The hypothesis that the level of chromatic polymorphism in intertidal isopods is related to their distribution and seasonal fluctuations in abundance was examined in northern Spain. Four species were used, Dynamene bidentata, Dynamene magnitorata, Cymodoce truncata and Cymodoce emarginata. Only for Dynamene species were results consistent with initial hypothesis. The most common colour morph in Dynamene bidentata was uniformis which is the most flexible phenotype, allowing effective concealment in most of the environments where the species occurs. Dynamene bidentata is the most abundant species of isopod in northern Spain, where it is abundant along the shore and throughout the year. Distribution of D. magnitorata, Cymodoce truncata and C. emarginata is restricted to macroalgal assemblages at low tidal levels. Seasonality is also important in D. magnitorata and C. truncata. The number of colour morphs and phenotypic diversity was larger in D. magnitorata than in D. bidentata. Only one colour morph was found in C. truncata and four in C. emarginata.

The behaviour of two intertidal chitons (Mollusca: Polyplacophora) from the western Indian Ocean (Acanthopleura gemmata and A. brevispinosa) and one from the Caribbean Sea (A. granulata) were analyzed in order to assess the spatial and temporal organization of their foraging activity. Individual paths were recorded in the field using a motographic method based on LED-tracking and the speed variation during each excursion used to reveal the places where the animals slowed down or stopped for the purpose of grazing. Foraging segments of each trajectory were selected according to a threshold speed which was individually calibrated. The three species of Acanthopleura exhibited graded foraging strategies of different spatial complexity. Acanthopleura gemmata focused its foraging on a few large feeding sites well separated from its permanent home. Acanthopleura brevispinosa exploited more subdivided feeding grounds not distinctly separated from its rest area. Acanthopleura granulata spreads its grazing activity over many small segments, throughout each excursion. Due to different tidal and diel constraints on their activity the three species allocated different absolute time to foraging, but the fraction of time spent foraging relative to the total excursion was similar in each.

The discrete habitat requirements of Ophelia bicornis from the Exe estuary are reported in relation to: the influence of tidal activity; the nature of the sandy substratum; the associated meiofauna; the interstitial bacteria; the interstitial water, organic matter and calcareous material; and the interstitial and sand-adsorbed free amino acids. The interrelationships of these features as potential limiting factors in the highly specific littoral distribution of O. bicornis is speculated upon.

The influence of temperature on the duration of the embryonic and larval development in Necora puber (L., 1767) was studied. Nine different temperatures were used for the eggs and seven for the larvae, in both cases ranging from 2 to 35°C. The temperature range where visible development was obtained was between 4 and 31°C, with the lowest lethal temperature (temperature at which the eggs did not show any sign of development and development did not resume when the eggs were placed at 15°C) being between 2 and 4°C and the highest lethal temperature between 31 and 35°C for both eggs and larvae.

Temperature was found to be inversely related to developmental time. The incubation period (D) fluctuated between 76 days at 10°C and 17·6 days at 25°C, with an increase in the rate of development (100/D) from 1·13 to 5·55 between these two temperatures. The larval period varied between 48·5 days at 15°C and 28 days at 25°C with rates of development of 2·08 and 3·57 respectively. The adjustment equations used show that temperature has a greater accelerating effect on eggs than on larvae. A simple potential equation, D=aT, describes the relationship between temperature and developmental time better than the Belehrádek equation, D=a(T-t).

Acording to the fitted equations developmental time from spawning to the first postlarval stage is completed in 91–105 days at temperatures of 13–15°C which is very close to our experimental data. The model proposed also fits most of the data from the available literature even those for other species such as Liocarcinus holsatus (Fabricius, 1798) and Carcinus maenas (L., 1758), which suggests that a similar response of developmental time vs temperature could be expected from other related Portunidae.

Back-calculated egg fertilization (spawned) dates and growth rates for young-of-the-year bass, Dicentrarchus labrax (L), captured from Loughor Estuary, Oxwich Bay and Ogmore Estuary, south Wales, UK, during 1988 and 1989 were compared. Spawned date frequency distributions indicated that the bass spawning season began in late February and continued until early June in 1988 and early July in 1989.

There were no significant differences in the frequency distributions of back-calculated spawned dates for the bass populations, between either sites or years, which suggested that any variations in growth rates were attributable to characteristics of their respective environments. Growth rates were determined for bass cohorts resulting from early, midor late-season spawnings at Oxwich and Loughor in 1988 and Oxwich, Loughor and Ogmore in 1989. There were only slight intra-annual differences between the mean growth rates of bass cohorts at the same site, suggesting that bass from early cohorts would be larger at any given time of year. In 1989, growth was considerably faster at Oxwich and Loughor than at Ogmore, where food supply was considered limiting. However, between-site variations in growth rate were small in comparison with inter-annual differences. The faster growth rates observed at Loughor and Oxwich in 1989 were attributed to higher water temperatures.

Relationships between growth rate and subsequent survival of young-of-the-year bass, and the relative importance of estuaries as nursery habitats for juvenile bass, are discussed.

The exposure of two species of talitrid amphipods (Orchestia gammarellus and Orchestia mediterranea) to a range of zinc and copper concentrations in solution has enabled the categorization of the mode of metal accumulation adopted by these supralittoral amphipods. Both species showed net accumulation of dissolved zinc and copper at all experimental exposures between 20 and 1000 μig Zng 1 and 13 and 1000 μg Cu 1 in artificial sea-water. Studies using Zn have shown that the zinc uptake rates of both species (0·430 μg Zn g d, SE 0·032 and 0·408 µg Zn g d, SE 0·073 for O. gammarellus and O. mediterranea respectively at 10°C in 31·6 μg Zn 1) are not significantly different, and are low in comparison with other crustaceans. Laboratory results are related to field conditions, and it is concluded that Firth of Clyde O. gammarellus are more dependent upon a food source in order to meet both their copper and zinc requirements than are O. mediterranea which are able to obtain sufficient metabolic copper from solution. The use of talitrid amphipods in zinc and copper biomonitoring programmes is also discussed.

The American oyster drill, Urosalpinx cinerea introduced to UK waters around the turn of the century, flourished in the Essex oyster grounds until the 1970s. Recent observations, 1987–1990, made in Goldhanger Creek, River Blackwater, indicate that the population level has been reduced to the point of scarcity and that those individuals remaining are old. All females examined exhibited imposex. In most, this masculinizing syndrome was developed to an advanced state that involved oviducal malformation; copulation and egg capsule formation are thought to have been inhibited and hence such affected females were sterile. Other, probably very old, females appeared infertile because of senility. No viable spawn was observed during the four summers of 1987 – 1990.

A meeting on Plant-Animal Interactions in the Marine Benthos was held in Liverpool in September 1990, organized by the Sy sterna tics Association in their Symposium Series, and supported by the Marine Biological Association. The following six papers were first presented at this meeting:

The various steps involved in experimental investigations of the causes of observed ecological patterns are examined. A sequence of different steps (observation, model, hypothesis, null hypothesis, test) is identifiable. The logical necessity for distinguishing and evaluating each of these steps is discussed. The potential usefulness of explicit recognition of the logical relationships between the various parts of the procedure is evaluated by reference to experimental studies to determine the causes of boundaries of vertical distribution of macro-algae in rocky intertidal habitats. Pitfalls of experimental procedures can sometimes be recognized as failures in the logical progress from one part to the next in the sequence of steps necessary in any study. Particularly important is the early recognition of the existence of many, potentially conflicting, but sometimes interactive, models to account for any observed pattern. Greater attention to the relation-ships between the components of the logical structure of an experimental study might aid in reduction of errors in the design, analysis and interpretation of ecological experimental data.

A literature review and new data are used to clarify geographical patterns of community response to release from heavy grazing by green sea urchins, Strongylocentrotus droebachiensis (O.F. Müller) within the north-west Atlantic region. Large geographical areas identified where urchin-removal experiments have not been conducted are the Passamaquoddy Bay area of the northern Bay of Fundy, the south and west coasts of Newfoundland, and southern Labrador. Within the north-west Atlantic region, there has been variation in the degree of domination by Laminaria species of post-urchin-removal communities. This is probably due, at least in part, to variation in the availability of Laminaria populations in refugia from urchin grazing. The following hypothesis is developed and given a preliminary test: in eastern Newfoundland, the absence of refugial Laminaria longicruris populations is due to periodic ice-scour. Despite the absence of significant Laminaria populations following short-term (<5 years) urchin-removal experiments in some areas, it is suggested that Laminaria spp. may be the natural, long-term community dominants in the absence of significant urchin grazing throughout the region. In view of the logistic problems involved in conducting long-term (6–15 years) urchin-removal experiments, it is suggested that urchin-removal/Laminaria-seeding experiments should be conducted within this region.

Traditionally, colonies of encrusting epiphytic bryozoans have been regarded as biotic factors reducing photosynthetic performance in benthic algae. In this study we determined under laboratory conditions the effects of Membranipora tuberculata on the photosynthetic efficiency of the rhodophyte Gelidium rex.

Encrusting bryozoans reduce to 44% the incident light reaching the algal thallus. However, concentrations of chlorophyll a and other accessory pigments are significantly higher in encrusted than in non-encrusted thalli. Consequently, photosynthetic efficiency is almost identical in both types of thalli. Although non-encrusted thalli showed a higher photosynthetic V due to higher levels of light reaching the algae, encrusted thalli exhibited a compensatory effect at low photon flux density and reached a similar P value. The detrimental effect of M. tuberculata on photosynthesis could be partially compensated by CO released from bryozoan cells, as G. rex preferred CO over HCO3 as a source of photosynthetic inorganic carbon. These results suggest that physiological interaction between bryozoans and algae, involving the interchange of metabolic substances, are likely to be important.

The brown alga Pilayella littoralis is common and widely distributed in the North Atlantic. In insular Newfoundland it is found year-round in the subtidal, but shows a distinct periodicity in the intertidal where it is a summer annual. Rapid growth begins in May and a maximum biomass is achieved in the summer with plants disappearing by October. Besides seasonal changes in abundance, seasonal changes in reproductive behaviour and calorific values of this alga also occur.

Pilayella littoralis is the most abundant consumable alga available to intertidal amphipods in Newfoundland. Newly hatched Gammarus lawrencianus grew faster and matured at a younger age on a diet of summer P. littoralis than on plants collected in the spring. Size at maturity and reproductive output (size of eggs, number of eggs) of maturing females did not vary with the time of collection of Pilayella.

Using laboratory experiments, this study examines the nature of the grazing relationship between the amphipod Hyale hirtipalma (Dana) and the red algae Iridaea spp., and the potential effects of grazing on the release and dispersal of algal spores. The results indicate that Hyale hirtipalma has a significant food preference for the cystocarpic stage of Iridaea laminarioides Bory when compared with consumption of Ulva rigida C. Ag. Hyale hirtipalma also shows a significantly greater food preference for cystocarpic tissues of Iridaea laminarioides and I. ciliata Kützing than for other karyological stages of these algae. By consuming the cystocarpic tissues, H. hirtipalma significantly increases the number of carpospores which are released and which settle at all measured distances from the mature cystocarpic I. laminarioides frond where measurements were taken. This evidence, together with information previously published, indicates that several Hyale species show similar food preferences towards the cystocarpic stage of Iridaea spp., and probably have the same ecological role as spore releasers and dispersal agents.

One of the most obvious effects of eutrophication in sheltered coastal areas and estuaries is enhanced growth of opportunistic macroalgae, which may form extensive mats over intertidal mudflats during the spring and summer. In the Ythan estuary, densities of the amphipod Corophium volutator (Pallas) in the sediment underlying weed mats were significantly lower than those in weed-free sediments, and are dominated by species characteristic of organically enriched, low oxygen environments such as Capitella capitata. Long-term data sets on Corophium abundance in the Ythan suggest that this species has declined dramatically throughout those parts of the estuary affected by weed mats.