Interannual phenological variability in two North-East Atlantic populations of Calanus finmarchicus

ABSTRACT

Phenological variations of the marine copepod Calanus finmarchicus were studied in Svalbard and northern Iceland, where samples were collected in summer and spring, respectively, over two decades. Four phenological indices, developed for copepodite stage-structured data, were used: the proportion of CV to total abundance (CVT), the population development index (PDI), the average weighted stage (AWS), and the average age in days (AAD). The variation of these indices was compared within and between locations to evaluate their suitability for the analysis of phenological effects. For both populations, phenology was related to local temperature and spring bloom dynamics, influenced by Atlantic water inflow. Large-scale climate was related to phenological variation only in the Svalbard population. C. finmarchicus phenology advanced under warmer conditions in both locations. We conclude that vertical phenological indices, i.e. based on interannual changes in copepodite stage structure, are useful to investigate zooplankton phenology, especially when data series covering the whole life cycle are unavailable. We suggest that AWS and AAD can be applied irrespective of sampling time, while PDI and CVT should be applied for early and late sampling seasons, respectively. When multiple phenological indices are needed, AAD in combination with either CVT or PDI should be preferred.

SUBJECT EDITOR:

• Audrey Geffen

KEYWORDS:

• Calanus spp
• phenology
• vertical life table approach

Acknowledgements

We are thankful to M. Daase (UiT The Arctic University of Norway) and A. Wold (Norwegian Polar Institute), S. Sigurgeirsdottir, H. Petursdottir (Marine and Freshwater Research Institute, Iceland) and S. Kwasniewski (Institute of Oceanology, Poland) for their help with data collection and analysis. The study was done with a support from the ARCTOS Research network.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by ConocoPhillips: [Grant Number NSBU-107021]; Lundin Norway [Grant Number C000353].