Coral reef food webs are out!

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biodiversity, coral reef, corals, food webs, marine communities, real world networks, trophic guild

The first paper dealing with our Caribbean coral reef work is finally out. This paper is really just a detailed account of the data and webs compilation, but the data are now available to all. Enjoy!

Roopnarine, Peter D. and Rachel Hertog. 2013. Detailed Food Web Networks of Three Greater Antillean Coral Reef Systems: The Cayman Islands, Cuba, and Jamaica. Dataset Papers in Ecology, Vol. 2013, Article ID 857470, 9 pages.

Abstract: Food webs represent one of the most complex aspects of community biotic interactions. Complex food webs are represented as networks of interspecific interactions, where nodes represent species or groups of species, and links are predator-prey interactions. This paper presents reconstructions of coral reef food webs in three Greater Antillean regions of the Caribbean: the Cayman Islands, Cuba, and Jamaica. Though not taxonomically comprehensive, each food web nevertheless comprises producers and consumers, single-celled and multicellular organisms, and species foraging on reefs and adjacent seagrass beds. Species are grouped into trophic guilds if their prey and predator links are indistinguishable. The data list guilds, taxonomic composition, prey guilds/species, and predators. Primary producer and invertebrate richness are regionally uniform, but vertebrate richness varies on the basis of more detailed occurrence data. Each region comprises 169 primary producers, 513 protistan and invertebrate consumer species, and 159, 178, and 170 vertebrate species in the Cayman Islands, Cuba, and Jamaica, respectively. Caribbean coral reefs are among the world’s most endangered by anthropogenic activities. The datasets presented here will facilitate comparisons of historical and regional variation, the assessment of impacts of species loss and invasion, and the application of food webs to ecosystem analyses.

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BBC News – Coral reefs heading for fishing and climate crisis

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climate change, coral reef, corals, extinction, marine communities, pollution

BBC News – Coral reefs heading for fishing and climate crisis.

Regional biases in Caribbean coral reef food webs?

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connectance, coral reef, corals

Cayman Islands coral reef vertebrates food web

We have now constructed models of three Greater Antillean coral reef communities: the Cayman Islands, Jamaica and Cuba. Granted, the models/communities are defined by political entities, but there is no denying that physical contiguity of the reefs within these nations far exceeds the connections between localities. So we’ll consider them as separate communities within a regional ecosystem. The question that we’re interested in is, are there significant differences among these reef communities that cannot be explained by stochastic processes, such as the vagaries of immigration, colonization and population persistence.

Cuba

The overall vertebrate (fish and reptiles) regional diversity in the models, or gamma diversity, is 169 species (a total of 735 species in the food web, including primary producers, invertebrates, etc.). The food web alpha diversities are: Caymans – 155, Cuba – 134 and Jamaica – 147. These diversities are all very close to each other, as well as the gamma diversity. But are they unbiased samples of gamma diversity? As a first test of this, we asked whether the connectance of the local food webs could be derived from the regional pool in unbiased fashion. We therefore constructed 1,000 food webs, at each level of alpha diversity, by drawing species randomly from the regional pool, calculating their connectances, and then comparing the observed to the “expected”. Interestingly, the answer is a resounding NO!

• Cayman connectance (C) = 0.0594606; randomizations, , p=0.295.
• Cuba C = 0.0594165; , p = 0.298.
• Jamaica C = 0.0620494; , p<0.00001.

Jamaica

You should notice that connectance bears no relation to alpha diversity. In fact, the randomizations fail to reject the hypothesis that the Cayman and Cuban reefs are anything other than random draws from the regional pool. Jamaica, however, stands out. Connectance of the Jamaican web is significantly greater than expected. This implies that if the Jamaican web were indeed drawn from the regional pool, then there would be a bias in favour of link-rich species. Translated ecologically, Jamaica is relatively depauperate in trophically specialized species (few links).

What could generate that bias? We hypothesize the more degraded state of Jamaican reefs relative to the Caymans, a proportionally smaller area of protected reefs, and greater fishing pressure. Interestingly, Cuba has fewer species included in our model, yet shows no biases, as expected given our hypothesized factors.

Do we care about the oceans?

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corals, food webs, trophic level

(CITES)

First there was the failure to place a ban on bluefin tuna. The decline and ultimate loss of this high trophic level species will reverberate throughout oceanic food web networks and human economic networks. This was followed by the failure to control international trade in red and pink corals (read the CITES press releases here), even though the major backer was the United States. In the same consideration, however, renewed sale of elephant ivory by Zambia and Tanzania was rightfully blocked. I can’t help but get the feeling that perhaps, if tuna and corals were embedded in the mentality of circus nostalgia to the extent that elephants are, or if Zambia and Tanzania counted as much on the global scale as do Canada and Japan (opponents of the ban on bluefin fishing), these decisions would have worked out a bit differently.

Coral reefs and climate change, a message for Copenhagen

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climate change, coral reef, corals

Coral reefs and climate change, a message for Copenhagen from Earth Touch on Vimeo.

Scientists Work To Protect Cuba’s Unspoiled Reefs

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coral reef, corals

Los Jardines de la Reina, Cuba (NPR photo)

Scientists Work To Protect Cuba’s Unspoiled Reefs

Coral reef fish food webs

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coral reef, corals, extinction, food webs, Network theory, real world networks, trophic level

Reef fish food web, Greater Antilles

Here are a couple of renderings of the vertebrate-only component of the coral reef food web. Reminder: the food web is what we expect to see for a reef in the Greater Antilles of the Caribbean, based on data collected around the mid-20th century. The vertebrate component comprises all fish and sea turtle species. The upper figure is the expected food web, and includes 196 species and 995 trophic interactions. Species are arranged on the periphery of the diagram, with interaction represented by the lines crossing the interior. The very busy, or hub species are higher trophic level predators, mostly carcharhinid sharks.

Jamaica coral reef fish food web

The lower figure is what we observe today in Jamaica. (Note: Jamaica is of particular interest for me as a starting comparison, both because of the excellent documentation of those reefs, and my Jamaican heritage; not picking on Jamaica). The number of species, out of 196, observed there over the past 10 years is dramatically smaller. Perhaps more obvious is the loss of interactions. I won’t present the actual data yet, since we will eventually prepare a paper to report all this, but the differences between the two food webs are obvious. We are currently rendering the complete food web, including primary producers and invertebrates, which will be an update of the figures presented in earlier posts. But there are a lot of species in there, and the computers have been churning now for about 17 hours!

Sobering

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coral reef, corals, extinction

I started to match our Caribbean coral reef food web data to assessments of Jamaican reefs today. I used 10 years of careful observations. I basically just sat there and watched my dataset fall apart as species after species failed to appear on the Jamaica list. Where have all the species gone? I’ve worked on extinction for quite some time now, I know many of the people who work on these systems well and we talk, and I talk a lot with relatives (mom included) who are Jamaican and remember the way that it was. It is depressing, it’s sobering, and it’s humbling. I don’t think that I’ve ever had a more depressing day of science. Our species is both remarkable, and remarkably stupid. Sigh.

Power law confirmed

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coral reef, corals, food webs, Network theory, networks, power law

Species-level trophic link distribution

Okay, this post just disappeared, so let’s try again. The updated and correct coral reef food web comprises 759 species. The incoming trophic link distribution, when expanded to the species level (compared to the guild level in the previous post), is a definite power law distribution. The log-transformed data (see figure) yield a function of , i.e. . See the earlier coral reef posts to understand why this is significant.

Coral reef trophic levels, & update

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coral reef, corals, food webs, Network theory, networks, power law, trophic level

Guild-level trophic link distribution

Spent a great week at the Annual Meeting of the Geological Society of America. The Paleontology Society session on Conservation Paleobiology was a lot of fun, and my students also presented great posters. Now back to the coral reef.

I’ve been cleaning up the data, because with some much data, errors are bound to creep in. I believe that the current data are now accurate, and the metanetwork statistics are 265 guilds (including primary producers) and 4,651 links. That yields a metanetwork connectance of 0.066. The link distribution should therefore also be different, and indeed it is. The figure shows the no. of links per guild, and the regression plot demonstrates that the distribution is still a power law distribution. The exponent is smaller than previously calculated, (), but this is the guild-level network and does not reflect species richnesses (yet).

Trophic level vs. no. of links

The next question that I’m looking at is the distribution of trophic levels among guilds and species. I therefore calculated trophic level for all guilds. The first figure (scatter plot) plots trophic level against the number of prey or incoming links to each guild. There are two things to notice: First, the variance of trophic levels decreases as the number of links, or diet generality of the guild increases. Second, the decrease in the variance is asymmetric, in that there is a bias against being a generalist of low trophic level. This is obvious if you look at all the empty space being vacated below the data points as no. of links increases. I can think of two non-exclusive explanations for this. If you think about a food chain, consumers toward the top of the chain simply have more prey to select from (on an evolutionary timescale), and therefore there should be a natural increase in the number of generalists as trophic level increases. Also, note that there are also many specialists of high trophic level. Perhaps the ability to exert power over other species, as a predator, combined with the previous statement, explains this observation. Finally, what is the distribution of trophic levels within the community? The second figure is a simple histogram plot of all non-primary consumer guilds (i.e. omnivores and carnivores). The distribution is approximately normal, with a definite central tendency. On average, most guilds in the reef are of similar trophic level! That’s very interesting. And referring to the previous scatter plot, we know that there is a biased composition in the tails of the distribution, in that the upper tail (higher trophic level) is a mixed composition of specialist to generalist guilds, but the lower tail is basically restricted to low trophic level specialists.

Guild trophic level distribution

Some of you may have noticed that our trophic levels are non-integer numbers. Primary producers all occupy trophic level 1, and primary consumers are trophic level 2. “Above” that, trophic level is calculated on the basis of the trophic levels of your prey. Exactly how we do that will remain a secret for now.