Species  diversity  and  association  in  the  rocky  intertidal  zone  of  Mount  Hope  Bay  Benjamin  Gibson    Roger  Williams  University    

Introduction  

Narragansett   Bay   is   a   predominantly  rocky-­‐intertidal   coastline   inhabited   by   an   array  of   invertebrate   species.   The   rocky   intertidal  zone   is   strongly   affected   by   the   forces   of  nature.  The  wind  waves,   tides,  and  currents  all  play   a   factor   in   the   organisms   that   call   this  harsh   environment   their   home.   The   shoreline  area   presents   marine   organisms   with   the  problems   of   exposure,   temperature  fluctuations,   and   salinity   fluctuations.   In   turn,  this   provides   terrestrial   organisms   with   the  problems   of   submersion,   desiccation,   and   high  salinity.   Any   of   the   organisms   that   attempt   to  colonize   in  the  rocky   intertidal  zone  have  to  be  outfitted   with   survival   traits   specific   to   this  environment.   Space   is   also   a   limiting   factor   in  the   rocky   intertidal   zone;   organisms   have   to  congregate   in   the   areas   resistant   to   the  constant  wave  and  tidal  action.  The  high  energy  dynamics   of   the   rocky-­‐intertidal   make   it   a  difficult  place  for  organisms  to  grown  within  the  water   column.     Organisms   that   live   within   the   rocky  intertidal   zone   have   to   adjust   to   the   physical  component   of   wave   action,   salinity,   and  temperature  changes,  but  also  need  to  compete  for   space  within   the   zone.  With   space   being   a  limiting   factor   within   the   eulittoral   zone,   and  predation   in   the   splash   zone,   it   is   difficult   for  any   organism   to   live   or   colonize   the   intertidal  area.    

                                                                                                                                                                                                                                                                                                                                                                                                 

Materials  and  Methods    

Scientific  tools  that  were  utilized:  

• Area  Measurements:  Quadrants  measuring   1X1   meter(s),   tape  measure  

• Identification:  Field  Guides    

The   research  was   conducted   in   an   area   of  Mt.  Hope   Bay,   the   northeastern   section   of  Narragansett   Bay,   Rhode   Island.   Specifically  targeting  the  area  to  the  north  and  the  south  of  the   Roger   Williams   University   Learning  Platform,   The   tidal   zone   was   measured   at   the  lowest  tide  which  insures  that  each  of  the  three  zones   is   equally   represented.   Each   group  surveys  a  portion  of  the  specific   intertidal  zone  with   a   quadrant,   a   1m2   area   tool   used   to   help  quantify   species   in   similar   experiments.   Each  group  surveys  a   lower,  middle,  and  upper   tidal  area  and  records  the  abundance  of  species  and  population   at   each   of   the   sections.   The   areas  were   sampled   on   September   8th,   2014,   with  overcast  weather  conditions  and  at  the  peak  of  low   tide.   All   produced   data   was   then   loaded  into   a   spreadsheet   (Excel).   Then   the   data   was  analyzed   using   Excel   to   find   the   Coles  coefficient  of  association  and  a  linear  regression  line   and   the   r2   value.   Both   of   these   tests  were  conducted  in  Excel.  

 

 

 

 

 

Results:  

Fig.  1  Comparison  between  groups  of  the  number  of  individuals  between  the  three  zones  

 

Fig.  2  Comparison  of  the  species  diversity,  using  number  of  species  in  each  of  the  three  intertidal  zones.  

R²  =  0.61856  

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Linear  (Regression)  

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  The   diversity   indices   of   the   rocky  intertidal  zone  down  by  the  learning  platform  at  Roger   Williams   University,   changed   with  distance   from   the   water.   Table   2   shows   the  relationship   between   species   diversity   and  distance   from   the  water.   The   three   zones   are:  the   upper   zone,   also   considered   the   splash  zone,  is  the  furthest  from  the  water.  The  middle  zone,   or   the   eulittoral   zone,   is   the   midpoint  between   the  upper  and   lower  zone.   Lastly,   the  lower   zone,   also   known   as   the   lower   eulittoral  zone,  is  almost  always  submerged  in  seawater.    

  Table   1   outlines   the   species   seen   at  each   of   the   three   zones,   and   it   can   be   stated  that   the   most   species   are   in   the   lower   zone.  However,   there   are   several   species   that   are  found   at   both   extremes,   one   such   example   is  the  periwinkle.    

  Figure   1   shows   the   number   of  individuals   that   are   present   in   each   zone,  with  

an  r2  value  of  0.62  and  a  regression  line  showing  this  value.  Figure  2  is  comparing  the  number  of  species  at  each  of   the   zones,   compared  by   the  groups.    

  Another  aspect  of  a  diversity  study  is  calculating  Cole’s  Coefficient  of  Association  (Ca)  which  is  outlined  in  table  3.  Taking  a  predator  and  known  prey  and  calculating  Ca  yields  how  likely  of  an  association  is  present  in  our  data.  

Discussion  

  As  seen  in  figure  1’s  regression  line,  there  is  an  r2  value  of  0.62,  which  indicates  that  62%  of  the  total  variance  in  the  number  of  individuals  is  explained  by  each  zone.  Figure  2  shows  the  number  of  species  discovered  by  each  group,  separated  by  zones.    

  Table   1   is   data   from   group   2,   which  outlines   the   species   diversity   at   each   of   the  different   zones.   The   most   diverse   zone   is   the  lower   zone   which   has   been   proven   by   both  studies   and   theory.     Not   only   was   the   lower  zone  the  most  diverse,  but  the  types  of  animals  there   were   ones   that   would   not   thrive   in   the  intense   conditions   that   the   middle   and   upper  zones  feature  during  low  tide.  These  organisms  included   algae   of   all   phylums,   polychaete  worms,   and   other   soft   bodied   species.   The  organisms  that  populated  the  middle  and  upper  zones  were  mostly  gastropods  and  crustaceans;  

Mean  n(n-­‐1)   Mean  N(N-­‐1)   Mean  Diversity  Index  

 

Upper  zone  

7525.5   19430   0.39    

Middle  zone  

12517.5   37754   0.33    

Lower  zone  

17573   47841   0.37    

Table  2.  Averaging  of  each  group’s  data,  the  approximate  diversity  index  of  the  area  can  be  found.  

 

Species   Upper   Middle   Lower  Asian  Shore  

Crab  3   9   11  

Green  Crab   0   1   0  

Barnacles   36   117   219  

Polychaete   0   0   1  

Beach  Flea   1   0   10  

Mud  Snails   0   33   60  

Tube  worms   0   0   9  

Slipper  Shells   0   0   18  

Mussels   0   0   19  

Quahog   0   0   1  

Oyster  drills   0   0   2  

Periwinkles   6   15   11  

Red  Algae   6   13   13  

Green  Algae   4   8   8  

Brown  Algae   0   3   5  Table  1.  Species  diversity  for  Group  2  at  the  upper,  middle,  and  lower  zones.  

 

gastropods  and  barnacles  are  able  to  withstand  the   harsh   conditions   of   the   middle   and   upper  zones  due  to  their  ability  to  reduce  their  risks  of  desiccation.   They   do   this   by   storing  water   and  closing   themselves   off,   through   the   use   of  either   an   operculum   or   plates.

Table   2   averages   and   summarizes   the   three  zones,   using   diversity   indices.   Averaging   the  sum   of   n(n-­‐1)   and   N(N-­‐1)   across   all   groups  supplied  the  average  diversity  index  for  each  pf  the   three   zones.   The   diversity   indices   were   all  relatively   close   to   each   other,   however   with   a  big   enough   sample   size,   there   would   be   a  notable  difference  between   the  upper,  middle,  and   lower   zones.   For   this   study,   the   diversity  indices  were   not  what  would  we   thought   they  would   be;   the   upper   zone   had   the   highest  diversity   index   of   0.39,   the   middle   had   the  lowest   index   of   0.33,   and   the   lower   zone   had  the   intermediate   diversity   index   of   0.37.   The  lower  zone  is  thought  to  be  the  most  diverse  of  the  three  zones.  

Table   3   outlines   Cole’s   Coefficient   of  association   and   how   likely   it   is   that   the   two  species   are   associated   with   each   other.   As  believed  due  to  them  being  related  as  predator  and   prey,   the   periwinkle   and   green   algae  respectively   are   associated   with   a   Ca   value   of  0.52.  This   suggests   that   the   two  are  associated  with   one   another.   This   value   was   calculated  using   the   equation   outlined   in   the   equation  section.    

 

 

 

 

 

 

 

 

Equation:  

 

𝑪𝒂 =  ( 𝟖 ∗ 𝟐 − 𝟏 ∗ 𝟐 )𝟖 + 𝟏 ∗ (𝟏 + 𝟐)

 

 

 

Conclusion  

  The   intertidal   zone   provides   a   difficult  environment   for   terrestrial   and   marine  organisms.   However,   the   data   was   not  supportive  of  the  original  hypothesis  that  it  was  the  lower  intertidal  one  that  would  present  the  largest   species   diversity.   The   middle   intertidal  zone   showed   the   largest   diversity   index   (.38),  and   suggests   that   the   middle   intertidal   is   the  most   species   diverse.   This   resulted   from  differences   in  the  data  analysis  methods  of  the  groups.   The   conducted   study   contained   too  

 

Periw

inkles  

 

Presen

t  

  8    

1  

2   2  

Absent  

Present   Absent  

    Green  Algae  

Table  3.  Cole’s  Coefficient  of  association  between  Green  Algae  and  Periwinkles.  8  is  the  number  of  quadrants  where  both  the  green  algae  and  periwinkles  are  present,  1  is  the  number  of  quadrants  where  green  algae  is  absent  but  periwinkles  are  present,  2  on  the  left  is  the  number  of  quadrants  where  green  algae  is  present  but  periwinkles  are  absent,  and  finally  the  2  on  the  right  represents  the  number  of  quadrants  where  both  green  algae  and  periwinkles  are  absent.  

many   different   data   collection   and   analysis  methods   to   suggest   a   significant   correlation  between  data  and  actual  habitat  diversity  of  the  Mt  Hope   Bay.   To   represent   the   organisms   and  species   diversity   in   the   bay   it   is   important   for  the  collection  methods   to  be  uniform.  Uniform  distances   separating   the   three   intertidal   zones.  Furthermore,   the   collecting   patterns   and  frequencies   require   more   standardization  among  all  groups  so  that  there  is  no  question  of  the  significance  of  the  data.  The  suggestion  that  the  periwinkle  and  green  algae  are  associated  in  the   intertidal   ecosystem   is   evident   in   the   data  collected.   Using   the   Coles   coefficient   it   was  determined   that   the   periwinkles,   being   the  natural   predator   of   various   species   of   green  algae,   are   associated   with   green   algae   in   this  

survey.   This   association   correlates   with   the  belief   that   periwinkles   are   predators   of   green  algae.