Monday, October 16, 2017

The reef

A stovepipe sponge
For our first few dives in Bonaire, my boyfriend and I started easy, diving on the reef just adjacent to our beachfront hotel. It was my first time diving on a coral reef, and I have just one thing to say: holy biodiversity, Batman.

We started the dive by jumping off the resort's pier and swimming seaward over the sand. There's a line leading divers out to the reef, which makes the journey very straight-forward. The sand had a smooth, gentle slope, but I could notice we were getting gradually deeper. At about 30 ft (9 m), the seafloor dropped off with a steep ledge, and that's where the reef began. Most coral reefs around Bonaire are located on similar sub-sea walls, about 30 - 130 ft (40 m) deep.

The first organism I remember noticing was a large purple sponge. Several long, thin tubes stretched up from a common base, and each tube was maybe 2 ft long. According to my identification guide, it's called the stovepipe sponge, Aplysina archeri. It was very common on the reef.
Hard corals on my first reef

The next thing I noticed were all the hard corals. There were four really common species, a brain coral (Colpophyllia natans, I believe), the blushing star coral (Stephanocoenia intersepta), lobed star coral (Orbicella annularis), and smooth flower cup coral (Eusmilia fastigiata). I've tried to point some of them out in the photo here at left. You'll notice the different growth forms - ridges versus clusters versus bumps. Reef-forming corals are actually colonies of clones, and every species has a slightly different pattern for how those clones are arranged. In the brain coral, they live in long sinewy lines, creating ridges in their colony's collective skeleton like a brain. Flower corals have large, single polyps that live in individual cups but are joined together at the base. For the star coral, you can actually see the coral individuals in this photo. Each one of the brown bumps is a polyp, and together they form a calcaerous mound.

A couple things surprised me about the reef. First was the sheer number of species in a small area. I knew there would probably be more species than other marine habitats I'm used to looking at, but I guess I didn't expect them all to be so obvious or in one place. I'm used to having to look under rocks or dig hard to find organisms in the intertidal; on the reef, I could see 30-50 species just by swimming for a few minutes. It was incredible!

A coral restoration project
The second thing that surprised me was actually how much empty space there was. Corals covered the vast majority of the seafloor, but there was still a measurable fraction left uncolonized. The substrata were obviously all old coral skeletons, so I started to wonder if the emptiness was normal or if coral recruitment has been declining in recent years. I suspect the latter, because right next to the reef were several tall stands with growing coral juveniles - a restoration project by the Coral Restoration Foundation Bonaire. I asked around and was told that the coral juveniles will be outplanted on the natural reefs once they are large enough, in the hopes that they will become established and reproduce on their own in later years.

I had a great first day exploring the resort's "house reef" and getting acquainted with the local system. Coral reefs are such beautiful, diverse habitats, and I look forward to exploring more!

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