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Oceanic dispersion

Oceanic dispersion

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Oceanic dispersion

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  1. Life cycle of coral reef fish LECCHINI David 33 mm Larvae Colonization Oceanic dispersion 33 mm Settlement Juveniles Recruitment 60 mm 0.6 mm Eggs Reproduction Adults 150 mm

  2. Cycle de vie des poissons des récifs coralliens : La plupart des poissons de récifs coralliens possède un cycle de vie complexe avec une phase larvaire océanique et pélagique de quelques semaines à quelques mois, suivie d'une phase récifale relativement sédentaire pour les juvéniles et les adultes. Au moment de la reproduction, des produits génitaux ou des œufs sont expulsés vers l'océan où ils se développent en larves pélagiques. Celles-ci s'éloignent plus ou moins loin de leur aire natale grâce aux processus hydrodynamiques et/ou à une dispersion active. Après cette phase océanique dispersive, les larves retournent vers le récif (d’origine ou non) pour continuer leur développement en juvénile, puis en adulte. Ces larves colonisent le récif en traversant la crête récifale (phase de colonisation). Dans les heures ou les jours qui suivent cette colonisation, les larves se métamorphosent et deviennent des juvéniles adaptés au milieu récifal. Ces derniers sont exposés à un environnement complexe dans lequel ils doivent choisir leur habitat parmi les nombreux substrats potentiels, les compétiteurs tant intra- qu'inter-spécifiques et les prédateurs (phase d’installation). Cette phase est ensuite suivie par le recrutement qui correspond à l'apport de nouveaux individus dans la population d’adultes. Les diapositives suivantes vous présentent succinctement la phase de reproduction, la phase de dispersion océanique et celle de la colonisation. Le cours qui a lieu à Moorea et à Perpignan vous présentera aussi les autres phases du cycle biologique des poissons.

  3. Reproduction strategies of coral reef fish: The reproduction is the process by which animals or plants perpetuate their species giving birth to egg. So egg is the first life stage of fish. There are 4 reproduction strategies: Oviparousspecies

  4. Main notions of fish reproduction: Pelagic eggs: 60% of families small size eggs (e.g. 0.6 mm for Centropyge flavissimus) float Laid in huge quantity (several hundreds of thousands) exported by lagoon currents to the ocean Time of incubation less than 48 hours 1. Aperçu de la phase pélagique 2 categories of layers : 1 Non-migrant layers (e.g. Chaetodontidae, Pomacanthidae, Labridae). Species of small size who lay near their habitat due to high vulnerability to the predation of bigger species ; Leave for a moment their habitat and swim quickly to the surface to release their genital products. => avoid eggs predation by reef predators and increase dipersion facilities by surface lagoon currents. 2 Migrant layers (e.g. Serranidae, Lutjanidae, Acanthuridae). Move to lay near reef zones with outgoing ocean (pass or outer slope). => quick dispersion of genital products in ocean, so limiting reef predation.

  5. Main notions of fish reproduction: 1. Aperçu de la phase pélagique Demersal eggs 35% of families Big size eggs (until 4mm) Laid on the substrate due to higher density than the seawater density Laid in less quantity (from 50 to 1000) After eclosion, larvae leave parental habitat to go in the ocean Time of incubation between 3 and 7 days (larvaes better developped than those of pelagic eggs.) Protection increased from parents: e.g. Pomacentridae lay eggs sticking to coral branchs due to adhesive filaments, while Apogonidae eggs are protected in male’s mouth.

  6. Reproduction strategies & Oceanic dispersion: Reproduction Dispersion

  7. Reproduction strategies & Oceanic dispersion: . 1995-1997 . 19 campagnes ALIS . 134 chalutages dont 93 examinés

  8. Nb. larves 500 400 300 200 100 0 0 200 400 600 distance à l’île (Km) Reproduction strategies & Oceanic dispersion: 1. Aperçu de la phase pélagique

  9. Reproduction strategies & Oceanic dispersion: 1. Aperçu de la phase pélagique

  10. Examples of fish larvae during their oceanic dispersion: 1. Aperçu de la phase pélagique

  11. Colonization phase of coral reef fish: Reproduction Colonization Dispersion

  12. Colonization phase & capture tools: Crest net The net (5.0 m long) had a rectangular mouth (2.0 m wide, 1.5 m height) and was made of a 1 mm mesh, which was fine enough to retain the majority of incoming fish larvae before settlement. The mouth of the net was open to the offshore. Two hinged panels (2.0 m long, 1.5 m height) of 0.7 mm mesh enlarged the mouth area of the net to 4 m. The crest net was divided into two chambers: the mouth where larvae entered and the cod-end where the larvae are captured. The whole structure was fastened secured by steel cables which were bolted firmly onto the reef-rock to prevent the net from being swept away during times of strong current. The cod-end was attached to the net at dusk (6 pm) to minimize the accumulation of debris in the net during the day when few larvae are usually captured and was cleared of catches at dawn (6 am). "Lagoon" species / quantitative data / passive tool

  13. Colonization phase & capture tools: Light trap The light trap is cylindrical in shape and is divided into three parts, all of which are fitted together when it is in operation. It is 1.3m in height and 0.45m at its widest point. 1) The codend is made of 5mm thick PVC and is cylindrical in shape with two drainage slits cut on either side, which are covered with 1mm plastic mesh. This allows constant flow through of seawater during the entirety of the trap deployment. 2) The second component is a case where the light radiates horizontally through 8 inward arranged vertical transparent baffles, each 6 mm apart. The baffles were made of 3-mm thick clear perspex cut into rectangular sheets of approximately 10 cm in width and 40 cm in length. 3) The light case is a PVC cylinder 12 cm in diameter and 40 cm in total length. This component of the trap encases the battery and the light source. The light is emitted through a clear cylindrical perspex plastic (20 cm in length) attached to the bottom of the case. 1: Codend 2: Baffle’s for larvae to enter trap 3: Light case "All" species / no quantitative data / active tool / positive phototropism

  14. Colonization patterns: Month cycles 60 000 2 000 Small larvae 1 800 Large larvae 50 000 1 600 1 400 40 000 1 200 Abundance of large larvae Abundance of smalllarvae 30 000 1 000 800 20 000 600 400 10 000 200 0 0 avr-97 avr-98 avr-99 avr-96 oct-97 oct-98 oct-96 oct-99 juil-97 juil-98 févr-98 févr-99 févr-00 juil-96 juil-99 févr-96 févr-97 nov-97 nov-98 nov-96 nov-99 juin-96 déc-96 juin-97 juin-99 déc-99 déc-97 juin-98 déc-98 janv-99 janv-96 janv-98 janv-00 janv-97 mai-97 mai-98 mai-99 mai-96 août-97 sept-97 août-96 sept-96 août-98 sept-98 août-99 sept-99 mars-98 mars-99 mars-00 mars-96 mars-97 dates (months)

  15. Colonization patterns: Lunar cycles

  16. Colonization patterns: Season cycles Cold season Hot season

  17. Colonization patterns: 4 25 1400 SSTanom 150 Annual cycles & ENSO Rangiroa 1996/2000 Flux Cum. Sum. SSTanom Flux cum 3 20 -350 1200 -850 2 15 1000 -1350 Cum. Sum SST anomaly SST anomaly 1 800 10 -1850 600 0 5 -2350 400 -1 0 -2850 200 -3350 -2 -5 s s s s m m m m jan99 jan00 jan96 jan97 jan98 date 0 -3850 El Niño La Niña date

  18. Colonization patterns: Annual cycles & ENSO Rangiroa 1996/2000

  19. Colonization patterns: Annual cycles & ENSO a- SST showing Nino Region 3.4 (solid line) and local anomaly (dashed line) b- West–east sea surface current vector, Uzo c- Chlorophyll-a data from SeaWIFS indicating patterns in primary production d- Larval supply of coral reef fishes measured as monthly means of daily catches.

  20. Colonization patterns: Annual cycles & ENSO a- Regression of SST anomaly vs. log (abundance of larvae) b- Regression of SST anomaly vs. chlorophyll-a concentration c- Regression of SST anomaly vs. west–east sea surface current vector d- No significant relationship between west–east sea surface current vector and abundance of larvae e- Regression coefficients between chlorophyll-a concentrations and abundance of larvae f- Regression between chlorophyll-a concentration with a 4-month lag and abundance of larvae. Where significant relationships were found, regression trends are shown with 95% confidence intervals and R2-values.

  21. Colonization patterns: Annual cycles & ENSO At Rangiroa, an intense El Nino (April 1997–May 1998) event between two periods of La Nina (January–March 1996 and August 1998–March 2000) conditions. El Nino = Strong relationship with current flow, ocean productivity (as measured by Chl-a) and larval supply. In the warm conditions of the event : increase of SST anomaly index (up to 3.5°C above mean values) decrease of the strength of westward surface current toward the reef low concentrations of Chl-a (mean: 0.06 mg/m3) 51% decline in larval supply La Nina SST anomalies were 2°C below mean values Strong westward surface current Chl-a concentration was 150% greater Larval supply was 249% greater Our results warming temperatures in the world’s oceans will have negative effects on the reproduction of reef fishes and survival of their larvae within the plankton, ultimately impacting on the replenishment of benthic populations.