Mission Journal 11 — Jim Leichter: Mission Day 6: Sunday, June 19th, 2004
t’s already Day 6, and it’s a beautiful sunny Saturday. At least that’s on the surface and some of that we can tell here on the bottom. Looking up at the surface it’s clearly quite calm today and the wavering spot of the sun is appears as a bright patch on the surface. One way to tell that it is Saturday is that during our dives we could hear many more boat engines today than on the weekdays. Even though the boats are not directly overhead (or at least they shouldn’t be inside the research area) the motor noise carries far underwater and it’s always a good idea to look up and check just in case. The early dive this morning was quite interesting because an especially cool, murky layer of water had moved onto the reef. We could see a layer of suspended particles in the top few meters of the cool water layer, and when this cool water spread up the reef we could clearly see the cloudy layer in the low lying depressions and grooves on the reef. As we swam over the reef it looked almost the way fog or smoke hugging the low valleys of a mountain side would look from an airplane. These thin layers right along the thermocline are likely to be full of phytoplankton and zooplankton (that’s why they appear cloudy). So in addition to the dissolved nutrients that are brought onto the reef, the cool water layers can be transporting important food particles for the reef suspension feeders as well as larvae of invertebrates and fish. There are many interesting and important implications of this transport; one is that periods of strong upwelling are likely to correspond to episodes of high delivery of new fish larvae onto the reefs. Another is that the supply of larvae (at least for some types of larvae) for the reefs can be coming from far offshore and from reefs far ‘up stream’ in the Florida current.