P.S.Z.N. I: Marine Ecology, 13 (1): 63-68 (1992) 8 1992 Paul Parey Scientific Publishers, Berlin and Hamburg

Accepted: January 7, 1991

ISSN 0173-9565

Respiratory Rate and Assessment of Secondary Production in the Holoth uroid Holofhuria tubulosa (Echinodermafa) from Mediterranean Seagrass Beds PIERRE COULON', MICHEL JANGOUX~,~ & PATRICK BULTEEL'

Laboratoire de Biologie marine (CP 160), Universitk Libre de Bruxelles, 50 av. F. D. Roosevelt, B-1050 Bruxelles, Belgium.

* Laboratoire de Biologie marine, Universit6 de Mons-Hainaut, 19 av. Maistriau, B-7000 Mons, Belgium.

With 1 figure and 3 tables

Key words: Holothuroids, respiratory rate, secondary production, seagrass beds.

Abstract. Respiration in Holothuriu tubulosa was investigated in individuals from the Posidonia oceunica meadow off Lacco Ameno (Ischia Island, Italy). Respiratory rates increase with increasing body weight and increasing sea water temperature. Oxygen consumption of an average individual (7g dw body wall) ranges from 0.409 (14°C) to 1.300 (26°C) mg 02.h-l . Data on population density, mean size of individuals, and annual sea water temperature variations allow an assessment of holothuroid production. Values of 45.65 and 13.75 kJ . m-*. y-1 were calculated for shallow (3 to 10m) and deep (25 to 33 m) areas of the Posidoniu meadow, respectively. Holothuroid production shows a bathymetric pattern similar to primary production of the Posidoniu-epiphytes complex and the production of Posidonia litter.

Problem

The aspidochirote holothuroid Holothuria tubulosa inhabits Mediterranean seagrass beds (Posidonia oceanica), where it often occurs in high densities (GUSTATO et al., 1982). H. tubulosa is a continuous deposit-feeder contributing to large-scale reworking of sediments within the Posidonia ecosystem (COULON & JANGOUX, 1991). Almost no studies have examined the ecological impact of H.tubulosa populations, even though this species significantly contributes to the overall energy budget of the ecosystem. The aim of the present paper is to assess, from measurements of respiratory rates', the production of a H. tubulosa population from a particular Posidonia meadow in the Gulf of Naples.

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66 COULON, JANGOUX & BULTEEL

2. Assessment of holothuroid production per square meter

Holothuroid production was tentatively assessed by using the empirical relation- ship between production (including reproductive output) and respiration estab- lished by Mc NEILL & LAWTON (1970) for poikilotherm animals. Production is considered as a power function of respiration in accordance with the formula log P = 0.8233 log R - 0.1273, where P denotes the production (kJ 9 m-2 y-l) and R the respiration (kJ * m-2 - y-*).

Population density in the Lacco Ameno meadow ranges from 3.7 to 0.34 individuals . m-z in the shallow (3 to 10 m) and deep (25 to 33 m) areas of the meadow, respectively (BULTEEL & COULON, unpubl. data). Mean individual size changes with depth, the smallest individuals occurring in shallow (mean weight: 2g dw body wall), the largest in the deeper areas (mean weight: 12g dw body wall) (BULTEEL etal., 1991). Annual sea water temperature differed according to depth: from 14 to 26°C and from 14 to 18°C in the shallow and deep areas, respectively. Consequently, production estimations were conducted assuming that water temparature remains constant over a 6-month period at each sampling station.

The above information enables calculation - for each sampling station -of the respiration of an average individual, the respiration of the holothuroid popula- tion per square meter, and holothuroid production per square meter (see Table 3). The results indicate that production is higher in the shallow than in the deeper areas of the meadow (45.65 versus 13.75 kJ . m-2. y-1).

Table 3. Calculation of Holothuria tubulosa respiration and production (for explanation see text).

depth respiration of an respiration of the production of the average individual (kJ . Y - 9

holothuroid population holothuroid population (kJ . y-l . mZ) (kJ . y-' . m-z)

6m 33 m

39.25 101.36

147.98 34.46

45.65 13.75

Discussion

The values obtained for holothuroid (Holothuria tubulosa) secondary produc- tion indicate a higher productivity in the shallow areas of the Lacco Ameno meadow. Production in the deeper meadow corresponds to ca. 30 % of that of the shallow meadow. These results agree with observations of COULON &JAN- GOUX (1991) that the turn-over of ingested sediment by the H.tubufosa popula- tion is from 50 to 100% higher in the shallow meadow. Interestingly, these results also fit the bathymetric pattern of both the primary production of the Posidonia-epiphytes complex (Om, 1980) and the litter biomass per square meter (PERGENT-MARTINI etal., 1991), both of which are much higher in the shallow part of the Lacco Ameno meadow. This suggests there is a similar bathymetric pattern in food availability for deposit-feeding organisms such as H. tubulosa.

Respiratory rate and production in Holothuria tubulosa 67

It should be pointed out, however, that H.tubulosa from the deeper meadow areas are much larger than those from shallow depths, and that only the former have significant reproductive output (BULTEEL etal., 1991). The observed size differences are interpreted to indicate that the environmental factors influencing holothuroid growth are less constraining at deeper depths. There, holothuroids live in calmer water and inhabit sparser meadows where detrital food, although less abundant, is more readily accessible.

These data provide a preliminary estimation of H . tubulosa secondary produc- tion. Bioenergetic data on this common and abundant species is lacking and classical approaches in population dynamics have failed in estimating holothuroid growth. The present data can therefore serve as a preliminary basis for more detailed studies that will consider aspects of the energy budget of this species.

Summary

An average Holothuria tubulosa individual (7g dw body wall) consumes from 0.409 (14°C) to 1.300 (26°C) mg O2.h-’. Calculated values for holothuroid production according to depth in the Posidonia meadow of Lacco Ameno are 45.65 kJ m-2. y-l (6 to 10m depth) and 13.75 kJ . m-z. y-l (30 to 35 m depth).

Acknowledgements

We thank Dr. L. MAZZELLA for providing facilities at the Laboratorio di Ecologia del Benthos (Stazione Zoologica di Napoli). This research was supported by the European Community Commis- sion (Environment Programme; ref. EV4V-0139-B) and by the “Service de la Programmation de la Politique Scientifique”, Belgium (ref. ENV/3 87-91). Contribution of the “Centre Interuniversitaire de Biologie Marine” (CIBIM).

References

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