Distribution, maturity and population structure of Meganyctiphanes norvegica and Thysanoessa inermis around Iceland in spring.

Teresa Silva,Olafur S Astthorsson,Astthor Gislason,Gudrún Marteinsdóttir,Erik V Thuesen

doi:10.1371/journal.pone.0187360

Teresa Silva, Olafur S Astthorsson + Show 3 more

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https://doi.org/10.1371/journal.pone.0187360

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Abstract

This study aims to explain the distribution, maturity and population structure of Meganyctiphanes norvegica and Thysanoessa inermis in springtime in relation to main hydrographic regions around Iceland: Atlantic in the southwest, Atlantic-Arctic mixture in the north and Arctic in the east. Krill were collected 14–29 May 2013 using a macrozooplankton trawl. Biomass of both species combined was significantly higher in the southwest than in north and east. M. norvegica clearly dominated in Atlantic waters, whereas T. inermis was more evenly distributed around the island, while the highest values were also observed in the southwest for this species. Simple linear regressions showed that the abundance of M. norvegica was positively related to temperature, salinity and phytoplankton concentration, while the abundance of T. inermis was negatively related to bathymetry. Multiple linear regression analyses did not add to this information of a positive relationship between abundance and temperature for M. norvegica, while T. inermis was shown to be negatively related to both temperature and bathymetry. During the latter half of May, the main spawning of both species was confined to the regions off the southwest coast. Sex ratio (males/females) of M. norvegica was higher in the southwest than in the north and east, whereas T. inermis showed a similar sex ratio all around the island. In all regions, M. norvegica appears to have a lifespan of 2 years while T. inermis of 1 year in the southwest and possibly 2 years in north and east.

Highlights

As in most other areas of the North Atlantic, krill play an important role in the Icelandic marine food web, as conveyors of energy from lower to higher trophic levels including several commercially exploited fish species, seabirds and marine mammals [1,2,3,4,5,6,7]
M. norvegica is distributed from the Mediterranean Sea northwards to the subarctic waters in the Norwegian and Greenland Seas [16], whereas T. inermis is mainly found in coastal and shelf break waters of the northern part of the North Atlantic and the Pacific [9, 16].The first systematic study of krill in Icelandic waters is that of Paulsen [18], who recorded occurrence and distribution
In cases where the telson or eyes were damaged, only the carapace length (CL) was measured. For these individuals (4280 individuals of a total of 7552 measured), the Total length (TL) was estimated using equations obtained by linear regressions between TL and CL for intact individuals (M. norvegica: TL = 3.100CL+7.166, r2 = 0.86, n = 694, P

Summary

Introduction

As in most other areas of the North Atlantic, krill play an important role in the Icelandic marine food web, as conveyors of energy from lower to higher trophic levels including several commercially exploited fish species, seabirds and marine mammals [1,2,3,4,5,6,7]. Meganyctiphanes norvegica and Thysanoessa inermis around Iceland ecosystem, there is limited information on the large-scale distribution of krill in Icelandic waters. In the North Atlantic, Meganyctiphanes norvegica and Thysanoessa inermis are important krill species in terms of abundance and biomass [1,9,10,11,12,13,14,15]. Both species usually inhabit the upper 400 m of the water column [12,13,16,17]. The other earlier studies on krill were restricted to specific geographic locations in the north [10,11] and southwest of Iceland [1]

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