Tuesday, March 13, 2012

Fiji: Diving the Mellow Yellow

For the past several years, the New England Aquarium has participated in a joint expedition to Fiji, along with the Monterey Bay Aquarium and other conservation-minded groups and individuals. The last expedition took place in October and November 2010. Stay tuned to this blog to follow the team as they dive to collect data on the health of the coral reefs, pick up trash where they find it, check in with the villagers to see how some conservation initiatives are faring and further develop connections with the people that live on these beautiful Pacific islands. 

Today's post and pictures come from Mark Rosenstein.

Diving today on Mellow Yellow, the brilliant yellow Chironephthia soft coral for which it is named was mostly limp. When the current is right, the corals inflate to form beautiful brightly colored "bushes."  But no dive here is ever boring. 

 Pulsing clouds of fish above the reef

Near the top of the pinnacle were huge pulsing clouds of fish. While it first seems chaotic, there are patterns here. Closest to the reef are damselfishes: several different species in shades of gray and brown. They never go more than a couple of feet above the protection of the coral. Beyond the damsels are brightly colored purple and orange fishes. These are anthias. The most numerous are scalefin anthias, Pseudanthias squamipinnis.  The females are all orange, and the males mostly magenta/purple. Mixed in with these are smaller numbers of slender anthias, Luzonichthys waitei, who are each orange above and purple below. The slender anthias range 4 to 5 feet above the reef, and the scalefins up to a couple of feet beyond that. And if you look very carefully, some of the slender anthias seem grayer than the others--those are actually fusilier damsels, Lepidozygus tapeinosoma, who mimic the more numerous anthias. Passing above these thousands of fish are groups of several dozen fusiliers, of four different species.

All of these fish are in constant motion. They are moving around in their groups feeding on microscopic bits of plankton. But more dramatically, entire populations move in towards the reef as larger predators such as trevally make passes through these fish looking for a quick lunch. Each time a predator comes through, all of the fish move in the blink of an eye towards the safety of the reef. The cloud of fish then gradually spread out again in the next 10 to 20 seconds. Some of these fish, in their rush to safety, may accidentally end up in the mouth of a patient hunter such as a peacock grouper. This dance is mesmerizing as I watch the food web in action.

Recently hatched black noddy chick

In lieu of a third dive, many of us visited Vatu-I-Ra, or Bird Island, instead. Through the efforts of Birdlife International, this island has been labeled an Important Bird Area because it has the densest nesting area of Black Noddies in the Pacific. A couple of years ago, BI assisted in eradicating rats from the island so that ground nesting birds would return. They have also mounted loudspeakers on the summit of the hill which play Fiji petrel calls each evening, trying to lure this critically endangered bird to come to the island for breeding. The Fiji petrel is currently only known to breed on the island of Gau, where both rats and house cats are present.

Of special interest during this visit was nesting crested terns. These are recently returned ground-nesters. BI had asked us to survey the nests. The terns are very skittish, and in spite of a cautious approach, they all fled when we were still 30 yards away. After some debate, we decided that just one of us (me) would go the rest of the way down the beach to where we could see some of the nests.  While frantic adults swooped at my head, I counted 27 eggs, each larger than a hen's egg, sitting in the sand. There may have been as many as twice that, but I didn't want to get any closer to further disturb the nesting terns while getting a more accurate count.

Leaving the terns, we explored the rest of the island, including climbing the 100 foot hill at the opposite end. Near the summit of this hill is the solar powered device which plays the petrel calls. From here we were also able to estimate that the island has about 250 small trees on it. If each tree has 20 to 25 black noddies in it, then there are 5000 to 6250 noddies on the island. These were by far the most numerous birds on the island. Many nests contained eggs, and a number of newborn chicks were present as well. 

As in past years, we collected trash from the island during our visit. The good news is that we found much less trash than on past visits. But we still found some. And with personnel from BI having visited the island just two weeks ago, this would be a lot of trash if they also carted away much of what they saw.

Marbled shrimp

Only a few of us went out on a night dive after dinner.  We dived the fringing reef around Vatu-i-ra Island. In a leisurely dive, we saw many sleeping fish showing their night colors. There were a few odd creatures. Pleurobranchs are foot-long maroon sea slugs who move slowly over the reef. A few salps, free-swimming jelly-like tunicates, were in the water and attracted to our lights. 

As is usual on night dives, pairs of shiny red dots were scattered around the reef.  These are the eyes of shrimp, whose night-vision adapted eyes reflect flashlights. Most shrimps are mottled patterns of red and white.  But this reef had a number of marbled shrimp, Saran sp., some with spectacular colors and patterns.  In dim light these were not too obvious, but in a flash-lit photograph they are very evident.

-- Mark Rosenstein

1 comment:

  1. An enjoyable read about your adventure. It's such a shame about the trash though, one I can't fathom (pardon the pun).