Quantifying Daily Migration in the Sea Urchin Paracentrotus Lividus

J. Mar. Biol. Ass. U.K. (2000), 80,177^178 Printed in the United Kingdom

Quantifying daily migration in the sea urchin Paracentrotus lividus

Anne C. Crook*, Maria Long and David K.A. Barnes Department of Zoology and Animal Ecology, University College Cork, Cork, Ireland. *Correspondence e-mail: [email protected]

In Ireland the purple sea urchin Paracentrotus lividus (Echinoidea) typically inhabits intertidal bored holes. At Lough Hyne, Co. Cork, a population occurs associated with rock scree in the shallow subtidal zone. This study provides unequivocal quantitative evidence to demonstrate diurnal migration in a population of P. lividus at Lough Hyne, Ireland. Most size groups/age-classes did not to migrate, the youngest always and oldest never occurring under rocks.Those that did migrate between the lower and upper surface of rocks (2 ,3 and 4 age categories) did so in exactly the reverse circadian patternto those described fromthe Mediterranean Sea. Paracentrotus lividus (Lamarck) exhibits a number of cyclical The number of P. lividus individuals on each of the rock patterns, the least variable being annual reproductive cycles surfaces (upper, side and lower) di¡ered signi¢cantly over a 24-h (Crapp & Willis, 1975). It is an important commercial species in period. The numbers on the upper surface peaked at 1200^1600, the Mediterranean Sea and has been described as a keystone compared to 1400^1800 for the sides and 0000^0400 for the species (through control of macroalgae) at the Marine Nature lower surfaces (Figure 1). The period of maximum change was Reserve of Lough Hyne, Co. Cork, Ireland. The P. lividus around 1000 although individuals began moving to the sides community at Lough Hyne was ¢rst noted by Renouf (1931) and and upper surfaces of rocks at 0700^0800. Similarly P. lividus has since been the subject of a number of population and individuals commenced returning to the lower surfaces after behavioural studies (Kitching & Ebling, 1961; Muntz et al., 1965; 1600, although the number of side dwellers appears to rise Kitching & Thain, 1983; Barnes et al., 1999). This population is because of transitory individuals travelling from the upper to unusual as, unlike the intertidal distribution of other populations lower surfaces. The majority of the sample population of outside of the Mediterranean Sea, it occurs in the subtidal zone. P. lividus were on the under surface at night (Figure 2). During Short distance circadian migrations have been described and crepuscular periods the majority of the sample population were suggested for a number of sublittoral zone macroinvertebrates, on the sides and during daylight most were on either the upper including certain populations of P. lividus (Ebling et al., 1966; or side surfaces. The proportion of the population involved in Dance, 1987). In the case of P. lividus both the actual movement migration/change of location (either from lower to side or side and the causes are unquanti¢ed and controversial, but sugges- to upper) was high diurnally and low nocturnally, but highest in tions have involved predator^prey separation. Here we present the morning and evening (Figure 2). Overall, the mean test our ¢ndings relating to the movement of individuals with a view diameter of individuals on the lower, side and upper surfaces of to providing a quantitative assessment of potential diurnal rocks di¡ered signi¢cantly (P50.05). migration in this species. We assessed the daily, circadian and A signi¢cant proportion (45% overall) was not involved in individual size components of P. lividus movement in the ¢eld. migrations. This proportion di¡ered across the population; few In addition, randomly chosen focal P. lividus specimens were small individuals migrated onto the sides or upper rock surfaces. tracked to study magnitude and variation of individual velocity. Conversely, very few large individuals migrated onto the lower Observations of P. lividus were made in situ at Lough Hyne, from surfaces of rocks. AugusttoNovember1998.Individualswerestudiedonthenorthern Preliminary studies of P. lividus at Lough Hyne have shore (North Wall), where the population reaches maximum suggested they may undergo a pattern of diurnal migration density (Barnes et al., 1999). In this location, P. lividus typically (Muntz et al., 1965; Ebling et al., 1966; Kitching & Thain, occur in 0.2^2 m depth on rock/cobble shallow sloping scree, thus 1983). The results from this study conducted during autumn, making observation possible using snorkelling techniques at most showed that there was signi¢cant variation in the numbers of times of the tide.The number of P. lividus individuals on the upper, individuals found on di¡erent rock surfaces with time of day. side and undersurfaces of rocks located within randomly placed The highest density of P. lividus recorded between 1200^1600 1m2 quadrats was recorded andtheir test diameters were measured were found on the upper surface of rocks; between 1400^1800 insituusingVerniercalipers.The proportionofeach size-class found P. lividus mainly occurred on rock sides, whereas during the onthe di¡erent rock surfaces at di¡erent times of the day was calcu- period between midnight and 0400, they were predominantly lated and compared with the ¢ndings of Ebling et al. (1966) and located in rock interstices. This supported the qualitative ¢nd- Barnes et al. (1999). Study periods involved data collection every ings of Muntz et al. (1965), Ebling et al. (1966) and Kitching & 2 h over 24 h periods, using underwater torches to aid data Thain (1983) whose data were recorded in a period when the collectionduring periodsof low visibility. density of the population was at least an order of magnitude The velocity of randomly chosen focal P. lividus was also greater and the algal density and diversity were correspondingly monitored within the 1m2 quadrats (during daylight sampling di¡erent (Barnes et al., 1999). In addition, although P. lividus periods only) by measuring the distance travelled per unit time. lives for up to nine years (Crapp & Willis, 1975) only 3 year- The distance moved by focal individuals was measured and classes (2 , 3 and 4 age groups) were found to take part in recorded every minute for periods of between one and ¢ve diurnal migrations in the present study. Barnes et al. (1999) hours. Focal individuals were identi¢ed by marking them with showed that these year groups represented approximately 41, 28 coloured tape on their dorsal spines. and 8% of the population, respectively.

Journal of the Marine Biological Association of the United Kingdom (2000)

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Figure 2. Proportion (%) Paracentrotus lividus individuals on under surfaces of rocks with time (*). Also shown; proportion of individuals migrating with time (*). Data are illustrated as mean with standard error. Arrows indicate crepuscular periods, dawn (left) and dusk (right).

tion is size/age speci¢c and occurs at particular times of day. Figure 1. Number of Paracentrotus lividus individuals on top and side surfaces of rocks at North Wall, Lough Hyne, Co. Cork. Data are The migrations at Lough Hyne are the inverse of those in the illustrated as mean with standard error. `nearby' Mediterranean Sea but di¡erences in potential predators or predation pressure are not evident. The fact that algal Muntz et al. (1965), Ebling et al. (1966) and Kitching & Thain resources and harmful irradiation are not evenly distributed (1983) suggested that the movement of P. lividus was the result of with depth may mean that it is advantageous for those indivi- circadian patterns in overall predator activity but this currently duals that are able, to migrate diurnally. lacks supporting data. The main cause of predation of P. lividus at This work was carried out under permit numbers R28/98 Lough Hyne is unknown but ballan wrasse (Labrus bergylta), crabs and R3/99 for which we are grateful to the O¤ce of Public (e.g. Necora puber), and sea-stars (e.g. Marthasterias glacialis), may Works, Wildlife and Parks Service and in particular Declan be in£uential (personal observation). If diurnal migration does O'Donnell. We would also like to thank Mr John Bohane for his serve to separate prey from potential predators (Ebling et al., continued support of the Lough Hyne Research Group. 1966; Kitching, 1987; Nelson & Vance,1979) then three paradoxes are established: (1) most P. lividus year groups do not migrate REFERENCES (45% of total population did not); (2) migration to the tops of Barnes, D.K.A., Steele, S., Maguire, D. & Turner, J., 1999. rocks during the day by the 2 to 4 age groups makes indivi- Population dynamics of the urchin Paracentrotus lividus at duals more visible to birds which have been suggested as potential Lough Hyne, Ireland. In Proceedings of the Fifth European Echinodermata Conference, Milano, Italy. predators (Ebling at al., 1966). In the same way, by remaining Crapp, G.B. & Willis, M.E., 1975. Age determination in the sea underneath rocks diurnally, smaller individuals (year groups 0 urchin Paracentrotus lividus (Lamarck) with notes on the repro- and 1 ) may be more susceptible to predation since crabs and ductive cycle. Journal of Experimental Marine Biology and Ecology, sea-stars also occur in this microhabitat; (3) M. glacialis, the sea- 20, 157^178. star that Ebling et al. (1966) and Kitching (1987) believed to be Dance, C., 1987. Patterns of activity of the sea urchin an important nocturnal hunter and P. lividus predator has not Paracentrotus lividus in the Bay of Port-Cros (Var, France, been established to be either (Frid,1992). Diurnal migration to the Mediterranean). Marine Ecology, 8, 131^142. upper surfaces of rocks may therefore not necessarily be a Ebling, F.J., Hawkins, A.D., Kitching, J.A., Muntz, L. & Pratt, response to predation pressure but instead may be driven by V.M., 1966. The ecology of Lough Hyne. XVI. Predation and diurnal migration in the Paracentrotus community. Journal of factors such as di¡erential food (algal) availability. Animal Ecology, 35, 559^566. In the Mediterranean P. lividus are nocturnal (Dance, 1987) Frid, C.L.J., 1992. Foraging behaviour of the star¢sh although they share some of the same potential predators as the Marthasterias glacialis in Lough Ine, Co. Cork. Marine population at Lough Hyne. In the Mediterranean, diurnally Behaviour and Physiology, 19, 227^239. hunting ¢sh are believed to be the most important predators of Kitching, J.A., 1987. Ecological studies at Lough Hyne. Advances P. lividus (Dance, 1987). It may therefore be adaptive for Medi- in Ecological Research, 7, 115^186. terranean P. lividus to forage nocturnally when predation pres- Kitching, J.A. & Ebling, F.J., 1961. The ecology of Lough Hyne. sure is least intense. This assumes predation is the driving force X. The control of algae by Paracentrotus lividus (Echinoidea). Journal of Animal Ecology, 30, 373^383. behind migrations and that ¢sh predation in Lough Hyne is Kitching, J.A. & Thain, V.M., 1983. The ecological impact of relatively unimportant. the sea urchin Paracentrotus lividus in Lough Ine, Ireland. Data analysis enabled assessment of individual speed and PhilosophicalTransactions of the Royal Society B, 300, 513^552. directionality of P. lividus movement at di¡erent times of day. Muntz, L., Ebling, F.J. & Kitching, J.A., 1965. The ecology of Between 0700^0800 of those P. lividus observed moving, the prin- Lough Hyne. XIV. Predatory activity of large crabs. Journal of cipal direction of movement was from the sides to the upper surface Animal Ecology, 34, 315^329. of rocks. From 1600 onwards, P. lividus were recorded moving Nelson, B.V. & Vance, R.R., 1979. Diel foraging patterns of the towards the undersurface of rocks. Thus providing the ¢rst unam- sea urchin Centrostephanus coronatus as a predator avoidance strategy. Marine Biology, 51, 251^258. biguous, quantitative evidence for diurnal migration at Lough Renouf, L.P.W.,1931. Preliminary work of a new biological station Hyne. (Lough Ine, Co. Cork, I.F.S.). Journal of Ecology, XIX, 410^438. Clearly diurnal migration is an important component in P. lividus behaviour at Lough Hyne. It is also clear that migra- Submitted 3 June 1999. Accepted 22 July 1999.

Journal of the Marine Biological Association of the United Kingdom (2000)