Does your character stand out?
First a couple of facts:
1. Oceans cover nearly 70 percent of the earth's surface.
2. Humans are terrestrial beings unable to survive underwater for longer than they can hold their breath unless they use specialized equipment.
3. Humans are not at the top of the food chain in the marine environment.
What better place to stage a crime?
My current work-in-progress includes a marine biologist in the cast of characters. Scientists tend to be focused, fact-driven, data junkies. Cops tend to be focused, evidence-driven, adrenaline junkies. So far so good. Biologists also tend to know A LOT of biology. Cops, not so much. Therein lies a problem. My solution to the conundrum was a research trip* to the island of Kauai. I'm still a bit dodgy on the science, but the sea taught me an unexpected lesson on characterization.
Hiding in plain sight
Sometimes characters blend with the crowd
Not all characters are deserving of special recognition. Too much description of a secondary character leads readers to believe that the waitress / neighbor / UPS delivery person will play a more important role than the writer intends. Individually, these Spanish Grunts are hard to distinguish, but collectively, they form schools that create a larger profile and confuse prey.
Not all villains look dangerous
Antagonists shouldn't have a scar, a maniacal laugh, wear a black cloak, and kick kittens. The most chilling villain is the one readers understand. The Crown of Thorns starfish is an invasive species with venomous spines, few natural predators, and a voracious appetite for coral polyps. It leaves a swath of dead coral reefs in its wake and has threatened the stability of many ecosystems.
Not all heroes look heroic
The Trident Trumpet Conch looks like Stephanie Plum, but acts like Jack Reacher. It is one of the few critters (scientific technical term) capable of getting the drop on the Crown of Thorns starfish. It grips its prey, saws through the starfish's armored skin, injects a paralyzing saliva, then feeds at its own pace.
Wait, this is a hero?
Depends on how I write it-- and whether you are the starfish or the coral.
That's the beauty of characterization.
*I love my job.