Studies in Canarium urceus (Linnaeus, 1758) Part 6: A new Canarium species from the Andaman Sea (Gastropoda: Strombidae) and discussion on related species

This part of the Canarium (Canarium) urceus-complex (Linnaeus, 1758) review after Abbott’s revision (Abbott, 1960) revision examines material from the Andaman Sea. At present, material from that region has been synonymised under the name Canarium (Canarium) urceus (Linnaeus, 1758). Canarium (Canarium) andamanense new species is known from the Andamanian Subprovince, a semi enclosed basin that is centered on the Andaman Sea and enclosed by the west coasts of Myanmar and Thailand and the Mergui Archipelago in the east, to the northern Malacca Strait in the south, and to the Andaman and Nicobar Islands in the west. This species is recognized and differentiated by solid, sturdy shells with a triangular body whorl, large knobs on the shoulder and bright orange aperture. This study further confirms that there is a high degree of bioregionalisation within the Canarium complex.

Paralomis White, 1856 (Crustacea: Decapoda: Anomura) from India, with morphological variability in Paralomis indica Alcock & Anderson, 1899

Deep-water king crabs of the genus Paralomis White, 1856 collected during three cruises of the Fishery Oceanographic Research Vessel Sagar Sampada in the western Bay of Bengal (528–777 m depths), one cruise in the eastern Bay of Bengal off Great Nicobar Island (337 m depth), and four cruises in the southeastern Arabian Sea (315–1245 m) were identified. They are referred to Paralomis ceres Macpherson, 1989, recorded for the first time from Indian waters and P. indica Alcock & Anderson, 1899, reported for the first time from the Bay of Bengal and the Andaman Sea. In addition, this study reports the morphological variability among the P. indica populations in the shape of the carapace and dorsal rostral spines, nature of the branchial and cardiac regions and abdominal marginal spines, and the relative lengths of pereopods 2–4. Mitochondrial Cytochrome oxidase I (594 base pairs) and 16S rRNA (503 bp) gene sequences of P. ceres and P. indica (602 and 497 bp, respectively) revealed that they formed distinct lineages. A key to the Indian Ocean species of Paralomis is provided.

Late monsoon threatens coral refugia in the Andaman Sea

Internal waves (IWs) mitigate thermal stress and provide refugia for corals against increasingly frequent mass bleaching. However, climate events may bring uncertainty regarding the resistance of such refugia. Here, using in situ observation data in the Andaman Sea (AS), we conduct a case study in which a monsoon anomaly associated with El Niño event threatens IW coral refugia. IW cooling in the AS coral reefs is modulated by the thermocline depth variation, which is significantly driven by Kelvin wave signals from the equator. In premonsoon period, distinct variations in IW cooling and surface heating form a time window of quickly-growing cumulative heat exposure. The El Niño induces a typical 2-week delayed summer monsoon, which prolongs the duration of thermal stress growth and brings severe bleaching risk to corals. As global warming increases the frequency of extreme El Niño events, IW coral refugia will face great challenges in the future.

Re-determination of normal dates of onset of southwest monsoon over India

The onset of southwest monsoon over various parts of the country can be early, timely or late as compared to a set of normal dates. Advance of monsoon could be either rapid or slow or sometimes there could be prolonged stagnation in the advance of monsoon. The timing of the monsoon onset is of vital importance to the agricultural sector and water replenishment. The climatological normal dates of onset which are being used at present are based on a much older data set (1901-1940) obtained from 149 stations. In this study, the climatology of the summer monsoon onset over different parts of India is derived using the mean pentad precipitation data of 569 stations spread all over the country, from 1971-2000. It has been observed that the revised dates of onset of monsoon over the Andaman Sea is 20 May, over Kerala is 1 June, over the northeastern parts is 5 June and the date of monsoon covering the entire country is 15 July (same as the existing dates). Considerable differences between the existing and the re-determined dates of onset are noticed over parts of south peninsula and western parts of central and adjoining northwest India where the re-determined dates are advanced by 1 to 3 days and delayed by 10 to 15 days respectively with respect to the existing normal dates of arrival of monsoon. The Standard Deviation of the re-determined normal dates ranges between 7 to 14 days with larger values over the northwest and west central parts and interior peninsular India.

Flexural strike-slip basins

Strike-slip faults are classically associated with pull-apart basins where continental crust is thinned between two laterally offset fault segments. We propose a subsidence mechanism to explain the formation of a new type of basin where no substantial segment offset or syn-strike-slip thinning is observed. Such “flexural strike-slip basins” form due to a sediment load creating accommodation space by bending the lithosphere. We use a two-way coupling between the geodynamic code ASPECT and surface-processes code FastScape to show that flexural strike-slip basins emerge if sediment is deposited on thin lithosphere close to a strike-slip fault. These conditions were met at the Andaman Basin Central fault (Andaman Sea, Indian Ocean), where seismic reflection data provide evidence of a laterally extensive flexural basin with a depocenter located parallel to the strike-slip fault trace.

A study of tides and storm surges in offshore waters of the Meghna estuary using a finite element model

Tropical Cyclones which develop in the Andaman Sea and the Bay of Bengal during the inter monsoon months (April-May, October-December), move either westwards affecting the east coast of India or recurve to the north or northeast and eventually cross the coast of Bangladesh or Myanmar. Extensive damage is caused to the life and property by the storm surge as much of the coastal land around the Bay of Bengal is densely populated. The damage caused by a cyclone induced surge depends to a considerable extent on whether the surge peaks at or close to high tide. The main purpose of the present study was to develop a combined time-surge model for the off-shore waters in the Meghna estuary. It seems clear that the strong, predominantly southward current measured at Site A, south of Sandwip Island, has substantial magnifying and delaying effect on tidal elevation and current. But the areal extent of this modification of the tide is unknown at present. Further, it is impossible to say whether the fast southward current forms a narrow jet or a broad current many kilometers wide, but it is important to know which is the case before the effect can be modelled satisfactorily.

The potential of the spiny lobster fishery in Aceh waters: A short review

The western-southern and northern coastal waters of Aceh are the potential fishing areas of spiny lobster, which faces the Indian Ocean and the Andaman Sea. Fishing gears that are widely used are lobster gill nets and hand-picking with compressors. In Indonesia, seven species of spiny lobsters are caught in these waters, including Panulirus homarus, P. penicillatus, P. versicolor, P. ornatus, P. polyphagus, P. longipes longipes, and P. longipes femoristiga. The habitat for spiny lobsters is spread from coral reefs, rock, sand, and muddy sand. Panulirus homarus is the most frequently caught species in these waters, followed by P. penicillatus and P. longipes. Panulirus homarus is mainly caught during the dry season (southwest wind) and high waves (May to July), where other lobster species experience a significant decrease in the catch. The stock of spiny lobster in Fisheries Management Area (FMA) 572 (including Aceh coastal waters) has been in an overfishing condition since 2008. Maximum sustainable yield (MSY) of spiny lobster in Aceh coastal waters part of Malacca Strait (FMA 571) is 188.60 tons.yr−1 with a total allowable catch (TAC) of 151.10 tons. yr−1. Furthermore, the MSY for Aceh coastal waters part of Indian Ocean is 292.09 tons.yr−1 with a TAC of 233.92 tons.yr−1. Spiny lobster fishing in Aceh coastal waters must ensure its use in the future, both ecologically, socially, and economically.

Internal Solitary Waves in the Andaman Sea Revealed by Long-term Mooring Observations

The complex behaviors of internal solitary waves (ISWs) in the Andaman Sea were revealed using data collected over nearly 22-month-long observation period completed by two moorings. Emanating from the submarine ridges northwest of Sumatra Island and south of Car Nicobar, two types of ISWs, referred to as S- and C-ISWs, respectively, were identified in the measurements, and S-ISWs were generally found to be stronger than C-ISWs. The observed S- and C-ISWs frequently appeared as multi-wave packets, accounting for 87% and 43% of their observed episodes, respectively. The simultaneous measurements collected by the two moorings featured evident variability along the S-ISW crests, with the average wave amplitude in the northern portion being 36% larger than that in the southern portion. The analyses of the arrival times revealed that the S-ISWs in the northern portion occurred more frequently and arrived more irregularly than those in the southern portion. Moreover, the temporal variability of ISWs drastically differed on monthly and seasonal time scales, characterized by relatively stronger S-ISWs in spring and autumn. Over interannual time scale, the temporal variations in ISWs were generally subtle. The monthly-to-annual variations of ISWs could be mostly explained by the variability in stratification, which could be modulated by the monsoons, the winds in equatorial Indian Ocean and the mesoscale eddies in Andaman Sea. From careful analyses preformed based on the long-term measurements, we argued that the observed ISWs were likely generated via internal tide release mechanism and their generation processes were obviously modulated by background circulations.