Sea urchins are being
collected as the major source of food and livelihood in the Philippines and
foreign market (Manuel et al., 2013). The roe of some sea urchin species
especially T. gratilla is considered as a delicacy in several countries and
communities in the Philippines while some are eaten raw. In aquaculture, it
yields up to 9.6 million pesos net income in 1998 (Junio-Meñez et al., 1998)
because the roe of T. gratilla is used as supplemental feeds and sold by
bottles in the Philippines (Schoppe, 2000).
Tripneustes gratilla plays a vital part of
the ecosystem (Pates et al., 2015; Wahbeh, 2009) by contributing significantly
to the nitrogen cycle through its excretions in the seagrass areas (Koike et
al., 1987). Moreover, the high presence of sea urchin may facilitate
colonization of some colonial seagrass species which lead to seagrass diversity
(Pates et al., 2015).
Effects of Temperature
and Climate Change to Echinoid Larvae
ecosystems and the living organism in it are in great danger because
near-future increase of temperature can affect the fertilization and early
development of the echinoids including T. gratilla (Brennand et al. (2010) as
cited by Sherman (2015)) because temperature has great effects in the various
biological processes of the organism (Ubaldo et al., 2007).
Byrne (2010) stated
that different species of larvae have various sensitivities to stressors. In
the study of Collin and Chan (2016), they discovered that on the tropical sea
urchin, Lytechinus variegatus, the cleavage, and early embryonic development
are more susceptible to thermal stress compared to the larvae. This is contrary to the studies claiming that
larval stage is the most vulnerable to thermal stress (Tangwancharoen &
Burton, 2014; Byrne et al., 2010).
On another study by
Brennand et al. (2010), embryos of the sea urchin T. gratilla were reared in
flow-through chambers filled with filtered seawater maintained at all
combinations of three different temperatures and three different pH values and
after five days of exposure, the growth and development of the larvae were
assessed. Results of the experiment revealed that the larvae reared at pH 7.6
and pH 7.8 had smaller post-oral arms when compared with those reared at
control pH. However, they reported that a +3°C warming diminished the negative
effects of low pH/high CO2. In addition, the total length of calcite rods is
largely comprised of the post-oral arms. The results of the study suggest that
the negative effects of a 0.35 to 0.55 CO2-induced decline in seawater pH on
the growth and calcification of the sea urchin T. gratilla can be largely
overcome by a 3°C increase in water temperature.
According to Byrne et
al. (2009), over the ranges of seawater pH and temperature they studied on
Heliocidaris erythrogramma, there was no effect of pH and no interaction
between temperature and pH on sea urchin egg fertilization. Seawater pH also
had no effect on the longer-term development of fertilized sea urchin eggs; but
they said that warming led to developmental failure at the upper warming (+4 to
+6°C) level, regardless of pH. They stated that gametes from H. erythrogramma
adults acclimated to 24°C would have successful development in a +4°C treatment.
They also noted that single stressor studies of thermo-tolerance in a diverse
suite of tropical and temperate sea urchins show that fertilization and early
development are robust to temperature well above ambient and the increases
expected from climate change, citing the work of Farmanfarmaian and Giese
(1963), Chen and Chen (1992) and Roller and Stickle (1993).
In the study of Rahman
et al. (2009), the lower and higher thermal tolerance of the embryonic
development of T. gratilla were 22°C and 29°C, respectively. However, outside
the range of temperature, the development showed abnormality within the
experiment. Early larvae of this species have the ability to survive the higher
temperature limit for short periods of time. For the two-hour period, prism and
two-arm pluteus larvae survived at temperatures between 30°C and 33°C, whereas
four-armed pluteus larvae survived at temperatures between 30°C and 36°C. The
results suggested that the larval thermal tolerance capability of T. gratilla
is stage dependent.