5  Hereditary material, deoxyribonucleic acid (Abbr.) (3)

 6  Marine Global Earth Observatory (Abbr.), directed by the Smithsonian’s Tennenbaum Marine Observatories Network (TMON) and is the first long-term, worldwide research program focusing on understanding coastal marine life and its role in maintaining resilient ecosystems around the world (6,3)

 9  CH4, second most prevalent greenhouse gas (7)

11 An organism that lives on or in a host and benefits at the expense of its host (8)

12 Bivalve, can be ordered "on the half shell," "The world is your ______" (6)

14 Heavy metal with the l symbol Hg, name of a planet in our solar system, last name of lead singer Freddie from the British band Queen (7)

15 Stinging invertebrate, most common example in the Chesapeake Bay is the sea nettle (9)

17 Popular term given to Loxo-parasitized mud crabs, reanimated undead being popular within the horror and fantasy genre (6,5)

18 Central American country that connects Atlantic and Pacific Oceans with man-made canal, is home to Smithsonian field stations, Van Halen song title from the album 1984 (6)

19 "Somewhere over the rainbow, ______ fly." (8)

 2  Largest estuary in the United States, known for its blue crabs (10,3)

 3  Small, grayish-white crustaceans that live on rocks, pilings, boat hulls and other hard surfaces, Spongebob Squarepants says this when frustrated (8)

 4  CO2, primary greenhouse gas (6,7)

 7  Scientist's Jell-O, lab staple derived from red seaweed (4)

 8  Smithsonian-wide competition based on votes, SERC's entry was the North American Orchid Conservation Center (orchids) and placed 3rd in the science category (6,8)

10 Rhymes with "harsh" (5)

13 Decapod with the scientific name Callinectes sapidus which comes from the Greek words for “beautiful” and “swimmer” (4,4)

16 Submerged Aquatic Vegetation (Abbr.) (3)