Surveying Coral Reefs of the Antillean Archipelago
Toward the end of 2014 I had the opportunity (and privilege) to join Professor Bob Steneck on his Eastern Caribbean expedition to survey the coral reefs of the Antillean archipelago. Amazingly, considering the amount of Caribbean reef-related research achieved over the last 30 or so years, very little is known about the condition of reefs around many of the eastern islands, possibly due to the lack of marine laboratories.
The low islands of the eastern Caribbean are dry and have little runoff, with Trade Winds and the north equatorial current bathing them in clear tropical seawater with a minimum of upstream pollution. Since all of the eastern Caribbean islands are in a relatively small north to south archipelago, it is reasonable that global warming and ocean acidification will affect the reefs in similar ways. So, by studying similar reef zones from island to island we can see if the reefs differ. If they do, it likely the result of local factors such as the fish fauna rather than pollution, climate or atmospheric stresses. This is not to say the other factors are unimportant but that they may not be the sole drivers of the health of coral reefs.
Given the correct conditions coral reefs demonstrate large variations in community composition and species abundances with associated high levels of resistance and resilience. The capacity to recover and regenerate following disturbance has ensured the dominance of hard corals in shallow tropical seas for many thousands of years, but this ability, in many areas, is now in sharp decline. Widespread disturbance from human activities such as overfishing, habitat destruction and pollution are working together with increasingly frequent natural phenomena causing large-scale reductions in biodiversity opening up the potential for dramatic shifts in species dominance.
A once majestic stand of Acropora palmata (Elkhorn Coral) now a skeleton which will eventually turn to rubble.
Daily life down below
Captain’s work station
Bob set out from his home in Maine, heading down the east coast of the States on Alaria, a 34ft Pacific Seacraft, out to Bermuda and then down to St Maarten (a fair old trek!) which is where I would meet up with him. I had a couple of days on land before Bob arrived, enough time to make acquaintance with the staff at the St Maarten Marine Park and track down a diving compressor which we would need to bolt to Alaria before we headed further south.
Bob (and crew) arrived after a short delay (to read an in-depth account of Bob’s journey see Bob’s blog). There was no messing around! The compressor was hauled out and promptly bolted to the boat. Then plans were made to dive the following day with the director of the marine park, using their dive boat.
I’ve dived a lot in the Caribbean but this has all been in the west, around the Bay Islands of Honduras and further south near Nicaragua, so I was intrigued to see how the reefs here compared. Obviously the species would all be the same but, seeing as there’s around 2500km of deep water between the eastern and western reefs there would no doubt be some noticeable variation. Bob had told me stories of Elkhorn coral forests which he’d dived 40yrs previously and this excited me. Extensive Acropora reefs, in general, are comparatively rare in the Caribbean, mostly killed off by white-band disease (a subject for another time) so it’s always a treat for the eyes to stumble across any significant Acropora colonies.
Heading out in the zodiac on a reconnaissance mission looking for potential survey sites.
Our survey methodology would loosely follow a protocol Bob helped develop around 20yrs ago and what has become known as the Atlantic and Gulf Rapid Reef Assessment, or AGRRA. It basically allows all reef organisms to be broadly characterised in a short amount of time – a good section of reef can be surveyed in just a few dives. Throughout the survey my main responsibility underwater was to count and identify species and assess body size of ‘important’ reef fish (‘important’ meaning those which have greatest influence on reef function, principally herbivores and predators). Essentially I would swim a 30m transect line and record all fish 2m either side of the line, while Bob would do the same looking at coral species, algae, and other reef-dwellers.
So we began what was to be 2 months of fairly intensive surveys. The sites we dived in St. Maarten were not really coral reefs rather thin veneers of coral over bedrock. However, because we were diving inside the marine park, and because enforcement here is relatively good, fish numbers, at least in retrospect, weren’t too bad. I’ve found throughout my diving in the Caribbean (both east and west) that numbers of large-bodied herbivores such as parrotfish are always alarmingly scarce. The same was true on St. Maarten, no doubt a result of years of spearfishing and trapping, but general diversity for sites with little in the way of coral seemed ok. I even saw a couple of Caribbean reef sharks which is a pretty rare thing these days!
After a few days diving St. Maarten, restocking supplies and saying goodbye to a couple of Bob’s long-haul crew members, we headed off to start the journey down the Antillean island chain. Initially though we headed north a short way across the channel to Anguilla where we spent another couple of days diving inside an apparent marine reserve (at least on paper). Fish numbers here were noticeably low and the reef in obvious decline no doubt, in part, due to the alarming number of fish traps we came across whilst diving. After a bit of research, it would seem the 5 marine reserves around Anguilla were set up to minimise the impact of anchor damage but still allow all forms of fishing. Other than that there isn’t much detail on any other conservation objectives.
One of the few healthy stands of Elkhorn coral we came across
From Anguilla we set sail southeast toward Antigua & Barbuda. This was an overnight trip and conditions were about as good as we could hope for. Bob had installed an autopilot mechanism which, on calm crossings, proved incredibly effective meaning when on watch, for the most part, you could sit back and relax…although as this was my first sailing trip I didn’t feel completely relaxed even on these calm crossings!
After a calm, moonlit night we came into the beautiful English Harbour, cruising around the south western edge of Antigua. We would base ourselves in Antigua for a couple of weeks, making short trips to the eastern reefs as well as a few days on Barbuda which is governed by Antigua.
From satellite imagery the reef development along the eastern coast of Antigua seems relatively extensive. A few years ago that would have been the case, as Bob confirmed from his surveys 30yrs ago. However, the majority of the reefs we dived in this area were in poor condition. In many cases there were remnants of once majestic reef-building corals, Acropora and Montastraea, but most of these were dead or dying, reduced to skeletons and rubble. Combined with fishing (by spear, traps and line) which, although small-scale, is fairly constant, the diversity on these reefs was noticeably low. Reef-building corals, as their name suggests, form the foundation of the reef providing a platform and refuge for many other species. They are essentially responsible for maintaining biodiversity and once they are gone so too is much of the associated marine life.
Tools of the trade
The reasons for the decline in these reefs, in fact reefs globally, are many and complex but essentially it is due to combined natural and human pressures. Historically, coral reefs have always had the capacity to recover and regenerate following disturbance. Natural disturbances such as hurricanes, periodic temperature rises, tsunamis etc have always occurred and reefs have always recovered, but coupled with human disturbances such as overfishing and pollution much of the resilience of corals has now been lost. Added to this the increased frequency of natural disturbances as a result of climate change and a large number of reefs around the world are really struggling. Once biodiversity begins to decline many reefs begin to undergo a process known as a phase shift whereby once dominant corals are replaced by faster growing species such as algae (seaweed). Once algae take hold it is very difficult for new corals to settle and so a once rich, diverse reef becomes barren and lifeless. This is happening to many of the world’s coral reefs but the Caribbean has been particularly susceptible, part. Over the last 30 or so years there have been a number of significant ecological events which have severely disrupted Caribbean reefs. As a result, there have been declines of up to 97% of some coral species. Two of the major reef-building corals are now on the IUCN Red List classed as critically endangered.
A staff member of the Barbuda marine park authority, fishing for lobster inside one their own reserves
Despite the relatively poor condition of many of the reefs, Antigua itself was undeniably beautiful. Some of our overnight anchorages were so perfect they were almost tropical clichés – deserted white sand beaches with water so clear and turquoise it almost hurt your eyes. After a few days diving the eastern reefs we made the short hop over to Barbuda where we’d arranged to dive with some of the staff from the marine park office.
Seeing as we were diving in a marine park we were cautiously optimistic. Unfortunately, our caution was justified – the reefs here were also not in great shape. After our last dive a member of the marine park staff proudly showed us his bag of spiny lobsters he’d just caught inside one of their reserves. With the exception of St. Maarten, where specific regulations were in place and enforcement was fairly effective, it would seem most of the other reserves we dived didn’t seem to meet any kind of conservation objectives. I would guess most were set up as a token gesture and maybe prevent a bit of anchor damage, but by continuing to allow fishing in whatever form the label ‘marine reserve/park’ is rather meaningless.
More dead coral
And even more dead coral
Barbuda itself was fascinating for its topography as well as its human and natural history. The island itself is barely visible, appearing only as a thin strip of sand on the horizon until you get relatively close. Its highest point of elevation is just 42 metres. It has a population of around 90,000 and it quickly becomes noticeable that many of the blokes are rather hefty, and by that I mean tall, lean and muscular. Apparently, according to some, this is due to the island once being used as a slave breeding ground in an attempt to produce the perfect slave…an awful thought indeed! Apart from the donkeys which appeared to outnumber people Barbuda is fairly well-known for its large colony of nesting Frigatebirds, undoubtedly an impressive sight and one which, unfortunately we didn’t get to see during our brief visit.