Southwest monsoon effects on the growth of juvenile abalone (Haliotis mariae Wood, 1828) along the western Dhofar coast, Arabian Sea, Sultanate of Oman

- We quantified seasonal incremental growth in juvenile abalone.
- We established a link between seasonal upwelling and abalone growth.
- We established the relationship between seasonal temperature and growth.
- We illuminated the importance of the south west monsoon on productivity and abalone growth.

An experimental tag and release/recapture experiment with juvenile H. mariae in three areas, Hassila, Haat and Raha, along the Dhofar coast of Oman demonstrated that the growth rates of H. mariae are driven by season and temperature. The winter NE monsoon and the summer SW monsoon have a significant effect on the monthly incremental growth of juvenile abalone (30-63 mm shell length, p<0.001). The peak average growth rates, up to 7.4 (SD  ±  2.5) mm and 8.4 (SD  ±  2.5) mm per month, occurred in October and September, respectively, with minimal growth of <1 mm occurring from March to May. The growth increases coincided with the blooming of Ulva sp. when the temperatures decreased and upwelling occurred. Growth also peaked when the kelp species Sargassum and Sargopsis were abundant. Complete growth inhibition occurred during April and May when very little algal biomass is available. The peak summer growth rates were approximately 3 times the lowest winter growth rates. A close relationship was identified between the chlorophyll-a levels and abalone growth. Increases in marine productivity are reflected in both the chlorophyll-a levels and the seasonal algal diversity, and the abundance is likely the most dominant driver of increased abalone growth along the Dhofar coast.