Diet and daily ration of two nototheniid fish on the shelf of the sub-Antarctic Prince Edward Islands

The seasonal dietary composition and estimates of daily consumption rate of Lepidonotothen larseni and Gobionotothen marionensis juveniles were obtained for the first time using fish collected near sub-Antarctic Prince Edward Islands during April 1999–2003. The diet of L. larseni consisted mainly of pelagic prey, with copepods and arrow worms making up the most significant prey groups and accounting for 46% and 40% of prey mass, respectively. The diet of G. marionensis was more diverse than that of L. larseni and was composed mainly of benthic prey, including bottom-dwelling decapods (Nauticaris marionis) and sedentary polychaetes, which accounted for 54% and 30% of prey mass, respectively. During the present study, dietary overlap between juveniles of L. larseni and G. marionensis was very low (<5%) indicating that competition for food resources between them was negligible. They not only relied on different prey species, both also exhibited different diel feeding regimes. Daily consumption rate of L. larseni and G. marionensis juveniles was estimated to be 4.5% and 5.2% of body dry mass, respectively. Stomach contents and stable isotope analyses suggested, that both L. larseni and G. marionensis occupy the forth-trophic level of the sub-Antarctic food web but depend mainly on allochthonous and autochthonous (kelp derived) organic matter, respectively.     

Algal communities at Gouqi Island in the Zhoushan archipelago, China

The kelp bed of Gouqi Island lies in the east of the East China Sea, in the Shengsi Archipelago. It is a key component of the island-reef ecosystem. This study evaluated kelp beds on intertidal and subtidal zones from 2004 to 2006. We evaluated seasonal variations in the community structure of macroalgae, and their relationship with water temperature, nitrogen and phytoplankton. The Gouqi Island kelp bed consists mainly of species of Sargassum. Sargassum horneri was the dominant species in subtidal zones, representing 90% of the total biomass. The dominant species in intertidal zones were S. fusiforme, S. horneri, S. thunbergii and Undaria pinnatifida. Fifty-four phytoplankton species were found in the Gouqi Island kelp bed, of which 51 species were found inside the kelp beds, 43 species outside the kelp beds, and 40 species were present both inside and outside the kelp beds. Diatoms were dominant both inside and outside the kelp beds. Except in winter, Skeletonema costatum was dominant, and its abundance in autumn was over 98% of the total abundance. Water temperature was found to be the primary factor influencing the growth of S. horneri in the Gouqi Island kelp bed. S. horneri grew slowly from November to March, and rapidly from March to June. The upper temperature limit for growth of S. horneri was about 18°C. Higher water temperatures can result in a decline in the kelp bed. Nitrogen seemed to be a limiting factor for macroalgal growth. This was particularly true for S. horneri and phytoplankton. Since nitrate is the primary nutrient for S. horneri, its absorption by S. horneri resulted in seasonal changes of nitrate in the ecosystem.     

Evidence for diet partitioning among three coexisting native freshwater fishes in South Africa's Cape Fold Ecoregion

The partitioning of limited resources commonly explains how different species can coexist within the same ecological community. In this 2010 study, the diets of three coexisting freshwater fishes (Cape galaxias Galaxias zebratus, n = 27; Cape kurper Sandelia capensis, n = 60; Breede River redfin Pseudobarbus burchelli, n = 77) were characterised and compared in three headwater streams in South Africa's Cape Fold Ecoregion using gut contents and stable isotope analyses. These data were analysed to ascertain whether the three species exploit distinct trophic niches. Both approaches provided evidence that these species occupy different trophic niches, though with some overlap. However, dietary differences among sites were not consistent and were probably influenced by site-specific factors like resource availability. Pseudobarbus burchelli had a broader niche breadth at Tierkloof Stream than the other two species, but not at Waaihoek or Tierstel Streams. Our results also suggest that P. burchelli consumed a more omnivorous diet than do the other two species, whereas S. capensis occupied a higher trophic position than the other two species and consumed vertebrates. Our findings suggest that these species occupy non-equivalent feeding niches in Cape Fold Ecoregion headwater streams, and that diet partitioning might facilitate their coexistence in these systems.     

Feeding ecology and seasonal diet overlap between Stellifer brasiliensis and Stellifer stellifer in a tropical estuarine ecocline

Seasonal freshwater discharge was important for defining habitat utilization by different ontogenetic phases of Stellifer brasiliensis and Stellifer stellifer along the estuarine ecocline. The middle estuary was important as a nursery and feeding ground for young‐of‐the‐year, and a feeding ground for sub‐adults and adults of both species. These species are zoobenthivorous, but during their life cycle and between different habitats and seasons, their trophic guild can change to opportunist and zooplanktivore. During the late rainy season in the lower estuary, all phases of both species, except juveniles of S. brasiliensis and adults of S. stellifer, showed a niche overlap indicating similarity in prey utilization. The diet composition was qualitatively similar, showing an evident niche overlap of intra and interspecific competition among the Stellifer spp. Although the niches of these species appeared to significantly overlap, some resource partitioning patterns were apparent. The niche overlap was significantly reduced due to the seasonal difference in habitat use and prey consumption along the ecocline of the estuary by different ontogenetic phases. The ingestion of blue nylon fragments by both species was observed and quantified.     

Demographic history,geographical distribution and reproductive isolation of distinct lineages of blue rockfish (Sebastes mystinus), a marine fish with a high dispersal potential

Understanding the barriers to genetic exchange in taxonomic groups that have a high dispersal potential will provide critical information on speciation in general. Blue rockfish (Sebastes mystinus) are good taxa to examine speciation because they are nonmigratory inhabitants of shallow rocky reef habitats along the eastern North Pacific with a pelagic larval stage lasting 3–5 months. The goal of this study was to analyse the evolutionary history and distribution patterns of different lineages within S. mystinus described previously and use this information to understand the speciation process in this group of high dispersal fish. The molecular data derived from specimens sampled over approximately 1650 km of the S. mystinus range revealed a northerly and southerly distribution for the two lineages. Almost equal frequencies of both lineages occurred at centrally located sample locations, with evidence of reproductive isolation between the lineages. A demographic analysis showed that the two lineages diverged and experienced sudden expansion prior to the last glacial maximum, which affected the observed pattern of genetic structure. The spatial distribution, demographic history and degree of genetic distinctiveness found from the genetic analysis, despite the high potential for dispersal in S. mystinus, suggest both lineages diverged in allopatry.     

Niche overlap between juvenile flatfishes, Platichthys flesus and Solea solea, in a southern European estuary and adjacent coastal waters

The distribution and abundance patterns as well as the feeding ecology of two flatfishes, Platichthys flesus (Linnaeus, 1758) and Solea solea (Linnaeus, 1758), were studied in the Douro estuary and adjacent coastal waters (Portugal) in order to evaluate the niche overlap between these species. Fish were collected during sampling surveys conducted every 2 months between November 2000 and March 2002 using a 12‐m otter‐trawl with 18 mm stretched mesh size, at 12 sites within the estuary and six sites in the adjacent coastal area. The highest densities of P. flesus were registered in the middle estuary; a peak density of 9.12 ind 1000 m^?2 was obtained in October 2001. Solea solea densities were low compared with P. flesus; the highest values were also recorded in the middle estuary in October 2001. For both species, the proportion of juveniles was above 90% within the estuary. Highest densities of P. flesus and S. solea were recorded at sites with low water depth and high densities of crustaceans and polychaetes, the main food items in the diet of these species. High values of spatial and diet niche overlap were found between these two flatfishes (0.97 and 0.92, respectively).     

Mortalities of kelp-forest fishes associated with large oceanic waves off central California, 1982–1983

Synopsis Observations of three incidents of the mass mortality of nearshore fishes are reported; each corresponded to periods of high-amplitude, long-period swells during the 1982–1983 El Niño event along the coast of central California. Members of the nearshore kelp forest fish assemblage, primarily of the genusSebastes, accounted for 96% of the observed mortalities andS. mystinus (blue rockfish) alone accounted for 72%.     

Systematic relationships of sympatric pipefishes (Syngnathus spp.): A mismatch between morphological and molecular variation

Analyses of mitochondrial DNA and morphological variation were performed on specimens of all five currently recognised Syngnathus pipefish species from the eastern Pacific Ocean with type localities currently considered to lie within the Californian marine biogeographic province: kelp pipefish Syngnathus californiensis, bay pipefish S. leptorhynchus, barred pipefish S. auliscus, barcheek pipefish S. exilis and chocolate pipefish S. euchrous. Results consistently differentiate S. auliscus from the other species and fail to distinguish all other specimens as distinct species, as indicated by extensive morphological overlap as well as incomplete lineage sorting and considerably low genetic divergence for 16s and coI genes(<1%). This study presents a taxonomic revision of eastern Pacific Syngnathus spp. and proposes the synonymy of S. leptorhynchus, S. euchrous and S. exilis, under the senior synonym, S. californiensis. There is still a need to study populations of Syngnathus spp. from north and south of the Californian province to assess whether these too are synonyms of the two-species recognised here.     

Sexual dimorphism in four species of rockfish genusSebastes (Scorpaenidae)

Synopsis Sexual dimorphisms, and factors influencing the evolution of these differences, have been investigated for four species of rockfish:Sebastes melanops, S. flavidus, S. mystinus, andS. serranoides. These four species, which have similar ecology, tend to aggregate by species with males and females staying together throughout the year. In all four species adult females reach larger sizes than males, which probably relates to their role in reproduction. The number of eggs produced increases with size, so that natural selection has favored larger females. It appears males were subjected to different selective pressures than females. It was more advantageous for males to mature quickly, to become reproductive, than to expend energy on growth. Other sexually dimorphic features include larger eyes in males of all four species and longer pectoral fin rays in males of the three piscivorous species:S. melanops, S. flavidus, andS. serranoides. The larger pectoral fins may permit smaller males to coexist with females by increasing acceleration and, together with the proportionately larger eye, enable the male to compete successfully with the female to capture elusive prey (the latter not necessarily useful for the planktivoreS. mystinus). Since the size of the eye is equivalent in both sexes of the same age, visual perception should be comparable for both sexes.     

Habitat selection and aggression as determinants of spatial segregation among damselfish on a coral reef

Adults of many closely related coral reef fish species are segregated along gradients of depth or habitat structure. Both habitat selection by new settlers and subsequent competitive interactions can potentially produce such patterns, but their relative importance is unclear. This study examines the potential roles of habitat selection and aggression in determining the spatial distribution of adults and juveniles of four highly aggressive damselfishes at Lizard Island, northern Great Barrier Reef. Dischistodus perspicillatus, D. prosopotaenia, D. melanotus, and D. pseudochrysopoecilus maintain almost non-overlapping distributions across reef zones, with adults of one species dominating each reef zone. Juveniles exhibit slightly broader distributional patterns suggesting that subsequent interactions reduce overlap among species. Although habitat choice experiments in aquaria suggest that associations between juveniles and substrata types in the field are partly due to habitat selection, large overlaps in the use of substrata by the different species were also found, suggesting that substratum selection alone is insufficient in explaining the discrete spatial distributions of adults. The strength of aggressive interactions among all four species was tested by a "bottle" experiment, in which an adult or juvenile of each species was placed in the territories of adult fish on the reef. The greatest levels of interspecific aggression were directed against adults and juveniles of neighbouring species. The highest levels of aggression were associated with species exhibiting the greatest levels of overlap in resource use. Evidently both habitat selection and interspecific aggression combine to determine the adult distributions of these species.     

Recruitment and growth of the sea urchin Strongylocentrotus droebachiensis (Muller) following mass mortalities off Nova Scotia,Canada

Recruitment of Strongylocentrotus droebachiensis (Muller) was monitored for four successive years following a mass mortality of this species on a subtidal boulder bottom in St. Margaret's Bay, Nova Scotia. Recently recruited juveniles (1–2 mm diameter) were observed in the fall (September–November) between (1982) and (1984), but not in (1985). Juveniles grew to 6–8 mm diameter at 1-yr post-settlement and 19 mm diameter ((1983) cohort) at 2-yr post-settlement. Individuals > 18 mm diameter had macroscopic gonads in the spring of their third year and spawning probably occurred at 2.75-yr post-settlement. The growth rate of juveniles (3–6 mm initial diameter) maintained in cages with coralline-covered rocks was similar to that of the natural population. Growth and gonad index increased significantly when kelp (Laminaria longicruris (Pylaie)) was added to cages, suggesting that juveniles were food limited in St. Margaret's Bay. Despite an abundance of kelp and other fleshy algae, they remained cryptic under rocks and were not observed grazing on attached plants. The effects of temperature and food supply on juvenile growth and survival were examined in laboratory experiments using factorial designs. Recently-metamorphosed juveniles (from laboratory cultures), maintained at three temperature regimes (5°C, ambient, 16 °C) and two feeding regimes (no added food, coralline algae added), had similar growth rates (over 9 mth) among treatment combinations. However, growth was asymptotic at 16 °C and ambient temperatures, suggesting food limitation. Survival of these juveniles was higher in treatments with coralline algae, but survival was not affected by temperature. Field-collected juveniles (3–6 mm diameter), maintained at three temperature regimes (5°C, ambient, 16 °C) and three feeding regimes (no added food, coralline algae added, and kelp and coralline algae added), grew only in treatments with kelp added as food. In these treatments, growth rates increased with temperature. However, the growth curve at variable ambient temperature regimes was linear, suggesting seasonal acclimation. Survival of the field-collected juveniles was highest in treatments at 5 °C and/or with added kelp.     

Habitat characteristics of juvenile cowcod, <Emphasis Type="Italic">Sebastes levis</Emphasis> (Scorpaenidae), in Southern California

We characterized habitat requirements of juvenile cowcod, Sebastes levis, using information from surveys conducted aboard the manned research submersible Delta. We conducted 303 dive surveys on rocky banks and outcrops in water depths between 28 and 365 m in southern and central California, covering 483 km (963,940 m²) of seafloor. We counted 549,263 fishes from at least 134 species; 216 individuals were juvenile cowcod, S. levis, of 45 cm or less in total length (TL). Juvenile cowcod occupied depths between 52 and 330 m and demonstrated ontogenetic shifts in their habitat associations. Small fish (5–20 cm TL) lived primarily among cobbles or cobbles and small boulders. As fish grew, they moved into high-relief rock habitats, including boulder fields and rock ridges. Small cowcods were found with pygmy, Sebastes wilsoni, and swordspine, Sebastes ensifer, rockfishes. Larger juveniles often associated with juvenile bocaccio, Sebastes paucispinis, juvenile widow rockfish, Sebastes entomelas, and squarespot rockfish, Sebastes hopkinsi. Our study resulted in a characterization of seafloor habitats on a small spatial scale that is relevant to juvenile cowcod nursery areas, which is important when considering effective management strategies for this overfished species.     

Experimental effects of kelp canopies on subtidal coralline algae

Plants are often grouped as canopy species or understorey species because it is thought that that these sets of taxa interact in predictable ways. Mensurative experiments in southern Australia demonstrated that the percentage cover of encrusting coralline algae was greater, and articulated (branching) coralline algae less, on boulders under a canopy of dense kelp (>7 plants per m²), Ecklonia radiata, than on boulders without kelp. Experimental clearances of kelp and reciprocal transplants of boulders between patches of E. radiata and patches without kelp showed that canopies maintained and facilitated the growth of encrusting coralline algae and reduced the cover of articulated coralline algae. Potential artefacts associated with clearing kelp and transplanting boulders were not detected when tested with a series of translocation controls. These results reject the model that the co‐occurrence of E. radiata and encrusting corallines is just an assemblage of plants caused by spatial and temporal coincidence. Instead, they support the model that kelp facilitates the growth and survival of understorey algae.     

The ecology of juvenile flat periwinkles

Juvenile Littorina live lower on the shore than adults of the same species, and they occupy distinct ecological niches. On Fucus serratus the juveniles live on the abaxial surface of submerged fronds, where the smaller ones resemble the surface protuberances. On F. vesiculosus they live in damaged air bladders on emersed fronds.     

An experimental study of the habitat preferences and movement patterns of copper,quillback, and brown rockfishes (Sebastes spp.)

Synopsis A study was designed to test whether habitat association affects the movement patterns and habitat preferences of copper, quillback, and brown rockfishes. Resighting of tagged rockfishes (512 tagged rockfishes and 726 resightings) from July 1986 through June 1988 indicated that home ranges, movements from reefs, and tendency to return from experimental displacement (up to 8.0 km) were significantly different on the three habitat types compared. On high relief rocky reefs, rockfishes maintained small home ranges (most within 30 m²) and displayed strong reef fidelity that was not affected by season; no off-reef movement was detected and rockfishes generally returned from displacements. On artificial reefs, rockfishes also maintained small home ranges (most within 30 m²), however, there were pronounced seasonal habitat preferences. In the summer, artificial reefs become less suitable; considerable off-reef movement occurred and rockfish did not return from displacements. In contrast, during fall and winter, rockfishes remained on artificial reefs and returned from displacements. On low relief rocky reefs, rockfishes maintained considerably larger home ranges (most within 400 m² and some up to 1500 m²) and habitat use was strongly affected by season; rockfishes only inhabited low relief reefs in the summer and only returned from displacements in the summer coincident when peak algal cover. In addition, there was substantial movement between artificial reefs and adjacent low relief reefs; many rockfishes leave artificial reefs in the summer, move to low relief reefs, and return to artificial reefs in the fall when kelp disappears on low relief reefs. Through habitat assessment, movement in response to habitat quality, and ability to home, these rockfish maintain a flexible behavior for optimal habitat use.     

Foraging ecology and niche overlap in pygmy (Kogia breviceps) and dwarf (Kogia sima) sperm whales from waters of the U.S. mid‐Atlantic coast

A complementary approach of stomach content and stable isotope analyses was used to characterize the foraging ecology and evaluate niche overlap between pygmy (Kogia breviceps) and dwarf (K. sima) sperm whales stranded on the U.S. mid‐Atlantic coast between 1998 and 2011. Food habits analysis demonstrated both species were primarily teuthophagous, with 35 species of cephalopods, and 2 species of mesopelagic fishes represented in their overall diets. Pianka's Index of niche overlap suggested high overlap between whale diets (O_n = 0.92), with squids from the families Histioteuthidae, Cranchidae, and Ommastrephidae serving as primary prey. Pygmy sperm whales consumed slightly larger prey sizes (mean mantle length [ML] = 10.8 cm) than dwarf sperm whales (mean ML = 7.8 cm). Mean prey sizes consumed by pygmy sperm whales increased with growth, but showed no trend in dwarf sperm whales. Significant differences were not detected in δ¹⁵N and δ¹³C values of muscle tissues from pygmy (10.8‰ ± 0.5‰, ?17.1‰ ± 0.6‰), and dwarf sperm whales (10.7‰ ± 0.5‰, ?17.0‰ ± 0.4‰), respectively. Isotopic niche widths also did not differ significantly and dietary overlap was high between the two species. Results suggest the feeding ecologies of the pygmy and dwarf sperm whales are similar and both species occupy equivalent trophic niches in the region.     

THE EFFECT OF SEAWEED DIETS ON GROWTH OF GREEN ABALONE,HALIOTIS FULGENS,FROM BAJA CALIFORNIA,MEXICO

Two abalone species: green Haliotis fulgens and yellow Halioti corrugata represent nearly 97% of the total production in the Mexican abalone fishery. It has been assumed that abalone feed on the kelp algae Macrocystis pyrifera. Regional hatcheries use this species as a main source of natural food. M. pyrifera does not occur at the southern limit of the distribution of abalone species along the Baja California Peninsula. In this study, growth rates of juveniles H. fulgens, 17.3 ± 2.2 mm shell length and 0.4 ± 0.2 g body weight, were evaluated. Juveniles were fed with common species in the benthic environments inhabited by abalone along the western coast of Baja California during 191 days. Three diets were based on algae: palm kelp, Eisenia arborea, giant kelp, M. pyrifera and Gelidium robustum, and one on seagrass, Phyllospadix torreyi. Shell length and body growth rates varied between 21.5 μm day^?1 and 2.2 mg day^?1 for E. arborea and between 45.9 μm day^?1 and 6.7 mg day^?1 for M. pyrifera. Higher specific growth rates (SGR) in length and weight were determined for M. pyrifera: 0.2% and 0.7% day^?1. Significant differences between values of juveniles fed M. pyrifera with the rest of the diets were found. The highest mortality (21%) was in juveniles fed the red algae G. robustum.     

Skinny kelp (Saccharina angustissima) provides valuable genetics for the biomass improvement of farmed sugar kelp (Saccharina latissima)

Saccharina latissima (sugar kelp) is one of the most widely cultivated brown marine macroalgae species in the North Atlantic and the eastern North Pacific Oceans. To meet the expanding demands of the sugar kelp mariculture industry, selecting and breeding sugar kelp that is best suited to offshore farm environments is becoming necessary. To that end, a multi-year, multi-institutional breeding program was established by the U.S. Department of Energy's (DOE) Advanced Research Projects Agency-Energy (ARPA-E) Macroalgae Research Inspiring Novel Energy Resources (MARINER) program. Hybrid sporophytes were generated using 203 unique gametophyte cultures derived from wild-collected Saccharina spp. for two seasons of farm trials (2019–2020 and 2020–2021). The wild sporophytes were collected from 10 different locations within the Gulf of Maine (USA) region, including both sugar kelp (Saccharina latissima) and the skinny kelp species (Saccharina angustissima). We harvested 232 common farm plots during these two seasons with available data. We found that farmed kelp plots with skinny kelp as parents had an average increased yield over the mean (wet weight 2.48?±?0.90 kg m^?1 and dry weight 0.32?±?0.10 kg m^?1) in both growing seasons. We also found that blade length positively correlated with biomass in skinny kelp x sugar kelp crosses or pure sugar kelp crosses. The skinny x sugar progenies had significantly longer and narrower blades than the pure sugar kelp progenies in both seasons. Overall, these findings suggest that sugar x skinny kelp crosses provide improved yield compared to pure sugar kelp crosses.

     

All Clone-mates are not Created Equal: Fitness Discounting Theory Predicts Pea Aphid Colony Structure

As many animals form aggregations, group-living is believed to be adaptive. It is not clear, though, if clonal aggregations should have spatial structure, as protecting clone-mates is the genetic equivalent of protecting self. ‘Fitness discounting’ theory states that immediate reproductive opportunities are of greater value than are delayed opportunities. Thus, we hypothesized that spatial structure should exist in colonies of unequal-aged, clonal organisms like aphids. We predicted that, compared to reproductive (5^th instar) individuals, young (2^nd and 3^rd instar) juveniles (i.e., the youngest instars capable of emitting an alarm signal) should occupy the most dangerous feeding positions. As individuals approach reproductive maturity and alarm signals decline (4^th instar), they should occupy increasingly safer feeding positions. We tested these predictions by documenting the spatial distribution of two (green and pink) pea aphid, Acyrthosiphon pisum, asexual lineages (“clones”) at 1, 3, 6, 24, 48, 72, 96, and 120 h after host plant colonization. Confirming our hypothesis, we found that early (2^nd and 3^rd) instar aphids occupied feeding positions with the highest predation risk. Upon reaching the penultimate (4^th) instar, individuals dispersed from the colony to colonize other leaves. Thus, pea aphid colonies are not random aggregations; aphid colony structure can be explained by fitness discounting theory.     

Seascape genetics of the stalked kelp Pterygophora californica and comparative population genetics in the Santa Barbara Channel

We conducted a population genetic analysis of the stalked kelp, Pterygophora californica, in the Santa Barbara Channel, California, USA. The results were compared with previous work on the genetic differentiation of giant kelp, Macrocystis pyrifera, in the same region. These two sympatric kelps not only share many life history and dispersal characteristics but also differ in that dislodged P. californica does not produce floating rafts with buoyant fertile sporophytes, commonly observed for M. pyrifera. We used a comparative population genetic approach with these two species to test the hypothesis that the ability to produce floating rafts increases the genetic connectivity among kelp patches in the Santa Barbara Channel. We quantified the association of habitat continuity and oceanographic distance with the genetic differentiation observed in stalked kelp, like previously conducted for giant kelp. We compared both overall (across all patches) and pairwise (between patches) genetic differentiation. We found that oceanographic transit time, habitat continuity, and geographic distance were all associated with genetic connectivity in P. californica, supporting similar previous findings for M. pyrifera. Controlling for differences in heterozygosity between kelp species using Jost's D_EST, we showed that global differentiation and pairwise differentiation were similar among patches between the two kelp species, indicating that they have similar dispersal capabilities despite their differences in rafting ability. These results suggest that rafting sporophytes do not play a significant role in effective dispersal of M. pyrifera at ecologically relevant spatial and temporal scales.