Climate–change and fish 1. Tropics Flashcards
What is macroecology?
? Doing work at a large scale, often not using the experimental work that forms the gold standard throughout other areas of research. By scaling the process up you can make the measurements on large scale so you don’t have to worry about scaling up. You lose the capacity to specifically identify other factors.
What coral reef topic areas should you be able to talk about?
How can we measure large-scale changes?
Bleaching events
Impacts on reef benthos, habitat, fish and fisheries
Caribbean coral reef degradation
Impacts on habitat complexity
Different origins of coral mortality
Other sources of damage: fishing, OA, nutrients, diseases
What types of experiment will have a higher strength of inference, and what types will have a higher environmental relevance?
Strength of inference – the greatest chance of actually relating the structure of the system to a particular factor. Done an experiment and shown that the factor has an effect.
Environmental relevance – relevant to policy and creating the evidence that we need in order to build a policy
- Randomly assign individuals are manipulative experiments. These are good experiments as you can get a definitive result for the factor.
- Other ends of the scale – no treatment available, where observational data is used. Observational data does not allow for a control, and you cannot rule out the roles of other factors. Often relies on a correlation.
- Macroecology - whilst it would be nice to do experiments for every factor, it is not feasible.
What threats are facing coral reefs?
Degradation of coral reefs
The last 50 years have seen what appear to be unprecedented large-scale events including coral and sea-urchin diseases, invasive species (e.g. lionfish), natural disasters (e.g. larger and more frequent cyclones), Saharan dust-storms (including iron, with is limiting nutrient and spores, coral and urchin disease events could have been caused by dust) nutrient inputs
To which are now added at least climate-related coral bleaching and ocean acidification
Warming, nutrients, cyclones, fishing, COT outbreaks
NICK paper
Bleaching events
Impacts on reef benthos,
Summary
(Graham et al, 2006)
Here we show that climate change-driven loss of live coral, and ultimately structural complexity, in the Seychelles results in local extinctions, substantial reductions in species richness, reduced taxonomic distinctness, and a loss of species within key functional groups of reef fish.
The importance of deteriorating physical structure to these patterns demonstrates the longer-term impacts of bleaching on reefs and raises questions over the potential for recovery. We suggest that isolated reef systems may be more susceptible to climate change, despite escaping many of the stressors impacting continental reefs.
1998 bleaching event right across the tropics, hit the Seychelles very badly.
NICK paper
Bleaching events
Impacts on reef benthos,
Findings
(Graham et al, 2006)
Comparing data before and a few years later. Straight comparison between the two dates, shows a significant separation of the two.
Branching and plating corals have suffered particularly – around 95% decline in cover. Important as they stick up to create the physical environment.
Study allows comparison before and after and between protected (crosshatching) and not protected sites
Complex corals and the three different kinds of reef that were looked at.
Branching and plating corals particular sensitive .
Compare protected corals to those that are not protected.
Sites that were chosen as MPAs would have had a lot of complex corals which would have been particularly vulnerable to bleaching
Fish exclusive eating coral were lost. Whether they died or moved to deeper water is unknown
21 sites, ranked according to the amount of physical habitat they have lost. When you do that and look at the structure of the fish community, gain and loss.
Coral feeders decline when the live corals die, even when structure remains. Fish may have moved rather than dies.
Basin-scale effects coral bleaching meta analysis - assesing different groups - NICK paper
Wilson et al. 2006
- In this paper – an analysis of a whole load of data from the western Indian ocean.
- When you look at the richness of all species, they are related to the depletion of corals at a large scale.
- Look at the obligate corallivores – can see a particularly strong effect
- Herbivores do not see such a strong trend (can consume algae)
- Planktivores and all species (Richness are showing some effect)
- Mixed diet – algae – may benefit
Our assessment of the impacts of the 1998 mass bleaching event on coral cover, reef structural complexity, and reef associated fishes spans 7 countries, 66 sites and 26 degrees of latitude in the Indian Ocean. Using Bayesian meta-analysis we show that changes in the size structure, diversity and trophic composition of the reef fish community have followed coral declines. Although the ocean scale integrity of these coral reef ecosystems has been lost, it is positive to see the effects are spatially variable at multiple scales, with impacts and vulnerability affected by geography but not management regime.
Existing no-take marine protected areas still support high biomass of fish, however they had no positive affect on the ecosystem response to large-scale disturbance.
Changes in Caribbean coral reefs
What causes the degradation of the reef - Nick paper
Gardner TA et al. 2003 Science 301: 958-960•Decline before and after urchin disease suggests something else involved here - different hypothesis include
Fishing removes grazers, leading to algal overgrowth
- Nutrients contribute to algal overgrowth and coral loss
- 90-99% mortality of urchins in 1982-83 led to algal overgrowth
Later data than Gardner et al study, regional effects tested
- Most coral loss by ~1981, related to Acropora white band disease
- Greatest macroalgal increase related to sea-urchin die-off
- Trends different among regions (especially Florida Keys)
fish size latitiude
Nick Paper
Stallings CD 2009 PLoS ONE 4 (5): e5333
The different countries are really different in the makeup of the fish communities
On the left-hand side there are lots of big fish which are important fisheries targets. These fish are lost towards the right
Driven by human population density and latitude
Many sharks, jacks, large groupers and snappers
(Human population density (also latitude effect))
Fewer large predators: trumpetfish, small groupers and snappers
Background
Understanding the current status of predatory fish communities, and the effects fishing has on them, is vitally important information for management. However, data are often insufficient at region-wide scales to assess the effects of extraction in coral reef ecosystems of developing nations.
Methodology/Principal Findings
Here, I overcome this difficulty by using a publicly accessible, fisheries-independent database to provide a broad scale, comprehensive analysis of human impacts on predatory reef fish communities across the greater Caribbean region. Specifically, this study analyzed presence and diversity of predatory reef fishes over a gradient of human population density. Across the region, as human population density increases, presence of large-bodied fishes declines, and fish communities become dominated by a few smaller-bodied species.
Conclusions/Significance
Complete disappearance of several large-bodied fishes indicates ecological and local extinctions have occurred in some densely populated areas. These findings fill a fundamentally important gap in our knowledge of the ecosystem effects of artisanal fisheries in developing nations, and provide support for multiple approaches to data collection where they are commonly unavailable
Calcification rate
Calcification rate will fall because of oceanic ‘acidification’ due to CO2
Coral reefs good tropical example of an ecosystem subject to multiple stressors, the outcome of which is hard to predict!
Kleypas JA et al. 1999. Science 284: 118-120
What other factors may effect meta analysis of coral reefs?
Dust storms with potential nutrient and disease consequences
List the factors degrading coral reefs, whats being effected and the Ecosystem-based management tools at different scales/.
Factors
- Bleaching
- Disease
- Acidification
- Storms
- Nutrients
- Runoff
Ecosystem
- Fish
- Corals
- Reef
- Algae
Management
- Society, policy, and management (international and local action)
- Subsistence employment, trade
- Goods, services
Summary
- Macroecological approaches have allowed us to analyse bleaching effects at the scale relevant to management and policy.
- Impacts on: reef benthos, habitat complexity, fish and potentially fisheries
- The Caribbean provides the most striking case of coral reef degradation, effects on habitat, ecosystem services, and fish
- Coral as Achilles heel; many threats including fishing, OA, nutrients, diseases
Importance of structural complexity in coral reefs.
methods
Graham and nash, 2013: The importance of structural complexity in coral reef ecosystems
- Methods: meta-analysis of the literature from 1972-2010 on Web of Science, papers only specifically related to reef structural components were retained
Importance of structural complexity in coral reefs.
Results
Graham and nash, 2013: The importance of structural complexity in coral reef ecosystems
Results:
- Resulted in 158 publications examining the role of structural complexity in coral reefs
- Cover of total live coral and branching coral was positively correlated with structural complexity
- Urchin densities negatively associated with structural complexity – relationship may be driven by urchins eroding reef or by gregarious behaviour when in open space
- The strongest relationship between fish density and biomass with increased structural complexity – the same as found in Wilson, 2007 – likely due to density-dependent competition and refuge from predation