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Starting Small and Vulnerable: The Babies of the Sea

collage of sea animals
Top Row, L to R: octopus (Photo: Jackie Sones); crab (Photo: Ellie Fairbairn); sea urchin (Photo: Alex Anderson). Bottom Row, L to R: abalone (Photo: Shelby Kawana); fish (Photo: Ellie Fairbairn); sea star (Photo: Alvaro Migotto, Flickr)

Quick, imagine an OCTOPUS! Picture in your mind a SEA URCHIN! Now a FISH! Now a CRAB! Now a SEASTAR! Now a SNAIL!

Did the images you conjured in your mind look like the ones above?

Probably not.

But these are the extraordinary embryos and larvae of the various sea critters I asked you to imagine.

When we think about the organisms in the ocean, we don't often think of these strange and beautiful early life stages that look very unlike the adults they grow into. But in order to become an adult crab or fish or octopus, a lot has to happen first.

Before we go any further, let's see, step by step, what it takes to be a triumphant animal in the large ocean.

Steps to success if you're a lonely sperm in the ocean:

  1. To effectively reproduce, you, the sperm, must find an egg of your species. Don't let the vast open ocean discourage you! The right egg is out there: swim!

  2. After fertilization, that single cell you've become must divide again and again, until you form a little embryo inside a thin shell. Be careful; you are very vulnerable at this stage to man-made pollution, ocean acidification, and other stressors.

  3. Then, little embryo, once you've grown, you must fight and squirm your way out of the shell and hatch.

  4. Now the real journey begins! Once hatched, you are now a larva! Roam free in the big ocean, keep growing and (most importantly) don't get eaten! (You're part of the plankton, and plankton are delicious to a lot of other animals.)

  5. As you float, you must navigate your way through the ocean and find the perfect home to settle into and become an adult.

  6. Here you will metamorphose from your strange larval body into the adult we know and love. Your body as you know it will disappear and be replaced by new tissues and organs; cross your tentacles and hope this crazy process goes well!

Phew! I'm exhausted just thinking about it. Embryonic and larval development are so perilous that the odds of a single sperm surviving to adulthood are less than one in a billion!

Below are a couple of videos of early embryo development that will hopefully give you an appreciation for how much is going on during early development, how elaborate and delicate the process is—and how lucky we all are to have survived it (YOU were an embryo once, too!).

This incredible video shows the spawning, fertilization, development, and metamorphosis of a sand dollar (these critters are very closely related to sea urchins).

This next video shows the early development of a fish embryo. First you'll see cells dividing quickly on top of the large yolk. Then the cells will begin to move around and organize themselves; suddenly, you'll recognize the body plan of a fish! The head and tail are wrapped around the yolk as the larva begins to wiggle and twitch within the thin shell that surrounds it.

Hopefully those videos convey to you how fascinating and COMPLICATED development is.

Embryonic development is an amazing process: After fertilization, a single cell goes on to form all the cells, tissues and organs of the larva as well as the adult animal. This is an incredibly intricate undertaking. Just imagine: the cells have to divide thousands of times, while at the same time continually rearranging themselves to form the necessary structures—this involves complicated communication pathways between the cells, so that they can in essence let one another know who is going to be what and where.

Stress can disturb this delicate dance of cells. In fact, the complex cellular orchestrations during early development have long been thought to be uniquely sensitive to environmental stressors, from changes in temperature, salinity, and pH, to exposure to man-made chemical pollution. At Bodega Marine Laboratory (BML), a lot of researchers are interested in the embryos of marine critters. For example:

  • From oil spills to endocrine disruptors, man-made chemical pollution can be especially detrimental to the early life stages of marine animals. Scientists in the toxicology lab at BML use powerful microscopes and other tools to determine the sensitivity of marine embryos to pollution.

  • The release of carbon dioxide into the atmosphere from human activities is affecting not only ocean temperatures but also the chemistry of the ocean. The Bodega Ocean Acidification Research (BOAR) group seeks to understand how seawater chemistry impacts marine invertebrates. Invertebrates that synthesize calcium carbonate shells are thought to be particularly vulnerable to ocean acidification; larval oysters raised in more acidic seawater have weaker shells and grow more slowly.

  • BML's White Abalone Captive Breeding Program has succeeded in breeding and raising the larvae of endangered white abalone that are held in captivity. There are now more white abalone in captivity than are thought to exist in the wild. To save this species from the brink of extinction scientists will soon begin to move some of the captive abalone out into the ocean.

  • After microscopic larvae are released from their parents into the big ocean, where do they go? The answer to that question is quite complicated, but can influence recreational and commercial fisheries, as well as how we determine the best locations for marine protected areas. Researchers at BML study larval dispersal and biological oceanography to address these and other questions.

As a student in the Coastal and Marine Sciences Pre-College Program you will have a chance to explore many of these research topics first hand. To learn more about these and other research programs at BML, visit our webpage.

Many things in the ocean start out small. But the ocean is ENORMOUSLY important, from providing seafood, tourism, and seaborne trade, to regulating earth's climate patterns. Understanding the threats to ocean ecosystems is critical to the conservation of the marine economy, as well as the beauty and wonder the ocean provides.