Studies of dispersal in marine organisms spanning from fish to invertebrates have benefitted imme... more Studies of dispersal in marine organisms spanning from fish to invertebrates have benefitted immensely from advances in larval tracking techniques, genetics, and biophysical modeling approaches. Increasing interest in marine connectivity and its application to management challenges have pushed marine ecologists to apply new approaches that change our view of marine dispersal, often illustrating greater population complexity than previous thought. Acknowledging differences in behavioural capacity in larval fishes and many larval invertebrates, the research communities focusing on these groups could learn much from each other. Nonetheless, aside from coral reef systems, the invertebrate and fish larval ecology research worlds remain largely disconnected. We begin by revisiting how similar drivers influence dispersal in these two research groups and then ask whether they have maximized how they share tools, models, genetic approaches, analyses, and literature. We find that although some tools and analytical approaches successfully transcend larval fish and invertebrate research approaches, the research communities, their interpretations of results, and their literature remain discouragingly separate.
The gastropods Lepetodrilus fucensis and Depressigyra globulus are abundant faunal components of ... more The gastropods Lepetodrilus fucensis and Depressigyra globulus are abundant faunal components of animal communities at deep-sea hydrothermal vents along the Juan de Fuca Ridge in the NE PaciWc. The population structure and recruitment pattern of both species were studied using modal decomposition of length-frequency distributions. Gastropod populations were collected from Axial Volcano and Endeavour Segment in 2002 and 2003. Polymodal size-frequency distributions, particularly at Axial Volcano vent sites, suggest a discontinuous recruitment pattern for D. globulus. In contrast, there were no distinct peaks visible in the distributions of L. fucensis, suggesting a continuous recruitment pattern for this species. For both species, distributions were positively skewed towards the smaller length-classes, implying post-settlement mortality is high. However, variations in growth, due to short-and long-term variability in environmental conditions in the hydrothermal vent habitat, as well as biological interactions, may also be inXuencing the distribution and abundance of subsequent life-history stages. Using maximum shell lengths from populations of known ages, the growth rate of L. fucensis was estimated as 9.6 m day ¡1 , indicating adulthood would be reached in »1 year. Our results suggest that, despite occupying the same habitat, abundance and population structure are regulated by diVerent biotic and abiotic processes in L. fucensis and D. globulus.
Journal of the Marine Biological Association of the United Kingdom, 2011
ABSTRACT Despite the importance of early life-history processes in regulating population assembla... more ABSTRACT Despite the importance of early life-history processes in regulating population assemblages of benthic invertebrates at hydrothermal vents, they remain poorly understood, mainly because of the inaccessibility of these habitats. Vestimentiferan tubeworms provide an excellent system to study settlement in these habitats; they inhabit tubes that remain intact for some period even after the occupants die, and thus provide a proxy for rates of settlement and post-settlement mortality. In 2007, we collected rocks supporting populations of Lamellibrachia sp. using a TV-grab, from Mussel Ridge hydrothermal vent field on Monowai Volcanic Complex, at the Tonga–Kermadec arc. Twenty-two discrete patches of similarly sized individuals and of discrete length–frequency distributions were identified and quantified. Mean length of individual tubeworms ranged from <0.5 to 6.38 cm, and abundance per patch ranged from 6.8 to 108 ind cm−2. Post-settlement mortality was ~5%. These results suggest that gregarious settlement of pulses of larvae is likely occurring by Lamellibrachia sp., a process that has not yet been described in deep-sea hydrothermal vent tubeworms. The abundance of adult tubeworms on Monowai was low, and allochthonous larval supply from neighbouring seamounts unlikely. Consequently, gregarious settlement can increase the probability of maintenance and expansion of the existing populations.
In any ecological system, the factors that regulate the abundance of species vary with spatial sc... more In any ecological system, the factors that regulate the abundance of species vary with spatial scale; therefore, the sources of spatial variability should be described. We examined different sources of variability in the spatial distribution of phytoplankton assemblages and biotic (e.g. planktonic and benthic micrograzers, mussels) and abiotic (e.g. nutrients, temperature, salinity, pH) factors that may regulate these assemblages in 4 tidepools a t each of 3 intertidal zones (mid, high and splash) on a rocky shore in Nova Scotia, Canada, over a period of 15 mo. Stratum (defined as the depth within a pool) was a significant source of variability, particularly for pennate diatoms which were consistently more abundant near the bottom of pools. There was no indication of vertical zonation of the phytoplankton assemblages along the intertidal gradient, and differences among zones rarely explained more than 30':: of the spatial vanabillty in phytoplankton abundance. Also, among-zone variation was not apparent for the biotic and abiotic factors. We suggest that among-zone variability in these factors does not adequately explain vertical variability in phytoplankton assemblages. All groups of phytoplankton vaned significantly among pools within intertidal zones on most sampling dates, and differences among pools explained up to 96% of the variability In phytoplankton abundance. Furthermore, there was significant variability among pools within zones for all biotic and abiotic characteristics of the pools on most sampling dates. We detected significant relationships between the density of benthic micrograzers and small mussels, and the concentration of nutrients in individual pools with the abundance of pennate diatoms, cryptomonads and chlorophytes Among the abiotic characteristics of the tidepools, there was a significant relationship between flushing rate and temperature of individual pools, with the abundance of cryptomonads and chlorophytes. We suggest that the factors that regulate phytoplankton assemblages in tidepools probably operate more a t the scale of the individual pool rather than the intertidal zone.
Journal of Experimental Marine Biology and Ecology, Jul 1, 2006
Larval loss of marine benthic invertebrates while in the plankton is extremely high, and although... more Larval loss of marine benthic invertebrates while in the plankton is extremely high, and although several sources of mortality have been proposed, the relative significance of each remains unknown. Despite suggestions that predation is a significant source of mortality, experimental manipulations using natural densities of prey have measured low predation rates. In part, structural, chemical and behavioural larval defenses may lead to these low rates. In the laboratory, we examined changes in the vertical distribution of echinoplutei (4-and 6-arm developmental stages) of Strongylocentrotus droebachiensis (Mueller) and veligers of Ostrea edulis (L.) in the presence of the ctenophore Bolinopsis infundibulum (Mueller), a known larval predator. Larvae were introduced 2-3 cm above the bottom of experimental plexiglas rectangular columns (60 × 10 × 10 cm). The ctenophores were held in baskets (10 × 10 × 10 cm), made of 0.63-μm Nitex mesh, which hung in the water at the top of the experimental columns. Empty baskets were used in "No predator" treatments. Echinoplutei of both stages, and reared under both high and low food rations, showed a strong response and were found lower in the columns in the presence than the absence of ctenophores. The population mean height above the bottom of the experimental columns was 12.2-15.2 and 9.4-16.2 cm's lower in the presence than in the absence of predators (for 4-and 6-arm larvae, respectively). Interestingly, there was little difference in the vertical distribution of veligers between the two treatments, suggesting that a behavioural defense to predation may not have evolved in all phyla. A behavioural avoidance of predators, such as the one shown by echinoplutei in our study, may reduce larval mortality and increase the probability for eventual recruitment to the benthos.
ABSTRACT We examined changes in phytoplankton assemblages in tidepools during the period of tidal... more ABSTRACT We examined changes in phytoplankton assemblages in tidepools during the period of tidal isolation, both at a time of low phytoplankton abundance (22 August 1991) and during the autumn bloom (9 October 1991) in the surrounding seawater. Four tidepools were sampled at each of three intertidal zones (mid, high and splash) on a rocky shore near Halifax, Nova Scotia, Canada. We sampled phytoplankton, micrograzers, and dissolved nutrients, and measured temperature, salinity and pH, immediately after the tide receded and immediately before the pools were flooded on the returning tide. Although we detected changes in phytoplankton abundance over the period of tidal isolation of the pools, these changes varied among phytoplankton groups and within groups between sampling dates. Nanoflagellates increased significantly within the period of isolation in August, probably due to population growth. Centric diatoms, and consequently total phytoplankton, decreased significantly over the period of tidal isolation in October, probably due to grazing. Temperature was the most variable physical factor within the tidal cycle on both dates, and salinity was the least variable. Nitrate + nitrite and density of benthic micrograzers decreased significantly within the isolation period in August, but no significant differences were detected in October. Variability in the chemical and physical environment over the period of pool isolation do not adequately explain the few recorded changes in phytoplankton abundance. The abundance of most phytoplankton groups differed significantly between the two sampling dates.
Page 1. AQUATIC BIOLOGY Aquat Biol Vol. 8: 8394, 2009 doi: 10.3354/ab00208 Published online Dece... more Page 1. AQUATIC BIOLOGY Aquat Biol Vol. 8: 8394, 2009 doi: 10.3354/ab00208 Published online December 29 INTRODUCTION The rocky subtidal ecosystem in the western North Atlantic has historically been dominated ...
Deep-water gorgonian corals are long-lived organisms found worldwide off continental margins and ... more Deep-water gorgonian corals are long-lived organisms found worldwide off continental margins and seamounts, usually occurring at depths of ,200-1,000 m. Most corals undergo sexual reproduction by releasing a planktonic larval stage that disperses; however, recruitment rates and the environmental and biological factors influencing recruitment in deep-sea species are poorly known. Here, we present results from a 4-year field experiment conducted in the Gulf of Maine (northwest Atlantic) at depths .650 m that document recruitment for 2 species of deep-water gorgonian corals, Primnoa resedaeformis and Paragorgia arborea. The abundance of P. resedaeformis recruits was high, and influenced by the structural complexity of the recipient habitat, but very few recruits of P. arborea were found. We suggest that divergent reproductive modes (P. resedaeformis as a broadcast spawner and P. arborea as a brooder) may explain this pattern. Despite the high recruitment of P. resedaeformis, severe mortality early on in the benthic stage of this species may limit the abundance of adult colonies. Most recruits of this species (,80%) were at the primary polyp stage, and less than 1% of recruits were at stage of 4 polyps or more. We propose that biological disturbance, possibly by the presence of suspension-feeding brittle stars, and limited food supply in the deep sea may cause this mortality. Our findings reinforce the vulnerability of these corals to anthropogenic disturbances, such as trawling with mobile gear, and the importance of incorporating knowledge on processes during the early life history stages in conservation decisions.
Distribution, abundance and demographic composition of populations of Oreaster reticulatus (Linna... more Distribution, abundance and demographic composition of populations of Oreaster reticulatus (Linnaeus, 1758) were sampled in mangrove, fringing reef, seagrass, and sand habitats at sand cayes off the southern coast of Belize. Density and biomass were 1.7-18.3 ind 100 m -2 and 0.9-5.5 kg 100 m -2 among six sites. Dispersion was random, except at a fringing reef where sea stars were aggregated at our sampling scale (15 m 2 ). Mean individual size (radius, R) ranged from 9.7 to 13.7 cm among sites. Populations in mangrove and reef habitats were mainly juveniles (R < 12 cm: 83% and 91% respectively), with characteristic cryptic coloration. Juveniles occurred primarily along mangrove banks and were closely associated with coral colonies in fringing reefs. The proportion of juveniles also was high on a sand flat (54%), although juvenile color morphs were not observed there. Most sea stars had their stomach everted on sediments or detrital matter, but sponge and ascidian prey also were consumed in a mangrove habitat. Mangrove and fringing reefs, like dense seagrass beds, may provide a protective environment for recruits that undergo an ontogenic shift to adult habitats, such as sand flats, as they mature reproductively. Our findings are comparable with previous studies of O. reticulatus in Panama and suggest that levels of recruitment in Central America may be higher than in other parts of the Caribbean.
ABSTRACT The diatom community that inhabits both the water-column and the benthos of tidepools po... more ABSTRACT The diatom community that inhabits both the water-column and the benthos of tidepools positioned along an intertidal gradient, during late spring and early summer is described. Samples from the water-column and benthos of five tidepools, ranging from 1.5 to 6.5 m, were collected on five dates, and the diatom community was recorded. Pelagic, centric diatom species decreased in density with increasing intertidal height, whereas benthic pennates increased, both in absolute and relative abundance, thus becoming the dominant genera in the higher pools. A number of benthic, centric diatom species exhibited distributions similar to those of the pennates. In the cluster analysis, the two lower and the two higher tidepools were grouped together on most occasions, while the intermediate-height pool grouped variably. Similar zonation patterns to those described here have been demonstrated for species of macroflora and fauna. This is the first study, however, that describes the distribution and abundance of microflora within tidepools in some detail.
This study examines the role of complex physical substrate structure on the colonization of hydro... more This study examines the role of complex physical substrate structure on the colonization of hydrothermal vent invertebrates to test the hypothesis that the diversity of colonizing species can be enhanced by the provision of complex physical structure. Colonization was studied over 1 yr intervals between 2001 and 2003 at 2 diffuse venting sites near Axial Volcano, on the Juan de Fuca Ridge (depth 1500 m), on 2 types of artificial substrates with the same planar area but different levels of structural complexity: a complex structure with interstitial spaces (sponge) and a mimic of the seafloor (basalt). Colonist assemblages were compared between substrate types using univariate and multivariate measures of community composition. While the most abundant taxa on both substrate types were gastropods and polychaetes, colonist assemblages were significantly dissimilar between substrate types, due to the greater relative abundances of polychaete and meiofaunal species colonizing sponges. Overall, the faunal assemblages colonizing sponge substrates had higher species richness, diversity and evenness than assemblages colonizing the basalts. Our results suggest that complex physical substrate structure can facilitate the colonization of a diverse faunal assemblage at diffuse hydrothermal vents on the Juan de Fuca Ridge.
Increased understanding of recruitment dynamics of vent species can provide greater insights into... more Increased understanding of recruitment dynamics of vent species can provide greater insights into the variability in adult populations and aid in identifying factors, such as physical and/or environmental stressors, which may obscure the temporal history of recruitment patterns. At anhydrite vents within the ASHES vent field (Axial Volcano, Juan de Fuca Ridge) the infrastructure is unstable, fluids contain low metal but high sulphide concentrations, and temperatures range from 10 to 200°C. Despite high levels of larval supply to these vents, there is a paucity of colonizing invertebrates, either because of the physical instability of the anhydrite substratum or the chemical composition of the fluid. Colonization panels were used to quantify recruitment to three anhydrite vents (Virgin, Virgin’s Daughter, Marshmallow) in the ASHES vent field over different time scales (1 vs. 2 yrs). Recruitment to anhydrite habitats did occur, but at lower levels compared to other vents in the field....
ABSTRACT Many larval sessile marine invertebrates exhibit settlement preferences, and larval beha... more ABSTRACT Many larval sessile marine invertebrates exhibit settlement preferences, and larval behavioral responses to cues at settlement can ultimately influence the distribution of adults and an individual&#39;s lifetime fitness. Two epifaunal bryozoans, the invasive Membranipora membranacea and the native Electra pilosa, commonly co-occur on kelp species in the subtidal habitats of Nova Scotia, Canada. Outbreaks of M. membranacea have been linked to mass defoliation of the kelp canopy; however, E. pilosa has not been associated with any significant effect on its host substrate. To examine whether larvae of M. membranacea and E. pilosa exhibit settlement preference for a particular location along the blades of the kelps Saccharina latissima and Laminaria digitata, abundances of newly settled colonies were quantified at different locations along the kelp blade. Algae were sampled at 2 sites on the southwestern shore of Nova Scotia (The Lodge and Feltzen South) from September 2009 to October 2010, over one complete cycle of the annual life cycle of M. membranacea, and thus over a wide range of bryozoan percent cover. Settlers of both bryozoans were significantly more abundant towards the younger, more proximal regions of blades of both kelps across all sampling periods. These patterns did not vary seasonally with increasing colony density. Both M. membranacea and E. pilosa larvae showed preferential settlement, suggesting that they can detect small-scale differences in habitat quality at the scale of a single kelp blade.
Studies of dispersal in marine organisms spanning from fish to invertebrates have benefitted imme... more Studies of dispersal in marine organisms spanning from fish to invertebrates have benefitted immensely from advances in larval tracking techniques, genetics, and biophysical modeling approaches. Increasing interest in marine connectivity and its application to management challenges have pushed marine ecologists to apply new approaches that change our view of marine dispersal, often illustrating greater population complexity than previous thought. Acknowledging differences in behavioural capacity in larval fishes and many larval invertebrates, the research communities focusing on these groups could learn much from each other. Nonetheless, aside from coral reef systems, the invertebrate and fish larval ecology research worlds remain largely disconnected. We begin by revisiting how similar drivers influence dispersal in these two research groups and then ask whether they have maximized how they share tools, models, genetic approaches, analyses, and literature. We find that although som...
We examlned the distribution and abundance of the hyperbenthos in tidepools on a rocky shore, nea... more We examlned the distribution and abundance of the hyperbenthos in tidepools on a rocky shore, near Halifax, Nova Scotia, Canada, at approximately monthly intervals between March and November 1991, and between April and June 1992. We sampled 4 pools at each of 3 intertidal heights: mid and high intertidal and splash zones. Additional samples were taken at the sea surface for comparison. Calanoid and harpacticoid copepods, cladocerans, forarniniferans, nematodes and rotifers were the most abundant groups within our samples. Significant differences in the abundance of these groups among zones were detected on only 5 out of 12 sampling dates. Total hyperbenthos, as well as calanoid and harpacticoid copepods, nematodes and rotifers, generally were more abundant in the high and/or the splash pools. The abundance of total hyperbenthos varied significantly among pools within zones from May to October 1991 and in June 1992. Significant differences in abundance among pools within zones were also detected for harpacticoid copepods and nematodes on 3 sampling dates, for calanoid copepods and rotifers on 5 s a m p h g dates, and for cladocerans and foraminiferans on 2 sampling dates. In most cases, the significant variability in abundance among pools arose within the high intertidal or the splash zones. Over the entire sampling period, the diversity of fauna1 groups was lower in the splash pools, possibly as a result of harsh conditions in these pools. The few groups that survived in these high pools, such as rotifers and the calanoid copepod Eurytemora affinis, reached densities of up to 106 ind. m-3. Dominant populations may be established in particular pools by founder effects and persist due to low flushing rates. Thus, variability among pools in the high intertidal and splash zones may exceed that observed among pools in lower intertidal zones.
Studies of dispersal in marine organisms spanning from fish to invertebrates have benefitted imme... more Studies of dispersal in marine organisms spanning from fish to invertebrates have benefitted immensely from advances in larval tracking techniques, genetics, and biophysical modeling approaches. Increasing interest in marine connectivity and its application to management challenges have pushed marine ecologists to apply new approaches that change our view of marine dispersal, often illustrating greater population complexity than previous thought. Acknowledging differences in behavioural capacity in larval fishes and many larval invertebrates, the research communities focusing on these groups could learn much from each other. Nonetheless, aside from coral reef systems, the invertebrate and fish larval ecology research worlds remain largely disconnected. We begin by revisiting how similar drivers influence dispersal in these two research groups and then ask whether they have maximized how they share tools, models, genetic approaches, analyses, and literature. We find that although some tools and analytical approaches successfully transcend larval fish and invertebrate research approaches, the research communities, their interpretations of results, and their literature remain discouragingly separate.
The gastropods Lepetodrilus fucensis and Depressigyra globulus are abundant faunal components of ... more The gastropods Lepetodrilus fucensis and Depressigyra globulus are abundant faunal components of animal communities at deep-sea hydrothermal vents along the Juan de Fuca Ridge in the NE PaciWc. The population structure and recruitment pattern of both species were studied using modal decomposition of length-frequency distributions. Gastropod populations were collected from Axial Volcano and Endeavour Segment in 2002 and 2003. Polymodal size-frequency distributions, particularly at Axial Volcano vent sites, suggest a discontinuous recruitment pattern for D. globulus. In contrast, there were no distinct peaks visible in the distributions of L. fucensis, suggesting a continuous recruitment pattern for this species. For both species, distributions were positively skewed towards the smaller length-classes, implying post-settlement mortality is high. However, variations in growth, due to short-and long-term variability in environmental conditions in the hydrothermal vent habitat, as well as biological interactions, may also be inXuencing the distribution and abundance of subsequent life-history stages. Using maximum shell lengths from populations of known ages, the growth rate of L. fucensis was estimated as 9.6 m day ¡1 , indicating adulthood would be reached in »1 year. Our results suggest that, despite occupying the same habitat, abundance and population structure are regulated by diVerent biotic and abiotic processes in L. fucensis and D. globulus.
Journal of the Marine Biological Association of the United Kingdom, 2011
ABSTRACT Despite the importance of early life-history processes in regulating population assembla... more ABSTRACT Despite the importance of early life-history processes in regulating population assemblages of benthic invertebrates at hydrothermal vents, they remain poorly understood, mainly because of the inaccessibility of these habitats. Vestimentiferan tubeworms provide an excellent system to study settlement in these habitats; they inhabit tubes that remain intact for some period even after the occupants die, and thus provide a proxy for rates of settlement and post-settlement mortality. In 2007, we collected rocks supporting populations of Lamellibrachia sp. using a TV-grab, from Mussel Ridge hydrothermal vent field on Monowai Volcanic Complex, at the Tonga–Kermadec arc. Twenty-two discrete patches of similarly sized individuals and of discrete length–frequency distributions were identified and quantified. Mean length of individual tubeworms ranged from &lt;0.5 to 6.38 cm, and abundance per patch ranged from 6.8 to 108 ind cm−2. Post-settlement mortality was ~5%. These results suggest that gregarious settlement of pulses of larvae is likely occurring by Lamellibrachia sp., a process that has not yet been described in deep-sea hydrothermal vent tubeworms. The abundance of adult tubeworms on Monowai was low, and allochthonous larval supply from neighbouring seamounts unlikely. Consequently, gregarious settlement can increase the probability of maintenance and expansion of the existing populations.
In any ecological system, the factors that regulate the abundance of species vary with spatial sc... more In any ecological system, the factors that regulate the abundance of species vary with spatial scale; therefore, the sources of spatial variability should be described. We examined different sources of variability in the spatial distribution of phytoplankton assemblages and biotic (e.g. planktonic and benthic micrograzers, mussels) and abiotic (e.g. nutrients, temperature, salinity, pH) factors that may regulate these assemblages in 4 tidepools a t each of 3 intertidal zones (mid, high and splash) on a rocky shore in Nova Scotia, Canada, over a period of 15 mo. Stratum (defined as the depth within a pool) was a significant source of variability, particularly for pennate diatoms which were consistently more abundant near the bottom of pools. There was no indication of vertical zonation of the phytoplankton assemblages along the intertidal gradient, and differences among zones rarely explained more than 30':: of the spatial vanabillty in phytoplankton abundance. Also, among-zone variation was not apparent for the biotic and abiotic factors. We suggest that among-zone variability in these factors does not adequately explain vertical variability in phytoplankton assemblages. All groups of phytoplankton vaned significantly among pools within intertidal zones on most sampling dates, and differences among pools explained up to 96% of the variability In phytoplankton abundance. Furthermore, there was significant variability among pools within zones for all biotic and abiotic characteristics of the pools on most sampling dates. We detected significant relationships between the density of benthic micrograzers and small mussels, and the concentration of nutrients in individual pools with the abundance of pennate diatoms, cryptomonads and chlorophytes Among the abiotic characteristics of the tidepools, there was a significant relationship between flushing rate and temperature of individual pools, with the abundance of cryptomonads and chlorophytes. We suggest that the factors that regulate phytoplankton assemblages in tidepools probably operate more a t the scale of the individual pool rather than the intertidal zone.
Journal of Experimental Marine Biology and Ecology, Jul 1, 2006
Larval loss of marine benthic invertebrates while in the plankton is extremely high, and although... more Larval loss of marine benthic invertebrates while in the plankton is extremely high, and although several sources of mortality have been proposed, the relative significance of each remains unknown. Despite suggestions that predation is a significant source of mortality, experimental manipulations using natural densities of prey have measured low predation rates. In part, structural, chemical and behavioural larval defenses may lead to these low rates. In the laboratory, we examined changes in the vertical distribution of echinoplutei (4-and 6-arm developmental stages) of Strongylocentrotus droebachiensis (Mueller) and veligers of Ostrea edulis (L.) in the presence of the ctenophore Bolinopsis infundibulum (Mueller), a known larval predator. Larvae were introduced 2-3 cm above the bottom of experimental plexiglas rectangular columns (60 × 10 × 10 cm). The ctenophores were held in baskets (10 × 10 × 10 cm), made of 0.63-μm Nitex mesh, which hung in the water at the top of the experimental columns. Empty baskets were used in "No predator" treatments. Echinoplutei of both stages, and reared under both high and low food rations, showed a strong response and were found lower in the columns in the presence than the absence of ctenophores. The population mean height above the bottom of the experimental columns was 12.2-15.2 and 9.4-16.2 cm's lower in the presence than in the absence of predators (for 4-and 6-arm larvae, respectively). Interestingly, there was little difference in the vertical distribution of veligers between the two treatments, suggesting that a behavioural defense to predation may not have evolved in all phyla. A behavioural avoidance of predators, such as the one shown by echinoplutei in our study, may reduce larval mortality and increase the probability for eventual recruitment to the benthos.
ABSTRACT We examined changes in phytoplankton assemblages in tidepools during the period of tidal... more ABSTRACT We examined changes in phytoplankton assemblages in tidepools during the period of tidal isolation, both at a time of low phytoplankton abundance (22 August 1991) and during the autumn bloom (9 October 1991) in the surrounding seawater. Four tidepools were sampled at each of three intertidal zones (mid, high and splash) on a rocky shore near Halifax, Nova Scotia, Canada. We sampled phytoplankton, micrograzers, and dissolved nutrients, and measured temperature, salinity and pH, immediately after the tide receded and immediately before the pools were flooded on the returning tide. Although we detected changes in phytoplankton abundance over the period of tidal isolation of the pools, these changes varied among phytoplankton groups and within groups between sampling dates. Nanoflagellates increased significantly within the period of isolation in August, probably due to population growth. Centric diatoms, and consequently total phytoplankton, decreased significantly over the period of tidal isolation in October, probably due to grazing. Temperature was the most variable physical factor within the tidal cycle on both dates, and salinity was the least variable. Nitrate + nitrite and density of benthic micrograzers decreased significantly within the isolation period in August, but no significant differences were detected in October. Variability in the chemical and physical environment over the period of pool isolation do not adequately explain the few recorded changes in phytoplankton abundance. The abundance of most phytoplankton groups differed significantly between the two sampling dates.
Page 1. AQUATIC BIOLOGY Aquat Biol Vol. 8: 8394, 2009 doi: 10.3354/ab00208 Published online Dece... more Page 1. AQUATIC BIOLOGY Aquat Biol Vol. 8: 8394, 2009 doi: 10.3354/ab00208 Published online December 29 INTRODUCTION The rocky subtidal ecosystem in the western North Atlantic has historically been dominated ...
Deep-water gorgonian corals are long-lived organisms found worldwide off continental margins and ... more Deep-water gorgonian corals are long-lived organisms found worldwide off continental margins and seamounts, usually occurring at depths of ,200-1,000 m. Most corals undergo sexual reproduction by releasing a planktonic larval stage that disperses; however, recruitment rates and the environmental and biological factors influencing recruitment in deep-sea species are poorly known. Here, we present results from a 4-year field experiment conducted in the Gulf of Maine (northwest Atlantic) at depths .650 m that document recruitment for 2 species of deep-water gorgonian corals, Primnoa resedaeformis and Paragorgia arborea. The abundance of P. resedaeformis recruits was high, and influenced by the structural complexity of the recipient habitat, but very few recruits of P. arborea were found. We suggest that divergent reproductive modes (P. resedaeformis as a broadcast spawner and P. arborea as a brooder) may explain this pattern. Despite the high recruitment of P. resedaeformis, severe mortality early on in the benthic stage of this species may limit the abundance of adult colonies. Most recruits of this species (,80%) were at the primary polyp stage, and less than 1% of recruits were at stage of 4 polyps or more. We propose that biological disturbance, possibly by the presence of suspension-feeding brittle stars, and limited food supply in the deep sea may cause this mortality. Our findings reinforce the vulnerability of these corals to anthropogenic disturbances, such as trawling with mobile gear, and the importance of incorporating knowledge on processes during the early life history stages in conservation decisions.
Distribution, abundance and demographic composition of populations of Oreaster reticulatus (Linna... more Distribution, abundance and demographic composition of populations of Oreaster reticulatus (Linnaeus, 1758) were sampled in mangrove, fringing reef, seagrass, and sand habitats at sand cayes off the southern coast of Belize. Density and biomass were 1.7-18.3 ind 100 m -2 and 0.9-5.5 kg 100 m -2 among six sites. Dispersion was random, except at a fringing reef where sea stars were aggregated at our sampling scale (15 m 2 ). Mean individual size (radius, R) ranged from 9.7 to 13.7 cm among sites. Populations in mangrove and reef habitats were mainly juveniles (R < 12 cm: 83% and 91% respectively), with characteristic cryptic coloration. Juveniles occurred primarily along mangrove banks and were closely associated with coral colonies in fringing reefs. The proportion of juveniles also was high on a sand flat (54%), although juvenile color morphs were not observed there. Most sea stars had their stomach everted on sediments or detrital matter, but sponge and ascidian prey also were consumed in a mangrove habitat. Mangrove and fringing reefs, like dense seagrass beds, may provide a protective environment for recruits that undergo an ontogenic shift to adult habitats, such as sand flats, as they mature reproductively. Our findings are comparable with previous studies of O. reticulatus in Panama and suggest that levels of recruitment in Central America may be higher than in other parts of the Caribbean.
ABSTRACT The diatom community that inhabits both the water-column and the benthos of tidepools po... more ABSTRACT The diatom community that inhabits both the water-column and the benthos of tidepools positioned along an intertidal gradient, during late spring and early summer is described. Samples from the water-column and benthos of five tidepools, ranging from 1.5 to 6.5 m, were collected on five dates, and the diatom community was recorded. Pelagic, centric diatom species decreased in density with increasing intertidal height, whereas benthic pennates increased, both in absolute and relative abundance, thus becoming the dominant genera in the higher pools. A number of benthic, centric diatom species exhibited distributions similar to those of the pennates. In the cluster analysis, the two lower and the two higher tidepools were grouped together on most occasions, while the intermediate-height pool grouped variably. Similar zonation patterns to those described here have been demonstrated for species of macroflora and fauna. This is the first study, however, that describes the distribution and abundance of microflora within tidepools in some detail.
This study examines the role of complex physical substrate structure on the colonization of hydro... more This study examines the role of complex physical substrate structure on the colonization of hydrothermal vent invertebrates to test the hypothesis that the diversity of colonizing species can be enhanced by the provision of complex physical structure. Colonization was studied over 1 yr intervals between 2001 and 2003 at 2 diffuse venting sites near Axial Volcano, on the Juan de Fuca Ridge (depth 1500 m), on 2 types of artificial substrates with the same planar area but different levels of structural complexity: a complex structure with interstitial spaces (sponge) and a mimic of the seafloor (basalt). Colonist assemblages were compared between substrate types using univariate and multivariate measures of community composition. While the most abundant taxa on both substrate types were gastropods and polychaetes, colonist assemblages were significantly dissimilar between substrate types, due to the greater relative abundances of polychaete and meiofaunal species colonizing sponges. Overall, the faunal assemblages colonizing sponge substrates had higher species richness, diversity and evenness than assemblages colonizing the basalts. Our results suggest that complex physical substrate structure can facilitate the colonization of a diverse faunal assemblage at diffuse hydrothermal vents on the Juan de Fuca Ridge.
Increased understanding of recruitment dynamics of vent species can provide greater insights into... more Increased understanding of recruitment dynamics of vent species can provide greater insights into the variability in adult populations and aid in identifying factors, such as physical and/or environmental stressors, which may obscure the temporal history of recruitment patterns. At anhydrite vents within the ASHES vent field (Axial Volcano, Juan de Fuca Ridge) the infrastructure is unstable, fluids contain low metal but high sulphide concentrations, and temperatures range from 10 to 200°C. Despite high levels of larval supply to these vents, there is a paucity of colonizing invertebrates, either because of the physical instability of the anhydrite substratum or the chemical composition of the fluid. Colonization panels were used to quantify recruitment to three anhydrite vents (Virgin, Virgin’s Daughter, Marshmallow) in the ASHES vent field over different time scales (1 vs. 2 yrs). Recruitment to anhydrite habitats did occur, but at lower levels compared to other vents in the field....
ABSTRACT Many larval sessile marine invertebrates exhibit settlement preferences, and larval beha... more ABSTRACT Many larval sessile marine invertebrates exhibit settlement preferences, and larval behavioral responses to cues at settlement can ultimately influence the distribution of adults and an individual&#39;s lifetime fitness. Two epifaunal bryozoans, the invasive Membranipora membranacea and the native Electra pilosa, commonly co-occur on kelp species in the subtidal habitats of Nova Scotia, Canada. Outbreaks of M. membranacea have been linked to mass defoliation of the kelp canopy; however, E. pilosa has not been associated with any significant effect on its host substrate. To examine whether larvae of M. membranacea and E. pilosa exhibit settlement preference for a particular location along the blades of the kelps Saccharina latissima and Laminaria digitata, abundances of newly settled colonies were quantified at different locations along the kelp blade. Algae were sampled at 2 sites on the southwestern shore of Nova Scotia (The Lodge and Feltzen South) from September 2009 to October 2010, over one complete cycle of the annual life cycle of M. membranacea, and thus over a wide range of bryozoan percent cover. Settlers of both bryozoans were significantly more abundant towards the younger, more proximal regions of blades of both kelps across all sampling periods. These patterns did not vary seasonally with increasing colony density. Both M. membranacea and E. pilosa larvae showed preferential settlement, suggesting that they can detect small-scale differences in habitat quality at the scale of a single kelp blade.
Studies of dispersal in marine organisms spanning from fish to invertebrates have benefitted imme... more Studies of dispersal in marine organisms spanning from fish to invertebrates have benefitted immensely from advances in larval tracking techniques, genetics, and biophysical modeling approaches. Increasing interest in marine connectivity and its application to management challenges have pushed marine ecologists to apply new approaches that change our view of marine dispersal, often illustrating greater population complexity than previous thought. Acknowledging differences in behavioural capacity in larval fishes and many larval invertebrates, the research communities focusing on these groups could learn much from each other. Nonetheless, aside from coral reef systems, the invertebrate and fish larval ecology research worlds remain largely disconnected. We begin by revisiting how similar drivers influence dispersal in these two research groups and then ask whether they have maximized how they share tools, models, genetic approaches, analyses, and literature. We find that although som...
We examlned the distribution and abundance of the hyperbenthos in tidepools on a rocky shore, nea... more We examlned the distribution and abundance of the hyperbenthos in tidepools on a rocky shore, near Halifax, Nova Scotia, Canada, at approximately monthly intervals between March and November 1991, and between April and June 1992. We sampled 4 pools at each of 3 intertidal heights: mid and high intertidal and splash zones. Additional samples were taken at the sea surface for comparison. Calanoid and harpacticoid copepods, cladocerans, forarniniferans, nematodes and rotifers were the most abundant groups within our samples. Significant differences in the abundance of these groups among zones were detected on only 5 out of 12 sampling dates. Total hyperbenthos, as well as calanoid and harpacticoid copepods, nematodes and rotifers, generally were more abundant in the high and/or the splash pools. The abundance of total hyperbenthos varied significantly among pools within zones from May to October 1991 and in June 1992. Significant differences in abundance among pools within zones were also detected for harpacticoid copepods and nematodes on 3 sampling dates, for calanoid copepods and rotifers on 5 s a m p h g dates, and for cladocerans and foraminiferans on 2 sampling dates. In most cases, the significant variability in abundance among pools arose within the high intertidal or the splash zones. Over the entire sampling period, the diversity of fauna1 groups was lower in the splash pools, possibly as a result of harsh conditions in these pools. The few groups that survived in these high pools, such as rotifers and the calanoid copepod Eurytemora affinis, reached densities of up to 106 ind. m-3. Dominant populations may be established in particular pools by founder effects and persist due to low flushing rates. Thus, variability among pools in the high intertidal and splash zones may exceed that observed among pools in lower intertidal zones.
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Papers by Anna Metaxas