Shallow Sea:
Noverian:Your species evolved rudimentary heat sensitivity. At night this is helpful for avoiding other creatures, but during the day the sun makes the water so warm that really its hard to tell what's what. It does seem to make avoiding nocturnal predators easier, as your species now moves to the coldest location it can find during the night. Finally you get a general idea of whats preying on you, its fairly large, its a large long creature. Its fairly rare, and they seem to be eating just about every warm spot (which you assume to be living things) nearby. Your population grows to 18.
Moplural: Soon your light sensitive cells develop the ability to pick out the edges of things. This gives you rather poor eyesight, but its more than most species have at this point. You are the first species to visually see the world in some level of definition. The benefits to this are astounding. Predation drops to almost zero as you are able to identify threats at a fair distance and hide preemptively. Furthermore, it lets your species locate food very very easily. All and all, this is a major step forward for these little creatures. Your population explodes to 1900! Algae is becoming more and more scarce due to overgrazing by several species.
Neophid: Your species develops small fleshy hooks on your head and butt. This unique evolution is rather ingenious, as it allows your species to hook plants and prevent them from floating away after the roots have been eaten. In fact, for the smaller seagrasses, your species pulls them completely under the sand and eat them in safety. The best food, the red plants, require several neophids to hold them down, but most attempts are successful. Other attempts end with greedy neophids unwillingly hitching rides on the floating plants. Your population grows to 390.
Klarnn: The Klarnn make a lead forward in evolution and develop a vacume-like organ in their throats. This allows them to suck in water, hopefully full of food, and then release the water without the food. Its a rather clever design for these blind manta-like creatures. It doesn't help devour larger prey, but the Klarnn find it fairly easy to just go over rocks like a vacuum cleaner and suck up everything in their path. Sometimes they find big food, and honestly your species tries to eat anything that moves, but always they manage to get some nourishment from vacuuming. Population grows to 19.
Microsis exertialum: Your species continues to grow, reaching 130,000! Your species has decimated most indigenous herbivorous microbes, most will go extinct in the wake of you rapid expansion. Algae cannot grow as fast as your species eats it, and large barren spots are starting to appear on typically algae covered rocks. Large creatures have started eating you, but your species has so many individuals that it barely makes a dent in your growing numbers.
Nasone: Your species remains unchanged. It's predators seems less interested in chasing them, and its quite capable of sniffing out food. Mostly its plants, but cubecrabs are also quite prevalent now. There is little need for change right now, and life seems quite pleasant for these nosy eel-worms. Population grows to 120.
Minor Event: Tiny cubecrabs are becoming much more common. They are are .5x.5 inches to 1x1 inches. It seems their food source is rapidly growing and they are taking advantage of that much more than other species.
Deep Sea
Brot worm: The brot worms make a large evolutionary leap! They develop a harpoon like structure within their mouth, and a small gas filled sac for propelling the harpoon. This allows them to take an active roll in hunting down food. Suddenly competition becomes prey, and the brot worms find that the species of deep sea cube crabs are quite tasty. The tristars are a bit too big to be eaten by brot worms however. Predation remains constant, as your harpoon does little against the sweeping tentacles of the floating stubbornians, who's bodies remain suspended far out of reach. Not that your blind brots would know that, they just shoot at moving things and hope its edible. The shoot first try and eat second strategy seems fairly effective and your population grows to 28.
Glivin: The Glivin's sit there. Waiting. Life goes on all around them, but they remain unchanged.
Stubbornians: The stubornians remain unchanged. They continue to dredge the seafloor looking for food, and it seems to still be working. Life goes on unchanged for these drifting wanderers. Their population grows to 41. Your species keep catching something that makes them sick and die. Without senses, you cannot tell exactly what it is.
Goobloids: Your species gains rudimentary vision, basically patches of photosensitive cells. While its a bit of a way from true vision, it does give you some insight into the world. That world is dark. Very very dark. However, your species glows constantly, and your goobloids can now locate eachother in the dark. Whats more, you notice at least two other luminescent signatures. Your species sees some lights far above that move quickly and a slow moving signature along the seabed. Your species still has no predators, and can now find mates very easily. Population grows to 424.
Chitter: Your species develops photosensitive slits in its faceplate armor. At first your creatures do not understand this, as it is incredibly dark down in the deep sea. However, it quickly becomes clear that one direction is lighter than all the others. Your species move in this direction and find themselves moving into the open ocean. Food is even more rare out here, but actually easier to find for your species. Its lighter here, and your species is able to tell generally where objects are (during the day). While your species isn't the strongest swimmer in the sea, it does manage to locate some food drifting through the endless waters. Predators of all sorts roam the open ocean, losses are heavy, but are offset by reproduction to some degree. Population drops to 13.
Major Event:
Volcanic activity is increasing across the world. More islands are forming, and a number of hydrothermal vents have opened up in the deep sea. Temperatures are decreasing slightly, and light levels are slightly less than they were, but not enough to decrease the effectiveness of photosynthesis. Silica is becoming more common in water chemistry.