Effect of patch size and in-patch location on the infaunal macroinvertebrate assemblages of Zostera marina seagrass beds.

Much recent work on patch-occupancy dynamics has been concentrated in terrestrial ecosystems, with few examples evident from soft-sediment marine habitats. Seagrass landscapes have recently been recognised to be potentially ideal marine models for the study of such ecological concepts. Infaunal macroinvertebrate assemblages of two patch sizes of the seagrass Zostera marina were compared: small (<15 m diameter) and large (>30 m diameter), using an unreplicated random block design. Further comparison was made between infaunal assemblage composition at the edge and centre of each patch. Univariate statistical analysis of data indicated significantly greater total numbers of taxa in samples from large patches than in small. Multivariate analyses indicated significant differences in assemblage composition due to both patch size and in-patch location, and revealed that differences were due to small changes in the relative abundances of many taxa. Possible mechanisms underlying the observed variations of assemblage composition with patch size and in-patch location are discussed. Although the present results support some of the theories relating to the control of infaunal assemblage composition, explanations are not applicable across all taxonomic groups. At the scale of the present study, seagrass patch size and edge-effects appear to be less significant than 'regional' factors, which relate to relatively small variation in environmental parameters, for the structuring of infaunal macroinvertebrate assemblages.

Lipid metabolism in pregnancy. VIII. Effects of dietary fat versus carbohydrate on lipoprotein and hepatic lipids and tissue triglyceride lipases.

UNLABELLED: We have asked, is hypertriglyceridemia in the fed state in pregnancy due to intolerance to exogenous fat, accumulation of endogenous triglycerides, or accumulation of remnants of d < 1.006 lipoprotein metabolism? To answer these questions, we fed fat-free diets high in starch or sucrose, or diets containing fat or fat plus cholesterol to pregnant and nonpregnant rats for 12 days until gestational day 21 (term = 22 days). Blood was obtained 0, 4, or 8 hr after removal of food from the cages. Lipid concentrations were determined in chylomicrons and very low, low, and high density lipoproteins. Hypertriglyceridemia in pregnancy exists on both starch and sucrose containing fat-free diets and is exaggerated 4 and 8 hr after food is removed from the cage. The triglyceride rise occurs in d < 1.006 lipoproteins. With fat feeding, chylomicron triglyceride concentrations are not significantly elevated in pregnant rats, 0 or 8 hr postabsorptively despite greater food intake in pregnancy. In contrast, very low density lipoprotein (VLDL) triglyceride concentrations are elevated at all times following fat feeding in pregnant compared to nonpregnant animals. A significant contribution of lipoprotein remnants to the triglyceride rise in d < 1.006 lipoproteins seems unlikely since an isolated increase in VLDL cholesterol is not observed. No statistically significant accumulation of hepatic triglycerides occurs on any diet in pregnancy. Diet induced shifts in adipose tissue and muscle lipoprotein lipase activity are exaggerated in pregnancy while hepatic lipase is unaffected. Fetal weight is similar on all diets except sucrose where weight is reduced. CONCLUSIONS: Hypertriglyceridemia in fed pregnant rats is due to an increase in endogenous triglycerides. Remnant lipid accumulation does not appear to contribute to the endogenous hypertriglyceridemia. There is no intolerance to exogenous (dietary) fat. The results are compatible with an unimpaired delivery of exogenous fat to fat oxidizing tissues thereby maximizing glucose availability for fetal growth.