Summer Below the Surface: Marine Animals in Our Summer Waters

Phytoplankton

As July sets in, the Lowcountry enters into the dog days of summer. There is no denying it’s hot! The best way to beat the heat is get out on the water—swimming, kayaking or boating. But the heat doesn’t only affect the air temperature, it also affects the water temperature. Coastal water temperatures can reach 90º on Hilton Head! So, how do our marine neighbors adapt to summer weather below the surface?

Zooplankton

Seasonal warming of coastal waters affects every step in the food chain, starting with microscopic free-floating phytoplankton and zooplankton. Increasing temperatures kick these tiny plants and animals into overdrive, and they grow and reproduce far more rapidly. As they do, their populations become far more dense, making their watery home more opaque. As a result, birds that fish aerially, hunting from above, can’t see fish to catch and migrate elsewhere. One such species, the bald eagle, is seen far more often in winter, when the water is clearer.

Blue Crab. Photo by Jarek Tuszyński / CC-BY-SA-3.0

Warmer water and increased planktons also cause coastal waters to be less oxygen-rich. Many local animals have adapted to breathe water with lower oxygen, such as the blue crab. These little crustaceans have larger gills than most crabs, which allow them to absorb more oxygen from the water. Crabs are very sensitive to temperature, and cannot survive in waters over 91º or below 45º. In winter, they migrate to open ocean areas and dig themselves a sandy den to hibernate in until temperatures rise again.
At the top of the food chain, sharks and dolphins have sophisticated adaptations allowing them to thrive in a variety of water temperatures. Dolphins and other whales have a variable layer of blubber and can go from very cold to very warm waters, gaining or losing their insulating layer of fat, as necessary. This adaptability allows marine mammals to focus on following their food sources. While most sharks are cold-blooded and behave like fish, Great White and Mako sharks can regulate their body temperatures like mammals. This allows them to migrate and adapt to warm and cold waters much like marine mammals.

This July, don’t let the heat get to you! Take a kayak or boat tour, cool down and learn about the fascinating creatures living in our local waterways.

Article by Jessie Renew, Outside Hilton Head

For more than 30 years, Outside Hilton Head has provided personalized adventures for all ages, from kayak, fishing, nature and dolphin tours to kids’ camps, history excursions, family outings and stand up paddleboarding. (843) 686-6996 or outsidehiltonhead.com.

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