Ontogenetic habitat shift,population growth,and burrowing behavior of the Indo-Pacific beach star, <Emphasis Type="Italic">Archaster typicus</Emphasis> (Echinodermata; Asteroidea)

Archaster typicus, a common sea star in Indo-Pacific regions, has been a target for the ornamental trade, even though little is known about its population biology. Spatial and temporal patterns of abundance and size structure of A. typicus were studied in the Davao Gulf, the Philippines (125°42.7′E, 7°0.6′N), from February 2008 to December 2009. Specimens of A. typicus were associated with intertidal mangrove prop roots, seagrass meadows, sandy beaches, and shoals. Among prop roots, specimens were significantly smaller and had highest densities (131 ind. m⁻²) between November and March. High organic matter in sediment and a relatively low predation rate seemed to support juvenile life among mangroves. Size and density analyses provided evidence that individuals gradually move to seagrass, sandy habitats, and shoals as they age. Specimens were significantly larger at a shoal (maximum radius R = 81 mm). New recruits were found between August and November in both 2008 and 2009. Timing of recruitment and population size frequencies confirmed a seasonal reproductive cycle. Juveniles had relatively high growth rates (2–7 mm month⁻¹) and may reach an R of 20–25 mm after 1 year. Growth rates of larger specimens (R > 30 mm) were generally <2 mm month⁻¹. The activity pattern of A. typicus was related to the tidal phase and not to time of day: Specimens moved over the sediment surface during low tides and were burrowed during high tides possibly avoiding predation. This is one of the first studies to document an ontogenetic habitat shift for sea stars and provides new biological information as a basis for management of harvested A. typicus populations.     

Distribution,life history,and production of three species of <Emphasis Type="Italic">Neomysis</Emphasis> in Akkeshi-ko estuary,northern Japan

Spatial and seasonal distribution pattern, life history and production of three species of Neomysis (Mysidacea) which commonly occur in northwestern subarctic Pacific coastal waters, were investigated throughout the year in the Akkeshi-ko estuary, northern Japan. The most abundant species Neomysis awatschensis (annual mean density: 179.8 inds. m⁻², biomass: 108.8 mg DW m⁻²) occurred at the inner part of the estuary including low salinity areas with no clear preference for the seagrass bed. The second most abundant Neomysis mirabilis (mean density: 95.8 inds. m⁻², biomass: 90.1 mg DW m⁻²) occurred at relatively saline seagrass site throughout the year. Occurrence of Neomysis czerniawskii in the estuary was limited to the seagrass bed during summer when their population mainly consisted of juveniles, suggesting that this species is a seasonal migrant between the estuary and the marine environment. Both N. awatschensis and N. mirabilis populations were composed of two generation types, a larger sized overwintering and smaller sized spring/summer generations; however, each species had a different reproductive strategy. N. awatschensis was characterized by fast growth to maturity at a smaller size than N. mirabilis with a relatively high fecundity during warm season, suggesting that this species is an r-strategist which can utilize opportunistically a wide variety of habitats. In contrast, the seagrass bed resident N. mirabilis was a K-strategist which matures at a larger size producing fewer but larger offspring. The annual production of N. awatschensis (0.57–0.70 g DW m⁻², mean of the whole estuary) and N. mirabilis (0.58–0.68 g DW m⁻², mean of the seagrass bed) at their respective habitats was comparable. Consequently, species-specific life history and distribution pattern are concluded to allow Neomysis spp. to coexist in the estuary and the high carrying capacity of seagrass bed is suggested to contribute to maintain their high biomass level.     

Microbial activity and carbon, nitrogen, and phosphorus content in a subtropical seagrass estuary (Florida Bay): evidence for limited bacterial use of seagrass production

Bacterial abundance, production, and extracellular enzyme activity were determined in the shallow water column, in the epiphytic community of Thalassia testudinum, and at the sediment surface along with total carbon, nitrogen, and phosphorus in Florida Bay, a subtropical seagrass estuary. Data were statistically reduced by principle components analysis (PCA) and multidimensional scaling and related to T. testudinum leaf total phosphorus content and phytoplankton biomass. Each zone (i.e., pelagic, epiphytic, and surface sediment community) was significantly dissimilar to each other (Global R = 0.65). Pelagic aminopeptidase and sum of carbon hydrolytic enzyme (esterase, peptidase, and α- and β-glucosidase) activities ranged from 8 to 284 mg N m⁻² day⁻¹ and 113–1,671 mg C m⁻² day⁻¹, respectively, and were 1–3 orders of magnitude higher than epiphytic and sediment surface activities. Due to the phosphorus-limited nature of Florida Bay, alkaline phosphatase activity was similar between pelagic (51–710 mg P m⁻² day⁻¹) and sediment (77–224 mg P m⁻² day⁻¹) zones but lower in the epiphytes (1.1–5.2 mg P m⁻² day⁻¹). Total (and/or organic) C (111–311 g C m⁻²), N (9.4–27.2 g N m⁻²), and P (212–1,623 mg P m⁻²) content were the highest in the sediment surface and typically the lowest in the seagrass epiphytes, ranging from 0.6 to 8.7 g C m⁻², 0.02–0.99 g N m⁻², and 0.5–43.5 mg P m⁻². Unlike nutrient content and enzyme activities, bacterial production was highest in the epiphytes (8.0–235.1 mg C m⁻² day⁻¹) and sediment surface (11.5–233.2 mg C m⁻² day⁻¹) and low in the water column (1.6–85.6 mg C m⁻² day⁻¹). At an assumed 50% bacterial growth efficiency, for example, extracellular enzyme hydrolysis could supply 1.8 and 69% of epiphytic and sediment bacteria carbon demand, respectively, while pelagic bacteria could fulfill their carbon demand completely by enzyme-hydrolyzable organic matter. Similarly, previously measured T. testudinum extracellular photosynthetic carbon exudation rates could not satisfy epiphytic and sediment surface bacterial carbon demand, suggesting that epiphytic algae and microphytobenthos might provide usable substrates to support high benthic bacterial production rates. PCA revealed that T. testudinum nutrient content was related positively to epiphytic nutrient content and carbon hydrolase activity in the sediment, but unrelated to pelagic variables. Phytoplankton biomass correlated positively with all pelagic components and sediment aminopeptidase activity but negatively with epiphytic alkaline phosphatase activity. In conclusion, seagrass production and nutrient content was unrelated to pelagic bacteria activity, but did influence extracellular enzyme hydrolysis at the sediment surface and in the epiphytes. This study suggests that seagrass-derived organic matter is of secondary importance in Florida Bay and that bacteria rely primarily on algal/cyanobacteria production. Pelagic bacteria seem coupled to phytoplankton, while the benthic community appears supported by epiphytic and/or microphytobenthos production.     

Delayed ontogenic dietary shift and high levels of omnivory in green turtles (<Emphasis Type="Italic">Chelonia mydas</Emphasis>) from the NW coast of Africa

Young green turtles (Chelonia mydas) spend their early lives as oceanic omnivores with a prevalence of animal prey. Once they settle into neritic habitats (recruitment), they are thought to shift rapidly to an herbivorous diet, as revealed by studies in the Greater Caribbean. However, the precise timing of the ontogenic dietary shift and the actual relevance of animal prey in the diet of neritic green turtles are poorly known elsewhere. Stable isotopes of carbon, sulfur and nitrogen in the carapace scutes of 19 green turtles from Mauritania (NW Africa), ranging from 26 to 102 cm in curved carapace length (CCLmin), were analyzed to test the hypothesis of a rapid dietary shift after recruitment. Although the length of residence time in neritic habitats increased with turtle length, as revealed by a significant correlation between turtle length and the δ¹³C and the δ³⁴S of the scutes, comparison of the δ¹⁵N of the innermost and outermost layers of carapace scutes demonstrated that consumption of macrophytes did not always start immediately after recruitment, and turtles often resumed an animal-based diet after starting to graze on seagrasses. As a consequence, seagrass consumption did not increase gradually with turtle size and animal prey largely contributed to the diet of turtles within the range 29–59 cm CCLmin (76–99% of assimilated nutrients). Seagrass consumption by turtles larger than 59 cm CCLmin was higher, but they still relied largely on animal prey (53–76% of assimilated nutrients). Thus, throughout most of their neritic juvenile life, green turtles from NW Africa would be better classified as omnivores rather than herbivores. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The effects of temperature,body size and growth rate on energy losses due to metabolism in early life stages of haddock (<Emphasis Type="Italic">Melanogrammus aeglefinus</Emphasis>)

Rates of routine respiration (R _R, μl O₂ fish⁻¹ h⁻¹) and total ammonia nitrogen excretion (E _R, μg NH₄–N + NH₃–N fish⁻¹ h⁻¹) were measured on larval and juvenile haddock (Melanogrammus aeglefinus) to ascertain how energy losses due to metabolism were influenced by temperature (T), dry body mass (M _D, mg) and specific growth rate (SGR, % per day). R _R and E _R increased with M _D according to y = a  · M _D ^b with b-values of 0.96, 0.98, 1.14, and 0.89, 0.78, 0.74, respectively, at 10, 7, and 4°C, respectively. Multiple regressions explained 98% of the variability in the combined effects of M _D and T on R _R and E _R in larval haddock: R _R = 0.97 · M _D ^0.98  · e^0.092 · T ; E _R = 0.06 · M _D ^0.79  · e^0.092 · T . In young juvenile (24–30 mm standard length) haddock, R _R tended to decline (P = 0.06) and E _R significantly declined (P = 0.02) with increasing SGR. O:N ratios significantly increased with increasing SGR suggesting that N was spared in relatively fast-growing individuals. Our results for young larval and juvenile haddock suggest: (1) nearly isometric scaling of R _R with increasing body size, (2) allometric scaling of E _R with increasing body size, (3) Q ₁₀ values of 2.5 for both R _R and E _R, (4) metabolic differences in substrate utilization between relatively fast- and slow-growing individuals, and (5) that rates of routine energy loss and growth were not positively related. The measurements in this study will provide robust parameter estimates for individual-based models that are currently being utilized to investigate how variability in climatic forcing influences the vital rates of early life stages of haddock. Our results also stress that inter-individual differences in rates of energy loss should not be overlooked as a factor influencing growth variability among individuals.     

Fish assemblages in seagrass beds are influenced by the proximity of mangrove forests

Mangrove forests and seagrass beds frequently occur as adjacent habitats in the temperate waters of southeastern Australia. At low tide when fish cannot occupy mangroves they might utilise adjacent habitats, including seagrass. We first sampled small fish from seagrass beds close to and far from mangroves in the Pittwater estuary, NSW, Australia. Seagrass beds close to mangroves had a greater density of fish species than beds far from mangroves (close: mean 16.0 species net⁻¹, SE 1.0; far: 13.2, 1.3; P < 0.05). In particular, juvenile fish were in greater densities near to than far from mangroves (close: 5.3, 0.4; far: 3.1, 0.4; P < 0.05). We then sampled the mangrove forests during the high tide and seagrass beds during the low tide, in beds along a continuum of distances from mangroves. Multivariate analysis showed that fish assemblages differed with distance from mangroves, and the differences were attributed to the composition of the fish assemblage (i.e. presence/absence of fish species), not the abundances of individual species. In particular, fish that utilise mangrove forests at high tide were found in greater species densities and species richness in seagrass nearer to mangroves. A negative relationship was found between the density of mangrove-utilising fish species and the distance of the bed from mangroves (R ² = 0.37, P < 0.05). This confirms the important connectivity between mangroves and seagrass for fish in temperate Australian waters.     

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.     

Migration,distribution, and diving behavior of adult male loggerhead sea turtles (<Emphasis Type="Italic">Caretta caretta</Emphasis>) following dispersal from a major breeding aggregation in the Western North Atlantic

Sixteen satellite-tagged adult male loggerhead sea turtles (Caretta caretta) dispersed widely from an aggregation near Port Canaveral, Florida, USA (28°23′N, −80°32′W) after breeding. Northbound males migrated further (990 ± 303 km) than southbound males (577 ± 168 km) and transited more rapidly (median initial dive duration = 6 (IQR = 4–16) versus 19 (IQR = 10–31) min, respectively).. Migration occurred along a depth corridor (20–40 m) except where constricted by a narrow continental shelf width. Males foraged in areas 27 ± 41 km² day⁻¹ at locations <1–80 km from shore for 100.1 ± 60.6 days, with variability in foraging patterns not explained by turtle size or geography. Post-breeding dispersal patterns were similar to patterns reported for adult female loggerhead sea turtles in this region and adult male loggerhead sea turtles elsewhere in the northern hemisphere; however, foraging ground distributions were most similar to adult female loggerhead sea turtles in this region.     

Caribbean mangroves and seagrass beds as daytime feeding habitats for juvenile French grunts, Haemulon flavolineatum

Caribbean seagrass beds are important feeding habitats for so-called nocturnally active zoobenthivorous fish, but the extent to which these fishes use mangroves and seagrass beds as feeding habitats during daytime remains unclear. We hypothesised three feeding strategies: (1) fishes feed opportunistically in mangroves or seagrass beds throughout the day and feed predominantly in seagrass beds during night-time; (2) fishes start feeding in mangroves or seagrass beds during daytime just prior to nocturnal feeding in seagrass beds; (3) after nocturnal feeding in seagrass beds, fishes complete feeding in mangroves or seagrass beds during the morning. We studied the effect of habitat type, fish size, social mode and time of day on resting and feeding behaviour of large juvenile (5–10 cm) and sub-adult (10–15 cm) Haemulon flavolineatum in mangroves and seagrass beds during daytime. Sub-adults occurred in mangroves only, spent most time on resting, and showed rare opportunistic feeding events (concordant with strategy 1), regardless of their social mode (solitary or schooling). In contrast, large juveniles were present in both habitat types and solitary fishes mainly foraged, while schooling fishes mainly rested. Exceptions were small juveniles (±5 cm) in seagrass beds which foraged intensively while schooling. Large juveniles showed more feeding activity in seagrass beds than in mangroves. In both habitat types, they showed benthic feeding, whereas pelagic feeding was observed almost exclusively in the seagrass beds. In both habitat types, their feeding activity was highest during 8:00–10:30 hours (concordant with strategy 3), and for seagrass fishes, it was also high during 17:30–18:30 hours (concordant with strategy 2). The study shows that both mangroves and seagrass beds provide daytime feeding habitats for some life-stages of H. flavolineatum, which is generally considered a nocturnal feeder.     

Flux by fin: fish-mediated carbon and nutrient flux in the northeastern Gulf of Mexico

Seagrass meadows are among the most productive ecosystems in the marine environment. It has been speculated that much of this production is exported to adjacent ecosystems via the movements of organisms. Our study utilized stable isotopes to track seagrass-derived production into offshore food webs in the northeastern Gulf of Mexico. We found that gag grouper (Myctereoperca microlepis) on reefs as far as 90 km from the seagrass beds incorporate a significant portion of seagrass-derived biomass. The muscle tissue of gag grouper, a major fisheries species, was composed on average of 18.5–25% seagrass habitat-derived biomass. The timing of this annual seagrass subsidy appears to be important in fueling gag grouper egg production. The δ³⁴S values of gag grouper gonad tissues varied seasonally and were δ³⁴S depleted during the spawning season indicating that gag utilize the seagrass-derived biomass to support reproduction. If such large scale trophic subsidies are typical of temperate seagrass systems, then loss of seagrass production or habitat would result in a direct loss of offshore fisheries productivity.     

Alimentary niche partitioning in the Galapagos sea lion, Zalophus wollebaeki

Sea lions are generally considered opportunistic feeders. However, studies from different areas suggest their diet consists mostly of four to five types of prey. Previous studies in Galapagos sea lions have identified at least three feeding strategies for this species, suggesting diversification of their diet. Diet diversification is favored in organisms with relatively high trophic position and subject to high intra-specific and low inter-specific competition. Zalophus wollebaeki meet these criteria as the only pinniped on San Cristobal Island, where three sea lion rookeries are located within 11 km: a distance considerably shorter than their 41 km foraging range. To measure the degree of diet diversification, we used scats and stable isotope analyses. A total of 270 scat samples from lactating females and 142 fur samples from sea lion pups were collected during the breeding season 2006. The scat analysis identified distinct diets among rookeries, with minimal trophic overlap (Cλ = 0.19), a trophic level TL = 4.5 (secondary–tertiary carnivore), and trophic breadth of a specialist predator (B _i  = 0.37). The mean δ¹⁵N and δ¹³C values were 13.07 ± 0.52 and −16.34 ± 0.37, respectively. No significant difference was found in the δ¹⁵N values from the sea lion rookeries, but differences were found inter- and intra-population in δ¹³C values for pups from different groups (ANOVA P < 0.05). Our results indicate that diet diversification is present in the Galapagos sea lion and may play important role to the survival of the species in a habitat where pinniped populations are limited.     

Spatial patterns and environmental correlates in leaf-associated epifaunal assemblages of temperate seagrass (<Emphasis Type="Italic">Zostera marina</Emphasis>) meadows

We estimated and tested variability of seagrass leaf-associated epifaunal assemblages at a range of scales. Sampling was performed in 36 seagrass (Zostera marina) meadows within three regions along the Swedish west coast following a hierarchical design (samples separated by 10 s m, km or 100 km). Results showed strongest variability (43–81%) at the intermediate amongst-meadow (km) scale using biomass of functional categories, while considering taxa composition the within-meadow (10 s m) scale contributed most to variability (60%). Using functional categories, we found that embayment exposure and seagrass shoot density were the most important predictor variables explaining part of the variability in biomass of suspension feeders (bivalves and barnacles) and grazers. In contrast, variability in epifaunal taxa composition was predicted mainly by sediment chemistry, substratum coverage and geographical positioning. Our findings suggest that models to develop predictive power and mechanistic understanding should focus on variables and processes varying at small and intermediate scales rather than those varying at larger scales.     

Feeding ecology of the grooved tiger shrimp <Emphasis Type="Italic">Penaeus semisulcatus</Emphasis> De Haan (Decapoda: Penaeidae) in inshore waters of Qatar,Arabian Gulf

The feeding ecology of the green tiger shrimp Penaeus semisulcatus was studied in inshore fishing grounds off Doha, Qatar, using a combination of stable isotope (δ¹³C and δ¹⁵N) analysis and gut contents examination. Samples of post-larvae, juvenile and adult shrimp and other organisms were collected from intertidal and subtidal zones during the spawning season (January–June). Shrimp collected from shallow water seagrass beds were mostly post-larvae and juveniles and were significantly smaller than the older juveniles and adults caught in deeper macroalgal beds. Gut content examination indicated that post-larvae and juvenile shrimp in seagrass beds fed mainly on benthos such as Foraminifera, polychaetes, benthic diatoms and small benthic crustaceans (amphipods, isopods and ostracoda), whereas larger shrimp in the macroalgal beds fed mainly on bivalve molluscs and to a lesser extent polychaetes. In shrimp from both seagrass and algal beds, unidentifiable detritus was also present in the gut (18, 32%). δ¹³C values for shrimp muscle tissue ranged from −9.5 ± 0.26 to −12.7 ± 0.05‰, and δ¹⁵N values increased with increasing shrimp size, ranging from 4.1 ± 0.03 to 7.7 ± 0.11‰. Both δ¹⁵N values and δ¹³C values for shrimp tissue were consistent with the dietary sources indicated by gut contents and the δ¹³C and δ¹⁵N values for primary producers and prey species. The combination of gut content and stable isotope data demonstrates that seagrass beds are important habitats for post-larvae and juvenile P. semisulcatus, while the transition to deeper water habitats in older shrimp involves a change in diet and source of carbon and nitrogen that is reflected in shrimp tissue stable isotope ratios. The results of the study confirm the linkage between sensitive shallow water habitats and the key life stages of an important commercially-exploited species and indicate the need for suitable assessment of the potential indirect impacts of coastal developments involving dredging and land reclamation.     

Human impact on <Emphasis Type="Italic">Paracentrotus lividus</Emphasis>: the result of harvest restrictions and accessibility of locations

The sea urchin Paracentrotus lividus is common in the Mediterranean Sea in shallow subtidal rocky habitats, and it is intensely harvested for commercial and recreational purposes. This study is aimed at investigating whether the effects of harvest restrictions of P. lividus in rocky reef habitats interact with the accessibility of locations in structuring sea urchin population (total and commercial-sized individuals). These results are important for generating hypotheses about the influence of human harvesting on P. lividus and for addressing suitable measures of conservation. Paracentrotus lividus was sampled after the end of the sea urchin harvesting period (May–July 2007) within the Gulf of Alghero (North West Sardinia), where the Capo Caccia–Isola Piana Marine Protected Area (MPA) was established since 2002. Paracentrotus lividus was sampled at sixteen locations and attributed in groups of four to 4 combinations of harvest restrictions (Restricted Harvest, RH, vs. Unlimited Harvest, UH) and accessibility (Boat vs. Car), which correspond to a gradient of potential human activity on P. lividus in the ranked order of very low (RHBoatfar), low (RHBoatclose), moderate (RHCar) and high (UHCar). At each location, two depth ranges of 3–7 and 8–12 m were considered. At each of these depths, two areas of about 100-m² size were chosen. The density of P. lividus was assessed in ten quadrats of 1 × 1 m, and the size of 100 individuals (test diameter) was considered. Human activity has been found to significantly affect population structure of P. lividus influencing the proportion of individuals larger than 50 mm. Although harvest was restricted by MPA regulations, a significantly lower abundance of large individuals was found at sites accessible by car. This result highlights that there is an effect of harvest restrictions in relation to accessibility and emphasizes the need to carefully address the enforcement of the MPA toward easily accessible sites. Thus, surveillance and investment in enforcement of marine reserves seem crucial points that may provide the greatest return on maintaining the ecological benefits to the fishery activities.     

Automated method for the determination of total arsenic and selenium in natural and drinking water by HG-AAS

A multicommutated flow system was designed and evaluated for the determination of total arsenic and selenium by Hydride Generation Atomic Absorption Spectrometry (HG-AAS). It was applied to the determination of arsenic and selenium in samples of natural and drinking water. Detection limits were 0.46 and 0.08 μg l⁻¹ for arsenic and selenium, respectively; sampling frequency was 120 samples h⁻¹ for arsenic and 160 samples h⁻¹ for selenium. Linear ranges found were 1.54–10 μg l⁻¹ (R = 0.999) for arsenic and 0.27–27 μg l⁻¹ (R = 0.999) for selenium. Accuracy was evaluated by spiking various water samples and using a reference material. Recoveries were in the range 95–116%. Analytical precision (s _r (%), n = 10) was 6% for both elements. Compared with the Standard Methods, APHA, 3114B manual method, the system consumes at least 10 times less sample per determination, and the quantities of acid and reducing agent used are significantly lower with a reduction in the generation of pollutants and waste. As an additional advantage, the system is very fast, efficient and environmentally friendly for monitoring total arsenic and selenium levels in waters.     

Among-habitat variation in herbivory on Sargassum spp. on a mid-shelf reef in the northern Great Barrier Reef

Herbivory is widely acknowledged as a key process determining the benthic community structure and resilience of coral reefs. Despite numerous studies that have examined herbivory across reef gradients in the Caribbean, few studies have directly quantified this process on Pacific reefs. Bioassays of two species of erect macroalgae (Sargassum swartzii and S. cristaefolium) were used to quantify variation in grazing intensity across seven habitats of varying depth and wave exposure on a mid-shelf reef in the northern Great Barrier Reef. Removal rates of Sargassum varied significantly among habitats, with both species displaying broadly similar patterns. The shallow habitats on the exposed aspect of the reef (i.e. reef crest, flat and back reef) experienced the highest reductions in mass (81.4–91.6% day⁻¹) for both S. swartzii and S. cristaefolium, while the deeper exposed habitats (reef slope and base) displayed the lowest reductions (3.8–13.4% day⁻¹) over a 24 h period. In contrast, the grazing intensity varied between the two species in the three habitats on the leeward aspect of the reef. Reductions in mass remained relatively high for S. swartzii on the patch reef and sheltered reef base and flat (62.7–76.5% day⁻¹) but were considerably lower for S. cristaefolium (37.9–63.5% day⁻¹) across the same habitats. Surprisingly, the rates of removal of Sargassum displayed no relationship with the density or biomass of roving herbivorous fishes or those species known to consume erect macroalgae, either collectively or independently. These results suggest that the relationship between browsing rates and herbivorous fish biomass is complex and may be driven by species that are underestimated in visual surveys. Direct quantification of browsing intensity using assays revealed a different pattern to inferences based on herbivore densities and highlights the potential difficulties of evaluating ecosystem processes based on visual census data alone.     

Spatial distribution,population dynamics and productivity of <Emphasis Type="Italic">Spisula subtruncata</Emphasis>: implications for <Emphasis Type="Italic">Spisula</Emphasis> fisheries in seaduck wintering areas

Bivalves are important in shallow marine habitats, not at least being the major food resource for seaducks such as the common scoter (Melanitta nigra), thousands of which are wintering on the Western Coastal Banks, near the Belgian-French border (North Sea). Next to this ecological importance, fishable stocks of one of these bivalves, Spisula subtruncata, occur in the area. This study aimed at investigating S. subtruncata’s spatial distribution, population dynamics and productivity and its implications for a sustainable Spisula fishery in seaduck wintering areas. The spatial distribution of S. subtruncata was studied in 1994 and 1997 in two areas of the Belgian Western Coastal Banks. The population dynamics and production were investigated by monthly sampling of two stations between April 1995 and April 1996 and a seasonal sampling between April 1996 and April 1998. Spisula subtruncata had a patchy distribution in the deeper (6 m), fine sandy (200 ± 20 μm) sediments of the Abra alba community, mainly found in the western most part of the Western Coastal Banks. In August 1995, an overwhelming and successful recruitment was observed in this area: local densities were as high as 150,000 ind m⁻². Minor, non-successful recruitments were detected in August 1996 and 1997. Due to space limitation, high densities of S. subtruncata are hypothesized to be responsible for the occurrence of aberrant shapes as observed from August 1996 onwards. Growth was described by a seasonally oscillating version of the von Bertalanffy growth function (VBGF): a growth stop was observed from late autumn till early spring. The VBGF parameters K (growth constant) and L _∞ (asymptotic length) were estimated at 0.7–0.9 and 31–33 mm. A combination of length and individual biomass increment showed: (1) a faster length increment of smaller individuals during the second growing period (catching-up phenomenon), (2) a constant length combined with a decreasing individual biomass during the suboptimal winter periods (except for the first winter, when the individual biomass slightly increased), (3) a positive relationship between the individual biomass decrease and the seawater temperature during the winter periods, and (4) a strong increase of the individual biomass in early spring (April 1997 and 1998) because of gametogenesis, followed by a decrease because of spawning (August 1997). The extremely high total production of the 1995 year class in the tidal gully (Potje) during the study period was estimated at approximately 1,500 g ash-free dry weight (ADW) m⁻² or 600 g ADW m⁻² on average per year. Shellfisheries for S. subtruncata within seaduck wintering areas, such as the Western Coastal Banks, should be carefully deliberated since (1) an important food resource for the seaducks will decrease, (2) the ecologically most diverse and rich macrobenthic A. alba community will be heavily affected, and (3) the recovery of Spisula populations after depletion is expected to be erratic.     

Distributional patterns of adult male loggerhead sea turtles (<Emphasis Type="Italic">Caretta caretta</Emphasis>) in the vicinity of Cape Canaveral,Florida, USA during and after a major annual breeding aggregation

Satellite transmitters were attached to 25 reproductively active and four inactive adult male loggerhead sea turtles (86.6–107.0 cm SCLmin) captured from the Port Canaveral, FL, USA shipping channel to assess horizontal and vertical distributions. During the breeding period, male loggerheads aggregated (44% of 755 turtle days) in a 117.6 km² core area that encompassed the shipping channel. Median dive duration during the breeding period was 27 min (IQR = 15–42 min) and males spent 4% (IQR = 3–5%) of the time at the surface, with significantly shorter dives associated with reproductively active males. Migrant and resident males dispersed concurrently, with residents shifting > 30 km east across the continental shelf over a more protracted departure schedule than migrants. Dive duration and time spent at the surface increased through the fall. Cluster analysis revealed the strongest association for dive duration with sea state during and after the breeding period, with significantly longer dives during more turbulent conditions. In contrast, univariate associations with surface interval duration were not elucidated.     

Feeding behaviour of the sea cucumber <Emphasis Type="Italic">Cucumaria frondosa</Emphasis> (Echinodermata: Holothuroidea) in the laboratory and the field: relationships between tentacle insertion rate,flow speed,and ingestion

The sea cucumber, Cucumaria frondosa, is a benthic suspension feeder that captures food particles on its tentacles and then inserts them into its mouth one at a time. Previous studies have suggested that tentacle insertion rate (TIR) could be a useful indicator of food intake. The present study determined whether flow velocity affects TIR and whether TIR is a good indicator of ingestion. Video observations of sea cucumbers in Passamaquoddy Bay (45°01.70N, 66°55.74W) in August 1995 showed that TIRs increased with velocities up to 55 cm s⁻¹ and decreased steadily at flows above that up to 130 cm s⁻¹. In October 2006, laboratory flume studies were carried out on specimens collected from the same site in the previous August. Temperature and salinity (12°C and 32) in the flume were the same as in the field at the time of collection. There was high individual variation in feeding behavior at free-stream velocities of 4–40 cm s⁻¹ and TIR was independent of flow. As the number of tentacle insertions increased in the flume experiments, the amount of chloropigments in the digestive tracts of the sea cucumbers also increased. This suggests that TIR, which can be measured non-intrusively using remote video techniques, could be a good indicator of feeding behavior and ingestion in C. frondosa.     

Oceanographic preferences of Atlantic bluefin tuna, <Emphasis Type="Italic">Thunnus thynnus</Emphasis>, on their Gulf of Mexico breeding grounds

Electronic tagging and remotely sensed oceanographic data were used to determine the oceanographic habitat use and preferences of Atlantic bluefin tuna (Thunnus thynnus L.) exhibiting behaviors associated with breeding in the Gulf of Mexico (GOM). Oceanographic habitats used by 28 Atlantic bluefin tuna exhibiting breeding behavior (259 days) were compared with available habitats in the GOM, using Monte Carlo tests and discrete choice models. Habitat utilization and preference patterns for ten environmental parameters were quantified: bathymetry, bathymetric gradient, SST, SST gradient, surface chlorophyll concentration, surface chlorophyll gradient, sea surface height anomaly, eddy kinetic energy, surface wind speed, and surface current speed. Atlantic bluefin tuna exhibited breeding behavior in the western GOM and the frontal zone of the Loop Current. Breeding areas used by the bluefin tuna were significantly associated with bathymetry, SST, eddy kinetic energy, surface chlorophyll concentration, and surface wind speed, with SST being the most important parameter. The bluefin tuna exhibited significant preference for areas with continental slope waters (2,800–3,400 m), moderate SSTs (24–25 and 26–27°C), moderate eddy kinetic energy (251–355 cm² s⁻²), low surface chlorophyll concentrations (0.10–0.16 mg m⁻³), and moderate wind speeds (6–7 and 9–9.5 m s⁻¹). A resource selection function of the bluefin tuna in the GOM was estimated using a discrete choice model and was found to be highly sensitive to SST. These habitat utilization and preference patterns exhibited by breeding bluefin tuna can be used to develop habitat models and estimate the probable breeding areas of bluefin tuna in a dynamic environment.