Dy­ing Sea Stars

Note­wor­thy

Oceans cover most of the Earth's sur­face and con­tain more than 97% of all our wa­ter. The oceans' im­por­tance in sup­port­ing life on our planet, in reg­u­lat­ing the cli­mate, and as a home for a vast amount of bio­di­ver­sity is un­de­ni­able. Yet, as land an­i­mals, we re­main largely un­aware of much of the on­go­ing be­neath the oceans' sur­face. 

Sun­flower Sea Star. Source

A re­cent pub­li­ca­tion high­lights one such case. Since 2013, an epi­demic called sea star wast­ing dis­ease (SSWD) has dev­as­tated pop­u­la­tions of sea stars along the Pa­cific Coast of North Amer­ica. The sun­flower sea star (Py­c­nopo­dia he­lianthoides), which is par­tic­u­larly sus­cep­ti­ble to the dis­ease, was once abun­dant from Baja Cal­i­for­nia to Alaska but is now al­most ex­tinct. But why should we be con­cerned with sea star mor­tal­ity? As with most species, sea stars are im­por­tant for the ecol­ogy of their en­vi­ron­ments. They prey on and con­trol pop­u­la­tions of sea urchins, which in turn graze on kelp forests. The loss of sea stars trans­lates into grow­ing sea urchin pop­u­la­tions and loss of kelp forests, which house thou­sands of ma­rine species and store car­bon.

In a re­cent study, re­searchers from Canada and the United States pinned down the cul­prit in­volved in this wast­ing dis­ease: Vib­rio pecteni­cida FHCF‑3. The au­thors car­ried out four years of con­trolled ex­po­sure ex­per­i­ments in which they ex­posed healthy sea stars to dis­eased sam­ples. They fol­lowed with se­quence analy­sis of dis­eased sea star sam­ples and iden­ti­fied V. pecteni­cida as the dom­i­nant bac­terium. The re-in­oc­u­la­tion of a& V. pecteni­cida iso­late into healthy in­di­vid­u­als re­sulted in dis­eased sea stars, ful­fill­ing Koch's pos­tu­lates. 

Elec­tron mi­cro­graph of a neg­a­tively stained cell of the king scal­lop (Pecten max­imus) pathogen V. pecteni­cida A365^T (Ma­rine Broth growth) show­ing the sin­gle po­lar fla­gel­lum. Bar, 1 µm. Source

Un­cov­er­ing agents of dis­ease in these sea stars re­quired care­ful ob­ser­va­tion in the field and ex­per­i­men­tal work in con­trolled set­tings. In the fu­ture, it will be pos­si­ble to screen and track the pathogen and hope­fully de­velop con­ser­va­tion strate­gies to main­tain healthy coastal ma­rine ecosys­tems. 

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