Morais, P, Chicharo, M.A. & Barbosa, A.. (in press) Phytoplankton Dynamics in a
coastal saline lake Acta Oecologica (aceite em Janeiro de 2003).
Chicharo MA, Chicharo L, Amaral A, Condinho S & Gaspar, M.B. Adenylic-derived
indices and reburying time as indicators of the effects of dredging-induced stress on the
clam Spisula solida. Marine Biology. (em publicação).
31 - Gaspar, M.B., Santos, M.N., Leitão, F., Chícharo, L., Chícharo, M.A. & Monteiro,
C.C. Recovery of substrates and macro-benthos after fishing trials with a new
Portuguese clam dredge. Journal Marine Biological Association U.K. (em publicação)
30 - Chícharo M.A., Amaral, A., Condinho, S., Gaspar, M.,. & Chícharo L. Study of
the chronic effects of dredging induced stress on the clam (Spisula solida) using nucleic
acids and lipids composition. Fisheries Research (em publicação)
29 - Gaspar, M.B., Leitão, F., Santos, M.N., Chícharo, L., Damásia, D. & Monteiro,
C.C. A comparison of direct macrofaunal mortality using three types of Portuguese
clam dredge. ICES Journal of Marine Science (em publicação)
28 - Alves F, Chícharo, L, Nogueira, A. & Regala, J. Changes in benthic communities
due to clam dredging in the Algarve coast (South Portugal): importance of seasonal
analysis for short-term impact studies. Journal of the Marine Biological Association of
the United Kingdom (em publicação)
27 - Alves, F.; Chícharo L.; Serrão, E, & Abreu A. Grazing by Diadema antillarum
(Philippi) upon algal communities on rocky substrates. Scientia Marina (em
publicação
Reburial time and indirect mortality of Spisula solida clams caused by dredging
Chícharo, L.; Regala, J.; Gaspar, M.; Alves, F. & Chícharo M.A.
Fisheries Research. (2002) 59 (1-2), 247-258.
Abstract
Clam-dredging results in the exposure of Spisula solida individuals not caught by the
dredge. Subsequent survival depends on clam damage, reburial time, and the time
needed by predators to reach the impacted area.We analyse these variables and discuss
the importance of predation on exposed S. solida caused by dredge fishing. Sampling
was performed in July 2000 off the southern coast of Portugal, at Vilamoura, a
traditional S. solida sandy fishing ground.We compared the time needed for S. solida
individuals to rebury themselves, relative to the abundance of potential predators.
Bivalves collected by divers were placed on the seabed, and the times required for
reburial were measured. These were compared with the times needed for reburial of the
clams exposed by dredge impact. At each of three dredge tracks, we analysed the
number of predators that entered three equal quadrats (0.0250 m2) per minute. These
results were compared with a non-affected control area. Impact caused by the fishing
dredge significantly increases the number of exposed S. solida clams (p < 0.05) and the
abundance of potential predatory species (p < 0.05). The brittle star Ophiura texturata
was the most abundant and first species to reach the dredge track (less than 3 min after
dredge impact). Other species reaching the dredge track were Pomatochistus spp. (6 min
after impact), Diogenes pugilator, and Nassarius reticulatus (both 9 min after impact).
Although predators reached the impacted area while S. solida bivalves were still
exposed, our results suggest that predation on the non-buried clams in the dredge track
is not a major factor for subsequent indirect mortality of S. solida.
Influence of mesh size and tooth spacing on the proportion of damaged organisms
in the catches of the Portuguese clam dredge fishery
Gaspar, M. B., Leitão, F., Santos, M. N., Sobral, M., Chícharo, L., Chícharo, A., and
Monteiro, C. C.
ICES Journal of Marine Science, . 2002, 59: 1228–1236.
Abstract
Experiments to assess the eff ect of mesh size and tooth spacing on the catch of Spisula
solida were undertaken with the aim of determining an optimal combination of these
two characteristics to minimize the dredging impact on by-catch species. However, our
data showed that tooth spacing, mesh size and the interactions between these two
factors did not affect the number of damaged macrofaunal individual’s caught. This
may be because infauna entered the dredge without passing through the space between
the teeth and the mesh of the net bag closed as it was stretched by the weight of the
contents, preventing the escape of the caught individuals. Thus, independently of mesh
size, when the dredge is towed over the sediment, the retained individuals were injured
due to abrasion between animals and/or between animals and debris. The severity of
injuries inflicted by dredging on diff erent macrobenthic species is related to their
morphology and fragility.
Size selectivity of the Spisula solida dredge in relation to tooth spacing and mesh
size.
Gaspar, M.B., Leitão, F., Santos, M.N., Sobral, M., Chícharo, L., Chícharo, M.A. &
Monteiro, C.C.
Fisheries Research (2003). 60 (2-3): 561-568
Abstract
A study was undertaken on the northwestern coast of Portugal to evaluate the selectivity
effect of both tooth spacing and mesh size on the catch of the white clam (Spisula
solida). Two typical clam dredges, equipped with different tooth spacing and mesh size,
were towed side by side. Three tooth spacing (20, 40 and 60 mm) and three mesh sizes
(35, 40 and 50 mm) were investigated. The dredge selectivity experiments were
performed by attaching a cover bag with a 20mm mesh to the gear. Individual hauls
were analysed by the SELECT model. The Fryer’s mixed model of between-haul
variation was also applied to data. The results showed that the space between teeth does
not have an effect on selectivity. Tooth length was directly related to the dredge’s
capture efficiency. The only factor that contributed to dredge size selection was mesh
size. The 50% retention lengths estimated for mesh sizes 30, 40 and 50mm were 25.68,
26.35 and 31.94 mm, respectively. For all mesh sizes, very narrow selection ranges
were observed. The most appropriate mesh size to be enforced within the Portuguese
northwestern S. solida fishery should be 40 mm.
Comparison of RNA/DNA ratios obtained with two methods for nucleic acid
quantification in gobiid larvae.
Esteves, E., Chicharo, M. A., Pina, T Coelho, M.L. & J.P. Andrade
J. Exp. Mar. Biol. Ecol., (2000) 243 (1): 81-94
Abstract
In this paper, RNA and DNA contents and RNA/DNA ratios obtained with two
fluorometric methods for the extraction and quantification of nucleic acids in individual
estuarine gobiid larvae are compared. A total of 141 gobiid larvae, collected in the Mira
and Guadiana estuaries (Portugal), were analysed. This study indicated that the nucleic
acids content and RNA/DNA ratios of individual larvae varied with the procedure used.
The two methods yielded similar log DNA values but different log RNA and log
(RNA/DNA). The differences could be due to a number of factors related to specific
steps of tested protocols. Comparison of nucleic acids contents and calibration of the
two methods by regression analysis provided a reasonable basis for comparison
although differences between estimates were evident.
The distribution of estuarine fish larvae: Nutritional condition and co-ocurrence
with predators and prey.
Esteves, E., Pina, T., Chicharo, M. A & J.P. Andrade
Acta Oecologica, (2000) 21 (3): 1-13
Abstract
Fish larvae were collected monthly between March and September 1997 in the Mira and
Guadiana estuaries (southern Portugal). Hydrological parameters were registered and
zooplankton samples were obtained simultaneously. Densities of fish larvae (ind·100
m–3) were calculated from 211 samples and larval nutritional condition measured as
RNA/DNA ratios were obtained for 346 individuals, using a fluorimetric method for
nucleic acid quantification. Correlating variables were further studied using multiple
regression analysis in order to assess the relative importance of abiotic and biotic factors
affecting within-year trends in abundance and nutritional condition of estuarine fish
larvae. Results indicated that: 1) the abundance of fish larvae seems conditioned by
temperature and predation; and 2) their nutritional condition is dependent on
temperature and prey availability. Temperature is an important variable structuring
estuaries and therefore conditions the behaviour and physiology of fish larvae.
Furthermore, the co-occurrence of predators and larvae might be related to similar
feeding patterns or comensalism. Whenever feeding conditions are suitable, they usually
determine enhanced growth and nutritional condition. However, predation seems to
control this latter relationship through its effect on larval mortality.
Algal cover and sea urchin spatial distribution at Madeira Island (NE Atlantic)
Alves,-F.M.A.; Chicharo,-L.M.; Serrao,-E.; Abreu,-A.D.
Scientia-Marina-Barcelona [Sci-Mar-Barc] 2001 vol. 65, no. 4, pp. 383-392
Abstract
This study describes sea urchin spatial distribution in relation to environmental factors,
and the relationship between Diadema antillarum density and algal abundance. Twentythree transects around Madeira Island were surveyed by scuba divers, and sea urchin
density and algal cover were determined in situ. Sampling sites along these transects
were characterised in terms of distance from the tide line, water depth, substratum type,
bottom declivity and water turbulence. Diadema antillarum was the dominant sea urchin
species. Paracentrotus lividus and Arbacia lixula occurred at shallower depths (2-6 m),
contrasting with the distribution of Sphaerechinus granularis, which occurs among D.
antillarum (4-20 m). Surveys found two alternative types of communities on rocky
shores: 1) a community with high algal cover and low numbers of sea urchins, along the
north and south-west coasts and; 2) a community with little algal cover and high
densities of sea urchins, along the south-east coast. Macroalgal cover and D. antillarum
densities were inversely correlated (adjusted R super(2)=75.6%; n = 429; p<0.05). The
results showed that water turbulence was the most important factor limiting the
distribution of D. antillarum on rocky substrates. We propose a multiple non-linear
regression model (using backward stepwise analysis) to explain D. antillarum
abundance on the rocky shores: D. antillarum/m super(2) ( square root square root )=
0.121 -0.209 distance from shore (in m) ( square root square root ) + 2.052 water depth
(in m) ( square root square root ) - 1.778 water turbulence level ( square root square root
) - 0.007 water turbulence level super(4) ( square root square root ); where square root
square root indicates data are square-root transformed (adjusted R super(2) = 60.99%; n
= 454; p<0.05).
The influence of dredge design on the catch of Callista chione (Linnaeus, 1758)
Gaspar,-M.B.; Dias,-M.D.; Campos,-A.; Monteiro,-C.; Santos,-M.N.; Chicharo,-A.;
Chicharo,-L.
Hydrobiologia 2001 vol. 465, no. 1-3, pp. 153-167
Abstract
To evaluate a possible introduction of a new dredge in the fishery of Callista chione
(Linnaeus, 1758), IPIMAR has conducted a study with the objective of comparing the
efficiency of two dredges (traditional dredge and the new dredge design) and evaluating
their impact on the benthic community. The experiments were carried out during March
1999 on the Southwest coast of Portugal, from a site off Troia. Three different tow
durations of 5, 10 and 20 min were investigated. A total of 24 hauls were accomplished,
4 for each tow duration and dredge. The experiments were conducted by attaching a
cover bag with a 20 mm mesh to the gear. After each haul, the catches in the bag and in
the cover were sorted separately. All individuals retained were attributed scores on a
scale of 1-4 in which 1 equates to good and 4 equates to dead. The results obtained
showed that catches from the traditional dredge (TD) are composed of a great fraction
of juveniles of C. chione, while in the new dredge (NDD) catches are composed, almost
entirely, by individuals with a superior size to the minimum legal length (50 mm). This
result indicates that the mesh of the bag of the TD used in the exploitation of this
resource is not adequate. For the 3 different tow durations, the mean fishing yield
obtained for the NDD was always superior to the TD, due to its greater efficiency in
capture. The proportion of by-catch is significantly higher when the TD is used. For all
3 tow duration, the TD caused mortalities on the target species and on the macrobenthic
community in the same order of magnitude as the NDD. Since the fishery of C. chione
is managed by daily quotas per boat, when using the NDD the impact on the
macrobenthic community is reduced by about 50% due to its greater efficiency of
capture. Another advantage in the usage of the NDD relatively to the TD, is to allow the
smallest individuals (independently of the species) to escape rapidly through the
metallic bars on the grid, increasing their probability of survival.
Macrofauna spatial differences within clam dredge-tracks and their implications
for short-term fishing effect studies
Chicharo,-L.; Regala,-J.; Gaspar,-M.; Alves,-F.; Chicharo,-A.
Fisheries-Research-Amsterdam [Fish-Res] 2002 vol. 54, no. 3, pp. 349-354
Abstract
In situ observations of clam dredging showed that the effects of the dredge on the
benthic macrofauna may not be constant during a tow. A sand buffer forms in front of
the gear approximately 10 m after the beginning of a tow, and this pushes the sediment
partially aside. In this study, we analyze differences in abundance, the number of taxa
present, diversity, and evenness within sections of dredge-tracks in a disturbed, fished
area and a non-fished area along the southern coast of Portugal. These areas were
sampled by divers before and after dredge-fishing activity. At each site, three dredgetracks were produced. These tracks were divided in three longitudinal sections (start,
middle and end) and two transverse sections (track and edge). Six quadrats were used to
sample macro.
Effects of environmental conditions on planktonic abundances, benthic
recruitment and growth rates of the bivalve mollusc Ruditapes decussates in a
Portuguese coastal lagoon
Chicharo,-L.; Chicharo,-M.A.
Fisheries-Research-Amsterdam [Fish-Res] 2001 vol. 53, no. 3, pp. 235-250
Abstract
Controlling environmental parameters for the early stages of marine invertebrates have
received little attention, particularly in field studies. This study involves measurement
of abundances and growth rates of the bivalve Ruditapes decussates Linnaeus 1758
during its planktonic larval and early benthic life stages in a coastal lagoon: Ria
Formosa, Portugal. Measured abundances were compared with tidal amplitude, water
temperature, salinity, wind velocity and direction, and a food availability indicator
(chlorophyll a). Data were obtained on abundance and prodissoconch length of the
larvae, measured two to three times per week, and of post-larval stages individuals that
had settled in artificial collectors over 10 months. Larval and juvenile cohorts were
identified using size-frequency distributions and larval ages estimated by larval shell
growth lines. Data were fitted to linear, exponential, and Laird-Gompertz growth
models. Larval growth rates best matched a linear model: 3.78 plus or minus 0.55 per
day, r super(2) = 0.75, p < 0.001. Early benthonic growth rates best matched a LairdGompertz model: 3.97 plus or minus 0.15 per month, r super(2) = 0.98, p < 0.001. It
was concluded that there was a significant relationship between planktonic and
recruitment abundances. Water temperature (as a coarse factor) and advection (as a fine
factor) effects were inferred to be the prime environmental factors affecting early life
stages of this species in this coastal lagoon system.
A juvenile recruitment prediction model for Ruditapes decussates (L.) (Bivalvia:
Mollusca)
Chicharo,-L.; Chicharo,-M.A.
Fisheries-Research-Amsterdam [Fish-Res] 2001 vol. 53, no. 3, pp. 219-233
Abstract
Despite the importance of larval abundance in determining the recruitment of benthic
marine invertebrates and as a major factor in marine benthic community structure,
relating planktonic larval abundance with post-settlement post-larvae and juveniles in
the benthos is difficult. It is hampered by several methodological difficulties, including
sampling frequency, ability to follow larval and post-larval or juvenile cohorts, and
ability to calculate growth and mortality rates. In our work, an intensive sampling
strategy was used. Larvae in the plankton were collected at weekly intervals, while postlarvae that settled into collectors were analyzed fortnightly. Planktonic larval and
benthic post-larval/juvenile cohorts were determined, and growth and mortality rates
calculated. Integration of all equations allowed the development of a theoretical
formulation that, based on the abundance and planktonic larval duration, permits an
estimation of the future abundance of post-larvae/juveniles during the first year of
benthic life. The model can be applied to a sample in which it was necessary only to
measure larval length.
An ecohydrologic study of the Guadiana estuary (south Portugal)
Um estudo ecohidrologico do estuario do Guadiana (sul de Portugal)
Chicharo,-M.A.; Chicharo,-L.M.; Galvao,-H.; Barbosa,-A.; Marques,-M.H.; Andrade,J.P.; Esteves,-E.; Gouveia,-I.; Miguel,-C.
Revista-de-Biologia [Rev-Biol-Lisboa] 2000 vol. 18, no. 1-4, pp. 139-156
Abstract
Ecohydrology is considered a tool for sustainable management of aquatic resources.
This is the basis of a study on the Guadiana Estuary carried out within the Fifth Phase of
UNESCO's International Hydrological Programme. The construction of the Alqueva
dam in the near future will pose problems for water quantity and quality in the Guadiana
Estuary. The aims of this study were to monitor basic hydrological and ecological
characteristics of the Guadiana Estuary before the construction of the Alqueva dam
(1996-1998). This was carried out to determine how environmental factors affect the
aquatic biota. The results of available information on the subcatchments of the estuary
(including urban, agricultural, forested areas and pollution point sources, both domestic
and industrial) were integrated into a geographic information system (GIS)-based
software program. Mean monthly river flow varied markedly on a seasonal and yearly
basis. The N/P ratios indicate some limitation by phosphorus, except for the end of
summer, when nitrogen limitation appeared. During this period, cyanobacterial blooms
usually occur in the upper/middle estuary. The fish larval life cycle phase, especially
sensitive to environmental alterations, was in a good ecophysiological condition with
high RNA/DNA ratios. It was concluded that the estuary subcatchment basin is under
low anthropogenic pressure and the aquatic biota characteristics seem to indicate a
general good water quality.
Status of the Guadiana Estuary (south Portugal) during 1996-1998: An
ecohydrological approach
Chicharo,-M.A.; Chicharo,-L.M.; Galvao,-H.; Barbosa,-A.; Marques,-M.H.; Andrade,J.P.; Esteves,-E.; Miguel,-C.; Gouveia,-I.
Aquatic-Ecosystem-Health-and-Management [Aquat-Ecosyst-Health-Manage] 2001
vol. 4, no. 1, pp. 73-89
Abstract
The aims of this study were to monitor basic hydrological and ecological characteristics
of the Guadiana Estuary (1996-1998) before the construction of the Alqueva dam. This
work was carried out to determine how environmental factors affect seasonal and tidal
variations of plankton populations in the estuary. The available information on the
subcatchment of the estuary (e.g., urban, agricultural and forested areas) was integrated
into a geographic information system-based software program. Mean monthly river
flow varied markedly on a seasonal and yearly basis. River flow near Mertola (ca 50 km
upstream from the mouth) reached 3400 x 10 super(6) m super(3) in winter and
decreased to 42x10 super(6) m super(3) in summer. With respect to nutrients, nitrogen
to phosphorus ratios indicated some limitation by phosphorus, except at the end of
summer, when nitrogen limitation appeared. During this period, cyanobacterial blooms
usually occurred in the upper/middle estuary. Estuarine Turbidity Maximum may
significantly influence the retention of zooplankton in the estuary. The fish larval life
cycle, especially sensitive to environmental alterations, showed high ratios of
ribonucleic to desoxyribonucleic acids indicating good physiological condition. It was
concluded that an ecohydrological approach, allowing integration of different elements
from the cellular to the habitat level into a geographic information system, can
contribute to a better understanding of the processes that influence the aquatic biota of
the estuary. The approach will be a useful assessment tool for monitoring the estuary
following dam completion.
Diel variation of the RNA/DNA ratios in Crassostrea angulata (Lamarck) and
Ruditapes decussatus (Linnaeus 1758) (Mollusca: Bivalvia)
Chicharo,-L.M.Z.; Chicharo,-M.A.; Alves,-F.; Amaral,-A.; Pereira,-A.; Regala,-J.
Journal-of-Experimental-Marine-Biology-and-Ecology [J-Exp-Mar-Biol-Ecol] 2001
vol. 259, no. 1, pp. 121-129
Abstract
The aim of this study was to investigate the effect of time of day on RNA/DNA ratios
among fed and starved Crassostrea angulata and Ruditapes decussatus juveniles.
Sampling to investigate the day and night condition of juveniles was carried out for 48
h. A highly sensitive method for nucleic acid quantification was applied to bivalves.
The results suggest that there is some variation in nucleic acid quantities with the time
of the day. For the two species analysed, the RNA/DNA ratio was particularly high
during the night and was higher in the fed animals. The results seem to indicate that
there is some endogenous rhythm in the production of RNA. If there are diel changes in
RNA/DNA ratios, it follows that average RNA/DNA ratios can be unrepresentative if
there is any day or night bias in sampling.
Marine plankton of the Bijagos Archipelago (Guinea-Bissau, West Africa) and its
relationship with fish eggs and larvae.
Poissons et Peches Africains Diversite et Utilisation
Esteves,-E.; Gomes,-T.M.; Anibal,-J.; Teixeira,-T.; Jardim,-J.E.; Chicharo,-L.;
Ferreira,-L.
International Conference for the Paradi Association and The Fisheries Society of Africa,
Grahamstown (South Africa), 13-18 Sept 1998
African-Fishes-and-Fisheries-Diversity-and-Utilisation-Poissons-et-Peches-AfricainsDiversite-et-Utilisation
Coetzee,-L.-(ed.);
Gon,-J.-(ed.);
Kulongowski,-C.-(ed.)
Grahamstown-South-Africa FISA; PARADI 1998 p. 275
Summary only.
Abstract
Results of the joint Guinean-Bissau (CIPA)/Portuguese (UCTRA) marine sciences
survey in the Bijagos Archipelago (Guinea-Bissau, West Africa) carried out in May
June 1995 are presented here. Water surface temperature and salinity were measured in
15 stations with T-probe and refractometer. Nitrite, ammonia and phosphates
concentrations were obtained from water samples collected at 1-m depth and analysed
using a Hach DR/3 portable photometer. In nine of these stations phytoplankton was
sampled with a Nansen bottle at 1m depth and zooplankton was collected with a FAO
conical net (0.37 x 1.60 m, 0.5 mm mesh size) towed 0.5 mm mesh size) towed 0.5 m
below the surface at a constant velocity of 3 knots. The system had lower salinity
(mean=34.4 ppm plus or minus 0.77 SD) and higher temperature (mean=28.6 degree C
plus or minus 2.02 SD) than surrounding open oceanic water. Nitrite, ammonia and
phosphates concentration ranged between 0.05-0.47,0.29 and 0.8-12.1 mu mol/L,
respectively. Phytoplankton abundance was greater in the periphery of the archipelago
and its diel variation at Canogo station seemed more related to tidal influence than with
hour of sampling. Malacrostaceans determined the general variability of the
zooplankton community. Fish eggs and larvae represented less than 5.5% of total
zooplankton abundance. A day-night rhythm of zooplankters abundance could be
depicted from the eulerian sampling plan done at Canogo station. Integrated analysis of
oceanographic data and the data collected did not permit us to establish interrelationships among factors.
Plankton of Guadiana Estuary: seasonal distribution and relation with
environmental parameters - preliminary results
Plancton do Estuario do Guadiana: sazonalidade e relacao com os parametros
ambientais - resultados preliminares
Gouveia,-I.; Miguel,-C.; Chicharo,-M.A.; Marques,-M.H.; Chicharo,-L.M.
Revista-de-Biologia [Rev-Biol-Lisboa] 1999 vol. 17, no. 1-4, pp. 179-192
Abstract
The aim of this study was to investigate the spatial and temporal distribution of
plankton communities from the Guadiana Estuary and related environmental
parameters. Between March 1997 and March 1998, with a variable periodicity,
sampling was done along five sampling stations (from the mouth of the river to 40 km
upstream) during flood tide. Temperature, salinity, turbidity (with a Secchi disc) and
chlorophyll a were measured. Mesozooplankton was sampled by sub-superficial tows,
of ten-minute duration, using a 500 mu m net. The plankton taxonomic composition and
density were determined. Phytoplankton and zooplankton abundance was higher in the
beginning and in the end of spring and summer, respectively than in the other months.
High densities of phytoplankton occurred generally in higher estuary, were the
Chlorophyceae dominated (namely Ankistrodesmus spirilliformis and Pediastrum
simplex). In the middle estuary the small flagellates and the Cryptophyceae were the
predominant, and in the lower estuary were the Baccillariophyceae (Leptocylindrus
danicus) and the small flagellates. The zooplankton abundance was higher in the lower
estuary. Crustacea dominated in the obtained samples, in spit of changes in it specific
composition along the estuary. So, in the lower estuary the Cladoceros (Podon, Evadne
e Penilia) and Decapoda larvae were the dominant, while in the upper estuary the
Copepodes and Cladoceros (Bosmina, Diaphanosoma and Ceriodaphnia) were the most
abundant. The environmental parameters significantly related with the planktonic
densities were the temperature and salinity, as well as, in an indirect way, the nutrients
chlorophyll a seems to act as an indicator of food availability, for the herbivore
mesozooplankton.
Estimation of the life history parameters of Mytilus galloprovincialis (Lamarck)
larvae in a coastal lagoon (Ria Formosa - south Portugal)
Chicharo,-L.M.Z.; Chicharo,-M.A.
Journal-of-Experimental-Marine-Biology-and-Ecology [J-Exp-Mar-Biol-Ecol] 2000
vol. 243, no. 1, pp. 81-94
Abstract
The life history parameters of early stages of marine invertebrates, particularly field
estimations, have received relatively little attention. The aim of this research was to
estimate in situ abundance and growth of Mytilus galloprovincialis planktonic larvae.
Plankton samples were filtered through gauze of 63 mu m mesh and identified, counted
and measured using an inverted microscope. Short-term fluctuations in Mytilus
galloprovincialis larvae abundance and environmental parameters (water temperature,
salinity, wind velocity direction, tidal amplitude and chlorophyll a) were monitored
(two to three times a week). Larval cohorts were identified using size-frequency
distributions and age estimates compared with larval shell growth lines. Data were fitted
to the linear, exponential, von Bertalanffy and Laird-Gompertz growth models. Larval
growth adjusted better to the Laird-Gompertz model (0.525 plus or minus 0.073 mu m d
super(- 1); r super(2) = 0.768; P < 0.05). Reduction of shell growth after 1 to 1.5 months
in the plankton suggests the occurrence, in this period, of a 'delay of metamorphosis'
phase. The results of our study indicate that advection and availability of settlement
substratum may be the key factors for the life history parameters of this species in a
coastal system such as the Ria Formosa.
Estimation of starvation and diel variation of the RNA/DNA ratios in field-caught
Sardina pilchardus larvae off the north of Spain
Chicharo,-M.A.; Chicharo,-L.; Valdes,-L.; Lopez-Jamar,-E.; Re,-P.
Mar.-Ecol.-Prog.-Ser. 1998 vol. 164, pp. 273-283
Incl. bibliogr.: 65 refs.
Abstract
The aim of this study was to analyse the general larval condition, to determine the
incidence of starvation and to investigate the effect of time of day on RNA/DNA ratios
among field-caught Sardina pilchardus larvae. The larvae were collected during 4
research cruises off northern Spain, during March, April, May and June 1992. A highly
sensitive fluorometric method for nucleic acid quantification was applied to larvae of S.
pilchardus. The means of the RNA/DNA ratio were relatively high, so the larvae
collected off northern Spain were generally in good condition. Low percentages of
starving larvae (RNA/DNA ratio less than 1.3), ranging from 0 to 3.23%, were found
over the 4 mo. The RNA/DNA ratios were significantly correlated with zooplankton
biomass. Larvae collected at night revealed higher RNA/DNA ratios compared to larvae
caught during the day. This seems to indicate that there is some endogenous rhythm in
the production of RNA. It would then follow that, if there are diel changes in RNA
concentrations, average RNA indices can be unrepresentative if there is any day /night
bias in sampling.
Starvation percentages in field caught Sardina pilchardus larvae off southern
Portugal
Chicharo,-M.A.
Sci.-Mar.-Barc. 1997 vol. 61, no. 4, pp. 507-516
Abstract
Starvation has been proposed as a major event only in small larvae that are learning to
feed on planktonic prey. However, there are few comparisons of percentages of starving
larvae either among locations, times or phases of larval development. The percentage of
starvation of Sardina pilchardus larvae of different lengths was analysed in four distinct
areas off southern Portugal. A highly sensitive fluorometric method for RNA/DNA
quantification was applied to field caught S. pilchardus larvae during April and May
1992. Using in situ determination of critical RNA/DNA ratio (1.3), we classified as
starving only a small percentage (2.22%) of first-feeding (<8 mm) sardine larvae, but
bigger larvae appeared to be more vulnerable to starvation. We concluded that sardine
larvae analysed were generally in good condition (total percentage of starving larvae 4.64%), but with some variation within each region.
Nutritional condition and starvation in Sardina pilchardus (L.) larvae off southern
Portugal compared with some environmental factors
Chicharo,-M.A.
J.-Exp.-Mar.-Biol.-Ecol. 1998 vol. 225, no. 1, pp. 123-137
Abstract
The aim of this study was to determine the condition and the incidence of starvation
among field-caught Sardina pilchardus larvae, using RNA/DNA ratios and to compare
them with various abiotic and biotic factors. S. pilchardus larvae were collected off
southern Portugal, during April and May 1992. A highly sensitive fluorometric method
for quantifying larvae nucleic acid was applied. Sardine larvae were generally in good
condition. The means of the RNA/DNA ratios were relatively high and low percentages
of starving larvae (RNA/DNA ratio < 1.3) were recorded, ranging from 0 to 12.5%.
These two results were associated with high prey availability, which contributes to
enhanced condition, and with a high density of potential predators, which may result in
fewer larvae in poor condition.
The DNA/RNA ratio as a useful indicator of the nutritional condition in juveniles
of Ruditapes decussatus
Chicharo,-L.M.Z.; Chicharo,-M.A.A.T.
8. Iberian Symposium on Marine Benthos Studies, Blanes (Spain), Feb 1994
SCI.-MAR.-BARC. 1995 vol. 59, no. supplement 1, pp. 95-101
Abstract
Condition indices have been widely used to assess how healthy individuals are under
certain circumstances. It has been shown that the RNA/DNA ratio is a good indicator of
the nutritional condition of several marine organisms. A very sensitive fluorometric
method for RNA/DNA quantification (Clemmesen, 1990) was applied to fed and
starved post-larvae laboratory-reared clam, Ruditapes decussatus. The presented study
shows that the RNA/DNA ratio is a useful indicator of nutritional stress for bivalve spat.
The decrease in RNA/DNA ratio recorded here, under starved conditions was lower
than in similar experiments on fish. A lower metabolic rate in clams may result in a
slower response with respect to RNA /DNA ratios than that observed in vertebrates.