The following is adapted from my field notes on a research trip to San Salvador Bahamas.
North Point is made of eolianites which are made of wind deposits of calcium-rich sand from the island mainland. The wet carbonate turns sold. A crust (caliche) forms on the surface and the then rest solidifies. These dunes are less than 500 years old. My professor, Fred said that sometimes the crust of the eolianites breaks and then is filled with sand which cements. It is harder than the rest of the eolianites so while the rest erodes it stays behind. Off of North Point, there is a shipwreck of a gas tanker. Fred saw a grey catbird (Dumetella carolinensis).These birds are named after their cat-like meowing sounds. Non breeding birds can be found as far south as the Bahamas. We also saw white-tailed tropic birds (Phaethon lepturus). They have very elegant long whitetails. They can be found in Hawaii as well. They don’t build nests and instead lay eggs on the bare ground. I saw several really small hermit crabs, which are also called soldier crabs (Coenobita clypeatus) taking advantage of old snail shells. This crab is one of two species that is commonly sold as pets. They are both herbivores and scavengers.
Winds come from the east here giving the east side low variability of marine ecosystems and high energy. The west side has high variability of marine ecosystems but low energy. This is due to storms with which can create blowouts which occur when waves wash out a huge part of the eolianites. There are also three zones of plants. Zone 1 contains low growing plants (due to wind pressure) on the east side. Zone 2 is in the middle. Zone 3 is tall shrubs on the west side of the point. There are different splash zones on the rocks. The tan zone is the farthest down zone, then the black zone followed by the white zone. The tan and black zones are bacteria-rich environments but contain distinct bacteria due to the different environments each species thrive in.
We looked at a tidal pool of snails and fuzzy chiton (Acanthopleura granulata). Chitons are ancient gastropods that have been around since the age of the dinosaurs. They have 6 plates on their back that can harden when they are attached to a surface or soften when they are moving. They have ideas around the perimeter of their body, instead of ” just 2 eyes. Chiton consumes algae, and “farm” the areas that they live in, traveling in circles to consume new algae growth. They consume algae at nighttime. The snails in the area with the chiton secrete an enzyme that then eats ways at the rock to create little pockets for themselves to protect themselves from wave action. There was lots of Knobbly Periwinkles (Echinolittorina malaccana) that live outside of the splash zone. These snails are very hearty and are only wet for a few hours a day. It is thought that the warty structures on their shells help to cool them. In the splash zone, there were Zebra Nerites (Neritina natalensis).