Richard G. Hartnoll

MATING IN THE BRACHYURA

[Bei den Superfamilien der Brachyura, die weibliche Genitalporen am Sternum besitzen - Corystoidea, Oxystomata, Brachyrhyncha und Oxyrhyncha - wurde die Begattung studiert. Die mannlichen Tiere kopulieren nur mit vollig erhartetem Integument, wie es auch bei den Weibchen mancher Arten der Fall ist. Bei anderen Arten jedoch kopulieren die Weibchen gleich nach der Hautung, wenn die Schale also noch weich ist. Es gibt nun zwei grundsatzlich verschiedene Typen der Begattung. Typus I: Das Weibchen kopuliert gleich nach der Hautung, das Mannchen begleitet das Weibchen langere Zeit vor der Hautung und nach der Begattung; die Balz-Anreizungen sind hauptsachlich in chemischen Mitteln und in der Beruhrung konzentriert. Typus II: Das Weibchen kopuliert erst wenn die Schale erhartet ist, es gibt nur ein kurzes Liebesspiel und Gesicht- und Gehor-Anreizungen sind dabei am wichtigsten. Bei den Cancridae, Portunidae und Hymenosomatidae gibt es die Kopulation nach Typus I, bei den Xanthidae, Grapsidae und Ocypodidae hingegen hauptsachlich nach Typus II. Bei den Majidae kann die erste Kopulation nach Typus I vorgehen, die folgenden Begattungen verlaufen jedoch nach Typus II. Typus I der Begattung gibt es oft kombiniert mit der einfachen Form der Vagina: beide Merkmale werden jedoch als primitiv betrachtet und es ist unbewiesen, dass es hier funktionelle Zusammenhange gibt., Bei den Superfamilien der Brachyura, die weibliche Genitalporen am Sternum besitzen - Corystoidea, Oxystomata, Brachyrhyncha und Oxyrhyncha - wurde die Begattung studiert. Die mannlichen Tiere kopulieren nur mit vollig erhartetem Integument, wie es auch bei den Weibchen mancher Arten der Fall ist. Bei anderen Arten jedoch kopulieren die Weibchen gleich nach der Hautung, wenn die Schale also noch weich ist. Es gibt nun zwei grundsatzlich verschiedene Typen der Begattung. Typus I: Das Weibchen kopuliert gleich nach der Hautung, das Mannchen begleitet das Weibchen langere Zeit vor der Hautung und nach der Begattung; die Balz-Anreizungen sind hauptsachlich in chemischen Mitteln und in der Beruhrung konzentriert. Typus II: Das Weibchen kopuliert erst wenn die Schale erhartet ist, es gibt nur ein kurzes Liebesspiel und Gesicht- und Gehor-Anreizungen sind dabei am wichtigsten. Bei den Cancridae, Portunidae und Hymenosomatidae gibt es die Kopulation nach Typus I, bei den Xanthidae, Grapsidae und Ocypodidae hingegen hauptsachlich nach Typus II. Bei den Majidae kann die erste Kopulation nach Typus I vorgehen, die folgenden Begattungen verlaufen jedoch nach Typus II. Typus I der Begattung gibt es oft kombiniert mit der einfachen Form der Vagina: beide Merkmale werden jedoch als primitiv betrachtet und es ist unbewiesen, dass es hier funktionelle Zusammenhange gibt.]

The Determination of Relative Growth in Crustacea

Relative growth in Crustacea is generally in accordance with the simple allometry rule, y = Bxα. The regulation of growth at each ecdysis is such as to result in the attainment, where possible, of the proportions dictated by this rule. Growth proceeds as a series of phases, each composed of from one to several instars. Within each phase there is simple allometric growth, but both the levels of allometry and the size of the variables often change at the transition between phases. These transition changes may be minimal, but they can be so prominent as to result in an obvious critical moult or metamorphosis. In Brachyura there is a consistent pattern of phases in the later post-larval life, the critical moults separating the final three phases being known as the pre-puberty and puberty moults respectively. There can be polymorphism of the terminal mature phase. The critical moults do not necessarily appear to have fixed positions in the sequence of post-larval instars.

Growth in Crustacea — twenty years on

Developments during the past 20 years are reviewed for four aspects of crustacean growth. These are the hormonal control of moulting, the effects of external factors on growth rate, the patterns of growth and the determination of age. Hormonal control. The nature and structure of Moult Inhibiting Hormone has been determined, though the mechanism by which it inhibits crustecdysone production is still unclear. A role in moult control by Crustacean Hyperglycaemic Hormone has been demonstrated, but needs clarification. Methyl farnesoate, a juvenile hormone like substance, occurs in Crustacea: however, a clear function as a juvenile hormone has yet to be shown. External factors. The effect of increased temperature in reducing moult increments is supported by further data. Reduced food supply causes smaller moult increments and longer intermoult periods: the latter effect is generally proportionately greater. A role for CHH in this process is hypothesised. Patterns of growth. Little advance has occurred in understanding the rationale for the diversity of growth patterns. Computer modelling offers promise, but is constrained by lack of data on natural mortality for validation. Determination of age. The basic methods available remain size frequency analysis and tagging programmes. There have been advances in technology and methods of analysis, but no major breakthrough. Novel methods include radionuclide ratios (expensive, complex and give only duration of current intermoult), lipofuschin pigment assay (promising, but needs further validation), and annular structures in the infra-cerebral organ (still very speculative).

A continental scale evaluation of the role of limpet grazing on rocky shores

It is critical for our knowledge of biodiversity and ecosystem processes to understand how individual species contribute to ecosystem processes and how these contributions vary in space and time. We used a manipulative field experiment in five locations over 17° of latitude [from southern Portugal to the Isle of Man (British Isles)] to determine the relative response of rocky intertidal algal assemblages released from control by the grazing of limpets. Response ratios showed that when limpets were removed there was a trend of effects from north to south. In the north, grazing had a strong effect on algal assemblages, but removing grazers reduced spatial variability in assemblages. In the south, the effect of limpet grazing was far weaker and removal of grazers had a much reduced impact on spatial variability. Here we show a clear trophic control of an ecosystem in that grazing by limpets not only determines macroalgal abundance overall but also modifies ecosystem stability via variability in cover of algae.

Settlement patterns of Semibalanus balanoides (L.) in the Isle of Man (1977–1981)

Recruitment of the barnacle Semibalanus balanoides (L.) was assessed for five years at Port St. Mary, Isle of Man. Counts were made of settling cyprids and metamorphosed juveniles on a set of exactly the same ten squares (0.1 × 0.1 m) of rock-surface, scraped once prior to settlement each spring. There was considerable variation in the onset, duration, and density of settlement. There was a trend for earlier onset each year from 1977 to 1981 which correlated with earlier algal blooms. There was a positive correlation between earliness and density of settlement. Daily patterns of cyprid settlement were examined in 1978 and 1979 at Port St. Mary; these showed marked but irregular maxima of short duration. In 1979 comparison of settlement on two different sides of the island revealed a good correlation with onshore winds. Density and timing of settlement on the Isle of Man were compared with nearby Anglesey. There was little correspondence, emphasizing the importance of local factors on barnacle recruitment. Settlement densities on the Isle of Man were low compared with mainland sites presumably due to the islands isolation from other populations.

Paradoxical selective feeding on a low-nutrient diet: why do mangrove crabs eat leaves?

Abstract. Sesarmid crabs dominate Indo West-Pacific mangroves, and consume large amounts of mangrove litter. This is surprising, since mangrove leaves have high tannin contents and C/N ratios that far exceed 17, normally taken as the maximum for sustainable animal nutrition. This paradox has led to the hitherto untested hypothesis that crabs let leaves age in burrows before consumption, thereby reducing tannin content and C/N ratio. We excavated burrows of Neosarmatium meinerti within high-shore Avicennia marina mangroves, and investigated whether burrow leaves had C, N or C/N values significantly different from those of senescent leaves. Leaves were found in <45% of burrows, mostly only as small fragments, and N concentrations and C/N ratios of burrow leaves never varied significantly from senescent leaves. The leaf-ageing hypothesis was therefore not supported. In the field N. meinerti and Sesarma guttatum fed on sediment in 76% and 66–69% of observations, respectively, and on leaves in <10% of observations. Sediments from two A. marina mangroves had a mean C/N ratio of 19.6. Our results, and the literature, show that mangrove leaves are unlikely to fulfil the N requirements of crabs, whether or not leaf ageing takes place. Sediment detritus could be a richer source of N, as shown by lower C/N ratios and regular ingestion by crabs. By fragmenting leaves crabs may be elevating the nutritional quality of the substrate detritus.

Spatial and temporal variation in settlement and recruitment of the intertidal barnacle Semibalanus balanoides (L.) (Crustacea : Cirripedia) over a European scale

Variation in the level of settlement and recruitment in the intertidal barnacle Semibalanus balanoides was studied using a hierarchical sampling programme. The effect of three spatial scales, 10s of metres (sites), 1000s of metres (shores) and 100s of kilometres (locations), was determined. The largest spatial scale represented the distance between four widely separated locations, Sweden, the Isle of Man, SW Ireland and SW England, covering a large part of the range of S. balanoides in Europe. Temporal variation was determined by comparison between two years, 1997 and 1998. The settlement period of S. balanoides varied in length and timing, being earlier and shorter at the most northerly location, Sweden. The duration of settlement showed little difference among shores within locations, but the pattern of settlement did vary. Estimates of total settlement throughout the settlement period and of recruitment at the end of this period both showed substantial variation among locations which was dependent on the year of study. There was little consistency in the ranking of locations between the two years. Recruitment showed significant variation at the lower spatial scales of shore and site. In addition, examination of variance components showed a high degree of variation between replicates within sites in 1997. There was a significant relationship between settlement and recruitment at three of the four locations. Across all locations variation in settlement explained between 29 and 99% of variation in recruitment. However, locations showed distinct differences in the level of post-settlement survival.

Patchiness and fluctuations on moderately exposed rocky shores

Abstract Small-scale changes in a mid-tide level patchy fucoid/barnacle community were investigated for 7 years on a moderately exposed shore in the Isle of Man. A fixed area was repeatedly sampled non-destructively to assess the abundance and spatial pattern of the major species present. Considerable natural change was recorded on this unpolluted shore, especially in seaweed cover and number of limpets. Concurrent manipulative field experiments were run to clarify the role of biological interactions in generating and maintaining the observed fluctuations and patchiness. Local reductions in Patella vulgata grazing induced development of Fucus vesiculosus clumps. Such clumps dislodged up to 80% of settling Semibalanus balanoides cyprids, but encouraged aggregation and recruitment of Patella, Actinia equina and Nucella lapillus. Dense barnacles inhibited Patella grazing and growth. A simple model of the generation and maintenance of patchiness is presented.

Food supply, grazing activity and growth rate in the limpet Patella vulgata L.: a comparison between exposed and sheltered shores.

The limpet Patella vulgata L. is an important microphagous grazer on intertidal rocky shores of north-west Europe, occurring across the wave exposure gradient. Groups of P. vulgata were selected at mid-tide level of two exposed shores and two sheltered, fucoid dominated shores on the Isle of Man, British Isles, and manipulated to equivalent densities and population structure. The level of grazing activity and growth rate were determined over a 1-year period. At the same time, the abundance of epilithic microalgae, measured as the concentration of chlorophyll a, was determined as an estimate of food supply. Microagal abundance showed a seasonal pattern in both exposed and sheltered conditions, with higher levels in winter compared to summer. In both seasons, the microalgal resource was more abundant on the sheltered shore studied. The level of grazing activity in P. vulgata showed a seasonal pattern on the exposed but not the sheltered shores. Averaged over the year, grazing activity on the exposed shores was over double that on sheltered shores. Thus, in sheltered conditions, food supply for limpets was high and grazing activity low; in exposed conditions, food supply was low and grazing activity high. The growth rate of P. vulgata, measured as increase in shell length, showed no significant difference between exposed and sheltered shores. Growth rate was also determined in P. vulgata at natural densities. Although the overall density declined with decreasing exposure to wave action, the density per unit area of grazeable substance was higher in shelter. In these populations, the mean growth rate was over twice as high on exposed compared to sheltered shores.

Foraging movements and homing in the limpet Patella vulgata L

In two populations of Patella vulgata in the Isle of Man foraging activity is restricted to daytime high waters, with about 75 per cent of the population foraging on any one day. Movement commences as the tide covers the limpets, and they travel an average of 0·4 m from their home sites to which they return at least an hour before the falling tide exposes them again. The mean speed on the outward and return journey is around 0·60 cm min−, and during the intervening browsing period about 0·08 cm min−. This behaviour contrasts with that of the same species in Alderney, where foraging is limited to nocturnal low waters: there is possibly a geographical trend in behaviour. P. vulgata, especially in the Isle of Man, is one of the more mobile limpets.