Seagrass-Watch Magazine Issue 47 - March 2013 | Page 51

Taking over
Seagrass meadow completely smothered by the moss balls.
Growth of Cladophora reaches nuisance proportions at times often
as a result of eutrophication.

proportions at times often as a result of fertiliser runoff and
sewage discharge. The macroalgae clumps fragment due to
tidal and wave action, and these fragments then multiply as
individual balls, multiplying in numbers. Due to their greater
multiplication potential, the algae starts competing with
seagrass for space and also spreads to adjacent barren areas.
The biomass of the algae was 2-4.5 kg.m-2(wet weight) at
established algal beds. It smothers the smaller leaved seagrass
species (Halophila spp. and Halodule spp.) and over time the
entire meadow become dead and decayed. Though the
quantitative algal cover estimates are missing from our survey,
observations from 2010 onwards record the expansion of the
algal mats across the region with its growth and successional
spread along the shore from village to village.
The Palk Bay region is influenced by the northeast monsoon
(October-December) and is prone to periodic nutrient inputs
that stimulate the productivity of the moss balls. Only Enhalus
acoroides with its greater canopy height successfully outcompetes these macroalgae, followed by Cymodocea
serrulata. The small leaved seagrass meadows of Halodule
spp. and Halophila spp. were completely smothered. To
worsen the scenario, as the algae die the substratum becomes
anoxic (deprived of oxygen) with high levels of sulphides.
Anoxic conditions were observed in the survey sites ranging
between 3.1 and -24.3 mV. Such hypoxic conditions
prevailing within the roots of seagrass pose a severe threat by
inhibiting growth. The debris of the decayed algal mats also
elevates turbidity in the water column and competes with large
leaved seagrasses.
The rapid growth of macroalgae in the region of Palk Bay is
alarming, with about sixty percent Thalassia hemprichii and
ninety percent of Halophila ovalis and Halodule meadows
already destroyed. This problem may ultimately lead to a
major ecological phase shift that must be prevented by suitable
management action plans.
Microscopical view of the macroalgae
showing varied degrees of branching

References
1. Dodds, W.K. and D. A. Gudder, 1992. The ecology of Cladophora: Review. J. Phycol., 28: 415-427.

MARCH 2013

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