Habitat-specific Differences Research Articles

Effects of Food Type, Habitat, and Fish Predation on the Relative Abundance of Two Amphipod Species, Gammarus fasciatus and Echinogammarus ischnus

We evaluated the abundance patterns of Gammarus fasciatus and Echinogammarus ischnus in dreissenid and macrophyte areas in Hatchery Bay, Lake Erie before (1997) and after round goby (2001, 2002) invaded the area. Total amphipod abundance was higher before round goby invasion in both habitats. In mussel beds, E. ischnus abundance was similar or significantly higher than G. fasciatus. In macrophytes, G. fasciatus was significantly more abundant than E. ischnus. In laboratory experiments, we compared amphipod survivorship and growth when fed mussel feces and pseudofeces (F+P) or macrophytes with epiphytes (M+E). Gammarus fasciatus survivorship and growth were higher when fed F+P than M+E. Echinogammarus ischnus showed similar survivorship under both diets, but significantly higher growth when fed M+E than F+P. Therefore inter-habitat differences in food resources cannot explain the abundance patterns observed in the lake. We also estimated the relative vulnerability of G. fasciatus and E. ischnus to yellow perch ( Perca flavescens) and round goby ( Neogobius melanostomus) predation in laboratory feeding trials using mussel colonies or macrophyte beds as substrate. Both fish strongly preferred E. ischnus in macrophytes, but consumed relatively more G. fasciatus than E. ischnus in dreissenid habitats. Our results suggest that dreissenid establishment may have facilitated the invasion of E. ischnus. However, habitat-specific differences in vulnerability to fish predation may mediate the coexistence of G. fasciatus and E. ischnus by minimizing expansion of E. ischnus to macrophyte areas. Our results also suggest that round goby invasion can alter amphipod abundance patterns in Lake Erie.

Growth of larval krill, Euphausia superba , in fall and winter west of the Antarctic Peninsula

A quantitative characterization of growth-related parameters for larval and juvenile Antarctic krill, Euphausia superba (Dana), is essential to understanding the early life history of this key species in the Southern Ocean ecosystem. To this end, instantaneous growth rate experiments were conducted with larval and juvenile krill to determine growth increments and molting frequency in situ. All experiments were carried out during fall and winter months (April through September) on nine separate cruises west of the Antarctic Peninsula between 1987 and 1999. A consistent seasonal pattern across years was observed: growth rates decreased during fall (April/May), were minimal in early winter (June), and increased to maximum rates by late winter (September). Habitat-specific differences (water column vs under-ice) in growth rates of larvae collected on the same cruise were not observed in early winter (June 1993; within-year comparison). However, in a between-year comparison, larvae from the under-ice habitat (June/July 1987) had significantly higher growth increments than larvae from the open-water habitat (July 1989). The difference between these two comparisons may be a function of the degree of contrast in food availability in the water column and the sea ice at different times in the winter. Daylength at the time of collection explained 74% of the variation in larval and juvenile growth rates. This correlation may be an indirect effect of the influence of diel cycles on krill behavior and/or primary production in both the water column and ice.

Grazer biomass correlates more strongly with production than with biomass of algal turfs on a coral reef

The biomass of large herbivorous grazing fish on the shallow reef crest of Myrmidon Reef, Great Barrier Reef, is 7.0 times that on the reef slope (15 m depth), and 2.3 times that on the reef flat. Biomass of algal turfs on the crest was only 1.4 and 1.0 times that on the slope and flat, respectively. In contrast, rate of production of algal turfs on the crest was 5.3 and 2.8 times that on the slope and flat, respectively. A multiple correlation between large grazer biomass, algal turf biomass, and algal turf production across the three zones showed that only rate of algal production correlated significantly with large grazer biomass (algal production p=0.007, algal biomass p=0.418). This result suggests that large grazers may aggregate in zones of highest algal turf production. The mechanisms by which fish respond to habitat-specific differences in food production remain unclear.

Influence of wave-induced disturbance on seasonal spawning patterns in the sabellariid polychaete Phragmatopoma lapidosa

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 256:123-133 (2003) - doi:10.3354/meps256123 Influence of wave-induced disturbance on seasonal spawning patterns in the sabellariid polychaete Phragmatopoma lapidosa Daniel A. McCarthy1,2,*, Craig M. Young1, Roland H. Emson2 1Department of Larval Ecology, Harbor Branch Oceanographic Institute, 5600 North, Fort Pierce, Florida 34946, USA 2Division of Life Sciences, King¹s College, University of London, 150 Stamford Street, London SE1 9NN, United Kingdom 3Present address: Smithsonian Marine Station at Fort Pierce, 701 Seaway Drive, Fort Pierce, Florida 34949-3140, USA *Email: mccarthy@sms.si.edu ABSTRACT: The effect of wave-induced disturbance on seasonal spawning patterns of the opportunistic polychaete Phragmatopoma lapidosa (Kinberg, 1867) was investigated by comparing seasonal fecundity, egg size and adult size between intertidal and subtidal worms at Boynton Beach, Florida. Fecundity patterns showed spawning peaks in summer and fall in both habitats, with reduced spawning in late fall and early winter. Subtidal females averaged 1015.2 eggs mm-1 body length (range 0 to 2000 eggs mm-1), while intertidal females averaged 607.4 eggs mm-1 (range 0 to 1520 eggs mm-1). Mean egg diameters were not significantly different between worms from the 2 habitats, ranging between 90.4 µm (SD = 3.7) and 89.5 µm (SD = 4.3) for intertidal and subtidal worms respectively. Inter- and intra-census comparisons of egg diameter, fecundity and adult length revealed few statistically significant relationships, suggesting that intertidal and subtidal worms were the same age. Adult lengths in both habitats did change seasonally. The smallest adult worms were found shortly after massive fall recruitment replaced a large percentage of individuals in both intertidal and subtidal populations. Stepwise multiple regression indicated that 76.2% of the variance in intertidal fecundity was explained by a negative correlation with wave height (40.4%), and a positive correlation with day length (34.7%). In contrast, 85.5% of the variance in subtidal fecundity was explained by a positive correlation with day length (77.4%), and a negative correlation with chlorophyll a concentration (8.1%). While habitat-specific differences in energy available for gametogenesis probably contribute towards the observed fecundity trends, the force of crashing waves could also influence fecundity, as it may affect frequency of spawning in intertidal but not subtidal habitats. KEY WORDS: Phragmatopoma · Polychaetes · Fecundity · Spawning · Reproductive plasticity Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 256. Online publication date: July 17, 2003 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2003 Inter-Research.

Impact of habitat edges on density and secondary production of seagrass-associated fauna

Species richness and abundance of seagrass-associated fauna are often positively correlated with seagrass biomass and structure complexity of the habitat. We found that while shoot density and plant biomass were greater in interior portions of turtle grass (Thalassia testudinum) beds than at edges, mean faunal density was significantly greater at edges than interior sites during 1994. This pattern was also observed in 1995, although differences were not significant. The four numerically dominant taxonomic groups showed varying degrees of elevated densitities at edges ofT. testudinum beds. Peracarids and polychaetes had significantly greater densities at edges oft. testudinum beds, while both decapods and gastropods showed dramatic temporal variability in density, with reversals in density between edge and interior occurring during the course of the study. This within-habitat variability in abundance may reflect both active accumulation of fauna at edges and settlement shadows for species with pelagic larvae. Active accumulation of highly mobile taxa seeking refuge in seagrass beds may explain the differences in density between edge and interior ofT. testudinum patches for peracarids in 1994 and in 1995. Active accumulation at edges may also explain differeces in density for some decapod taxa. Chauges in gastropod densities between habitats may reflect larval settlement patterns. Results showed a distinct settlement shadow for the gastropodCaecum nitidum whose densities (primarily second stage protoconch) increased by more than an order of magnitude in 1994. Settlement shadows and post-settlement processes may also explain density differences of polychaetes between the edge and interior ofT. testudinum patches. The differences in faunal densities between edge and interior habitat resulted in habitat specific differences in secondary production among the major taxonomic groups. On four of five dates in 1994 and in 1995, secondary production was greater at edge than interior locations. These unexpected results suggest that differences in faunal densities and secondary production between edges and interiors of seagrass patches represent a potentially vital link in seagrass trophic dynamics. If this elevated secondary production leads to increases in trophic transfer, then edges may serve as a significant trophic conduit to higher-level consumers in this system.

Factors affecting invasion and persistence of broomCytisus scopariusin Australia

Summary 1 The effective management of invasive plants requires an understanding of their invasiveness in contrasting environments. The effects of disturbance on recruitment of broom Cytisus scoparius , a European shrub invading parts of Australasia, was assessed in a 7-year experiment carried out in two countries, respectively, in its native and exotic ranges. This paper presents the results for Australia and their implications for the biological control of this weed. 2 Disturbance treatments involved removal (cut or cut plus cultivation) and grazing effects on broom seed banks and recruitment, in mature and immature stands and in three habitats, ranging from improved, largely exotic pasture to unimproved native grassland. 3 The time between recruitment and flowering varied between 5 and 7 years depending on habitat, the slowest being in native unimproved grassland. In cultivated plots, regeneration was faster in immature compared with mature broom stands. 4 Following broom removal, whether the ground was cultivated or not had little effect on the speed of regeneration, indicating weak suppression from the ground flora in uncultivated plots. In contrast, grazing tended to increase the rate of regeneration. 5 The timing of seedling establishment had little effect on survival to reproduction, in marked contrast to European populations. The overall rates of seedling mortality were greater in Australia compared with Europe. 6 A simulation model, parameterized from the field data, was used to explore the likely impact of biological control from pre-dispersal seed predation. 7 The simulation studies demonstrated large habitat-specific differences in seed rain requirement for broom persistence and the potential impact of seed predators. Seed rain requirements were fivefold less in improved exotic pasture vs. native grassland. Seed loss of 62% was theoretically sufficient to suppress broom in native grassland, whereas > 97% was required in exotic pasture. 8 This study suggests that successful broom control in Australia is likely to be site dependent, because while broom seed has greater opportunities for recruitment in Australia than in Europe, immature plant mortality can be very high, particularly in native grassland.

Variación fenotípica y genética en el tunicado Pyura praeputialis (Heller, 1878) en el área norte de la Bahía de Antofagasta, Chile

The morphology of “sea squirts” (Urochordata: Tunicata) is highly variable and is expressed in habitat-specific differences intra- and interspecific variation pattern that had hindered the interpretation of such differences as well as their taxonomical, ecological or evolutionary meaning. Here we describe the population genetic structure of three morphotypes (squat, intermediate and tall “sea squirt”) observed in populations of the “piure de Antofagasta”, Pyura praeputialis by enzyme electrophoresis. The study was carried out in three localities in the northern sac of the Bay of Antofagasta, Chile, and distributed along a wave exposure gradient. A total of 17 enzymatic loci were assayed by horizontal starch-gel electrophoresis, three of which (IDH-1, MDH-1 and PGM-1) were polymorphic. The results showed significant genetic differences among localities, but not among morphotypes. These results are contrasted with similar studies conducted on the same species in Australia, on the base that P. praeputialis has recently colonized Antofagasta from Australia. It is suggested that the differences among the morphotypes from Antofagasta are intraspecifics and those from Australia are interspecifics. The possible explanations for the genetic and morphological differences among localities are discussed.

Evaluation of RNA concentration as an indicator of growth in young-of-the-year winter flounder Pseudopleuronectes americanus and tautog Tautoga onitis

White muscle tissue RNA concentration was evaluated as an indirect measure of fish growth. Young-of-the-year winter flounder Pseudopleuronectes americanus and tautog Tautoga onitis were grown in short-term caging experiments conducted during 1994 and 1995 within 3 geographically distinct estuarine systems in the NE of the USA: the Hammonasset River along the Connecticut coast of Long Island Sound, the Navesink River located in the Hudson-Raritan Bay estu- ary in northern New Jersey, and Great Bay-Little Egg Harbor estuary in southern New Jersey. Fish were caged in each of 5 habitat types including: eelgrass, macroalgae, unvegetated areas adjacent to eelgrass, unvegetated areas adjacent to macroalgae, and tidal marsh creeks. White muscle tissue RNA concentration (µg per mg wet tissue wt) was measured in winter flounder and tautog recovered from the cages and compared to instantaneous growth rate measurements of these same fish. RNA concentration was significantly correlated with growth rate measured as length (r = 0.83) and weight (r = 0.79) in winter flounder and length (r = 0.69) and weight (r = 0.73) in tautog. In most cases, estu- ary- and habitat-specific differences in growth rate, as determined by RNA concentration, were sim- ilar to those determined by measuring instantaneous growth. These results validate the use of RNA concentration as an indirect measure of growth in young-of-the-year winter flounder and tautog.

Seasonal and local spatial patterns in the upper thermal limits of corals on the inshore Central Great Barrier Reef

Experimental studies of the upper thermal limits of corals from Orpheus Island, an inshore reef in the central Great Barrier Reef, show that Acropora formosa has a 5-day 50%-bleaching threshold of between 31 and 32 °C in summer, only 2 to 3 °C higher than local mean summer temperatures (29 °C). Summer bleaching thresholds for Pocillopora damicornis and A. elseyi were 1 °C higher (between 32 and 33 °C). The winter bleaching threshold of Pocillopora damicornis was 1 °C lower than its summer threshold, indicating that seasonal acclimatisation may take place. This seasonal difference raises the possibility that at least some corals may be capable of short-term thermal acclimatisation. Neither P. damicornis nor A. elseyi showed habitat-specific (reef flat versus reef slope) differences in bleaching thresholds. Further, colonies of P. damicornis collected from sites 3 km apart also showed no difference in bleaching threshold despite populations of this species responding differently at these two sites during a natural bleaching event. The bleaching thresholds determined in this study are best considered as the maximum tolerable temperatures for local populations of these species because they were determined in the absence of additional stressors (e.g. high light) which often co-occur during natural bleaching events. We consider the 5-day 50% bleaching thresholds determined in these experiments to be fair indicators of upper thermal limits, because >50% of a sample population died when allowed to recover in situ. We found a delay of up to a month in the bleaching response of corals following thermal stress, a result that has implications for identifying the timing of stressful conditions in natural bleaching events.

The value of tethering fishes (winter flounder and tautog) as a tool for assessing predation rates

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 163:45-51 (1998) - doi:10.3354/meps163045 The value of tethering fishes (winter flounder and tautog) as a tool for assessing predation rates Mary Carla Curran1,*, Kenneth W. Able2 1University of South Carolina Beaufort, 801 Carteret St., Beaufort, South Carolina 29902, USA 2Marine Field Station, Institute of Marine and Coastal Sciences, Rutgers University, 800 Great Bay Blvd, c/o 132 Great Bay Blvd, Tuckerton, New Jersey 08087-2004, USA *E-mail: ibfrt34@vm.sc.edu We evaluated the effect of tethering 2 species of juvenile fishes on their behaviour and susceptibility to predation under laboratory conditions in order to determine whether these fishes can be effectively used in field studies designed to assess predation rates. More specifically, this laboratory study investigated: (1) the effect of tethering, which required puncturing the body, on 2 mobile fish prey: the winter flounder Pseudopleuronectes americanus (42 to 85 mm total length, TL), and the tautog Tautoga onitis (47 to 91 mm TL); and (2) whether the predators, the summer flounder Paralichthys dentatus and the blue crab Callinectes sapidus, preferentially preyed upon tethered individuals. The behaviour of tethered individuals varied between species. Tethered P. americanus buried more extensively (i.e. greater percentage of body covered by sand) than untethered individuals. Therefore, tethering this species may reduce predation by visual predators because individuals are less visible. Tethered T. onitis were more likely than untethered individuals to occupy open areas of the experimental pool rather than to be found near shelter. In this case, tethering may increase potential predatory attacks because tethered fish are more accessible. Despite differences in behaviour caused by tethering P. americanus, there was no significant difference between the rates of predation by P. dentatus on tethered versus untethered individuals. However, as predicted by the change in T. onitis behaviour, P. dentatus preyed more frequently on tethered individuals than untethered ones. C. sapidus, a predator that uses olfactory cues, preferentially selected tethered P. americanus. The preference for tethered individuals may depend in part upon the release of prey body fluids and subsequent detection by predators that use olfactory cues. Furthermore, tethered individuals may change their shelter-seeking behaviour, and thus confound potential habitat-specific differences in relative predation rates. As a result, tethering as a tool to determine predation rates should be used cautiously for fishes. At a minimum, laboratory observations to detect tethering artifacts should be conducted before field experiments. Tethering · Predation · Prey behaviour · Prey susceptibility Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 163. Publication date: March 12, 1998 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1998 Inter-Research.

PHENOTYPIC PLASTICITY IN THE FOOT SIZE OF AN INTERTIDAL SNAIL

The risk of dislodgment due to hydrodynamic forces on rocky intertidal shores is greater on wave-exposed than on protected shores, and this is believed to represent an important selective force in intertidal communities. For intertidal snails, the probability of dislodgment by a given flow is determined, in part, by shell size and shape, and by the attachment strength of the foot. This study addressed two questions. First, do habitat-specific differences in traits that reduce the risk of dislodgment of an intertidal snail (Littorina obtusata) parallel differences in wave energies? To address this question, I measured variation in (1) shell size (defined as the maximum projected surface area, MPSA); (2) foot size; (3) maximum shear dislodgment force; and (4) tenacity (dislodgment force per unit foot size) of two wave-exposed and three protected snail populations. Second, are habitat-specific differences in foot size, and hence attachment strength, the product of selection or of phenotypic plasticity in response to increased hydrodynamic stress? I conducted field transplant experiments and a laboratory flume experiment that manipulated water velocity to test for plasticity in foot size. Wave-exposed snails exhibited traits that reduce the risk of dislodgment. Their shells were smaller (MPSA) and more squat (shell height relative to MPSA and shell length) than were shells of protected conspecifics. Wave-exposed snails also had larger foot sizes and were thus able to resist greater shear dislodgment forces than protected conspecifics of similar MPSA. Neither wave exposure nor collection site influenced tenacity, indicating that the greater dislodgment forces of wave-exposed snails were due to their larger foot sizes. Assuming that MPSA is proportional to speed-specific drag, which is reasonable for bluff bodies, I found that dislodgment force was proportional to drag. Foot size scaled isometrically with MPSA, and dislodgment force scaled isometrically with foot size, indicating that the risk of dislodgment does not change as snails grow. The field and laboratory flume experiments provide the first clear demonstration that increased hydrodynamic stress induces plastic increases in foot size. Protected snails raised on a wave-exposed shore produced a larger foot than controls raised on their native shore. Selection on the foot size of protected snails raised on both shores was not detected in either habitat. Protected snails also produced larger foot sizes when raised in high-velocity flumes relative to snails raised under low-velocity flow. In contrast, wave-exposed snails exhibited no change in foot size when raised under both high- and low-velocity flow. Hence, variation in the foot size of wave-exposed snails is less flexible than that of protected conspecifics. If natural selection favors plasticity in heterogeneous environments, an asymmetry may be favored as well, especially if there are risks associated with improper adjustments to unpredictable environmental cues.

Demographic change and microhabitat Variability in a Grassland Endemic, Silene Douglasii Var. oraria (Caryophyllaceae)

Variable spatial and temporal environments are known to affect the population dynamics of plants, but studies of local scale variability and its relationship to demographic change within a population remain limited. Using mapped plants, we examined the population dynamics of a coastal grassland endemic, Silene douglasii var. oraria, in two habitats over 10 yr. We hypothesized that ecological differences between rocky and grassy habitats might influence demographic parameters, including adult survival, growth, and density. Soil pH, soil moisture. and other abiotic variables differed little between habitats, but microsite differences in light, soil depth. and vegetation height were related to variation in Silene density and plant circumference. We also found significantly higher population densities, lower adult mortality, and more juvenile recruitment in rocky areas. Finite rates of population growth varied across years and habitats (lambda = 0.82-1.12). with different patterns evident in the two habitats. In both, observed population sizes in 1992 were similar to matrix projections using 1982-1985 data. Populations declined in size in some years despite high adult survivorship and variable recruitment. More intensive study of seedlings is needed, including experimental evaluation of the role of light and competition. However, the habitat-specific differences we observed imply that ecological studies and conservation plans developed for rare plants should consider the effect of local scale variability on demography.

Heat resistance and energy budget in different Scandinavian plants

Heat resistance and energy budget in different Scandinavian plants