Seasonality in East Africa's coastal waters

Abstract

A review of existing literature and data on seasonal patterns in East Africa's coastal waters indicates distinct seasonality in physical, chemical and biological oceanographic parameters. Seasonal patterns are dictated by the behavior of the Inter-Tropical Convergence Zone (ITCZ) which creates 2 distinct seasonsthe northeast and southeast monsoons. SE monsoon (March to October) meteorological parameters are characterized by high cloud cover, rainfall, river discharge, terrestrial runoff and wind energy while solar insolation and temperatures are low; SE monsoon oceanographic parameters are characterized by cool water, a deep thermocline, high water-column mixing and wave energy, fast currents, low s a h~t y and high phosphorus. These parameters are reversed during the NE monsoon. Nitrogen availability and planktonic primary productivity are high along the Somali coast and estuarine and river discharge areas during the southeast monsoons due to nutrient upwelling and terrestrial runoff. In near-shore waters off Tanzania, nitrogen fixation is the major source of nitrogen and is highest during NE monsoons when the water column is stable. Coral reef benthic algal biomass and diversity is greatest during the SE monsoons. Fish catch and reproduction are highest during NE monsoons in Kenya and Tanzania. Transition periods between monsoons may also be important times in determining productivity and reproduction.

Grouper and Napoleon Wrasse ecology in Laamu Atoll, Republic of Maldives: Part 2. Timing, location, and characteristics of spawning aggregations

“…However, spawning may occur during the other monsoonal shift occurring SeptemberOctober. There is limited evidence that bimonsoonal spawning occurs for some species and locations in the Western Indian Ocean (Morgans, 1962;Nzioka, 1979;Ntiba and Jaccarini, 1990), but other evidence suggests otherwise (McClanahan, 1988). Courtship behavior of P. areoloatus was similar to that of P. leopardus observed on the Great Barrier Reef, Australia by Samoilys and Squire (1994).…”

Annual cyclicity in high‐resolution stable carbon and oxygen isotope ratios in the wood of the mangrove tree Rhizophora mucronata

“…The rainfall along the Kenyan coast shows a bimodal distribution, which is locally expressed in terms of the long rains (from April to July) and the short rains (from October to November) (McClanahan 1988), with a mean annual precipitation of 1144 mm (data for Mombasa, 1890-1985) (Lieth et al 1999). The monthly average temperature ranges from 23.3 to 29.9 ∞C with a mean annual temperature of 26.4 ∞C (1931-1990) (Lieth et al 1999).…”

The breeding pattern and variations in timing and reproductive output of the commercial sea cucumber Holothuria fuscogilva in Kenya

“…The Kenyan coast occurs at the equator and is exposed to monsoonal seasonality with varying oceanographic conditions of temperature, light, and productivity (McClanahan, 1988). Studies along the Kenyan coast are therefore suitable for testing the effects of monsoonal seasonality on breeding patterns of marine invertebrates.…”