Ecology of two littoral species of caprellid amphipods (Crustacea) from Washington,USA

Ecology of 2 littoral species of caprellid amphipods is compared. Populations of Caprella laeviuscula, a periphyton scraper/filter-feeder, are most dense on eelgrass Zostera marina L. In the absence of C. laeviuscula, periphyton biomass increases 411% in protected Z. marina beds. The light absorption spectra of periphyton and Z. marina are similar, and C. laeviuscula, by its periphyton removal, may allow Z. marina to grow in areas where it would otherwise be excluded. C. laeviuscula is aggressively dominant over sympatric caprellids, and seasonal predators of C. laeviuscula are absent during winter, the period when periphyton would be most limiting to Z. marina. Populations of Deutella californica, a predator, are most dense on the hydroid Obelia dichotoma (L.). In the O. dichotoma epibiotic community, D. californica is the primary predator, but removal did not change the composition of the community structure. In the absence of other macropredators, the structure of the O. dichotoma epibiotic community depends more on the seasonality of O. dichotoma occurrence than on organismal interactions.     

Annual variation in the growth rate of Yoldia notabilis (Bivalvia: Nuculanidae) in Otsuchi Bay,northeastern Japan,analyzed using shell microgrowth patterns

Annual variation in the growth rate of the protobranch bivalve Yoldia notabilis (collected in Otsuchi Bay, northeastern Japan between 1989 and 1991) was determined by measuring shell length at successive growth lines. Factors affecting growth rates were assessed by examining long-term environmental data. Shell cross-sections of Y. notabilis showed a clear pattern of internal growth lines which formed simultaneously with the annual external lines on the outer shell surface. Hence, they were used as an age marker. A maximum lifespan of 17 yr was determined for this species, and a sigmoidal growth curve was obtained by the internal growth line analysis. Examination of the growth lines also revealed a large annual variation in growth rate, fluctuating as much as 32-fold during the past 9 yr. The variation correlated negatively with water temperature and positively with chlorophyll a content in the water column. It is suggested that the variation in annual growth rate is dependent on food supply during the spring phytoplankton bloom which varies from year to year according to the flow of the cold Oyashio current each spring.     

Effects of preservation on wet weight,dry weight,nitrogen and carbon contents of Calanus helgolandicus (Crustacea: Copepoda)

The lengths, wet and dry weights, nitrogen and carbon contents of fresh, frozen and formaldehyde-fixed specimens of Calanus helgolandicus (Claus) were determined. Samples were collected during May 1980 in the Celtic Sea. Individual Copepodite Stages 3, 4, 5, and Adult Male and Female Stage 6 were measured and analysed, and 36 linear regression equations derived for these variables together with mean values, standard deviations and 95% confidence limits. The range of nitrogen values in the fresh material, expressed as a percentage of dry weight, ranged from 8.08%±0.80 (Copepodite Stage 3) to 10.89%±0.27 (adult female); carbon values changed from 41.6%±3.05 (mean ±95% confidence limits) for Copepodite Stage 3 to 50.97%±2.63 in Copepodite Stage 5. The adult females had a high nitrogen and relatively low carbon content, while the converse was true for Stage 5 copepodites. There was a loss of dry weight from the frozen samples (57%) and the fixed samples (38%) compared with the mean of the fresh dry weight of all stages. The material lost from the copepods was rich in nitrogen, thus, artificially high percentage carbon values were determined from the frozen and fixed samples (52.0 to 60.3% and 44.7 to 58.5%, respectively).     

Trophic diversity of idoteids (Crustacea, Isopoda) inhabiting the Posidonia oceanica litter

The coexistence of three idoteid species in Posidonia oceanica litter raises the question of trophic diversity and their role in the litter degradation process. Hence, diet composition of Idotea balthica, Idotea hectica and Cleantis prismatica was studied using a combination of gut contents and stable isotopes analysis. Gut content observations indicate that P. oceanica dead leaves are an important part of the ingested food for the three species, although their tissues are constituted of only a small to medium fraction of P. oceanica carbon. Our results also underlined the potential role of these species in the degradation of P. oceanica litter by mechanically fragmenting the litter and by assimilating a small to medium fraction of carbon. Moreover, we showed that there were considerable inter- and intra-specific differences in diet composition. Diet differed between juveniles and adults for I. balthica. Crustaceans are an important food source for adults of I. balthica, while I. hectica indicated a major contribution of algal material. C. prismatica showed an intermediate diet. This trophic diversity is probably one of the factors allowing these species to coexist in the same biotope.     

Fatty acid composition as a dietary indicator of the invasive caprellid, Caprella mutica (Crustacea: Amphipoda)

The invasive caprellid amphipod Caprella mutica is one of the most widely dispersed marine non-native species globally. Originating in sub-boreal north-east Asia, it has now been found in both the northern and the southern hemispheres. One potential reason why this species is such a successful invader is its ability to utilise a wide variety of food sources. The contribution of different food sources to the diet of C. mutica was estimated using fatty acids as biomarkers. Caprella mutica was collected from three field sites, including sea cages stocked with Atlantic salmon Salmo salar, shellfish longlines stocked with the blue mussel Mytilus edulis and mooring lines marking the Loch Linnhe Artificial Reef (>2 km from caged finfish aquaculture), where established populations of this species are known to occur. In addition, the fatty acid compositions of C. mutica held in aquaria and either fed the microalga, Dunaliella tertiolecta, or the diatom, Phaeodactylum tricornutum, for a period of 21 days were investigated. The fatty acid composition of the diatom and the microalgal diets was also examined. The results showed that C. mutica contained high levels of polyunsaturated fatty acids, particularly 20:5(n-3); other dominant fatty acids included 18:1(n-9), 22:6(n-3) and 16:0 (in decreasing order based on abundance). Significant differences in the fatty acid profiles between caprellids fed on the microalgae and the diatom diets and between C. mutica collected from the field sites were observed. These results provide evidence that lipid biomarkers can be successfully used to provide evidence of feeding strategy for C. mutica and that the flexibility observed in this strategy may play an important role in its invasion success.     

Daytime surface swarming of Euphausia pacifica (Crustacea: Euphausiacea) in the Sanriku coastal waters of northeastern Japan

Biological characteristics of daytime surface swarming of Euphausia pacifica were investigated. Swarms in the Sanriku coastal waters consisted almost exclusively of mature individuals and seemed to be related to breeding behavior. Although maturation of ovarian eggs occurred both at the beginning and the end of the swarming period, females with attached spermatophore were most frequent at the end of the period. Since stomachs of swarming individuals were nearly empty throughout this period, swarming behavior was probably not related to feeding. Swarming individuals did not seem to be transported to the surface by vertical water movement caused by tidal streams, because the daily catch per boat did not differ between spring and neap tides.     

Vertical distribution of larvae of Euphausia nana and E. similis (Crustacea: Euphausiacea) in Sagami Bay and Suruga Bay,Central Japan

Vertical distributions of the larval stages of Euphausia nana Brinton and E. similis G. O. Sars in Sagami Bay and Suruga Bay, Central Japan were studied. Most of the metanauplius larvae of E. nana occurred between 25 and 80 m depth, and they were found at greater depths than the eggs and calyptopis larvae. The nauplii and metanauplii of e. similis were mainly found between 50 and 100 m depth, and they also occurred deeper than the eggs and calyptopes. The larvae of the two species from calyptopis I demonstrate diurnal vertical migration. However, this phenomenon was not clear in the season (March) when a seasonal thermocline was absent. Calyptopes and fruciliae of E. similis occurred deeper and migrated over greater vertical distances than those of E. nana. The distance of migration of furcilia I larvae of E. similis was estimated to be about 200 m.     

Selection of unicellular algae by the littoral amphipods Gammarus oceanicus and Calliopius laeviusculus (Crustacea)

The effect of microalgal strength of adhesion to surfaces was examined with regard to their susceptibility to grazing by Gammarus oceanicus Segerstråle and Calliopius laeviusculus (Krøyer). Observations of the feeding behaviour and two feeding experiments were carried out under laboratory conditions. Naturally attached periphyton (strongly attached cells), homogenized periphyton (loosely attached cells), filtered phytoplankton (unattached cells) and bare surfaces (controls) were randomly located in a grid and offered for grazing to a fixed number of amphipods of each species separately. The number of individuals visiting each type of food presented in the grid was recorded for 24-h periods. The feeding habit of each species, their effect on food distribution and their efficiency at collecting small particles were also recorded. G. oceanicus has a low efficiency at collecting particles and does not select a particular type of food, owing to its feeding habit of indiscriminately resuspending loosely attached particles. C. laeviusculus is a highly efficient and selective grazer, preferring homogenized periphyton and phytoplankton to naturally attached periphyton. For epibenthic diatoms, strong adhesion to surfaces is advantageous to avoid grazers.     

Interannual, seasonal, local and body size variations in reproduction of the prawn Penaeus (Marsupenaeus) japonicus (Crustacea: Decapoda: Penaeidae) in the Ariake Sea and Tachibana Bay, Japan

 The reproductive biology of female Penaeus japonicus Bate was investigated in the Ariake Sea and Tachibana Bay (located outside the Ariake Sea), Japan from 1994 to 1996. Interannual, seasonal, individual female body size and spatial influences on the incidence of spawning were examined. The proportion of inseminated females, increased with increasing body size up to 170 mm body length (BL) and decreased thereafter. The minimum size at maturity was similar between years; 130 to 140 mm BL. The minimum size of individuals with developing ovaries or spermatophores differed from that of ripe females by 20 to 25 mm. Spawning occurred in the central part of the Ariake Sea and Tachibana Bay but rarely in the inner part. P. japonicus had a clear reproductive cycle. Spawning started earlier and ended later, occurring from mid-May to mid-October, in the eastern central part of and outside of the Ariake Sea compared with the western central part, where spawning occurred from mid-June to mid-September. Spawning dynamics differed across seasons, body sizes and areas but not across years. The seasonal peak in the proportion of ripe females varied with body size. In small individuals (130 to 169 mm BL), no peak was observed, whereas in large individuals (>170 mm BL) the proportion of ripe individuals peaked in June. The proportion of ripe individuals increased with increasing body size and was high outside the Ariake Sea. Factors causing the variation in spawning dynamics are discussed. Received: 30 November 1998 / Accepted: 12 October 1999     

Spatio-temporal changes in diversity and community structure of planktonic copepods in Sagami Bay, Japan

Seasonal changes in diversity and community structure of planktonic copepods at a shelf site in Sagami Bay, Japan was studied in relation to cross-shelf interaction of species components. Seasonal mesozooplankton samples were collected from the shelf station (St. M) of the north-west part of Sagami Bay from 1995 to 1997. Vertical multi-layered samples were collected near the center of Sagami Bay (St. P) in June 1996. A total 185 copepod species were identified from the two stations. We observed a clear seasonal succession in calanoid diversity and community structure at St. M from a simple shelf water community (>11 species) during spring blooming periods to highly diverse and mixed communities (ca 20–30 species) of shelf water species coupled with various Kuroshio Current species during late summer to autumn. Cluster and non-metric multidimensional scaling ordination analyses showed two distinct calanoid community groups. One group, which included samples of St. M and the surface layer of St. P, consisted of shelf water species, such as Calanus sinicus, Ctenocalanus vanus, Paracalanus spp., and Kuroshio species, such as, Canthocalanus pauper, Scolecithrix danae, etc. The other cluster was restricted to the samples collected from mid and deep layers at St. P, which consisted of meso- and bathypelagic species and Oyashio species (cold-current species, such as Neocalanus cristatus, Pseudocalanus spp., Eucalanus bungii and Metridia pacifica). In the mid and deep layers at St. P, the population of dormant copepodid stage V (CV) of Eucalanus californicus and C. sinicus were dominant. The deep CV population of C. sinicus might be ecologically discriminated from the surface and shelf water population due to their larger body length and dormant life cycle. E. californicus was also collected at the shelf site during each spring bloom period, whereas the population might descend into the mid- and deep-layers of the central bay before summer. Our results suggest that the seasonal fluctuation of community structure in the shelf water was controlled by both physical (Kuroshio Current) and biological factors, i.e., spring bloom and ontogenetic vertical migration of E. californicus. In particular, transport and diffusion processes of Kuroshio Current in Sagami Bay played a key role in controlling the shelf water calanoid community.     

Effects of the 1983-El Niño on growth and carbon and nitrogen metabolism ofPleurophycus gardneri (Phaeopyceae: Laminariales) in the northeastern Pacific

Growth and compounds of carbon and nitrogen of the northeast Pacific kelpPleurophycus gardneri (Laminariales, Laminariaceae) were assessed before, during and after the 1983-El Niño Souther Oscillation event. This 2-yr study provides evidence that reduced ambient levels of nitrate and phosphate from March until August/September, 1983, in combination with elevated seawater temperature, caused a significant impairment of growth. Blade surface area, blade length, total fresh weight, and dry weight on an areal basis were significantly reduced in 1983 compared to 1982 (P<0.01). They were also significantly smaller in 1984 than in 1983 (P<0.05). The C:N values obtained both in May and July 1983 were considerably higher than in 1982, while those in May 1984 were strikingly smaller than in both 1982 and 1983. Mannitol content of the mibrid in May 1983, exhibited the highest levels recorded during the 2-yr study period, with ca. 19% dry weight and significantly exceeded mannitol content measured in May 1982 (average: 13%) and in May 1984 (average: 8%). The concentration factor for internal vs external nitrate in the midrib was 700 x ambient in May 1982 and 1984 compared with 20 x in May 1983. Ninhydrin positive substances (NPS) averaged 117 mol g dry wt^-1 in May 1984 compared with ca. 50 mol in May 1982 and 1983. The pigment ratios chlorophyllc: chlorophylla and fucoxanthin: chlorophylla in May 1983 were similar to those obtained in 1982, but were significantly different in May 1984. It is suggested that the interactive effects of temperature stress and nutrient limitation in 1983 caused a disruptive influence on C- and N-metabolism ofPleurophycus gardneri, which still affected growth performance in 1984.     

Microbial activity and carbon, nitrogen, and phosphorus content in a subtropical seagrass estuary (Florida Bay): evidence for limited bacterial use of seagrass production

Bacterial abundance, production, and extracellular enzyme activity were determined in the shallow water column, in the epiphytic community of Thalassia testudinum, and at the sediment surface along with total carbon, nitrogen, and phosphorus in Florida Bay, a subtropical seagrass estuary. Data were statistically reduced by principle components analysis (PCA) and multidimensional scaling and related to T. testudinum leaf total phosphorus content and phytoplankton biomass. Each zone (i.e., pelagic, epiphytic, and surface sediment community) was significantly dissimilar to each other (Global R = 0.65). Pelagic aminopeptidase and sum of carbon hydrolytic enzyme (esterase, peptidase, and α- and β-glucosidase) activities ranged from 8 to 284 mg N m⁻² day⁻¹ and 113–1,671 mg C m⁻² day⁻¹, respectively, and were 1–3 orders of magnitude higher than epiphytic and sediment surface activities. Due to the phosphorus-limited nature of Florida Bay, alkaline phosphatase activity was similar between pelagic (51–710 mg P m⁻² day⁻¹) and sediment (77–224 mg P m⁻² day⁻¹) zones but lower in the epiphytes (1.1–5.2 mg P m⁻² day⁻¹). Total (and/or organic) C (111–311 g C m⁻²), N (9.4–27.2 g N m⁻²), and P (212–1,623 mg P m⁻²) content were the highest in the sediment surface and typically the lowest in the seagrass epiphytes, ranging from 0.6 to 8.7 g C m⁻², 0.02–0.99 g N m⁻², and 0.5–43.5 mg P m⁻². Unlike nutrient content and enzyme activities, bacterial production was highest in the epiphytes (8.0–235.1 mg C m⁻² day⁻¹) and sediment surface (11.5–233.2 mg C m⁻² day⁻¹) and low in the water column (1.6–85.6 mg C m⁻² day⁻¹). At an assumed 50% bacterial growth efficiency, for example, extracellular enzyme hydrolysis could supply 1.8 and 69% of epiphytic and sediment bacteria carbon demand, respectively, while pelagic bacteria could fulfill their carbon demand completely by enzyme-hydrolyzable organic matter. Similarly, previously measured T. testudinum extracellular photosynthetic carbon exudation rates could not satisfy epiphytic and sediment surface bacterial carbon demand, suggesting that epiphytic algae and microphytobenthos might provide usable substrates to support high benthic bacterial production rates. PCA revealed that T. testudinum nutrient content was related positively to epiphytic nutrient content and carbon hydrolase activity in the sediment, but unrelated to pelagic variables. Phytoplankton biomass correlated positively with all pelagic components and sediment aminopeptidase activity but negatively with epiphytic alkaline phosphatase activity. In conclusion, seagrass production and nutrient content was unrelated to pelagic bacteria activity, but did influence extracellular enzyme hydrolysis at the sediment surface and in the epiphytes. This study suggests that seagrass-derived organic matter is of secondary importance in Florida Bay and that bacteria rely primarily on algal/cyanobacteria production. Pelagic bacteria seem coupled to phytoplankton, while the benthic community appears supported by epiphytic and/or microphytobenthos production.     

Calorific,ash, carbon and nitrogen content in relation to length and dry weight of Parathemisto gaudichaudi (Amphipoda: Hyperiidea) in the North East Atlantic Ocean

The calorific, ash, carbon and nitrogen content, length and dry weight were determined for the hyperiid Parathemisto gaudichaudi (Guerin). Regression equations for all these variables were determined so that they can be estimated by calculation from measurements of length of the hyperiid. Mean values for total nitrogen and carbon were 7.79±0.85% and 36.80±4.18% of the dry weight, respectively. The carbon to calorific equivalent for P. gaudichaudi was 10.37 kcal g^-1 carbon (9.13 kcal g^-1 when corrected for nitrogen). The calorific value for ash-free adult P. gaudichaudi was 5.138 kcal g^-1±1.309 (4.510 kcal g^-1 when corrected for nitrogen). This large variation in the calorific content (coefficient of variation of 25.84%) can be accounted for largely by variation in the ash content (coefficient of variation of 21.84%). The calorific value determined for P. gaudichaudi is similar to that measured for other carnivorous crustaceans and adds support to the hypothesis that animals with high calorific content have a low fecundity and an energy-rich store which can be used as a buffer during unfavourable periods in their life.     

Modeling the seasonal autochthonous sources of dissolved organic carbon and nitrogen in the upper Chesapeake Bay

In this paper we investigate the seasonal autochthonous sources of dissolved organic carbon (DOC) and nitrogen (DON) in the euphotic zone at a station in the upper Chesapeake Bay using a new mass-based ecosystem model. Important features of the model are: (1) carbon and nitrogen are incorporated by means of a set of fixed and varying C:N ratios; (2) dissolved organic matter (DOM) is separated into labile, semi-labile, and refractory pools for both C and N; (3) the production and consumption of DOM is treated in detail; and (4) seasonal observations of light, temperature, nutrients, and surface layer circulation are used to physically force the model. The model reasonably reproduces the mean observed seasonal concentrations of nutrients, DOM, plankton biomass, and chlorophyll a. The results suggest that estuarine DOM production is intricately tied to the biomass concentration, ratio, and productivity of phytoplankton, zooplankton, viruses, and bacteria. During peak spring productivity phytoplankton exudation and zooplankton sloppy feeding are the most important autochthonous sources of DOM. In the summer when productivity peaks again, autochthonous sources of DOM are more diverse and, in addition to phytoplankton exudation, important ones include viral lysis and the decay of detritus. The potential importance of viral decay as a source of bioavailable DOM from within the bulk DOM pool is also discussed. The results also highlight the importance of some poorly constrained processes and parameters. Some potential improvements and remedies are suggested. Sensitivity studies on selected parameters are also reported and discussed.     

Locomotor activity patterns and feeding habits in the prawn Palaemon xiphias (Crustacea: Decapoda: Palaemonidae) in Alfacs Bay,Ebro Delta (northwest Mediterranean)

Diel activity rhythms of the prawn Palaemon xiphias Risso, 1818 from Alfacs Bay, Ebro Delta, were studied by time-lapse videorecordings. Activity displayed an endogenous circadian rhythm, with maximum activity at night. Feeding habits were studied by frequency of occurrence and by the points method. The food of P. xiphias consisted mainly of crustaceans; the remains of amphipods, isopods, mysids, copepods, decapods and ostracods were identified. The remaining items consisted of molluscs, polychaetes, ophiuroids, plant material, sand, and unidentified organic debris. The results indicate that P. xiphias is a predator of benthic invertebrates rather than a scavenger or detritus feeder. Diet composition changes with increasing size of the prawn.     

The breeding cycles of two species of grapsid crabs (Crustacea: Decapoda) from the North Coast of Kyushu,Japan

The incidence of ovigerous females in populations of two grapsid crabs, Hemigrapsus penicillatus (de Haan, 1835) and Sesarma (Parasesarma) pictum (de Haan, 1835) were followed from August 1975 to November 1976. H. penicillatus, which inhabits the lower intertidal region near the mouth of Tatara-Umi Estuary, breeds from March to November. S. pictum, which inhibits crevices and abandoned holes of other species and is abundant at and above the upper intertidal region of the estuary, breeds from May to September. H. penicillatus matures when the female reaches 6 to 7 mm carapace width, whereas S. pictum becomes mature when the carapace width is 12 to 13 mm, although the maximum size attained by females of both species is almost the same. H. penicillatus produces 5 to 6 broods, S. pictum 2 to 3 broods, during a breeding season. The size of a newly laid egg of H. penicillatus is smaller than that of S. pictum. The number of eggs produced by a female H. penicillatus is greater than that of S. pictum during a breeding season. In both species the peak of the breeding season is during summer, at which time the ovarian activity is also apparently accelerated. The major environmental factor which controls the breeding in these crabs appears to be temperature. H. penicillatus is submerged at every high tide, and is relatively inactive from late November to February when the ambient water and air temperatures are rather low. S. pictum is dormant in crevices or understones of the splash zone from November to March. The length of the breeding season of these crabs appears to be inversely proportional to the period of their winter dormancy.     

Some aspects of the life history of the subarctic copepodNeocalanus cristatus (Calanoida) in Sagami Bay,central Japan

A typical subarctic copepod,Neocalanus cristatus, occurred in the mesopelagic layer (500 to 1000 m) in Sagami Bay, central Japan, throughout the year. Specimens were collected from 1982 to 1986. A small number of adult females were distributed from 800 to 900 m only, but no adult males were collected. This species appeared to be abundant in April and August, when intermediate Oyashio water flowed strongly into Sagami Bay. Mean prosome lengths of copepodite stages IV and V and adults were 4.33, 6.87 and 6.87 mm, respectively. The condition factor [wet wt/(prosome length)³ × 100] of copepodite stage V did not vary remarkably, and mean values ranged from 4.7 to 5.0. Prosome length, body weight and condition factor ofN. cristatus collected from Sagami Bay were smaller than those of copepods in the northern North Pacific.N. cristatus transported from the north cannot molt to adult stages (except for those originating in mesopelagic waters) due to the adverse environmental conditions in Sagami Bay; instead, they die in the mesopelagic layer and sink to the bathypelagic layer (1 000 to 1 400 m), close to the bottom. Since nauplii and early copepodite stages did not occur in any season,N. cristatus probably do not reproduce in Sagami Bay.     

Complete carbon and nitrogen budgets for the hydromedusaCladonema californicum (Anthomedusa: Cladonemidae)

Complete carbon and nitrogen budgets were constructed for a single cohort of the hydromedusaCladonema californicum Hyman, 1947, collected in 1984 from Santa Catalina Island, California, USA. The budgets accounted for 62 to 84% (average = 74%) of ingested C and 60 to 108% (average = 84%) of ingested N. During most of the medusan life cycle, expenditures for growth exceeded those for metabolism and dissolved organic release (DOR). The gross growth efficiency was lower for C than for N; different conversion rates of C and N are discussed in terms of C:N ratios and budget balances for predator and prey. Growth rates, egg production, and C and N composition ofC. californicum were quite different from those of neritic ctenophores, indicating that gelatinous predators may be a physiologically diverse group.Please address all correspondence and requests for reprints to Dr Costello at his present address: Biology Department, Providence College, Providence, Rhode Island 02918-0001, USA     

Temperature tolerance of the estuarine prawn Upogebia africana (Anomura,Crustacea)

Continuous temperature measurements were made in a typical South East African estuary. Mean summer (November to March) temperatures were in the range 19° to 24°C, and in winter (June to August) from 13° to 16°C. Large daily temperature fluctuations of 6° to 10°C occurred in summer; these appear to result from tidal movement of cool sea water into the estuary. In winter, temperature fluctuations were much smaller (3° to 5°C). The burrowing prawn Upogebia africana (Obtmann) was found to have an upper lethal temperature of 29°C in both winter and summer. The resistance time of prawns to temperatures above 30°C was much greater in summer than in winter. It was possible to acclimate winter prawns and increase their resistance time to a level comparable to that of summer individuals. A latent period of 40 h occurred before acclimation effects were detectable. Long-term exposure of prawns to high temperatures did not increase their resistance above that of summer prawns. Water at a temperature above this upper lethal temperature is not pumped through the burrows. This avoidance behaviour considerably increases the ability of U. africana to withstand short-lived temperature extremes.     

Feeding habits of the pebble crab Eriphia smithi (Crustacea,Brachyura, Menippidae)

Eriphia smithi is a very common East African intertidal xanthoid crab. Its dietary input is based mainly in algal grazing (during the day) and predation (particularly at night). Predation appears quite opportunistic and mostly directed at crustaceans and molluscs, among which bivales largely predominate. Echinoderms are actively avoided and, contrary to common belief, predation on Prosobranchia is only accessory.