Growth in Culture Mytilus Galloprovincialis Lmk

VERTIMAR-2005 Symposium on Marine Accidental Oil Spills

Growth performance of mussel recruits on raft culture after Prestige oil spill

Laura G. PETEIRO, José MF BABARRO, Uxío LABARTA and María José FERNÁNDEZ REIRIZ

Instituto de Investigaciones Marinas CSIC, 36208 Vigo Spain Phone: +34986 231930 Fax: +34986 292762 Email: [email protected]

ABSTRACT Growth of mussel seed (Mytilus galloprovincialis) from four origins along the Galician coastline with different degree of exposure to the Prestige oil spill was studied. Samples were collected monthly for a year, covering both phases of the culture, from seed to thinning-out (mar-03/aug-03) and from thinning-out to harvest (aug-03/febr-04). During the first phase of the culture, mussels from Pindo showed lower growth rates for total and tissue dry weight as compared to mussel populations less affected by the spill (p<0.05). During the second phase of the culture, from thinning out to harvest, mussels from Pindo and Bueu showed lower growth rate values for both total and tissue dry weight as compared to the rest of populations (p<0.05). At harvest, mean shell length values of mussels from Pindo were significantly lower (63.5 mm; P<0.001) than those observed for the rest of populations (66.3-67.3 mm) as well as condition index values (CI), for the former population (Pindo) towards the end of the culture (p<0.005). Growth values may be considered a good stress index of hydrocarbons exposure during Prestige oil spill, highlighting a significant reduction of growth in the mussel seed population from the most affected area (Pindo).

1. INTRODUCTION

Despite that fact that oil from Prestige spill, in November 2002, didn’t affect the inner part of the estuaries significantly, where the commercial raft culture of mussels is carried out in Galicia, it had a strong effect on an extensive area where mussel seed is gathered for its culture. Growth integrates a number of internal biological processes of the animal and could be used as a good stress index (Salazar et al., 1995; Dame, 1996). The latter authors have reported that both natural and pollution stresses are related to a reduction of growth rates in length and weight, although both corporal parameters may have different regulations. Similarly, CI can also be identified with episodes of stress, associated with losses in weight of soft tissues which in turn are related to the mobilization of energetic reserves (Dame, 1996). The aim of this survey was to characterize growth patterns of the first mussel’s post- Prestige generation under raft culture in the Ría de Sada, and to identify differences related to the origin of mussel seed and their degree of exposure to the oil.

2. RESULTS AND DISCUSSION

Growth patterns of all mussel populations under study varied with both phase of culture and origin of mussel seed. All mussel populations showed higher values in shell growth rate during the seed-thinning out period (>6 mm/m) as compared to the second phase of the culture (2-3 mm/m; fig.1). Nevertheless, growth rate values for total and tissue dry weights remained rather similar all over the culture (0.5-1 g total dry weight/month and 0.06-0.14 g tissue dry weight/month; fig. 1). During seed-thinning out phase, mussels from Pindo showed lower growth rates in total and tissue dry weight as compared to mussels from the other populations (p<0.05; fig.1) whereas during the thinning out-harvest phase, mussels from Pindo and Bueu showed lower values of growth rate in both weight values than the other populations (p<0.05; fig.1). Condition index average values were significantly lower during the first phase of the culture as compared to the second phase, for all populations under study (p<0.05; fig.2). During the first phase from seed to thinning-out, mussels from Redes showed significantly higher CI values than those from Pindo (p<0.05; fig.2). After thinning-out procedure, all mussel populations showed an abrupt increase of CI, concomitant with the phytoplankton bloom recorded in September in Ría de Sada (fig.2). At that moment mussels from Pindo presented similar values than the rest of mussel populations, being reported a decrease in the following months for CI of all origins without significant differences among them until January 2004, when mussels from Pindo showed lower CI values than the rest of populations (p<0.001; fig.2). The latter pattern VERTIMAR-2005 Symposium on Marine Accidental Oil Spills was also maintained in February between Pindo and both Bueu and Miranda mussels (p<0.005 for both cases; fig.2). In general, mussels from Pindo belonged to an area highly affected by the oil spill and it could be observed lower growth rate values in weight (P<0.05), lower condition index at the end of the culture (P<0.005) as well as lower adjusted length at harvest (P<0.001) for that mussel population. In agreement with our results, lower growth rates of Mytilus edulis have been reported in different studies when individuals are exposed to many pollutant agents (Salazar et al, 1991; Strömgren, 1982) and also specifically to different forms of hydrocarbons (Strömgren et al, 1986). A reduction of growth as a sub-lethal response to hydrocarbons exposure can be considered in our case a good stress index that pointed out mussel seed from Pindo as the most affected population by the spill.

Seed-Thinning out Thinning out-Harvest

1 0 1 0 8 < 2 , 4 < 2 8 6 6 4 4 * * 2 2 0 0 R e d e s 1 M i r a n d a 2 P i n d o 3 B u e u 4 R e d e s 1 M i r a n d a 2 P i n d o 3 B u e u 4

0 , 2 > 1 , 2 0 , 2 > 3 , 4 > 3 0 , 1 5 < 1 , 2 , 4 0 , 1 5 0 , 1 0 , 1 * * 0 , 0 5 * 0 , 0 5 * 0 0 R e d e s 1 M i r a n d a 2 P i n d o 3 B u e u 4 R e d e s 1 M i r a n d a 2 P i n d o 3 B u e u 4

> 2 1 , 2 > 1 , 3 , 4 1 , 2 1 > 3 , 4 1 0 , 8 < 1 , 4 0 , 8 0 , 6 0 , 6 * * 0 , 4 0 , 4 * * 0 , 2 0 , 2 0 0 R e d e s 1 M i r a n d a 2 P i n d o 3 B u e u 4 R e d e s 1 M i r a n d a 2 P i n d o 3 B u e u 4

Fig.1 Growth rate values in shell length, total and tissue dry weight for all mussel populations during the two phases of the culture.* p<0.05 Bueu 35 9 Redes 30 8 Miranda

l Pindo

6 g Chl a μ I 20 5 (

10 C 2 5 1 0 0

h e t r r c n s e e ry r u u b b a a j g o m u m u t e r a c c b o e fe d

Fig.2 Condition index values for all mussel populations throughout the raft culture (mar-03/feb-04) and variation of average values of chlorophyll-a (Chl-a μg/l). VERTIMAR-2005 Symposium on Marine Accidental Oil Spills

REFERENCES

Dame, R.F. (1996) Bivalves as components of ecosystem health. In The ecology of marine bivalves. An ecosystem approach (ed. R.F.Dame), pp 213-226.CRC Marine Science Series, CRC Press, Inc. Salazar, M.H. & Salazar, S. M. (1995) In-situ bioassays using transplanted mussels: I. Estimating chemical exposure and bioeffects with bioaccumulation and growth. In Environmental toxicology and risk assessment- Third volume, (eds. J. S. Hughes, G. R. Biddinger & E. Mones), pp 216-241. American Society for Testing and Materials, Philadelphia. Salazar, M.H. & Salazar, S. M. (1991) Assessing site-specific effects of TBT Contamination with mussel growth rates. Marine Environmental Research, 32: 131-150 Strömgren, T. (1982) Effects of heavy metals (Zn, Hg, Cu, Cd, Pb, Ni) on the length growth of Mytilus edulis. Marine Biology, 72: 69-72 Strömgren, T., Nielsen, M.V. & Ueland, K. (1986) Short-term effect of microencapsulated hydrocarbons on shell growth of Mytilus edulis. Marine Biology, 91: 33-39