Effects of ocean acidification on the settlement and metamorphosis of marine invertebrate and fish larvae: a review

Abstract

Most marine organisms present an indirect lifecycle where a planktonic larval stage reaches competency before settling to the substrate and metamorphosing. Despite the critical importance of these early life history stages, little is known about how global change-related stressors, in particular ocean acidification (OA), affect marine larval settlement and metamorphosis. To date, 48 studies have investigated the effects of OA on larval settlement, focussing mostly on tropical corals (16), echinoderms (11) and fish (8). Most studies show negative effects of OA during settlement and post-settlement processes. For instance, reduced settlement is typically seen along natural pH gradients and in experimentally lowered pH treatments. This generally results in reduced settlement selectivity and metamorphosis and poorer post-settlement fitness. Carryover effects of OA exposure can also occur, with larval environmental history influencing early post-settlement performance. We conclude that OA may (1) alter larval supply for settlement by altering horizontal swimming behaviour or vertical migration; (2) directly influence settlement success through changes in the nature and distribution of suitable settlement substrates (e.g. biofilm, crustose coralline algae); and (3) mediate carryover effects at settlement by altering larval development or larval energy budgets. In contrast to fish larvae, there is little evidence for most invertebrate larvae that their perception of settlement cues is directly influenced by reduced pH. A summation of how OA affects the settlement and metamorphosis of marine invertebrates is timely, since altered settlement rates will influence the future distributions, abundances and ecology of marine benthic communities.

Ocean acidification affects microbial community and invertebrate settlement on biofilms

“…Presently, there is limited information on the potential effects of OA on the settlement process 20,47 . Mostly, it has shown that OA has a negative impact on settlement in marine invertebrates, however these conclusions are based on relatively few taxa, and mostly within the Cnidaria and Echinoderm phyla.…”

“…While reduced pH has been linked to decreases in the settlement success of vermetids 14 , corals [14][15][16][17][18] , sea stars 11 , and sea urchins 19 , our understanding regarding the OA effects on the settlement processes of marine invertebrates remains limited. In this respect, a recent review by Espinel et al 20 found less than 50 published studies, with the majority indicated neutral or negative changes in settlement under reduced pH. Within these studies, only a small number examined the outcomes of pH induced changes of substrates (biofilms and CCAs) on settlement, and these indicated a reduction in settlement rate in taxa such as coral and sea stars 20 .…”

“…In this respect, a recent review by Espinel et al 20 found less than 50 published studies, with the majority indicated neutral or negative changes in settlement under reduced pH. Within these studies, only a small number examined the outcomes of pH induced changes of substrates (biofilms and CCAs) on settlement, and these indicated a reduction in settlement rate in taxa such as coral and sea stars 20 .…”

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

“…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. ).…”

“…Larvae with external calcified structures will very likely suffer more extreme physical deformities than non‐calcifying larvae or those with internally buffered calcium structures as pH declines, though increasing evidence points to maladaptive behavior in low pH conditions across a range of taxa which could impact dispersal (Espinel‐Velasco et al. ). Species that release swimming larvae should better adapt to changes in current flow and stratification than free‐spawning species that release passive gametes and embryos, particularly in upwelling regions where offshore and equatorward transport is expected to strengthen.…”