In the past year there has been a notable amount of publications on climate driven impacts on coral reef fishes. This post will attempt to review a portion of this literature, taking a look at three specific articles which were of interest and relevance to this blog.
The first paper of choice looks at reef fish responses to coral recovery following El Niño disturbances. I chose this paper because it looks at long term coral and fish responses from the 1982-1983 as opposed to the 1997-1998 bleaching event where long term analysis isn't possible just yet. After being reduced to 0% coral cover in Uva Island Reef, Panama, coral response was minimal in the following 10 years, with notable response (35%) occurring by 2010. The study found that following the 1982-83 bleaching event coral fish densities varied little over the sampling period of 30 year,s however there was a sharp response in recovery when coral cover recovered between 0 and 20%, waning after 20% recovery. They propose that fish diversity was related to the diversity and availability of food and shelter resources which also followed this parabolic trend. Following coral reef degradation and coral rubble transformation, the presence of cryptic invertebrates increases which, according to this article, provides prey for fish consumers, allowing populations to bounce back and recover.
The rather positive outlook of the previous article is contrasted by a study by Brooker et al published last year which much like what was explained in a short lecture in a previous post stresses the danger of local level extinctions of marine species. This article raises awareness to the local extinction of the corallivorous reef fish Oxymonacanthus longirostris following an intense mass bleaching event. They found that this extinction was due to loss of a key prey species Acropora millepora (Am) despite overall coral cover remained high. Further to this they found that the fish chose to feed on the bleached coral as opposed to alternative unaffected species in an experimental test that compared their feeding habits with healthy Am, bleached Am, and healthy Acropora noblilis (An). The continued selection of Am, regardless of condition, suggests that even when bleached Am either is a superior resource or that inherent preferences persist despite changing conditions. This article makes me reflect on the findings of the previous article that solely looks at the response of invertebrate feeding fish and those that don't have such a specified diet. As discovered with this article, responses are clearly more complex when corallivorous species are considered and/or those with behavioural inflexibility.
The third and final article in this review emphasises the role of structural complexity and the difference between coral mortality and eventual coral erosion. Ecologically driven coral mortality (for example the introduction of coral eating sea stars in this case) differs significantly from climate driven events (post Tropical cyclone) which normally induces complete skeletal erosion in the coming years/decades. When the latter occurs, a lack of structure significantly impacts the ability of fish species to survive, which has implications for short term studies on fish species response, as more significant responses are seen on longer timescales. The results of this article highlight the ability of disturbance type to influence rate at which structural complexity declines post mortality and therefore the impacts on reef associated fish species. The results from this article bears significance as it highlights that climate driven as opposed to ecologically driven changes are most detrimental, but also emphasises the value and need for long term studies.
While all of these articles produce interesting (and sometimes conflicting results) I think scale is an important constraint to the applicability of the results. Obviously it is incredibly difficult and resource consuming to produce a long term metaanalysis of coral reef and fish response to global bleaching events at a number of sites. I hope that as scientists and academics scramble to the sites where this year's bleaching event is impacting, there are collaborative efforts to look at differences (or indeed similarities) between sites.
No comments:
Post a Comment