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D. M. MARTYNOVA AND A. V. GORDEEVA

j

LIGHT-DEPENDENT BEHAVIOR OF ABUNDANT ZOOPLANKTON SPECIES

Species and their biogeographical characteristic

Season

Feeding preferences

Developmental stage

Water layer

Light response

Significance of light response, P

Significance of starvation acclimation to light response intensification, P

Acartia spp.,

August

Omnivore

CI-CVI

Photic

þ

**

No data

boreal Pseudpcalanus

March

Predominantly

CIII-CV

2/2

þ

**

*

minutus, arctic

herbivore 2/2 2/2 ?

CIII-CV CIV-CVI CI-CVI

Aphotic 2/2 2/2

þ þ 0

** ** **

* No data 0.54

Oncaea borealis, arctic

August March

**P , 0.01; *P , 0.05. Np, naupliar stages; SI-CV, young and pre-mature copepodites; CVI, mature copepodites. Phototaxis (light response) pattern: þ, positive; 2, negative; 0, indifferent.

0.38

0.52

0.34

0.23

**

*

0.62

0.45

** *

Darkness Light

able II: Light-induced (U , 280 nm) behavioral responses of investigated zooplankton species inhabiting the White Sea

Significance of duration of light acclimation to light response intensification, P

light, during the same season and the effects of all the acclimation factors were not significant (Table II).

DISCUSSION

Almost all the studied species, such as Acartia spp.,

  • C.

    hamatus, E. nordmanni, C. glacialis, M. longa, T. longicornis,

  • P.

    minutus, O. similis, and Polychaeta larvae, were light-

sensitive. However, they showed different responses to light. For example, some species were characterized by positive response to RY light during the whole life cycle, whereas others changed their behavior depending on the season and developmental stage. Light did not affect the behavior of O. borealis. We hypothesize that the species inhabiting the upper water layers or feeding close to the surface should depend on light more than deep-dwelling or eurybiont forms. Generall , marine copepods can be divided into several trophic groups inhabiting specific depth horizons. For example, predo- minantly herbivorous species tend to occupy the upper (photic) water layer, detritus consumers are linked with bottom layers, whereas predatory and omnivorous crus- taceans have an intermediate position (Vinogradov, 1968). However, such division is not observed clearly in the relatively shallow White Sea, (average depth 60 m,

maximum depth

species

exhibit

up to 340 seasonal

m). Nevertheless, certain

ontogenetic

migrations

(Prygunkova,

1974).

The

White

Sea

copepods

may

be

clearly divided into several feeding patterns. All stages

groups depending on their of C. glacialis and P. minutus,

and younger copepodite stages of the

Centropagpidaf (T.

longicornis, C. hamatus,

are

herbivorous

or

predominantly

superfamily Acartia spp.) herbivorous

(Martynova, 2004; Martynova et al., unpublished results) and depend on phytoplankton availability (Martynova et al., submitted for publication). Omnivorous species are represented by younger stages of M. longa and elder copepodite stages of Centropagoids, whereas predation is characteristic of elder M. longa copepodites (Perueva, 1982; Martynova, 2004). Trophic characteristics of O. borealis and O. similis are still unclear; however, there is evidence that Onceidae are suctorial predators, whereas cyclopoids (O. similis) feed on faecal pellets of other copepods (Nielsen and Sabatini, 1996). In addition to grouping based on feeding patterns, all studied species may be divided into migrating and non- migrating. We hypothesize that migrating forms may have higher light sensitivity than non-migrating. The diurnal patterns of distribution of different copepod species in the White Sea are different. For example, Bogorov (1974) considered migrating females of C. gla- cialis and P. minutus, younger copepodites of M. longa and older copepodites of O. borealis. Kosobokova (1989) also distinguished the White Sea M. longa, O. borealis and C. glacialis as species characterized by pronounced diurnal migrations. Beare and McKenzie (Beare and McKenzie, 1999) documented diel vertical migration in a related species Calanus finmarchicus. Diurnal vertical migrations are characteristic of T. longicornis, M. longa and P. minutus (Kutcheva, personal communication). All the above-mentioned species tend to occupy water layers with specific illumination levels, rising into upper layers during the dark period and descending deeper during the day. At the same time, in summer (the end of July) Acartia is characterized by a bimodal distribution

pattern, and animals of water surface (0–3 m)

all age groups migrate to the twice, first, around midnight

451

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