The tidal regimes of three indian ocean atolls and some ecological implications

Pugh, David; Rayner, Ralph

doi:10.1016/s0302-3524(81)80036-9

Cited by 24 publications

(16 citation statements)

References 13 publications

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“…data). It has been observed previously (Sheppard 1999a) that corals in all the deep (25 to 60 m) lagoons (all except Egmont, which is extremely shallow) survived considerably better than corals on seaward slopes, and it was supposed that because lagoonal corals were more regularly subjected to elevated water temperatures (Pugh & Rayner 1981), they perhaps acclimated better to it. It can be speculated that these lagoons may be a reservoir of surviving adults that have led to such successful recruitment throughout.…”

Section: Shallow Zone Recoverymentioning

confidence: 90%

Archipelago-wide coral recovery patterns since 1998 in the Chagos Archipelago, central Indian Ocean

Sheppard¹,

Harris²,

Sheppard³

2008

Mar. Ecol. Prog. Ser.

114

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Patterns of coral recovery are analysed across reefs of the Chagos Archipelago, which spans 400 × 250 km in the central Indian Ocean. This archipelago mostly lacks direct human impacts and is subject only to global changes such as a rise in sea surface temperature. Following very heavy coral mortality (mostly > 90%) caused by the 1998 warming event, and despite 2 further sub-lethal bleaching events, the recovery of coral cover, colony numbers and juvenile recruitment has been good in many parts of the archipelago. There was little discrimination between atolls and depths, with a notable exception of 1 atoll where a repeat of heavy mortality had occurred in 2005. In 2006, coral cover was almost restored to pre-1998 values at most shallow sites, but had recovered much less in deeper waters. However, in shallow water, coral cover values alone are a poor indication of recovery, because present, shallow cover mainly comes from Acropora palifera and other corals that are largely encrusting in juvenile form, in contrast to their mature condition, in which they provide a 3-dimensional 'forest' structure. Recruitment of juvenile colonies in 2006 ranged from 6 to 28 m -2 . Total juvenile density showed no significant pattern with atolls or with depth, but, taking each genus of juveniles in turn, many genera showed a marked depth preference. No shift was observed towards algal domination, or to assemblages dominated by Porites or faviids, as has been reported elsewhere. Recovery in Chagos 8 yr after massive coral and soft coral mortality is discussed in relation to an absence of other, locally manageable factors such as pollution, over-fishing and sedimentation.

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Section: Shallow Zone Recoverymentioning

confidence: 90%

Archipelago-wide coral recovery patterns since 1998 in the Chagos Archipelago, central Indian Ocean

Sheppard¹,

Harris²,

Sheppard³

2008

Mar. Ecol. Prog. Ser.

114

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“…First, the increased chlorophyll region is associated with cooler water, whereas the lagoon water would be warmer than the surroundings (Pugh and Rayner, 1981). Second, even if the entire lagoon water were exchanged each tidal cycle, the volume of water could not cause the vertical and horizontal coverage of enhanced productivity that was observed.…”

Section: Discussionmentioning

confidence: 99%

“…It rises steeply (about 25°) from the abyssal plain at 4000 m. If considered as a cylinder facing a predominantly northwestward flow, a representative radius would be 10 km. It consists of a ring of small islands enclosing a large, shallow lagoon (average depth 4 m, approximate area 200 x 10 6 m 2 , Pugh and Rayner, 1981). The principal means of exchange of lagoon water with the open ocean is the Main Channel situated at the western end of the northern shore.…”

Section: Data Collectionmentioning

confidence: 99%

“…Since the lagoon is large and shallow, it will be a source of warmer, saltier water every tidal cycle. Pugh and Rayner (1981) estimate that the excess temperature of the outflow water from such lagoons may be as large as 2°C during sunny, windless conditions. The Cosmoledo island group, lying about 1 0 to the east of Aldabra, is more circular in shape but slightly smaller; its radius is about 7 km.…”

Section: Data Collectionmentioning

confidence: 99%

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The effects of flow disturbance by an oceanic island

Heywood¹,

Barton²,

Simpson³

1990

J Mar Res

128

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We present CTD and ADCP surveys around the Indian Ocean coral atolls of Aldabra (46°20'E, 9°25/S) and Cosmoledo (47°30E, 9°45'S) during April-July 1987. These isolated, steep-sided islands situated in deep (4000 m) water in the South Equatorial Current provide examples of flow disturbance which are compared to laboratory studies of eddy generation by a circular cylinder in a channel.For sufficiently strong and steady flows, a doming of the isopycnals is observed in the lee of the islands. The sea-surface temperature decreases and the salinity increases as cool, saline water is mixed from below. Just as in the case of islands in tidally dominated shelf seas, we observe an increase in the chlorophyll content of the water behind the island, indicative of enhanced phytoplankton productivity caused by the flow disturbance. This anomalous region may be associated with an eddy trapped downstream of the island. The incident flows were not strong enough to generate a vortex street of eddies spun off in a wake. When the incident flows are weak and fluctuating, no evidence for eddies is seen; and there is no doming of the isopycnals leading to low sea-surface temperature and high chlorophyll content.

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“…A flushing index of 0.22 obtained in the present study is within values given by Gilmartin and Revelante (1978) for coastal lagoons of the Gulf of California. Nevertheless, as a first attempt, to know the flushing condition of the SAMARE, this approach has been used, and the obtained time period is comparable with flushing time of some other lagoons including Aldabra Atoll (Pugh & Rayner 1981) and Cocos Islands lagoon (Kench 1994). As a consequence of shallow depths in a tidal regimen where the mean tidal range is about 0.8 m, the flushing index of 0.22 predicted in this investigation is low compared with Ohuira and Yavaros Lagoons, where the flushing indexes were 0.55 and 0.56 respectively ( Table 2).…”

Section: Discussionmentioning

confidence: 99%

Assessment of the tidal currents and pollutants dynamics associated with shrimp aquaculture effluents in SAMARE coastal lagoon (NW Mexico)

Ley

Osuna

2012

Aquac Res

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The pollutant dispersion induced by the tidal hydrodynamics was investigated through a modified model in Santa María-La Reforma coastal lagoon, a body water that receives effluents containing chemicals that are used in shrimp aquaculture. Maxima tidal currents (0.7 ms À1 ) were predicted within the main channel. Residual currents, of the order of 0.01 ms À1 , were also predicted. The hypothetical pollutant, released at four selected sites that receive effluents from shrimp aquaculture and agriculture within the lagoon, spread towards the northern and southern inlets. The advection and diffusion processes allow the pollutant in most of the cases, to reach the inlets in about 120 h. The spreading of the pollutant in the coastal lagoon seems to be modulated by the tidal velocity fields. The presence of an area where tidal currents converge in the eastern part of Talchichitle Island suggests that a potential accumulation of pollutants occurs in this site.

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The tidal regimes of three indian ocean atolls and some ecological implications

Cited by 24 publications

References 13 publications

Archipelago-wide coral recovery patterns since 1998 in the Chagos Archipelago, central Indian Ocean

Archipelago-wide coral recovery patterns since 1998 in the Chagos Archipelago, central Indian Ocean

The effects of flow disturbance by an oceanic island

Assessment of the tidal currents and pollutants dynamics associated with shrimp aquaculture effluents in SAMARE coastal lagoon (NW Mexico)

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