beach) were located on opposite sides of Lizard Island. Live gnathiids were collected with light traps in November 2005 to investigate species differences between sites. At both sites, the most abundant gnathiid species was exclusive to that site. More gnathiid larvae emerged at night, and emergence of fed gnathiids (pranizae) and flabelliferan isopods was almost exclusively nocturnal. Diurnal emergence was greater at Coconut Beach than Casuarina Beach. Although emergence counts were not consistently affected by parameters such as habitat, site, or sampling period, gnathiid size and feeding state were. Where significant differences existed, gnathiids were larger and more often fed over reef borders than centrally. We suggest first stage larvae (Z1) have the largest influence on total abundance and are patchily distributed in accordance with adults from which they have recently hatched. As later stage larvae depend on fish, more successful (fed) and older larvae are found on the edges of reefs where appropriate hosts may be more abundant, or predation is lower. Gnathiids were over-dispersed in all habitats investigated, including apparently homogeneous beds of coral rubble and sand. This indicates that their distributions may be better predicted by very fine scale differences in substrate or that aggregations are the result of gregariousness and may be difficult to predict on the basis of substrate. Emergence traps collected comparatively few parasitic flabelliferan isopods. This community differed greatly from the previously described community of scavenging isopods at Lizard Island. These differences are probably the result of differences in trapping methodology.     

Domoic acid in benthic flatfish on the continental shelf of Monterey Bay,California, USA

Within Monterey Bay, California, USA, the food web transfer of domoic acid (DA), a neurotoxin produced by diatoms of the genus Pseudo-nitzschia, has led to major mortality events of marine mammals and birds. Less visible, and less well known, is whether invertebrates and fish associated with the benthos are also affected by blooms of DA-producing Pseudo-nitzschia spp. This study examines the presence of DA in benthic flatfish offshore of Davenport, California, (37°0′36″N, 122°13′12″W) and within Monterey Bay, California (36°45′0″N, 122°1′48″W), including species that feed primarily in the sediment (benthic-feeding) and species that feed primarily in the water column (benthopelagic-feeding). Flatfish caught between 10 December 2002 and 17 November 2003 at depths of 30–180 m had concentrations of DA in the viscera ranging from 3 to 26 μg DA g⁻¹ of viscera. Although the DA values reported are relatively low, benthic-feeding flatfish were frequently contaminated with DA, especially as compared with the frequency of contamination of flatfish species that feed in the water column. Furthermore, on days in which both benthic-feeding and benthopelagic-feeding flatfish were collected, the former had significantly higher concentrations of DA in the viscera. Curlfin turbot, Pleuronicthys decurrens, the flatfish with both the highest level and frequency of DA contamination, are reported to feed exclusively on polychaetes, suggesting that these invertebrates may be an important vector of the toxin in benthic communities and may pose a risk to other benthic-feeding organisms. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Interpreting seawater temperature range using oxygen isotopes and zooid size variation in Pentapora foliacea (Bryozoa)

This is the first investigation of how two independent proxies for seawater temperature inference (zooid size variation and oxygen isotope ratios of skeletal carbonate) relate to the actual measured ranges of temperature experienced by cheilostome bryozoan colonies. Nine specimens of the bimineralic marine cheilostome bryozoan Pentapora foliacea (Ellis and Solander, 1786) were analysed, collected from ~18-m depth at two localities in Wales, UK—four from Skomer Island (51°42′510″N, 5°13′42.60″W) and five from Porth Ysgaden, Lleyn Peninsula (52°54′6.75″N, 4°38′47.34″W). The annual range of temperature implied by zooid size variability provides a good approximation of the actual range of temperature recorded by a datalogger. However, annual ranges of temperature reconstructed from skeletal oxygen isotope ratios were narrower, typically not showing the lowest temperatures experienced by the colonies. This can be explained by progressive thickening of zooid skeletal walls during the life of the colony that homogenises the temperature signal by time-averaging over the lifetime of the colonies. Our study provides evidence that a combined morphological isotope approach has great potential in the reconstruction of annual ranges in seawater temperatures from historical and fossil bryozoans, particularly for species that lack ontogenetic skeletal wall thickening and bimineralic skeletal composition. As cheilostome bryozoans have been common in benthic communities since the Late Cretaceous, they represent a valuable and underutilised resource for the interpretation of environmental regimes.     

The relationship between lunar periodicity and activity of fish-parasitic gnathiid isopods in the Caribbean

Gnathiid isopod larvae are members of the marine demersal zooplankton community and are common ectoparasites of coral reef fishes, emerging from the substratum, mostly at night and crepuscular periods to feed on fish blood. Given that the activity of many marine organisms is often linked to changes in the phase of the moon, we examined the relationship between lunar phase and activity in gnathiid isopods on Caribbean reefs. We employed two sampling methods to quantify gnathiid activity: (1) Emergence traps set on reefs over a 24 h period; and (2) live fish placed in cages on reefs and retrieved during night and dawn peaks in gnathiid activity. These were compared during discrete phases as well as a continuous metric, the lunar “angle”, and an estimate of ambient light availability (luminance). Lunar phase and angle varied in their statistical effect on gnathiid activity patterns by sampling method and/or year. Luminance had a significant but inconsistent effect on measures of gnathiid activity. Our results suggest that changes in the lunar cycle are not a strong predictor of gnathiid activity at our shallow reef study sites.     

The reproductive ecology of the invasive ascidian, <Emphasis Type="Italic">Styela clava,</Emphasis> in Auckland Harbour,New Zealand

The ascidian Styela clava, native to the north-west Pacific, is an invasive species affecting New Zealand’s marine ecosystems, biodiversity and aquaculture operations. To provide detailed information on the reproductive biology of S. clava in New Zealand for post-border biosecurity management, long-term seasonal patterns of gametogenesis were determined from May 2006 to May 2008 in Auckland’s Waitemata Harbour (36°49′20″S, 174°45′85″E). Of particular interest was whether the critical 15°C threshold spawning temperature for reproduction observed in the Northern Hemisphere applied here to the first Southern Hemisphere study. S. clava gametogenesis followed a regular seasonal cycle with ripe gametes appearing as early as September and persisting to June; this time frame corresponds to the period when sea surface temperatures in the region first reach 15°C and with spawning occurring mainly during late summer to early autumn. From photoperiod manipulation, it was determined that spawning occurred at approximately 18:20. The extended reproductive period and a short generation time in the Waitemata Harbour provides a lengthy opportunity for S. clava to spread. Findings are discussed in relation to S. clava’s post-border management.     

Does spawning behavior minimize exposure to environmental stressors for encapsulated gastropod embryos on rocky shores?

Adults of motile intertidal invertebrates are able to seek shelter to avoid environmental stress associated with low tides, but embryos within egg masses are effectively sessile for the duration of their encapsulation. Gastropod egg masses from 34 taxa on two rocky shores in SE Australia (34°37′08″S, 150°92′03″E and 34°35′45″S, 150°53′20″E) were surveyed over 2 years (June 2002–May 2004) to test the hypothesis that eggs are deposited in patterns that minimize exposure to environmental stress. Egg masses were expected to be predominantly deposited in shaded habitats not prone to environmental extremes. It was also anticipated that the deposition of egg masses in habitats exposed to UVR, desiccation, and/or extremes in temperature would occur when exposure to these abiotic factors was minimized. Among the taxa investigated, only four species spawned in full sun (Bembicium nanum, Nerita morio, Siphonaria zelandica and S. denticulata). Summer had the highest UVR index, water temperature, and air temperature as well as the lowest daytime tides. Univariate and multivariate analyses confirmed that egg mass abundance was highest during summer, with no change in egg mass size. This study shows that those species depositing egg masses on the surfaces of rock platforms do not adjust the seasonal timing or macrohabitat location of their spawning to avoid physiologically stressful conditions, particularly UVR. Alternate reasons for the evolution of egg mass deposition behavior in apparently sub-optimal habitats are discussed, and it is almost certainly the complex interplay of a variety of highly species-specific factors that is responsible for the patterns observed.     

Recovery after trampling disturbance in a canopy-forming seaweed population

The recovery of Ascophyllum nodosum, and the associated benthic community, was followed after repeated trampling disturbance at different intensities, from 2005 to 2010, at its southern limit (41°41′27″N; 8°50′57″W). The cover of A. nodosum and associated organisms and the demography of A. nodosum individuals in the most disturbed areas were followed over a recovery period of 54 months. Recovery of A. nodosum assemblages was negatively affected by increasing trampling intensity. After 54 months, the highest intensity plots were still significantly different from control plots. Growth and mortality rates of A. nodosum increased shortly after disturbance but progressively recovered to levels close to control plots. The results of this study demonstrate the sensitivity of this habitat-building species to human trampling and also show its plasticity to cope with disturbance events.     

Geographic and ontogenetic variation in the diet and daily ration of the bonnethead shark, <Emphasis Type="Italic">Sphyrna tiburo</Emphasis>, from the eastern Gulf of Mexico

To examine variation in diet and daily ration of the bonnethead shark, Sphyrna tiburo (Linnaeus 1758), animals were collected from three areas in the eastern Gulf of Mexico: northwest Florida (∼29°40′N, 85°13′W), Tampa Bay near Anclote Key (∼28°10′N, 82°42.5′W), and Florida Bay (∼24°50′N, 80°48′W) from March through September, 1998–2000. In each area, diet was assessed by life stage (young-of-the year, juveniles, and adults) and quantified using five indices: percent by number (%N), percent by weight (%W), frequency of occurrence (%O), index of relative importance expressed on a percent basis (%IRI), and %IRI based on diet category (%IRI_DC). Diet could not be assessed for young-of-the-year in Tampa Bay or Florida Bay owing to low sample size. Diet analysis showed an ontogenetic shift in northwest Florida. Young-of-the-year stomachs from northwest Florida (n = 68, 1 empty) contained a mix of seagrass and crustaceans while juvenile stomachs (n = 82, 0 empty) contained a mix of crabs and seagrass and adult stomachs (n = 39, 1 empty) contained almost exclusively crabs. Crabs made up the majority of both juvenile and adult diet in Tampa Bay (n = 79, 2 empty, and n = 88, 1 empty, respectively). Juvenile stomachs from Florida Bay (n = 72, 0 empty) contained seagrass and a mix of crustaceans while adult stomachs contained more shrimp and cephalopods (n = 82, 3 empty). Diets in northwest Florida and Tampa Bay were similar. The diet in Florida Bay was different from those in the other two areas, consisting of fewer crabs and more cephalopods and lobsters. Plant material was found in large quantities in all stomachs examined from all locations (>15 %IRI_DC in 6 of the 7 life stage-area combinations, >30 %IRI_DC in 4 of the 7 combinations, and 62 %IRI_DC in young-of-the-year diet in northwest Florida). Using species- and area-specific inputs, a bioenergetic model was constructed to estimate daily ration. Models were constructed under two scenarios: assuming plant material was and was not part of the diet. Overall, daily ration was significantly different by sex, life stage, and region. The bioenergetic model predicted increasing daily ration with decreasing latitude and decreasing daily ration with ontogeny regardless of the inclusion or exclusion of plant material. These results provide evidence that bonnetheads continuously exposed to warmer temperatures have elevated metabolism and require additional energy consumption to maintain growth and reproduction. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The effects of symbiotic state on heterotrophic feeding in the temperate sea anemone <Emphasis Type="Italic">Anthopleura elegantissima</Emphasis>

The temperate sea anemone Anthopleura elegantissima is facultatively symbiotic with unicellular algae. Symbiotic A. elegantissima can supplement heterotrophic feeding with excess photosynthate from their algal partners, while asymbiotic individuals must rely solely on heterotrophy. A. elegantissima individuals were collected from Swirl Rocks, Washington (48°25′6″ N, 122°50′58″ W) in July 2010, and prey capture and feeding characteristics were measured to determine whether asymbiotic individuals are more efficient predators. Feeding abilities were then measured again after a 3-week exposure to full sunlight or shaded conditions. Freshly collected asymbiotic anemones had larger nematocysts, but symbiotic individuals showed greater nematocyte sensitivity. Sunlight enhanced digestion and reduced cnida density in all anemones regardless of symbiotic state. Results suggest that the phototropic potential of A. elegantissima, as influenced by symbiotic condition, has little effect on heterotrophic capacity. The anemones appear to maximize heterotrophic energy input independent of the presence or identity of their algal symbionts.     

Effect of MS-222 on response to light and rate of metabolism of the little skate Raja erinacea

The effect of tricaine methanesulfonate (MS-222) on the standard (SMR) and routine (RMR) metabolic rates of Raja erinacea was estimated from oxygen-consumption measurements. Data were gathered from a computerized, flow-through respirometry system. Individual trials were run for 96 h at 10 °C on anesthetized and untreated fish. The resulting rates, SMR = 20.1 ± 1.99 SE and RMR = 48.3± 2.5 SE mg O₂ kg⁻¹ h⁻¹, for an unanesthetized skate of 0.5 kg standardized weight, are the lowest reported for any elasmobranch. Periodogram analysis revealed a significant light-response component to the oxygen consumption of these fish, indicating a pattern of nocturnal and crepuscular activity. This activity pattern was disrupted in skates subjected to anesthesia. The use of low-dosage MS-222 in conjunction with the respirometry trials provides positive preliminary evidence that this technique may be useful in giving quick, accurate estimates of SMR in the more intractable elasmobranch fishes. Received: 15 January 1997 / Accepted: 6 February 1997     

Characterizing the resident, fermentative microbial consortium in the hindgut of the temperate-zone herbivorous fish, Hermosilla azurea (Teleostei: Kyphosidae)

The zebraperch, Hermosilla azurea Jenkins and Evermann, a warm-temperate marine fish species with a strictly macroalgal diet, has a relatively long digestive tract with an enlarged hindgut and an associated blind caecum (HC). In zebraperch sampled off Santa Catalina Island, California (33°19′42′′N; 118°18′37′′W) in years 1995 through 2001, direct cell counts, gut epithelium assessment of bacterial attachment, and short-chain fatty acid (SCFA) analyses verified that the zebraperch HC possesses a dense and morphologically diverse, fermentative microbiota. Bacterial cell counts and morphological diversity were significantly higher in HC contents compared to anterior gut regions, suggesting that microbial populations were growing along the digestive tract. Similarly, electron micrographs of the HC epithelium revealed attached microbes, further supporting the possibility that these organisms constitute resident microbiota. Five different SCFAs were detected in all three regions of the digestive tract, but levels were up to three times greater in HC contents. Acetate was consistently the prevailing SCFA in all gut regions. Sequence analysis of bacterial 16S rDNA was used to identify predominant bacterial groups in HC contents. Of the seven main bacterial types identified, Enterovibrio spp. were the dominant bacteria in HC contents followed by species of Bacteroides,Faecalibacterium, and Desulfovibrio. Taken together, our findings show that the zebraperch HC harbors a consortium of microbes that appears to assist in the breakdown of algal polysaccharides in the herbivorous diet of the fish.     

Relative intensity of predation on the French grunt, Haemulon flavolineatum, during diurnal, dusk, and nocturnal periods on a coral reef

Established hypotheses state that the rate of predation on coral reef fish should be highest during crepuscular periods (dawn and dusk) intermediate diurnally, and lowest nocturnally. We examined the relative risk of predation on juvenile French grunts (Haemulon flavolineatum Desmarest) during diurnal, dusk, and nocturnal periods on the fore- and back-reef at Teague Bay, U.S. Virgin Islands in July and August 1996. Tethering-devices recorded the exact amount of time between attaching a prey fish to its tether and subsequent predation on the prey fish. As tethering of prey usually inflates the actual rate of predation, times from our tethering devices were used to establish only the relative predation risk among treatments. During 3-h diurnal and nocturnal tethering experiments, relative predation was significantly higher during the nocturnal period, and differences between side of reef were not significant. In 30-min tethering experiments, which included all three time periods, the relative predation risk was significantly higher during dusk and nocturnal periods than during the diurnal period. Relative predation was not significantly different between the dusk and nocturnal periods, or between side of reef during any time period. The unexpected finding that the diurnal period had the lowest relative risk of predation indicates that the timing of predation events on reefs, as well as the adaptive reasons for nocturnal larval settlement, may need to be re-examined. Received: 11 February 1997 / Accepted: 21 October 1998     

Size and spatial structure in deep versus shallow populations of the Mediterranean gorgonian <Emphasis Type="Italic">Eunicella singularis</Emphasis> (Cap de Creus,northwestern Mediterranean Sea)

In the Western Mediterranean Sea, the gorgonian Eunicella singularis (Esper, 1794) is found at high densities on sublittoral bottoms at depths from 10 to 70 m. Shallow colonies have symbiotic zooxanthellae that deeper colonies lack. While knowledge of the ecology of the shallow populations has increased during the last decades, there is almost no information on the ecology of the deep sublittoral populations. In October and November 2004 at Cap de Creus (42°19′12″ N; 03°19′34″ E), an analysis of video transects made by a remotely operated vehicle showed that shallow populations (10–25 m depth) were dominated by small, non-reproductive colonies, while deep sublittoral populations (50–67 m depth) were dominated by medium-sized colonies. Average and maximum colony heights were greater in the deeper populations, with these deeper populations also forming larger patch sizes and more extensive regions of continuous substrate coverage. These results suggest that shallow habitats are suitable for E. singularis, as shown by the high recruitment rate, but perturbations may limit or delay the development of these populations into a mature stage. This contrasts with the deep sublittoral habitats where higher environmental stability may allow the development of mature populations dominated by larger, sexually mature colonies.     

Increasing heterogeneity of sensitive assemblages as a consequence of human impact in submarine caves

Submarine caves are considered as a top priority for conservation, but the effects of common pressures are poorly known for these habitats. Here, we examined the effect of recreational human visitation on a selection of submarine caves in a Mediterranean Marine Protected Area (40°35′40″N; 8°11′39″E) where diving activities are regulated. Sampling was conducted in visited and not visited caves to assess whether diving activities have a significant effect on cave habitats, what are the components of biodiversity most affected by this disturbance, and its potential effects on spatial heterogeneity of benthic assemblages. Results clearly showed that human visitation could significantly affect spatial patterns of benthic assemblages. Organisms with erect growth forms were significantly more abundant and homogeneously distributed where diving activities are forbidden. An increase in the small-scale heterogeneity of assemblages and a decrease in their three-dimensional structure could be the ultimate consequences of human visitation. The interaction between specific stressors and the patterns of distribution of species and assemblages can drive their spatial heterogeneity also in unique habitats like marine caves, representing an early warning for the development of appropriate management measures.     

Emergence of an oocytic circumnuclear ring in response to increasing day length in Atlantic herring (<Emphasis Type="Italic">Clupea harengus</Emphasis>)

Understanding physiological and environmental variables that initiate sexual maturity would provide fundamental information on life history dynamics. The aim of this study was to test the usefulness of the common circumnuclear ring (CNR), an oocytic structure similar to the Balbiani body, which appears just prior to oocyte development as a predictor of first maturation in Atlantic herring (Clupea harengus). The relative roles of physiology (e.g. fat) and photoperiod as triggers of maturation were also investigated. Samples were collected in May 2008 (72°26′–73°84′N/11°26′–18°40′E) and February 2009 (56°12′–59°45′N/00°25′–03°06′W). These data suggested that thresholds in body size may influence the decision to mature. We also found that short days (winter solstice) may be the photoperiod trigger for a first-decision window for both Norwegian spring-spawning (NSS) and North Sea autumn-spawning (NSAS) herring. The second-decision window for NSAS herring maturation appears to be triggered by longer days (spring equinox), while a decreasing rate of day lengthening may trigger NSS herring maturation. So, photoperiodic cycle is a key determinate of the timing of maturation in Atlantic herring.     

Avoidance of feeding opportunities by the whelk Buccinanops globulosum in the presence of damaged conspecifics

Feeding decisions under predation risk can be a key in the life of scavenger organisms, and tuned recognition of predation alarm cues and flexibility in the response are fundamental. The effect of injured conspecifics on the response behavior of the whelk Buccinanops globulosum to feeding opportunities was experimentally evaluated in a Patagonian Bay (40°45′S, 64°56′W, Argentina) in September 2010. The effect of sex, size, body condition, or starvation on anti-predatory behavior was assessed. The number of B. globulosum feeding on carrion was reduced by half when damaged conspecifics were present. Smaller, lighter, and starved individuals responded less to the presence of damaged conspecifics. These results indicate that, under natural conditions, feeding avoidance after detecting damaged conspecifics is a common and important anti-predatory strategy of B. globulosum and show that morphology and starvation are significant factors in the context of the trade-off between feeding and avoiding predation risk.     

Scarred limpets at hydrothermal vents: evidence of predation by deep-sea whelks

The chaotic physical and chemical environment at deep-sea hydrothermal vents has been associated with an ecosystem with few predators, arguably allowing the habitat to provide refuge for vulnerable species. The dominance of endemic limpets with thin, open-coiled shells at north Pacific vents may support this view. To test their vulnerability to predation, the incidence of healed repair scars, which are argued to reflect non-lethal encounters with predators, were examined on the shells of over 5,800 vent limpets of Lepetodrilus fucensis McLean (1988) that were collected from 13 to 18 August 1996. Three vent fields on the Juan de Fuca Ridge at ca. 2,200 m depth were sampled, two within 70 m of 47°56.87′N 129°05.91′W, and one at 47°57.85′N 129°05.15′W with the conspicuous potential limpet predators, the zoarcid fish Pachycara gymninium Anderson and Peden (1988), the galatheid crab Munidopsis alvisca Williams (1988), and the buccinid snail Buccinum thermophilum Harasewych and Kantor (2002). Limpets from the predator-rich vent were most often scarred, a significant difference created by the high incidence of scars on small (<4 mm long) limpets in this sample. Collected with the limpets were small (median shell diameter 4.4 mm) buccinids. They, rather than the larger, more conspicuous mobile fishes and crabs are argued to be the shell-damaging predator. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Interception and dispersal of artificial food falls by scavenging fishes in the abyssal Northeast Atlantic: early-season observations prior to annual deposition of phytodetritus

The hypothesis that the behaviour of deep-sea scavenging fishes is influenced by seasonal input of organic matter from the ocean surface was investigated by observing responses to baits placed on the sea floor at 4800 m depth in the NE Atlantic (48°50′N; 16°30′W) during spring (April 1994). Data from the present study are compared with those from previous studies of the same location made in summer 1989. The first fishes to arrive at baits were the grenadier Coryphaenoides (Nematonurus) armatus and the eel Histiobranchus bathybius, after delays of 28 and 29 min, respectively; these results are not significantly different from those of summer 1989. Similarly, other indices of activity (staying time and swimming speed) showed no evidence of differences between years/seasons. However, the rate of radial dispersal of bait (0.009 m s⁻¹) by C. (N.) armatus was much slower than in all previous studies. A change in the size distribution of C. (N.) armatus to smaller individuals in spring 1994 was also evident. It is suggested that the fish on the abyssal plain may not comprise a steady-state population and that major episodic or seasonal migrations may occur. Received: 18 October 1996 / Accepted: 20 December 1996     

Spatiotemporal variation in the population ecology of scaly slipper lobsters <Emphasis Type="Italic">Scyllarides squammosus</Emphasis> in the Northwestern Hawaiian Islands

Scaly slipper lobster (Scyllarides squammosus) population ecology was examined using tag/recapture information at Necker Island (23°30′N; 164°35′W), Gardner Pinnacles (25°00′N; 168°50′W), Maro Reef (25°30′N; 170°45′W), and Laysan Island (25°48′N; 171°45′W) in the Northwestern Hawaiian Islands (NWHI) USA from 2002 to 2008. Although many aspects of S. squammosus life history and population dynamics were similar to those of other scyllarids, somatic growth differed from its congers. Scyllarides squammosus growth abruptly declined at maturity and, because of this, growth at length was better described using the Schnute as opposed to the more commonly von Bertalanffy growth model. Growth varied among locations, and survival varied among years; thereby being the first documentation of variability in the life history of a scyllarid. This study has expanded knowledge of scyllarid biology and documented that spatiotemporal variability in biological characteristics must be considered to understand and describe the population ecology of this species and probably of other scyllarids.