Crab Megalopae Research Articles

Effects of various salinities on Na+-K+-ATPase, Hsp70 and Hsp90 expression profiles in juvenile mitten crabs, Eriocheir sinensis

Eriocheir sinensis is a euryhaline crab migrating from sea to freshwater habitats during the juvenile stage. We used quantitative real-time polymerase chain reaction (qRT-PCR) to investigate the gene expression profile of Na(+)-K(+)-ATPase, Hsp70 (heat shock protein 70) and Hsp90 in megalopa exposed to salinities of 0, 2, 5, 10, and 15 parts per thousand. Both low and high salinities markedly stimulated expression of Na(+)-K(+)-ATPase, Hsp70 and Hsp90 genes of Chinese mitten crab megalopa; salinity had different effects on Na(+)-K(+)-ATPase, Hsp70 and Hsp90 levels depending on the duration of salinity stress, implying that Na(+)-K(+)-ATPase, Hsp70 and Hsp90 may play an important role in salinity tolerance in this crab species.

Behavioural Response Thresholds in New Zealand Crab Megalopae to Ambient Underwater Sound

A small number of studies have demonstrated that settlement stage decapod crustaceans are able to detect and exhibit swimming, settlement and metamorphosis responses to ambient underwater sound emanating from coastal reefs. However, the intensity of the acoustic cue required to initiate the settlement and metamorphosis response, and therefore the potential range over which this acoustic cue may operate, is not known. The current study determined the behavioural response thresholds of four species of New Zealand brachyuran crab megalopae by exposing them to different intensity levels of broadcast reef sound recorded from their preferred settlement habitat and from an unfavourable settlement habitat. Megalopae of the rocky-reef crab, Leptograpsus variegatus, exhibited the lowest behavioural response threshold (highest sensitivity), with a significant reduction in time to metamorphosis (TTM) when exposed to underwater reef sound with an intensity of 90 dB re 1 µPa and greater (100, 126 and 135 dB re 1 µPa). Megalopae of the mud crab, Austrohelice crassa, which settle in soft sediment habitats, exhibited no response to any of the underwater reef sound levels. All reef associated species exposed to sound levels from an unfavourable settlement habitat showed no significant change in TTM, even at intensities that were similar to their preferred reef sound for which reductions in TTM were observed. These results indicated that megalopae were able to discern and respond selectively to habitat-specific acoustic cues. The settlement and metamorphosis behavioural response thresholds to levels of underwater reef sound determined in the current study of four species of crabs, enables preliminary estimation of the spatial range at which an acoustic settlement cue may be operating, from 5 m to 40 km depending on the species. Overall, these results indicate that underwater sound is likely to play a major role in influencing the spatial patterns of settlement of coastal crab species.

Common sea anemones Actinia equina are predominantly sessile intertidal scavengers

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 430:147-155 (2011) - DOI: https://doi.org/10.3354/meps08861 Common sea anemones Actinia equina are predominantly sessile intertidal scavengers J. Davenport*, T. V. Moloney, J. Kelly School of Biological, Earth & Environmental Sciences, University College Cork, Distillery Fields, North Mall, Cork, Ireland *Email: j.davenport@ucc.ie ABSTRACT: Coelenteron contents of anemones Actinia equina collected from 2 shore heights (upper and lower) on 3 shores (exposed, semi-exposed and sheltered) in south-west Ireland were investigated in summer 2009. Diets of exposed and semi-exposed shore anemones were dominated by small mussels Mytilus edulis, mostly (>90%) with broken/cracked shells. The diet of anemones on the sheltered shore was dominated by insects, particularly on the upper shore. On all shores, larger food items (isopods, mussels, insects) were broken or fragmented; only small gammarid amphipods, crab megalopae, midges and mosquitos were found whole. Laboratory behavioural experiments showed that A. equina were unselective at small prey size, but were limited by their own size, which restricted the maximum size of prey that could be ingested. Whole mussels were ingested, but egested alive after mean elapsed times of 0.75 to 1.95 h (depending upon anemone size). In contrast, mussels with cut adductor muscles, and incapable of shell valve closure, were fully digested, empty shells not being egested until 8.70 to 8.95 h after ingestion. Whole, live mealworms Tenebrio molitor were eaten by anemones, but were egested after a mean 1.30 h with no signs of digestion or fragmentation. Mealworms with mechanically perforated exoskeletons were held in the coelenterons of A. equina for a mean of 5.90 h and all soft tissues were digested. It was concluded that A. equina pre­dominantly ­scavenges on macrofaunal carrion, as well as preying upon smaller food items. KEY WORDS: Sea anemones · Actinia equina · Scavengers · Carrion Full text in pdf format PreviousNextCite this article as: Davenport J, Moloney TV, Kelly J (2011) Common sea anemones Actinia equina are predominantly sessile intertidal scavengers. Mar Ecol Prog Ser 430:147-155. https://doi.org/10.3354/meps08861 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 430. Online publication date: May 26, 2011 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2011 Inter-Research.

Emigration behaviour during sea-to-land transition of the coconut crab Birgus latro: Effects of gastropod shells, substrata, shelters and humidity

Populations of the coconut crab, Birgus latro, have been severely depleted on most inhabited islands throughout the Indo-Pacific because of over-harvesting and environmental degradation. Coconut crabs emigrate from the sea as megalopae carrying gastropod shells. Better knowledge of emigration behaviour can assist in conservation of coconut crab populations through understanding and protecting the habitats indispensable for completing their life cycle. We examined the behaviour of coconut crabs during sea-to-land transition by culturing megalopae and juveniles in containers that hold sea-water and hard substrate simulating an intertidal microhabitat in nature. The test environmental factors were availability of gastropod shells and substrata (small and coarse coral sands) including shelters on land, and humidity (relative humidity, 76% and 98%). Megalopae matured their nature for acquiring shells and emigration from the sea in around 10 days. Humidity and shell availability affected animal behaviour. Low humidity decreased the proportion of animals on land, and burrowing behaviour was stimulated in low humidity and shell-less conditions. Animals in low humidity had a low survival rate. Shelters and shells stimulated the proportion of animals on land at low humidity, and animals concentrated under the shelters on land. Shells, burrows and shelters should act to protect animals from desiccation by keeping microclimates around animals on high humidity. Thus, coconut crab megalopae and juveniles preferred a humid environment, and high-humidity conditions stimulated emigration from the sea. Our findings highlight the importance of a humid environment around the seashore in sustaining the recruits for coconut crab populations.

Supply of crab larvae to an estuary in the eastern Atlantic upwelling system exhibits predictable and haphazard variation at different temporal scales

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 425:113-124 (2011) - DOI: https://doi.org/10.3354/meps08992 Supply of crab larvae to an estuary in the eastern Atlantic upwelling system exhibits predictable and haphazard variation at different temporal scales Carla P. Domingues1,*, Maria João Almeida1, Jesus Dubert2, Rita Nolasco2, Nuno Cordeiro2, Silke Waap3, Ana Sequeira1, Sofia Tavares1, Henrique Queiroga1 1CESAM & Departamento de Biologia, Universidade de Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal 2CESAM & Departamento de Física, Universidade de Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal 3Faculdade de Ciências do Mar e do Ambiente, Universidade do Algarve, Campus de Gambelas, 8005-196 Faro, Portugal *Email: cdomingues@ua.pt ABSTRACT: We measured variability in daily supply levels of shore crab megalopae in an estuary on the northwest Portuguese coast, Ria de Aveiro, located in the eastern Atlantic upwelling system. The 5 yr study covered the shore crab larval season (generally February to July) in 2002 and from 2006 to 2009. We addressed the possible effects of wind- and tide-driven circulation, number of flood hours during darkness, and chlorophyll a concentration in coastal waters on larval supply variation. Megalopae supply measured over the years was an episodic phenomenon, and observations showed some predictable and haphazard patterns. In some episodes, supply was highest around spring tides and was enhanced by southerly winds, as predicted, although not all episodes fitted this pattern. The relationships between supply levels and number of flood hours during darkness or chlorophyll a concentration were ambiguous throughout the time series, although in some years increased levels of supply were positively correlated with number of flood hours during the night. The analysis of multiple years conducted in this study showed that shore crab megalopae supply patterns to Ria de Aveiro are more variable than previously assumed, suggesting the participation of several delivery mechanisms that vary within and among years. However, a proportion of supply variation exists that cannot be explained by the mechanisms we propose. KEY WORDS: Larval supply · Carcinus maenas · Wind · Tides · Flood hours · Chlorophyll a Full text in pdf format PreviousNextCite this article as: Domingues CP, Almeida MJ, Dubert J, Nolasco R and others (2011) Supply of crab larvae to an estuary in the eastern Atlantic upwelling system exhibits predictable and haphazard variation at different temporal scales. Mar Ecol Prog Ser 425:113-124. https://doi.org/10.3354/meps08992 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 425. Online publication date: March 14, 2011 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2011 Inter-Research.

Gut Content Analysis of Selected Commercially Important Species of Coral Reef Fish in the Southwest Part of Iligan Bay, Northern Mindanao, Phillippines

The diet composition of selected economically important reef fishes was described. Sampling for fish and plankton was done every month from July to December 2004 in eight sampling stations located in Maigo and Kauswagan, lanao del Norte. Nine fish species were selected for the gut content study. The nine species belong to seven families: the Gerreidae (Gerres oyena), Leiognathidae (Leiognathus splendens), Lethrinidae (Lethrinus insulindicus), Scaridae (Scarus bowersi), Siganidae (Siganus guttatus and Siganus vermiculatus), Theraponidae (Therapon jarbua and Therapon sp.) and Mullidae (Upeneus caeruleus). The result of the stomach or gut content analysis showed that majority of the fish species preyed on zooplankton and benthic animals. These fishes were categorized as generalist species based on Costello's method. They are represented by Gerres oyena, Leiognathaus splendens, Lethrinus insulindicus, Therapon jarbua, Therapon sp. and Upeneus caeruleus except for fishes belonging to Family Scaridae (Scarus bowersi) and Family Siganidae (Siganus guttatus and Siganus vermiculatus) which exclusively fed on algae and were categorized as strict herbivores. A total of 46 zooplankton groups were identified and 76.51% of the total population was composed of copepods which included calanoida, cyclopoida, harpacticoida, copepod nauplius and eggs. Comparison between the abundance of zooplankton between stations in Maigo, and Kauswagan, Lanao del Norte showed no significant difference (p > 0.05) in both areas. This study showed that out of the nine economically important reef fishes, six fish species preferred to prey on zooplankton species. This further showed that despite the abundance of zooplankton in the environment, planktivorous fishes preferred to prey on some zooplankton groups like copepods, amphipods and crab megalopa. Hence, zooplankton as prey of selected economically important reef fishes should be conserved and harvesting of commercial fishes should be controlled.

Catching the prey: Sampling juvenile fish and invertebrate prey fields of juvenile coho and Chinook salmon during their early marine residence

Marine diets of juvenile coho ( Oncorhynchus kisutch) and Chinook salmon ( Oncorhynchus tshawytscha) in the northern California Current are made up primarily of micronekton prey including juvenile fish, adult euphausiids, and large crab megalopae. However, these animals are seldom caught in the conventional plankton gears used to define juvenile salmon prey fields in ocean salmon programs. Four types of sampling gears with various mouth openings and configurations were examined for the ability to catch known juvenile salmon prey. Samples were examined for differences in species composition, relative biomass, length distribution, and taxonomic overlap with prey in the diets of salmon sampled concurrently. The herring, Marinovich, and Methot trawl nets generally caught juvenile prey fish such as hexagrammids, rockfish, cottids, and osmerids. These prey were in the 15–95 mm fork-length range, consistent with the type and size eaten by juvenile salmon. The bongo net sampled smaller invertebrate prey, which are rarely eaten by juvenile salmon, but instead are common prey of the juvenile fish that salmon consume. Overlap between prey fields and salmon diets was moderate for samples from the larger gear types but low for those from bongo nets towed in the same area. The fact that no gear matched exactly with coho and Chinook salmon diets was related to differences in catchability of the prey in different gears but may also in part be probably due to the high mobility of juvenile salmon, which enables these fish to consume food in locations distant from where they are sampled, and also to selectively feed in areas of high prey concentration. Based on our analysis, we recommend the use of micronekton gears with larger mouth openings and mesh sizes for better filtration rather than standard plankton gears (i.e., bongo nets) for direct estimates of available prey resources for juvenile coho or Chinook salmon. Sampling the abundance, size, and distribution of prey fields for juvenile salmon during their first summer in the ocean, a period of high natural mortality, may help us to better understand the mechanisms of bottom-up forcing on interannual changes in salmon mortality.

Shelf and estuarine transport mechanisms affecting the supply of competent larvae in a suite of brachyuran crabs with different life histories

Supply of competent larvae to the benthic habitat is a major determinant of population dynamics in coastal and estuarine invertebrates with an indirect life cycle. Larval delivery may depend not only on physical transport mechanisms, but also on larval behavior and physiological progress to the competent stage. Yet, the combined analysis of such factors has seldom been attempted. We used time-series analyses to examine tide- and wind-driven mechanisms responsible for the supply of crab megalopae to an estuarine river under a major marine influence in SW Spain, and monitored the vertical distribution of upstream moving megalopae, their net flux and competent state. The species Panopeus africanus (estuarine), Brachynotus sexdentatus (euryhaline) and Nepin- notheres pinnotheres (coastal) comprised 80% of the whole sample, and responded in a similar way to tide and wind forcing. Tidal range was positively correlated to supply, with maxima 0 to 1 d after spring tides, suggesting selective tidal stream transport. Despite being extensively subjected to upwelling, downwind drift under the effect of westerlies, not Ekman transport, explained residual supply variation at our sampling area. Once in the estuary, net flux and competence state matched the expected trends. Net upstream flux increased from B. sexdentatus to P. africanus, favoring trans- port to a sheltered coastal habitat (N. pinnotheres), or to the upper estuary (P. africanus). Competence state was highest in N. pinnotheres, intermediate in B. sexdentatus and lowest in P. africanus ,a s expected if larvae respond to cues from adequate benthic habitat. P. africanus megalopae were found close to the bottom, not above, rendering slower upstream transport than anticipated.

Molting of megalopae of the Asian shore crab Hemigrapsus sanguineus in intertidal habitats of Northeastern North America

Planktonic larvae of many benthic taxa settle and metamorphose in response to certain habitat cues. Although laboratory investigations of the importance of potential cues are numerous, field experiments are less common. We modified a field caging technique first developed for analysis of molting specificity of fiddler crab megalopae to test potential habitat cues affecting molting of megalopae of the non-native Asian shore crab Hemigrapsus sanguineus (de Haan). Potential cues consisted of waterborne substances from 2 potential habitats (cobble beach and salt marsh), and the material used to construct experimental cages. Experiments were conducted in 2002, 2003, and 2004 in Massachusetts and New York (USA). Megalopae (4 or 5 d post molt) were placed in either nylon mesh (500 μm) cages open to flooding seawater or transparent glass jars containing filtered seawater. Cages and jars were placed at identical intertidal heights at the field sites and retrieved 3 or 4 d later. The proportion of megalopae molting to the first crab stage was determined after the period of field exposure and for 2 d thereafter. More megalopae molted in cages than jars placed in the adult habitat (cobble beach) and in a marsh without adults. The cage mesh had little effect on molting response. We conclude that waterborne cues stimulate molting of H. sanguineus megalopae, and that cues are present in both the adult habitat and marsh. Molting of H. sanguineus megalopae is substantially less habitat-specific than molting of native fiddler crab megalopae.

Induction of settlement in crab megalopae by ambient underwater reef sound

The larvae of a number of crab species have been found to orientate and swim toward ambient underwater sound emanating from coastal settlement habitats. This current study examined whether ambient underwater sound also has the potential to trigger settlement responses in crab larvae. The effect of exposure to reef sound on the settlement behavior and time to metamorphosis (TTM) was examined in the megalopae of 5 common crab species, 3 from temperate waters and 2 from tropical waters. The megalopae of all 5 crab species showed marked changes in swimming behavior and a significant decrease in TTM when exposed to replayed ambient underwater reef sound compared with a silent (control) treatment. Megalopae exposed to sound decreased swimming activity earlier and displayed crawling behavior that was a precursor to both settlement and metamorphosis. Sound exposure decreased the median TTM by 33 h in Hemigrapsus sexdentatus and by 75 h in Grapsidae sp. 2. The consistent results among all species examined indicate that ambient underwater sound is likely to be an important settlement cue for the megalopae of many crab species. The wider ecological significance of acoustic settlement cues in crab larvae, in relation to other settlement cues and processes, now needs to be determined.

The capacity of crab megalopae to autotomize body appendages and the consequences upon their feeding ability–the price to pay to live another day

During the mass settlement events of brachyuran crabs, there is a significant chance of density-dependent injury in the megalopae (last larval stage) because cannibalism can occur by larger conspecifics. Laboratory observations revealed that the appendages that are more prone to injury are eyestalks, as well as first (P1) and fifth (P5) pereiopods. The ability of Carcinus maenas megalopae to autotomize these structures and the effect of such injuries in their feeding ability and metamorphosis were investigated. All tested specimens were able to autotomize one or both of their P1 and P5, but not their eyestalks. Megalopae missing a single P1, as well as one or both P5, were able to capture and ingest prey, as well as intact specimens. Megalopae with either P1 and P5 appendages or at least one damaged eyestalk failed to ingest sufficient food to reach the nutritional threshold required to successfully metamorphose.

Impacts of biochemical cues on horizontal swimming behavior of individual crab larvae

To determine if larval crabs alter their horizontal swimming behavior in response to biochemical cues in the water, fiddler crab (Uca pugnax) and blue crab (Callinectes sapidus) megalopae were video recorded in a laminar-flow flume while putative cues were introduced and allowed to establish a gradient in the flow field. Changes in horizontal orientation, distribution, and swimming velocity were observed for six different cue treatments. Overall results show that crab megalopae can detect biochemical cues in ambient water and that they adjust their horizontal swimming behavior in response to these cues. The dominant response was a change in swimming velocity in the presence of a cue. While this response may affect the dynamics of larval patches, it is not clear if swimming in the horizontal plane has a substantial effect on the spatial aggregation of the larvae in the field.

Habitat selectivity of megalopae and juvenile mud crabs (Scylla serrata): implications for recruitment mechanism

Megalopae of several crab species exhibit active habitat selection when settling. These megalopae usually select structurally complex habitats which can provide refuge and food. The portunid mud crab, Scylla serrata, is commonly found within the muddy estuaries of the Indo-West Pacific after attaining a carapace width >40 mm. Despite substantial efforts, the recruitment mechanism of juvenile mud crabs to estuaries is not understood because their megalopae and early stage crablets (carapace width <30 mm) are rarely found. We used laboratory experiments to determine whether megalopae and early stage crablets are selective among three estuarine habitats which commonly occur in Queensland, Australia. These animals were placed in arenas where they had a choice of habitats: seagrass, mud or sand, and arenas where they had no choice. Contrary to the associations exhibited by other portunid crab megalopae, S. serrata megalopae were not selective among these estuarine habitats, suggesting that they tend not to encounter these habitats, or, gain no advantage by selecting one over the others. The crablets, however, strongly selected seagrass, suggesting that residing within seagrass is beneficial to the crablets and likely increases survival. This supports the model that for S. serrata, crablets and not megalopae tend to colonise estuaries, since a selective behaviour has evolved within crablets but not megalopae.

Mesozooplankton Responses to Climate Change and Variability in a Southeastern U.S. Estuary (1981–2003)

Abstract Long-term trends and relationships between large mesozooplankton (1.5–20 mm) and the physical environment were used to investigate impacts of climate change and variability in the North Inlet estuary, South Carolina. Biweekly collections (365 μm) from 1981 to 2003 demonstrated distinct seasonal patterns and large interannual fluctuations in abundances. Significant long-term decreases in abundances were observed for total zooplankton and 12 taxa (e.g., Gobiosoma larvae, chaetognaths, and adult shrimps), whereas 14 others, including some of the most abundant constituents, did not change (e.g., mysids, amphipods, crab megalopae, and Palaemonetes larvae). The composition of the fauna was similar at the beginning and end of the 23-year period. A significant long-term increase in winter water temperature (2.6°C) and a decrease in summer salinity (3.2) were determined. Relationships between physical conditions and taxa varied in strength and direction, and most did not agree with their long-term trends....

Pilot Evaluation of Early Juvenile Blue Crab Stock Enhancement Using a Replicated BACI Design

We quantified whether local populations of early juvenile blue crabs (J1–2) could be enhanced through the translocation of crabs to underutilized nursery habitats, and if enhancement success, survival, and potential impacts of stocked crabs on their benthic prey varied in a density-dependent manner. Using plankton nets, ∼143,000 blue crab megalopae were collected as they ingressed into Pamlico Sound, NC. Of these, ∼13,800 early juvenile blue crabs (J1–2 stages) were then stocked at potential nursery sites relatively far removed (32–70 km) from their initial settlement areas using a replicated before-after control impact (BACI) experimental design. On average, there was negative enhancement success (−34%) five weeks after local crab enhancement, and no evidence of density-dependent enhancement success, mortality, or impact on potential crab prey. Poor stocking success was likely due to pelagic emigration from enhancement sites relative to controls. Attempts to assess the feasibility of stocking blue crabs at local scales of small coves should (i) probably not consider J1–2 stages because of their apparent propensity to emigrate from these areas, or (ii) further assess the effects of geomorphology and wind fetch of release sites on density-dependent emigration.

Size-Specific Predation on Marine Invertebrate Larvae

Predation on planktonic larval stages is frequently a major source of mortality for the offspring of benthic marine invertebrates. Mortality rate likely varies with larval size and developmental stage, but few experiments have measured how these factors affect predation rates. I used experimental reductions in egg size to test how variation in larval size affects the likelihood of predation during planktonic development. Blastomeres of the sand dollar Dendraster excentricus were separated at the two-cell stage to produce half-sized zygotes. Larvae resulting from this manipulation were tested for their susceptibility to predation relative to whole-sized siblings at four ages. Individuals from each size class were simultaneously presented as prey items to five predators (crab zoeae, crab megalopae, chaetognaths, solitary tunicates, and postlarval fish) in the laboratory. Four predators consumed significantly more half-sized larvae than whole-sized larvae, but one predator type (postlarval fish) consumed more whole-sized larvae. Predators that consumed more half-sized larvae also preferentially consumed younger larvae. In contrast, postlarval fish showed no significant prey preference based on larval age. These results suggest that assumptions of constant mortality rates during development should be modified to account for the effects of larval size and age.

Behavioural responses of zooplankton to the presence of predatory jellyfish

The major objective of this study was to investigate the behavioural responses of several zooplankton species to the presence of the scyphozoan jellyfish, Catostylus mosaicus. Specific aims included: identifying taxa that were not captured by C. mosaicus; investigating whether some of these taxa were able to detect and avoid water that had been exposed to C. mosaicus; and determining if positive phototaxis of crab megalopae was suppressed in the presence of C. mosaicus. Zooplankton not caught by C. mosaicus were identified by comparing the zooplankton present in the water column to those on the oral arms of the jellyfish. C. mosaicus mainly caught mollusc veligers and copepods, but did not catch crab megalopae, small prawns or post-flexion fish larvae. The hypothesis that these taxa were able to avoid swimming in water exposed to C. mosaicus was tested using water-choice experiments in a flume tank. A significant proportion (18–25%) of larval barramundi ( Lates calcarifer) avoided swimming in the plume of water that had been exposed to C. mosaicus but mud crab ( Scylla serrata) megalopae and juvenile prawns showed no response. The effect of C. mosaicus on the positive phototaxis of S. serrata megalopae was tested using 1 m tall glass towers. Megalopae were exposed to one of four treatments: filtered seawater (a control), an oral arm of C. mosaicus, an oral arm that had been sealed in plastic, and mucus from C. mosaicus. Megalopae migrated higher into the water column in the control than in treatments containing cues from the jellyfish. These findings suggest that blooms of jellyfish may induce behavioural changes in some zooplankton.

Stimulation of molting in megalopae of the Asian shore crab Hemigrapsus sanguineus: physical and chemical cues

The Asian shore crab Hemigrapsus sanguineus is a recent invader and abundant mem- ber of rocky intertidal coastlines of the eastern USA. Understanding factors influencing the settlement and metamorphosis of its larvae is important for predict- ing colonization of the species. For many species of brachyuran crustaceans studied to date, chemical cues in the natural environment stimulate molting of megalopae, the final larval stage, to the first crab stage, whereas physical cues alone have little or no effect. However, physical structure can influence the abundance of juvenile and adult crabs. In this study, I tested whether physical/structural and chemical cues stimulate molting of H. sanguineus in the labo- ratory. Molting rates of megalopae exposed to exu- dates from adult crabs (H. sanguineus and the green crab Carcinus maenas) and different physical cues varying in structural complexity (rocks with or with- out biofilms, silt particles, nylon mesh used in aqua- culture) were monitored. Megalopae molted sooner to the first crab stage in the presence of exudates of both crab species, rocks with and without biofilms, and all nylon meshes tested regardless of the size of mesh openings. By separating the effects of chem- ical and physical cues, this study shows both to be important during settlement and metamorphosis of Asian shore crab megalopae, potentially contributing to its successful colonization of North Atlantic coast- lines.

Wind and tidal influences on larval crab recruitment to an Oregon estuary

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 351:177-188 (2007) - DOI: https://doi.org/10.3354/meps07130 Wind and tidal influences on larval crab recruitment to an Oregon estuary G. Curtis Roegner1,*, David A. Armstrong2, Alan L. Shanks3 1NOAA Fisheries, Northwest Fisheries Science Center, Point Adams Biological Field Station, PO Box 155, Hammond, Oregon 97013, USA 2School of Aquatic and Fisheries Science, PO Box 355020, University of Washington, Seattle, Washington 98195, USA 3University of Oregon, Oregon Institute of Marine Biology, PO Box 5389, Charleston, Oregon 97420, USA *Email: curtis.roegner@noaa.gov ABSTRACT: We investigated wind and tidal forcings that may facilitate transport of crab megalopae to a northeast Pacific coastal estuary. Daily abundance of crab megalopae was estimated from light trap collections made from March 1998 through December 2001 in Coos Bay, Oregon, USA. The Dungeness crab Cancer magister dominated the catch; Cancer Group I (C. productus and C. oregonensis), Hemigrapsus oregonensis and Pachygrapsus crassipes megalopae were also abundant enough for statistical evaluation. The abundance time series data were analyzed in relation to mean daily wind stress, maximum daily tidal range, and mean daily temperature residuals using cross-correlation and cross-Fourier techniques. Variation in wind stress had little relation to variation in crab megalopae abundance. Rather, crab megalopae were found to recruit to the estuary at periods close to the spring–neap tidal frequencies. Increased catches were not coincident with spring tides; most tests indicated that ingress occurred at times ranging from several days after spring tide to near the neap tide, but this varied among species and years. Tidal forcing appears to control crab recruitment to this estuarine system. KEY WORDS: Ocean-estuary coupling · Larval transport · Cancer magister · Hemigrapsus oregonensis · Pachygrapsus crassipes · Light trap · Northeast Pacific Full text in pdf format PreviousNextCite this article as: Roegner GC, Armstrong DA, Shanks AL (2007) Wind and tidal influences on larval crab recruitment to an Oregon estuary. Mar Ecol Prog Ser 351:177-188. https://doi.org/10.3354/meps07130 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 351. Online publication date: December 06, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.

Planktonic availability and settlement of Carcinus maenas megalopae at high temporal resolution in the lower Mira Estuary (SW Portugal)

The current conceptual model of reinvasion and settlement for estuarine brachyuran crabs in mesotidal systems is that megalopae undergo selective tidal stream transport, in an upstream direction, and settle by the end of the flood tide. Recent studies on recruitment processes of Carcinus maenas (L.) have reported a clear decoupling between supply, as larval influx, and settlement events in the lower Mira Estuary (SW Portugal). We investigated, at high temporal resolution, whether overestimation of planktonic abundances and/or deviations of megalopal responses from the conceptual model were responsible for such decoupling. Daily settlement of megalopae was analyzed using regression and spectral analyses to identify periodicities and correlated with tidal amplitude. Hydrological parameters and supply, net flux and hourly concentration of megalopae in the plankton were addressed as factors influencing short, intermediate and long-term settlement, through 50 h sampling series. Supply and surface net flux levels of megalopae were similar and clearly decoupled from settlement on bottom-deployed collectors. Both hourly planktonic concentra- tion and settlement patterns of megalopae fitted the conceptual model at high temporal resolution, with some deviations in terms of light intensity influences. Furthermore, our results suggest that processes preventing settlement and capable of overriding the influence of light intensities — such as turbulence — may explain the decoupling between supply and settlement of shore crab megalopae in the lower Mira Estuary.