Tropical seas, nutrients

Nutrients are often the key limiting factors to primary production in the tropical seas, and symbioses are frequently observed in these types of oligotrophic habitats. From his many microscopy observations, Norris (1967) speculated that a considerable part of the biota in the open ocean were involved at one time or another in a consortium, either temporary or more permanent. Forming a symbiotic association might then be considered an ecological adaptation to life in the oligotrophic ocean. 

One aspect of sedimentary 7 8 chlorite formation which is particularly interesting is the fact that these minerals are never found forming at depths greater than 80 meters in recent sediments. Porrenga (1967b) thinks that they are characteristic of tropical sediments and their formation is thus temperature dependent. This appears invalid since they are known to form in recent sediments in a Scottish loch (Rohrlich, e al.. 1969). Nevertheless there does seem to be a bathymetric control on their occurrence. This is probably not a pressure effect but more likely some sort of factor related to organic activity in the sediments which is controlled by the biotic factors of sea depth, temperature, nutrients, etc. 

DiTullio GR, Smith WO Jr (1996) Spatial patterns in phytoplankton biomass and pigment distributions in the Ross Sea. J Geophys Res 101 18467-18477 DiTullio GR, Hutchins DA, Bruland KW (1993) Interaction of iron and major nutrients controls phytoplankton growth and species composition in the tropical north Pacific Ocean. Limnol Oceanogr 38 495-508 DiTullio GR, Grebmeier JM, Arrigo KR, Lizotte MP, Robinson DH, Leventer A, Barry JP, VanWoert ML, Dunbar RB (2000) Rapid and early export of Phae-ocystis antarctica blooms in the Ross Sea, Antarctica. Nature 404 595-598... 

One key factor for tropical diazotrophs may be water temperature. For example, the distribution of Trkhodesmium spp. is roughly limited by the 20°C isotherm, and other planktonic cyanobacteria are likewise primarily tropical or subtropical in distribution. MetabolicaUy active populations of Trkhodesmium have been observed at 18.3°C in the North Atlantic (McCarthy and Carpenter, 1979), but activity was low, and substantial growth is typically not seen until water temperature exceeds 20°C (Carpenter, 1983a,b). Moreover, water temperature co-varies inversely with surface nutrient concentrations (Kamykowski and Zentara, 1986). Indeed, in previous studies we have used sea surface temperature as a proxy for oligotrophic waters in order to estimate the areal range of Trkhodesmium (Capone et al., 2005). 

Nutrient requirements of fish have mainly been defined for small juvenile animals held under optimum environmental conditions. In contrast, the majority of aquaculture is conducted outdoors and where fish are subject to periods of sub-optimum environmental conditions (Carter etal, 2005), which are likely to increase due to climate change and threaten the sustainability of aquaculture. To further understand environment-nutrient interactions in relation to protein and energy requirements two model fish species were selected (Carter et al., 2005 Katersky and Carter, 2007). Temperate Atlantic salmon Salmo solar) and tropical barramrmdi or Asian sea bass Bates calcarifer) perform well in aquaculture over a wide temperature range (Katersky and Carter, 2007). 

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