Gianluca Sarà

Impact on the water column biogeochemistry of a Mediterranean mussel and fish farm

We investigated and compared the impact of organic loads due to the biodeposition of mussel and fish farms on the water column of a coastal area of the Tyrrhenian Sea (Western Mediterranean). Physico-chemical data (including oxygen, nutrients. DOC and particulate organic matter), microbial variables (picoplankton and picophytoplankton density and biomass) and phytoplankton biomass (as chlorophyll-a) were determined on a monthly basis from March 1997 to February 1998. The results of this study indicate that both fish farm and mussel culture did not alter significantly dissolved inorganic phosphorus and chlorophyll-a values, while inorganic nitrogen concentrations were higher in mussel farm area. However, waters overlying the fish farm presented significantly higher DOC concentrations. In contrast, no significant differences were observed comparing particulate matter concentrations. The increased DOC concentrations determined a response of the heterotrophic fraction of picoplankton, while picophytoplankton, likewise phytoplankton. did not display differences among fish or mussel farms and control site. From the analysis of the different microbial components, it is possible to conclude that the impact of fish farms is evident only for the heterotrophic components. The comparative analysis of the mussel biodeposition and fish-farm impact revealed that mussel farms induced a considerably lower disturbance, apparently limited to an increased density and biomass of microbial assemblages beneath the mussel cultures.

Enzymatically hydrolyzable protein and carbohydrate sedimentary pools as indicators of the trophic state of detritus sink systems: A case study in a Mediterranean coastal lagoon

In order to classify the trophic state of detritus sink systems, instead of the conventional indicators based on inorganic nutrient availability and algal biomass and productivity in the water column, we used new biochemical descriptors based on the amount of sedimentary organic carbon (C) and nitrogen (N) potentially available to heterotrophs. We investigated spatial and temporal changes in microphytobenthic biomass, organic matter biochemical composition, and enzymatically hydrolyzable protein and carbohydrate pools along a north-south transect in the Marsala lagoon (Mediterranean Sea, Italy) at three stations characterized by different hydrodynamic conditions and organic matter content in the sediment. In the Marsala lagoon water currents decreased from north to south and this pattern was reflected by organic matter distribution and composition. Sediment organic matter concentrations were among the highest reported in the literature and, in the central area where large meadows of the seagrassPosidonia oceanica were present, display a strong dominance of highly refractory carbohydrates. The protein to carbohydrate ratio was always < 1, indicating the dominance of aged organic detritus. Microphytobenthic biomass displayed an increasing pattern southward, and its contribution to the biopolymeric C pools ranged from negligible in the central sector of the lagoon to 50% in its northern part, indicating that sources of sediment organic C also changed along the hydrodynamic gradient. The percentage contribution of the enzymatically hydrolyzable fraction of proteins and carbohydrates was inversely related to total protein and total carbohydrate concentrations, respectively, suggesting that bioavailability of organic C and N increased with decreasing organic matter content in the sediment and with increasing hydrodynamic regime. Microphytobenthic contribution to biopolymeric C (as a proxy of autotrophic organic C) and the ratio of the enzymatically digestible fraction to biopolymeric C (as an indicator of organic matter liability) were significantly correlated, suggesting that chlorophylla sediment content might be used as an indicator of food promptly available to consumers. The present study also highlighted that the ratio of labile (i.e., enzymatically digestible) versus biopolymeric organic C in the sediments tends to decrease with increasing organic matter content, due to the increase of the refractory fraction of organic C.

The effect of fish farming organic waste on food availability for bivalve molluscs (Gaeta Gulf, Central Tyrrhenian, MED): stable carbon isotopic analysis

Abstract Stable carbon isotope ( δ 13 C) analysis was used in a fish-farming impacted Mediterranean area (the Gulf of Gaeta, Central Tyrrhenian) to determine the predominant carbon sources available to bivalve molluscs cultivated around fish cages. Whether the organic matter generated by fish farming was taken up by the bivalve molluscs was also investigated. Stable carbon isotope values were measured in the particulate organic carbon (POC) of samples from potential organic matter sources such as fish-pelleted feed, mollusc faecal waste and bivalve flesh. The sources of organic matter affecting the study area water column and benthic communities appeared to be terrigenous-continental, autochthonous (phytoplankton) and anthropogenic inputs due mainly to fish-farming and bivalve mollusc activities. The POC was dominated by organic waste isotopic signatures, while the bivalve mixed diet was composed of organic matter with different isotopic signatures (phytoplankton, waste material from the bivalves themselves and surplus uneaten pelletted feed). Organic waste appears to be the dominant trophic resource in the deeper-cultivated clam diet, while phytoplankton organic carbon plays a more important role in the diet of the mussel. We propose that bivalve organic matter uptake may play an effective role in reducing the environmental impact of fish organic waste. The organic matter produced by bivalves (faecal material) under these hydrodynamic conditions (low current velocities) can be recycled through the filtration activities of the bivalves themselves, together with most of the organic matter produced by fish-farming activities (uneaten feed and faecal material). Bivalve cultivation around cages may reduce the environmental impact of organic waste from fish-farming activities and increase the profitability of fish culture activities.

Seasonal and spatial changes in the sediment organic matter of a semi-enclosed marine system (W-Mediterranean Sea)

The composition of sediment organic matter and the related role of microphytobenthic biomass have been investigated during one-year in a semi-enclosed marine system (Marsala lagoon, Mediterranean Sea). Monthly samples from June 1993 to May 1994 were analysed for carbohydrate, protein, lipid, photosynthetic pigment and total organic matter.The three main biochemical classes of organic compounds (i.e. carbohydrates, proteins and lipids) showed higher concentrations than reported in the literature. However, photosynthetic pigment was quite low, compared to other enclosed marine basins or Mediterranean coastal lagoons. As a result, the contribution of primary organic carbon to the sedimentary biopolymeric fraction of organic matter was low (on average 2.2%), indicating that most of the sedimentary organic matter in the study area originated from sources other than micro-algae. The sedimentary organic matter, dominated by carbohydrates (on average 51.2%) followed by proteins (39.0%) and lipids (9.8%), as well as the low protein to carbohydrate ratio, indicate the presence of large amounts of non-living and/or aged organic matter. Comparing data on spatial distribution of sedimentary and suspended organic matter, the dynamic balance of resuspension vs. sedimentation along a north-south axis is invoked as one major factor affecting the distribution and composition of the main classes of organic compounds. The macroalgal and vascular plant coverage is suggested to be another major factor affecting both amounts and composition of sedimentary organic matter. The northern area, characterised by partially unvegetated sediments, showed higher amounts of proteins, whilst moving southward and approaching a luxuriant Posidonia oceanica reef, carbohydrates became more important relative to proteins. As only the biopolymeric fraction of sediment organic matter showed significant seasonal changes, the quantity of sediment OM behaves as an emerging property. By contrast, OM quality is strictly connected to algal coverage as well as to episodic inputs of primary organic matter from deposited phytoplankton and/or microphytobenthos. The uncoupling between large amounts and relatively low nutritional value of sedimentary OM suggests that this particular environment behaves as a detrital ‘trap’.

Beyond long-term averages: making biological sense of a rapidly changing world

Biological responses to climate change are typically communicated in generalized terms such as poleward and altitudinal range shifts, but adaptation efforts relevant to management decisions often require forecasts that incorporate the interaction of multiple climatic and nonclimatic stressors at far smaller spatiotemporal scales. We argue that the desire for generalizations has, ironically, contributed to the frequent conflation of weather with climate, even within the scientific community. As a result, current predictions of ecological responses to climate change, and the design of experiments to understand underlying mechanisms, are too often based on broad-scale trends and averages that at a proximate level may have very little to do with the vulnerability of organisms and ecosystems. The creation of biologically relevant metrics of environmental change that incorporate the physical mechanisms by which climate trains patterns of weather, coupled with knowledge of how organisms and ecosystems respond to these changes, can offer insight into which aspects of climate change may be most important to monitor and predict. This approach also has the potential to enhance our ability to communicate impacts of climate change to nonscientists and especially to stakeholders attempting to enact climate change adaptation policies.

Combining heat-transfer and energy budget models to predict thermal stress in Mediterranean intertidal mussels

Recent studies have emphasised that organisms can experience physiological stress well within their geographic range limits. Developing methods for mechanistically predicting the presence, absence and physiological performance of organisms is therefore important because of the ongoing effects of climate change. In this study, we merged a biophysical–ecological (BE) model that estimates the aquatic (high tide) and aerial (low tide) body temperatures of Mytilus galloprovincialis with a Dynamic Energy Budget (DEB) model to predict growth, reproduction and mortality of this Mediterranean mussel in both intertidal and subtidal environments. Using weather and chlorophyll-a data from three Mediterranean sites along the Italian coasts, we show that predictions of sublethal and lethal (acute) stress can potentially explain the observed distribution (both presence and absence) of mussels in the intertidal and subtidal zones, and the maximum size of animals in the subtidal zones. Importantly, our results suggest that different mechanisms limit the intertidal distribution of mussels, and that these mechanisms do not follow a simple latitudinal gradient. At the northernmost site (Palermo), M. galloprovincialis appears to be excluded from the intertidal zone due to persistent exposure to lethal aerial temperatures, whereas at the southernmost sites (Porto Empedocle and Lampedusa) sublethal stress is the most important driver of mussel intertidal distribution. Our predictions provide a set of hypotheses for future work on the role of climate change in limiting intertidal distribution of mussels in the Mediterranean.

Cultivation of the Mediterranean amberjack, Seriola dumerili (Risso, 1810), in submerged cages in the Western Mediterranean Sea

Abstract The growth rate, survival and food conversion ratio (FCR) of the Mediterranean amberjack ( Seriola dumerili , Risso, 1810) was ascertained in cultivation using submerged net cages in the Gulf of Castellammare (NW Sicily), from September to December 1994. Two net cages (volume=75 m 3 ) were placed at a depth of 10 m in a sheltered area 1000 m off the coast. Juveniles (mean total length=141.4±34.2 mm; mean total wet weight=48±28.1 g) were caught in the gulf under floating wreckage with a purse seine and transplanted to the cages ( n =800 per cage) in August. Fish in one cage, group A, were fed with fish scraps whilst fish in group B were fed with pellets. The total length and body wet weight were recorded each month and compared with the wild population of the gulf. Negligible mortality occurred due to capture and transportation to the cages and no diseases were found during the rearing period. Group A reached a final size of 438.1±25.3 mm and 1149±172.2 g, while group B reached 347±25.6 mm and 576±139 g. At this time the wild population was 404.13±17 mm and 777±89.4 g. Food conversion ratios of 1.22 for group A and 3.51 for group B were in the low range compared with other research on S. dumerili in the Mediterranean. S. dumerili seemed to find fish scraps more appetising than pellets. The low level of investment required, limited breeding period and compatibility with small-scale fishing make submerged net cages a promising system of cultivation for the conversion of coastal fishing.

The relationship between food availability and growth in Mytilus galloprovincialis in the open sea (southern Mediterranean)

Abstract With the aim of gathering information about the possibility of culturing mussels ( Mytilus galloprovincialis ) in a south Mediterranean oligotrophic area, different lots of mussels were placed in culture at depths of −5 m and −15 m and their growth monitored on a monthly basis. Temperature and salinity were measured in situ and water samples were collected at different depths each month. Total suspended matter (TSM) and its inorganic (ISM) and organic (OSM) fractions were analysed by gravimetry and loss on ignition. Photosynthetic pigments (chlorophyll- a and phaeopigments), particulate organic carbon (POC) and nitrogen (PON), particulate carbohydrate (CHO), protein (PRT) and lipid concentration (LIP) were also measured. The chlorophyll- a concentrations highlighted the high degree of oligotrophy of the study site. Moreover, the inorganic fraction of total seston, which exceeded the organic fraction throughout the study period, highlighted the importance of the allochthonous input of suspended particles. Two main phytoplankton abundance peaks were observed, in spring and autumn. These peaks were mirrored by the biochemical composition of the biopolymeric fraction of particulate organic matter (POM, the sum of PRT, CHO and LIP concentrations). The relatively high values of the POC:PON ratio indicated that the major fraction of particulate organic matter in the study area was of detrital origin. A clear dilution effect on the organic matter, caused by high concentrations of suspended inorganic material, was also revealed by the LPOM/TSM ratio, used as a qualitative food index. The mussels were found to activate physiological compensatory mechanisms in order to maintain a constant absorption rate of organic matter from the total available seston. In this case study, the mussels survived in an environment in which the quantities of available food were frequently time-varied. The mussels placed in culture as juveniles (total length=11.20±4.02 mm) reached a length of approximately 40 mm after 12 months, while the mussels placed in culture as sub-adults (total length=43.16±7.5 mm) reached the commercial size of about 60 mm in the same time interval. The sub-adult mussels spawned in autumn and spring, indicating that they acclimatised well, despite the high degree of oligotrophy of the water.

Effects of nautical traffic and noise on foraging patterns of Mediterranean damselfish (Chromis chromis).

Chromis chromis is a key species in the Mediterranean marine coastal ecosystems where, in summer, recreational boating and its associated noise overlap. Anthropogenic noise could induce behavioural modifications in marine organisms, thereby affecting population dynamics. In the case of an important species for the ecosystem like C. chromis, this could rebound on the community structure. Here, we measured nautical traffic during the summer of 2007 in a Southern Mediterranean Marine Protected Area (MPA) and simultaneously the feeding behaviour of C. chromis was video-recorded, within both the no-take A-zone and the B-zone where recreational use is allowed. Feeding frequencies, escape reaction and school density were analysed. C. chromis specimens were also collected from 2007 to 2008 to evaluate their physiological state using the Body Condition Index as a proxy of feeding efficiency. The MPA was more exploited by nautical tourism during holidays than on weekdays, particularly in the middle of the day. Greater traffic volume corresponded with lower feeding frequencies. The escape reaction was longer in duration (>1 min) when boat passed nearby, while moored boats did not induce an escape response. We found no differences in density between schools in the A- and B-zones and worse body conditions among those individuals inhabiting the B-zone in one area only. Overall, our findings revealed a significant modification of the daily foraging habits of C. chromis due to boat noise, which was slightly buffered by no-take zones established within the MPA.

δ13C and δ15N variability in Posidonia oceanica associated with seasonality and plant fraction

Abstract The carbon and nitrogen isotopic compositions of fractions of the seagrass Posidonia oceanica (L.) Delile in a Mediterranean shallow environment (Stagnone di Marsala, western Sicily) were investigated seasonally throughout 1998. The stable isotope ratios of seagrass leaves (intermediate and adult), rhizomes, leaf litter and aegagropiles were compared over 1 year in order to distinguish between seasonal and plant part variability. Significant differences in the isotopic composition tested using ANOVA were observed as a function of both plant fraction and season. There was an overall trend towards less discrimination against 13 C in summer (average δ 13 C ∼ −10‰) than in winter (average δ 13 C ∼ −13‰). In contrast, greater δ 15 N enrichment was observed in winter (average ∼ 5‰) than in summer (average ∼ 3‰). The possibility of a link between δ 13 C and δ 15 N seasonal variability and seagrass physiology such as plant carbon balance and reserve dynamics is proposed to explain the observed patterns. The demonstration of seasonal and plant fraction variability in P. oceanica isotopic composition provides a broader perspective to seagrass ecological and physiological studies. Overall, the observed variability can be up to 4 and 5‰ for δ 13 C and δ 15 N , respectively, a range that largely exceeds that associated with the transition between consecutive trophic levels (1 and 3.5‰ for δ 13 C and δ 15 N , respectively).Our results corroborate the need for, at least, seasonal sampling designs to obtain a good understanding of organic matter fluxes into food webs and highlight the limitations in drawing general conclusions about food webs where a low seasonal sampling effort has been applied. They also suggest that stable carbon and nitrogen isotope ratios deserve attention as a possible valuable approach in seagrass ecophysiological studies.