Paradigm Lost: Ocean Acidification Will Overturn the Concept of Larval-Fish Biophysical Dispersal

Abstract

Most marine ecologists have in the past 25 years changed from supporting a passive-dispersal paradigm for larval marine fishes to supporting a biophysical-dispersal paradigm wherein the behaviour of larvae plays a central role. Research shows larvae of demersal perciform fishes have considerable swimming and orientation abilities over a major portion of their pelagic larval duration. These abilities depend on sensory function, and some recent research has indicated anthropogenic acidification of the oceans will by the end of the century result in sensory dysfunction. This could strongly alter the ability of fish larvae to orientate in the pelagic environment, to locate suitable settlement habitat, to bet-hedge, and to colonize new locations. This paper evaluates the available publications on the effects of acidification on senses and behaviours relevant to dispersal of fish early life-history stages. A large majority of studies tested CO 2 values predicted for the middle to end of the century. Larvae of fourteen families-all but two perciform-were studied. However, half of studies used Damselfishes (Pomacentridae), and except for swimming, most studies used settlement-stage larvae or later stages. In spite of these taxonomic and ontogenetic restrictions, all but two studies on sensory function (chemosensation, hearing, vision, detection of estuarine cues) found deleterious effects from acidification. The four studies on lateralization and settlement timing all found deleterious effects from acidification. No clear effect of acidification on swimming ability was found. If fish larvae cannot orientate due to sensory dysfunction, their dispersal will, in effect, conform to the passive dispersal paradigm. Modelling incorporating larval behaviour derived from empirical studies indicates that relative to active larvae, passive larvae will have less self-recruitment, higher median and mean dispersal distances, and lower settlement rates: further, bet hedging and colonization of new locations will decrease. The biophysical dispersal paradigm will be lost in theory and in fact, which is predicted to result in lower recruitment and less bet hedging for demersal, perciform fishes. More research is required to determine if the larvae of other Orders will be effected in the same way, or if warm-and cold-water fish faunas will be similarly effected.

Biodiversity of coral reef cryptobiota shuffles but does not decline under the combined stressors of ocean warming and acidification

“…Acidification, on the other hand, has been found to have more direct negative effects across a wider range of phyla and life stages than elevated temperature ( 21 – 23 ) with calcifying larvae being particularly vulnerable to lethal and sublethal responses during development ( 23 , 26 , 57 ). Acidification-induced changes in larval development times, dispersal distances, and shifts in microbial biofilms used as settlement cues for larvae have also been shown to alter recruitment and settlement dynamics ( 58 – 61 ), all of which could have contributed to the diminished richness observed within the Acidified treatment.…”

Development of the visual system of anchovy larvae, Engraulis anchoita: A microanatomical description

“…Frommel et al (, ) found alterations specifically in the retina of the larvae associated with a pH reduction (e.g., an abnormal shape in the pigmented epithelial layer), and also observed vacuolation in the cornea, and damage to the lens. Alterations in larval retina could damage the vision producing severe effects, among them, affecting the way of perceiving the intensity of light influencing its orientation (Leis, ). The ocean acidification may act as an additional source of natural mortality, affecting fish populations, particularly those subject to fishing exploitation because the population is destabilized and its ability to respond to climate change is reduced (Le Quesne & Pinnegar, ).…”

“…Frommel et al (, ) found alterations in the retina of the larvae associated with acidification. This could affect vision causing a variety of harmful effects in the larvae, for example, affecting light intensity perception and influencing larval orientation (Leis, ). Teleost fishes are especially vulnerable during the early stages of their life cycle because they lack specialized physiological mechanisms for pH regulation.…”

Larval dispersal in a changing ocean with an emphasis on upwelling regions

“…). Reduced sensory ability combined with reduced swimming ability for many species could effectively result in passive dispersal (Leis ). Changes in chemical cue or cue source can reduce settlement success, such as changes in the algal community and cue integrity reducing coral settlement (Albright , Nagelkerken and Munday , Espinel‐Velasco et al.…”