Micronecton analysis from the insular shelf of the Kerguelen Islands the amphipod gaudichaudii's case

0 ^Af Oceanographic Laboratory of Villefranche, UMR7093 University Pierre and Marie Curie (UPMC) upmc Supervisor: J-Ph. Labat, e-mail:[email protected] Carmen David, e-mail:[email protected] >aai SQRBQNNI

Introduction

The hyperiid amphipod Themisto gaudichaudiiis a representative of the subantarctic pelagic communities, having a circumpolar distribution limited at north by the Subtropical Convergence and at south by the Antarctic Polar Front. This study’s objective was to describe the distribution of T. ga in the Kerguelen Islands Waters (Fig.l), Southern Indian Ocean, based on the analysis of the speciesabundance and size spectra in the SKALP stations. Our results were compared with the data of the Birds Zooplankton Interactions Program (IOZ), representingT.gaudichaudii's the population of the Morbihan Gulf (Kerguelen Islands) and the individuals from the stomachs of the island's birds for the same period of the year.

Fig.l Kerguelen Islands - Latitude 49°S Longitude 69°E Large Marine Ecosystems - source: NOAA Materials and Methods Sampling technique (SKIF SKALP cruise, February 1987) ■ Bongo net (o 64 cm; 500 pm mesh)(Fig.2) « ■ 0 - 200m depth diagonal haul \ ■ fixed with formaldehyde Sampling treatment (Fig.3) rinsed with freshwater

divided with Motoda box Fig.3 Image analysis platform sub samples -200 individuals sort and identification Data analysis counting ■ Correspondence Analysis ■ abundances of juveniles/adults (ind.nr3)* morphometries Ltotai=L2 +L3+L4 (TL = total body length)(Fig.4) ■ size spectra presented as 1 mm classes* * georeferenced data as GIS maps (Fig.5 & 6)

Fig.2 Bongo net (source: kc-denmark.dk) Fig.4 T. gaudichaudii -body lengths measurements Results

65° E 66° E 67° E 68° E 69° E 70° E 71° E 72° E

115 Spatial distribution 47° S - 114 t e Correspondence Analysis C C 185' 113 ■ density decreases from coastal to open waters ■124 ■ Juveniles and medium size individuals well explained

.J 123 stations 48° S - ■ Adults larger than 20 mm poorly represented(Fig.7) ■ maximal density of 10 ind.nr3 in the south-west 111 122

131 coastal stations 49° S - 171 132 175 ■ minimal density of 0,07 ind.nr3 at the southern 161

50° S - Î63 151 stations(Fig.5) ' , 164 191 152 165 temperature (°C) 153 AFC IOZ - SKIF 51° S - Value 145jP*te M7Â> ¡ High : 8 154 Legend

— A size classes 65° E 66° E 67° E 68° E 69° E 70° E 71° E 72° E Low : 0 I__ 52° S - H SKALP stations 46° S - X26 H IOZ stations (Morbihan Gulf) 5 .4 5 -10.99 (ind.nr3) H birds gut content 2.43 - 5.44 Antarctic Polar F«®* 0.96 - 2.42 53° S - * juvenils CO — 0.42 - 0.95 X24AX23 a X22 47° S - 0.08 - 0.41 adults 182 ° ▲ X25 0147 sO 0s ap96m CN o Fig.5 Density distribution ofT. gaudichaudii in the SKALP stations (February 1987) 1^ CN - 48° S - CNÍ X28 . X21 X20

CN 175o 164 E ° „126 b 49° S - X19 „115 r ▲ Moibihan Gulf Size spectra analysis evidences three cohorts o bp96m r 111-181185 172 m ° X18 oozni 50° S - (Fig.6 & 7) : 171 oX4.1°4 1 é3 1bp96nBi 705 q f f A ' 161- a 1 4 319°I1 . QP r „ 4 0 1 02<1 T p tp sS n n O - 131 °<>0 X5* A Juveniles (TL<10 mm) dominate the SKALP 151 124 * xa 141122-1765C »>$47 stations Ïllifê0inio2 X12 >^“3 80602 51° S - 11102 2010^21102 82401 A First year individuals (TL 10-20 mm) associated 1 -3 -2 -1 0 Log (ïnd.rrr') with the Gulf of Morbihan stations (IOZ) 52° S - Juvenils Dim 1 (35.09%) 1st year individuals A Second year individuals (TL>20 mm) 2nd year individuals associated with few open waters SKALP stations Fig.7 Correspondence Analysis of the size classesT.gaudichaudii of in the IOZ i (Bocher et.al. 2001) and SKALP stations; size classes from the diet of are Fig.6 Size spectra distribution ofT. gaudichaudii in SKALP stations (February 1987) illustratively projected

Discussion

■ The pattern of spatial distribution is a steep gradient coast - open waters, the values corresponding to other zones at the same latitude. ■ A dominance of juvenilesin the SKALP stations at the end of southern summer is in contrast with the IOZ population dynamics studied in the area. ■ The use of differentsampling technique: sampling at the SKALP stations used a Bongo net (500 pm) which is adapted to smaller size individuals; the sampling in the Morbihan Gulf (IOZ) used a bigger mesh size net, the Omori net (1 mm), therefore the results showed the dominance of the medium size individuals. ■ The absence of larger individuals from the costal stations suggestsmigration a of the adults to the open ocean waters after their first year of life. ■ The above assumptions are supported by the gut contents of the seabirds living on the islands which feed mainly on

Main bibliographic sources: • Bocher, P., Cherel, Y., Labat, J.-Ph., Mayzaud, P., Razouls, S., Jouventin, P., (2001). Amphipod-based foodThemisto web: gaudichaudii caught in nets and by seabirds in Kerguelen waters, Southern Indian Ocean. Mar. Ecol. Progr. Ser. 223: 261-276. • Labat, J.-Ph., Mayzaud, P., Sabini, S., 2005. Population dynamicsThemisto of gaudichaudii in Kerguelen Islands waters, Southern Indian Ocean. Polar Biol. 28 (10), 776-783 • Watts, J., Tarling, A., 2011. Population dynamics and productionThemisto of gaudichaudii (, ) at South Georgia, Antarctica.Deep-Sea Research //, doi: 10.1016/j.dsr2.2011.05.001.