Diversity of Benthic Invertebrates Fauna and Secondary Production in Southern Caspian Sea Basin, Case Study on Tajan River Estuary
Macro benthic invertebrate assemblages were investigated
monthly, from March 2006 to March 2007, at six stations in Tajan river
estuary, a south eastern Caspian Sea coastal estuary, in order to estimate
secondary production consumable for extensive finger fish releasing and
to investigate the factors affecting this production. Benthic assemblages
comprised 9 taxa, of which Ballanus sp., Chironomus plumosus
and Cerastoderma lamarki were the main contributors to both overall
biomass and secondary production. Annual secondary production varied from
4.55 g AFDW m-2 year-1 (Ash Free Dry Weight), in
the upper Tajan estuary, to 78.06 g AFDW m-2 year-1
(Ash Free Dry Weight) in the center of the estuary area. Multivariate
correlations between environmental variables and the Macro benthic assemblage
biomass highlighted the role of the water level, temperature, sediment
organic carbon content and dissolved oxygen in the differentiation of
the communities in the estuary. Composition, biomass and secondary annual
production of Macro benthic communities were dramatically affected by
changes in water residence time and summer drought crises. The isolation
of this habitat limits the recovery of other invertebrate benthic assemblages
during drought periods. Only populations of two species, Balanus sp.
and C. plumosus, seemed to be able to recover quickly after the
drought crises, which, in turn, could compromise the overall secondary
production, with negative effects on the released fish survival. During
summer water renewal, when agricultural activity is intense and nutrient
inputs should be regulated in this estuary to reduce the risk of benthic
mass mortality and to ensure a sustainability of this environment.
Temperate coastal estuaries which are influenced by river discharges,
are very unpredictable systems characterized by marked seasonal and daily
variations of several chemical-physical parameters. Under these conditions
only highly adaptable invertebrate species can survive and grow. Thus,
brackish water benthic assemblages include euryhaline species which prefer
a shallow, sheltered environment and opportunistic species with a high
tolerance to stress and to disturbance (Cognetti and Maltagliati, 2000).
Macro invertebrate benthic communities in estuaries and coastal lagoons
may show high secondary production that can be exploited by fish and shorebirds
(Wilson, 2002). For this reason many coastal river estuary are used worldwide
for extensive and semi-intensive fish releasing because of losses in natural
fish stocks in the adjacent seas (Barnes, 1991). Southern Caspian sea
rivers have traditionally been exploited for fish releasing in order to
repair fish stocks, there is three decades (from 1970s).
Recently, they have been increasingly subjected to human intervention
and greatly affected by eutrophication or mass mortality of fish and other
aquatic organisms. Tajan river estuary complex, located north of the Tajan
river (Caspian sea south basin region), is characterized by hypereutrophic
conditions and dense blooms of diatoms which result in a drastic depletion
of zooplankton, mass mortality of benthic fauna and lack of sea grasses
(Heijs et al., 2000). In spite of their reduced environmental quality,
some areas are still exploited for extensive aquaculture in the upper
river. Fish are released in deep areas of the river once upon a year often
in spring and early summer, allowed to grow during few months and then
going on to the sea where, they encounter natural fish stocks. This kind
of human intervention does not require an external food supply, a high
capital investment or specialized skills. The success of extensive fish
releasing depends on the natural primary and secondary productions. Composition,
biomass and production of macro benthic assemblages can provide useful
information on the sustainability of this kind of interventions. The aims
of the present study were to: (1) analyze variations in the composition
and biomass of the macro benthic assemblages in a coastal river estuary
exploited for finger ling fish releasing; (2) estimate the annual secondary
production; (3) investigate factors affecting this production and(4) consumption
of this production by fish or other consumers of the Tajan river estuary.
MATERIALS AND METHODS
The Tajan estuary is one of the largest estuaries on the south east
coast of Caspian Sea. The climate is mild with a mean air temperature
of 16.3Â°C and total annual precipitation of 700 mm. The estuary has
a broad shallow bay covering an area of about 2 km2 (Fig.
1 ) and is located in the most populated area of North of Iran. Seawater
enters the estuary through a deep narrow inlet channel and sea water is
mixed with fresh water from the Tajan river. The Tajan river drains an
area of 86000 km2 and the estuary also receives effluent discharges,
mainly from urban, industrial and agricultural sources.
||Map of Tajan River estuary situation. Circles show the
six selected stations in the studied area. Stations 1 to 4 and 6 being
in the estuarine area, station 5 is located in the plume area in the
||Comparison among Tajan discharge in m3 sec-1
averages of 48 years maxima ()
during present study and ()
averages of 48 years minima. This figure suggests that, this study
was carried out in a relatively dry year compared to maximum points
of discharge value. Also from June to September, river debit was not
enough to allow water current inflow to the Caspian Sea
The river flow fluctuates seasonally with an average monthly discharge
varying from 1.5 in summer to 81.3 m3 sec-1 in winter
(Fig. 2) which corresponds to a water residence time
of 26 and 8 days, respectively. The present study was conducted at an
area located close to the Caspian Sea Ecologic Institute, in the middle
Tajan estuary (Fig. 1 ). The exact location of the studied
stations is shown in this Fig. 1 . Six sampling stations
were considered, selected after a pre-sampling of 12 stations and selected
by multivariate analysis and clustering method, hereafter designed by
stations l to 6. Stations differed in relation to distance from the estuary
and also in relation to their plank tonic communities and physical and
The location of the sampling stations was chosen in order to study the
benthic communities located in a polluted area of the Tajan estuary, the
Tajan river, where several industrial plants are located along its coasts.
Therefore, station 1 and 2 were located along the Tajan river and station
3 at the same longitude but separated from the river by enlarging the
river. Station 4, chosen as a control station, was located in the middle
of the estuary, away from the influence of industrial discharges. Station
5 in the sea but influenced by Tajan estuary discharge and station 6 in
the estuary of a river closely ending to the estuary`s estuary.
In each stations benthic invertebrate composition, nutrient content
and physical parameters as pH, conductivity, salinity and temperature
were measured. Then utilizing a multivariate analysis, 6 functioning stations
were selected where differences among them (in term of Euclidian distance)
were maxima. Sampling size and time in these stations remaining constant
in the rest of study. Sampling was carried out once per month in the same
time for the whole stations. Sampled parameters consisted of biotic and
abiotic components of water column (chemical and physical components,
invertebrate taxa determination and its composition).
Benthic samples were taken monthly from March 2006 to February 2007.
In each station, four samples were randomly taken; using a modified Van-Veen
grab of 15x15 cm. Samples were sieved (0.3 mm mesh) and preserved using
a buffered solution of 4% formaldehyde. The sieve mesh size of 0.3 mm
was chosen to retain the juveniles of macro benthic species. On each sampling
occasion, water depth, water and sediment temperature, salinity (in the
Practical Salinity Scale), conductivity, pH and dissolved oxygen were
measured near the bottom using electronic probes and a sediment sample
was collected to analyze the organic carbon content and granulometry measurements.
The animals retained by sieve were identified to the lowest possible taxonomic
level and counted. Biomass was measured as Ash Free Dry Weight (AFDW),
firstly drying samples in 50Â°C (48 h) and then ash weight was calculated
after ignition at 700Â°C. The organic content of the sediments was
determined as per cent loss of weight on ignition (LOI %: Loss Of Ignition)
at 550Â°C for 8 h after drying at 95Â°C for 24 h (King et al.,
Daily river flow data for Tajan River were provided by Study Bureau of
Mahab Ghods of Islamic Republic of Iran. Salinity and temperature measurements
were obtained using thermosaline meter (WTW Tetracon 325 Japan). Discrete
sampling was carried out on sub-surface (1 m below the surface) by using
5 L Niskin water samplers, fitted with non-toxic silicone tubing. Samples
for the identification of benthic species composition were preserved on
board with an acid lugol solution. Benthic species were identified and
counted by microscopic examination on an 100xloop (Zeiss). Net and gross
secondary production rates were measured during the entire year of study
considering their absolute values differences. The experimental design
was based on the measurement production of benthos content in samples
based on biomass (AFDW) variations upon months. Benthos fluctuations during
months and among stations was calculated, considering differences between
two successive values in total biomass in g m-2; when values
are additive, it was translated to a production compared to last sampling
(here one month ago) and when there was a decrease of this value (here
on month later) it is suggested that a consumption of this production
compared to last month. The origin of consumption could be of different
kinds. It can be consumed in place by other benthic invertebrates or birds
feeding activity or be derived from the place by currents or only it was
decomposed by bacterial recycling. However, in present study these compartment
are not studied per case and effect of all of them is expressed in term
of secondary production consumption (net or gross). Secondary production
can be estimated by several methods. Most of the classical methodologies,
based on the recognition of cohorts or on size frequency and mass specific
growth rate, are expensive and time consuming (Cusson and Bourget, 2005).
Although less accurate, a number of empirical models based on equations
relating production to biomass and lifespan, maximum individual body weight
and environmental variables like temperature (Tumbiolo and Downing, 1994)
and depth (Tumbiolo and Downing, 1994) have been proposed. In present
study, but in this study, secondary production of benthic community was
calculated based on variations in biomass content of benthic communities.
Descending values suggested that there was a decrease in produced live
measured materials, thus it was estimated that, loss in benthic values
could be a result of consumption where the origin is not clearly understood.
To better understand the patterns of biomass and secondary production,
macro benthic invertebrate assemblages were analyzed using univariate
and multivariate analysis. Faunal biomass, as Ash-Free Dry Weight (AFDW),
was estimated from the number of specimens of each taxon. Although there
is a risk of this method introducing an error into the biomass estimate,
it has been widely applied in studies aimed to assess the secondary production
of a whole community. Abundance, biomass and number of Species (S), were
calculated for each replicate sample and analyzed by two way Analysis
of Variance (ANOVA) with stations and dates as fixed factors. Cochran`s
C test was used to check the assumption of homogeneity of variances and,
when necessary, appropriate transformations were applied to the data.
If variances were heterogeneous even after transformation the analysis
were run at Î± = 0.01 for significance test. Student Newman Kuels
(SNK) post-hoc test was used for multiple comparisons.
Sediment and Water Variables
Results of sediment granulometry (size classifying) (Table
1) of overall stations from 1 to 6 and in 4 seasons indicate that
water discharge and depth of station 6 situated in the estuary of auxiliary
stream to the Tajan river estuary is less but water velocity is more than
the main Tajan river. This condition results that station 6 to have more
instable sediments and erosion could be more important than the main river,
here thin sediments could be washed from this station and exported to
the Tajan river estuary. Size studies of station 6 show that important
fractions of sediments are composed from thick materials as sand (near
to 93). Because of permanent erosion mainly in winter and spring TOM (Total
Organic Matter ) content of station 6 was less than other studied stations.
Although there was not any important variety among seasons in whole stations
but cruds of winter washed main part of thin sediments which was exported
to the sea. Considering what mentioned above, TOM (Total Organic Matter
) content in the main river (Stations from 1 to 5) during the studied
year was more than station 6. This pattern conduct to characterize station
6 as sandy, stations 1 as clay and other stations situated relative to
the estuary having silt texture. Organic materials of sandy bottoms are
simply washed and transported by river flow, because of important porosity
||Result of sediment granulometry ( grain size) and TOM
of sampling stations in studied area, Tajan estuary
||Salinity (S%), pH, water temperature (TÂ°C), Total
Suspended Substances (TSS) mg L-1, N-NO3, N-NO2
and ammonium for water column of six stations in the Tajan estuary.
Values are averages from monthly sampling throughout one year
Thus this kind of substrate has less fractions of TOM. Although thin
particles of clay are more stable than silt ones, but clay permeability
to organic materials is less than silt which contains more organic materials.
The general pattern of the Tajan river flow rates recorded during the
2006 annual discharge (Fig. 2) followed a seasonal variation
characterized by maximal values in fall and winter (seasonally averages;
1.45 and 1.30 m3 sec-1, respectively) and minimal
values during summer (average of the season; 0.48 m3 sec-1).
Many high discharges were observed during spring season in this study
with an average of 1.16 m3 sec-1. Low
discharge during summer led to high residence time beyond the lack of
nutrient inflow from upper Tajan river.
Physical and Chemical Variables
Water temperatures ranged between 25.83Â°C in station 6 and 28.24Â°C
in station 4 and no significant differences were found between stations
(Table 2). Salinity ranged between 3.51 and 12.5% throughout
the year. Salinity values were higher during summer months and were reduced
by increased rainfall and river input. For whole water column, station
1 had significantly (p<0.001) lower salinity than other stations, because
it is the closest station to the Tajan River; pH values were constant
throughout the year with an average value of 8.01Â±0.45. TSS was
relatively constant throughout the year and annual means ranged between
3142.96 and 11274.81 mg L-1 TSS values were significantly (p<0.05)
higher for station 5 and significantly (p<0.01) lower for station 1
The studied period corresponded to a dry year and the Tajan annual river
flow value was less than half of the average of the last 30 years. River
flow fluctuated greatly during the study period with a maximum value in
November (81.3 m3 sec-1) and a minimum in August
(1.5 m3 sec-1). These values correspond, approximately,
to water residence times in the upper estuary of 8 and 26 days, respectively.
With the exceptions of June, October and November, water residence times
were considerably higher than average values (Fig. 2).
Benthic Invertebrates Gross Production
Fluctuation of benthic biomass leads to concretise benthic gross production
and its consumption in 6 stations of study area. Stations could be categorised
by their gross secondary production into three classes (Fig.
||Station 1 and 6 where flowing behaviour
of rivers leads to low annual secondary benthic production of 3.8
and 24.0 g m-2 year-1, respectively (Fig.
4). Station 1 situated in the upper part of Tajan estuary receiving
inflow of Tajan river, is exposed to high concentrations of nutrients
and low water residence time which seems to be the main cause of low
production. This station receives major part of vegetative material
in the form of detritus DOM (Detritus Organic Materials) but not phytoplankton
production of its proper station. Station 6 situated near to the sea
estuary of estuary is charged by draining waters of agricultural wastes
and pollutants, thus low concentration of phytoplankton production
necessary to benthic growth and production. This station probably
play the role of nutrient supply to the Tajan estuary and by this
way participate to its high primary and secondary productions. Also
its sand size bottom substrata seem to contribute to its low accumulation
of benthic communities
category consists of station 2, 3 and 4 where benthic production during
the year exceeds its consumption (Fig. 3). In station
2 consumption values of 13.46 g m-2 30 days-1
begin in spring which will be compensated by high production to 29.4
g m-2 30 days-1 in the end of spring. This production
decreases abruptly in early summer, because of dramatic decrease of
water flow in this period. Production continues until fall and winter
months probably related to lack of consumers (fish and macro invertebrates).
Two marked consumption peaks in early spring and end of fall can be
related to Anadromous fish migration in order to their natural reproduction
which takes place in the river. Two stations of 3 and 4 did not so
suffered from losses in water discharge during summer months. Considering
the lather stations situated in the estuary of Tajan river and being
influenced more by sea currents and waves than the river, they can
support loss of water inlet from river thus stay independent from
river dryness in summer months. Both of them exhibit decreased values
of production (consumed) in early spring and at the end of fall, which
probably due to Caspian Sea fish recruitment during these two periods
5 represent 3rd category with relatively mild lack of production in
spring and early summer but consumption is compensated by benthic
production up to 6.40 and 12.66 g m-2 30 days-1
in early fall and the end of winter, respectively. Considering the
location of this station in the sea and being at the front of Tajan
estuary, where, sediment are so instable, benthic production may be
replaced by zooplankton production stimulated by phytoplankton front
existing during spring and early summer
||Fluctuation of benthic
secondary production and consumption in stations of studied area.
net production and consumptions in stations of studied area, Tajan
of benthic biomass leads to concretise benthic gross production and
its consumption in stations of studied area
Production and Consumption along Stations
Comparing net production and consumptions in studied stations, show variation
of both of values. In stations 1 to 6, efficiencies of benthic net production
compared to benthic consumption (in term of g m-2 year-1)
were 58, 40, 47, 60, 87 and 49 %. In total efficiencies of these stations
were near to 60 %. This estuary has an annual production of 393.8 g m-2
year-1 compared to a consumption of 117.4 g m-2
year-1, where, net production efficiency is 70% (276.4 g m-2
year-1) which may be transported to the sea. Station 2 in the
estuary of Tajan river is dominant by its 78.0 g m-2 year-1
benthic net production as an annual yield. But this 40% of this important
benthic production is consumed in this station (52.2 g m-2
year-1). Station 5 having mild production have been the most
production efficiency, compared to other studied stations. This station
situated in front of the estuary could profit from phytoplankton front
formed in this region. Instable sediments under action of waves can reduce
consumers of benthic materials produced (Fig. 4).
Dispersion of species in 6 studied station show that fresh water specific
species like C. plumosus and Simulium sp. and Hydropsyche
sp. were found only in river-situated stations of 1, 2 and 6. Simulium
sp. being characteristic of medium quality waters indicates that the quality
of station 6 adjacent directly to the Tajan estuary, is predominate by
the estuary itself and not by the water current of the stream. C. lamarki
which is a brakish-marine species was present in all stations except station
1 in upper estuary (Table 3).
This species benefiting from high concentrations of phytoplankton materials
for its filter feeding behaviour, ascend near to upper estuary and is
omnipresent in estuarine and marine stations. However Nereis diversicolor,
which is an exotic species and transported to Caspian sea by Russian program
of species introduction to the Caspian sea as early as 1940s, was found
only in absolute marine station (5) and not in marine places affected
by estuarine waters with salinity variability. Presence of Balanus
sp. in stations 3 and 4 and its absence in station 5 which was marine
station in present studies, suggest that its absence in station 5 was
not due to high salinities of this station but its is so sensible to lack
of habitat as it has a sessile life.
Results of the total macro benthic invertebrate secondary net production
are better explained by analyzing the whole assemblages. Table
4 demonstrates, production and consumption of each station related
to its dominant species. Considering station 1 in the upper Tajan estuary,
where, water residence time is lowest compared to other stations. In this
station the annual benthic production and consumption were 4.55 and 1.5
g m-2 year-1, respectively. Regarding the dominant
species Chironomus plumosus which is characteristic of polluted
waters with low quality, this point could suffer from high trophic inputs.
However organic materials in this station were lower than other studied
points and important part of POM (Particulate Organic Materials) are transported
due to river flow and sandy bottom of the river. Approaching to the river
estuary in station 2 Chironomid dominance is replaced by filter feeding
communities of Cerastoderma lamarki specimens where, benthic production
and consumption were 78.6 and 52.26 g m-2 year-1,
respectively. Only at the beginning of summer, Chironomids were representative,
since, river discharge decreased to its lowest values or this species
tolerate high variation of water temperature. Two stations of 3 and 4
located near to the sea where production/consumption efficiencies were
higher in present study are also dominated by filter feeder communities
of C. lamarki. By exception, at the end of summer dominant species
in both of them was communities of Dreissena polymorpha. After
summer their dominant state was replaced by C. lamarki. In station
5 which is entirely situated in the sea in front of estuary, C. lamarki
was dominant for the entire year. Present observation indicating dominant
species fluctuations in this small estuary of south Caspian basin showed
that benthic communities are not
entirely dependent to their substratum and this study proves that seasonality
can play an important role in benthic population dynamics. Station 6 which
inlets directly to the little estuary showed the medium state between
river and estuary where filter feeders were dominant during spring with
relatively important fresh water inputs. In the rest of the year D.
polymorpha was dominant species. The annual benthic production and
consumption of this station were 24.02 g m-2 year-1
compared to 12.39 g m-2 year-1. Considering evolution
of dominant species in estuarine stations (3, 4, 5 and 6) one can observe
that during fall and winter settled dominant species tend to increase
their production (as a result of enhancing biomass values). While, in
river situated points as, 1 and 2 where, benthic communities are much
more influenced by water input from river and low residence time doesn`t
allow to have a local production. Production and consumption values remained
relatively constant during months. In these stations important consumptions
were happened during dry months of summer.
river benthic invertebrate composition in studied station
indicate presence of genera (even if in one sampling time)
species, monthly production and consumption of 6 studied stations
with annual sum of these values. Abbreviations indicate as: C.p :
Chironomus plumosus, C.l : Cerastoderma lamarki, D.p
: Dreissena polymorpha
In Tajan river estuary, the wide availability of organic matter in the
sediment, coupled with low water exchange and high temperatures during
the summer may promote dystrophic crises. In addition, the water inlet
of the adjacent small stream, issued from agricultural activity, is very
likely to be enriched by remains of fertilizers, faeces and nutrients
(Sorokin et al., 1999). This leads to an increase in primary and
secondary production and may contribute to the establishment of dystrophic
conditions (Sorokin et al., 1999). Azzoni et al. (2001)
showed that, in this kind of lagoons, there was an accumulation of free
sulphide in the rhizosphere of aquatic plants during late summer as a
result of an imbalance between sulphate reduction rates and sulphide reoxidation
rates. As well as directly inhibiting macrophyte growth, dystrophic events
undoubtedly have a lethal effect on macro benthic fauna. Consequently,
decreases in macro benthic abundance and biomass might be related not
only to the oxygen depletion, but also to the high production of toxic
free sulphide, as has already been documented in the Comacchio lagoon
complex. The macro benthic assemblage structure and composition and the
environmental conditions found in Tajan river estuary, were very similar
to those found in a shallow lagoon in the Bay of Cadiz. However the number
of species was relatively low compared to the assemblages described in
the other estuaries such as Valli di Comacchio estuary and other brackish
water ones (Mistri, 2002) and same estuaries in northern Adriatic lagoons.
After the late summer crisis, the macro benthic assemblages had an appearance
of greater homogeneity among the stations as a consequence of an overall
reduction in abundance and biomass. This aspect is likely to be most relevant
for species that have limited dispersion due to a short pelagic phase
or direct development such as Cerastoderma lamarki, Chironomus
plumosus and Dreissena polymorpha. The degree of isolation
could also explain the local diminution of Cerastoderma lamarki
after the dystrophic event. On the other hand, Ballanus sp. and
Chironomus plumosus appeared to recover quite quickly after
the dystrophic crises. Ballanus sp. communities were able to overcome
the dystrophic crises due both to their ability to remain at the air/water
interface and their continuous breeding strategy (Barnes, 1999). The larvae
of C. plumosus are periodically restored at each reproduction cycle
since adults fly from neighbouring aquatic habitats. Although the dryness
crises affect the community structure, however the secondary production
in Tajan river estuary appeared very high. Secondary macrobenthic production
is sustained by a small number of species. Dreissena polymorpha.,
larvae of Chironomus plumosus and Cerastoderma lamarki emerged
as the most important species in terms of both biomass and production.
They represented dominant species in all of our studied stations. The
somatic productivity is traditionally expressed by the production-to-biomass
ratio (P/B ratio). The estimated P/B ratio of C. plumosus, was
in the range 9.1-11.9 year-1 and is in good accordance with
the mean value of 12.7 year-1, obtained in Cadiz Bay (Spain),
with the size-frequency method. The P/B ratio of Ballanus sp.,
in Tajan river estuary ranged from 6.1 to 7.8 year-1. These
values was slightly higher than the ratios found in literature for the
same species obtained by cohort or size frequency analysis, which appeared
highly variable ranging from 1.8 to 6.1 year-1 according to
the study stations (Drake and Arias, 1995; Lillebo et al., 1999).
Most of this kind studies were carried out in the northern European tidal
flats, where habitat characteristics and lower temperatures can limit
the productivity of the Ballanus sp. In our study, the P/B ratios
for Cerastoderma lamarki vary according to the sampling stations
from 2.3 to 3.9 year-1. In spite of the high mortality observed
at the time of the dryness crisis, the annual turnover of C. lamarki
was in good accordance with the value of 3.2 year-1, calculated
using the Tumbiolo and Downing (1994) method, from the Sacca di Goro,
another coastal lagoon (Mistri et al., 2001). Present results based
on variations of benthic biomass showed that this estuary export the sum
of 245.99 g m-2 year-1 of benthic production to
the south Caspian Sea basin. 117.37 g m-2 year-1
is consumed locally in the estuary by estuarine proper animals or removed
by Caspian Sea euryhaline fishes living in the near shore of the bay.
Although the assemblage composition and environmental conditions found
in Tajan river estuary were very similar to those found by, a direct comparison
of the estimated secondary production is impossible due to the different
methods applied. As (Mistri et al., 2001) conceded, their estimation
of macro benthic production using methods widely underestimates the production
of the multivoltine chironomids, which fall in the range 0.3 to 5 mm.
Many studies have demonstrated that vegetated bottoms support higher secondary
production compared to the surrounding unvegetated bottoms (Edgar et
al., 1994; Dolbeth et al., 2003, 2005). However, total biomass
was dramatically affected by dryness crises, especially in low deep areas.
Macro benthic secondary production in Tajan river estuary supported a
large biomass of predators, largely reared finger ling fish species, issued
from stock restoration organized by Iranian fisheries organization, in
particular Acipenseridae species and Caspian Roach (Rutillus firissi
Kutum) released into the estuary each spring. The reduction of biomass
may reduce the secondary production and lead to negative effects on the
growth of the commercial fish, beginning with those like Caspian Roach,
Rutilus rutilus (frissi kutum), Huso huso, Acipenser
persicus, A. guldenstadtii and A. stellatus, which mainly
feed on benthic macroinvertebrates during their juvenile life stage (Pita
et al., 2002) and are released in huge quantities from spring to
early summer by Iranian fisheries organization. In Tajan river estuary,
it was found that they mainly feed on nereid polychaetes, bivalves like
juveniles of Cerastoderma lamark, amphipods like Gammarus
sp., larvae of Chironomus plumosus and on the Ballanus sp.
However, results from this study show that biomass community structures
and secondary macro benthic production are negatively affected by the
drought events. Management of these kinds of coastal lagoons focuses mainly
on fish releasing but often the importance of the benthic assemblages
is neglected. Monitoring programs generally take into account only a few
environmental variables, like dissolved oxygen concentration and water
temperature, apart from the health of the benthic community structure.
Since it is very difficult to operate directly on the oxygen concentration
and water temperature in the field, the management practices should try
to prevent the dry periods by limiting nutrient inputs and by ensuring
an adequate water renewal. Moreover, it is very important to remember
that any severe alteration of the macro benthic secondary production will
inevitably be reflected, through the food chain, up to the higher trophic
levels, i.e., the released fish. Although empirical methods for secondary
production estimation are less accurate than the direct methods, especially
when the assemblages are not in steady state, they are widely applicable
and can provide a reliable and practical tool for monitoring and management
purposes. There are thus grounds for suggesting that monitoring programs
of the fish releasing managed for stock restoration should also include
the macro benthic assemblage composition in terms of biomass.
Special thanks to all of colleagues who cooperated in this project. This
article was complied from Ph.D Shapoori project.
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