[Coral-List] Impact of nutrient enrichment on coral reefs

Sun Mar 16 16:41:27 EDT 2014

Dennis,

thank you for your comments! Regarding the role of fish there have been important new insights. For instance, fish species commonly thought to prevent phase shifts to reefs dominated by macroalgae (e.g. parrotfish) might not be able to reverse them (Bellwood et al, 2006 Current Biology 16, 2434–2439). Moreover, I saw recently a talk by Chris Perry during which he showed a parrotfish reducing an Acropora colony to rubble. Therefore, having too many parrotfishes might not necessarily be the best for the reef and top predators are certainly required to keep a healthy balance. Overfishing thus carries a high risk that species with as yet unrecognised functions in stabilising reef resilience might be removed. Additionally, fish assemblages might show an unfavourable dominance of certain species. Overall, I feel that both nutrient effects of corals and the role of fish in coral reef ecosystem functioning deserve continued attention in the future!

Best,

Joerg

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Prof. Dr. Jörg Wiedenmann
University of Southampton, Waterfront Campus, NOCS
Southampton, SO14 3ZH, U.K.
http://noc.ac.uk/corals
email: joerg.wiedenmann at noc.soton.ac.uk
Mobile: +44 (0)7912564356

Projects on thermal stress tolerance of corals:
http://www.southampton.ac.uk/oes/research/projects/coral_bleaching.page
http://www.southampton.ac.uk/oes/research/projects/gulf_corals.page

<http://www.mobitec.com/cms/products/bio/07_fluores_tec/eosfp.html>
________________________________
From: Dennis Hubbard [dennis.hubbard at oberlin.edu]
Sent: Friday, March 14, 2014 2:18 PM
To: Wiedenmann J.
Cc: coral-list at coral.aoml.noaa.gov
Subject: Re: [Coral-List] Impact of nutrient enrichment on coral reefs

Joerg:

Thanks very much for bringing this paper to our attention. It will be very useful to myself and to my students. In class, we have just completed a first look at the intersection between top-down and bottom-up stresses and I used a home-grown modeling simulation that requires them to do multiple runs at varying levels of nutrient enrichment and overfishing. Because each "event" in the model (e.g., fish eating an encountered alga, coral recruitment, negative macro-algal impacts on a specific coral) has a different degree of randomness applied to it, this "fuzzy logic" dictates that a) successive runs do not produce absolutely intical results and b) the system behaves in a very non-linear way both as it crashes and as stresses are removed to encourage "recovery".

While this approach gives them (and many are non-science majors) a healthy appreciation of the non-linearity of natural systems going into discussions of climate change as the third leg of the stool (and the relative economics of avoiding the problem at today's costs versus fixing it at discounted rates in the future), I found myself remembering papers a couple of decades back that challenged the importance of nutrient loading. A number of equally thoughtful papers followed that argued otherwise. However, I never developed a clear sense of what folks wrestling with this ultimately decided.

So, first, thanks for what appears like an excellent overview. Second, and to the larger "brain trust", do the seemingly realistic ideas reflected in this manuscript reflect the larger opinions on this important topic? I'm less concerned over arguments over the primacy of particular stresses (i.e., is climate change or local stress the gorilla in the room?) than I am about where the science on nutrient impacts relative to overfishing has come over the past decade. This is not a semantic question and there is no hidden agenda. I am asking purely out of ignorance and interest.

Best,

Dennis

On Fri, Mar 14, 2014 at 3:14 AM, Wiedenmann J. <joerg.wiedenmann at noc.soton.ac.uk<mailto:joerg.wiedenmann at noc.soton.ac.uk>> wrote:
Dear all,

our new publication on the impact of nutrient enrichment on corals and coral reefs can now be freely downloaded from the COSUST page: http://www.sciencedirect.com/science/article/pii/S1877343513001917

We discuss, among other issues, the role that the competition for nutrients by phytoplankton might play in disturbing the nutrient balance in reef ecosystems. The abstract is attached below.

Best wishes,

Joerg

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Prof. Dr. Jörg Wiedenmann
University of Southampton, Waterfront Campus, NOCS
Southampton, SO14 3ZH, U.K.
http://noc.ac.uk/corals
email: joerg.wiedenmann at noc.soton.ac.uk<mailto:joerg.wiedenmann at noc.soton.ac.uk>
Mobile: +44 (0)7912564356<tel:%2B44%20%280%297912564356>
Projects on thermal stress tolerance of corals:
http://www.southampton.ac.uk/oes/research/projects/coral_bleaching.page
http://www.southampton.ac.uk/oes/research/projects/gulf_corals.page
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

D’Angelo, C., Wiedenmann, J., 2014. Impacts of nutrient enrichment on coral reefs: new perspectives and implications for coastal management and reef survival. Current Opinion in Environmental Sustainability 7, 82-93.
Anthropogenic nutrient enrichment is often associated with coral reef decline. Consequently, there is a large consent that increased nutrient influxes in reef waters have negative longterm consequences for corals. However, the mechanisms by which dissolved inorganic nutrients can disturb corals and their symbiotic algae are subject to controversial debate. Herein, we discuss recent studies that demonstrate how nutrient enrichment affects the heat and light stress tolerance of corals and their bleaching susceptibility. We integrate direct and indirect effects of nutrient enrichment on corals in a model that explains why healthy coral reefs can exist over a rather broad range of natural nutrient environments at the lower end of the concentration scale and that anthropogenic nutrient enrichment can disturb the finely balanced processes via multiple pathways. We conceptualise that corals can suffer from secondary negative nutrient effects due to the alteration of their natural nutrient environment by increased phytoplankton loads. In this context, we suggest that phytoplankton represents a likely vector that can translate nutrients effects, induced for instance by coastal run-off, into nutrient stress on coral reefs in considerable distance to the site of primary nutrient enrichment. The presented synthesis of the literature suggests that the effects of nutrient enrichment and eutrophication beyond certain thresholds are negative for the physiological performance of the coral individual and for ecosystem functioning. Hence, the immediate implementation of knowledge-based nutrient management strategies is crucial for coral reef survival.
<http://www.mobitec.com/cms/products/bio/07_fluores_tec/eosfp.html>
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--
Dennis Hubbard
Chair, Dept of Geology-Oberlin College Oberlin OH 44074
(440) 775-8346

 "When you get on the wrong train.... every stop is the wrong stop"
 Benjamin Stein: "Ludes, A Ballad of the Drug and the Dream"

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