Lower pH kills spirorbids but favors sponges
A 0.2-unit drop in seawater pH over 100 days thins calcareous tube worms and algae while sponges and some sea squirts increase.
Source
Acidification effects on biofouling communities: winners and losers
Study at a glance
- Design
- Animal / in-vitro — 100-day flow-through aquarium experiment comparing biofouling at pH 7.9 vs 7.7
- N
- N=50 · Spirorbid counts analysed with n=50 quadrats/surfaces; algal scores n=11
- Population
- Ria Formosa biofouling communities on pipes, HDPE, limestone, and tank walls
- Outcome
- Live spirorbid density, mortality, and shifts toward sponges/ascidians under acidification
Structured fields used in claim comparison tables when every cited study has a complete layer.
What they did
Researchers held Ria Formosa biofouling communities at pH 7.9 versus 7.7 for 100 days in a flow-through aquarium, tracking established assemblages on pipes and new colonization of HDPE, limestone tiles, and tank walls.
What they found
At pH 7.7, live spirorbids fell from 11.1 to 2.0 per 10 cm² and 72.8% of tubes were dead (versus 23.3% in controls). Sponges rose 2.5-fold and Molgula ascidians fourfold. New spirorbid settlement dropped several-fold on all surfaces; algal films were thinner (score 1.8 vs 4.4).
The limits
What it doesn't show
The pH drop (0.2) is milder than some 2100 projections, tanks were at a fixed 23°C, and 100 days cannot capture century-scale evolution or open-coast food webs.
Key terms
- Ocean acidification
- Decline in seawater pH as the ocean absorbs rising atmospheric CO2.
- Biofouling community
- Sessile organisms that colonize hard surfaces in shallow seawater, including worms, sponges, ascidians, and algae.
- Spirorbid
- A calcareous tube-dwelling polychaete, here Neodexiospira pseudocorrugata, that dominated control pipes.
- Calcite / aragonite saturation
- Whether calcium carbonate minerals are thermodynamically stable in seawater; both remained saturated at pH 7.7 here.
- Succession
- The repeatable sequence of species that colonize a new marine surface.
Flashcards
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The acidification treatment was:
Common questions
Did skeletons dissolve because seawater was undersaturated?
No. Neither calcite nor aragonite was undersaturated at pH 7.7, yet spirorbids still died and tubes looked breached.
Who were the winners?
The sponge Leucosolenia and the ascidian Molgula increased; Aplidium and spirorbids declined.
Did new surfaces still get fouled?
Yes, but spirorbid densities were 3.5- to 6-fold lower, and algal films were much thinner.
Why do biofouling communities matter economically?
Managing fouling on ships, desalination plants, and power plants costs billions of dollars a year.
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