Abstract
Resting eggs are important phases in the life strategy of many coastal and estuarine copepods. The egg mortality in the sediment layers where they are buried, as well as re-suspension from the sediment into the water column where eggs may hatch are factors that affect the success of this life strategy. Considering that fishing effort in some coastal areas is high and trawling leads to re-suspension of the bottom sediments, it is important to understand these effects on the biology of organisms that utilize sediment habitats in part of their life cycle. This study examined the re-suspension and the hatching success of copepod resting eggs in the wake of two different demersal fishing gear components (doors and discs) that are in contact with the seabed, in two areas off the coast of Scotland that are rarely worked by fishermen. Sediment cores were taken and analysed for resting eggs quantity and hatching performance and compared with samples taken in the water column right after re-suspension of sediment by the gear components. This study demonstrated for the first time that although eggs are re-suspended in the water column together with the sediment, providing them with the opportunity to hatch and recruit nauplii to the pelagic, egg viability was reduced by the passage of the gear components. This study also suggests that the viability is dependent on the gear component and accordingly potential effects must be considered for at this level.
Highlights
Resting eggs are produced by around 50 species of calanoid copepods [1,2] and are known to be produced to survive harsh environmental conditions [3]
This study examined the re-suspension and the hatching success of copepod resting eggs in the wake of two different demersal fishing gear components that are in contact with the seabed, in two areas off the coast of Scotland that are rarely worked by fishermen
Sediment cores were taken and analysed for resting eggs quantity and hatching performance and compared with samples taken in the water column right after re-suspension of sediment by the gear components
Summary
Resting eggs are produced by around 50 species of calanoid copepods [1,2] and are known to be produced to survive harsh environmental conditions [3]. There are: immediate survival strategies (quiescent eggs), short-term resting strategies (e.g. delayed hatching eggs), and long-term survival strategies (diapause) where eggs accumulate in the sediment as an egg bank, saving these genes for the future [6,7,8,9,10]. It is, difficult to separate eggs according to these categories when sampled from the sea bed because diapause and delayed hatching eggs for which hatching is maternally controlled may lie in the sediment under quiescence once their refractory period is over. Morphological approaches for the identification of eggs often produce contradictory results and must be used cautiously [11,12,13]
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