Factors affecting variability of foraging excursions in a population of the limpet Patella vulgata (Mollusca,Gastropoda)

Paths moved by the limpet Patella vulgata L. were monitored on a sheltered vertical rocky shore in North Wales using time-lapse photography throughout nocturnal low tides in April and November 1992, roughly corresponding to periods of minimum and maximum gonad ripeness, respectively. Various motion parameters, including total duration, total length, and maximum distance reached from home were computed from 124 complete foraging routes obtained from 18 higher-zoned and 18 lower-zoned limpets. P. vulgata typically performed a single loop per night (average total length, ca. 70 cm), moving from the individual home scar to graze the surrounding algal grounds (average maximum distance, ca. 25 cm), then following its own trail back home. On the average, limpets moved from the home scar during three of four available nocturnal low tides and exploited about half the emersion time. Evidence for size-related variability in behaviour was found, as a positive correlation was assessed between both total duration and legth of the excursions, and shell length. In addition, zonation was proved to affect the limpets' foraging behaviour, since low-shore limpets moved faster and covered greater distances than high-shore ones. Moreover, consistent seasonal variation in foraging behaviour emerged, since in April the excursions were longer and longer-lasting than in November, but limpets exploited a larger fraction of potential activity phases in November than in April. The within-population variability in the temporal and spatial characteristics of the foraging excursions is discussed in relation to the available data on zonal and seasonal variation of food resources and in relation to physiological changes due to reproductive cycle.     

Assessment of factors affecting heart rate of the limpet Patella vulgata on the natural shore

 Heart rate variations of a population of the limpet Patella vulgata were monitored in the natural environment (Lough Hyne, southern Ireland) by non-invasive, optoelectronic recording. The heart rates of 145 limpets of different sizes, living on vertical and horizontal substrata, were measured both in air and water at different environmental temperatures, while the animals were inactive on their home scars. The heart rates of emersed, inactive limpets were positively related to air temperature and negatively related to limpet size. These relationships were similar for limpets on vertical and horizontal substrates. In contrast, no significant relationship between heart rate and temperature was found in submerged limpets, probably due to the narrow thermal range of the water during the study period. During submersion, a significant negative relationship between heart rate and size was evident for limpets on vertical surfaces but not for limpets on horizontal surfaces. In general, submerged limpets had a higher heart rate, 1.16 times that of limpets exposed to air. Moreover, the heart rates of nine animals were recorded while they were moving and while inactive on their home scars. Active limpets had a faster heart rate, 1.6 times that of limpets resting on their home scars. The dependence of heart rate on environmental temperature, size, respiratory medium and activity, as observed in limpets on the shore, agrees well with laboratory data and with previous findings of the correlation of oxygen consumption with the same factors. Such in situ measurements may, therefore, prove useful in attempts to determine natural levels of energy expenditure in models on the behaviour of foraging molluscs. Received: 5 September 1999 / Accepted: 17 April 2000     

Compressibility and shell failure in the European Atlantic <Emphasis Type="Italic">Patella</Emphasis> limpets

The specimens of Patella intermedia, Patella rustica, Patella ulyssiponensis and Patella vulgata were analysed for morphological and morphometric characters, and for the resistance to compression and crushing to a force applied at the apex. Shell shape in these species ranged from the high symmetrical cone, with a rounded base of P. rustica, to the flat, asymmetrical, narrow-pear-shaped base of P. ulyssiponensis. P. intermedia and P. vulgata showed intermediate morphologies. Shell thickness increased linearly with age, but differed in the four limpets. P. rustica had the thickest shells, and P. ulyssiponensis and P. vulgata had the thinnest shells. P. intermedia displayed intermediate shell thickness. Considering deformability and toughness, P. intermedia shells usually needed the highest force to compress in height, the highest pressure to collapse, and were appreciably deformed at collapse. On the opposite side, P. ulyssiponensis shells usually needed the lowest force to compress in height, the lowest pressure to collapse, and were much less deformed at collapse. P. intermedia shells were therefore the most deformable and tough, and P. ulyssiponensis, the most stiff and fragile. P. rustica and P. vulgata shells displayed intermediate behaviour. However, numerical simulations based on the finite element method using the experimentally determined shells’ geometry and thickness, but considering similar shells’ material and structure in the four species, predicted that shell toughness should be decreased in the order P. rustica >> P. intermedia > P. vulgata >> P. ulyssiponensis. P. rustica shells’ geometry (a high and centred cone) and thickness (very thick) were therefore, theoretically, the most fitted for shells to resist crushing by compression. Yet, in the experimental tests, they were not the most resistant shells. It was concluded that resistance to crushing was not a direct function of shell morphology and morphometry, but appeared to be mainly determined by shell deformability. This is most probably related to differences in the internal composition and architecture of the shell in the four species. By comparison with data reported in the literature on the pressures normally exerted by ocean waves, it was concluded that these limpets have resistances to crushing in far excess to pressures normally endured in nature, being therefore unlikely that these species are crushed by the action of even very strong waves on shores. Hard objects, like logs and boulders, can be hurled onto the shore by waves, and constitute a much greater threat to limpets than the waves themselves. The high toughness of the limpet shell can be related to resistance to the impact of incidental hard objects. There was no direct relationship between the habit preferences of these limpets and the resistance to crushing. Other factors are involved in the distribution of these species in the shores.     

Foraging and homing behaviour in the high-shore, crevice-dwelling limpet Helcion pectunculus (Prosobranchia: Patellidae)

The foraging activity of the high-shore, crevice-dwelling limpet Helcion pectunculus (Gmelin, 1791) (Prosobranchia: Patellidae) from an exposed shore on the eastern Cape coast of South Africa was monitored. Activity was compared during spring and neap tides and between spring, summer, autumn and winter. Rhythms of activity in this limpet varied depending upon microhabitat; individuals inhabiting both east- and west-facing rock surfaces were active during nocturnal low tides, but limpets on west-facing rock surfaces were also active during daytime low tides, whilst in the shade. Individuals travelled further during foraging excursions in winter (xˉ=85.53 cm) than in either spring (xˉ=55.7 cm) or summer (xˉ=48.8 cm) and also during spring low tides (xˉ=89.8 cm) compared with neaps (xˉ=40.9 cm). H. pectunculus exhibited rigid homing to a fixed scar within a crevice, and feeding excursions were found to consist of three distinct phases: a relatively rapid outward phase, a much slower foraging phase and a rapid homeward phase. Whether or not these limpets graze throughout an excursion is not known. Foraging was always highly directional, with a mean vector which took limpets onto an area of the rock face with the highest microalgal biomass. The fact that H. pectunculus took advantage of optimal feeding areas and memorized their location to enable return visits suggests a learning component in herbivorous gastropod foraging behaviour. Received: 29 December 1997 / Accepted: 8 May 1998     

Movement patterns of the limpet Cellana grata (Gould) observed over a continuous period through a changing tidal regime

Time-lapse videography of limpets mounted with light-emitting diodes was used to monitor the movements of a population of the non-homing Cellana grata on a vertical gully wall in Hong Kong. Animals were monitored for >7 days to examine spatial and temporal variation in their behaviour as the tides transited from a semi-diurnal to an almost diurnal pattern. Movement was synchronised with the tides, irrespective of the day–night cycles. Limpets rested low on the shore and were stimulated to move by the rising tide. Individuals moved up shore with the flooding tide, maintaining themselves in the awash zone, and then down shore on the ebbing tide, until they reached a resting height when the tide then fell beneath them, exhibiting ‘zonal shuttling’. A tight coupling of limpet position to tide height persisted through the changing tidal pattern, and almost all animals displayed the same organisation of activity over all tides. Initiation of activity and maximum height reached were probably controlled by the tides, but the cessation of activity may have been controlled by an internal clock. The pattern observed is consistent with the threat of attack from aquatic predators coupled with the need to minimise physical stresses while exposed. It is also consistent with the avoidance of grazing lower on the shore where interspecific competition may be more intense. Limpets showed two peaks of activity per tide, corresponding to when the rate of change of tide height was the greatest, except when tides became much reduced during the transit to a diurnal pattern. Movement was triphasic: an initial rapid phase, followed by a slower phase in the high shore and then a rapid phase before the limpets stopped moving. This structure is common in limpets and in this case is likely to be a consequence of animals maintaining themselves within the awash zone. Tide height appears to determine foraging activity, but with modifications in the behaviour in response to factors operating at more local temporal and spatial scales.     

Migratory and reproductive movements of male leatherback turtles (<Emphasis Type="Italic">Dermochelys coriacea</Emphasis>)

The biology of the endangered leatherback turtle (Dermochelys coriacea) at sea is poorly understood. As research has been almost exclusively limited to studies of nesting females, the movements of male turtles and the timing and location of mating activity have remained unknown. We report on the first deployments of satellite tags on male leatherbacks. Male migration to and residency in waters adjacent low-latitude nesting beaches in the western Atlantic suggest that this is where mating occurs, and return migration to these areas reveals male fidelity for breeding sites. Rate of travel decreased markedly after arriving in coastal breeding areas, where males remained for up to 96 days before assuming northward migrations. The initiation of these northward migrations coincided with peak nesting activity in adjacent nesting colonies. Data from satellite-linked time-depth recorders attached to two males revealed diel dive patterns in breeding areas and marked differences in diving behaviour between migratory and breeding periods in one turtle. When male turtles were in waters adjacent nesting colonies, their movements differed from those reported for nesting females, with females ranging farther from shore. Our results suggest that male leatherbacks may be vulnerable to entanglement in coastal fishing gear in waters adjacent nesting beaches.Communicated by R.J. Thompson, St. Johns     

Ecological studies on a tropical limpet Cellana radiata

Some aspects of the habitat zones, distribution pattern, and population density with reference to tidal levels of the tropical limpet Cellana radiata (Born) are presented. Observations have also been made on the homing behaviour of the limpet. Unlike the temperate limpets, no migration to different tidal levels during different seasons was observed in C. radiata.     

Effect of cholinergic antagonists on the bradycardic response of limpets to copper

The effect of cholinergic antagonists on the bradycardia induced by waterborne copper in the Mediterranean limpet Patella caerulea was investigated by using non-invasive recording of cardiac activity of whole animals. Preliminary tests were conducted to check the role of cholinergic and serotoninergic systems in the control of heart rate of P. caerulea. Superfusing the whole limpets with carbachol (cholinergic agonist) at 5×10^–5 M produced a negative inotropic and chronotropic effect (bradycardia), while superfusion with 5-hydroxytryptamine produced a positive inotropic and chronotropic effect (tachycardia). Exposure of limpets to a solution of copper in artificial seawater (0.25 mg l^–1, 3 h) reduced their heart rate to about 80% the value recorded in copper-free water. This bradycardia was inhibited by injecting the limpets with atropine (cholinergic muscarinic antagonist) at 21 g g^–1 wet flesh weight and with benzoquinonium [cholinergic nicotinic antagonist blocking the K⁺ mediated acetylcholine (ACh) response] at 10 and 100 g g^–1 prior to copper exposure. In contrast, D-tubocurarine (cholinergic nicotinic antagonist blocking Na⁺ mediated ACh response) had no effect at 85 g g^–1. These results agree with the involvement of the cholinergic system in the bradycardic response of limpets to copper, and support the view that gastropod ACh receptors do not fit the vertebrate nicotinic–muscarinic classification.Communicated by R. Cattaneo-Vietti, Genova     

Genetic variability in littoral gastropods: Phosphoglucose isomerase and phosphoglucomutase in Patella vulgata and P. aspera

Genetic variability of the phosphoglucose isomerase (PGI) and phosphoglucomutase (PGM) loci are compared in Patella vulgata L. and P. aspera Lamark from two sites on the west and south coasts of Ireland. P. vulgata was less variable than P. aspera at these 2 loci, and in only 1 of 7 other loci briefly examined was P. vulgata more variable. Evidence is also presented that the PGI enzyme in P. vulgata is more stable at high temperature than that of P aspera. The significance of these observations is discussed in the light of, the different zonal distributions of these species on the shore.     

Analyses of limpet defense and predator offense in the field

Between November 1982 and August 1984 diving observations of two intertidal limpets' defensive behaviours in response to two predatory species were made near the Seto Marine Biological Laboratory of Kyoto University, in Wakayama Prefecture, Japan, for over 800 h. The focus of the observations was a simple isolated rock, 0.9 m² in area with an inclination of 75°. The pulmonate homing limpet Siphonaria sirius responded by fleeing from its home in response to the whelk Thais clavigera and by calmping tightly to its home scar in response to the starfish Coscinasterias acutispina. Both behaviours were successful for avoiding predation. After a whelk moved far away, limpets returned to their homes. The patellid limpet Cellana toreuma showed mantle folding behaviour or fled for an average distance of 8 cm vertically upwards in response to the whelk and for an average distance of 21 cm vertically upwards in response to the starfish. The amount of time predators spent foraging increased in the low intertidal zone relative to the mid and high zones, and most predator attacks were observed during the limpets' resting periods (submersion in late afternoon or nighttime). The upward directional flight displayed by C. toreuma was related to the upward orientation of the limpets' heads when they are in a resting position. Half of the limpets observed fleeing downward away from a starfish, a movement elicited by a downward attack, received a second attack. These limpets were preyed upon at the second encounter 67% of the time. The upward fleeing behaviour of C. toreuma resulted in the shifting of its resting site higher up the study site where fewer attacks occurred and where the mortality rate was at its lowest. It is suggested that the homing behaviour of S. sirius and the upward fleeing behaviour of C. toreuma are mechanisms by means of which interspecific competition between limpets is reduced and coexistence on a small rock surface is maintained.     

Ecdysial rhythms in megalopae and first instars of the Dungeness crab Cancer magister

Diel molting cycles of megalopae and first instar Dungeness crabs Cancer magister Dana captured in the Grays Harbor estuary (46° 55N; 124° 05 W) in May 1991 were studied under laboratory conditions. Sixtyone percent of the megalopae and 76% of the first instar crabs molted during periods of ambient darkness under a normal light — dark diel regime, and molting pattern was not affected by changes in the photoperiod (24 h daylight or 24 h darkness). Time until metamorphic molt increased as conspecific density increased. Habitat type (shell or mud) did not affect time until molt of megalopae and first instar crabs, nor did it affect daily molting rhythm of first instars. We hypothesize that nightly ecdysis of megalopae and first instar Dungeness crabs and density-dependent molting may be an adaptive response to predation and cannibalism among young-of-the-year.Contribution No. 875 from the School of Fisheries, WH-10, University of Washington, Seattle, Washington     

Plasticity in the temporal organization of behaviour in the limpet <Emphasis Type="Italic">Cellana grata</Emphasis>

The behaviour of intertidal consumers is often tightly constrained to tidal movements, although activity patterns can vary within these constraints. Spatio-temporal variability in behaviour of a limpet, Cellana grata, was analysed over different tidal conditions (spring and neap tides) and during different times of the year (one summer and one winter) at sites in Hong Kong. Activity was generally dictated by tidal movements, being concentrated when animals were awash. Plasticity in behaviour was observed, with some limpets anticipating activity during the summer period and delaying activity during winter time. Limpets were active for a time equal, or slightly less, than time awash. As the time awash exceeded ~14–16 h, however, activity duration decreased. Within this general pattern, tidal variation as well as variation among times of the year was noted, with the lowest dependence on time awash being recorded during winter neap tides. Limpets showed a slight preference for being active during nighttime, which was particularly evident when animals were emersed during the summer period. Although the basic activity in C. grata is constrained to a specific temporal window, this limpet is able to modulate its foraging strategies and resting height, according to local, daily changes in environmental conditions.     

Encounters between Antarctic limpets, <Emphasis Type="Italic">Nacella concinna</Emphasis>, and predatory sea stars, <Emphasis Type="Italic">Lysasterias</Emphasis> sp., in laboratory and field experiments

Antarctic limpets, Nacella concinna, from the Admiralty Bay (King George Island, South Shetlands) for at least part of the year (austral winter) co-exist with predatory sea stars Lysasterias sp. Our laboratory and field experiments established that the presence of Lysasterias sp. or its odour had considerable influence upon their behaviour. Limpets’ responses, consisting of shell mushrooming, shell rotation and flight, were distinctly different from their reaction to other stimuli, such as food and conspecific odours, or mechanical stimulation. Moreover, a significant impact of sea star presence on limpets’ activity was observed, with limpets fleeing to a distance of 60 cm from the predator. Such reactions allow limpets to lower the incidence of sea star predation, but at the cost of presumptive disrupting of foraging and an additional energy expended for locomotion. A visible difference was noted between two limpet populations, with the rockpool limpets responding only after physical contact with being touched by a sea star, and the subtidal ones responding at a distance of up to 20 cm.     

Shell parameters in relation to zonation in mediterranean limpets

The relation of shell form to habitat in the Mediterranean limpets Patella caerulea (L.) and P. lusitanica (Gmelin) was investigated. P. caerulea shells were significantly longer, broader, but lower in height than P. lusitanica shells. The regression of the ratio (length plus breadth)/2 on the height of the shell was found to characterize the two limpet populations, with a small degree of overlap reflecting the distribution of the two limpets on the shore.     

Daily energy requirements and trophic positioning of the sand shrimp<Emphasis Type="Italic"> Crangon septemspinosa</Emphasis>

Sand shrimp, Crangon septemspinosa Say, are important to the trophic dynamics of coastal systems in the northwestern Atlantic. To evaluate predatory impacts of sand shrimp, daily energy requirements (J ind.^–1 day^–1) were calculated for this species from laboratory estimates of energy losses due to routine (R_R), active (R_A), and feeding (R_SDA) oxygen consumption rates (J ind.^–1 h^–1), coupled with measurements of diel motile activity. Shrimp used in this study were collected biweekly from the Niantic River, Connecticut (41°33N; 72°19W) during late spring and summer of 2000 and 2001. The rates of shrimp energy loss due to R_R and R_A increased exponentially with increasing temperature, with the magnitude of increase greater between 6°C and 10°C (Q₁₀=3.01) than between 10°C and 14°C (Q₁₀=2.85). Rates of R_R doubled with a twofold increase in shrimp mass, and R_SDA was 0.130 J h^–1+R_R, irrespective of shrimp body size. Shrimp motile activity was significantly greater during dark periods relative to light periods, indicating nocturnal behavior. Nocturnal activity also increased significantly at higher temperatures, and at 20°C shifted from a unimodal to a bimodal pattern. Laboratory estimates of daily metabolic expenditures (1.7–307.4 J ind.^–1 day^–1 for 0.05 and 1.5 g wet weight shrimp, respectively, between 0°C and 20°C) were combined with results from previous investigations to construct a bioenergetic model and make inferences regarding the trophic positioning of C. septemspinosa. Bioenergetic model estimates indicated that juvenile and adult shrimp could meet daily energy demands via opportunistic omnivory, selectively preying upon items of high energy content (e.g. invertebrate and fish tissue) and compensating for limited prey availability by ingesting readily accessible lower energy food (e.g. detritus and plant material).Electronic Supplementary Material Supplementary material is available in the online version of this article at Communicated by J.P. Grassle, New Brunswick     

Day/night differences in determination of growth rate of mackerel Scomber scombrus larvae during a patch-study in the Celtic Sea

The growth rate of mackerel, Scomber scombrus, larvae was calculated by analysing mean cohort length over time. The study took place on the central spawning ground of mackcrel in the Celtic Sea (Great Sole Bank) in April 1986. In order to minimize horizontal catch variability, repeated small-scale sampling with the Mocness plankton net was undertaken close to a satellite-tracked drifting buoy during a period of 78 h. Eighteen samples from nine hauls distributed over the whole sampling period were considered. One hundred larvae per sample were measured using a semi-automatic method. The proportion of larger larvae was significantly higher in night catches than in day catches. Independently calculated growth rates were 0.18 mm d^-1 for day catches and 0.14 mm d^-1 for night catches. This difference was not statistically significant. However, confidence in the calculation of growth rate, computed from night sampling, was much higher than that for day sampling. This may result as an effect of avoidance behaviour by larvae in daylight. Thus, night sampling seems to be a more reliable tool in the study of larval growth and should be used more extensively than daylight sampling.This paper was presented at the Early life history of fish symposium, Bergen, October 3 to 5, 1988     

Diurnal gut pigment rhythm and metabolic rate of<Emphasis Type="Italic"> Calanus euxinus</Emphasis> in the Black Sea

The vertical distribution, diel gut pigment content and oxygen consumption of Calanus euxinus were studied in April and September 1995 in the Black Sea. Gut pigment content of C. euxinus females was associated with diel vertical migration of the individuals, and it varied with depth and time. Highest gut pigment content was observed during the nighttime, when females were in the chlorophyll a (chl a) rich surface waters, but significant feeding also occurred in the deep layer. Gut pigment content throughout the water column varied from 0.8 to 22.0 ng pigment female^–1 in April and from 0.2 to 21 ng pigment female^–1 in September 1995. From the diel vertical migration pattern, it was estimated that female C. euxinus spend 7.5 h day^–1 in April and 10.5 h day^–1 in September in the chl a rich surface waters. Daily consumption by female C. euxinus in chl a rich surface waters was estimated by taking into account the feeding duration and gut pigment concentrations. Daily carbon rations of female C. euxinus, derived from herbivorous feeding in the euphotic zone, ranged from 6% to 11% of their body carbon weight in April and from 15% to 35% in September. Oxygen consumption rates of female and copepodite stage V (CV) C. euxinus were measured at different temperatures and at different oxygen concentrations. Oxygen consumption rates at oxygen-saturated concentration ranged from an average of 0.67 g O₂ mg^–1 dry weight (DW) h^–1 at 5°C to 2.1 g O₂ mg^–1 DW h^–1 at 23°C for females, and ranged from 0.48 g O₂ mg^–1 DW h^–1 at 5°C to 1.5 g O₂ mg^–1 DW h^–1 at 23°C for CVs. The rate of oxygen consumption at 16°C varied from 0.62 g O₂ mg^–1 DW h^–1 at 0.65 mg O₂ l^–1 to 1.57 g O₂ mg^–1 DW h^–1 at 4.35 mg O₂ l^–1 for CVs, and from 0.74 g O₂ mg^–1 DW h^–1 at 0.57 mg O₂ l^–1 to 2.24 g O₂ mg^–1 DW h^–1 at 4.37 mg O₂ l^–1 for females. From the oxygen consumption rates, daily requirements for the routine metabolism of females were estimated, and our results indicate that the herbivorous daily ration was sufficient to meet the routine metabolic requirements of female C. euxinus in April and September in the Black Sea.Communicated by O. Kinne, Oldendorf/Luhe     

Egg-capsule deposition and how behavioral interactions influence spawning rate in the squid<Emphasis Type="Italic"> Loligo opalescens</Emphasis> in Monterey Bay,California

Recent evidence suggests that, contrary to what was believed previously, most Loligo spp. females spawn multiple times and do not die immediately following a single spawning event. The present study used sustained focal observations of male/female pairs of the opalescent inshore squid Loligo opalescens Berry to examine the structure and behavior of near-bottom spawning groups. The study was carried out in a small area (10 km²) of Monterey Bay, California (36°36.1N; 121°53.4W), at depths of 25–45 m, using video cameras mounted on remotely operated vehicles. Behavioral observations were made primarily during daylight hours over known spawning beds in April and November 2000, and August 2001. Squid formed large aggregations in the water column where pairing occurred. Most commonly, only small numbers of active spawners were found at the substrate depositing egg capsules, and the mean operational sex ratio in the spawning groups was 1.87 males:1 female (range=1.0–8.5), although the ratio fluctuated rapidly as roving lone males joined and departed from the small spawning groups. On average, females (n=40) deposited 2.67 capsules (range 2–7) per focal observation at an average interval of 8.47 min between depositions (n=67). Following deposition of the capsules, females broke away from their consort males and jetted upwards to rejoin large schools located many meters above the substrate. Egg-capsule deposition was often interrupted by lone males seeking a mate, or by the approach of predators including fish and marine mammals. The results suggest that most of the communal egg beds in southern Monterey Bay are built up slowly through daily intermittent spawning, not in large big bang reproductive events as often depicted for L. opalescens.Communicated by J.P. Grassle, New Brunswick     

Temporal patterns of shell-gape in Mytilus edulis

Hitherto published evidence of the presence or absence of endogenous activity rhythms in bivalve molluscs is equivocal. Mytilus edulis L. were collected from a North Wales (UK) estuary in 1985, and shell-gaping was investigated in individual mussels under constant conditions in the laboratory. Results suggest that there is no endogenous circatidal rhythm of shell-gaping in this species, This is consistent with the view that, unlike mobile species, sessile intertidal species are much more likely to exhibit exogenous rather than endogenous responses to tidal fluctuations. There is some evidence of weak circadian rhythmicity of shell-gaping in M. edulis, with greater duration of shell-closure during hours of expected daylight. Such behaviour could represent an adaptational defence against visually-feeding predators.     

Effect of sunlight intensity and albinism on the covering response of the Caribbean sea urchin<Emphasis Type="Italic"> Tripneustes ventricosus</Emphasis>

At Discovery Bay, Jamaica, Tripneustes ventricosus lives in beds of the turtle grass Thalassia testudinum. Especially during daylight hours, it covers its aboral surface with fragments of this plant and other objects. Normally pigmented, wild-type sea urchins covered themselves significantly less with Thalassia when sunlight was experimentally decreased to 66% or 32% ambient intensity. Consistent with this result, naturally occurring sea urchins exhibited significantly less covering at a deep (3.5 m) site than at a shallow (1 m) site, where light intensities at the bottom were 619 and 946 mol s^–1 m^–2, respectively. The graded covering response to light intensity suggests that covering is a defense against damaging solar radiation. Albino sea urchins covered themselves significantly more with Thalassia than wild-type sea urchins in both full and 66% sunlight. In addition, at the shallow site where they accounted for about 4% of the population, they showed significantly greater covering than wild-type urchins. The greater covering response of albino sea urchins suggests a greater susceptibility to solar radiation.Communicated by P. W. Sammarco, Chauvin