Noses baffled by ocean acidification

18 04 2017

Clown fish couple (Amphiprion percula) among the tentacles of anemone Heteractis magnifica in Kimbe Bay (Papua New Guinea) – courtesy of Mark McCormick. Clownfish protect anemones from predators and parasites in exchange of shelter and food. The fish tolerates the host’s venom because its skin is protected by a mucus layer some 2-3× thicker than phylogenetically related species (12); clownfish fabricate the mucus themselves and seem to obtain anemone antigens through a period of acclimation (13), but whether protection is acquired or innate is still debated. Clownfish are highly social bony fish, forming groups with one reproductive pair (up to 11 cm in length each) and several smaller, non-reproductive males. Reproduction is protandrous (also known as sequential hermaphroditism), so larvae are born male and, as soon as the reproductive female dies, her widower becomes female and the largest of the subsidiary males becomes the alpha male. The IUCN lists clownfish, generically named ‘anemone fish’, as threatened by the pet-trade industry and habitat degradation, although surprisingly, only 1 species has been assessed (A. sandaracinos). The clown anemone fish A. ocellaris is the species that inspired Nemo in the 2003 Academy-Award fiction movie – contrary to the logical expectation that the Oscars Red Carpet would generate support for conservation on behalf of Hollywood, of the 1568 species represented in the movie, only 16 % of those evaluated are threatened (14).

Smell is like noise, the more scents we breathe in one sniff, the more difficult it is to distinguish them to the point of olfactory saturation. Experimental work with clownfish reveals that the increase in dissolved carbon dioxide in seawater, mimicking ocean acidification, alters olfactory physiology, with potential cascading effects on the demography of species.

Places such as a restaurant, a hospital or a library have a characteristic bouquet, and we can guess the emotional state of other people by their scents. Smell is critical between predators and prey of many species because both have evolved to detect each other without the aid of vision. At sea, the smell of predators dissolves in water during detection, attack, capture, and ingestion of prey, and many fishes use this information to assess the risk of ending up crunched by enemy teeth (1, 2). But predator-prey interactions can be modified by changes in the chemical composition of seawater and are therefore highly sensitive to ongoing ocean acidification (see global measuring network here). Experts regard ocean acidification as the ‘other CO2 problem’ of climate change (3) — just to emphasize that anthropogenic climate-change impacts terrestrial and aquatic ecosystems alike. Acidification occurs because the ocean absorbs CO2 at a rate proportional with the concentration of this gas in the atmosphere and, once dissolved, CO2 becomes carbonic acid (H2CO3), which in turn releases protons (H+) — in simple terms, pH is the concentration of protons (see video about ocean acidification): Read the rest of this entry »





Noisy oceans

20 01 2014
killers & boats
Killer whales are social animals that navigate all oceans and seas between the Arctic and Antarctica – they can be regarded eusocial since reproduction ceases around 40 years of age and menopausal females help care for offspring: like humans [13, 14]. Group cohesion in killer whales relies on a complex repertoire of vocalisations including clicks, whistles and calls. Sounds are instrumental for prey searching, orientation and communication. Foote [5] focused on calls, which are made up of series of discrete sounds that resemble squeaks, screams, and squawks to the human ear. It has been postulated that individuals learn to vocalise by imitation of peers of the same pod, and that only the base structure has a genetic, hence heritable, component [15]. Regardless, pods develop regional dialects. Those dialects, along with aspects of diet, genetics, morphology and behaviour, differentiate the three main lineages of killer whales (resident, transient and open sea) that might have been genetically isolated for ~ 150 to 700 thousand years and, potentially represent different taxa [16, 17]. The species might abandon the IUCN conservation category of ‘Data Deficient’ as soon its taxonomic uncertainty is resolved.Resident killer whales form matrilineal groups of 2 to 15 individuals  (the matriarch and her offspring) – known as pods, in turn subdivided into subpods centred around grandmothers and great-grandmothers. The Southern Resident population is regarded as an acoustic clan comprising 3 pods currently numbering 81 individuals = 26 (J pod) + 19 (K pod) + 36 (L pod) (2013 survey), among whom the matriarch Granny is the oldest at 103 years! This clan feeds mainly on fish, and dwells in the coastal waters between British Columbia (Canada) and Washington State (USA), particularly south of Vancouver Island – nothing is known about where they spend the winter. The clan lost 20 % of its members between 1995 & 2001, and 13 more by 2013, and now faces the decline of its main prey: Chinook salmon (Oncorhynchus tshawytscha) [18]. The two pics show two sub pods of this clan swimming close to a whale-watching boat near Friday Harbour (San Juan Island) and a Chinese ship at Puget Sound (Seatle, USA). Photo credits: Marla Holt, NOAA/NMFS Northwest Fisheries Sciences Center.

Acoustic pollution has become a transnational issue, particularly in marine ecosystems [1] by virtue of the physical fact that sounds travel in water farther and faster than in air. In our noisy, modern world, many species are now forced to modify their vocal repertoire in response to noise. The pivotal social role that vocalisations play in all cetacean species makes these predators and filter feeders particularly vulnerable to this environmental problem.

Last night, an ambulance siren woke me, only seconds before the neighbour’s washing machine started spinning, and a good friend of mine rang from overseas. Gradually more and more people are living in societies plugged in to noisy mechanical and electronic devices 24 hours a day, 356 days a year.

Engine-powered vehicles are the main source of anthropogenic noise, and their numbers can grow even at a higher rate than the human population – so spreading not only diseases [2] but also decibels over a global network of travelling routes. In an ecological context, we refer to noise as a kind of sound (= energy wave detected by an auditory system) that is not considered a biologically meaningful cue by wildlife (including us) and might also cause physiological stress. Experts refer to ‘masking’ as those situations in which noise interferes the perception or emission of sounds that matter to the life history of species – a global concern in both terrestrial [3] and aquatic [4] ecosystems.

Andy Foote [5] has assessed the effect of vessel traffic on the vocal behaviour of the three pods forming the Southern Resident population of killer whales (Orcinus orca¸ see video). He recorded calls from these cetaceans from a ship, and through an array of submarine microphones in Haro Straight, between San Juan Island (Washington State, USA) and Vancouver Island (British Columbia, Canada). Between the 1990s and the 2000s, local traffic density had multiplied by a factor of 5 and currently, > 20 whale-watching vessels follow these killer whales daily among an active fleet of > 70 commercial vessels. Foote compared call length through 35 hours of underwater killer whale recordings over three periods (1977-1981, 1989-1992, 2001-2003), each comprising situations in which the pods were exposed to both noisy and quiet environments. Over the study, call length varied between 0.3 and 2.0 seconds; while on average, L-pod calls were the shortest (0.6-0.8 seconds), and J-pod calls the longest (0.9-1.0 seconds). Read the rest of this entry »





You know it’s hot when it’s too hot to ….

16 01 2014
© T. Brandon

© T. Brandon

My post’s title might be a good candidate title for a punk song in the 2030s (maybe by a re-incarnation of the Dead Kennedys).

I am currently sitting under my solar-powered ceiling fan as Adelaide is declared the world’s hottest city (and not in the funky, cultural, fun way), and I can’t help but contemplate climate change models predicting the fate of biodiversity over the coming decades. Because it’s far, far too hot to work outside, I’m perusing the latest interesting articles on the subject and I came across this recent little gem.

Also recommended on F1000Prime by Ary Hoffman, the paper, Using physiology to predict the responses of ants to climatic warming, by Sarah Diamond and colleagues touches on many aspects of climate predictions that need to be considered. I summarise these briefly here.

While no physiologist, I have dabbled in the past, although up until quite recently I didn’t see that physiology per se had much to do with conservation. It turns out that climate change has spawned an entire sub-discipline called ‘conservation physiology‘, which focuses inter alia on how species can/will/might respond and adapt to a warmer, climatically disrupted world.

What struck me about Diamond & colleagues’ paper was that yet again, it’s not as simple as heat-stressing a species experimentally and making a prediction on its future distribution (ecology is complex). No, the complexity comes in various forms that makes each species a little different from each other. Using North American ant species subjected to various warming scenarios in large (5 m) enclosures, they found the following: Read the rest of this entry »