Barbara Niehoff, Nicole Hildebrandt, Vanessa Köhler
Using the optical plankton recorder LOKI (Lightframe On-sight Key species
Investigations) to elucidate high-resolution vertical distribution patterns of Arctic key zooplankton species in Fram Stait
BREMERHAVEN Am Handelshafen 12 27570 Bremerhaven Telefon 0471 4831-0 www.awi.de
Rationale: Optical measurements are increasingly important in zooplankton studies as they allow for covering wide spatial ranges and study the distribution of the dominant taxa in greater detail than classical net tows. In the Fram Strait, hydrographical conditions change quickly due the prevailing current system. Thus, zooplankton depth distribution may change on short spatial scales.
Methods: We studied the community composition, abundance and depth distribution of the mesozooplankton species in the Fram Strait.
Two hauls from 1000 m depth to the surface were taken with LOKI (Lightframe on-sight key species investigations), an optical plankton recorder, during a RV Polarstern cruise in July/August 2015 (PS93.2) to the “AWI-Hausgarten”. We sampled at the most northern (N5;
79°56’35”N, 3°11’45”E) and at the most southern station (S3;
78°35’97”N, 5°4”11”E). All organisms were measured and identified in the pictures taken by LOKI.
LOKI (Lightframe On-sight Key species Investigations)
• Vertical tows down to 1000 m depth (Fig. 1A)
• 27 high resolution pictures sec-1(Fig. 1B,C)
• One cm mesh on top that no large zooplankton clog the cuvette
• Equipped with net of 150 µm mesh size
• Depth, Sal, T, O2, and fluorescence recorded simultaneously
Fig. 1C: Examples of non-copepod zooplankton; (a) Aglantha digitale, (b) Siphonophora, (c) Radiolaria, (d) Chaetognatha, (e) Ctenophora, (f) Euphausiacea, (g) Amphipoda, (h) Polychaeta, (i) Ostracoda
Fig. 1B: Examples of copepods; (a) Aetideopsis sp., (b) Microcalanus sp., (c) nauplius, (d) Calanus spp. Stage CV, (e) Oithona sp., (f) Oncaea sp. female with egg sacks, (g) Gaetanus sp. female, (h) Calanus spp. Stage CIV, (i) Paraeuchaeta sp. female with egg sack, (j) Metridia sp.
female, (k) Heterorhabdus sp.
Fig. 1A: LOKI, deployed in the Fram Strait
A
C B
Results
245 383 258 175 337 327 338 253 490 282 436 329
458 526 315 254 409 591 570 414 580 585 590 494
C O PE PO D S NO N- C O PE PO D S A M PH I PO D A C A LA NUS C H A E T O G NA T H A C NI D A R I AE UPH A USI A C E AM E T R I D I A M I C R O C A LA NU SO NC A E A O ST R A C O D AR A D I O LA R I A
DEPTH(m)
Station 48 Station 60
Fig. 4
Mean-weighted depths
Copepod community composition
Total zooplankton distribution (S3) Total zooplankton distribution (N5)
S3 N5
Total mesozooplankton abundance 2x higher at N5 than at S3 (Fig. 2)
Copepod species composition similar at S3 and N5 (Fig. 3) Mean weighted depth ~150 m deeper at N5 (Fig. 4, 5) Vertical distribution and hydrography
→ related to deeper North Atlantic current and deeper Return Atlantic Intermediate Water, dominant species reside at greater depth at N5
N5 S3
Depth[m]Depth[m]
N5
S3 S3 N5
Depth distribution of Oncaeaspp. Depth distribution of Calanusspp.
Fig. 2
Fig. 3
Fig. 5
