Recursos Marinos y Pesquerías

Spatial dynamics of a local population of Maja [Conference]

22/06/05 ,

A Corgos, N Sánchez & J Freire (2005). Dynamics of the small-scale spatial structure of a local population of the spider crab, Maja brachydactyla .Sixth International Crustacean Congress, University of Glasgow, Scotland, 18-22 July 2005.
POSTER (pdf)
WORKING PAPER v.1, Jun 2005 (pdf)

Mark-recapture analysis of growth in Maja brachydactyla [Working paper]

13/05/05 ,

A. Corgos, M. P. Sampedro, E.
González-Gurriarán and J. Freire. Growth at moult, intermoult period
and moulting seasonality of the spider crab Maja
brachydactyla: combining information from mark-recapture and experimental
studies. (Working paper, v.1, May 2005) [pdf]

An analysis of growth at moult (for
both the prepubertal and terminal moults), moulting seasonality and the
intermoult period in the spider crab Maja squinado in the Ría de A Coruña (NW
Spain) was carried out based on a mark-recapture experiment. Crabs between 70
and 130 mm carapace length (CL) undergo a mean increase at moult of 32.4% from
their pre-moult size. Generalised Linear Models (GLMs) were used to construct
growth models, employing a combination of information from the mark-recapture
study and other previous studies performed in both laboratory and extensive
culture, to estimate the effects of the biological variables and the study
method. No differences were found in the growth rate between males and females.
However, the effects of the study method, the premoult CL and the interaction between
them were significant. The smallest-sized crabs undergo a greater increase in
size in the laboratory and culture studies, while the largest individuals
undergo greater growth in the field. The mean intermoult period estimated for
prepubertal moults in the field ranged from 50 to 86 days, which is similar to
the 84.7 days observed in the laboratory study. The  prepubertal moults occurred primarily in
spring and autumn in the field, while under culture conditions, the crabs
moulted mainly in the spring. The intermoult period for terminal moults was
estimated to be around 90 days, slightly lower than the value of 104 days
obtained in the laboratory. The terminal moult took place generally in summer
(June-September) both at sea as well as in culture experiments. The intermoult
period of juveniles at sea was highly variable, and some of the specimens did
not moult for more than 5 months.

Reproductive strategies of Maja brachydactyla [Working paper]

13/05/05 ,

Antonio Corgos, Patricia Verísimo and Juan Freire.
Estacionalidad de la muda terminal y la migración reproductiva en la centolla, Maja brachydactyla: evidencias de
estrategias de apareamiento alternativas. Working paper (v.1, Jul 2005) [pdf]

Versión en castellano (v.1, May 2005) [pdf]

Timing and synchronisation at individual and population levels of the processes related to the terminal moult, gonad maturation, accumulation of energy reserves and migration in the spider crab Maja brachydactyla are analyzed. Also, the intra- and intersexual variability is established. Two hypotheses are tested to explain the temporal and population variability:1) physiological hypothesis: males and females begin migration when they reach the appropriate physiological stage (the optimum level of energy reserves); and 2) mating opportunities hypothesis: the timing of the migration maximise mating opportunities and mate quality. Our results show that males carry out the terminal moult before females, the former having a peak in July and the latter in August. The onset of gonad maturity in females occurs between two and three months after they have reached morphometric maturity (starting in October), coinciding with the period prior to and during the mating migration to deep waters. In an analysis of the spermathecae of primiparous females, it was found that practically no mating activity occurred in shallow waters, while the first copulations took place in the migration corridor. However probably most of the mating activity occurs in deep mating grounds. Males reached gonad maturity prior to morphometric maturity. On average, males started migrating on 8 October, while females began migration on 16 October, which would corroborate previous evidence pointing to an earlier starting date for males. No differences were observed in the physiological status (muscle, gonad and hepatopancreas relative mass) between migrating and non-migrating crabs, which is a clear indication that the physiological hypothesis does not hold true for this species. A higher percentage of postmoult crabs were caught in the migration corridor than in shallow waters. The physiological condition improved over time in both males and females in the specimens caught in the shallow area as well as in the migration corridor. Therefore, the crabs that start migrating first did so in poorer physiological condition. Moreover, the early migrators had a significantly lower mean size than the late migrators. Our results would suggest that variability within populations and between sexes is related to the different reproductive strategies and not to a physiological limitation. Thus, the poor-quality males (with a reduced competitive ability) would migrate at the beginning of the season (prior to or in synchronisation with the first females), whereas the high-quality males might delay migration until they have accumulated a high level of reserves, because they would be able to displace low-quality males at mating habitats.

Versión en castellano en la continuación

Continue reading Reproductive strategies of Maja brachydactyla [Working paper]…

Distribution and habitat use in coastal decapods [Working paper]

10/05/05 ,

A Pallas, B García-Calvo, A Corgos, C Bernárdez, J
Freire. Inter-specific comparative analysis of distribution and
habitat use patterns of benthic decapod crustaceans in shallow waters. Working paper (v.1, May 2005). [pdf]

ABSTRACT: Coastal areas have been widely considered as
nurseries for many marine species. New approaches to this concept take into
account interactions among environmental variables and ecological variations
related to geographical location, as well as complex life cycles of marine
invertebrates. We present a comparative approach to assess the relevance of
environmental variables on the determination of patterns of distribution and
habitat use of benthic decapod species in coastal areas. We hypothesize that
this approach allows us to infer processes originating these patterns and to
identify the main habitat use models. An intensive fine-grain sampling design
was used to take into account the environmental gradients occurring at
different spatial scales (defined by substrate type, depth, exposure and
geographical location) in a temperate oceanic bay (Ria de A Coruña, Spain). A
high proportion of juveniles were found in most populations, but the results do
not allow us to generalize the idea of coastal areas as potential nurseries,
except for few species with a marked spatial segregation between juveniles and
adults. Larval transport seems to be the main process regulating mesoscale
distribution patterns, while microscale distribution responds to a complex interaction
among different processes, i. e. habitat selection at settlement, differential
mortality among habitats, post-settlement dispersal and ontogenetic habitat
shifts. Sandy substrates showed low-diversity communities dominated by hermit
crabs. In rocky bottoms, variability in spatial patterns was mostly related to
substrate type and geographical location. Caridean shrimps showed higher
densities on flat rock surfaces, with similar juvenile and adult patterns.
Anomuran species occurred mainly on cobbles. Distribution patterns of
brachyurans varied among species, but did not change greatly from juveniles to
adults.

Plankton and larval fish dynamics (Prog. Oceanogr.)

17/01/05 ,

Franco-Gordo C, E Godínez-Domínguez, AE Filonov, IE Tereshchenko & J Freire (2004). Plankton and larval fish dynamics prior and during El Niño period (1997-98) in the central Pacific coast of Mexico. Progress in Oceanography 63:99-123. [pdf]

The temporal and spatial distributions of zooplankton biomass and larval fish recorded during 27 months (December 1995–December 1998) off the Pacific coast of central México are analyzed. A total of 316 samples were obtained by surface (from 40–68 to 0 m) oblique hauls at 12 sampling sites using a Bongo net. Two well-defined periods were observed: a pre-ENSO period (December 1995–march 1997) and an ENSO event (July 1997–September 1998) characterized by impoverishment of the pelagic habitat. The highest biomass concentrations occurred at coastal stations during the pre-ENSO period. During the El Niño period no spatial patterns were found in coastal waters. The months with highest biomass were those in which the lowest sea surface temperature (SST) occurred (January–May), and this pattern was also observed during the ENSO period. A typical, although attenuated, seasonal environmental pattern with enhanced phytoplankton (diatoms and dinoflagellates) was prevalent during the El Niño event in nearshore waters. During the El Niño period the phytoplankton was mainly small diatoms (microphytoplankton), while dinoflagellates were practically absent. The most parsimonious generalized linear models explaining spatial and temporal distribution of larval fish species included the ENSO index (MEI), upwelling index (UI) and distance to the coast. The environmental variability defined on an interannual time-scale by the ENSO event and the seasonal hydroclimatic pattern defined by the UI (intra-annualscale) controlled the ecosystem productivity patterns. The small-scale distribution patterns (defined by a cross-shore gradient) of plankton were related to the hydroclimatic seasonality and modulated by interannual anomalies.

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