Identifying trophic relationships within the high Arctic benthic community: how much can fatty acids tell?

Multivariate analysis of fatty acids (FA) profiles proved to be a useful tool for demonstrating feeding preferences of Arctic invertebrates belonging to several taxonomic groups collected during summer and winter seasons in the Spitsbergen fjords (Arctic). Within phytodetrivorous taxa, the enhanced proportions of 16:1n-7, C16 polyunsaturated fatty acids (PUFA) and 20:5n-3 in crustaceans clearly reflected selective ingestion of diatoms, while high amounts of 22:6n-3 and C18 FAs found in molluscs indicated flagellate-based nutrition. High levels of C20 PUFA and 16:1n-7 together with the typical bacterial FAs were found in winter specimens of deposit-feeding polychaetes showing their reliance on highly reworked organic matter during this season. Our results suggest that 18:1n-9 may not be a reliable marker of carnivory feeding within benthic taxa. Lipid signatures of omnivores and carnivores/detrivores usually originated from a variety of dietary sources, of which few possess highly characteristic FA features. Still, elevated levels of Calanus markers (20:1 and 22:1 moieties) characterized species linked to the pelagic food chains, while 20:4n-6 proved to be a useful indicator of foraminiferan consumption. We highlight the need for a multimethod approach, since complexity of benthic food webs along with general lack of unambiguous FA trophic markers prevents tracking of trophic relationships with use of FA analysis alone. Based on their FA composition, we showed that benthic species represent a source of essential PUFA and could play a fundamental role in the Arctic food webs transferring energy derived from variable pelagic and benthic resources to upper trophic levels.     

Effects of algae-enriched rotifers on winter flounder (Pseudopleuronectes americanus) gene expression during metamorphosis

The aim of this study was to evaluate the effect of a dietary highly unsaturated fatty acid (HUFA) deficiency on winter flounder Pseudopleuronectes americanus metamorphosis by examining the growth and the expression of genes involved in some key metabolic processes: lipid digestion, oxidative stress, and growth. Three groups of fish were fed rotifers enriched with different blends of microalgae providing different HUFA profiles: (1) a diet comprising a mixture of three microalgae, Nannochloropsis oculata, Isochrysis galbana, and Pavlova lutheri (Cocktail diet), which contained a balanced combination of ecosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and arachidonic acid (AA); (2) the N. oculata diet (Nanno diet), with a low level of DHA; and (3) the I. galbana diet (Tiso diet), characterized by low levels of EPA and AA. The results indicate that the need for DHA increased from settlement and for EPA and AA from 15 days after settlement. The lower HUFA content in the Tiso and Nanno diets did not affect larval development or lipid reserve accumulation. The superoxide dismutase gene expression suggests a reduced oxidative stress in the Cocktail group, and overall results indicate that gh gene expression could be a valuable indicator of development at the molecular level in response to dietary HUFA quality during metamorphosis in winter flounder.     

Mass mortality and slow recovery of Diadema antillarum: Could compromised immunity be a factor?

Long-spined sea urchins (Diadema antillarum-a) began dying in January 1983 and over the next year virtually disappeared from the Caribbean. Decades later, Diadema densities remain low, with only very limited recovery in some areas. Ecological extinction of Diadema is a factor in the transformation of coral to barren algae-covered rock that has occurred in the Caribbean during the past 25 years. Working with sea urchins collected from St. Croix, United States Virgin Islands, we asked whether the immune system of Diadema differs from those of other common Caribbean urchins that did not experience the die-off. Using isolated coelomocytes, we tested humoral responses of the urchins with classic stimulators in numerous humoral immune assays. All coelomocytes responded to stimulators—with one notable and statistically significant exception—D. antillarum did not respond to lipopolysaccharide. Our results indicate that Diadema may have a weakness in its humoral defense response that is independent of local stressors and may help explain why Caribbean Diadema was vulnerable to the 1983 epidemic and has shown slow and limited recovery since then.     

Constancy and change in marine predator diets across a shift in oceanographic conditions in the Northern California Current

Variable ocean conditions can greatly impact prey assemblages and predator foraging in marine ecosystems. Our goal was to better understand how a change in ocean conditions influenced dietary niche overlap among a suite of midtrophic-level predators. We examined the diets of three fishes and one seabird off central Oregon during two boreal summer upwelling periods with contrasting El Niño (2010) and La Niña (2011) conditions. We found greater niche specialization during El Niño and increased niche overlap during La Niña in both the nekton and micronekton diet components, especially in the larger, more offshore predators. However, only the two smaller, more nearshore predators exhibited interannual variation in diet composition. Concurrent trawl surveys confirmed that changes in components of predator diets reflected changes in the prey community. Using multiple predators across diverse taxa and life histories provided a comprehensive understanding of food-web dynamics during changing ocean conditions.     

Fine-scale genetic structure in the surface brooding Caribbean octocoral,Antillogorgia elisabethae

Larval dispersal is a critical component of marine species’ life histories because it controls their population dynamics. Dispersal distance can be inferred by the presence and scale of spatial genetic structure (SGS). The larvae of Antillogorgia elisabethae, a surface brooding Caribbean octocoral, have been observed to settle within meters of maternal colonies, although many disperse over greater distances. Using a spatially hierarchical sampling design, A. elisabethae recruits were collected from a site off the coast of Great Abaco, The Bahamas, in June of 2009–2011. Seven microsatellite loci were used to determine whether genetic structure was present among recruits on scales of <1 m to 10s of meters. Multilocus genotypes were autocorrelated within spatial distance classes using Moran’s I coefficient as an estimate of genetic similarity, and Rousset’s genetic distance (â). Genetic structure was present on a scale of <10 m in 2010, but not in the other 2 years, suggesting that larval dispersal was more localized in 2010. Moran’s I coefficients were positive and significant for 0–1, 1–2 and 2–5 m classes in 2010, and the average genetic distance (â) among recruits in the 0–1 m class was significantly lower than the other classes. Autocorrelograms suggested that genetic patch sizes were 7.5 m in 2010, and 20 m in 2009 and 2011. Differences in the SGS of recruits between years might reflect temporal variation in temperature, wind and/or current speeds affecting larval dispersal, or variation in reproduction at the site.     

Does temporal and spatial segregation explain the complex population structure of humpback whales on the coast of West Africa?

Humpback whales (Megaptera novaeangliae) in the Southeastern Atlantic Ocean (International Whaling Commission ‘Breeding Stock B’—BSB) are distributed from the Gulf of Guinea to Western South Africa. Genetic data suggest that this stock may be sub-structured, but it remains unknown if this is due to reproductive segregation. This paper evaluates the spatial and temporal population structure of BSB humpback whales using a combination of maternally and bi-parentally inherited markers. The genetic differentiation that we identify in this study could be due to a combination of (1) spatial and/or temporal segregation on breeding grounds in the greater Gulf of Guinea, (2) the possibility of maternally inherited site fidelity to specific feeding grounds and (3) the use of two generalized but exclusive migratory routes (coastal and offshore) between feeding and breeding areas. Further, photo-identification and genetic sampling efforts in other areas of the Sub-Saharan Western Africa winter range and targeted deployment of satellite tags would help to clarify some of the apparent complexity in the population structure of animals biopsied in this region.     

Recent expansion led to the lack of genetic structure of Sargassum aquifolium populations in Southeast Asia

Phylogeographical study of the brown macroalga, Sargassum aquifolium using nuclear internal transcribed spacer 2, plastidal RuBisCo spacer, and mitochondrial cytochrome oxidase subunit-III revealed the populations in Southeast Asia to be homogeneous. On the other hand, genetic differences were detected between populations from Southeast Asia and western Pacific Islands/Guam, suggesting the presence of genetic break between these regions. This further suggests that populations of S. aquifolium may have survived east of Sunda Shelf during the Last Glacial Maximum and recent recolonization led to homogeneity of the populations in the Sunda Shelf region. Recolonization could be facilitated by year-round reproduction of the populations and dispersal of germlings on floating thalli by coastal currents. Restricted current flow across Maluku Sea and directional equatorial current flows could have isolated the Pacific Island and Guam populations from those of Southeast Asia. Our results support the presence of multiple refugia as the source of different lineages of S. aquifolium populations with a lack of secondary contact in the post-glacial dispersal between Southeast Asia and western Pacific as the mechanisms behind the phylogeographical patterns observed.     

Demographic parameters of two populations of red coral (Corallium rubrum L. 1758) in the North Western Mediterranean

The demographic and reproductive structure of populations represents the main data set needed for conservation and management plans. Mediterranean red coral Corallium rubrum has been exploited for 2,000 years, but only recently management plans have been solicited by the international community. We examined and compared the demographic features of two red coral shallow populations located in distinct geographic locations: Portofino (Italy) and Cap de Creus (Spain). Adults and juveniles density, growth rates, population size and age structure, fecundity and fertility were examined. Juveniles were the dominant class (33 %) in both populations. The analysis of the gamete content of 653 colonies revealed that the populations have balanced sex ratios and similar fertility and polyp fecundity. The average annual growth rate, determined on 119 colonies by annual growth rings count, was similar in both populations (0.24 mm year^?1), decreasing with colony age. Maximum life span of 99 % of the colonies was 60 and 40 years at Portofino and Cap de Creus, respectively. Minimum harvestable size (7 mm basal diameter) was reached in 30–35 years, and the percentage of colonies above it was 6.7 % at Portofino and 2.1 % at Cap de Creus, where juvenile and adult colony densities were significantly lower and the percentage of commercial-sized colonies reduced by 25 % in just a few years. Notwithstanding similar growth and fecundity, the two populations showed different densities and size/age structures suggesting local factors, together with different fishing pressures, have to be taken into account in the management plans for this species.     

Abundance of harbour porpoises (Phocoena phocoena) in the western Baltic,Belt Seas and Kattegat

In July 2012, a ship-board double-platform line-transect survey was conducted to assess harbour porpoise (Phocoena phocoena) abundance in the Kattegat, Belt Seas and the Western Baltic. A total of 826 km of track lines were surveyed between the 2nd and 21st of July 2012, and 169 observations were made by the primary observers, comprising a total of 230 porpoises. Fifty-seven observations were identified as duplicate sightings observed by both tracker and primary observers and were used to correct for availability and perception bias of the primary detections. Using Mark–Recapture Distance Sampling analysis, we produced a model using the half-normal key function, including sightability as the only covariate to estimate the density and abundance of harbour porpoise within the 51,511 km² survey area. Estimated detection probability on the transect line, known as g(0), was at 0.571 (±0.074; CV = 0.130). Using a point independence model of the detection function, the abundance of harbour porpoises within the survey area was estimated at 40,475 animals (95 % CI 25,614–65,041, CV = 0.235) with an associated density of 0.786 animals km^?2 (95 % CI 0.498–1.242, CV = 0.235) and an average group size of 1.488 animals. These results reflect densities obtained during the SCANS surveys in 1994 and 2005, indicating no significant population trend in the area. However, it should be noted that the survey area covers more than one population and that results are therefore not necessarily reflecting local population trends. Until proper population borders are obtained, the abundance estimate provides baseline data for future monitoring and is an important input to the assessment of the conservation status of harbour porpoises in the area.     

Predation of calanoid copepods on their own and other copepods’ offspring

Predation of eggs and nauplii by adult copepods is often used to explain unexpected death rates in population dynamics studies, but the phenomenon has been rarely investigated or quantified. Therefore, we studied the predatory feeding of adult females (Acartia clausi, Centropages hamatus, Centropages typicus, and Temora longicornis) on their own and other species’ eggs and young nauplii with different densities of single animal-prey, mixtures of animal-prey and in the presence of diatoms. All species preyed on eggs and nauplii of their own and all other species. Maximal egg predation varied between 7 and 64 eggs fem^?1 day^?1. Ingestion of Centropages spp. eggs was lowest, potentially due to the spiny egg surface. Maximal feeding rates on nauplii ranged from 5 to 45 nauplii fem^?1 day^?1. T. longicornis preferred eggs, when eggs and nauplii were offered together at the same densities, and the other predators selected for nauplii. At a diatom concentration of 60 μg C l^?1 predation on eggs by C. typicus was higher than without algae, whereas A. clausi and T. longicornis did not change their uptake of eggs. Feeding on nauplii in the presence of diatoms was again enhanced in C. typicus, and unaffected in A. clausi and C. hamatus. T. longicornis reduced its feeding on nauplii in the presence of diatoms. Calculated predation rates, using field abundances of predators and prey, suggest that predation of copepods on their own young stages may account for ca. 30 % of total mortality of young stages in North Sea copepod populations.     

Temporal shifts in the fatty acid profiles of rocky intertidal invertebrates

Fatty acid profiles were determined in rocky intertidal suspension-feeders (mussels and polychaetes) and grazers (limpets and sea urchins) on a monthly basis over 1 year to assess potential dietary overlap between consumers occupying the same trophic guild, and any temporal shifts in diets. Both reproductive and non-reproductive tissues were assessed in an attempt to separate influences of food quality with those of life cycle. Relative variability in fatty acids over time could not be predicted from the feeding guild occupied by a consumer, and influential factors of the temporal shifts included both dietary and reproductive dynamics (even in muscle tissues). Species in the same trophic guild occupied separate trophic niches throughout the year, hence minimising competitive interactions regarding food acquisition. Based on overall variation in fatty acid profiles of muscle tissues, the suspension-feeders Perna perna and Gunnarea gaimardi and the grazing limpet Cymbula oculus occupied narrower feeding niches relative to the grazing sea urchin Parechinus angulosus. Our results provide compelling evidence for potentially large changes in the lipid composition of intertidal invertebrate populations over relatively small temporal scales (i.e. month to month), and these have important implications for short-term field collections intended for assessing invertebrate diets.     

Seasonal changes in movements and habitat preferences of the scalloped hammerhead shark (Sphyrna lewini) while refuging near an oceanic island

Movements and habitat preferences of sharks relative to a central location are widely documented for many species; however, the reasons for such behaviors are currently unknown. Do movements vary spatially or temporally or between individuals? Do sharks have seasonal habitat and environmental preferences or simply perform movements at random at any time of the year? To help understand requirements for the designation of critical habitats for an endangered top predator and to develop zoning and management plans for key habitats, we examined vertical and horizontal movements, and determined habitat and environmental preferences of scalloped hammerhead sharks (Sphyrna lewini). We tracked seven hammerheads for 19–96 h at Wolf Island (1.38ºN, 91.82ºW) between 2007 and 2009 using ultrasonic transmitters with depth and temperature sensors, and we profiled temperature through the water column. Movements of individual hammerheads fell in two classes: constrained (remaining near the island) and dispersive (moving offshore to pelagic environments). The central activity space or kernel off the southeast side of Wolf Island was small and common to most, but the area varied among individuals (mean ± SE 0.25 ± 0.2 km²), not exceeding 0.6 km² for any of the sharks, and not changing significantly between seasons. In general, hammerheads showed preference for the up-current habitat on the eastern side of Wolf Island in both the warm and cold seasons. However, the depth of sharks varied with season, apparently in response to seasonal changes in the vertical structure of temperature. Hammerheads performed frequent vertical excursions above the thermocline during offshore movements and, in general, were observed to prefer temperatures of 23–26 °C found above the thermocline. At times, though individuals moved into the thermocline and made brief dives below it. Our results provided evidence that hammerheads (1) are highly selective of location (i.e., habitat on up-current side of island) and depth (i.e., top of the thermocline) while refuging, where they may carry out essential activities such as cleaning and thermoregulation, and (2) perform exploratory vertical movements by diving the width of the mixed layer and occasionally diving below the thermocline while moving offshore, most likely for foraging.     

Interactions among sea otters, sea stars, and suspension-feeding invertebrates in the western Aleutian archipelago

The structuring and organizing effects of apex predators on ecosystems are becoming increasingly well documented. The enhancement of kelp forests via sea otter predation on herbivorous sea urchins is among the earliest and best known examples. This study provides evidence for direct and indirect trophic interactions among sea otters, predatory sea stars, and filter-feeding mussels (Mytilus trossulus) and barnacles (Semibalanus cariosis). In western Massacre Bay at Attu Island (173°E, 53°N), subtidal transects showed sea star body size and biomass density declined markedly between 1983 and 1994 as sea otters reinhabited this area. Mussels and barnacles translocated from the rocky intertidal zone to shallow subtidal habitats to assess loss rates from sea star predation showed lower mortality rates after the arrival of sea otters. Prey mortality rates in subtidal caged controls were consistently low and similar to those of intertidal controls in both years. These findings elucidate a trophic pathway by which sea otters can influence ecosystems separate from the well-known sea otter/sea urchin/macroalgae cascade.     

Shift in nutrient and plankton community in eutrophic lake following introduction of a freshwater bivalve

The impact of the freshwater bivalve Corbicula leana on plankton community dynamics was examined during a cyanobacterial bloom period. Nutrient and chlorophyll concentrations, primary productivity, and phytoplankton and zooplankton communities in the experimental enclosures were measured at 2-3 day intervals. The introduction of mussels reduced net primary productivity and phytoplankton and chlorophyll. Chlorophyll decreased immediately following addition of 100 mussels and then increased over time. After 600 mussels were added, chlorophyll decreased continuously from 87to 25 microg l(-1), approaching that in the mussel-free enclosure. Simultaneously, water transparency increased and concentrations of suspended solids and total phosphorus decreased. Mussel addition caused short-term increases in nutrient concentrations, especially following high-density treatment: phytoplankton density decreased, while cell density in the mussel-free enclosure increased. Zooplankton densities in the two enclosures were similar; however, carbon biomass in the mussel enclosure increased, associated with an increase in large zooplankton. The trophic relationship between phytoplankton and zooplankton was positive in the mussel-free enclosure and negative in the mussel-treatment enclosure, possibly reflecting effects of mussels on both consumer and resource control in the plankton community. Thus, filter feeding by Corbicula affects nutrient recycling and plankton community structure in a freshwater ecosystem through direct feeding and competition for food resources.     

Geographical and seasonal variation of trace metal bioavailabilities in the Gulf of Gdansk,Baltic Sea using mussels (<Emphasis Type="Italic">Mytilus trossulus</Emphasis>) and barnacles (<Emphasis Type="Italic">Balanus improvisus</Emphasis>) as biomonitors

The barnacle Balanus improvisus and the mussel Mytilus trossulus have been used as biomonitors of the trace metals Cu, Zn, Cd, Fe, Pb, Mn and Ni at five sublittoral sites in the Gulf of Gdansk (Baltic Sea) between February 2000 and September 2001. The study has established a benchmark against which future biomonitoring programmes will be able to establish changes in local metal pollution, particularly if metal loadings in the river Vistula (draining into the Gulf) alter in the future. The study highlighted differences in trace metal bioavailabilities to both barnacles and mussels, geographically and over time. Accumulated metal concentrations of Cu, Zn, Fe, Pb and Ni, but not Cd or Mn, were correlated in the barnacles and mussels, suggesting that the bioavailabilities of the former metals to the two biomonitors were similar. The barnacles showed greater discriminatory power than the mussels as trace metal biomonitors. Concentrations of trace metals in surficial sediments (<63 m) did not correlate significantly with accumulated metal concentrations in either barnacles or mussels, indicating that sediment metal concentrations are not necessarily good proxy measures of ambient trace metal bioavailabilities to the local coastal filter feeders.Communicated by J.P. Thorpe, Port Erin     

High intertidal community organization on a rocky headland in Maine,USA

A mosaic patchwork of the barnacle Balanus balanoides L., the mussel Mytilus edulis L., and the alga Fucus vesiculosus L. was found in the transitional region between the mid and high intertidal zones on a rocky headland on Mount Desert Island, Maine, USA. The development of the mosaic was observed by following recruitment and survival of B. balanoides in denuded patches located at the same tidal level along a 60 m stretch of shore. Barnacle recruitment was least under canopies of F. vesiculosus and greatest in open areas kept moist at low tide by surf. Barnacle survival after settlement was least under the F. vesiculosus canopy due to the whiplash effect of the algal fronds in the surf and greatest in open areas free from competition from mussels. In open areas, early mortality was correlated with settlement density. In areas of dense settlement (60 spat cm^-2) up to 90% mortality resulted within 5 months from crowding associated with growth. In older individuals crowding produced hummocks of elongated, weakly attached barnacles which were more prone to removal by surf than uncrowded barnacles. Mussels exerted competitive dominance over barnacles for space and the presence of mussel beds prevented further barnacle recruitment. Mussels suffered extensive mortality during winter storms when surf removed dense mats of weakly attached mussels. The patchy distribution of mussels and barnacles results from irregular rock substrata producing numerous environmental patches with respect to wave exposure and drainage at low tide, and from densitydependent mortality of both mussels and barnacles which creates patches of new colonizable space within each environmental patch.     

Coexisting generalist scavengers occupy different feeding niches

Generalist scavengers are perceived to exhibit broad feeding niches, and therefore, it is predicted that coexisting generalist scavengers should exhibit extensive food niche overlap. However, ecological theory suggests that no two species can coexist while using the same limited resources in the same manner because competitive differences between the species will result in one species being outcompeted. Thus, some differentiation of the diets of coexisting generalist scavengers must exist in order to avoid competitive exclusion. In this study, I analyzed the feeding niches of two species of coexisting generalist scavengers (hermit crabs; Clibanarius digueti and Paguristes perrieri) to determine whether the species overlap in their: (1) preferred food items and (2) past diets. Food choice experiments conducted in the field showed that the species’ preferences for the food items offered largely overlapped. However, gut content and stable isotope analyses of collected specimens revealed significant differences in the past diets of the species. These analyses suggest that C. digueti consumes more photosynthetic materials than P. perrieri. The results suggest that the species differentiate their diets despite both feeding opportunistically on carrion and detritus washed into the intertidal zone by the tides.     

Description of a Tetraclita stalactifera panamensis community on a rocky intertidal Pacific shore of Panama

The midlittoral zone at Paitilla Beach, Panama, Is occupied by a group of organisms closely associated with Tetraclita stalactifera panamensis. Upon death, this cirripede provides housing for a number of species bound by common substrata and interacting with each other due to their close physical proximity; the faunistic group associated with each barnacle qualifies then, as a small, well-defined community which represents a subsample of the more comprehensive midlittoral community dominated by T. stalactifera panamensis. In patches where it is abundant, T. stalactifera panamensis occupies 28% of the surface area available. It has a relative abundance of only 1% of the specimens found in the zone, but all the other 95 species (with an average of 26, 810 individuals/m²) identified from the area are associated either with the parietal canals, or the external or internal surfaces of T. stalactifera panamensis tests. Each one of these structures represents a habitat which provides surface for attachment, shelter, or both, to 37 species of polychaetes, 32 of mollusks, 20 of crustaceans, 3 of actiniarians, 2 of pycogonids, 2 of sipunculans and an unknown number of tanaid, nemertean and turbellarian species. The single most diverse space-niche is represented by the parietal canals (H=0.783), occupied mostly by polychaetes. dead barnacles harbor an average of 131 individuals per test, which compose a fauna of higher diversity (H=0.678) than that associated with live barnacles (H=0.163). The latter contain 53 specimens per test on the average. Although there is considerable overlapping of species associated with the different T. stalactifera panamensis space-niches, mollusks are clearly more abundant on internal surfaces, polychaetes in parietal, canals; Balanus spp. on external surfaces, and anemones at the base of the parapet on the external surfaces of the tests. Over 220 species of macro-invertebrates were identified from the rocky intertidal at Paitilla. Most of the species are concentrated in the lower (157 species, 1824 specimens/m²) and midlittoral (96 species, 26, 810 specimens/m²) intertidal zones. Splash zone is depauperate (6 species, 1578 specimens/m²). Of the entire fauna identified from the intertidal, 73 species (33%) occur in more than one zone and 147 (67%) are restricted to a particular belt. This last category of zone-restricted species breaks down into 42% for the lower intertidal, 17% for the midlittoral, 6% for the intermediate zone, and 2% for the splash zone.     

Temporal and spatial variability in stable isotope ratios of SPM link to local hydrography and longer term SPM averages suggest heavy dependence of mussels on nearshore production

Temporal changes in hydrography affect suspended particulate matter (SPM) composition and distribution in coastal systems, potentially influencing the diets of suspension feeders. Temporal variation in SPM and in the diet of the mussel Perna perna, were investigated using stable isotope analysis. The δ¹³C and δ¹⁵ N ratios of SPM, mussels and macroalgae were determined monthly, with SPM samples collected along a 10 km onshore–offshore transect, over 14 months at Kenton-on-Sea, on the south coast of South Africa. Clear nearshore (0 km) to offshore (10 km) carbon depletion gradients were seen in SPM during all months and extended for 50 km offshore on one occasion. Carbon enrichment of coastal SPM in winter (June–August 2004 and May 2005) indicated temporal changes in the nearshore detrital pool, presumably reflecting changes in macroalgal detritus, linked to local changes in coastal hydrography and algal seasonality. Nitrogen patterns were less clear, with SPM enrichment seen between July and October 2004 from 0 to 10 km. Nearshore SPM demonstrated cyclical patterns in carbon over 24-h periods that correlated closely with tidal cycles and mussel carbon signatures, sampled monthly, demonstrated fluctuations that could not be correlated to seasonal or monthly changes in SPM. Macroalgae showed extreme variability in isotopic signatures, with no discernable patterns. IsoSource mixing models indicated over 50% reliance of mussel tissue on nearshore carbon, highlighting the importance of nearshore SPM in mussel diet. Overall, carbon variation in SPM at both large and small temporal scales can be related to hydrographic processes, but is masked in mussels by long-term isotope integration.     

Seston composition of the bottom waters of Great Lameshur Bay,St. John,US Virgin Islands

Seston composition [particulate organic carbon (POC), particulate nitrogen (PN), phyto- and microzooplankton numbers and biomass] was investigated in the bottom waters of Great Lameshur Bay, St. John, Virgin Islands (USA), in October, 1970 during Tektite II Mission 17–50. Mean values of 67.4 g POC · I^-1 and 7.2 g PN · I^-1 were determined. A mean phytoplankton carbon content of 42.2 g · I^-1 and zooplankton carbon content of 5.5 g · I^-1 were calculated from counts. The phytoplankton consisted mainly of dinoflagellates 71.2% phytoplankton carbon. Copepods were the dominant zooplankters (61.8% zooplankton carbon), followed by larvaceans (30.9% zooplankton carbon). Organic carbon content of counted zooplankton faecal pellets ranged between 0.4 and 1.6 g · I^-1, and amounted probably to about 15% of the total zooplankton carbon value. Plankton and detritus components as possible food for coral-reef animals are discussed. The ratio carbon: nitrogen of suspended particles is compared to that of sedimented matter.