Bivalve mollusc circadian clock genes can run at tidal frequency

Marine coastal habitats are complex cyclic environments as a result of sun and moon interactions. In contrast with the well-known circadian orchestration of the terrestrial animal rhythmicity (approx. 24 h), the mechanism responsible for the circatidal rhythm (approx. 12.4 h) remains largely elusive in marine organisms. We revealed in subtidal field conditions that the oyster Crassostrea gigas exhibits tidal rhythmicity of circadian clock genes and clock-associated genes. A free-running (FR) experiment showed an endogenous circatidal rhythm. In parallel, we showed in the field that oysters' valve behaviour exhibited a strong tidal rhythm combined with a daily rhythm. In the FR experiment, all behavioural rhythms were circatidal, and half of them were also circadian. Our results fuel the debate on endogenous circatidal mechanisms. In contrast with the current hypothesis on the existence of an independent tidal clock, we suggest that a single ‘circadian/circatidal’ clock in bivalves is sufficient to entrain behavioural patterns at tidal and daily frequencies.

Biological and environmental rhythms in (dark) deep-sea hydrothermal ecosystems

During 2011, two deep-sea observatories focusing on hydrothermal vent ecology were up and running in the Atlantic (Eiffel Tower, Lucky Strike vent field) and the Northeast Pacific Ocean (NEP) (Grotto, Main Endeavour Field). Both ecological modules recorded imagery and environmental variables jointly for a time span of 23 days (7–30 October 2011) and environmental variables for up to 9 months (October 2011–June 2012). Community dynamics were assessed based on imagery analysis and rhythms in temporal variation for both fauna and environment were revealed. Tidal rhythms were found to be at play in the two settings and were most visible in temperature and tubeworm appearances (at NEP). A ∼ 6 h lag in tidal rhythm occurrence was observed between Pacific and Atlantic hydrothermal vents, which corresponds to the geographical distance and time delay between the two sites.

Biological and environmental rhythms in (dark) deep-sea hydrothermal ecosystems

During 2011, two deep-sea observatories focusing on hydrothermal vent ecology were up and running in the Atlantic (Eiffel Tower, Lucky Strike vent field) and the North-East Pacific Ocean (NEP) (Grotto, Main Endeavour field). Both ecological modules recorded imagery and environmental variables jointly for a time span of 23 days (7–30 October 2011) and environmental variables for up to 9 months (October 2011 to June 2012). Community dynamics were assessed based on imagery analysis and rhythms in temporal variation for both fauna and environment were revealed. Tidal rhythms were found to be at play in the two settings and were most visible in temperature and tubeworm appearances (at NEP). A 6-hour lag in tidal rhythm occurrence was observed between Pacific and Atlantic hydrothermal vents which corresponds to the geographical distance and time delay between the two sites.

RECRUITMENT PATTERN OF JUVENILE FISHES INTO PAMI RIVER ESTUARY (WEST PAPUA, INDONESIA

Recruitment pattern of juvenile fishes into Pami River estuary, West Papua, Indonesia (S 00.80970, E.134.06050), was studied from July to October 2005. The study purposes were 1) to observe fish diversity in family level, 2) to observe fish abundance of each family, 3) to observe recruitment pattern related to abundance and tidal rhythm. Samples were collected using line transect method and identification procedure were done based on morphological characteristics. A total of 19 Families were identified, namely Acanthuridae, Ambassidae, Anguillidae, Apogonidae, Carangidae, Chlopsidae, Clupeidae, Congeridae, Elopidae, Engraulidae, Gerreidae, Gobiidae, Mugillidae, Platycephalidae, Callyonimidae, Siganidae, Syngnathidae, Terapontidae, Tetraodontidae. Fishes composition varied each month. Family of Gobiidae was the most dominant juvenile fishes recruiting during this study with 32%, 69.5%, 84.3%, 71.3%, respectively. Other 8 families (Ambassidae, Engraulidae, Elopidae, Chlopsidae , Siganidae, Syngnathidae, Congeridae , and Callyonimidae) had the lowest composition varied from 0.4% to 3.2%. Three different patterns in abundance during the recruitment time of juvenile fishes, 1) early night (18.00-21.00) was represented by Ambassidae, Chlopsidae, Clupeidae, Gerreidae, Terapontidae, 2) mid-night (22.00-01.00) was represented by Callyonimidae, Congeridae, Engraulidae, Mugilidae, Platycephalidae, Tetraodontidae, and 3) late night (02.00-05.00) represented by Acanthuridae, Apogonidae, Carangidae, Elopidae, Gobiidae, Siganidae, Syngnathidae. However, the peak of abundance occurred at late night (>50 specimens caught), and recruitment pattern of all juvenile fishes has been associated with tidal rhythm.

The retention of fish larvae in estuaries: among-tide variability at Beaufort Inlet, North Carolina, USA

Sixty-eight tides were sampled consecutively to study the retention of fish larvae transported into estuaries. The experiment was conducted at Beaufort Inlet, North Carolina, USA, in March 1996. The inlet is primarily tide-driven and meteorological forcing has a minor influence. Four species of winter-spawning fish were abundant in the samples: Atlantic menhaden, Brevoortia tyrannus; Atlantic croaker, Micropogonias undulatus; spot, Leiostomus xanthurus; and pinfish, Lagodon rhomboides. Across-shore winds significantly affected flow and physico-chemical characteristics of the water. Across-shore winds also positively influenced the larval retention provided larvae did not present a clear tidal rhythm of vertical migration within the water column and that winds pushed in the water during flood tides. The retention of larvae migrating vertically in respect to the direction of the flow was independent of meteorological forcing of the water.