Browsing by Author "Fernández, M"

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    Active brood care in Cancer setosus (Crustacea: Decapoda)
    (2002) Baeza, JA; Fernández, M
    1. Previous studies have shown that oxygen is limiting in embryo masses of marine invertebrates. It has been suggested that several behaviours found in brooding females of brachyuran crabs are used to ventilate and provide oxygen to the embryo masses.
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    Cannibalism in Dungeness crab Cancer magister
    (1999) Fernández, M
    Cannibalism between age classes has been reported for Dungeness crab Cancer magister Dana, and hypothesized to cause the cyclic behavior of the fishery. Recently, cannibalism among young-of-the-year (YOY) Dungeness crabs has been documented, and proposed as an alternative hypothesis to explain recruitment failure of later cohorts of megalopae in intertidal shell habitats already occupied by older YOY crabs. Furthermore, cannibalism among juveniles has also recently been reported for other crab species. This study experimentally addressed whether: (1) cannibalism rate by age classes 0+, 1+ and 2+ of Dungeness crabs Cancer magister of both sexes on YOY conspecifics is affected by habitat type; (2) cannibalism rate among YOY is affected by conspecific density and prey-predator asymmetry; and (3) YOY mutual interference and prey-predator asymmetry affect consumption rate. Predation rate by older crabs (age classes 1 and 2) on YOY was highest in mud habitat, intermediate in low shell density, and lowest in the high shell density treatment. These results show that shell habitat enhances production of YOY crabs by increasing survival. Despite the fact that shell habitat decreased cannibalism rate of larger conspecifics on YOY, it did not affect cannibalism rate among juveniles. YOY crabs did not consume carapaces of conspecifics, while larger crabs consumed entire prey; this difference in amount of hard parts consumed suggests that although cannibalism may be common among YOY, it may not be detected by stomach analysis. Consumption of megalopae was affected by prey density, and also by the asymmetry between the prey and the predator. As predator density increased, the total consumption of megalopae increased, but proportional mortality per predator decreased. When other instar stages were used as prey, prey-predator asymmetry and prey density were not as important factors as predator density on cannibalism rate. Megalopae were the most vulnerable prey, and under certain circumstances YOY conspecifics may be able to decimate cohorts of settling megalopae. However, megalopae may find refuge from cannibalism when predator-prey size ratio is low, predator density is high, and probably when relative abundance of alternative prey is high (laboratory experiments were conducted using only conspecifics as prey). Cannibalism, or other processes that may have evolved in response to cannibalism, may be important factors regulating crab recruitment in natural populations and limiting crab production in artificial habitats.
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    Effect of oxygen availability in determining clutch size in Acanthina monodon
    (2002) Lardies, MA; Fernández, M
    Most taxa of aquatic invertebrates exhibit (1) strong variation in number and size of offspring, and (2) an association between adult size and mode of development, and also between mode of development and size of the clutch. These patterns suggest that a similar set of constraints affects both critical life-history traits and physiology of most taxa, Evidence suggests that oxygen is limiting during early development in aggregated egg masses of marine invertebrates. We studied whether oxygen availability during early development could be a determinant of clutch size in the gastropod Acanthina monodon. We estimated intra- and extracapsubar oxygen availability throughout embryo development using optic fibers and incubated capsules at different oxygen partial pressures (hypoxia, normoxia and hyperoxia) throughout development, We also compared the ratio between nurse eggs and embryos in capsules collected in situ as well as in experimental capsules. We found that intracapsular oxygen availability decreased as embryos developed (80% air saturation in early stages to 40% air saturation in late stages), The mean number of embryos increased as oxygen availability increased from hypoxia to hyperoxia, while the total number of eggs remained constant, The mean number of embryos that developed under normoxia was similar to that recorded in field-collected capsules, We suggest that oxygen availability determines clutch size in this species, probably as a result of oxygen competition among siblings, This may also occur in other taxa of marine invertebrates, since oxygen is limiting in egg masses in general.
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    Full time mothers
    (2002) Ruiz-Tagle, N; Fernández, M; Pörtner, HO
    Daily rhythms in activity have been reported for marine and terrestrial organisms, including brooding behaviors which supply oxygen to the embryos of marine invertebrates. Considering that oxygen is a limiting factor in embryo masses of Brachyuran crabs and that female crabs play a critical role in supplying oxygen to the embryos, we studied and compared daily patterns of (1) brooding and nonbrooding behaviors in brooding females, (2) behaviors in nonbrooding females, and (3) oxygen provision to the embryos in a Xanthid crab (Homalaspis plana). We also experimentally evaluated whether daily patterns of nonbrooding behaviors were related to food intake. Behaviors were identified using video recordings and correlated with oxygen analyses in the center of the egg masses by use of microoptodes. According to PO2 recordings abdominal flapping was identified as the single, most important behavior supplying oxygen to the center of the egg mass, maintained at a constant rate during both day and night. Furthermore, the lack of a daily pattern in oxygen availability in the center of the embryo mass is consistent with the lack of daily pattern in abdominal flapping. In contrast, locomotor activity (walking) and maxilliped movements remained unrelated to PO2 oscillations and showed a pronounced diurnal pattern, increasing during the night. This strong diurnal rhythmicity in walking behavior decreased as embryos developed. The frequency of locomotor activity and egg ventilation increased as embryo development progressed. The increase in egg ventilation throughout embryo development may be a response to the increase in embryonic oxygen demand during development. The change in locomotor activity was unrelated to feeding activity, but may serve to make the ventilation process more efficient. These findings emphasize that oxygen is a crucial factor during early development, affecting the normal rate of development of embryos. In consequence, females permanently provide oxygen to the brood despite daily cycles in other behaviors. (C) 2002 Elsevier Science B.V. All rights reserved.
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    Latitudinal trends of species diversity in rocky intertidal herbivore assemblages
    (2002) Rivadeneira, MM; Fernández, M; Navarrete, SA
    In this study we assessed the impact of the spatial scale of analysis on patterns of latitudinal diversity of rocky intertidal invertebrates and on the relationship between local and regional species richness. Fifty-three wave-exposed sites were sampled along the coast of Chile between 18degrees40'S and 42degrees35'S, covering a range of over 2600 km and 25degrees of latitude. Three spatial scales were defined to analyze latitudinal trends of diversity: (1) regional, based on species range limits across the entire region (100s of km), (2) site, corresponding to hundreds of square meters sampled at each location, (3) sampling unit scale, corresponding roughly with a square meter of rocky shore. The analysis showed that spatial patterns of species richness and species turnover varied according to the scale used. At a regional scale, species richness showed a mid-latitudinal peak (i.e. around 30 to 32degreesS), decreasing toward northern and southern latitudes. No clear latitudinal trends in diversity were detected at site and especially at sampling unit scales. Despite the fact that at regional scale species turnover was low and geographically uniform, at the site scale beta diversity showed the existence of 2 zones of higher species turnover (19 to 20degreesS and 30 to 32 S), which may be attributed to changes in ecological and oceanographical regimes. The relationship between regional and local species richness changed depending on the 'local' scale used; unsaturated patterns (linear positive relationship between local and regional diversity) were evident at site scale, whereas saturated patterns (quadratic trend between local and regional diversity) were observed when the local scale was defined in terms of the sampling unit. We suggest that different regulating processes, operating at different spatial scales, may explain the latitudinal trends in diversity at site and sampling unit scales. While regional processes may set an upper limit in species richness at site scale, species interactions (e.g. competition) may control species richness at sampling unit scales. These findings question the current idea of the disproportionate prevalence of regional factors over local ones in determining diversity of local assemblages. They also suggest that regulation of local diversity results from the interplay of regional and local processes.
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    Patterns of oxygen supply in embryo masses of brachyuran crabs throughout development
    (2002) Fernández, M; Pardo, LM; Baeza, JA
    Different patterns of variation in oxygen availability throughout development have been observed in embryo masses of brooding species of marine invertebrates, and this variation seems to be related to the strategy to solve the oxygen limitation problem of the broods. As yet, little is known about patterns of oxygen availability and female brooding behavior (abdominal flapping) throughout development in brachyuran crabs, and about which factors trigger abdominal flapping. These issues were experimentally studied in 2 crab species of similar body size (Cancer setosus and Homalaspis plana). In addition, oxygen consumption of crab embryos and 2 potential factors that could trigger changes in female brooding behavior were studied (oxygen partial pressure and non-identified chemical cues produced by the embryos). Optic fibers were used to monitor oxygen partial pressure (pO(2)) in the embryo mass as female behavior was videotaped; optic fibers do not affect female behavior. Microchambers were used to determine oxygen consumption of the embryos. Females carrying early stage embryos connected to containers with water under different treatments were used to evaluate the effect of pO(2) and chemical cues on female behavior. A cyclic pattern in pO(2) was detected in masses of early stage embryos and constant high pO(2) for late stages. As changes in pO(2) in the embryo mass occurred, an increase in oxygen demand by the embryos and an increase in abdominal flapping frequency were detected in both species. Abdominal flapping seems to be affected by low pO(2) in the embryo mass and also by the presence of late stage embryos. These results support previous findings suggesting that oxygen provision to embryos seems to be a critical factor determining parental investment across taxa of marine invertebrates.
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    Recruitment of Homalaspis plana in intertidal habitats of central Chile and implications for the current use of Management and Marine Protected Areas
    (2000) Fernández, M; Castilla, JC
    Information about the life history of the stone crab Homalaspis plana was necessary to investigate the possible reasons for the failure of Marine Protected Area (MPA) and Management and Exploitation Area (MEA) in increasing stone crab abundance, in contrast with other exploited benthic species. In this study, we analyzed some aspects of the early Life history of the stone crab, focusing especially on (1) recruitment patterns among habitats and between years in intertidal zones, (2) habitat preferences, including some intra- and interspecific interactions that may affect habitat use, and (3) intraspecific interactions that may affect survival. We also evaluated the percent cover of suitable habitats for juvenile stone crabs in a MPA and a MEA. Sheltered habitats showed higher densities of juvenile H, plana than exposed areas, and sand with boulders showed the highest crab densities, followed by shell hash with boulders. Differences in mean densities were detected for all benthic stages among sheltered substrates, except for megalopae. Bare substrates (without boulders) showed the lowest density. Throughout the settlement period, abundance of smaller instars (J4 were twice as high in 1996 than in 1995. Neither intra- nor interspecific space competition seems to explain the distribution of juvenile stone crabs in the field. However, cannibalism among juveniles may have an important effect on survival. Cannibalism among juveniles is density-dependent, and may have greater effects as the abundance of larger conspecifics increases since mutual interference does not affect proportional prey mortality per predator. We suggest that losses are high in low quality habitats (probably through emigration, predation or habitat disturbance due to wave impact), and cannibalism is an important source of mortality in high quality habitats (where crab density is high). Although substrate type and post-settlement processes can help explain the distribution of juvenile stone crabs, wave action seems to be the major determinant of juvenile distribution. Neither sheltered habitats nor the most suitable substrate are common in the MPA and MEA studied. These factors are not currently being considered in the assignation of MEAs or planning of MPAs, although they could explain the lack of effect of both protection strategies in increasing the abundance of the stone crabs in Chile in comparison to other exploited benthic species.
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    Reproductive investment in the crab Cancer setosus along a latitudinal cline
    (2003) Brante, A; Fernández, M; Eckerle, L; Mark, F; Pörtner, HO; Arntz, W
    Reproductive output (RO) is commonly used as a proxy for reproductive effort (RE) among Brachyuran crabs and other marine invertebrates, and so far no attempt has been made to incorporate the cost of brooding into RE to obtain a more reliable estimate of reproductive investment, nor to compare it along a temperature (latitudinal) gradient. We compared RO among 3 sites (ca. 20, 30 and 40degrees S, reflecting mean annual sea-surface temperatures of 18, 14 and 10degreesC, respectively), and the cost of brooding (oxygen provision) at those temperatures, in order to obtain a more reliable pattern of reproductive investment along an extended latitudinal gradient. A total of 187 brooding females of Cancer setosus were collected to estimate RO. Fecundity, volume and weight of the embryos, and embryo losses were also estimated. Laboratory experiments were carried out at the characteristic temperatures of those sites (acclimating females from central Chile) to determine (1) patterns of oxygen provision to the embryos, (2) patterns of brooding behavior, and (3) to quantify the cost of embryo ventilation. Optic fibers, video recording and respiration chambers were used to meet these goals. Results showed that (1) RO, (2) fecundity, and (3) volume and weight of embryos varied with latitude, and that temperature affects (1) period of embryo ventilation (oxygen provision) events, (2) flapping frequency, (3) embryo losses throughout the brooding period, and (4) cost of embryo ventilation per unit of time. While RO increased with latitude, the cost of embryo ventilation decreased with temperature, suggesting a trade-off between investment in eggs and the cost of providing oxygen to the embryos at different temperatures (latitudes). This pattern may not be exclusive to Brachyuran crabs, but may also apply to other marine invertebrates since oxygen limitation during early development occurs in other brooding species.
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    The cost of being a caring mother
    (2000) Fernández, M; Bock, C; Pörtner, HO
    Investment in reproduction ranges from gamete production to active parental care, and marine invertebrates span this range. However, the cost of parental care has not yet been systematically quantified, nor incorporated into life history studies of marine invertebrates, in contrast to most other animal taxa. Since oxygen is a limiting factor in egg masses of marine invertebrates, we studied patterns of oxygen partial pressure over time in embryo masses of Brachyuran crabs, and correlated these results with the cost of providing oxygen to the embryos. We found that: (1) oxygen is limiting in the embryo masses, (2) female crabs show an active brooding behaviour that we think helps to provide oxygen to the embryo mass, and (3) there is a substantial parental investment associated with brooding behaviours. Oxygen limitation and parental investment seem to be associated in many taxa of marine invertebrates, and we suggest that oxygen provision to the embryos may be a critical factor determining parental investment in this group.
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    Two oceans, two taxa and one mode of development
    (2003) Astorga, A; Fernández, M; Boschi, EE; Lagos, N
    The latitudinal gradient of species diversity is a widely recognized but poorly understood phenomenon. In marine systems, differences in dispersal abilities among species may pose an additional problem in identifying the processes that affect diversity. We compared latitudinal diversity gradients along two parallel continental coasts, the east and west coasts of South America, of two groups of Crustacea (Brachyura and Anomura), which exclusively exhibit planktonic development. We also evaluated the species-area and the energy-input hypotheses. Diversity decreased with increasing latitude for both groups in both oceans. Results suggest that the spatial structure of sea surface temperature (SST) explains diversity of both groups at large, but not small (<5 degrees), scales. Range size and latitude were not correlated. We hypothesize that SST differentially affects taxa with contrasting modes of development, influencing patterns of diversity. We suggest that developmental modes of marine organisms should be considered in future diversity analyses.