Uniform size spectra comprising bacteria through macrofauna characterize six intertidal communities when biomass concentration is expressed as a function of logarithmic intervals of organism size. Although total community biomass ranged from 70 cm3/m2 to 1283 cm3/m2, biomass distribution patterns are consistent over the entire size spectrum. Three biomass peaks, at 0.5–1 μm equivalent spherical diameter (29–81 cm3/m2), 64–125 μm (0.5–4 cm3/m2), and > 2 mm (2.4–1283 cm3/m2) were separated by typically low biomasses near 8 μm (0–0.04 cm3/m2) and 500 μm–1 mm (0–1.5 cm3/m2). The peaks correspond to bacteria, interstitial meiofauna, and macrofauna, respectively. Size discontinuities between grain colonizers and interstitial microfauna or epibenthic microflora near 8 μm, and between interstitial meiofauna and burrowing or sedentary macrofauna near 500–1000 μm, are reflected in low biomass values in these size intervals. Comparison of the data with recast published data for other locales shows that similar size distributions characterize a wide variety of benthic communities, including estuarine to abyssal. This study is the first to describe quantitatively, in detail, the size composition of marine benthic communities.Key words: benthic, community, bacteria, meiofauna, macrofauna, size, biomass, Sheldon spectrum

Published data on production of natural populations of benthic organisms were used to derive allometric equations relating annual production per unit biomass (P: B ratio) to mean individual body mass (time and biomass weighted) in the population on which production was measured. Separate equations were derived for meiofauna and macrofauna. Since no published data on production and size-structure in natural bacterial populations were found, P:B ratios for bacteria were calculated by extrapolation from an all-inclusive regression. In situ respiration was then calculated from production assuming the two to be approximately equal over an annual cycle for bacteria and benthc microalgae, and using an empirical relation between annual respiration and production in marine benthic animals for meiofauna and macrofauna. Monthly observations of benthic biomass spectra at Pecks Cove, an intertidal site in the upper Bay of Fundy, were used to estimate production and respiration in bacteria, microalgae, meiofauna, and macrofauna from the allometric equations. These estimates compared well with measured production for Corophjum volutator and Macoma balthjca, the 2 dominant macrofaunal species, and w~t h gross primary production by benthic microalgae, but not with total community respiration as measured by sediment oxygen consumption. Calculated values for production by bactena were of an expected magnitude ~f between 1 and 10 O/ O of the total biomass was assumed to be active. The contribution of meiofauna and macrofauna to total community production (8 to 19 %, depending on the assumphon for bacterial achvity) was d~spropor-tionately small compared to their relahve biomass (47 to 52 %, also depending on what proportion of bacterial biomass was considered to be actlve). Estimates of respiration were much higher than measured rates of sediment oxygen consurnphon (2.5 to 5.5 times), although both followed closely sirmlar seasonal trends. Bacterial produchon in nature must be directly measured before the validity of our calculations can be assessed. However, we conclude that it 1s possible to obtain reasonable estimates of annual production and its distribution among slze groups in natural benthic comn~unities of eukaryotic organisms using allometric P : B scal~ng.

Benthic communities in the Bay of Fundy are characterized by the distribution of biomass among logarithmic size classes of organisms ranging from 0.25 p m to 64 mm equivalent spherical diameter. This distribution, a biornass spectrum, exhibits features that are conservative over a wide range of environmental conditions and over a seasonal cycle, having 3 distinct size groups of heterotrophic organisms: grain surface dwellers (bacteria), interstitial fauna (rneiofauna), and macroscopic surface dwellers (rnacrofauna). Causal analysis was used to construct plausible, hypothetical models of interactions among macrofauna, meiofauna, micro-algae, bacteria, and environmental variables. In the models, macrofaunal biomass was largely a function of exogenous predation and sediment disturbance, meiofauna were most abundant in fluid, fine-grained sedirnents where algal biornass was high, and there was evidence of size-dependent competition for food between macrofauna and rneiofauna. Benthic micro-algae at an intertidal station appeared to be controlled by rnacrofaunal cropping and nutrient conditions in the sediment. Bacteria showed a very strong positive relationship with macrofauna and sediment carbon over a seasonal cycle and, spatially, with grain surface area and carbon content of sedirnents.

We conducted a 3‐year experiment on the effects of otter trawling on benthic habitat and communities on a sandy‐bottom ecosystem of the Grand Banks of Newfoundland that has supported commercial fisheries. Each year, three 13‐km‐long corridors were trawled 12 times with an Engel 145 otter trawl, creating a disturbance zone 120–250 m wide. Using a variety of oceanographic instruments, measurements were made before and after trawling to document effects. Trawling had no detectable effect on sediment grain size. Tracks made by trawl doors were readily visible on the sea floor immediately after trawling and 10 weeks later; in some cases they were still faintly visible after 1 year. Acoustic data indicated that trawling increased the topographic relief or roughness of surficial sediments and changed small‐scale biogenic sediment structures down to depths of 4.5 cm. Video observations in trawled corridors revealed that organisms and shells tended to be organized into linear features parallel to the corridor axis. They also demonstrated that trawling reduces both surficial biogenic sediment structure and the abundance of flocculated organic matter; untrawled sediments had a hummocky, mottled appearance, whereas trawled sediments were smoother and cleaner. These changes combined to give the trawled corridors a lighter appearance in color. It appears that the physical effects of otter trawling observed in this experiment are moderate and that recovery occurs in about a year. The biological effects of this experimental trawling have yet to be examined. Efectos del Arrastre Experimental en las Propiedades de Sedimentos Superficiales de un Ecosistema de Fondo Arenoso de los Grande Bancos de Terranova Un experimento de tres años sobre los efectos del arrastre en hábitat bentónico y sus comunidades fue realizado en un ecosistema arenoso que soporta pesquerías comerciales de los Grandes Bancos de Terranova. Cada año, tres corredores de 13 km de largo fueron arrastrados 12 veces con una red de arrastre Engel, creando una zona de perturbación de 120‐250 m de ancho. Para documentar los efectos se realizaron mediciones antes y después del arrastre usando una variedad de instrumentos oceanográficos. Los arrastres no tuvieron efectos detectables en el tamaño de grano del sedimento. Las marcas hechas por las puertas del arrastre fueron fácilmente visibles en el fondo inmediatamente después del arrastre y hasta 10 semanas después; en algunos casos las marcas fueron visibles después de un año. Los datos acústicos indican que el arrastre incrementa el relieve topográfico o la aspereza del sedimento superficial y cambia las estructuras biogénicas de pequeña escala del sedimento hasta una profundidad de 4.5 cm. Observaciones de video en corredores de arrastre revelan que los organismos y conchas tienden a estar organizados en forma lineal y paralelos a los ejes del corredor. Los videos también demostraron que el arrastre reduce tanto la estructura biogénica superficial del sedimento como la abundancia de materia orgánica floculada; sediment...

Ratios of stable carbon isotopes (δ 13C) have been measured in components of an intertidal mudflat ecosystem located near the head of the Bay of Fundy. Special attention was given to the isolation and analysis of carbon source materials including phytoplankton, benthic algae, marsh grass (Spartina alterniflora), size-fractionated detritus, and "mineral" sediment. Bulk sediment and suspended matter were also analyzed. For most of the year the two major primary producers, Spartina and benthic diatoms (dominated by Gyrosigma spp.), had similar δ 13C values (−13 to −14‰). Some Spartina detritus, presumably "fresh" material, also had similar δ 13C values. It was therefore imposible to estimate the relative importance of carbon from these sources to the nutrition of consumer organisms. Zooplankton, benthic-feeding fish, and benthic fauna had δ 13C values mostly in the range of −12 to −15‰, suggesting that live Spartina, "fresh" detritus, and benthic diatoms could be major carbon sources. Phytoplankton and other isotopically light carbon sources including "aged" detritus, bulk and "mineral" sediment, do not appear to be major carbon sources for mudflat organisms. We found Spartina detritus to be abundant both in sediments and suspended matter outside the salt marshes, but the δ 13C values of most of the detritus were much lighter (−17 to −20‰) than those of live Spartina. The mechanism of this isotopic alteration is not known and we were not able to demonstrate it clearly in laboratory experiments. Although the δ 13C method has helped to assess the relative importance of some isotopically distinct carbon sources, we were unable to detect any 13C enrichment in various trophic levels of mudflat organisms and benthic-feeding fish.Key words: stable carbon isotope ratio, detritus, decomposition, mudflat ecosystem, Pecks Cove, Bay of Fundy