Some Ecological Consequences Of The Physiological And Biochemical Effects Of Petroleum Compounds On Marine Mollusks

The problems of relating the results of experiments in the laboratory to events in nature are twofold: to equate the response to a single variable (hydrocarbons) with the natural variability in the biological material in a multivariate environment, and to consider whether the response established experimentally has any relevance to the animal's chances of survival and reproduction (i.e. its fitness) in the natural population. Recent studies of the effects of petroleum hydrocarbons on marine invertebrates are reviewed, with an emphasis on the physiological and cytochemical responses by bivalve molluscs. The dose-response relations that emerge suggest the intensity of the 'signal' that must be detected in nature if the chronic, sublethal effects of petroleum pollution are to be measured. The natural variability in these physiological and cytochemical processes are then reviewed and the main causes of variability in natural populations, both endogenous and exogenous, discussed. These results indicate the extent of the `noise' above which the signal from possible pollution effects must be detected. The results from recent field studies on the common mussel, Mytilus edulis, are discussed. The results are as complex as expected, but it proves possible to reduce the variance in the measured responses so that pollution effects, including those due to hydrocarbons, can be detected. The ecological consequences of the observed effects of petroleum hydrocarbons are then discussed in terms of reproductive effort and reproductive value. Considerable variation between populations exists here also and this can be used to help in the interpretation of the extent of the impact of the environment on the ecology of the population. The result is to place the findings of the laboratory experiments in an ecological context of natural variability and of the physiological costs of adaptation.

Some Practical Considerations In The Measurement Of Pollution Effects On Bivalve Mollusks And Some Possible Ecological Consequences

A consideration of some physiological (rates of oxygen consumption, the scope for growth) and cellular (the cytochemical latency of a lysosomal enzyme) processes in bivalve molluscs suggests that animal size and seasonal changes related to the gametogenic cycle are important sources of natural variability. Correcting for size using regression techniques, and limiting measurements to one part of the gametogenic cycle, reduces observed natural variability considerably. Differences between populations are then still apparent, but the results of laboratory experiments with hydrocarbons from crude oil suggest that it should be possible to detect sub-lethal effects due to pollution (the ‘signal’) in the presence of the remaining natural variability (the ‘noise’). Statistical considerations, taken together with results from current studies on Mytilus edulis and Scobicularia plana, indicate that sample sizes of 10–15 individuals should suffice for the detection of possible pollution effects. The physiological effects to be expected in the presence of sub-lethal levels of polluting hydrocarbons are on a scaie that can cause significant ecological damage to a population through a reduction in fecundity and the residual reproductive value of the individuals.

Effects Of Oil On Digestive Cells In Mussels - Quantitative Alterations In Cellular And Lysosomal Structure

Structural changes were observed in the digestive tubule epithelial cells of Mytilus edulis following long-term exposure to the water accommodated fraction (WAF) of North Sea crude oil (30 μg · l−1 total oil derived aromatic hydrocarbons). The changes observed involved a reduction in the height of the digestive cells beyond that demonstrated in a normal feeding cycle. In addition there was a loss of the normal synchrony of the digestive cells to a point where nearly all the tubules exhibited an appearance similar to that which is usually termed ‘reconstituting’. These alterations were quantified using an image analysis technique and the mean height of the digestive cells used as an index of digestive function or state. Long-term exposure also induced a radical alteration of the structure of secondary lysosomes within the digestive cells, resulting in the formation of large lysosomes, believed to be autolysosomes. Stereological analyses showed that these lysosomes are reduced in numbers and greatly increased in volume in comparison with controls. There is a concomitant increase in surface area of lysosomes per unit volume of digestive cell compared with control conditions. These alterations are indicative of fundamental changes in secondary lysosomal function involving an autophagic response to oil derived hydrocarbons. which would contribute to the reduction of digestive cell cytoplasm. These cellular alterations are discussed in terms of their use as indices of cell injury, in response to oil.

Laboratory Simulation Of Chemical Processes Induced By Estuarine Mixing - The Behavior Of Iron And Phosphate In Estuaries

A series of well stirred tank reactors has been shown to provide an adaptable laboratory analogue of a one-dimensional estuarine mixing profile which can be applied dynamically to the study of the chemistry of estuarine mixing. Simulations of the behaviour of iron and phosphate in the low salinity region of an estuary have been achieved with this system. The well documented general features of iron removal, involving rapid aggregation of river-borne colloids, were reproduced. Phosphate removal is attributable in part to the coagulation process, although specific adsorption of phosphate by colloids also appears to be significant.

Leucine Aminopeptidase (Aminopeptidase-I) N-Acetyl-Beta-Hexosaminidase And Lysosomes In The Mussel Mytilus-Edulis-L In Response To Salinity Changes

The intracellular distribution of aminopeptidase-I in the intestinal and digestive cells of Mytilus edulishas been shown to be the same as the lysosomal marker enzymes β-glucuronidase and N-acetyl-β-hexosaminidase. Activity for these enzymes was also associated with the intestinal apical cytoplasm and microvillous border where there was pronounced staining for aminopeptidase-I. Experimental alterations of salinity induced changes in both microdensitometrically and spectrophotometrically determined aminopeptidase-I activity, as an increase with raised salinity and a decrease with lowered salinity. Lysosomal hexosaminidase showed similar changes in activity with altered salinity. Cytochemically determined lysosomal stability was also responsive to salinity changes, indicative of alterations in lysosomal functional capability. The lysosomal distribution of aminopeptidase-I is discussed in terms of the function of lysosomes in intracellular protein turnover, their high concentrations of free amino acids, and the possible roles which these might play in intracellular osmoregulation in response to salinity change.

Ecological And Metabolic Studies On Free-Living Nematodes From An Estuarine Mud-Flat

Nematodes from a mud-flat in the river Lynher estuary, Cornwall, U.K., have a population density ranging between 8 and 9 × 106 m−2 in the winter months, corresponding to a dry weight of 1·4 and 1·6 g m−2. They reach a peak abundance of 22·86 × 106 m−2 (3·4 g) in May. About 40 species are present, and the species composition remained seasonally stable over the period of study. Analysis of age-structure suggests that the major species have continuous asynchronous reproduction. Respiration rates of 16 species have been determined at 20 °C using Cartesian diver respirometry. For five species, respiration/body size regressions were obtained in the form log10R = log10a+b log10V, where R = respiration in nl O2 ind−1 h−1 and V = body volume in nl: Mesotheristus setosus (log10a = −0·04,b = 0·74), Sphaerolaimus hirsutus (log10a = 0·11, b = 0·68), Axonolaimus paraspinosus (log10a = 0·00, b = 0·79), Metachromadora vivipara (log10a = −0·59, b = 1·07), Praeacanthonchus punctatus (log10a = 0·00, b = 0·55). For the remaining 11 species, several animals were used in each diver and, by assuming b = 0·75, log10a′ values were calculated: Viscosia viscosa (log10a′ = 0·188), Innocuonema tentabundum (−0·012), Ptycholaimellus ponticus (−0·081), Odontophora setosa (−0·092), Sphaerolaimus balticus (−0·112), Dichromadora cephalata (−0·133), Atrochromadora microlaima (−0·142), Cylindrotheristus normandicus (−0·150), Terschellingialongicaudata (−0·170), Sabatieria pulchra (−0·197), Terschellingia communis (−0·277). These values are compared with recalculated values for other species from the literature. Annual respiration of the nematode community is 28·01 O2 m−2, equivalent to 11·2 g carbon metabolised. Community respiration is compared with figures from N. American saltmarshes. At 20 °C, a respiration of about 61 O2 m−2 year−1 g−1 wet weight of nematodes appears to be typical. Annual production is estimated to be 6·6 g C m−2. The correlation between feeding-group, body-size, habitat and the repiration rate of individual species is discussed.

Combined Effects Of Body Size Food Concentration And Season On Physiology Of Mytilus-Edulis

Multivariate experiments are used to study the effects of body size, food concentration, and season on the oxygen consumption, ammonia excretion, food assimilation efficiency and filtration rate of Mytilus edulis adults. Food concentrations and season affect both the intercept and the slope of the allometric equation describing oxygen uptake as a function of body size. Multiple regression and response surface techniques are used to describe and illustrate the complex relationship between metabolic rate, ration, season and the body size of M. edulis. Filtration rate has a relatively low weight exponent Q> = 038) and the intercept for the allometric equation is not significantly affected by food concentration, season or acclimation temperatures between 5 and 20 °C. Food assimilation efficiency declines exponentially with increasing food concentration and is dependent on body size at high food levels. The rate of ammonia excretion shows a similar seasonal cycle to that of oxygen consumption. They are both minimal in the autumn/winter and reach a maximum in the spring /summer.

Cytology And Cytochemistry Of Hemocytes Of Mytilus-Edulis And Their Responses To Experimentally Injected Carbon Particles

Hemocytes of Mytilus edulis were examined cytologically and cytochemically. On the basis of structure, staining reactions, and phagocytic behavior, they were divided into two main groups: basophilic hemocytes and eosinophilic granular hemocytes (granulocytes). The basophilic cells were further divided into small lymphocytes and larger phagocytic macrophages reactive for lysosomal hydrolases. Mitosis was observed in granulocytes and in small lymphoid cells, believed to be the stem cells for the basophilic cell line. A few cells appeared to be intermediate between lymphocytes and small granulocytes. Macrophages were the main cell type involved in the clearance of injected carbon particles. However, granulocytes did show some phagocytic activity. Brown cells displaying apparent amoebocytic behavior were found to contain Fe3+ and Pb2+ in cytoplasmic inclusions, some of which were also reactive for β-glucuronidase and glucosaminidase. These cells appear to have a separate origin from the hemocytes.